Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P10721 (c-kit)
 6,575 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Stem cell factor (SCF)/c-kit plays an important role in the regulation of hematopoiesis, melanogenesis, and spermatogenesis. In the testis, the SCF/c-kit system is believed to regulate germ cell proliferation, meiosis, and apoptosis. Studies with type A spermatogonia in vivo and in vitro have indicated that SCF induces DNA synthesis and proliferation. However, the signaling pathway for this function of SCF/c-kit has not been elucidated. We now demonstrate that SCF activates phosphoinositide 3-kinase (PI3-K) and p70 S6 kinase (p70S6K) and that rapamycin, a FRAP/mammalian target of rapamycin-dependent inhibitor of p70S6K, completely inhibited bromodeoxyuridine incorporation induced by SCF in primary cultures of spermatogonia. SCF induced cyclin D3 expression and phosphorylation of the retinoblastoma protein through a pathway that is sensitive to both wortmannin and rapamycin. Furthermore, AKT, but not protein kinase C-zeta, is used by SCF/c-kit/PI3-K to activate p70S6K. Dominant negative AKT-K179M completely abolished p70S6K phosphorylation induced by the constitutively active PI3-K catalytic subunit p110. Constitutively active v-AKT highly phosphorylated p70S6K, which was totally inhibited by rapamycin. Thus, SCF/c-kit uses a rapamycin-sensitive PI3-K/AKT/p70S6K/cyclin D3 pathway to promote spermatogonial cell proliferation.
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PMID:Stem cell factor/c-kit up-regulates cyclin D3 and promotes cell cycle progression via the phosphoinositide 3-kinase/p70 S6 kinase pathway in spermatogonia. 1084 22

Establishment of the mammalian germ line is a prerequisite for fertility of the adult animal but we know surprisingly little about the molecular mechanisms regulating germ-line development in mammals. Signaling from the c-Kit receptor tyrosine kinase is essential for primordial germ cell (PGC) growth both in vivo and in vitro. Many downstream effectors of the c-Kit signaling pathway have been identified in other cell types but how these molecules control PGC survival and proliferation are unknown. Determination of the c-Kit effectors acting in PGCs has been hampered by the lack of effective methods to easily manipulate gene expression in these cells. We overcame this problem by testing the efficacy of retroviral-mediated gene transfer for manipulating gene expression in mammalian germ cells. We found that PGCs can be successfully infected with a variety of types of retroviruses. We used this method to demonstrate an important role for the AKT kinase in regulating PGC growth. Such technology for manipulating gene expression in PGCs will allow many of the molecular mechanisms regulating germ cell growth, behavior, and differentiation to be comprehensively analyzed.
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PMID:Dissection of the c-Kit signaling pathway in mouse primordial germ cells by retroviral-mediated gene transfer. 1214 Mar 61

Mutations in the proto-oncogene c-kit cause constitutive kinase activity of its product, KIT protein, and are associated with human mastocytosis and gastrointestinal stromal tumors (GISTs). Although currently available tyrosine kinase inhibitors are effective in the treatment of GISTs, there has been limited success in the treatment of mastocytosis. 17-Allylamino-17-demethoxygeldanamycin (17-AAG), a benzoquinoid ansamycin antibiotic, which binds to heat shock protein 90 (hsp90) causes destabilization of various hsp90-dependent kinases important in oncogenesis. Treatment with 17-AAG of the mast cell line HMC-1.2, harboring the Asp816Val and Val560Gly KIT mutations, and the cell line HMC-1.1, harboring a single Val560Gly mutation, causes both the level and activity of KIT and downstream signaling molecules AKT and STAT3 to be down-regulated following drug exposure. These data were validated using Cos-7 cells transfected with wild-type and mutated KIT. 17-AAG promotes cell death of both HMC mast cell lines. In addition, neoplastic mast cells isolated from patients with mastocytosis, incubated with 17-AAG ex vivo, are selectively sensitive to the drug compared to the mononuclear fraction. These data provide compelling evidence that 17-AAG may be effective in the treatment of c-kit-related diseases including mastocytosis, GISTs, mast cell leukemia, subtypes of acute myelogenous leukemia, and testicular cancer.
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PMID:17-Allylamino-17-demethoxygeldanamycin (17-AAG) is effective in down-regulating mutated, constitutively activated KIT protein in human mast cells. 1455 Nov 38

