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Dong Y, Yu Z, Li Y, Huang B, Bai Q, Gao Y, Chen Q, Li N, He L, Zhao Y. Structural insight into the allosteric inhibition of human sodium-calcium exchanger NCX1 by XIP and SEA0400. EMBO J 2024; 43:14-31. [PMID: 38177313 PMCID: PMC10897212 DOI: 10.1038/s44318-023-00013-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 11/10/2023] [Accepted: 11/15/2023] [Indexed: 01/06/2024] Open
Abstract
Sodium-calcium exchanger proteins influence calcium homeostasis in many cell types and participate in a wide range of physiological and pathological processes. Here, we elucidate the cryo-EM structure of the human Na+/Ca2+ exchanger NCX1.3 in the presence of a specific inhibitor, SEA0400. Conserved ion-coordinating residues are exposed on the cytoplasmic face of NCX1.3, indicating that the observed structure is stabilized in an inward-facing conformation. We show how regulatory calcium-binding domains (CBDs) assemble with the ion-translocation transmembrane domain (TMD). The exchanger-inhibitory peptide (XIP) is trapped within a groove between the TMD and CBD2 and predicted to clash with gating helices TMs1/6 at the outward-facing state, thus hindering conformational transition and promoting inactivation of the transporter. A bound SEA0400 molecule stiffens helix TM2ab and affects conformational rearrangements of TM2ab that are associated with the ion-exchange reaction, thus allosterically attenuating Ca2+-uptake activity of NCX1.3.
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Affiliation(s)
- Yanli Dong
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Zhuoya Yu
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yue Li
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bo Huang
- Beijing StoneWise Technology Co Ltd., 15 Haidian street, Haidian district, Beijing, China
| | - Qinru Bai
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yiwei Gao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Qihao Chen
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Na Li
- Heart Center and Beijing Key Laboratory of Hypertension, Beijing Chaoyang Hospital, Capital Medical University, Beijing, 100020, China
| | - Lingli He
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Yan Zhao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China.
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
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Khananshvili D. Neuronal and astrocyte NCX isoform/splice variants: How do they participate in Na + and Ca 2+ signalling? Cell Calcium 2023; 116:102818. [PMID: 37918135 DOI: 10.1016/j.ceca.2023.102818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 10/20/2023] [Accepted: 10/22/2023] [Indexed: 11/04/2023]
Abstract
NCX1, NCX2, and NCX3 gene isoforms and their splice variants are characteristically expressed in different regions of the brain. The tissue-specific splice variants of NCX1-3 isoforms show specific expression profiles in neurons and astrocytes, whereas the relevant NCX isoform/splice variants exhibit diverse allosteric modes of Na+- and Ca2+-dependent regulation. In general, overexpression of NCX1-3 genes leads to neuroprotective effects, whereas their ablation gains the opposite results. At this end, the partial contributions of NCX isoform/splice variants to neuroprotective effects remain unresolved. The glutamate-dependent Na+ entry generates Na+ transients (in response to neuronal cell activities), whereas the Na+-driven Ca2+ entry (through the reverse NCX mode) raises Ca2+ transients. This special mode of signal coupling translates Na+ transients into the Ca2+ signals while being a part of synaptic neurotransmission. This mechanism is of general interest since disease-related conditions (ischemia, metabolic stress, and stroke among many others) trigger Na+ and Ca2+ overload with deadly outcomes of downstream apoptosis and excitotoxicity. The recently discovered mechanisms of NCX allosteric regulation indicate that some NCX variants might play a critical role in the dynamic coupling of Na+-driven Ca2+ entry. In contrast, the others are less important or even could be dangerous under altered conditions (e.g., metabolic stress). This working hypothesis can be tested by applying advanced experimental approaches and highly focused computational simulations. This may allow the development of structure-based blockers/activators that can selectively modulate predefined NCX variants to lessen the life-threatening outcomes of excitotoxicity, ischemia, apoptosis, metabolic deprivation, brain injury, and stroke.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Faculty of Medicine, Tel-Aviv University, Tel Aviv 69978, Israel.
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Xue J, Zeng W, Han Y, John S, Ottolia M, Jiang Y. Structural mechanisms of the human cardiac sodium-calcium exchanger NCX1. Nat Commun 2023; 14:6181. [PMID: 37794011 PMCID: PMC10550945 DOI: 10.1038/s41467-023-41885-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 09/22/2023] [Indexed: 10/06/2023] Open
Abstract
Na+/Ca2+ exchangers (NCX) transport Ca2+ in or out of cells in exchange for Na+. They are ubiquitously expressed and play an essential role in maintaining cytosolic Ca2+ homeostasis. Although extensively studied, little is known about the global structural arrangement of eukaryotic NCXs and the structural mechanisms underlying their regulation by various cellular cues including cytosolic Na+ and Ca2+. Here we present the cryo-EM structures of human cardiac NCX1 in both inactivated and activated states, elucidating key structural elements important for NCX ion exchange function and its modulation by cytosolic Ca2+ and Na+. We demonstrate that the interactions between the ion-transporting transmembrane (TM) domain and the cytosolic regulatory domain define the activity of NCX. In the inward-facing state with low cytosolic [Ca2+], a TM-associated four-stranded β-hub mediates a tight packing between the TM and cytosolic domains, resulting in the formation of a stable inactivation assembly that blocks the TM movement required for ion exchange function. Ca2+ binding to the cytosolic second Ca2+-binding domain (CBD2) disrupts this inactivation assembly which releases its constraint on the TM domain, yielding an active exchanger. Thus, the current NCX1 structures provide an essential framework for the mechanistic understanding of the ion transport and cellular regulation of NCX family proteins.
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Affiliation(s)
- Jing Xue
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Weizhong Zeng
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yan Han
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Scott John
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Youxing Jiang
- Howard Hughes Medical Institute and Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
- Department of Biophysics, The University of Texas Southwestern Medical Center, Dallas, TX, USA.
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Takei GL, Ogura Y, Ujihara Y, Toyama F, Hayashi K, Fujita T. Hamster Sperm Possess Functional Na +/Ca 2+-Exchanger 1: Its Implication in Hyperactivation. Int J Mol Sci 2023; 24:ijms24108905. [PMID: 37240252 DOI: 10.3390/ijms24108905] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 05/12/2023] [Accepted: 05/16/2023] [Indexed: 05/28/2023] Open
Abstract
Previous studies demonstrated that hamster sperm hyperactivation is suppressed by extracellular Na+ by lowering intracellular Ca2+ levels, and Na+/Ca2+-exchanger (NCX) specific inhibitors canceled the suppressive effects of extracellular Na+. These results suggest the involvement of NCX in the regulation of hyperactivation. However, direct evidence of the presence and functionality of NCX in hamster spermatozoa is still lacking. This study aimed to reveal that NCX is present and is functional in hamster spermatozoa. First, NCX1 and NCX2 transcripts were detected via RNA-seq analyses of hamster testis mRNAs, but only the NCX1 protein was detected. Next, NCX activity was determined by measuring the Na+-dependent Ca2+ influx using the Ca2+ indicator Fura-2. The Na+-dependent Ca2+ influx was detected in hamster spermatozoa, notably in the tail region. The Na+-dependent Ca2+ influx was inhibited by the NCX inhibitor SEA0400 at NCX1-specific concentrations. NCX1 activity was reduced after 3 h of incubation in capacitating conditions. These results, together with authors' previous study, showed that hamster spermatozoa possesses functional NCX1 and that its activity was downregulated upon capacitation to trigger hyperactivation. This is the first study to successfully reveal the presence of NCX1 and its physiological function as a hyperactivation brake.
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Affiliation(s)
- Gen L Takei
- Department of Pharmacology and Toxicology, Dokkyo Medical University, 880 Kitakobayashi, Mibu, Tochigi 321-0293, Japan
| | - Yuhei Ogura
- Department of Electrical and Mechanical Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
| | - Yoshihiro Ujihara
- Department of Electrical and Mechanical Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
| | - Fubito Toyama
- School of Engineering, Utsunomiya University, Yoto 7-1-2, Utsunomiya 321-8585, Japan
| | - Keitaro Hayashi
- Department of Pharmacology and Toxicology, Dokkyo Medical University, 880 Kitakobayashi, Mibu, Tochigi 321-0293, Japan
| | - Tomoe Fujita
- Department of Pharmacology and Toxicology, Dokkyo Medical University, 880 Kitakobayashi, Mibu, Tochigi 321-0293, Japan
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Bkaily G, Jacques D. Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System. Int J Mol Sci 2023; 24:ijms24108803. [PMID: 37240147 DOI: 10.3390/ijms24108803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Revised: 05/06/2023] [Accepted: 05/10/2023] [Indexed: 05/28/2023] Open
Abstract
Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.
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Affiliation(s)
- Ghassan Bkaily
- Department of Immunology and Cell Biology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Danielle Jacques
- Department of Immunology and Cell Biology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
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Structure-Based Function and Regulation of NCX Variants: Updates and Challenges. Int J Mol Sci 2022; 24:ijms24010061. [PMID: 36613523 PMCID: PMC9820601 DOI: 10.3390/ijms24010061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 12/14/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
The plasma-membrane homeostasis Na+/Ca2+ exchangers (NCXs) mediate Ca2+ extrusion/entry to dynamically shape Ca2+ signaling/in biological systems ranging from bacteria to humans. The NCX gene orthologs, isoforms, and their splice variants are expressed in a tissue-specific manner and exhibit nearly 104-fold differences in the transport rates and regulatory specificities to match the cell-specific requirements. Selective pharmacological targeting of NCX variants could benefit many clinical applications, although this intervention remains challenging, mainly because a full-size structure of eukaryotic NCX is unavailable. The crystal structure of the archaeal NCX_Mj, in conjunction with biophysical, computational, and functional analyses, provided a breakthrough in resolving the ion transport mechanisms. However, NCX_Mj (whose size is nearly three times smaller than that of mammalian NCXs) cannot serve as a structure-dynamic model for imitating high transport rates and regulatory modules possessed by eukaryotic NCXs. The crystal structures of isolated regulatory domains (obtained from eukaryotic NCXs) and their biophysical analyses by SAXS, NMR, FRET, and HDX-MS approaches revealed structure-based variances of regulatory modules. Despite these achievements, it remains unclear how multi-domain interactions can decode and integrate diverse allosteric signals, thereby yielding distinct regulatory outcomes in a given ortholog/isoform/splice variant. This article summarizes the relevant issues from the perspective of future developments.
