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Ottolia M, John S, Hazan A, Goldhaber JI. The Cardiac Na + -Ca 2+ Exchanger: From Structure to Function. Compr Physiol 2021; 12:2681-2717. [PMID: 34964124 DOI: 10.1002/cphy.c200031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ca2+ homeostasis is essential for cell function and survival. As such, the cytosolic Ca2+ concentration is tightly controlled by a wide number of specialized Ca2+ handling proteins. One among them is the Na+ -Ca2+ exchanger (NCX), a ubiquitous plasma membrane transporter that exploits the electrochemical gradient of Na+ to drive Ca2+ out of the cell, against its concentration gradient. In this critical role, this secondary transporter guides vital physiological processes such as Ca2+ homeostasis, muscle contraction, bone formation, and memory to name a few. Herein, we review the progress made in recent years about the structure of the mammalian NCX and how it relates to function. Particular emphasis will be given to the mammalian cardiac isoform, NCX1.1, due to the extensive studies conducted on this protein. Given the degree of conservation among the eukaryotic exchangers, the information highlighted herein will provide a foundation for our understanding of this transporter family. We will discuss gene structure, alternative splicing, topology, regulatory mechanisms, and NCX's functional role on cardiac physiology. Throughout this article, we will attempt to highlight important milestones in the field and controversial topics where future studies are required. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.
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Affiliation(s)
- Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, California, USA
| | - Adina Hazan
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
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2
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Wanichawan P, Skogestad J, Lunde M, Støle TP, Stensland M, Nyman TA, Sjaastad I, Sejersted OM, Aronsen JM, Carlson CR. Design of a Proteolytically Stable Sodium-Calcium Exchanger 1 Activator Peptide for In Vivo Studies. Front Pharmacol 2021; 12:638646. [PMID: 34163352 PMCID: PMC8215385 DOI: 10.3389/fphar.2021.638646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 05/14/2021] [Indexed: 11/13/2022] Open
Abstract
The cardiac sodium–calcium exchanger (NCX1) is important for normal Na+- and Ca2+-homeostasis and cardiomyocyte relaxation and contraction. It has been suggested that NCX1 activity is reduced by phosphorylated phospholemman (pSer68-PLM); however its direct interaction with PLM is debated. Disruption of the potentially inhibitory pSer68-PLM-NCX1 interaction might be a therapeutic strategy to increase NCX1 activity in cardiac disease. In the present study, we aimed to analyze the binding affinities and kinetics of the PLM-NCX1 and pSer68-PLM-NCX1 interactions by surface plasmon resonance (SPR) and to develop a proteolytically stable NCX1 activator peptide for future in vivo studies. The cytoplasmic parts of PLM (PLMcyt) and pSer68-PLM (pSer68-PLMcyt) were found to bind strongly to the intracellular loop of NCX1 (NCX1cyt) with similar KD values of 4.1 ± 1.0 nM and 4.3 ± 1.9 nM, but the PLMcyt-NCX1cyt interaction showed higher on/off rates. To develop a proteolytically stable NCX1 activator, we took advantage of a previously designed, high-affinity PLM binding peptide (OPT) that was derived from the PLM binding region in NCX1 and that reverses the inhibitory PLM (S68D)-NCX1 interaction in HEK293. We performed N- and C-terminal truncations of OPT and identified PYKEIEQLIELANYQV as the minimum sequence required for pSer68-PLM binding. To increase peptide stability in human serum, we replaced the proline with an N-methyl-proline (NOPT) after identification of N-terminus as substitution tolerant by two-dimensional peptide array analysis. Mass spectrometry analysis revealed that the half-life of NOPT was increased 17-fold from that of OPT. NOPT pulled down endogenous PLM from rat left ventricle lysate and exhibited direct pSer68-PLM binding in an ELISA-based assay and bound to pSer68-PLMcyt with a KD of 129 nM. Excess NOPT also reduced the PLMcyt-NCX1cyt interaction in an ELISA-based competition assay, but in line with that NCX1 and PLM form oligomers, NOPT was not able to outcompete the physical interaction between endogenous full length proteins. Importantly, cell-permeable NOPT-TAT increased NCX1 activity in cardiomyocytes isolated from both SHAM-operated and aorta banded heart failure (HF) mice, indicating that NOPT disrupted the inhibitory pSer68-PLM-NCX1 interaction. In conclusion, we have developed a proteolytically stable NCX1-derived PLM binding peptide that upregulates NCX1 activity in SHAM and HF cardiomyocytes.
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Affiliation(s)
- Pimthanya Wanichawan
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Jonas Skogestad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Marianne Lunde
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Thea Parsberg Støle
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Maria Stensland
- Department of Immunology, Institute of Clinical Medicine, University of Oslo and Rikshospitalet Oslo, Oslo, Norway
| | - Tuula A Nyman
- Department of Immunology, Institute of Clinical Medicine, University of Oslo and Rikshospitalet Oslo, Oslo, Norway
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Ole M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Jan Magnus Aronsen
- Department of Molecular Medicine, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Oslo, Norway.,Department of Pharmacology, Oslo University Hospital Rikshospitalet, Oslo, Norway
| | - Cathrine Rein Carlson
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,The KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway
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Yap JQ, Seflova J, Sweazey R, Artigas P, Robia SL. FXYD proteins and sodium pump regulatory mechanisms. J Gen Physiol 2021; 153:211866. [PMID: 33688925 PMCID: PMC7953255 DOI: 10.1085/jgp.202012633] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 02/03/2021] [Indexed: 12/12/2022] Open
Abstract
The sodium/potassium-ATPase (NKA) is the enzyme that establishes gradients of sodium and potassium across the plasma membrane. NKA activity is tightly regulated for different physiological contexts through interactions with single-span transmembrane peptides, the FXYD proteins. This diverse family of regulators has in common a domain containing a Phe-X-Tyr-Asp (FXYD) motif, two conserved glycines, and one serine residue. In humans, there are seven tissue-specific FXYD proteins that differentially modulate NKA kinetics as appropriate for each system, providing dynamic responsiveness to changing physiological conditions. Our understanding of how FXYD proteins contribute to homeostasis has benefitted from recent advances described in this review: biochemical and biophysical studies have provided insight into regulatory mechanisms, genetic models have uncovered remarkable complexity of FXYD function in integrated physiological systems, new posttranslational modifications have been identified, high-resolution structural studies have revealed new details of the regulatory interaction with NKA, and new clinical correlations have been uncovered. In this review, we address the structural determinants of diverse FXYD functions and the special roles of FXYDs in various physiological systems. We also discuss the possible roles of FXYDs in protein trafficking and regulation of non-NKA targets.
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Affiliation(s)
- John Q Yap
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Ryan Sweazey
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
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4
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Cheung JY, Wang J, Zhang XQ, Song J, Davidyock JM, Prado FJ, Shanmughapriya S, Worth AM, Madesh M, Judenherc-Haouzi A, Haouzi P. Methylene Blue Counteracts H 2S-Induced Cardiac Ion Channel Dysfunction and ATP Reduction. Cardiovasc Toxicol 2019; 18:407-419. [PMID: 29603116 DOI: 10.1007/s12012-018-9451-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
We have previously demonstrated that methylene blue (MB) counteracts the effects of hydrogen sulfide (H2S) cardiotoxicity by improving cardiomyocyte contractility and intracellular Ca2+ homeostasis disrupted by H2S poisoning. In vivo, MB restores cardiac contractility severely depressed by sulfide and protects against arrhythmias, ranging from bundle branch block to ventricular tachycardia or fibrillation. To dissect the cellular mechanisms by which MB reduces arrhythmogenesis and improves bioenergetics in myocytes intoxicated with H2S, we evaluated the effects of H2S on resting membrane potential (Em), action potential (AP), Na+/Ca2+ exchange current (INaCa), depolarization-activated K+ currents and ATP levels in adult mouse cardiac myocytes and determined whether MB could counteract the toxic effects of H2S on myocyte electrophysiology and ATP. Exposure to toxic concentrations of H2S (100 µM) significantly depolarized Em, reduced AP amplitude, prolonged AP duration at 90% repolarization (APD90), suppressed INaCa and depolarization-activated K+ currents, and reduced ATP levels in adult mouse cardiac myocytes. Treating cardiomyocytes with MB (20 µg/ml) 3 min after H2S exposure restored Em, APD90, INaCa, depolarization-activated K+ currents, and ATP levels toward normal. MB improved mitochondrial membrane potential (∆ψm) and oxygen consumption rate in myocytes in which Complex I was blocked by rotenone. We conclude that MB ameliorated H2S-induced cardiomyocyte toxicity at multiple levels: (1) reversing excitation-contraction coupling defects (Ca2+ homeostasis and L-type Ca2+ channels); (2) reducing risks of arrhythmias (Em, APD, INaCa and depolarization-activated K+ currents); and (3) improving cellular bioenergetics (ATP, ∆ψm).
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MESH Headings
- Action Potentials
- Adenosine Triphosphate/metabolism
- Animals
- Arrhythmias, Cardiac/chemically induced
- Arrhythmias, Cardiac/metabolism
- Arrhythmias, Cardiac/physiopathology
- Arrhythmias, Cardiac/prevention & control
- Calcium Channels, L-Type/drug effects
- Calcium Channels, L-Type/metabolism
- Calcium Signaling/drug effects
- Energy Metabolism/drug effects
- Heart Rate/drug effects
- Hydrogen Sulfide/toxicity
- Ion Channels/drug effects
- Ion Channels/metabolism
- Membrane Potential, Mitochondrial/drug effects
- Methylene Blue/pharmacology
- Mice
- Mitochondria, Heart/drug effects
- Mitochondria, Heart/metabolism
- Myocardial Contraction/drug effects
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Oxygen Consumption/drug effects
- Potassium Channels, Voltage-Gated/drug effects
- Potassium Channels, Voltage-Gated/metabolism
- Sodium-Calcium Exchanger/drug effects
- Sodium-Calcium Exchanger/metabolism
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Affiliation(s)
- Joseph Y Cheung
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA.
- Department of Medicine, Lewis Katz School of Medicine of Temple University, Philadelphia, PA, 19140, USA.
| | - JuFang Wang
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Xue-Qian Zhang
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Jianliang Song
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - John M Davidyock
- Department of Medicine, Lewis Katz School of Medicine of Temple University, Philadelphia, PA, 19140, USA
| | - Fabian Jana Prado
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Santhanam Shanmughapriya
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Alison M Worth
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Muniswamy Madesh
- Center of Translational Medicine, Lewis Katz School of Medicine of Temple University, 3500 N. Broad Street, MERB 958, Philadelphia, PA, 19140, USA
| | - Annick Judenherc-Haouzi
- Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
| | - Philippe Haouzi
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Pennsylvania State University College of Medicine, Hershey, PA, 17033, USA
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5
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Hormonal regulation of Na +-K +-ATPase from the evolutionary perspective. CURRENT TOPICS IN MEMBRANES 2019; 83:315-351. [PMID: 31196608 DOI: 10.1016/bs.ctm.2019.01.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Na+-K+-ATPase, an α/β heterodimer, is an ancient enzyme that maintains Na+ and K+ gradients, thus preserving cellular ion homeostasis. In multicellular organisms, this basic housekeeping function is integrated to fulfill the needs of specialized organs and preserve whole-body homeostasis. In vertebrates, Na+-K+-ATPase is essential for many fundamental physiological processes, such as nerve conduction, muscle contraction, nutrient absorption, and urine excretion. During vertebrate evolution, three key developments contributed to diversification and integration of Na+-K+-ATPase functions. Generation of novel α- and β-subunits led to formation of multiple Na+-K+-ATPase isoenyzmes with distinct functional characteristics. Development of a complex endocrine system enabled efficient coordination of diverse Na+-K+-ATPase functions. Emergence of FXYDs, small transmembrane proteins that regulate Na+-K+-ATPase, opened new ways to modulate its function. FXYDs are a vertebrate innovation and an important site of hormonal action, suggesting they played an especially prominent role in evolving interaction between Na+-K+-ATPase and the endocrine system in vertebrates.
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6
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van Opbergen CJ, van der Voorn SM, Vos MA, de Boer TP, van Veen TA. Cardiac Ca2+ signalling in zebrafish: Translation of findings to man. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 138:45-58. [DOI: 10.1016/j.pbiomolbio.2018.05.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 04/09/2018] [Accepted: 05/04/2018] [Indexed: 02/07/2023]
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7
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Cheung JY, Wang J, Zhang XQ, Song J, Tomar D, Madesh M, Judenherc-Haouzi A, Haouzi P. Methylene blue counteracts cyanide cardiotoxicity: cellular mechanisms. J Appl Physiol (1985) 2018; 124:1164-1176. [PMID: 29420146 PMCID: PMC6050200 DOI: 10.1152/japplphysiol.00967.2017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 01/09/2018] [Accepted: 02/01/2018] [Indexed: 11/22/2022] Open
Abstract
In adult left ventricular mouse myocytes, exposure to sodium cyanide (NaCN) in the presence of glucose dose-dependently reduced contraction amplitude, with ~80% of maximal inhibitory effect attained at 100 µM. NaCN (100 µM) exposure for 10 min significantly decreased contraction and intracellular Ca2+ concentration ([Ca2+]i) transient amplitudes, systolic but not diastolic [Ca2+]i, and maximal L-type Ca2+ current ( ICa) amplitude, indicating acute alteration of [Ca2+]i homeostasis largely accounted for the observed excitation-contraction abnormalities. In addition, NaCN depolarized resting membrane potential ( Em), reduced action potential (AP) amplitude, prolonged AP duration at 50% (APD50) and 90% repolarization (APD90), and suppressed depolarization-activated K+ currents but had no effect on Na+-Ca2+ exchange current ( INaCa). NaCN did not affect cellular adenosine triphosphate levels but depolarized mitochondrial membrane potential (ΔΨm) and increased superoxide (O2·-) levels. Methylene blue (MB; 20 µg/ml) added 3 min after NaCN restored contraction and [Ca2+]i transient amplitudes, systolic [Ca2+]i, Em, AP amplitude, APD50, APD90, ICa, depolarization-activated K+ currents, ΔΨm, and O2·- levels toward normal. We conclude that MB reversed NaCN-induced cardiotoxicity by preserving intracellular Ca2+ homeostasis and excitation-contraction coupling ( ICa), minimizing risks of arrhythmias ( Em, AP configuration, and depolarization-activated K+ currents), and reducing O2·- levels. NEW & NOTEWORTHY Cyanide poisoning due to industrial exposure, smoke inhalation, and bioterrorism manifests as cardiogenic shock and requires rapidly effective antidote. In the early stage of cyanide exposure, adenosine triphosphate levels are normal but myocyte contractility is reduced, largely due to alterations in Ca2+ homeostasis because of changes in oxidation-reduction environment of ion channels. Methylene blue, a drug approved by the U.S. Food and Drug Administration, ameliorates cyanide toxicity by normalizing oxidation-reduction state and Ca2+ channel function.
