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Uechi Y, Fujikane R, Morita S, Tamaoki S, Hidaka M. Bloom syndrome DNA helicase mitigates mismatch repair-dependent apoptosis. Biochem Biophys Res Commun 2024; 723:150214. [PMID: 38850810 DOI: 10.1016/j.bbrc.2024.150214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2024] [Revised: 05/26/2024] [Accepted: 05/31/2024] [Indexed: 06/10/2024]
Abstract
Generation of O6-methylguanine (O6-meG) by DNA-alkylating agents such as N-methyl N-nitrosourea (MNU) activates the multiprotein mismatch repair (MMR) complex and the checkpoint response involving ATR/CHK1 and ATM/CHK2 kinases, which may in turn trigger cell cycle arrest and apoptosis. The Bloom syndrome DNA helicase BLM interacts with the MMR complex, suggesting functional relevance to repair and checkpoint responses. We observed a strong interaction of BLM with MMR proteins in HeLa cells upon treatment with MNU as evidenced by co-immunoprecipitation as well as colocalization in the nucleus as revealed by dual immunofluorescence staining. Knockout of BLM sensitized HeLa MR cells to MNU-induced cell cycle disruption and enhanced expression of the apoptosis markers cleaved caspase-9 and PARP1. MNU-treated BLM-deficient cells also exhibited a greater number of 53BP1 foci and greater phosphorylation levels of H2AX at S139 and RPA32 at S8, indicating the accumulation of DNA double-strand breaks. These findings suggest that BLM prevents double-strand DNA breaks during the MMR-dependent DNA damage response and mitigates O6-meG-induced apoptosis.
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Affiliation(s)
- Yuka Uechi
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan; Department of Oral Growth and Development, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan
| | - Ryosuke Fujikane
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan; Oral Medicine Research Center, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan.
| | - Sho Morita
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan
| | - Sachio Tamaoki
- Department of Oral Growth and Development, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan
| | - Masumi Hidaka
- Department of Physiological Science and Molecular Biology, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan; Oral Medicine Research Center, Fukuoka Dental College, 2-15-1, Tamura, Sawaraku, Fukuoka, 814-0193, Japan
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2
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Miller AK, Mao G, Knicely BG, Daniels HG, Rahal C, Putnam CD, Kolodner RD, Goellner EM. Rad5 and Its Human Homologs, HLTF and SHPRH, Are Novel Interactors of Mismatch Repair. Front Cell Dev Biol 2022; 10:843121. [PMID: 35784486 PMCID: PMC9243396 DOI: 10.3389/fcell.2022.843121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 05/16/2022] [Indexed: 12/02/2022] Open
Abstract
DNA mismatch repair (MMR) repairs replication errors, and MMR defects play a role in both inherited cancer predisposition syndromes and in sporadic cancers. MMR also recognizes mispairs caused by environmental and chemotherapeutic agents; however, in these cases mispair recognition leads to apoptosis and not repair. Although mutation avoidance by MMR is fairly well understood, MMR-associated proteins are still being identified. We performed a bioinformatic analysis that implicated Saccharomyces cerevisiae Rad5 as a candidate for interacting with the MMR proteins Msh2 and Mlh1. Rad5 is a DNA helicase and E3 ubiquitin ligase involved in post-replicative repair and damage tolerance. We confirmed both interactions and found that the Mlh1 interaction is mediated by a conserved Mlh1-interacting motif (MIP box). Despite this, we did not find a clear role for Rad5 in the canonical MMR mutation avoidance pathway. The interaction of Rad5 with Msh2 and Mlh1 is conserved in humans, although each of the Rad5 human homologs, HLTF and SHPRH, shared only one of the interactions: HLTF interacts with MSH2, and SHPRH interacts with MLH1. Moreover, depletion of SHPRH, but not HLTF, results in a mild increase in resistance to alkylating agents although not as strong as loss of MMR, suggesting gene duplication led to specialization of the MMR-protein associated roles of the human Rad5 homologs. These results provide insights into how MMR accessory factors involved in the MMR-dependent apoptotic response interact with the core MMR machinery and have important health implications into how human cells respond to environmental toxins, tumor development, and treatment choices of tumors with defects in Rad5 homologs.
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Affiliation(s)
- Anna K. Miller
- College of Medicine Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, United States
| | - Guogen Mao
- College of Medicine Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, United States
| | - Breanna G. Knicely
- College of Medicine Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, United States
| | - Hannah G. Daniels
- College of Medicine Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, United States
| | - Christine Rahal
- Ludiwg Institute for Cancer Research San Diego, San Diego, CA, United States
| | - Christopher D. Putnam
- Ludiwg Institute for Cancer Research San Diego, San Diego, CA, United States
- Department of Medicine, University of California San Diego, San Diego, CA, United States
| | - Richard D. Kolodner
- Ludiwg Institute for Cancer Research San Diego, San Diego, CA, United States
- Moores-UCSD Cancer Center, San Diego, CA, United States
- Institute of Genomic Medicine, San Diego, CA, United States
- Department of Cellular and Molecular Medicine, University of California San Diego, San Diego, CA, United States
| | - Eva M. Goellner
- College of Medicine Department of Toxicology and Cancer Biology, University of Kentucky, Lexington, KY, United States
- Markey Cancer Center, University of Kentucky, Lexington, KY, United States
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3
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Negishi T, Yamada K, Miyamoto K, Mori E, Taira K, Fujii A, Goto Y, Arimoto-Kobayashi S, Okamoto K. Mismatch repair systems might facilitate the chromosomal recombination induced by N-nitrosodimethylamine, but not by N-nitrosodiethylamine, in Drosophila. Mutagenesis 2020; 35:197-206. [PMID: 32109288 DOI: 10.1093/mutage/geaa008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 02/03/2020] [Indexed: 11/14/2022] Open
Abstract
Mismatch repair (MMR) systems play important roles in maintaining the high fidelity of genomic DNA. It is well documented that a lack of MMR increases the mutation rate, including base exchanges and small insertion/deletion loops; however, it is unknown whether MMR deficiency affects the frequency of chromosomal recombination in somatic cells. To investigate the effects of MMR on chromosomal recombination, we used the Drosophila wing-spot test, which efficiently detects chromosomal recombination. We prepared MMR (MutS)-deficient flies (spel1(-/-)) using a fly line generated in this study. The spontaneous mutation rate as measured by the wing-spot test was slightly higher in MutS-deficient flies than in wild-type (spel1(+/-)) flies. Previously, we showed that N-nitrosodimethylamine (NDMA)-induced chromosomal recombination more frequently than N-nitrosodiethylamine (NDEA) in Drosophila. When the wing-spot test was performed using MMR-deficient flies, unexpectedly, the rate of NDMA-induced mutation was significantly lower in spel1(-/-) flies than in spel1(+/-) flies. In contrast, the rate of mutation induced by NDEA was higher in spel1(-/-) flies than in spel1(+/-) flies. These results suggest that in Drosophila, the MutS homologue protein recognises methylated DNA lesions more efficiently than ethylated ones, and that MMR might facilitate mutational chromosomal recombination due to DNA double-strand breaks via the futile cycle induced by MutS recognition of methylated lesions.