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Akerberg AA, Trembley M, Butty V, Schwertner A, Zhao L, Beerens M, Liu X, Mahamdeh M, Yuan S, Boyer L, MacRae C, Nguyen C, Pu WT, Burns CE, Burns CG. RBPMS2 Is a Myocardial-Enriched Splicing Regulator Required for Cardiac Function. Circ Res 2022; 131:980-1000. [PMID: 36367103 PMCID: PMC9770155 DOI: 10.1161/circresaha.122.321728] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 10/27/2022] [Accepted: 11/01/2022] [Indexed: 11/13/2022]
Abstract
BACKGROUND RBPs (RNA-binding proteins) perform indispensable functions in the post-transcriptional regulation of gene expression. Numerous RBPs have been implicated in cardiac development or physiology based on gene knockout studies and the identification of pathogenic RBP gene mutations in monogenic heart disorders. The discovery and characterization of additional RBPs performing indispensable functions in the heart will advance basic and translational cardiovascular research. METHODS We performed a differential expression screen in zebrafish embryos to identify genes enriched in nkx2.5-positive cardiomyocytes or cardiopharyngeal progenitors compared to nkx2.5-negative cells from the same embryos. We investigated the myocardial-enriched gene RNA-binding protein with multiple splicing (variants) 2 [RBPMS2)] by generating and characterizing rbpms2 knockout zebrafish and human cardiomyocytes derived from RBPMS2-deficient induced pluripotent stem cells. RESULTS We identified 1848 genes enriched in the nkx2.5-positive population. Among the most highly enriched genes, most with well-established functions in the heart, we discovered the ohnologs rbpms2a and rbpms2b, which encode an evolutionarily conserved RBP. Rbpms2 localizes selectively to cardiomyocytes during zebrafish heart development and strong cardiomyocyte expression persists into adulthood. Rbpms2-deficient embryos suffer from early cardiac dysfunction characterized by reduced ejection fraction. The functional deficit is accompanied by myofibril disarray, altered calcium handling, and differential alternative splicing events in mutant cardiomyocytes. These phenotypes are also observed in RBPMS2-deficient human cardiomyocytes, indicative of conserved molecular and cellular function. RNA-sequencing and comparative analysis of genes mis-spliced in RBPMS2-deficient zebrafish and human cardiomyocytes uncovered a conserved network of 29 ortholog pairs that require RBPMS2 for alternative splicing regulation, including RBFOX2, SLC8A1, and MYBPC3. CONCLUSIONS Our study identifies RBPMS2 as a conserved regulator of alternative splicing, myofibrillar organization, and calcium handling in zebrafish and human cardiomyocytes.
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Affiliation(s)
- Alexander A. Akerberg
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Michael Trembley
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Vincent Butty
- BioMicroCenter, Department of Biology (V.B.), Massachusetts Institute of Technology, Cambridge‚ MA
- Department of Biology (V.B., L.B.), Massachusetts Institute of Technology, Cambridge‚ MA
| | - Asya Schwertner
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Long Zhao
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Manu Beerens
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
- Division of Cardiovascular Medicine, Brigham and Women’s Hospital, Boston, MA (M.B., C.M.)
| | - Xujie Liu
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Mohammed Mahamdeh
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Shiaulou Yuan
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
| | - Laurie Boyer
- Department of Biology (V.B., L.B.), Massachusetts Institute of Technology, Cambridge‚ MA
- Department of Biological Engineering (L.B.), Massachusetts Institute of Technology, Cambridge‚ MA
| | - Calum MacRae
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
- Division of Cardiovascular Medicine, Brigham and Women’s Hospital, Boston, MA (M.B., C.M.)
| | - Christopher Nguyen
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
- Cardiovascular Innovation Research Center, Heart Vascular & Thoracic Institute, Cleveland Clinic‚ Cleveland‚ OH (C.N.)
| | - William T. Pu
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
- Harvard Stem Cell Institute, Cambridge, MA (W.T.P., C.E.B.)
| | - Caroline E. Burns
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
- Harvard Stem Cell Institute, Cambridge, MA (W.T.P., C.E.B.)
| | - C. Geoffrey Burns
- Division of Basic and Translational Cardiovascular Research, Department of Cardiology, Boston Children’s Hospital, Boston‚ MA (A.A.A., M.T., X.L., W.T.P., C.E.B., C.G.B.)
- Cardiovascular Research Center, Massachusetts General Hospital, Charlestown‚ MA (A.A.A., A.S., L.Z., M.M., S.Y., C.N., C.E.B., C.G.B.)
- Harvard Medical School, Boston, MA (A.A.A., M.T., A.S., L.Z., M.B., X.L., M.M., S.Y., C.M., C.N., W.T.P., C.E.B., C.G.B.)
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8
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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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Kohajda Z, Loewe A, Tóth N, Varró A, Nagy N. The Cardiac Pacemaker Story-Fundamental Role of the Na +/Ca 2+ Exchanger in Spontaneous Automaticity. Front Pharmacol 2020; 11:516. [PMID: 32410993 PMCID: PMC7199655 DOI: 10.3389/fphar.2020.00516] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 04/01/2020] [Indexed: 01/01/2023] Open
Abstract
The electrophysiological mechanism of the sinus node automaticity was previously considered exclusively regulated by the so-called "funny current". However, parallel investigations increasingly emphasized the importance of the Ca2+-homeostasis and Na+/Ca2+ exchanger (NCX). Recently, increasing experimental evidence, as well as insight through mechanistic in silico modeling demonstrates the crucial role of the exchanger in sinus node pacemaking. NCX had a key role in the exciting story of discovery of sinus node pacemaking mechanisms, which recently settled with a consensus on the coupled-clock mechanism after decades of debate. This review focuses on the role of the Na+/Ca2+ exchanger from the early results and concepts to recent advances and attempts to give a balanced summary of the characteristics of the local, spontaneous, and rhythmic Ca2+ releases, the molecular control of the NCX and its role in the fight-or-flight response. Transgenic animal models and pharmacological manipulation of intracellular Ca2+ concentration and/or NCX demonstrate the pivotal function of the exchanger in sinus node automaticity. We also highlight where specific hypotheses regarding NCX function have been derived from computational modeling and require experimental validation. Nonselectivity of NCX inhibitors and the complex interplay of processes involved in Ca2+ handling render the design and interpretation of these experiments challenging.
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Affiliation(s)
- Zsófia Kohajda
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Axel Loewe
- Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Noémi Tóth
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - András Varró
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Norbert Nagy
- MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.,Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
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10
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Formisano L, Guida N, Mascolo L, Serani A, Laudati G, Pizzorusso V, Annunziato L. Transcriptional and epigenetic regulation of ncx1 and ncx3 in the brain. Cell Calcium 2020; 87:102194. [PMID: 32172011 DOI: 10.1016/j.ceca.2020.102194] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 03/03/2020] [Accepted: 03/04/2020] [Indexed: 01/26/2023]
Abstract
Sodium-calcium exchanger (NCX) 1 and 3, have been demonstrated to play a relevant role in controlling the intracellular homeostasis of sodium and calcium ions in physiological and patho-physiological conditions. While NCX1 and NCX3 knocking-down have been both implicated in brain ischemia, several aspects of the epigenetic regulation of these two antiporters transcription were not yet well characterized. In response to stroke, NCX1 and NCX3 transcriptional regulation occurs from specific promoter sequences. Several evidences have shown that the expression of NCX1 and NCX3 can be determined by epigenetic modifications, consisting in changes of the histone acetylation levels on their promoter sequences. An interesting issue is that histone modifications at the NCX1 and NCX3 promoters could be linked to neurodegeneration occurring after stroke. Therefore, identifying the epigenetic regulation at the NCX1 and NCX3 promoters could permit to identify new molecular targets that can open new strategies for stroke treatment. The current review reassumes the recent knowledge of histone modifications of NCX1 and NCX3 genes in brain in physiological and patho-physiological conditions.
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Affiliation(s)
- Luigi Formisano
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, Federico II University of Naples, Via Pansini, 5, 80131, Naples, Italy.
| | - Natascia Guida
- IRCCS SDN Naples, Via Emanuele Gianturco 113, 80143, Naples, Italy
| | - Luigi Mascolo
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, Federico II University of Naples, Via Pansini, 5, 80131, Naples, Italy
| | - Angelo Serani
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, Federico II University of Naples, Via Pansini, 5, 80131, Naples, Italy
| | - Giusy Laudati
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, Federico II University of Naples, Via Pansini, 5, 80131, Naples, Italy
| | - Vincenzo Pizzorusso
- Division of Pharmacology, Department of Neuroscience, Reproductive and Dentistry Sciences, School of Medicine, Federico II University of Naples, Via Pansini, 5, 80131, Naples, Italy
| | - Lucio Annunziato
- IRCCS SDN Naples, Via Emanuele Gianturco 113, 80143, Naples, Italy
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11
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Multipurpose Na + ions mediate excitation and cellular homeostasis: Evolution of the concept of Na + pumps and Na +/Ca 2+ exchangers. Cell Calcium 2020; 87:102166. [PMID: 32006802 DOI: 10.1016/j.ceca.2020.102166] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 01/21/2020] [Indexed: 12/14/2022]
Abstract
Ionic signalling is the most ancient form of regulation of cellular functions in response to environmental challenges. Signals, mediated by Na+ fluxes and spatio-temporal fluctuations of Na+ concentration in cellular organelles and cellular compartments contribute to the most fundamental cellular processes such as membrane excitability and energy production. At the very core of ionic signalling lies the Na+-K+ ATP-driven pump (or NKA) which creates trans-plasmalemmal ion gradients that sustain ionic fluxes through ion channels and numerous Na+-dependent transporters that maintain cellular and tissue homeostasis. Here we present a brief account of the history of research into NKA, Na+ -dependent transporters and Na+ signalling.
