Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Epigenetic events in early breast cancer

ABSTRACT: Subpopulations of primary Human Mammary Epithelial Cells (HMEC) have the unique ability to escape a period of growth arrest and continue to proliferate. These cells, called post-selection or variant cells (vHMEC), share features with premalignant breast cancer lesions, including p16INK4A promoter hypermethylation. Epigenetic silencing of tumour suppressor genes through DNA methylation and histone modification is an early event in tumorigenesis. One of the main challenges is to find genes or gene pathways that are commonly silenced to provide early epigenetic diagnostic and therapeutic cancer targets. To identify very early epigenetic events that occur in breast cancer, we used microarrays to screen for gene pathways that were suppressed in post-selection HMECs, but reactivated after treatment with the demethylation agent 5-Aza-2â-deoxycytidine (5-Aza-dC). We found several members of the Transforming Growth Factor Beta (TGFb) signalling pathway (THBS1, TGFb2, TGFb R1 & TGFb R2) were consistently down-regulated in the post-selection HMEC population. Gene suppression was not associated with DNA methylation but was associated with chromatin remodelling, involving a decrease in histone H3 lysine 27 (H3K27) tri-methylation and an increase in histone H3 lysine 9 (H3K9) di-methylation and H3K9 de-acetylation. Similar epigenetic repression was also identified MDAMB453 breast cancer cells and in breast tumour samples. These results demonstrate for the first time that TGFb2, its receptors TGFb R1 & TGFb R2 and activator THBS1 are concordantly suppressed early in breast carcinogenesis by repressive histone modifications and indicate that the TGFb signalling pathway is a novel target for gene activation by epigenetic therapy. Keywords: cell differentiation, breast cancer, gene silencing, epigenetics Two-colour reference design was used. Two biological replicates were included in the study - Bre60 and Bre-80. Each cell line was sampled at pre-selection stage, post-selection stage and post AZA treatment. The post-selection stage was chosen as the reference sample, and a control post-post hybridisation included to assess variability across the assay.

ORGANISM(S): Homo sapiens

SUBMITTER: Susan Clark

PROVIDER: E-GEOD-8007 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Concordant epigenetic silencing of transforming growth factor-beta signaling pathway genes occurs early in breast carcinogenesis.

Hinshelwood Rebecca A RA Huschtscha Lily I LI Melki John J Stirzaker Clare C Abdipranoto Andrea A Vissel Bryce B Ravasi Timothy T Wells Christine A CA Hume David A DA Reddel Roger R RR Clark Susan J SJ Clark Susan J SJ

Cancer research 20071201 24

Human mammary epithelial cells (HMEC) grown under standard cell culture conditions enter a growth phase referred to as selection, but a subpopulation is able to escape from arrest and continue to proliferate. These cells, called post-selection or variant HMECs, may be derived from progenitor cells found in normal mammary epithelium that subsequently acquire premalignant lesions, including p16(INK4A) promoter hypermethylation. Epigenetic silencing of tumor suppressor genes through DNA methylation ...[more]