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Affiliation(s)
- Tomoe Negishi
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan.,Department of Pharmaceutical and Medical Business Sciences, Nihon Pharmaceutical University, Ina, Kita-Adachi-gun, Saitama, Japan
| | - Kenji Yamada
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Keiko Miyamoto
- Faculty of Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Emiko Mori
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Kentaro Taira
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Asei Fujii
- Faculty of Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Yuki Goto
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Sakae Arimoto-Kobayashi
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
| | - Keinosuke Okamoto
- Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Tsushima-naka, Kita-ku, Okayama, Japan
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4
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Gupta D, Heinen CD. The mismatch repair-dependent DNA damage response: Mechanisms and implications. DNA Repair (Amst) 2019; 78:60-69. [PMID: 30959407 DOI: 10.1016/j.dnarep.2019.03.009] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Revised: 02/25/2019] [Accepted: 03/16/2019] [Indexed: 12/22/2022]
Abstract
An important role for the DNA mismatch repair (MMR) pathway in maintaining genomic stability is embodied in its conservation through evolution and the link between loss of MMR function and tumorigenesis. The latter is evident as inheritance of mutations within the major MMR genes give rise to the cancer predisposition condition, Lynch syndrome. Nonetheless, how MMR loss contributes to tumorigenesis is not completely understood. In addition to preventing the accumulation of mutations, MMR also directs cellular responses, such as cell cycle checkpoint or apoptosis activation, to different forms of DNA damage. Understanding this MMR-dependent DNA damage response may provide insight into the full tumor suppressing capabilities of the MMR pathway. Here, we delve into the proposed mechanisms for the MMR-dependent response to DNA damaging agents. We discuss how these pre-clinical findings extend to the clinical treatment of cancers, emphasizing MMR status as a crucial variable in selection of chemotherapeutic regimens. Also, we discuss how loss of the MMR-dependent damage response could promote tumorigenesis via the establishment of a survival advantage to endogenous levels of stress in MMR-deficient cells.
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Affiliation(s)
- Dipika Gupta
- Center for Molecular Oncology, UConn Health, Farmington, CT 06030, USA
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5
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Abstract
Reverse gyrase introduces positive supercoils to circular DNA and is implicated in genome stability maintenance in thermophiles. The extremely thermophilic crenarchaeon Sulfolobus encodes two reverse gyrase proteins, TopR1 (topoisomerase reverse gyrase 1) and TopR2, whose functions in thermophilic life remain to be demonstrated. Here, we investigated the roles of TopR1 in genome stability maintenance in S. islandicus in response to the treatment of methyl methanesulfonate (MMS), a DNA alkylation agent. Lethal MMS treatment induced two successive events: massive chromosomal DNA backbone breakage and subsequent DNA degradation. The former occurred immediately after drug treatment, leading to chromosomal DNA degradation that concurred with TopR1 degradation, followed by chromatin protein degradation and DNA-less cell formation. To gain a further insight into TopR1 function, the expression of the enzyme was reduced in S. islandicus cells using a CRISPR-mediated mRNA interference approach (CRISPRi) in which topR1 mRNAs were targeted for degradation by endogenous III-B CRISPR-Cas systems. We found that the TopR1 level was reduced in the S. islandicus CRISPRi cells and that the cells underwent accelerated genomic DNA degradation during MMS treatment, accompanied by a higher rate of cell death. Taken together, these results indicate that TopR1 probably facilitates genome integrity maintenance by protecting DNA breaks from thermo-degradation in vivo.
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6
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Kadyrova LY, Dahal BK, Kadyrov FA. The Major Replicative Histone Chaperone CAF-1 Suppresses the Activity of the DNA Mismatch Repair System in the Cytotoxic Response to a DNA-methylating Agent. J Biol Chem 2016; 291:27298-27312. [PMID: 27872185 DOI: 10.1074/jbc.m116.760561] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/15/2016] [Indexed: 11/06/2022] Open
Abstract
The DNA mismatch repair (MMR) system corrects DNA mismatches in the genome. It is also required for the cytotoxic response of O6-methylguanine-DNA methyltransferase (MGMT)-deficient mammalian cells and yeast mgt1Δ rad52Δ cells to treatment with Sn1-type methylating agents, which produce cytotoxic O6-methylguanine (O6-mG) DNA lesions. Specifically, an activity of the MMR system causes degradation of irreparable O6-mG-T mispair-containing DNA, triggering cell death; this process forms the basis of treatments of MGMT-deficient cancers with Sn1-type methylating drugs. Recent research supports the view that degradation of irreparable O6-mG-T mispair-containing DNA by the MMR system and CAF-1-dependent packaging of the newly replicated DNA into nucleosomes are two concomitant processes that interact with each other. Here, we studied whether CAF-1 modulates the activity of the MMR system in the cytotoxic response to Sn1-type methylating agents. We found that CAF-1 suppresses the activity of the MMR system in the cytotoxic response of yeast mgt1Δ rad52Δ cells to the prototypic Sn1-type methylating agent N-methyl-N'-nitro-N-nitrosoguanidine. We also report evidence that in human MGMT-deficient cell-free extracts, CAF-1-dependent packaging of irreparable O6-mG-T mispair-containing DNA into nucleosomes suppresses its degradation by the MMR system. Taken together, these findings suggest that CAF-1-dependent incorporation of irreparable O6-mG-T mispair-containing DNA into nucleosomes suppresses its degradation by the MMR system, thereby defending the cell against killing by the Sn1-type methylating agent.
