Tyrosine-protein kinase that acts as a cell-surface receptor for VEGFA, VEGFC and VEGFD. Plays an essential role in the regulation of angiogenesis, vascular development, vascular permeability, and embryonic hematopoiesis. Promotes proliferation, survival, migration and differentiation of endothelial cells. Promotes reorganization of the actin cytoskeleton. Isoforms lacking a transmembrane domain, such as isoform 2, may function as decoy receptors for VEGFA, VEGFC and/or VEGFD. Isoform 2 plays an important role as a negative regulator of VEGFA- and VEGFC-mediated lymphangiogenesis by limiting the amount of free VEGFA and/or VEGFC and by preventing their binding to FLT4. Modulates FLT1 and FLT4 signaling by forming heterodimers. Binding of vascular growth factors to isoform 1 leads to the activation of several signaling cascades. Activation of PLCG1 leads to the production of the cellular signaling molecules diacylglycerol and inositol 1,4,5-trisphosphate and the activation of protein kinase C. Mediates activation of MAPK1/ERK2, MAPK3/ERK1 and the MAP kinase signaling pathway, as well as of the AKT1 signaling pathway. Mediates phosphorylation of PIK3R1, the regulatory subunit of phosphatidylinositol 3-kinase, reorganization of the actin cytoskeleton and activation of PTK2/FAK1. Required for VEGFA-mediated induction of NOS2 and NOS3, leading to the production of the signaling molecule nitric oxide (NO) by endothelial cells. Phosphorylates PLCG1. Promotes phosphorylation of FYN, NCK1, NOS3, PIK3R1, PTK2/FAK1 and SRC. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Present in an inactive conformation in the absence of bound ligand. Binding of VEGFA, VEGFC or VEGFD leads to dimerization and activation by autophosphorylation on tyrosine residues. May be regulated by hydrogen sulfide (H(2)S) levels via a sensitive intracellular disulfide bond (By similarity). Homodimer in the presence of bound dimeric VEGFA, VEGFC or VEGFD ligands; monomeric in the absence of bound ligands. Can also form heterodimers with FLT1/VEGFR1 and KDR/VEGFR2. Interacts (tyrosine phosphorylated) with LFYN, NCK1, PLCG1. Interacts (tyrosine-phosphorylated active form preferentially) with DAB2IP (via C2 domain and active form preferentially); the interaction occurs at the late phase of VEGFA response and inhibits KDR/VEGFR2 activity. Interacts with SHBSH2D2A/TSAD, GRB2, MYOF, CBL and PDCD6 (PubMed:12796773, PubMed:12881528, PubMed:15026417, PubMed:15673613, PubMed:17702744, PubMed:19668192, PubMed:7681362, PubMed:8356051). Interacts (via C-terminus domain) with ERN1 (via kinase domain); the interaction is facilitated in a XBP1 isoform 1- and vascular endothelial growth factor (VEGF)-dependent manner in endothelial cells (By similarity). Interacts (via juxtamembrane region) with chaperone PDCL3 (via thioredoxin fold region); the interaction leads to increased KDR/VEGFR2 abundance through inhibition of its ubiquitination and degradation (By similarity). Interacts (tyrosine phosphorylated) with CCDC88A/GIV (via SH2-like region); binding requires autophosphorylation of the KDR/VEGFR2 C-terminal region (By similarity). Interacts with isoform 2 of BSG (By similarity). Colocalizes with ERN1 and XBP1 in the endoplasmic reticulum in endothelial cells in a vascular endothelial growth factor (VEGF)-dependent manner (By similarity). Localized with RAP1A at cell-cell junctions. Detected on caveolae-enriched lipid rafts at the cell surface. Is recycled from the plasma membrane to endosomes and back again. Phosphorylation triggered by VEGFA binding promotes internalization and subsequent degradation. VEGFA binding triggers internalization and translocation to the nucleus (By similarity). Expressed in endothelial cells (at protein level). Detected in embryonic endothelial cells, as well as hematopoietic stem and progenitor cells. Detected in vascular endothelium. Expressed at high levels in adult heart, lung, kidney, brain and skeletal muscle, but is also expressed at lower levels in most other adult tissues. Expressed in endothelial cells of allantois/umbilical vessels at 8.5 dpc (at protein level). Increases moderately during pregnancy (maximum 2.7-fold at 19 days), and increases further during lactation (maximum 3.7-fold increase on day 7). The second and third Ig-like C2-type (immunoglobulin-like) domains are sufficient for VEGFC binding. N-glycosylated. Ubiquitinated. Tyrosine phosphorylation of the receptor promotes its poly-ubiquitination, leading to its degradation via the proteasome or lysosomal proteases (By similarity). Autophosphorylated on tyrosine residues upon ligand binding. Autophosphorylation occurs in trans, i.e. one subunit of the dimeric receptor phosphorylates tyrosine residues on the other subunit. Phosphorylation at Tyr-949 is important for interaction with SH2D2A/TSAD and VEGFA-mediated reorganization of the actin cytoskeleton. Phosphorylation at Tyr-1173 is important for interaction with PLCG1 and SHB. Phosphorylation at Tyr-1212 is important for interaction with NCK1 and FYN. Dephosphorylated by PTPRJ at Tyr-799, Tyr-949, Tyr-994, Tyr-1052, Tyr-1057, Tyr-1173 and Tyr-1212 (By similarity). The inhibitory disulfide bond between Cys-1022 and Cys-1043 may serve as a specific molecular switch for H(2)S-induced modification that regulates KDR/VEGFR2 function. Embryonic lethality at 8.5 to 9.5 dpc, due to early defects in the development of hematopoietic and endothelial cells, leading to defects in vasculogenesis and endocardium development. At 7.5 dpc, there are no blood islands in the yolk sac. Organized blood vessels are absent in the yolk sac and in the embryo. Belongs to the protein kinase superfamily. Tyr protein kinase family. CSF-1/PDGF receptor subfamily.