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Venkadakrishnan J, Lahane G, Dhar A, Xiao W, Bhat KM, Pandita TK, Bhat A. Implications of Translesion DNA Synthesis Polymerases on Genomic Stability and Human Health. Mol Cell Biol 2023; 43:401-425. [PMID: 37439479 PMCID: PMC10448981 DOI: 10.1080/10985549.2023.2224199] [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: 01/31/2023] [Revised: 05/03/2023] [Accepted: 06/01/2023] [Indexed: 07/14/2023] Open
Abstract
Replication fork arrest-induced DNA double strand breaks (DSBs) caused by lesions are effectively suppressed in cells due to the presence of a specialized mechanism, commonly referred to as DNA damage tolerance (DDT). In eukaryotic cells, DDT is facilitated through translesion DNA synthesis (TLS) carried out by a set of DNA polymerases known as TLS polymerases. Another parallel mechanism, referred to as homology-directed DDT, is error-free and involves either template switching or fork reversal. The significance of the DDT pathway is well established. Several diseases have been attributed to defects in the TLS pathway, caused either by mutations in the TLS polymerase genes or dysregulation. In the event of a replication fork encountering a DNA lesion, cells switch from high-fidelity replicative polymerases to low-fidelity TLS polymerases, which are associated with genomic instability linked with several human diseases including, cancer. The role of TLS polymerases in chemoresistance has been recognized in recent years. In addition to their roles in the DDT pathway, understanding noncanonical functions of TLS polymerases is also a key to unraveling their importance in maintaining genomic stability. Here we summarize the current understanding of TLS pathway in DDT and its implication for human health.
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Affiliation(s)
| | - Ganesh Lahane
- Department of Pharmacy, Birla Institute of Technology and Sciences Pilani, Hyderabad Campus, Hyderabad, India
| | - Arti Dhar
- Department of Pharmacy, Birla Institute of Technology and Sciences Pilani, Hyderabad Campus, Hyderabad, India
| | - Wei Xiao
- Department of Biochemistry, Microbiology and Immunology, University of Saskatchewan, Saskatoon, Canada
| | - Krishna Moorthi Bhat
- Department of Molecular Medicine, University of South Florida, Tampa, Florida, USA
| | - Tej K. Pandita
- Center for Genomics and Precision Medicine, Texas A&M College of Medicine, Houston, Texas, USA
| | - Audesh Bhat
- Center for Molecular Biology, Central University of Jammu, UT Jammu and Kashmir, India
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Firlej M, Weir JR. Unwinding during stressful times: Mechanisms of helicases in meiotic recombination. Curr Top Dev Biol 2022; 151:191-215. [PMID: 36681470 DOI: 10.1016/bs.ctdb.2022.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Successful meiosis I requires that homologous chromosomes be correctly linked before they are segregated. In most organisms this physical linkage is achieved through the generation of crossovers between the homologs. Meiotic recombination co-opts and modifies the canonical homologous recombination pathway to successfully generate crossovers One of the central components of this pathway are a number of conserved DNA helicases. Helicases couple nucleic acid binding to nucleotide hydrolysis and use this activity to modify DNA or protein-DNA substrates. During meiosis I it is necessary for the cell to modulate the canonical DNA repair pathways in order to facilitate the generation of interhomolog crossovers. Many of these meiotic modulations take place in pathways involving DNA helicases, or with a meiosis specific helicase. This short review explores what is currently understood about these helicases, their interaction partners, and the role of regulatory modifications during meiosis I. We focus in particular on the molecular structure and mechanisms of these helicases.
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Affiliation(s)
- Magdalena Firlej
- Structural Biochemistry of Meiosis Group, Friedrich Miescher Laboratory of the Max Planck Society, Tuebingen, Germany
| | - John R Weir
- Structural Biochemistry of Meiosis Group, Friedrich Miescher Laboratory of the Max Planck Society, Tuebingen, Germany.
