1
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Xie B, Sanford EJ, Hung SH, Wagner M, Heyer WD, Smolka MB. Multi-step control of homologous recombination via Mec1/ATR suppresses chromosomal rearrangements. EMBO J 2024; 43:3027-3043. [PMID: 38839993 PMCID: PMC11251156 DOI: 10.1038/s44318-024-00139-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 05/19/2024] [Accepted: 05/22/2024] [Indexed: 06/07/2024] Open
Abstract
The Mec1/ATR kinase is crucial for genome stability, yet the mechanism by which it prevents gross chromosomal rearrangements (GCRs) remains unknown. Here we find that in cells with deficient Mec1 signaling, GCRs accumulate due to the deregulation of multiple steps in homologous recombination (HR). Mec1 primarily suppresses GCRs through its role in activating the canonical checkpoint kinase Rad53, which ensures the proper control of DNA end resection. Upon loss of Rad53 signaling and resection control, Mec1 becomes hyperactivated and triggers a salvage pathway in which the Sgs1 helicase is recruited to sites of DNA lesions via the 911-Dpb11 scaffolds and phosphorylated by Mec1 to favor heteroduplex rejection and limit HR-driven GCR accumulation. Fusing an ssDNA recognition domain to Sgs1 bypasses the requirement of Mec1 signaling for GCR suppression and nearly eliminates D-loop formation, thus preventing non-allelic recombination events. We propose that Mec1 regulates multiple steps of HR to prevent GCRs while ensuring balanced HR usage when needed for promoting tolerance to replication stress.
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Affiliation(s)
- Bokun Xie
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Ethan James Sanford
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Shih-Hsun Hung
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA, USA
| | - Mateusz Wagner
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Wolf-Dietrich Heyer
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA, USA
| | - Marcus B Smolka
- Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA.
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2
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Remines M, Schoonover MG, Knox Z, Kenwright K, Hoffert KM, Coric A, Mead J, Ampfer J, Seye S, Strome ED. Profiling the compendium of changes in Saccharomyces cerevisiae due to mutations that alter availability of the main methyl donor S-Adenosylmethionine. G3 (BETHESDA, MD.) 2024; 14:jkae002. [PMID: 38184845 PMCID: PMC10989883 DOI: 10.1093/g3journal/jkae002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Revised: 11/17/2023] [Accepted: 12/16/2023] [Indexed: 01/09/2024]
Abstract
The SAM1 and SAM2 genes encode for S-Adenosylmethionine (AdoMet) synthetase enzymes, with AdoMet serving as the main cellular methyl donor. We have previously shown that independent deletion of these genes alters chromosome stability and AdoMet concentrations in opposite ways in Saccharomyces cerevisiae. To characterize other changes occurring in these mutants, we grew wildtype, sam1Δ/sam1Δ, and sam2Δ/sam2Δ strains in 15 different Phenotypic Microarray plates with different components and measured growth variations. RNA-Sequencing was also carried out on these strains and differential gene expression determined for each mutant. We explored how the phenotypic growth differences are linked to the altered gene expression, and hypothesize mechanisms by which loss of the SAM genes and subsequent AdoMet level changes, impact pathways and processes. We present 6 stories, discussing changes in sensitivity or resistance to azoles, cisplatin, oxidative stress, arginine biosynthesis perturbations, DNA synthesis inhibitors, and tamoxifen, to demonstrate the power of this novel methodology to broadly profile changes due to gene mutations. The large number of conditions that result in altered growth, as well as the large number of differentially expressed genes with wide-ranging functionality, speaks to the broad array of impacts that altering methyl donor abundance can impart. Our findings demonstrate that some cellular changes are directly related to AdoMet-dependent methyltransferases and AdoMet availability, some are directly linked to the methyl cycle and its role in production of several important cellular components, and others reveal impacts of SAM gene mutations on previously unconnected pathways.
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Affiliation(s)
- McKayla Remines
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Makailyn G Schoonover
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Zoey Knox
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Kailee Kenwright
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Kellyn M Hoffert
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Amila Coric
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - James Mead
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Joseph Ampfer
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Serigne Seye
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
| | - Erin D Strome
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099, USA
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3
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Li Y, Zhang Y, Shah SB, Chang CY, Wang H, Wu X. MutSβ protects common fragile sites by facilitating homology-directed repair at DNA double-strand breaks with secondary structures. Nucleic Acids Res 2024; 52:1120-1135. [PMID: 38038265 PMCID: PMC10853791 DOI: 10.1093/nar/gkad1112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/14/2023] [Accepted: 11/07/2023] [Indexed: 12/02/2023] Open
Abstract
Common fragile sites (CFSs) are regions prone to chromosomal rearrangements, thereby contributing to tumorigenesis. Under replication stress (RS), CFSs often harbor under-replicated DNA regions at the onset of mitosis, triggering homology-directed repair known as mitotic DNA synthesis (MiDAS) to complete DNA replication. In this study, we identified an important role of DNA mismatch repair protein MutSβ (MSH2/MSH3) in facilitating MiDAS and maintaining CFS stability. Specifically, we demonstrated that MutSβ is required for the increased mitotic recombination induced by RS or FANCM loss at CFS-derived AT-rich and structure-prone sequences (CFS-ATs). We also found that MSH3 exhibits synthetic lethality with FANCM. Mechanistically, MutSβ is required for homologous recombination (HR) especially when DNA double-strand break (DSB) ends contain secondary structures. We also showed that upon RS, MutSβ is recruited to Flex1, a specific CFS-AT, in a PCNA-dependent but MUS81-independent manner. Furthermore, MutSβ interacts with RAD52 and promotes RAD52 recruitment to Flex1 following MUS81-dependent fork cleavage. RAD52, in turn, recruits XPF/ERCC1 to remove DNA secondary structures at DSB ends, enabling HR/break-induced replication (BIR) at CFS-ATs. We propose that the specific requirement of MutSβ in processing DNA secondary structures at CFS-ATs underlies its crucial role in promoting MiDAS and maintaining CFS integrity.
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Affiliation(s)
- Youhang Li
- Beijing Key Laboratory of DNA Damage Response and College of Life Sciences, Capital Normal University, Beijing 100048, China
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Yunkun Zhang
- Beijing Key Laboratory of DNA Damage Response and College of Life Sciences, Capital Normal University, Beijing 100048, China
| | - Sameer Bikram Shah
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Chia-Yu Chang
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Hailong Wang
- Beijing Key Laboratory of DNA Damage Response and College of Life Sciences, Capital Normal University, Beijing 100048, China
| | - Xiaohua Wu
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
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4
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Oh JM, Kang Y, Park J, Sung Y, Kim D, Seo Y, Lee E, Ra J, Amarsanaa E, Park YU, Lee S, Hwang J, Kim H, Schärer O, Cho S, Lee C, Takata KI, Lee J, Myung K. MSH2-MSH3 promotes DNA end resection during homologous recombination and blocks polymerase theta-mediated end-joining through interaction with SMARCAD1 and EXO1. Nucleic Acids Res 2023; 51:5584-5602. [PMID: 37140056 PMCID: PMC10287916 DOI: 10.1093/nar/gkad308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 04/04/2023] [Accepted: 04/27/2023] [Indexed: 05/05/2023] Open
Abstract
DNA double-strand break (DSB) repair via homologous recombination is initiated by end resection. The extent of DNA end resection determines the choice of the DSB repair pathway. Nucleases for end resection have been extensively studied. However, it is still unclear how the potential DNA structures generated by the initial short resection by MRE11-RAD50-NBS1 are recognized and recruit proteins, such as EXO1, to DSB sites to facilitate long-range resection. We found that the MSH2-MSH3 mismatch repair complex is recruited to DSB sites through interaction with the chromatin remodeling protein SMARCAD1. MSH2-MSH3 facilitates the recruitment of EXO1 for long-range resection and enhances its enzymatic activity. MSH2-MSH3 also inhibits access of POLθ, which promotes polymerase theta-mediated end-joining (TMEJ). Collectively, we present a direct role of MSH2-MSH3 in the initial stages of DSB repair by promoting end resection and influencing the DSB repair pathway by favoring homologous recombination over TMEJ.
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Affiliation(s)
- Jung-Min Oh
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Oral Biochemistry, Dental and Life Science Institute, School of Dentistry, Pusan National University, Yangsan 50612, Republic of Korea
| | - Yujin Kang
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Jumi Park
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Yubin Sung
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Dayoung Kim
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Yuri Seo
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Eun A Lee
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Jae Sun Ra
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Enkhzul Amarsanaa
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Young-Un Park
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Seon Young Lee
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Jung Me Hwang
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
| | - Hongtae Kim
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Orlando Schärer
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Seung Woo Cho
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Changwook Lee
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Kei-ichi Takata
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Ja Yil Lee
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biological Sciences, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
| | - Kyungjae Myung
- Center for Genomic Integrity, Institute for Basic Science (IBS), Ulsan 44919, Republic of Korea
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan44919, Republic of Korea
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5
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Remines M, Schoonover M, Knox Z, Kenwright K, Hoffert KM, Coric A, Mead J, Ampfer J, Seye S, Strome ED. Profiling The Compendium Of Changes In Saccharomyces cerevisiae Due To Mutations That Alter Availability Of The Main Methyl Donor S-Adenosylmethionine. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.09.544294. [PMID: 37333147 PMCID: PMC10274911 DOI: 10.1101/2023.06.09.544294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
The SAM1 and SAM2 genes encode for S-AdenosylMethionine (AdoMet) synthetase enzymes, with AdoMet serving as the main methyl donor. We have previously shown that independent deletion of these genes alters chromosome stability and AdoMet concentrations in opposite ways in S. cerevisiae. To characterize other changes occurring in these mutants, we grew wildtype, sam1∆/sam1∆, and sam2∆/sam2∆ strains in 15 different Phenotypic Microarray plates with different components, equal to 1440 wells, and measured for growth variations. RNA-Sequencing was also carried out on these strains and differential gene expression determined for each mutant. In this study, we explore how the phenotypic growth differences are linked to the altered gene expression, and thereby predict the mechanisms by which loss of the SAM genes and subsequent AdoMet level changes, impact S. cerevisiae pathways and processes. We present six stories, discussing changes in sensitivity or resistance to azoles, cisplatin, oxidative stress, arginine biosynthesis perturbations, DNA synthesis inhibitors, and tamoxifen, to demonstrate the power of this novel methodology to broadly profile changes due to gene mutations. The large number of conditions that result in altered growth, as well as the large number of differentially expressed genes with wide-ranging functionality, speaks to the broad array of impacts that altering methyl donor abundance can impart, even when the conditions tested were not specifically selected as targeting known methyl involving pathways. Our findings demonstrate that some cellular changes are directly related to AdoMet-dependent methyltransferases and AdoMet availability, some are directly linked to the methyl cycle and its role is production of several important cellular components, and others reveal impacts of SAM gene mutations on previously unconnected pathways.
