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Gałgańska H, Jarmuszkiewicz W, Gałgański Ł. Carbon dioxide and MAPK signalling: towards therapy for inflammation. Cell Commun Signal 2023; 21:280. [PMID: 37817178 PMCID: PMC10566067 DOI: 10.1186/s12964-023-01306-x] [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: 06/13/2023] [Accepted: 09/05/2023] [Indexed: 10/12/2023] Open
Abstract
Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.
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Affiliation(s)
- Hanna Gałgańska
- Faculty of Biology, Molecular Biology Techniques Laboratory, Adam Mickiewicz University in Poznan, Uniwersytetu Poznanskiego 6, 61-614, Poznan, Poland
| | - Wieslawa Jarmuszkiewicz
- Faculty of Biology, Department of Bioenergetics, Adam Mickiewicz University in Poznan, Institute of Molecular Biology and Biotechnology, Uniwersytetu Poznanskiego 6, 61-614, Poznan, Poland
| | - Łukasz Gałgański
- Faculty of Biology, Department of Bioenergetics, Adam Mickiewicz University in Poznan, Institute of Molecular Biology and Biotechnology, Uniwersytetu Poznanskiego 6, 61-614, Poznan, Poland.
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2
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Song C, Yue Q, Moseley A, Al-Khalili O, Wynne BM, Ma H, Wang L, Eaton DC. Myristoylated alanine-rich C kinase substrate-like protein-1 regulates epithelial sodium channel activity in renal distal convoluted tubule cells. Am J Physiol Cell Physiol 2020; 319:C589-C604. [PMID: 32639874 DOI: 10.1152/ajpcell.00218.2020] [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] [Indexed: 12/21/2022]
Abstract
The epithelial sodium channel (ENaC) regulates blood pressure by fine-tuning distal nephron sodium reabsorption. Our previous work has shown that ENaC gating is regulated by anionic phospholipid phosphates, including phosphatidylinositol 4,5-bisphosphate (PIP2). The PIP2-dependent regulation of ENaC is mediated by the myristoylated alanine-rich protein kinase C substrate-like protein-1 (MLP-1). MLP-1 binds to and is a reversible source of PIP2 at the plasma membrane. We examined MLP-1 regulation of ENaC in distal convoluted tubule clonal cell line DCT-15 cells. Wild-type MLP-1 runs at an apparent molecular mass of 52 kDa despite having a predicted molecular mass of 21 kDa. Native MLP-1 consists of several distinct structural elements: an effector domain that is highly positively charged, sequesters PIP2, contains serines that are the target of PKC, and controls MLP-1 association with the membrane; a myristoylation domain that promotes association with the membrane; and a multiple homology 2 domain of previously unknown function. To further examine MLP-1 in DCT-15 cells, we constructed several MLP-1 mutants: WT, a full-length wild-type protein; S3A, three substitutions in the effector domain to prevent phosphorylation; S3D mimicked constitutive phosphorylation by replacing three serines with aspartates; and GA replaced the myristoylation site glycine with alanine, so GA could not be myristoylated. Each mutant was tagged with either NH2-terminal 3XFLAG or COOH-terminal mCherry or V5. Transfection with MLP mutants modified ENaC activity in DCT-15 cells: activity was highest in S3A and lowest in S3D, and the activity after transfection with either construct was significantly different from WT. In Western blots, when transfected with 3XFLAG-tagged MLP-1 mutants, the expression of the full length of MLP-1 at 52 kDa increased in mutant S3A-MLP-1-transfected DCT-15 cells and decreased in S3D-MLP-1-transfected DCT-15 cells. Several lower molecular mass bands were also detected that correspond to potential presumptive calpain cleavage products. Confocal imaging shows that the different mutants localize in different subcellular compartments consistent with their preferred location in the membrane or in the cytosol. Activation of protein kinase C increases phosphorylation of endogenous MLP-1 and reduces ENaC activity. Our results suggest a complicated role for proteolytic processing in MLP-1 regulation of ENaC.
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Affiliation(s)
- Chang Song
- Department of Neurology, The Second Affiliated Hospital of Harbin Medical University, Harbin, China.,Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia.,Department of Physiology, Emory University, Atlanta, Georgia
| | - Qiang Yue
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Auriel Moseley
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Otor Al-Khalili
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Brandi M Wynne
- Division of Nephrology & Hypertension, Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Heping Ma
- Department of Physiology, Emory University, Atlanta, Georgia
| | - Lihua Wang
- Department of Neurology, The Second Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Douglas C Eaton
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
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3
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Hamacher J, Hadizamani Y, Borgmann M, Mohaupt M, Männel DN, Moehrlen U, Lucas R, Stammberger U. Cytokine-Ion Channel Interactions in Pulmonary Inflammation. Front Immunol 2018; 8:1644. [PMID: 29354115 PMCID: PMC5758508 DOI: 10.3389/fimmu.2017.01644] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/10/2017] [Indexed: 12/12/2022] Open
Abstract
The lungs conceptually represent a sponge that is interposed in series in the bodies’ systemic circulation to take up oxygen and eliminate carbon dioxide. As such, it matches the huge surface areas of the alveolar epithelium to the pulmonary blood capillaries. The lung’s constant exposure to the exterior necessitates a competent immune system, as evidenced by the association of clinical immunodeficiencies with pulmonary infections. From the in utero to the postnatal and adult situation, there is an inherent vital need to manage alveolar fluid reabsorption, be it postnatally, or in case of hydrostatic or permeability edema. Whereas a wealth of literature exists on the physiological basis of fluid and solute reabsorption by ion channels and water pores, only sparse knowledge is available so far on pathological situations, such as in microbial infection, acute lung injury or acute respiratory distress syndrome, and in the pulmonary reimplantation response in transplanted lungs. The aim of this review is to discuss alveolar liquid clearance in a selection of lung injury models, thereby especially focusing on cytokines and mediators that modulate ion channels. Inflammation is characterized by complex and probably time-dependent co-signaling, interactions between the involved cell types, as well as by cell demise and barrier dysfunction, which may not uniquely determine a clinical picture. This review, therefore, aims to give integrative thoughts and wants to foster the unraveling of unmet needs in future research.
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Affiliation(s)
- Jürg Hamacher
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Internal Medicine V - Pneumology, Allergology, Respiratory and Environmental Medicine, Faculty of Medicine, Saarland University, Saarbrücken, Germany.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Yalda Hadizamani
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Michèle Borgmann
- Internal Medicine and Pneumology, Lindenhofspital, Bern, Switzerland.,Lungen- und Atmungsstiftung Bern, Bern, Switzerland
| | - Markus Mohaupt
- Internal Medicine, Sonnenhofspital Bern, Bern, Switzerland
| | | | - Ueli Moehrlen
- Paediatric Visceral Surgery, Universitäts-Kinderspital Zürich, Zürich, Switzerland
| | - Rudolf Lucas
- Department of Pharmacology and Toxicology, Vascular Biology Center, Medical College of Georgia, Augusta, GA, United States
| | - Uz Stammberger
- Lungen- und Atmungsstiftung Bern, Bern, Switzerland.,Novartis Institutes for Biomedical Research, Translational Clinical Oncology, Novartis Pharma AG, Basel, Switzerland
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Berman JM, Mironova E, Stockand JD. Physiological regulation of the epithelial Na + channel by casein kinase II. Am J Physiol Renal Physiol 2017; 314:F367-F372. [PMID: 29021227 DOI: 10.1152/ajprenal.00469.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
epithelial Na+ channel, ENaC, is the final arbiter of sodium excretion in the kidneys. As such, discretionary control of ENaC by hormones is critical to the fine-tuning of electrolyte and water excretion and, consequently, blood pressure. Casein kinase 2 (CK2) phosphorylates ENaC. Phosphorylation by CK2 is necessary for normal ENaC activity. We tested the physiological importance of CK2 regulation of ENaC as the degree to which ENaC activity is dependent on CK2 phosphorylation in the living organism is unknown. This was addressed using patch-clamp analysis of ENaC in completely split-open collecting ducts and whole animal physiological studies of sodium excretion in mice. We also used ENaC-harboring CK2 phosphorylation site mutations to elaborate the mechanism. We found that ENaC activity in ex vivo preparations of murine collecting duct had a significant decrease in activity in response to selective antagonism of CK2. In whole animal experiments selective antagonism of CK2 caused a natriuresis similar to benzamil, but not additive to benzamil, suggesting an ENaC-dependent mechanism. Regulation of ENaC by CK2 was abolished by mutation of the canonical CK2 phosphorylation sites in beta and gamma ENaC. Together, these results demonstrate that the appropriate regulation of ENaC by CK2 is necessary for the normal physiological role played by this key renal ion channel in the fine-tuning of sodium excretion.
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Affiliation(s)
- Jonathan M Berman
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - Elena Mironova
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
| | - James D Stockand
- Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
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Role of Smad3 and p38 Signalling in Cigarette Smoke-induced CFTR and BK dysfunction in Primary Human Bronchial Airway Epithelial Cells. Sci Rep 2017; 7:10506. [PMID: 28874823 PMCID: PMC5585359 DOI: 10.1038/s41598-017-11038-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 08/18/2017] [Indexed: 01/26/2023] Open
Abstract
Mucociliary clearance (MCC) is a major airway host defence system that is impaired in patients with smoking-associated chronic bronchitis. This dysfunction is partially related to a decrease of airway surface liquid (ASL) volume that is in part regulated by apically expressed cystic fibrosis transmembrane conductance regulator (CFTR) and large-conductance, Ca2+-activated, and voltage dependent K+ (BK) channels. Here, data from human bronchial epithelial cells (HBEC) confirm that cigarette smoke not only downregulates CFTR activity but also inhibits BK channel function, thereby causing ASL depletion. Inhibition of signalling pathways involved in cigarette smoke-induced channel dysfunction reveals that CFTR activity is downregulated via Smad3 signalling whereas BK activity is decreased via the p38 cascade. In addition, pre-treatment with pirfenidone, a drug presently used to inhibit TGF-β signalling in idiopathic pulmonary fibrosis, ameliorated BK dysfunction and ASL volume loss. Taken together, our results highlight the importance of not only CFTR but also BK channel function in maintaining ASL homeostasis and emphasize the possibility that pirfenidone could be employed as a novel therapeutic regimen to help improve MCC in smoking-related chronic bronchitis.
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6
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Ruhs S, Nolze A, Hübschmann R, Grossmann C. 30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Nongenomic effects via the mineralocorticoid receptor. J Endocrinol 2017; 234:T107-T124. [PMID: 28348113 DOI: 10.1530/joe-16-0659] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Accepted: 03/27/2017] [Indexed: 12/12/2022]
Abstract
The mineralocorticoid receptor (MR) belongs to the steroid hormone receptor family and classically functions as a ligand-dependent transcription factor. It is involved in water-electrolyte homeostasis and blood pressure regulation but independent from these effects also furthers inflammation, fibrosis, hypertrophy and remodeling in cardiovascular tissues. Next to genomic effects, aldosterone elicits very rapid actions within minutes that do not require transcription or translation and that occur not only in classical MR epithelial target organs like kidney and colon but also in nonepithelial tissues like heart, vasculature and adipose tissue. Most of these effects can be mediated by classical MR and its crosstalk with different signaling cascades. Near the plasma membrane, the MR seems to be associated with caveolin and striatin as well as with receptor tyrosine kinases like EGFR, PDGFR and IGF1R and G protein-coupled receptors like AT1 and GPER1, which then mediate nongenomic aldosterone effects. GPER1 has also been named a putative novel MR. There is a close interaction and functional synergism between the genomic and the nongenomic signaling so that nongenomic signaling can lead to long-term effects and support genomic actions. Therefore, understanding nongenomic aldosterone/MR effects is of potential relevance for modulating genomic aldosterone effects and may provide additional targets for intervention.
