CKIT

KIT is a type III receptor tyrosine kinase encoded by a gene locus on the long arm of chromosome 4. It is closely related to Fms-like tyrosine kinase 3 (FLT3), platelet-derived growth factor receptor alpha and beta (PDGFRa, PDGFRß), and colony-stimulating factor 1 receptor (CSF1R). Depending on its degree of glycosylation, the molecular mass of KIT is 140-160 kD. KIT is normally expressed on the surface of hematopoietic stem and progenitor cells, mast cells, melanocytes, germ cells, and interstitial cells of Cajal. There are both transmembrane and soluble forms of KIT; however, the transmembrane form is believed to be biologically active, while the role of soluble KIT is poorly understood. The ligand for KIT is stem cell factor (SCF), also known as steel factor or mast cell growth factor. Both soluble and membrane-bound forms of SCF exist, resulting from alternative splicing of exon 6 (Broudy, Blood 90:1345-1364, 1997; Heinrich et al., J Clin Oncol 20:1692-1703, 2002; Lennartsson and Ronnstrand, Curr Cancer Drug Targets 6:65-75, 2006).