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Affiliation(s)
- Joseph Y Cheung
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
- Department of Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - JuFang Wang
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - Xue-Qian Zhang
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - Jianliang Song
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - Dhanendra Tomar
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - Muniswamy Madesh
- Center of Translational Medicine, Lewis Katz School of Medicine, Temple University , Philadelphia, Pennsylvania
| | - Annick Judenherc-Haouzi
- Heart and Vascular Institute, Pennsylvania State University College of Medicine , Hershey, Pennsylvania
| | - Philippe Haouzi
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Pennsylvania State University College of Medicine , Hershey, Pennsylvania
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8
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Lariccia V, Amoroso S. Calcium- and ATP-dependent regulation of Na/Ca exchange function in BHK cells: Comparison of NCX1 and NCX3 exchangers. Cell Calcium 2018; 73:95-103. [PMID: 29705719 DOI: 10.1016/j.ceca.2018.04.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 04/16/2018] [Indexed: 12/27/2022]
Abstract
Na+/Ca2+ exchangers (NCX) mediate bidirectional Ca2+ fluxes across cell membranes and contribute to Ca2+ homeostasis in many cell types. Exchangers are regulated by gating reactions that depend on Na+ and Ca2+ binding to transport and regulatory sites. A Na+i-dependent inactivation is prominent in all isoforms, whereas Ca2+i-dependent regulation varies among isoforms. Here we characterize new details of NCX operation and describe differences and similarities between NCX3 and NCX1 regulation by intracellular Ca2+ and ATP. To compare isoforms, we employed BHK cells expressing NCX3 or NCX1 constitutively and exchange activity was analysed in whole-cell and excised patch recordings under "zero-trans" conditions (i.e., with only one transported ion species on each side). Using BHK cells with low cytoplasmic Ca2+ buffering, outward (reverse) currents, reflecting Ca2+ influx, are activated by applying extracellular Ca2+ (Cao) in the presence of Na+ on the cytoplasmic side. When firstly activated, peak outward NCX3 currents rapidly decay over seconds and then typically develop a secondary transient peak with slower kinetics, until Cao removal abolishes all outward current. The delayed rise of outward current is the signature of an activating process since peak outward NCX3 currents elicited at subsequent Cao bouts remain stimulated for minutes and slower decline towards a non-zero level during continued Cao application. Secondary transient peaks and current stimulation are suppressed by increasing the intracellular Ca2+ buffer capacity or by replacing cytoplasmic ATP with the analogues AMP-PNP or ATPγS. In BHK cells expressing NCX1, outward currents activated under identical settings decay to a steady-state level during single Cao application and are significantly larger, causing strong and long-lived run down of subsequent outward currents. NCX1 current run down is not prevented by increasing cytoplasmic Ca2+ buffering but secondary transient peaks in the outward current profile can be resolved in the presence of ATP. Finally, inward currents recorded in patches excised from NCX3-expressing cells reveal a proteolysis-sensitive, Ca-dependent inactivation process that is unusual for NCX1 forward activity. Together, our results suggest that NCX function is regulated more richly than appreciated heretofore, possibly including processes that are lost in excised membrane patches.
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Affiliation(s)
- Vincenzo Lariccia
- Department of Biomedical Science and Public Health, School of Medicine, University "Politecnica delle Marche", Ancona, Italy.
| | - Salvatore Amoroso
- Department of Biomedical Science and Public Health, School of Medicine, University "Politecnica delle Marche", Ancona, Italy.
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Lubelwana Hafver T, Wanichawan P, Manfra O, de Souza GA, Lunde M, Martinsen M, Louch WE, Sejersted OM, Carlson CR. Mapping the in vitro interactome of cardiac sodium (Na + )-calcium (Ca 2+ ) exchanger 1 (NCX1). Proteomics 2017; 17. [PMID: 28755400 DOI: 10.1002/pmic.201600417] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 07/03/2017] [Accepted: 07/26/2017] [Indexed: 11/07/2022]
Abstract
The sodium (Na+ )-calcium (Ca2+ ) exchanger 1 (NCX1) is an antiporter membrane protein encoded by the SLC8A1 gene. In the heart, it maintains cytosolic Ca2+ homeostasis, serving as the primary mechanism for Ca2+ extrusion during relaxation. Dysregulation of NCX1 is observed in end-stage human heart failure. In this study, we used affinity purification coupled with MS in rat left ventricle lysates to identify novel NCX1 interacting proteins in the heart. Two screens were conducted using: (1) anti-NCX1 against endogenous NCX1 and (2) anti-His (where His is histidine) with His-trigger factor-NCX1cyt recombinant protein as bait. The respective methods identified 112 and 350 protein partners, of which several were known NCX1 partners from the literature, and 29 occurred in both screens. Ten novel protein partners (DYRK1A, PPP2R2A, SNTB1, DMD, RABGGTA, DNAJB4, BAG3, PDE3A, POPDC2, STK39) were validated for binding to NCX1, and two partners (DYRK1A, SNTB1) increased NCX1 activity when expressed in HEK293 cells. A cardiac NCX1 protein-protein interaction map was constructed. The map was highly connected, containing distinct clusters of proteins with different biological functions, where "cell communication" and "signal transduction" formed the largest clusters. The NCX1 interactome was also significantly enriched with proteins/genes involved in "cardiovascular disease" which can be explored as novel drug targets in future research.
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Affiliation(s)
- Tandekile Lubelwana Hafver
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Pimthanya Wanichawan
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Ornella Manfra
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Gustavo Antonio de Souza
- Department of Immunology and Centre for Immune Regulation, Oslo University Hospital HF Rikshospitalet, University of Oslo, Oslo, Norway.,The Brain Institute, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil.,Bioinformatics Multidisciplinary Environment, Instituto Metrópole Digital, UFRN, Natal, RN, Brazil
| | - Marianne Lunde
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Marita Martinsen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - William Edward Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Ole Mathias Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
| | - Cathrine Rein Carlson
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
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10
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Ang SY, Uebersohn A, Spencer CI, Huang Y, Lee JE, Ge K, Bruneau BG. KMT2D regulates specific programs in heart development via histone H3 lysine 4 di-methylation. Development 2016; 143:810-21. [PMID: 26932671 PMCID: PMC4813342 DOI: 10.1242/dev.132688] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
KMT2D, which encodes a histone H3K4 methyltransferase, has been implicated in human congenital heart disease in the context of Kabuki syndrome. However, its role in heart development is not understood. Here, we demonstrate a requirement for KMT2D in cardiac precursors and cardiomyocytes during cardiogenesis in mice. Gene expression analysis revealed downregulation of ion transport and cell cycle genes, leading to altered calcium handling and cell cycle defects. We further determined that myocardial Kmt2d deletion led to decreased H3K4me1 and H3K4me2 at enhancers and promoters. Finally, we identified KMT2D-bound regions in cardiomyocytes, of which a subset was associated with decreased gene expression and decreased H3K4me2 in mutant hearts. This subset included genes related to ion transport, hypoxia-reoxygenation and cell cycle regulation, suggesting that KMT2D is important for these processes. Our findings indicate that KMT2D is essential for regulating cardiac gene expression during heart development primarily via H3K4 di-methylation. Highlighted article: Cardiac-specific depletion of the H3K4 methyltransferase KMT2D causes dysregulation of genes associated with cell cycle regulation, ion homeostasis and hypoxia signaling.
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Affiliation(s)
- Siang-Yun Ang
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA Roddenberry Center for Stem Cell Biology and Medicine at Gladstone, San Francisco, CA 94158, USA Biomedical Sciences Graduate Program, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Alec Uebersohn
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA Roddenberry Center for Stem Cell Biology and Medicine at Gladstone, San Francisco, CA 94158, USA
| | - C Ian Spencer
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA Roddenberry Center for Stem Cell Biology and Medicine at Gladstone, San Francisco, CA 94158, USA
| | - Yu Huang
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA Roddenberry Center for Stem Cell Biology and Medicine at Gladstone, San Francisco, CA 94158, USA
| | - Ji-Eun Lee
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Kai Ge
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - Benoit G Bruneau
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94158, USA Roddenberry Center for Stem Cell Biology and Medicine at Gladstone, San Francisco, CA 94158, USA Biomedical Sciences Graduate Program, University of California, San Francisco, San Francisco, CA 94158, USA Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143, USA Department of Pediatrics, University of California, San Francisco, San Francisco, CA 94143, USA
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Development of a high-affinity peptide that prevents phospholemman (PLM) inhibition of the sodium/calcium exchanger 1 (NCX1). Biochem J 2016; 473:2413-23. [PMID: 27247424 PMCID: PMC4964977 DOI: 10.1042/bcj20160465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 05/31/2016] [Indexed: 11/17/2022]
Abstract
NCX1 (Na+/Ca2+ exchanger 1) is an important regulator of intracellular Ca2+ and a potential therapeutic target for brain ischaemia and for diastolic heart failure with preserved ejection fraction. PLM (phospholemman), a substrate for protein kinases A and C, has been suggested to regulate NCX1 activity. However, although several studies have demonstrated that binding of phosphorylated PLM (pSer68-PLM) leads to NCX1 inhibition, other studies have failed to demonstrate a functional interaction of these proteins. In the present study, we aimed to analyse the biological function of the pSer68-PLM–NCX1 interaction by developing high-affinity blocking peptides. PLM was observed to co-fractionate and co-immunoprecipitate with NCX1 in rat left ventricle, and in co-transfected HEK (human embryonic kidney)-293 cells. For the first time, the NCX1–PLM interaction was also demonstrated in the brain. PLM binding sites on NCX1 were mapped to two regions by peptide array assays, containing the previously reported PASKT and QKHPD motifs. Conversely, the two NCX1 regions bound identical sequences in the cytoplasmic domain of PLM, suggesting that NCX1-PASKT and NCX1-QKHPD might bind to each PLM monomer. Using two-dimensional peptide arrays of the native NCX1 sequence KHPDKEIEQLIELANYQVLS revealed that double substitution of tyrosine for positions 1 and 4 (K1Y and D4Y) enhanced pSer68-PLM binding 8-fold. The optimized peptide blocked binding of NCX1-PASKT and NCX1-QKHPD to PLM and reversed PLM(S68D) inhibition of NCX1 activity (both forward and reverse mode) in HEK-293 cells. Altogether our data indicate that PLM interacts directly with NCX1 and inhibits NCX1 activity when phosphorylated at Ser68.
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Feldman AM, Gordon J, Wang J, Song J, Zhang XQ, Myers VD, Tilley DG, Gao E, Hoffman NE, Tomar D, Madesh M, Rabinowitz J, Koch WJ, Su F, Khalili K, Cheung JY. BAG3 regulates contractility and Ca(2+) homeostasis in adult mouse ventricular myocytes. J Mol Cell Cardiol 2016; 92:10-20. [PMID: 26796036 PMCID: PMC4789075 DOI: 10.1016/j.yjmcc.2016.01.015] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Revised: 01/14/2016] [Accepted: 01/17/2016] [Indexed: 12/22/2022]
Abstract
Bcl2-associated athanogene 3 (BAG3) is a 575 amino acid anti-apoptotic protein that is constitutively expressed in the heart. BAG3 mutations, including mutations leading to loss of protein, are associated with familial cardiomyopathy. Furthermore, BAG3 levels have been found to be reduced in end-stage non-familial failing myocardium. In contrast to neonatal myocytes in which BAG3 is found in the cytoplasm and involved in protein quality control and apoptosis, in adult mouse left ventricular (LV) myocytes BAG3 co-localized with Na(+)-K(+)-ATPase and L-type Ca(2+) channels in the sarcolemma and t-tubules. BAG3 co-immunoprecipitated with β1-adrenergic receptor, L-type Ca(2+) channels and phospholemman. To simulate decreased BAG3 protein levels observed in human heart failure, we targeted BAG3 by shRNA (shBAG3) in adult LV myocytes. Reducing BAG3 by 55% resulted in reduced contraction and [Ca(2+)]i transient amplitudes in LV myocytes stimulated with isoproterenol. L-type Ca(2+) current (ICa) and sarcoplasmic reticulum (SR) Ca(2+) content but not Na(+)/Ca(2+) exchange current (INaCa) or SR Ca(2+) uptake were reduced in isoproterenol-treated shBAG3 myocytes. Forskolin or dibutyryl cAMP restored ICa amplitude in shBAG3 myocytes to that observed in WT myocytes, consistent with BAG3 having effects upstream and at the level of the receptor. Resting membrane potential and action potential amplitude were unaffected but APD50 and APD90 were prolonged in shBAG3 myocytes. Protein levels of Ca(2+) entry molecules and other important excitation-contraction proteins were unchanged in myocytes with lower BAG3. Our findings that BAG3 is localized at the sarcolemma and t-tubules while modulating myocyte contraction and action potential duration through specific interaction with the β1-adrenergic receptor and L-type Ca(2+) channel provide novel insight into the role of BAG3 in cardiomyopathies and increased arrhythmia risks in heart failure.
