| 1. |
- Kazi, Julhash U., et al.
(författare)
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Src-Like Adaptor Protein (SLAP) differentially regulates normal and oncogenic c-Kit signaling
- 2014
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Ingår i: Journal of Cell Science. - : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 127:3, s. 653-662
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Tidskriftsartikel (refereegranskat)abstract
- The Src-Like Adaptor Protein (SLAP) is an adaptor protein sharing considerable structural homology with Src. SLAP is expressed in variety of cells regulating receptor tyrosine kinase signaling by direct association. In this report, we show that SLAP associates with both wild-type and oncogenic c-Kit (c-Kit-D816V). The association involves SLAP SH2 domain and receptor phosphotyrosine residues different from those mediating Src interaction. Association of SLAP triggers c-Kit ubiquitination which, in turn, is followed by receptor degradation. Although SLAP depletion potentiates c-Kit downstream signaling by stabilizing the receptor, it remains non-functional in c-Kit-D816V signaling. Ligand-stimulated c-Kit or c-Kit-D816V did not alter membrane localization of SLAP. Interestingly oncogenic c-Kit-D816V, but not wild-type c-Kit, phosphorylates SLAP on Y120, Y258 and Y273 residues. Physical interaction between c-Kit-D816V and SLAP is mandatory for the phosphorylation to take place. Although tyrosine phosphorylated SLAP does not affect c-Kit-D816V signaling, mutation of these tyrosine sites to phenylalanine can restore SLAP activity. Taken together the data demonstrate that SLAP negatively regulates wild-type c-Kit signaling, but not its oncogenic counterpart, indicating a possible mechanism by which the oncogenic c-Kit bypasses the normal cellular negative feedback control.
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| 2. |
- Lennartsson, Johan, et al.
(författare)
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C-Kit signal transduction and involvement in cancer
- 2005
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Ingår i: Cancer Therapy. ; 3, s. 5-28
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Forskningsöversikt (refereegranskat)abstract
- Receptor tyrosine kinases, such as c-Kit, are proteins whose function it is to transduce signals from the environment into the cell leading to complex behaviors such as proliferation, migration, survival and differentiation. Many of these behaviors are deregulated in cancer, which is characterized by uncontrolled proliferation, insensitivity towards death stimuli, migration of tumor cells away from the primary tumor site and in some cases also block of cellular differentiation leaving the cell in an immature proliferative state. To be able to target these processes it is vital to have a detailed understanding of the receptor function and the downstream pathways activated. In this article we will review the mechanisms by which c-Kit induces signal transduction as well as describing tumors in which c-Kit function is perturbed.
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| 3. |
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| 4. |
- Phung, Bengt, et al.
(författare)
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C-KIT Signaling Depends on Microphthalmia-Associated Transcription Factor for Effects on Cell Proliferation.
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- The development of melanocytes is regulated by the tyrosine kinase receptor c-KIT and the basic-helix-loop-helix-leucine zipper transcription factor Mitf. These essential melanocyte survival regulators are also well known oncogenic factors in malignant melanoma. Despite their importance, not much is known about the regulatory mechanisms and signaling pathways involved. In this study, we therefore sought to identify the signaling pathways and mechanisms involved in c-KIT mediated regulation of Mitf. We report that c-KIT stimulation leads to the activation of Mitf specifically through the c-KIT phosphorylation sites Y721 (PI3 kinase binding site), Y568 and Y570 (Src binding site). Our study not only confirms the involvement of Ras-Erk signaling pathway in the activation of Mitf, but also establishes that Src kinase binding to Y568 and Y570 of c-KIT is required. Using specific inhibitors we observe and verify that c-KIT induced activation of Mitf is dependent on PI3-, Akt-, Src-, p38- or Mek kinases. Moreover, the proliferative effect of c-KIT is dependent on Mitf in HEK293T cells. In contrast, c-KIT Y568F and Y721F mutants are less effective in driving cell proliferation, compared to wild type c-KIT. Our results reveal novel mechanisms by which c-KIT signaling regulates Mitf, with implications for understanding both melanocyte development and melanoma.
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| 5. |
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| 6. |
- Sun, Jianmin, et al.
(författare)
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GAB2 is involved in differential pi3-kinase signaling by two splice forms of C-kit.
