Role of SGK in hormonal regulation of epithelial sodium channel in A6 cells

The purpose of this study was to examine the role of the serum- and glucocorticoid-induced kinase (SGK) in the activation of the epithelial sodium channel (ENaC) by aldosterone, arginine vasopressin (AVP), and insulin. We used a tetracycline-inducible system to control the expression of wild-type (SGK wtT ), constitutively active (S425D mutation; SGK S425DT ), or inactive (K130M mutation; SGK K130MT ) SGK in A6 cells independently of hormonal stimulation. The effect of SGK expression on ENaC activity was monitored by measuring transepithelial amiloride-sensitive short-circuit current ( I sc) of transfected A6 cell lines. Expression of SGK wtT or SGK S425DT and aldosterone stimulation have additive effects on I sc. Although SGK could play some role in the aldosterone response, our results suggest that other mechanisms take place. SGK S425DT abrogates the responses to AVP and insulin; hence, in the signaling pathways of these hormones there is a shared step that is stimulated by SGK. Because AVP and insulin induce fusion of vesicles to the apical membrane, our results support the notion that SGK promotes incorporation of channels in the apical membrane.