The activation of protein kinase B by H2O2 or heat shock is mediated by phosphoinositide 3-kinase and not by mitogen-activated protein kinase-activated protein kinase-2

Protein kinase B (PKB) isoforms became activated [and glycogen synthase kinase-3 (GSK3) became inhibited] when mouse Swiss 3T3 fibroblasts were exposed to oxidative stress (H2O2) or heat shock, but not when they were exposed to osmotic shock (0.5 M sorbitol or 0.7 M NaCl), chemical stress (sodium arsenite), the protein-synthesis inhibitor anisomycin, or UV radiation. In contrast, all seven stimuli activated mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP-K2). The activation of MAPKAP-K2 was suppressed by the drug SE 203580, but not by inhibitors of phosphoinositide (phosphatidylinositide, PI) 3-kinase. In contrast, the activation of PKB isoforms and the inhibition of GSK3 by oxidative stress or heat shock were prevented by inhibitors of PI 3-kinase, but not by SE 203580. Thus the activation of PKB by oxidative stress or heat shock is mediated by PI 3-kinase and not by MAPKAP-K2. PKB alpha and PKB gamma were also activated by heat shock and oxidative stress in human embryonic kidney 293 cells and PKB gamma was activated by heat shock in NIH 3T3 cells; in each case activation was suppressed by inhibitors of PI 3-kinase. The activation of PKB isoforms by H2O2 may underlie some of the insulin-mimetic effects of this compound.