1
|
Yang G, Pillich H, White R, Czikora I, Pochic I, Yue Q, Hudel M, Gorshkov B, Verin A, Sridhar S, Isales CM, Eaton DC, Hamacher J, Chakraborty T, Lucas R. Listeriolysin O Causes ENaC Dysfunction in Human Airway Epithelial Cells. Toxins (Basel) 2018; 10:toxins10020079. [PMID: 29439494 PMCID: PMC5848180 DOI: 10.3390/toxins10020079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Revised: 02/01/2018] [Accepted: 02/07/2018] [Indexed: 01/22/2023] Open
Abstract
Pulmonary permeability edema is characterized by reduced alveolar Na⁺ uptake capacity and capillary barrier dysfunction and is a potentially lethal complication of listeriosis. Apical Na⁺ uptake is mainly mediated by the epithelial sodium channel (ENaC) and initiates alveolar liquid clearance. Here we examine how listeriolysin O (LLO), the pore-forming toxin of Listeria monocytogenes, impairs the expression and activity of ENaC. To that purpose, we studied how sub-lytic concentrations of LLO affect negative and positive regulators of ENaC expression in the H441 airway epithelial cell line. LLO reduced expression of the crucial ENaC-α subunit in H441 cells within 2 h and this was preceded by activation of PKC-α, a negative regulator of the channel's expression. At later time points, LLO caused a significant reduction in the phosphorylation of Sgk-1 at residue T256 and of Akt-1 at residue S473, both of which are required for full activation of ENaC. The TNF-derived TIP peptide prevented LLO-mediated PKC-α activation and restored phospho-Sgk-1-T256. The TIP peptide also counteracted the observed LLO-induced decrease in amiloride-sensitive Na⁺ current and ENaC-α expression in H441 cells. Intratracheally instilled LLO caused profound pulmonary edema formation in mice, an effect that was prevented by the TIP peptide; thus indicating the therapeutic potential of the peptide for the treatment of pore-forming toxin-associated permeability edema.
Collapse
Affiliation(s)
- Guang Yang
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
| | - Helena Pillich
- Institute of Medical Microbiology, Justus-Liebig University Giessen, 35392 Gießen, Germany.
| | - Richard White
- Department of Pharmacology and Toxicology, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
- Department of Biomedical Sciences, Georgia Campus-Philadelphia College of Osteopathic Medicine, Atlanta, GA 30224, USA.
| | - Istvan Czikora
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
| | - Isabelle Pochic
- Biochemical Pharmacology, University of Konstanz, 78464 Konstanz, Germany.
- Sandoz Inc., 83607 Holzkirchen, Germany.
| | - Qiang Yue
- Department of Physiology, Emory School of Medicine, Atlanta, GA 30307, USA.
| | - Martina Hudel
- Institute of Medical Microbiology, Justus-Liebig University Giessen, 35392 Gießen, Germany.
| | - Boris Gorshkov
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
| | - Alexander Verin
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
| | - Supriya Sridhar
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
| | - Carlos M Isales
- Department of Medicine, Medical College of Georgia, Augusta, GA 30901, USA.
| | - Douglas C Eaton
- Department of Physiology, Emory School of Medicine, Atlanta, GA 30307, USA.
| | - Jürg Hamacher
- Biochemical Pharmacology, University of Konstanz, 78464 Konstanz, Germany.
- Department of Pneumology, Lindenhofspital, 3001 Bern, Switzerland.
- Internal, Pulmonary and Critical Care Medicine, Saarland University, 66424 Homburg/Saar, Germany.
- Lungen-und Atmungsstifung, 3001 Bern, Switzerland.
| | - Trinad Chakraborty
- Institute of Medical Microbiology, Justus-Liebig University Giessen, 35392 Gießen, Germany.
| | - Rudolf Lucas
- Vascular Biology Center, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
- Department of Pharmacology and Toxicology, Medical College of Georgia at Augusta University, Room CB-3213B, Augusta, GA 30912-2500, USA.
