Vascular endothelial growth factor receptor-2 (VEGFR-2/Flk-1/KDR) is the primary receptor for VEGF in endothelial cells. Other VEGFR family members, VEGFR-1 (Flt-1) and VEGFR-3 (Flt-4), can also transduce the intracellular signals of VEGF. However, the role of VEGFR-1 is observed mainly during embryonic angiogenesis and VEGFR-3 signaling may be restricted to specific types of endothelial cells. Major autophosphorylation sites of VEGFR-2 are located in the kinase insert domain (Tyr-951/996) and in the tyrosine kinase catalytic domain (Tyr-1054/1059). Other sites, Tyr-1175 and Tyr-1212 provide docking sites for downstream signaling molecules. Activation of VEGFR-2 also phosphorylates Tyr-801, leading to PI3-kinase-Akt activation and increases in endothelial nitric oxide synthase activity. Phosphorylation of mutliple sites in VEGFR-2 is required for downstream activation of several signaling pathways that control proliferation, chemotaxis, and sprouting during angiogenesis.