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Ler AAL, Carty MP. DNA Damage Tolerance Pathways in Human Cells: A Potential Therapeutic Target. Front Oncol 2022; 11:822500. [PMID: 35198436 PMCID: PMC8859465 DOI: 10.3389/fonc.2021.822500] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 12/30/2021] [Indexed: 12/26/2022] Open
Abstract
DNA lesions arising from both exogenous and endogenous sources occur frequently in DNA. During DNA replication, the presence of unrepaired DNA damage in the template can arrest replication fork progression, leading to fork collapse, double-strand break formation, and to genome instability. To facilitate completion of replication and prevent the generation of strand breaks, DNA damage tolerance (DDT) pathways play a key role in allowing replication to proceed in the presence of lesions in the template. The two main DDT pathways are translesion synthesis (TLS), which involves the recruitment of specialized TLS polymerases to the site of replication arrest to bypass lesions, and homology-directed damage tolerance, which includes the template switching and fork reversal pathways. With some exceptions, lesion bypass by TLS polymerases is a source of mutagenesis, potentially contributing to the development of cancer. The capacity of TLS polymerases to bypass replication-blocking lesions induced by anti-cancer drugs such as cisplatin can also contribute to tumor chemoresistance. On the other hand, during homology-directed DDT the nascent sister strand is transiently utilised as a template for replication, allowing for error-free lesion bypass. Given the role of DNA damage tolerance pathways in replication, mutagenesis and chemoresistance, a more complete understanding of these pathways can provide avenues for therapeutic exploitation. A number of small molecule inhibitors of TLS polymerase activity have been identified that show synergy with conventional chemotherapeutic agents in killing cancer cells. In this review, we will summarize the major DDT pathways, explore the relationship between damage tolerance and carcinogenesis, and discuss the potential of targeting TLS polymerases as a therapeutic approach.
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Affiliation(s)
- Ashlynn Ai Li Ler
- Biochemistry, School of Biological and Chemical Sciences, The National University of Ireland (NUI) Galway, Galway, Ireland
| | - Michael P. Carty
- Biochemistry, School of Biological and Chemical Sciences, The National University of Ireland (NUI) Galway, Galway, Ireland
- DNA Damage Response Laboratory, Centre for Chromosome Biology, NUI Galway, Galway, Ireland
- *Correspondence: Michael P. Carty,
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Veerabhadrappa B, Subramanian S, S J S, Dyavaiah M. Evaluating the genetic basiss of anti-cancer property of Taxol in Saccharomyces cerevisiae model. FEMS Microbiol Lett 2021; 368:6307513. [PMID: 34156070 DOI: 10.1093/femsle/fnab077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 06/18/2021] [Indexed: 01/24/2023] Open
Abstract
Taxol has been regarded as one of the most successful anti-cancer drugs identified from natural sources to date. Although Taxol is known to sensitize cells by stabilizing microtubules, its ability to cause DNA damage in peripheral blood lymphocytes and to induce oxidative stress and apoptosis indicates that Taxol may have other modes of cytotoxic action. This study focuses on identifying the additional targets of Taxol that may contribute to its multifaceted cell killing property, using Saccharomyces cerevisiae. We show that yeast oxidative stress response mutants (sod1Δ, tsa1Δ and cta1Δ) and DNA damage response mutants (mre11∆, sgs1∆ and sub1∆) are highly sensitive to Taxol. Our results also show that Taxol increases the level of reactive oxygen species (ROS) in yeast oxidative stress response mutant strains. Further, 4',6-Diamidino-2'-phenylindole (DAPI) and acridine orange/ethidium bromide (AO/EB) staining show that Taxol induces apoptotic features such as nuclear fragmentation and chromatin condensation in DNA repair mutants. On the whole, our results suggest that Taxol's cytotoxic property is attributed to its multifaceted mechanism of action. Yeast S. cerevisiae anti-oxidant and DNA repair gene mutants are sensitive to Taxol compared to wild-type, suggesting yeast model can be used to identify the genetic targets of anti-cancer drugs.
