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Chen S, Lai W, Li Y, Liu Y, Jiang J, Li X, Jiang G, Wang H. Aberrant DNA N 6 -methyladenine incorporation via adenylate kinase 1 is suppressed by ADAL deaminase-dependent 2'-deoxynucleotide pool sanitation. EMBO J 2023:e113684. [PMID: 37366109 PMCID: PMC10390868 DOI: 10.15252/embj.2023113684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 05/30/2023] [Accepted: 06/15/2023] [Indexed: 06/28/2023] Open
Abstract
Intracellular decay of N6 -methyladenine (m6A)-containing RNA potentially induces aberrant N6 -methyl-2'-adenine (6mdA) misincorporation into DNA. Biophysically, misincorporated 6mdA may destabilize the DNA duplex in a manner similar to bona fide methylated 6mdA DNA, thereby affecting DNA replication and transcription. Utilizing heavy stable isotope labeling and ultrasensitive UHPLC-MS/MS assay, we demonstrate that intracellular m6A-RNA decay does not generate free 6mdA species, nor lead to any misincorporated DNA 6mdA in most mammalian cell lines tested, unveiling the existence of a sanitation mechanism that prevents 6mdA misincorporation. Depletion of deaminase ADAL increases the levels of free 6mdA species, concomitant with the presence of DNA-misincorporated 6mdA resulting from intracellular RNA m6A decay, suggesting that ADAL catabolizes 6mdAMP in vivo. Furthermore, we show that the overexpression of adenylate kinase 1 (AK1) promotes 6mdA misincorporation, while AK1 knockdown diminishes 6mdA incorporation, in ADAL-deficient cells. We conclude that ADAL together with other factors (such as MTH1) contributes to 2'-deoxynucleotide pool sanitation in most cells but compromised sanitation (e.g., in NIH3T3 cells) and increased AK1 expression may facilitate aberrant 6mdA incorporation. This sanitation mechanism may provide a framework for the maintenance of the epigenetic 6mdA landscape.
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Affiliation(s)
- Shaokun Chen
- The State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Weiyi Lai
- The State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
| | - Yanan Li
- Institute of Environment and Health, Institute for Advanced Study, UCAS, Hangzhou, China
| | - Yan Liu
- The State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
| | - Jie Jiang
- Shenzhen Center for Disease Control and Prevention, Shenzhen, China
| | - Xiangjun Li
- School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Guibin Jiang
- The State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- Institute of Environment and Health, Institute for Advanced Study, UCAS, Hangzhou, China
| | - Hailin Wang
- The State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- Institute of Environment and Health, Institute for Advanced Study, UCAS, Hangzhou, China
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Pospíšil Š, Panattoni A, Gracias F, Sýkorová V, Hausnerová VV, Vítovská D, Šanderová H, Krásný L, Hocek M. Epigenetic Pyrimidine Nucleotides in Competition with Natural dNTPs as Substrates for Diverse DNA Polymerases. ACS Chem Biol 2022; 17:2781-2788. [PMID: 35679536 PMCID: PMC9594043 DOI: 10.1021/acschembio.2c00342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Five 2'-deoxyribonucleoside triphosphates (dNTPs) derived from epigenetic pyrimidines (5-methylcytosine, 5-hydroxymethylcytosine, 5-formylcytosine, 5-hydroxymethyluracil, and 5-formyluracil) were prepared and systematically studied as substrates for nine DNA polymerases in competition with natural dNTPs by primer extension experiments. The incorporation of these substrates was evaluated by a restriction endonucleases cleavage-based assay and by a kinetic study of single nucleotide extension. All of the modified pyrimidine dNTPs were good substrates for the studied DNA polymerases that incorporated a significant percentage of the modified nucleotides into DNA even in the presence of natural nucleotides. 5-Methylcytosine dNTP was an even better substrate for most polymerases than natural dCTP. On the other hand, 5-hydroxymethyl-2'-deoxyuridine triphosphate was not the best substrate for SPO1 DNA polymerase, which naturally synthesizes 5hmU-rich genomes of the SPO1 bacteriophage. The results shed light onto the possibility of gene silencing through recycling and random incorporation of epigenetic nucleotides and into the replication of modified bacteriophage genomes.