Stem cell factor (SCF) is essential for the development of primordial follicles. One of its functions is to prevent oocytes from apoptosis. However, the underlying mechanism remains largely unknown. By using cultured ovaries that are rich in primordial follicles, the anti-apoptotic action of SCF and the potential signal transduction pathways were investigated. The apoptosis was evaluated by means of in situ 3'-end labeling. The expressions of proteins were analyzed with immunohistochemistry and Western blot. The data showed that SCF significantly prevented oocytes from apoptosis in the cultured organs. Addition of a specific pharmacological inhibitor of PI3K abolished the anti-apoptotic action of SCF while that of a MEK inhibitor did not. The phosphorylation of two mitogen activated protein kinases (MAPKs) (p42 and p44) and AKT, the respective substrates of MEK and PI3K, were enhanced by SCF treatment. Not surprisingly, the MAPK activation occurred only in theca cells. The expressions of apoptosis-related gene products, the Bcl-2 family proteins, in response to SCF treatment were also investigated. While SCF up-regulated the expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL, it did the opposite to the pro-apoptotic factor Bax. The PI3K inhibitor reversed the regulation of SCF on Bcl-xL and Bax but not on Bcl-2. Therefore, it seemed that SCF initiated an anti-apoptotic signal starting from its membrane receptor c-kit to Bcl-2 family members through PI3K/AKT and other signaling cascades in the oocytes of primordial follicles.
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PMID:Anti-apoptotic action of stem cell factor on oocytes in primordial follicles and its signal transduction. 1551 61

The Kasumi-1 cell line is an intensively investigated model system of Acute Myeloid Leukemia with t(8;21) translocation, that represents 1 of the 2 main subtypes of Core Binding Factor Leukemia (CBFL). Since establishment in 1991 the Kasumi-1 cell line has provided the tool to study the peculiar molecular, morphologic, immunophenotypic findings of AML with t(8;21) and the functional consequences of the AML1-ETO fusion oncogene on myeloid differentiation. Leukemogenesis involves multiple genetic changes and, as suggested by murine experiments and other findings in humans, AML1-ETO expression may not be sufficient for full blown leukemia. In agreement with the "two hits" model of leukemogenesis, based on the cooperation between 1 class of mutations that impair hematopoietic differentiation and a second class of mutations that confer a proliferative and/or survival advantage to hematopoietic progenitors an activating mutation in the tyrosine kinase domain of the c-kit gene was identified in the AML1/ETO expressing Kasumi-1 cell line. The dosage of the Asn822Lys mutated allele was shown to be about 5-fold compared to the normal allele and c-kit amplification was found to map to minute 4cen-q11 marker chromosomes, likely derived from the extra chromosome 4 recorded in the newly established cell line. The combination of t(8;21) and trisomy 4 leading to enhanced dosage of a mutated kit allele is a feature of a few CBFL patients reproduced by the Kasumi-1 cell model. The Kasumi-1 cell line, paralleling the commitment stage of CBF leukemia also provides a valuable resource to investigate the effect of tyrosine kinase kit mutant on the main KIT-regulated signal transduction pathways, i.e. MAPK, PI3K/AKT and STAT3 and the diverse inhibitory effect exerted by STI 571 on these KIT mutant activated pathways. PI3K-dependent activation of AKT and STAT activation was observed in Kasumi-1 cells. Contrary to the expectations for an amplified tyrosine kinase kit mutant, we found that STI 571 inhibited KIT Asn822Lys tyrosine phosphorylation and downstream JNK and STAT3 effectors in Kasumi-1 cells, but had no effect on constitutive activation of AKT, suggesting that signaling by tyrosine kinases other than KIT may be responsible for its activation in Kasumi-1 cells. Independent findings on the same model system provide complementary insights into designing strategies for treatment of CBF leukemia associated with mutations in the KIT catalytic domain.
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PMID:The Kasumi-1 cell line: a t(8;21)-kit mutant model for acute myeloid leukemia. 1562 9

