Nucleobase Modifiers Identify TET Enzymes as Bifunctional DNA Dioxygenases Capable of Direct N-Demethylation.
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ABSTRACT:
SUBMITTER: Ghanty U
PROVIDER: S-EPMC7332413 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The methylation of cytosine and subsequent oxidation constitutes a fundamental epigenetic modification in mammalian genomes, and its abnormalities are intimately coupled to various pathogenic processes including cancer development. Enzymes of the Ten-eleven translocation (TET) family catalyze the stepwise oxidation of 5-methylcytosine in DNA to 5-hydroxymethylcytosine and further oxidation products. These oxidized 5-methylcytosine derivatives represent intermediates in the reversal of cytosine methylation, and also serve as stable epigenetic modifications that exert distinctive regulatory roles. It is becoming increasingly obvious that TET proteins and their catalytic products are key regulators of embryonic development, stem cell functions and lineage specification. Over the past several years, the function of TET proteins as a barrier between normal and malignant states has been extensively investigated. Dysregulation of TET protein expression or function is commonly observed in a wide range of cancers. Notably, TET loss-of-function is causally related to the onset and progression of hematologic malignancy in vivo. In this review, we focus on recent advances in the mechanistic understanding of DNA methylation-demethylation dynamics, and their potential regulatory functions in cellular differentiation and oncogenic transformation.
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Project description:DNA methylation has a profound impact on genome stability, transcription and development. Although enzymes that catalyse DNA methylation have been well characterized, those that are involved in methyl group removal have remained elusive, until recently. The transformative discovery that ten-eleven translocation (TET) family enzymes can oxidize 5-methylcytosine has greatly advanced our understanding of DNA demethylation. 5-Hydroxymethylcytosine is a key nexus in demethylation that can either be passively depleted through DNA replication or actively reverted to cytosine through iterative oxidation and thymine DNA glycosylase (TDG)-mediated base excision repair. Methylation, oxidation and repair now offer a model for a complete cycle of dynamic cytosine modification, with mounting evidence for its significance in the biological processes known to involve active demethylation.
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Project description:Mammalian genomes are subjected to epigenetic modifications, including cytosine methylation by DNA methyltransferases (Dnmt) and further oxidation by Ten-eleven-translocation (Tet) family of dioxygenases. Cytosine methylation plays key roles in multiple processes such as genomic imprinting and X-chromosome inactivation. However, the functional significance of cytosine methylation and the further oxidation has remained undetermined in mouse embryogenesis. Here we show that global inactivation of all three Tet genes in mice led to consistent defects in gastrulation. The defects include reduced specification of the axial mesoderm and paraxial mesoderm, mimicking phenotypes in embryos with gain-of-function Nodal signaling, a cardinal cue for gastrulation. Introduction of a single mutant allele of Nodal in the Tet mutant background partially restored patterning, suggesting that hyperactive Nodal signaling is a leading cause for the gastrulation failure of Tet mutants. Increased Nodal signaling is likely due to diminished expression of the Lefty1 and Lefty2 genes, inhibitors of Nodal signaling. Moreover, reduction in the Lefty gene expression can be ascribed to elevated DNA methylation as both Lefty-Nodal signaling and normal morphogenesis are largely restored in Tet-deficient embryos when the Dnmt3a and Dnmt3b genes are disrupted. Additionally, specific inactivation of Tet by point mutations abolishing the dioxygenase activity causes similar molecular and gastrulation abnormalities. Taken together, our results show that Tet-mediated DNA oxidation modulates the Lefty-Nodal signaling by promoting demethylation of the shared target genes with Dnmt3a and Dnmt3b. These findings reveal a fundamental epigenetic mechanism featuring dynamic DNA methylation and demethylation and their role in the regulation of key signaling in body plan formation during early embryogenesis. Examine RNA expression and DNA methylation differences between Tet-null and wild type samples of mouse epiblast in E6.5.
2016-10-27 | E-GEOD-76261 | biostudies-arrayexpress
Project description:Iron(II) and 2-oxoglutarate (2OG)-dependent dioxygenases involved in histone and DNA/RNA demethylation convert the cosubstrate 2OG and oxygen to succinate and carbon dioxide, resulting in hydroxylation of the methyl group of the substrates and subsequent demethylation. Recent evidence has shown that these 2OG dioxygenases play vital roles in a variety of biological processes, including transcriptional regulation and gene expression. In this review, the structure and function of these dioxygenases in histone and nucleic acid demethylation will be discussed. Given the important roles of these 2OG dioxygenases, detailed analysis and comparison of the 2OG dioxygenases will guide the design of target-specific small-molecule chemical probes and inhibitors.
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Project description:Vitamin C serves as a cofactor for Fe(II) and 2-oxoglutarate-dependent dioxygenases including TET family enzymes, which catalyze the oxidation of 5-methylcytosine into 5-hydroxymethylcytosine and further oxidize methylcytosines. Loss-of-function mutations in epigenetic regulators such as TET genes are prevalent in hematopoietic malignancies. Vitamin C deficiency is frequently observed in cancer patients. In this review, we discuss the role of vitamin C and TET proteins in cancer, with a focus on hematopoietic malignancies, T regulatory cells, and other immune system cells.
