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Query: UNIPROT:P10721 (c-kit)
 6,575 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Germline mutations at the Dominant White Spotting (W) and Steel (Sl) loci have provided conclusive genetic evidence that c-kit mediated signal transduction pathways are essential for normal mouse development. We have analysed the interactions of normal and mutant W/c-kit gene products with cytoplasmic signalling proteins, using transient c-kit expression assays in COS cells. In addition to the previously identified c-kit gene product (Kit+), a second normal Kit isoform (KitA+) containing an in-frame insertion, Gly-Asn-Asn-Lys, within the extracellular domain, was detected in murine mast cell cultures and mid-gestation placenta. Both Kit+ and KitA+ isoforms showed increased autophosphorylation and enhanced association with phosphatidylinositol (PI) 3' kinase and PLC gamma 1, when stimulated with recombinant soluble Steel factor. No association or increase in phosphorylation of GAP and two GAP-associated proteins, p62 and p190, was observed. The two isoforms had distinct activities in the absence of exogenous soluble Steel factor; Kit+, but not KitA+, showed constitutive tyrosine phosphorylation that was accompanied by a low constitutive level of association with PI-3' kinase and PLC gamma 1. Introduction of the point substitutions associated with W37 (Glu582----Lys) or W41 (Val831----Met) mutant alleles into c-kit expression constructs abolished (W37) or reduced (W41) the Steel factor-induced association of the Kit receptor with signalling proteins in a manner proportional to the overall severity of the corresponding W mutant phenotype. These data suggest a diversity of normal Kit signalling pathways and indicate that W mutant phenotypes result from primary defects in the Kit receptor that affect its interaction with cytoplasmic signalling proteins.
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PMID:Signal transduction by normal isoforms and W mutant variants of the Kit receptor tyrosine kinase. 171 77

Homozygous mutant rats at the newly found white spotting (Ws) locus were anemic and deficient in mast cells and melanocytes. Because the phenotype of Ws/Ws rats resembled the phenotype of mice possessing a double-gene dose of mutant alleles at the W locus and because the c-kit gene was mapped at the W locus of mice, we characterized the c-kit gene of Ws/Ws rats. The authentic sequence of the rat c-kit cDNA was determined by using a cDNA library prepared from the hippocampus of Sprague-Dawley rats. The c-kit cDNA of Ws/Ws and normal (+/+) control rats was obtained by reverse transcriptase modification of the polymerase chain reaction. When compared with the authentic sequence, a deletion of 12 bases was found in the c-kit cDNA of Ws/Ws rats. This change was shown to be a result of the deletion of the genomic DNA. Four amino acids encoded by the deleted 12 bases (ie, Val-Lys-Gly-Asn) were located at two amino acids downstream from the tyrosine autophosphorylation site in the c-kit kinase and were conserved not only in mouse and human c-kit kinases but also in mouse and human c-fms kinases (ie, receptors of colony-stimulating factor-1). Taken together, the Ws/Ws rat is the first characterized mutant of the c-kit gene in an animal species other than the mouse.
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PMID:Characterization of Ws mutant allele of rats: a 12-base deletion in tyrosine kinase domain of c-kit gene. 191 77

FDC-P1 haemopoietic cells were used to select mutations of c-fms that constitutively activate the receptor for macrophage-colony stimulating factor (M-CSF or CSF-1). One mutation changed Ser 929 to Gly within a Ser/Gly rich region of the C-terminal tail and a second changed a nearby, highly conserved Leu 926 for Pro. A third mutation (D802V) changed Asp 802 to Val within the alpha L12/beta 9 region of the tyrosine kinase domain, so supporting the crystallographic evidence that this region triggers kinase activation. A c-kit mutation exactly equivalent to D802V was previously identified in a leukamic cell line and was demonstrated here to be transforming. Surprisingly, although D802V potently transformed FDC-P1 cells, it could not induce Rat-2 fibroblast foci, even in the presence of M-CSF. It is suggested that the accelerated receptor degradation induced by D802V may account for its cell specific effect.
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PMID:Selection of activating mutations of c-fms in FDC-P1 cells. 747 56