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Affiliation(s)
- Stefanie Ruhs
- Julius Bernstein Institute of PhysiologyMartin Luther University Halle-Wittenberg, Halle, Germany
| | - Alexander Nolze
- Julius Bernstein Institute of PhysiologyMartin Luther University Halle-Wittenberg, Halle, Germany
| | - Ralf Hübschmann
- Julius Bernstein Institute of PhysiologyMartin Luther University Halle-Wittenberg, Halle, Germany
| | - Claudia Grossmann
- Julius Bernstein Institute of PhysiologyMartin Luther University Halle-Wittenberg, Halle, Germany
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Li Y, Chang J, Cui Y, Zhao R, Ding Y, Hou Y, Zhou Z, Ji HL, Nie H. Novel mechanisms for crotonaldehyde-induced lung edema. Oncotarget 2017; 8:83509-83522. [PMID: 29137360 PMCID: PMC5663532 DOI: 10.18632/oncotarget.17840] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 04/25/2017] [Indexed: 12/13/2022] Open
Abstract
Background Crotonaldehyde is a highly noxious α,β-unsaturated aldehyde in cigarette smoke that causes edematous acute lung injury. Objective To understand how crotonaldehyde impairs lung function, we examined its effects on human epithelial sodium channels (ENaC), which are major contributors to alveolar fluid clearance. Methods We studied alveolar fluid clearance in C57 mice and ENaC activity was examined in H441 cells. Expression of α- and γ-ENaC was measured at protein and mRNA levels by western blot and real-time PCR, respectively. Intracellular ROS levels were detected by the dichlorofluorescein assay. Heterologous αβγ-ENaC activity was observed in an oocyte model. Results Our results showed that crotonaldehyde reduced transalveolar fluid clearance in mice. Furthermore, ENaC activity in H441 cells was inhibited by crotonaldehyde dose-dependently. Expression of α- and γ-subunits of ENaC was decreased at the protein and mRNA level in H441 cells exposed to crotonaldehyde, which was probably mediated by the increase in phosphorylated extracellular signal-regulated protein kinases 1 and 2. ROS levels increased time-dependently in cells exposed to crotonaldehyde. Heterologous αβγ-ENaC activity was rapidly eliminated by crotonaldehyde. Conclusion Our findings suggest that crotonaldehyde causes edematous acute lung injury by eliminating ENaC activity at least partly via facilitating the phosphorylation of extracellular signal-regulated protein kinases 1 and 2 signal molecules. Long-term exposure may decrease the expression of ENaC subunits and damage the cell membrane integrity, as well as increase the levels of cellular ROS products.
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Affiliation(s)
- Yue Li
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
| | - Jianjun Chang
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
| | - Yong Cui
- Department of Anesthesiology, First Affiliated Hospital of China Medical University, Shenyang 110001, Liaoning, China
| | - Runzhen Zhao
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA
| | - Yan Ding
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
| | - Yapeng Hou
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
| | - Zhiyu Zhou
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas 75708, USA.,Texas Lung Injury Institute, University of Texas Health Northeast, Tyler, Texas 75708, USA
| | - Hongguang Nie
- Institute of Metabolic Disease Research and Drug Development, China Medical University, Shenyang 110122, Liaoning, China
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8
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Ong GSY, Young MJ. Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways. J Mol Endocrinol 2017; 58:R33-R57. [PMID: 27821439 DOI: 10.1530/jme-15-0318] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 11/06/2016] [Indexed: 12/22/2022]
Abstract
The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.
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Affiliation(s)
- Gregory S Y Ong
- Cardiovascular Endocrinology LaboratoryCentre for Endocrinology and Metabolism, Hudson Institute of Medical Research, Clayton, Victoria, Australia
- Department of MedicineSchool of Clinical Sciences, Monash University, Clayton, Victoria, Australia
| | - Morag J Young
- Cardiovascular Endocrinology LaboratoryCentre for Endocrinology and Metabolism, Hudson Institute of Medical Research, Clayton, Victoria, Australia
- Department of PhysiologySchool of Biomedical Sciences, Monash University, Clayton, Victoria, Australia
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9
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The Epithelial Sodium Channel and the Processes of Wound Healing. BIOMED RESEARCH INTERNATIONAL 2016; 2016:5675047. [PMID: 27493961 PMCID: PMC4963570 DOI: 10.1155/2016/5675047] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 06/15/2016] [Indexed: 12/19/2022]
Abstract
The epithelial sodium channel (ENaC) mediates passive sodium transport across the apical membranes of sodium absorbing epithelia, like the distal nephron, the intestine, and the lung airways. Additionally, the channel has been involved in the transduction of mechanical stimuli, such as hydrostatic pressure, membrane stretch, and shear stress from fluid flow. Thus, in vascular endothelium, it participates in the control of the vascular tone via its activity both as a sodium channel and as a shear stress transducer. Rather recently, ENaC has been shown to participate in the processes of wound healing, a role that may also involve its activities as sodium transporter and as mechanotransducer. Its presence as the sole channel mediating sodium transport in many tissues and the diversity of its functions probably underlie the complexity of its regulation. This brief review describes some aspects of ENaC regulation, comments on evidence about ENaC participation in wound healing, and suggests possible regulatory mechanisms involved in this participation.
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10
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Martínez-Mármol R, Comes N, Styrczewska K, Pérez-Verdaguer M, Vicente R, Pujadas L, Soriano E, Sorkin A, Felipe A. Unconventional EGF-induced ERK1/2-mediated Kv1.3 endocytosis. Cell Mol Life Sci 2015; 73:1515-28. [PMID: 26542799 DOI: 10.1007/s00018-015-2082-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Revised: 10/14/2015] [Accepted: 10/26/2015] [Indexed: 12/13/2022]
Abstract
The potassium channel Kv1.3 plays roles in immunity, neuronal development and sensory discrimination. Regulation of Kv1.3 by kinase signaling has been studied. In this context, EGF binds to specific receptors (EGFR) and triggers tyrosine kinase-dependent signaling, which down-regulates Kv1.3 currents. We show that Kv1.3 undergoes EGF-dependent endocytosis. This EGF-mediated mechanism is relevant because is involved in adult neural stem cell fate determination. We demonstrated that changes in Kv1.3 subcellular distribution upon EGFR activation were due to Kv1.3 clathrin-dependent endocytosis, which targets the Kv1.3 channels to the lysosomal degradative pathway. Interestingly, our results further revealed that relevant tyrosines and other interacting motifs, such as PDZ and SH3 domains, were not involved in the EGF-dependent Kv1.3 internalization. However, a new, and yet undescribed mechanism, of ERK1/2-mediated threonine phosphorylation is crucial for the EGF-mediated Kv1.3 endocytosis. Our results demonstrate that EGF triggers the down-regulation of Kv1.3 activity and its expression at the cell surface, which is important for the development and migration of adult neural progenitors.
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Affiliation(s)
- Ramón Martínez-Mármol
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Barcelona, Spain.,Departament de Biologia Celular, Universitat de Barcelona, Barcelona, Spain
| | - Núria Comes
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Barcelona, Spain
| | - Katarzyna Styrczewska
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Barcelona, Spain
| | - Mireia Pérez-Verdaguer
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Barcelona, Spain
| | - Rubén Vicente
- Laboratory of Molecular Physiology and Channelopathies, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain
| | - Lluís Pujadas
- Departament de Biologia Celular, Universitat de Barcelona, Barcelona, Spain
| | - Eduardo Soriano
- Departament de Biologia Celular, Universitat de Barcelona, Barcelona, Spain.,Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, Madrid, Spain.,Vall d´Hebron Institute of Research (VHIR) and Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
| | - Alexander Sorkin
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Antonio Felipe
- Molecular Physiology Laboratory, Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Barcelona, Spain. .,Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Avda. Diagonal 643, 08028, Barcelona, Spain.
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11
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Matalon S, Bartoszewski R, Collawn JF. Role of epithelial sodium channels in the regulation of lung fluid homeostasis. Am J Physiol Lung Cell Mol Physiol 2015; 309:L1229-38. [PMID: 26432872 DOI: 10.1152/ajplung.00319.2015] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 09/25/2015] [Indexed: 01/11/2023] Open
Abstract
In utero, fetal lung epithelial cells actively secrete Cl(-) ions into the lung air spaces while Na(+) ions follow passively to maintain electroneutrality. This process, driven by an electrochemical gradient generated by the Na(+)-K(+)-ATPase, is responsible for the secretion of fetal fluid that is essential for normal lung development. Shortly before birth, a significant upregulation of amiloride-sensitive epithelial channels (ENaCs) on the apical side of the lung epithelial cells results in upregulation of active Na(+) transport. This process is critical for the reabsorption of fetal lung fluid and the establishment of optimum gas exchange. In the adult lung, active Na(+) reabsorption across distal lung epithelial cells limits the degree of alveolar edema in patients with acute lung injury and cardiogenic edema. Cl(-) ions are transported either paracellularly or transcellularly to preserve electroneutrality. An increase in Cl(-) secretion across the distal lung epithelium has been reported following an acute increase in left atrial pressure and may result in pulmonary edema. In contrast, airway epithelial cells secrete Cl(-) through apical cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels and absorb Na(+). Thus the coordinated action of Cl(-) secretion and Na(+) absorption is essential for maintenance of the volume of epithelial lining fluid that, in turn, maximizes mucociliary clearance and facilitates clearance of bacteria and debris from the lungs. Any factor that interferes with Na(+) or Cl(-) transport or dramatically upregulates ENaC activity in airway epithelial cells has been associated with lung diseases such as cystic fibrosis or chronic obstructive lung disease. In this review we focus on the role of the ENaC, the mechanisms involved in ENaC regulation, and how ENaC dysregulation can lead to lung pathology.
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Affiliation(s)
- Sadis Matalon
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Department of Cell, Developmental, and Integrative Biology, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Pulmonary Injury and Repair Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Gregory Fleming James Cystic Fibrosis Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
| | - Rafal Bartoszewski
- Department of Biology and Pharmaceutical Botany, Medical University of Gdansk, Gdansk, Poland
| | - James F Collawn
- Department of Cell, Developmental, and Integrative Biology, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Pulmonary Injury and Repair Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; Gregory Fleming James Cystic Fibrosis Center, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama; and
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12
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Xu X, Balsiger R, Tyrrell J, Boyaka PN, Tarran R, Cormet-Boyaka E. Cigarette smoke exposure reveals a novel role for the MEK/ERK1/2 MAPK pathway in regulation of CFTR. Biochim Biophys Acta Gen Subj 2015; 1850:1224-32. [PMID: 25697727 DOI: 10.1016/j.bbagen.2015.02.004] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Revised: 01/19/2015] [Accepted: 02/06/2015] [Indexed: 12/22/2022]
Abstract
BACKGROUND Cystic fibrosis transmembrane conductance regulator plays a key role in maintenance of lung fluid homeostasis. Cigarette smoke decreases CFTR expression in the lung but neither the mechanisms leading to CFTR loss, nor potential ways to prevent its loss have been identified to date. METHODS The molecular mechanisms leading to down-regulation of CFTR by cigarette smoke were determined using pharmacologic inhibitors and silencing ribonucleic acids (RNAs). RESULTS Using human bronchial epithelial cells, here we show that cigarette smoke induces degradation of CFTR that is attenuated by lysosomal inhibitors, but not proteasome inhibitors. Cigarette smoke can activate multiple signaling pathways in airway epithelial cells, including the MEK/Erk1/2 MAPK (MEK: mitogen-activated protein kinase/ERK kinase Erk1/2: extracellular signal-regulated kinase 1/2 MAPK: Mitogen-activated protein kinase) pathway regulating cell survival. Interestingly, pharmacological inhibition of the MEK/Erk1/2 MAPK pathway prevented the loss of plasma membrane CFTR upon cigarette smoke exposure. Similarly, decreased expression of Erk1/2 using silencing RNAs prevented the suppression of CFTR protein by cigarette smoke. Conversely, specific inhibitors of the c-Jun N-terminal kinase (JNK) or p38 MAPK pathways had no effect on CFTR decrease after cigarette smoke exposure. In addition, inhibition of the MEK/Erk1/2 MAPK pathway prevented the reduction of the airway surface liquid observed upon cigarette smoke exposure of primary human airway epithelial cells. Finally, addition of the antioxidant N-acetylcysteine inhibited activation of Erk1/2 by cigarette smoke and precluded the cigarette smoke-induced decrease of CFTR. CONCLUSIONS These results show that the MEK/Erk1/2 MAPK pathway regulates plasma membrane CFTR in human airway cells. GENERAL SIGNIFICANCE The MEK/Erk1/2 MAPK pathway should be considered as a target for strategies to maintain/restore CFTR expression in the lung of smokers.
