title: Serum- and glucocorticoid-induced kinase 3 in recycling endosomes mediates acute activation of Na+/H+ exchanger NHE3 by glucocorticoids.
abstract: Na(+)/H(+) exchanger 3 (NHE3) is the major Na(+) transporter in the intestine. Serum- and glucocorticoid-induced kinase (SGK) 1 interacts with NHE regulatory factor 2 (NHERF2) and mediates activation of NHE3 by dexamethasone (Dex) in cultured epithelial cells. In this study, we compared short-term regulation of NHE3 by Dex in SGK1-null and NHERF2-null mice. In comparison to wild-type mice, loss of SGK1 or NHERF2 significantly attenuated regulation of NHE3 by Dex but did not completely obliterate the effect. We show that transfection of SGK2 or SGK3 in PS120 cells resulted in robust activation of NHE3 by Dex. However, unlike SGK1 or SGK2, SGK3 rapidly activated NHE3 within 15 min of Dex treatment in both PS120 and Caco-2bbe cells. Immunofluorescence analysis showed that SGK3 colocalized with NHE3 in recycling endosomes, whereas SGK1 and SGK2 were diffusely distributed. Mutation of Arg-90 of SGK3 disrupted the endosomal localization of SGK3 and delayed NHE3 activation. Activation of SGK3 and NHE3 by Dex was dependent on phosphoinositide 3-kinase (PI3K) and phosphoinositide-dependent kinase 1 (PDK1), and Dex induced translocation of PDK1 to endosomes. Our study identifies SGK3 as a novel endosomal kinase that acutely regulates NHE3 in a PI3K-dependent mechanism.
authors.affiliation: Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, GA 30324, USA.
authors.forename: Peijian
authors.initials: P
authors.lastname: He
authors.forename: Sei-Jung
authors.initials: SJ
authors.lastname: Lee
authors.forename: Songbai
authors.initials: S
authors.lastname: Lin
authors.forename: Ursula
authors.initials: U
authors.lastname: Seidler
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: Geza
authors.initials: G
authors.lastname: Fejes-Toth
authors.forename: Aniko
authors.initials: A
authors.lastname: Naray-Fejes-Toth
authors.forename: C Chris
authors.initials: CC
authors.lastname: Yun
mesh_terms: D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology*; D011992:Endosomes / Q000187:drug effects* / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D005786:Gene Expression Regulation; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010957:Plasmids; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D015398:Signal Transduction / Q000235:genetics*; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D003907:Dexamethasone; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D012964:Sodium; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000099184:Serum-Glucocorticoid Regulated Kinases; C000631429:PDK1 protein, human; C000631433:Pdk1 protein, mouse; C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; C093376:sodium-hydrogen exchanger regulatory factor; C504729:Sgk2 protein, mouse; C523602:Sgk3 protein, mouse