Background information
p21-activated kinases (PAKs) belong to the family of serine/threonine kinases involved in the control of various cellular processes, including the cell cycle, dynamics of the cytoskeleton, apoptosis, oncogenic transformation, and transcription. All PAK family members are characterized by the presence of p21-binding domain. p21-activated kinases are regulated by the small GTP-binding proteins Rac and Cdc42, and lipids, which stimulate autophosphorylation and phosphorylation of exogenous substrates. Serine (Ser-474) is the likely autophosphorylation site in the kinase domain of PAK4 in vivo. Phosphospecific directed against serine 474 detect activated PAK4 on the Golgi membrane when PAK4 is co-expressed with activated Cdc42. Current data strongly implicates PAK-4 in oncogenesis. PAK4 is frequently overexpressed in human tumor cell lines of various tissue origins. Serine/threonine protein kinase that plays a role in a variety of different signaling pathways including cytoskeleton regulation, cell migration, proliferation or cell survival. Activation by various effectors including growth factor receptors or active CDC42 and RAC1 results in a conformational change and a subsequent autophosphorylation on several serine and/or threonine residues. Phosphorylates the proto-oncogene RAF1 and stimulates its kinase activity. Promotes cell survival by phosphorylating the BCL2 antagonist of cell death BAD. Phosphorylates CTNND1, probably to regulate cytoskeletal organization and cell morphology. Keeps microtubules stable through MARK2 inhibition and destabilizes the F-actin network leading to the disappearance of stress fibers and focal adhesions.
