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

• Published in: Pflügers Archiv 2004-04, Vol.448 (1), p.29-35
• Main Authors: Zecevic, Marija, Heitzmann, Dirk, Camargo, Simone M R, Verrey, Francois
• Format: Article
• Language: English
• Subjects: Aldosterone - pharmacology; Animals; Blotting, Western; Electrophoresis, Polyacrylamide Gel; Epithelial Sodium Channels; Female; Gene Expression; Immediate-Early Proteins; Kidney Tubules, Collecting - metabolism; Kidneys; Large Neutral Amino Acid-Transporter 1 - metabolism; Membrane Proteins - metabolism; Nuclear Proteins - genetics; Nuclear Proteins - physiology; Oocytes - metabolism; Protein Transport; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - physiology; Rodents; Sodium; Sodium Channels - metabolism; Sodium-Phosphate Cotransporter Proteins; Sodium-Potassium-Exchanging ATPase - genetics; Sodium-Potassium-Exchanging ATPase - metabolism; Symporters - metabolism; Xenopus laevis
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s00424-003-1222-9

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 glucocorticoid-regulated 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 alpha 1- and Xenopus laevis beta 1-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,K-ATPase 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.