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12
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Basic and editing mechanisms underlying ion transport and regulation in NCX variants. Cell Calcium 2020; 85:102131. [DOI: 10.1016/j.ceca.2019.102131] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 11/20/2019] [Accepted: 11/20/2019] [Indexed: 12/28/2022]
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13
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An Evolutionary Mechanism for the Generation of Competing RNA Structures Associated with Mutually Exclusive Exons. Genes (Basel) 2018; 9:genes9070356. [PMID: 30018239 PMCID: PMC6071210 DOI: 10.3390/genes9070356] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 07/06/2018] [Accepted: 07/13/2018] [Indexed: 12/31/2022] Open
Abstract
Alternative splicing is a commonly-used mechanism of diversifying gene products. Mutually exclusive exons (MXE) represent a particular type of alternative splicing, in which one and only one exon from an array is included in the mature RNA. A number of genes with MXE do so by using a mechanism that depends on RNA structure. Transcripts of these genes contain multiple sites called selector sequences that are all complementary to a regulatory element called the docking site; only one of the competing base pairings can form at a time, which exposes one exon from the cluster to the spliceosome. MXE tend to have similar lengths and sequence content and are believed to originate through tandem genomic duplications. Here, we report that pre-mRNAs of this class of exons have an increased capacity to fold into competing secondary structures. We propose an evolutionary mechanism for the generation of such structures via duplications that affect not only exons, but also their adjacent introns with stem-loop structures. If one of the two arms of a stem-loop is duplicated, it will generate two selector sequences that compete for the same docking site, a pattern that is associated with MXE splicing. A similar partial duplication of two independent stem-loops produces a pattern that is consistent with the so-called bidirectional pairing model. These models explain why tandem exon duplications frequently result in mutually exclusive splicing.
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Sherkhane P, Kapfhammer JP. Chronic pharmacological blockade of the Na + /Ca 2+ exchanger modulates the growth and development of the Purkinje cell dendritic arbor in mouse cerebellar slice cultures. Eur J Neurosci 2017; 46:2108-2120. [PMID: 28715135 DOI: 10.1111/ejn.13649] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 07/11/2017] [Accepted: 07/11/2017] [Indexed: 01/22/2023]
Abstract
The Na+ /Ca2+ exchanger (NCX) is a bidirectional plasma membrane antiporter involved in Ca2+ homeostasis in eukaryotes. NCX has three isoforms, NCX1-3, and all of them are expressed in the cerebellum. Immunostaining on cerebellar slice cultures indicates that NCX is widely expressed in the cerebellum, including expression in Purkinje cells. The pharmacological blockade of the forward mode of NCX (Ca2+ efflux mode) by bepridil moderately inhibited growth and development of Purkinje cell dendritic arbor in cerebellar slice cultures. However, the blockade of the reverse mode (Ca2+ influx mode) by KB-R7943 severely reduced the dendritic arbor and induced a morphological change with thickened distal dendrites. The effect of KB-R7943 on dendritic growth was unrelated to the activity of voltage-gated calcium channels and was also apparent in the absence of bioelectrical activity indicating that it was mediated by NCX expressed in Purkinje cells. We have used additional NCX inhibitors including CB-DMB, ORM-10103, SEA0400, YM-244769, and SN-6 which have higher specificity for NCX isoforms and target either the forward, reverse, or both modes. These inhibitors caused a strong dendritic reduction similar to that seen with KB-R7943, but did not elicit thickening of distal dendrites. Our findings indicate that disturbance of the NCX-dependent calcium transport in Purkinje cells induces a reduction of dendritic arbor, which is presumably caused by changes in the calcium handling, and underline the importance of the calcium equilibrium for the dendritic development in cerebellar Purkinje cells.
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Affiliation(s)
- Pradeep Sherkhane
- Department of Biomedicine, Anatomical Institute, University of Basel, Pestalozzistrasse 20, CH-4056, Basel, Switzerland
| | - Josef P Kapfhammer
- Department of Biomedicine, Anatomical Institute, University of Basel, Pestalozzistrasse 20, CH-4056, Basel, Switzerland
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15
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Sommer B, Flores-Soto E, Gonzalez-Avila G. Cellular Na+ handling mechanisms involved in airway smooth muscle contraction (Review). Int J Mol Med 2017; 40:3-9. [PMID: 28534960 PMCID: PMC5466399 DOI: 10.3892/ijmm.2017.2993] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 04/20/2017] [Indexed: 12/17/2022] Open
Abstract
A decrease in bronchial diameter is designated as bronchoconstriction (BC) and impedes the flow of air through the airway. Asthma is characterized by inflammation of the airways, reversible BC and nonspecific hyperreactivity. These last two symptoms are dependent on airway smooth muscle. Stimuli that trigger contraction can be characterized as chemical (neurotransmitters, cytokines and terpenoids) and physical (volume inspired, air pressure). Both stimuli activate signaling pathways by acting on membrane proteins and facilitating the passage of ions through the membrane, generating a voltage change and a subsequent depolarization. Na+ plays an important role in preserving the resting membrane potential; this ion is extracted from the cells by the Na+/K+ ATPase (NKA) or introduced into the cytoplasm by the Na+/Ca2+ exchanger (NCX). During depolarization, Na+ appears to accumulate in specific regions beneath the plasma membrane, generating local concentration gradients which determine the handling of Ca2+. At rest, the smooth muscle has a basal tone that is preserved by the continuous adjustment of intracytoplasmic concentrations of Ca2+ and Na+. At homeostasis, the Na+ concentration is primarily dependent on three structures: the NKA, the NCX and non-specific cation channels (NSCC). These three structures, their functions and the available evidence of the probable role of Na+ in asthma are described in the present review.
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Affiliation(s)
- Bettina Sommer
- Department of Bronchial Hyperreactivity, National Institute of Respiratory Diseases 'Ismael Cosio Villegas', CP 14080 Mexico City, Mexico
| | - Edgar Flores-Soto
- Department of Pharmacology, Faculty of Medicine, National Autonomous University of Mexico, CP 04510 Mexico City, Mexico
| | - Georgina Gonzalez-Avila
- Biomedical Oncology Laboratory, Department of Chronic‑Degenerative Diseases, National Institute of Respiratory Diseases 'Ismael Cosio Villegas', CP 14080 Mexico City, Mexico
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16
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Structure-based dynamic arrays in regulatory domains of sodium-calcium exchanger (NCX) isoforms. Sci Rep 2017; 7:993. [PMID: 28428550 PMCID: PMC5430519 DOI: 10.1038/s41598-017-01102-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 03/24/2017] [Indexed: 02/06/2023] Open
Abstract
Mammalian Na+/Ca2+ exchangers, NCX1 and NCX3, generate splice variants, whereas NCX2 does not. The CBD1 and CBD2 domains form a regulatory tandem (CBD12), where Ca2+ binding to CBD1 activates and Ca2+ binding to CBD2 (bearing the splicing segment) alleviates the Na+-induced inactivation. Here, the NCX2-CBD12, NCX3-CBD12-B, and NCX3-CBD12-AC proteins were analyzed by small-angle X-ray scattering (SAXS) and hydrogen-deuterium exchange mass-spectrometry (HDX-MS) to resolve regulatory variances in the NCX2 and NCX3 variants. SAXS revealed the unified model, according to which the Ca2+ binding to CBD12 shifts a dynamic equilibrium without generating new conformational states, and where more rigid conformational states become more populated without any global conformational changes. HDX-MS revealed the differential effects of the B and AC exons on the folding stability of apo CBD1 in NCX3-CBD12, where the dynamic differences become less noticeable in the Ca2+-bound state. Therefore, the apo forms predefine incremental changes in backbone dynamics upon Ca2+ binding. These observations may account for slower inactivation (caused by slower dissociation of occluded Ca2+ from CBD12) in the skeletal vs the brain-expressed NCX2 and NCX3 variants. This may have physiological relevance, since NCX must extrude much higher amounts of Ca2+ from the skeletal cell than from the neuron.