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Affiliation(s)
- Lyudmila Y Kadyrova
- From the Department of Biochemistry and Molecular Biology, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901
| | - Basanta K Dahal
- From the Department of Biochemistry and Molecular Biology, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901
| | - Farid A Kadyrov
- From the Department of Biochemistry and Molecular Biology, Southern Illinois University, School of Medicine, Carbondale, Illinois 62901
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7
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Olivera Harris M, Kallenberger L, Artola Borán M, Enoiu M, Costanzo V, Jiricny J. Mismatch repair-dependent metabolism of O6-methylguanine-containing DNA in Xenopus laevis egg extracts. DNA Repair (Amst) 2015; 28:1-7. [PMID: 25697728 DOI: 10.1016/j.dnarep.2015.01.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Revised: 01/15/2015] [Accepted: 01/20/2015] [Indexed: 11/27/2022]
Abstract
The cytotoxicity of SN1-type alkylating agents such as N-methyl-N'-nitrosourea (MNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), or the cancer chemotherapeutics temozolomide, dacarbazine and streptozotocin has been ascribed to the persistence of O(6)-methylguanine ((me)G) in genomic DNA. One hypothesis posits that (me)G toxicity is caused by futile attempts of the mismatch repair (MMR) system to process (me)G/C or (me)G/T mispairs arising during replication, while an alternative proposal suggests that the latter lesions activate DNA damage signaling, cell cycle arrest and apoptosis directly. Attempts to elucidate the molecular mechanism of (me)G-induced cell killing in vivo have been hampered by the fact that the above reagents induce several types of modifications in genomic DNA, which are processed by different repair pathways. In contrast, defined substrates studied in vitro did not undergo replication. We set out to re-examine this phenomenon in replication-competent Xenopus laevis egg extracts, using either phagemid substrates containing a single (me)G residue, or methylated sperm chromatin. Our findings provide further support for the futile cycling hypothesis.
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Affiliation(s)
- Maite Olivera Harris
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Biology, Swiss Federal Institute of Technology (ETH), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Lia Kallenberger
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Mariela Artola Borán
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Milica Enoiu
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - Vincenzo Costanzo
- IFOM-European Institute of Oncology Campus, Via Adamello 16, 20139 Milano, Italy
| | - Josef Jiricny
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Biology, Swiss Federal Institute of Technology (ETH), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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8
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Abstract
DNA repair mechanisms are critical for maintaining the integrity of genomic DNA, and their loss is associated with cancer predisposition syndromes. Studies in Saccharomyces cerevisiae have played a central role in elucidating the highly conserved mechanisms that promote eukaryotic genome stability. This review will focus on repair mechanisms that involve excision of a single strand from duplex DNA with the intact, complementary strand serving as a template to fill the resulting gap. These mechanisms are of two general types: those that remove damage from DNA and those that repair errors made during DNA synthesis. The major DNA-damage repair pathways are base excision repair and nucleotide excision repair, which, in the most simple terms, are distinguished by the extent of single-strand DNA removed together with the lesion. Mistakes made by DNA polymerases are corrected by the mismatch repair pathway, which also corrects mismatches generated when single strands of non-identical duplexes are exchanged during homologous recombination. In addition to the true repair pathways, the postreplication repair pathway allows lesions or structural aberrations that block replicative DNA polymerases to be tolerated. There are two bypass mechanisms: an error-free mechanism that involves a switch to an undamaged template for synthesis past the lesion and an error-prone mechanism that utilizes specialized translesion synthesis DNA polymerases to directly synthesize DNA across the lesion. A high level of functional redundancy exists among the pathways that deal with lesions, which minimizes the detrimental effects of endogenous and exogenous DNA damage.
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9
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Ghodgaonkar MM, Lazzaro F, Olivera-Pimentel M, Artola-Borán M, Cejka P, Reijns MA, Jackson AP, Plevani P, Muzi-Falconi M, Jiricny J. Ribonucleotides misincorporated into DNA act as strand-discrimination signals in eukaryotic mismatch repair. Mol Cell 2013; 50:323-32. [PMID: 23603115 PMCID: PMC3653069 DOI: 10.1016/j.molcel.2013.03.019] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Revised: 01/30/2013] [Accepted: 03/14/2013] [Indexed: 11/28/2022]
Abstract
To improve replication fidelity, mismatch repair (MMR) must detect non-Watson-Crick base pairs and direct their repair to the nascent DNA strand. Eukaryotic MMR in vitro requires pre-existing strand discontinuities for initiation; consequently, it has been postulated that MMR in vivo initiates at Okazaki fragment termini in the lagging strand and at nicks generated in the leading strand by the mismatch-activated MLH1/PMS2 endonuclease. We now show that a single ribonucleotide in the vicinity of a mismatch can act as an initiation site for MMR in human cell extracts and that MMR activation in this system is dependent on RNase H2. As loss of RNase H2 in S.cerevisiae results in a mild MMR defect that is reflected in increased mutagenesis, MMR in vivo might also initiate at RNase H2-generated nicks. We therefore propose that ribonucleotides misincoporated during DNA replication serve as physiological markers of the nascent DNA strand.
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Affiliation(s)
- Medini Manohar Ghodgaonkar
- Institute of Molecular Cancer Research of the University of Zurich and ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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10
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Exonuclease 1 (Exo1) is required for activating response to S(N)1 DNA methylating agents. DNA Repair (Amst) 2012; 11:951-64. [PMID: 23062884 DOI: 10.1016/j.dnarep.2012.09.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 09/08/2012] [Accepted: 09/11/2012] [Indexed: 11/23/2022]
Abstract
S(N)1 DNA methylating agents are genotoxic agents that methylate numerous nucleophilic centers within DNA including the O(6) position of guanine (O(6)meG). Methylation of this extracyclic oxygen forces mispairing with thymine during DNA replication. The mismatch repair (MMR) system recognizes these O(6)meG:T mispairs and is required to activate DNA damage response (DDR). Exonuclease I (EXO1) is a key component of MMR by resecting the damaged strand; however, whether EXO1 is required to activate MMR-dependent DDR remains unknown. Here we show that knockdown of the mouse ortholog (mExo1) in mouse embryonic fibroblasts (MEFs) results in decreased G2/M checkpoint response, limited effects on cell proliferation, and increased cell viability following exposure to the S(N)1 methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), establishing a phenotype paralleling MMR deficiency. MNNG treatment induced formation of γ-H2AX foci with which EXO1 co-localized in MEFs, but mExo1-depleted MEFs displayed a significant diminishment of γ-H2AX foci formation. mExo1 depletion also reduced MSH2 association with DNA duplexes containing G:T mismatches in vitro, decreased MSH2 association with alkylated chromatin in vivo, and abrogated MNNG-induced MSH2/CHK1 interaction. To determine if nuclease activity is required to activate DDR we stably overexpressed a nuclease defective form of human EXO1 (hEXO1) in mExo1-depleted MEFs. These experiments indicated that expression of wildtype and catalytically null hEXO1 was able to restore normal response to MNNG. This study indicates that EXO1 is required to activate MMR-dependent DDR in response to S(N)1 methylating agents; however, this function of EXO1 is independent of its nucleolytic activity.
