CpG Island Hypermethylation Mediated by DNMT3A Is a Consequence of AML Progression.
ABSTRACT: DNMT3A mutations occur in ?25% of acute myeloid leukemia (AML) patients. The most common mutation, DNMT3AR882H, has dominant negative activity that reduces DNA methylation activity by ?80% in vitro. To understand the contribution of DNMT3A-dependent methylation to leukemogenesis, we performed whole-genome bisulfite sequencing of primary leukemic and non-leukemic cells in patients with or without DNMT3AR882 mutations. Non-leukemic hematopoietic cells with DNMT3AR882H displayed focal methylation loss, suggesting that hypomethylation antedates AML. Although virtually all AMLs with wild-type DNMT3A displayed CpG island hypermethylation, this change was not associated with gene silencing and was essentially absent in AMLs with DNMT3AR882 mutations. Primary hematopoietic stem cells expanded with cytokines were hypermethylated in a DNMT3A-dependent manner, suggesting that hypermethylation may be a response to, rather than a cause of, cellular proliferation. Our findings suggest that hypomethylation is an initiating phenotype in AMLs with DNMT3AR882, while DNMT3A-dependent CpG island hypermethylation is a consequence of AML progression.
Project description:Aberrant DNA methylation of gene promoters is a hallmark of AML. To define how cytosine methylation is redistributed in AML more precisely 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. These patients featured a unique gene expression profile featuring deregulated expression of RAS pathway that was not linked to DNA methylation. Overall design: Enhanced Reduced Representation Bisulfite Sequencing (ERRBS) was performed on 119 AML samples, which are a subset of those profiled using HELP in PMC3008568.
Project description: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. Overall design: Enhanced Reduced Representation Bisulfite Sequencing (ERRBS) was performed on Idh2, Dnmt3a, and Idh2/Dnmt3a mutant mice. Idh2 mouse profiling is detailed in PMID: 28193779 and deposited here (LSK controls are deposited under GSE57114). Dnmt3a mutant and LSK control mouse profiling is detailed in PMID: 26710888 and deposited under GSE86827 with a set of LSK controls under GEO series GSE74165
Project description:Trisomy 8 acute myeloid leukemia (AML) is the commonest numerical aberration in AML. Here we present a global analysis of trisomy 8 AML using methylated DNA immunoprecipitation-sequencing (MeDIP-seq). The study is based on three diagnostic trisomy 8 AML and their parallel relapse status in addition to nine non-trisomic AML and four normal bone marrows (NBMs). In contrast to non-trisomic DNA samples, trisomy 8 AML showed a characteristic DNA methylation distribution pattern because an increase in the frequency of the hypermethylation signals in chromosome 8 was associated with an increase in the hypomethylation signals in the rest of the chromosomes. Chromosome 8 hypermethylation signals were found mainly in the CpG island (CGI) shores and interspersed repeats. Validating the most significant differentially methylated CGI (P = 7.88 × 10(-11)) identified in trisomy 8 AML demonstrated a specific core region within the gene body of HHEX, which was significantly correlated with HHEX expression in both diagnostic and relapse trisomy 8 AMLs. Overall, the existence of extra chromosome 8 was associated with a global impact on the DNA methylation distribution with identification of HHEX gene methylation as a potential diagnostic marker for trisomy 8 AML.
Project description:Eukaryotic DNA methylation prevents genomic instability by regulating the expression of oncogenes and tumor-suppressor genes. The negative effects of dysregulated DNA methylation are highlighted by a strong correlation between mutations in the de novo DNA methyltransferase gene DNA methyltransferase 3? (DNMT3A) and poor prognoses among acute myeloid leukemia (AML) patients. We show here that clinically observed DNMT3A mutations dramatically alter enzymatic activity, including mutations that lead to 6-fold hypermethylation and 3-fold hypomethylation of the human cyclin-dependent kinase inhibitor 2B (CDKN2B or p15) gene promoter. Our results provide insights into the clinically observed heterogeneity of p15 methylation in AML. Cytogenetically normal AML (CN-AML) constitutes 40-50% of all AML cases and is the most epigenetically diverse AML subtype with pronounced changes in non-CpG DNA methylation. We identified a subset of DNMT3A mutations that enhance the enzyme's ability to perform non-CpG methylation by 2-8-fold. Many of these mutations mapped to DNMT3A regions known to interact with proteins that themselves contribute to AML, such as thymine DNA glycosylase (TDG). Using functional mapping of TDG-DNMT3A interactions, we provide evidence that TDG and DNMT3-like (DNMT3L) bind distinct regions of DNMT3A. Furthermore, DNMT3A mutations caused diverse changes in the ability of TDG and DNMT3L to affect DNMT3A function. Cell-based studies of one of these DNMT3A mutations (S714C) replicated the enzymatic studies and revealed that it causes dramatic losses of genome-wide methylation. In summary, mutations in DNMT3A lead to diverse levels of activity, interactions with epigenetic machinery components and cellular changes.