Stem cell factor (SCF) or c-kit ligand is a growth factor cytokine produced by stromal cells that is known to influence mast cell proliferation and differentiation. We hypothesized that SCF may also influence the adhesion of mast cells to connective tissue matrix. To examine this hypothesis, we stimulated MCP5/L mast cells or murine bone marrow-derived cultured mast cells (BMCMC) with either SCF or PMA and observed adhesion to fibronectin (FN). As expected, 80 to 90% of PMA-activated MCP5/L cells or BMCMC adhered to FN. In addition, SCF promoted MCP5/L cell or BMCMC adhesion to FN in a dose-response fashion with 50 to 60% of BMCMC adhering to FN at a concentration 10 ng/ml of SCF. BMCMC adhesion was observed with as little as 200 pg/ml of SCF. Adhesion of SCF stimulated BMCMC to FN did not require IL-3, but was dependent on the concentration of FN used to coat the assay surface. Mast cell adhesion in the presence of SCF appeared to occur through an integrin receptor as adhesion was calcium dependent and could be blocked by an RGD (Ang, Gly, Asp)-containing peptide. SCF did not directly mediate adhesion through interaction with c-kit, as FN-coated surfaces exposed to SCF before initiation of the adhesion assay did not promote adhesion in the absence of soluble SCF. Rather, SCF appeared to stimulate adhesion to FN by activating mast cells through its interaction with c-kit. Thus, antibody to SCF blocked adhesion, and rat and murine SCF stimulated BMCMC adhesion to FN, but human SCF, which does not bind to murine c-kit, did not stimulate adhesion. Genistein, which inhibits tyrosine kinase activity, partially inhibited SCF-induced adhesion. SCF thus stimulates mast cell adhesion and, because SCF is produced normally in tissues, it may be a major factor responsible for the adhesion of mast cells to connective tissue matrix under physiologic conditions.
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PMID:Stem cell factor induces mast cell adhesion to fibronectin. 750 10

The c-kit proto-oncogene encodes a receptor tyrosine kinase that is known to play a crucial role in mast cell growth and differentiation. In a human mast cell leukemia cell line (HMC-1), KitR was found to be constitutively phosphorylated on tyrosine, activated and associated with phosphatidylinositol 3-kinase (P13K) in the absence of autocrine production of SCF. Sequencing of c-kit cDNA revealed that c-kit genes of HMC-1 cells were composed of a normal, wild-type allele and a mutant allele with two point mutations in codon 560 and codon 816, resulting in intracellular amino acid substitutions of Gly-560 for Val and Val-816 for Asp, respectively. Murine c-kit mutants encoding Gly-559 and/or Val-814, corresponding to human Gly-560 and/or Val-816, were constructed by site-directed mutagenesis and expressed in cells of a human embryonic kidney cell line (293T). In the transfected cells, KitR (Gly-559 + Val-814) and KitR (Val-814) were strikingly phosphorylated on tyrosine and activated in the absence of SCF, whereas tyrosine phosphorylation and activation of KitR (Gly-559) or wild-type KitR was modest or little, respectively. These results suggest that constitutive activation of KitR in HMC-1 results from the activating mutations of c-kit gene, and raise the possibility that the activating mutations, particularly at codon 814 of murine c-kit or at codon 816 of human c-kit, may participate in oncogenesis of mast cells.
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PMID:Activating mutations of the c-kit proto-oncogene in a human mast cell leukemia cell line. 751 80

