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Epigenetic identity in AML is mostly dependent on disruption of non-promoter regulatory elements and reveals potentially antagonistic effects of mutations in epigenetic modifiers [mouse]

ABSTRACT: Aberrant DNA methylation of gene promoters is a hallmark of AML. To define more precisely how cytosine methylation is redistributed in AML, we performed base-pair resolution methylome sequencing in 119 patients. We find that leukemic DNA methylation patterning is tightly linked to somatic mutations and primarily driven by regulatory elements outside of promoters and by CpG shores as opposed to CpG islands. Active enhancers displayed much stronger focal differential methylation than promoters and were generally aberrantly hypomethylated except in IDH2 mutant and CEBPA silenced AMLs. AMLs with dominant hypermethylation feature greater epigenetic disruption of promoters. Those with dominant hypomethylation, such as DNMT3A mutated AMLs, display greater disruption of distal and intronic regions. IDH mutant AMLs manifest profound hypermethylation whereas DNMT3A mutant AMLs manifest profound hypomethylation of a different set of CpGs. In striking contrast, AMLs with co-occurring IDH1 and DNMT3A mutations exhibited epigenetic antagonism in which most CpGs affected by either mutation alone were no longer affected in the double mutant cases.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE96744 | GEO | 2017/04/28

SECONDARY ACCESSION(S): PRJNA384797

REPOSITORIES: GEO

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Project description:Since DNMT3A is a de novo DNA methyltransferase, transcriptional differences in WT versus Dnmt3a-/- HSCs upon infection suggest a possible role for epigenetic regulation in the HSC transcriptional response to inflammation. Therefore, we wanted to investigate if differences in stress and presence of Dnmt3a affect the methylome overall, and specific IFNg responses genes. 100000 LT-HSCs (LK CD150+ CD48- were sorted into lysis buffer from the pools of naive or 1-month (M. avium) infected WT/ Dnmt3-/-_x0001_ mice (n = 7-8 per group). Around 300 ng of DNA per group was extracted with AllPrep DNA/RNA Mini Kit. NEBNext Ultra II DNA library prep kit was used for library preparation. Bisulfite conversion step was added after ‘‘methylated’’ adaptor ligation and USER excision. Then, methylated adaptor ligated DNA fragment was treated with bisulfite conversion using EZ DNA methylationlightning kit. These modified DNA fragments were then amplified with index primers with Kapa HiFi urasil+ specialized polymerase for bisulfite converted DNA. For WGBS library sequencing, 150-high output kit from illumine was used. Samples (400 million reads/ sample (15-20X coverage)) were run in NovaSeq S1 FC (2, lanes 1,600 Million reads). Global methylation of Dnmt3a-/- cells was more divergent upon infection compared to WT. There were vastly more hyper- and hypomethylated regions in infected versus naive Dnmt3a-/- HSCs compared to WT. Among the altered regions, both WT and Dnmt3a-/- HSCs showed slightly more hypomethylated than hypermethylated regions, although changes in both directions were present. In the WT background, regions of hyper- and hypomethylation were mostly restricted to CpG islands. By contrast, highly significant differences in hypomethylation were found in the Dnmt3a-/- HSCs in CpG islands, shores, enhancers, and promoters DNMT3A is highly active in HSCs during infection and that the loss of DNMT3A function results in significant global changes in methylation, including both hyper- and hypomethylation, in genome regions that likely affect gene transcription. we examined the methylation of Batf2, Jun, and Fos. All 3 of these prodifferentiation genes showed increased methylation in the promoter region in the Dnmt3a-/- background as compared to the WT background. Hypermethylation of these promoter regions is consistent with their transcriptional repression.

Project description:Background Thousands of mammalian promoters are defined by co-enrichment of the histone tail modifications H3K27me3 (repressive) and H3K4me3 (activating) and are thus termed bivalent. It was previously observed that bivalent genes in human ES cells (hESC) are frequent targets for hypermethylation in human cancers, and depletion of DNA methylation in mouse embryonic stem cells has a marked impact on H3K27me3 distribution at bivalent promoters. However, only a fraction of bivalent genes in stem cells are targets of hypermethylation in cancer, and it is currently unclear whether all bivalent promoters are equally sensitive to DNA hypomethylation and whether H3K4me3 levels play a role in the interplay between DNA methylation and H3K27me3. Results We report the sub-classification of bivalent promoters into two groups—promoters with a high H3K27me3:H3K4me3 (hiBiv) ratio or promoters with a low H3K27me3:H3K4me3 ratio (loBiv). HiBiv are enriched in canonical Polycomb components, show a higher degree of local intrachromosomal contacts and are highly sensitive to DNA hypomethylation in terms of H3K27me3 depletion from broad Polycomb domains. In contrast, loBiv promoters are enriched in non-canonical Polycomb components, show lower intrachromosomal contacts and are less sensitive to DNA hypomethylation at the same genomic resolution. Multiple systems reveal that hiBiv promoters are more depleted of Polycomb complexes than loBiv promoters following a reduction in DNA methylation, and we demonstrate that H3K27me3 re-accumulates at promoters when DNA methylation is restored. In human cancer, we show that hiBiv promoters lose H3K27me3 and are more susceptible to DNA hypermethylation than loBiv promoters. Conclusion We conclude that bivalency as a general term to describe mammalian promoters is an over-simplification and our sub-classification has revealed novel insights into the interplay between the largely antagonistic presence of DNA methylation and Polycomb systems at bivalent promoters. This approach redefines molecular pathologies underlying disease in which global DNA methylation is aberrant or where Polycomb mutations are present.

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Epigenetic identity in AML is mostly dependent on disruption of non-promoter regulatory elements and reveals potentially antagonistic effects of mutations in epigenetic modifiers [mouse]

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