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

Interaction of a tyrosine kinase type receptor and its ligand induces receptor-dimerization or -oligomerization followed by transphosphorylation and activation of its intrinsic kinase, which leads to a series of intracellular signals. We have previously reported that the membrane-bound form of Steel factor (SLF) induces more persistent tyrosine kinase activation and longer life span of c-kit encoded protein (KIT) than its soluble form (Miyazawa et al, Blood 85:641, 1995). In this study, we used YB5.B8 monoclonal antibody (MoAb) that recognizes the extracellular domain of KIT to investigate whether immobilized anti-KIT MoAb can substitute for SLF as a potent activator of KIT by cross-linking receptors and further compared its effect with each SLF isoform in a factor-dependent cell line M07e. YB5.B8 MoAb in a soluble state suppressed SLF-induced M07e cell proliferation in a dose-dependent manner. By contrast, once this antibody was immobilized on the goat-antimouse MoAb (GAM)-coated culture plates, it supported the growth of M07e cells in the absence of any growth factors, whereas culture the cells in GAM alone or YB5.B8 without GAM-coated plates resulted in rapid cell-death within 24 hours. As with the natural ligand SLF, immobilized YB5.B8 MoAb synergized with granulocyte-macrophage colony-stimulating factor (GM-CSF) in inducing cell proliferation compared with either YB5.B8 MoAb or GM-CSF alone. Immunoblotting with antiphosphotyrosine MoAb showed that interaction of M07e cells with immobilized YB5.B8 induced tyrosine phosphorylation of a series of intracellular proteins including KIT (145 kD). In addition, cross-linking studies using a water-soluble cross linking reagent bis-sulfosuccinimidyl-suberate showed that immobilized YB5.B8 MoAb induced dimerization and activation of KIT. However, as with stimulation by the membrane-bound form of SLF, the kinetics of KIT activation with YB5.B8 MoAb was more prolonged compared with the cells treated with recombinant soluble SLF. Flow cytometry showed that, unlike the cells treated with soluble SLF, no downmodulation of cell-surface KIT expression was observed in M07e cells cultured with immobilzed YB5.B8 MoAb. These data suggest that immobilized antibodies against hematopoietic receptors may replace their ligand-stimulators; however, their activities may resemble the membrane-bound form rather than the soluble form of natural ligands.
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PMID:Immobilized anti-KIT monoclonal antibody induces ligand-independent dimerization and activation of Steel factor receptor: biologic similarity with membrane-bound form of Steel factor rather than its soluble form. 863 Mar 83

Characteristic of Philadelphia (Ph)+ chronic myelogenous leukemia (CML) is the presence of the chimeric BCR/ABL (p210) protein possessing elevated protein tyrosine kinase activity relative to the normal c-abl tyrosine kinase. Our previous studies demonstrated subtle differences in the growth, phenotypic and morphologic characteristics of the most primitive subpopulations of primary lin-Ph+ chronic phase CML blasts and comparable primary lin- normal blasts. Recently, in comparing proteins phosphorylated on tyrosine in these cell populations, we reported a prominent 62 kDa phosphotyrosyl (P-tyr) protein constitutively present in primary primitive lin- CML chronic phase blasts which was virtually undetectable in primary primitive lin- normal blasts. In the present studies, we demonstrate that this P-tyr p62 from primary primitive lin- chronic phase CML blasts co-immunoprecipitates with ras-GAP. Furthermore, in addition to the p210 protein, we show in whole cell lysates the presence of other clearly consistent but less prominent P-tyr proteins with molecular weights of approximately 155, 140, 110, 55 and 45 kDa as well as more minor P-tyr proteins of approximately 190, 85, 52, 42 and 39 kDa constitutively present in primary primitive lin- chronic phase CML blasts. In analyzing proteins tyrosine phosphorylated in primary primitive lin- normal blasts in response to various hematopoietic growth factors, we found a striking similarity in the phosphorylation of four major (approximately 140, 110, 62 and 56 kDa) and three minor (approximately 51, 45 and 42 kDa) P-tyr proteins after stimulation with c-kit ligand and the P-tyr proteins constitutively phosphorylated in primary primitive lin- chronic phase CML blasts. Other growth factors tested (ie GM-CSF, G-CSF, IL-3, FLT3 ligand and EPO) were much less active or stimulated phosphorylation of other proteins. It is provocative that at least seven proteins rapidly and transiently phosphorylated on tyrosine in the c-kit ligand signal transduction pathway in lin- normal blasts may be constitutive substrates for the p210 activated tyrosine kinase in comparable lin- chronic phase CML blasts. In addition, it is intriguing that some of the biological effects on hematopoietic progenitors attributed to the c-kit ligand may be similar to some of the observed biological consequences of the p210 protein, including survival and expansion of a more mature stem cell population, probably at the time of lineage commitment rather than at the level of the earliest self-renewing stem cell.
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PMID:c-kit ligand stimulates tyrosine phosphorylation of a similar pattern of phosphotyrosyl proteins in primary primitive normal hematopoietic progenitors that are constitutively phosphorylated in comparable primitive progenitors in chronic phase chronic myelogenous leukemia. 863 31