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Affiliation(s)
- McKayla Remines
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Makailyn Schoonover
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Zoey Knox
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Kailee Kenwright
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Kellyn M. Hoffert
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Amila Coric
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - James Mead
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Joseph Ampfer
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Serigne Seye
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
| | - Erin D. Strome
- Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY 41099
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6
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Trost H, Merkell A, Lopezcolorado FW, Stark J. Resolution of sequence divergence for repeat-mediated deletions shows a polarity that is mediated by MLH1. Nucleic Acids Res 2023; 51:650-667. [PMID: 36620890 PMCID: PMC9881173 DOI: 10.1093/nar/gkac1240] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 11/07/2022] [Accepted: 01/04/2023] [Indexed: 01/10/2023] Open
Abstract
Repeat-mediated deletions (RMDs) are a type of chromosomal rearrangement between two homologous sequences that causes loss of the sequence between the repeats, along with one of the repeats. Sequence divergence between repeats suppresses RMDs; the mechanisms of such suppression and of resolution of the sequence divergence remains poorly understood. We identified RMD regulators using a set of reporter assays in mouse cells that test two key parameters: repeat sequence divergence and the distances between one repeat and the initiating chromosomal break. We found that the mismatch repair factor MLH1 suppresses RMDs with sequence divergence in the same pathway as MSH2 and MSH6, and which is dependent on residues in MLH1 and its binding partner PMS2 that are important for nuclease activity. Additionally, we found that the resolution of sequence divergence in the RMD product has a specific polarity, where divergent bases that are proximal to the chromosomal break end are preferentially removed. Moreover, we found that the domain of MLH1 that forms part of the MLH1-PMS2 endonuclease is important for polarity of resolution of sequence divergence. We also identified distinctions between MLH1 versus TOP3α in regulation of RMDs. We suggest that MLH1 suppresses RMDs with sequence divergence, while also promoting directional resolution of sequence divergence in the RMD product.
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Affiliation(s)
- Hannah Trost
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | - Arianna Merkell
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | | | - Jeremy M Stark
- To whom correspondence should be addressed. Tel: +1 626 218-6346; Fax: +1 626 218 8892;
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7
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Sakellariou D, Bak ST, Isik E, Barroso SI, Porro A, Aguilera A, Bartek J, Janscak P, Peña-Diaz J. MutSβ regulates G4-associated telomeric R-loops to maintain telomere integrity in ALT cancer cells. Cell Rep 2022; 39:110602. [PMID: 35385755 DOI: 10.1016/j.celrep.2022.110602] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 12/17/2021] [Accepted: 03/10/2022] [Indexed: 12/24/2022] Open
Abstract
Up to 15% of human cancers maintain their telomeres through a telomerase-independent mechanism, termed "alternative lengthening of telomeres" (ALT) that relies on homologous recombination between telomeric sequences. Emerging evidence suggests that the recombinogenic nature of ALT telomeres results from the formation of RNA:DNA hybrids (R-loops) between telomeric DNA and the long-noncoding telomeric repeat-containing RNA (TERRA). Here, we show that the mismatch repair protein MutSβ, a heterodimer of MSH2 and MSH3 subunits, is enriched at telomeres in ALT cancer cells, where it prevents the accumulation of telomeric G-quadruplex (G4) structures and R-loops. Cells depleted of MSH3 display increased incidence of R-loop-dependent telomere fragility and accumulation of telomeric C-circles. We also demonstrate that purified MutSβ recognizes and destabilizes G4 structures in vitro. These data suggest that MutSβ destabilizes G4 structures in ALT telomeres to regulate TERRA R-loops, which is a prerequisite for maintenance of telomere integrity during ALT.
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Affiliation(s)
- Despoina Sakellariou
- Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark; Danish Cancer Society Research Center, 2100 Copenhagen, Denmark
| | - Sara Thornby Bak
- Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Esin Isik
- Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland
| | - Sonia I Barroso
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, University of Seville-CSIC-UPO, Seville, Spain
| | - Antonio Porro
- Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, University of Seville-CSIC-UPO, Seville, Spain
| | - Jiri Bartek
- Danish Cancer Society Research Center, 2100 Copenhagen, Denmark; Division of Genome Biology, Department of Medical Biochemistry and Biophysics, Science for Life Laboratory, Karolinska Institute, 17177 Stockholm, Sweden; Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 14300 Prague, Czech Republic
| | - Pavel Janscak
- Institute of Molecular Cancer Research, University of Zurich, 8057 Zürich, Switzerland; Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 14300 Prague, Czech Republic.
| | - Javier Peña-Diaz
- Center for Healthy Aging, Department of Neuroscience and Pharmacology, University of Copenhagen, 2200 Copenhagen, Denmark.
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8
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Al-Zain AM, Symington LS. The dark side of homology-directed repair. DNA Repair (Amst) 2021; 106:103181. [PMID: 34311272 DOI: 10.1016/j.dnarep.2021.103181] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 07/16/2021] [Accepted: 07/16/2021] [Indexed: 10/20/2022]
Abstract
DNA double strand breaks (DSB) are cytotoxic lesions that can lead to genome rearrangements and genomic instability, which are hallmarks of cancer. The two main DSB repair pathways are non-homologous end joining and homologous recombination (HR). While HR is generally highly accurate, it has the potential for rearrangements that occur directly or through intermediates generated during the repair process. Whole genome sequencing of cancers has revealed numerous types of structural rearrangement signatures that are often indicative of repair mediated by sequence homology. However, it can be challenging to delineate repair mechanisms from sequence analysis of rearrangement end products from cancer genomes, or even model systems, because the same rearrangements can be generated by different pathways. Here, we review homology-directed repair pathways and their consequences. Exploring those pathways can lead to a greater understanding of rearrangements that occur in cancer cells.
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Affiliation(s)
- Amr M Al-Zain
- Program in Biological Sciences, Columbia University, New York, NY, 10027, United States; Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY, 10032, United States
| | - Lorraine S Symington
- Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY, 10032, United States; Department of Genetics & Development, Columbia University Irving Medical Center, New York, NY, 10032, United States.
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9
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Mendez-Dorantes C, Tsai LJ, Jahanshir E, Lopezcolorado FW, Stark JM. BLM has Contrary Effects on Repeat-Mediated Deletions, based on the Distance of DNA DSBs to a Repeat and Repeat Divergence. Cell Rep 2021; 30:1342-1357.e4. [PMID: 32023454 PMCID: PMC7085117 DOI: 10.1016/j.celrep.2020.01.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Revised: 12/08/2019] [Accepted: 12/31/2019] [Indexed: 12/30/2022] Open
Abstract
Repeat-mediated deletions (RMDs) often involve repetitive elements (e.g., short interspersed elements) with sequence divergence that is separated by several kilobase pairs (kbps). We have examined RMDs induced by DNA double-strand breaks (DSBs) under varying conditions of repeat sequence divergence (identical versus 1% and 3% divergent) and DSB/repeat distance (16 bp–28.4 kbp). We find that the BLM helicase promotes RMDs with long DSB/repeat distances (e.g., 28.4 kbp), which is consistent with a role in extensive DSB end resection, because the resection nucleases EXO1 and DNA2 affect RMDs similarly to BLM. In contrast, BLM suppresses RMDs with sequence divergence and intermediate (e.g., 3.3 kbp) DSB/repeat distances, which supports a role in heteroduplex rejection. The role of BLM in heteroduplex rejection is not epistatic with MSH2 and is independent of the annealing factor RAD52. Accordingly, the role of BLM on RMDs is substantially affected by DSB/repeat distance and repeat sequence divergence. Mendez-Dorantes et al. identify the BLM helicase as a key regulator of repeat-mediated deletions (RMDs). BLM, EXO1, and DNA2 mediate RMDs with remarkably long DNA break/repeat distances. BLM suppresses RMDs with sequence divergence that is optimal with a long non-homologous tail and is independent of MSH2 and RAD52.
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Affiliation(s)
- Carlos Mendez-Dorantes
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA; Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | - L Jillianne Tsai
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA; Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | - Eva Jahanshir
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA
| | | | - Jeremy M Stark
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA; Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
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10
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Mackenroth B, Alani E. Collaborations between chromatin and nuclear architecture to optimize DNA repair fidelity. DNA Repair (Amst) 2021; 97:103018. [PMID: 33285474 PMCID: PMC8486310 DOI: 10.1016/j.dnarep.2020.103018] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 10/18/2020] [Accepted: 11/05/2020] [Indexed: 01/22/2023]
Abstract
Homologous recombination (HR), considered the highest fidelity DNA double-strand break (DSB) repair pathway that a cell possesses, is capable of repairing multiple DSBs without altering genetic information. However, in "last resort" scenarios, HR can be directed to low fidelity subpathways which often use non-allelic donor templates. Such repair mechanisms are often highly mutagenic and can also yield chromosomal rearrangements and/or deletions. While the choice between HR and its less precise counterpart, non-homologous end joining (NHEJ), has received much attention, less is known about how cells manage and prioritize HR subpathways. In this review, we describe work focused on how chromatin and nuclear architecture orchestrate subpathway choice and repair template usage to maintain genome integrity without sacrificing cell survival. Understanding the relationships between nuclear architecture and recombination mechanics will be critical to understand these cellular repair decisions.
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Affiliation(s)
- Beata Mackenroth
- Department of Molecular Biology and Genetics, Cornell University, 459 Biotechnology Building, Ithaca, NY, 14853-2703, United States
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, 459 Biotechnology Building, Ithaca, NY, 14853-2703, United States.
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11
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Datta A, Dhar S, Awate S, Brosh RM. Synthetic Lethal Interactions of RECQ Helicases. Trends Cancer 2020; 7:146-161. [PMID: 33041245 DOI: 10.1016/j.trecan.2020.09.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Revised: 08/20/2020] [Accepted: 09/04/2020] [Indexed: 02/06/2023]
Abstract
DNA helicases have risen to the forefront as genome caretakers. Their prominent roles in chromosomal stability are demonstrated by the linkage of mutations in helicase genes to hereditary disorders with defects in DNA repair, the replication stress response, and/or transcriptional activation. Conversely, accumulating evidence suggests that DNA helicases in cancer cells have a network of pathway interactions such that codeficiency of some helicases and their genetically interacting proteins results in synthetic lethality (SL). Such genetic interactions may potentially be exploited for cancer therapies. We discuss the roles of RECQ DNA helicases in cancer, emphasizing some of the more recent developments in SL.