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Affiliation(s)
- Bhavana Veerabhadrappa
- Department of Biochemistry and Molecular Biology Pondicherry University Pondicherry - 605014, India
| | - Subasri Subramanian
- Department of Biochemistry and Molecular Biology Pondicherry University Pondicherry - 605014, India
| | - Sudharshan S J
- Department of Biochemistry and Molecular Biology Pondicherry University Pondicherry - 605014, India
| | - Madhu Dyavaiah
- Department of Biochemistry and Molecular Biology Pondicherry University Pondicherry - 605014, India
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Álvarez V, Frattini C, Sacristán MP, Gallego-Sánchez A, Bermejo R, Bueno A. PCNA Deubiquitylases Control DNA Damage Bypass at Replication Forks. Cell Rep 2020; 29:1323-1335.e5. [PMID: 31665643 DOI: 10.1016/j.celrep.2019.09.054] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 08/01/2019] [Accepted: 09/17/2019] [Indexed: 01/06/2023] Open
Abstract
DNA damage tolerance plays a key role in protecting cell viability through translesion synthesis and template switching-mediated bypass of genotoxic polymerase-blocking base lesions. Both tolerance pathways critically rely on ubiquitylation of the proliferating-cell nuclear antigen (PCNA) on lysine 164 and have been proposed to operate uncoupled from replication. We report that Ubp10 and Ubp12 ubiquitin proteases differentially cooperate in PCNA deubiquitylation, owing to distinct activities on PCNA-linked ubiquitin chains. Ubp10 and Ubp12 associate with replication forks in a fashion determined by Ubp10 dependency on lagging-strand PCNA residence, and they downregulate translesion polymerase recruitment and template switch events engaging nascent strands. These findings reveal PCNAK164 deubiquitylation as a key mechanism for the modulation of lesion bypass during replication, which might set a framework for establishing strand-differential pathway choices. We propose that damage tolerance is tempered at replication forks to limit the extension of bypass events and sustain chromosome replication rates.
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Affiliation(s)
- Vanesa Álvarez
- Instituto de Biología Molecular y Celular del Cáncer (USAL/CSIC), Salamanca, Spain
| | | | - María P Sacristán
- Instituto de Biología Molecular y Celular del Cáncer (USAL/CSIC), Salamanca, Spain; Departamento de Microbiología y Genética, Universidad de Salamanca, Salamanca, Spain
| | | | | | - Avelino Bueno
- Instituto de Biología Molecular y Celular del Cáncer (USAL/CSIC), Salamanca, Spain; Departamento de Microbiología y Genética, Universidad de Salamanca, Salamanca, Spain.
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Resolvases, Dissolvases, and Helicases in Homologous Recombination: Clearing the Road for Chromosome Segregation. Genes (Basel) 2020; 11:genes11010071. [PMID: 31936378 PMCID: PMC7017083 DOI: 10.3390/genes11010071] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 12/29/2019] [Accepted: 01/01/2020] [Indexed: 12/13/2022] Open
Abstract
The execution of recombinational pathways during the repair of certain DNA lesions or in the meiotic program is associated to the formation of joint molecules that physically hold chromosomes together. These structures must be disengaged prior to the onset of chromosome segregation. Failure in the resolution of these linkages can lead to chromosome breakage and nondisjunction events that can alter the normal distribution of the genomic material to the progeny. To avoid this situation, cells have developed an arsenal of molecular complexes involving helicases, resolvases, and dissolvases that recognize and eliminate chromosome links. The correct orchestration of these enzymes promotes the timely removal of chromosomal connections ensuring the efficient segregation of the genome during cell division. In this review, we focus on the role of different DNA processing enzymes that collaborate in removing the linkages generated during the activation of the homologous recombination machinery as a consequence of the appearance of DNA breaks during the mitotic and meiotic programs. We will also discuss about the temporal regulation of these factors along the cell cycle, the consequences of their loss of function, and their specific role in the removal of chromosomal links to ensure the accurate segregation of the genomic material during cell division.
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Cerritelli SM, Crouch RJ. RNase H2-RED carpets the path to eukaryotic RNase H2 functions. DNA Repair (Amst) 2019; 84:102736. [PMID: 31761672 PMCID: PMC6936605 DOI: 10.1016/j.dnarep.2019.102736] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Accepted: 10/15/2019] [Indexed: 11/24/2022]
Abstract
Eukaryotic RNases H2 have dual functions in initiating the removal of ribonucleoside monophosphates (rNMPs) incorporated by DNA polymerases during DNA synthesis and in cleaving the RNA moiety of RNA/DNA hybrids formed during transcription and retrotransposition. The other major cellular RNase H, RNase H1, shares the hybrid processing activity, but not all substrates. After RNase H2 incision at the rNMPs in DNA the Ribonucleotide Excision Repair (RER) pathway completes the removal, restoring dsDNA. The development of the RNase H2-RED (Ribonucleotide Excision Defective) mutant enzyme, which can process RNA/DNA hybrids but is unable to cleave rNMPs embedded in DNA has unlinked the two activities and illuminated the roles of RNase H2 in cellular metabolism. Studies mostly in Saccharomyces cerevisiae, have shown both activities of RNase H2 are necessary to maintain genome integrity and that RNase H1 and H2 have overlapping as well as distinct RNA/DNA hybrid substrates. In mouse RNase H2-RED confirmed that rNMPs in DNA during embryogenesis induce lethality in a p53-dependent DNA damage response. In mammalian cell cultures, RNase H2-RED helped identifying DNA lesions produced by Top1 cleavage at rNMPs and led to determine that RNase H2 participates in the retrotransposition of LINE-1 elements. In this review, we summarize the studies and conclusions reached by utilization of RNase H2-RED enzyme in different model systems.