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Affiliation(s)
- Xiaohua Xu
- Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, USA
| | - Robert Balsiger
- Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, USA
| | - Jean Tyrrell
- Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA
| | - Prosper N Boyaka
- Department of Veterinary Biosciences, The Ohio State University, Columbus, OH, USA
| | - Robert Tarran
- Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina, Chapel Hill, NC, USA
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13
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Chen Z, Zhao R, Zhao M, Liang X, Bhattarai D, Dhiman R, Shetty S, Idell S, Ji HL. Regulation of epithelial sodium channels in urokinase plasminogen activator deficiency. Am J Physiol Lung Cell Mol Physiol 2014; 307:L609-17. [PMID: 25172911 DOI: 10.1152/ajplung.00126.2014] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial sodium channels (ENaC) govern transepithelial salt and fluid homeostasis. ENaC contributes to polarization, apoptosis, epithelial-mesenchymal transformation, etc. Fibrinolytic proteases play a crucial role in virtually all of these processes and are elaborated by the airway epithelium. We hypothesized that urokinase-like plasminogen activator (uPA) regulates ENaC function in airway epithelial cells and tested that possibility in primary murine tracheal epithelial cells (MTE). Both basal and cAMP-activated Na(+) flow through ENaC were significantly reduced in monolayers of uPA-deficient cells. The reduction in ENaC activity was further confirmed in basolateral membrane-permeabilized cells. A decrease in the Na(+)-K(+)-ATPase activity in the basolateral membrane could contribute to the attenuation of ENaC function in intact monolayer cells. Dysfunctional fluid resolution was seen in uPA-disrupted cells. Administration of uPA and plasmin partially restores ENaC activity and fluid reabsorption by MTEs. ERK1/2, but not Akt, phosphorylation was observed in the cells and lungs of uPA-deficient mice. On the other hand, cleavage of γ ENaC is significantly depressed in the lungs of uPA knockout mice vs. those of wild-type controls. Expression of caspase 8, however, did not differ between wild-type and uPA(-/-) mice. In addition, uPA deficiency did not alter transepithelial resistance. Taken together, the mechanisms for the regulation of ENaC by uPA in MTEs include augmentation of Na(+)-K(+)-ATPase, proteolysis, and restriction of ERK1/2 phosphorylation. We demonstrate for the first time that ENaC may serve as a downstream signaling target by which uPA controls the biophysical profiles of airway fluid and epithelial function.
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Affiliation(s)
- Zaixing Chen
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Runzhen Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Meimi Zhao
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; School of Pharmacy, China Medical University, Liaoning Shenyang, China
| | - Xinrong Liang
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Deepa Bhattarai
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Rohan Dhiman
- Department of Pulmonary Immunology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Sreerama Shetty
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Steven Idell
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and Department of Medicine, The University of Texas Health Science Center at Tyler, Tyler, Texas
| | - Hong-Long Ji
- Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, Texas; Texas Lung Injury Institute, The University of Texas Health Science Center at Tyler, Tyler, Texas; and
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14
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Eaton AF, Yue Q, Eaton DC, Bao HF. ENaC activity and expression is decreased in the lungs of protein kinase C-α knockout mice. Am J Physiol Lung Cell Mol Physiol 2014; 307:L374-85. [PMID: 25015976 DOI: 10.1152/ajplung.00040.2014] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We used a PKC-α knockout model to investigate the regulation of alveolar epithelial Na(+) channels (ENaC) by PKC. Primary alveolar type II (ATII) cells were subjected to cell-attached patch clamp. In the absence of PKC-α, the open probability (Po) of ENaC was decreased by half compared with wild-type mice. The channel density (N) was also reduced in the knockout mice. Using in vivo biotinylation, membrane localization of all three ENaC subunits (α, β, and γ) was decreased in the PKC-α knockout lung, compared with the wild-type. Confocal microscopy of lung slices showed elevated levels of reactive oxygen species (ROS) in the lungs of the PKC-α knockout mice vs. the wild-type. High levels of ROS in the knockout lung can be explained by a decrease in both cytosolic and mitochondrial superoxide dismutase activity. Elevated levels of ROS in the knockout lung activates PKC-δ and leads to reduced dephosphorylation of ERK1/2 by MAP kinase phosphatase, which in turn causes increased internalization of ENaC via ubiquitination by the ubiquitin-ligase Nedd4-2. In addition, in the knockout lung, PKC-δ activates ERK, causing a decrease in ENaC density at the apical alveolar membrane. PKC-δ also phosphorylates MARCKS, leading to a decrease in ENaC Po. The effects of ROS and PKC-δ were confirmed with patch-clamp experiments on isolated ATII cells in which the ROS scavenger, Tempol, or a PKC-δ-specific inhibitor added to patches reversed the observed decrease in ENaC apical channel density and Po. These results explain the decrease in ENaC activity in PKC-α knockout lung.
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Affiliation(s)
- Amity F Eaton
- Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
| | - Qiang Yue
- Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
| | - Douglas C Eaton
- Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
| | - Hui-Fang Bao
- Department of Physiology and the Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia
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15
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Yusef YR, Thomas W, Harvey BJ. Estrogen increases ENaC activity via PKCδ signaling in renal cortical collecting duct cells. Physiol Rep 2014; 2:2/5/e12020. [PMID: 24872356 PMCID: PMC4098747 DOI: 10.14814/phy2.12020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The most active estrogen, 17β‐estradiol (E2), has previously been shown to stimulate a female sex‐specific antisecretory response in the intestine. This effect is thought to contribute to the increase in whole body extracellular fluid (ECF) volume which occurs in high estrogen states, such as in the implantation window during estrous cycle. The increased ECF volume may be short‐circuited by a renal compensation unless estrogen exerts a proabsorptive effect in the nephron. Thus, the effect of E2 on ENaC in kidney cortical collecting duct (CCD) cells is of interest to understand estrogen regulation of ECF volume. Previous studies showed a rapid stimulatory effect of estrogen on ENaC in bronchial epithelium. In this study we examined if such a rapid effect on Na+ absorption could occur in the kidney. Experiments were carried out on murine M1‐CCD cell cultures. E2 (25 nmol/L) treatment caused a rapid‐onset (<15 min) and sustained increase in the amiloride‐sensitive Na+ current (INa) in CCD monolayers mounted in Ussing chambers (control, 1.9 ± 0.2 μA/cm2; E2, 4.7 ± 0.3 μA/cm2; n = 43, P < 0.001), without affecting the ouabain‐sensitive Na+/K+ pump current. The INa response to E2 was inhibited by PKCδ activity antagonism with rottlerin (5 μmol/L), inhibition of matrix metalloproteinases activity with GM6001 (1 μmol/L), inhibition of EGFR activity with AG1478 (10 μmol/L), inhibition of PLC activity with U‐73122 (10 μmol/L), and inhibition of estrogen receptors with the general ER antagonist ICI‐182780 (100 nmol/L). The estrogen activation of INa could be mimicked by the ERα agonist PPT (1 nmol/L). The nuclear excluded estrogen dendrimer conjugate (EDC) induced similar stimulatory effects on INa comparable to free E2. The end target for E2 stimulation of PKCδ was shown to be an increased abundance of the γ‐ENaC subunit in the apical plasma membrane of CCD cells. We have demonstrated a novel rapid “nongenomic” function of estrogen to stimulate ENaC via ERα‐EGFR transactivation in kidney CCD cells. We propose that the salt‐retaining effect of estrogen in the kidney together with its antisecretory action in the intestine are the molecular mechanisms causing the expanded ECF volume in high‐estrogen states. Estrogen stimulates sodium absorption in kidney cells. This rapid “nongenomic” response to estrogen is transduced via estrogen receptor transactivation of the epidermal growth factor receptor. The ER‐EGFR transactivation triggers a protein kinase signaling cascade which culminates in the insertion of sodium channel subunits into the cell membrane. Estrogen is a novel salt‐retaining hormone with proabsorptive effects in kidney and antisecretory actions in intestine.
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Affiliation(s)
- Yamil R Yusef
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI Education and Research Centre, Beaumont Hospital, Dublin, Ireland
| | - Warren Thomas
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI Education and Research Centre, Beaumont Hospital, Dublin, Ireland
| | - Brian J Harvey
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, RCSI Education and Research Centre, Beaumont Hospital, Dublin, Ireland
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16
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Gille T, Randrianarison-Pellan N, Goolaerts A, Dard N, Uzunhan Y, Ferrary E, Hummler E, Clerici C, Planès C. Hypoxia-induced inhibition of epithelial Na(+) channels in the lung. Role of Nedd4-2 and the ubiquitin-proteasome pathway. Am J Respir Cell Mol Biol 2014; 50:526-37. [PMID: 24093724 DOI: 10.1165/rcmb.2012-0518oc] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Transepithelial sodium transport via alveolar epithelial Na(+) channels (ENaC) and Na(+),K(+)-ATPase constitutes the driving force for removal of alveolar edema fluid. Alveolar hypoxia associated with pulmonary edema may impair ENaC activity and alveolar Na(+) absorption through a decrease of ENaC subunit expression at the apical membrane of alveolar epithelial cells (AECs). Here, we investigated the mechanism(s) involved in this process in vivo in the β-Liddle mouse strain mice carrying a truncation of β-ENaC C-terminus abolishing the interaction between β-ENaC and the ubiquitin protein-ligase Nedd4-2 that targets the channel for endocytosis and degradation and in vitro in rat AECs. Hypoxia (8% O2 for 24 h) reduced amiloride-sensitive alveolar fluid clearance by 69% in wild-type mice but had no effect in homozygous mutated β-Liddle littermates. In vitro, acute exposure of AECs to hypoxia (0.5-3% O2 for 1-6 h) rapidly decreased transepithelial Na(+) transport as assessed by equivalent short-circuit current Ieq and the amiloride-sensitive component of Na(+) current across the apical membrane, reflecting ENaC activity. Hypoxia induced a decrease of ENaC subunit expression in the apical membrane of AECs with no change in intracellular expression and induced a 2-fold increase in α-ENaC polyubiquitination. Hypoxic inhibition of amiloride-sensitive Ieq was fully prevented by preincubation with the proteasome inhibitors MG132 and lactacystin or with the antioxidant N-acetyl-cysteine. Our data strongly suggest that Nedd4-2-mediated ubiquitination of ENaC leading to endocytosis and degradation of apical Na(+) channels is a key feature of hypoxia-induced inhibition of transepithelial alveolar Na(+) transport.
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Affiliation(s)
- Thomas Gille
- 1 Université Paris 13, Sorbonne Paris Cité, Laboratoire Réponses Cellulaires et Fonctionnelles à l'Hypoxie (EA 2363), Bobigny, France
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17
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Staruschenko A, Safonova TA. PC and PKC: in vivo vs. in vitro. Am J Physiol Renal Physiol 2014; 306:F507-8. [PMID: 24370588 DOI: 10.1152/ajprenal.00678.2013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Alexander Staruschenko
- Dept. of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226.
