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Dong Y, Li H, Ilie A, Gao Y, Boucher A, Zhang XC, Orlowski J, Zhao Y. Structural basis of autoinhibition of the human NHE3-CHP1 complex. SCIENCE ADVANCES 2022; 8:eabn3925. [PMID: 35613257 PMCID: PMC9132474 DOI: 10.1126/sciadv.abn3925] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 04/11/2022] [Indexed: 06/15/2023]
Abstract
Sodium-proton exchanger 3 (NHE3/SLC9A3) located in the apical membrane of renal and gastrointestinal epithelia mediates salt and fluid absorption and regulates pH homeostasis. As an auxiliary regulatory factor of NHE proteins, calcineurin B homologous protein 1 (CHP1) facilitates NHE3 maturation, plasmalemmal expression, and pH sensitivity. Dysfunctions of NHE3 are associated with renal and digestive system disorders. Here, we report the cryo-electron microscopy structure of the human NHE3-CHP1 complex in its inward-facing conformation. We found that a cytosolic helix-loop-helix motif in NHE3 blocks the intracellular cavity formed between the core and dimerization domains, functioning as an autoinhibitory element and hindering substrate transport. Furthermore, two phosphatidylinositol molecules are found to bind to the peripheric juxtamembrane sides of the complex, function as anchors to stabilize the complex, and may thus enhance its transport activity.
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Affiliation(s)
- Yanli Dong
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hang Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Alina Ilie
- Department of Physiology, McGill University, Montreal, Canada
| | - Yiwei Gao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Annie Boucher
- Department of Physiology, McGill University, Montreal, Canada
| | - Xuejun Cai Zhang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - John Orlowski
- Department of Physiology, McGill University, Montreal, Canada
| | - Yan Zhao
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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Hendus-Altenburger R, Vogensen J, Pedersen ES, Luchini A, Araya-Secchi R, Bendsoe AH, Prasad NS, Prestel A, Cardenas M, Pedraz-Cuesta E, Arleth L, Pedersen SF, Kragelund BB. The intracellular lipid-binding domain of human Na +/H + exchanger 1 forms a lipid-protein co-structure essential for activity. Commun Biol 2020; 3:731. [PMID: 33273619 PMCID: PMC7713384 DOI: 10.1038/s42003-020-01455-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 11/03/2020] [Indexed: 12/03/2022] Open
Abstract
Dynamic interactions of proteins with lipid membranes are essential regulatory events in biology, but remain rudimentarily understood and particularly overlooked in membrane proteins. The ubiquitously expressed membrane protein Na+/H+-exchanger 1 (NHE1) regulates intracellular pH (pHi) with dysregulation linked to e.g. cancer and cardiovascular diseases. NHE1 has a long, regulatory cytosolic domain carrying a membrane-proximal region described as a lipid-interacting domain (LID), yet, the LID structure and underlying molecular mechanisms are unknown. Here we decompose these, combining structural and biophysical methods, molecular dynamics simulations, cellular biotinylation- and immunofluorescence analysis and exchanger activity assays. We find that the NHE1-LID is intrinsically disordered and, in presence of membrane mimetics, forms a helical αα-hairpin co-structure with the membrane, anchoring the regulatory domain vis-a-vis the transport domain. This co-structure is fundamental for NHE1 activity, as its disintegration reduced steady-state pHi and the rate of pHi recovery after acid loading. We propose that regulatory lipid-protein co-structures may play equally important roles in other membrane proteins.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Jens Vogensen
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Emilie Skotte Pedersen
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
| | - Alessandra Luchini
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark
| | - Raul Araya-Secchi
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark
| | - Anne H Bendsoe
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Nanditha Shyam Prasad
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Andreas Prestel
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark
| | - Marité Cardenas
- Biofilms Research Center for Biointerfaces, Malmö University, Per Albin Hanssons Väg 35, 214 32, Malmö, Sweden
| | - Elena Pedraz-Cuesta
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark
| | - Lise Arleth
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen Ø, Denmark.
| | - Stine F Pedersen
- Cell Biology and Physiology, Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen Ø, Denmark.
| | - Birthe B Kragelund
- Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200, Copenhagen N, Denmark.