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Brem R, Karran P. Oxidation-mediated DNA cross-linking contributes to the toxicity of 6-thioguanine in human cells. Cancer Res 2012; 72:4787-95. [PMID: 22822082 DOI: 10.1158/0008-5472.can-12-1278] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The thiopurines azathioprine and 6-mercaptopurine have been extensively prescribed as immunosuppressant and anticancer agents for several decades. A third member of the thiopurine family, 6-thioguanine (6-TG), has been used less widely. Although known to be partly dependent on DNA mismatch repair (MMR), the cytotoxicity of 6-TG remains incompletely understood. Here, we describe a novel MMR-independent pathway of 6-TG toxicity. Cell killing depended on two properties of 6-TG: its incorporation into DNA and its ability to act as a source of reactive oxygen species (ROS). ROS targeted DNA 6-TG to generate potentially lethal replication-arresting DNA lesions including interstrand cross-links. These triggered processing by the Fanconi anemia and homologous recombination DNA repair pathways. Allopurinol protected against 6-TG toxicity by acting as a ROS scavenger and preventing DNA damage. Together, our findings provide mechanistic evidence to support the proposed use of thiopurines to treat HR-defective tumors and for the coadministration of 6-TG and allopurinol as an immunomodulation strategy in inflammatory disorders.
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Affiliation(s)
- Reto Brem
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, United Kingdom
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12
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Groth P, Ausländer S, Majumder MM, Schultz N, Johansson F, Petermann E, Helleday T. Methylated DNA causes a physical block to replication forks independently of damage signalling, O(6)-methylguanine or DNA single-strand breaks and results in DNA damage. J Mol Biol 2010; 402:70-82. [PMID: 20643142 DOI: 10.1016/j.jmb.2010.07.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2010] [Revised: 07/01/2010] [Accepted: 07/12/2010] [Indexed: 11/27/2022]
Abstract
Even though DNA alkylating agents have been used for many decades in the treatment of cancer, it remains unclear what happens when replication forks encounter alkylated DNA. Here, we used the DNA fibre assay to study the impact of alkylating agents on replication fork progression. We found that the alkylator methyl methanesulfonate (MMS) inhibits replication elongation in a manner that is dose dependent and related to the overall alkylation grade. Replication forks seem to be completely blocked as no nucleotide incorporation can be detected following 1 h of MMS treatment. A high dose of 5 mM caffeine, inhibiting most DNA damage signalling, decreases replication rates overall but does not reverse MMS-induced replication inhibition, showing that the replication block is independent of DNA damage signalling. Furthermore, the block of replication fork progression does not correlate with the level of DNA single-strand breaks. Overexpression of O(6)-methylguanine (O6meG)-DNA methyltransferase protein, responsible for removing the most toxic alkylation, O6meG, did not affect replication elongation following exposure to N-methyl-N'-nitro-N-nitrosoguanidine. This demonstrates that O6meG lesions are efficiently bypassed in mammalian cells. In addition, we find that MMS-induced gammaH2AX foci co-localise with 53BP1 foci and newly replicated areas, suggesting that DNA double-strand breaks are formed at MMS-blocked replication forks. Altogether, our data suggest that N-alkylations formed during exposure to alkylating agents physically block replication fork elongation in mammalian cells, causing formation of replication-associated DNA lesions, likely double-strand breaks.
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Affiliation(s)
- Petra Groth
- Department of Genetics, Microbiology and Toxicology, Stockholm University, S-106 91 Stockholm, Sweden
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13
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Rajesh P, Rajesh C, Wyatt MD, Pittman DL. RAD51D protects against MLH1-dependent cytotoxic responses to O(6)-methylguanine. DNA Repair (Amst) 2010; 9:458-67. [PMID: 20133210 DOI: 10.1016/j.dnarep.2010.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Revised: 01/08/2010] [Accepted: 01/11/2010] [Indexed: 10/19/2022]
Abstract
S(N)1-type methylating agents generate O(6)-methyl guanine (O(6)-meG), which is a potently mutagenic, toxic, and recombinogenic DNA adduct. Recognition of O(6)-meG:T mismatches by mismatch repair (MMR) causes sister chromatid exchanges, which are representative of homologous recombination (HR) events. Although the MMR-dependent mutagenicity and toxicity caused by O(6)-meG has been studied, the mechanisms of recombination induced by O(6)-meG are poorly understood. To explore the HR and MMR genetic interactions in mammals, we used the Rad51d and Mlh1 mouse models. Ablation of Mlh1 did not appreciably influence the developmental phenotypes conferred by the absence of Rad51d. Mouse embryonic fibroblasts (MEFs) deficient in Rad51d can only proliferate in p53-deficient background. Therefore, Rad51d(-/-)Mlh1(-/-)Trp53(-/-) MEFs with a combined deficiency of HR and MMR were generated and comparisons between MLH1 and RAD51D status were made. To our knowledge, these MEFs are the first mammalian model system for combined HR and MMR defects. Rad51d-deficient MEFs were 5.3-fold sensitive to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) compared to the Rad51d-proficient MEFs. A pronounced G2/M arrest in Rad51d-deficient cells was accompanied by an accumulation of gamma-H2AX and apoptosis. Mlh1-deficient MEFs were resistant to MNNG and showed no G2/M arrest or apoptosis at the doses used. Importantly, loss of Mlh1 alleviated sensitivity of Rad51d-deficient cells to MNNG, in addition to reducing gamma-H2AX, G2/M arrest and apoptosis. Collectively, the data support the hypothesis that MMR-dependent sensitization of HR-deficient cells is specific for O(6)-meG and suggest that HR resolves DNA intermediates created by MMR recognition of O(6)-meG:T. This study provides insight into recombinogenic mechanisms of carcinogenesis and chemotherapy resulting from O(6)-meG adducts.