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Affiliation(s)
- Arindam Datta
- Section on DNA Helicases, Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Srijita Dhar
- Section on DNA Helicases, Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Sanket Awate
- Section on DNA Helicases, Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Robert M Brosh
- Section on DNA Helicases, Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
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12
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A Genome-Wide Screen for Genes Affecting Spontaneous Direct-Repeat Recombination in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2020; 10:1853-1867. [PMID: 32265288 PMCID: PMC7263696 DOI: 10.1534/g3.120.401137] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Homologous recombination is an important mechanism for genome integrity maintenance, and several homologous recombination genes are mutated in various cancers and cancer-prone syndromes. However, since in some cases homologous recombination can lead to mutagenic outcomes, this pathway must be tightly regulated, and mitotic hyper-recombination is a hallmark of genomic instability. We performed two screens in Saccharomyces cerevisiae for genes that, when deleted, cause hyper-recombination between direct repeats. One was performed with the classical patch and replica-plating method. The other was performed with a high-throughput replica-pinning technique that was designed to detect low-frequency events. This approach allowed us to validate the high-throughput replica-pinning methodology independently of the replicative aging context in which it was developed. Furthermore, by combining the two approaches, we were able to identify and validate 35 genes whose deletion causes elevated spontaneous direct-repeat recombination. Among these are mismatch repair genes, the Sgs1-Top3-Rmi1 complex, the RNase H2 complex, genes involved in the oxidative stress response, and a number of other DNA replication, repair and recombination genes. Since several of our hits are evolutionarily conserved, and repeated elements constitute a significant fraction of mammalian genomes, our work might be relevant for understanding genome integrity maintenance in humans.
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13
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Wang H, Cao Q, Zhao Q, Arfan M, Liu W. Mechanisms used by DNA MMR system to cope with Cadmium-induced DNA damage in plants. CHEMOSPHERE 2020; 246:125614. [PMID: 31883478 DOI: 10.1016/j.chemosphere.2019.125614] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Revised: 12/07/2019] [Accepted: 12/09/2019] [Indexed: 05/27/2023]
Abstract
Cadmium (Cd) is found widely in soil and is severely toxic for plants, causing oxidative damage in plant cells because of its heavy metal characteristics. The DNA damage response (DDR) is triggered in plants to cope with the Cd stress. The DNA mismatch repair (MMR) system known for its mismatch repair function determines DDR, as mispairs are easily generated by a translesional synthesis under Cd-induced genomic instability. Cd-induced mismatches are recognized by three heterodimeric complexes including MutSα (MSH2/MSH6), MutSβ (MSH2/MSH3), and MutSγ (MSH2/MSH7). MutLα (MLH1/PMS1), PCNA/RFC, EXO1, DNA polymerase δ and DNA ligase participate in mismatch repair in turn. Meanwhile, ATR is preferentially activated by MSH2 to trigger DDR including the regulation of the cell cycle, endoreduplication, cell death, and recruitment of other DNA repair, which enhances plant tolerance to Cd. However, plants with deficient MutS will bypass MMR-mediated DDR and release the multiple-effect MLH1 from requisition of the MMR system, which leads to weak tolerance to Cd in plants. In this review, we systematically illustrate how the plant DNA MMR system works in a Cd-induced DDR, and how MMR genes regulate plant tolerance to Cd. Additionally, we also reviewed multiple epigenetic regulation systems acting on MMR genes under stress.
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Affiliation(s)
- Hetong Wang
- Liaoning Key Laboratory of Urban Integrated Pest Management and Ecological Security, College of Life Science and Bioengineering, Shenyang University, Shenyang, 110044, PR China.
| | - Qijiang Cao
- Liaoning Key Laboratory of Urban Integrated Pest Management and Ecological Security, College of Life Science and Bioengineering, Shenyang University, Shenyang, 110044, PR China.
| | - Qiang Zhao
- Agricultural College, Shenyang Agricultural University, Shenyang, 110866, PR China.
| | - Muhammad Arfan
- Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, PR China.
| | - Wan Liu
- Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, PR China.
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14
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Gonzalez V, Spampinato CP. The mismatch repair protein MSH6 regulates somatic recombination in Arabidopsis thaliana. DNA Repair (Amst) 2020; 87:102789. [PMID: 31945543 DOI: 10.1016/j.dnarep.2020.102789] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 11/29/2019] [Accepted: 01/08/2020] [Indexed: 11/28/2022]
Abstract
The mismatch repair (MMR) pathway promotes genome stability by controlling the fidelity of replication and recombination. The first step of the pathway involves recognition of the mismatch by heterodimers composed of MutS homologs (MSH). Although MSH6 has been well characterized in yeasts and humans, the role of the plant protein has not been extensively studied. We first analyzed gene expression in Arabidopsis thaliana. The use of transgenic plants expressing the β-glucuronidase (GUS) reporter gene under the control of approximately 1-kb region upstream of the start codon of the AtMSH6 gene demonstrated that MSH6 is preferentially expressed in undifferentiated cells with an intense cell division rate. We then examined protein function in meiotic and somatic recombination. Suppression of AtMSH6 did not affect the rate of meiotic recombination, but increased the frequency of recombination between two homeologous repeats of a marker gene by 3-fold relative to wild-type plants. Expression of the AtMSH6 gene under the control of its own promoter in msh6 homozygous mutant plants rescued the altered somatic recombination phenotype. We conclude that MSH6 shows a functional conservation across different biological kingdoms and a functional specificity in plants.
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Affiliation(s)
- Valentina Gonzalez
- Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000, Rosario, Argentina
| | - Claudia P Spampinato
- Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000, Rosario, Argentina.
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15
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Chakraborty U, Mackenroth B, Shalloway D, Alani E. Chromatin Modifiers Alter Recombination Between Divergent DNA Sequences. Genetics 2019; 212:1147-1162. [PMID: 31221666 PMCID: PMC6707472 DOI: 10.1534/genetics.119.302395] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 06/18/2019] [Indexed: 02/07/2023] Open
Abstract
Recombination between divergent DNA sequences is actively prevented by heteroduplex rejection mechanisms. In baker's yeast, such antirecombination mechanisms can be initiated by the recognition of DNA mismatches in heteroduplex DNA by MSH proteins, followed by recruitment of the Sgs1-Top3-Rmi1 helicase-topoisomerase complex to unwind the recombination intermediate. We previously showed that the repair/rejection decision during single-strand annealing recombination is temporally regulated by MSH (MutShomolog) protein levels and by factors that excise nonhomologous single-stranded tails. These observations, coupled with recent studies indicating that mismatch repair (MMR) factors interact with components of the histone chaperone machinery, encouraged us to explore roles for epigenetic factors and chromatin conformation in regulating the decision to reject vs. repair recombination between divergent DNA substrates. This work involved the use of an inverted repeat recombination assay thought to measure sister chromatid repair during DNA replication. Our observations are consistent with the histone chaperones CAF-1 and Rtt106, and the histone deacetylase Sir2, acting to suppress heteroduplex rejection and the Rpd3, Hst3, and Hst4 deacetylases acting to promote heteroduplex rejection. These observations, and double-mutant analysis, have led to a model in which nucleosomes located at DNA lesions stabilize recombination intermediates and compete with MMR factors that mediate heteroduplex rejection.
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Affiliation(s)
- Ujani Chakraborty
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
| | - Beata Mackenroth
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
| | - David Shalloway
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
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16
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Rogers DW, McConnell E, Ono J, Greig D. Spore-autonomous fluorescent protein expression identifies meiotic chromosome mis-segregation as the principal cause of hybrid sterility in yeast. PLoS Biol 2018; 16:e2005066. [PMID: 30419022 PMCID: PMC6258379 DOI: 10.1371/journal.pbio.2005066] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 11/26/2018] [Accepted: 10/29/2018] [Indexed: 11/19/2022] Open
Abstract
Genome-wide sequence divergence between populations can cause hybrid sterility through the action of the anti-recombination system, which rejects crossover repair of double strand breaks between nonidentical sequences. Because crossovers are necessary to ensure proper segregation of homologous chromosomes during meiosis, the reduced recombination rate in hybrids can result in high levels of nondisjunction and therefore low gamete viability. Hybrid sterility in interspecific crosses of Saccharomyces yeasts is known to be associated with such segregation errors, but estimates of the importance of nondisjunction to postzygotic reproductive isolation have been hampered by difficulties in accurately measuring nondisjunction frequencies. Here, we use spore-autonomous fluorescent protein expression to quantify nondisjunction in both interspecific and intraspecific yeast hybrids. We show that segregation is near random in interspecific hybrids. The observed rates of nondisjunction can explain most of the sterility observed in interspecific hybrids through the failure of gametes to inherit at least one copy of each chromosome. Partially impairing the anti-recombination system by preventing expression of the RecQ helicase SGS1 during meiosis cuts nondisjunction frequencies in half. We further show that chromosome loss through nondisjunction can explain nearly all of the sterility observed in hybrids formed between two populations of a single species. The rate of meiotic nondisjunction of each homologous pair was negatively correlated with chromosome size in these intraspecific hybrids. Our results demonstrate that sequence divergence is not only associated with the sterility of hybrids formed between distantly related species but may also be a direct cause of reproductive isolation in incipient species.
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Affiliation(s)
- David W. Rogers
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany
- Department of Microbial Population Biology, Max Planck Institute for Evolutionary Biology, Plön, Germany
- * E-mail:
| | - Ellen McConnell
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany
- Department of Microbial Population Biology, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Jasmine Ono
- Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
| | - Duncan Greig
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany
- Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
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17
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Li S, Wehrenberg B, Waldman BC, Waldman AS. Mismatch tolerance during homologous recombination in mammalian cells. DNA Repair (Amst) 2018; 70:25-36. [PMID: 30103093 DOI: 10.1016/j.dnarep.2018.07.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Revised: 07/19/2018] [Accepted: 07/30/2018] [Indexed: 12/13/2022]
Abstract
We investigated the homology dependency of recombination in thymidine kinase (tk)-deficient mouse fibroblasts. Cells were transfected with DNA constructs harboring a herpes tk gene (the "recipient") rendered non-functional by an oligonucleotide containing the recognition site for endonuclease I-SceI. Constructs also contained a "donor" tk sequence that could restore function to the recipient gene through spontaneous gene conversion or via repair of a double-strand break (DSB) at the I-SceI site. Recombination events were recoverable by selection for tk-positive clones. Three different donors were used containing 16, 25, or 33 mismatches relative to the recipient. The mismatches were clustered, forming an interval of "homeology" relative to the recipient sequences. We show that when homeologous sequences were surrounded by high homology, mismatches were frequently included in gene conversion events. Notably, conversion tracts from spontaneous recombination included either all or none of the mismatches, suggesting that recombination must begin and end in high homology. This requirement was relaxed for events that occurred near an induced DSB, as a significant number of these latter conversion tracts had one end positioned within homeology. Knock-down of mismatch repair showed that incorporation of mismatches into gene conversion tracts can involve repair of mismatched heteroduplex intermediates, indicating that mismatch repair does not necessarily impede homeologous genetic exchange. Our results illustrate (1) genetic exchange between homeologous sequences in a mammalian genome is enabled by nearby homology, (2) proximity to a DSB impacts the homology requirements for where genetic exchange may begin and end, and (3) mismatch correction and previously documented anti-recombination activity are separable functions of the mismatch repair machinery in mammalian cells.
