Human Vascular endothelial growth factor receptor 1(VEGFR-1, FLT-1) is a member of the the class III subfamily of receptor tyrosine kinases (RTKs) and Tyr protein kinase family and CSF-1/PDGF receptor subfamily. VEGFR-1 is widely expressed in human tissues including normal lung, placenta, liver, kidney, heart and brain tissues. It is specifically expressed in most of the vascular endothelial cellsand peripheral blood monocytes. VEGFR-1 contains seven Ig-like C2-type domains and one protein kinase domain. VEGFR-1is an essential receptor tyrosine kinase and plays an important role in theregulation of VEGF family-mediated vasculogenesis, angiogenesis, and lymphangiogenesis. It is also mediators of neurotrophic activity and regulators of hematopoietic development. VEGFR-1 is a receptor for VEGF, VEGFB and PGF. It has a tyrosine-protein kinase activity. Tyrosine-protein kinase that acts as a cell-surface receptor for VEGFA, VEGFB and PGF.It may play an essential role as a negative regulator of embryonic angiogenesis by inhibiting excessive proliferation of endothelial cells and promote endothelial cell proliferation, survival and angiogenesis in adulthood. Its function in promoting cell proliferation seems to be cell-type specific. VEGFR-1 can also promote PGF-mediated proliferation of endothelial cells, proliferation of some types of cancer cells, but does not promote proliferation of normal fibroblasts (in vitro).