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Affiliation(s)
- Preeti Rajesh
- Department of Pharmaceutical and Biomedical Sciences, University of South Carolina, Columbia, 29208, United States
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14
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Mastrocola AS, Heinen CD. Nuclear reorganization of DNA mismatch repair proteins in response to DNA damage. DNA Repair (Amst) 2010; 9:120-33. [PMID: 20004149 PMCID: PMC2819642 DOI: 10.1016/j.dnarep.2009.11.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2009] [Revised: 10/16/2009] [Accepted: 11/04/2009] [Indexed: 12/16/2022]
Abstract
The DNA mismatch repair (MMR) system is highly conserved and vital for preserving genomic integrity. Current mechanistic models for MMR are mainly derived from in vitro assays including reconstitution of strand-specific MMR and DNA binding assays using short oligonucleotides. However, fundamental questions regarding the mechanism and regulation in the context of cellular DNA replication remain. Using synchronized populations of HeLa cells we demonstrated that hMSH2, hMLH1 and PCNA localize to the chromatin during S-phase, and accumulate to a greater extent in cells treated with a DNA alkylating agent. In addition, using small interfering RNA to deplete hMSH2, we demonstrated that hMLH1 localization to the chromatin is hMSH2-dependent. hMSH2/hMLH1/PCNA proteins, when associated with the chromatin, form a complex that is greatly enhanced by DNA damage. The DNA damage caused by high doses of alkylating agents leads to a G(2) arrest after only one round of replication. In these G(2)-arrested cells, an hMSH2/hMLH1 complex persists on chromatin, however, PCNA is no longer in the complex. Cells treated with a lower dose of alkylating agent require two rounds of replication before cells arrest in G(2). In the first S-phase, the MMR proteins form a complex with PCNA, however, during the second S-phase PCNA is missing from that complex. The distinction between these complexes may suggest separate functions for the MMR proteins in damage repair and signaling. Additionally, using confocal immunofluorescence, we observed a population of hMSH6 that localized to the nucleolus. This population is significantly reduced after DNA damage suggesting that the protein is shuttled out of the nucleolus in response to damage. In contrast, hMLH1 is excluded from the nucleolus at all times. Thus, the nucleolus may act to segregate a population of hMSH2-hMSH6 from hMLH1-hPMS2 such that, in the absence of DNA damage, an inappropriate response is not invoked.
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Affiliation(s)
- Adam S. Mastrocola
- Neag Comprehensive Cancer Center and Center for Molecular Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Christopher D. Heinen
- Neag Comprehensive Cancer Center and Center for Molecular Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
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15
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Abstract
Suicide gene therapy with herpes simplex virus thymidine kinase and ganciclovir is notable for producing multi-log cytotoxicity in a unique pattern of delayed cytotoxicity in S-phase. Because hydroxyurea, a ribonucleotide reductase inhibitor that activates mismatch repair, can increase sensitivity to ganciclovir, we evaluated the role of MLH1, an essential mismatch repair protein, in ganciclovir cytotoxicity. Using HCT116TK (HSV-TK-expressing) colon carcinoma cells that express or lack MLH1, cell survival studies demonstrated greater ganciclovir sensitivity in the MLH1 deficient cells, primarily at high concentrations. This could not be explained by differences in ganciclovir metabolism, as the less sensitive MLH1-expresssing cells accumulated more ganciclovir triphosphate and incorporated more of the analog into DNA. SiRNA suppression of MLH1 in U251 glioblastoma or SW480 colon carcinoma cells also enhanced sensitivity to high concentrations of ganciclovir. Studies in a panel of yeast deletion mutants confirmed the results with MLH1, and further suggested a role for homologous recombination repair and several cell cycle checkpoint proteins in ganciclovir cytotoxicity. These data suggest that MLH1 can prevent cytotoxicity with ganciclovir. Targeting mismatch repair-deficient tumors may increase efficacy of this suicide gene therapy approach to cancer treatment.
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16
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O6-methylguanine-induced cell death involves exonuclease 1 as well as DNA mismatch recognition in vivo. Proc Natl Acad Sci U S A 2009; 106:576-81. [PMID: 19124772 DOI: 10.1073/pnas.0811991106] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Alkylation-induced O(6)-methylguanine (O(6)MeG) DNA lesions can be mutagenic or cytotoxic if unrepaired by the O(6)MeG-DNA methyltransferase (Mgmt) protein. O(6)MeG pairs with T during DNA replication, and if the O(6)MeG:T mismatch persists, a G:C to A:T transition mutation is fixed at the next replication cycle. O(6)MeG:T mismatch detection by MutSalpha and MutLalpha leads to apoptotic cell death, but the mechanism by which this occurs has been elusive. To explore how mismatch repair mediates O(6)MeG-dependent apoptosis, we used an Mgmt-null mouse model combined with either the Msh6-null mutant (defective in mismatch recognition) or the Exo1-null mutant (impaired in the excision step of mismatch repair). Mouse embryonic fibroblasts and bone marrow cells derived from Mgmt-null mice were much more alkylation-sensitive than wild type, as expected. However, ablation of either Msh6 or Exo1 function rendered these Mgmt-null cells just as resistant to alkylation-induced cytotoxicity as wild-type cells. Rapidly proliferating tissues in Mgmt-null mice (bone marrow, thymus, and spleen) are extremely sensitive to apoptosis induced by O(6)MeG-producing agents. Here, we show that ablation of either Msh6 or Exo1 function in the Mgmt-null mouse renders these rapidly proliferating tissues alkylation-resistant. However, whereas the Msh6 defect confers total alkylation resistance, the Exo1 defect leads to a variable tissue-specific alkylation resistance phenotype. Our results indicate that Exo1 plays an important role in the induction of apoptosis by unrepaired O(6)MeGs.
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17
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Roos WP, Nikolova T, Quiros S, Naumann SC, Kiedron O, Zdzienicka MZ, Kaina B. Brca2/Xrcc2 dependent HR, but not NHEJ, is required for protection against O6-methylguanine triggered apoptosis, DSBs and chromosomal aberrations by a process leading to SCEs. DNA Repair (Amst) 2009; 8:72-86. [DOI: 10.1016/j.dnarep.2008.09.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 08/18/2008] [Accepted: 09/01/2008] [Indexed: 10/21/2022]
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18
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Hsieh P, Yamane K. DNA mismatch repair: molecular mechanism, cancer, and ageing. Mech Ageing Dev 2008; 129:391-407. [PMID: 18406444 PMCID: PMC2574955 DOI: 10.1016/j.mad.2008.02.012] [Citation(s) in RCA: 291] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2007] [Revised: 02/22/2008] [Accepted: 02/28/2008] [Indexed: 02/09/2023]
Abstract
DNA mismatch repair (MMR) proteins are ubiquitous players in a diverse array of important cellular functions. In its role in post-replication repair, MMR safeguards the genome correcting base mispairs arising as a result of replication errors. Loss of MMR results in greatly increased rates of spontaneous mutation in organisms ranging from bacteria to humans. Mutations in MMR genes cause hereditary nonpolyposis colorectal cancer, and loss of MMR is associated with a significant fraction of sporadic cancers. Given its prominence in mutation avoidance and its ability to target a range of DNA lesions, MMR has been under investigation in studies of ageing mechanisms. This review summarizes what is known about the molecular details of the MMR pathway and the role of MMR proteins in cancer susceptibility and ageing.
