Hypothetical model for the role of αv integrins in angiogenesis. Angiogenic stimulus by growth factors induces expression of αvβ3 and causes cells to invade the surrounding ECM and enter the cell cycle. When ligation of αv integrins is blocked, proliferating vascular cells undergo apoptosis, accompanied by an increase in p53 activity. Angiogenic growth factors induce the activation of Ras/MAP kinase in vascular cells and lead to cell proliferation, differentiation, and migration.