P70 S6 KINASE IS ACTIVATED BY SODIUM ARSENITE IN ADULT-RAT CARDIOMYOCYTES - ROLES FOR PHOSPHATIDYLINOSITOL 3-KINASE AND P38 MAP KINASE

p70 S6 kinase (p70 S6k) is important in regulating a variety of cellul ar functions including mRNA translation and cell cycle progression and is activated by mitogens and hormones, Unexpectedly, we have found th at, in adult rat cardiomyocytes, arsenite, which generally induces str ess responses, markedly and rapidly activates p70 S6k, This activation of p70 S6k is completely blocked by rapamycin but only partially prev ented by inhibitors of phosphatidylinositol 3-kinase. In trying to del ineate the mechanism underlying this effect, we found that arsenite di d not activate protein kinase B, JNK or MAP kinase, but did activate p 38 MAP kinase in cardiac myocytes. A specific inhibitor of p38 MAP kin ase (SB203580) partially attenuated the stimulation of p70 S6k by arse nite. These data indicate that the activation of p70 S6k by arsenite i nvolves p38 MAP kinase and phosphatidylinositol 3-kinase but not PKB. (C) 1997 Academic Press.