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Noor S, Mohammad T, Ashraf GM, Farhat J, Bilgrami AL, Eapen MS, Sohal SS, Yadav DK, Hassan MI. Mechanistic insights into the role of serum-glucocorticoid kinase 1 in diabetic nephropathy: A systematic review. Int J Biol Macromol 2021; 193:562-573. [PMID: 34715204 DOI: 10.1016/j.ijbiomac.2021.10.165] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 10/21/2021] [Accepted: 10/23/2021] [Indexed: 12/13/2022]
Abstract
Aberrant expression of serum-glucocorticoid kinase 1 (SGK1) contributes to the pathogenesis of multiple disorders, including diabetes, hypertension, obesity, fibrosis, and metabolic syndrome. SGK1 variant is expressed in the presence of insulin and several growth factors, eventually modulating various ion channels, carrier proteins, and transcription factors. SGK1 also regulates the enzymatic activity of Na+ K+ ATPase, glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, and phosphomannose mutase impacting cell cycle regulation, neuroexcitation, and apoptosis. Ample evidence supports the crucial role of aberrant SGK1 expression in hyperglycemia-mediated secondary organ damage. Diabetic nephropathy (DN), a dreadful microvascular complication of diabetes, is the leading cause of end-stage renal failures with high morbidity and mortality rate. The complex pathogenesis of DN encompasses several influencing factors, including transcriptional factors, inflammatory markers, cytokines, epigenetic modulators, and abnormal enzymatic activities. SGK1 plays a pivotal role by controlling various physiological functions associated with the occurrence and progression of DN; therefore, targeting SGK1 may favorably influence the clinical outcome in patients with DN. This review aimed to provide mechanistic insights into SGK1 regulated DN pathogenesis and summarize the evidence supporting the therapeutic potential of SGK1 inhibition and its consequences on human health.
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Affiliation(s)
- Saba Noor
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi 110025, India
| | - Taj Mohammad
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi 110025, India
| | - Gulam M Ashraf
- Pre-Clinical Research Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Joviana Farhat
- College of Pharmacy, Al Ain University, Abu Dhabi 112612, United Arab Emirates
| | - Anwar L Bilgrami
- Deanship of Scientific Research, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Entomology, Rutgers University, New Brunswick, NJ 08901, USA
| | - Mathew Suji Eapen
- Respiratory Translational Research Group, Department of Laboratory Medicine, School of Health Sciences, College of Health and Medicine, University of Tasmania, Launceston, TAS, Australia
| | - Sukhwinder Singh Sohal
- Respiratory Translational Research Group, Department of Laboratory Medicine, School of Health Sciences, College of Health and Medicine, University of Tasmania, Launceston, TAS, Australia
| | - Dharmendra Kumar Yadav
- College of Pharmacy, Gachon University of Medicine and Science, Hambakmoeiro, Yeonsu-gu, Incheon City 21924, South Korea.
| | - Md Imtaiyaz Hassan
- Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi 110025, India.
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Lu YT, Fan P, Zhang D, Zhang Y, Meng X, Zhang QY, Zhao L, Yang KQ, Zhou XL. Overview of Monogenic Forms of Hypertension Combined With Hypokalemia. Front Pediatr 2020; 8:543309. [PMID: 33569358 PMCID: PMC7868374 DOI: 10.3389/fped.2020.543309] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 12/29/2020] [Indexed: 12/26/2022] Open
Abstract
Hypertension is an important risk factor in many conditions and creates a heavy burden of disease and mortality globally. Polygenic hypertension is the most common form; however, it is increasingly recognized that monogenic hypertension is not rare, especially in patients with electrolyte disorders. Single genetic alterations are associated with plasma volume expansion and catecholamines/sympathetic excess with simultaneously increased potassium excretion in the urine and potassium intracellular shift. Early-onset refractory hypertension and profound hypokalemia are characteristics of monogenic hypertension. However, accumulated evidence shows the existence of phenotypic heterogeneity in monogenic hypertension meaning that, even for mild symptoms, clinicians cannot easily exclude the possibility of monogenic hypertension. Genetic, epigenetic and non-genetic factors are all possible mechanisms influencing phenotypic diversity. Genetic sequencing is a precise and efficient method that can broaden the mutant gene spectrum of the disease and is very helpful for understanding the pathophysiology of monogenic hypertension. Genetic sequencing, along with biochemical tests and imaging modalities, is essential for the early diagnosis and targeted management of monogenic hypertension to avoid long-term catastrophic complications.
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Affiliation(s)
- Yi-Ting Lu
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Peng Fan
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Di Zhang
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Ying Zhang
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Xu Meng
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Qiong-Yu Zhang
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Lin Zhao
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Kun-Qi Yang
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Xian-Liang Zhou
- Department of Cardiology, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
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Lou Y, Zhang F, Luo Y, Wang L, Huang S, Jin F. Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis. Int J Mol Sci 2016; 17:ijms17081307. [PMID: 27517916 PMCID: PMC5000704 DOI: 10.3390/ijms17081307] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 08/02/2016] [Accepted: 08/03/2016] [Indexed: 12/13/2022] Open
Abstract
The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na+/K+-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na+ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na+ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na+ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.
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Affiliation(s)
- Yiyun Lou
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Department of Gynaecology, Hangzhou Hospital of Traditional Chinese Medicine, Hangzhou 310007, Zhejiang, China.
| | - Fan Zhang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Yuqin Luo
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Liya Wang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Shisi Huang
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
| | - Fan Jin
- Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University, Hangzhou 310006, Zhejiang, China.
- Key Laboratory of Reproductive Genetics, National Ministry of Education (Zhejiang University), Women's Reproductive Healthy Laboratory of Zhejiang Province, Hangzhou 310058, Zhejiang, China.
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4
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López-Barradas A, González-Cid T, Vázquez N, Gavi-Maza M, Reyes-Camacho A, Velázquez-Villegas LA, Ramírez V, Zandi-Nejad K, Mount DB, Torres N, Tovar AR, Romero MF, Gamba G, Plata C. Insulin and SGK1 reduce the function of Na+/monocarboxylate transporter 1 (SMCT1/SLC5A8). Am J Physiol Cell Physiol 2016; 311:C720-C734. [PMID: 27488665 DOI: 10.1152/ajpcell.00104.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 07/27/2016] [Indexed: 11/22/2022]
Abstract
SMCTs move several important fuel molecules that are involved in lipid, carbohydrate, and amino acid metabolism, but their regulation has been poorly studied. Insulin controls the translocation of several solutes that are involved in energetic cellular metabolism, including glucose. We studied the effect of insulin on the function of human SMCT1 expressed in Xenopus oocytes. The addition of insulin reduced α-keto-isocaproate (KIC)-dependent 22Na+ uptake by 29%. Consistent with this result, the coinjection of SMCT1 with SGK1 cRNA decreased the KIC-dependent 22Na+ uptake by 34%. The reduction of SMCT1 activity by SGK1 depends on its kinase activity, and it was observed that the coinjection of SMCT1 with S442D-SGK1 (a constitutively active mutant) decreased the KIC-dependent 22Na+ uptake by 50%. In contrast, an SMCT1 coinjection with K127M-SGK1 (an inactive mutant) had no effect on the KIC-dependent Na+ uptake. The decreasing SMCT1 function by insulin or SGK1 was corroborated by measuring [1-14C]acetate uptake and the electric currents of SMCT1-injected oocytes. Previously, we found that SMCT2/Slc5a12-mRNA, but not SMCT1/Slc5a8-mRNA, is present in zebrafish pancreas (by in situ hybridization); however, SLC5a8 gene silencing was associated with the development of human pancreatic cancer. We confirmed that the mRNA and protein of both transporters were present in rat pancreas using RT-PCR with specific primers, Western blot analysis, and immunohistochemistry. Additionally, significant propionate-dependent 22Na+ uptake occurred in pancreatic islets and was reduced by insulin treatment. Our data indicate that human SMCT1 is regulated by insulin and SGK1 and that both SMCTs are present in the mammalian pancreas.