Antisense methods to control aberrant gene expression have been investigated as therapeutic strategies. A proto-oncogene c-kit, which encodes a transmembrane tyrosine kinase, is overexpressed in some malignancies, including small-cell lung cancer (SCLC), and is thought to be involved in their pathogenesis. To test the feasibility of using adenovirus vectors for antisense strategies and to target c-kit in SCLC therapy, we constructed replication-deficient recombinant adenovirus vectors which express fragments of c-kit transcripts in antisense (Ad.kitAS) or sense orientation (Ad.kitS: control). In vitro infection of SBC-1 cells, which are c-Kit protein-producing SCLC cells, by these vectors resulted in the expression of artificial c-kit transcripts. The Ad.kitAS-infected SBC-1 cells showed reductions in the amount of c-Kit protein. As expected, at 10 days after infection (1 multiplicity of infection), Ad.kitAS-infected SBC-1 cells showed approximately 40% growth inhibition compared to uninfected or Ad.kitS-infected cells in vitro. Such a significant growth inhibition by Ad.kitAS was not induced in SBC-5 cells, which are SCLC cells producing no c-Kit protein. These results demonstrate the usefulness of adenovirus vectors in antisense strategies, and the feasibility of targeting c-kit in the therapy of c-Kit-producing SCLC.
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PMID:Specific growth inhibition of small-cell lung cancer cells by adenovirus vector expressing antisense c-kit transcripts. 864 92

To understand the signalling mechanisms involved in the dual stimulatory effects of endothelin-1 (ET-1) on DNA synthesis and melanization in cultured human melanocytes, we analysed the biological profile of ET-1 receptor and determined the effects of ET-1 on the protein kinase C, cyclic AMP system and mitogen-activated protein kinase (MAP kinase) in comparison with their relevant stimulants. The photoaffinity labelling of ET-1 receptors with Denny-Jaff reagents revealed an ET-1 receptor with a molecular mass of 51 kDa in human melanocytes. The ET(A) receptor subtype-sensitive antagonist BQ123(50 nM) or pertussis toxin (100 ng/ml) significantly suppressed the ET-1-induced intracellular calcium mobilization, indicating the presence of pertussis toxin-sensitive G-protein-coupled ET(A) receptors. An assay of protein kinase C activity revealed that 10nM ET-1 translocated cytosolic protein kinase C to membrane-bound protein kinase C within 5 min of the start of incubation. In contrast, receptor-mediated melanocyte activation by ET-1 was accompanied by an elevated level of cyclic AMP (4-fold over control) after 10-60 min of incubation, whereas 60 min of incubation of human melanocytes with c-Kit or c-Met ligands such as stem cell factor (10 nM) or basic fibroblast growth factor (10 nM) did not elevate the cyclic AMP level. We have also demonstrated that a specific tyrosine kinase inhibitor, tyrphostin B-42 (10 microM), inhibited the ET-1-induced growth stimulation, suggesting the involvement of the tyrosine kinase pathway in growth stimulation. Consistently, an assay of MAP kinase revealed that ET-1 caused a 10-fold activation of MAP kinase after 5 min of incubation with human melanocytes in a similar way to tyrosine kinase ligands such as stem cell factor and hepatocyte growth factor. Further, the DNA synthesis stimulated by the c-Kit ligand stem cell factor at a concentration of 1 nM was synergistically enhanced by 5 nM ET-1. These results suggest that ET-induced dual cellular events in human melanocytes are closely associated with cross-talk between the protein kinase C and A and tyrosine kinase pathways.
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PMID:Signalling mechanisms of endothelin-induced mitogenesis and melanogenesis in human melanocytes. 866 Feb 99

