Regulates vascular tubulogenesis in vivo. Inhibits platelet-derived growth factor (PDGF)-BB-induced smooth muscle cell migration and promotes endothelial cell adhesion to the extracellular matrix and angiogenesis. Interacts with ITGAV/ITGB3 in an RGD-dependent manner, increasing endothelial cell's motility. Expressed specifically by endothelial cells of the highly vascularized organs heart, lung and kidney. Expressed early during mouse embryogenesis in the yolk sac mesoderm and in the developing vascular system. At 7.5 dpc, it is expressed in the primitive blood islands where the first endothelial cells differentiate. At 10.5 and 13.5 dpc expression is restricted to endothelial cells.