- Department of Medicine, Medical College of Georgia, Augusta, GA 30901, USA.
| |
Collapse
|
2
|
He J, Qi D, Wang DX, Deng W, Ye Y, Feng LH, Zhu T, Zhao Y, Zhang CR. Insulin upregulates the expression of epithelial sodium channel in vitro and in a mouse model of acute lung injury: Role of mTORC2/SGK1 pathway. Exp Cell Res 2015; 331:164-175. [DOI: 10.1016/j.yexcr.2014.09.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 09/03/2014] [Accepted: 09/18/2014] [Indexed: 01/04/2023]
|
3
|
Althaus M, Urness KD, Clauss WG, Baines DL, Fronius M. The gasotransmitter hydrogen sulphide decreases Na⁺ transport across pulmonary epithelial cells. Br J Pharmacol 2012; 166:1946-63. [PMID: 22352810 DOI: 10.1111/j.1476-5381.2012.01909.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND AND PURPOSE The transepithelial absorption of Na(+) in the lungs is crucial for the maintenance of the volume and composition of epithelial lining fluid. The regulation of Na(+) transport is essential, because hypo- or hyperabsorption of Na(+) is associated with lung diseases such as pulmonary oedema or cystic fibrosis. This study investigated the effects of the gaseous signalling molecule hydrogen sulphide (H(2) S) on Na(+) absorption across pulmonary epithelial cells. EXPERIMENTAL APPROACH Ion transport processes were electrophysiologically assessed in Ussing chambers on H441 cells grown on permeable supports at air/liquid interface and on native tracheal preparations of pigs and mice. The effects of H(2)S were further investigated on Na(+) channels expressed in Xenopus oocytes and Na(+) /K(+)-ATPase activity in vitro. Membrane abundance of Na(+) /K(+)-ATPase was determined by surface biotinylation and Western blot. Cellular ATP concentrations were measured colorimetrically, and cytosolic Ca(2+) concentrations were measured with Fura-2. KEY RESULTS H(2)S rapidly and reversibly inhibited Na(+) transport in all the models employed. H(2)S had no effect on Na(+) channels, whereas it decreased Na(+) /K(+)-ATPase currents. H(2)S did not affect the membrane abundance of Na(+) /K(+)-ATPase, its metabolic or calcium-dependent regulation, or its direct activity. However, H(2)S inhibited basolateral calcium-dependent K(+) channels, which consequently decreased Na(+) absorption by H441 monolayers. CONCLUSIONS AND IMPLICATIONS H(2) S impairs pulmonary transepithelial Na(+) absorption, mainly by inhibiting basolateral Ca(2+)-dependent K(+) channels. These data suggest that the H(2)S signalling system might represent a novel pharmacological target for modifying pulmonary transepithelial Na(+) transport.
Collapse
Affiliation(s)
- M Althaus
- Institute of Animal Physiology, Justus-Liebig University of Giessen, Giessen, Germany.
| | | | | | | | | |
Collapse
|
4
|
Ji HL, Zhao RZ, Chen ZX, Shetty S, Idell S, Matalon S. δ ENaC: a novel divergent amiloride-inhibitable sodium channel. Am J Physiol Lung Cell Mol Physiol 2012; 303:L1013-26. [PMID: 22983350 DOI: 10.1152/ajplung.00206.2012] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The fourth subunit of the epithelial sodium channel, termed delta subunit (δ ENaC), was cloned in human and monkey. Increasing evidence shows that this unique subunit and its splice variants exhibit biophysical and pharmacological properties that are divergent from those of α ENaC channels. The widespread distribution of epithelial sodium channels in both epithelial and nonepithelial tissues implies a range of physiological functions. The altered expression of SCNN1D is associated with numerous pathological conditions. Genetic studies link SCNN1D deficiency with rare genetic diseases with developmental and functional disorders in the brain, heart, and respiratory systems. Here, we review the progress of research on δ ENaC in genomics, biophysics, proteomics, physiology, pharmacology, and clinical medicine.
