PAK4 and cancer: Of relevance to cancer, several cell cycle regulating genes were found, such as G1/S-specific cyclin E [61], p19INK4d [58], prostate tumor overexpressed gene, serine protease hepsin [57] and those encoding the serine/threonine kinases associated with cell cycle regulation, p21-activated kinase 4 (PAK4) and homeodomain-interacting protein kinase 4.