SGK1 increases Na,K-ATP cell-surface expression and function in Xenopus laevis oocytes

Abstract

The Na + -retaining hormone aldosterone increases the cell-surface expression of the luminal epithelial sodium channel (ENaC) and the basolateral Na + pump (Na,K-ATPase) in aldosterone-sensitive distal nephron cells in a coordinated fashion. To address the question of whether aldosterone-induced serum and glucocorticoidregulated kinase-1 (SGK1) might be involved in mediating this regulation of Na,K-ATPase subcellular localization, similar to that of the epithelial Na + channel (ENaC), we co-expressed the Na,K-ATPase (rat α1-and Xenopus laevis β1-subunits) and Xenopus SGK1 in Xenopus oocytes. Measurements of the Na + pump current showed that wild-type SGK1 increases the function of exogenous Na,K-ATPase at the surface of Xenopus oocytes. This appeared to be secondary to an increase in Na,K-ATPase cell-surface expression as visualized by Western blotting of surface-biotinylated proteins. In contrast, the functional surface expression of two other exogenous transporters, the heterodimeric amino acid transporter LAT1-4F2hc and the Na + /phosphate cotransporter NaPi-IIa, was not increased by SGK1 co-expression. The total pool of exogenous Na,K-ATPase was increased by the co-expression of SGK1, and similarly also by ENaC co-expression. This latter effect depended on the [Na + ] of the buffer and was not additive to that of SGK1. When the total Na,KATPase was increased by ENaC co-expression, SGK1 still increased Na,K-ATPase cell-surface expression. These observations in Xenopus oocytes suggest the possibility that SGK1 induction and/or activation could participate in the coordinated regulation of Na,K-ATPase and ENaC cell-surface expression in the aldosterone-sensitive distal nephron.

Orphan Transporter SLC6A18 Is Renal Neutral Amino Acid Transporter B0AT3

“…Protein Preparation and Western Blot Analysis-Oocyte homogenization and protein preparation was done as described previously (14). Surface labeling of oocytes expressing XT2 alone or co-expressed with ACE2 or Collectrin using MTSEABiotin (Sigma) and streptavidin precipitation were performed as previously described (15).…”

Role of Epithelial Sodium Channels and Their Regulators in Hypertension

“…SGK1 may also indirectly enhance ENaC P o through effects on membrane-bound channel-activating serine proteases (53,66). Furthermore, in addition to its effects on ENaC, SGK1 has been shown to stimulate the activity of the basolateral Na ϩ ,K ϩ -ATPase, which separately increases ENaC-mediated Na ϩ transport (67,68). The relative importance of these effects compared with the Nedd4-2-dependent inhibition has, however, not been determined (63).…”

Resistance of mice lacking the serum- and glucocorticoid-inducible kinase SGK1 against salt-sensitive hypertension induced by a high-fat diet

“…Besides ENaC, SGK1 enhances the activity of further renal transport systems, including the apical K ϩ channel (ROMK) (56,76), the Na ϩ -K ϩ -ATPase (36,61,77), the Na ϩ -K ϩ -2Cl Ϫ cotransporter (NKCC2) (46), the epithelial Ca 2ϩ channel (TRPV5) (30,54), the Na ϩ /H ϩ exchanger type 3 (NHE3) (75,76), and the K ϩ channel (KCNE1) (29). Considering the significance of renal Na ϩ transport for blood pressure regulation (47,49), the effects of SGK1 on ENaC were expected to influence blood pressure.…”