Protein kinase B and rac are activated in parallel within a phosphatidylinositide 3OH-kinase-controlled signaling pathway.

The GTPase Rac and the protein kinase B (PKB) are downstream targets of phosphatidylinositide 3OH-kinase in platelet-derived growth factor-stimulated signaling pathways. We have generated PAE cell lines inducibly expressing mutants of Rac. Use of these cell lines suggests that Rac is involved in both platelet-derived growth factor-stimulated membrane ruffling and the activation of p70(S6K) but not in the activation of PKB. Furthermore, expression of constitutively active alleles of PKB in PAE cells suggests that PKB is able to regulate the activity of p70(S6K) but not the cytoskeletal changes underlying membrane ruffling. Thus, our results indicate that Rac and PKB are on separate pathways downstream of phosphatidylinositide 3OH-kinase in these cells but that both of these pathways are involved in the regulation of p70(S6K).