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Affiliation(s)
- Peggy Hsieh
- Genetics & Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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19
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Interplay of DNA repair pathways controls methylation damage toxicity in Saccharomyces cerevisiae. Genetics 2008; 179:1835-44. [PMID: 18579505 DOI: 10.1534/genetics.108.089979] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Methylating agents of S(N)1 type are widely used in cancer chemotherapy, but their mode of action is poorly understood. In particular, it is unclear how the primary cytotoxic lesion, O(6)-methylguanine ((Me)G), causes cell death. One hypothesis stipulates that binding of mismatch repair (MMR) proteins to (Me)G/T mispairs arising during DNA replication triggers cell-cycle arrest and cell death. An alternative hypothesis posits that (Me)G cytotoxicity is linked to futile processing of (Me)G-containing base pairs by the MMR system. In this study, we provide compelling genetic evidence in support of the latter hypothesis. Treatment of 4644 deletion mutants of Saccharomyces cerevisiae with the prototypic S(N)1-type methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) identified MMR as the only pathway that sensitizes cells to MNNG. In contrast, homologous recombination (HR), postreplicative repair, DNA helicases, and chromatin maintenance factors protect yeast cells against the cytotoxicity of this chemical. Notably, DNA damage signaling proteins played a protective rather than sensitizing role in the MNNG response. Taken together, this evidence demonstrates that (Me)G-containing lesions in yeast must be processed to be cytotoxic.
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20
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Feitsma H, Akay A, Cuppen E. Alkylation damage causes MMR-dependent chromosomal instability in vertebrate embryos. Nucleic Acids Res 2008; 36:4047-56. [PMID: 18522974 PMCID: PMC2475609 DOI: 10.1093/nar/gkn341] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
SN1-type alkylating agents, like N-methyl-N-nitrosourea (MNU) and N-ethyl-N-nitrosourea (ENU), are potent mutagens. Exposure to alkylating agents gives rise to O6-alkylguanine, a modified base that is recognized by DNA mismatch repair (MMR) proteins but is not repairable, resulting in replication fork stalling and cell death. We used a somatic mutation detection assay to study the in vivo effects of alkylation damage on lethality and mutation frequency in developing zebrafish embryos. Consistent with the damage-sensing role of the MMR system, mutant embryos lacking the MMR enzyme MSH6 displayed lower lethality than wild-type embryos after exposure to ENU and MNU. In line with this, alkylation-induced somatic mutation frequencies were found to be higher in wild-type embryos than in the msh6 loss-of-function mutants. These mutations were found to be chromosomal aberrations that may be caused by chromosomal breaks that arise from stalled replication forks. As these chromosomal breaks arise at replication, they are not expected to be repaired by non-homologous end joining. Indeed, Ku70 loss-of-function mutants were found to be equally sensitive to ENU as wild-type embryos. Taken together, our results suggest that in vivo alkylation damage results in chromosomal instability and cell death due to aberrantly processed MMR-induced stalled replication forks.
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Affiliation(s)
| | | | - Edwin Cuppen
- *To whom correspondence should be addressed. +31 30 2121969+31 30 2516554
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21
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Mojas N, Lopes M, Jiricny J. Mismatch repair-dependent processing of methylation damage gives rise to persistent single-stranded gaps in newly replicated DNA. Genes Dev 2008; 21:3342-55. [PMID: 18079180 DOI: 10.1101/gad.455407] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
O(6)-Methylguanine ((Me)G) is a highly cytotoxic DNA modification generated by S(N)1-type methylating agents. Despite numerous studies implicating DNA replication, mismatch repair (MMR), and homologous recombination (HR) in (Me)G toxicity, its mode of action has remained elusive. We studied the molecular transactions in the DNA of yeast and mammalian cells treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Although replication fork progression was unaffected in the first cell cycle after treatment, electron microscopic analysis revealed an accumulation of (Me)G- and MMR-dependent single-stranded DNA (ssDNA) gaps in newly replicated DNA. Progression into the second cell cycle required HR, while the following G(2) arrest required the continued presence of (Me)G. Yeast cells overcame this block, while mammalian cells generally failed to recover, and those that did contained multiple sister chromatid exchanges. Notably, the arrest could be abolished by removal of (Me)G after the first S phase. These new data provide compelling support for the hypothesis that MMR attempts to correct (Me)G/C or (Me)G/T mispairs arising during replication. Due to the persistence of (Me)G in the exposed template strand, repair synthesis cannot take place, which leaves single-stranded gaps behind the replication fork. During the subsequent S phase, these gaps cause replication fork collapse and elicit recombination and cell cycle arrest.
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Affiliation(s)
- Nina Mojas
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
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22
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Liskay RM, Wheeler LJ, Mathews CK, Erdeniz N. Involvement of deoxycytidylate deaminase in the response to S(n)1-type methylation DNA damage in budding yeast. Curr Biol 2008; 17:R755-7. [PMID: 17803923 PMCID: PMC2405937 DOI: 10.1016/j.cub.2007.07.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- R Michael Liskay
- Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239-3098, USA.