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Affiliation(s)
- Shen Li
- Department of Biological Sciences, University of South Carolina, Coker Life Sciences Building, 700 Sumter Street, Columbia, South Carolina, 29208, USA
| | - Bryan Wehrenberg
- Department of Biological Sciences, University of South Carolina, Coker Life Sciences Building, 700 Sumter Street, Columbia, South Carolina, 29208, USA
| | - Barbara C Waldman
- Department of Biological Sciences, University of South Carolina, Coker Life Sciences Building, 700 Sumter Street, Columbia, South Carolina, 29208, USA
| | - Alan S Waldman
- Department of Biological Sciences, University of South Carolina, Coker Life Sciences Building, 700 Sumter Street, Columbia, South Carolina, 29208, USA.
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18
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Chakraborty U, Dinh TA, Alani E. Genomic Instability Promoted by Overexpression of Mismatch Repair Factors in Yeast: A Model for Understanding Cancer Progression. Genetics 2018; 209:439-456. [PMID: 29654124 PMCID: PMC5972419 DOI: 10.1534/genetics.118.300923] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Accepted: 04/12/2018] [Indexed: 02/04/2023] Open
Abstract
Mismatch repair (MMR) proteins act in spellchecker roles to excise misincorporation errors that occur during DNA replication. Curiously, large-scale analyses of a variety of cancers showed that increased expression of MMR proteins often correlated with tumor aggressiveness, metastasis, and early recurrence. To better understand these observations, we used The Cancer Genome Atlas and Gene Expression across Normal and Tumor tissue databases to analyze MMR protein expression in cancers. We found that the MMR genes MSH2 and MSH6 are overexpressed more frequently than MSH3, and that MSH2 and MSH6 are often cooverexpressed as a result of copy number amplifications of these genes. These observations encouraged us to test the effects of upregulating MMR protein levels in baker's yeast, where we can sensitively monitor genome instability phenotypes associated with cancer initiation and progression. Msh6 overexpression (two- to fourfold) almost completely disrupted mechanisms that prevent recombination between divergent DNA sequences by interacting with the DNA polymerase processivity clamp PCNA and by sequestering the Sgs1 helicase. Importantly, cooverexpression of Msh2 and Msh6 (∼eightfold) conferred, in a PCNA interaction-dependent manner, several genome instability phenotypes including increased mutation rate, increased sensitivity to the DNA replication inhibitor HU and the DNA-damaging agents MMS and 4-nitroquinoline N-oxide, and elevated loss-of-heterozygosity. Msh2 and Msh6 cooverexpression also altered the cell cycle distribution of exponentially growing cells, resulting in an increased fraction of unbudded cells, consistent with a larger percentage of cells in G1. These novel observations suggested that overexpression of MSH factors affected the integrity of the DNA replication fork, causing genome instability phenotypes that could be important for promoting cancer progression.
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Affiliation(s)
- Ujani Chakraborty
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
| | - Timothy A Dinh
- Curriculum in Genetics and Molecular Biology, Biological and Biomedical Sciences Program, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853-2703
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19
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DNA mismatch repair and its many roles in eukaryotic cells. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2017; 773:174-187. [PMID: 28927527 DOI: 10.1016/j.mrrev.2017.07.001] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 07/01/2017] [Accepted: 07/06/2017] [Indexed: 02/06/2023]
Abstract
DNA mismatch repair (MMR) is an important DNA repair pathway that plays critical roles in DNA replication fidelity, mutation avoidance and genome stability, all of which contribute significantly to the viability of cells and organisms. MMR is widely-used as a diagnostic biomarker for human cancers in the clinic, and as a biomarker of cancer susceptibility in animal model systems. Prokaryotic MMR is well-characterized at the molecular and mechanistic level; however, MMR is considerably more complex in eukaryotic cells than in prokaryotic cells, and in recent years, it has become evident that MMR plays novel roles in eukaryotic cells, several of which are not yet well-defined or understood. Many MMR-deficient human cancer cells lack mutations in known human MMR genes, which strongly suggests that essential eukaryotic MMR components/cofactors remain unidentified and uncharacterized. Furthermore, the mechanism by which the eukaryotic MMR machinery discriminates between the parental (template) and the daughter (nascent) DNA strand is incompletely understood and how cells choose between the EXO1-dependent and the EXO1-independent subpathways of MMR is not known. This review summarizes recent literature on eukaryotic MMR, with emphasis on the diverse cellular roles of eukaryotic MMR proteins, the mechanism of strand discrimination and cross-talk/interactions between and co-regulation of MMR and other DNA repair pathways in eukaryotic cells. The main conclusion of the review is that MMR proteins contribute to genome stability through their ability to recognize and promote an appropriate cellular response to aberrant DNA structures, especially when they arise during DNA replication. Although the molecular mechanism of MMR in the eukaryotic cell is still not completely understood, increased used of single-molecule analyses in the future may yield new insight into these unsolved questions.
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20
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Chakraborty U, Alani E. Understanding how mismatch repair proteins participate in the repair/anti-recombination decision. FEMS Yeast Res 2016; 16:fow071. [PMID: 27573382 PMCID: PMC5976031 DOI: 10.1093/femsyr/fow071] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 06/24/2016] [Accepted: 08/24/2016] [Indexed: 01/06/2023] Open
Abstract
Mismatch repair (MMR) systems correct DNA mismatches that result from DNA polymerase misincorporation errors. Mismatches also appear in heteroduplex DNA intermediates formed during recombination between nearly identical sequences, and can be corrected by MMR or removed through an unwinding mechanism, known as anti-recombination or heteroduplex rejection. We review studies, primarily in baker's yeast, which support how specific factors can regulate the MMR/anti-recombination decision. Based on recent advances, we present models for how DNA structure, relative amounts of key repair proteins, the timely localization of repair proteins to DNA substrates and epigenetic marks can modulate this critical decision.
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Affiliation(s)
- Ujani Chakraborty
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
| | - Eric Alani
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
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21
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Wang Y, Li S, Smith K, Waldman BC, Waldman AS. Intrachromosomal recombination between highly diverged DNA sequences is enabled in human cells deficient in Bloom helicase. DNA Repair (Amst) 2016; 41:73-84. [PMID: 27100209 DOI: 10.1016/j.dnarep.2016.03.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Accepted: 03/21/2016] [Indexed: 11/30/2022]
Abstract
Mutation of Bloom helicase (BLM) causes Bloom syndrome (BS), a rare human genetic disorder associated with genome instability, elevation of sister chromatid exchanges, and predisposition to cancer. Deficiency in BLM homologs in Drosophila and yeast brings about significantly increased rates of recombination between imperfectly matched sequences ("homeologous recombination," or HeR). To assess whether BLM deficiency provokes an increase in HeR in human cells, we transfected an HeR substrate into a BLM-null cell line derived from a BS patient. The substrate contained a thymidine kinase (tk)-neo fusion gene disrupted by the recognition site for endonuclease I-SceI, as well as a functional tk gene to serve as a potential recombination partner for the tk-neo gene. The two tk sequences on the substrate displayed 19% divergence. A double-strand break was introduced by expression of I-SceI and repair events were recovered by selection for G418-resistant clones. Among 181 events recovered, 30 were accomplished via HeR with the balance accomplished by nonhomologous end-joining. The frequency of HeR events in the BS cells was elevated significantly compared to that seen in normal human fibroblasts or in BS cells complemented for BLM expression. We conclude that BLM deficiency enables HeR in human cells.
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Affiliation(s)
- Yibin Wang
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Shen Li
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Krissy Smith
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | | | - Alan S Waldman
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
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22
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A Delicate Balance Between Repair and Replication Factors Regulates Recombination Between Divergent DNA Sequences in Saccharomyces cerevisiae. Genetics 2015; 202:525-40. [PMID: 26680658 DOI: 10.1534/genetics.115.184093] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 12/07/2015] [Indexed: 11/18/2022] Open
Abstract
Single-strand annealing (SSA) is an important homologous recombination mechanism that repairs DNA double strand breaks (DSBs) occurring between closely spaced repeat sequences. During SSA, the DSB is acted upon by exonucleases to reveal complementary sequences that anneal and are then repaired through tail clipping, DNA synthesis, and ligation steps. In baker's yeast, the Msh DNA mismatch recognition complex and the Sgs1 helicase act to suppress SSA between divergent sequences by binding to mismatches present in heteroduplex DNA intermediates and triggering a DNA unwinding mechanism known as heteroduplex rejection. Using baker's yeast as a model, we have identified new factors and regulatory steps in heteroduplex rejection during SSA. First we showed that Top3-Rmi1, a topoisomerase complex that interacts with Sgs1, is required for heteroduplex rejection. Second, we found that the replication processivity clamp proliferating cell nuclear antigen (PCNA) is dispensable for heteroduplex rejection, but is important for repairing mismatches formed during SSA. Third, we showed that modest overexpression of Msh6 results in a significant increase in heteroduplex rejection; this increase is due to a compromise in Msh2-Msh3 function required for the clipping of 3' tails. Thus 3' tail clipping during SSA is a critical regulatory step in the repair vs. rejection decision; rejection is favored before the 3' tails are clipped. Unexpectedly, Msh6 overexpression, through interactions with PCNA, disrupted heteroduplex rejection between divergent sequences in another recombination substrate. These observations illustrate the delicate balance that exists between repair and replication factors to optimize genome stability.
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23
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The role of Drosophila mismatch repair in suppressing recombination between diverged sequences. Sci Rep 2015; 5:17601. [PMID: 26616528 PMCID: PMC4663472 DOI: 10.1038/srep17601] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 11/02/2015] [Indexed: 11/08/2022] Open
Abstract
DNA double-strand breaks (DSBs) must be accurately repaired to maintain genomic integrity. DSBs can be repaired by homologous recombination (HR), which uses an identical sequence as a template to restore the genetic information lost at the break. Suppression of recombination between diverged sequences is essential to the repair of DSBs without aberrant and potentially mutagenic recombination between non-identical sequences, such as Alu repeats in the human genome. The mismatch repair (MMR) machinery has been found to suppress recombination between diverged sequences in murine cells. To test if this phenomenon is conserved in whole organisms, two DSB repair systems were utilized in Drosophila melanogaster. The DR-white and DR-white.mu assays provide a method of measuring DSB repair outcomes between identical and diverged sequences respectively. msh6–/– flies, deficient in MMR, were not capable of suppressing recombination between sequences with 1.4% divergence, and the average gene conversion tract length did not differ between msh6–/+ and msh6–/–flies. These findings suggest that MMR has an early role in suppressing recombination between diverged sequences that is conserved in Drosophila.
