p21 (CDKN1A)-activated kinase 4; Activates the JNK pathway. Plays a role in the reorganization of the actin cytoskeleton and in the formation of filopodia. Phosphorylates and inactivates the protein phosphatase SSH1, leading to increased inhibitory phosphorylation of the actin binding/depolymerizing factor cofilin. Decreased cofilin activity may lead to stabilization of actin filaments. Phosphorylates ARHGEF2 (By similarity) (593 aa)