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Affiliation(s)
- Adriana López-Barradas
- Department of Physiology of Nutrition, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Tania González-Cid
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Norma Vázquez
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico.,Molecular Physiology Unit, Instituto de Investigaciones Biomédicas, UNAM, Tlalpan, Mexico City, Mexico
| | - Marisol Gavi-Maza
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Adriana Reyes-Camacho
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Laura A Velázquez-Villegas
- Department of Physiology of Nutrition, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Victoria Ramírez
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | | | - David B Mount
- Renal Division, Brigham and Women's Hospital, Boston, Massachusetts.,Veterans Affairs Boston Healthcare System, Boston, Massachusetts; and
| | - Nimbe Torres
- Department of Physiology of Nutrition, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Armando R Tovar
- Department of Physiology of Nutrition, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico
| | - Michael F Romero
- Physiology & Biomedical Engineering, Nephrology & Hypertension, Mayo Clinic College of Medicine, Rochester, Minnesota
| | - Gerardo Gamba
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico.,Molecular Physiology Unit, Instituto de Investigaciones Biomédicas, UNAM, Tlalpan, Mexico City, Mexico
| | - Consuelo Plata
- Department of Nephrology & Mineral Metabolism, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Tlalpan, Mexico City, Mexico;
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Abstract
Aldosterone is a major regulator of Na(+) absorption and acts primarily by controlling the epithelial Na(+) channel (ENaC) function at multiple levels including transcription. ENaC consists of α, β, and γ subunits. In the classical model, aldosterone enhances transcription primarily by activating mineralocorticoid receptor (MR). However, how aldosterone induces chromatin alternation and thus leads to gene activation or repression remains largely unknown. Emerging evidence suggests that Dot1a-Af9 complex plays an important role in repression of αENaC by directly binding and modulating targeted histone H3 K79 hypermethylation at the specific subregions of αENaC promoter. Aldosterone impairs Dot1a-Af9 formation by decreasing expression of Dot1a and Af9 and by inducing Sgk1, which, in turn, phosphorylates Af9 at S435 to weaken Dot1a-Af9 interaction. MR counterbalances Dot1a-Af9 action by competing with Dot1a for binding Af9. Af17 derepresses αENaC by competitively interacting with Dot1a and facilitating Dot1a nuclear export. Consistently, MR(-/-) mice have impaired ENaC expression at day 5 after birth, which may contribute to progressive development of pseudohypoaldosteronism type 1 in a later stage. Af17(-/-) mice have decreased ENaC expression, renal Na(+) retention, and blood pressure. In contrast, Dot1l(AC) mice have increased αENaC expression, despite a 20% reduction of the principal cells. This chapter reviews these findings linking aldosterone action to ENaC transcription through chromatin modification. Future direction toward the understanding the role of Dot1a-Af9 complex beyond ENaC regulation, in particular, in renal fibrosis is also briefly discussed.
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Affiliation(s)
- Lihe Chen
- Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas, USA; Division of Renal Diseases and Hypertension, Department of Internal Medicine, University of Texas Medical School at Houston, Houston, Texas, USA
| | - Xi Zhang
- Division of Renal Diseases and Hypertension, Department of Internal Medicine, University of Texas Medical School at Houston, Houston, Texas, USA
| | - Wenzheng Zhang
- Graduate School of Biomedical Sciences, The University of Texas Health Science Center at Houston, Houston, Texas, USA; Division of Renal Diseases and Hypertension, Department of Internal Medicine, University of Texas Medical School at Houston, Houston, Texas, USA.
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Alsop TA, McLeod BJ, Butt AG. Variations in epithelial Na(+) transport and epithelial sodium channel localisation in the vaginal cul-de-sac of the brushtail possum, Trichosurus vulpecula, during the oestrous cycle. Reprod Fertil Dev 2014; 28:328-36. [PMID: 25056576 DOI: 10.1071/rd13277] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 05/27/2014] [Indexed: 11/23/2022] Open
Abstract
The fluid in the vaginal cul-de-sac of the brushtail possum, Trichosurus vulpecula, is copious at ovulation when it may be involved in sperm transport or maturation, but is rapidly reabsorbed following ovulation. We have used the Ussing short-circuit current (Isc) technique and measurements of transcript and protein expression of the epithelial Na(+) channel (ENaC) to determine if variations in electrogenic Na(+) transport are associated with this fluid absorption. Spontaneous Isc (<20µAcm(-2) during anoestrus, 60-80µAcm(-2) in cycling animals) was inhibited by serosal ouabain. Mucosal amiloride (10µmolL(-1)), an inhibitor of ENaC, had little effect on follicular Isc but reduced luteal Isc by ~35%. This amiloride-sensitive Isc was dependent on mucosal Na(+) and the half-maximal inhibitory concentration (IC50)-amiloride (0.95μmolL(-1)) was consistent with ENaC-mediated Na(+) absorption. Results from polymerase chain reaction with reverse transcription (RT-PCR) indicate that αENaC mRNA is expressed in anoestrous, follicular and luteal phases. However, in follicular animals αENaC immunoreactivity in epithelial cells was distributed throughout the cytoplasm, whereas immunoreactivity was restricted to the apical pole of cells from luteal animals. These data suggest that increased Na(+) absorption contributes to fluid absorption during the luteal phase and is regulated by insertion of ENaC into the apical membrane of cul-de-sac epithelial cells.
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Affiliation(s)
- T-A Alsop
- Department of Physiology, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand
| | - B J McLeod
- AgResearch Invermay, Private Bag 50034 Mosgiel 9053, New Zealand
| | - A G Butt
- Department of Physiology, Otago School of Medical Sciences, University of Otago, PO Box 56, Dunedin 9054, New Zealand
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Oztekin O, Akyol M, Kalay S, Tezel G, Akcakus M, Oygur N. Investigation of the serum glucocorticoid kinase 1 gene in patients with transient tachypnea of the newborn. J Matern Fetal Neonatal Med 2013; 26:990-4. [PMID: 23339546 DOI: 10.3109/14767058.2013.766709] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE The aim of this study was to investigate whether there is a role of the serum glucocorticoid kinase (SGK) 1 gene, which has an effect on the control of the epithelial sodium channels. MATERIALS AND METHOD This study included patients who were diagnosed with transient tachypnea of the newborn (TTN) with more than 37 weeks of gestation. As the control group, healthy newborns of the same gestational age were included. From each group, within the first 5 d of their lives, 2 cc of whole blood was taken in EDTA tubes, and stored at -80 °C. The DNA extraction was performed. RESULTS There were 32 patients in the TTN, and also 32 patients in the control group. The heterozygous allele rs1057293 (3/28) and rs1743966 (8/28) were located in the encoder region of the SGK 1 gene. In addition, in encoding region of the SGK 1 gene, the Arg97Ile (1/28), which causes the amino acid changes, had a genotype frequency of 0.0357, and a mutation was identified in Arg97Ile. DISCUSSION We have defined polymorphisms rs1057293 and rs1743966 in the SGK 1 gene, and the Arg97Ile mutation, for the first time in patients with TTN. This pilot study gave us some clues about a genetic basis of TTN phenotype, next to the lack of the pulmonary maturation.