Collapse
Affiliation(s)
- Hong-Long Ji
- Department of Cellular and Molecular Biology, University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
| | | | | | | | | | | |
Collapse
|
5
|
Watt GB, Ismail NAS, Caballero AG, Land SC, Wilson SM. Epithelial Na⁺ channel activity in human airway epithelial cells: the role of serum and glucocorticoid-inducible kinase 1. Br J Pharmacol 2012; 166:1272-89. [PMID: 22250980 PMCID: PMC3417446 DOI: 10.1111/j.1476-5381.2012.01860.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 11/24/2011] [Accepted: 12/05/2011] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND AND PURPOSE Glucocorticoids appear to control Na⁺ absorption in pulmonary epithelial cells via a mechanism dependent upon serum and glucocorticoid-inducible kinase 1 (SGK1), a kinase that allows control over the surface abundance of epithelial Na⁺ channel subunits (α-, β- and γ-ENaC). However, not all data support this model and the present study re-evaluates this hypothesis in order to clarify the mechanism that allows glucocorticoids to control ENaC activity. EXPERIMENTAL APPROACH Electrophysiological studies explored the effects of agents that suppress SGK1 activity upon glucocorticoid-induced ENaC activity in H441 human airway epithelial cells, whilst analyses of extracted proteins explored the associated changes to the activities of endogenous protein kinase substrates and the overall/surface expression of ENaC subunits. KEY RESULTS Although dexamethasone-induced (24 h) ENaC activity was dependent upon SGK1, prolonged exposure to this glucocorticoid did not cause sustained activation of this kinase and neither did it induce a coordinated increase in the surface abundance of α-, β- and γ-ENaC. Brief (3 h) exposure to dexamethasone, on the other hand, did not evoke Na⁺ current but did activate SGK1 and cause SGK1-dependent increases in the surface abundance of α-, β- and γ-ENaC. CONCLUSIONS AND IMPLICATIONS Although glucocorticoids activated SGK1 and increased the surface abundance of α-, β- and γ-ENaC, these responses were transient and could not account for the sustained activation of ENaC. The maintenance of ENaC activity did, however, depend upon SGK1 and this protein kinase must therefore play an important but permissive role in glucocorticoid-induced ENaC activation.
Collapse
Affiliation(s)
- Gordon B Watt
- Centre for Cardiovascular and Lung Research, Division of Medical Sciences, College of Medicine, Dentistry & Nursing, University of Dundee, Dundee, UK
| | | | | | | | | |
Collapse
|
6
|
Mansley MK, Wilson SM. Effects of nominally selective inhibitors of the kinases PI3K, SGK1 and PKB on the insulin-dependent control of epithelial Na+ absorption. Br J Pharmacol 2011; 161:571-88. [PMID: 20880397 DOI: 10.1111/j.1476-5381.2010.00898.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND AND PURPOSE Insulin-induced Na(+) retention in the distal nephron may contribute to the development of oedema/hypertension in patients with type 2 diabetes. This response to insulin is usually attributed to phosphatidylinositol-3-kinase (PI3K)/serum and glucocorticoid-inducible kinase 1 (SGK1) but a role for protein kinase B (PKB) has been proposed. The present study therefore aimed to clarify the way in which insulin can evoke Na(+) retention. EXPERIMENTAL APPROACH We examined the effects of nominally selective inhibitors of PI3K (wortmannin, PI103, GDC-0941), SGK1 (GSK650394A) and PKB (Akti-1/2) on Na(+) transport in hormone-deprived and insulin-stimulated cortical collecting duct (mpkCCD) cells, while PI3K, SGK1 and PKB activities were assayed by monitoring the phosphorylation of endogenous proteins. KEY RESULTS Wortmannin substantially inhibited basal Na(+) transport whereas PI103 and GDC-0941 had only very small effects. However, these PI3K inhibitors all abolished insulin-induced Na(+) absorption and inactivated PI3K, SGK1 and PKB fully. GSK650394A and Akti-1/2 also inhibited insulin-evoked Na(+) absorption and while GSK650394A inhibited SGK1 without affecting PKB, Akti-1/2 inactivated both kinases. CONCLUSION AND IMPLICATIONS While studies undertaken using PI103 and GDC-0941 show that hormone-deprived cells can absorb Na(+) independently of PI3K, PI3K seems to be essential for insulin induced Na(+) transport. Akti-1/2 does not act as a selective inhibitor of PKB and data obtained using this compound must therefore be treated with caution. GSK650394A, on the other hand, selectively inhibits SGK1 and the finding that GSK650394A suppressed insulin-induced Na(+) absorption suggests that this response is dependent upon signalling via PI3K/SGK1.
