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Tissue-Biased Expansion of DNMT3A-Mutant Clones in a Mosaic Individual Is Associated with Conserved Epigenetic Erosion.

ABSTRACT: DNA methyltransferase 3A (DNMT3A) is the most commonly mutated gene in clonal hematopoiesis (CH). Somatic DNMT3A mutations arise in hematopoietic stem cells (HSCs) many years before malignancies develop, but difficulties in comparing their impact before malignancy with wild-type cells have limited the understanding of their contributions to transformation. To circumvent this limitation, we derived normal and DNMT3A mutant lymphoblastoid cell lines from a germline mosaic individual in whom these cells co-existed for nearly 6 decades. Mutant cells dominated the blood system, but not other tissues. Deep sequencing revealed similar mutational burdens and signatures in normal and mutant clones, while epigenetic profiling uncovered the focal erosion of DNA methylation at oncogenic regulatory regions in mutant clones. These regions overlapped with those sensitive to DNMT3A loss after DNMT3A ablation in HSCs and in leukemia samples. These results suggest that DNMT3A maintains a conserved DNA methylation pattern, the erosion of which provides a distinct competitive advantage to hematopoietic cells.

SUBMITTER: Tovy A

PROVIDER: S-EPMC7494054 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Tissue-Biased Expansion of DNMT3A-Mutant Clones Associated with Conserved Epigenetic Alterations

Project description:DNA methyltransferase 3A (DNMT3A) is the most frequently mutated gene in clonal hematopoiesis (CH) and serves as a key tumor suppressor in the hematopoietic system. Somatic mutations in DNMT3A arise in hematopoietic stem and progenitor cells (HSPCs) many years before malignancies develop, but how they prime cells for transformation remains unknown, partly due to our inability to compare mutant to equivalent wild-type cells before frank disease. To overcome this challenge, we derived multiple normal and DNMT3A-mutant lymphoblastoid cell clones from a germ-line mosaic individual in whom these cells co-existed for nearly six decades. Although arising early in gestation, mutant cells dominated the blood, but not other tissues. Deep sequencing revealed similar mutational burdens and mutational signatures across normal and mutant clones. In contrast, epigenetic profiling uncovered focal erosion of DNA methylation at oncogenic regulatory regions in mutant clones. These regions overlapped with those sensitive to DNMT3A loss after DNMT3A ablation in HSPCs and with those present in leukemia samples. These results suggest that DNMT3A is responsible for maintaining a conserved DNA methylation pattern that is maintained for decades and across cell types and states. Erosion of this pattern confers a distinct competitive advantage, increasing the likelihood of malignant transformation

2020-07-15 | GSE150515 | GEO

Tissue-Biased Expansion of DNMT3A-Mutant Clones Associated with Conserved Epigenetic Alterations

Project description:Tissue-Biased Expansion of DNMT3A-Mutant Clones Associated with Conserved Epigenetic Alterations

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Injury prevents Ras mutant cell expansion in mosaic skin.

Project description:Healthy skin is a mosaic of wild-type and mutant clones1,2. Although injury can cooperate with mutated Ras family proteins to promote tumorigenesis3-12, the consequences in genetically mosaic skin are unknown. Here we show that after injury, wild-type cells suppress aberrant growth induced by oncogenic Ras. HrasG12V/+ and KrasG12D/+ cells outcompete wild-type cells in uninjured, mosaic tissue but their expansion is prevented after injury owing to an increase in the fraction of proliferating wild-type cells. Mechanistically, we show that, unlike HrasG12V/+ cells, wild-type cells respond to autocrine and paracrine secretion of EGFR ligands, and this differential activation of the EGFR pathway explains the competitive switch during injury repair. Inhibition of EGFR signalling via drug or genetic approaches diminishes the proportion of dividing wild-type cells after injury, leading to the expansion of HrasG12V/+ cells. Increased proliferation of wild-type cells via constitutive loss of the cell cycle inhibitor p21 counteracts the expansion of HrasG12V/+ cells even in the absence of injury. Thus, injury has a role in switching the competitive balance between oncogenic and wild-type cells in genetically mosaic skin.

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Injury prevents Ras mutant cell expansion in mosaic skin

Project description:Healthy skin is a tapestry of wild-type and mutant clones. Although injury can cooperate with Ras mutations to promote tumorigenesis, the consequences in genetically mosaic skin are unknown. Here, we show that wild-type cells suppress oncogenic Ras-induced aberrant growth after injury. While HrasG12V/+ and KrasG12D/+ cells outcompete wild-type cells in uninjured, mosaic tissue, their expansion is prevented after injury due to an increase in the fraction of proliferating wild-type cells. Mechanistically, we show that, unlike HrasG12V/+ cells, wild-type cells respond to autocrine and paracrine secretion of EGFR ligands, and this differential activation of the EGFR pathway explains the competitive switch during injury-repair. Inhibition of EGFR by both drug and genetic approaches diminished the proportion of dividing wild-type cells after injury, leading to the expansion of HrasG12V/+ cells. Increased wild-type cell proliferation through a global loss of the cell cycle inhibitor p21 counteracted the expansion of HrasG12V/+ cells even without injury. Thus, injury plays an unanticipated role in switching the competitive balance between oncogenic and wild-type cells in genetically mosaic skin.

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The strand-biased mitochondrial DNA methylome and its regulation by DNMT3A.

