Extracellular matrix-bound vascular endothelial growth factor promotes endothelial cell adhesion, migration, and survival through integrin ligation

Vascular endothelial growth factor (VEGF), a major factor mediating endothelial cell survival, migration, and proliferation during angiogenesis, is expressed as five splice variants (121, 145, 165, 189, and 206 aminoacids) encoded by a single gene. Although the three shorter isoforms are mainly diffusible, the two longer ones are sequestered in cell membranes after secretion. However, their potential role as true components of the extracellular matrix has not been investigated. We determined that endothelial cells could adhere and spread on VEGF(189) and VEGF(165), but not on VEGF(121). Adhesion was mediated by the alpha3beta1 and alphavbeta3 integrins and other alphav integrins but not by the cognate VEGF receptors. Cells migrated on VEGF(165) and VEGF(189) and displayed a stellate morphology with numerous lamellopodia and FAK staining but no actin stress fibers. Tumstatin, an antiangiogenic peptide that interacts with the alphavbeta3 integrin, could inhibit adhesion on VEGF, and this effect was potentiated by anti-alphavbeta3 blocking antibody. Immobilized VEGF almost totally abolished endothelial cell apoptosis through interactions with integrins. The inhibition of alphavbeta3 engagement with immobilized VEGF by tumstatin inhibited most of its survival activity. We have thus determined a new VEGF receptor-independent role for immobilized VEGF in supporting cell adhesion and survival through interactions with integrins.