Required for the proper formation of vascular structures that develop via both vasculogenesis and angiogenesis. Acts as a critical and vascular-specific regulator of GTPase signaling, cell architecture, and adhesion, which is essential for endothelial cell morphogenesis and blood vessel tubulogenesis. Regulates the activity of Rho GTPases in part by recruiting ARHGAP29 and suppressing RhoA signaling and dampening ROCK and MYH9 activities in endothelial cells. May act as effector for Golgi-bound HRAS and other Ras-like proteins. May promote HRAS-mediated transformation. Negative regulator of amino acid starvation-induced autophagy (By similarity). Interacts with Ras family members that have been activated by GTP binding. Interacts with HRAS, RAP1A, RAP2, RRAS, RAF1 and RRAS2 (By similarity). Interacts with MYH9 and ARHGAP29. Associated with perinuclear vesicles. Is recruited to Golgi stacks by activated HRAS (By similarity). Detected in kidney, heart, skeletal muscle, small intestine and lung. Specifically expressed in the endothelium of the developing blood vessels in embryos.