Plexin-A's are GAPs for the Ras family GTPase R-Ras. On stimulation with Rnd-1, plexin-A directly and specifically down regulates R-Ras activity. R-Ras activity is critical for PI3K activation and ECM-mediated beta1 integrin activation and cell migration. Inactivation of R-Ras by Sema3A/Plexin-A1 reduces integrin-mediated adhesions. It has been suggested that the final step in the Sema3A repulsive signaling pathway is inhibition of integrin activity. Reduced integrin activity allows detachment from the substratum and subsequent cell retraction.