Project description:How individual genes are regulated from a mitochondrial polycistronic transcript to have variable expression remains an enigma. Here, through bisulfite sequencing and strand-specific mapping, we show mitochondrial genomes in humans and other animals are strongly biased to light (L)-strand non-CpG methylation with conserved peak loci preferentially located at gene-gene boundaries, which was also independently validated by MeDIP and FspEI digestion. Such mtDNA methylation patterns are conserved across different species and developmental stages but display dynamic local or global changes during development and aging. Knockout of DNMT3A alone perturbed mtDNA regional methylation patterns, but not global levels, and altered mitochondrial gene expression, copy number, and oxygen respiration. Overexpression of DNMT3A strongly increased mtDNA methylation and strand bias. Overall, methylation at gene bodies and boundaries was negatively associated with mitochondrial transcript abundance and also polycistronic transcript processing. Furthermore, HPLC-MS confirmed the methylation signals on mitochondria DNA. Together, these data provide high-resolution mtDNA methylation maps that revealed a strand-specific non-CpG methylation, its dynamic regulation, and its impact on the polycistronic mitochondrial transcript processing.

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Clonal expansion and epigenetic reprogramming following deletion or amplification of mutant <i>IDH1</i>.

Project description:IDH1 mutation is the earliest genetic alteration in low-grade gliomas (LGGs), but its role in tumor recurrence is unclear. Mutant IDH1 drives overproduction of the oncometabolite d-2-hydroxyglutarate (2HG) and a CpG island (CGI) hypermethylation phenotype (G-CIMP). To investigate the role of mutant IDH1 at recurrence, we performed a longitudinal analysis of 50 IDH1 mutant LGGs. We discovered six cases with copy number alterations (CNAs) at the IDH1 locus at recurrence. Deletion or amplification of IDH1 was followed by clonal expansion and recurrence at a higher grade. Successful cultures derived from IDH1 mutant, but not IDH1 wild type, gliomas systematically deleted IDH1 in vitro and in vivo, further suggestive of selection against the heterozygous mutant state as tumors progress. Tumors and cultures with IDH1 CNA had decreased 2HG, maintenance of G-CIMP, and DNA methylation reprogramming outside CGI. Thus, while IDH1 mutation initiates gliomagenesis, in some patients mutant IDH1 and 2HG are not required for later clonal expansions.

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DNMT3A co-mutation in an IDH1-mutant glioblastoma.

Project description:Glioblastomas are highly aggressive, infiltrative, and genetically heterogeneous primary brain tumors that arise de novo or secondarily progress over time from low-grade tumors. Along with well-established signature mutational profiles, emerging research suggests that the epigenetic tumor landscape plays an important role in gliomagenesis via transcriptional regulation, DNA methylation, and histone modifications. The pursuit of targeted therapeutic approaches, based not only on expression profiles but also on somatic mutations, is fundamental to the effort of improving survival in patients with glioblastoma. Here, we describe a missense DNMT3A p.P904S mutation in an IDH1-mutant glioblastoma. Although never previously reported in gliomas, this mutation is predicted to be pathogenic and has been reported in several other malignancies. Our report suggests that elucidating epigenetic control is important to understanding glioblastoma biology and may likely unveil targets potentially important to glioblastoma treatment in an effort to improve survival.

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Dnmt3a is an epigenetic mediator of adipose insulin resistance.

Project description:Insulin resistance results from an intricate interaction between genetic make-up and environment, and thus may be orchestrated by epigenetic mechanisms like DNA methylation. Here, we demonstrate that DNA methyltransferase 3a (Dnmt3a) is both necessary and sufficient to mediate insulin resistance in cultured mouse and human adipocytes. Furthermore, adipose-specific Dnmt3a knock-out mice are protected from diet-induced insulin resistance and glucose intolerance without accompanying changes in adiposity. Unbiased gene profiling studies revealed Fgf21 as a key negatively regulated Dnmt3a target gene in adipocytes with concordant changes in DNA methylation at the Fgf21 promoter region. Consistent with this, Fgf21 can rescue Dnmt3a-mediated insulin resistance, and DNA methylation at the FGF21 locus was elevated in human subjects with diabetes and correlated negatively with expression of FGF21 in human adipose tissue. Taken together, our data demonstrate that adipose Dnmt3a is a novel epigenetic mediator of insulin resistance in vitro and in vivo.

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Injury prevents Ras mutant cell expansion in mosaic skin

Project description:Injury prevents Ras mutant cell expansion in mosaic skin

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The DNMT3A R882H mutant displays altered flanking sequence preferences.

Project description:The DNMT3A R882H mutation is frequently observed in acute myeloid leukemia (AML). It is located in the subunit and DNA binding interface of DNMT3A and has been reported to cause a reduction in activity and dominant negative effects. We investigated the mechanistic consequences of the R882H mutation on DNMT3A showing a roughly 40% reduction in overall DNA methylation activity. Biochemical assays demonstrated that R882H does not change DNA binding affinity, protein stability or subnuclear distribution of DNMT3A. Strikingly, DNA methylation experiments revealed pronounced changes in the flanking sequence preference of the DNMT3A-R882H mutant. Based on these results, different DNA substrates with selected flanking sequences were designed to be favored or disfavored by R882H. Kinetic analyses showed that the R882H favored substrate was methylated by R882H with 45% increased rate when compared with wildtype DNMT3A, while methylation of the disfavored substrate was reduced 7-fold. Our data expand the model of the potential carcinogenic effect of the R882H mutation by showing CpG site specific activity changes. This result suggests that R882 is involved in the indirect readout of flanking sequence preferences of DNMT3A and it may explain the particular enrichment of the R882H mutation in cancer patients by revealing mutation specific effects.

| S-EPMC5887309 | biostudies-literature

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