The c-kit receptor tyrosine kinase (KIT) is activated upon ligand binding, thereby leading to a variety of signaling events that play a fundamental role in hematopoiesis. In addition to ligand-dependent activation, we have previously shown that KIT is constitutively activated in a ligand-independent manner by two point mutations, Val-559-->Gly (G559) mutation in the juxtamembrane domain and Asp-814-->Val (V814) mutation in the phosphotransferase domain. To investigate the biochemical consequence and biologic significance of these mutations, retroviral vectors encoding KITG559 or KITV814 were introduced into murine pro-B-type Ba/F3 cells and myeloid FDC-P1 cells, both of which require interleukin-3 (IL-3) for their growth and survival. In the cells, KITG559 or KITV814 were found to be constitutively phophorylated on tyrosine in the absence of stem cell factor (SCF) that is a ligand for KIT. Chemical cross-linking analysis showed that a substantial fraction of the phosphorylated KITG559 underwent dimerization even in the absence of SCF, whereas the phosphorylated KITV814 did not, suggesting the distinct mechanisms underlying constitutive activation of KIT by G559 and V814 mutations. Furthermore, the cells expressing either KITG559 or KITV814 were found to show a factor-independent growth, whereas the cells expressing wild-type KIT (KITWT) proliferated in response to SCF as well as IL-3. Moreover, subcutaneous injection of Ba/F3 cells expressing KITG559 or KITV814 into nude mice resulted in production of large tumors at all sites of the injection within 2 weeks, and all nude mice quickly succumbed to leukemia and died. These results suggest that, although the mechanisms underlying constitutive activation of KITG559 or KITV814 may be different, both of the activating mutations have a function to induce a factor-independent and tumorigenic phenotype. Also, the data of this study raise the possibility that the constitutively activating mutations of c-kit may play a causal role in development of hematologic malignancies.
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PMID:Constitutively activating mutations of c-kit receptor tyrosine kinase confer factor-independent growth and tumorigenicity of factor-dependent hematopoietic cell lines. 753 May 9

Because mutations in receptor tyrosine kinases may contribute to cellular transformation, studies were undertaken to examine c-kit in human leukemia. Isoforms of c-kit have been characterized in the human megakaryoblastic leukemia cell line M-07. Deletion of the four amino acids Gly-Asn-Asn-Lys in the extracellular domain represents an alternatively spliced isoform that has been shown by others, in mice, to be associated with constitutive receptor autophosphorylation (Reith et al, EMBO J 10:2451, 1991). Additional isoforms differ in the inclusion or exclusion of a serine residue in the interkinase domain, a region that contains the binding site for phosphatidylinositol 3-kinase. By RNase protection analysis, we have shown coexpression of the Gly-Asn-Asn-Lys+ and Gly-Asn-Asn-Lys- isoforms, with dominance of the Gly-Asn-Asn-Lys- transcript, in normal human bone marrow, normal melanocytes, a range of tumor cell lines, and the blasts of 23 patients with acute myeloid leukemia. Analysis of transcripts for the Ser+ and Ser- isoforms also showed coexpression in all normal and leukemic cells examined. The ratios of isoform expression for both the Gly-Asn-Asn-Lys and Ser variants were relatively constant, providing no evidence in the tumors examined that upregulation of one isoform contributes to the neoplastic process.
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PMID:Expression of isoforms of the human receptor tyrosine kinase c-kit in leukemic cell lines and acute myeloid leukemia. 768 88

The c-kit proto-oncogene encodes a receptor tyrosine kinase. Binding of c-kit ligand, stem cell factor (SCF) to c-kit receptor (c-kitR) is known to activate c-kitR tyrosine kinase, thereby leading to autophosphorylation of c-kitR on tyrosine and to association of c-kitR with substrates such as phosphatidylinositol 3-kinase (PI3K). In a human mast cell leukemia cell line HMC-1, c-kitR was found to be constitutively phosphorylated on tyrosine, activated, and associated with PI3K without the addition of SCF. The expression of SCF mRNA transcript in HMC-1 cells was not detectable by means of PCR after reverse transcription (RT-PCR) analysis, suggesting that the constitutive activation of c-kitR was ligand independent. Sequencing of whole coding region of c-kit cDNA revealed that c-kit genes of HMC-1 cells were composed of a normal, wild-type allele and a mutant allele with two point mutations resulting in intracellular amino acid substitutions of Gly-560 for Val and Val-816 for Asp. Amino acid sequences in the regions of the two mutations are completely conserved in all of mouse, rat, and human c-kit. In order to determine the causal role of these mutations in the constitutive activation, murine c-kit mutants encoding Gly-559 and/or Val-814, corresponding to human Gly-560 and/or Val-816, were constructed by site-directed mutagenesis and expressed in a human embryonic kidney cell line, 293T cells. In the transfected cells, both c-kitR (Gly-559, Val-814) and c-kitR (Val-814) were abundantly phosphorylated on tyrosine and activated in immune complex kinase reaction in the absence of SCF, whereas tyrosine phosphorylation and activation of c-kitR (Gly-559) or wild-type c-kitR was modest or little, respectively. These results suggest that conversion of Asp-816 to Val in human c-kitR may be an activating mutation and responsible for the constitutive activation of c-kitR in HMC-1 cells.
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PMID:Identification of mutations in the coding sequence of the proto-oncogene c-kit in a human mast cell leukemia cell line causing ligand-independent activation of c-kit product. 769 85