| S-EPMC7498365 | biostudies-literature
Project description:Mammalian genomes are subjected to epigenetic modifications, including cytosine methylation by DNA methyltransferases (Dnmt) and further oxidation by Ten-eleven-translocation (Tet) family of dioxygenases. Cytosine methylation plays key roles in multiple processes such as genomic imprinting and X-chromosome inactivation. However, the functional significance of cytosine methylation and the further oxidation has remained undetermined in mouse embryogenesis. Here we show that global inactivation of all three Tet genes in mice led to consistent defects in gastrulation. The defects include reduced specification of the axial mesoderm and paraxial mesoderm, mimicking phenotypes in embryos with gain-of-function Nodal signaling, a cardinal cue for gastrulation. Introduction of a single mutant allele of Nodal in the Tet mutant background partially restored patterning, suggesting that hyperactive Nodal signaling is a leading cause for the gastrulation failure of Tet mutants. Increased Nodal signaling is likely due to diminished expression of the Lefty1 and Lefty2 genes, inhibitors of Nodal signaling. Moreover, reduction in the Lefty gene expression can be ascribed to elevated DNA methylation as both Lefty-Nodal signaling and normal morphogenesis are largely restored in Tet-deficient embryos when the Dnmt3a and Dnmt3b genes are disrupted. Additionally, specific inactivation of Tet by point mutations abolishing the dioxygenase activity causes similar molecular and gastrulation abnormalities. Taken together, our results show that Tet-mediated DNA oxidation modulates the Lefty-Nodal signaling by promoting demethylation of the shared target genes with Dnmt3a and Dnmt3b. These findings reveal a fundamental epigenetic mechanism featuring dynamic DNA methylation and demethylation and their role in the regulation of key signaling in body plan formation during early embryogenesis.
2016-10-27 | GSE76261 | GEO
Project description:As one of the most induced genes in activated macrophages, immune-responsive gene 1 (IRG1) encodes a mitochondrial metabolic enzyme catalysing the production of itaconic acid (ITA). Although ITA has an anti-inflammatory property, the underlying mechanisms are not fully understood. Here we show that ITA is a potent inhibitor of the TET-family DNA dioxygenases. ITA binds to the same site on TET2 as the co-substrate α-ketoglutarate, inhibiting TET2 catalytic activity. Lipopolysaccharide treatment, which induces Irg1 expression and ITA accumulation, inhibits Tet activity in macrophages. Transcriptome analysis reveals that TET2 is a major target of ITA in suppressing lipopolysaccharide-induced genes, including those regulated by the NF-κB and STAT signalling pathways. In vivo, ITA decreases the levels of 5-hydroxymethylcytosine, reduces lipopolysaccharide-induced acute pulmonary oedema as well as lung and liver injury, and protects mice against lethal endotoxaemia, depending on the catalytic activity of Tet2. Our study thus identifies ITA as an immune modulatory metabolite that selectively inhibits TET enzymes to dampen the inflammatory responses.
| S-EPMC9305987 | biostudies-literature
Project description:Methylation of cytosines is a major epigenetic modification in mammalian genomes. The levels and patterns of DNA methylation are the results of the opposing actions of methylating and demethylating machineries. Over the past two decades, great progress has been made in elucidating the methylating machinery including the identification and functional characterization of the DNA methyltransferases (Dnmts). However, the mechanisms of demethylation and the major players involved had been elusive. A major breakthrough came in 2009, when the ten-eleven translocation (Tet) family of proteins was discovered as 5-methylcytosine (5mC) dioxygenases that convert 5mC to 5-hydroxymethylcytosine (5hmC). Studies in the past several years have established that 5hmC serves as an intermediate in DNA demethylation and that Tet proteins have important roles in epigenetic reprogramming in early embryos and primordial germ cells. In this review, we discuss recent advances in this exciting field, focusing on the role of Tet proteins in mammalian development.
| S-EPMC3977598 | biostudies-literature
Project description:Since the discovery of methylcytosine oxidase ten-eleven translocation (TET) proteins, we have witnessed an exponential increase in studies examining their roles in epigenetic regulation. TET family proteins catalyze the sequential oxidation of 5-methylcytosine (5mC) to oxidized methylcytosines including 5-hydroxymethylcytosine (5hmC), 5-formylcytosine, and 5-carboxylcytosine. TETs contribute to the regulation of lineage-specific gene expression via modulating DNA 5mC/5hmC balances at the proximal and distal regulatory elements of cell identity genes, and therefore enhance chromatin accessibility and gene transcription. Emerging evidence suggests that TET dioxygenases participate in the establishment and/or maintenance of hypomethylated bivalent domains at multiple differentiation-associated genes, and thus ensure developmental plasticity. Here, we review the current state of knowledge concerning TET family proteins, DNA hydroxymethylation, their distribution, and function in endoderm, mesoderm, and neuroectoderm specification. We will summarize the evidence pertaining to their crucial regulatory roles in lineage commitment and development.
| S-EPMC6172806 | biostudies-literature
Project description:In mammals, active DNA demethylation involves oxidation of 5-methylcytosine (5mC) into 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) by Tet dioxygenases and excision of these two oxidized bases by thymine DNA glycosylase (TDG). Although TDG is essential for active demethylation in embryonic stem cells and induced pluripotent stem cells, it is hardly expressed in mouse zygotes and dispensable in pronuclear DNA demethylation. To search for other factors that might contribute to demethylation in mammalian cells, we performed a functional genomics screen based on a methylated luciferase reporter assay. UNG2, one of the glycosylases known to excise uracil residues from DNA, was found to reduce DNA methylation, thus activating transcription of a methylation-silenced reporter gene when co-transfected with Tet2 into HEK293T cells. Interestingly, UNG2 could decrease 5caC from the genomic DNA and a reporter plasmid in transfected cells, like TDG. Furthermore, deficiency in Ung partially impaired DNA demethylation in mouse zygotes. Our results suggest that UNG might be involved in Tet-mediated DNA demethylation.
| S-EPMC4705393 | biostudies-literature