Browsing by Subject "genetic transcription"

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    Differential p21 expression after ionizing and UVC radiation in EBV-transformed lymphoblastoid cells
    (2000) Moyret-Lalle, C.; Lalle P.; Pedeux, R.; Guillot, C.; Martel, S.; Magaud J.-P.; Puisieux, A.; Ozturk, M.
    Responses to DNA-damaging agents appear to be coordinated by p53 through transcriptional activation of critical target genes. Among them, p21WAF1 encodes a protein preventing cells from entering S phase. It is not clear whether p53-mediated response varies depending on the type of DNA damage. Here, we have decided to compare the p53-mediated response of EBV-transformed lymphoblasts to ionizing radiation and UVC irradiation. We have shown that these cells respond to ionizing radiation by a cell cycle arrest as expected. Surprisingly they failed to do so after UVC treatment. Accordingly there was no significant induction of p21 protein in UVC exposed cells despite p53 accumulation. Using isogenic EBV-transformed lymphoblastoid cells expressing E6 protein of HPV18, we have demonstrated that there was no evidence of p53-dependent cell cycle arrest after UVC irradiation. These observations suggest that the p53-mediated response to UVC, in contrast to ionizing radiation, was compromised in EBV-transformed cells and might be cell type-dependent.
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    SIP1 is downregulated in hepatocellular carcinoma by promoter hypermethylation
    (2011) Acun, T.; Oztas, E.; Yagci, T.; Yakicier, M.C.
    Background: Smad interacting protein-1 is a transcription factor that is implicated in transforming growth factor-β/bone morphogenetic protein signaling and a repressor of E-cadherin and human telomerase reverse transcriptase. It is also involved in epithelial-mesenchymal transition and tumorigenesis. However, genetic and epigenetic alterations of SIP1 have not been fully elucidated in cancers. In this study, we investigated mutations and promoter hypermethylation of the SIP1 gene in human hepatocellular carcinomas.Methods: SIP1 expression was analyzed in HCC cell lines and primary tumors in comparison to normal and non-tumor liver tissues by using semi-quantitative RT-PCR, quantitative real-time RT-PCR and immunohistochemistry. Mutation and deletion screening of the SIP1 gene were performed by direct sequencing in HCC-derived cells. Restoration of SIP1 expression was sought by treating HCC cell lines with the DNA methyl transferase inhibitor, 5-AzaC, and the histone deacetylase inhibitor, TSA. SIP1 promoter methylation was analyzed by the combined bisulfite restriction analysis assay in in silico-predicted putative promoter and CpG island regions.Results: We found that the expression of SIP1 was completely lost or reduced in five of 14 (36%) HCC cell lines and 17 of 23 (74%) primary HCC tumors. Immunohistochemical analysis confirmed that SIP1 mRNA downregulation was associated with decreased expression of the SIP1 protein in HCC tissues (82.8%). No somatic mutation was observed in SIP1 exons in any of the 14 HCC cell lines. Combined treatment with DNA methyl transferase and histone deacetylase inhibitors synergistically restored SIP1 expression in SIP1-negative cell lines. Analysis of three putative gene regulatory regions revealed tumor-specific methylation in more than half of the HCC cases.Conclusions: Epigenetic mechanisms contribute significantly to the downregulation of SIP1 expression in HCC. This finding adds a new level of complexity to the role of SIP1 in hepatocarcinogenesis. © 2011 Acun et al; licensee BioMed Central Ltd.