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Pedersen SF, Counillon L. The SLC9A-C Mammalian Na +/H + Exchanger Family: Molecules, Mechanisms, and Physiology. Physiol Rev 2019; 99:2015-2113. [PMID: 31507243 DOI: 10.1152/physrev.00028.2018] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Na+/H+ exchangers play pivotal roles in the control of cell and tissue pH by mediating the electroneutral exchange of Na+ and H+ across cellular membranes. They belong to an ancient family of highly evolutionarily conserved proteins, and they play essential physiological roles in all phyla. In this review, we focus on the mammalian Na+/H+ exchangers (NHEs), the solute carrier (SLC) 9 family. This family of electroneutral transporters constitutes three branches: SLC9A, -B, and -C. Within these, each isoform exhibits distinct tissue expression profiles, regulation, and physiological roles. Some of these transporters are highly studied, with hundreds of original articles, and some are still only rudimentarily understood. In this review, we present and discuss the pioneering original work as well as the current state-of-the-art research on mammalian NHEs. We aim to provide the reader with a comprehensive view of core knowledge and recent insights into each family member, from gene organization over protein structure and regulation to physiological and pathophysiological roles. Particular attention is given to the integrated physiology of NHEs in the main organ systems. We provide several novel analyses and useful overviews, and we pinpoint main remaining enigmas, which we hope will inspire novel research on these highly versatile proteins.
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Affiliation(s)
- S F Pedersen
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
| | - L Counillon
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark; and Université Côte d'Azur, CNRS, Laboratoire de Physiomédecine Moléculaire, LP2M, France, and Laboratories of Excellence Ion Channel Science and Therapeutics, Nice, France
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4
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Babich V, Henry MK, Di Sole F. Application of Electrophysiology Measurement to Study the Activity of Electro-Neutral Transporters. J Vis Exp 2018. [PMID: 29443070 DOI: 10.3791/56630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The transport of ions through cell membranes ensures the fine control of ion content within and outside the cell that is indispensable for cell survival. These transport mechanisms are mediated by the activities of specialized transporter proteins. Specifically,pH dynamics are finely controlled by plasma membrane proton (H+) extrusion systems, such as the Na+/H+ exchanger (NHE) protein family. Despite extensive efforts to study the mechanisms underlying NHE regulation, our current understanding of the biophysical and molecular properties of the NHE family is inadequate because of the limited availability of methods to effectively measure NHE activity. In this manuscript, we used H+-selective electrodes during whole-cell patch clamping recording to measure NHE-induced H+ flux. We proposed this approach to overcome some limitations of typically used methods to measure NHE activity, such as radioactive uptake and fluorescent membrane permeants. Measurement of NHE activity using the described method enables high sensitivity and time resolution and more efficient control of intracellular H+ concentrations. H+-selective electrodes are based on the fact that transporter activity creates an ion gradient in close proximity to the cell membrane. An H+-selective electrode moving up to and away from the cell membrane in a repetitive, oscillatory fashion records a voltage difference that is dependent on H+ flux. While H+-selective electrodes are used to detect H+ flux moving out of the cell, the patch clamp method in the whole-cell configuration is used to control the intracellular ion composition. Moreover, application of the giant patch clamp technique allows modification of the intracellular composition of not only ions but also lipids. The transporter activity of NHE isoform 3 (NHE3) was measured using this technical approach to study the molecular basis of NHE3 regulation by phosphoinositides.
