title: The serum and glucocorticoid-inducible kinase SGK1 and the Na+/H+ exchange regulating factor NHERF2 synergize to stimulate the renal outer medullary K+ channel ROMK1.
abstract: Mineralocorticoids stimulate Na(+) reabsorption and K(+) secretion in principal cells of connecting tubule and collecting duct. The involved ion channels are ENaC and ROMK1, respectively. In Xenopus oocytes, the serum and glucocorticoid-sensitive kinase SGK1 has been shown to increase ENaC activity by enhancing its abundance in the plasma membrane. With the same method, ROMK1 appeared to be insensitive to regulation by SGK1. On the other hand, ROMK1 has been shown to colocalize with NHERF2, a protein mediating targeting and trafficking of transport proteins into the cell membrane. The present study has been performed to test whether NHERF2 is required for regulation of ROMK1 by SGK1. Coexpression of neither NHERF2 nor SGK1 with ROMK1 increases ROMK1 activity. However, coexpression of NHERF2 and SGK1 together with ROMK1 markedly increases K(+) channel activity. The combined effect of SGK1 and NHERF2 does not significantly alter the I/V relation of the channel but increases the abundance of the channel in the membrane and decreases the decay of channel activity after inhibition of vesicle insertion with brefeldin. Coexpression of NHERF2 and SGK1 does not modify cytosolic pH but leads to a slight shift of pK(a) of ROMK1 to more acidic values. In conclusion, NHERF2 and SGK1 interact to enhance ROMK1 activity in large part by enhancing the abundance of channel protein within the cell membrane. This interaction allows the integration of genomic regulation and activation of SGK1 and NHERF2 in the control of ROMK1 activity and renal K(+) excretion.
authors.affiliation: Department of Medicine, Division of Digestive Disease, Emory University, Atlanta, Georgia, USA.
authors.forename: C Chris
authors.initials: CC
authors.lastname: Yun
authors.forename: Monica
authors.initials: M
authors.lastname: Palmada
authors.forename: Hamdy M
authors.initials: HM
authors.lastname: Embark
authors.forename: Olga
authors.initials: O
authors.lastname: Fedorenko
authors.forename: Yuxi
authors.initials: Y
authors.lastname: Feng
authors.forename: Guido
authors.initials: G
authors.lastname: Henke
authors.forename: Iwan
authors.initials: I
authors.lastname: Setiawan
authors.forename: Christoph
authors.initials: C
authors.lastname: Boehmer
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Weinman
authors.forename: Sabrina
authors.initials: S
authors.lastname: Sandrasagra
authors.forename: Christoph
authors.initials: C
authors.lastname: Korbmacher
authors.forename: Philip
authors.initials: P
authors.lastname: Cohen
authors.forename: David
authors.initials: D
authors.lastname: Pearce
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000502:physiology*; D005260:Female; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D009865:Oocytes; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017923:Sodium-Hydrogen Exchangers; D014982:Xenopus laevis; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D020126:Brefeldin A; D003598:Cytoskeletal Proteins; D017874:Immediate-Early Proteins; D009687:Nuclear Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D017923:Sodium-Hydrogen Exchangers; D000099184:Serum-Glucocorticoid Regulated Kinases; C510692:Kcnj1 protein, rat; C498832:Slc9a3r2 protein, rat