- 2008
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 283:41, s. 27444-27451
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Tidskriftsartikel (refereegranskat)abstract
- The stem cell factor receptor/c-Kit plays an important physiological role in hematopoesis, melanogenesis and gametogenesis. It has also been implicated in numerous human malignancies. Signal transduction pathways shown to be of importance for c-Kit mediated transformation include the PI3-kinase/Akt pathway. We have previously shown that two alternative splice forms of c-Kit, denoted GNNK- and GNNK+ respectively, mediate distinctively different signals. In this study we find that in the hematopoietic cell line Ba/F3, the GNNK- c-Kit mediates a substantially stronger activation of PI3-kinase/Akt than the GNNK+ c-Kit. This difference in signaling was shown to be dependent on the association of the scaffolding protein Gab2 to c-Kit and Src-mediated phosphorylation of Gab2, to be independent of the direct association of PI3-kinase with c-Kit. Furthermore, proliferation and survival of Ba/F3 cells expressing a mutant of c-Kit that fails to bind to PI3-kinase directly was slightly decreased compared to wild-type c-Kit expressing cells. Using siRNA technology we further verified a role of Gab2 in inducing activation of PI3-kinase/Akt downstream of c-Kit. To summarize, we show that PI3-kinase activation by c-Kit is both splice form dependent and cell type specific. Furthermore, activation of PI3-kinase by c-Kit is dependent both on the direct PI3-kinase binding site in c-Kit as well as on the phosphorylation of Gab2. The fact that c-Kit has been found mutated in numerous human malignancies including acute myeloid leukemia and that Gab2 often is overexpressed in acute myeloid leukemia suggests a potential role of Gab2 mediated PI3-kinase activation in transformation.
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| 7. |
- Sun, Jianmin, et al.
(författare)
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Grb2 mediates negative regulation of stem cell factor receptor/c-Kit signaling by recruitment of Cbl.
- 2007
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Ingår i: Experimental Cell Research. - : Elsevier BV. - 1090-2422 .- 0014-4827. ; 313:18, s. 3935-3942
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Tidskriftsartikel (refereegranskat)abstract
- Aberrant activation of c-Kit is involved in a number of human diseases including cancers and leukemias. Certain receptor tyrosine kinases, such as epidermal growth factor receptor, have been shown to indirectly recruit Cbl through the adapter protein Grb2, leading to receptor ubiquitination and degradation. In order to study the role of Grb2 in c-Kit degradation, a series of mutations of the Grb2 binding sites in c-Kit were generated (Y703F, Y936F, and Y703F/Y936F). Since other signal transduction molecules are also known to bind Y703 and Y936, the more selective asparagine-to-alanine (N-to-A) mutants N705A, N938A, and N705A/N938A were generated. We could clearly demonstrate that binding of Grb2 was dependent on intact phosphorylation sites Y703 and Y936. Furthermore, we could demonstrate the presence of Cbl in a complex with Grb2 and c-Kit. Thus, Grb2 is able to indirectly recruit Cbl to c-Kit. In the N-to-A mutants, Cbl phosphorylation was strongly reduced, which correlated with reduced ubiquitination of c-Kit as well as decreased internalization and degradation of the receptor. Taken together, we have demonstrated that, in addition to its role in positive signaling via the Ras/Erk pathway, Grb2 mediates c-Kit degradation through recruitment of Cbl to c-Kit, leading to ubiquitination of c-Kit followed by internalization and degradation.
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| 8. |
- Sun, Jianmin, et al.
(författare)
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The D816V mutation of c-Kit circumvents a requirement for Src family kinases in c-Kit signal transduction.
