TRANSLOCATION AND ACTIVATION OF AKT2 IN RESPONSE TO STIMULATION BY INSULIN

The AKT2 oncogene encodes a protein-serine/threonine ki nase that was recently shown to be activated by a variety of growth factors. In addi tion, we previously showed that AKT2 is abundant in brown fat and skel etal muscle, tissues that are highly insulin responsive and that play a role in glucose metabolism. In this study, we demonstrate that AKT2 is activated in response to stimulation by insulin in a dose- and time -dependent manner in human ovarian carcinoma cells and that activation of AKT2 is abolished in cells pretreated with wortmannin, an inhibito r of phosphatidylinositol 3-kinase (PI 3-kinase). Activation of AKT2 i s manifested by changes in its phosphorylation state. Immunofluorescen ce experiments demonstrate that AKT2 is translocated to the plasma mem brane after insulin stimulation, and this translocation is abolished b y wortmannin. Both wild-type AKT2 activated by insulin and constitutiv ely active AKT2, which has been targeted to the membrane by the additi on of a myristoylation signal, were found to inactivate glycogen synth ase kinase-3 (GSK-3) in vitro. GSK-3 was not inactivated by a catalyti cally inactive AKT2 mutant. Collectively, these data indicate that act ivation of AKT2 by insulin is mediated by PI 3-kinase and that GSK-3 i s a downstream target of AKT2, suggesting a potentially important role of AKT2 in glycogen synthesis and other GSK-3 signaling pathways. J. Cell. Biochem. 70:433-441, 1998. (C) 1998 Wiley-iiss, Inc.