INVOLVEMENT OF PHOSPHATIDYLINOSITIDE 3'-KINASE AND RAC IN PLATELET-DERIVED GROWTH FACTOR-INDUCED ACTIN REORGANIZATION AND CHEMOTAXIS

Previous work has suggested a role for phosphatidylinositide 3'-kinase (PI3-kinase) in platelet-derived growth factor (PDGrF)-induced actin reorganization and chemotaxis. In support of this notion, we show in t his report that the PI3-kinase inhibitor wortmannin inhibits chemotaxi s of PDGrF beta-receptor expressing porcine aortic endothelial (PAE/PD GFR-beta) cells. Treatment with wortmannin resulted in a dose-dependen t decrease in chemotaxis with an IC50 value of about 15 - 20 nM. Highe r concentrations of wortmannin also reduced basal random migration of transfected cells in the absence of PDGF. We also investigated the rol e of Rac in PDGF-induced actin reorganization and cell motility, Overe xpression of wt Rac in PAE/PDGFR-beta cells led to an increased cell m otility and edge ruffling in response to PDGF-BB, compared to control cells, In PAE/PDGFR-beta cells transfected with inducible V12Rac (a co nstitutively active Rac mutant), membrane ruffling occurred in the abs ence of PDGF stimulation and was independent of PI3-kinase activity. O n the other hand, PAE/PDGFR-beta cells transfected with inducible N17R ac (a dominant negative Rac mutant) failed to show membrane ruffling i n response to PDGF stimulation. Together with previous observations th ese data indicate that activation of PI3-kinase is crucial for initiat ion of PDGF-induced cell motility responses and that Rac has a major r ole downstream of PI3-kinase, in this pathway. (C) 1997 Academic Press .