Flt-3

The Flt3 (fms-like tyrosine kinase) receptor, also named Flk2 (fetal liver kinase) and Stk1 (stem cell tyrosine kinase) is a member of the class III subfamily of receptor tyrosine kinases that also includes KIT, the receptor for SCF and FMS, the receptor for MCSF. The extracellular region of these receptors contains five immunoglobulin-like domains and the intracellular region contains a split kinase domain. Human Flt3 cDNA encodes a 993 amino acid (aa) residue type I membrane protein with a 26 aa residue signal peptide, a 515 aa extracellular domain with 10 potential N-linked glycosylation sites, a 21 aa residue transmembrane domain and a 431 aa residue cytoplasmic domain. Mouse Flt3 has also been cloned and shown to share 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.