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24
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White TB, Morales ME, Deininger PL. Alu elements and DNA double-strand break repair. Mob Genet Elements 2015; 5:81-85. [PMID: 26942043 DOI: 10.1080/2159256x.2015.1093067] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 08/31/2015] [Accepted: 09/04/2015] [Indexed: 12/30/2022] Open
Abstract
Alu elements represent one of the most common sources of homology and homeology in the human genome. Homeologous recombination between Alu elements represents a major form of genetic instability leading to deletions and duplications. Although these types of events have been studied extensively through genomic sequencing to assess the impact of Alu elements on disease mutations and genome evolution, the overall abundance of Alu elements in the genome often makes it difficult to assess the relevance of the Alu elements to specific recombination events. We recently reported a powerful new reporter gene system that allows the assessment of various cis and trans factors on the contribution of Alu elements to various forms of genetic instability. This allowed a quantitative measurement of the influence of mismatches on Alu elements and instability. It also confirmed that homeologous Alu elements are able to stimulate non-homologous end joining events in their vicinity. This appears to be dependent on portions of the mismatch repair pathway. We are now in a position to begin to unravel the complex influences of Alu density, mismatch and location with alterations of DNA repair processes in various tissues and tumors.
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Affiliation(s)
- Travis B White
- Tulane Cancer Center; Tulane University Health Sciences Center ; New Orleans, LA USA
| | - Maria E Morales
- Tulane Cancer Center; Tulane University Health Sciences Center ; New Orleans, LA USA
| | - Prescott L Deininger
- Tulane Cancer Center; Tulane University Health Sciences Center ; New Orleans, LA USA
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25
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Morales ME, White TB, Streva VA, DeFreece CB, Hedges DJ, Deininger PL. The contribution of alu elements to mutagenic DNA double-strand break repair. PLoS Genet 2015; 11:e1005016. [PMID: 25761216 PMCID: PMC4356517 DOI: 10.1371/journal.pgen.1005016] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 01/22/2015] [Indexed: 11/18/2022] Open
Abstract
Alu elements make up the largest family of human mobile elements, numbering 1.1 million copies and comprising 11% of the human genome. As a consequence of evolution and genetic drift, Alu elements of various sequence divergence exist throughout the human genome. Alu/Alu recombination has been shown to cause approximately 0.5% of new human genetic diseases and contribute to extensive genomic structural variation. To begin understanding the molecular mechanisms leading to these rearrangements in mammalian cells, we constructed Alu/Alu recombination reporter cell lines containing Alu elements ranging in sequence divergence from 0%-30% that allow detection of both Alu/Alu recombination and large non-homologous end joining (NHEJ) deletions that range from 1.0 to 1.9 kb in size. Introduction of as little as 0.7% sequence divergence between Alu elements resulted in a significant reduction in recombination, which indicates even small degrees of sequence divergence reduce the efficiency of homology-directed DNA double-strand break (DSB) repair. Further reduction in recombination was observed in a sequence divergence-dependent manner for diverged Alu/Alu recombination constructs with up to 10% sequence divergence. With greater levels of sequence divergence (15%-30%), we observed a significant increase in DSB repair due to a shift from Alu/Alu recombination to variable-length NHEJ which removes sequence between the two Alu elements. This increase in NHEJ deletions depends on the presence of Alu sequence homeology (similar but not identical sequences). Analysis of recombination products revealed that Alu/Alu recombination junctions occur more frequently in the first 100 bp of the Alu element within our reporter assay, just as they do in genomic Alu/Alu recombination events. This is the first extensive study characterizing the influence of Alu element sequence divergence on DNA repair, which will inform predictions regarding the effect of Alu element sequence divergence on both the rate and nature of DNA repair events. DNA double-strand breaks (DSBs) are a highly mutagenic form of DNA damage that can be repaired through one of several pathways with varied degrees of sequence preservation. Faithful repair of DSBs often occurs through gene conversion in which a sister chromatid is used as a repair template. Unfaithful repair of DSBs can occur through non-allelic homologous or homeologous recombination, which leads to chromosomal abnormalities such as deletions, duplications, and translocations and has been shown to cause several human genetic diseases. Substrates for these homologous and homeologous events include Alu elements, which are approximately 300 bp elements that comprise ~11% of the human genome. We use a new reporter assay to show that repair of DSBs results in Alu-mediated deletions that resolve through several distinct repair pathways. Either single-strand annealing (SSA) repair or microhomology-mediated end joining occurs ‘in register’ between two Alu elements when Alu sequence divergence is low. However, with more diverged Alu elements, like those typically found in the human genome, repair of DSBs appears to use the Alu/Alu homeology to direct non-homologous end joining in the general vicinity of the Alu elements. Mutagenic NHEJ repair involving divergent Alu elements may represent a common repair event in primate genomes.
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Affiliation(s)
- Maria E. Morales
- Tulane Cancer Center and Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Travis B. White
- Tulane Cancer Center and Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Vincent A. Streva
- Tulane Cancer Center and Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, Louisiana, United States of America
| | - Cecily B. DeFreece
- Department of Biology, Xavier University of Louisiana, New Orleans, Louisiana, United States of America
| | - Dale J. Hedges
- Division of Human Genetics, Department of Internal Medicine, The Ohio State University, Columbus, Ohio, United States of America
| | - Prescott L. Deininger
- Tulane Cancer Center and Department of Epidemiology, Tulane University Health Sciences Center, New Orleans, Louisiana, United States of America
- * E-mail:
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Abstract
Homologous recombination (HR) and mismatch repair (MMR) are inextricably linked. HR pairs homologous chromosomes before meiosis I and is ultimately responsible for generating genetic diversity during sexual reproduction. HR is initiated in meiosis by numerous programmed DNA double-strand breaks (DSBs; several hundred in mammals). A characteristic feature of HR is the exchange of DNA strands, which results in the formation of heteroduplex DNA. Mismatched nucleotides arise in heteroduplex DNA because the participating parental chromosomes contain nonidentical sequences. These mismatched nucleotides may be processed by MMR, resulting in nonreciprocal exchange of genetic information (gene conversion). MMR and HR also play prominent roles in mitotic cells during genome duplication; MMR rectifies polymerase misincorporation errors, whereas HR contributes to replication fork maintenance, as well as the repair of spontaneous DSBs and genotoxic lesions that affect both DNA strands. MMR suppresses HR when the heteroduplex DNA contains excessive mismatched nucleotides, termed homeologous recombination. The regulation of homeologous recombination by MMR ensures the accuracy of DSB repair and significantly contributes to species barriers during sexual reproduction. This review discusses the history, genetics, biochemistry, biophysics, and the current state of studies on the role of MMR in homologous and homeologous recombination from bacteria to humans.
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Affiliation(s)
- Maria Spies
- Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242
| | - Richard Fishel
- Department of Molecular Virology, Immunology, and Medical Genetics, The Ohio State University Medical Center and Comprehensive Cancer Center, Columbus, Ohio 43210 Human Genetics Institute, The Ohio State University Medical Center, Columbus, Ohio 43210 Physics Department, The Ohio State University, Columbus, Ohio 43210
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Rakshambikai R, Srinivasan N, Nishant KT. Structural insights into Saccharomyces cerevisiae Msh4-Msh5 complex function using homology modeling. PLoS One 2013; 8:e78753. [PMID: 24244354 PMCID: PMC3828297 DOI: 10.1371/journal.pone.0078753] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Accepted: 09/20/2013] [Indexed: 11/18/2022] Open
Abstract
The Msh4–Msh5 protein complex in eukaryotes is involved in stabilizing Holliday junctions and its progenitors to facilitate crossing over during Meiosis I. These functions of the Msh4–Msh5 complex are essential for proper chromosomal segregation during the first meiotic division. The Msh4/5 proteins are homologous to the bacterial mismatch repair protein MutS and other MutS homologs (Msh2, Msh3, Msh6). Saccharomyces cerevisiae msh4/5 point mutants were identified recently that show two fold reduction in crossing over, compared to wild-type without affecting chromosome segregation. Three distinct classes of msh4/5 point mutations could be sorted based on their meiotic phenotypes. These include msh4/5 mutations that have a) crossover and viability defects similar to msh4/5 null mutants; b) intermediate defects in crossing over and viability and c) defects only in crossing over. The absence of a crystal structure for the Msh4–Msh5 complex has hindered an understanding of the structural aspects of Msh4–Msh5 function as well as molecular explanation for the meiotic defects observed in msh4/5 mutations. To address this problem, we generated a structural model of the S. cerevisiae Msh4–Msh5 complex using homology modeling. Further, structural analysis tailored with evolutionary information is used to predict sites with potentially critical roles in Msh4–Msh5 complex formation, DNA binding and to explain asymmetry within the Msh4–Msh5 complex. We also provide a structural rationale for the meiotic defects observed in the msh4/5 point mutations. The mutations are likely to affect stability of the Msh4/5 proteins and/or interactions with DNA. The Msh4–Msh5 model will facilitate the design and interpretation of new mutational data as well as structural studies of this important complex involved in meiotic chromosome segregation.
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Affiliation(s)
| | | | - Koodali Thazath Nishant
- School of Biology, Indian Institute of Science Education and Research, Thiruvananthapuram, India
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Distinct requirements within the Msh3 nucleotide binding pocket for mismatch and double-strand break repair. J Mol Biol 2013; 425:1881-1898. [PMID: 23458407 DOI: 10.1016/j.jmb.2013.02.024] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Revised: 02/21/2013] [Accepted: 02/22/2013] [Indexed: 11/20/2022]
Abstract
In Saccharomyces cerevisiae, repair of insertion/deletion loops is carried out by Msh2-Msh3-mediated mismatch repair (MMR). Msh2-Msh3 is also required for 3' non-homologous tail removal (3' NHTR) in double-strand break repair. In both pathways, Msh2-Msh3 binds double-strand/single-strand junctions and initiates repair in an ATP-dependent manner. However, the kinetics of the two processes appear different; MMR is likely rapid in order to coordinate with the replication fork, whereas 3' NHTR has been shown to be a slower process. To understand the molecular requirements in both repair pathways, we performed an in vivo analysis of well-conserved residues in Msh3 that are hypothesized to be required for MMR and/or 3' NHTR. These residues are predicted to be involved in either communication between the DNA-binding and ATPase domains within the complex or nucleotide binding and/or exchange within Msh2-Msh3. We identified a set of aromatic residues within the FLY motif of the predicted Msh3 nucleotide binding pocket that are essential for Msh2-Msh3-mediated MMR but are largely dispensable for 3' NHTR. In contrast, mutations in other regions gave similar phenotypes in both assays. Based on these results, we suggest that the two pathways have distinct requirements with respect to the position of the bound ATP within Msh3. We propose that the differences are related, at least in part, to the kinetics of each pathway. Proper binding and positioning of ATP is required to induce rapid conformational changes at the replication fork, but is less important when more time is available for repair, as in 3' NHTR.