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17
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Abstract
The Na+-Ca 2+ exchanger is a secondary active antiporter found in all excitable cells. This transporter couples transmembrane fluxes of Na+ to opposite fluxes of Ca2+. Under normal conditions, the energy stored in the electrochemical Na+ gradient is used to export Ca 2+ from the cytoplasm, thus contributing to cellular Ca2+ homeostasis, such as termination of Ca2+ transients during synaptic transmission in nerve terminals. The reversible and electrogenic properties of the Na+-Ca2+ exchanger suggest an interesting additional role of controlled Ca2+ entry, e.g., during action potential generation in axons. Moreover, under pathological conditions, such as anoxia/ischemia, the exchanger may function either to help extrude damaging Ca2+ loads entering via other pathways in neurons or mediate Ca2+ overload in axons. Cell geometry will influence the rate and extent of collapse of the Na+ gradient and membrane potential, the two main driving forces acting on the exchanger, which will in turn dictate to what extent and in which direction Ca2+ will be transported. The Na+-Ca2+ exchanger is subject to complex regulatory control by several ions and chemical messengers, and several recently identified isoforms are undoubtedly tailored for specific roles in different regions of the CNS. NEUROSCIENTIST 2:162-171, 1996
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Affiliation(s)
| | - Peter K. Stys
- Neurosciences Loeb Institute Ottawa Civic Hospital Ottawa,
Ontario
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18
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Giladi M, Tal I, Khananshvili D. Structural Features of Ion Transport and Allosteric Regulation in Sodium-Calcium Exchanger (NCX) Proteins. Front Physiol 2016; 7:30. [PMID: 26903880 PMCID: PMC4746289 DOI: 10.3389/fphys.2016.00030] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 01/19/2016] [Indexed: 01/14/2023] Open
Abstract
Na(+)/Ca(2+) exchanger (NCX) proteins extrude Ca(2+) from the cell to maintain cellular homeostasis. Since NCX proteins contribute to numerous physiological and pathophysiological events, their pharmacological targeting has been desired for a long time. This intervention remains challenging owing to our poor understanding of the underlying structure-dynamic mechanisms. Recent structural studies have shed light on the structure-function relationships underlying the ion-transport and allosteric regulation of NCX. The crystal structure of an archaeal NCX (NCX_Mj) along with molecular dynamics simulations and ion flux analyses, have assigned the ion binding sites for 3Na(+) and 1Ca(2+), which are being transported in separate steps. In contrast with NCX_Mj, eukaryotic NCXs contain the regulatory Ca(2+)-binding domains, CBD1 and CBD2, which affect the membrane embedded ion-transport domains over a distance of ~80 Å. The Ca(2+)-dependent regulation is ortholog, isoform, and splice-variant dependent to meet physiological requirements, exhibiting either a positive, negative, or no response to regulatory Ca(2+). The crystal structures of the two-domain (CBD12) tandem have revealed a common mechanism involving a Ca(2+)-driven tethering of CBDs in diverse NCX variants. However, dissociation kinetics of occluded Ca(2+) (entrapped at the two-domain interface) depends on the alternative-splicing segment (at CBD2), thereby representing splicing-dependent dynamic coupling of CBDs. The HDX-MS, SAXS, NMR, FRET, equilibrium (45)Ca(2+) binding and stopped-flow techniques provided insights into the dynamic mechanisms of CBDs. Ca(2+) binding to CBD1 results in a population shift, where more constraint conformational states become highly populated without global conformational changes in the alignment of CBDs. This mechanism is common among NCXs. Recent HDX-MS studies have demonstrated that the apo CBD1 and CBD2 are stabilized by interacting with each other, while Ca(2+) binding to CBD1 rigidifies local backbone segments of CBD2, but not of CBD1. The extent and strength of Ca(2+)-dependent rigidification at CBD2 is splice-variant dependent, showing clear correlations with phenotypes of matching NCX variants. Therefore, diverse NCX variants share a common mechanism for the initial decoding of the regulatory signal upon Ca(2+) binding at the interface of CBDs, whereas the allosteric message is shaped by CBD2, the dynamic features of which are dictated by the splicing segment.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University Tel Aviv, Israel
| | - Inbal Tal
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University Tel Aviv, Israel
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University Tel Aviv, Israel
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19
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Radhakrishnan VM, Kojs P, Ramalingam R, Midura-Kiela MT, Angeli P, Kiela PR, Ghishan FK. Experimental colitis is associated with transcriptional inhibition of Na+/Ca2+ exchanger isoform 1 (NCX1) expression by interferon γ in the renal distal convoluted tubules. J Biol Chem 2015; 290:8964-74. [PMID: 25648899 DOI: 10.1074/jbc.m114.616516] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Indexed: 01/20/2023] Open
Abstract
NCX1 is a Na(+)/Ca(2+) exchanger, which is believed to provide a key route for basolateral Ca(2+) efflux in the renal epithelia, thus contributing to renal Ca(2+) reabsorption. Altered mineral homeostasis, including intestinal and renal Ca(2+) transport may represent a significant component of the pathophysiology of the bone mineral density loss associated with Inflammatory Bowel Diseases (IBD). The objective of our research was to investigate the effects of TNBS and DSS colitis and related inflammatory mediators on renal Ncx1 expression. Colitis was associated with decreased renal Ncx1 expression, as examined by real-time RT-PCR, Western blotting, and immunofluorescence. In mIMCD3 cells, IFNγ significantly reduced Ncx1 mRNA and protein expression. Similar effects were observed in cells transiently transfected with a reporter construct bearing the promoter region of the kidney-specific Ncx1 gene. This inhibitory effect of IFNγ is mediated by STAT1 recruitment to the proximal promoter region of Ncx1. Further in vivo study with Stat1(-/-) mice confirmed that STAT1 is indeed required for the IFNγ mediated Ncx1 gene regulation. These results strongly support the hypothesis that impaired renal Ca(2+) handling occurs in experimental colitis. Negative regulation of NCX1- mediated renal Ca(2+) absorption by IFNγ may significantly contribute to the altered Ca(2+) homeostasis in IBD patients and to IBD-associated loss of bone mineral density.
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Affiliation(s)
| | - Pawel Kojs
- From the Departments of Pediatrics, Steele Children's Research Center and
| | | | | | - Peter Angeli
- Zanvyl Krieger School of Arts and Sciences Johns Hopkins University, Baltimore, Maryland 21218
| | - Pawel R Kiela
- From the Departments of Pediatrics, Steele Children's Research Center and Immunobiology, University of Arizona Health Sciences Center, Tucson, Arizona 85724, and
| | - Fayez K Ghishan
- From the Departments of Pediatrics, Steele Children's Research Center and
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20
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Towards Understanding the Role of the Na+-Ca2+ Exchanger Isoform 3. Rev Physiol Biochem Pharmacol 2015; 168:31-57. [DOI: 10.1007/112_2015_23] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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21
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Scheff NN, Yilmaz E, Gold MS. The properties, distribution and function of Na(+)-Ca(2+) exchanger isoforms in rat cutaneous sensory neurons. J Physiol 2014; 592:4969-93. [PMID: 25239455 PMCID: PMC4259538 DOI: 10.1113/jphysiol.2014.278036] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 09/10/2014] [Indexed: 11/08/2022] Open
Abstract
The Na(+)-Ca(2+) exchanger (NCX) appears to play an important role in the regulation of the high K(+)-evoked Ca(2+) transient in putative nociceptive dorsal root ganglion (DRG) neurons. The purpose of the present study was to (1) characterize the properties of NCX activity in subpopulations of DRG neurons, (2) identify the isoform(s) underlying NCX activity, and (3) begin to assess the function of the isoform(s) in vivo. In retrogradely labelled neurons from the glabrous skin of adult male Sprague-Dawley rats, NCX activity, as assessed with fura-2-based microfluorimetry, was only detected in putative nociceptive IB4+ neurons. There were two modes of NCX activity: one was evoked in response to relatively large and long lasting (∼325 nm for >12 s) increases in the concentration of intracellular Ca(2+) ([Ca(2+)]i), and a second was active at resting [Ca(2+)]i > ∼150 nm. There also were two modes of evoked activity: one that decayed relatively rapidly (<5 min) and a second that persisted (>10 min). Whereas mRNA encoding all three NCX isoforms (NCX1-3) was detected in putative nociceptive cutaneous neurons with single cell PCR, pharmacological analysis and small interfering RNA (siRNA) knockdown of each isoform in vivo suggested that NCX2 and 3 were responsible for NCX activity. Western blot analyses suggested that NCX isoforms were differentially distributed within sensory neurons. Functional assays of excitability, action potential propagation, and nociceptive behaviour suggest NCX activity has little influence on excitability per se, but instead influences axonal conduction velocity, resting membrane potential, and nociceptive threshold. Together these results indicate that the function of NCX in the regulation of [Ca(2+)]i in putative nociceptive neurons may be unique relative to other cells in which these exchanger isoforms have been characterized and it has the potential to influence sensory neuron properties at multiple levels.
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Affiliation(s)
- N N Scheff
- The Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA, USA Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, PA, USA
| | - E Yilmaz
- The Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA, USA Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, PA, USA
| | - M S Gold
- The Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA, USA Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, PA, USA
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22
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Sharma V, O'Halloran DM. Recent structural and functional insights into the family of sodium calcium exchangers. Genesis 2013; 52:93-109. [PMID: 24376088 DOI: 10.1002/dvg.22735] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 12/04/2013] [Accepted: 12/08/2013] [Indexed: 01/08/2023]
Abstract
Maintenance of calcium homeostasis is necessary for the development and survival of all animals. Calcium ions modulate excitability and bind effectors capable of initiating many processes such as muscular contraction and neurotransmission. However, excessive amounts of calcium in the cytosol or within intracellular calcium stores can trigger apoptotic pathways in cells that have been implicated in cardiac and neuronal pathologies. Accordingly, it is critical for cells to rapidly and effectively regulate calcium levels. The Na(+) /Ca(2+) exchangers (NCX), Na(+) /Ca(2+) /K(+) exchangers (NCKX), and Ca(2+) /Cation exchangers (CCX) are the three classes of sodium calcium antiporters found in animals. These exchanger proteins utilize an electrochemical gradient to extrude calcium. Although they have been studied for decades, much is still unknown about these proteins. In this review, we examine current knowledge about the structure, function, and physiology and also discuss their implication in various developmental disorders. Finally, we highlight recent data characterizing the family of sodium calcium exchangers in the model system, Caenorhabditis elegans, and propose that C. elegans may be an ideal model to complement other systems and help fill gaps in our knowledge of sodium calcium exchange biology.
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Affiliation(s)
- Vishal Sharma
- Department of Biological Sciences, The George Washington University, Washington, DC; Institute for Neuroscience, The George Washington University, Washington, DC
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23
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Khananshvili D. Sodium-calcium exchangers (NCX): molecular hallmarks underlying the tissue-specific and systemic functions. Pflugers Arch 2013; 466:43-60. [PMID: 24281864 DOI: 10.1007/s00424-013-1405-y] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2013] [Revised: 11/06/2013] [Accepted: 11/09/2013] [Indexed: 12/19/2022]
Abstract
NCX proteins explore the electrochemical gradient of Na(+) to mediate Ca(2+)-fluxes in exchange with Na(+) either in the Ca(2+)-efflux (forward) or Ca(2+)-influx (reverse) mode, whereas the directionality depends on ionic concentrations and membrane potential. Mammalian NCX variants (NCX1-3) and their splice variants are expressed in a tissue-specific manner to modulate the heartbeat rate and contractile force, the brain's long-term potentiation and learning, blood pressure, renal Ca(2+) reabsorption, the immune response, neurotransmitter and insulin secretion, apoptosis and proliferation, mitochondrial bioenergetics, etc. Although the forward mode of NCX represents a major physiological module, a transient reversal of NCX may contribute to EC-coupling, vascular constriction, and synaptic transmission. Notably, the reverse mode of NCX becomes predominant in pathological settings. Since the expression levels of NCX variants are disease-related, the selective pharmacological targeting of tissue-specific NCX variants could be beneficial, thereby representing a challenge. Recent structural and biophysical studies revealed a common module for decoding the Ca(2+)-induced allosteric signal in eukaryotic NCX variants, although the phenotype variances in response to regulatory Ca(2+) remain unclear. The breakthrough discovery of the archaebacterial NCX structure may serve as a template for eukaryotic NCX, although the turnover rates of the transport cycle may differ ~10(3)-fold among NCX variants to fulfill the physiological demands for the Ca(2+) flux rates. Further elucidation of ion-transport and regulatory mechanisms may lead to selective pharmacological targeting of NCX variants under disease conditions.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel,
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Khananshvili D. The SLC8 gene family of sodium-calcium exchangers (NCX) - structure, function, and regulation in health and disease. Mol Aspects Med 2013; 34:220-35. [PMID: 23506867 DOI: 10.1016/j.mam.2012.07.003] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2011] [Accepted: 03/08/2012] [Indexed: 01/12/2023]
Abstract
The SLC8 gene family encoding Na(+)/Ca(2+) exchangers (NCX) belongs to the CaCA (Ca(2+)/Cation Antiporter) superfamily. Three mammalian genes (SLC8A1, SLC8A2, and SLC8A3) and their splice variants are expressed in a tissue-specific manner to mediate Ca(2+)-fluxes across the cell-membrane and thus, significantly contribute to regulation of Ca(2+)-dependent events in many cell types. A long-wanted mitochondrial Na(+)/Ca(2+) exchanger has been recently identified as NCLX protein, representing a gene product of SLC8B1. Distinct NCX isoform/splice variants contribute to excitation-contraction coupling, long-term potentiation of the brain and learning, blood pressure regulation, immune response, neurotransmitter and insulin secretion, mitochondrial bioenergetics, etc. Altered expression and regulation of NCX proteins contribute to distorted Ca(2+)-homeostasis in heart failure, arrhythmia, cerebral ischemia, hypertension, diabetes, renal Ca(2+) reabsorption, muscle dystrophy, etc. Recently, high-resolution X-ray structures of Ca(2+)-binding regulatory domains of eukaryotic NCX and of full-size prokaryotic NCX have become available and the dynamic properties have been analyzed by advanced biophysical approaches. Molecular silencing/overexpression of NCX in cellular systems and organ-specific KO mouse models provided useful information on the contribution of distinct NCX variants to cellular and systemic functions under various pathophysiological conditions. Selective inhibition or activation of predefined NCX variants in specific diseases might have clinical relevance, although this breakthrough has not yet been realized. A better understanding of the underlying molecular mechanisms as well as the development of in vitro procedures for high-throughput screening of "drug-like" compounds may lead to selective pharmacological targeting of NCX variants.