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Affiliation(s)
- Šimon Pospíšil
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, CZ-16000 Prague 6, Czech Republic,Department
of Organic Chemistry, Faculty of Science, Charles University, Hlavova 8, CZ-12843 Prague 2, Czech Republic
| | - Alessandro Panattoni
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, CZ-16000 Prague 6, Czech Republic
| | - Filip Gracias
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, CZ-16000 Prague 6, Czech Republic
| | - Veronika Sýkorová
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, CZ-16000 Prague 6, Czech Republic
| | - Viola Vaňková Hausnerová
- Lab.
of Microbial Genetics and Gene Expression, Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, CZ-14220 Prague 4, Czech Republic
| | - Dragana Vítovská
- Lab.
of Microbial Genetics and Gene Expression, Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, CZ-14220 Prague 4, Czech Republic
| | - Hana Šanderová
- Lab.
of Microbial Genetics and Gene Expression, Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, CZ-14220 Prague 4, Czech Republic
| | - Libor Krásný
- Lab.
of Microbial Genetics and Gene Expression, Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, CZ-14220 Prague 4, Czech Republic
| | - Michal Hocek
- Institute
of Organic Chemistry and Biochemistry, Czech
Academy of Sciences, Flemingovo nam. 2, CZ-16000 Prague 6, Czech Republic,Department
of Organic Chemistry, Faculty of Science, Charles University, Hlavova 8, CZ-12843 Prague 2, Czech Republic,E-mail:
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Yamagishi K, Kikuta Y. Nucleoside derivatives of 5-methylcytosine suppress 5-azacytidine-induced reactivation of a silent transgene in suspension-cultured tobacco cells. PLANT BIOTECHNOLOGY (TOKYO, JAPAN) 2021; 38:173-178. [PMID: 34177339 PMCID: PMC8215451 DOI: 10.5511/plantbiotechnology.20.1126b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 11/26/2020] [Indexed: 06/13/2023]
Abstract
Epigenetic modifications, including DNA methylation, are involved in the regulatory mechanisms of gene expression in animals and plants. In this study, we investigated whether the action of 5-azacytidine (5-aza-Cd), which is a well-known DNA methylation inhibitor, in suspension-cultured tobacco cells is affected by treatment with nucleoside derivatives of 5-methylcytosine (5-mCs), namely 5-methylcytidine (5-mCd) and 5-methyl-2'-deoxycytidine (5-mdCd). In a tobacco cell line, 5-aza-Cd treatment reactivated an epigenetically silenced transgene containing the cauliflower mosaic virus 35S promoter fused to the β-glucuronidase coding region and the nopaline synthase polyadenylation signal. The reactivation was evident on the fifth day of treatment and was augmented during culture with application of 5-aza-Cd at every subcultivation. This treatment, provided only once in the initial culture, resulted in transient transgene reactivation, followed by attenuation of its activity. The reactivation induced by 5-aza-Cd was suppressed by concomitant treatment with either 5-mCd or 5-mdCd. These results suggest that the 5-mCs derivatives inhibit and/or reverse 5-aza-Cd-induced reactivation of a silent transgene in tobacco cells.
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Affiliation(s)
- Kazutoshi Yamagishi
- Laboratory of Crop Physiology, Faculty of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo, Hokkaido 060-8589, Japan
- Department of Food and Nutrition, Koen Gakuen Women’s Junior College, 3-1-1 Makomanai-kamimachi, Minami-ku, Sapporo, Hokkaido 005-0012, Japan
| | - Yoshio Kikuta
- Laboratory of Crop Physiology, Faculty of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo, Hokkaido 060-8589, Japan
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4
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Abstract
Cells require nucleotides to support DNA replication and to repair damaged DNA. In addition to de novo synthesis, cells recycle nucleotides from the DNA of dying cells or from cellular material ingested through the diet. Salvaged nucleosides come with the complication that they can contain epigenetic modifications. Since epigenetic inheritance of DNA methylation mainly relies on copying of the modification pattern from parental strands1-3, random incorporation of pre-modified bases during replication could have profound implications for epigenome fidelity and yield adverse cellular phenotypes. Although the salvage mechanism of 5-methyl-2′deoxycytidine (5mdC) has been investigated before4-6, currently it remains unknown how cells deal with the recently identified oxidised forms of 5mdC – 5-hydroxymethyl-2′deoxycytidine (5hmdC), 5-formy-2′deoxycytidine (5fdC) and 5-carboxyl-2′deoxycytidine (5cadC)7-10. Here we demonstrate that enzymes of the nucleotide salvage pathway display substrate selectivity, effectively protecting newly synthesized DNA from the incorporation of epigenetically modified forms of cytosine. Thus cell lines and animals can tolerate high doses of these modified cytidines without any deleterious effects on physiology. Interestingly, by screening cancer cell lines for growth defects following exposure to 5hmdC, we unexpectedly identify a subset of cell lines where 5hmdC or 5fdC administration leads to cell lethality. Using genomic approaches we discover that the susceptible cell lines overexpress cytidine deaminase (CDA). CDA converts 5hmdC and 5fdC into variants of uridine that are incorporated into DNA, resulting in accumulation of DNA damage and ultimately, cell death. Our observations extend current knowledge of the nucleotide salvage pathway by revealing the metabolism of oxidised epigenetic bases, and suggest a therapeutic option for cancers, such as pancreatic cancer, that have CDA overexpression and are resistant to treatment with other cytidine analogues11.