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MESH Headings
- Action Potentials/drug effects
- Adaptor Proteins, Signal Transducing/biosynthesis
- Adaptor Proteins, Signal Transducing/genetics
- Animals
- Apoptosis Regulatory Proteins/biosynthesis
- Apoptosis Regulatory Proteins/genetics
- Arrhythmias, Cardiac/genetics
- Arrhythmias, Cardiac/metabolism
- Arrhythmias, Cardiac/pathology
- Calcium/metabolism
- Calcium Channels, L-Type/metabolism
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Dilated/metabolism
- Cardiomyopathy, Dilated/pathology
- Excitation Contraction Coupling
- Heart Failure/genetics
- Heart Failure/metabolism
- Heart Failure/pathology
- Heart Ventricles/metabolism
- Heart Ventricles/pathology
- Homeostasis
- Humans
- Isoproterenol/administration & dosage
- Membrane Proteins/metabolism
- Mice
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Phosphoproteins/metabolism
- RNA, Small Interfering/genetics
- Receptors, Adrenergic, beta-1/metabolism
- Sarcolemma/metabolism
- Sodium-Potassium-Exchanging ATPase/metabolism
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Affiliation(s)
- Arthur M Feldman
- Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA; Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Jennifer Gordon
- Comprehensive NeuroAIDS Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - JuFang Wang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Jianliang Song
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Xue-Qian Zhang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Valerie D Myers
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Douglas G Tilley
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Erhe Gao
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Nicholas E Hoffman
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Dhanendra Tomar
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Muniswamy Madesh
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Joseph Rabinowitz
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Walter J Koch
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Feifei Su
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA 19140, USA; Department of Cardiology, Tangdu Hospital, the Fourth Military Medical University, Xi'an, China
| | - Kamel Khalili
- Comprehensive NeuroAIDS Center, Temple University School of Medicine, Philadelphia, PA 19140, USA
| | - Joseph Y Cheung
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA; Department of Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
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13
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Hafver TL, Hodne K, Wanichawan P, Aronsen JM, Dalhus B, Lunde PK, Lunde M, Martinsen M, Enger UH, Fuller W, Sjaastad I, Louch WE, Sejersted OM, Carlson CR. Protein Phosphatase 1c Associated with the Cardiac Sodium Calcium Exchanger 1 Regulates Its Activity by Dephosphorylating Serine 68-phosphorylated Phospholemman. J Biol Chem 2015; 291:4561-79. [PMID: 26668322 DOI: 10.1074/jbc.m115.677898] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Indexed: 11/06/2022] Open
Abstract
The sodium (Na(+))-calcium (Ca(2+)) exchanger 1 (NCX1) is an important regulator of intracellular Ca(2+) homeostasis. Serine 68-phosphorylated phospholemman (pSer-68-PLM) inhibits NCX1 activity. In the context of Na(+)/K(+)-ATPase (NKA) regulation, pSer-68-PLM is dephosphorylated by protein phosphatase 1 (PP1). PP1 also associates with NCX1; however, the molecular basis of this association is unknown. In this study, we aimed to analyze the mechanisms of PP1 targeting to the NCX1-pSer-68-PLM complex and hypothesized that a direct and functional NCX1-PP1 interaction is a prerequisite for pSer-68-PLM dephosphorylation. Using a variety of molecular techniques, we show that PP1 catalytic subunit (PP1c) co-localized, co-fractionated, and co-immunoprecipitated with NCX1 in rat cardiomyocytes, left ventricle lysates, and HEK293 cells. Bioinformatic analysis, immunoprecipitations, mutagenesis, pulldown experiments, and peptide arrays constrained PP1c anchoring to the K(I/V)FF motif in the first Ca(2+) binding domain (CBD) 1 in NCX1. This binding site is also partially in agreement with the extended PP1-binding motif K(V/I)FF-X5-8Φ1Φ2-X8-9-R. The cytosolic loop of NCX1, containing the K(I/V)FF motif, had no effect on PP1 activity in an in vitro assay. Dephosphorylation of pSer-68-PLM in HEK293 cells was not observed when NCX1 was absent, when the K(I/V)FF motif was mutated, or when the PLM- and PP1c-binding sites were separated (mimicking calpain cleavage of NCX1). Co-expression of PLM and NCX1 inhibited NCX1 current (both modes). Moreover, co-expression of PLM with NCX1(F407P) (mutated K(I/V)FF motif) resulted in the current being completely abolished. In conclusion, NCX1 is a substrate-specifying PP1c regulator protein, indirectly regulating NCX1 activity through pSer-68-PLM dephosphorylation.
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Affiliation(s)
- Tandekile Lubelwana Hafver
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Kjetil Hodne
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway, the Department of Basic Sciences and Aquatic Medicine, Norwegian University of Life Sciences (NMBU), 0454 Oslo, Norway
| | - Pimthanya Wanichawan
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Jan Magnus Aronsen
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the Bjørknes College, Oslo, Norway
| | - Bjørn Dalhus
- the Department of Microbiology, Oslo University Hospital, Rikshospitalet, 0424 Oslo, Norway, the Department of Medical Biochemistry, Institute for Clinical Medicine, University of Oslo, 0424 Oslo, Norway and
| | - Per Kristian Lunde
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Marianne Lunde
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Marita Martinsen
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Ulla Helene Enger
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - William Fuller
- the Cardiovascular and Diabetes Medicine, School of Medicine, University of Dundee, Dundee, Scotland, United Kingdom DD1 9SY
| | - Ivar Sjaastad
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - William Edward Louch
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Ole Mathias Sejersted
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway
| | - Cathrine Rein Carlson
- From the Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0450 Oslo, Norway, the KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, 0316 Oslo, Norway,
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14
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Zhang XQ, Wang J, Song J, Rabinowitz J, Chen X, Houser SR, Peterson BZ, Tucker AL, Feldman AM, Cheung JY. Regulation of L-type calcium channel by phospholemman in cardiac myocytes. J Mol Cell Cardiol 2015; 84:104-11. [PMID: 25918050 PMCID: PMC4468006 DOI: 10.1016/j.yjmcc.2015.04.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 03/24/2015] [Accepted: 04/21/2015] [Indexed: 11/26/2022]
Abstract
We evaluated whether phospholemman (PLM) regulates L-type Ca(2+) current (ICa) in mouse ventricular myocytes. Expression of α1-subunit of L-type Ca(2+) channels between wild-type (WT) and PLM knockout (KO) hearts was similar. Compared to WT myocytes, peak ICa (at -10 mV) from KO myocytes was ~41% larger, the inactivation time constant (τ(inact)) of ICa was ~39% longer, but deactivation time constant (τ(deact)) was similar. In the presence of isoproterenol (1 μM), peak ICa was ~48% larger and τ(inact) was ~144% higher in KO myocytes. With Ba(2+) as the permeant ion, PLM enhanced voltage-dependent inactivation but had no effect on τ(deact). To dissect the molecular determinants by which PLM regulated ICa, we expressed PLM mutants by adenovirus-mediated gene transfer in cultured KO myocytes. After 24h in culture, KO myocytes expressing green fluorescent protein (GFP) had significantly larger peak ICa and longer τ(inact) than KO myocytes expressing WT PLM; thereby independently confirming the observations in freshly isolated myocytes. Compared to KO myocytes expressing GFP, KO myocytes expressing the cytoplasmic domain truncation mutant (TM43), the non-phosphorylatable S68A mutant, the phosphomimetic S68E mutant, and the signature PFXYD to alanine (ALL5) mutant all resulted in lower peak ICa. Expressing PLM mutants did not alter expression of α1-subunit of L-type Ca(2+) channels in cultured KO myocytes. Our results suggested that both the extracellular PFXYD motif and the transmembrane domain of PLM but not the cytoplasmic tail were necessary for regulation of peak ICa amplitude. We conclude that PLM limits Ca(2+) influx in cardiac myocytes by reducing maximal ICa and accelerating voltage-dependent inactivation.
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Affiliation(s)
- Xue-Qian Zhang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA
| | - JuFang Wang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA
| | - Jianliang Song
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA
| | - Joseph Rabinowitz
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA
| | - Xiongwen Chen
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA, USA
| | - Steven R Houser
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA, USA
| | - Blaise Z Peterson
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Amy L Tucker
- Cardiovascular Division, Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, VA, USA
| | - Arthur M Feldman
- Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, PA, USA
| | - Joseph Y Cheung
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA.
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15
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Guo K, Wang YP, Zhou ZW, Jiang YB, Li W, Chen XM, Li YG. Impact of phosphomimetic and non-phosphorylatable mutations of phospholemman on L-type calcium channels gating in HEK 293T cells. J Cell Mol Med 2015; 19:642-50. [PMID: 25656605 PMCID: PMC4369820 DOI: 10.1111/jcmm.12484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Accepted: 10/10/2014] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND Phospholemman (PLM) is an important phosphorylation substrate for protein kinases A and C in the heart. Until now, the association between PLM phosphorylation status and L-type calcium channels (LTCCs) gating has not been fully understood. We investigated the kinetics of LTCCs in HEK 293T cells expressing phosphomimetic or nonphosphorylatable PLM mutants. METHODS The LTCCs gating was measured in HEK 293T cells transfected with LTCC and wild-type (WT) PLM, phosphomimetic or nonphosphorylatable PLM mutants: 6263AA, 6869AA, AAAA, 6263DD, 6869DD or DDDD. RESULTS WT PLM significantly slowed LTCCs activation and deactivation while enhanced voltage-dependent inactivation (VDI). PLM mutants 6869DD and DDDD significantly increased the peak of the currents. 6263DD accelerated channel activation, while 6263AA slowed it more than WT PLM. 6869DD significantly enhanced PLM-induced increase of VDI. AAAA slowed the channel activation more than 6263AA, and DDDD accelerated the channel VDI more than 6869DD. CONCLUSIONS Our results demonstrate that phosphomimetic PLM could stimulate LTCCs and alter their dynamics, while PLM nonphosphorylatable mutant produced the opposite effects.
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Affiliation(s)
- Kai Guo
- Department of Cardiology, Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China
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16
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Boguslavskyi A, Pavlovic D, Aughton K, Clark JE, Howie J, Fuller W, Shattock MJ. Cardiac hypertrophy in mice expressing unphosphorylatable phospholemman. Cardiovasc Res 2014; 104:72-82. [PMID: 25103111 PMCID: PMC4174889 DOI: 10.1093/cvr/cvu182] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
AIMS Elevation of intracellular Na in the failing myocardium contributes to contractile dysfunction, the negative force-frequency relationship, and arrhythmias. Although phospholemman (PLM) is recognized to form the link between signalling pathways and Na/K pump activity, the possibility that defects in its regulation contribute to elevation of intracellular Na has not been investigated. Our aim was to test the hypothesis that the prevention of PLM phosphorylation in a PLM(3SA) knock-in mouse (in which PLM has been rendered unphosphorylatable) will exacerbate cardiac hypertrophy and cellular Na overload. Testing this hypothesis should determine whether changes in PLM phosphorylation are simply bystander effects or are causally involved in disease progression. METHODS AND RESULTS In wild-type (WT) mice, aortic constriction resulted in hypophosphorylation of PLM with no change in Na/K pump expression. This under-phosphorylation of PLM occurred at 3 days post-banding and was associated with a progressive decline in Na/K pump current and elevation of [Na]i. Echocardiography, morphometry, and pressure-volume (PV) catheterization confirmed remodelling, dilation, and contractile dysfunction, respectively. In PLM(3SA) mice, expression of Na/K ATPase was increased and PLM decreased such that net Na/K pump current under quiescent conditions was unchanged (cf. WT myocytes); [Na(+)]i was increased and forward-mode Na/Ca exchanger was reduced in paced PLM(3SA) myocytes. Cardiac hypertrophy and Na/K pump inhibition were significantly exacerbated in banded PLM(3SA) mice compared with banded WT. CONCLUSIONS Decreased phosphorylation of PLM reduces Na/K pump activity and exacerbates Na overload, contractile dysfunction, and adverse remodelling following aortic constriction in mice. This suggests a novel therapeutic target for the treatment of heart failure.
