The p21 activated protein kinases (PAK) are a growing family of serine/threonine protein kinases which are activated in response to extracellular signals and regulate diverse cellular functions including cytoskeletal actin assembly, neurite outgrowth, cell cycle control and apoptosis.The GTPase family proteins Cdc42 and Rac are the major activators of PAKs. The GTP bound forms of Cdc42 and Rac regulate assembly of the actin cytoskeleton, in part by stimulation of PAKs and in part by activation of the intermediate switch proteins, WASP and N-WASP. PAKs respond to receptor mediated signals that direct their recruitment to the plasma membrane followed by their activation. Major receptors that activate PAK signaling include RTK and integrins...