PAK4 is a member of the PAK family of serine/threonine p21-activating kinases. PAK4 is a target for the GTP-bound Rho GTPase, CDC42, and is an important factor that links Rho GTPases such as Ras to transformation. In this context, PAK4 is highly transforming, and has been found to be highly expressed in some tumor cell lines. PAK4 has been demonstrated to activate the JNK pathway and mediate the formation of filopodia and the reorganization of the actin cytoskeleton. PAK4 has also been found to function as a regulator of prosurvival pathways and senescence.