Tyrosine-protein kinase that acts as cell-surface receptor for the cytokine FLT3LG and regulates differentiation, proliferation and survival of hematopoietic progenitor cells and of dendritic cells. Promotes phosphorylation of SHC1 and AKT1, and activation of the downstream effector MTOR. Promotes activation of RAS signaling and phosphorylation of downstream kinases, including MAPK1/ERK2 and/or MAPK3/ERK1. Promotes phosphorylation of FES, FER, PTPN6/SHP, PTPN11/SHP-2, PLCG1, and STAT5A and/or STAT5B. Activation of wild-type FLT3 causes only marginal activation of STAT5A or STAT5B. Mutations that cause constitutive kinase activity promote cell proliferation and resistance to apoptosis via the activation of multiple signaling pathways. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Present in an inactive conformation in the absence of bound ligand. FLT3LG binding leads to dimerization and activation by autophosphorylation. Monomer in the absence of bound FLT3LG. Homodimer in the presence of bound FLT3LG. Interacts with FIZ1 following ligand activation (By similarity). Interacts with FES, FER, LYN, FGR, HCK, SRC and GRB2. Interacts with PTPRJ/DEP-1 and PTPN11/SHP2. Interacts with RNF115 and RNF126 (By similarity). (Microbial infection) Interacts with human cytomegalovirus protein UL7. Constitutively activated mutant forms with internal tandem duplications are less efficiently transported to the cell surface and a significant proportion is retained in an immature form in the endoplasmic reticulum lumen. The activated kinase is rapidly targeted for degradation. Detected in bone marrow, in hematopoietic stem cells, in myeloid progenitor cells and in granulocyte/macrophage progenitor cells (at protein level). Detected in bone marrow, liver, thymus, spleen and lymph node, and at low levels in kidney and pancreas. Highly expressed in T-cell leukemia. The juxtamembrane autoregulatory region is important for normal regulation of the kinase activity and for maintaining the kinase in an inactive state in the absence of bound ligand. Upon tyrosine phosphorylation, it mediates interaction with the SH2 domains of numerous signaling partners. In-frame internal tandem duplications (ITDs) result in constitutive activation of the kinase. The activity of the mutant kinase can be stimulated further by FLT3LG binding. N-glycosylated, contains complex N-glycans with sialic acid. Autophosphorylated on several tyrosine residues in response to FLT3LG binding. FLT3LG binding also increases phosphorylation of mutant kinases that are constitutively activated. Dephosphorylated by PTPRJ/DEP-1, PTPN1, PTPN6/SHP-1, and to a lesser degree by PTPN12. Dephosphorylation is important for export from the endoplasmic reticulum and location at the cell membrane. Rapidly ubiquitinated by UBE2L6 and the E3 ubiquitin-protein ligase SIAH1 after autophosphorylation, leading to its proteasomal degradation. The gene represented in this entry may be involved in disease pathogenesis. Somatic mutations that lead to constitutive activation of FLT3 are frequent in AML patients. These mutations fall into two classes, the most common being in-frame internal tandem duplications of variable length in the juxtamembrane region that disrupt the normal regulation of the kinase activity. Likewise, point mutations in the activation loop of the kinase domain can result in a constitutively activated kinase. Can be used as diagnostic tool to establish the exact cause of acute myeloid leukemia, and to determine the optimal therapy. Belongs to the protein kinase superfamily. Tyr protein kinase family. CSF-1/PDGF receptor subfamily.