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Transcriptional repression of BRCA1 by aberrant cytosine methylation, histone hypoacetylation and chromatin condensation of the BRCA1 promoter.

ABSTRACT: BRCA1 expression is repressed by aberrant cytosine methylation in sporadic breast cancer. We hypothesized that aberrant cytosine methylation of the BRCA1 promoter was associated with the transcriptionally repressive effects of histone hypoacetylation and chromatin condensation. To address this question, we developed an in vitro model of study using normal cells and sporadic breast cancer cells with known levels of BRCA1 transcript to produce a 1.4 kb 5-methylcytosine map of the BRCA1 5' CpG island. While all cell types were densely methylated upstream of -728 relative to BRCA1 transcription start, all normal and BRCA1 expressing cells were non-methylated downstream of -728 suggesting that this region contains the functional BRCA1 5' regulatory region. In contrast, the non-BRCA1 expressing UACC3199 cells were completely methylated at all 75 CpGs. Chromatin immunoprecipitations showed that the UACC3199 cells were hypoacetylated at both histones H3 and H4 in the BRCA1 promoter compared to non-methylated BRCA1 expressing cells. The chromatin of the methylated UACC3199 BRCA1 promoter was inaccessible to DNA-protein interactions. These data indicate that the epigenetic effects of aberrant cytosine methylation, histone hypoacetylation and chromatin condensation act together in a discrete region of the BRCA1 5' CpG island to repress BRCA1 transcription in sporadic breast cancer.

SUBMITTER: Rice JC

PROVIDER: S-EPMC110706 | biostudies-literature | 2000 Sep

REPOSITORIES: biostudies-literature

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Transcriptional repression of BRCA1 by aberrant cytosine methylation, histone hypoacetylation and chromatin condensation of the BRCA1 promoter.

Rice J C JC Futscher B W BW

Nucleic acids research 20000901 17

BRCA1 expression is repressed by aberrant cytosine methylation in sporadic breast cancer. We hypothesized that aberrant cytosine methylation of the BRCA1 promoter was associated with the transcriptionally repressive effects of histone hypoacetylation and chromatin condensation. To address this question, we developed an in vitro model of study using normal cells and sporadic breast cancer cells with known levels of BRCA1 transcript to produce a 1.4 kb 5-methylcytosine map of the BRCA1 5' CpG isla ...[more]

PMID: 10954590

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Project description:FOXA1 expression correlates with the breast cancer luminal subtype and patient survival. RNA and protein analysis of a panel of breast cancer cell lines revealed that BRCA1 deficiency is associated with the downregulation of FOXA1 expression. Knockdown of BRCA1 resulted in the downregulation of FOXA1 expression and enhancement of FOXA1 promoter methylation in MCF-7 breast cancer cells, whereas the reconstitution of BRCA1 in Brca1-deficent mouse mammary epithelial cells (MMECs) promoted Foxa1 expression and methylation. These data suggest that BRCA1 suppresses FOXA1 hypermethylation and silencing. Consistently, the treatment of MMECs with the DNA methylation inhibitor 5-aza-2'-deoxycitydine induced Foxa1 mRNA expression. Furthermore, treatment with GSK126, an inhibitor of EZH2 methyltransferase activity, induced FOXA1 expression in BRCA1-deficient but not in BRCA1-reconstituted MMECs. Likewise, the depletion of EZH2 by small interfering RNA enhanced FOXA1 mRNA expression. Chromatin immunoprecipitation (ChIP) analysis demonstrated that BRCA1, EZH2, DNA methyltransferases (DNMT)1/3a/3b and H3K27me3 are recruited to the endogenous FOXA1 promoter, further supporting the hypothesis that these proteins interact to modulate FOXA1 methylation and repression. Further co-immunoprecipitation and ChIP analysis showed that both BRCA1 and DNMT3b form complexes with EZH2 but not with each other, consistent with the notion that BRCA1 binds to EZH2 and negatively regulates its methyltransferase activity. We also found that EZH2 promotes and BRCA1 impairs the deposit of the gene silencing histone mark H3K27me3 on the FOXA1 promoter. These associations were validated in a familial breast cancer patient cohort. Integrated analysis of the global gene methylation and expression profiles of a set of 33 familial breast tumours revealed that FOXA1 promoter methylation is inversely correlated with the transcriptional expression of FOXA1 and that BRCA1 mutation breast cancer is significantly associated with FOXA1 methylation and downregulation of FOXA1 expression, providing physiological evidence to our findings that FOXA1 expression is regulated by methylation and chromatin silencing and that BRCA1 maintains FOXA1 expression through suppressing FOXA1 gene methylation in breast cancer.

Dataset Information

Transcriptional repression of BRCA1 by aberrant cytosine methylation, histone hypoacetylation and chromatin condensation of the BRCA1 promoter.

Publications

Transcriptional repression of BRCA1 by aberrant cytosine methylation, histone hypoacetylation and chromatin condensation of the BRCA1 promoter.

Similar Datasets

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