Hematopoietic tyrosine kinase receptors (HGF-TKRs or class III TKRs) are essential for the growth and differentiation of hematopoietic cells. In this report we present a novel method that generates expression profiles of these receptors. The method was tested and optimized using the myeloblastic/ promyelocytic cell line KG1. The method involves PCR of cDNA using class III-specific degenerate primers and subsequent restriction enzyme digests of the 147 bp amplicons followed by fractionation on denaturing poly-acrylamide gels. This primary fingerprint of KG1 revealed equal expression of c-kit and flt3 and to a lesser extent PDGF-R alpha and c-fms. One residual band of unknown origin was seen and appeared to be the proto-oncogene RET following cloning and sequence analysis. This tyrosine kinase receptor is known to play an important role in neural development. In order to detect less abundantly expressed sequences, a secondary fingerprint was generated by pre-digestion of the receptors present in the primary expression profile and subsequent amplification of the residual band. No other tyrosine kinase receptors were observed in KG1. In conclusion, this method allows direct visualization of expression of the HGF-TKRs and has the potential to detect novel homologous receptors.
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PMID:Direct display of hematopoietic tyrosine kinase receptor expression profiles in KG1 cells by PCR using degenerate primers. 870 51

We have previously studied the expression of protein tyrosine kinases in different preparations of insulin producing cells by polymerase chain reaction (PCR). Among the tyrosine kinases thus identified were the fibroblast growth factor receptor-4 (FGFR-4), c-Kit, the insulin-like growth factor (IGF-I) receptor, and the cytoplasmic tyrosine kinase Jak2, which associates with the activated receptor for growth hormone (GH). To elucidate the putative biological effects of the receptors identified, fetal islet-like structures were cultured in the absence or presence of the ligands to the receptors identified, namely, acidic FGF (aFGF), stem-cell factor (SCF), IGF-I, and GH, whereafter insulin and DNA contents as well as insulin secretion to the culture medium were determined. Nerve growth factor (NGF), the ligand to the tyrosine kinase receptor Trk-A, was also included. aFGF and GH were found to stimulate insulin release to the culture medium, whereas SCF augmented insulin contents/DNA as well as islet DNA contents. No effects of NGF or IGF-I were detected. Immunohistochemical studies of fetal rat pancreas showed localization of the c-Kit protein to the pancreatic ducts, whereas immuno-reactivity against FGFR-4 could be detected in both endocrine and exocrine parts of the pancreas as well as in the pancreatic ducts. It is concluded that tyrosine kinase receptors may be involved in the maturation of pancreatic beta cells.
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PMID:Effects of certain growth factors on in vitro maturation of rat fetal islet-like structures. 874 Mar 98

c-kit ligand (KL) is a hematopoietic growth factor that plays a major role in the survival, expansion and differentiation of hematopoietic progenitor cells of various lineages. The biological actions elicited by KL are initiated by binding to its cognate receptor, c-kit, which is a transmembrane tyrosine kinase. The resulting ligand/receptor complex rapidly activates the intrinsic kit receptor tyrosine kinase and subsequent phosphorylation of specific intracellular substrates that are involved in downstream signaling events. In the present studies, we demonstrate that KL stimulates the rapid tyrosine phosphorylation of the proto-oncogene, c-Cbl, in two KL-responsive human hematopoietic cell lines, MO7e and TF-1. In both these cell lines we found a constitutive in vivo association between c-Cbl and the adaptor protein Grb2 and demonstrate (in vitro) that c-Cbl binds primarily to the N-terminal SH3 domain of Grb2. Furthermore, the stoichiometry of this association was not significantly affected upon c-kit receptor activation. We also provide evidence that c-Cbl is not stably associated with the kit receptor either prior to or following KL stimulation. Our findings suggest that c-Cbl is an important component in the KL signaling pathway in human hematopoietic progenitor cells.
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PMID:c-kit ligand stimulates tyrosine phosphorylation of the c-Cbl protein in human hematopoietic cells. 875 59

