SGK1, Active

SGK1 is a member of the serum- and glucocorticoid-induced protein kinase that is activated in vitro by 3-phosphoinositide-dependent protein kinase-1 (PDK1) and in vivo in response to signals that activate phosphatidylinositol (PI) 3-kinase (1). SGK1, mRNA is expressed in all tissues and the levels of SGK1 mRNA is increased by stimulation with serum or dexamethasone. SGK1 promotes cell survival by phosphorylating and inactivating FKHRL1. SGK and Akt display differences with respect to the efficacy with which they phosphorylate the three regulatory sites on FKHRL1. While both kinases can phosphorylate Thr-32, SGK1 displays a marked preference for Ser-315 whereas Akt favors Ser-253. These findings suggest that SGK1 and Akt may coordinately regulate the function of FKHRL1 by phosphorylating this transcription factor at distinct sites. Like PKB, SGK1 preferentially phosphorylate Ser and Thr residues that lie in Arg-Xaa-Arg-Xaa-Xaa-Ser/Thr motifs. SGK1 gene has recently been identified as an important aldosterone-induced protein kinase that mediates trafficking of the renal epithelial Na(+) channel (ENaC) to the cell membrane. Thus, SGK1 is an appealing candidate for blood pressure regulation and possibly essential hypertension (3).