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George CM, Alani E. Multiple cellular mechanisms prevent chromosomal rearrangements involving repetitive DNA. Crit Rev Biochem Mol Biol 2012; 47:297-313. [PMID: 22494239 PMCID: PMC3337352 DOI: 10.3109/10409238.2012.675644] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Repetitive DNA is present in the eukaryotic genome in the form of segmental duplications, tandem and interspersed repeats, and satellites. Repetitive sequences can be beneficial by serving specific cellular functions (e.g. centromeric and telomeric DNA) and by providing a rapid means for adaptive evolution. However, such elements are also substrates for deleterious chromosomal rearrangements that affect fitness and promote human disease. Recent studies analyzing the role of nuclear organization in DNA repair and factors that suppress non-allelic homologous recombination (NAHR) have provided insights into how genome stability is maintained in eukaryotes. In this review, we outline the types of repetitive sequences seen in eukaryotic genomes and how recombination mechanisms are regulated at the DNA sequence, cell organization, chromatin structure, and cell cycle control levels to prevent chromosomal rearrangements involving these sequences.
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Affiliation(s)
- Carolyn M George
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853-2703, USA
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The DNA damage checkpoint allows recombination between divergent DNA sequences in budding yeast. DNA Repair (Amst) 2011; 10:1086-94. [PMID: 21978436 DOI: 10.1016/j.dnarep.2011.07.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 07/23/2011] [Accepted: 07/25/2011] [Indexed: 11/22/2022]
Abstract
In the early steps of homologous recombination, single-stranded DNA (ssDNA) from a broken chromosome invades homologous sequence located in a sister or homolog donor. In genomes that contain numerous repetitive DNA elements or gene paralogs, recombination can potentially occur between non-allelic/divergent (homeologous) sequences that share sequence identity. Such recombination events can lead to lethal chromosomal deletions or rearrangements. However, homeologous recombination events can be suppressed through rejection mechanisms that involve recognition of DNA mismatches in heteroduplex DNA by mismatch repair factors, followed by active unwinding of the heteroduplex DNA by helicases. Because factors required for heteroduplex rejection are hypothesized to be targets and/or effectors of the DNA damage response (DDR), a cell cycle control mechanism that ensures timely and efficient repair, we tested whether the DDR, and more specifically, the RAD9 gene, had a role in regulating rejection. We performed these studies using a DNA repair assay that measures repair by single-strand annealing (SSA) of a double-strand break (DSB) using homeologous DNA templates. We found that repair of homeologous DNA sequences, but not identical sequences, induced a RAD9-dependent cell cycle delay in the G2 stage of the cell cycle. Repair through a divergent DNA template occurred more frequently in RAD9 compared to rad9Δ strains. However, repair in rad9Δ mutants could be restored to wild-type levels if a G2 delay was induced by nocodazole. These results suggest that cell cycle arrest induced by the Rad9-dependent DDR allows repair between divergent DNA sequences despite the potential for creating deleterious genome rearrangements, and illustrates the importance of additional cellular mechanisms that act to suppress recombination between divergent DNA sequences.
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Multiple factors insulate Msh2-Msh6 mismatch repair activity from defects in Msh2 domain I. J Mol Biol 2011; 411:765-80. [PMID: 21726567 DOI: 10.1016/j.jmb.2011.06.030] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 06/13/2011] [Accepted: 06/14/2011] [Indexed: 01/16/2023]
Abstract
DNA mismatch repair (MMR) is a highly conserved mutation avoidance mechanism that corrects DNA polymerase misincorporation errors. In initial steps in MMR, Msh2-Msh6 binds mispairs and small insertion/deletion loops, and Msh2-Msh3 binds larger insertion/deletion loops. The msh2Δ1 mutation, which deletes the conserved DNA-binding domain I of Msh2, does not dramatically affect Msh2-Msh6-dependent repair. In contrast, msh2Δ1 mutants show strong defects in Msh2-Msh3 functions. Interestingly, several mutations identified in patients with hereditary non-polyposis colorectal cancer map to domain I of Msh2; none have been found in MSH3. To understand the role of Msh2 domain I in MMR, we examined the consequences of combining the msh2Δ1 mutation with mutations in two distinct regions of MSH6 and those that increase cellular mutational load (pol3-01 and rad27). These experiments reveal msh2Δ1-specific phenotypes in Msh2-Msh6 repair, with significant effects on mutation rates. In vitro assays demonstrate that msh2Δ1-Msh6 DNA binding is less specific for DNA mismatches and produces an altered footprint on a mismatch DNA substrate. Together, these results provide evidence that, in vivo, multiple factors insulate MMR from defects in domain I of Msh2 and provide insights into how mutations in Msh2 domain I may cause hereditary non-polyposis colorectal cancer.
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Balasubramanian N, Bai P, Buchek G, Korza G, Weller SK. Physical interaction between the herpes simplex virus type 1 exonuclease, UL12, and the DNA double-strand break-sensing MRN complex. J Virol 2010; 84:12504-14. [PMID: 20943970 PMCID: PMC3004347 DOI: 10.1128/jvi.01506-10] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Accepted: 10/05/2010] [Indexed: 12/16/2022] Open
Abstract
The herpes simplex virus type 1 (HSV-1) alkaline nuclease, encoded by the UL12 gene, plays an important role in HSV-1 replication, as a UL12 null mutant displays a severe growth defect. The HSV-1 alkaline exonuclease UL12 interacts with the viral single-stranded DNA binding protein ICP8 and promotes strand exchange in vitro in conjunction with ICP8. We proposed that UL12 and ICP8 form a two-subunit recombinase reminiscent of the phage lambda Red α/β recombination system and that the viral and cellular recombinases contribute to viral genome replication through a homologous recombination-dependent DNA replication mechanism. To test this hypothesis, we identified cellular interaction partners of UL12 by using coimmunoprecipitation. We report for the first time a specific interaction between UL12 and components of the cellular MRN complex, an important factor in the ATM-mediated homologous recombination repair (HRR) pathway. This interaction is detected early during infection and does not require viral DNA or other viral or cellular proteins. The region of UL12 responsible for the interaction has been mapped to the first 125 residues, and coimmunoprecipitation can be abolished by deletion of residues 100 to 126. These observations support the hypothesis that cellular and viral recombination factors work together to promote efficient HSV-1 growth.
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Affiliation(s)
- Nandakumar Balasubramanian
- Department of Molecular, Microbial and Structural Biology and The Molecular Biology and Biochemistry Graduate Program, The University of Connecticut Health Center, Farmington, Connecticut 06030
| | - Ping Bai
- Department of Molecular, Microbial and Structural Biology and The Molecular Biology and Biochemistry Graduate Program, The University of Connecticut Health Center, Farmington, Connecticut 06030
| | - Gregory Buchek
- Department of Molecular, Microbial and Structural Biology and The Molecular Biology and Biochemistry Graduate Program, The University of Connecticut Health Center, Farmington, Connecticut 06030
| | - George Korza
- Department of Molecular, Microbial and Structural Biology and The Molecular Biology and Biochemistry Graduate Program, The University of Connecticut Health Center, Farmington, Connecticut 06030
| | - Sandra K. Weller
- Department of Molecular, Microbial and Structural Biology and The Molecular Biology and Biochemistry Graduate Program, The University of Connecticut Health Center, Farmington, Connecticut 06030
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Amin AD, Chaix ABH, Mason RP, Badge RM, Borts RH. The roles of the Saccharomyces cerevisiae RecQ helicase SGS1 in meiotic genome surveillance. PLoS One 2010; 5:e15380. [PMID: 21085703 PMCID: PMC2976770 DOI: 10.1371/journal.pone.0015380] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2010] [Accepted: 09/01/2010] [Indexed: 11/24/2022] Open
Abstract
Background The Saccharomyces cerevisiae RecQ helicase Sgs1 is essential for mitotic and meiotic genome stability. The stage at which Sgs1 acts during meiosis is subject to debate. Cytological experiments showed that a deletion of SGS1 leads to an increase in synapsis initiation complexes and axial associations leading to the proposal that it has an early role in unwinding surplus strand invasion events. Physical studies of recombination intermediates implicate it in the dissolution of double Holliday junctions between sister chromatids. Methodology/Principal Findings In this work, we observed an increase in meiotic recombination between diverged sequences (homeologous recombination) and an increase in unequal sister chromatid events when SGS1 is deleted. The first of these observations is most consistent with an early role of Sgs1 in unwinding inappropriate strand invasion events while the second is consistent with unwinding or dissolution of recombination intermediates in an Mlh1- and Top3-dependent manner. We also provide data that suggest that Sgs1 is involved in the rejection of ‘second strand capture’ when sequence divergence is present. Finally, we have identified a novel class of tetrads where non-sister spores (pairs of spores where each contains a centromere marker from a different parent) are inviable. We propose a model for this unusual pattern of viability based on the inability of sgs1 mutants to untangle intertwined chromosomes. Our data suggest that this role of Sgs1 is not dependent on its interaction with Top3. We propose that in the absence of SGS1 chromosomes may sometimes remain entangled at the end of pre-meiotic replication. This, combined with reciprocal crossing over, could lead to physical destruction of the recombined and entangled chromosomes. We hypothesise that Sgs1, acting in concert with the topoisomerase Top2, resolves these structures. Conclusions This work provides evidence that Sgs1 interacts with various partner proteins to maintain genome stability throughout meiosis.
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Affiliation(s)
- Amit Dipak Amin
- Department of Genetics, University of Leicester, Leicester, United Kingdom
| | | | - Robert P. Mason
- Department of Genetics, University of Leicester, Leicester, United Kingdom
| | - Richard M. Badge
- Department of Genetics, University of Leicester, Leicester, United Kingdom
| | - Rhona H. Borts
- Department of Genetics, University of Leicester, Leicester, United Kingdom
- * E-mail:
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A two-pathway analysis of meiotic crossing over and gene conversion in Saccharomyces cerevisiae. Genetics 2010; 186:515-36. [PMID: 20679514 DOI: 10.1534/genetics.110.121194] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Several apparently paradoxical observations regarding meiotic crossing over and gene conversion are readily resolved in a framework that recognizes the existence of two recombination pathways that differ in mismatch repair, structures of intermediates, crossover interference, and the generation of noncrossovers. One manifestation of these differences is that simultaneous gene conversion on both sides of a recombination-initiating DNA double-strand break ("two-sidedness") characterizes only one of the two pathways and is promoted by mismatch repair. Data from previous work are analyzed quantitatively within this framework, and a molecular model for meiotic double-strand break repair based on the concept of sliding D-loops is offered as an efficient scheme for visualizing the salient results from studies of crossing over and gene conversion, the molecular structures of recombination intermediates, and the biochemical competencies of the proteins involved.