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Affiliation(s)
| | - Davor Pavlovic
- Cardiovascular Division, King's College London, London, UK
| | - Karen Aughton
- Cardiovascular Division, King's College London, London, UK
| | - James E Clark
- Cardiovascular Division, King's College London, London, UK
| | - Jacqueline Howie
- Division of Cardiovascular and Diabetes Medicine, University of Dundee, Dundee, UK
| | - William Fuller
- Division of Cardiovascular and Diabetes Medicine, University of Dundee, Dundee, UK
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17
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Wang J, Song J, Gao E, Zhang XQ, Gu T, Yu D, Koch WJ, Feldman AM, Cheung JY. Induced overexpression of phospholemman S68E mutant improves cardiac contractility and mortality after ischemia-reperfusion. Am J Physiol Heart Circ Physiol 2014; 306:H1066-77. [PMID: 24486513 DOI: 10.1152/ajpheart.00861.2013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM), when phosphorylated at Ser(68), inhibits cardiac Na+ / Ca2+ exchanger 1 (NCX1) and relieves its inhibition on Na+ -K+ -ATPase. We have engineered mice in which expression of the phosphomimetic PLM S68E mutant was induced when dietary doxycycline was removed at 5 wk. At 8-10 wk, compared with noninduced or wild-type hearts, S68E expression in induced hearts was ∼35-75% that of endogenous PLM, but protein levels of sarco(endo)plasmic reticulum Ca2+ -ATPase, α1- and α2-subunits of Na+ -K+ -ATPase, α1c-subunit of L-type Ca2+ channel, and phosphorylated ryanodine receptor were unchanged. The NCX1 protein level was increased by ∼47% but the NCX1 current was depressed by ∼34% in induced hearts. Isoproterenol had no effect on NCX1 currents but stimulated Na+ -K+ -ATPase currents equally in induced and noninduced myocytes. At baseline, systolic intracellular Ca2+ concentrations ([Ca2+]i), sarcoplasmic reticulum Ca2+ contents, and [Ca(2+)]i transient and contraction amplitudes were similar between induced and noninduced myocytes. Isoproterenol stimulation resulted in much higher systolic [Ca2+]i, sarcoplasmic reticulum Ca2+ content, and [Ca2+]i transient and contraction amplitudes in induced myocytes. Echocardiography and in vivo close-chest catheterization demonstrated similar baseline myocardial function, but isoproterenol induced a significantly higher +dP/dt in induced compared with noninduced hearts. In contrast to the 50% mortality observed in mice constitutively overexpressing the S68E mutant, induced mice had similar survival as wild-type and noninduced mice. After ischemia-reperfusion, despite similar areas at risk and left ventricular infarct sizes, induced mice had significantly higher +dP/dt and -dP/dt and lower perioperative mortality compared with noninduced mice. We propose that phosphorylated PLM may be a novel therapeutic target in ischemic heart disease.
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Affiliation(s)
- JuFang Wang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania
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18
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Monfredi O, Maltsev VA, Lakatta EG. Modern concepts concerning the origin of the heartbeat. Physiology (Bethesda) 2014; 28:74-92. [PMID: 23455768 DOI: 10.1152/physiol.00054.2012] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Physiological processes governing the heart beat have been under investigation for several hundred years. Major advances have been made in the recent past. A review of the present paradigm is presented here, including a look back at important steps that led us to where we are today, alongside a glimpse into the exciting future of pacemaker research.
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Affiliation(s)
- Oliver Monfredi
- Institute of Cardiovascular Sciences, University of Manchester, Manchester, UK
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19
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Correll RN, Eder P, Burr AR, Despa S, Davis J, Bers DM, Molkentin JD. Overexpression of the Na+/K+ ATPase α2 but not α1 isoform attenuates pathological cardiac hypertrophy and remodeling. Circ Res 2013; 114:249-256. [PMID: 24218169 DOI: 10.1161/circresaha.114.302293] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE The Na+ / K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+ / Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse-mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance. OBJECTIVE To determine whether maintaining lower intracellular Na+ levels by NKA overexpression in the heart would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 to protect the heart. METHODS AND RESULTS Cardiac-specific transgenic mice overexpressing either NKA-α1 or NKA-α2 were generated and subjected to pressure overload hypertrophic stimulation. We found that although increased expression of NKA-α1 had no protective effect, overexpression of NKA-α2 significantly decreased cardiac hypertrophy after pressure overload in mice at 2, 10, and 16 weeks of stimulation. Remarkably, total NKA protein expression and activity were not altered in either of these 2 transgenic models because increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. NKA-α2 overexpression but not NKA-α1 led to significantly faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. Mechanistically, overexpressed NKA-α2 showed greater affinity for Na+ compared with NKA-α1, leading to more efficient clearance of this ion. Furthermore, overexpression of NKA-α2 but not NKA-α1 was coupled to a decrease in phospholemman expression and phosphorylation, which would favor greater NKA activity, NCX1 activity, and Ca2+ removal. CONCLUSIONS Our results suggest that the protective effect produced by increased expression of NKA-α2 on the heart after pressure overload is due to more efficient Ca2+ clearance because this isoform of NKA preferentially enhances NCX1 activity compared with NKA-α1.
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Affiliation(s)
- Robert N Correll
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Petra Eder
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.,Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany
| | - Adam R Burr
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Sanda Despa
- Department of Pharmacology, UC Davis, Davis, California, USA
| | - Jennifer Davis
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Donald M Bers
- Department of Pharmacology, UC Davis, Davis, California, USA
| | - Jeffery D Molkentin
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.,Howard Hughes Medical Institute, Cincinnati, Ohio, USA
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20
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Wang J, Gao E, Chan TO, Zhang XQ, Song J, Shang X, Koch WJ, Feldman AM, Cheung JY. Induced overexpression of Na(+)/Ca(2+) exchanger does not aggravate myocardial dysfunction induced by transverse aortic constriction. J Card Fail 2013; 19:60-70. [PMID: 23273595 DOI: 10.1016/j.cardfail.2012.11.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Revised: 11/06/2012] [Accepted: 11/08/2012] [Indexed: 11/30/2022]
Abstract
BACKGROUND Alterations in expression and activity of cardiac Na(+)/Ca(2+) exchanger (NCX1) have been implicated in the pathogenesis of heart failure. METHODS AND RESULTS Using transgenic mice in which expression of rat NCX1 was induced at 5 weeks of age, we performed transverse aortic constriction (TAC) at 8 weeks and examined cardiac and myocyte function at 15-18 weeks after TAC (age 23-26 weeks). TAC induced left ventricular (LV) and myocyte hypertrophy and increased myocardial fibrosis in both wild-type (WT) and NCX1-overexpressed mice. NCX1 and phosphorylated ryanodine receptor expression was increased by TAC, whereas sarco(endo)plasmic reticulum Ca(2+)-ATPase levels were decreased by TAC. Action potential duration was prolonged by TAC, but to a greater extent in NCX1 myocytes. Na(+)/Ca(2+) exchange current was similar between WT-TAC and WT-sham myocytes, but was higher in NCX1-TAC myocytes. Both myocyte contraction and [Ca(2+)](i) transient amplitudes were reduced in WT-TAC myocytes, but restored to WT-sham levels in NCX1-TAC myocytes. Despite improvement in single myocyte contractility and Ca(2+) dynamics, induced NCX1 overexpression in TAC animals did not ameliorate LV hypertrophy, increase ejection fraction, or enhance inotropic (maximal first derivative of LV pressure rise, +dP/dt) responses to isoproterenol. CONCLUSIONS In pressure-overload hypertrophy, induced overexpression of NCX1 corrected myocyte contractile and [Ca(2+)](i) transient abnormalities but did not aggravate or improve myocardial dysfunction.
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Affiliation(s)
- Jufang Wang
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
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21
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Miller BA, Wang J, Hirschler-Laszkiewicz I, Gao E, Song J, Zhang XQ, Koch WJ, Madesh M, Mallilankaraman K, Gu T, Chen SJ, Keefer K, Conrad K, Feldman AM, Cheung JY. The second member of transient receptor potential-melastatin channel family protects hearts from ischemia-reperfusion injury. Am J Physiol Heart Circ Physiol 2013; 304:H1010-22. [PMID: 23376831 DOI: 10.1152/ajpheart.00906.2012] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The second member of the transient receptor potential-melastatin channel family (TRPM2) is expressed in the heart and vasculature. TRPM2 channels were expressed in the sarcolemma and transverse tubules of adult left ventricular (LV) myocytes. Cardiac TRPM2 channels were functional since activation with H2O2 resulted in Ca(2+) influx that was dependent on extracellular Ca(2+), was significantly higher in wild-type (WT) myocytes compared with TRPM2 knockout (KO) myocytes, and inhibited by clotrimazole in WT myocytes. At rest, there were no differences in LV mass, heart rate, fractional shortening, and +dP/dt between WT and KO hearts. At 2-3 days after ischemia-reperfusion (I/R), despite similar areas at risk and infarct sizes, KO hearts had lower fractional shortening and +dP/dt compared with WT hearts. Compared with WT I/R myocytes, expression of the Na(+)/Ca(2+) exchanger (NCX1) and NCX1 current were increased, expression of the α1-subunit of Na(+)-K(+)-ATPase and Na(+) pump current were decreased, and action potential duration was prolonged in KO I/R myocytes. Post-I/R, intracellular Ca(2+) concentration transients and contraction amplitudes were equally depressed in WT and KO myocytes. After 2 h of hypoxia followed by 30 min of reoxygenation, levels of ROS were significantly higher in KO compared with WT LV myocytes. Compared with WT I/R hearts, oxygen radical scavenging enzymes (SODs) and their upstream regulators (forkhead box transcription factors and hypoxia-inducible factor) were lower, whereas NADPH oxidase was higher, in KO I/R hearts. We conclude that TRPM2 channels protected hearts from I/R injury by decreasing generation and enhancing scavenging of ROS, thereby reducing I/R-induced oxidative stress.
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Affiliation(s)
- Barbara A Miller
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA, USA
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22
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Cheung JY, Zhang XQ, Song J, Gao E, Chan TO, Rabinowitz JE, Koch WJ, Feldman AM, Wang J. Coordinated regulation of cardiac Na(+)/Ca (2+) exchanger and Na (+)-K (+)-ATPase by phospholemman (FXYD1). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:175-90. [PMID: 23224879 DOI: 10.1007/978-1-4614-4756-6_15] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Phospholemman (PLM) is the founding member of the FXYD family of regulators of ion transport. PLM is a 72-amino acid protein consisting of the signature PFXYD motif in the extracellular N terminus, a single transmembrane (TM) domain, and a C-terminal cytoplasmic tail containing three phosphorylation sites. In the heart, PLM co-localizes and co-immunoprecipitates with Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and L-type Ca(2+) channel. The TM domain of PLM interacts with TM9 of the α-subunit of Na(+)-K(+)-ATPase, while its cytoplasmic tail interacts with two small regions (spanning residues 248-252 and 300-304) of the proximal intracellular loop of Na(+)/Ca(2+) exchanger. Under stress, catecholamine stimulation phosphorylates PLM at serine(68), resulting in relief of inhibition of Na(+)-K(+)-ATPase by decreasing K(m) for Na(+) and increasing V(max), and simultaneous inhibition of Na(+)/Ca(2+) exchanger. Enhanced Na(+)-K(+)-ATPase activity lowers intracellular Na(+), thereby minimizing Ca(2+) overload and risks of arrhythmias. Inhibition of Na(+)/Ca(2+) exchanger reduces Ca(2+) efflux, thereby preserving contractility. Thus, the coordinated actions of PLM during stress serve to minimize arrhythmogenesis and maintain inotropy. In acute cardiac ischemia and chronic heart failure, either expression or phosphorylation of PLM or both are altered. PLM regulates important ion transporters in the heart and offers a tempting target for development of drugs to treat heart failure.
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Affiliation(s)
- Joseph Y Cheung
- Center of Translational Medicine, Temple University School of Medicine, Philadelphia, PA 19140, USA.
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23
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Fuller W, Tulloch LB, Shattock MJ, Calaghan SC, Howie J, Wypijewski KJ. Regulation of the cardiac sodium pump. Cell Mol Life Sci 2012; 70:1357-80. [PMID: 22955490 PMCID: PMC3607738 DOI: 10.1007/s00018-012-1134-y] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 07/27/2012] [Accepted: 08/13/2012] [Indexed: 01/24/2023]
Abstract
In cardiac muscle, the sarcolemmal sodium/potassium ATPase is the principal quantitative means of active transport at the myocyte cell surface, and its activity is essential for maintaining the trans-sarcolemmal sodium gradient that drives ion exchange and transport processes that are critical for cardiac function. The 72-residue phosphoprotein phospholemman regulates the sodium pump in the heart: unphosphorylated phospholemman inhibits the pump, and phospholemman phosphorylation increases pump activity. Phospholemman is subject to a remarkable plethora of post-translational modifications for such a small protein: the combination of three phosphorylation sites, two palmitoylation sites, and one glutathionylation site means that phospholemman integrates multiple signaling events to control the cardiac sodium pump. Since misregulation of cytosolic sodium contributes to contractile and metabolic dysfunction during cardiac failure, a complete understanding of the mechanisms that control the cardiac sodium pump is vital. This review explores our current understanding of these mechanisms.
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Affiliation(s)
- W Fuller
- Division of Cardiovascular and Diabetes Medicine, Medical Research Institute, College of Medicine Dentistry and Nursing, University of Dundee, Dundee, UK.