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Affiliation(s)
- Osman Oztekin
- Department of Pediatrics, Division of Neonatology, Akdeniz University Medical School, Antalya, Turkey
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Lang F, Shumilina E. Regulation of ion channels by the serum- and glucocorticoid-inducible kinase SGK1. FASEB J 2012; 27:3-12. [PMID: 23012321 DOI: 10.1096/fj.12-218230] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The ubiquitously expressed serum- and glucocorticoid-inducible kinase-1 (SGK1) is genomically regulated by cell stress (including cell shrinkage) and several hormones (including gluco- and mineralocorticoids). SGK1 is activated by insulin and growth factors through PI3K and 3-phosphoinositide-dependent kinase PDK1. SGK1 activates a wide variety of ion channels (e.g., ENaC, SCN5A, TRPV4-6, ROMK, Kv1.3, Kv1.5, Kv4.3, KCNE1/KCNQ1, KCNQ4, ASIC1, GluR6, ClCKa/barttin, ClC2, CFTR, and Orai/STIM), which participate in the regulation of transport, hormone release, neuroexcitability, inflammation, cell proliferation, and apoptosis. SGK1-sensitive ion channels participate in the regulation of renal Na(+) retention and K(+) elimination, blood pressure, gastric acid secretion, cardiac action potential, hemostasis, and neuroexcitability. A common (∼3-5% prevalence in Caucasians and ∼10% in Africans) SGK1 gene variant is associated with increased blood pressure and body weight as well as increased prevalence of type II diabetes and stroke. SGK1 further contributes to the pathophysiology of allergy, peptic ulcer, fibrosing disease, ischemia, tumor growth, and neurodegeneration. The effect of SGK1 on channel activity is modest, and the channels do not require SGK1 for basic function. SGK1-dependent ion channel regulation may thus become pathophysiologically relevant primarily after excessive (pathological) expression. Therefore, SGK1 may be considered an attractive therapeutic target despite its broad range of functions.
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Affiliation(s)
- Florian Lang
- Department of Physiology, University of Tuebingen, Gmelinstrasse 5, 72076 Tuebingen, Germany.
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Abstract
PURPOSE OF REVIEW The serum and glucocorticoid regulated kinase (SGK) family of protein kinases shares similar biochemical and hormonal signaling properties; however, the SGK kinases also exhibit distinct differences in regulating renal sodium (Na(+)) transport. This review will highlight recent advances in our understanding of the specificity of SGK kinase signaling and regulation of renal Na(+) transport. RECENT FINDINGS Differential expression of SGK kinases at the cellular and subcellular levels contributes to signaling specificity. New evidence indicates that SGK1 associates with the apical cell membrane of cortical collecting duct cells to regulate open probability of the epithelial Na(+) channel (ENaC). Scaffold proteins can also recruit SGK1 to multiprotein complexes for regulation of ENaC expression in the apical membrane. Recent SGK1 knockout models have implicated the NaCl co-transporter (NCC) as another target of SGK1 regulation. Less is known about the function of SGK2 or SGK3, but both kinases can regulate Na(+)/H(+) exchanger 3 (NHE3) activity. SUMMARY The SGK kinases assume distinct roles in regulating Na transport in both proximal and distal elements of the kidney tubule. Future examination of the molecular mechanisms by which the SGK kinases regulate specific substrates will inform our understanding of how these kinases contribute to the physiology of renal Na(+) transport.
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Affiliation(s)
- Alan C Pao
- Division of Nephrology, Department of Medicine, Stanford University School of Medicine, Stanford, California, USA
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10
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Aguilar-Sánchez C, Hernández-Díaz I, Lorenzo-Díaz F, Navarro JF, Hughes TE, Giraldez T, Alvarez de la Rosa D. Identification of permissive insertion sites for generating functional fluorescent mineralocorticoid receptors. Endocrinology 2012; 153:3517-25. [PMID: 22621960 DOI: 10.1210/en.2012-1210] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily of transcription factors, is activated by aldosterone and mediates its natriferic action in tight epithelia. MR is also expressed in nonepithelial tissues. Importantly, it mediates the deleterious effects of inappropriately high aldosterone levels in the heart, in which it induces the development of cardiac fibrosis. Antagonism of MR in humans is useful in the treatment of severe cardiac failure and some forms of hypertension. Despite the important pathophysiological and pharmacological role of this receptor, many important questions about its cellular biology and functional roles remain unanswered. A major challenge in the study of MR is the unavailability of fully functional fluorescent derivatives of the receptor. In this study we have created a library of MR mutants with insertions of the yellow fluorescent protein in various internal locations in the receptor using a random-insertion transposon-based technique. Screening of this library using a transactivation assay allowed us to identify several fluorescent constructs that retain functionality. Detailed characterization of one of these construct showed that it induces aldosterone-target genes such as the epithelial Na(+) channel subunits and the serum and glucocorticoid-induced kinase 1 at physiological concentrations of aldosterone to an equal extent than the wild-type receptor. Furthermore, aldosterone affinity, hormone-induced nuclear translocation, DNA binding and regulation of nongenomic pathways are all indistinguishable from the wild-type receptor. This new set of fluorescent MR derivatives provides a useful tool for studying the cell biology of the receptor.
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Affiliation(s)
- Cristina Aguilar-Sánchez
- Department of Physiology and Instituto de Tecnologías Biomédicas, University of La Laguna, 38071 Tenerife, Spain
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11
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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.
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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
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12
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Faresse N, Lagnaz D, Debonneville A, Ismailji A, Maillard M, Fejes-Toth G, Náray-Fejes-Tóth A, Staub O. Inducible kidney-specific Sgk1 knockout mice show a salt-losing phenotype. Am J Physiol Renal Physiol 2012; 302:F977-85. [PMID: 22301619 DOI: 10.1152/ajprenal.00535.2011] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The expression of the serum- and glucocorticoid-regulated kinase 1 (Sgk1) is induced by mineralocorticoids and, in turn, upregulates the renal epithelial Na(+) channel (ENaC). Total inactivation of Sgk1 has been associated with transient urinary Na(+) wasting with a low-Na(+) diet, while the aldosterone-mediated ENaC channel activation was unchanged in the collecting duct. Since Sgk1 is ubiquitously expressed, we aimed to study the role of renal Sgk1 and generated an inducible kidney-specific knockout (KO) mouse. We took advantage of the previously described TetOn/CreLoxP system, in which rtTA is under the control of the Pax8 promotor, allowing inducible inactivation of the floxed Sgk1 allele in the renal tubules (Sgk1fl/fl/Pax8/LC1 mice). We found that under a standard Na(+) diet, renal water and Na(+)/K(+) excretion had a tendency to be higher in doxycycline-treated Sgk1 KO mice compared with control mice. The impaired ability of Sgk1 KO mice to retain Na(+) increased significantly with a low-salt diet despite higher plasma aldosterone levels. On a low-Na(+) diet, the Sgk1 KO mice were also hyperkaliuric and lost body weight. This phenotype was accompanied by a decrease in systolic and diastolic blood pressure. At the protein level, we observed a reduction in phosphorylation of the ubiquitin protein-ligase Nedd4-2 and a decrease in the expression of the Na(+)-Cl(-)-cotransporter (NCC) and to a lesser extent of ENaC.
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Affiliation(s)
- Nourdine Faresse
- Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, Lausanne, Switzerland
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Abstract
The epithelial Na(+) channel (ENaC) and acid-sensitive ion channel (ASIC) branches of the ENaC/degenerin superfamily of cation channels have drawn increasing attention as potential therapeutic targets in a variety of diseases and conditions. Originally thought to be solely expressed in fluid absorptive epithelia and in neurons, it has become apparent that members of this family exhibit nearly ubiquitous expression. Therapeutic opportunities range from hypertension, due to the role of ENaC in maintaining whole body salt and water homeostasis, to anxiety disorders and pain associated with ASIC activity. As a physiologist intrigued by the fundamental mechanics of salt and water transport, it was natural that Dale Benos, to whom this series of reviews is dedicated, should have been at the forefront of research into the amiloride-sensitive sodium channel. The cloning of ENaC and subsequently the ASIC channels has revealed a far wider role for this channel family than was previously imagined. In this review, we will discuss the known and potential roles of ENaC and ASIC subunits in the wide variety of pathologies in which these channels have been implicated. Some of these, such as the role of ENaC in Liddle's syndrome are well established, others less so; however, all are related in that the fundamental defect is due to inappropriate channel activity.