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Affiliation(s)
- Victor Babich
- Physiology and Pharmacology Department, Des Moines University; School of Liberal Arts and Sciences, Mercy College of Health Sciences
| | - Matthew K Henry
- Physiology and Pharmacology Department, Des Moines University
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Yin J, Tse CM, Cha B, Sarker R, Zhu XC, Walentinsson A, Greasley PJ, Donowitz M. A common NHE3 single-nucleotide polymorphism has normal function and sensitivity to regulatory ligands. Am J Physiol Gastrointest Liver Physiol 2017; 313:G129-G137. [PMID: 28495802 PMCID: PMC5582881 DOI: 10.1152/ajpgi.00044.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 05/01/2017] [Accepted: 05/05/2017] [Indexed: 01/31/2023]
Abstract
Na+/H+ exchanger NHE3 mediates the majority of intestinal and renal electroneutral sodium absorption. Dysfunction of NHE3 is associated with a variety of diarrheal diseases. We previously reported that the NHE3 gene (SLC9A3) has more than 400 single-nucleotide polymorphisms (SNPs) but few nonsynonymous polymorphisms. Among the latter, one polymorphism (rs2247114-G>A), which causes a substitution from arginine to cysteine at amino acid position 799 (p.R799C), is common in Asian populations. To improve our understanding of the population distribution and potential clinical significance of the NHE3-799C variant, we investigated the frequency of this polymorphism in different ethnic groups using bioinformatics analyses and in a cohort of Japanese patients with cardiovascular or renal disease. We also characterized the function of human NHE3-799C and its sensitivity to regulatory ligands in an in vitro model. NHE3-799C had an allele frequency of 29.5-57.6% in Asian populations, 11.1-23.6% in European populations, and 10.2-22.7% in African populations. PS120/FLAG-NHERF2 fibroblasts stably expressing NHE3-799C had lower total protein expression but a higher percentage of surface expression than those expressing NHE3-799R. NHE3-799C had similar basal activity to NHE3-799R and was similarly stimulated or inhibited, by serum or forskolin, respectively. Tenapanor, a small-molecule NHE3 inhibitor, dose-dependently inhibited NHE3-799R and NHE3-799C activities. The IC50 values of tenapanor for NHE3-799C and NHE3-799R were significantly different, but both were in the nanomolar range. These results suggest that NHE3-799C is a common variant enriched in Asian populations, is not associated with compromised function or abnormal regulation, and is unlikely to contribute to clinical disease.NEW & NOTEWORTHY This study reports results on the functional significance of human NHE3-799C under basal conditions and in response to regulatory ligands, including a novel NHE3 inhibitor called tenapanor. We demonstrate that NHE3-799C is a common variant of NHE3 that is enriched in Asian populations; however, in contrast to our previous studies using rabbit NHE3, its presence seems to have limited clinical significance in humans and is not associated with compromised function or abnormal transport regulation.
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Affiliation(s)
- Jianyi Yin
- 1Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
| | - Chung-Ming Tse
- 1Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
| | - Boyoung Cha
- 1Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
| | - Rafiquel Sarker
- 1Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
| | - Xinjun C. Zhu
- 2Department of Medicine, Division of Gastroenterology and Hepatology, Albany Medical College, Albany, New York; and
| | | | | | - Mark Donowitz
- Department of Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland;
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Sarker R, Cha B, Kovbasnjuk O, Cole R, Gabelli S, Tse CM, Donowitz M. Phosphorylation of NHE3-S 719 regulates NHE3 activity through the formation of multiple signaling complexes. Mol Biol Cell 2017; 28:1754-1767. [PMID: 28495796 PMCID: PMC5491184 DOI: 10.1091/mbc.e16-12-0862] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 03/09/2017] [Accepted: 05/04/2017] [Indexed: 12/02/2022] Open
Abstract
CK2 regulates NHE3 by phosphorylating a single C-terminal amino acid, which, when mutated, reduces basal NHE3 activity and its acute stimulation and inhibition. It also is necessary for binding of proteins throughout the C-terminus, which means that it determines the C-terminal structure. Casein kinase 2 (CK2) binds to the NHE3 C-terminus and constitutively phosphorylates a downstream site (S719) that accounts for 40% of basal NHE3 activity. The role of CK2 in regulation of NHE3 activity in polarized Caco-2/bbe cells was further examined by mutation of NHE3-S719 to A (not phosphorylated) or D (phosphomimetic). NHE3-S719A but not -S719D had multiple changes in NHE3 activity: 1) reduced basal NHE3 activity—specifically, inhibition of the PI3K/AKT-dependent component; 2) reduced acute stimulation of NHE3 activity by LPA/LPA5R stimulation; and 3) reduced acute inhibition of NHE3 activity—specifically, elevated Ca2+ related (carbachol/Ca2+ ionophore), but there was normal inhibition by forskolin and hyperosmolarity. The S719A mutant had reduced NHE3 complex size, reduced expression in lipid rafts, increased BB mobile fraction, and reduced binding to multiple proteins that bind throughout the NHE3 intracellular C-terminus, including calcineurin homologous protein, the NHERF family and SNX27 (related PDZ domains). These studies show that phosphorylation of the NHE3 at a single amino acid in the distal part of the C-terminus affects multiple aspects of NHE3 complex formation and changes the NHE3 lipid raft distribution, which cause changes in specific aspects of basal as well as acutely stimulated and inhibited Na+/H+ exchange activity.
