Acts as a ligand for the urokinase plasminogen activator surface receptor. Plays a role in angiogenesis by inducing endothelial cell migration and the formation of vascular network (cords). Involved in cellular migration and adhesion. Increases the phosphorylation levels of FAK. Interacts with and increases the mitogenic activity of HGF. Promotes synapse formation. Required for ultrasonic vocalizations. Forms homooligomers. Interacts with PLAUR (via the UPAR/Ly6 domains), ADAMTS4 and CTSB. Interacts with HGF; the interaction increases the mitogenic activity of HGF (By similarity). Expressed in angiogenic endothelial cells (at protein level). Contains chondroitin sulfate chains. Truncated N-terminus. Truncated N-terminus.