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Affiliation(s)
- Yawar J Qadri
- Department of Physiology and Biophysics, University of Alabama at Birmingham, AL 35294, USA
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14
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Wallace K, Long Q, Fairhall EA, Charlton KA, Wright MC. Serine/threonine protein kinase SGK1 in glucocorticoid-dependent transdifferentiation of pancreatic acinar cells to hepatocytes. J Cell Sci 2011; 124:405-13. [PMID: 21224398 DOI: 10.1242/jcs.077503] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Elevated glucocorticoid levels result in the transdifferentiation of pancreatic acinar cells into hepatocytes through a process that requires a transient repression of WNT signalling upstream of the induction of C/EBP-β. However, the mechanism by which glucocorticoid interacts with WNT signalling is unknown. A screen of microarray data showed that the serine/threonine protein kinase SGK1 (serum- and glucocorticoid-regulated kinase 1) was markedly induced in the model B-13 pancreatic rat acinar cell line after glucocorticoid treatment (which converts them into hepatocyte-like 'B-13/H' cells) and this was confirmed at the level of mRNA (notably an alternatively transcribed SGK1C form) and protein. Knockdown of SGK1 using an siRNA designed to target all variant transcripts inhibited glucocorticoid-dependent transdifferentiation, whereas overexpression of the human C isoform (and also the human SGK1F isoform, for which no orthologue in the rat has been identified) alone - but not the wild-type A form - inhibited distal WNT signalling Tcf/Lef transcription factor activity, and converted B-13 cells into B-13/H cells. These effects were lost when the kinase functions of SGK1C and SGK1F were mutated. Inhibition of SGK1 kinase activity also inhibited glucocorticoid-dependent transdifferentiation. Expression of SGK1C and SGK1F resulted in the appearance of phosphorylated β-catenin, and recombinant SGK1 was shown to directly phosphorylate purified β-catenin in vitro in an ATP-dependent reaction. These data therefore demonstrate a crucial role for SGK1 induction in B-13 cell transdifferentiation to B-13/H hepatocytes and suggest that direct phosphorylation of β-catenin by SGK1C represents the mechanism of crosstalk between glucocorticoid and WNT signalling pathways.
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Affiliation(s)
- Karen Wallace
- Institute of Cellular Medicine, Newcastle University, Newcastle Upon Tyne NE24HH, UK
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15
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Soundararajan R, Pearce D, Hughey RP, Kleyman TR. Role of epithelial sodium channels and their regulators in hypertension. J Biol Chem 2010; 285:30363-9. [PMID: 20624922 PMCID: PMC2945528 DOI: 10.1074/jbc.r110.155341] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The kidney has a central role in the regulation of blood pressure, in large part through its role in the regulated reabsorption of filtered Na(+). Epithelial Na(+) channels (ENaCs) are expressed in the most distal segments of the nephron and are a target of volume regulatory hormones. A variety of factors regulate ENaC activity, including several aldosterone-induced proteins that are present within an ENaC regulatory complex. Proteases also regulate ENaC by cleaving the channel and releasing intrinsic inhibitory tracts. Polymorphisms or mutations within channel subunits or regulatory pathways that enhance channel activity may contribute to an increase in blood pressure in individuals with essential hypertension.
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Affiliation(s)
| | - David Pearce
- From the Division of Nephrology, Department of Medicine, and
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143 and
| | - Rebecca P. Hughey
- the Departments of Medicine and of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Thomas R. Kleyman
- the Departments of Medicine and of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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Xie GL, Yan H, Lu ZF. Inhibition of glucocorticoid-induced changes of Na(+), K(+)-ATPase in rat lens by a glucocorticoid receptor antagonist RU486. Exp Eye Res 2010; 91:544-9. [PMID: 20637751 DOI: 10.1016/j.exer.2010.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2010] [Revised: 07/06/2010] [Accepted: 07/08/2010] [Indexed: 01/24/2023]
Abstract
Cataract formation can be induced by prolonged use of glucocorticoids. The underlying mechanism is not fully understood yet. The presence of the functional glucocorticoid receptor (GR) in human and rat lens epithelial cells suggests that glucocorticoids target lens epithelial cells directly and specifically. Na(+), K(+)-ATPase has long been recognized for its role in regulating electrolyte concentration in the lens, contributing to lens transparency. We previously reported that the inactivation of Na(+), K(+)-ATPase induced by a glucocorticoid in rat lens. Therefore, the question is whether the changes of Na(+), K(+)-ATPase can be induced through the specific GR activation in glucocorticoid-induced cataract formation. Clear rat lenses were cultured in vitro and were treated with or without dexamethasone (Dex) or RU486 (a GR antagonist). The lenses were cultured for 7 days and photographed daily to record the development of opacity. The activity of Na(+), K(+)-ATPase was determined by using spectrophotometric analysis. The mRNA and protein level expressions of Na(+), K(+)-ATPase α1 were examined by reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry analysis, respectively. Our findings are presented in this study and show that mist-like opacity of the lens was observed as early as 5 days after incubation with dexamethasone. The opacity was more obvious at day 7 in the Dex group. The lenses of the untreated group and the RU486+Dex group remained transparent throughout the incubation. The activity of Na(+), K(+)-ATPase in the Dex-treated group decreased in a time-dependent manner. There was no significant loss of enzyme activity in either the control or the RU486+Dex group throughout the incubation period. Both the protein and mRNA expression levels of Na(+), K(+)-ATPase α1 in the capsule-epithelium of lenses decreased in the Dex-treated group. The GR antagonist RU486 inhibited the decrease of the expression of Na(+), K(+)-ATPase α1 induced by Dex. All of the above results suggested that the GR-mediated reduction of Na(+), K(+)-ATPase may contribute to the formation of steroid-induced cataract. Intervention in this pathway maybe helpful to avoid glucocorticoids-cataract formation.
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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.
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Regulation of Epithelial Na+ Channel (ENaC) in the Salivary Cell Line SMG-C6. Exp Biol Med (Maywood) 2009; 234:522-31. [DOI: 10.3181/0806-rm-209] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Glucocorticoids and mineralocorticoids modulate Na+ transport via epithelial Na+ channels (ENaC). The rat submandibular epithelial cell line, SMG-C6, expresses α-ENaC mRNA and protein and exhibits amiloride-sensitive Na+ transport when grown in low-serum (2.5%) defined medium, therefore, we examined the effects of altering the composition of the SMG-C6 cell growth medium on ENaC expression and function. No differences in basal or amiloride-sensitive short-circuit current (Isc) were measured across SMG-C6 monolayers grown in the absence of thyroid hormone, insulin, transferrin, or EGF. In the absence of hydrocortisone, basal and amiloride-sensitive Isc significantly decreased. Similarly, monolayers grown in 10% serum-supplemented medium had lower basal Isc and no response to amiloride. Adding hydrocortisone (1.1 μM) to either the low or 10% serum medium increased basal and amiloride-sensitive Isc, which was blocked by RU486, the glucocorticoid and progesterone receptor antagonist. Aldosterone also induced an increase in α-ENaC expression and Na+ transport, which was also blocked by RU486 but not by the mineralocorticoid receptor antagonist spironolactone. Thus, in the SMG-C6 cell line, hydrocortisone and aldosterone increased ENaC expression and basal epithelial Na+ transport. The absence of endogenous ENaC expression in culture conditions devoid of steroids makes the properties of this cell line an excellent model for investigating pathways regulating ENaC expression and Na+ transport.
