PROTEIN-KINASE-B AND RAC ARE ACTIVATED IN PARALLEL WITHIN A PHOSPHATIDYLINOSITIDE 30H-KINASE-CONTROLLED SIGNALING PATHWAY

The GTPase Rac and the protein kinase B (PKB) are downstream targets o f phosphatidylinositide 30H-kinase in platelet-derived growth factor-s timulated signaling pathways. We have generated PAE cell lines inducib ly expressing mutants of Rac, Use of these cell lines suggests that Ra c is involved in both platelet-derived growth factor-stimulated membra ne ruffling and the activation of p70(S6K) but not in the activation o f PRE. Furthermore, expression of constitutively active alleles of PKB in PAE cells suggests that PKB is able to regulate the activity of p7 0(S6K) but not the cytoskeletal changes underlying membrane ruffling. Thus, our results indicate that Rac and PRE are on separate pathways d ownstream of phosphatidylinositide SOH-kinase in these cells but that both of these pathways are involved in the regulation of p70(S6K).