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Humeniuk R, Menon LG, Mishra PJ, Gorlick R, Sowers R, Rode W, Pizzorno G, Cheng YC, Kemeny N, Bertino JR, Banerjee D. Decreased levels of UMP kinase as a mechanism of fluoropyrimidine resistance. Mol Cancer Ther 2009; 8:1037-44. [PMID: 19383847 DOI: 10.1158/1535-7163.mct-08-0716] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
5-Fluorouracil (5-FU) continues to be widely used for treatment of gastrointestinal cancers. Because many tumors show primary or acquired resistance, it is important to understand the molecular basis underlying the mechanism of resistance to 5-FU. In addition to its effect on thymidylate synthase inhibition and DNA synthesis, 5-FU may also influence RNA metabolism. Our previous studies revealed that colorectal cancer cells resistant to bolus 5-FU (HCT-8/4hFU) showed significantly decreased incorporation of the drug into RNA. Resistance to bolus 5-FU was associated with lower expression of UMP kinase (UMPK), an enzyme that plays an important role in the activation of 5-FU to 5-FUTP and its incorporation into RNA. Activities of other 5-FU-metabolizing enzymes (e.g., thymidine kinase, uridine phosphorylase, thymidine phosphorylase, and orotate phosphoribosyltransferase) remained unchanged between sensitive and resistant cell lines. Herein, we show that UMPK down-regulation in 5-FU-sensitive cells (HCT-8/P) induces resistance to bolus 5-FU treatment. Moreover, HCT-8/4hFU cells are even more cross-resistant to treatment with 5-fluorouridine, consistent with the current understanding of 5-fluorouridine as a RNA-directed drug. Importantly, colorectal cancer hepatic metastases isolated from patients clinically resistant to weekly bolus 5-FU/leucovorin treatment exhibited decreased mRNA expression of UMPK but not thymidylate synthase or dihydropyrimidine dehydrogenase compared with tumor samples of patients not previously exposed to 5-FU. Our findings provide new insights into the mechanisms of acquired resistance to 5-FU in colorectal cancer and implicate UMPK as an important mechanism of clinical resistance to pulse 5-FU treatment in some patients.
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Affiliation(s)
- Rita Humeniuk
- The Graduate School of Biomedical Sciences, Department of Pharmacology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08903, USA
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7
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Nonaka M, Tsuchimoto D, Sakumi K, Nakabeppu Y. Mouse RS21-C6 is a mammalian 2'-deoxycytidine 5'-triphosphate pyrophosphohydrolase that prefers 5-iodocytosine. FEBS J 2009; 276:1654-66. [PMID: 19220460 DOI: 10.1111/j.1742-4658.2009.06898.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Free nucleotides in living cells play important roles in a variety of biological reactions, and often undergo chemical modifications of their base moieties. As modified nucleotides may have deleterious effects on cells, they must be eliminated from intracellular nucleotide pools. We have performed a screen for ITP-binding proteins because ITP is a deaminated product of ATP, the most abundant nucleotide, and identified RS21-C6 protein, which bound not only ITP but also ATP. Purified, recombinant RS21-C6 hydrolyzed several canonical nucleoside triphosphates to the corresponding nucleoside monophosphates. The pyrophosphohydrolase activity of RS21-C6 showed a preference for deoxynucleoside triphosphates and cytosine bases. The k(cat)/K(m) (s(-1) m(-1)) values were 3.11 x 10(4), 4.49 x 10(3) and 1.87 x 10(3) for dCTP, dATP and dTTP, respectively, and RS21-C6 did not hydrolyze dGTP. Of the base-modified nucleotides analyzed, 5-I-dCTP showed an eightfold higher k(cat)/K(m) value compared with that of its corresponding unmodified nucleotide, dCTP. RS21-C6 is expressed in both proliferating and non-proliferating cells, and is localized to the cytoplasm. These results show that RS21-C6 produces dCMP, an upstream precursor for the de novo synthesis of dTTP, by hydrolyzing canonical dCTP. Moreover, RS21-C6 may also prevent inappropriate DNA methylation, DNA replication blocking or mutagenesis by hydrolyzing modified dCTP.
