title: Epithelial sodium channel regulation by cell surface-associated serum- and glucocorticoid-regulated kinase 1.
abstract: Serum- and glucocorticoid-regulated kinase 1 (sgk1) participates in diverse biological processes, including cell growth, apoptosis, and sodium homeostasis. In the cortical collecting duct of the kidney, sgk1 regulates sodium transport by stimulating the epithelial sodium channel (ENaC). Control of subcellular localization of sgk1 may be an important mechanism for modulating specificity of sgk1 function; however, which subcellular locations are required for sgk1-regulated ENaC activity in collecting duct cells has yet to be established. Using cell surface biotinylation studies, we detected endogenous sgk1 at the apical cell membrane of aldosterone-stimulated mpkCCD(c14) collecting duct cells. The association of sgk1 with the cell membrane was enhanced when ENaC was co-transfected with sgk1 in kidney cells, suggesting that ENaC brings sgk1 to the cell surface. Furthermore, association of endogenous sgk1 with the apical cell membrane of mpkCCD(c14) cells could be modulated by treatments that increase or decrease ENaC expression at the apical membrane; forskolin increased the association of sgk1 with the apical surface, whereas methyl-β-cyclodextrin decreased the association of sgk1 with the apical surface. Single channel recordings of excised inside-out patches from the apical membrane of aldosterone-stimulated A6 collecting duct cells revealed that the open probability of ENaC was sensitive to the sgk1 inhibitor GSK650394, indicating that endogenous sgk1 is functionally active at the apical cell membrane. We propose that the association of sgk1 with the apical cell membrane, where it interacts with ENaC, is a novel means by which sgk1 specifically enhances ENaC activity in aldosterone-stimulated collecting duct cells.
authors.affiliation: Department of Medicine, Division of Nephrology, Stanford University, Stanford, California 94305, USA.
authors.forename: Sheela V
authors.initials: SV
authors.lastname: Thomas
authors.forename: Paru P
authors.initials: PP
authors.lastname: Kathpalia
authors.forename: Madhumitha
authors.initials: M
authors.lastname: Rajagopal
authors.forename: Carol
authors.initials: C
authors.lastname: Charlton
authors.forename: Jianning
authors.initials: J
authors.lastname: Zhang
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Eaton
authors.forename: My N
authors.initials: MN
authors.lastname: Helms
authors.forename: Alan C
authors.initials: AC
authors.lastname: Pao
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D047392:beta-Cyclodextrins / Q000494:pharmacology; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D000450:Aldosterone; D001565:Benzoates; D019086:Bridged Bicyclo Compounds, Heterocyclic; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D017346:Protein Serine-Threonine Kinases; D012964:Sodium; D047392:beta-Cyclodextrins; D000099184:Serum-Glucocorticoid Regulated Kinases; C108732:methyl-beta-cyclodextrin; C532254:2-cyclopentyl-4-(5-phenyl-1H-pyrrolo(2,3-b)pyridin-3-yl)-benzoic acid