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Meyer DJ, Díaz-García CM, Nathwani N, Rahman M, Yellen G. The Na +/K + pump dominates control of glycolysis in hippocampal dentate granule cells. eLife 2022; 11:e81645. [PMID: 36222651 PMCID: PMC9592084 DOI: 10.7554/elife.81645] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 10/11/2022] [Indexed: 11/13/2022] Open
Abstract
Cellular ATP that is consumed to perform energetically expensive tasks must be replenished by new ATP through the activation of metabolism. Neuronal stimulation, an energetically demanding process, transiently activates aerobic glycolysis, but the precise mechanism underlying this glycolysis activation has not been determined. We previously showed that neuronal glycolysis is correlated with Ca2+ influx, but is not activated by feedforward Ca2+ signaling (Díaz-García et al., 2021a). Since ATP-powered Na+ and Ca2+ pumping activities are increased following stimulation to restore ion gradients and are estimated to consume most neuronal ATP, we aimed to determine if they are coupled to neuronal glycolysis activation. By using two-photon imaging of fluorescent biosensors and dyes in dentate granule cell somas of acute mouse hippocampal slices, we observed that production of cytoplasmic NADH, a byproduct of glycolysis, is strongly coupled to changes in intracellular Na+, while intracellular Ca2+ could only increase NADH production if both forward Na+/Ca2+ exchange and Na+/K+ pump activity were intact. Additionally, antidromic stimulation-induced intracellular [Na+] increases were reduced >50% by blocking Ca2+ entry. These results indicate that neuronal glycolysis activation is predominantly a response to an increase in activity of the Na+/K+ pump, which is strongly potentiated by Na+ influx through the Na+/Ca2+ exchanger during extrusion of Ca2+ following stimulation.
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Affiliation(s)
- Dylan J Meyer
- Department of Neurobiology, Harvard Medical SchoolBostonUnited States
| | | | - Nidhi Nathwani
- Department of Neurobiology, Harvard Medical SchoolBostonUnited States
| | - Mahia Rahman
- Department of Neurobiology, Harvard Medical SchoolBostonUnited States
| | - Gary Yellen
- Department of Neurobiology, Harvard Medical SchoolBostonUnited States
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Meyer DJ, Bijlani S, de Sautu M, Spontarelli K, Young VC, Gatto C, Artigas P. FXYD protein isoforms differentially modulate human Na/K pump function. J Gen Physiol 2021; 152:211559. [PMID: 33231612 PMCID: PMC7690937 DOI: 10.1085/jgp.202012660] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 10/29/2020] [Indexed: 12/28/2022] Open
Abstract
Tight regulation of the Na/K pump is essential for cellular function because this heteromeric protein builds and maintains the electrochemical gradients for Na+ and K+ that energize electrical signaling and secondary active transport. We studied the regulation of the ubiquitous human α1β1 pump isoform by five human FXYD proteins normally located in muscle, kidney, and neurons. The function of Na/K pump α1β1 expressed in Xenopus oocytes with or without FXYD isoforms was evaluated using two-electrode voltage clamp and patch clamp. Through evaluation of the partial reactions in the absence of K+ but presence of Na+ in the external milieu, we demonstrate that each FXYD subunit alters the equilibrium between E1P(3Na) and E2P, the phosphorylated conformations with Na+ occluded and free from Na+, respectively, thereby altering the apparent affinity for Na+. This modification of Na+ interaction shapes the small effects of FXYD proteins on the apparent affinity for external K+ at physiological Na+. FXYD6 distinctively accelerated both the Na+-deocclusion and the pump-turnover rates. All FXYD isoforms altered the apparent affinity for intracellular Na+ in patches, an effect that was observed only in the presence of intracellular K+. Therefore, FXYD proteins alter the selectivity of the pump for intracellular ions, an effect that could be due to the altered equilibrium between E1 and E2, the two major pump conformations, and/or to small changes in ion affinities that are exacerbated when both ions are present. Lastly, we observed a drastic reduction of Na/K pump surface expression when it was coexpressed with FXYD1 or FXYD6, with the former being relieved by injection of PKA's catalytic subunit into the oocyte. Our results indicate that a prominent effect of FXYD1 and FXYD6, and plausibly other FXYDs, is the regulation of Na/K pump trafficking.
