Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.1.1.37 (DNA methyltransferase)
4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chronic dietary insufficiency of the lipotropic nutrients choline and methionine is hepatocarcinogenic in male rats and certain mouse strains. Despite the fact that DNA hypomethylation is a hallmark of most cancer genomes, the tissue-specific consequences of this alternation with respect to tumorigenesis remain to be determined. In the present study, the folate/methyl deficient model of multistage hepatocarcinogenesis was used to evaluate in vivo alterations in DNA methylation in the liver, the carcinogenesis target tissue, and in non-target tissues, including pancreas, spleen, kidney, and thymus, of male F344 rats. By utilizing the HpaII/MspI-based cytosine extension assay, we demonstrated that the percent of CpG sites that lost methyl groups on both strands progressively increased in liver tissue after 9, 18, and 36 weeks of folate/methyl deficiency. The endogenous activity of DNA methyltransferase in liver of rats fed with folate/methyl deficient diet for the 36-week period gradually increased with time. In contrast, non-target tissues displayed no changes in DNA methylation level or activity of DNA methyltransferase. The failure of DNA methyltransferase to restore and maintain DNA methylation patterns in preneoplastic liver tissue may lead to the establishment of tumor-specific DNA methylation and DNA methyltransferase profiles that are not expressed in normal liver. These results provide additional information about alterations in DNA methylation during early preneoplastic stages of carcinogenesis. They also demonstrate that DNA hypomethylation is localized to tissue that undergoes carcinogenesis, and is not altered in non-target tissues.
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PMID:Genomic hypomethylation is specific for preneoplastic liver in folate/methyl deficient rats and does not occur in non-target tissues. 1506 36

EcoRII DNA methyltransferase (M.EcoRII) recognizes the 5' em leader CC*T/AGG em leader 3' DNA sequence and catalyzes the transfer of the methyl group from S-adenosyl-l-methionine to the C5 position of the inner cytosine residue (C*). Here, we study the mechanism of inhibition of M.EcoRII by DNA containing 2-pyrimidinone, a cytosine analogue lacking an NH(2) group at the C4 position of the pyrimidine ring. Also, DNA containing 2-pyrimidinone was used for probing contacts of M.EcoRII with functional groups of pyrimidine bases of the recognition sequence. 2-Pyrimidinone was incorporated into the 5' em leader CCT/AGG em leader 3' sequence replacing the target and nontarget cytosine and central thymine residues. Study of the DNA stability using thermal denaturation of 2-pyrimidinone containing duplexes pointed to the influence of the bases adjacent to 2-pyrimidinone and to a greater destabilizing influence of 2-pyrimidinone substitution for thymine than that for cytosine. Binding of M.EcoRII to 2-pyrimidinone containing DNA and methylation of these DNA demonstrate that the amino group of the outer cytosine in the EcoRII recognition sequence is not involved in the DNA-M.EcoRII interaction. It is probable that there are contacts between the functional groups of the central thymine exposed in the major groove and M.EcoRII. 2-Pyrimidinone replacing the target cytosine in the EcoRII recognition sequence forms covalent adducts with M.EcoRII. In the absence of the cofactor S-adenosyl-l-methionine, proton transfer to the C5 position of 2-pyrimidinone occurs and in the presence of S-adenosyl-l-methionine, methyl transfer to the C5 position of 2-pyrimidinone occurs.
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PMID:2-Pyrimidinone as a probe for studying the EcoRII DNA methyltransferase-substrate interaction. 1518 54

