Gene Summary: Kit gene encodes the human homolog of the proto-oncogene c-kit. C-kit was first identified as the cellular homolog of the feline sarcoma viral oncogene v-kit. This C-kit protein is a type 3 transmembrane receptor for MGF (mast cell growth factor, also known as stem cell factor). Mutations in this Kit gene are associated with gastrointestinal stromal tumors, mast cell disease, acute myelogenous lukemia, and piebaldism. Multiple transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]General information above from NCBI
Catalytic activity: ATP + a [protein]-L-tyrosine = ADP + a [protein]-L-tyrosine phosphate.
Enzyme regulation: Present in an inactive conformation in the absence of bound ligand. KITLG/SCF binding leads to dimerization and activation by autophosphorylation on tyrosine residues. Activity is down-regulated by PRKCA-mediated phosphorylation on serine residues. Inhibited by imatinib/STI-571 (Gleevec) and sunitinib; these compounds maintain the kinase in an inactive conformation.
Subunit structure: Monomer in the absence of bound KITLG/SCF. Homodimer in the presence of bound KITLG/SCF, forming a heterotetramer with two KITLG/SCF molecules. Interacts (via phosphorylated tyrosine residues) with the adapter proteins GRB2 and GRB7 (via SH2 domain), and SH2B2/APS. Interacts (via C-terminus) with MPDZ (via the tenth PDZ domain). Interacts (via phosphorylated tyrosine residues) with PIK3R1 and PIK3 catalytic subunit. Interacts (via phosphorylated tyrosine) with CRK (isoform Crk-II), FYN, SHC1 and MATK/CHK (via SH2 domain). Interacts with LYN and FES/FPS. Interacts (via phosphorylated tyrosine residues) with the protein phosphatases PTPN6/SHP-1 (via SH2 domain), PTPN11/SHP-2 (via SH2 domain) and PTPRU. Interacts with PLCG1. Interacts with DOK1 and TEC.
Subcellular location: Isoform 1: Cell membrane; Single-pass type I membrane protein.
Isoform 2: Cell membrane; Single-pass type I membrane protein.
Isoform 3: Cytoplasm. Note=Detected in the cytoplasm of spermatozoa, especially in the equatorial and subacrosomal region of the sperm head.
Tissue specificity: Isoform 1 and isoform 2 are detected in spermatogonia and Leydig cells. Isoform 3 is detected in round spermatids, elongating spermatids and spermatozoa (at protein level). Widely expressed. Detected in the hematopoietic system, the gastrointestinal system, in melanocytes and in germ cells.
Induction: Up-regulated by cis-retinoic acid in neuroblastoma cell lines.
Post-translational: Ubiquitinated by SOCS6. KIT is rapidly ubiquitinated after autophosphorylation induced by KITLG/SCF binding, leading to internalization and degradation.
Autophosphorylated on tyrosine residues. KITLG/SCF binding enhances autophosphorylation. Isoform 1 shows low levels of tyrosine phosphorylation in the absence of added KITLG/SCF (in vitro). Kinase activity is down-regulated by phosphorylation on serine residues by protein kinase C family members. Phosphorylation at Tyr-568 is required for interaction with PTPN11/SHP-2, CRK (isoform Crk-II) and members of the SRC tyrosine-protein kinase family. Phosphorylation at Tyr-570 is required for interaction with PTPN6/SHP-1. Phosphorylation at Tyr- 703, Tyr-823 and Tyr-936 is important for interaction with GRB2. Phosphorylation at Tyr-721 is important for interaction with PIK3R1. Phosphorylation at Tyr-823 and Tyr-936 is important for interaction with GRB7.
Involvement in disease: Piebald trait (PBT) [MIM:172800]: Autosomal dominant genetic developmental abnormality of pigmentation characterized by congenital patches of white skin and hair that lack melanocytes. Note=The disease is caused by mutations affecting the gene represented in this entry.
Gastrointestinal stromal tumor (GIST) [MIM:606764]: Common mesenchymal neoplasms arising in the gastrointestinal tract, most often in the stomach. They are histologically, immunohistochemically, and genetically different from typical leiomyomas, leiomyosarcomas, and schwannomas. Most GISTs are composed of a fairly uniform population of spindle-shaped cells. Some tumors are dominated by epithelioid cells or contain a mixture of spindle and epithelioid morphologies. Primary GISTs in the gastrointestinal tract commonly metastasize in the omentum and mesenteries, often as multiple nodules. However, primary tumors may also occur outside of the gastrointestinal tract, in other intra-abdominal locations, especially in the omentum and mesentery. Note=The gene represented in this entry is involved in disease pathogenesis.
Testicular germ cell tumor (TGCT) [MIM:273300]: A common malignancy in males representing 95% of all testicular neoplasms. TGCTs have various pathologic subtypes including: unclassified intratubular germ cell neoplasia, seminoma (including cases with syncytiotrophoblastic cells), spermatocytic seminoma, embryonal carcinoma, yolk sac tumor, choriocarcinoma, and teratoma. Note=The gene represented in this entry may be involved in disease pathogenesis.
Leukemia, acute myelogenous (AML) [MIM:601626]: A subtype of acute leukemia, a cancer of the white blood cells. AML is a malignant disease of bone marrow characterized by maturational arrest of hematopoietic precursors at an early stage of development. Clonal expansion of myeloid blasts occurs in bone marrow, blood, and other tissue. Myelogenous leukemias develop from changes in cells that normally produce neutrophils, basophils, eosinophils and monocytes. Note=The gene represented in this entry is involved in disease pathogenesis. Somatic mutations that lead to constitutive activation of KIT are detected 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 kinase domain can result in a constitutively activated kinase.
Sequence similarities: Belongs to the protein kinase superfamily. Tyr protein kinase family. CSF-1/PDGF receptor subfamily.
Contains 5 Ig-like C2-type (immunoglobulin-like) domains.
Contains 1 protein kinase domain.
General information above from UniProt