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Affiliation(s)
- Rafiquel Sarker
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Boyoung Cha
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Olga Kovbasnjuk
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Robert Cole
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Sandra Gabelli
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Chung Ming Tse
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Mark Donowitz
- Department of Physiology and Department of Medicine, GI Division, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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7
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Babich V, Di Sole F. The Na+/H+ Exchanger-3 (NHE3) Activity Requires Ezrin Binding to Phosphoinositide and Its Phosphorylation. PLoS One 2015; 10:e0129306. [PMID: 26042733 PMCID: PMC4455992 DOI: 10.1371/journal.pone.0129306] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 05/08/2015] [Indexed: 11/19/2022] Open
Abstract
Na+/H+ exchanger-3 (NHE3) plays an essential role in maintaining sodium and fluid homeostasis in the intestine and kidney epithelium. Thus, NHE3 is highly regulated and its function depends on binding to multiple regulatory proteins. Ezrin complexed with NHE3 affects its activity via not well-defined mechanisms. This study investigates mechanisms by which ezrin regulates NHE3 activity in epithelial Opossum Kidney cells. Ezrin is activated sequentially by phosphatidylinositol-4,5-bisphosphate (PIP2) binding and phosphorylation of threonine 567. Expression of ezrin lacking PIP2 binding sites inhibited NHE3 activity (-40%) indicating that ezrin binding to PIP2 is required for preserving NHE3 activity. Expression of a phosphomimetic ezrin mutated at the PIP2 binding region was sufficient not only to reverse NHE3 activity to control levels but also to increase its activity (+80%) similar to that of the expression of ezrin carrying the phosphomimetic mutation alone. Calcineurin Homologous Protein-1 (CHP1) is part, with ezrin, of the NHE3 regulatory complex. CHP1-mediated activation of NHE3 activity was blocked by expression of an ezrin variant that could not be phosphorylated but not by an ezrin variant unable to bind PIP2. Thus, for NHE3 activity under baseline conditions not only ezrin phosphorylation, but also ezrin spatial-temporal targeting on the plasma membrane via PIP2 binding is required; however, phosphorylation of ezrin appears to overcome the control of NHE3 transport. CHP1 action on NHE3 activity is not contingent on ezrin binding to PIP2 but rather on ezrin phosphorylation. These findings are important in understanding the interrelation and dynamics of a CHP1-ezrin-NHE3 regulatory complex.