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Li T, Koshy S, Folkesson HG. IL-1beta-induced cortisol stimulates lung fluid absorption in fetal guinea pigs via SGK-mediated Nedd4-2 inhibition. Am J Physiol Lung Cell Mol Physiol 2009; 296:L527-33. [PMID: 19136575 DOI: 10.1152/ajplung.90506.2008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that interleukin (IL)-1beta-induced cortisol synthesis stimulates distal lung fluid absorption in fetal guinea pigs via induction of serum- and glucocorticoid-regulated kinase (SGK) and inhibition of neural precursor cell expressed, developmentally downregulated protein 4-2 (Nedd4-2). IL-1beta was subcutaneously administered daily to timed-pregnant guinea pigs over 3 days. Fetuses were obtained by abdominal hysterotomy at gestation day (GD)61 and GD68 and instilled with an isosmolar 5% albumin solution into the lungs. Distal lung fluid movement was measured over 1 h from the change in distal air space protein concentration. Fetal lungs were secreting lung fluid at GD61 while absorbing lung fluid at GD68. Distal lung fluid absorption was induced at GD61 by IL-1beta but unaffected at GD68. Plasma cortisol concentrations were increased by IL-1beta at GD61 and endogenously at GD68. Distal lung fluid absorption was measured and correlated to SGK and Nedd4-2 expression and to alpha-epithelial Na channel (ENaC) expression. SGK was increased by IL-1beta and late during gestation (GD68), while Nedd4-2 was decreased by IL-1beta and late during gestation. alpha-ENaC was induced by IL-1beta at GD61 and increased late during gestation. Thus our study suggests that cortisol-stimulated fetal lung fluid absorption is mediated by increased ENaC expression and may be governed by the SGK/Nedd4-2 pathway. These observations may explain why babies delivered preterm after intrauterine inflammation have a reduced risk of developing severe respiratory distress.
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Affiliation(s)
- Tianbo Li
- Department of Integrative Medical Sciences, Northeastern Ohio Universities Colleges of Medicine and Pharmacy, Rootstown, Ohio 44272-0095, USA
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20
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Epigenetics and the control of epithelial sodium channel expression in collecting duct. Kidney Int 2008; 75:260-7. [PMID: 18818687 DOI: 10.1038/ki.2008.475] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In eukaryotic nuclei, genomic DNA is compacted with histone and nonhistone proteins into a dynamic polymer termed chromatin. Reorganization of chromatin structure through histone modifications, the action of chromatin factors, or DNA methylation, can profoundly change gene expression. These epigenetic modifications allow heritable and potentially reversible changes in gene functioning to occur without altering the DNA sequence, thus extending the information potential of the genetic code. This review provides an introduction to epigenetic concepts for renal investigators and an overview of our work detailing an epigenetic pathway for aldosterone signaling and the control of epithelial Na(+) channel-alpha (ENaCalpha) subunit gene expression in the collecting duct. This new pathway involves a nuclear repressor complex, consisting of histone H3 Lys-79 methyltransferase disruptor of telomeric silencing-1a (Dot1a), ALL1 fused gene from chromosome 9 (Af9), a sequence-specific DNA-binding protein that binds the ENaCalpha promoter, and potentially other nuclear proteins. This complex regulates targeted histone H3 Lys-79 methylation of chromatin associated with the ENaCalpha promoter, thereby suppressing its transcriptional activity. Aldosterone disrupts the Dot1a-Af9 interaction by serum- and glucocorticoid-induced kinase-1 phosphorylation of Af9, and inhibits Dot1a and Af9 expression, resulting in histone H3 Lys-79 hypomethylation at specific subregions, and derepression of the ENaCalpha promoter. The Dot1a-Af9 pathway may also be involved in the control of genes implicated in renal fibrosis and hypertension.
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21
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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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Fejes-Tóth G, Frindt G, Náray-Fejes-Tóth A, Palmer LG. Epithelial Na+channel activation and processing in mice lacking SGK1. Am J Physiol Renal Physiol 2008; 294:F1298-305. [DOI: 10.1152/ajprenal.00579.2007] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Amiloride-sensitive Na+channel activity was examined in the cortical collecting ducts of a mouse line (SGK1−/−) deficient in the serum- and glucocorticoid-dependent protein kinase SGK1. This activity was correlated with changes in renal Na handling and in the maturation of epithelial Na+channel (ENaC) protein. Neither SGK1−/−mice nor paired SGK1+/+animals expressed detectable channel activity, measured as amiloride-sensitive whole-cell current ( INa), under control conditions with standard chow. Administration of aldosterone (0.5 μg/h via osmotic minipump for 7 days) increased INato a similar extent in SGK1+/+(378 ± 61 pA/cell at −100 mV) and in SGK1−/−(350 ± 57 pA/cell) animals. However, the maturation of ENaC, assessed as the ratio of cleaved to full-length forms of γ-ENaC, was more pronounced in SGK+/+mice. The SGK1−/−animals exhibited a salt-wasting phenotype when kept on a low-Na diet for up to 2 days, losing significantly more Na in the urine than wild-type mice. Under these conditions, INawas enhanced more in SGK1−/−(94 ± 14 pA/cell) than in SGK+/+(23 ± 5 pA/cell) genotypes. Despite the larger currents, the ratio of cleaved to full-length γ-ENaC was lower in the knockout animals. The mice also expressed a smaller amount of Na+-Cl−cotransporter protein under Na-depleted conditions. These results indicated that SGK1 is essential for optimal processing of ENaC but is not required for activation of the channel by aldosterone.
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Náray-Fejes-Tóth A, Boyd C, Fejes-Tóth G. Regulation of epithelial sodium transport by promyelocytic leukemia zinc finger protein. Am J Physiol Renal Physiol 2008; 295:F18-26. [PMID: 18448589 DOI: 10.1152/ajprenal.00573.2007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Aldosterone is the principal regulator of Na homeostasis, and thereby blood pressure. One of the main targets of aldosterone is the epithelial Na channel (ENaC) located in the apical membrane of target cells. Previous studies identified several genes involved in the regulation of ENaC such as SGK1; however, SGK1 knockout mice have only a mild salt-losing phenotype, indicating that further genes must be involved in the action of aldosterone. In our search for further aldosterone-regulated genes, we discovered that aldosterone, at physiological concentrations, induces the expression of the promyelocytic leukemia zinc finger protein (PLZF) in renal cortical collecting duct (CCD) cell lines that stably express mineralocorticoid receptors (MRs). This effect is rapid and does not require de novo protein synthesis, suggesting a direct action. Surprisingly, stable overexpression of human or mouse PLZF isoforms significantly decreased transepithelial Na transport in CCD cells while having no effect on the integrity of the monolayers. In parallel with the decline in Na transport, PLZF suppressed the mRNA levels of beta- and gamma-ENaC subunits. These observations suggest that PLZF is a negative regulator of ENaC in renal epithelial cells and might be part of a negative feedback loop that limits aldosterone's stimulatory effects on sodium reabsorption.
