GTPase-activating protein for p21-rac and a phorbol ester receptor. Involved in the assembly of neuronal locomotor circuits as a direct effector of EPHA4 in axon guidance (By similarity). Interacts with EPHA4; effector of EPHA4 in axon guidance linking EPHA4 activation to RAC1 regulation. Phosphorylated. Phosphorylation is EPHA4 kinase activity-dependent (By similarity).