Collapse
Affiliation(s)
- Morag K Mansley
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine, Dentistry and Nursing, University of Dundee, Dundee, UK
| | | |
Collapse
|
7
|
Amiloride-sensitive sodium channels and pulmonary edema. Pulm Med 2010; 2011:830320. [PMID: 21637371 PMCID: PMC3100597 DOI: 10.1155/2011/830320] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Accepted: 12/01/2010] [Indexed: 01/11/2023] Open
Abstract
The development of pulmonary edema can be considered as a combination of alveolar flooding via increased fluid filtration, impaired alveolar-capillary barrier integrity, and disturbed resolution due to decreased alveolar fluid clearance. An important mechanism regulating alveolar fluid clearance is sodium transport across the alveolar epithelium. Transepithelial sodium transport is largely dependent on the activity of sodium channels in alveolar epithelial cells. This paper describes how sodium channels contribute to alveolar fluid clearance under physiological conditions and how deregulation of sodium channel activity might contribute to the pathogenesis of lung diseases associated with pulmonary edema. Furthermore, sodium channels as putative molecular targets for the treatment of pulmonary edema are discussed.
Collapse
|
8
|
Rubenstein RC, Lockwood SR, Lide E, Bauer R, Suaud L, Grumbach Y. Regulation of endogenous ENaC functional expression by CFTR and ΔF508-CFTR in airway epithelial cells. Am J Physiol Lung Cell Mol Physiol 2010; 300:L88-L101. [PMID: 20935229 DOI: 10.1152/ajplung.00142.2010] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The functional expression of the epithelial sodium channel (ENaC) appears elevated in cystic fibrosis (CF) airway epithelia, but the mechanism by which this occurs is not clear. We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) alters the trafficking of endogenously expressed human ENaC in the CFBE41o⁻ model of CF bronchial epithelia. Functional expression of ENaC, as defined by amiloride-inhibited short-circuit current (I(sc)) in Ussing chambers, was absent under control conditions but present in CFBE41o⁻ parental and ΔF508-CFTR-overexpressing cells after treatment with 1 μM dexamethasone (Dex) for 24 h. The effect of Dex was mimicked by incubation with the glucocorticoid hydrocortisone but not with the mineralocorticoid aldosterone. Application of trypsin to the apical surface to activate uncleaved, "near-silent" ENaC caused an additional increase in amiloride-sensitive I(sc) in the Dex-treated cells and was without effect in the control cells, suggesting that Dex increased ENaC cell surface expression. In contrast, Dex treatment did not stimulate amiloride-sensitive I(sc) in CFBE41o⁻ cells that stably express wild-type (wt) CFTR. CFBE41o⁻ wt cells also had reduced expression of α- and γ-ENaC compared with parental and ΔF508-CFTR-overexpressing cells. Furthermore, application of trypsin to the apical surface of Dex-treated CFBE41o⁻ wt cells did not stimulate amiloride-sensitive I(sc), suggesting that ENaC remained absent from the surface of these cells even after Dex treatment. We also tested the effect of trafficking-corrected ΔF508-CFTR on ENaC functional expression. Incubation with 1 mM 4-phenylbutyrate synergistically increased Dex-induced ENaC functional expression in ΔF508-CFTR-overexpressing cells. These data support the hypothesis that wt CFTR can regulate the whole cell, functional, and surface expression of endogenous ENaC in airway epithelial cells and that absence of this regulation may foster ENaC hyperactivity in CF airway epithelia.