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Taruno A, Niisato N, Marunaka Y. Intracellular calcium plays a role as the second messenger of hypotonic stress in gene regulation of SGK1 and ENaC in renal epithelial A6 cells. Am J Physiol Renal Physiol 2007; 294:F177-86. [PMID: 17959754 DOI: 10.1152/ajprenal.00250.2007] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In A6 cells, a renal cell line derived from Xenopus laevis, hypotonic stress stimulates the amiloride-sensitive Na(+) transport. Hypotonic action on Na(+) transport consists of two phases, a nongenomic early phase and a genomic delayed phase. Although it has been reported that, during the genomic phase, hypotonic stress stimulates transcription of Na(+) transport-related genes, such as serum- and glucocorticoid-inducible kinase 1 (SGK1) and subunits of the epithelial Na(+) channel (ENaC), increasing Na(+) transport, the mechanism remains unknown. We focused the present study on the role of intracellular Ca(2+) in hypotonicity-induced SGK1 and ENaC subunit transcription. Since hypotonic stress raises intracellular Ca(2+) concentration in A6 cells, we hypothesized that Ca(2+)-dependent signals participate in the genomic action. Using real-time quantitative RT-PCR and Western blot techniques and measuring short-circuit currents, we observed that 1) BAPTA-AM and W7 blunted the hypotonicity-induced expression of SGK1 mRNA and protein, 2) ionomycin dose dependently stimulated expression of SGK1 mRNA and protein under an isotonic condition and the time course of the stimulatory effect of ionomycin on SGK1 mRNA was remarkably similar to that of hypotonic action on SGK1 mRNA, 3) hypotonic stress stimulated transcription of three ENaC subunits in an intracellular Ca(2+)-dependent manner, and 4) BAPTA-AM retarded the delayed phase of hypotonic stress-induced Na(+) transport but had no effect on the early phase. These observations indicate for the first time that intracellular Ca(2+) plays a role as the second messenger in hypotonic stress-induced Na(+) transport by stimulating transcription of SGK1 and ENaC subunits.
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Affiliation(s)
- Akiyuki Taruno
- Department of Molecular Cell Physiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan
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Abstract
Steroid-induced posterior subcapsular cataracts (PSCs) exhibit three main distinctive characteristics: (i) association only with steroids possessing glucocorticoid activity, (ii) involvement of aberrant migrating lens epithelial cells, and (iii) a central posterior location. The first characteristic suggests a key role for glucocorticoid receptor activation and subsequent changes to the transcription of specific genes. Glucocorticoid receptor activation is associated in many cell types with proliferation, suppressed differentiation, a reduced susceptibility to apoptosis, altered transmembrane transport, and enhancement of reactive oxygen species activity. Glucocorticoids may be capable of inducing changes to the transcription of genes in lens epithelial cells that are related to many of these cellular processes. This review examines the various mechanisms that have been proposed to account for the development of PSC in the context of recent DNA array studies. Additionally, given that the glucocorticoid receptor can also engender wide-ranging indirect activities, glucocorticoids could also indirectly affect the lens through the responses of other cells within the ocular compartment and/or through effects on cells at more remote locations. These indirect mechanisms, which, for example, could be mediated through alterations to the intraocular levels of growth factors that normally orchestrate lens development and maintain lens homeostasis, are also discussed. Although the mechanism of steroid cataract induction remains unknown, glucocorticoid-induced gene transcription events in lens epithelial cells, and also other intraocular or systemic cells, likely interact to generate steroid cataracts. Finally, although evidence for glucocorticoid-protein adduct formation in the lens is inconclusive, the generation of such adducts cannot yet be discounted as a contributing factor and must necessarily be retained in discussions of the etiology of steroid cataract.
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Husted RF, Volk KA, Sigmund RD, Stokes JB. Discordant effects of corticosteroids and expression of subunits on ENaC activity. Am J Physiol Renal Physiol 2007; 293:F813-20. [PMID: 17609289 DOI: 10.1152/ajprenal.00225.2007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In renal distal nephron and airway epithelial cells, adrenocortical steroids increase epithelial Na+ channel (ENaC) activity and also markedly increase the expression of the α-subunit. The present experiments were designed to reconstitute this steroid effect in ENaC-expressing cells by overexpressing the subunits whose expression is enhanced by corticosteroids. In renal collecting duct monolayers, corticosteroids increased ENaC activity 5- to 8-fold, endogenous α-ENaC mRNA and protein ∼10-fold, and β-ENaC protein and mRNA 1.2- to 2-fold. γ-ENaC expression was unchanged. To determine whether this increase in expression was sufficient to increase ENaC activity, we used a regulated adenovirus system to increase expression of each subunit alone and in combination. Unexpectedly, increased expression of the α- and/or β-subunit had no effect on ENaC activity in collecting duct cells or lung epithelial cells. In contrast, a small increase in γ-ENaC expression increased ENaC activity about threefold. This increase in activity was additive to the effect of steroids. Thus, even though corticosteroids strongly increase α-ENaC expression and moderately increase β-ENaC expression, these effects are not, by themselves, sufficient to increase ENaC activity. Knockdown experiments are consistent with the idea that the increased expression of α-ENaC is necessary for the full steroid effect on ENaC. Increased expression of γ-ENaC and corticosteroid treatment enhances ENaC activity by parallel, noninteracting pathways. These results underscore the importance of other actions of steroid hormones for long-term enhancement of ENaC activity and raise new possibilities for regulation of ENaC activity by γ-ENaC expression.
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Affiliation(s)
- Russell F Husted
- Department of Internal Medicine, 200 Hawkins Drive, University of Iowa, Iowa City, IA 52246, USA
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Martel JA, Michael D, Fejes-Tóth G, Náray-Fejes-Tóth A. Melanophilin, a novel aldosterone-induced gene in mouse cortical collecting duct cells. Am J Physiol Renal Physiol 2007; 293:F904-13. [PMID: 17609287 DOI: 10.1152/ajprenal.00365.2006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The molecular mechanisms of aldosterone-regulated Na+ transport are not entirely clear. The goal of this study was to identify aldosterone-induced genes potentially involved in the trafficking of the epithelial Na+ channel (ENaC). We report that the transcript levels of melanophilin (MLPH), a protein involved in vesicular trafficking in melanocytes, are rapidly increased by aldosterone in cortical collecting duct (CCD) cells. This effect was near maximal at physiological aldosterone concentrations, indicating that it is mediated by the mineralocorticoid receptor. De novo protein synthesis is not required for the induction of MLPH mRNA by aldosterone. To determine whether this induction has functional consequences on transepithelial Na+ current, we generated clonal CCD cell lines that express a tetracycline-inducible MLPH. Induction of MLPH in these cells led to a relatively modest, but statistically significant, increase in amiloride-sensitive Na+ current, suggesting the MLPH may be involved in ENaC trafficking. MyosinVc, the epithelial-specific class V myosin that is highly homologous to MyosinVa, another component of the melanosome trafficking complex, has putative consensus sites for serum and glucocorticoid-induced kinase 1 (SGK1), an early aldosterone-induced kinase that mediates some of aldosterone's effects on Na+ transport. Our results indicate that MyosinVc is phosphorylated by endogenous SGK1, suggesting that this complex may be involved in the aldosterone-regulated trafficking of ENaC in the CCD. These results suggest potential mechanisms by which aldosterone may regulate Na+ transport both directly, by increasing the abundance of MLPH, and indirectly by increasing the transcription of SGK1, which in turn regulates the activity of MyosinVc.
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Affiliation(s)
- Jessica A Martel
- Dartmouth Medical School, 1 Medical Center Drive, Lebanon, NH 03756, USA
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Abstract
The hormone aldosterone increases extracellular fluid volume and blood pressure by activating epithelial Na+ channels (ENaCs). Serum- and glucocorticoid-induced kinase 1 (SGK1) is an aldosterone-stimulated signaling molecule that enhances distal nephron Na+ transport, in part by preventing the internalization of ENaCs from the plasma membrane. In this issue of the JCI, Zhang et al. demonstrate that SGK1 enhances transcription of the alpha subunit of ENaC by preventing histone methylation, providing an additional mechanism by which SGK1 increases ENaC-mediated Na+ transport in the distal nephron (see the related article beginning on page 773).
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Affiliation(s)
- David Pearce
- Division of Nephrology, Department of Medicine, UCSF, San Francisco, California, USA.
Renal-Electrolyte Division, Department of Medicine, and Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Thomas R. Kleyman
- Division of Nephrology, Department of Medicine, UCSF, San Francisco, California, USA.