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Affiliation(s)
- Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel.
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Giladi M, Hiller R, Hirsch JA, Khananshvili D. Population shift underlies Ca2+-induced regulatory transitions in the sodium-calcium exchanger (NCX). J Biol Chem 2013; 288:23141-9. [PMID: 23798674 DOI: 10.1074/jbc.m113.471698] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In eukaryotic Na(+)/Ca(2+) exchangers (NCX) the Ca(2+) binding CBD1 and CBD2 domains form a two-domain regulatory tandem (CBD12). An allosteric Ca(2+) sensor (Ca3-Ca4 sites) is located on CBD1, whereas CBD2 contains a splice-variant segment. Recently, a Ca(2+)-driven interdomain switch has been described, albeit how it couples Ca(2+) binding with signal propagation remains unclear. To resolve the dynamic features of Ca(2+)-induced conformational transitions we analyze here distinct splice variants and mutants of isolated CBD12 at varying temperatures by using small angle x-ray scattering (SAXS) and equilibrium (45)Ca(2+) binding assays. The ensemble optimization method SAXS analysis demonstrates that the apo and Mg(2+)-bound forms of CBD12 are highly flexible, whereas Ca(2+) binding to the Ca3-Ca4 sites results in a population shift of conformational landscape to more rigidified states. Population shift occurs even under conditions in which no effect of Ca(2+) is observed on the globally derived Dmax (maximal interatomic distance), although under comparable conditions a normal [Ca(2+)]-dependent allosteric regulation occurs. Low affinity sites (Ca1-Ca2) of CBD1 do not contribute to Ca(2+)-induced population shift, but the occupancy of these sites by 1 mM Mg(2+) shifts the Ca(2+) affinity (Kd) at the neighboring Ca3-Ca4 sites from ∼ 50 nM to ∼ 200 nM and thus, keeps the primary Ca(2+) sensor (Ca3-Ca4 sites) within a physiological range. Thus, Ca(2+) binding to the Ca3-Ca4 sites results in a population shift, where more constraint conformational states become highly populated at dynamic equilibrium in the absence of global conformational transitions in CBD alignment.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Functional comparison of the reverse mode of Na+/Ca2+ exchangers NCX1.1 and NCX1.5 expressed in CHO cells. Acta Pharmacol Sin 2013; 34:691-8. [PMID: 23564083 DOI: 10.1038/aps.2013.4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
AIM To investigate the reverse mode function of Na(+)/Ca(2+) exchangers NCX1.1 and NCX1.5 expressed in CHO cells as well as their modulations by PKC and PKA. METHODS CHO-K1 cells were transfected with pcDNA3.1 (+) plasmid carrying cDNA of rat cardiac NCX1.1 and brain NCX1.5. The expression of NCX1.1 and NCX1.5 was examined using Western blot analysis. The intracellular Ca(2+) level ([Ca(2+)]i) was measured using Ca(2+) imaging. Whole-cell NCX currents were recorded using patch-clamp technique. Reverse mode NCX activity was elicited by perfusion with Na(+)-free medium. Ca(2+) paradox was induced by Ca(2+)-free EBSS medium, followed by Ca(2+)-containing solution (1.8 or 3.8 mmol/L CaCl2). RESULTS The protein levels of NCX1.1 and NCX1.5 expressed in CHO cells had no significant difference. The reverse modes of NCX1.1 and NCX1.5 in CHO cells exhibited a transient increase of [Ca(2+)]i, which was followed by a Ca(2+) level plateau at higher external Ca(2+) concentrations. In contrast, the wild type CHO cells showed a steady increase of [Ca(2+)]i at higher external Ca(2+) concentrations. The PKC activator PMA (0.3-10 μmol/L) and PKA activator 8-Br-cAMP (10-100 μmol/L) significantly enhanced the reverse mode activity of NCX1.1 and NCX1.5 in CHO cells. NCX1.1 was 2.4-fold more sensitive to PKC activation than NCX1.5, whereas the sensitivity of the two NCX isoforms to PKA activation had no difference. Both PKC- and PKA-enhanced NCX reverse mode activities in CHO cells were suppressed by NCX inhibitor KB-R7943 (30 μmol/L). CONCLUSION Both NCX1.1 and NCX1.5 are functional in regulating and maintaining stable [Ca(2+)]i in CHO cells and differentially regulated by PKA and PKC. The two NCX isoforms might be useful drug targets for heart and brain protection.
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Ota Y, Kawanai T, Watanabe R, Nishimura A, Ago Y, Takuma K, Matsuda T. Effect of overexpression of the brain-specific Na(+)/Ca(2+) exchanger splice variant NCX1.5 on NO cytotoxicity in HEK293 cells. J Pharmacol Sci 2013; 121:351-4. [PMID: 23538676 DOI: 10.1254/jphs.13012sc] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
Nitric oxide (NO) induces cytotoxicity in neuronal and glial cells via activation of the Na(+)/Ca(2+) exchanger (NCX). This study examined the role of the predominant brain-specific NCX splice variant NCX1.5 in NO-induced cytotoxicity in the HEK293 cell expression system. Cells were transfected with the plasmid construct pcDNA3.1/V5-His containing full-length rat NCX1.5 cDNA. There was no difference in the cytotoxic effects of the NO donors sodium nitroprusside and S-nitroso-N-acetylpenicillamine between control and transfected cells. These results suggest that NO cytotoxicity is not dependent on NCX1.5.
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Affiliation(s)
- Yuki Ota
- Laboratory of Medicinal Pharmacology, Graduate School of Pharmaceutical Sciences, Osaka University, Japan
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Yang YC, Kao LS. Regulation of sodium-calcium exchanger activity by creatine kinase. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:163-73. [PMID: 23224878 DOI: 10.1007/978-1-4614-4756-6_14] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
It has been shown that in rat heart NCX1 exists in a macromolecular -complex including PKA, PKA-anchoring protein, PKC, and phosphatases PP1 and PP2A. In addition, several lines of evidence suggest that the interactions of the exchanger with other molecules are closely associated with its function in regulation of [Ca(2+)](i). NCX contains a large intracellular loop (NCXIL) that is responsible for regulating NCX activity. We used the yeast two-hybrid method to screen a human heart cDNA library and found that the C-terminal region of sarcomeric mitochondrial creatine kinase (sMiCK) interacted with NCX1IL. Among the four creatine kinase (CK) isozymes, both sMiCK and the muscle-type cytosolic creatine kinase (CKM) co-immunoprecipitated with NCX1. Both sMiCK and CKM were able to produce a recovery in the decreased NCX1 activity that was lost under energy-compromised conditions. This regulation is mediated through a putative PKC phosphorylation site of sMiCK and CKM. The catalytic activity of sMiCK and CKM is not required for their regulation of NCX1 activity. Our results suggest a novel mechanism for the regulation of NCX1 activity and a novel role for CK.
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Affiliation(s)
- Ya-Chi Yang
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan, Republic of China
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Giladi M, Friedberg I, Fang X, Hiller R, Wang YX, Khananshvili D. G503 is obligatory for coupling of regulatory domains in NCX proteins. Biochemistry 2012; 51:7313-20. [PMID: 22924554 DOI: 10.1021/bi300739z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In multidomain proteins, interdomain linkers allow an efficient transfer of regulatory information, although it is unclear how the information encoded in the linker structure coins dynamic coupling. Allosteric regulation of NCX proteins involves Ca(2+)-driven tethering of regulatory CBD1 and CBD2 (through a salt bridge network) accompanied by alignment of CBDs and Ca(2+) occlusion at the interface of the two CBDs. Here we investigated "alanine-walk" substitutions in the CBD1-CBD2 linker (501-HAGIFT-506) and found that among all linker residues, only G503 is obligatory for Ca(2+)-induced reorientations of CBDs and slow dissociation of occluded Ca(2+). Moreover, swapping between positions A502 and G503 in the CBD1-CBD2 linker results in a complete loss of slow dissociation of occluded Ca(2+), meaning that dynamic coupling of CBDs requires an exact pose of glycine at position 503. Therefore, accumulating data revealed that position 503 occupied by glycine is absolutely required for Ca(2+)-driven tethering of CBDs, which in turn limits the linker's flexibility and, thus, restricts CBD movements. Because G503 is extremely well conserved in eukaryotic NCX proteins, the information encoded in G503 is essential for dynamic coupling of the two-domain CBD tandem and, thus, for propagation of the allosteric signal.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Abstract
The binding of Ca(2+) to two adjacent Ca(2+)-binding domains, CBD1 and CBD2, regulates ion transport in the Na(+)/Ca(2+) exchanger. As sensors for intracellular Ca(2+), the CBDs form electrostatic switches that induce the conformational changes required to initiate and sustain Na(+)/Ca(2+) exchange. Depending on the presence of a few key residues in the Ca(2+)-binding sites, zero to four Ca(2+) ions can bind with affinities between 0.1 to 20 μm. Importantly, variability in CBD2 as a consequence of alternative splicing modulates not only the number and affinities of the Ca(2+)-binding sites in CBD2 but also the Ca(2+) affinities in CBD1.