The polygenic nature of complex psychiatric disorders suggests a common pathway that may be involved in the down-regulation of multiple genes through an epigenetic mechanism. To investigate the role of methylation in down-regulating the expression of mRNAs that may be associated with the schizophrenia phenotype, we have adopted a cell-culture model amenable to this line of investigation. We have administered methionine (2 mM) to primary cultures of cortical neurons prepared from embryonic day 16 mice and show that this treatment down-regulated reelin and glutamic acid decarboxylase 67 (GAD67) mRNA expression but not that corresponding to neuron-specific enolase mRNA. Moreover, methionine increased methylation of the reelin promoter, suggesting a possible mechanism for the observed change. These cultures contain a mixed population of neurons and glia. Approximately 83% of the neurons are GABAergic based on GAD immunoreactivity, and these neurons coexpress high levels of reelin and DNA methyltransferase (Dnmt) 1 immunoreactivity. To examine whether Dnmt1 regulates reelin gene expression, we used an antisense approach to reduce (knock down) Dnmt1 expression. The reduced Dnmt1 mRNA and protein were accompanied by increased reelin mRNA expression. More importantly, the Dnmt1 knockdown blocked the methionine-induced reelin and GAD67 mRNA down-regulation. These data support the hypothesis that the reduced amounts of reelin and GAD67 mRNAs documented in postmortem schizophrenia brain may be the consequence of a Dnmt1-mediated hypermethylation of the corresponding promoters.
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PMID:DNA methyltransferase 1 regulates reelin mRNA expression in mouse primary cortical cultures. 1567 Nov 76

Folate is an essential co-factor in the remethylation of homocysteine to methionine, thereby ensuring the supply of S-adenosylmethionine, the methyl group donor for most biological methylations, including that of DNA. Aberrant patterns and dysregulation of DNA methylation are consistent events in carcinogenesis and hence, DNA methylation is considered to be mechanistically related to the development of cancer. Folate deficiency appears to increase the risk of several malignancies, and aberrant DNA methylation has been considered to be a leading mechanism by which folate deficiency enhances carcinogenesis. Although diets deficient in methyl group donors (choline, folate, methionine and vitamin B12) have been consistently observed to induce DNA hypomethylation, the effect of an isolated folate deficiency on DNA methylation remains highly controversial and unresolved. Whether or not isolated folate deficiency can modulate DNA methylation is an important issue because it would establish a mechanistic link between folate deficiency and cancer. We examined the effects of isolated folate deficiency on methionine cycle intermediates, genomic and site-specific DNA methylation and DNA methyltransferase in an in vitro model of folate deficiency, using untransformed NIH/3T3 and CHO-K1 cells, and human HCT116 and Caco-2 colon cancer cells. Our data demonstrate that the effect of folate deficiency on the methionine cycle pathway and DNA methylation in these cells is highly complex and appears to depend on the cell type and stage of transformation, and may be gene and site-specific. The direction of changes of methionine cycle intermediates in response to folate deficiency is not uniformly consistent with the known biochemical effect of folate on the methionine cycle pathway. Moreover, the effect of folate deficiency on DNA methylation appears to be mediated by both methionine cycle intermediate-dependent and independent pathways.
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PMID:Cell and stage of transformation-specific effects of folate deficiency on methionine cycle intermediates and DNA methylation in an in vitro model. 1569 36

DNA methyltransferases (DNMTs) comprise a family of proteins involved in the establishment and maintenance of DNA methylation patterns in the mammalian genome. DNA methylation involves the transfer of the methyl group of the coenzyme S-adenosyl-L-methionine to the 5 position of cytosine residues within CpG dinucleotides. DNA methylation is implicated in the control of imprinted genes expression, X chromosome silencing, development of certain types of cancer, and embryonic development. DNA methylation is also believed to protect the genome from parasitic elements such as transposons, retrotransposons, and viruses. The aim of this study was to analyze the expression patterns of DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L genes in rhesus macaque (Macaca mulatta) oocytes and preimplantation stage embryos from fertilization to the hatched blastocyst stage, and to compare these results with the expression profiles in the mouse and other mammalian species. We describe species-dependent differences as well as similarities in expression patterns of DNMT genes among mammals.
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PMID:Species-dependent expression patterns of DNA methyltransferase genes in mammalian oocytes and preimplantation embryos. 1615 59