Renal-Electrolyte Division, Department of Medicine, and Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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Zhang W, Xia X, Reisenauer MR, Rieg T, Lang F, Kuhl D, Vallon V, Kone BC. Aldosterone-induced Sgk1 relieves Dot1a-Af9-mediated transcriptional repression of epithelial Na+ channel alpha. J Clin Invest 2007; 117:773-83. [PMID: 17332896 PMCID: PMC1804379 DOI: 10.1172/jci29850] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2006] [Accepted: 01/02/2007] [Indexed: 01/17/2023] Open
Abstract
Aldosterone plays a major role in the regulation of salt balance and the pathophysiology of cardiovascular and renal diseases. Many aldosterone-regulated genes--including that encoding the epithelial Na+ channel (ENaC), a key arbiter of Na+ transport in the kidney and other epithelia--have been identified, but the mechanisms by which the hormone modifies chromatin structure and thus transcription remain unknown. We previously described the basal repression of ENaCalpha by a complex containing the histone H3 Lys79 methyltransferase disruptor of telomeric silencing alternative splice variant a (Dot1a) and the putative transcription factor ALL1-fused gene from chromosome 9 (Af9) as well as the release of this repression by aldosterone treatment. Here we provide evidence from renal collecting duct cells and serum- and glucocorticoid-induced kinase-1 (Sgk1) WT and knockout mice that Sgk1 phosphorylated Af9, thereby impairing the Dot1a-Af9 interaction and leading to targeted histone H3 Lys79 hypomethylation at the ENaCalpha promoter and derepression of ENaCalpha transcription. Thus, Af9 is a physiologic target of Sgk1, and Sgk1 negatively regulates the Dot1a-Af9 repressor complex that controls transcription of ENaCalpha and likely other aldosterone-induced genes.
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Affiliation(s)
- Wenzheng Zhang
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Xuefeng Xia
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Mary Rose Reisenauer
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Timo Rieg
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Florian Lang
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Dietmar Kuhl
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Volker Vallon
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
| | - Bruce C. Kone
- Departments of Internal Medicine and Integrative Biology and Pharmacology, University of Texas Medical School at Houston, Houston, Texas, USA.
Departments of Medicine and Pharmacology, University of California, San Diego, and VA Medical Center, San Diego, California, USA.
Department of Physiology, University of Tübingen, Tübingen, Germany.
Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany.
Brown Foundation Institute of Molecular Medicine for the Prevention of Human Diseases, Houston, Texas, USA
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Lang F, Böhmer C, Palmada M, Seebohm G, Strutz-Seebohm N, Vallon V. (Patho)physiological significance of the serum- and glucocorticoid-inducible kinase isoforms. Physiol Rev 2006; 86:1151-78. [PMID: 17015487 DOI: 10.1152/physrev.00050.2005] [Citation(s) in RCA: 515] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocorticoids). Similar to its isoforms SGK2 and SGK3, SGK1 is activated by insulin and growth factors via phosphatidylinositol 3-kinase and the 3-phosphoinositide-dependent kinase PDK1. SGKs activate ion channels (e.g., ENaC, TRPV5, ROMK, Kv1.3, KCNE1/KCNQ1, GluR1, GluR6), carriers (e.g., NHE3, GLUT1, SGLT1, EAAT1-5), and the Na+-K+-ATPase. They regulate the activity of enzymes (e.g., glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, phosphomannose mutase-2) and transcription factors (e.g., forkhead transcription factor FKHRL1, beta-catenin, nuclear factor kappaB). SGKs participate in the regulation of transport, hormone release, neuroexcitability, cell proliferation, and apoptosis. SGK1 contributes to Na+ retention and K+ elimination of the kidney, mineralocorticoid stimulation of salt appetite, glucocorticoid stimulation of intestinal Na+/H+ exchanger and nutrient transport, insulin-dependent salt sensitivity of blood pressure and salt sensitivity of peripheral glucose uptake, memory consolidation, and cardiac repolarization. A common ( approximately 5% prevalence) SGK1 gene variant is associated with increased blood pressure and body weight. SGK1 may thus contribute to metabolic syndrome. SGK1 may further participate in tumor growth, neurodegeneration, fibrosing disease, and the sequelae of ischemia. SGK3 is required for adequate hair growth and maintenance of intestinal nutrient transport and influences locomotive behavior. In conclusion, the SGKs cover a wide variety of physiological functions and may play an active role in a multitude of pathophysiological conditions. There is little doubt that further targets will be identified that are modulated by the SGK isoforms and that further SGK-dependent in vivo physiological functions and pathophysiological conditions will be defined.
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Affiliation(s)
- Florian Lang
- Department of Physiology, University of Tuebingen, Tuebingen, Germany.
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Dagenais A, Fréchette R, Clermont ME, Massé C, Privé A, Brochiero E, Berthiaume Y. Dexamethasone inhibits the action of TNF on ENaC expression and activity. Am J Physiol Lung Cell Mol Physiol 2006; 291:L1220-31. [PMID: 16877633 DOI: 10.1152/ajplung.00511.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have reported that TNF, a proinflammatory cytokine present in several lung pathologies, decreases the expression and activity of the epithelial Na(+) channel (ENaC) by approximately 70% in alveolar epithelial cells. Because dexamethasone has been shown to upregulate ENaC mRNA expression and is well known to downregulate proinflammatory genes, we tested if it could alleviate the effect of TNF on ENaC expression and activity. In cotreatment with TNF, we found that dexamethasone reversed the inhibitory effect of TNF and upregulated alpha, beta, and gammaENaC mRNA expression. When the cells were pretreated for 24 h with TNF before cotreatment, dexamethasone was still able to increase alphaENaC mRNA expression to 1.8-fold above control values. However, in these conditions, beta and gammaENaC mRNA expression was reduced to 47% and 14%, respectively. The potential role of TNF and dexamethasone on alphaENaC promoter activity was tested in A549 alveolar epithelial cells. TNF decreased luciferase (Luc) expression by approximately 25% in these cells, indicating that the strong diminution of alphaENaC mRNA must be related to posttranscriptional events. Dexamethasone raised Luc expression by fivefold in the cells and augmented promoter activity by 2.77-fold in cotreatment with TNF. In addition to its effect on alphaENaC gene expression, dexamethasone was able to maintain amiloride-sensitive current as well as the liquid clearance abilities of TNF-treated cells within the normal range. All these results suggest that dexamethasone alleviates the downregulation of ENaC expression and activity in TNF-treated alveolar epithelial cells.
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Affiliation(s)
- André Dagenais
- Centre de recherche, Centre hospitalier de l'Université de Montréal (CHUM)-Hôtel-Dieu, Université de Montréal, Montréal, Québec, Canada.