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18
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Bao HF, Thai TL, Yue Q, Ma HP, Eaton AF, Cai H, Klein JD, Sands JM, Eaton DC. ENaC activity is increased in isolated, split-open cortical collecting ducts from protein kinase Cα knockout mice. Am J Physiol Renal Physiol 2014; 306:F309-20. [PMID: 24338818 PMCID: PMC3920049 DOI: 10.1152/ajprenal.00519.2013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 12/04/2013] [Indexed: 11/22/2022] Open
Abstract
The epithelial Na channel (ENaC) is negatively regulated by protein kinase C (PKC) as shown using PKC activators in a cell culture model. To determine whether PKCα influences ENaC activity in vivo, we examined the regulation of ENaC in renal tubules from PKCα⁻/⁻ mice. Cortical collecting ducts were dissected and split open, and the exposed principal cells were subjected to cell-attached patch clamp. In the absence of PKCα, the open probability (P₀) of ENaC was increased three-fold vs. wild-type SV129 mice (0.52 ± 0.04 vs. 0.17 ± 0.02). The number of channels per patch was also increased. Using confocal microscopy, we observed an increase in membrane localization of α-, β-, and γ-subunits of ENaC in principal cells in the cortical collecting ducts of PKCα⁻/⁻ mice compared with wild-type mice. To confirm this increase, one kidney from each animal was perfused with biotin, and membrane protein was pulled down with streptavidin. The nonbiotinylated kidney was used to assess total protein. While total ENaC protein did not change in PKCα⁻/⁻ mice, membrane localization of all the ENaC subunits was increased. The increase in membrane ENaC could be explained by the observation that ERK1/2 phosphorylation was decreased in the knockout mice. These results imply a reduction in ENaC membrane accumulation and P₀ by PKCα in vivo. The PKC-mediated increase in ENaC activity was associated with an increase in blood pressure in knockout mice fed a high-salt diet.
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Affiliation(s)
- Hui-Fang Bao
- Emory Univ. School of Medicine, Dept. of Physiology, Whitehead Biomedical Research Bldg., 615 Michael St., Atlanta, GA 30322.
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19
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Yu L, Al-Khalili O, Duke BJ, Stockand JD, Eaton DC, Bao HF. The inhibitory effect of Gβγ and Gβ isoform specificity on ENaC activity. Am J Physiol Renal Physiol 2013; 305:F1365-73. [PMID: 23863469 DOI: 10.1152/ajprenal.00009.2013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Epithelial Na(+) channel (ENaC) activity, which determines the rate of renal Na(+) reabsorption, can be regulated by G protein-coupled receptors. Regulation of ENaC by Gα-mediated downstream effectors has been studied extensively, but the effect of Gβγ dimers on ENaC is unclear. A6 cells endogenously contain high levels of Gβ1 but low levels of Gβ3, Gβ4, and Gβ5 were detected by Q-PCR. We tested Gγ2 combined individually with Gβ1 through Gβ5 expressed in A6 cells, after which we recorded single-channel ENaC activity. Among the five β and γ2 combinations, β1γ2 strongly inhibits ENaC activity by reducing both ENaC channel number (N) and open probability (Po) compared with control cells. In contrast, the other four β-isoforms combined with γ2 have no significant effect on ENaC activity. By using various inhibitors to probe Gβ1γ2 effects on ENaC regulation, we found that Gβ1γ2-mediated ENaC inhibition involved activation of phospholipase C-β and its enzymatic products that induce protein kinase C and ERK1/2 signaling pathways.
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Affiliation(s)
- Ling Yu
- College of Resources and Environmental Sciences, Nanjing Agricultural Univ., Nanjing 210095, China.
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20
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Wang Q, Traynor JR. Modulation of μ-opioid receptor signaling by RGS19 in SH-SY5Y cells. Mol Pharmacol 2013; 83:512-20. [PMID: 23197645 PMCID: PMC3558815 DOI: 10.1124/mol.112.081992] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Accepted: 11/29/2012] [Indexed: 02/03/2023] Open
Abstract
Regulator of G-protein signaling protein 19 (RGS19), also known as Gα-interacting protein (GAIP), acts as a GTPase accelerating protein for Gαz as well as Gαi/o subunits. Interactions with GAIP-interacting protein N-terminus and GAIP-interacting protein C-terminus (GIPC) link RGS19 to a variety of intracellular proteins. Here we show that RGS19 is abundantly expressed in human neuroblastoma SH-SY5Y cells that also express µ- and δ- opioid receptors (MORs and DORs, respectively) and nociceptin receptors (NOPRs). Lentiviral delivery of short hairpin RNA specifically targeted to RGS19 reduced RGS19 protein levels by 69%, with a similar reduction in GIPC. In RGS19-depleted cells, there was an increase in the ability of MOR (morphine) but not of DOR [(4-[(R)-[(2S,5R)-4-allyl-2,5-dimethylpiperazin-1-yl](3-methoxyphenyl)methyl]-N,N-diethylbenzamide (SNC80)] or NOPR (nociceptin) agonists to inhibit forskolin-stimulated adenylyl cyclase and increase mitogen-activated protein kinase (MAPK) activity. Overnight treatment with either MOR [D-Ala, N-Me-Phe, Gly-ol(5)-enkephalin (DAMGO) or morphine] or DOR (D-Pen(5)-enkephalin or SNC80) agonists increased RGS19 and GIPC protein levels in a time- and concentration-dependent manner. The MOR-induced increase in RGS19 protein was prevented by pretreatment with pertussis toxin or the opioid antagonist naloxone. Protein kinase C (PKC) activation alone increased the level of RGS19 and inhibitors of PKC 5,6,7,13-tetrahydro-13-methyl-5-oxo-12H-indolo[2,3-a]pyrrolo[3,4-c]carbazole-12-propanenitrile and mitogen-activated protein kinase kinase 1 2-(2-amino-3-methoxyphenyl)-4H-chromen-4-one, but not protein kinase A (H89), completely blocked DAMGO-induced RGS19 protein accumulation. The findings show that RGS19 and GIPC are jointly regulated, that RGS19 is a GTPase accelerating protein for MOR with selectivity over DOR and NOPR, and that chronic MOR or DOR agonist treatment increases RGS19 levels by a PKC and the MAPK pathway-dependent mechanism.
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MESH Headings
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/metabolism
- Adenylyl Cyclases/genetics
- Adenylyl Cyclases/metabolism
- Animals
- Benzamides/pharmacology
- Colforsin/pharmacology
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- HEK293 Cells
- Humans
- Mitogen-Activated Protein Kinases/genetics
- Mitogen-Activated Protein Kinases/metabolism
- Morphine/pharmacology
- Opioid Peptides/pharmacology
- PC12 Cells
- Piperazines/pharmacology
- Protein Kinase C/genetics
- Protein Kinase C/metabolism
- RGS Proteins/genetics
- RGS Proteins/metabolism
- Rats
- Receptors, Opioid/genetics
- Receptors, Opioid/metabolism
- Receptors, Opioid, delta/agonists
- Receptors, Opioid, delta/genetics
- Receptors, Opioid, delta/metabolism
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
- Signal Transduction/drug effects
- Nociceptin Receptor
- Nociceptin
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Affiliation(s)
- Qin Wang
- Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109-5632, USA
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21
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Kuntzsch D, Bergann T, Dames P, Fromm A, Fromm M, Davis RA, Melzig MF, Schulzke JD. The plant-derived glucocorticoid receptor agonist Endiandrin A acts as co-stimulator of colonic epithelial sodium channels (ENaC) via SGK-1 and MAPKs. PLoS One 2012; 7:e49426. [PMID: 23152905 PMCID: PMC3496671 DOI: 10.1371/journal.pone.0049426] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 10/07/2012] [Indexed: 11/23/2022] Open
Abstract
In a search for secondary plant compounds that bind to the glucocorticoid receptor (GR), the cyclobutane lignan endiandrin A was discovered from the rainforest tree Endiandra anthropophagorum Domin. Our present study aims to characterize the effect of endiandrin A on GR-dependent induction of colonic sodium transport. The effect of endiandrin A was analyzed in GR-expressing colonic HT-29/B6 cells (HT-29/B6-GR). GR transactivation and subcellular localization were investigated by reporter gene assay and immunofluorescence. Epithelial sodium channel (ENaC) was analyzed by qRT-PCR and by measuring amiloride-sensitive short-circuit current (Isc) in Ussing chambers. Endiandrin A (End A) has been identified as GR receptor binder. However, it did not cause significant GR transactivation as pGRE-luciferase activity was only 7% of that of the maximum effect of dexamethasone. Interestingly, endiandrin A had a significant impact on dexamethasone-dependent sodium absorption in cells co-exposed to tumor necrosis factor (TNF)-α. This was in part due to up-regulation of β- and γ-ENaC subunit expression. Endiandrin A potentiated GR-mediated transcription by increasing GR protein expression and phosphorylation. It inhibited c-Jun N-terminal kinase (JNK) activation induced by dexamethasone and/or TNF-α and increased levels of GR localized to the nucleus. Additionally, endiandrin A increased the serum- and glucocorticoid-induced kinase (sgk)-1 via activation of p38. Finally, the regulation of ENaC function by endiandrin A was confirmed in rat native colon. In conclusion, endiandrin A potentiates glucocorticoid-driven activation of colonic epithelial sodium channels via JNK inhibition and p38 activation due to transcriptional up-regulation of β- and γ-ENaC-subunits along with induction of sgk-1.
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Affiliation(s)
- Dana Kuntzsch
- Department of Gastroenterology, Division of Nutritional Medicine, Charité, Campus Benjamin Franklin, Berlin, Germany
| | - Theresa Bergann
- Department of Gastroenterology, Division of Nutritional Medicine, Charité, Campus Benjamin Franklin, Berlin, Germany
| | - Petra Dames
- Department of Gastroenterology, Division of Nutritional Medicine, Charité, Campus Benjamin Franklin, Berlin, Germany
| | - Anja Fromm
- Institute of Clinical Physiology, Charité, Campus Benjamin Franklin, Berlin, Germany
| | - Michael Fromm
- Institute of Clinical Physiology, Charité, Campus Benjamin Franklin, Berlin, Germany
| | - Rohan A. Davis
- Eskitis Institute, Griffith University, Brisbane, Queensland, Australia
| | - Matthias F. Melzig
- Institute of Pharmacy, Pharmaceutical Biology, Freie Universität Berlin, Berlin, Germany
| | - Joerg D. Schulzke
- Department of Gastroenterology, Division of Nutritional Medicine, Charité, Campus Benjamin Franklin, Berlin, Germany
- * E-mail:
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22
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Soundararajan R, Ziera T, Koo E, Ling K, Wang J, Borden SA, Pearce D. Scaffold protein connector enhancer of kinase suppressor of Ras isoform 3 (CNK3) coordinates assembly of a multiprotein epithelial sodium channel (ENaC)-regulatory complex. J Biol Chem 2012; 287:33014-25. [PMID: 22851176 DOI: 10.1074/jbc.m112.389148] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hormone regulation of ion transport in the kidney tubules is essential for fluid and electrolyte homeostasis in vertebrates. A large body of evidence has suggested that transporters and channels exist in multiprotein regulatory complexes; however, relatively little is known about the composition of these complexes or their assembly. The epithelial sodium channel (ENaC) in particular is tightly regulated by the salt-regulatory hormone aldosterone, which acts at least in part by increasing expression of the serine-threonine kinase SGK1. Here we show that aldosterone induces the formation of a 1.0-1.2-MDa plasma membrane complex, which includes ENaC, SGK1, and the ENaC inhibitor Nedd4-2, a key target of SGK1. We further show that this complex contains the PDZ domain-containing protein connector enhancer of kinase suppressor of Ras isoform 3 (CNK3). CNK3 physically interacts with ENaC, Nedd4-2, and SGK1; enhances the interactions among them; and stimulates ENaC function in a PDZ domain-dependent, aldosterone-induced manner. These results strongly suggest that CNK3 is a molecular scaffold, which coordinates the assembly of a multiprotein ENaC-regulatory complex and hence plays a central role in Na(+) homeostasis.