Project description:Acute myeloid leukemia (AML) often harbors mutations in epigenetic regulators, and also has frequent DNA hypermethylation, including the presence of CpG island methylator phenotypes (CIMPs). Although global hypomethylation is well known in cancer, the question of whether distinct demethylator phenotypes (DMPs) exist remains unanswered. Using Illumina 450k arrays for 194 patients from The Cancer Genome Atlas, we identified two distinct DMPs by hierarchical clustering: DMP.1 and DMP.2. DMP.1 cases harbored mutations in NPM1 (94%), FLT3 (71%) and DNMT3A (61%). Surprisingly, only 40% of patients with DNMT3A mutations were DMP.1, which has implications for mechanisms of transformation by this mutation. In contrast, DMP.2 AML was comprised of patients with t(8;21), inv(16) or t(15;17), suggesting common methylation defects connect these disparate rearrangements. RNA-seq revealed upregulated genes functioning in immune response (DMP.1) and development (DMP.2). We confirmed these findings by integrating independent 450k data sets (236 additional cases), and found prognostic effects by DMP status, independent of age and cytogenetics. The existence of DMPs has implications for AML pathogenesis and may augment existing tools in risk stratification.
Project description:Loss of the de novo DNA methyltransferases Dnmt3a and Dnmt3b in embryonic stem cells obstructs differentiation; however, the role of these enzymes in somatic stem cells is largely unknown. Using conditional ablation, we show that Dnmt3a loss progressively impairs hematopoietic stem cell (HSC) differentiation over serial transplantation, while simultaneously expanding HSC numbers in the bone marrow. Dnmt3a-null HSCs show both increased and decreased methylation at distinct loci, including substantial CpG island hypermethylation. Dnmt3a-null HSCs upregulate HSC multipotency genes and downregulate differentiation factors, and their progeny exhibit global hypomethylation and incomplete repression of HSC-specific genes. These data establish Dnmt3a as a critical participant in the epigenetic silencing of HSC regulatory genes, thereby enabling efficient differentiation.
Project description:DNMT3A is frequently mutated in acute myeloid leukemia (AML). To explore the features of human AML with the hotspot DNMT3A R882H mutation, we generated Dnmt3a R878H conditional knockin mice, which developed AML with enlarged Lin-Sca1+cKit+ cell compartments. The transcriptome and DNA methylation profiling of bulk leukemic cells and the single-cell RNA sequencing of leukemic stem/progenitor cells revealed significant changes in gene expression and epigenetic regulatory patterns that cause differentiation arrest and growth advantage. Consistent with leukemic cell accumulation in G2/M phase, CDK1 was up-regulated due to mTOR activation associated with DNA hypomethylation. Overexpressed CDK1-mediated EZH2 phosphorylation resulted in an abnormal trimethylation of H3K27 profile. The mTOR inhibitor rapamycin elicited a significant therapeutic response in Dnmt3aR878H/WT mice.
Project description:The extent and role of aberrant DNA methylation in promoter CpG islands (CGIs) have been extensively studied in leukemia and other malignancies. Still, CGIs represent only a small fraction of the methylome. We aimed to characterize genome-wide differential methylation of cytogenetically normal AML (CN-AML) cells compared with normal CD34(+) bone marrow cells using the Illumina 450K methylation array. Differential methylation in CN-AML was most prominent in genomic areas far from CGIs, in so called open sea regions. Furthermore, differential methylation was specifically found in genes encoding transcription factors (TFs), with WT1 being the most differentially methylated TF. Among genetic mutations in AML, DNMT3A mutations showed the most prominent association with the DNA methylation pattern, characterized by hypomethylation of CGIs (as compared with DNMT3A wild type cases). The differential methylation in DNMT3A mutant cells vs. wild type cells was predominantly found in HOX genes, which were hypomethylated. These results were confirmed and validated in an independent CN-AML cohort. In conclusion, we show that, in CN-AML, the most pronounced changes in DNA methylation occur in non-CGI regions and that DNMT3A mutations confer a pattern of global hypomethylation that specifically targets HOX genes.
Project description:We have developed an enhanced form of reduced representation bisulfite sequencing with extended genomic coverage, which resulted in greater capture of DNA methylation information of regions lying outside of traditional CpG islands. Applying this method to primary human bone marrow specimens from patients with Acute Myelogeneous Leukemia (AML), we demonstrated that genetically distinct AML subtypes display diametrically opposed DNA methylation patterns. As compared to normal controls, we observed widespread hypermethylation in IDH mutant AMLs, preferentially targeting promoter regions and CpG islands neighboring the transcription start sites of genes. In contrast, AMLs harboring translocations affecting the MLL gene displayed extensive loss of methylation of an almost mutually exclusive set of CpGs, which instead affected introns and distal intergenic CpG islands and shores. When analyzed in conjunction with gene expression profiles, it became apparent that these specific patterns of DNA methylation result in differing roles in gene expression regulation. However, despite this subtype-specific DNA methylation patterning, a much smaller set of CpG sites are consistently affected in both AML subtypes. Most CpG sites in this common core of aberrantly methylated CpGs were hypermethylated in both AML subtypes. Therefore, aberrant DNA methylation patterns in AML do not occur in a stereotypical manner but rather are highly specific and associated with specific driving genetic lesions.