The role of phosphatidylinositol 3-kinase in vascular endothelial growth factor signaling

Vascular endothelial growth factor (VEGF) receptor Flk-1/KDR in endothelial cells is activated during vasculogenesis and angiogenesis upon ligand-rece ptor interaction. Activated Flk-1/KDR has been shown to recruit Src homolog y 2 domain-containing signaling molecules that are known to serve as links to the activation of the mitogen-activated protein (MAP) kinase signaling p athway. To define the functional significance of phosphatidylinositol (PI) 3-kinase in VEGF signaling, we have examined its role in human umbilical ve in endothelial cell (HUVEC) cycle progression. We show herein that p85, the regulatory subunit of PI 3-kinase, is constitutively associated with Flk-1 /KDR. The treatment of HUVECs with VEGF promoted tyrosine autophosphorylati on of Flk-1/KDR and also induced phosphorylation of p85, This was followed by an increase in the PI 3-kinase activity, which was sensitive to wortmann in, a potent PI 3-kinase inhibitor, VEGF also induced a striking activation of MAP kinase in a time-dependent manner. Inhibition studies with both a d ominant-negative p85 mutant and the PI 3-kinase inhibitor, wortmannin, were employed to show for the first time that VEGF-stimulated PI 3-kinase modul ates MAP kinase activation and nuclear events such as transcription from c- fos promoter and entry into the synthesis (S)-phase, Our data demonstrate t he importance of PI 3-kinase as a necessary signaling component of VEGF-med iated cell cycle progression.