Oncogene
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Retinoids signal biological effects through retinoic acid receptors (RAR) and retinoid X receptors (RXR) and their co-regulators. We previously reported that all-trans retinoic acid (RA) triggers terminal differentiation in the human embryonal carcinoma cell line NTERA-2 clone D1 (NT2/D1), through an RARgamma dependent pathway. RARgamma repression in NT2/D1-R1 cells accounts for RA resistance in this line. ⋯ Semi-quantitative reverse transcription-polymerase chain reaction (RT - PCR) assays of total RNA from 4HPR-treated NT2/D1 and NT2/D1-R1 cells did not reveal RARgamma induction. Since 4HPR signals in RA-resistant NT2/D1-R1 cells having an RARgamma transcriptional block, these results indicate that 4HPR triggers apoptosis but not differentiation through an RARgamma independent pathway. Taken together, these findings implicate a therapeutic role for 4HPR mediated apoptosis in germ cell tumors even when a maturation block is present.
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One prominent effect of IFNs is their cell growth-inhibitory activity. The mechanism behind this inhibition of proliferation is still not fully understood. In this study, the effect of IFN-alpha treatment on cell cycle progression has been analysed in three lymphoid cell lines, Daudi, U-266 and H9. ⋯ Moreover, elevated levels of p27 correlated with a dissociation of cyclin E/Cdk2-p130 or p107 complexes to yield cyclin E/Cdk2-p27 complexes. In resistant H9 cells, which possess a homozygous deletion of the p15/p16 genes and lack p21 protein expression, IFN-alpha causes no detectable changes in p27 expression and, furthermore, no effects are observed on either pocket proteins in this cell line. Taken together, these data suggest that the early decline in G1 Cdk activity, subsequent changes in phosphorylation of pocket proteins, and G1/G0 arrest following IFN-alpha treatment, is not primarily due to loss of the G1 kinase components, but result from the inhibitory action of CKIs on these complexes.
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Human T-cells immortalized (interleukin-2 [IL-2] dependent) by the human T-cell lymphotropic/leukemia virus type I (HTLV-I), in time, become transformed (IL-2 independent). To understand the biochemical basis of this transition, we have used the sibling HTLV-I-infected T-cell lines, N1186 (IL-2 dependent) and N1186-94 (IL-2 independent), as models to assess the responses to antiproliferative signals. In N1186 cells arrested in G1 after serum/interleukin-2 (IL-2) deprivation, downregulation of the cyclin E-CDK2 kinase activity correlated with decreased phosphorylation of CDK2 and accumulation of p27Kip1 bound to the cyclin E-CDK2 complex, as seen in normal activated PBMCs (peripheral blood mononuclear cells). ⋯ In fact, the amount of p27Kip1 protein was lower in most HTLV-I-transformed (IL-2-independent) than in the immortalized (IL-2-dependent) HTLV-I-infected T-cells. Furthermore, specific inhibitors of the phosphatidylinositol 3-kinase (P13K) induced an increase of p27Kip1 protein levels, which correlated with G1 arrest, in both IL-2-dependent and IL-2-independent HTLV-I-infected T-cells. Altogether, these results suggest that maintaining a low level of expression of p27Kip1 is a key event in HTLV-I transformation.
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Hereditary papillary renal carcinoma (HPRC) is characterized by multiple, bilateral papillary renal carcinomas. Previously, we demonstrated missense mutations in the tyrosine kinase domain of the MET proto-oncogene in HPRC and a subset of sporadic papillary renal carcinomas. In this study, we screened a large panel of sporadic papillary renal carcinomas and various solid tumors for mutations in the MET proto-oncogene. ⋯ These mutations caused constitutive phosphorylation of MET when transfected into NIH3T3 cells. Molecular modeling studies suggest that these activating mutations interfere with the intrasteric mechanism of tyrosine kinase autoinhibition and facilitate transition to the active form of the MET kinase. The low frequency of MET mutations in noninherited papillary renal carcinomas (PRC) suggests that noninherited PRC may develop by a different mechanism than hereditary papillary renal carcinoma.
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The novel synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) has been shown to induce apoptosis in various tumor cell lines including human non-small cell lung carcinoma (NSCLC) cells, which are resistant to the natural all-trans retinoic acid and to many synthetic receptor-selective retinoids. Although the mechanism of this effect was not elucidated, it was found to be independent of nuclear retinoid receptors. In the present study, we analysed the mechanisms by which CD437 induces apoptosis in two human NSCLC cell lines: H460 with wild-type p53 and H1792 with mutant p53. ⋯ CD437 induced the expression of the p53 gene and its target genes, p21, Bax, and Killer/DR5, only in the H460 cells. These results suggest that CD437-induced apoptosis is more extensive in NSCLC cells that express wild-type p53, possibly due to the involvement of the p53 regulated genes Killer/DR5, and Bax although CD437 can also induce apoptosis by means of a p53-independent mechanism. Both pathways of CD437-induced apoptosis appear to involve activation of CPP32-like caspase.