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)

The DNA methylation status of the protozoan parasite Entamoeba histolytica was heretofore unknown. In the present study, we developed a new technique, based on the affinity of methylated DNA to 5-methylcytosine antibodies, to identify methylated DNA in this parasite. Ribosomal DNA and ribosomal DNA circles were isolated by this method and we confirmed the validity of our approach by sodium bisulfite sequencing. We also report the identification and the characterization of a gene, Ehmeth, encoding a DNA methyltransferase strongly homologous to the human DNA methyltransferase 2 (Dnmt2). Immunofluorescence microscopy using an antibody raised against a recombinant Ehmeth showed that Ehmeth is concentrated in the nuclei of trophozoites. The recombinant Ehmeth has a weak but significant methyltransferase activity when E.histolytica genomic DNA is used as substrate. 5-Azacytidine (5-AzaC), an inhibitor of DNA methyltransferase, was used to study in vivo the role of DNA methylation in E.histolytica. Genomic DNA of trophozoites grown with 5-AzaC (23 microM) was undermethylated and the ability of 5-AzaC-treated trophozoites to kill mammalian cells or to cause liver abscess in hamsters was strongly impaired.
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PMID:Characterization of cytosine methylated regions and 5-cytosine DNA methyltransferase (Ehmeth) in the protozoan parasite Entamoeba histolytica. 1471 27

Using a direct somatic embryogenesis system in carrot, we examined the role of DNA methylation in the change of cellular differentiation state, from somatic to embryogenic. 5-Azacytidine (aza-C), an inhibitor of DNA methylation suppressed the formation of embryogenic cell clumps from epidermal carrot cells. Aza-C also downregulated the expression of DcLEC1c, a LEC1-like embryonic gene in carrot, during morphogenesis of embryos. A carrot DNA methyltransferase gene, Met1-5 was expressed transiently after the induction of somatic embryogenesis by 2,4-dichlorophenoxyacetic acid (2,4-D), before the formation of embryogenic cell clumps. These findings suggested the significance of DNA methylation in acquiring the embryogenic competence in somatic cells in carrot.
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PMID:Formation of embryogenic cell clumps from carrot epidermal cells is suppressed by 5-azacytidine, a DNA methylation inhibitor. 1570 Apr 20

5-Azacytidine- and 5-aza-deoxycytidine (5-aza-CdR)-mediated reactivation of tumor suppressor genes silenced by promoter methylation has provided an alternate approach in cancer therapy. Despite the importance of epigenetic therapy, the mechanism of action of DNA-hypomethylating agents in vivo has not been completely elucidated. Here we report that among three functional DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B), the maintenance methyltransferase, DNMT1, was rapidly degraded by the proteasomal pathway upon treatment of cells with these drugs. The 5-aza-CdR-induced degradation, which occurs in the nucleus, could be blocked by proteasomal inhibitors and required a functional ubiquitin-activating enzyme. The drug-induced degradation occurred even in the absence of DNA replication. Treatment of cells with other nucleoside analogs modified at C-5, 5-fluorodeoxyuridine and 5-fluorocytidine, did not induce the degradation of DNMT1. Mutation of cysteine at the catalytic site of Dnmt1 (involved in the formation of a covalent intermediate with cytidine in DNA) to serine (CS) did not impede 5-aza-CdR-induced degradation. Neither the wild type nor the catalytic site mutant of Dnmt3a or Dnmt3b was sensitive to 5-aza-CdR-mediated degradation. These results indicate that covalent bond formation between the enzyme and 5-aza-CdR-incorporated DNA is not essential for enzyme degradation. Mutation of the conserved KEN box, a targeting signal for proteasomal degradation, to AAA increased the basal level of Dnmt1 and blocked its degradation by 5-aza-CdR. Deletion of the catalytic domain increased the expression of Dnmt1 but did not confer resistance to 5-aza-CdR-induced degradation. Both the nuclear localization signal and the bromo-adjacent homology domain were essential for nuclear localization and for the 5-aza-CdR-mediated degradation of Dnmt1. Polyubiquitination of Dnmt1 in vivo and its stabilization upon treatment of cells with a proteasomal inhibitor indicate that the level of Dnmt1 is controlled by ubiquitin-dependent proteasomal degradation. Overexpression of the substrate recognition component, Cdh1 but not Cdc20, of APC (anaphase-promoting complex)/cyclosome ubiquitin ligase reduced the level of Dnmt1 in both untreated and 5-aza-CdR-treated cells. In contrast, the depletion of Cdh1 with small interfering RNA increased the basal level of DNMT1 that blocked 5-aza-CdR-induced degradation. Dnmt1 interacted with Cdh1 and colocalized in the nucleus at discrete foci. Both Dnmt1 and Cdh1 were phosphorylated in vivo, but only Cdh1 was significantly dephosphorylated upon 5-aza-CdR treatment, suggesting its involvement in initiating the proteasomal degradation of DNMT1. These results demonstrate a unique mechanism for the selective degradation of DNMT1, the maintenance DNA methyltransferase, by well-known DNA-hypomethylating agents.
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PMID:5-Aza-deoxycytidine induces selective degradation of DNA methyltransferase 1 by a proteasomal pathway that requires the KEN box, bromo-adjacent homology domain, and nuclear localization signal. 2971 69