The development of in vitro models for testicular toxicity may provide important tools for investigating specific mechanisms of toxicity in the testis. Although various systems have been reported, their application in toxicological studies has been limited by the poor ability to replicate the complex biochemical, molecular, and functional interactions observed in the testis. In the present study, we evaluated a significantly improved Sertoli cell/gonocyte co-culture (SGC) system that employs a 3-dimensional extracellular matrix Matrigel (ECM) applied as an overlay instead of a substratum. We explored the dose- and time-dependent effects of the addition of such an ECM overlay on cytoskeletal and morphological changes in the SGC system, and the resulting effects on cellular integrity. Furthermore, we correlated the latter effects with the ECM-dependent modulation of stress and survival signaling pathways and, most critically, the expression levels of the spermatogonia-specific protein, c-Kit. Finally, we applied this co-culture system to investigate the dose- and time-dependent effects on the morphology and induction of apoptosis of cadmium. We observed that the dose-dependent addition of an ECM overlay led to an enhanced attachment of Sertoli cells and facilitated the establishment of SGC communication and cytoskeletal structure, with a dramatic improvement in cell viability. The latter was consistent with the observed dose- and time-dependent modulation of both stress signaling pathways (SAPK/JNK) and survival signaling pathways (ERK and AKT) in the presence of the ECM overlay. Furthermore, the dose-dependent stabilization of c-Kit protein expression confirmed the functional integrity of this co-culture system. We conclude that this modified SGC system will provide investigators with a simple, efficient, and highly reproducible alternative in the screen for testicular cell-specific cytotoxicity and the assessment of molecular mechanisms associated with both normal development and reproductive toxicity induced by environmental toxicants.
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PMID:Essential role of extracellular matrix (ECM) overlay in establishing the functional integrity of primary neonatal rat Sertoli cell/gonocyte co-cultures: an improved in vitro model for assessment of male reproductive toxicity. 1565 72

Imatinib mesylate (IM) is a tyrosine kinase inhibitor, which inhibits phosphorylation of downstream proteins involved in BCR-ABL signal transduction. It has proved beneficial in treating patients with chronic myeloid leukaemia (CML). In addition, IM demonstrates activity against malignant cells expressing c-kit and platelet-derived growth factor receptor (PDGF-R). The activity of IM in the blastic crisis of CML and against various myeloma cell lines suggests that this drug may also target other cellular components. In the light of the important role of telomerase in malignant transformation, we evaluated the effect of IM on telomerase activity (TA) and regulation in various malignant cell lines. Imatinib mesylate caused a dose-dependent inhibition of TA (up to 90% at a concentration of 15 microM IM) in c-kit-expressing SK-N-MC (Ewing sarcoma), SK-MEL-28 (melanoma), RPMI 8226 (myeloma), MCF-7 (breast cancer) and HSC 536/N (Fanconi anaemia) cells as well as in ba/F3 (murine pro-B cells), which do not express c-kit, BCR-ABL or PDGF-R. Imatinib mesylate did not affect the activity of other DNA polymerases. Inhibition of TA was associated with 50% inhibition of proliferation. The inhibition of proliferation was associated with a decrease in the S-phase of the cell cycle and an accumulation of cells in the G2/M phase. No apoptosis was observed. Inhibition of TA was caused mainly by post-translational modifications: dephosphorylation of AKT and, to a smaller extent, by early downregulation of hTERT (the catalytic subunit of the enzyme) transcription. Other steps of telomerase regulation were not affected by IM. This study demonstrates an additional cellular target of IM, not necessarily mediated via known tyrosine kinases, that causes inhibition of TA and cell proliferation.
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PMID:Imatinib mesylate (Gleevec) downregulates telomerase activity and inhibits proliferation in telomerase-expressing cell lines. 1587 Jul 11

Activating mutations of c-KIT lead to ligand-independent growth. Internal tandem duplications (ITDs) of exon 11, which encodes the juxtamembrane domain (JMD), are constitutively activating mutations found in 7% of gastrointestinal stromal tumors (GISTs) but have not been described in childhood acute myeloid leukemia (AML). DNA and cDNA from 60 children with AML were screened by polymerase chain reaction (PCR) for mutations of the JMD. A complex ITD (kit cITD) involving exon 11 and exon 12 was identified with a relative frequency of 7% (4/60). The human kit cITDs were inserted into the murine c-Kit backbone and expressed in Ba/F3 cells. KIT cITD induced factorindependent growth and apoptosis resistance, and exhibited constitutive autophosphorylation. KIT cITD constitutively activated the PI3K/AKT pathway and phosphorylated STAT1, STAT3, STAT5, and SHP-2. Imatinib (IM) or rapamycin (Rap) led to complete inhibition of growth, with IC50 values at nanomolar levels. IM and Rap synergistically inhibited growth and surmounted KIT cITD-induced apoptosis resistance. IM but not LY294002 inhibited phosphorylation of STAT3 and STAT5, suggesting aberrant cross talk between PI3K- and STAT-activating pathways. The findings presented may have immediate therapeutic impact for a subgroup of childhood AML-expressing c-KIT mutations.
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PMID:Newly identified c-KIT receptor tyrosine kinase ITD in childhood AML induces ligand-independent growth and is responsive to a synergistic effect of imatinib and rapamycin. 1684 Jul 25