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Affiliation(s)
- Mari Nonaka
- Division of Neurofunctional Genomics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka, Japan
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8
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O'Handley SF, Dunn CA, Bessman MJ. Orf135 from Escherichia coli Is a Nudix hydrolase specific for CTP, dCTP, and 5-methyl-dCTP. J Biol Chem 2001; 276:5421-6. [PMID: 11053429 DOI: 10.1074/jbc.m004100200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Orf135 from Escherichia coli is a new member of the Nudix (nucleoside diphosphate linked to some other moiety, x) hydrolase family of enzymes with substrate specificity for CTP, dCTP, and 5-methyl-dCTP. The gene has been cloned for overexpression, and the protein has been overproduced, purified, and characterized. Orf135 is most active on 5-methyl-dCTP (k(cat)/K(m) = 301,000 M(-1) s(-1)), followed by CTP (k(cat)/K(m) = 47,000 M(-1) s(-1)) and dCTP (k(cat)/K(m) = 18,000 M(-1) s(-1)). Unlike other nucleoside triphosphate pyrophophohydrolases of the Nudix hydrolase family discovered thus far, Orf135 is highly specific for pyrimidine (deoxy)nucleoside triphosphates. Like other Nudix hydrolases, the enzyme cleaves its substrates to produce a nucleoside monophosphate and inorganic pyrophosphate, has an alkaline pH optimum, and requires a divalent metal cation for catalysis, with magnesium yielding optimal activity. Because of the nature of its substrate specificity, Orf135 may play a role in pyrimidine biosynthesis, lipid biosynthesis, and in controlling levels of 5-methyl-dCTP in the cell.
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Affiliation(s)
- S F O'Handley
- Department of Biology and the McCollum-Pratt Institute, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
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9
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Van Rompay AR, Johansson M, Karlsson A. Phosphorylation of nucleosides and nucleoside analogs by mammalian nucleoside monophosphate kinases. Pharmacol Ther 2000; 87:189-98. [PMID: 11008000 DOI: 10.1016/s0163-7258(00)00048-6] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Nucleoside monophosphate kinases catalyze the reversible phosphotransferase reaction between nucleoside triphosphates and monophosphates, i.e., monophosphates are converted to their corresponding diphosphate form. These enzymes play an important role in the synthesis of nucleotides that are required for a variety of cellular metabolic processes, as well as for RNA and DNA synthesis. Human tissues contain a thymidylate kinase, a uridylate-cytidylate kinase, five isozymes of adenylate kinase, and several guanylate kinases. Nucleoside monophosphate kinases are also required for the pharmacological activation of therapeutic nucleoside and nucleotide analogs. This overview is focused on the substrate specificity, tissue distribution, and subcellular location of the mammalian monophosphate kinases and their role in the activation of nucleoside and nucleotide analogs.
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Affiliation(s)
- A R Van Rompay
- Division of Clinical Virology, Karolinska Institute, Huddinge University Hospital, S-141 86, Stockholm, Sweden
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10
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Van Rompay AR, Johansson M, Karlsson A. Phosphorylation of deoxycytidine analog monophosphates by UMP-CMP kinase: molecular characterization of the human enzyme. Mol Pharmacol 1999; 56:562-9. [PMID: 10462544 DOI: 10.1124/mol.56.3.562] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phosphorylation of deoxycytidine analogs by cellular enzymes is a prerequisite for the activity of these compounds. We have investigated the kinetic parameters for the phosphorylation of 1-beta-D-arabinofuranosylcytosine (araC) and 2', 2'-difluorodeoxycytidine (dFdC) to their diphosphate forms catalyzed by human UMP-CMP kinase. We cloned the cDNA of this enzyme to enable characterization of the recombinant protein, determine its expression in different tissues, and determine the chromosome location of the gene. We showed that the recombinant UMP-CMP kinase phosphorylated CMP, dCMP, and UMP with highest efficiency and dUMP, AMP, and dAMP with lower efficiency. The monophosphates of araC and dFdC were shown to be phosphorylated with similar efficiency as dCMP and CMP. We further showed, in a combined enzymatic assay, that human deoxycytidine kinase and UMP-CMP kinase together phosphorylated araC, dFdC, and 2',3'-dideoxycytidine to their diphosphate forms. Northern blot analysis showed that the UMP-CMP kinase mRNA was ubiquitously present in human tissues as a 3.9-kb transcript with highest levels in pancreas, skeletal muscle, and liver. The human UMP-CMP kinase gene was localized to chromosome 1p34.1-1p33 by radiation hybrid analysis. We further expressed the UMP-CMP kinase as a fusion protein to the green fluorescent protein in Chinese hamster ovary cells, and showed that the fusion protein was located in the cytosol and nucleus.
