Functions as a GTPase-activating protein (GAP) for RHOA and CDC42. Downstream partner of ARF1 which may control Golgi apparatus structure and function. Also required for CTNNA1 recruitment to adherens junctions (By similarity). Interacts with CTNNA1 (By similarity). Interacts with GTP-bound ARF1 and probably ARF6. Localization to the Golgi is dependent on interaction with GTP-bound ARF1. Sumoylated with SUMO2 and SUMO3 in proliferating lymphocytes.