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Affiliation(s)
- Mark Hilge
- Center for Cellular Imaging and NanoAnalytics (C-CINA), Biozentrum, University Basel, CH-4058 Basel, Switzerland.
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Giladi M, Bohbot H, Buki T, Schulze DH, Hiller R, Khananshvili D. Dynamic features of allosteric Ca2+ sensor in tissue-specific NCX variants. Cell Calcium 2012; 51:478-85. [PMID: 22571864 DOI: 10.1016/j.ceca.2012.04.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 04/10/2012] [Accepted: 04/12/2012] [Indexed: 11/19/2022]
Abstract
The Na(+)-Ca(2+) exchanger (NCX) mediated Ca(2+) fluxes are essential for handling Ca(2+) homeostasis in many cell-types. Eukaryotic NCX variants contain regulatory CBD1 and CBD2 domains, whereas in distinct variants the Ca(2+) binding to Ca3-Ca4 sites of CBD1 results either in sustained activation, inhibition or no effect. CBD2 contains an alternatively spliced segment, which is expressed in a tissue-specific manner although its impact on allosteric regulation remains unclear. Recent studies revealed that the Ca(2+) binding to Ca3-Ca4 sites results in interdomain tethering of CBDs, which rigidifies CBDs movements with accompanied slow dissociation of "occluded" Ca(2+). Here we investigate the effects of CBD2 variants on Ca(2+) occlusion in the two-domain construct (CBD12). Mutational studies revealed that both sites (Ca3 and Ca4) contribute to Ca(2+) occlusion, whereas after dissociation of the first Ca(2+) ion the second Ca(2+) ion becomes occluded. This mechanism is common for the brain, kidney and cardiac splice variants of CBD12, although the occluded Ca(2+) exhibits 20-50-fold difference in off-rates among the tested variants. Therefore, the spliced exons on CBD2 affect the rate-limiting step of the occluded Ca(2+) dissociation at the primary regulatory sensor to shape dynamic features of allosteric regulation in NCX variants.
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Affiliation(s)
- Moshe Giladi
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv, Israel
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Hnatowich M, Le HD, DeMoissac D, Ranson K, Yurkov V, Gilchrist JS, Omelchenko A, Hryshko LV. μ-Calpain-mediated deregulation of cardiac, brain, and kidney NCX1 splice variants. Cell Calcium 2012; 51:164-70. [DOI: 10.1016/j.ceca.2011.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2011] [Revised: 12/08/2011] [Accepted: 12/09/2011] [Indexed: 11/26/2022]
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Abstract
Nuclear lipid metabolism is implicated in various processes, including transcription, splicing, and DNA repair. Sphingolipids play roles in numerous cellular functions, and an emerging body of literature has identified roles for these lipid mediators in distinct nuclear processes. Different sphingolipid species are localized in various subnuclear domains, including chromatin, the nuclear matrix, and the nuclear envelope, where sphingolipids exert specific regulatory and structural functions. Sphingomyelin, the most abundant nuclear sphingolipid, plays both structural and regulatory roles in chromatin assembly and dynamics in addition to being an integral component of the nuclear matrix. Sphingosine-1-phosphate modulates histone acetylation, sphingosine is a ligand for steroidogenic factor 1, and nuclear accumulation of ceramide has been implicated in apoptosis. Finally, nuclear membrane-associated ganglioside GM1 plays a pivotal role in Ca(2+) homeostasis. This review highlights research on the factors that control nuclear sphingolipid metabolism and summarizes the roles of these lipids in various nuclear processes.
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Affiliation(s)
- Natasha C Lucki
- School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
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34
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Abstract
GM1 and GD1a gangliosides occur in both membranes of the nuclear envelope (NE) together with two isoforms of neuraminidase. The Neu3 isoform of neuraminidase occurs in the inner membrane of the NE and Neu1 in the outer membrane. Both isoforms convert GD1a to GM1 within the respective membranes. GM1 in the inner membrane is tightly associated with a Na(+) /Ca(2+) exchanger (NCX) and potentiates the latter's activity. The NCX/GM1 complex mediates transfer of nucleoplasmic Ca(2+) to the NE lumen and hence to the endoplasmic reticulum (ER) with which it is continuous. Since cytoplasmic- and nucleoplasmic Ca(2+) are in homeostatic equilibrium (via nuclear pores), the nuclear NCX/GM1 complex acts to gate Ca(2+) transfer from cytosol to ER via nucleoplasm and NE. This constitutes an alternate route to the SERCA pump, indicating the influence of nuclear NCX/GM1 on whole cell Ca(2+) homeostasis. Use of cameleon-fluorescent Ca(2+) indicators (R. Tsien) demonstrated no Ca(2+) transfer from cytosol/nucleoplasm to ER in cells lacking nuclear NCX (Jurkat), and significantly reduced Ca(2+) transfer in cells lacking nuclear GM1 (NG-CR72). NCX/GM1 appears in the NE of neurons as they differentiate and serves a cytoprotective function, as seen in the high susceptibility of GalNAcT-/- knockout mice to kainate-induced seizure activity. This was alleviated by intraperitoneal injections of LIGA-20 a derivative of GM1 that is able (unlike GM1 itself) to traverse the blood brain barrier and neuronal plasma membrane and insert into the NE where it restores NCX exchanger activity. Absence or loss of nuclear GM1 renders cells vulnerable to apoptotic elimination.
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Affiliation(s)
- Robert Ledeen
- Department of Neurology & Neurosciences, New Jersey Medical School, UMDNJ, Newark, NJ 07103, USA.
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Liu B, Peel SE, Fox J, Hall IP. Reverse mode Na+/Ca2+ exchange mediated by STIM1 contributes to Ca2+ influx in airway smooth muscle following agonist stimulation. Respir Res 2010; 11:168. [PMID: 21126331 PMCID: PMC3012663 DOI: 10.1186/1465-9921-11-168] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2009] [Accepted: 12/02/2010] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Agonist stimulation of airway smooth muscle (ASM) results in IP3 mediated Ca2+ release from the sarcoplasmic reticulum followed by the activation of store operated and receptor operated non-selective cation channels. Activation of these non-selective channels also results in a Na+ influx. This localised increase in Na+ levels can potentially switch the Na+/Ca2+ exchanger into reverse mode and so result in a further influx of Ca2+. The aim of this study was to characterise the expression and physiological function of the Na+/Ca2+ exchanger in cultured human bronchial smooth muscle cells and determine its contribution to agonist induced Ca2+ influx into these cells. METHODS The expression profile of NCX (which encodes the Na+/Ca2+ exchanger) homologues in cultured human bronchial smooth muscle cells was determined by reverse transcriptase PCR. The functional activity of reverse mode NCX was investigated using a combination of whole cell patch clamp, intracellular Ca2+ measurements and porcine airway contractile analyses. KB-R7943 (an antagonist for reverse mode NCX) and target specific siRNA were utilised as tools to inhibit NCX function. RESULTS NCX1 protein was detected in cultured human bronchial smooth muscle cells (HBSMC) cells and NCX1.3 was the only mRNA transcript variant detected. A combination of intracellular Na+ loading and addition of extracellular Ca2+ induced an outwardly rectifying current which was augmented following stimulation with histamine. This outwardly rectifying current was inhibited by 10 μM KB-R7943 (an antagonist of reverse mode NCX1) and was reduced in cells incubated with siRNA against NCX1. Interestingly, this outwardly rectifying current was also inhibited following knockdown of STIM1, suggesting for the first time a link between store operated cation entry and NCX1 activation. In addition, 10 μM KB-R7943 inhibited agonist induced changes in cytosolic Ca2+ and induced relaxation of porcine peripheral airways. CONCLUSIONS Taken together, these data demonstrate a potentially important role for NCX1 in control of Ca2+ homeostasis and link store depletion via STIM1 directly with NCX activation.
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Affiliation(s)
- Bo Liu
- Division of Therapeutics and Molecular Medicine, Respiratory Biomedical Research Unit, Queens Medical Centre, Nottingham, UK
| | - Samantha E Peel
- Division of Therapeutics and Molecular Medicine, Respiratory Biomedical Research Unit, Queens Medical Centre, Nottingham, UK
| | - Jane Fox
- Division of Therapeutics and Molecular Medicine, Respiratory Biomedical Research Unit, Queens Medical Centre, Nottingham, UK
| | - Ian P Hall
- Division of Therapeutics and Molecular Medicine, Respiratory Biomedical Research Unit, Queens Medical Centre, Nottingham, UK
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Ledeen RW, Wu G. In Search of a Solution to the Sphinx-Like Riddle of GM1. Neurochem Res 2010; 35:1867-74. [DOI: 10.1007/s11064-010-0286-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/28/2010] [Indexed: 11/30/2022]
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Martinez Y, N'Gouemo P. Blockade of the sodium calcium exchanger exhibits anticonvulsant activity in a pilocarpine model of acute seizures in rats. Brain Res 2010; 1366:211-6. [PMID: 20888801 DOI: 10.1016/j.brainres.2010.09.100] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Revised: 09/23/2010] [Accepted: 09/24/2010] [Indexed: 11/28/2022]
Abstract
Recent evidence suggests that the sodium calcium exchanger (NCX) may contribute to the etiology of pentylenetetrazol-induced seizures. Here we further investigated the role of NCX in the etiology of seizures by quantifying the effects of KB-R7943 and SN-6, potent inhibitors of the reverse mode of NCX subtypes 3 (NCX3) and 1 (NCX1), respectively, on the occurrence of acute seizures and status epilepticus induced by intraperitoneal administration of pilocarpine, a muscarinic acetylcholine receptor agonist. Pretreatment with KB-R7943 significantly reduced the incidence of pilocarpine-induced seizures and status epilepticus in 22-56% of treated animals. In the remaining animals that exhibited seizures, KB-R7943 pretreatment delayed the onset of seizures and status epilepticus, and reduced seizure severity. Delayed onset of seizures and reduced seizure severity also were seen following pretreatment with SN-6. These findings suggest that altered NCX activity may contribute to the pathophysiology of pilocarpine-induced seizures and status epilepticus.