- 2009
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 284:17, s. 11039-11047
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Tidskriftsartikel (refereegranskat)abstract
- The receptor tyrosine kinase c-Kit plays a critical role in hematopoiesis and gain-of-function mutations of the receptor are frequently seen in several malignancies, including acute myeloid leukemia (AML), gastrointestinal stromal tumors and testicular carcinoma. The most common mutation of c-Kit in these disorders is a substitution of the aspartic acid residue in position 816 to a valine (D816V), leading to constitutive activation of the receptor. In this study we aimed to investigate the role of Src family kinases in c-Kit/D816V signaling. Src family kinases are necessary for the phosphorylation of wild-type c-Kit as well as of activation of downstream signaling pathways including receptor ubiquitination and the Ras/Mek/Erk pathway. Our data demonstrate that, unlike wild-type c-Kit, the phosphorylation of c-Kit/D816V is not dependent on Src family kinases. In addition we found that neither receptor ubiquitination nor Erk activation by c-Kit/D816V required activation of Src family kinases. In vitro kinase assay using synthetic peptides revealed that c-Kit/D816V had an altered substrate specificity resembling Src and Abl tyrosine kinases. We further present evidence that, in contrast to wild-type c-Kit, Src family kinases are dispensable for c-Kit/D816V cell survival, proliferation and colony formation. Taken together, we demonstrate that the signal transduction pathways mediated by c-Kit/D816V are markedly different from those activated by wild-type c-Kit and that altered substrate specificity of c-Kit circumvents a need for Src family kinases in signaling of growth and survival, thereby contributing to the transforming potential of c-Kit/D816V.
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| 9. |
- Yuan, Bin, et al.
(författare)
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Dose-effect relationship of apoptosis induced by fission-neutron in murine thymocytes
- 2000
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Ingår i: Chinese Journal of Radiological Medical Protection. ; 20, s. 87-87
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Tidskriftsartikel (refereegranskat)abstract
- Objective To investigate the effectiveness of high LET fission-neutron to induce apoptosis in murine thymocytes and to compare it with that of low LET 60Co γ-ray. Methods Apoptosis induction was studied qualitatively by light and transmission electron microscopy and DNA gel electrophoresis,also quantitatively by flow cytometry(FCM) and diphenylamine (DPA)methods. Results DNA ladders of murine thymocytes were detectable,the typical apoptosis of thymocytes could be observed morphologically by means of light and electron microscopy at 6 h after fission-neutron irradiation with doses ranging from 0.5 to 5.0 Gy,meanwhile the percentages of apoptosis increased with increasing doses.After exposure to γ-rays with doses ranging from 1.0 to 30 Gy,the expermiental results were similar to those from neutron radiation.The incidence of apoptosis peaked at about 20 Gy，the percentages did not increase further when doses increased. Conclusion Apoptosis of murine thymocytes can be induced when mice are exposed to either fission-neutron (0.5-5.0 Gy) or to γ-ray (1-30 Gy).Although the relationship between apoptosis and radiation doses is similar,the percentage of apoptosis induced by neutron irradiation is higher than that induced by γ-irradiation.The RBE values of fission-neutron for inducing apoptosis murine thymocytes are 2.09 (by FCM method) and 2.37 (by DPA method),respectively.These results also suggest that fission-neutron-induced murine immune tissue is more severe than that induced by γ-rays at several hours post-irradiation and this might be the basis for heavy damage to immune tissues induced by fission-neutron-irradiation in later period.
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| 10. |
- Zadjali, F, et al.
(författare)
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Structural Basis for c-KIT Inhibition by the Suppressor of Cytokine Signaling 6 (SOCS6) Ubiquitin Ligase
- 2011
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 286:1, s. 480-490
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Tidskriftsartikel (refereegranskat)abstract
- The c-KIT receptor tyrosine kinase mediates the cellular response to stem cell factor (SCF). Whereas c-KIT activity is important for the proliferation of hematopoietic cells, melanocytes and germ cells, uncontrolled c-KIT activity contributes to the growth of diverse human tumors. Suppressor of cytokine signaling 6 (SOCS6) is a member of the SOCS family of E3 ubiquitin ligases that can interact with c-KIT and suppress c-KIT-dependent pathways. Here, we analyzed the molecular mechanisms that determine SOCS6 substrate recognition. Our results show that the SH2 domain of SOCS6 is essential for its interaction with c-KIT pY568. The 1.45-A crystal structure of SOCS6 SH2 domain bound to the c-KIT substrate peptide (c-KIT residues 564-574) revealed a highly complementary and specific interface giving rise to a high affinity interaction (K(d) = 0.3 mum). Interestingly, the SH2 binding pocket extends to substrate residue position pY+6 and envelopes the c-KIT phosphopeptide with a large BG loop insertion that contributes significantly to substrate interaction. We demonstrate that SOCS6 has ubiquitin ligase activity toward c-KIT and regulates c-KIT protein turnover in cells. Our data support a role of SOCS6 as a feedback inhibitor of SCF-dependent signaling and provides molecular data to account for target specificity within the SOCS family of ubiquitin ligases.
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