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23
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Erdeniz N, Nguyen M, Deschênes SM, Liskay RM. Mutations affecting a putative MutLalpha endonuclease motif impact multiple mismatch repair functions. DNA Repair (Amst) 2007; 6:1463-70. [PMID: 17567544 PMCID: PMC2366940 DOI: 10.1016/j.dnarep.2007.04.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Accepted: 04/16/2007] [Indexed: 12/11/2022]
Abstract
Mutations in DNA mismatch repair (MMR) lead to increased mutation rates and higher recombination between similar, but not identical sequences, as well as resistance to certain DNA methylating agents. Recently, a component of human MMR machinery, MutLalpha, has been shown to display a latent endonuclease activity. The endonuclease active site appears to include a conserved motif, DQHA(X)(2)E(X)(4)E, within the COOH-terminus of human PMS2. Substitution of the glutamic acid residue (E705) abolished the endonuclease activity and mismatch-dependent excision in vitro. Previously, we showed that the PMS2-E705K mutation and the corresponding mutation in Saccharomyces cerevisiae were both recessive loss of function alleles for mutation avoidance in vivo. Here, we show that mutations impacting this endonuclease motif also significantly affect MMR-dependent suppression of homeologous recombination in yeast and responses to S(n)1-type methylating agents in both yeast and mammalian cells. Thus, our in vivo results suggest that the endonuclease activity of MutLalpha is important not only in MMR-dependent mutation avoidance but also for recombination and damage response functions.
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Affiliation(s)
- Naz Erdeniz
- Department of Molecular and Medical Genetics, Oregon Health & Science University L103, 3181 SW, Sam Jackson Park Road, Portland, OR 97239-3098, United States
| | - Megan Nguyen
- Department of Molecular and Medical Genetics, Oregon Health & Science University L103, 3181 SW, Sam Jackson Park Road, Portland, OR 97239-3098, United States
| | - Suzanne M. Deschênes
- Department of Biology, Sacred Heart University, 5151 Park Ave., Fairfield, CT 06825, United States
| | - R. Michael Liskay
- Department of Molecular and Medical Genetics, Oregon Health & Science University L103, 3181 SW, Sam Jackson Park Road, Portland, OR 97239-3098, United States
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24
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Nowosielska A, Marinus MG. DNA mismatch repair-induced double-strand breaks. DNA Repair (Amst) 2007; 7:48-56. [PMID: 17827074 PMCID: PMC2175267 DOI: 10.1016/j.dnarep.2007.07.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Revised: 05/21/2007] [Accepted: 07/18/2007] [Indexed: 11/26/2022]
Abstract
Escherichia coli dam mutants are sensitized to the cytotoxic action of base analogs, cisplatin and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), while their mismatch repair (MMR)-deficient derivatives are tolerant to these agents. We showed previously, using pulse field gel electrophoresis (PFGE), that MMR-mediated double-strand breaks (DSBs) are produced by cisplatin in dam recB(Ts) cells at the non-permissive temperature. We demonstrate here that the majority of these DSBs require DNA replication for their formation, consistent with a model in which replication forks collapse at nicks or gaps formed during MMR. DSBs were also detected in dam recB(Ts) ada ogt cells exposed to MNNG in a dose- and MMR-dependent manner. In contrast to cisplatin, the formation of these DSBs was not affected by DNA replication and it is proposed that two separate mechanisms result in DSB formation. Replication-independent DSBs arise from overlapping base excision and MMR repair tracts on complementary strands and constitute the majority of detectable DSBs in dam recB(Ts) ada ogt cells exposed to MNNG. Replication-dependent DSBs result from replication fork collapse at O(6)-methylguanine (O(6)-meG) base pairs undergoing MMR futile cycling and are more likely to contribute to cytotoxicity. This model is consistent with the observation that fast-growing dam recB(Ts) ada ogt cells, which have more chromosome replication origins, are more sensitive to the cytotoxic effect of MNNG than the same cells growing slowly.
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Affiliation(s)
- Anetta Nowosielska
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA
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25
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Abstract
The eukaryotic mismatch repair protein Msh6 shares five domains in common with other MutS members. However, it also contains several hundred additional residues at its N-terminus. A few of these residues bind to PCNA, but the functions of the other amino acids in the N-terminal region (NTR) are unknown. Here we demonstrate that the Msh6 NTR binds to duplex DNA in a salt-sensitive, mismatch-independent manner. Partial proteolysis, DNA affinity chromatography and mass spectrometry identified a fragment comprised of residues 228–299 of yeast Msh6 that binds to DNA and is rich in positively charged residues. Deleting these residues, or replacing lysines and arginines with glutamate, reduces DNA binding in vitro and elevates spontaneous mutation rates and resistance to MNNG treatment in vivo. Similar in vivo defects are conferred by alanine substitutions in a highly conserved motif in the NTR that immediately precedes domain I of MutS proteins, the domain that interacts with mismatched DNA. These data suggest that, in addition to PCNA binding, DNA binding and possibly other functions in the amino terminal region of Msh6 are important for eukaryotic DNA mismatch repair and cellular response to alkylation damage.
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Affiliation(s)
- Alan B. Clark
- Laboratory of Structural Biology and Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
| | - Leesa Deterding
- Laboratory of Structural Biology and Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
| | - Kenneth B. Tomer
- Laboratory of Structural Biology and Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
| | - Thomas A. Kunkel
- Laboratory of Structural Biology and Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
- *To whom correspondence should be addressed. 919-541-2644919-541-7613
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26
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Wyatt MD, Pittman DL. Methylating agents and DNA repair responses: Methylated bases and sources of strand breaks. Chem Res Toxicol 2007; 19:1580-94. [PMID: 17173371 PMCID: PMC2542901 DOI: 10.1021/tx060164e] [Citation(s) in RCA: 314] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The chemical methylating agents methylmethane sulfonate (MMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) have been used for decades as classical DNA damaging agents. These agents have been utilized to uncover and explore pathways of DNA repair, DNA damage response, and mutagenesis. MMS and MNNG modify DNA by adding methyl groups to a number of nucleophilic sites on the DNA bases, although MNNG produces a greater percentage of O-methyl adducts. There has been substantial progress elucidating direct reversal proteins that remove methyl groups and base excision repair (BER), which removes and replaces methylated bases. Direct reversal proteins and BER, thus, counteract the toxic, mutagenic, and clastogenic effects of methylating agents. Despite recent progress, the complexity of DNA damage responses to methylating agents is still being discovered. In particular, there is growing understanding of pathways such as homologous recombination, lesion bypass, and mismatch repair that react when the response of direct reversal proteins and BER is insufficient. Furthermore, the importance of proper balance within the steps in BER has been uncovered with the knowledge that DNA structural intermediates during BER are deleterious. A number of issues complicate the elucidation of the downstream responses when direct reversal is insufficient or BER is imbalanced. These include inter-species differences, cell-type-specific differences within mammals and between cancer cell lines, and the type of methyl damage or BER intermediate encountered. MMS also carries a misleading reputation of being a radiomimetic, that is, capable of directly producing strand breaks. This review focuses on the DNA methyl damage caused by MMS and MNNG for each site of potential methylation to summarize what is known about the repair of such damage and the downstream responses and consequences if the damage is not repaired.