The class of DNA methyltransferase inhibitors is represented by azacitidine and decitabine. Azacitidine is approved for the treatment of patients in both low- and high-risk subtypes of myelodysplastic syndrome (MDS), and decitabine is currently under review by the FDA. Azacitidine phase III trial data, based upon the Cancer and Leukemia Group B (CALGB) study 9221, showed durable clinical and symptomatic improvement in bone marrow function, a reduction in the risk of leukemic transformation, and significant improvements in the quality of life of patients treated with azacitidine compared with supportive care alone. This study also provided data suggestive of improvement in survival in MDS patients. The experience with decitabine comprises a number of phase I/II studies and a phase III trial yet to be published. While there is a strong base of experience supporting the efficacy of DNA methyltransferase inhibitors in the treatment of MDS, a number of practical issues need to be explored further. These include the optimization of the timing and duration of treatment, and the prediction of response to therapy. Along with current experience, future studies will lead to the development of treatment algorithms, strategies for selecting patients (e.g. according to age, risk, classification, and cytogenetic profile), and the combination strategies, particularly with histone deacetylase inhibitors, in the management of MDS.
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PMID:Methylation inhibitor therapy in the treatment of myelodysplastic syndrome. 1634 Dec 36

Azacitidine (Vidaza, Pharmion Corp., Boulder, CO, USA) and decitabine (Dacogentrade mark, SuperGen, Inc., Dublin, CA, USA, and MGI Pharma, Inc., Bloomington, MN, USA) are DNA methyltransferase (DNMT) inhibitors that have clinical activity in patients with myelodysplastic syndromes. Mechanism-based laboratory studies suggest that clinical optimization of therapy with DNMT inhibitors needs to include optimizing intracellular drug uptake and maximizing drug exposure over time while still using lower doses to avoid cytotoxicity. Clinical studies suggest that increased dose intensity and multiple cycles of administration substantially increase response rates. Other strategies for optimizing the efficacy of DNMT inhibitor therapy also include identification of patients that are best qualified for treatment, and defining in vivo mechanisms of patient responses. In the future, combination strategies to increase gene reactivation and to take advantage of increased expression of target genes may be critical for achieving optimal results.
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PMID:Optimizing therapy with methylation inhibitors in myelodysplastic syndromes: dose, duration, and patient selection. 1634 Dec 37

Epigenetic silencing of regulatory genes by aberrant methylation contributes to tumorigenesis. DNA methyltransferase inhibitors (DNMTI) represent promising new drugs for anti-cancer therapies. The DNMTI 5-Azacytidine is effective against myelodysplastic syndrome, but induces switching of latent to lytic Epstein-Barr virus (EBV) in vitro and results in EBV DNA demethylation with the potential of induction of lytic EBV in vivo. This is of considerable concern given that recurrent lytic EBV has been linked with an increased incidence of EBV-associated lymphomas. Based on the distinct properties of action we hypothesized that the newer DNMTI Zebularine might differ from 5-Azacytidine in its potential to induce switching from latent to lytic EBV. Here we show that both 5-Azacytidine and Zebularine are able to induce expression of E-cadherin, a cellular gene frequently silenced by hypermethylation in cancers, and thus demonstrate that both DNMTI are active in our experimental setting consisting of EBV-harboring Burkitt's lymphoma Akata cells. Quantification of mRNA expression of EBV genes revealed that 5-Azacytidine induces switching from latent to lytic EBV and, in addition, that the immediate-early lytic infection progresses to early and late lytic infection. Furthermore, 5-Azacytidine induced upregulation of the latent EBV genes LMP2A, LMP2B, and EBNA2 in a similar fashion as observed following switching of latent to lytic EBV upon cross-linking of the B-cell receptor. In striking contrast, Zebularine did not exhibit any effect neither on lytic nor on latent EBV gene expression. Thus, Zebularine might be safer than 5-Azacytidine for the treatment of cancers in EBV carriers and could also be applied against EBV-harboring tumors, since it does not induce switching from latent to lytic EBV which may result in secondary EBV-associated malignancies.
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PMID:Zebularine reactivates silenced E-cadherin but unlike 5-Azacytidine does not induce switching from latent to lytic Epstein-Barr virus infection in Burkitt's lymphoma Akata cells. 1721 5

