Flt-3

The Flt-3 (fms-like tyrosine kinase) receptor, also named Flk-2 (fetal liver kinase) and Stk1 (stem cell tyrosine kinase) and designated CD135, is a member of the class III subfamily of receptor tyrosine kinases. This familay includes KIT, the receptor for SCF, and C-FMS, the receptor for M-CSF. The extracellular region of these receptors contains five immunoglobulin-like domains and the intracellular region contains a split kinase domain. Mouse Flt3 cDNA encodes a 992 amino acid (aa) residue type I membrane protein with a 27 aa residue signal peptide, a 517 aa extracellular domain with 10 potential N-linked glycosylation sites, a 20 aa residue transmembrane domain and a 428 aa residue cytoplasmic domain. Mouse Flt-3 shares 85% amino acid sequence identity with human Flt3. Flt3 expression has been detected in various tissues, including placenta, gonads, and tissues of nervous and hematopoietic origin. Among hematopoietic cells, the expression of Flt3 was found to be restricted to the highly enriched stem/progenitor cell populations. The ligand for Flt3 (FL) has been identified to be a transmembrane protein with structural homology to M-CSF and SCF. Recombinant soluble Flt3 Fc chimeric protein has been shown to bind FL with high affinity and is a potent FL antagonist.