CD117 c-KIT (v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog), SCFR(stem cell factor receptor)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Bone Marrow
Hematopoietic Cell
Myeloid Cell
Testis
Progenitor Cell
Leukemia cell
Melanocyte
Fibroblast
Mast Cell
Liver
Kidney
Lung
Brain
Cancer cell
Stem Cell
NK Cell
Dendritic Cell
Megakaryocyte
Erythroid Cell
T Cell
B Cell
145 / 145

Expression
CD117 is expressed by the earliest hemopoietic stem cells through to committed progenitors of myeloid, erythroid, megakaryocytic, NK, and dendritic cells as well as pro-B and T cells and tissue mast cells.  Expression is weakest in early hemopoietic stem cells and is strongest in more mature progenitor cells.  CD117 is expressed on 1%-4% of bone marrow stromal cells, the majority of which 50%-70% express CD34 and comprise pluripotent hematopoietic progenitor cells.  CD117 is expressed on fibroblasts and in liver, lung, kidney, testis, brain, and acute myeloid leukemic cells. Expression is found in small cell lung, breast and colorectal carcinomas, gynecological tumors, neuroblastoma, gastrointestinal stomal tumor, seminoma germ cell tumors, choroidal melanomas, and acute myeloid leukemias and mastocytosis.  In the mouse, CD117 is expressed on almost all hematopoietic progenitor cells including colony-forming cells reactive to IL-3, GM-CSF and M-CSF, but not on B-lineage progenitors which form colonies in response to IL-7.  It is also expressed on the surface of mouse tissue mast cells, melanocytes, spermatogonia and oocytes.



Structure
MOLECULAR FAMILY NAME: Belongs to the tyrosine kinease receptor family. 

CD117 is a single-chain type-1 976 aa  glycoprotein.  It contains a 23 aa N-terminus signal sequence, a 497 aa extracellular region which contains of 4 Ig-like C2-type domains, (the first 3 Ig domains are involved in ligand binding), and 1 Ig-like V-type domain and has 9 potential N-glycosylation sites, a 23 aa hydrophobic transmembrane domain and a 433 aa intracellular cytoplasmic domain which contains a consensus ATP binding site and a split tyrosine kinase-homologous sequence.  Ligand binding leads to dimerization and stabilization of the dimeric complex as well as increasing the local concentration of kinase domains which assists autophosphorylation and activation of the intrinsic kinase activity of CD117.  CD117 belongs to subclass 3 within the family of growth factor receptors with tyrosine kinase activity, that also includes CD115 M-CSFR and the PDGF receptors type A and B CD140a and CD140b.  CD117L is expressed both on the cell surface and, following proteolytic cleavage, in a soluble form.  Both membrane bound and secreted c-kitL are biologically active.  The soluble form, and presumably also the membrane bound form, exists as a dimer.  Intramolecular disulfide bonds are formed between Cys4-89 and 43-138 and the molecule contains considerable secondary structure including a helices and b sheets.  Together both N- and O-linked glycosylation accounts for approximately 30% of the total weight of c-kitL.  Alternative splicing gives rise to a 2nd form of the molecule that lacks 28 aa including 1 of the 5 potential N-linked glycosylation sites and the protease recognition site, which therefore yields soluble c-kitL less efficiently and is predominantly membrane bound.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
AML cells, cell lines 145 kDa 145 kDa

MOLECULAR MASS OF c-kitL
Cell Type Unreduced Reduced
Soluble form 28 - 36 kDa 28 - 36 kDa

POST-TRANSCRIPTIONAL MODIFICATION

Alternative splicing yields 4 difference isoforms.  The splicing results in isoforms with or without four extracellular membrane proximal amino acids (GNNK).  The shorter variant has been shown to bind and activate Src family kinases more efficiently.  Other splice variants are characterized by the presence or absense of a serine (SFKs) more efficiently.                 

POST-TRANSLATIONAL MODIFICATION

CD117 contains the N-linked glycosylation of the extracellular domain and the ligand-dependent tyrosine phosphorylation of the cytoplasmic domain.

Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD117

c-kitL binds to CD117 which is a cell surface receptor with Tyr kinase activity.  The natural ligand for CD117 is a c-kit ligand, also known as stem cell growth factor (SCF), steel factor (SF), and mast cell growth factor (MGF).  This growth factor is biologically active in both membrane-bound and soluble form.  CD117 transduces transmembrane signals by interaction with phosphatidylinositol 3-kinase PI-3 kinase), Raf1 and, to some extent, phospholipase Cg.  CD117 is associated with SCF, also known as SF, MGF and the kit ligand (KL).