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Toh GWL, Sugawara N, Dong J, Toth R, Lee SE, Haber JE, Rouse J. Mec1/Tel1-dependent phosphorylation of Slx4 stimulates Rad1-Rad10-dependent cleavage of non-homologous DNA tails. DNA Repair (Amst) 2010; 9:718-26. [PMID: 20382573 PMCID: PMC4352089 DOI: 10.1016/j.dnarep.2010.02.013] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 02/09/2010] [Accepted: 02/24/2010] [Indexed: 01/22/2023]
Abstract
Budding yeast Slx4 interacts with the Rad1-Rad10 endonuclease that is involved in nucleotide excision repair (NER), homologous recombination (HR) and single-strand annealing (SSA). We previously showed that Slx4 is dispensable for NER but is essential for SSA. Slx4 is phosphorylated by the Mec1 and Tel1 kinases after DNA damage on at least six Ser/Thr residues, and mutation of all six residues to Ala reduces the efficiency of SSA. In this study, we further investigated the role of Slx4 phosphorylation in SSA, specifically in regulating cleavage of 3' non-homologous (NH) DNA tails by Rad1-Rad10 during SSA and HR. Slx4 became phosphorylated after induction of a single double-strand break (DSB) during SSA and dephosphorylation coincided approximately with completion of repair. Slx4 is recruited to 3' NH tails during DSB repair, but this does not require phosphorylation of Slx4. However, we identified a specific damage-dependent Mec1/Tel1 site of Slx4 phosphorylation, Thr 113, that is required for efficient cleavage of NH tails by Rad1-Rad10. Consistent with these data, deletion of both Mec1 and Tel1 severely reduces the efficiency of NH DNA tail cleavage during HR. These data show that phosphorylation of Slx4 by Mec1 and Tel1 plays an important role in facilitating NH DNA tail cleavage during HR.
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Affiliation(s)
- Geraldine W.-L. Toh
- MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Neal Sugawara
- Rosentiel Basic Medical Sciences Research Centre, Waltham, Massachusetts
| | - Junchao Dong
- Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, TX 78245, USA
| | - Rachel Toth
- MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Sang Eun Lee
- Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, TX 78245, USA
| | - James E. Haber
- Rosentiel Basic Medical Sciences Research Centre, Waltham, Massachusetts
| | - John Rouse
- MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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36
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Song L, Yuan F, Zhang Y. Does a helicase activity help mismatch repair in eukaryotes? IUBMB Life 2010; 62:548-53. [DOI: 10.1002/iub.349] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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An essential DNA strand-exchange activity is conserved in the divergent N-termini of BLM orthologs. EMBO J 2010; 29:1713-25. [PMID: 20389284 DOI: 10.1038/emboj.2010.61] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Accepted: 03/15/2010] [Indexed: 11/08/2022] Open
Abstract
The gene mutated in Bloom's syndrome, BLM, encodes a member of the RecQ family of DNA helicases that is needed to suppress genome instability and cancer predisposition. BLM is highly conserved and all BLM orthologs, including budding yeast Sgs1, have a large N-terminus that binds Top3-Rmi1 but has no known catalytic activity. In this study, we describe a sub-domain of the Sgs1 N-terminus that shows in vitro single-strand DNA (ssDNA) binding, ssDNA annealing and strand-exchange (SE) activities. These activities are conserved in the human and Drosophila orthologs. SE between duplex DNA and homologous ssDNA requires no cofactors and is inhibited by a single mismatched base pair. The SE domain of Sgs1 is required in vivo for the suppression of hyper-recombination, suppression of synthetic lethality and heteroduplex rejection. The top3Delta slow-growth phenotype is also SE dependent. Surprisingly, the highly divergent human SE domain functions in yeast. This work identifies SE as a new molecular function of BLM/Sgs1, and we propose that at least one role of SE is to mediate the strand-passage events catalysed by Top3-Rmi1.
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Mechanisms of recombination between diverged sequences in wild-type and BLM-deficient mouse and human cells. Mol Cell Biol 2010; 30:1887-97. [PMID: 20154148 DOI: 10.1128/mcb.01553-09] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged ("homeologous") sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally < or =100 bp, even in Msh2(-)(/)(-) cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.
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Tay YD, Sidebotham JM, Wu L. Mph1 requires mismatch repair-independent and -dependent functions of MutSalpha to regulate crossover formation during homologous recombination repair. Nucleic Acids Res 2010; 38:1889-901. [PMID: 20047969 PMCID: PMC2847250 DOI: 10.1093/nar/gkp1199] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In budding yeast the DNA helicase Mph1 prevents genome rearrangements during ectopic homologous recombination (HR) by suppressing the formation of crossovers (COs). Here we show that during ectopic HR repair, the anti-CO function of Mph1 is intricately associated with the mismatch repair (MMR) factor, MutSα. In particular, during HR repair using a completely homologous substrate, we reveal an MMR-independent function of MutSα in generating COs that is specifically antagonized by Mph1, but not Sgs1. In contrast, both Mph1 and MutSα are required to efficiently suppress COs in the presence of a homeologous substrate. Mph1 acts redundantly with Sgs1 in this respect since mph1Δ sgs1Δ double mutant cells pheno-copy MutSα mutants and completely fail to discriminate homologous and homeologous sequences during HR repair. However, this defect of mph1Δ sgs1Δ cells is not due to an inability to carry out MMR but rather is accompanied by elevated levels of gene conversion (GC) and bi-directional GC tracts specifically in non-crossover products. Models describing how Mph1, MutSα and Sgs1 act in concert to suppress genome rearrangements during ectopic HR repair are discussed.
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Affiliation(s)
- Ye Dee Tay
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Headington Oxford, OX3 9DS, UK
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Manthey GM, Naik N, Bailis AM. Msh2 blocks an alternative mechanism for non-homologous tail removal during single-strand annealing in Saccharomyces cerevisiae. PLoS One 2009; 4:e7488. [PMID: 19834615 PMCID: PMC2759526 DOI: 10.1371/journal.pone.0007488] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 09/25/2009] [Indexed: 11/19/2022] Open
Abstract
Chromosomal translocations are frequently observed in cells exposed to agents that cause DNA double-strand breaks (DSBs), such as ionizing radiation and chemotherapeutic drugs, and are often associated with tumors in mammals. Recently, translocation formation in the budding yeast, Saccharomyces cerevisiae, has been found to occur at high frequencies following the creation of multiple DSBs adjacent to repetitive sequences on non-homologous chromosomes. The genetic control of translocation formation and the chromosome complements of the clones that contain translocations suggest that translocation formation occurs by single-strand annealing (SSA). Among the factors important for translocation formation by SSA is the central mismatch repair (MMR) and homologous recombination (HR) factor, Msh2. Here we describe the effects of several msh2 missense mutations on translocation formation that suggest that Msh2 has separable functions in stabilizing annealed single strands, and removing non-homologous sequences from their ends. Additionally, interactions between the msh2 alleles and a null allele of RAD1, which encodes a subunit of a nuclease critical for the removal of non-homologous tails suggest that Msh2 blocks an alternative mechanism for removing these sequences. These results suggest that Msh2 plays multiple roles in the formation of chromosomal translocations following acute levels of DNA damage.
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Affiliation(s)
- Glenn M. Manthey
- Division of Molecular Biology, Beckman Research Institute, City of Hope National Medical Center, Duarte, California, United States of America
| | - Nilan Naik
- Scripps College Post-Baccalaureate Premedical Program, Claremont, California, United States of America
| | - Adam M. Bailis
- Division of Molecular Biology, Beckman Research Institute, City of Hope National Medical Center, Duarte, California, United States of America
- * E-mail:
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Kaniak A, Dzierzbicki P, Rogowska AT, Malc E, Fikus M, Ciesla Z. Msh1p counteracts oxidative lesion-induced instability of mtDNA and stimulates mitochondrial recombination in Saccharomyces cerevisiae. DNA Repair (Amst) 2009; 8:318-29. [DOI: 10.1016/j.dnarep.2008.11.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Revised: 11/02/2008] [Accepted: 11/05/2008] [Indexed: 01/01/2023]
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Yodh JG, Stevens BC, Kanagaraj R, Janscak P, Ha T. BLM helicase measures DNA unwound before switching strands and hRPA promotes unwinding reinitiation. EMBO J 2009; 28:405-16. [PMID: 19165145 PMCID: PMC2646154 DOI: 10.1038/emboj.2008.298] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2008] [Accepted: 12/17/2008] [Indexed: 01/27/2023] Open
Abstract
Bloom syndrome (BS) is a rare genetic disorder characterized by genomic instability and a high predisposition to cancer. The gene defective in BS, BLM, encodes a member of the RecQ family of 3'-5' DNA helicases, and is proposed to function in recombinational repair during DNA replication. Here, we have utilized single-molecule fluorescence resonance energy transfer microscopy to examine the behaviour of BLM on forked DNA substrates. Strikingly, BLM unwound individual DNA molecules in a repetitive manner, unwinding a short length of duplex DNA followed by rapid reannealing and reinitiation of unwinding in several successions. Our results show that a monomeric BLM can 'measure' how many base pairs it has unwound, and once it has unwound a critical length, it reverses the unwinding reaction through strand switching and translocating on the opposing strand. Repetitive unwinding persisted even in the presence of hRPA, and interaction between wild-type BLM and hRPA was necessary for unwinding reinitiation on hRPA-coated DNA. The reported activities may facilitate BLM processing of stalled replication forks and illegitimately formed recombination intermediates.
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Affiliation(s)
- Jaya G Yodh
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Benjamin C Stevens
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | | | - Pavel Janscak
- Institute of Molecular Cancer Research, University of Zurich, Zurich, Switzerland
- Institute of Molecular Genetics AS CR, Prague, Czech Republic
| | - Taekjip Ha
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL, USA
- Howard Hughes Medical Institute, Urbana, IL, USA
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SRS2 and SGS1 prevent chromosomal breaks and stabilize triplet repeats by restraining recombination. Nat Struct Mol Biol 2009; 16:159-67. [PMID: 19136956 DOI: 10.1038/nsmb.1544] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Accepted: 12/04/2008] [Indexed: 01/30/2023]
Abstract
Several molecular mechanisms have been proposed to explain trinucleotide repeat expansions. Here we show that in yeast srs2Delta cells, CTG repeats undergo both expansions and contractions, and they show increased chromosomal fragility. Deletion of RAD52 or RAD51 suppresses these phenotypes, suggesting that recombination triggers trinucleotide repeat instability in srs2Delta cells. In sgs1Delta cells, CTG repeats undergo contractions and increased fragility by a mechanism partially dependent on RAD52 and RAD51. Analysis of replication intermediates revealed abundant joint molecules at the CTG repeats during S phase. These molecules migrate similarly to reversed replication forks, and their presence is dependent on SRS2 and SGS1 but not RAD51. Our results suggest that Srs2 promotes fork reversal in repetitive sequences, preventing repeat instability and fragility. In the absence of Srs2 or Sgs1, DNA damage accumulates and is processed by homologous recombination, triggering repeat rearrangements.