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Affiliation(s)
- Susana M Cerritelli
- SFR, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Robert J Crouch
- SFR, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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Menin L, Colombo CV, Maestrini G, Longhese MP, Clerici M. Tel1/ATM Signaling to the Checkpoint Contributes to Replicative Senescence in the Absence of Telomerase. Genetics 2019; 213:411-429. [PMID: 31391264 PMCID: PMC6781906 DOI: 10.1534/genetics.119.302391] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Accepted: 07/27/2019] [Indexed: 11/18/2022] Open
Abstract
Telomeres progressively shorten at every round of DNA replication in the absence of telomerase. When they become critically short, telomeres trigger replicative senescence by activating a DNA damage response that is governed by the Mec1/ATR and Tel1/ATM protein kinases. While Mec1/ATR is known to block cell division when extended single-stranded DNA (ssDNA) accumulates at eroded telomeres, the molecular mechanism by which Tel1/ATM promotes senescence is still unclear. By characterizing a Tel1-hy184 mutant variant that compensates for the lack of Mec1 functions, we provide evidence that Tel1 promotes senescence by signaling to a Rad9-dependent checkpoint. Tel1-hy184 anticipates senescence onset in telomerase-negative cells, while the lack of Tel1 or the expression of a kinase-defective (kd) Tel1 variant delays it. Both Tel1-hy184 and Tel1-kd do not alter ssDNA generation at telomeric DNA ends. Furthermore, Rad9 and (only partially) Mec1 are responsible for the precocious senescence promoted by Tel1-hy184. This precocious senescence is mainly caused by the F1751I, D1985N, and E2133K amino acid substitutions, which are located in the FRAP-ATM-TRAPP domain of Tel1 and also increase Tel1 binding to DNA ends. Altogether, these results indicate that Tel1 induces replicative senescence by directly signaling dysfunctional telomeres to the checkpoint machinery.
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Affiliation(s)
- Luca Menin
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Chiara Vittoria Colombo
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Giorgia Maestrini
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Maria Pia Longhese
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
| | - Michela Clerici
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Milano 20126, Italy
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Saatchi F, Kirchmaier AL. Tolerance of DNA Replication Stress Is Promoted by Fumarate Through Modulation of Histone Demethylation and Enhancement of Replicative Intermediate Processing in Saccharomyces cerevisiae. Genetics 2019; 212:631-654. [PMID: 31123043 PMCID: PMC6614904 DOI: 10.1534/genetics.119.302238] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Accepted: 05/07/2019] [Indexed: 12/28/2022] Open
Abstract
Fumarase is a well-characterized TCA cycle enzyme that catalyzes the reversible conversion of fumarate to malate. In mammals, fumarase acts as a tumor suppressor, and loss-of-function mutations in the FH gene in hereditary leiomyomatosis and renal cell cancer result in the accumulation of intracellular fumarate-an inhibitor of α-ketoglutarate-dependent dioxygenases. Fumarase promotes DNA repair by nonhomologous end joining in mammalian cells through interaction with the histone variant H2A.Z, and inhibition of KDM2B, a H3 K36-specific histone demethylase. Here, we report that Saccharomyces cerevisiae fumarase, Fum1p, acts as a response factor during DNA replication stress, and fumarate enhances survival of yeast lacking Htz1p (H2A.Z in mammals). We observed that exposure to DNA replication stress led to upregulation as well as nuclear enrichment of Fum1p, and raising levels of fumarate in cells via deletion of FUM1 or addition of exogenous fumarate suppressed the sensitivity to DNA replication stress of htz1Δ mutants. This suppression was independent of modulating nucleotide pool levels. Rather, our results are consistent with fumarate conferring resistance to DNA replication stress in htz1Δ mutants by inhibiting the H3 K4-specific histone demethylase Jhd2p, and increasing H3 K4 methylation. Although the timing of checkpoint activation and deactivation remained largely unaffected by fumarate, sensors and mediators of the DNA replication checkpoint were required for fumarate-dependent resistance to replication stress in the htz1Δ mutants. Together, our findings imply metabolic enzymes and metabolites aid in processing replicative intermediates by affecting chromatin modification states, thereby promoting genome integrity.