In this study, we investigated the cytotoxicity of 5-azacytidine, a DNA methyltransferase inhibitor, against multiple myeloma (MM) cells, and characterized DNA damage-related mechanisms of cell death. 5-Azacytidine showed significant cytotoxicity against both conventional therapy-sensitive and therapy-resistant MM cell lines, as well as multidrug-resistant patient-derived MM cells, with IC(50) of approximately 0.8-3 micromol/L. Conversely, 5-azacytidine was not cytotoxic to peripheral blood mononuclear cells or patient-derived bone marrow stromal cells (BMSC) at these doses. Importantly, 5-azacytidine overcame the survival and growth advantages conferred by exogenous interleukin-6 (IL-6), insulin-like growth factor-I (IGF-I), or by adherence of MM cells to BMSCs. 5-Azacytidine treatment induced DNA double-strand break (DSB) responses, as evidenced by H2AX, Chk2, and p53 phosphorylations, and apoptosis of MM cells. 5-Azacytidine-induced apoptosis was both caspase dependent and independent, with caspase 8 and caspase 9 cleavage; Mcl-1 cleavage; Bax, Puma, and Noxa up-regulation; as well as release of AIF and EndoG from the mitochondria. Finally, we show that 5-azacytidine-induced DNA DSB responses were mediated predominantly by ATR, and that doxorubicin, as well as bortezomib, synergistically enhanced 5-azacytidine-induced MM cell death. Taken together, these data provide the preclinical rationale for the clinical evaluation of 5-azacytidine, alone and in combination with doxorubicin and bortezomib, to improve patient outcome in MM.
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PMID:5-Azacytidine, a DNA methyltransferase inhibitor, induces ATR-mediated DNA double-strand break responses, apoptosis, and synergistic cytotoxicity with doxorubicin and bortezomib against multiple myeloma cells. 1757 3

Why systemic lupus erythematosus primarily affects women is unknown. Recent evidence indicates that human lupus is an epigenetic disease characterized by impaired T cell DNA methylation. Women have two X chromosomes; one is inactivated by mechanisms including DNA methylation. We hypothesized that demethylation of sequences on the inactive X may cause gene overexpression uniquely in women, predisposing them to lupus. We therefore compared expression and methylation of CD40LG, a B cell costimulatory molecule encoded on the X chromosome, in experimentally demethylated T cells from men and women and in men and women with lupus. Controls included TNFSF7, a methylation-sensitive autosomal B cell costimulatory molecule known to be demethylated and overexpressed in lupus. Bisulfite sequencing revealed that CD40LG is unmethylated in men, while women have one methylated and one unmethylated gene. 5-Azacytidine, a DNA methyltransferase inhibitor, demethylated CD40LG and doubled its expression on CD4(+) T cells from women but not men, while increasing TNFSF7 expression equally between sexes. Similar studies demonstrated that CD40LG demethylates in CD4(+) T cells from women with lupus, and that women but not men with lupus overexpress CD40LG on CD4(+) T cells, while both overexpress TNFSF7. These studies demonstrate that regulatory sequences on the inactive X chromosome demethylate in T cells from women with lupus, contributing to CD40LG overexpression uniquely in women. Demethylation of CD40LG and perhaps other genes on the inactive X may contribute to the striking female predilection of this disease.
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PMID:Demethylation of CD40LG on the inactive X in T cells from women with lupus. 1794 13

Epigenetic factors such as DNA methylation and histone deacetylation are known to contribute to the malignant transformation of cells by silencing critical genes. Drugs that inhibit DNA methyltransferases or histone deacetylases were shown to have the potential to reactivate silenced genes and induce differentiation or apoptosis of malignant cells. The most intensively studied class of such agents is DNA methyltransferase inhibitors, including 5-azacytidine (azacitidine) and 5-aza-2'-deoxycytidine (decitabine). In 2004, azacitidine was approved for the treatment of myelodysplastic syndrome on the basis of phase II and III studies that showed a response rate (complete and partial responses) of 15%. Azacitidine is also being evaluated in clinical trials for other malignant diseases. Decitabine has response rates of 17-49% in myelodysplastic syndrome in multiple phase II and III studies and also activity in acute and chronic myelogenous leukemia. Histone deacetylase inhibitors belong to another class of epigenetic modifying agents that include depsipeptide, butyrate derivatives, suberoylanilide hydroxamic acid and valproic acid. No agent in this class has been studied in a phase III trial, but several agents have been or are being studied in phase II trials. Further research is needed to determine the appropriate patient selection and dosing schedules.
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PMID:Review: recent clinical trials in epigenetic therapy. 1847 69

DNA methyltransferases (DNMTs) are important regulators of gene transcription and their roles in carcinogenesis have been a topic of considerable interest in the last few years. Diverse classes of chemical compounds including nucleotide analogues, adenosine analogues, aminobenzoic derivatives, polyphenols, hydrazines, phthalides, disulfides and antisenses are being discovered and evaluated as DNMT inhibitors targeting DNA hypermethylation. Among them, 5-Azacytidine 5 and Decitabine 6 were launched recently. Several other compounds are under clinical trials. Some of these compounds were discovered from structure-based drug design. These compounds exert their DNA methylation inhibitory by different mechanisms. This review will present a brief account of various DNA methyltransferases and their biological functions, with focus on actuality of design and synthesis of various inhibitors of DNA hypermethylation as anticancer drugs.
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PMID:Anticancer drug discovery targeting DNA hypermethylation. 1853 14


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