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Affiliation(s)
- Michael D Wyatt
- Department of Basic Pharmaceutical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina 29208, USA.
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27
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Yoshioka KI, Yoshioka Y, Hsieh P. ATR kinase activation mediated by MutSalpha and MutLalpha in response to cytotoxic O6-methylguanine adducts. Mol Cell 2006; 22:501-10. [PMID: 16713580 PMCID: PMC2423943 DOI: 10.1016/j.molcel.2006.04.023] [Citation(s) in RCA: 209] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2005] [Revised: 02/15/2006] [Accepted: 04/26/2006] [Indexed: 10/24/2022]
Abstract
S(N)1-type alkylating agents that produce cytotoxic O(6)-methyl-G (O(6)-meG) DNA adducts induce cell cycle arrest and apoptosis in a manner requiring the DNA mismatch repair (MMR) proteins MutSalpha and MutLalpha. Here, we show that checkpoint signaling in response to DNA methylation occurs during S phase and requires DNA replication that gives rise to O(6)-meG/T mispairs. DNA binding studies reveal that MutSalpha specifically recognizes O(6)-meG/T mispairs, but not O(6)-meG/C. In an in vitro assay, ATR-ATRIP, but not RPA, is preferentially recruited to O(6)-meG/T mismatches in a MutSalpha- and MutLalpha-dependent manner. Furthermore, ATR kinase is activated to phosphorylate Chk1 in the presence of O(6)-meG/T mispairs and MMR proteins. These results suggest that MMR proteins can act as direct sensors of methylation damage and help recruit ATR-ATRIP to sites of cytotoxic O(6)-meG adducts to initiate ATR checkpoint signaling.
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Affiliation(s)
- Ken-ichi Yoshioka
- Genetics and Biochemistry Branch National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland 20892
| | - Yoshiko Yoshioka
- Genetics and Biochemistry Branch National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland 20892
| | - Peggy Hsieh
- Genetics and Biochemistry Branch National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health Bethesda, Maryland 20892
- Correspondence:
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28
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York SJ, Modrich P. Mismatch repair-dependent iterative excision at irreparable O6-methylguanine lesions in human nuclear extracts. J Biol Chem 2006; 281:22674-83. [PMID: 16772289 PMCID: PMC2234603 DOI: 10.1074/jbc.m603667200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
The response of mammalian cells to Sn1 DNA methylators depends on functional MutSalpha and MutLalpha. Cells deficient in either of these activities are resistant to the cytotoxic effects of this class of chemotherapeutic drug. Because killing by Sn1 methylators has been attributed to O6-methylguanine (MeG), we have constructed nicked circular heteroduplexes that contain a single MeG-T mispair, and we have examined processing of these molecules by mismatch repair in nuclear extracts of human cells. Excision provoked by MeG-T is restricted to the incised heteroduplex strand, leading to removal of the MeG when it resides on this strand. However, when the MeG is located on the continuous strand, the heteroduplex is irreparable. MeG-T-dependent repair DNA synthesis is observed on both reparable and irreparable 3' and 5' heteroduplexes as judged by [32P]dAMP incorporation. Labeling with [alpha-32P]dATP followed by a cold dATP chase has demonstrated that newly synthesized DNA on irreparable molecules is subject to re-excision in a reaction that is MutLalpha-dependent, an effect attributable to the presence of MeG on the template strand. Processing of the irreparable 3' heteroduplex is also associated with incision of the discontinuous strand of a few percent of molecules near the thymidylate of the MeG-T base pair. These results provide the first direct evidence for mismatch repair-mediated iterative processing of DNA methylator damage, an effect that may be relevant to damage signaling events triggered by this class of chemotherapeutic agent.
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Affiliation(s)
- Sally J. York
- Howard Hughes Medical Institute and Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710
- Howard Hughes Medical Institute and Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710
| | - Paul Modrich
- Howard Hughes Medical Institute and Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710
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29
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Abstract
By removing biosynthetic errors from newly synthesized DNA, mismatch repair (MMR) improves the fidelity of DNA replication by several orders of magnitude. Loss of MMR brings about a mutator phenotype, which causes a predisposition to cancer. But MMR status also affects meiotic and mitotic recombination, DNA-damage signalling, apoptosis and cell-type-specific processes such as class-switch recombination, somatic hypermutation and triplet-repeat expansion. This article reviews our current understanding of this multifaceted DNA-repair system in human cells.
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Affiliation(s)
- Josef Jiricny
- Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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Current awareness on yeast. Yeast 2006. [DOI: 10.1002/yea.1285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Trouiller B, Schaefer DG, Charlot F, Nogué F. MSH2 is essential for the preservation of genome integrity and prevents homeologous recombination in the moss Physcomitrella patens. Nucleic Acids Res 2006; 34:232-42. [PMID: 16397301 PMCID: PMC1325206 DOI: 10.1093/nar/gkj423] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
MSH2 is a central component of the mismatch repair pathway that targets mismatches arising during DNA replication, homologous recombination (HR) and in response to genotoxic stresses. Here, we describe the function of MSH2 in the moss Physcomitrella patens, as deciphered by the analysis of loss of function mutants. Ppmsh2 mutants display pleiotropic growth and developmental defects, which reflect genomic instability. Based on loss of function of the APT gene, we estimated this mutator phenotype to be at least 130 times higher in the mutants than in wild type. We also found that MSH2 is involved in some but not all the moss responses to genotoxic stresses we tested. Indeed, the Ppmsh2 mutants were more tolerant to cisplatin and show higher sensitivity to UV-B radiations. PpMSH2 gene involvement in HR was studied by assessing gene targeting (GT) efficiency with homologous and homeologous sequences. GT efficiency with homologous sequences was slightly decreased in the Ppmsh2 mutant compared with wild type. Strikingly GT efficiency with homeologous sequences decreased proportionally to sequence divergence in the wild type whereas it remained unaffected in the mutants. Those results demonstrate the role of PpMSH2 in the maintenance of genome integrity and in homologous and homeologous recombination.
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Affiliation(s)
| | - Didier G. Schaefer
- Département de biologie moléculaire végétale, Université de LausanneCH-1015 Lausanne, Switzerland
| | | | - Fabien Nogué
- To whom correspondence should be addressed. Tel: +33 1 30833009; Fax: +33 1 30833319;
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