Collapse
Affiliation(s)
- Ronald C Rubenstein
- The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, USA.
| | | | | | | | | | | |
Collapse
|
9
|
Althaus M, Pichl A, Clauss WG, Seeger W, Fronius M, Morty RE. Nitric oxide inhibits highly selective sodium channels and the Na+/K+-ATPase in H441 cells. Am J Respir Cell Mol Biol 2010; 44:53-65. [PMID: 20139350 DOI: 10.1165/2009-0335oc] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Nitric oxide (NO) is an important regulator of Na(+) reabsorption by pulmonary epithelial cells and therefore of alveolar fluid clearance. The mechanisms by which NO affects epithelial ion transport are poorly understood and vary from model to model. In this study, the effects of NO on sodium reabsorption by H441 cell monolayers were studied in an Ussing chamber. Two NO donors, (Z)-1-[N-(3-aminopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate and diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate, rapidly, reversibly, and dose-dependently reduced amiloride-sensitive, short-circuit currents across H441 cell monolayers. This effect was neutralized by the NO scavenger hemoglobin and was not observed with inactive NO donors. The effects of NO were not blocked by 8-bromoguanosine-3',5'-cyclic monophosphate or by soluble guanylate cyclase inhibitors (methylene blue and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) and were therefore independent of soluble guanylate cyclase signaling. NO targeted apical, highly selective, amiloride-sensitive Na(+) channels in basolaterally permeabilized H441 cell monolayers. NO had no effect on the activity of the human epithelial sodium channel heterologously expressed in Xenopus oocytes. NO decreased Na(+)/K(+)-ATPase activity in apically permeabilized H441 cell monolayers. The inhibition of Na(+)/K(+)-ATPase activity by NO was reversed by mercury and was mimicked by N-ethylmaleimide, which are agents that reverse and mimic, respectively, the reaction of NO with thiol groups. Consistent with these data, S-NO groups were detected on the Na(+)/K(+)-ATPase α subunit in response to NO-donor application, using a biotin-switch approach coupled to a Western blot. These data demonstrate that, in the H441 cell model, NO impairs Na(+) reabsorption by interfering with the activity of highly selective Na(+) channels and the Na(+)/K(+)-ATPase.
Collapse
Affiliation(s)
- Mike Althaus
- Department of Internal Medicine (Pulmonology), University of Giessen Lung Center, Justus Liebig University, Giessen, Germany
| | | | | | | | | | | |
Collapse
|
10
|
Wilson SM, Mansley MK, Getty J, Husband EM, Inglis SK, Hansen MK. Effects of peroxisome proliferator-activated receptor gamma agonists on Na+ transport and activity of the kinase SGK1 in epithelial cells from lung and kidney. Br J Pharmacol 2010; 159:678-88. [PMID: 20105179 DOI: 10.1111/j.1476-5381.2009.00564.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, such as rosiglitazone and pioglitazone, sensitize cells to insulin, and are therefore used to treat type 2 diabetes. However, in some patients, these drugs induce oedema, and the present study tests the hypothesis that this side effect reflects serum and glucocorticoid-inducible kinase 1 (SGK1)-dependent enhancement of epithelia Na(+) absorption. EXPERIMENTAL APPROACH Na(+) absorbing epithelial cells (H441 cells, mpkCCD cells) on permeable membranes were mounted in Ussing chambers, and the effects of rosiglitazone (2 microM) and pioglitazone (10 microM) on transepithelial Na(+) absorption were quantified electrometrically. Changes in SGK1 activity were assessed by monitoring phosphorylation of residues within an endogenous protein. KEY RESULTS Both cell types absorbed Na(+) via an electrogenic process that was enhanced by insulin. In mpkCCD cells, this stimulation of Na(+) transport was associated with increased activity of SGK1, whereas insulin regulated Na(+) transport in H441 cells through a mechanism that did not involve activation of this kinase. Rosiglitazone and pioglitazone had no discernible effect on transepithelial Na(+) absorption in unstimulated or insulin-stimulated cells and failed to alter cellular SGK1 activity. CONCLUSIONS AND IMPLICATIONS Our results do not support the view that PPARgamma agonists stimulate epithelial Na(+) absorption or alter the control of cellular SGK1 activity. It is therefore likely that other mechanisms are involved in PPARgamma-mediated fluid retention, and a better understanding of these mechanisms may help with the identification of patients likely to develop oedema or heart failure when treated with these drugs.
