Dynamics of MBD2 deposition across methylated DNA regions during malignant transformation of human mammary epithelial cells.

DNA methylation is thought to induce transcriptional silencing through the combination of two mechanisms: the repulsion of transcriptional activators unable to bind their target sites when methylated, and the recruitment of transcriptional repressors with specific affinity for methylated DNA. The Methyl CpG Binding Domain proteins MeCP2, MBD1 and MBD2 belong to the latter category. Here, we present MBD2 ChIPseq data obtained from the endogenous MBD2 in an isogenic cellular model of oncogenic transformation of human mammary cells. In immortalized (HMEC-hTERT) or transformed (HMLER) cells, MBD2 was found in a large proportion of methylated regions and associated with transcriptional silencing. A redistribution of MBD2 on methylated DNA occurred during oncogenic transformation, frequently independently of local DNA methylation changes. Genes downregulated during HMEC-hTERT transformation preferentially gained MBD2 on their promoter. Furthermore, depletion of MBD2 induced an upregulation of MBD2-bound genes methylated at their promoter regions, in HMLER cells. Among the 3,160 genes downregulated in transformed cells, 380 genes were methylated at their promoter regions in both cell lines, specifically associated by MBD2 in HMLER cells, and upregulated upon MBD2 depletion in HMLER. The transcriptional MBD2-dependent downregulation occurring during oncogenic transformation was also observed in two additional models of mammary cell transformation. Thus, the dynamics of MBD2 deposition across methylated DNA regions was associated with the oncogenic transformation of human mammary cells.

[Rapid detection of BRCA-1 germline mutations by the protein truncation test in Tunisian families]. / Depistage rapide des mutations germinales du gene BRCA 1 par le test de la proteine tronquee chez des familles tunisiennes.

UNLABELLED: Early-onset breast cancer characterize genetic predisposition to cancer in women. BRCA-1 gene was identified as one of the predisposition genes of breast/ovarian cancer. About 90% of the reported mutations in the hereditary breast and ovarian cancer gene, BRCA-1, result in truncated proteins. The aim of our study is to detect rapidly BRCA-1 mutations by the protein truncation test (PTT) in Tunisian women with early breast cancer. Population and methods. We underwent molecular analysis in families with more than: (a) a women under 40 years-old with breast cancer, uni or bilateral; (b) two 1st degree relatives women under 50 years-old with beast cancer. Sixteen women from 12 families were studied by PTT to screen mutations in exon 11 which encodes 61% of BRCA-1. RESULTS: PTT analysis of exon 11 revealed a normal and truncated protein in one patient between 16 from 12 families. CONCLUSION: BRCA-1 gene seems to contribute to at least 1/16 or 6.25% in women with hereditary predisposition to breast/ovarian cancer in Tunisia. PTT promises to be a valuable technique in detecting BRCA-1 mutations in our country.