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Affiliation(s)
- Yuris Martinez
- Department of Pediatrics, Bldg D, Room 285, Georgetown University Medical Center, 3900 Reservoir Rd, NW, Washington DC 20057, USA
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Giladi M, Boyman L, Mikhasenko H, Hiller R, Khananshvili D. Essential role of the CBD1-CBD2 linker in slow dissociation of Ca2+ from the regulatory two-domain tandem of NCX1. J Biol Chem 2010; 285:28117-25. [PMID: 20587421 PMCID: PMC2934676 DOI: 10.1074/jbc.m110.127001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Revised: 06/28/2010] [Indexed: 11/06/2022] Open
Abstract
In NCX proteins CBD1 and CBD2 domains are connected through a short linker (3 or 4 amino acids) forming a regulatory tandem (CBD12). Only three of the six CBD12 Ca(2+)-binding sites contribute to NCX regulation. Two of them are located on CBD1 (K(d) = approximately 0.2 microM), and one is on CBD2 (K(d) = approximately 5 microM). Here we analyze how the intrinsic properties of individual regulatory sites are affected by linker-dependent interactions in CBD12 (AD splice variant). The three sites of CBD12 and CBD1 + CBD2 have comparable K(d) values but differ dramatically in their Ca(2+) dissociation kinetics. CBD12 exhibits multiphasic kinetics for the dissociation of three Ca(2+) ions (k(r) = 280 s(-1), k(f) = 7 s(-1), and k(s) = 0.4 s(-1)), whereas the dissociation of two Ca(2+) ions from CBD1 (k(f) = 16 s(-1)) and one Ca(2+) ion from CBD2 (k(r) = 125 s(-1)) is monophasic. Insertion of seven alanines into the linker (CBD12-7Ala) abolishes slow dissociation of Ca(2+), whereas the kinetic and equilibrium properties of three Ca(2+) sites of CBD12-7Ala and CBD1 + CBD2 are similar. Therefore, the linker-dependent interactions in CBD12 decelerate the Ca(2+) on/off kinetics at a specific CBD1 site by 50-80-fold, thereby representing Ca(2+) "occlusion" at CBD12. Notably, the kinetic and equilibrium properties of the remaining two sites of CBD12 are "linker-independent," so their intrinsic properties are preserved in CBD12. In conclusion, the dynamic properties of three sites are specifically modified, conserved, diversified, and integrated by the linker in CBD12, thereby generating a wide range dynamic sensor.
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Affiliation(s)
- Moshe Giladi
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Liron Boyman
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Helen Mikhasenko
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Reuben Hiller
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Daniel Khananshvili
- From the Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Elbaz B, Valitsky M, Davidov G, Rahamimoff H. Cyclophilin A Is Involved in Functional Expression of the Na+−Ca2+ Exchanger NCX1. Biochemistry 2010; 49:7634-42. [DOI: 10.1021/bi1008722] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Benayahu Elbaz
- Department of Biochemistry and Molecular Biology, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel
| | - Michael Valitsky
- Department of Biochemistry and Molecular Biology, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel
| | - Geula Davidov
- Department of Biochemistry and Molecular Biology, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel
| | - Hannah Rahamimoff
- Department of Biochemistry and Molecular Biology, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel
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Yang YC, Fann MJ, Chang WH, Tai LH, Jiang JH, Kao LS. Regulation of sodium-calcium exchanger activity by creatine kinase under energy-compromised conditions. J Biol Chem 2010; 285:28275-85. [PMID: 20576602 DOI: 10.1074/jbc.m110.141424] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Na(+)/Ca(2+) exchanger (NCX) is one of the major mechanisms for removing Ca(2+) from the cytosol especially in cardiac myocytes and neurons, where their physiological activities are triggered by an influx of Ca(2+). NCX contains a large intracellular loop (NCXIL) that is responsible for regulating NCX activity. Recent evidence has shown that proteins, including kinases and phosphatases, associate with NCX1IL to form a NCX1 macromolecular complex. To search for the molecules that interact with NCX1IL and regulate NCX1 activity, we used the yeast two-hybrid method to screen a human heart cDNA library and found that the C-terminal region of sarcomeric mitochondrial creatine kinase (sMiCK) interacted with NCX1IL. Moreover, both sMiCK and the muscle-type creatine kinase (CKM) coimmunoprecipitated with NCX1 using lysates of cardiacmyocytes and HEK293T cells that transiently expressed NCX1 and various creatine kinases. Both sMiCK and CKM were able to produce a recovery in the decreased NCX1 activity that was lost under energy-compromised conditions. This regulation is mediated through a putative PKC phosphorylation site of sMiCK and CKM. The autophosphorylation and the catalytic activity of sMiCK and CKM are not required for their regulation of NCX1 activity. Our results suggest a novel mechanism for the regulation of NCX1 activity.
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Affiliation(s)
- Ya-Chi Yang
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei 112, Taiwan, Republic of China
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Algara-Suárez P, Mejía-Elizondo R, Sims SM, Saavedra-Alanis VM, Espinosa-Tanguma R. The 1.3 isoform of Na+-Ca 2+ exchanger expressed in guinea pig tracheal smooth muscle is less sensitive to KB-R7943. J Physiol Biochem 2010; 66:117-25. [PMID: 20428991 DOI: 10.1007/s13105-010-0016-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Accepted: 04/13/2010] [Indexed: 10/19/2022]
Abstract
The sodium-calcium exchanger (NCX) plays a major role in the regulation of cytosolic Ca(2+) in muscle cells. In this work, we performed force experiments to explore the role of NCX during contraction and relaxation of Cch-stimulated guinea pig tracheal smooth muscle strips. This tissue showed low sensitivity to NCX inhibitor KB-R7943 (IC50, 57 +/- 2 microM), although a complete relaxation was obtained by NCX inhibition at 100 microM. Interestingly, relaxation after washing the agonist was prolonged in the absence of external Na(+), whereas washing without Na(+) and in the presence of KB-R7943 resembled control conditions with physiological solution. Altogether, this suggests the reversal of NCX to a Ca(2+) influx mode by the manipulation on the Na(+) gradient, which can be inhibited by KB-R7943. In order to understand the low sensitivity to KB-R7943, we studied the molecular aspects of the NCX expressed in this tissue and found that the isoform of NCX expressed is 1.3, similar to that described in human tracheal smooth muscle. Sequencing revealed that amino acid 19 in exon B is phenylalanine, whereas in its human counterpart is leucine, and that the first amino acid after exon D is aspartate instead of glutamate in humans. Results herein presented are discussed in term of their possible functional implications in the exchanger activity and thus in airway physiology.
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Affiliation(s)
- Paola Algara-Suárez
- Department of Physiology, Facultad de Medicina de la Universidad Autónoma de San Luis Potosí, Av. V. Carranza 2405, San Luis Potosí, San Luis Potosí 78210, Mexico
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43
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Breukels V, Vuister GW. Binding of calcium is sensed structurally and dynamically throughout the second calcium-binding domain of the sodium/calcium exchanger. Proteins 2010; 78:1813-24. [DOI: 10.1002/prot.22695] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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Kepp K, Org E, Sõber S, Kelgo P, Viigimaa M, Veldre G, Tõnisson N, Juhanson P, Putku M, Kindmark A, Kozich V, Laan M. Hypervariable intronic region in NCX1 is enriched in short insertion-deletion polymorphisms and showed association with cardiovascular traits. BMC MEDICAL GENETICS 2010; 11:15. [PMID: 20109173 PMCID: PMC2832636 DOI: 10.1186/1471-2350-11-15] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Accepted: 01/28/2010] [Indexed: 01/07/2023]
Abstract
Background Conserved non-coding regions (CNR) have been shown to harbor gene expression regulatory elements. Genetic variations in these regions may potentially contribute to complex disease susceptibility. Methods We targeted CNRs of cardiovascular disease (CVD) candidate gene, Na(+)-Ca(2+) exchanger (NCX1) with polymorphism screening among CVD patients (n = 46) using DHPLC technology. The flanking region (348 bp) of the 14 bp indel in intron 2 was further genotyped by DGGE assay in two Eastern-European CVD samples: essential hypertension (HYPEST; 470 cases, 652 controls) and coronary artery disease, CAD (CADCZ; 257 cases, controls 413). Genotype-phenotype associations were tested by regression analysis implemented in PLINK. Alignments of primate sequences were performed by ClustalW2. Results Nine of the identified NCX1 variants were either singletons or targeted by commercial platforms. The 14 bp intronic indel (rs11274804) was represented with substantial frequency in HYPEST (6.82%) and CADCZ (14.58%). Genotyping in Eastern-Europeans (n = 1792) revealed hypervariable nature of this locus, represented by seven alternative alleles. The alignments of human-chimpanzee-macaque sequences showed that the major human variant (allele frequency 90.45%) was actually a human-specific deletion compared to other primates. In humans, this deletion was surrounded by other short (5-43 bp) deletion variants and a duplication (40 bp) polymorphism possessing overlapping breakpoints. This indicates a potential indel hotspot, triggered by the initial deletion in human lineage. An association was detected between the carrier status of 14 bp indel ancestral allele and CAD (P = 0.0016, OR = 2.02; Bonferroni significance level alpha = 0.0045), but not with hypertension. The risk for the CAD development was even higher among the patients additionally diagnosed with metabolic syndrome (P = 0.0014, OR = 2.34). Consistent with the effect on metabolic processes, suggestive evidence for the association with heart rate, serum triglyceride and LDL levels was detected (P = 0.04). Conclusions Compared to SNPs targeted by large number of locus-specific and genome-wide assays, considerably less attention has been paid to short indel variants in the human genome. The data of genome dynamics, mutation rate and population genetics of short indels, as well as their impact on gene expressional profile and human disease susceptibility is limited. The characterization of NCX1 intronic hypervariable non-coding region enriched in human-specific indel variants contributes to this gap of knowledge.
