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DNA Methylation Regulates Alternative Polyadenylation via CTCF and the Cohesin Complex

ABSTRACT: Alternative cleavage and polyadenylation (APA) is a form of transcriptional regulation via shifts in how frequently multiple polyadenylation (polyA) sites within genes are used across biological conditions. APA can result in transcripts with varying length and information content, and has been linked to gene regulation in both cancer and development. While trans-acting regulatory factors can cause changes in APA, the process of cleavage and polyadenylation is often co-transcriptional. We hypothesized that epigenetic changes, such as DNA methylation, may regulate APA co-transcriptionally. To identify genes where DNA methylation may regulate APA, we performed a genome-wide quantification of polyA site usage using a next generation sequencing technique. By priming the polyA-tails of an RNA library, we mapped cleavage sites and abundances with base-pair resolution across the genomes of two cell lines. The HCT116 cell line is derived from colon cancer, and contains cancer-associated DNA hypermethylation. The DKO cell line is derived from the parental HCT116 line, but has a near-complete depletion of DNA methylation due to mutations in DNA methyltransferase enzymes. Previous studies have used this sytem to detect genes where promoter DNA methylation regulates the gene expression of tumor suppressors. Analogously, detecting APA between HCT116 and DKO reveals candidate genes where DNA methylation may regulate the process of APA. Mechanistic experiments can further interrogate cross-talk between DNA methylation and APA at these loci, and contribute to the understanding of the function of non-promoter differentially methylated regions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE86178 | GEO | 2020/03/18

REPOSITORIES: GEO

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Project description:This is one of expressional parts of the study. These data were correlated to epigenetic changes and CG density of genes in analyzed cells. The whole study has a following summary: To elucidate possible roles of DNA methylation and chromatin marks in transcription, we performed epigenetic profiling of chromosome 19 in human bronchial epithelial cells (HBEC) and in the colorectal cancer cell line HCT116 as well as its counterpart with double knockout of DNMT1 and DNMT3B (HCT116-DKO). We found that H3K9me3 forms intragenic chromatin blocks along genes with low CpG density in the gene body. Analysis of H3K36me3 profiles indicated that this mark associates either with active genes with low CpG density and H3K9me3 in the gene body or with active genes with high CpG density and DNA hypermethylation in the gene body. In HCT116 cells with double knockout of DNMT1 and DNMT3B, transcription of genes with low CpG density in the gene body was highly elevated and associated with promoter DNA demethylation and rearrangement of H3K9me3 and H3K36me3 occupation. Our finding suggests that similar to DNA methylation, H3K9me3 may play a role in intragenic gene regulation. Further, we observed that a combination of low CpG density in gene bodies together with H3K9me3 and H3K36me3 marking is a specific epigenetic feature of zinc finger (ZNF) genes, which comprise 90% of all genes carrying both histone marks on chromosome 19. For high CpG density genes, transcription and H3K36me3 occupancy were not changed in condition of partial or intensive loss of DNA methylation in gene bodies in the HCT116-DKO cell line. siRNA experiments with SETD2 knockdown in both HBEC and HCT116-DKO cell lines failed to reduce DNA methylation in gene bodies under conditions of H3K36me3 depletion. Our study suggests that the H3K36me3 and DNA methylation marks in gene bodies are established independently from each other and points to similar functional roles of intragenic DNA methylation and intragenic H3K9me3 for CpG-rich and CpG-poor genes, respectively. To elucidate how a loss of DNA methylation affects a gene expression and epigenome we studied colon cancer cell line HCT116 and its derivative, HCT116 DNMT1-/- DNMT3b -/- (HCT116-DKO). According to previous studies HCT116-DKO is characterized by 95% of loss of DNA methylation. In HCT116 and HCT116-DKO cells, we profiled diverse epigenetic marks and gene expression. Further a crosstalk between epigenetic changes and transcriptional changes was analyzed. This is the expressional part of study.

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DNA Methylation Regulates Alternative Polyadenylation via CTCF and the Cohesin Complex

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