Cell type-specific methylation of an intronic CpG island controls expression of the MCJ gene
ABSTRACT Over 50% of human genes are associated with CpG islands and DNA methylation within such CpG islands has been clearly correlated with inhibition of expression. Whereas changes in DNA methylation play a key role in a number of human diseases, in particular cancer, in normal DNA CpG islands are nearly always methylation free, regardless of the expression status of the associated gene. Only limited evidence supports a role for DNA methylation in controlling tissue-specific expression in adult somatic tissue. Loss of expression of the MCJ gene has previously been linked to increased chemotherapeutic drug resistance in ovarian cancer. We report that loss of expression of MCJ in drug-resistant ovarian cancer cell lines depends on methylation of a CpG island within its first exon, but is independent of methylation within the promoter region. Furthermore, cell type-specific expression of the MCJ gene in normal cells also depends on the methylation status of the CpG island within its first exon. The MCJ CpG island is methylated and the gene is not expressed in cells of epithelial origin, but unmethylated and expressed in cells of lymphocyte or fibroblast origin. Chromatin immunoprecipitation assays determined that MCJ CpG island methylation was associated with loss of histone acetylation in ovarian epithelial cells compared with unmethylated fibroblast cells. Reduced acetylation was observed not only within the CpG island, but also within the promoter region, suggesting that CpG island methylation may direct alterations in chromatin structure within the promoter region, leading to gene inactivation.
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ABSTRACT: Mitochondria have a central role in the intrinsic pathway of apoptosis and involve activation of several transmembrane channels leading to release of death factors. Reduced expression of a mitochondrial J-protein DnaJC15 was associated with the development of chemoresistance in ovarian cancer cells. DnaJC15 was found to be a part of mitochondrial protein-transport machinery, though its connection with cell death mechanisms is still unclear. In the present study, we have provided evidence towards a novel function of DnaJC15 in regulation of mitochondrial permeability transition pore (MPTP) complex in normal and cancer cells. Overexpression of DnaJC15 resulted in MPTP opening and induction of apoptosis, whereas reduced amount of protein suppressed MPTP activation, upon cisplatin treatment. DnaJC15 was found to exert its proapoptotic function through the essential component of MPTP, cyclophilin D (CypD). Our results reveal a specific role of DnaJC15 in recruitment and coupling of CypD with mitochondrial permeability transition. In summary, our analysis provides first-time insights on the functional connection between mitochondrial inner membrane protein translocation machinery-associated J-protein DnaJC15 and regulation of cell death pathways.Cell Death & Disease 03/2014; 5:e1101. DOI:10.1038/cddis.2014.72 · 5.18 Impact Factor
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ABSTRACT: Genetic alterations alone cannot account for the complexity of ovarian cancer. The potential reversibility of epigenetic mechanisms makes them attractive candidates for the prevention and/or treatment of ovarian carcinoma. Detection of the epigenetic signature of each cancer cell may be useful in the identification of candidate biomarkers for disease detection, classification and monitoring and may also facilitate personalized cancer treatment. In ovarian cancer, in addition to other non‑gynaecological cancers, two opposite epigenetic phenomena occur. The first involves an overall global decrease in DNA methylation of heterochromatin leading to demethylation of several oncogenes, while the second involves specific CpG island hypermethylation associated with the promoters of tumor suppressor genes. Early studies focused on the methylation patterns of single genes associated with tumorigenesis. However, newer genome-wide methods have identified a group of genes whose regulation is altered by DNA methylation during ovarian cancer progression.Molecular Medicine Reports 05/2014; 10(1). DOI:10.3892/mmr.2014.2221 · 1.48 Impact Factor