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Affiliation(s)
- A R Van Rompay
- Division of Clinical Virology, Karolinska Institute, Huddinge University Hospital, Stockholm, Sweden
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11
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Affiliation(s)
- R Holliday
- CSIRO Division of Molecular Science, Sydney Laboratory, North Ryde, NSW, Australia.
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12
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Holliday R, Ho T. Evidence for gene silencing by endogenous DNA methylation. Proc Natl Acad Sci U S A 1998; 95:8727-32. [PMID: 9671746 PMCID: PMC21144 DOI: 10.1073/pnas.95.15.8727] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/1997] [Accepted: 04/21/1998] [Indexed: 02/08/2023] Open
Abstract
Transformed cells can spontaneously silence genes by de novo methylation, and it is generally assumed that this is due to DNA methyltransferase activity. We have tested the alternative hypothesis that gene silencing could be due to the uptake of 5-methyl-dCMP into DNA, via the di- and triphosphonucleotides. 5-Methyl-dCMP would be present in cells from the ongoing repair of DNA. We have isolated a strain of Chinese hamster ovary (CHO) cells, designated HAM-, which spontaneously silences two tested genes at a very high frequency. We have shown that this strain incorporates 5-[3H]methyldeoxycytidine into 5-methylcytosine and thymine in DNA. It also has low 5-methyl-dCMP deaminase activity. Another HAM+ strain has high deaminase activity and a very low frequency of gene silencing. The starting strain, CHO K1, has a phenotype intermediate between HAM- and HAM+.
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Affiliation(s)
- R Holliday
- Commonwealth Scientific and Industrial Research Organization, Molecular Science, Sydney Laboratory, P.O. Box 184, North Ryde NSW 2113, Australia
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13
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Abstract
It is known that transformed mammalian cells can spontaneously inactivate genes at low frequency by the de novo methylation of promoter sequences. It is usually assumed that this is due to DNA methyl transferase activity, but an alternative possibility is that 5-methyldCTP is present in these cells and can be directly incorporated into DNA. The ongoing repair of DNA containing 5-methylcytosine will produce 5-methyldeoxycytidine monophosphate (5-methyldCMP), so the question arises whether this can be phosphorylated to 5-methyldCTP. We have tested this using three strains of CHO cells with different levels of 5-methyldCMP deaminase activity. That with the lowest enzyme activity, designated HAM-, has previously been shown to incorporate tritium labelled 5-methyldeoxycytidine into 5-methylcytosine in DNA, with a greater amount of label in thymine. This strain is phenotypically unstable producing cells resistant to bromodeoxyuridine (BrdU) and 6-thioguanine (6-TG) at high frequency. In contrast, the strain with the highest 5-methyldCMP deaminase, designated HAM+, is extremely stable, and the starting strain K1 HAMsl is intermediate between the HAM- and HAM+ phenotypes. We have also shown that human diploid fibroblast strain MRC-5 has a phenotype like HAM+, whereas its SV40 transformed derivative, MRC-5V2 resembles HAM- in having low 5-methyl dCMP deaminase activity, and is phenotypically unstable with regard to 6-TG resistance. It seems that 5-methyldCMP deaminase can be down-regulated in transformed cells, and this can promote de novo methylation by incorporation of 5-methyldCTP derived from 5-methyldCMP.
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Affiliation(s)
- R Holliday
- Division of Molecular Science, Sydney Laboratory P.O. Box 184, North Ryde, NSW, Sydney, Australia
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Vilpo JA, Vilpo LM. Prevention of DNA 5-methylcytosine reutilization in human cells. SOMATIC CELL AND MOLECULAR GENETICS 1995; 21:285-8. [PMID: 8525434 DOI: 10.1007/bf02255783] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
DNA methylation is an important process contributing to transcriptional regulation in animal and plant cells. The well known reutilization of DNA nucleotide bases indicated that DNA degradation occurs in many cells and tissues. On the other hand, the reutilization of 5-methyl-2'-deoxycytidine monophosphate in the DNA synthesis would have deleterious effects on gene regulation. Recent molecular insights into the exclusion of exogenous 5-methylcytosine from DNA are the subject of this review.
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Affiliation(s)
- J A Vilpo
- Department of Clinical Chemistry, Tampere University Hospital, Finland
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Counts JL, Goodman JI. Hypomethylation of DNA: an epigenetic mechanism involved in tumor promotion. Mol Carcinog 1994; 11:185-8. [PMID: 7999259 DOI: 10.1002/mc.2940110402] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- J L Counts
- Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48824
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