KDR, also named as VEGFR-2, FLK1 and CD309, is a receptor for VEGF or VEGFC. KDR which belongs to the protein kinase superfamily, has a tyrosine-protein kinase activity. The VEGF-kinase ligand/receptor signaling system plays a key role in vascular development and regulation of vascular permeability. In case of HIV-1 infection, the interaction with extracellular viral Tat protein seems to enhance angiogenesis in Kaposi's sarcoma lesions. KDR functions as the main mediator of VEGF-induced endothelial proliferation, survival, migration, tubular morphogenesis and sprouting. Mutations of this gene are implicated in infantile capillary hemangiomas.