PMID: 18089780

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Project description:Background Epigenetic changes are involved in the extinction of the B-cell gene expression program of classical Hodgkin lymphoma. However, little is known regarding epigenetic similarities between classical Hodgkin lymphoma and plasma cell myeloma cells, both of which share an extinction of the gene expression program of mature B-cells. Design and methods Global histone H3 acetylation patterns were determined in cell lines derived from classical Hodgkin lymphoma, plasma cell myeloma and B-cell lymphoma by chromatin immunoprecipitation and subsequent hybridization onto promoter tiling arrays. H3K27 trimethylation was analyzed by chromatin immunoprecipitation and real-time DNA-PCR for selected genes. Epigenetic modifications were compared to gene expression data. Results B-cell characteristic genes were hypoacetylated in classical Hodgkin lymphoma and plasma cell myeloma cell lines, as demonstrated by comparison of their histone H3 acetylation patterns to those of B-cell lines. However, the number of genes jointly hyperacetylated and expressed in classical Hodgkin lymphoma and plasma cell myeloma cell lines, such as IFR4/MUM1 and RYBP, is limited. Moreover, H3K27 trimethylation for selected B-cell characteristic genes revealed that this additional epigenetic silencing is much more prevalent in classical Hodgkin lymphoma as compared to plasma cell myeloma. Conclusion Our epigenetic data support the view that classical Hodgkin lymphoma is characterized by an abortive plasma cell differentiation with a down-regulation of B-cell characteristic genes but without activation of most plasma cell typical genes. Combined 5-aza-dC/TSA (A/T) treatment: The diffuse large B-cell lymphoma (DLBCL)-derived cell lines SU-DHL4, SU-DHL6 and HT and the Burkitt lymphoma-derived cell lines Daudi, Namalwa and Raji were treated with 5-aza-dC at a concentration of 3 µM for 6 days. 5-aza-dC and medium was replaced at day 2 and 5. At the fifth day - in addition to 3 µM 5-aza-dC - cells were incubated for 24 hours with 625 nM TSA. RNA was isolated according to standard protocols (Qiagen, Hilden, Germany) and used for Affymetrix GeneChip hybridization (HG-U133A). Microarrays were normalized using RMA and differential expression was calculated using moderated t-test. The gene expression profiles of the untreated and treated cell lines (with the exception of HT) were generated in duplicates. Microarray data (CEL files) for AZA/TSA-treated BL-derived cell lines Raji, Daudi and Namalwa were previously published (GEO accession GSE8388).

Project description:Expression profiling the response to inhibition of DNA methylation and histone deacetylation. Comparison of expression in HepG2 cells treated with 5-aza-dC, Trichostatin A, both, or none (control) to change methylation and acetylation status. Backgroubd: DNA methylation and histone deacetylation are epigenetic mechanisms that play major roles in eukaryotic gene regulation. We hypothesize that many genes in the human hepatoma cell line HepG2 are regulated by DNA methylation and histone deacetylation. Treatment with 5-aza-2'-deoxycytidine (5-aza-dC) to inhibit DNA methylation with and/or Trichostatin A (TSA) to inhibit histone deacetylation should allow us to identify genes that are regulated epigenetically in hepatoma cells. RESULTS: 5-aza-dC had a much larger effect on gene expression in HepG2 cells than did TSA, as measured using Affymetrix HG-U133 Plus 2.0 microarrays. The expression of 1504 probe sets was affected by 5-aza-dC (at p < 0.01), 535 probe sets by TSA, and 1929 probe sets by the combination of 5-aza-dC and TSA. 5-aza-dC treatment turned on the expression of 211 probe sets that were not detectably expressed in its absence. Expression of imprinted genes regulated by DNA methylation, such as H19 and NNAT, was turned on or greatly increased in response to 5-aza-dC. Genes involved in liver processes such as xenobiotic metabolism (CYP3A4, CYP3A5, and CYP3A7) and steroid biosynthesis (CYP17A1 and CYP19A1), and genes encoding CCAAT element-binding proteins (C/EBPalpha, C/EBPbeta, and C/EBPgamma) were affected by 5-aza-dC or the combination. Many of the genes that fall within these groups are also expressed in the developing fetal liver and adult liver. Quantitative real-time RT-PCR assays confirmed selected gene expression changes seen in microarray analyses. CONCLUSION: Epigenetics play a role in regulating the expression of several genes involved in essential liver processes such as xenobiotic metabolism and steroid biosynthesis in HepG2 cells. Many genes whose expression is normally silenced in these hepatoma cells were re-expressed by 5-aza-dC treatment. DNA methylation may be a factor in restricting the expression of fetal genes during liver development and in shutting down expression in hepatoma cells

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Dataset Information

Epigenetic events in early breast cancer

Publications

Concordant epigenetic silencing of transforming growth factor-beta signaling pathway genes occurs early in breast carcinogenesis.

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