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Affiliation(s)
- Rama Soundararajan
- Division of Nephrology, Department of Medicine, University of California, San Francisco, California 94143, USA
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23
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Niisato N, Ohta M, Eaton DC, Marunaka Y. Hypotonic stress upregulates β- and γ-ENaC expression through suppression of ERK by inducing MKP-1. Am J Physiol Renal Physiol 2012; 303:F240-52. [PMID: 22573375 DOI: 10.1152/ajprenal.00198.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
We investigated a physiological role for ERK, a member of the MAPK family, in the hypotonic stimulation of epithelial Na(+) channel (ENaC)-mediated Na(+) reabsorption in renal epithelial A6 cells. We show that hypotonic stress causes a major dephosphorylation of ERK following a rapid transient phosphorylation. PD98059 (a MEK inhibitor) increases dephosphorylated ERK and enhances the hypotonic-stress-stimulated Na(+) reabsorption. ERK dephosphorylation is mediated by MAPK phosphatase (MKP). Hypotonic stress activates p38, which in turn induces MKP-1 and to a lesser extent MKP-3 mRNA expression. Inhibition of p38 suppresses MKP-1 induction, preventing hypotonic stress from dephosphorylating ERK. Inhibition of MKP-1 and -3 by the inhibitor NSC95397 also suppresses the hypotonicity-induced dephosphorylation of ERK. NSC95397 reduces both β- and γ-ENaC mRNA expression and ENaC-mediated Na(+) reabsorption stimulated by hypotonic stress. In contrast, pretreatment with PD98059 significantly enhances mRNA and protein expression of β- and γ-ENaC even under isotonic conditions. However, PD98059 only stimulates Na(+) reabsorption in response to hypotonic stress, suggesting that ERK inactivation by itself (i.e., under isotonic conditions) is not sufficient to stimulate Na(+) reabsorption, even though ERK inactivation enhances β- and γ-ENaC expression. Based on these results, we conclude that hypotonic stress stimulates Na(+) reabsorption through at least two signaling pathways: 1) induction of MKP-1 that suppresses ERK activity and induces β- and γ-ENaC expression, and 2) promotion of translocation of the newly synthesized ENaC to the apical membrane.
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Affiliation(s)
- Naomi Niisato
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan
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Soundararajan R, Lu M, Pearce D. Organization of the ENaC-regulatory machinery. Crit Rev Biochem Mol Biol 2012; 47:349-59. [PMID: 22506713 DOI: 10.3109/10409238.2012.678285] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The control of fluid and electrolyte homeostasis in vertebrates requires the integration of a diverse set of signaling inputs, which control epithelial Na(+) transport, the principal ionic component of extracellular fluid. The key site of regulation is a segment of the kidney tubules, frequently termed the aldosterone-sensitive distal nephron, wherein the epithelial Na(+) channel (or ENaC) mediates apical ion entry. Na(+) transport in this segment is strongly regulated by the salt-retaining hormone, aldosterone, which acts through the mineralocorticoid receptor (MR) to influence the expression of a selected set of target genes, most notably the serine-threonine kinase SGK1, which phosphorylates and inhibits the E3 ubiquitin ligase Nedd4-2. It has long been known that ENaC activity is tightly regulated in vertebrate epithelia. Recent evidence suggests that SGK1 and Nedd4-2, along with other ENaC-regulatory proteins, physically associate with each other and with ENaC in a multi-protein complex. The various components of the complex are regulated by diverse signaling networks, including steroid receptor-, PI3-kinase-, mTOR-, and Raf-MEK-ERK-dependent pathways. In this review, we focus on the organization of the targets of these pathways by multi-domain scaffold proteins and lipid platforms into a unified complex, thereby providing a molecular basis for signal integration in the control of ENaC.
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Affiliation(s)
- Rama Soundararajan
- Division of Nephrology, Department of Medicine, University of California San Francisco, San Francisco, CA 94143, USA
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Sun P, Yue P, Wang WH. Angiotensin II stimulates epithelial sodium channels in the cortical collecting duct of the rat kidney. Am J Physiol Renal Physiol 2012; 302:F679-87. [PMID: 22169010 PMCID: PMC3311319 DOI: 10.1152/ajprenal.00368.2011] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Accepted: 12/06/2011] [Indexed: 02/07/2023] Open
Abstract
We examined the effect of angiotensin II (ANG II) on epithelial Na(+) channel (ENaC) in the rat cortical collecting duct (CCD) with single-channel and the perforated whole cell patch-clamp recording. Application of 50 nM ANG II increased ENaC activity, defined by NP(o) (a product of channel numbers and open probability), and the amiloride-sensitive whole cell Na currents by twofold. The stimulatory effect of ANG II on ENaC was absent in the presence of losartan, suggesting that the effect of ANG II on ENaC was mediated by ANG II type 1 receptor. Moreover, depletion of intracellular Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM failed to abolish the stimulatory effect of ANG II on ENaC but inhibiting protein kinase C (PKC) abolished the effect of ANG II, suggesting that the effect of ANG II was the result of stimulating Ca(2+)-independent PKC. This notion was also suggested by the experiments in which stimulation of PKC with phorbol ester derivative mimicked the effect of ANG II and increased amiloride-sensitive Na currents in the principal cell, an effect that was not abolished by treatment of the CCD with BAPTA-AM. Also, inhibition of NADPH oxidase (NOX) with diphenyleneiodonium chloride abolished the stimulatory effect of ANG II on ENaC and application of superoxide donors, pyrogallol or xanthine and xanthine oxidase, significantly increased ENaC activity. Moreover, addition of ANG II or H(2)O(2) diminished the arachidonic acid (AA)-induced inhibition of ENaC in the CCD. We conclude that ANG II stimulates ENaC in the CCD through a Ca(2+)-independent PKC pathway that activates NOX thereby increasing superoxide generation. The stimulatory effect of ANG II on ENaC may be partially the result of blocking AA-induced inhibition of ENaC.
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Affiliation(s)
- Peng Sun
- Dept. of Pharmacology, New York Medical College, 15 Dana Rd., Valhalla, NY 10595, USA
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Soukup B, Benjamin A, Orogo-Wenn M, Walters D. Physiological effect of protein kinase C on ENaC-mediated lung liquid regulation in the adult rat lung. Am J Physiol Lung Cell Mol Physiol 2011; 302:L133-9. [PMID: 21949158 DOI: 10.1152/ajplung.00031.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Tight control of lung liquid (LL) regulation is vital for pulmonary function. The aim of this work was to determine whether PKC activation is involved in the physiological regulation of LL volume in a whole lung preparation. Rat lungs were perfused with a modified Ringer solution, and the lumen was filled with the same solution without glucose. LL volume was measured during a control period and after modulating drugs were administered, and net LL transepithelial movement (J(v)) was calculated. When the PKC activator PMA (10(-5) M) and the Ca(2+) ionophore ionomycin (10(-6) M) were instilled into the lung together, J(v) was significantly reduced (P = 0.03). This reduction was blocked by the PKC inhibitor chelerythrine chloride (10(-6) M; P = 0.56) and by a second PKC inhibitor GF109203X (10(-5) M; P = 0.98). When PMA and ionomycin were added with the β-adrenergic agonist terbutaline, the terbutaline-induced increase in J(v) was abolished. Addition of PMA and ionomycin with the epithelial Na(+) channel (ENaC) blocker amiloride had no additional inhibitory effect. Together, these results suggest that PKC is likely to be involved in LL absorption, and the ability of PMA/ionomycin to block the terbutaline-induced increase in J(v) suggests that the downstream target of PKC is ENaC.
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Affiliation(s)
- Benjamin Soukup
- Division of Biomedical Sciences, St. George's University of London, London, United Kingdom
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Epidermal growth factor-mediated proliferation and sodium transport in normal and PKD epithelial cells. Biochim Biophys Acta Mol Basis Dis 2010; 1812:1301-13. [PMID: 20959142 DOI: 10.1016/j.bbadis.2010.10.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 09/30/2010] [Accepted: 10/11/2010] [Indexed: 02/07/2023]
Abstract
Members of the epidermal growth factor (EGF) family bind to ErbB (EGFR) family receptors which play an important role in the regulation of various fundamental cell processes including cell proliferation and differentiation. The normal rodent kidney has been shown to express at least three members of the ErbB receptor family and is a major site of EGF ligand synthesis. Polycystic kidney disease (PKD) is a group of diseases caused by mutations in single genes and is characterized by enlarged kidneys due to the formation of multiple cysts in both kidneys. Tubule cells proliferate, causing segmental dilation, in association with the abnormal deposition of several proteins. One of the first abnormalities described in cell biological studies of PKD pathogenesis was the abnormal mislocalization of the EGFR in cyst lining epithelial cells. The kidney collecting duct (CD) is predominantly an absorptive epithelium where electrogenic Na(+) entry is mediated by the epithelial Na(+) channel (ENaC). ENaC-mediated sodium absorption represents an important ion transport pathway in the CD that might be involved in the development of PKD. A role for EGF in the regulation of ENaC-mediated sodium absorption has been proposed. However, several investigations have reported contradictory results indicating opposite effects of EGF and its related factors on ENaC activity and sodium transport. Recent advances in understanding how proteins in the EGF family regulate the proliferation and sodium transport in normal and PKD epithelial cells are discussed here. This article is part of a Special Issue entitled: Polycystic Kidney Disease.
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McEneaney V, Dooley R, Yusef YR, Keating N, Quinn U, Harvey BJ, Thomas W. Protein kinase D1 modulates aldosterone-induced ENaC activity in a renal cortical collecting duct cell line. Mol Cell Endocrinol 2010; 325:8-17. [PMID: 20434520 DOI: 10.1016/j.mce.2010.04.019] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Revised: 04/14/2010] [Accepted: 04/21/2010] [Indexed: 01/31/2023]
Abstract
Aldosterone treatment of M1-CCD cells stimulated an increase in epithelial Na(+) channel (ENaC) alpha-subunit expression that was mainly localized to the apical membrane. PKD1-suppressed cells constitutively expressed ENaCalpha at low abundance, with no increase after aldosterone treatment. In the PKD1-suppressed cells, ENaCalpha was mainly localized proximal to the basolateral surface of the epithelium both before and after aldosterone treatment. Apical membrane insertion of ENaCbeta in response to aldosterone treatment was also sensitive to PKD1 suppression as was the aldosterone-induced rise in the amiloride-sensitive, trans-epithelial current (I(TE)). The interaction of the mineralocorticoid receptor (MR) with specific elements in the promoters of aldosterone responsive genes is stabilized by ligand interaction and phosphorylation. PKD1 suppression inhibited aldosterone-induced SGK-1 expression. The nuclear localization of MR was also blocked by PKD1 suppression and MEK antagonism implicating both these kinases in MR nuclear stabilization. PKD1 thus modulates aldosterone-induced ENaC activity through the modulation of sub-cellular trafficking and the stabilization of MR nuclear localization.
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Affiliation(s)
- Victoria McEneaney
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, Education and Research Centre, Smurfit Building, Beaumont Hospital, Dublin 9, Ireland
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Pondugula SR, Raveendran NN, Marcus DC. Ion transport regulation by P2Y receptors, protein kinase C and phosphatidylinositol 3-kinase within the semicircular canal duct epithelium. BMC Res Notes 2010; 3:100. [PMID: 20398257 PMCID: PMC2862037 DOI: 10.1186/1756-0500-3-100] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Accepted: 04/14/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The ionic composition of the luminal fluid in the vestibular labyrinth is maintained within tight limits by the many types of epithelial cells bounding the lumen. Regulatory mechanisms include systemic, paracrine and autocrine hormones along with their associated intracellular signal pathways. The epithelium lining the semicircular canal duct (SCCD) is a tissue that is known to absorb sodium and calcium and to secrete chloride. FINDINGS Transport function was assessed by measurements of short circuit current (Isc) and gene transcript expression was evaluated by microarray. Neither ATP nor UTP (100 microM) on the apical side of the epithelium had any effect on Isc. By contrast, basolateral ATP transiently increased Isc and transepithelial resistance dropped significantly after basolateral ATP and UTP. P2Y2 was the sole UTP-sensitive purinergic receptor expressed. Isc was reduced by 42%, 50% and 63% after knockdown of alpha-ENaC, stimulation of PKC and inhibition of PI3-K, while the latter two increased the transepithelial resistance. PKCdelta, PKCgamma and PI3-K were found to be expressed. CONCLUSIONS These observations demonstrate that ion transport by the SCCD is regulated by P2Y2 purinergic receptors on the basolateral membrane that may respond to systemic or local agonists, such as ATP and/or UTP. The sodium absorption from endolymph mediated by ENaC in SCCD is regulated by signal pathways that include the kinases PKC and PI3-K. These three newly-identified regulatory components may prove to be valuable drug targets in the control of pathologic vestibular conditions involving dysfunction of transport homeostasis in the ear, such as Meniere's disease.
