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CpG island hypermethylation and CpG-poor region hypomethylation drive gastric cancer risk after Helicobacter pylori eradication

ABSTRACT: Aberrant DNA methylation is deeply involved in the development of gastric cancer (GC) and has emerged as a promising biomarker for risk prediction. In this study, we performed comprehensive DNA methylation profiling of tumor and non-tumor gastric mucosa from patients who developed GC after Helicobacter pylori (H. pylori) eradication (post-eradication GC, PEGC). The normal mucosa of PEGC patients exhibited substantial CpG island (CGI) hypermethylation, comparable to that observed in H. pylori-infected tissues and intestinal metaplasia. We also identified approximately 4,000 CpG sites recurrently hypomethylated in GC using The Cancer Genome Atlas (TCGA)-STAD data, many of which were already hypomethylated in normal mucosa of PEGC. Majority of the hypomethylated sites are located outside of CGIs, and several of them are located near oncogenes such as CDH17, HNF4A, and CD44, and their methylation levels inversely correlated with gene expression. Importantly, we found a strong positive correlation between CGI hypermethylation and CpG hypomethylation, suggesting that both types of epigenetic alterations occur simultaneously from the early stages of carcinogenesis. These findings indicate that CGI hypermethylation and non-CGI hypomethylation are not independent events but represent a coordinated epigenetic landscape that may contribute to persistent GC risk after H. pylori eradication.

ORGANISM(S): Homo sapiens

PROVIDER: GSE296326 | GEO | 2025/11/01

REPOSITORIES: GEO

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Project description:Aberrant DNA hypermethylation of CpG island (CGI) promoters are associated with transcriptional repression of many tumor suppressor genes and lead to tumor progression in many cancers. Most recently, one research group observed that aberrantly hypermethylated genes in multiple cancers are already repressed, but their promoters are maintained in a hypomethylated state in pre-cancerous tissues.Their studies didn't provide a clue to explain by what mechanisms those genes were repressed in pre-cancerous tissues. Another research group found that many genes with de novo promoter hypermethylation in colon cancer were among the subset of genes "bivalently" marked in embryonic stem cells and adult stem/progenitor cells by repressive Polycomb group proteins (PcG), which are known for maintaining low, but poised, transcription.These observations provide a clue that CGI promoter hypermethylation in cancers is associated with PcG target genes in pre-cancerous tissues.we took advantage of ChIP-BS-seq technology and applied it to examine H3K27me3 and H3K4me3 profiles for one normal lymphoblastoid cell line (YH) and three cancer cell lines including one cervical cancer cell line (Hela) and two gastric cancer (GC) cell lines (BGC-823 and AGS). We aplied ChIP-BS technology to examine H3K27me3 marks, which are catalyzed by the SET domain histone methyltransferase EZH2 and have a repressive function with 50bp pair-end sequencing. found H3K27me3 marks were enriched preferentially at CpG islands, (+/-500) transcription start sites (TSSs) and exons in two GC cell lines (BGC-823 and AGS). In YH cells, H3K27me3 marks were only preferentially enriched at CpG islands. In contrast, Hela cells presented a reverse pattern with highest H3K27me3 enrichment in intergenic regions. To confirm this result in Hela cells, we performed two independent replicates of ChIP-Seq and ChIP-BS-seq. Cause of useful was relative small. we still sequenced one 100bp pe reads replicate for H3K4me3 and two replicate for H3K27me3 ChIP-BS-seq.

Project description:The model describing that aberrant CpG island (CGI) methylation leads to transcription repression of tumor suppressor genes and thereby is implicated in tumor progression has been established in many cancers. However, recent studies indicated aberrantly hypermethylated genes in multiple cancers are already repressed in pre-cancerous tissues despite their promoters are hypomethylated. Here, we hypothesized that the occurrence of CGI promoter hypermethylation in cancers are associated with Polycomb-repressive complex and the associated H3K27me3 mark in pre-cancerous tissues. By using a ChIP-BS-seq technology that examines methylation of the DNA fragments precipitated by the antibodies to histone modifications, we provided direct evidences showing that genes highly enriched with H3K27me3 marks both in cancer and normal cells became aberrantly hypermethylated in CGI promoters in cancer cells in comparison with normal cells. Furthermore, we confirmed that these genes consistently were significantly hypermethylated in TCGA primary cancer in comparison with normal tissues. Thus, we provided direct evidences supporting that the presence of H3K27m3 may serve as a guide to promoter hypermethylation. This will spur future work on epigenetic signature of combined histone and DNA methylation that could define a cancerM-bM-^@M-^Ys epigenetic abnormalities, therefore helping distinguish subtypes of cancers and aiding future diagnosis and therapeutics of cancers. We applied ChIP-BS technology to examine H3K27me3 marks, which are catalyzed by the SET domain histone methyltransferase EZH2 and have a repressive function with 50bp pair-end sequencing. found H3K27me3 marks were enriched preferentially at CpG islands, (+/-500) transcription start sites (TSSs) and exons in two GC cell lines (BGC-823 and AGS). In YH cells, H3K27me3 marks were only preferentially enriched at CpG islands. In contrast, Hela cells presented a reverse pattern with highest H3K27me3 enrichment in intergenic regions. To confirm this result in Hela cells, we performed two independent replicates of ChIP-Seq and ChIP-BS-seq. Cause of useful was relative small. we still sequenced one 100bp pe reads replicate for H3K4me3 and two replicate for H3K27me3 ChIP-BS-seq.

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CpG island hypermethylation and CpG-poor region hypomethylation drive gastric cancer risk after Helicobacter pylori eradication

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