CpG island hypermethylation occurs in most cases of cancer, typically resulting in the transcriptional silencing of critical cancer genes. Procainamide has been shown to inhibit DNA methyltransferase activity and reactivate silenced gene expression in cancer cells by reversing CpG island hypermethylation. We report here that procainamide specifically inhibits the hemimethylase activity of DNA methyltransferase 1 (DNMT1), the mammalian enzyme thought to be responsible for maintaining DNA methylation patterns during replication. At micromolar concentrations, procainamide was found to be a partial competitive inhibitor of DNMT1, reducing the affinity of the enzyme for its two substrates, hemimethylated DNA and S-adenosyl-l-methionine. By doing so, procainamide significantly decreased the processivity of DNMT1 on hemimethylated DNA. Procainamide was not a potent inhibitor of the de novo methyltransferases DNMT3a and DNMT3b2. As further evidence of the specificity of procainamide for DNMT1, procainamide failed to lower genomic 5-methyl-2'-deoxycytidine levels in HCT116 colorectal cancer cells when DNMT1 was genetically deleted but significantly reduced genomic 5-methyl-2'-deoxycytidine content in parental HCT116 cells and in HCT116 cells where DNMT3b was genetically deleted. Because many reports have strongly linked DNMT1 with epigenetic alterations in carcinogenesis, procainamide may be a useful drug in the prevention of cancer.
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PMID:Procainamide is a specific inhibitor of DNA methyltransferase 1. 1623 Mar 60

Aberrations in methylation profile of the genome occur in human cancers induced by folate deficiency. To elucidate the underlying mechanism, male F344 rats were fed a diet deficient in l-methionine and devoid of folic acid and choline (FMD diet), which is known to induce hepatocellular carcinomas. We investigated changes in the DNA methylation machinery, namely, de novo DNA methyltransferases (Dnmt3a and 3b), maintenance DNA methyltransferase (Dnmt1), and methyl CpG binding proteins (MBDs), in rat livers during early stages of tumorigenesis. RT-PCR and Western blot analyses revealed differential expression of these proteins in the livers of rats fed the FMD diet. Although the hepatic Dnmt1 mRNA level declined with age (P < 0.001), it was elevated (P < 0.001) in deficient rats compared with controls. The changes in hepatic Dnmt1 protein level with the diet correlated with its mRNA levels (r = 0.60, P = 0.002). Similarly, the Dnmt3a mRNA level was elevated in rats fed the FMD diet (P < 0.001), whereas the Dnmt3b level (mRNA and protein) was not affected by diet or age. Compared with controls, hepatic MBD1-3 RNA levels increased (P < 0.001) and the protein levels of MBD1, 2, and 4 were elevated (P < 0.001) in the deficient rats. In both diet groups, hepatic MBD2 protein decreased (P < 0.001), whereas MeCP2 protein increased (P < 0.001) with age. These results demonstrate that a combined folate and methyl deficiency alters components of the DNA methylation machinery by both transcriptional and posttranscriptional mechanisms during early stages of hepatocarcinogenesis.
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PMID:A folate- and methyl-deficient diet alters the expression of DNA methyltransferases and methyl CpG binding proteins involved in epigenetic gene silencing in livers of F344 rats. 1670 15