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Affiliation(s)
- Faeze Saatchi
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
- Purdue University Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907
| | - Ann L Kirchmaier
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
- Purdue University Center for Cancer Research, Purdue University, West Lafayette, Indiana 47907
- Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907
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Crickard J, Xue C, Wang W, Kwon Y, Sung P, Greene E. The RecQ helicase Sgs1 drives ATP-dependent disruption of Rad51 filaments. Nucleic Acids Res 2019; 47:4694-4706. [PMID: 30916344 PMCID: PMC6511845 DOI: 10.1093/nar/gkz186] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 03/06/2019] [Accepted: 03/20/2019] [Indexed: 12/21/2022] Open
Abstract
DNA helicases of the RecQ family are conserved among the three domains of life and play essential roles in genome maintenance. Mutations in several human RecQ helicases lead to diseases that are marked by cancer predisposition. The Saccharomyces cerevisiae RecQ helicase Sgs1 is orthologous to human BLM, defects in which cause the cancer-prone Bloom's Syndrome. Here, we use single-molecule imaging to provide a quantitative mechanistic understanding of Sgs1 activities on single stranded DNA (ssDNA), which is a central intermediate in all aspects of DNA metabolism. We show that Sgs1 acts upon ssDNA bound by either replication protein A (RPA) or the recombinase Rad51. Surprisingly, we find that Sgs1 utilizes a novel motor mechanism for disrupting ssDNA intermediates bound by the recombinase protein Rad51. The ability of Sgs1 to disrupt Rad51-ssDNA filaments may explain some of the defects engendered by RECQ helicase deficiencies in human cells.
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Affiliation(s)
- J Brooks Crickard
- Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Chaoyou Xue
- Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Weibin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, TX 78229, USA
| | - Youngho Kwon
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, TX 78229, USA
| | - Patrick Sung
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, TX 78229, USA
| | - Eric C Greene
- Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY 10032, USA
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Genome Instability Is Promoted by the Chromatin-Binding Protein Spn1 in Saccharomyces cerevisiae. Genetics 2018; 210:1227-1237. [PMID: 30301740 DOI: 10.1534/genetics.118.301600] [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: 06/05/2018] [Accepted: 10/02/2018] [Indexed: 02/06/2023] Open
Abstract
Cells expend a large amount of energy to maintain their DNA sequence. DNA repair pathways, cell cycle checkpoint activation, proofreading polymerases, and chromatin structure are ways in which the cell minimizes changes to the genome. During replication, the DNA-damage tolerance pathway allows the replication forks to bypass damage on the template strand. This avoids prolonged replication fork stalling, which can contribute to genome instability. The DNA-damage tolerance pathway includes two subpathways: translesion synthesis and template switch. Post-translational modification of PCNA and the histone tails, cell cycle phase, and local DNA structure have all been shown to influence subpathway choice. Chromatin architecture contributes to maintaining genome stability by providing physical protection of the DNA and by regulating DNA-processing pathways. As such, chromatin-binding factors have been implicated in maintaining genome stability. Using Saccharomyces cerevisiae, we examined the role of Spn1 (Suppresses postrecruitment gene number 1), a chromatin-binding and transcription elongation factor, in DNA-damage tolerance. Expression of a mutant allele of SPN1 results in increased resistance to the DNA-damaging agent methyl methanesulfonate, lower spontaneous and damage-induced mutation rates, along with increased chronological life span. We attribute these effects to an increased usage of the template switch branch of the DNA-damage tolerance pathway in the spn1 strain. This provides evidence for a role of wild-type Spn1 in promoting genome instability, as well as having ties to overcoming replication stress and contributing to chronological aging.