The chimaeric bcr/abl oncogene is detected in virtually all cases of chronic myelogenous leukaemia (CML). It encodes a constitutively active tyrosine kinase of 210 kDalton, p210bcr/abl, which stimulates a variety of cytosolic signalling intermediates. The effects of bcr/abl on the activity of growth factor receptors are less well known. In order to investigate interaction of p210bcr/abl with the receptor tyrosine kinase p145c-kit, we used two myeloid, factor-dependent cell lines, MO7 and 32D, to generate bcr/abl positive sublines, MO7p210 and 32Dp210, by transfection with the bcr/abl gene. Since 32D and 32Dp210 cells did not express p145c-kit, a c-kit retrovirus was used to generate c-kit positive cell lines (32Dkit, 32Dp210kit). In contrast to MO7 and 32Dkit cells, MO7p210 and 32Dp210kit cells were factor independent and did not respond to the growth-promoting effects of recombinant human Steel factor (rhSF). Preincubation with a monoclonal antibody (MAb) neutralizing the binding of SF to p145c-kit did not affect the growth of MO7p210 cells, thus eliminating the possibility of an autocrine SF secretion. 32Dkit cells transfected with bcr/abl containing an inactivating point mutation (Lys-->Arg271) in the Abl kinase domain (32Dp210(Arg271)kit) retained their responsiveness to the effects of rhSF. Immune complex kinase assays showed that the kinase activity of p145c-kit was several-fold higher in MO7p210 and 32Dp210kit cells than in MO7, 32Dkit and 32Dp210(Arg271)kit cells, suggesting that Abl kinase activity was necessary to activate p145c-kit. Co-immunoprecipitation experiments with anti-Kit and anti-Abl MAbs demonstrated that p145c-kit and p210bcr/abl were associated in an intracellular complex in human bcr/abl positive, c-kit positive cell lines (MO7p210; GM/SO). Finally, colony assays with bone marrow from bcr/abl positive CML patients showed that the haemopoietic progenitors of three of four patients did not respond to rhSF. Taken together, the results suggest that p145c-kit can be activated by p210bcr/abl via an Abl-kinase dependent mechanism involving the complex formation of both proteins. These findings could explain some clinical features (basophilia, increase of immature myeloid cells) of chronic-phase CML.
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PMID:Interaction of the receptor tyrosine kinase p145c-kit with the p210bcr/abl kinase in myeloid cells. 875 2

Expression profiles were generated for the haemopoietic tyrosine kinase receptors (HGF-TKRs or class III TKRs) by PCR on cDNA samples (RT-PCR) using a degenerate primer set. Each profile consisted of primary and secondary, i.e. enriched for less-expressed sequences, fingerprints. This method was applied on FACS-purified haemopoietic CD34+ cells, both from bone marrow (BM) and umbilical cord blood (UCB), and on mature cells from peripheral blood. CD34+ BM cells showed expression of c-fms. flt3, whereas CD34+ UCB cells expressed c-fms and, to a lesser extent, c-kit and flt3. In mature blood cells, only c-fms was observed in monocytes and a weaker flt3 expression in monocytes and T lymphocytes, whereas no known class III TKRs were detected in B lymphocytes and polymorphonuclear cells (PMNs). In all fractions a novel band could be observed, which appeared to be RET. Expression of RET was confirmed by RT-PCR and showed the highest levels in monocytes, followed by PMNs and CD34+ cells. B lymphocytes revealed low levels of expression. RET is known to be essential in neural development. Our results suggest a possible role for this receptor in haemopoiesis.
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PMID:Haemopoietic growth factor tyrosine kinase receptor expression profiles in normal haemopoiesis. 875 81

The cbl oncogene was first identified as part of a transforming retrovirus which arose in a mouse pre-B cell lymphoma. Its protein product, p120cbl, is cytoplasmic and has several distinctive domains including a highly basic region, a RING finger motif and a large proline-rich domain. A mutation to cbl in the 70Z/3 pre-B cell lymphoma produces an oncogenic protein which exhibits a marked enhancement of tyrosine phosphorylation. Parallel studies have demonstrated that p120cbl is a substrate of protein Tyrosine kinases activated by engagement of the T cell antigen receptor and that cbl is phosphorylated by oncogenic forms of the Abl tyrosine kinase. These studies also demonstrated a constitutive association between cbl and the SHS domains of the Grb2 and Nck adaptor proteins in a range of haemopoietic cell lines. More recently it has been found that cbl is rapidly phosphorylated following stimulation of the EGF receptor, Fcy receptor, c-Kit receptor and CSF-1 receptor. A genetic analysis in Caenorhabditis elegans has identified a cbl homologue, called sli-1, that negatively regulates the LET-23 tyrosine kinase receptor. These characteristics indicate a central role for cbl in the regulation of intracellular signals that are mediated by growth factors and antigenic stimuli which activate protein tyrosine kinases.
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PMID:The cbl oncogene: a novel substrate of protein tyrosine kinases. 877 Mar 64


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