STIMULATION OF ENDOTHELIAL-CELL MIGRATION BY VASCULAR-PERMEABILITY FACTOR VASCULAR ENDOTHELIAL GROWTH-FACTOR THROUGH COOPERATIVE MECHANISMSINVOLVING THE ALPHA(V)BETA(3) INTEGRIN, OSTEOPONTIN, AND THROMBIN

We have identified several mechanisms by which the angiogenic cytokine vascular permeability factor/vascular endothelial growth factor (VPF/ VEGF) likely regulates endothelial cell (EC) migration. VPF/VEGF induc ed dermal microvascular EC expression of mRNAs encoding to the alpha(v ) and beta(3) integrin subunits resulting in increased levels of the a lpha(v) beta(3) heterodimer at the cell surface, and VPF/VEGF also ind uced mRNA encoding osteopontin (OPN), an alpha(v) beta(3) ligand. OPN promoted EC migration in vitro; and VPF/VEGF induction of alpha(v) bet a(3) was accompanied by increased EC migration toward OPN. Because thr ombin cleavage of OPN results in substantial enhancement of OPN's adhe sive properties, and because VPF/VEGF promotes increased microvascular permeability leading to activation of the extrinsic coagulation pathw ay, we also investigated whether VPF/VEGF facilitates thrombin cleavag e of OPN in vivo. Consistent with this hypothesis, co-injection of VPF /VEGF together with OPN resulted in rapid cleavage of OPN by endogenou s thrombin. Furthermore, in comparison with native OPN, thrombin-cleav ed OPN stimulated a greater rate of EC migration in vitro, which was a dditive to the increased migration associated with induction of alpha( v) beta(3). Thus, these data demonstrate cooperative mechanisms for VP F/VEGF regulation of EC migration involving the alpha(v) beta(3) integ rin, the alpha(v) beta(3) ligand OPN, and thrombin cleavage of OPN. Th ese findings also illustrate an operational link between VPF/VEGF indu ction of EC gene expression and VPF/VEGF enhancement of microvascular permeability, suggesting that these distinct biological activities may act coordinately to stimulate EC migration during angiogenesis.