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Ko B, Kamsteeg EJ, Cooke LL, Moddes LN, Deen PMT, Hoover RS. RasGRP1 stimulation enhances ubiquitination and endocytosis of the sodium-chloride cotransporter. Am J Physiol Renal Physiol 2010; 299:F300-9. [PMID: 20392800 DOI: 10.1152/ajprenal.00441.2009] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The sodium-chloride cotransporter (NCC) is the principal salt-absorptive pathway in the distal convoluted tubule. Recently, we described a novel pathway of NCC regulation in which phorbol esters (PE) stimulate Ras guanyl-releasing protein 1 (RasGRP1), triggering a cascade ultimately activating ERK1/2 MAPK and decreasing NCC cell surface expression (Ko B, Joshi LM, Cooke LL, Vazquez N, Musch MW, Hebert SC, Gamba G, Hoover RS. Proc Natl Acad Sci USA 104: 20120-20125, 2007). Little is known about the mechanisms which underlie these effects on NCC activity. Regulation of NCC via changes in NCC surface expression has been reported, but endocytosis of NCC has not been demonstrated. In this study, utilizing biotinylation, internalization assays, and a dynamin dominant-negative construct, we demonstrate that the regulation of NCC by PE occurs via an enhancement in internalization of NCC and is dynamin dependent. In addition, immunoprecipitation of NCC and subsequent immunoblotting for ubiquitin showed increased ubiquitination of NCC with phorbol ester treatment. MEK1/2 inhibitors and gene silencing of RasGRP1 indicated that this effect was dependent on RasGRP1 and ERK1/2 activation. Inhibition of ubiquitination prevents any PE-mediated decrease in NCC surface expression as measured by biotinylation or NCC activity as measured by radiotracer uptake. These findings confirmed that the PE effect on NCC is mediated by endocytosis of NCC. Furthermore, ubiquitination of NCC is essential for this process and this ubiquitination is dependent upon RasGRP1-mediated ERK1/2 activation.
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Affiliation(s)
- Benjamin Ko
- Department of Medicine, University of Chicago, Illinois, USA
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Abstract
The epithelial cells of Reissner's membrane (RM) are capable of transporting Na(+) out of endolymph via epithelial Na(+) channel (ENaC). However, much remains to be known as to mechanism of regulation of Na(+) absorption in RM. We investigated P2Y signaling as a possible regulatory mechanism of ENaC in gerbil RM using voltage-sensitive vibrating probe technique and immunohistochemistry. Results showed that UTP induced partial inhibition of the amiloride-sensitive short-circuit current but did not change short-circuit current when applied in the presence of amiloride. The inhibitory effect of UTP was not completely reversible in minutes. The response to UTP was inhibited by reactive blue-2 and 2',3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate but not by suramin or pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid, which indicates this P2Y receptor as the P2Y(4) subtype. The phospholipase C (PLC) inhibitors 1-[6[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione and 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine markedly inhibited the effect of UTP on ENaC. In contrast, neither modulation of protein kinase C nor application of 2-aminoehoxydiphenyl borate affected P2Y(4)-mediated inhibition of ENaC. Immunoreactive staining for P2Y(4) was observed in the RM, apical membrane of stria vascularis, spiral ligament, and organ of Corti, including outer hair cell, inner hair cell, outer pillar cell, Deiters' cell, and Hensen cell. These results suggest that the physiological role of P2Y(4) receptor in RM is likely to regulate Na(+) homeostasis in the endolymph. The acute inhibition of ENaC activity by activation of P2Y(4) receptor is possibly mediated by decrease of phosphatidylinositol 4,5-biphosphate in the plasma membrane through PLC activation.
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Mironova E, Stockand JD. Activation of a latent nuclear localization signal in the NH2 terminus of γ-ENaC initiates feedback regulation of channel activity. Am J Physiol Renal Physiol 2010; 298:F1188-96. [PMID: 20147367 DOI: 10.1152/ajprenal.00600.2009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proteolytic enzymes cleave the epithelial Na(+) channel (ENaC) at several positions releasing, in part, the NH(2) terminus of the γ-subunit. Cleavage increases ENaC activity by increasing open probability; however, the role of polypeptides cleaved from the channel core remains unclear. We find that the cytosolic NH(2) terminus of γ-ENaC unexpectedly targets to the nucleus being particularly strong in nucleoli. In contrast, the cytosolic COOH terminus targets to the cytoplasm and plasma membrane in a manner similar to full-length subunits. Targeting of the cytosolic NH(2) terminus of γ-ENaC to the nucleus has functional consequences for coexpression of eGFP-fusion proteins containing this segment of the channel, but not the COOH terminus, decrease ENaC activity in a dose-dependent manner. The mechanism of this negative regulation is associated with a decrease in the functional half-life of ENaC at the plasma membrane. Inspection of the primary amino acid sequence of γ-ENaC reveals possible nuclear localization signals (NLS) conserved at the extreme NH(2) terminus and just preceding the first transmembrane domain. Disruption of the putative NLS preceding the first transmembrane domain in γ-ENaC but not that at the extreme NH(2) terminus abolishes both targeting to the nucleus and negative regulation of ENaC activity. These findings are consistent with the release of the NH(2) terminus of γ-ENaC following cleavage being functionally important for signaling to the nucleus in a manner similar to Notch signaling and release of the cytosolic COOH-terminal tail of polycystin-1.
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Affiliation(s)
- Elena Mironova
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA
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Pochynyuk O, Kucher V, Boiko N, Mironova E, Staruschenko A, Karpushev AV, Tong Q, Hendron E, Stockand J. Intrinsic voltage dependence of the epithelial Na+ channel is masked by a conserved transmembrane domain tryptophan. J Biol Chem 2009; 284:25512-21. [PMID: 19620245 DOI: 10.1074/jbc.m109.015917] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Tryptophan residues critical to function are frequently located at the lipid-water interface of transmembrane domains. All members of the epithelial Na+ channel (ENaC)/Degenerin (Deg) channel superfamily contain an absolutely conserved Trp at the base of their first transmembrane domain. Here, we test the importance of this conserved Trp to ENaC/Deg function. Targeted substitution of this Trp in mouse ENaC and rat ASIC subunits decrease channel activity. Differential substitution with distinct amino acids in alpha-mENaC shows that it is loss of this critical Trp rather than introduction of residues having novel properties that changes channel activity. Surprisingly, Trp substitution unmasks voltage sensitivity. Mutant ENaC has increased steady-state activity at hyperpolarizing compared with depolarizing potentials associated with transient activation and deactivation times, respectively. The times of activation and deactivation change 1 ms/mV in a linear manner with rising and decreasing slopes, respectively. Increases in macroscopic currents at hyperpolarizing potentials results from a voltage-dependent increase in open probability. Voltage sensitivity is not influenced by divalent cations; however, it is Na+-dependent with a 63-mV decrease in voltage required to reach half-maximal activity per log increase in [Na+]. Mutant channels are particularly sensitive to intracellular [Na+] for removing this sodium abolishes voltage dependence. We conclude that the conserved Trp at the base of TM1 in ENaC/Deg channels protects against voltage by masking an inhibitory allosteric or pore block mechanism, which decreases activity in response to intracellular Na+.
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Affiliation(s)
- Oleh Pochynyuk
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA
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Epithelial sodium channel regulated by differential composition of a signaling complex. Proc Natl Acad Sci U S A 2009; 106:7804-9. [PMID: 19380724 DOI: 10.1073/pnas.0809892106] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Hormonal control of transepithelial sodium (Na(+)) transport utilizes phosphatidylinositide 3'-kinase (PI3K) and Raf-MAPK/ERK kinase (MEK)-ERK-dependent signaling pathways, which impact numerous cell functions. How signals transmitted by these pathways are sorted and appropriately transmitted to alter Na(+) transport without altering other physiologic processes is not well understood. Here, we report the identification of a signaling complex that selectively modulates the cell surface expression of the epithelial sodium channel (ENaC), an ion channel that is essential for fluid and electrolyte balance in mammals. Raf-1 and the ubiquitin ligase, Nedd4-2, are constitutively-expressed inhibitory components of this ENaC regulatory complex, which interact with, and decrease the expression of, cell surface ENaC. The activities of Nedd4-2 and Raf-1 are inhibited cooperatively by the PI3K-dependent kinase serum- and glucocorticoid-induced kinase 1 (SGK1), and the Raf-1-interacting protein glucocorticoid-induced leucine zipper (GILZ1), which are aldosterone-stimulated components of the complex. Together, SGK1 and GILZ1 synergistically stimulate ENaC cell surface expression. Interestingly, GILZ1 and SGK1 do not have synergistic, and in fact have opposite, effects on an unrelated activity, FKHRL1-driven gene transcription. Together, these data suggest that GILZ1 and SGK1 provide a physical and functional link between the PI3K- and Raf-1-dependent signaling modules and represent a unique mechanism for specifically controlling Na(+) transport without inappropriately activating other cell functions.
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Edinger RS, Lebowitz J, Li H, Alzamora R, Wang H, Johnson JP, Hallows KR. Functional regulation of the epithelial Na+ channel by IkappaB kinase-beta occurs via phosphorylation of the ubiquitin ligase Nedd4-2. J Biol Chem 2009; 284:150-157. [PMID: 18981174 PMCID: PMC2610498 DOI: 10.1074/jbc.m807358200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Revised: 10/28/2008] [Indexed: 12/31/2022] Open
Abstract
We have previously shown that IkappaB kinase-beta (IKKbeta) interacts with the epithelial Na+ channel (ENaC) beta-subunit and enhances ENaC activity by increasing its surface expression in Xenopus oocytes. Here, we show that the IKKbeta-ENaC interaction is physiologically relevant in mouse polarized kidney cortical collecting duct (mpkCCDc14) cells, as RNA interference-mediated knockdown of endogenous IKKbeta in these cells by approximately 50% resulted in a similar reduction in transepithelial ENaC-dependent equivalent short circuit current. Although IKKbeta binds to ENaC, there was no detectable phosphorylation of ENaC subunits by IKKbeta in vitro. Because IKKbeta stimulation of ENaC activity occurs through enhanced channel surface expression and the ubiquitin-protein ligase Nedd4-2 has emerged as a central locus for ENaC regulation at the plasma membrane, we tested the role of Nedd4-2 in this regulation. IKKbeta-dependent phosphorylation of Xenopus Nedd4-2 expressed in HEK-293 cells occurred both in vitro and in vivo, suggesting a potential mechanism for regulation of Nedd4-2 and thus ENaC activity. 32P labeling studies utilizing wild-type or mutant forms of Xenopus Nedd4-2 demonstrated that Ser-444, a key SGK1 and protein kinase A-phosphorylated residue, is also an important IKKbeta phosphorylation target. ENaC stimulation by IKKbeta was preserved in oocytes expressing wild-type Nedd4-2 but blocked in oocytes expressing either a dominant-negative (C938S) or phospho-deficient (S444A) Nedd4-2 mutant, suggesting that Nedd4-2 function and phosphorylation by IKKbeta are required for IKKbeta regulation of ENaC. In summary, these results suggest a novel mode of ENaC regulation that occurs through IKKbeta-dependent Nedd4-2 phosphorylation at a recognized SGK1 and protein kinase A target site.