Collapse
Affiliation(s)
- Stuart M Wilson
- Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine, Dentistry and Nursing, University of Dundee, Dundee, UK.
| | | | | | | | | | | |
Collapse
|
11
|
Abstract
Compelling evidence is accumulating indicating a pathophysiological role of the serum-and-glucocorticoid-inducible-kinase-1 (SGK1) in the development and complications of diabetes. SGK1 is ubiquitously expressed with exquisitely high transcriptional volatility. Stimulators of SGK1 expression include hyperglycemia, cell shrinkage, ischemia, glucocorticoids and mineralocorticoids. SGK1 is activated by insulin and growth factors via PI3K, 3-phosphoinositide dependent kinase PDK1 and mTOR. SGK1 activates ion channels (including ENaC, TRPV5, ROMK, KCNE1/KCNQ1 and CLCKa/Barttin), carriers (including NCC, NKCC, NHE3, SGLT1 and EAAT3), and the Na(+)/K(+)-ATPase. It regulates the activity of several enzymes (e.g., glycogen-synthase-kinase-3, ubiquitin-ligase Nedd4-2, phosphomannose-mutase-2), and transcription factors (e.g., forkhead-transcription-factor FOXO3a, beta-catenin and NF-kappaB). A common SGK1 gene variant ( approximately 3 - 5% prevalence in Caucasians, approximately 10% in Africans) is associated with increased blood pressure, obesity and type 2 diabetes. In patients suffering from type 2 diabetes, SGK1 presumably contributes to fluid retention and hypertension, enhanced coagulation and increased deposition of matrix proteins leading to tissue fibrosis such as diabetic nephropathy. Accordingly, targeting SGK1 may favourably influence occurrence and course of type 2 diabetes.
Collapse
Affiliation(s)
- Florian Lang
- Eberhard-Karls-University of Tuebingen, Department of Physiology, Gmelinstrasse 5, Tuebingen 72076, Germany.
| | | | | |
Collapse
|
12
|
The physiological impact of the serum and glucocorticoid-inducible kinase SGK1. Curr Opin Nephrol Hypertens 2009; 18:439-48. [PMID: 19584721 DOI: 10.1097/mnh.0b013e32832f125e] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW The role of serum and glucocorticoid-inducible kinase 1 (SGK1) in renal physiology and pathophysiology is reviewed with particular emphasis on recent advances. RECENT FINDINGS The mammalian target of rapamycin complex 2 has been shown to phosphorylate SGK1 at Ser422 (the so-called hydrophobic motif). Ser397 and Ser401 are two additional SGK1-phosphorylation sites required for maximal SGK1 activity. A 5' variant alternate transcript of human Sgk1 has been identified that is widely expressed and shows improved stability, enhanced membrane association, and greater stimulation of epithelial Na+ transport. SGK1 is essential for optimal processing of the epithelial sodium channel and also regulates the expression of the Na+-Cl- cotransporter. With regard to pathophysiology, SGK1 participates in the stimulation of renal tubular glucose transport in diabetes, the renal profibrotic effect of both angiotensin II and aldosterone, and in fetal programing of arterial hypertension. SUMMARY The outlined recent findings advanced our understanding of the molecular regulation of SGK1 as well as the role of the kinase in renal physiology and the pathophysiology of renal disease and hypertension. Future studies using pharmacological inhibitors of SGK1 will reveal the utility of the kinase as a new therapeutic target.
