Vascular endothelial growth factor signals endothelial cell production of nitric oxide and prostacyclin through Flk-1/KDR activation of c-Src

Vascular endothelial growth factor (VEGF) is a potent endothelial cell- specific mitogen that promotes angiogenesis, vascular hyperpermeability, and vasodilation by autocrine mechanisms involving nitric oxide (NO) and prostacyclin (PGI₂) production. These experiments used immunoprecipitation and immunoassay procedures to characterize the signaling pathways by which VEGF induces NO and PGI₂ formation in cultured endothelial cells. The data showed that VEGF stimulates complex formation of the flk-1/kinase-insert domain-containing receptor (KDR) VEGF receptor with c-Src and that Src activation is required for VEGF induction of phospholipase C γ1 activation and inositol 1,4,5-trisphosphate formation. Reporter cell assays showed that VEGF promotes a ~50-fold increase in NO formation, which peaks at 5-20 min. This effect is mediated by a signaling cascade initiated by flk-1/KDR activation of c-Src, leading to phospholipase C γ1 activation, inositol 1,4,5-trisphosphate formation, release of [Ca²⁺](i) and nitric oxide synthase activation. Immunoassays of VEGF-induced 6-keto prostaglandin F(1α) formation as an indicator of PGI₂ production revealed a 3-4-fold increase that peaked at 45-60 min. The PGI₂ signaling pathway follows the NO pathway through release of [Ca²⁺](i), but diverges prior to NOS activation and also requires activation of mitogen-activated protein kinase. These results suggest that NO and PGI₂ function in parallel in mediating the effects of VEGF.