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Affiliation(s)
- Victor Babich
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Francesca Di Sole
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, United States of America
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
- Physiology and Pharmacology Department, Des Moines University, Iowa, United States of America
- * E-mail:
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8
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Zhu XC, Sarker R, Horton JR, Chakraborty M, Chen TE, Tse CM, Cha B, Donowitz M. Nonsynonymous single nucleotide polymorphisms of NHE3 differentially decrease NHE3 transporter activity. Am J Physiol Cell Physiol 2015; 308:C758-66. [PMID: 25715704 DOI: 10.1152/ajpcell.00421.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 02/23/2015] [Indexed: 12/24/2022]
Abstract
Genetic determinants appear to play a role in susceptibility to chronic diarrhea, but the genetic abnormalities involved have only been identified in a few conditions. The Na⁺/H⁺ exchanger 3 (NHE3) accounts for a large fraction of physiologic intestinal Na⁺ absorption. It is highly regulated through effects on its intracellular COOH-terminal regulatory domain. The impact of genetic variation in the NHE3 gene, such as single nucleotide polymorphisms (SNPs), on transporter activity remains unexplored. From a total of 458 SNPs identified in the entire NHE3 gene, we identified three nonsynonymous mutations (R474Q, V567M, and R799C), which were all in the protein's intracellular COOH-terminal domain. Here we evaluated whether these SNPs affect NHE3 activity by expressing them in a mammalian cell line that is null for all plasma membrane NHEs. These variants significantly reduced basal NHE3 transporter activity through a reduction in intrinsic NHE3 function in variant R474Q, abnormal trafficking in variant V567M, or defects in both intrinsic NHE3 function and trafficking in variant R799C. In addition, variants NHE3 R474Q and R799C failed to respond to acute dexamethasone stimulation, suggesting cells with these mutant proteins might be defective in NHE3 function during postprandial stimulation and perhaps under stressful conditions. Finally, variant R474Q was shown to exhibit an aberrant interaction with calcineurin B homologous protein (CHP), an NHE3 regulatory protein required for basal NHE3 activity. Taken together, these results demonstrate decreased transport activity in three SNPs of NHE3 and provide mechanistic insight into how these SNPs impact NHE3 function.
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Affiliation(s)
- Xinjun Cindy Zhu
- Department of Medicine, Division of Gastroenterology and Hepatology, Center of Cardiovascular Sciences, Albany Medical Center, Albany, New York; Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Rafiquel Sarker
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - John R Horton
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia
| | - Molee Chakraborty
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Tian-E Chen
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - C Ming Tse
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Boyoung Cha
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Mark Donowitz
- Departments of Physiology and Medicine, Division of Gastroenterology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
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9
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Phospho-NHE3 forms membrane patches and interacts with beta-actin to sense and maintain constant direction during cell migration. Exp Cell Res 2014; 324:13-29. [PMID: 24657527 DOI: 10.1016/j.yexcr.2014.03.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Revised: 02/28/2014] [Accepted: 03/02/2014] [Indexed: 01/14/2023]
Abstract
The Na(+)/H(+) exchanger NHE3 colocalizes with beta-actin at the leading edge of directionally migrating cells. Using human osteosarcoma cells (SaOS-2), rat osteoblasts (calvaria), and human embryonic kidney (HEK) cells, we identified a novel role for NHE3 via beta-actin in anode and cathode directed motility, during electrotaxis. NHE3 knockdown by RNAi revealed that NHE3 expression is required to achieve constant directionality and polarity in migrating cells. Phosphorylated NHE3 (pNHE3) and beta-actin complex formation was impaired by the NHE3 inhibitor S3226 (IC50 0.02µM). Fluorescence cross-correlation spectroscopy (FCCS) revealed that the molecular interactions between NHE3 and beta-actin in membrane protrusions increased 1.7-fold in the presence of a directional cue and decreased 3.3-fold in the presence of cytochalasin D. Data from flow cytometric analysis showed that membrane potential of cells (Vmem) decreases in directionally migrating, NHE3-deficient osteoblasts and osteosarcoma cells whereas only Vmem of wild type osteoblasts is affected during directional migration. These findings suggest that pNHE3 has a mechanical function via beta-actin that is dependent on its physiological activity and Vmem. Furthermore, phosphatidylinositol 3,4,5-trisphosphate (PIP3) levels increase while PIP2 remains stable when cells have persistent directionality. Both PI3 kinase (PI3K) and Akt expression levels change proportionally to NHE3 levels. Interestingly, however, the content of pNHE3 level does not change when PI3K/Akt is inhibited. Therefore, we conclude that NHE3 can act as a direction sensor for cells and that NHE3 phosphorylation in persistent directional cell migration does not involve PI3K/Akt during electrotaxis.
