The p21-activated kinase (PAK) family of serine/threonine kinases is engaged in multiple cellular processes, including cytoskeletal recognization, MAPK signaling, apoptotic signaling, control of phagocytes, NADPH oxidase and growth factor-induced neurite outgrowth. Research indicates that phosphorylation of serine 139 of PAK3 which is located in the kinase inhibitory domain, affects the kinase activity.