Function
CD117 is a receptor for growth stem cell factor (SCF) and is required for normal hematopoiesis, pigmentation, gut function and reproduction.  CD117 and C-kitL is an early-acting hematopoietic growth factor receptor, critical to the development of several distinct lineages from hematopoietic progenitors.  C-kitL also stimulates the proliferation of mast cells, as well as myeloid and lymphoid progenitors in bone marrow cultures, and functions as a survival factor for primordial germ cells.  The interaction of c-kitL with CD117 is crucial for the development of hematopoietic, gonadal and pigment stem cells.  CD117 also increases the sensitivity of human mucosal mast cells to crosslinking of the high affinity IgE receptor.  Ligand binding results in autophosphorylation of intracellular tyrosine residues that in turn become binding sites for signal transduction reproduction.  In vitro CD117 can activate several signaling pathways including P13K pathway which is involved in adhesion, anti-apoptotic signaling and proliferation.  Loss of the P13K binding site results in defective gametogenesis.  SCF binding activates the Janus kinase-signal transducers and activates of transcription (JAK-STAT) pathway.  In some studies, this was found to be a requirement for maximal SCF-proliferation of progenitor cells but not for mast cell proliferation.  CD117 mediates activation of Ras-Erk pathway is important for hemopoietic differentiation.  Activation of CD117 also leads to a rapid increase in Src family kinase (SFK) activity.  SFKs are necessary for CD117 internalization after ligand binding and survival and migration of hemopoietic precursors.  Activation of the phospholipase Cγ pathway protects CD117 expressing cells from apoptosis induced by irradiation or the cytotoxin daunorubicin.  CD117 can interact with some cytokine receptors such as the IL-7 receptor and the Epo receptor which in the presence of SCF results in synergistic signaling.  Negative regulation of CD117 signaling is potentially mediated by serine and threonine kinases belonging to the PKC family, the tyrosine phosphatase SHP-1 and the ubiquitin ligase Cbl.

BIOCHEMICAL ACTIVITY

CD117 is a SCF receptor and tyrosine kinase.

DISEASE RELEVANCE AND FUNCTION OF CD117 IN INTACT ANIMAL

In mice, mutations of the W and S1 loci, which encode CD117 and c-kitL respectively, lead to the alteration of coat color showing white spotting, defective lymphopoeisis, splenomegaly, anemia and defective gonad development.  CD117 is deleted or defective in W mutant mice resulting in anemia, lack of mast cells, pigmentation defects and infertility.  In humans, naturally occurring mutations within the CD117 gene have been identified as the cause of piebaldism, an autosomal dominant disorder of pigmentation.  A truncated and mutated form, v-Kit, is the transforming element encoded by the Hardy-Zuckerman 4 feline sarcoma virus.  In humans, CD117 mutations are associated with gastrointestinal stromal tumors, mast cell disease, acute myelogenous leukemia and piebaldism.  CD117 is ectopically expressed in small cell lung cancer and is mutated and constitutively active in systemic mastocytosis arising from myelodysplastic syndrome.

Comments
The feline v-kit oncogene has lost the extracellular and transmembrane domains as well as the proximal cytoplasmic and the C-terminal aa.  The last 49 aa have been replaced by 5 aa due to fusion with the feline leukemia polymerase gene.

C-kitL is analogous to PDGF and M-CSF, insofar as each growth factor is dimeric and their receptors CD117 c-kitL, PDGFRA/PDGFRB CD140a/CD140b and CD115 c-fms constitute subclass 3 within the family of growth factor receptors with Tyr kinase activity.

MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD117: No information.

SUBSTRATES
Molecule Comment
PI 3 kinase p85 regulatory subunit Signaling molecules recruited to the receptor include p85 regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cg1, Tec kinase, Shc and Vav
PLCg1 Signaling molecules recruited to the receptor include p85 regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cg1, Tec kinase, Shc and Vav
Tec kinase Signaling molecules recruited to the receptor include p85 regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cg1, Tec kinase, Shc and Vav
Shc Signaling molecules recruited to the receptor include p85 regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cg1, Tec kinase, Shc and Vav
Vav Signaling molecules recruited to the receptor include p85 regulatory subunit of phosphatidylinositol 3-kinase, phospholipase Cg1, Tec kinase, Shc and Vav

ENZYMES WHICH MODIFY CD117
Molecule Comment
SHP phosphatase
Protein kinase C May downregulate Kit signaling

ADDITIONAL INSIGHTS

A soluble form of the CD117 protein in serum has been reported.  Interaction of CD117 with the membrane form of SCF may mediate cell adhesion.

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 3815P10721
MouseS00474P05532Y00864
MouseA35972P20826M38436
RatB35974P21581M59966
Antibodies
104D2   View Reactivity
2B8   View Reactivity

Revised June 25, 2008


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