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10
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Singh V, Lin R, Yang J, Cha B, Sarker R, Tse CM, Donowitz M. AKT and GSK-3 are necessary for direct ezrin binding to NHE3 as part of a C-terminal stimulatory complex: role of a novel Ser-rich NHE3 C-terminal motif in NHE3 activity and trafficking. J Biol Chem 2014; 289:5449-61. [PMID: 24398676 DOI: 10.1074/jbc.m113.521336] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Basal activity of the BB Na(+)/H(+) exchanger NHE3 requires multiprotein complexes that form on its C terminus. One complex stimulates basal NHE3 activity and contains ezrin and phosphoinositides as major components; how it stimulates NHE3 activity is not known. This study tested the hypothesis that ezrin dynamically associates with this complex, which sets ezrin binding. NHE3 activity was reduced by an Akti. This effect was eliminated if ezrin binding to NHE3 was inhibited by a point mutant. Recombinant AKT phosphorylated NHE3 C terminus in the domain ezrin directly binds. This domain (amino acids 475-589) is predicted to be α-helical and contains a conserved cluster of three serines (Ser(515), Ser(522), and Ser(526)). Point mutations of two of these (S515A, S515D, or S526A) reduced basal NHE3 activity and surface expression and had no Akti inhibition. S526D had NHE3 activity equal to wild type with normal Akti inhibition. Ezrin binding to NHE3 was regulated by Akt, being eliminated by Akti. NHE3-S515A and -S526D did not bind ezrin; NHE3-S515D had reduced ezrin binding; NHE3-S526D bound ezrin normally. NHE3-Ser(526) is predicted to be a GSK-3 kinase phosphorylation site. A GSK-3 inhibitor reduced basal NHE3 activity as well as ezrin-NHE3 binding, and this effect was eliminated in NHE3-S526A and -S526D mutants. The conclusions were: 1) NHE3 basal activity is regulated by a signaling complex that is controlled by sequential effects of two kinases, Akt and GSK-3, which act on a Ser cluster in the same NHE3 C-terminal domain that binds ezrin; and 2) these kinases regulate the dynamic association of ezrin with NHE3 to affect basal NHE3 activity.
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Affiliation(s)
- Varsha Singh
- From the Departments of Physiology and Medicine, Gastroenterology Division, Johns, Hopkins University School of Medicine, Baltimore, Maryland 21205 and
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11
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Hendus-Altenburger R, Kragelund BB, Pedersen SF. Structural dynamics and regulation of the mammalian SLC9A family of Na⁺/H⁺ exchangers. CURRENT TOPICS IN MEMBRANES 2014; 73:69-148. [PMID: 24745981 DOI: 10.1016/b978-0-12-800223-0.00002-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mammalian Na⁺/H⁺ exchangers of the SLC9A family are widely expressed and involved in numerous essential physiological processes. Their primary function is to mediate the 1:1 exchange of Na⁺ for H⁺ across the membrane in which they reside, and they play central roles in regulation of body, cellular, and organellar pH. Their function is tightly regulated through mechanisms involving interactions with multiple protein and lipid-binding partners, phosphorylations, and other posttranslational modifications. Biochemical and mutational analyses indicate that the SLC9As have a short intracellular N-terminus, 12 transmembrane (TM) helices necessary and sufficient for ion transport, and a C-terminal cytoplasmic tail region with essential regulatory roles. No high-resolution structures of the SLC9As exist; however, models based on crystal structures of the bacterial NhaAs support the 12 TM organization and suggest that TMIV and XI may form a central part of the ion-translocation pathway, whereas pH sensing may involve TMII, TMIX, and several intracellular loops. Similar to most ion transporters studied, SLC9As likely exist as coupled dimers in the membrane, and this appears to be important for the well-studied cooperativity of H⁺ binding. The aim of this work is to summarize and critically discuss the currently available evidence on the structural dynamics, regulation, and binding partner interactions of SLC9As, focusing in particular on the most widely studied isoform, SLC9A1/NHE1. Further, novel bioinformatic and structural analyses are provided that to some extent challenge the existing paradigm on how ions are transported by mammalian SLC9As.
