Role of serum and glucocorticoid-regulated protein kinase (SGK) on insulin signaling pathway

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1. Identification of SGK1 interacting proteinIn order to identify protein(s) which interact with SGK1, two hybrid screen was carried out using human brain cDNA library. Adaptor protein Mint2 which possesses two PDZ domains and phosphotyrosine binding domain (PBD) was identified. SGK1 interacted with PDZ domain which exists at C-terminal but not with N-terminal PDZ domain and PBD. The interaction of SGK1 and Mint2 proteins was increased by treatment of cells with hydrogen peroxide, one of the activator of SGK1.2. Involvement of SGK isoforms in regulation of K+ channelsSGK1 was originally identified as a glucocoticoid sensitive gene. Subsequently SGK1 was shown to activate ion channels including K+ channel. Recently two homologous kinases, SGK2 and SGK3 have been cloned. To elucidate the role of SGK isoforms on regulation of K+ channel, effect of expression of these isoforms on electrical properties of renal epithelial cells. Transfection of SGK1, SGK2 or SGK3 increased the voltage-gated K+ current indicating strong stimulating effect of all three isoforms of SGK on K.+ channels.