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24
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Moshitzky S, Asher C, Garty H. Intracellular trafficking of FXYD1 (phospholemman) and FXYD7 proteins in Xenopus oocytes and mammalian cells. J Biol Chem 2012; 287:21130-41. [PMID: 22535957 DOI: 10.1074/jbc.m112.347807] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
FXYD proteins are a group of short single-span transmembrane proteins that interact with the Na(+)/K(+) ATPase and modulate its kinetic properties. This study characterizes intracellular trafficking of two FXYD family members, FXYD1 (phospholemman (PLM)) and FXYD7. Surface expression of PLM in Xenopus oocytes requires coexpression with the Na(+)/K(+) ATPase. On the other hand, the Na(+)/Ca(2+) exchanger, another PLM-interacting protein could not drive it to the cell surface. The Na(+)/K(+) ATPase-dependent surface expression of PLM could be facilitated by either a phosphorylation-mimicking mutation at Thr-69 or a truncation of three terminal arginine residues. Unlike PLM, FXYD7 could translocate to the cell surface of Xenopus oocytes independently of the coexpression of α1β1 Na(+)/K(+) ATPase. The Na(+)/K(+) ATPase-independent membrane translocation of FXYD7 requires O-glycosylation of at least two of three conserved threonines in its ectodomain. Subsequent experiments in mammalian cells confirmed the role of conserved extracellular threonine residues and demonstrated that FXYD7 protein, in which these have been mutated to alanine, is trapped in the endoplasmic reticulum and Golgi apparatus.
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Affiliation(s)
- Shiri Moshitzky
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
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25
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Role of protein kinase C in phospholemman mediated regulation of α2β1 isozyme of Na+/K+-ATPase in caveolae of pulmonary artery smooth muscle cells. Biochimie 2012; 94:991-1000. [DOI: 10.1016/j.biochi.2011.12.020] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 12/22/2011] [Indexed: 11/19/2022]
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26
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Mirza MA, Lane S, Yang Z, Karaoli T, Akosah K, Hossack J, McDuffie M, Wang J, Zhang XQ, Song J, Cheung JY, Tucker AL. Phospholemman deficiency in postinfarct hearts: enhanced contractility but increased mortality. Clin Transl Sci 2012; 5:235-42. [PMID: 22686200 DOI: 10.1111/j.1752-8062.2012.00403.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Phospholemman (PLM) regulates [Na(+) ](i), [Ca(2+)](i) and contractility through its interactions with Na(+)-K(+)-ATPase (NKA) and Na(+) /Ca(2+) exchanger (NCX1) in the heart. Both expression and phosphorylation of PLM are altered after myocardial infarction (MI) and heart failure. We tested the hypothesis that absence of PLM regulation of NKA and NCX1 in PLM-knockout (KO) mice is detrimental. Three weeks after MI, wild-type (WT) and PLM-KO hearts were similarly hypertrophied. PLM expression was lower but fractional phosphorylation was higher in WT-MI compared to WT-sham hearts. Left ventricular ejection fraction was severely depressed in WT-MI but significantly less depressed in PLM-KO-MI hearts despite similar infarct sizes. Compared with WT-sham myocytes, the abnormal [Ca(2+) ], transient and contraction amplitudes observed in WT-MI myocytes were ameliorated by genetic absence of PLM. In addition, NCX1 current was depressed in WT-MI but not in PLM-KO-MI myocytes. Despite improved myocardial and myocyte performance, PLM-KO mice demonstrated reduced survival after MI. Our findings indicate that alterations in PLM expression and phosphorylation are important adaptations post-MI, and that complete absence of PLM regulation of NKA and NCX1 is detrimental in post-MI animals.
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Affiliation(s)
- M Ayoub Mirza
- Cardiovascular Division, Department of Medicine, University of Virginia Medical Center, Charlottesville, Virginia, USA
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27
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Petkova-Kirova PS, London B, Salama G, Rasmusson RL, Bondarenko VE. Mathematical modeling mechanisms of arrhythmias in transgenic mouse heart overexpressing TNF-α. Am J Physiol Heart Circ Physiol 2011; 302:H934-52. [PMID: 22081697 DOI: 10.1152/ajpheart.00493.2011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transgenic mice overexpressing tumor necrosis factor-α (TNF-α mice) possess many of the features of human heart failure, such as dilated cardiomyopathy, impaired Ca(2+) handling, arrhythmias, and decreased survival. Although TNF-α mice have been studied extensively with a number of experimental methods, the mechanisms of heart failure are not completely understood. We created a mathematical model that reproduced experimentally observed changes in the action potential (AP) and Ca(2+) handling of isolated TNF-α mice ventricular myocytes. To study the contribution of the differences in ion currents, AP, Ca(2+) handling, and intercellular coupling to the development of arrhythmias in TNF-α mice, we further created several multicellular model tissues with combinations of wild-type (WT)/reduced gap junction conductance, WT/prolonged AP, and WT/decreased Na(+) current (I(Na)) amplitude. All model tissues were examined for susceptibility to Ca(2+) alternans, AP propagation block, and reentry. Our modeling results demonstrated that, similar to experimental data in TNF-α mice, Ca(2+) alternans in TNF-α tissues developed at longer basic cycle lengths. The greater susceptibility to Ca(2+) alternans was attributed to the prolonged AP, resulting in larger inactivation of I(Na), and to the decreased SR Ca(2+) uptake and corresponding smaller SR Ca(2+) load. Simulations demonstrated that AP prolongation induces an increased susceptibility to AP propagation block. Programmed stimulation of the model tissues with a premature impulse showed that reduced gap junction conduction increased the vulnerable window for initiation reentry, supporting the idea that reduced intercellular coupling is the major factor for reentrant arrhythmias in TNF-α mice.
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Affiliation(s)
- Polina S Petkova-Kirova
- Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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28
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Song J, Gao E, Wang J, Zhang XQ, Chan TO, Koch WJ, Shang X, Joseph JI, Peterson BZ, Feldman AM, Cheung JY. Constitutive overexpression of phosphomimetic phospholemman S68E mutant results in arrhythmias, early mortality, and heart failure: potential involvement of Na+/Ca2+ exchanger. Am J Physiol Heart Circ Physiol 2011; 302:H770-81. [PMID: 22081699 DOI: 10.1152/ajpheart.00733.2011] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression and activity of cardiac Na(+)/Ca(2+) exchanger (NCX1) are altered in many disease states. We engineered mice in which the phosphomimetic phospholemman S68E mutant (inhibits NCX1 but not Na(+)-K(+)-ATPase) was constitutively overexpressed in a cardiac-specific manner (conS68E). At 4-6 wk, conS68E mice exhibited severe bradycardia, ventricular arrhythmias, increased left ventricular (LV) mass, decreased cardiac output (CO), and ∼50% mortality compared with wild-type (WT) littermates. Protein levels of NCX1, calsequestrin, ryanodine receptor, and α(1)- and α(2)-subunits of Na(+)-K(+)-ATPase were similar, but sarco(endo)plasmic reticulum Ca(2+)-ATPase was lower, whereas L-type Ca(2+) channels were higher in conS68E hearts. Resting membrane potential and action potential amplitude were similar, but action potential duration was dramatically prolonged in conS68E myocytes. Diastolic intracellular Ca(2+) ([Ca(2+)](i)) was higher, [Ca(2+)](i) transient and maximal contraction amplitudes were lower, and half-time of [Ca(2+)](i) transient decline was longer in conS68E myocytes. Intracellular Na(+) reached maximum within 3 min after isoproterenol addition, followed by decline in WT but not in conS68E myocytes. Na(+)/Ca(2+) exchange, L-type Ca(2+), Na(+)-K(+)-ATPase, and depolarization-activated K(+) currents were decreased in conS68E myocytes. At 22 wk, bradycardia and increased LV mass persisted in conS68E survivors. Despite comparable baseline CO, conS68E survivors at 22 wk exhibited decreased chronotropic, inotropic, and lusitropic responses to isoproterenol. We conclude that constitutive overexpression of S68E mutant was detrimental, both in terms of depressed cardiac function and increased arrhythmogenesis.
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Affiliation(s)
- Jianliang Song
- Division of Nephrology, Thomas Jefferson Univ., 833 Chestnut St., Suite 700, Philadelphia, PA 19107, USA
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29
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Fearnley CJ, Roderick HL, Bootman MD. Calcium signaling in cardiac myocytes. Cold Spring Harb Perspect Biol 2011; 3:a004242. [PMID: 21875987 DOI: 10.1101/cshperspect.a004242] [Citation(s) in RCA: 186] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Calcium (Ca(2+)) is a critical regulator of cardiac myocyte function. Principally, Ca(2+) is the link between the electrical signals that pervade the heart and contraction of the myocytes to propel blood. In addition, Ca(2+) controls numerous other myocyte activities, including gene transcription. Cardiac Ca(2+) signaling essentially relies on a few critical molecular players--ryanodine receptors, voltage-operated Ca(2+) channels, and Ca(2+) pumps/transporters. These moieties are responsible for generating Ca(2+) signals upon cellular depolarization, recovery of Ca(2+) signals following cellular contraction, and setting basal conditions. Whereas these are the central players underlying cardiac Ca(2+) fluxes, networks of signaling mechanisms and accessory proteins impart complex regulation on cardiac Ca(2+) signals. Subtle changes in components of the cardiac Ca(2+) signaling machinery, albeit through mutation, disease, or chronic alteration of hemodynamic demand, can have profound consequences for the function and phenotype of myocytes. Here, we discuss mechanisms underlying Ca(2+) signaling in ventricular and atrial myocytes. In particular, we describe the roles and regulation of key participants involved in Ca(2+) signal generation and reversal.
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Affiliation(s)
- Claire J Fearnley
- Laboratory of Signalling and Cell Fate, The Babraham Institute, Babraham, Cambridge CB22 3AT, United Kingdom
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30
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Zhang XQ, Wang J, Song J, Ji AM, Chan TO, Cheung JY. Residues 248-252 and 300-304 of the cardiac Na+/Ca2+ exchanger are involved in its regulation by phospholemman. Am J Physiol Cell Physiol 2011; 301:C833-40. [PMID: 21734189 PMCID: PMC3191572 DOI: 10.1152/ajpcell.00069.2011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Accepted: 07/05/2011] [Indexed: 11/22/2022]
Abstract
Using split cardiac Na(+)/Ca(2+) exchangers (NCX1), we previously demonstrated that phospholemman (PLM) regulates NCX1 by interacting with the proximal linker domain (residues 218-358) of the intracellular loop of NCX1. With the use of overlapping loop deletion mutants, interaction sites are localized to two regions spanning residues 238-270 and residues 300-328 of NCX1. In this study, we used alanine (Ala) linker scanning to pinpoint the residues in the proximal linker domain involved in regulation of NCX1 by PLM. Transfection of human embryonic kidney (HEK)293 cells with wild-type (WT) NCX1 or its Ala mutants but not empty vector resulted in NCX1 current (I(NaCa)). Coexpression of PLM with WT NCX1 inhibited I(NaCa). Mutating residues 248-252 (PASKT) or 300-304 (QKHPD) in WT NCX1 to Ala resulted in loss of inhibition of I(NaCa) by PLM. By contrast, inhibition of I(NaCa) by PLM was preserved when residues 238-242, 243-247, 253-257, 258-262, 263-267, 305-309, 310-314, 315-319, 320-324, or 325-329 were mutated to Ala. While mutating residue 301 to alanine completely abolished PLM inhibition, mutation of any single residue 250-252, 300, or 302-304 resulted in partial reduction in inhibition. Mutating residues 248-252 to Ala resulted in significantly weaker association with PLM. The NCX1-G503P mutant that lacks Ca(2+)-dependent activation retained its sensitivity to PLM. We conclude that residues 248-252 and 300-304 in the proximal linker domain of NCX1 were involved in its inhibition by PLM.
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Affiliation(s)
- Xue-Qian Zhang
- Division of Nephrology, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
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31
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Tulloch LB, Howie J, Wypijewski KJ, Wilson CR, Bernard WG, Shattock MJ, Fuller W. The inhibitory effect of phospholemman on the sodium pump requires its palmitoylation. J Biol Chem 2011; 286:36020-36031. [PMID: 21868384 DOI: 10.1074/jbc.m111.282145] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM), the principal sarcolemmal substrate for protein kinases A and C in the heart, regulates the cardiac sodium pump. We investigated post-translational modifications of PLM additional to phosphorylation in adult rat ventricular myocytes (ARVM). LC-MS/MS of tryptically digested PLM immunoprecipitated from ARVM identified cysteine 40 as palmitoylated in some peptides, but no information was obtained regarding the palmitoylation status of cysteine 42. PLM palmitoylation was confirmed by immunoprecipitating PLM from ARVM loaded with [(3)H]palmitic acid and immunoblotting following streptavidin affinity purification from ARVM lysates subjected to fatty acyl biotin exchange. Mutagenesis identified both Cys-40 and Cys-42 of PLM as palmitoylated. Phosphorylation of PLM at serine 68 by PKA in ARVM or transiently transfected HEK cells increased its palmitoylation, but PKA activation did not increase the palmitoylation of S68A PLM-YFP in HEK cells. Wild type and unpalmitoylatable PLM-YFP were all correctly targeted to the cell surface membrane, but the half-life of unpalmitoylatable PLM was reduced compared with wild type. In cells stably expressing inducible PLM, PLM expression inhibited the sodium pump, but PLM did not inhibit the sodium pump when palmitoylation was inhibited. Hence, palmitoylation of PLM controls its turnover, and palmitoylated PLM inhibits the sodium pump. Surprisingly, phosphorylation of PLM enhances its palmitoylation, probably through the enhanced mobility of the phosphorylated intracellular domain increasing the accessibility of cysteines for the palmitoylating enzyme, with interesting theoretical implications. All FXYD proteins have conserved intracellular cysteines, so FXYD protein palmitoylation may be a universal means to regulate the sodium pump.
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Affiliation(s)
- Lindsay B Tulloch
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Jacqueline Howie
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Krzysztof J Wypijewski
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Catherine R Wilson
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - William G Bernard
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom
| | - Michael J Shattock
- Cardiovascular Division, The Rayne Institute, St. Thomas' Hospital, King's College London, London SE1 7EH, United Kingdom
| | - William Fuller
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine Dentistry & Nursing, University of Dundee, Dundee DD1 9SY, United Kingdom.
