VASCULAR ENDOTHELIAL GROWTH FACTOR-INDUCED IN-VITRO ANGIOGENESIS AND PLASMINOGEN-ACTIVATOR EXPRESSION ARE DEPENDENT ON ENDOGENOUS BASIC FIBROBLAST GROWTH-FACTOR

Induction of in vitro angiogenesis and upregulation of urokinase-and t issue type-plasminogen activator (uPA, tPA) expression are two hallmar ks of vascular endothelial growth factor (VEGF) activity on cultured e ndothelial cells. We report here that neutralizing antibodies to basic fibroblast growth factor (bFGF) inhibit VEGF-induced in vitro angioge nesis in bovine microvascular endothelial (BME) cells, Analysis of VEG F receptor-2 (VEGFR-2) expression revealed no alteration in VEGFR-2 mR NA or total protein in anti-bFGF antibody-treated BME or bovine aortic endothelial (BAE) cells, Ethidium bromide/agarose gel electrophoresis on the cytosolic fraction of BME cells revealed a basal level of frag mented DNA that was increased by anti-bFGF antibodies to an extent not exceeding that observed in parallel cultures incubated with concentra tions of transforming growth factor-pr that increase VEGF-induced in v itro angiogenesis, In both BME and BAE cells, antibodies to bFGF also decreased basal levels of cell-associated uPA activity, and completely blocked the VEGF-mediated increase in uPA and tPA expression observed in parallel cultures incubated with VEGP alone. In contrast, PA inhib itor-1 expression was strongly upregulated in BME and BAE cells incuba ted with antibodies to bFGF, either alone or in combination with VEGF, These findings demonstrate that: (1) VEGF-induced in vitro angiogenes is and PA expression are dependent on endogenous bFGF, (2) that this p henomenon is not mediated by a decrease in VEGFR-2 expression and that apoptosis does not necessarily correlate with inhibition of invasion, and (3) that inhibition of endogenous bFGF in VEGF-treated cells resu lts in a net antiproteolytic (and possibly also anti-adherent) effect, which could account in part for the inhibitory effect of the anti-bFG F antibodies, These findings point to a novel and unsuspected role for endogenous bFGF in regulating VEGF-induced in vitro angiogenesis.