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Abstract
Mammalian cells frequently depend on homologous recombination (HR) to repair DNA damage accurately and to help rescue stalled or collapsed replication forks. The essence of HR is an exchange of nucleotides between identical or nearly identical sequences. Although HR fulfills important biological roles, recombination between inappropriate sequence partners can lead to translocations or other deleterious rearrangements and such events must be avoided. For example, the recombination machinery must follow stringent rules to preclude recombination between the many repetitive elements in a mammalian genome that share significant but imperfect homology. This paper takes a conceptual approach in addressing the homology requirements for recombination in mammalian genomes as well as the general strategy used by cells to reject recombination between similar but imperfectly matched sequences. A mechanism of heteroduplex rejection that involves the unwinding of recombination intermediates that may form between mismatched sequences is discussed.
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Affiliation(s)
- Alan S Waldman
- Department of Biological Sciences, University of South Carolina, Biological Sciences, 700 Sumter Street, Columbia, SC 29208, USA.
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Mutants defective in Rad1-Rad10-Slx4 exhibit a unique pattern of viability during mating-type switching in Saccharomyces cerevisiae. Genetics 2008; 179:1807-21. [PMID: 18579504 DOI: 10.1534/genetics.108.090654] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Efficient repair of DNA double-strand breaks (DSBs) requires the coordination of checkpoint signaling and enzymatic repair functions. To study these processes during gene conversion at a single chromosomal break, we monitored mating-type switching in Saccharomyces cerevisiae strains defective in the Rad1-Rad10-Slx4 complex. Rad1-Rad10 is a structure-specific endonuclease that removes 3' nonhomologous single-stranded ends that are generated during many recombination events. Slx4 is a known target of the DNA damage response that forms a complex with Rad1-Rad10 and is critical for 3'-end processing during repair of DSBs by single-strand annealing. We found that mutants lacking an intact Rad1-Rad10-Slx4 complex displayed RAD9- and MAD2-dependent cell cycle delays and decreased viability during mating-type switching. In particular, these mutants exhibited a unique pattern of dead and switched daughter cells arising from the same DSB-containing cell. Furthermore, we observed that mutations in post-replicative lesion bypass factors (mms2Delta, mph1Delta) resulted in decreased viability during mating-type switching and conferred shorter cell cycle delays in rad1Delta mutants. We conclude that Rad1-Rad10-Slx4 promotes efficient repair during gene conversion events involving a single 3' nonhomologous tail and propose that the rad1Delta and slx4Delta mutant phenotypes result from inefficient repair of a lesion at the MAT locus that is bypassed by replication-mediated repair.
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Abstract
DNA mismatch repair (MMR) is a highly conserved biological pathway that plays a key role in maintaining genomic stability. The specificity of MMR is primarily for base-base mismatches and insertion/deletion mispairs generated during DNA replication and recombination. MMR also suppresses homeologous recombination and was recently shown to play a role in DNA damage signaling in eukaryotic cells. Escherichia coli MutS and MutL and their eukaryotic homologs, MutSalpha and MutLalpha, respectively, are key players in MMR-associated genome maintenance. Many other protein components that participate in various DNA metabolic pathways, such as PCNA and RPA, are also essential for MMR. Defects in MMR are associated with genome-wide instability, predisposition to certain types of cancer including hereditary non-polyposis colorectal cancer, resistance to certain chemotherapeutic agents, and abnormalities in meiosis and sterility in mammalian systems.
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Maloisel L, Fabre F, Gangloff S. DNA polymerase delta is preferentially recruited during homologous recombination to promote heteroduplex DNA extension. Mol Cell Biol 2008; 28:1373-82. [PMID: 18086882 PMCID: PMC2258756 DOI: 10.1128/mcb.01651-07] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Revised: 10/26/2007] [Accepted: 12/05/2007] [Indexed: 01/30/2023] Open
Abstract
DNA polymerases play a central role during homologous recombination (HR), but the identity of the enzyme(s) implicated remains elusive. The pol3-ct allele of the gene encoding the catalytic subunit of DNA polymerase delta (Poldelta) has highlighted a role for this polymerase in meiotic HR. We now address the ubiquitous role of Poldelta during HR in somatic cells. We find that pol3-ct affects gene conversion tract length during mitotic recombination whether the event is initiated by single-strand gaps following UV irradiation or by site-specific double-strand breaks. We show that the pol3-ct effects on gene conversion are completely independent of mismatch repair, indicating that shorter gene conversion tracts in pol3-ct correspond to shorter extensions of primed DNA synthesis. Interestingly, we find that shorter repair tracts do not favor synthesis-dependent strand annealing at the expense of double-strand-break repair. Finally, we show that the DNA polymerases that have been previously suspected to mediate HR repair synthesis (Polepsilon and Poleta) do not affect gene conversion during induced HR, including in the pol3-ct background. Our results argue strongly for the preferential recruitment of Poldelta during HR.
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Sharma S, Brosh RM. Unique and important consequences of RECQ1 deficiency in mammalian cells. Cell Cycle 2008; 7:989-1000. [PMID: 18414032 DOI: 10.4161/cc.7.8.5707] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Five members of the RecQ subfamily of DEx-H-containing DNA helicases have been identified in both human and mouse, and mutations in BLM, WRN, and RECQ4 are associated with human diseases of premature aging, cancer, and chromosomal instability. Although a genetic disease has not been linked to RECQ1 mutations, RECQ1 helicase is the most highly expressed of the human RecQ helicases, suggesting an important role in cellular DNA metabolism. Recent advances have elucidated a unique role of RECQ1 to suppress genomic instability. Embryonic fibroblasts from RECQ1-deficient mice displayed aneuploidy, chromosomal instability, and increased load of DNA damage.(1) Acute depletion of human RECQ1 renders cells sensitive to DNA damage and results in spontaneous gamma-H2AX foci and elevated sister chromatid exchanges, indicating aberrant repair of DNA breaks.(2) Consistent with a role in DNA repair, RECQ1 relocalizes to irradiation-induced nuclear foci and associates with chromatin.(2) RECQ1 catalytic activities(3) and interactions with DNA repair proteins(2,4,5) are likely to be important for its molecular functions in genome homeostasis. Collectively, these studies provide the first evidence for an important role of RECQ1 to confer chromosomal stability that is unique from that of other RecQ helicases and suggest its potential involvement in tumorigenesis.
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Affiliation(s)
- Sudha Sharma
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland, USA
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Nag DK, Cavallo SJ. Effects of mutations in SGS1 and in genes functionally related to SGS1 on inverted repeat-stimulated spontaneous unequal sister-chromatid exchange in yeast. BMC Mol Biol 2007; 8:120. [PMID: 18166135 PMCID: PMC2254439 DOI: 10.1186/1471-2199-8-120] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Accepted: 12/31/2007] [Indexed: 11/11/2022] Open
Abstract
Background The presence of inverted repeats (IRs) in DNA poses an obstacle to the normal progression of the DNA replication machinery, because these sequences can form secondary structures ahead of the replication fork. A failure to process and to restart the stalled replication machinery can lead to the loss of genome integrity. Consistently, IRs have been found to be associated with a high level of genome rearrangements, including deletions, translocations, inversions, and a high rate of sister-chromatid exchange (SCE). The RecQ helicase Sgs1, in Saccharomyces cerevisiae, is believed to act on stalled replication forks. To determine the role of Sgs1 when the replication machinery stalls at the secondary structure, we measured the rates of IR-associated and non-IR-associated spontaneous unequal SCE events in the sgs1 mutant, and in strains bearing mutations in genes that are functionally related to SGS1. Results The rate of SCE in sgs1 cells for both IR and non-IR-containing substrates was higher than the rate in the wild-type background. The srs2 and mus81 mutations had modest effects, compared to sgs1. The exo1 mutation increased SCE rates for both substrates. The sgs1 exo1 double mutant exhibited synergistic effects on spontaneous SCE. The IR-associated SCE events in sgs1 cells were partially MSH2-dependent. Conclusions These results suggest that Sgs1 suppresses spontaneous unequal SCE, and SGS1 and EXO1 regulate spontaneous SCE by independent mechanisms. The mismatch repair proteins, in contradistinction to their roles in mutation avoidance, promote secondary structure-associated genetic instability.
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Affiliation(s)
- Dilip K Nag
- Division of Molecular Medicine, Wadsworth Center, Center for Medical Sciences, 150 New Scotland Avenue, Albany, NY 12208, USA.
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Human RECQ1 is a DNA damage responsive protein required for genotoxic stress resistance and suppression of sister chromatid exchanges. PLoS One 2007; 2:e1297. [PMID: 18074021 PMCID: PMC2111050 DOI: 10.1371/journal.pone.0001297] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2007] [Accepted: 11/14/2007] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND DNA helicases are ubiquitous enzymes that unwind DNA in an ATP-dependent and directionally specific manner. Unwinding of double-stranded DNA is essential for the processes of DNA repair, recombination, transcription, and DNA replication. Five human DNA helicases sharing sequence similarity with the E. coli RecQ helicase have been identified. Three of the human RecQ helicases are implicated in hereditary diseases (Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome) which display clinical symptoms of premature aging and cancer. RECQ1 helicase is the most highly expressed of the human RecQ helicases; however, a genetic disease has yet not been linked to mutations in the RECQ1 gene, and the biological functions of human RECQ1 in cellular DNA metabolism are not known. METHODOLOGY/PRINCIPAL FINDINGS In this study, we report that RECQ1 becomes phosphorylated upon DNA damage and forms irradiation-induced nuclear foci that associate with chromatin in human cells. Depletion of RECQ1 renders human cells sensitive to DNA damage induced by ionizing radiation or the topoisomerase inhibitor camptothecin, and results in spontaneous gamma-H2AX foci and elevated sister chromatid exchanges, indicating aberrant repair of DNA breaks. Consistent with a role in homologous recombinational repair, endogenous RECQ1 is associated with the strand exchange protein Rad51 and the two proteins directly interact with high affinity. CONCLUSION/SIGNIFICANCE Collectively, these results provide the first evidence for a role of human RECQ1 in the response to DNA damage and chromosomal stability maintenance and point to the vital importance of RECQ1 in genome homeostasis.
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