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Affiliation(s)
- Ruth Hendus-Altenburger
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark; Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Birthe B Kragelund
- Section for Biomolecular Sciences, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Stine Falsig Pedersen
- Section for Cell and Developmental Biology, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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Regulation of the cardiac Na⁺/H⁺ exchanger in health and disease. J Mol Cell Cardiol 2013; 61:68-76. [PMID: 23429007 DOI: 10.1016/j.yjmcc.2013.02.007] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 02/07/2013] [Accepted: 02/11/2013] [Indexed: 11/21/2022]
Abstract
The Na(+) gradient produced across the cardiac sarcolemma by the ATP-dependent Na(+)-pump is a constant source of energy for Na(+)-dependent transporters. The plasma membrane Na(+)/H(+) exchanger (NHE) is one such secondary active transporter, regulating intracellular pH, Na(+) concentration, and cell volume. NHE1, the major isoform found in the heart, is activated in response to a variety of stimuli such as hormones and mechanical stress. This important characteristic of NHE1 is intimately linked to heart diseases, including maladaptive cardiac hypertrophy and subsequent heart failure, as well as acute ischemic-reperfusion injury. NHE1 activation results in elevation of pH and intracellular Na(+) concentration, which potentially enhance downstream signaling cascades in the myocardium. Therefore, in addition to determining the mechanism underlying regulation of NHE1 activity, it is important to understand how the ionic signal produced by NHE1 is transmitted to the downstream targets. Extensive studies have identified many accessory factors that interact with NHE1. Here, we have summarized the recent progress on understanding the molecular mechanism underlying NHE1 regulation and have shown a possible signaling pathway leading to cardiac remodeling, which is initiated from NHE1. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes".
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Kondapalli KC, Kallay LM, Muszelik M, Rao R. Unconventional chemiosmotic coupling of NHA2, a mammalian Na+/H+ antiporter, to a plasma membrane H+ gradient. J Biol Chem 2012; 287:36239-50. [PMID: 22948142 DOI: 10.1074/jbc.m112.403550] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human NHA2, a newly discovered cation proton antiporter, is implicated in essential hypertension by gene linkage analysis. We show that NHA2 mediates phloretin-sensitive Na(+)-Li(+) counter-transport (SLC) activity, an established marker for hypertension. In contrast to bacteria and fungi where H(+) gradients drive uptake of metabolites, secondary transport at the plasma membrane of mammalian cells is coupled to the Na(+) electrochemical gradient. Our findings challenge this paradigm by showing coupling of NHA2 and V-type H(+)-ATPase at the plasma membrane of kidney-derived MDCK cells, resulting in a virtual Na(+) efflux pump. Thus, NHA2 functionally recapitulates an ancient shared evolutionary origin with bacterial NhaA. Although plasma membrane H(+) gradients have been observed in some specialized mammalian cells, the ubiquitous tissue distribution of NHA2 suggests that H(+)-coupled transport is more widespread. The coexistence of Na(+) and H(+)-driven chemiosmotic circuits has implications for salt and pH regulation in the kidney.
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Affiliation(s)
- Kalyan C Kondapalli
- Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Abstract
Diverse biological processes including cell growth and survival require transient association of proteins with cellular membranes. A large number of these proteins are drawn to a bilayer through binding of their modular domains to phosphoinositide (PI) lipids. Seven PI isoforms are found to concentrate in distinct pools of intracellular membranes, and this lipid compartmentalization provides an efficient way for recruiting PI-binding proteins to specific cellular organelles. The atomic-resolution structures and membrane docking mechanisms of a dozen PI effectors have been elucidated in the last decade, offering insight into the molecular basis for regulation of the PI-dependent signaling pathways. In this chapter, I summarize the mechanistic aspects of deciphering the 'PI code' by the most common PI-recognizing domains and discuss similarities and differences in the membrane anchoring mechanisms.
