NITRIC-OXIDE PRODUCTION CONTRIBUTES TO THE ANGIOGENIC PROPERTIES OF VASCULAR ENDOTHELIAL GROWTH-FACTOR IN HUMAN ENDOTHELIAL-CELLS

Vascular endothelial growth factor (VEGF) is a regulator of vasculogen esis and angiogenesis. To investigate the role of nitric oxide (NO) in VEGF-induced proliferation and in vitro angiogenesis, human umbilical vein endothelial cells (HUVEC) were used. VEGF stimulated the growth of HUVEC in an NO-dependent manner, In addition, VEGF promoted the NO- dependent formation of network-like structures in HUVEC cultured in th ree dimensional (3D) collagen gels. Exposure of cells to VEGF led to a concentration-dependent increase in cGMP levels, an indicator of NO p roduction, that was inhibited by nitro-L-arginine methyl ester, VEGF-s timulated NO production required activation of tyrosine kinases and in creases in intracellular calcium, since tyrosine kinase inhibitors and calcium chelators attenuated VEGF-induced NO release. Moreover, two c hemically distinct phosphoinositide 3 kinase (PI-3K) inhibitors attenu ated NO release after VEGF stimulation. In addition, HUVEC incubated w ith VEGF for 24 h showed an increase in the amount of endothelial NO s ynthase (eNOS) protein and the release of NO, In summary, both short-a nd long-term exposure of human EC to VEGF stimulates the release of bi ologically active NO. While long-term exposure increases eNOS protein levels, short-term stimulation with VEGF promotes NO release through m echanisms involving tyrosine and PI-3K kinases, suggesting that NO med iates aspects of VEGF signaling required for EC proliferation and orga nization in vitro.