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Affiliation(s)
- Dylan J Meyer
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Sharan Bijlani
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Marilina de Sautu
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Victoria C Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Craig Gatto
- School of Biological Sciences, Illinois State University. Normal, IL
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
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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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Phospholemman, a major regulator of skeletal muscle Na+/K+-ATPase, is not mutated in probands with hypokalemic periodic paralysis. Exp Ther Med 2017; 14:3229-3232. [DOI: 10.3892/etm.2017.4848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 02/24/2017] [Indexed: 11/05/2022] Open
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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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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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7
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Gong XM, Ding Y, Yu J, Yao Y, Marassi FM. Structure of the Na,K-ATPase regulatory protein FXYD2b in micelles: implications for membrane-water interfacial arginines. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:299-306. [PMID: 24794573 DOI: 10.1016/j.bbamem.2014.04.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/19/2014] [Accepted: 04/23/2014] [Indexed: 01/06/2023]
Abstract
FXYD2 is a membrane protein responsible for regulating the function of the Na,K-ATPase in mammalian kidney epithelial cells. Here we report the structure of FXYD2b, one of two splice variants of the protein, determined by NMR spectroscopy in detergent micelles. Solid-state NMR characterization of the protein embedded in phospholipid bilayers indicates that several arginine side chains may be involved in hydrogen bond interactions with the phospholipid polar head groups. The structure and the NMR data suggest that FXYD2b could regulate the Na,K-ATPase by modulating the effective membrane surface electrostatics near the ion binding sites of the pump.
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Affiliation(s)
- Xiao-Min Gong
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yi Ding
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Jinghua Yu
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Yong Yao
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Francesca M Marassi
- Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.
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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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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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10
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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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11
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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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Ilies M, Di Costanzo L, Dowling DP, Thorn KJ, Christianson DW. Binding of α,α-disubstituted amino acids to arginase suggests new avenues for inhibitor design. J Med Chem 2011; 54:5432-43. [PMID: 21728378 DOI: 10.1021/jm200443b] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Arginase is a binuclear manganese metalloenzyme that hydrolyzes L-arginine to form L-ornithine and urea, and aberrant arginase activity is implicated in various diseases such as erectile dysfunction, asthma, atherosclerosis, and cerebral malaria. Accordingly, arginase inhibitors may be therapeutically useful. Continuing our efforts to expand the chemical space of arginase inhibitor design and inspired by the binding of 2-(difluoromethyl)-L-ornithine to human arginase I, we now report the first study of the binding of α,α-disubstituted amino acids to arginase. Specifically, we report the design, synthesis, and assay of racemic 2-amino-6-borono-2-methylhexanoic acid and racemic 2-amino-6-borono-2-(difluoromethyl)hexanoic acid. X-ray crystal structures of human arginase I and Plasmodium falciparum arginase complexed with these inhibitors reveal the exclusive binding of the L-stereoisomer; the additional α-substituent of each inhibitor is readily accommodated and makes new intermolecular interactions in the outer active site of each enzyme. Therefore, this work highlights a new region of the protein surface that can be targeted for additional affinity interactions, as well as the first comparative structural insights on inhibitor discrimination between a human and a parasitic arginase.
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Affiliation(s)
- Monica Ilies
- Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104-2875, United States
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Bibert S, Liu CC, Figtree GA, Garcia A, Hamilton EJ, Marassi FM, Sweadner KJ, Cornelius F, Geering K, Rasmussen HH. FXYD proteins reverse inhibition of the Na+-K+ pump mediated by glutathionylation of its beta1 subunit. J Biol Chem 2011; 286:18562-72. [PMID: 21454534 DOI: 10.1074/jbc.m110.184101] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The seven members of the FXYD protein family associate with the Na(+)-K(+) pump and modulate its activity. We investigated whether conserved cysteines in FXYD proteins are susceptible to glutathionylation and whether such reactivity affects Na(+)-K(+) pump function in cardiac myocytes and Xenopus oocytes. Glutathionylation was detected by immunoblotting streptavidin precipitate from biotin-GSH loaded cells or by a GSH antibody. Incubation of myocytes with recombinant FXYD proteins resulted in competitive displacement of native FXYD1. Myocyte and Xenopus oocyte pump currents were measured with whole-cell and two-electrode voltage clamp techniques, respectively. Native FXYD1 in myocytes and FXYD1 expressed in oocytes were susceptible to glutathionylation. Mutagenesis identified the specific cysteine in the cytoplasmic terminal that was reactive. Its reactivity was dependent on flanking basic amino acids. We have reported that Na(+)-K(+) pump β(1) subunit glutathionylation induced by oxidative signals causes pump inhibition in a previous study. In the present study, we found that β(1) subunit glutathionylation and pump inhibition could be reversed by exposing myocytes to exogenous wild-type FXYD3. A cysteine-free FXYD3 derivative had no effect. Similar results were obtained with wild-type and mutant FXYD proteins expressed in oocytes. Glutathionylation of the β(1) subunit was increased in myocardium from FXYD1(-/-) mice. In conclusion, there is a dependence of Na(+)-K(+) pump regulation on reactivity of two specifically identified cysteines on separate components of the multimeric Na(+)-K(+) pump complex. By facilitating deglutathionylation of the β(1) subunit, FXYD proteins reverse oxidative inhibition of the Na(+)-K(+) pump and play a dynamic role in its regulation.
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Affiliation(s)
- Stéphanie Bibert
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne 1005, Switzerland
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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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