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Upregulation of dNTP Levels After Telomerase Inactivation Influences Telomerase-Independent Telomere Maintenance Pathway Choice in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2018; 8:2551-2558. [PMID: 29848621 PMCID: PMC6071591 DOI: 10.1534/g3.118.200280] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In 10–15% of cancers, telomere length is maintained by a telomerase-independent, recombination-mediated pathway called alternative lengthening of telomeres (ALT). ALT mechanisms were first seen, and have been best studied, in telomerase-null Saccharomyces cerevisiae cells called “survivors”. There are two main types of survivors. Type I survivors amplify Y′ subtelomeric elements while type II survivors, similar to the majority of human ALT cells, amplify the terminal telomeric repeats. Both types of survivors require Rad52, a key homologous recombination protein, and Pol32, a non-essential subunit of DNA polymerase δ. A number of additional proteins have been reported to be important for either type I or type II survivor formation, but it is still unclear how these two pathways maintain telomeres. In this study, we performed a genome-wide screen to identify novel genes that are important for the formation of type II ALT-like survivors. We identified 23 genes that disrupt type II survivor formation when deleted. 17 of these genes had not been previously reported to do so. Several of these genes (DUN1, CCR4, and MOT2) are known to be involved in the regulation of dNTP levels. We find that dNTP levels are elevated early after telomerase inactivation and that this increase favors the formation of type II survivors.
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Sgs1 Binding to Rad51 Stimulates Homology-Directed DNA Repair in Saccharomyces cerevisiae. Genetics 2017; 208:125-138. [PMID: 29162625 PMCID: PMC5753853 DOI: 10.1534/genetics.117.300545] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 11/16/2017] [Indexed: 12/23/2022] Open
Abstract
Accurate repair of DNA breaks is essential to maintain genome integrity and cellular fitness. Sgs1, the sole member of the RecQ family of DNA helicases in Saccharomyces cerevisiae, is important for both early and late stages of homology-dependent repair. Its large number of physical and genetic interactions with DNA recombination, repair, and replication factors has established Sgs1 as a key player in the maintenance of genome integrity. To determine the significance of Sgs1 binding to the strand-exchange factor Rad51, we have identified a single amino acid change at the C-terminal of the helicase core of Sgs1 that disrupts Rad51 binding. In contrast to an SGS1 deletion or a helicase-defective sgs1 allele, this new separation-of-function allele, sgs1-FD, does not cause DNA damage hypersensitivity or genome instability, but exhibits negative and positive genetic interactions with sae2Δ, mre11Δ, exo1Δ, srs2Δ, rrm3Δ, and pol32Δ that are distinct from those of known sgs1 mutants. Our findings suggest that the Sgs1-Rad51 interaction stimulates homologous recombination (HR). However, unlike sgs1 mutations, which impair the resection of DNA double-strand ends, negative genetic interactions of the sgs1-FD allele are not suppressed by YKU70 deletion. We propose that the Sgs1-Rad51 interaction stimulates HR by facilitating the formation of the presynaptic Rad51 filament, possibly by Sgs1 competing with single-stranded DNA for replication protein A binding during resection.
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Fasullo MT, Sun M. Both RAD5-dependent and independent pathways are involved in DNA damage-associated sister chromatid exchange in budding yeast. AIMS GENETICS 2017; 4:84-102. [PMID: 28596989 PMCID: PMC5460634 DOI: 10.3934/genet.2017.2.84] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Sister chromatids are preferred substrates for recombinational repair after cells are exposed to DNA damage. While some agents directly cause double-strand breaks (DSBs), others form DNA base adducts which stall or impede the DNA replication fork. We asked which types of DNA damage can stimulate SCE in budding yeast mutants defective in template switch mechanisms and whether PCNA polyubiquitination functions are required for DNA damage-associated SCE after exposure to potent recombinagens. We measured spontaneous and DNA damage-associated unequal sister chromatid exchange (uSCE) in yeast strains containing two fragments of his3 after exposure to MMS, 4-NQO, UV, X rays, and HO endonuclease-induced DSBs. We determined whether other genes in the pathway for template switching, including UBC13, MMS2, SGS1, and SRS2 were required for DNA damage-associated SCE. RAD5 was required for DNA damage-associated SCE after exposure to UV, MMS, and 4-NQO, but not for spontaneous, X-ray-associated, or HO endonuclease-induced SCE. While UBC13, MMS2, and SGS1 were required for MMS and 4NQO-associated SCE, they were not required for UV-associated SCE. DNA damage-associated recombination between his3 recombination substrates on non-homologous recombination was enhanced in rad5 mutants. These results demonstrate that DNA damaging agents that cause DSBs stimulate SCE by RAD5-independent mechanisms, while several potent agents that generate bulky DNA adducts stimulate SCE by multiple RAD5-dependent mechanisms. We suggest that DSB-associated recombination that occurs in G2 is RAD5-independent.