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Riazi S, Khan O, Tiwari S, Hu X, Ecelbarger CA. Rosiglitazone regulates ENaC and Na-K-2Cl cotransporter (NKCC2) abundance in the obese Zucker rat. Am J Nephrol 2006; 26:245-57. [PMID: 16757903 DOI: 10.1159/000093783] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Accepted: 04/26/2006] [Indexed: 11/19/2022]
Abstract
BACKGROUND/AIMS Progressive diabetes is associated renal remodeling, which we previously showed correlated to reduced protein abundance of several major renal sodium transporters and channel subunits in the obese Zucker rat. Here we test whether rosiglitazone (RGZ), a peroxisome proliferator-activated subtype gamma receptor agonist, would be protective and attenuate these changes. METHODS Male, obese and lean Zucker rats (9 weeks old) were randomly divided (n = 6/group) to receive control diet with or without RGZ at 3 mg/kg.bw/day for 12 weeks. RESULTS RGZ normalized blood glucose and plasma fructosamine levels in obese rats. Obese control rats had relatively increased fractional excretion of sodium (FE(Na), sodium excretion relative to creatinine). Nonetheless, both obese and RGZ-treated rats had relatively higher 24-hour net sodium balances. Immunoblotting revealed obese rats had significantly reduced renal cortical protein abundances of the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) and the sodium hydrogen exchanger (NHE3). RGZ normalized NKCC2 abundance and increased the abundance of the alpha-subunit of the epithelial sodium channel (ENaC). In contrast, in the outer medulla, obese rats had increased abundance of NKCC2, gamma-ENaC (85-kDa), and endothelial NOS. Furthermore, RGZ caused a decrease in the abundance of cortical beta- and gamma-ENaC (85-kDa). Finally, the whole kidney abundances of alpha-1 Na-K-ATPase, alpha- beta-, and gamma-ENaC (70-kDa band) positively correlated with net sodium balance, whereas NKCC2 was negatively correlated to FE(Na). CONCLUSION Chronic RGZ treatment of obese Zucker rats may preserve renal sodium reabsorptive capacity by its indirect actions to attenuate hyperglycemia as well as direct effects on transporter abundance and activity.
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Affiliation(s)
- Shahla Riazi
- Department of Medicine, Division of Endocrinology and Metabolism, Georgetown University, Washington, DC 20057-1412, USA
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Zhang W, Xia X, Jalal DI, Kuncewicz T, Xu W, Lesage GD, Kone BC. Aldosterone-sensitive repression of ENaCalpha transcription by a histone H3 lysine-79 methyltransferase. Am J Physiol Cell Physiol 2005; 290:C936-46. [PMID: 16236820 PMCID: PMC3009459 DOI: 10.1152/ajpcell.00431.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Aldosterone is a major regulator of epithelial Na(+) absorption. One of its principal targets is the epithelial Na(+) channel alpha-subunit (ENaCalpha), principally expressed in the kidney collecting duct, lung, and colon. Models of aldosterone-mediated trans-activation of the ENaCalpha gene have focused primarily on interactions of liganded nuclear receptors with the ENaCalpha gene promoter. Herein, we demonstrate that the murine histone H3 lysine-79 methyltransferase, murine disruptor of telomeric silencing alternative splice variant "a" (mDot1a), is a novel component in the aldosterone signaling network controlling transcription of the ENaCalpha gene. Aldosterone downregulated mDot1a mRNA levels in murine inner medullary collecting ducts cells, which was associated with histone H3 K79 hypomethylation in bulk histones and at specific sites in the ENaCalpha 5'-flanking region, and trans-activation of ENaCalpha. Knockdown of mDot1a by RNA interference increased activity of a stably integrated ENaCalpha promoter-luciferase construct and expression of endogenous ENaCalpha mRNA. Conversely, overexpression of EGFP-tagged mDot1a resulted in hypermethylation of histone H3 K79 at the endogenous ENaCalpha promoter, repression of endogenous ENaCalpha mRNA expression, and decreased activity of the ENaCalpha promoter-luciferase construct. mDot1a-mediated histone H3 K79 hypermethylation and repression of ENaCalpha promoter activity was abolished by mDot1a mutations that eliminate its methyltransferase activity. Collectively, our data identify mDot1a as a novel aldosterone-regulated histone modification enzyme, and, through binding the ENaCalpha promoter and hypermethylating histone H3 K79 associated with the ENaCalpha promoter, a negative regulator of ENaCalpha transcription.
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Affiliation(s)
- Wenzheng Zhang
- Department of Internal Medicine, The University of Texas Medical School at Houston, 6431 Fannin, MSB 1.150, Houston, TX 77030, USA
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Velic A, Gabriëls G, Hirsch JR, Schröter R, Edemir B, Paasche S, Schlatter E. Acute rejection after rat renal transplantation leads to downregulation of NA+ and water channels in the collecting duct. Am J Transplant 2005; 5:1276-85. [PMID: 15888031 DOI: 10.1111/j.1600-6143.2005.00890.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Renal transplantation is associated with alterations of tubular functions and of the renin-angiotensin-aldosterone system. The underlying cellular and molecular mechanisms are unclear. We used an allogeneic rat renal transplantation model of acute rejection with and without immunosuppression by cyclosporine A (CsA) and a syngeneic model as control. Uninephrectomized Lewis or Lewis-Brown-Norway (LBN) rats received a kidney from LBN-rats. Renal transporters and receptors were analyzed by immunohistochemistry, semiquantitative RT-PCR and Western-blot analysis. Intracellular Na(+) was analyzed microfluorimetrically in isolated cortical collecting ducts. mRNA expression and function of the epithelial Na(+)-channel (ENaC) and mRNA and protein expression of the water-channel AQP2 were downregulated in transplanted kidneys undergoing rejection. Expression of the serum- and glucocorticoid-kinase (Sgk1) was decreased and that of the ubiquitin-protein ligase Nedd4-2 was increased. These changes were absent under CsA-therapy and in syngeneic model. Expression and function of the Na(+)-K(+)-ATPase, expression of the secretory K(+)-channel and of the mineralocorticoid receptor remained unchanged. Reduced ENaC function is likely due to decreased Sgk1- and increased Nedd4-2 mRNA expression leading to reduced ENaC expression in the membrane. These acute downregulations of ENaC and AQP2 may be triggered to reduce energy consumption in the distal nephron to protect the kidney immediately after transplantation.
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Affiliation(s)
- Ana Velic
- Universitätsklinikum Münster, Medizinische Klinik und Poliklinik D, Experimentelle Nephrologie, Münster, Germany
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Helms MN, Yu L, Malik B, Kleinhenz DJ, Hart CM, Eaton DC. Role of SGK1 in nitric oxide inhibition of ENaC in Na+-transporting epithelia. Am J Physiol Cell Physiol 2005; 289:C717-26. [PMID: 15843443 DOI: 10.1152/ajpcell.00006.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Several studies have shown that nitric oxide (NO) inhibits Na(+) transport in renal and alveolar monolayers. However, the mechanisms by which NO alters epithelial Na(+) channel (ENaC) activity is unclear. Therefore, we examined the effect of applying the NO donor drug l-propanamine 3,2-hydroxy-2-nitroso-1-propylhidrazino (PAPA-NONOate) to cultured renal epithelial cells. A6 and M1 cells were maintained on permeable supports in medium containing 1.5 microM dexamethasone and 10% bovine serum. After 1.5 microM PAPA-NONOate was applied, amiloride-sensitive short-circuit current measurements decreased 29% in A6 cells and 44% in M1 cells. This differed significantly from the 3% and 19% decreases in A6 and M1 cells, respectively, treated with control donor compound (P < 0.0005). Subsequent application of PAPA-NONOate to amiloride-treated control (no NONOate) A6 and M1 cells did not further decrease transepithelial current. In single-channel patch-clamp studies, NONOate significantly decreased ENaC open probability (P(o)) from 0.186 +/- 0.043 to 0.045 +/- 0.009 (n = 7; P < 0.05) without changing the unitary current. We also showed that aldosterone significantly decreased NO production in primary cultures of alveolar type II (ATII) epithelial cells. Because inducible nitric oxide synthase (iNOS) coimmunoprecipitated with the serum- and glucocorticoid-inducible kinase (SGK1) and both proteins colocalized in the cytoplasm (as shown in our studies in mouse ATII cells), SGK1 may also be important in regulating NO production in the alveolar epithelium. Our study also identified iNOS as a novel SGK1 phosphorylated protein (at S733 and S903 residues in miNOS) suggesting that one way in which SGK1 could increase Na(+) transport is by altering iNOS production of NO.
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Affiliation(s)
- My N Helms
- Dept. of Physiology, Emory University of School of Medicine, Atlanta, GA 30322, USA
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