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Affiliation(s)
- Katrin Kepp
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
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Sakamoto K, Owada Y, Shikama Y, Wada I, Waguri S, Iwamoto T, Kimura J. Involvement of Na+/Ca2+ exchanger in migration and contraction of rat cultured tendon fibroblasts. J Physiol 2009; 587:5345-59. [PMID: 19770194 DOI: 10.1113/jphysiol.2009.172080] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In response to injury and inflammation of tendons, tendon fibroblasts are activated, migrate to the wound, and eventually induce contraction of the extracellular matrices to repair the tissue. Under such conditions, Ca(2+) signalling is involved in motility and contractility of tendon fibroblasts. Using cultured tendon fibroblasts isolated from rat Achilles tendons, we investigated functional expression of Na(+)/Ca(2+) exchangers (NCX). The fluorometric study showed that the intracellular Ca(2+) concentration ([Ca(2+)](i)) was increased by reducing extracellular Na(+) concentration ([Na(+)](o)) in tendon fibroblasts. Selective NCX inhibitors, KB-R7943 and SEA0400, both attenuated [Na(+)](o)-dependent [Ca(2+)](i) elevation and the resting [Ca(2+)](i) in tendon fibroblasts. RT-PCR, Western blots and sequence analyses revealed that NCX1.3 and NCX1.7 were expressed in cultured tendon fibroblasts. NCX2 mRNA was undetected. NCX3 expression was negligibly low. Immunofluorescence microscopy indicated that NCX1 protein localized in the plasma membrane especially at the microspikes of tendon fibroblasts. In the wound-healing scratch assay, the cells migrated toward the space created by a scratch and almost completely filled the space within 48 h. This phenomenon was significantly suppressed by KB-R7943 and SEA0400. Furthermore, the NCX inhibitors abrogated the tendon fibroblast-mediated collagen-matrix contractions. Two types of siRNAs for NCX1 also suppressed the migration and contraction of tendon fibroblasts. We conclude that NCX is expressed and mediates Ca(2+) influx in cultured tendon fibroblasts. Since the pharmacological inhibitors and siRNA for NCX1 suppressed motility and contractility of tendon fibroblasts, NCX may play an important role in the function of tendon fibroblasts in the wound healing.
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Affiliation(s)
- Kazuho Sakamoto
- Department of Pharmacology, Fukushima Medical University, School of Medicine, Hikarigaoka, Fukushima, Japan.
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Sodium-calcium exchanger complexed with GM1 ganglioside in nuclear membrane transfers calcium from nucleoplasm to endoplasmic reticulum. Proc Natl Acad Sci U S A 2009; 106:10829-34. [PMID: 19541636 DOI: 10.1073/pnas.0903408106] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The inner membrane of the nuclear envelope (NE) was previously shown to contain a Na/Ca exchanger (NCX) tightly linked to GM1 ganglioside that mediates transfer of nucleoplasmic Ca(2+) to the NE lumen and constitutes a cytoprotective mechanism. This transfer was initially observed with isolated nuclei and is now demonstrated in living cells in relation to subcellular Ca(2+) dynamics. Four cell lines with varying expression of NCX and GM1 in the NE were transfected with cameleon-fluorescent Ca(2+) indicators genetically targeted to NE/endoplasmic reticulum (ER) and nucleoplasm to monitor [Ca(2+)](ne/er) and [Ca(2+)](n) respectively. Cytosolic Ca(2+) ([Ca(2+)](cyt)) was indicated with fura-2. Thapsigargin caused progressive loss of [Ca(2+)](ne/er), which was rapidly replaced on addition of extrinsic Ca(2+) to those cells containing fully functional NCX/GM1: differentiated NG108-15 and C6 cells. Reduced elevation of [Ca(2+)](ne/er) following thapsigargin depletion occurred in cells containing little or no GM1 in the NE: undifferentiated NG108-15 and NG-CR72 cells. No change in [Ca(2+)](ne/er) due to applied Ca(2+) was seen in Jurkat cells, which entirely lack NCX. Ca(2+) entry to NE/ER was also blocked by KB-R7943, inhibitor of NCX. [Ca(2+)](n) and [Ca(2+)](cyt) were elevated independent of [Ca(2+)](ne/er) and remained in approximate equilibrium with each other. Ca(2+) rise in the ER originated in the NE region and extended to the entire ER network. These results indicate the nuclear NCX/GM1 complex acts to gate Ca(2+) transfer from cytosol to ER, an alternate route to the sarcoplasmic/endoplasmic reticulum calcium ATPase pump. They also suggest a possible contributory mechanism for independent regulation of nuclear Ca(2+).
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Boyman L, Mikhasenko H, Hiller R, Khananshvili D. Kinetic and Equilibrium Properties of Regulatory Calcium Sensors of NCX1 Protein. J Biol Chem 2009; 284:6185-93. [DOI: 10.1074/jbc.m809012200] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Hamming KSC, Riedel MJ, Soliman D, Matemisz LC, Webster NJ, Searle GJ, MacDonald PE, Light PE. Splice variant-dependent regulation of beta-cell sodium-calcium exchange by acyl-coenzyme As. Mol Endocrinol 2008; 22:2293-306. [PMID: 18635667 DOI: 10.1210/me.2008-0053] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The sodium-calcium exchanger isoform 1 (NCX1) is intimately involved in the regulation of calcium (Ca(2+)) homeostasis in many tissues including excitation-secretion coupling in pancreatic beta-cells. Our group has previously found that intracellular long-chain acyl-coenzyme As (acyl CoAs) are potent regulators of the cardiac NCX1.1 splice variant. Despite this, little is known about the biophysical properties of beta-cell NCX1 splice variants and the effects of intracellular modulators on their important physiological function in health and disease. Here, we show that the forward-mode activity of beta-cell NCX1 splice variants is differentially modulated by acyl-CoAs and is dependent both upon the intrinsic biophysical properties of the particular NCX1 splice variant as well as the side chain length and degree of saturation of the acyl-CoA moiety. Notably, saturated long-chain acyl-CoAs increased both peak and total NCX1 activity, whereas polyunsaturated long-chain acyl-CoAs did not show this effect. Furthermore, we have identified the exon within the alternative splicing region that bestows sensitivity to acyl-CoAs. We conclude that the physiologically relevant forward-mode activity of NCX1 splice variants expressed in the pancreatic beta-cell are sensitive to acyl-CoAs of different saturation and alterations in intracellular acyl-CoA levels may ultimately lead to defects in Ca(2+)-mediated exocytosis and insulin secretion.
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Affiliation(s)
- Kevin S C Hamming
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Boyman L, Hiller R, Lederer WJ, Khananshvili D. Direct Loading of the purified endogenous inhibitor into the cytoplasm of patched cardiomyocytes blocks the ion currents and calcium transport through the NCX1 protein. Biochemistry 2008; 47:6602-11. [PMID: 18507397 PMCID: PMC3522518 DOI: 10.1021/bi8004279] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Na(+)-Ca(2+) exchanger in mammalian heart muscle (NCX1) is the central transporter protein that regulates extrusion of Ca(2+) from the heart cell. However, the functional biochemistry and physiology of NCX1 have been severely hampered by the absence of any specific high-affinity inhibitor. Here we describe advanced procedures for purifying a candidate inhibitor, previously called endogenous inhibitor factor (NCX(IF)), and demonstrate its direct actions on NCX1 activities in the single-cell system. A combination of advanced HILIC (hydrophilic interaction liquid chromatography) procedures with analytical tests suggests that the properties of NCX(IF) resemble those of a small (disaccharide size) polar molecule lacking any aromatic rings, conjugated bonds, or a primary amino group. The effects of NCX(IF) on the NCX1-mediated ion currents (I(NCX)) and cytosolic Ca(2+) extrusion were detected by a combination of patch-clamp and confocal microscopy under conditions in which the purified NCX(IF) was directly loaded into the cytoplasm of patched cardiomyocytes. It was demonstrated that cytosolic NCX(IF) blocks the Ca(2+)-activated NCX1 inward current and the accompanying extrusion of Ca(2+) from the cell with high efficacy. A constant fraction of NCX1 inhibition was observed under conditions in which the cytosolic [Ca(2+)](i) was varied at fixed doses of NCX(IF), suggesting that the degree of inhibition is controlled by NCX(IF) dose and not by cytosolic Ca(2+) concentration. NCX(IF) blocks equally well both the Ca(2+) extrusion and Ca(2+) entry modes of NCX1, consistent with thermodynamic principles expected for the functioning of a bidirectional "carrier-type" transport system. We concluded that NCX(IF) interacts with a putative regulatory domain from the cytosolic side and, thus, may play an important regulatory role in controlling Ca(2+) signaling in the heart. This may represent a new potential tool for developing novel treatments for cardiac Ca(2+) signaling dysfunction.
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Affiliation(s)
- Liron Boyman
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - Reuben Hiller
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
| | - W. Jonathan Lederer
- Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201
| | - Daniel Khananshvili
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Israel
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Guerini D, Coletto L, Carafoli E. Exporting calcium from cells. Cell Calcium 2008; 38:281-9. [PMID: 16102821 DOI: 10.1016/j.ceca.2005.06.032] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Accepted: 06/28/2005] [Indexed: 01/11/2023]
Abstract
All eukaryotic cells import Ca2+ through a number of variously gated plasma membrane channels. Once inside cells, Ca2+ transmits information to a large number of (enzyme) targets. Eventually, it must be exported again, to prevent the overloading of the cytosol with Ca2+. Two systems export Ca2+ from cells: a high affinity, low capacity Ca2+-ATPase, and a lower affinity, but much larger capacity, Na+/Ca2+ exchanger. The ATPase (commonly called the Ca2+ pump) is the fine-tuner of cell Ca2+, as it functions well even if the concentration of the ion drops below the microM level. It is a large enzyme, with 10 transmembrane domains and a C-terminal cytosolic tail that contains regulatory sites, including a calmodulin-binding domain. Four distinct gene products plus a large number of splice variants have been described. Some are tissue specific, the isoform 2 being specifically expressed in the sensorial cells of the Corti organ in the inner-ear. Its genetic absence causes deafness in mice. Two different families of the Na+/Ca2+ exchanger exist, one of which, originally described in photoreceptors, transports K+ and Ca2+ in exchange for Na+. The exchanger is particularly active in excitable cells, e.g., heart, where the necessity cyclically arises to rapidly eject large amounts of Ca2+. In addition to heart, the exchanger is particularly important to neurons: the cleavage of the most important neuronal isoform (NCX3) by calpains activated by excitotoxic treatments generates Ca2+ overload and eventually cell death.
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