Rac and Cdc42 induce actin polymerization and G1 cell cycle progression independently of p65(PAK) and the JNK/SAPK MAP kinase cascade

Rac and Cdc42 regulate a variety of responses in mammalian cells including formation of lamellipodia and filopodia, activation of the JNK MAP kinase cascade, and induction of G1 cell cycle progression. Pac is also one of the downstream targets required for Ras-induced malignant transformation. Pac and Cdc42 containing a Y40C effector site substitution no longer intact with the Ser/Thr kinase p65(PAK) and are unable to activate the JNK MAP kinase pathway. However, they still induce cytoskeletal changes and G1 cell cycle progression. Rac containing an F37A effector site substitution, on the other hand, no longer interacts with the Ser/Thr kinase p160(ROCK) and is unable to induce lamellipodia or G1 progression. We conclude that Pac and Cdc42 control MAP kinase pathways and actin cytoskeleton organization independently through distinct downstream targets.