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Affiliation(s)
- Robert S Edinger
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Jonathan Lebowitz
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Hui Li
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Rodrigo Alzamora
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Huamin Wang
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - John P Johnson
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261; Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Kenneth R Hallows
- Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261; Renal-Electrolyte Division, Departments of Medicine and Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
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SGK1 activity in Na+ absorbing airway epithelial cells monitored by assaying NDRG1-Thr346/356/366 phosphorylation. Pflugers Arch 2008; 457:1287-301. [PMID: 18787837 DOI: 10.1007/s00424-008-0587-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Accepted: 08/29/2008] [Indexed: 01/02/2023]
Abstract
Studies of HeLa cells and serum- and glucocorticoid-regulated kinase 1 (SGK1) knockout mice identified threonine residues in the n-myc downstream-regulated gene 1 protein (NDRG1-Thr(346/356/366)) that are phosphorylated by SGK1 but not by related kinases (Murray et al., Biochem J 385:1-12, 2005). We have, therefore, monitored the phosphorylation of NDRG1-Thr(346/356/366) in order to explore the changes in SGK1 activity associated with the induction and regulation of the glucocorticoid-dependent Na(+) conductance (G (Na)) in human airway epithelial cells. Transient expression of active (SGK1-S422D) and inactive (SGK1-K127A) SGK1 mutants confirmed that activating SGK1 stimulates NDRG1-Thr(346/356/366) phosphorylation. Although G (Na) is negligible in hormone-deprived cells, these cells displayed basal SGK1 activity that was sensitive to LY294002, an inhibitor of 3-phosphatidylinositol phosphate kinase (PI3K). Dexamethasone (0.2 muM) acutely activated SGK1 and the peak of this response (2-3 h) coincided with the induction of G (Na), and both responses were PI3K-dependent. While these data suggest that SGK1 might mediate the rise in G (Na), transient expression of the inactive SGK1-K127A mutant did not affect the hormonal induction of G (Na) but did suppress the activation of SGK1. Dexamethasone-treated cells grown on permeable supports formed confluent epithelial sheets that generated short circuit current due to electrogenic Na(+) absorption. Forskolin and insulin both stimulated this current and the response to insulin, but not forskolin, was LY294002-sensitive and associated with the activation of SGK1. While these data suggest that SGK1 is involved in the control of G (Na), its role may be minor, which could explain why sgk1 knockout has different effects upon different tissues.
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Bhalla V, Hallows KR. Mechanisms of ENaC regulation and clinical implications. J Am Soc Nephrol 2008; 19:1845-54. [PMID: 18753254 DOI: 10.1681/asn.2008020225] [Citation(s) in RCA: 180] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The epithelial Na+ channel (ENaC) transports Na+ across tight epithelia, including the distal nephron. Different paradigms of ENaC regulation include extrinsic and intrinsic factors that affect the expression, single-channel properties, and intracellular trafficking of the channel. In particular, recent discoveries highlight new findings regarding proteolytic processing, ubiquitination, and recycling of the channel. Understanding the regulation of this channel is critical to the understanding of various clinical phenomena, including normal physiology and several diseases of kidney and lung epithelia, such as blood pressure (BP) control, edema, and airway fluid clearance. Significant progress has been achieved in this active field of research. Although ENaC is classically thought to be a mediator of BP and volume status through Na+ reabsorption in the distal nephron, several studies in animal models highlight important roles for ENaC in lung pathophysiology, including in cystic fibrosis. The purpose of this review is to highlight the various modes and mechanisms of ENaC regulation, with a focus on more recent studies and their clinical implications.
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Affiliation(s)
- Vivek Bhalla
- Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, California, USA
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Bugaj V, Pochynyuk O, Mironova E, Vandewalle A, Medina JL, Stockand JD. Regulation of the epithelial Na+ channel by endothelin-1 in rat collecting duct. Am J Physiol Renal Physiol 2008; 295:F1063-70. [PMID: 18667482 DOI: 10.1152/ajprenal.90321.2008] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
We used patch-clamp electrophysiology to investigate regulation of the epithelial Na+ channel (ENaC) by endothelin-1 (ET-1) in isolated, split-open rat collecting ducts. ET-1 significantly decreases ENaC open probability by about threefold within 5 min. ET-1 decreases ENaC activity through basolateral membrane ETB but not ETA receptors. In rat collecting duct, we find no role for phospholipase C or protein kinase C in the rapid response of ENaC to ET-1. ET-1, although, does activate src family tyrosine kinases and their downstream MAPK1/2 effector cascade in renal principal cells. Both src kinases and MAPK1/2 signaling are necessary for ET-1-dependent decreases in ENaC open probability in the split-open collecting duct. We conclude that ET-1 in a physiologically relevant manner rapidly suppresses ENaC activity in native, mammalian principal cells. These findings may provide a potential mechanism for the natriuresis observed in vivo in response to ET-1, as well as a potential cause for the salt-sensitive hypertension found in animals with impaired endothelin signaling.
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Affiliation(s)
- Vladislav Bugaj
- Department of Physiology 7756, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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40
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Hoffmann HH, Palese P, Shaw ML. Modulation of influenza virus replication by alteration of sodium ion transport and protein kinase C activity. Antiviral Res 2008; 80:124-34. [PMID: 18585796 PMCID: PMC2614658 DOI: 10.1016/j.antiviral.2008.05.008] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 05/15/2008] [Accepted: 05/15/2008] [Indexed: 11/10/2022]
Abstract
In recent years, increasing levels of resistance to the four FDA-approved anti-influenza virus drugs have been described and vaccine manufacturers have experienced demands that exceed their capacity. This situation underlines the urgent need for novel antivirals as well as innovations in vaccine production in preparation for the next influenza epidemic. Here we report the development of a cell-based high-throughput screen which we have used for the identification of compounds that modulate influenza virus growth either negatively or positively. We screened a library of compounds with known biological activity and identified distinct groups of inhibitors and enhancers that target sodium channels or protein kinase C (PKC). We confirmed these results in viral growth assays and find that treatment with a sodium channel opener or PKC inhibitor significantly reduces viral replication. In contrast, inhibition of sodium channels or activation of PKC leads to enhanced virus production in tissue culture. These diametrically opposing effects strongly support a role for PKC activity and the regulation of Na+ currents in influenza virus replication and both may serve as targets for antiviral drugs. Furthermore, we raise the possibility that compounds that result in increased viral titers may be beneficial for boosting the production of tissue culture-grown influenza vaccines.
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Affiliation(s)
- H-Heinrich Hoffmann
- Department of Microbiology, Mount Sinai School of Medicine, New York, NY 10029, USA
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Harvey BJ, Alzamora R, Stubbs AK, Irnaten M, McEneaney V, Thomas W. Rapid responses to aldosterone in the kidney and colon. J Steroid Biochem Mol Biol 2008; 108:310-7. [PMID: 17951051 DOI: 10.1016/j.jsbmb.2007.09.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Aldosterone is a crucial modulator of ion transport across high resistance epithelia and regulates whole body electrolyte balance through its effects on the kidney and colon. The net consequence of aldosterone release is to promote salt conservation. The genomic mechanism of aldosterone action is relatively well characterized and the role of the classical mineralocorticoid receptor as a ligand-dependent transcription factor is well established. The rapid effects of aldosterone on target tissues are less well understood and there is still controversy over the identity of the aldosterone non-genomic receptor. Greater understanding of the physiological consequences of aldosterone's rapid responses in the kidney and colon has been achieved through the identification of definite and putative membrane targets and their signaling regulators.
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Affiliation(s)
- Brian J Harvey
- Department of Molecular Medicine, Royal College of Surgeons in Ireland, Beaumont Hospital, Dublin 9, Ireland.
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Falin RA, Cotton CU. Acute downregulation of ENaC by EGF involves the PY motif and putative ERK phosphorylation site. ACTA ACUST UNITED AC 2007; 130:313-28. [PMID: 17724164 PMCID: PMC2151644 DOI: 10.1085/jgp.200709775] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The epithelial sodium channel (ENaC) is expressed in a variety of tissues, including the renal collecting duct, where it constitutes the rate-limiting step for sodium reabsorption. Liddle's syndrome is caused by gain-of-function mutations in the β and γ subunits of ENaC, resulting in enhanced Na reabsorption and hypertension. Epidermal growth factor (EGF) causes acute inhibition of Na absorption in collecting duct principal cells via an extracellular signal–regulated kinase (ERK)–dependent mechanism. In experiments with primary cultures of collecting duct cells derived from a mouse model of Liddle's disease (β-ENaC truncation), it was found that EGF inhibited short-circuit current (Isc) by 24 ± 5% in wild-type cells but only by 6 ± 3% in homozygous mutant cells. In order to elucidate the role of specific regions of the β-ENaC C terminus, Madin-Darby canine kidney (MDCK) cell lines that express β-ENaC with mutation of the PY motif (P616L), the ERK phosphorylation site (T613A), and C terminus truncation (R564stop) were created using the Phoenix retroviral system. All three mutants exhibited significant attenuation of the EGF-induced inhibition of sodium current. In MDCK cells with wild-type β-ENaC, EGF-induced inhibition of Isc (<30 min) was fully reversed by exposure to an ERK kinase inhibitor and occurred with no change in ENaC surface expression, indicative of an effect on channel open probability (Po). At later times (>30 min), EGF-induced inhibition of Isc was not reversed by an ERK kinase inhibitor and was accompanied by a decrease in ENaC surface expression. Our results are consistent with an ERK-mediated decrease in ENaC open probability and enhanced retrieval of sodium channels from the apical membrane.
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Affiliation(s)
- Rebecca A Falin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
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Pochynyuk O, Tong Q, Medina J, Vandewalle A, Staruschenko A, Bugaj V, Stockand JD. Molecular determinants of PI(4,5)P2 and PI(3,4,5)P3 regulation of the epithelial Na+ channel. ACTA ACUST UNITED AC 2007; 130:399-413. [PMID: 17893193 PMCID: PMC2151653 DOI: 10.1085/jgp.200709800] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) are physiologically important second messengers. These molecules bind effector proteins to modulate activity. Several types of ion channels, including the epithelial Na+ channel (ENaC), are phosphoinositide effectors capable of directly interacting with these signaling molecules. Little, however, is known of the regions within ENaC and other ion channels important to phosphoinositide binding and modulation. Moreover, the molecular mechanism of this regulation, in many instances, remains obscure. Here, we investigate modulation of ENaC by PI(3,4,5)P3 and PI(4,5)P2 to begin identifying the molecular determinants of this regulation. We identify intracellular regions near the inner membrane interface just following the second transmembrane domains in β- and γ- but not α-ENaC as necessary for PI(3,4,5)P2 but not PI(4,5)P2 modulation. Charge neutralization of conserved basic amino acids within these regions demonstrated that these polar residues are critical to phosphoinositide regulation. Single channel analysis, moreover, reveals that the regions just following the second transmembrane domains in β- and γ-ENaC are critical to PI(3,4,5)P3 augmentation of ENaC open probability, thus, defining mechanism. Unexpectedly, intracellular domains within the extreme N terminus of β- and γ-ENaC were identified as being critical to down-regulation of ENaC activity and Po in response to depletion of membrane PI(4,5)P2. These regions of the channel played no identifiable role in a PI(3,4,5)P3 response. Again, conserved positive-charged residues within these domains were particularly important, being necessary for exogenous PI(4,5)P2 to increase open probability. We conclude that β and γ subunits bestow phosphoinositide sensitivity to ENaC with distinct regions of the channel being critical to regulation by PI(3,4,5)P3 and PI(4,5)P2. This argues that these phosphoinositides occupy distinct ligand-binding sites within ENaC to modulate open probability.
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Affiliation(s)
- Oleh Pochynyuk
- University of Texas Health Science Center, Department of Physiology, San Antonio, TX 78229, USA
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Pochynyuk O, Bugaj V, Vandewalle A, Stockand JD. Purinergic control of apical plasma membrane PI(4,5)P2 levels sets ENaC activity in principal cells. Am J Physiol Renal Physiol 2007; 294:F38-46. [PMID: 17913833 DOI: 10.1152/ajprenal.00403.2007] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Activity of the epithelial sodium channel (ENaC) is limiting for Na(+) reabsorption at the distal nephron. Phosphoinositides, such as phosphatidylinositol 4,5-biphosphate [PI(4,5)P(2)] modulate the activity of this channel. Activation of purinergic receptors triggers multiple events, including activation of PKC and PLC, with the latter depleting plasma membrane PI(4,5)P(2). Here, we investigate regulation of ENaC in renal principal cells by purinergic receptors via PLC and PI(4,5)P(2). Purinergic signaling rapidly decreases ENaC open probability and apical membrane PI(4,5)P(2) levels with similar time courses. Moreover, inhibiting purinergic signaling with suramin rescues ENaC activity. The PLC inhibitor U73122, but not U73343, its inactive analog, recapitulates the action of suramin. In contrast, modulating PKC signaling failed to affect purinergic regulation of ENaC. Unexpectedly, inhibiting either purinergic receptors or PLC in resting cells dramatically increased ENaC activity above basal levels, indicating tonic activation of purinergic signaling in these polarized renal epithelial cells. Increased ENaC activity was associated with elevation of apical membrane PI(4,5)P(2) levels. Subsequent treatment with ATP in the presence of inhibited purinergic signaling failed to decrease ENaC activity and apical membrane PI(4,5)P(2) levels. Dwell-time analysis reveals that depletion of PI(4,5)P(2) forces ENaC toward a closed state. In contrast, increasing PI(4,5)P(2) levels above basal values locks the channel in an open state interrupted by brief closings. Thus our results suggest that purinergic control of apical membrane PI(4,5)P(2) levels is a major regulator of ENaC activity in renal epithelial cells.