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32
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Wanichawan P, Louch WE, Hortemo KH, Austbø B, Lunde PK, Scott JD, Sejersted OM, Carlson CR. Full-length cardiac Na+/Ca2+ exchanger 1 protein is not phosphorylated by protein kinase A. Am J Physiol Cell Physiol 2011; 300:C989-97. [PMID: 21289289 DOI: 10.1152/ajpcell.00196.2010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cardiac Na(+)/Ca(2+) exchanger 1 (NCX1) is an important regulator of intracellular Ca(2+) homeostasis and cardiac function. Several studies have indicated that NCX1 is phosphorylated by the cAMP-dependent protein kinase A (PKA) in vitro, which increases its activity. However, this finding is controversial and no phosphorylation site has so far been identified. Using bioinformatic analysis and peptide arrays, we screened NCX1 for putative PKA phosphorylation sites. Although several NCX1 synthetic peptides were phosphorylated by PKA in vitro, only one PKA site (threonine 731) was identified after mutational analysis. To further examine whether NCX1 protein could be PKA phosphorylated, wild-type and alanine-substituted NCX1-green fluorescent protein (GFP)-fusion proteins expressed in human embryonic kidney (HEK)293 cells were generated. No phosphorylation of full-length or calpain- or caspase-3 digested NCX1-GFP was observed with purified PKA-C and [γ-(32)P]ATP. Immunoblotting experiments with anti-PKA substrate and phosphothreonine-specific antibodies were further performed to investigate phosphorylation of endogenous NCX1. Phospho-NCX1 levels were also not increased after forskolin or isoproterenol treatment in vivo, in isolated neonatal cardiomyocytes, or in total heart homogenate. These data indicate that the novel in vitro PKA phosphorylation site is inaccessible in full-length as well as in calpain- or caspase-3 digested NCX1 protein, suggesting that NCX1 is not a direct target for PKA phosphorylation.
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Affiliation(s)
- Pimthanya Wanichawan
- Institute for Experimental Medical Research, Oslo Univ. Hospital, Ullevaal, Oslo, Norway.
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33
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Brini M, Carafoli E. The plasma membrane Ca²+ ATPase and the plasma membrane sodium calcium exchanger cooperate in the regulation of cell calcium. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a004168. [PMID: 21421919 DOI: 10.1101/cshperspect.a004168] [Citation(s) in RCA: 204] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Calcium is an ambivalent signal: it is essential for the correct functioning of cell life, but may also become dangerous to it. The plasma membrane Ca(2+) ATPase (PMCA) and the plasma membrane Na(+)/Ca(2+) exchanger (NCX) are the two mechanisms responsible for Ca(2+) extrusion. The NCX has low Ca(2+) affinity but high capacity for Ca(2+) transport, whereas the PMCA has a high Ca(2+) affinity but low transport capacity for it. Thus, traditionally, the PMCA pump has been attributed a housekeeping role in maintaining cytosolic Ca(2+), and the NCX the dynamic role of counteracting large cytosolic Ca(2+) variations (especially in excitable cells). This view of the roles of the two Ca(2+) extrusion systems has been recently revised, as the specific functional properties of the numerous PMCA isoforms and splicing variants suggests that they may have evolved to cover both the basal Ca(2+) regulation (in the 100 nM range) and the Ca(2+) transients generated by cell stimulation (in the μM range).
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Affiliation(s)
- Marisa Brini
- Department of Biological Chemistry, University of Padova, Viale G. Colombo 3, 35131 Padova, Italy.
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34
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Wang J, Gao E, Rabinowitz J, Song J, Zhang XQ, Koch WJ, Tucker AL, Chan TO, Feldman AM, Cheung JY. Regulation of in vivo cardiac contractility by phospholemman: role of Na+/Ca2+ exchange. Am J Physiol Heart Circ Physiol 2010; 300:H859-68. [PMID: 21193587 DOI: 10.1152/ajpheart.00894.2010] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM), when phosphorylated at serine 68, relieves its inhibition on Na(+)-K(+)-ATPase but inhibits Na(+)/Ca(2+) exchanger 1 (NCX1) in cardiac myocytes. Under stress when catecholamine levels are high, enhanced Na(+)-K(+)-ATPase activity by phosphorylated PLM attenuates intracellular Na(+) concentration ([Na(+)](i)) overload. To evaluate the effects of PLM on NCX1 on in vivo cardiac contractility, we injected recombinant adeno-associated virus (serotype 9) expressing either the phosphomimetic PLM S68E mutant or green fluorescent protein (GFP) directly into left ventricles (LVs) of PLM-knockout (KO) mice. Five weeks after virus injection, ∼40% of isolated LV myocytes exhibited GFP fluorescence. Expression of S68E mutant was confirmed with PLM antibody. There were no differences in protein levels of α(1)- and α(2)-subunits of Na(+)-K(+)-ATPase, NCX1, and sarco(endo)plasmic reticulum Ca(2+)-ATPase between KO-GFP and KO-S68E LV homogenates. Compared with KO-GFP myocytes, Na(+)/Ca(2+) exchange current was suppressed, but resting [Na(+)](i), Na(+)-K(+)-ATPase current, and action potential amplitudes were similar in KO-S68E myocytes. Resting membrane potential was slightly lower and action potential duration at 90% repolarization (APD(90)) was shortened in KO-S68E myocytes. Isoproterenol (Iso; 1 μM) increased APD(90) in both groups of myocytes. After Iso, [Na(+)](i) increased monotonically in paced (2 Hz) KO-GFP but reached a plateau in KO-S68E myocytes. Both systolic and diastolic [Ca(2+)](i) were higher in Iso-stimulated KO-S68E myocytes paced at 2 Hz. Echocardiography demonstrated similar resting heart rate, ejection fraction, and LV mass between KO-GFP and KO-S68E mice. In vivo closed-chest catheterization demonstrated enhanced contractility in KO-S68E compared with KO-GFP hearts stimulated with Iso. We conclude that under catecholamine stress when [Na(+)](i) is high, PLM minimizes [Na(+)](i) overload by relieving its inhibition of Na(+)-K(+)-ATPase and preserves inotropy by simultaneously inhibiting Na(+)/Ca(2+) exchanger.
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Affiliation(s)
- Jufang Wang
- Division of Nephrology and Center of Translational Medicine, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
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Cheung JY, Zhang XQ, Song J, Gao E, Rabinowitz JE, Chan TO, Wang J. Phospholemman: a novel cardiac stress protein. Clin Transl Sci 2010; 3:189-96. [PMID: 20718822 DOI: 10.1111/j.1752-8062.2010.00213.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Phospholemman (PLM), a member of the FXYD family of regulators of ion transport, is a major sarcolemmal substrate for protein kinases A and C in cardiac and skeletal muscle. In the heart, PLM co-localizes and co-immunoprecipitates with Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and L-type Ca(2+) channel. Functionally, when phosphorylated at serine(68), PLM stimulates Na(+)-K(+)-ATPase but inhibits Na(+)/Ca(2+) exchanger in cardiac myocytes. In heterologous expression systems, PLM modulates the gating of cardiac L-type Ca(2+) channel. Therefore, PLM occupies a key modulatory role in intracellular Na(+) and Ca(2+) homeostasis and is intimately involved in regulation of excitation-contraction (EC) coupling. Genetic ablation of PLM results in a slight increase in baseline cardiac contractility and prolongation of action potential duration. When hearts are subjected to catecholamine stress, PLM minimizes the risks of arrhythmogenesis by reducing Na(+) overload and simultaneously preserves inotropy by inhibiting Na(+)/Ca(2+) exchanger. In heart failure, both expression and phosphorylation state of PLM are altered and may partly account for abnormalities in EC coupling. The unique role of PLM in regulation of Na(+)-K(+)-ATPase, Na(+)/Ca(2+) exchanger, and potentially L-type Ca(2+) channel in the heart, together with the changes in its expression and phosphorylation in heart failure, make PLM a rational and novel target for development of drugs in our armamentarium against heart failure. Clin Trans Sci 2010; Volume 3: 189-196.
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Affiliation(s)
- Joseph Y Cheung
- Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
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Guo K, Wang X, Gao G, Huang C, Elmslie KS, Peterson BZ. Amino acid substitutions in the FXYD motif enhance phospholemman-induced modulation of cardiac L-type calcium channels. Am J Physiol Cell Physiol 2010; 299:C1203-11. [PMID: 20720179 DOI: 10.1152/ajpcell.00149.2010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have found that phospholemman (PLM) associates with and modulates the gating of cardiac L-type calcium channels (Wang et al., Biophys J 98: 1149-1159, 2010). The short 17 amino acid extracellular NH(2)-terminal domain of PLM contains a highly conserved PFTYD sequence that defines it as a member of the FXYD family of ion transport regulators. Although we have learned a great deal about PLM-dependent changes in calcium channel gating, little is known regarding the molecular mechanisms underlying the observed changes. Therefore, we investigated the role of the PFTYD segment in the modulation of cardiac calcium channels by individually replacing Pro-8, Phe-9, Thr-10, Tyr-11, and Asp-12 with alanine (P8A, F9A, T10A, Y11A, D12A). In addition, Asp-12 was changed to lysine (D12K) and cysteine (D12C). As expected, wild-type PLM significantly slows channel activation and deactivation and enhances voltage-dependent inactivation (VDI). We were surprised to find that amino acid substitutions at Thr-10 and Asp-12 significantly enhanced the ability of PLM to modulate Ca(V)1.2 gating. T10A exhibited a twofold enhancement of PLM-induced slowing of activation, whereas D12K and D12C dramatically enhanced PLM-induced increase of VDI. The PLM-induced slowing of channel closing was abrogated by D12A and D12C, whereas D12K and T10A failed to impact this effect. These studies demonstrate that the PFXYD motif is not necessary for the association of PLM with Ca(V)1.2. Instead, since altering the chemical and/or physical properties of the PFXYD segment alters the relative magnitudes of opposing PLM-induced effects on Ca(V)1.2 channel gating, PLM appears to play an important role in fine tuning the gating kinetics of cardiac calcium channels and likely plays an important role in shaping the cardiac action potential and regulating Ca(2+) dynamics in the heart.
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Affiliation(s)
- Kai Guo
- Cardiovascular Research Institute, Renmin Hospital of Wuhan University, Wuhan, Hubei, China
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Gronich N, Kumar A, Zhang Y, Efimov IR, Soldatov NM. Molecular remodeling of ion channels, exchangers and pumps in atrial and ventricular myocytes in ischemic cardiomyopathy. Channels (Austin) 2010; 4:101-7. [PMID: 20090424 PMCID: PMC2891309 DOI: 10.4161/chan.4.2.10975] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Existing molecular knowledge base of cardiovascular diseases is rudimentary because of lack of specific attribution to cell type and function. The aim of this study was to investigate cell-specific molecular remodeling in human atrial and ventricular myocytes associated with ischemic cardiomyopathy. Our strategy combines two technological innovations, laser-capture microdissection of identified cardiac cells in selected anatomical regions of the heart and splice microarray of a narrow catalog of the functionally most important genes regulating ion homeostasis. We focused on expression of a principal family of genes coding for ion channels, exchangers and pumps (CE&P genes) that are involved in electrical, mechanical and signaling functions of the heart and constitute the most utilized drug targets. We found that (1) CE&P genes remodel in a cell-specific manner: ischemic cardiomyopathy affected 63 CE&P genes in ventricular myocytes and 12 essentially different genes in atrial myocytes. (2) Only few of the identified CE&P genes were previously linked to human cardiac disfunctions. (3) The ischemia-affected CE&P genes include nuclear chloride channels, adrenoceptors, cyclic nucleotide-gated channels, auxiliary subunits of Na(+), K(+) and Ca(2+) channels, and cell-surface CE&Ps. (4) In both atrial and ventricular myocytes ischemic cardiomyopathy reduced expression of CACNG7 and induced overexpression of FXYD1, the gene crucial for Na(+) and K(+) homeostasis. Thus, our cell-specific molecular profiling defined new landmarks for correct molecular modeling of ischemic cardiomyopathy and development of underlying targeted therapies.
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Affiliation(s)
- Naomi Gronich
- National Institute on Aging; National Institutes of health; Baltimore, MD USA
| | - Azad Kumar
- National Institute on Aging; National Institutes of health; Baltimore, MD USA
| | - Yuwei Zhang
- National Institute on Aging; National Institutes of health; Baltimore, MD USA
| | | | - Nikolai M. Soldatov
- National Institute on Aging; National Institutes of health; Baltimore, MD USA
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Abstract
During activation of the sympathetic nervous system, cardiac performance is increased as part of the fight-or-flight stress response. The increase in contractility with sympathetic stimulation is an orchestrated combination of intrinsic inotropic, lusitropic, and chronotropic effects, mediated in part by activation of beta-adrenergic receptors and protein kinase A. This causes phosphorylation of several Ca cycling proteins in cardiac myocytes (increasing Ca entry via L-type Ca channels, sarcoplasmic reticulum Ca pumping, and the dissociation rate of Ca from the myofilaments). Here, we discuss how stimulation of the Na/K-ATPase, mediated by phosphorylation of phospholemman (a small sarcolemmal protein that associates with and modulates Na/K-ATPase), is an additional important player in the sympathetic fight-or-flight response. Enhancement of Na/K- ATPase activity limits the rise in [Na](i) caused by the higher level of Na influx and by doing so limits the rise in cellular and sarcoplasmic reticulum Ca load by favoring Ca extrusion via the Na/Ca exchanger. Thus, phospholemman-mediated activation of the Na/K-ATPase may prevent Ca overload and triggered arrhythmias during stress.