The DNMT3-like protein, DNMT3L, is required for germ line DNA methylation, although it is inactive as a DNA methyltransferase per se. Previous studies have shown that DNMT3L physically associates with the active de novo DNA methyltransferases, DNMT3A and DNMT3B, and stimulates their catalytic activities in a cell culture system. However, the mechanism by which DNMT3L stimulates de novo methylation remains unclear. Here, we have purified the full-length human DNMT3A2 and DNMT3L proteins and determined unique conditions that allow for the proper reconstitution of the stimulation of DNMT3A2 de novo methyltransferase activity by DNMT3L. These conditions include the use of buffers resembling physiological conditions and the preincubation of the two proteins. Under these conditions, maximal stimulation is reached at equimolar amounts of DNMT3L and DNMT3A2 proteins, and the catalytic efficiency of DNMT3A2 is increased up to 20-fold. Biochemical analysis revealed that whereas DNMT3L on its own does not significantly bind to the methyl group donor, S-adenosyl-L-methionine (SAM), it strongly increases the binding of SAM to DNMT3A2. DNA binding, on the contrary, was not appreciably improved. Analysis of DNA methyltransferase complexes in solution using size exclusion chromatography revealed that DNMT3A2 forms large structures of heterogeneous sizes, whereas DNMT3L appears as a monomer. Binding of DNMT3L to DNMT3A2 promotes a dramatic reorganization of DNMT3A2 subunits and leads to the formation of specific complexes with enhanced DNA methyltransferase activity and increased SAM binding.
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PMID:Reconstitution and mechanism of the stimulation of de novo methylation by human DNMT3L. 1682 25

DNA methylation is an important epigenetic mechanism of transcriptional control, which plays an essential role in maintaining cellular function. Role of one-carbon transfer agents/methyl donors namely folate, choline and methionine in DNA methylation has been the subject of extensive investigation. The methylation pattern of DNA is established during embryogenesis by DNA methyltransferase 3 (dnmt3) and is subsequently maintained by maintenance methylation activity of the enzyme DNA methyltransferase 1 (dnmt1). Ionizing radiation is known to extensively damage the DNA. Sufficient dietary availability of methyl donors is known to contribute towards one-carbon transfer mediated repair of damaged DNA where folate is involved in nucleotide base synthesis. In the present study, modification in activities of dnmt1 and dnmt3 by methyl donor starvation followed by gamma-irradiation was observed. Assays were based on the catalytic transfer of (3)H-methyl groups from S-adenosyl-L: -methionine to a DNA substrate. Experiments showed a dose and methyl donors starvation dependent attenuation in dnmt1 activity. Attenuation of dnmt1 activity was most significant for diet deprived of all the three-methyl donors. No significant change in nuclear or cytoplasmic dnmt3 activity was observed when either or all the three possible source of dietary methyl group supply were removed. Ionizing radiation and methyl donor deficiency were observed to act synergistically towards inhibiting dnmt1 activity. Present results suggested possibility of interaction among folate, methionine and choline deficiency to potentiate symptoms of ionizing radiation stress. These enzymatic modifications might contribute to altered DNA methylation after chronic feeding of methyl donor free diets followed by gamma irradiation. These results suggested that dietary availability of methyl donors and gamma-radiation stress might significantly alter the dnmt1 profile.
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PMID:Modulation of DNA methyltransferase profile by methyl donor starvation followed by gamma irradiation. 1685 92

DNA methyltransferase (DNMT) enzymes catalyze the addition of a methyl group to cytosine residues in DNA. Appropriate cytosine methylation of CpG dinucleotides is required for normal mammalian development and homeostasis, and quantitative methods are necessary to assess DNMT activity in various cell extracts. The method described in this report utilizes incorporation of S-[methyl-(3)H]-adenosyl-L-methionine into hemi-methylated or unmethylated oligonucleotides to distinguish between maintenance and de novo DNMT activity, respectively. However, unlike previously described methods, this protocol uses native polyacrylamide gel electrophoresis to detect the incorporation of radioactivity into substrate oligonucleotides. This approach distinguishes between incorporation of radioactivity into target substrate oligonucleotides and incorporation into non-specific cellular DNA that often contaminates nuclear extracts, and permits the reproducible quantitation and comparison of de novo and maintenance DNMT activities in various cell lines. Electrophoretic separation of the methylated substrates is a cost-effective, specific, and reproducible approach to quantitate DNMT activities in nuclear extracts.
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PMID:PAGE separation of hemi-methylated or unmethylated oligonucleotide substrates to distinguish between maintenance and de novo DNA methyltranferase activity. 1690 46


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