Ras-related protein Rab-21 (RAB21) belongs to the Ras superfamily of small GTP-binding proteins. Rab21 is an integrin-associated protein and a positive regulator of integrin traffic. Rab21 associates with the cytoplasmic domains of alpha-integrin chains and their expression influences the endo/exocytic traffic of integrins. This function of Rab21 depends on its GTP/GDP cycle and right membrane targeting.