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Affiliation(s)
- Tatiana G Kutateladze
- Department of Pharmacology, University of Colorado Denver School of Medicine, Aurora, CO 80045, USA.
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Abu Jawdeh BG, Khan S, Deschênes I, Hoshi M, Goel M, Lock JT, Shinlapawittayatorn K, Babcock G, Lakhe-Reddy S, DeCaro G, Yadav SP, Mohan ML, Naga Prasad SV, Schilling WP, Ficker E, Schelling JR. Phosphoinositide binding differentially regulates NHE1 Na+/H+ exchanger-dependent proximal tubule cell survival. J Biol Chem 2011; 286:42435-42445. [PMID: 22020933 DOI: 10.1074/jbc.m110.212845] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tubular atrophy predicts chronic kidney disease progression, and is caused by proximal tubular epithelial cellcaused by proximal tubular epithelial cell (PTC) apoptosis. The normally quiescent Na(+)/H(+) exchanger-1 (NHE1) defends against PTC apoptosis, and is regulated by PI(4,5)P(2) binding. Because of the vast array of plasma membrane lipids, we hypothesized that NHE1-mediated cell survival is dynamically regulated by multiple anionic inner leaflet phospholipids. In membrane overlay and surface plasmon resonance assays, the NHE1 C terminus bound phospholipids with low affinity and according to valence (PIP(3) > PIP(2) > PIP = PA > PS). NHE1-phosphoinositide binding was enhanced by acidic pH, and abolished by NHE1 Arg/Lys to Ala mutations within two juxtamembrane domains, consistent with electrostatic interactions. PI(4,5)P(2)-incorporated vesicles were distributed to apical and lateral PTC domains, increased NHE1-regulated Na(+)/H(+) exchange, and blunted apoptosis, whereas NHE1 activity was decreased in cells enriched with PI(3,4,5)P(3), which localized to basolateral membranes. Divergent PI(4,5)P(2) and PI(3,4,5)P(3) effects on NHE1-dependent Na(+)/H(+) exchange and apoptosis were confirmed by selective phosphoinositide sequestration with pleckstrin homology domain-containing phospholipase Cδ and Akt peptides, PI 3-kinase, and Akt inhibition in wild-type and NHE1-null PTCs. The results reveal an on-off switch model, whereby NHE1 toggles between weak interactions with PI(4,5)P(2) and PI(3,4,5)P(3). In response to apoptotic stress, NHE1 is stimulated by PI(4,5)P(2), which leads to PI 3-kinase activation, and PI(4,5)P(2) phosphorylation. The resulting PI(3,4,5)P(3) dually stimulates sustained, downstream Akt survival signaling, and dampens NHE1 activity through competitive inhibition and depletion of PI(4,5)P(2).
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Affiliation(s)
- Bassam G Abu Jawdeh
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109
| | - Shenaz Khan
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109
| | - Isabelle Deschênes
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109; Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Malcolm Hoshi
- Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Monu Goel
- Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Jeffrey T Lock
- Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Krekwit Shinlapawittayatorn
- Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Gerald Babcock
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109; Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Sujata Lakhe-Reddy
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109
| | - Garren DeCaro
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109
| | - Satya P Yadav
- Department of Cleveland Clinic Foundation, Case Western Reserve University, Cleveland, Ohio 44109
| | - Maradumane L Mohan
- Department of Cleveland Clinic Foundation, Case Western Reserve University, Cleveland, Ohio 44109
| | | | - William P Schilling
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109; Departments of Physiology and Biophysics, Lerner Research Institute, Case Western Reserve University, Cleveland, Ohio 44109
| | - Eckhard Ficker
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109
| | - Jeffrey R Schelling
- Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44109.
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