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Wang J, Gao E, Song J, Zhang XQ, Li J, Koch WJ, Tucker AL, Philipson KD, Chan TO, Feldman AM, Cheung JY. Phospholemman and beta-adrenergic stimulation in the heart. Am J Physiol Heart Circ Physiol 2009; 298:H807-15. [PMID: 20008271 DOI: 10.1152/ajpheart.00877.2009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phosphorylation at serine 68 of phospholemman (PLM) in response to beta-adrenergic stimulation results in simultaneous inhibition of cardiac Na(+)/Ca(2+) exchanger NCX1 and relief of inhibition of Na(+)-K(+)-ATPase. The role of PLM in mediating beta-adrenergic effects on in vivo cardiac function was investigated with congenic PLM-knockout (KO) mice. Echocardiography showed similar ejection fraction between wild-type (WT) and PLM-KO hearts. Cardiac catheterization demonstrated higher baseline contractility (+dP/dt) but similar relaxation (-dP/dt) in PLM-KO mice. In response to isoproterenol (Iso), maximal +dP/dt was similar but maximal -dP/dt was reduced in PLM-KO mice. Dose-response curves to Iso (0.5-25 ng) for WT and PLM-KO hearts were superimposable. Maximal +dP/dt was reached 1-2 min after Iso addition and declined with time in WT but not PLM-KO hearts. In isolated myocytes paced at 2 Hz. contraction and intracellular Ca(2+) concentration ([Ca(2+)](i)) transient amplitudes and [Na(+)](i) reached maximum 2-4 min after Iso addition, followed by decline in WT but not PLM-KO myocytes. Reducing pacing frequency to 0.5 Hz resulted in much smaller increases in [Na(+)](i) and no decline in contraction and [Ca(2+)](i) transient amplitudes with time in Iso-stimulated WT and PLM-KO myocytes. Although baseline Na(+)-K(+)-ATPase current was 41% higher in PLM-KO myocytes because of increased alpha(1)- but not alpha(2)-subunit activity, resting [Na(+)](i) was similar between quiescent WT and PLM-KO myocytes. Iso increased alpha(1)-subunit current (I(alpha1)) by 73% in WT but had no effect in PLM-KO myocytes. Iso did not affect alpha(2)-subunit current (I(alpha2)) in WT and PLM-KO myocytes. In both WT and NCX1-KO hearts, PLM coimmunoprecipitated with Na(+)-K(+)-ATPase alpha(1)- and alpha(2)-subunits, indicating that association of PLM with Na(+)-K(+)-ATPase did not require NCX1. We conclude that under stressful conditions in which [Na(+)](i) was high, beta-adrenergic agonist-mediated phosphorylation of PLM resulted in time-dependent reduction in inotropy due to relief of inhibition of Na(+)-K(+)-ATPase.
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Affiliation(s)
- JuFang Wang
- Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Wang J, Chan TO, Zhang XQ, Gao E, Song J, Koch WJ, Feldman AM, Cheung JY. Induced overexpression of Na+/Ca2+ exchanger transgene: altered myocyte contractility, [Ca2+]i transients, SR Ca2+ contents, and action potential duration. Am J Physiol Heart Circ Physiol 2009; 297:H590-601. [PMID: 19525383 DOI: 10.1152/ajpheart.00190.2009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have produced mice in which expression of the rat cardiac Na(+)/Ca(2+) exchanger (NCX1) transgene was switched on when doxycycline was removed from the feed at 5 wk. At 8 to 10 wk, NCX1 expression in induced (Ind) mouse hearts was 2.5-fold higher but protein levels of sarco(endo)plasmic reticulum Ca(2+)-ATPase, alpha(1)- and alpha(2)-subunits of Na(+)-K(+)-ATPase, phospholamban, ryanodine receptor, calsequestrin, and unphosphorylated and phosphorylated phospholemman were unchanged compared with wild-type (WT) or noninduced (non-Ind) hearts. There was no cellular hypertrophy since WT, non-Ind, and Ind myocytes had similar whole cell membrane capacitance. In Ind myocytes, NCX1 current amplitude was approximately 42% higher, L-type Ca(2+) current amplitude was unchanged, and action potential duration was prolonged compared with WT or non-Ind myocytes. Contraction and intracellular Ca(2+) concentration ([Ca(2+)](i)) transient amplitudes in Ind myocytes were lower at 0.6, not different at 1.8, and higher at 5.0 mM extracellular Ca(2+) concentration ([Ca(2+)](o)) compared with WT or non-Ind myocytes. Despite similar Ca(2+) current amplitude and sarcoplasmic reticulum (SR) Ca(2+) uptake, SR Ca(2+) content at 5.0 mM [Ca(2+)](o) was significantly higher in Ind compared with non-Ind myocytes, indicating that NCX1 directly contributed to SR Ca(2+) loading. Echocardiography demonstrated that heart rate, left ventricular mass, ejection fraction, stroke volume, and cardiac output were similar among the three groups of animals. In vivo close-chest catheterization demonstrated similar contractility and relaxation among the three groups of mice, both at baseline and after stimulation with isoproterenol. We conclude that induced expression of NCX1 transgene resulted in altered [Ca(2+)](i) homeostasis, myocyte contractility, and action potential morphology. In addition, heart failure did not occur 3 to 5 wk after NCX1 transgene was induced to be expressed at levels found in diseased hearts.
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Affiliation(s)
- JuFang Wang
- Department of Medicine, Division of Nephrology, Center of Translational Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Zhang XQ, Wang J, Carl LL, Song J, Ahlers BA, Cheung JY. Phospholemman regulates cardiac Na+/Ca2+ exchanger by interacting with the exchanger's proximal linker domain. Am J Physiol Cell Physiol 2009; 296:C911-21. [PMID: 19158404 DOI: 10.1152/ajpcell.00196.2008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM) belongs to the FXYD family of small ion transport regulators. When phosphorylated at Ser(68), PLM inhibits cardiac Na(+)/Ca(2+) exchanger (NCX1). We previously demonstrated that the cytoplasmic tail of PLM interacts with the proximal intracellular loop (residues 218-358), but not the transmembrane (residues 1-217 and 765-938) or Ca(2+)-binding (residues 371-508) domains, of NCX1. In this study, we used intact Na(+)/Ca(2+) exchanger with various deletions in the intracellular loop to map the interaction sites with PLM. We first demonstrated by Western blotting and confocal immunofluorescence microscopy that wild-type (WT) NCX1 and its deletion mutants were expressed in transfected HEK-293 cells. Cotransfection with PLM and NCX1 (or its deletion mutants) in HEK-293 cells did not decrease expression of NCX1 (or its deletion mutants). Coexpression of PLM with WT NCX1 inhibited NCX1 current (I(NaCa)). Deletion of residues 240-679, 265-373, 250-300, or 300-373 from WT NCX1 resulted in loss of inhibition of I(NaCa) by PLM. Inhibition of I(NaCa) by PLM was preserved when residues 229-237, 270-300, 328-330, or 330-373 were deleted from the intracellular loop of NCX1. These results suggest that PLM mediated inhibition of I(NaCa) by interacting with two distinct regions (residues 238-270 and 300-328) of NCX1. Indeed, I(NaCa) measured in mutants lacking residues 238-270, 300-328, or 238-270 + 300-328 was not affected by PLM. Glutathione S-transferase pull-down assays confirmed that PLM bound to fragments corresponding to residues 218-371, 218-320, 218-270, 238-371, and 300-373, but not to fragments encompassing residues 250-300 and 371-508 of NCX1, indicating that residues 218-270 and 300-373 physically associated with PLM. Finally, acute regulation of I(NaCa) by PLM phosphorylation observed with WT NCX1 was absent in 250-300 deletion mutant but preserved in 229-237 deletion mutant. We conclude that PLM mediates its inhibition of NCX1 by interacting with residues 238-270 and 300-328.
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Affiliation(s)
- Xue-Qian Zhang
- Division of Nephrology, Thomas Jefferson Univ., 833 Chestnut St., Suite 700, Philadelphia, PA 19107, USA
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Rao YJ, Xi L. Pivotal effects of phosphodiesterase inhibitors on myocyte contractility and viability in normal and ischemic hearts. Acta Pharmacol Sin 2009; 30:1-24. [PMID: 19060915 DOI: 10.1038/aps.2008.1] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Phosphodiesterases (PDEs) are enzymes that degrade cellular cAMP and cGMP and are thus essential for regulating the cyclic nucleotides. At least 11 families of PDEs have been identified, each with a distinctive structure, activity, expression, and tissue distribution. The PDE type-3, -4, and -5 (PDE3, PDE4, PDE5) are localized to specific regions of the cardiomyocyte, such as the sarcoplasmic reticulum and Z-disc, where they are likely to influence cAMP/cGMP signaling to the end effectors of contractility. Several PDE inhibitors exhibit remarkable hemodynamic and inotropic properties that may be valuable to clinical practice. In particular, PDE3 inhibitors have potent cardiotonic effects that can be used for short-term inotropic support, especially in situations where adrenergic stimulation is insufficient. Most relevant to this review, PDE inhibitors have also been found to have cytoprotective effects in the heart. For example, PDE3 inhibitors have been shown to be cardioprotective when given before ischemic attack, whereas PDE5 inhibitors, which include three widely used erectile dysfunction drugs (sildenafil, vardenafil and tadalafil), can induce remarkable cardioprotection when administered either prior to ischemia or upon reperfusion. This article provides an overview of the current laboratory and clinical evidence, as well as the cellular mechanisms by which the inhibitors of PDE3, PDE4 and PDE5 exert their beneficial effects on normal and ischemic hearts. It seems that PDE inhibitors hold great promise as clinically applicable agents that can improve cardiac performance and cell survival under critical situations, such as ischemic heart attack, cardiopulmonary bypass surgery, and heart failure.
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Kang TM. PKC-Independent Stimulation of Cardiac Na/Ca Exchanger by Staurosporine. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2008; 12:259-65. [PMID: 19967065 DOI: 10.4196/kjpp.2008.12.5.259] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
[Ca(2+)](i) transients by reverse mode of cardiac Na(+)/Ca(2+) exchanger (NCX1) were recorded in fura-2 loaded BHK cells with stable expression of NCX1. Repeated stimulation of reverse NCX1 produced a long-lasting decrease of Ca(2+) transients ('rundown'). Rundown of NCX1 was independent of membrane PIP(2) depletion. Although the activation of protein kinase C (PKC) was observed during the Ca(2+) transients, neither a selective PKC inhibitor (calphostin C) nor a PKC activator (PMA) changed the degrees of rundown. By comparison, a non-specific PKC inhibitor, staurosporine (STS), reversed rundown in a dose-dependent and reversible manner. The action of STS was unaffected by pretreatment of the cells with calphostin C, PMA, or forskolin. Taken together, the results suggest that the stimulation of reverse NCX1 by STS is independent of PKC and/or PKA inhibition.
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Affiliation(s)
- Tong Mook Kang
- Department of Physiology, SBRI, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea
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Rasmussen MK, Kristensen M, Juel C. Exercise-induced regulation of phospholemman (FXYD1) in rat skeletal muscle: implications for Na+/K+-ATPase activity. Acta Physiol (Oxf) 2008; 194:67-79. [PMID: 18373741 DOI: 10.1111/j.1748-1716.2008.01857.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Na(+)/K(+)-ATPase activity is upregulated during muscle exercise to maintain ionic homeostasis. One mechanism may involve movement of alpha-subunits to the outer membrane (translocation). AIM We investigated the existence of exercise-induced translocation and phosphorylation of phospholemman (PLM, FXYD1) protein in rat skeletal muscle and exercise-induced changes in V(max) and K(m) for Na(+) of the Na(+)/K(+)-ATPase. METHODS Two membrane fractionation methods and immunoprecipitation were used. RESULTS Both fractionation methods revealed a 200-350% increase in PLM in the sarcolemma after 30 min of treadmill running, while the phosphorylation of Ser-68 of PLM appeared to be unchanged. Exercise did not change V(max) or K(m) for Na(+) of the Na(+)/K(+)-ATPase in muscle homogenate, but induced a 67% increase in V(max) in the sarcolemmal giant vesicle preparation; K(m) for Na(+) remained constant. The main part of the increase in V(max) is related to a 36-53% increase in the level of alpha-subunits; the remainder may be related to increased PLM content. Similar results were obtained with another membrane purification method. In resting muscle, 29% and 32% of alpha(1)- and alpha(2)-subunits, respectively, were co-immunoprecipitated by PLM antibodies. In muscle homogenate prepared after exercise, immunoprecipitation of alpha(1)-subunits was increased to 227%, whereas the fraction of precipitated alpha(2) remained constant. CONCLUSION Exercise translocates PLM to the muscle outer membrane and increases its association with mainly the alpha(1)-subunit, which may contribute to the increased V(max) of the Na(+)/K(+)-ATPase.