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Affiliation(s)
- Michael T Fasullo
- College of Nanoscale Sciences and Engineering, SUNY Polytechnic Institute, 257 Fuller Road, Albany, New York 12203, United States
| | - Mingzeng Sun
- College of Nanoscale Sciences and Engineering, SUNY Polytechnic Institute, 257 Fuller Road, Albany, New York 12203, United States
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15
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DNA Damage Tolerance Pathway Choice Through Uls1 Modulation of Srs2 SUMOylation in Saccharomyces cerevisiae. Genetics 2017; 206:513-525. [PMID: 28341648 DOI: 10.1534/genetics.116.196568] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Accepted: 03/09/2017] [Indexed: 01/24/2023] Open
Abstract
DNA damage tolerance and homologous recombination pathways function to bypass replication-blocking lesions and ensure completion of DNA replication. However, inappropriate activation of these pathways may lead to increased mutagenesis or formation of deleterious recombination intermediates, often leading to cell death or cancer formation in higher organisms. Post-translational modifications of PCNA regulate the choice of repair pathways at replication forks. Its monoubiquitination favors translesion synthesis, while polyubiquitination stimulates template switching. Srs2 helicase binds to small ubiquitin-related modifier (SUMO)-modified PCNA to suppress a subset of Rad51-dependent homologous recombination. Conversely, SUMOylation of Srs2 attenuates its interaction with PCNA Sgs1 helicase and Mus81 endonuclease are crucial for disentanglement of repair intermediates at the replication fork. Deletion of both genes is lethal and can be rescued by inactivation of Rad51-dependent homologous recombination. Here we show that Saccharomyces cerevisiae Uls1, a member of the Swi2/Snf2 family of ATPases and a SUMO-targeted ubiquitin ligase, physically interacts with both PCNA and Srs2, and promotes Srs2 binding to PCNA by downregulating Srs2-SUMO levels at replication forks. We also identify deletion of ULS1 as a suppressor of mus81Δ sgs1Δ synthetic lethality and hypothesize that uls1Δ mutation results in a partial inactivation of the homologous recombination pathway, detrimental in cells devoid of both Sgs1 and Mus81 We thus propose that Uls1 contributes to the pathway where intermediates generated at replication forks are dismantled by Srs2 bound to SUMO-PCNA. Upon ULS1 deletion, accumulating Srs2-SUMO-unable to bind PCNA-takes part in an alternative PCNA-independent recombination repair salvage pathway(s).
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16
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Mutator Phenotype and DNA Double-Strand Break Repair in BLM Helicase-Deficient Human Cells. Mol Cell Biol 2016; 36:2877-2889. [PMID: 27601585 PMCID: PMC5108877 DOI: 10.1128/mcb.00443-16] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Accepted: 08/25/2016] [Indexed: 12/16/2022] Open
Abstract
Bloom syndrome (BS), an autosomal recessive disorder of the BLM gene, predisposes sufferers to various cancers. To investigate the mutator phenotype and genetic consequences of DNA double-strand breaks (DSBs) in BS cells, we developed BLM helicase-deficient human cells by disrupting the BLM gene. Cells with a loss of heterozygosity (LOH) due to homologous recombination (HR) or nonhomologous end joining (NHEJ) can be restored with or without site-directed DSB induction. BLM cells exhibited a high frequency of spontaneous interallelic HR with crossover, but noncrossover events with long-tract gene conversions also occurred. Despite the highly interallelic HR events, BLM cells predominantly produced hemizygous LOH by spontaneous deletion. These phenotypes manifested during repair of DSBs. Both NHEJ and HR appropriately repaired DSBs in BLM cells, resulting in hemizygous and homozygous LOHs, respectively. However, the magnitude of the LOH was exacerbated in BLM cells, as evidenced by large deletions and long-tract gene conversions with crossover. BLM helicase suppresses the elongation of branch migration and crossover of double Holliday junctions (HJs) during HR repair, and a deficiency in this enzyme causes collapse, abnormal elongation, and/or preferable resolution to crossover of double HJs, resulting in a large-scale LOH. This mechanism underlies the predisposition for cancer in BS.