The c-kit proto-oncogene encodes a receptor tyrosine kinase that is crucial to hematopoiesis, melanogenesis, and gametogeneis. Although the enzymatic activity of the c-kit product (KIT) is regulated by its ligand, both the Val559-->Gly (G559) mutation in the juxtamembrane domain and the Asp814-->Val (V814) mutation in the phosphotransferase domain lead to constitutive activation of KIT. By retroviral infection of hematopoietic progenitor cells with KIT(G559) or KIT(V814), KIT(G559) induced development of granulocyte/macrophage and mast-cell colonies in vitro without the addition of exogenous growth factors. KIT(V814) induced factor-independent growth of various types of hematopoietic progenitor cells, resulting in the development of mixed erythroid/myeloid colonies in addition to granulocyte/macrophage and mast-cell colonies. Furthermore, transplantation of KIT(G559) and KIT(V814)-infected bone marrow cells led to development of acute leukemia in one of 10 and six of 10 transplanted mice, respectively. No mice developed hematologic malignancies after transplantation of wild-type KIT-infected cells. Furthermore, transgenic mice expressing KIT(V814) developed acute leukemia or malignant lymphoma. These results demonstrate a direct role of the mutant KITs, particularly KIT(V814), in tumorigenesis of hematopoietic cells and suggest that similar mutations may contribute to the development of human hematologic malignancies.
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PMID:Neoplastic transformation of normal hematopoietic cells by constitutively activating mutations of c-kit receptor tyrosine kinase. 870 59

The term mastocytosis denotes a heterogenous group of disorders characterized by abnormal growth and accumulation of mast cells in one or more organs. Cutaneous and systemic variants of the disease have been described. Mast cell disorders have also been categorized according to other aspects, such as family history, age, course of disease, or presence of a concomitant myeloid neoplasm. However, so far, generally accepted disease criteria are missing. Recently, a number of diagnostic (disease-related) markers have been identified in mastocytosis research. These include the mast cell enzyme tryptase, CD2, and mast cell growth factor receptor c-kit (CD117). Several gain-of-function-mutations in the kinase domain of c-kit appear to occur in mastocytosis supporting the clonal (neoplastic) nature of the disease. Also, certain point mutations appear to be associated with distinct variants of mastocytosis, i.e. Asp-816-->Val with a subset of sporadic persistent (systemic) mastocytosis (mostly adults), and Gly-839-->Lys with (a subset of) typical pediatric (mostly cutaneous) mastocytosis. Another potential indicator of mast cell neoplasm is the T-/NK-cell-associated marker CD2. This antigen (LFA-2) is abnormally expressed on neoplastic mast cells in cases of systemic mastocytosis or mast cell leukemia, but not found on normal mast cells. The mast cell enzyme tryptase is increasingly used as a serum- and immunohistochemical marker to estimate the actual spread of disease (burden of neoplastic mast cells). The clinical significance of novel mastocytosis markers is currently under investigation. First results indicate that they may be useful to define reliable criteria for the delineation of the disease.
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PMID:Recent advances in mastocytosis research. Summary of the Vienna Mastocytosis Meeting 1998. 1052 83


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