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Affiliation(s)
- Oleh Pochynyuk
- Department of Physiology, University of Texas Health Science Center, 7703 Floyd Curl Dr., San Antonio TX 78229-3900, USA.
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Choi JY, Choi YS, Kim SJ, Son EJ, Choi HS, Yoon JH. Interleukin-1β suppresses epithelial sodium channel β-subunit expression and ENaC-dependent fluid absorption in human middle ear epithelial cells. Eur J Pharmacol 2007; 567:19-25. [PMID: 17499239 DOI: 10.1016/j.ejphar.2007.04.026] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 04/02/2007] [Accepted: 04/04/2007] [Indexed: 10/23/2022]
Abstract
Recent reports have shown that cytokines inhibit fluid absorption by suppressing Na(+) channel activity in various epithelia. In this study, we investigated the role of epithelial sodium channel (ENaC) in fluid absorption in normal human middle ear epithelial (NHMEE) cells, as well as the effects of Interleukin (IL)-1beta on ENaC expression and fluid absorption in NHMEE cells. We confirmed that ENaC alpha, beta and gamma were predominantly expressed on the apical surface of the NHMEE cells by immunocytochemistry. Addition of amiloride, a potent ENaC blocker, to apical membranes of NHMEE cells decreased the fluid absorption rate in a dose-dependent manner. Treatment with 10 ng/ml IL-1beta for 24 h suppressed ENaC beta expression, the ENaC-dependent short-circuit current (Isc), and ENaC-dependent fluid absorption. When the NHMEE cells were pretreated with a phospholipase C (PLC)inhibitor (U73122, 10 microM), a protein kinase C (PKC) inhibitor (Calphostin C, 0.1 microM), or extracellular signal regulated kinase (ERK) 1/2 inhibitor (PD98059, 10 microM), the amiloride-sensitive currents in IL-1beta-treated cells were reversed to control levels; an effect not seen with SB202190 (an inhibitor of p38 mitogen-activated protein (MAP) kinase) or SP600125 (a reversible inhibitor of c-Jun N-terminal kinase). In this study we showed that ENaC is essential for fluid absorption in NHMEE cells and that IL-1beta suppresses the ENaC-dependent current via the PLC-PKC-ERK1/2 pathway. These results suggest that IL-1beta may contribute to fluid retention in otitis media with effusion by changing electrolyte transport and reducing middle ear epithelial fluid absorption.
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Affiliation(s)
- Jae Young Choi
- Department of Otorhinolaryngology, Yonsei University College of Medicine, Seoul, Republic of Korea
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46
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Affiliation(s)
- David W Good
- Department of Medicine, University of Texas Medical Branch, Galveston 77555-0562, USA.
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Bhalla V, Oyster NM, Fitch AC, Wijngaarden MA, Neumann D, Schlattner U, Pearce D, Hallows KR. AMP-activated Kinase Inhibits the Epithelial Na+ Channel through Functional Regulation of the Ubiquitin Ligase Nedd4-2. J Biol Chem 2006; 281:26159-69. [PMID: 16844684 DOI: 10.1074/jbc.m606045200] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
We recently found that the metabolic sensor AMP-activated kinase (AMPK) inhibits the epithelial Na+ channel (ENaC) through decreased plasma membrane ENaC expression, an effect requiring the presence of a binding motif in the cytoplasmic tail of the beta-ENaC subunit for the ubiquitin ligase Nedd4-2. To further examine the role of Nedd4-2 in the regulation of ENaC by AMPK, we studied the effects of AMPK activation on ENaC currents in Xenopus oocytes co-expressing ENaC and wild-type (WT) or mutant forms of Nedd4-2. ENaC inhibition by AMPK was preserved in oocytes expressing WT Nedd4-2 but blocked in oocytes expressing either a dominant-negative (DN) or constitutively active (CA) Nedd4-2 mutant, suggesting that AMPK-dependent modulation of Nedd4-2 function is involved. Similar experiments utilizing WT or mutant forms of the serum- and glucocorticoid-regulated kinase (SGK1), modulators of protein kinase A (PKA), or extracellular-regulated kinase (ERK) did not affect ENaC inhibition by AMPK, suggesting that these pathways known to modulate the Nedd4-2-ENaC interaction are not responsible. AMPK-dependent phosphorylation of Nedd4-2 expressed in HEK-293 cells occurred both in vitro and in vivo, suggesting a potential mechanism for modulation of Nedd4-2 and thus cellular ENaC activity. Moreover, cellular AMPK activation significantly enhanced the interaction of the beta-ENaC subunit with Nedd4-2, as measured by co-immunoprecipitation assays in HEK-293 cells. In summary, these results suggest a novel mechanism for ENaC regulation in which AMPK promotes ENaC-Nedd4-2 interaction, thereby inhibiting ENaC by increasing Nedd4-2-dependent ENaC retrieval from the plasma membrane. AMPK-dependent ENaC inhibition may limit cellular Na+ loading under conditions of metabolic stress when AMPK becomes activated.
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Affiliation(s)
- Vivek Bhalla
- Division of Nephrology, Department of Medicine, University of California at San Francisco, San Francisco, California 94107, USA
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48
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Yamagata T, Yamagata Y, Massé C, Tessier MC, Brochiero E, Dagenais A, Berthiaume Y. Modulation of Na+ transport and epithelial sodium channel expression by protein kinase C in rat alveolar epithelial cells. Can J Physiol Pharmacol 2006; 83:977-87. [PMID: 16391706 DOI: 10.1139/y05-071] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Although the amiloride-sensitive epithelial sodium channel (ENaC) plays an important role in the modulation of alveolar liquid clearance, the precise mechanism of its regulation in alveolar epithelial cells is still under investigation. Protein kinase C (PKC) has been shown to alter ENaC expression and activity in renal epithelial cells, but much less is known about its role in alveolar epithelial cells. The objective of this study was to determine whether PKC activation modulates ENaC expression and transepithelial Na+ transport in cultured rat alveolar epithelial cells. Alveolar type II cells were isolated and cultured for 3 to 4 d before they were stimulated with phorbol 12-myristate 13-acetate (PMA 100 nmol/L) for 4 to 24 h. PMA treatment significantly decreased alpha, beta, and gammaENaC expression in a time-dependent manner, whereas an inactive form of phorbol ester had no apparent effect. This inhibitory action was seen with only 5-min exposure to PMA, which suggested that PKC activation was very important for the reduction of alphaENaC expression. The PKC inhibitors bisindolylmaleimide at 2 micromol/L and Gö6976 at 2 micromol/L diminished the PMA-induced suppression of alphaENaC expression, while rottlerin at 1 micromol/L had no effect. PMA elicited a decrease in total and amiloride-sensitive current across alveolar epithelial cell monolayers. This decline in amiloride-sensitive current was not blocked by PKC inhibitors except for a partial inhibition with bisindolylmaleimide. PMA induced a decrease in rubidium uptake, indicating potential Na+-K+-ATPase inhibition. However, since ouabain-sensitive current in apically permeabilized epithelial cells was similar in PMA-treated and control cells, the inhibition was most probably related to reduced Na+ entry at the apical surface of the cells. We conclude that PKC activation modulates ENaC expression and probably ENaC activity in alveolar epithelial cells. Ca2+-dependent PKC is potentially involved in this response.
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Affiliation(s)
- Toshiyuki Yamagata
- Département de médecine, Centre de recherche, Centre hospitalier de l'Université de Montréal Hôtel-Dieu, Montreal, QC, Canada
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Yan W, Suaud L, Kleyman TR, Rubenstein RC. Differential modulation of a polymorphism in the COOH terminus of the α-subunit of the human epithelial sodium channel by protein kinase Cδ. Am J Physiol Renal Physiol 2006; 290:F279-88. [PMID: 16174865 DOI: 10.1152/ajprenal.00277.2005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The A663T polymorphism of the α-subunit of the human epithelial sodium channel (hENaC) increases the functional and surface expression of αβγ-hENaC in Xenopus laevis oocytes. The context of this residue in the COOH terminus of α-hENaC is important for this effect, as a homologous change in murine ENaC (mENaC), A692T, does not alter functional and surface expression of mENaC. Query of a phosphoprotein database suggested that the α-T663 residue might be phosphorylated by PKCδ. General inhibition of PKC with calphostin C decreased the functional and surface expression of αT663-hENaC and not αA663-hENaC, and was without effect on αA692-mENaC, αT692-mENaC, and a chimeric m(1–678)/h(650–669)αT663, mβγ-ENaC. These data suggest that residues outside of the α-hENaC COOH terminus are important for modulation of αT663-hENaC trafficking by PKC. In contrast, expression of PKCδ decreased the functional and surface expression of αT663-hENaC and the functional expression of m(1–678)/h(650–669)αT663, mβγ-ENaC, and was without effect on αA663-hENaC, αA692-mENaC, or αT692-mENaC. PKCδ did not phosphorylate the COOH terminus of either αT663-hENaC or αA663-hENaC in vitro, suggesting that it acts indirectly to regulate hENaC trafficking. αT663-hENaC was retrieved from the oocyte membrane more slowly than αA663-hENaC, and calphostin C increased the rate of αT663-hENaC removal from the oocyte membrane to a rate similar to that of αA663-hENaC. In contrast, PKCδ did not alter the rate of removal of αT663-hENaC from the oocyte membrane, suggesting that PKCδ altered rates of αT663-hENaC biosynthesis and/or delivery to the plasma membrane. These data are consistent with PKC isoform-specific effects on the intracellular trafficking of αT663- vs. αA663-hENaC.
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Affiliation(s)
- Wusheng Yan
- Renal-Electrolyte Division, Department of Medicine, A919 Scaife Hall, 3550 Terrace St., Pittsburgh, PA 15261, USA
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Abstract
The epithelial Na(+) channel (ENaC) is a pathway for Na(+) transport across epithelia, including the kidney collecting duct, lung, and distal colon. ENaC is critical for Na(+) homeostasis and blood pressure control; defects in ENaC function and regulation are responsible for inherited forms of hypertension and hypotension and may contribute to the pathogenesis of cystic fibrosis and other lung diseases. An emerging theme is that epithelial Na(+) transport is regulated in large part through trafficking mechanisms that control ENaC expression at the cell surface. ENaC trafficking is regulated at multiple steps. Delivery of channels to the cell surface is regulated by aldosterone (and corticosteroids) and vasopressin, which increase ENaC synthesis and exocytosis, respectively. Conversely, endocytosis and degradation is controlled by a sequence located in the C terminus of alpha, beta, and gammaENaC (PPPXYXXL). This sequence functions as an endocytosis motif and as a binding site for Nedd4-2, an E3 ubiquitin protein ligase that targets ENaC for degradation. Mutations that delete or disrupt this motif cause accumulation of channels at the cell surface, resulting in Liddle's syndrome, an inherited form of hypertension. Nedd4-2 is a central convergence point for ENaC regulation by aldosterone and vasopressin; both induce phosphorylation of a common set of three Nedd4-2 residues, which blocks Nedd4-2 binding to ENaC. Thus, aldosterone and vasopressin regulate epithelial Na(+) transport in part by altering ENaC trafficking to and from the cell surface.
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Affiliation(s)
- Peter M Snyder
- Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, 52242, USA.
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