Collapse
|
13
|
Abstract
The role of SGK1 (serum- and glucocorticoid-induced protein kinase 1) in the glucocorticoid induction of α-ENaC (epithelial Na+ channel α subunit) gene transcription was explored by monitoring the transcriptional activity of a luciferase-linked, α-ENaC reporter gene construct (pGL3-KR1) expressed in H441 airway epithelial cells. Dexamethasone evoked a concentration-dependent (EC50∼4 μM) increase in transcriptional activity dependent upon a glucocorticoid response element in the α-ENaC sequence. Although dexamethasone also activated endogenous SGK1, artificially increasing cellular SGK1 activity by expressing a constitutively active SGK1 mutant (SGK1-S422D) in hormone-deprived cells did not activate pGL3-KR1. Moreover, expression of catalytically inactive SGK1 (SGK1-K127A) suppressed the activation of endogenous SGK1 without affecting the transcriptional response to dexamethasone. Increasing cellular PI3K (phosphoinositide 3-kinase) activity by expressing a membrane-anchored form of the catalytic PI3K-P110α subunit [CD2 (cluster of differentiation 2)-P110α] also activated endogenous SGK1 without affecting pGL3-KR1activity. A catalytically inactive form of CD2-P110α (R1130P), on the other hand, prevented the dexamethasone-induced activation of SGK1, but did not inhibit the activation of pGL3-KR1. However, expression of SGK1-S422D or CD2-P110α enhanced the transcriptional responses to maximally effective concentrations of dexamethasone and this effect occurred with no change in EC50. Dexamethasone-induced (0.3–300 nM) activation of pGL3-KR1 was unaffected by inhibitors of PI3K (PI-103 and wortmanin) and by rapamycin, a selective inhibitor of the TORC1 (target of rapamycin complex 1) signalling complex. Dexamethasone-induced activation of the α-ENaC gene promoter can thus occur independently of SGK1/PI3K, although this pathway does provide a mechanism that allows this transcriptional response to dexamethasone to be enhanced.
Collapse
|
14
|
Gallacher M, Brown SG, Hale BG, Fearns R, Olver RE, Randall RE, Wilson SM. Cation currents in human airway epithelial cells induced by infection with influenza A virus. J Physiol 2009; 587:3159-73. [PMID: 19403603 DOI: 10.1113/jphysiol.2009.171223] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Influenza A viruses cause lung disease via an incompletely understood mechanism that involves the accumulation of liquid within the lungs. The accumulation of lung liquid is normally prevented by epithelial Na(+) absorption, a transport process regulated via several pathways including phosphoinositide-3-kinase (PI3K). Since the influenza A virus encodes a non-structural protein (NS1) that can activate this kinase, we now explore the effects of NS1 upon the biophysical properties of human airway epithelial cells. Transient expression of NS1 depolarized electrically isolated cells maintained in glucocorticoid-free medium by activating a cation conductance identical to the glucocorticoid-induced conductance seen in single cells. This response involved PI3K-independent and PI3K-dependent mechanisms. Infecting glucocorticoid-deprived cells with influenza A virus disrupted the normal electrical coupling between neighbouring cells, but also activated a conductance identical to that induced by NS1. This response to virus infection was only partially dependent upon NS1-mediated activation of PI3K. The presence of NS1 allows influenza A to modify the biophysical properties of infected cells by activating a Na(+)-permeable conductance. Whilst the activation of Na(+)-permeable channels may be expected to increase the rate of Na(+) absorption and thus reduce the volume of liquid in the lung, liquid does normally accumulate in influenza A-infected lungs. The overall effect of influenza A on lung liquid volume may therefore reflect a balance between the activation and inhibition of Na(+)-permeable channels.
Collapse
Affiliation(s)
- M Gallacher
- Centre for Cardiovascular and Lung Research, University of Dundee, UK
| | | | | | | | | | | | | |
Collapse
|
15
|
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.
Collapse
|