Flk-1/CD309
CD309 corresponds to VEGF receptor 2, called KDR in humans and Flk-1 in the mouse, the principal endothelial receptor tyrosine kinase transmitting VEGF-A signals during vascular development. VEGFR2 contains seven extracellular immunoglobulin-like domains and a split intracellular kinase, and upon ligand binding it autophosphorylates to activate the PLC-gamma/ERK, PI3K-AKT, and SRC cascades that drive endothelial proliferation, migration, and survival. The receptor is essential for embryonic vasculogenesis, as its deletion halts blood island formation in mice, and it remains the dominant pro-angiogenic receptor in tumors. Consequently VEGFR2 is the target of monoclonal antibodies, TKIs, and tumor-vascular imaging agents, and recombinant CD309 is used extensively in anti-angiogenic drug screening.