Mutation of the platelet-derived growth factor receptor-alpha (PDGFRA) gene has been well documented as an alternative oncogenic mechanism in a subset of gastrointestinal stromal tumors (GISTs) lacking c-kit mutations. However, the role of PDGFRA immunohistochemistry in the diagnosis of GISTs has not been well studied. We investigated PDGFRA immunoreactivity in GISTs and in other intra-abdominal mesenchymal tumors, and correlated PDGFRA expression with CD117 positivity and with the mutational status of PDGFRA and c-kit genes. In addition, expression of phosphorylated AKT, an activated downstream molecule in the PDGFRA and c-kit signaling pathways, was correlated with PDGFRA and CD117 status. A total of 39 GISTs and 20 other mesenchymal tumors in the abdomen were included in this study. Thirty-five of 39 GIST cases (89.7%) were positive for PDGFRA and 19 of these 35 positive cases were strongly positive. Five of 20 non-GIST lesions (25%) were positive for PDGFRA, but none of these cases were strongly positive. With one exception, PDGFRA-positive cases were also positive for CD117. Phosphorylated AKT positivity was not associated with the immunoreactivity or mutation of PDGFRA and c-kit, suggesting that the activation of AKT is probably independent of the activation of PDGFRA and c-kit in GISTs. Of 14 GISTs assayed, 4 had mutations in c-kit at exons 11 or 17, and 4 had mutations in PDGFRA at exons 12 or 18. Three of 4 GIST cases with PDGFRA mutations show epithelioid morphology and strong PDGFRA immunoreactivity with prominent perinuclear dotlike accentuation (so-called Golgi pattern). In conclusion, strong PDGFRA positivity with Golgi pattern is a useful adjunct in the diagnosis of GISTs with PDGFRA mutation.
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PMID:Strong PDGFRA positivity is seen in GISTs but not in other intra-abdominal mesenchymal tumors: Immunohistochemical and mutational analyses. 1712 34

In acute myeloid leukemia (AML), autocrine or paracrine activation of receptor tyrosine kinases such as c-kit and FLT3 contributes to proliferation and apoptosis resistance of leukemic blasts. This provided the rationale for a multicenter clinical trial in patients with refractory AML with SU5416, a small molecule kinase inhibitor which blocks phosphorylation of c-kit, FLT3, VEGFR-1, VEGFR-2 (KDR) and VEGFR-3. The levels of VEGF mRNA expression were investigated in peripheral blood leukemic blasts taken from AML patients before and during treatment with SU5416. Rapid down regulation of VEGF was observed in AML blasts from 72% (13 of 18) of patients analysed. Patients initially expressing high VEGF-levels had a stronger downregulation and a higher clinical response rate (mean 865-fold, n = 10, P = 0,01) than patients initially expressing low VEGF-levels (mean four-fold, n = 8). These results suggest that abnormal high VEGF expression is downregulated by SU5416 treatment, and furthermore that decreases in VEGF mRNA levels may provide an early marker of therapeutic response with anti-angiogenic therapy. Additionally, protein expression of STAT5 and AKT was assessed by western blotting in these patient samples, as well as in the leukemia cell line, M-07e, treated in vitro with SU5416 as a model system. In the AML patient samples, parallel downregulation of both STAT5 and AKT was observed in several cases (STAT5 in four of 15; AKT in three of six examined patients). These effects were confirmed with the cell line M-07e after incubation with SU5416 in vitro using concentrations that are achievable in patients. In summary, our data show suppression of the expression of VEGF and key signal transduction intermediates in AML blasts during treatment with SU5416.
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PMID:Downregulation of VEGF-A, STAT5 and AKT in acute myeloid leukemia blasts of patients treated with SU5416. 1716 5


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