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Affiliation(s)
- M K Rasmussen
- Department of Molecular Biology, Copenhagen Muscle Research Centre, University of Copenhagen, Denmark
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Davis KA, Samson SE, Hammel KE, Kiss L, Fulop F, Grover AK. Functional linkage of Na+-Ca2+-exchanger to sarco/endoplasmic reticulum Ca2+ pump in coronary artery: comparison of smooth muscle and endothelial cells. J Cell Mol Med 2008; 13:1775-1783. [PMID: 18752635 DOI: 10.1111/j.1582-4934.2008.00480.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
An increase in cytosolic Ca(2+) concentration in coronary artery smooth muscle causes a contraction but in endothelium it causes relaxation. Na(+)-Ca(2+)-exchanger (NCX) may play a role in Ca(2+) dynamics in both the cell types. Here, the NCX-mediated (45)Ca(2+) uptake was compared in Na(+)-loaded pig coronary artery smooth muscle and endothelial cells. In both the cell types, this uptake was inhibited by KB-R7943, SEA 0400 and by monensin, but not by cariporide. Prior loading of the cells with the Ca(2+) chelator BAPTA increased the NCX-mediated (45)Ca(2+) uptake in smooth muscle but not in endothelial cells. In the presence or absence of BAPTA loading, the Na(+)-mediated (45)Ca(2+) uptake was greater in endothelial than in smooth muscle cells. In smooth muscle cells without BAPTA loading, thapsigargin diminished the NCX-mediated (45)Ca(2+) entry. This effect was not observed in endothelial cells or in either cell type after BAPTA loading. The results in the smooth muscle cells are consistent with a limited diffusional space model in which the NCX-mediated (45)Ca(2+) uptake was enhanced by chelation of cytosolic Ca(2+) or by its sequestration by the sarco/endoplasmic reticulum Ca(2+) pump (SERCA). They suggest a functional linkage between NCX and SERCA in the smooth muscle but not in the endothelial cells. The concept of a linkage between NCX and SERCA in smooth muscle was also confirmed by similar distribution of NCX and SERCA2 proteins when detergent-treated microsomes were fractionated by flotation on sucrose density gradients. Thus, the coronary artery smooth muscle and endothelial cells differ not only in the relative activities of NCX but also in its functional linkage to SERCA.
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Affiliation(s)
- Kim A Davis
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Sue E Samson
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Kaitlin E Hammel
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Lorand Kiss
- Institute of Pharmaceutical Chemistry, University of Szeged, Szeged, Eotvo, Hungary
| | - Ferenc Fulop
- Institute of Pharmaceutical Chemistry, University of Szeged, Szeged, Eotvo, Hungary
| | - Ashok K Grover
- Department of Biology, McMaster University, Hamilton, Ontario, Canada.,Department of Medicine, McMaster University, Hamilton, Ontario, Canada
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Song J, Zhang XQ, Wang J, Cheskis E, Chan TO, Feldman AM, Tucker AL, Cheung JY. Regulation of cardiac myocyte contractility by phospholemman: Na+/Ca2+ exchange versus Na+ -K+ -ATPase. Am J Physiol Heart Circ Physiol 2008; 295:H1615-25. [PMID: 18708446 DOI: 10.1152/ajpheart.00287.2008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM) regulates cardiac Na(+)/Ca(2+) exchanger (NCX1) and Na(+)-K(+)-ATPase in cardiac myocytes. PLM, when phosphorylated at Ser(68), disinhibits Na(+)-K(+)-ATPase but inhibits NCX1. PLM regulates cardiac contractility by modulating Na(+)-K(+)-ATPase and/or NCX1. In this study, we first demonstrated that adult mouse cardiac myocytes cultured for 48 h had normal surface membrane areas, t-tubules, and NCX1 and sarco(endo)plasmic reticulum Ca(2+)-ATPase levels, and retained near normal contractility, but alpha(1)-subunit of Na(+)-K(+)-ATPase was slightly decreased. Differences in contractility between myocytes isolated from wild-type (WT) and PLM knockout (KO) hearts were preserved after 48 h of culture. Infection with adenovirus expressing green fluorescent protein (GFP) did not affect contractility at 48 h. When WT PLM was overexpressed in PLM KO myocytes, contractility and cytosolic Ca(2+) concentration ([Ca(2+)](i)) transients reverted back to those observed in cultured WT myocytes. Both Na(+)-K(+)-ATPase current (I(pump)) and Na(+)/Ca(2+) exchange current (I(NaCa)) in PLM KO myocytes rescued with WT PLM were depressed compared with PLM KO myocytes. Overexpressing the PLMS68E mutant (phosphomimetic) in PLM KO myocytes resulted in the suppression of I(NaCa) but had no effect on I(pump). Contractility, [Ca(2+)](i) transient amplitudes, and sarcoplasmic reticulum Ca(2+) contents in PLM KO myocytes overexpressing the PLMS68E mutant were depressed compared with PLM KO myocytes overexpressing GFP. Overexpressing the PLMS68A mutant (mimicking unphosphorylated PLM) in PLM KO myocytes had no effect on I(NaCa) but decreased I(pump). Contractility, [Ca(2+)](i) transient amplitudes, and sarcoplasmic reticulum Ca(2+) contents in PLM KO myocytes overexpressing the S68A mutant were similar to PLM KO myocytes overexpressing GFP. We conclude that at the single-myocyte level, PLM affects cardiac contractility and [Ca(2+)](i) homeostasis primarily by its direct inhibitory effects on Na(+)/Ca(2+) exchange.
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Affiliation(s)
- Jianliang Song
- Division of Nephrology, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Green HJ, Duhamel TA, Stewart RD, Tupling AR, Ouyang J. Dissociation between changes in muscle Na+-K+-ATPase isoform abundance and activity with consecutive days of exercise and recovery. Am J Physiol Endocrinol Metab 2008; 294:E761-7. [PMID: 18230697 DOI: 10.1152/ajpendo.00751.2007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The early plasticity of vastus lateralis Na(+)-K(+)-ATPase to the abrupt onset of prolonged submaximal cycling was studied in 12 untrained participants (Vo(2 peak) 44.8 +/- 2.0 ml x kg(-1) x min(-1), mean +/- SE) using a 6-day protocol (3 days of exercise plus 3 days of recovery). Tissue samples were extracted prior to (Pre) and following exercise (Post) on day 1 (E1) and day 3 (E3) and on each day of recovery (R1, R2, R3) and analyzed for changes in maximal protein (beta(max)) (vanadate-facilitated [(3)H]ouabain binding), alpha- and beta-isoform concentration (quantitative immunoblotting) and maximal Na(+)-K(+)-ATPase activity (V(max)) (3-O-methylfluorescein K(+)-stimulated phosphatase assay). For beta(max) (pmol/g wet wt), an increase (P < 0.05) of 11.8% was observed at R1 compared with E1-Pre (340 +/- 14 vs 304 +/- 17). For the alpha-isoforms alpha(1), alpha(2), and alpha(3), increases (P < 0.05) of 46, 42, and 31% were observed at R1, respectively. For the beta-isoform, beta(1) and beta(2) increased (P < 0.05) by 19 and 28% at R1, whereas beta(3) increased (P < 0.05) by 18% at R2. With the exception of alpha(2) and alpha(3), the increases in the isoforms persisted at R3. Exercise resulted in an average decrease (P < 0.05) in V(max) by 14.3%. No differences were observed in V(max) at E1 - Pre and E3 - Pre or between R1, R2, and R3. It is concluded that 3 days of prolonged exercise is a powerful stimulus for the rapid upregulation of the Na(+)-K(+)-ATPase subunit isoforms. Contrary to our hypothesis, the increase in subunit expression is not accompanied by increases in the maximal catalytic activity.
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Affiliation(s)
- H J Green
- Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada, N2L 3G1.
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Despa S, Tucker AL, Bers DM. Phospholemman-mediated activation of Na/K-ATPase limits [Na]i and inotropic state during beta-adrenergic stimulation in mouse ventricular myocytes. Circulation 2008; 117:1849-55. [PMID: 18362230 DOI: 10.1161/circulationaha.107.754051] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Cardiac Na/K-ATPase (NKA) regulates intracellular Na ([Na](i)), which in turn affects intracellular Ca and thus contractility via Na/Ca exchange. Recent evidence shows that phosphorylation of the NKA-associated small transmembrane protein phospholemman (PLM) mediates beta-adrenergic-induced NKA stimulation. METHODS AND RESULTS Here, we tested whether PLM phosphorylation during beta-adrenergic activation limits the rise in [Na](i), Ca transient amplitude, and triggered arrhythmias in mouse ventricular myocytes. In myocytes from wild-type (WT) mice, [Na](i) increased on field stimulation at 2 Hz from 11.1+/-1.8 mmol/L to a plateau of 15.2+/-1.5 mmol/L. Isoproterenol induced a decrease in [Na](i) to 12.0+/-1.2 mmol/L. In PLM knockout (PLM-KO) mice in which beta-adrenergic stimulation does not activate NKA, [Na](i) also increased at 2 Hz (from 10.4+/-1.2 to 17.0+/-1.5 mmol/L) but was unaltered by isoproterenol. The PLM-mediated decrease in [Na](i) in WT mice could limit the isoproterenol-induced inotropic state. Indeed, the isoproterenol-induced increase in the amplitude of Ca transients was significantly smaller in the WT mice (5.2+/-0.4- versus 7.1+/-0.5-fold in PLM-KO mice). This also was the case for the sarcoplasmic reticulum Ca content, which increased by 1.27+/-0.09-fold in WT mice versus 1.53+/-0.09-fold in PLM-KO mice. The higher sarcoplasmic reticulum Ca content in PLM-KO versus WT mice was associated with an increased propensity for spontaneous Ca transients and contractions in PLM-KO mice. CONCLUSIONS These data suggest that PLM phosphorylation and NKA stimulation are an integral part of the sympathetic fight-or-flight response, tempering the rise in [Na](i) and cellular Ca loading and perhaps limiting Ca overload-induced arrhythmias.
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Affiliation(s)
- Sanda Despa
- Department of Physiology, Loyola University Chicago, Maywood, Ill, USA
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Beevers AJ, Kukol A. Phospholemman Transmembrane Structure Reveals Potential Interactions with Na+/K+-ATPase. J Biol Chem 2007; 282:32742-8. [PMID: 17698851 DOI: 10.1074/jbc.m703676200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM) is a 72-residue bitopic cardiac transmembrane protein, which acts as a modulator of the Na(+)/K(+)-ATPase and the Na(+)/Ca(2+) exchanger and possibly forms taurine channels in nonheart tissue. This work presents a high resolution structural model obtained from a combination of site-specific infrared spectroscopy and experimentally constrained high throughput molecular dynamics (MD) simulations. Altogether, 37 experimental constraints, including nine long range orientational constraints, have been used during MD simulations in an explicit lipid bilayer/water system. The resulting tetrameric alpha-helical bundle has an average helix tilt of 7.3 degrees and a crossing angle close to 0 degrees . It does not reveal a hydrophilic pore, but instead strong interactions between various residues occlude any pore. The helix-helix packing is unusual, with Gly(19) and Gly(20) pointing to the outside of the helical bundle, facilitating potential interaction with other transmembrane proteins, thus providing a structural basis for the modulatory effect of PLM on the Na(+)/K(+)-ATPase. A two-stage model of interaction between PLM and the Na(+)/K(+)-ATPase is discussed involving PLM-ATPase interaction and subsequent formation of an unstable PLM trimer, which readily interacts with surrounding ATPase molecules. Further unconstrained MD simulations identified other packing models of PLM, one of which could potentially undergo a conformational transition to an open pore.
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Affiliation(s)
- Andrew J Beevers
- Department of Chemistry, University of Warwick, Coventry, United Kingdom
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Abstract
Mammalian Na+/Ca2+ exchangers are members of three branches of a much larger family of transport proteins [the CaCA (Ca2+/cation antiporter) superfamily] whose main role is to provide control of Ca2+ flux across the plasma membranes or intracellular compartments. Since cytosolic levels of Ca2+ are much lower than those found extracellularly or in sequestered stores, the major function of Na+/Ca2+ exchangers is to extrude Ca2+ from the cytoplasm. The exchangers are, however, fully reversible and thus, under special conditions of subcellular localization and compartmentalized ion gradients, Na+/Ca2+ exchangers may allow Ca2+ entry and may play more specialized roles in Ca2+ movement between compartments. The NCX (Na+/Ca2+ exchanger) [SLC (solute carrier) 8] branch of Na+/Ca2+ exchangers comprises three members: NCX1 has been most extensively studied, and is broadly expressed with particular abundance in heart, brain and kidney, NCX2 is expressed in brain, and NCX3 is expressed in brain and skeletal muscle. The NCX proteins subserve a variety of roles, depending upon the site of expression. These include cardiac excitation-contraction coupling, neuronal signalling and Ca2+ reabsorption in the kidney. The NCKX (Na2+/Ca2+-K+ exchanger) (SLC24) branch of Na+/Ca2+ exchangers transport K+ and Ca2+ in exchange for Na+, and comprises five members: NCKX1 is expressed in retinal rod photoreceptors, NCKX2 is expressed in cone photoreceptors and in neurons throughout the brain, NCKX3 and NCKX4 are abundant in brain, but have a broader tissue distribution, and NCKX5 is expressed in skin, retinal epithelium and brain. The NCKX proteins probably play a particularly prominent role in regulating Ca2+ flux in environments which experience wide and frequent fluctuations in Na+ concentration. Until recently, the range of functions that NCKX proteins play was generally underappreciated. This situation is now changing rapidly as evidence emerges for roles including photoreceptor adaptation, synaptic plasticity and skin pigmentation. The CCX (Ca2+/cation exchanger) branch has only one mammalian member, NCKX6 or NCLX (Na+/Ca2+-Li+ exchanger), whose physiological function remains unclear, despite a broad pattern of expression.
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Affiliation(s)
- Jonathan Lytton
- Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute of Alberta, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
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