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Replication intermediates that escape Dna2 activity are processed by Holliday junction resolvase Yen1. Nat Commun 2016; 7:13157. [PMID: 27779184 PMCID: PMC5093310 DOI: 10.1038/ncomms13157] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 09/08/2016] [Indexed: 12/29/2022] Open
Abstract
Cells have evolved mechanisms to protect, restart and repair perturbed replication forks, allowing full genome duplication, even under replication stress. Interrogating the interplay between nuclease-helicase Dna2 and Holliday junction (HJ) resolvase Yen1, we find the Dna2 helicase activity acts parallel to homologous recombination (HR) in promoting DNA replication and chromosome detachment at mitosis after replication fork stalling. Yen1, but not the HJ resolvases Slx1-Slx4 and Mus81-Mms4, safeguards chromosome segregation by removing replication intermediates that escape Dna2. Post-replicative DNA damage checkpoint activation in Dna2 helicase-defective cells causes terminal G2/M arrest by precluding Yen1-dependent repair, whose activation requires progression into anaphase. These findings explain the exquisite replication stress sensitivity of Dna2 helicase-defective cells, and identify a non-canonical role for Yen1 in the processing of replication intermediates that is distinct from HJ resolution. The involvement of Dna2 helicase activity in completing replication may have implications for DNA2-associated pathologies, including cancer and Seckel syndrome.
DNA replication stress drives genome instability and cancer. Here, Ölmezer and colleagues show that the helicase activity of multifunctional enzyme Dna2 suppresses dead-end replication structures that impair chromosome segregation if not removed by Holliday junction resolvase Yen1 in yeast.
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18
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Bermúdez-López M, Aragon L. Smc5/6 complex regulates Sgs1 recombination functions. Curr Genet 2016; 63:381-388. [PMID: 27664093 PMCID: PMC5422486 DOI: 10.1007/s00294-016-0648-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 09/02/2016] [Accepted: 09/03/2016] [Indexed: 11/07/2022]
Abstract
The family of RecQ helicases is evolutionary conserved from bacteria to humans and play key roles in genome stability. The budding yeast RecQ helicase Sgs1 has been implicated in several key processes during the repair of DNA damage by homologous recombination as part of the STR complex (Sgs1-Top3-Rmi1). Limited information on how is Sgs1 recruited and regulated at sites of damage is available. Recently, we and others have uncover a direct link between the Smc5/6 complex and Sgs1. Most roles of Sgs1 during recombination, including DNA end resection, Holiday junction dissolution, and crossover suppression, are regulated through Mms21-dependent SUMOylation. Smc5/6 first acts as a recruiting platform for STR and then SUMOylates STR components to regulate their function. Importantly, the assembly of STR is totally independent of Smc5/6. Here, we provide a brief overview of STR regulation by Smc5/6.
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Affiliation(s)
| | - Luis Aragon
- Cell Cycle Group, MRC Clinical Sciences Centre, Imperial College, London, W12 0NN, UK.
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19
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Lee KJ, Saha J, Sun J, Fattah KR, Wang SC, Jakob B, Chi L, Wang SY, Taucher-Scholz G, Davis AJ, Chen DJ. Phosphorylation of Ku dictates DNA double-strand break (DSB) repair pathway choice in S phase. Nucleic Acids Res 2015; 44:1732-45. [PMID: 26712563 PMCID: PMC4770226 DOI: 10.1093/nar/gkv1499] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 12/11/2015] [Indexed: 12/16/2022] Open
Abstract
Multiple DNA double-strand break (DSB) repair pathways are active in S phase of the cell cycle; however, DSBs are primarily repaired by homologous recombination (HR) in this cell cycle phase. As the non-homologous end-joining (NHEJ) factor, Ku70/80 (Ku), is quickly recruited to DSBs in S phase, we hypothesized that an orchestrated mechanism modulates pathway choice between HR and NHEJ via displacement of the Ku heterodimer from DSBs to allow HR. Here, we provide evidence that phosphorylation at a cluster of sites in the junction of the pillar and bridge regions of Ku70 mediates the dissociation of Ku from DSBs. Mimicking phosphorylation at these sites reduces Ku's affinity for DSB ends, suggesting that phosphorylation of Ku70 induces a conformational change responsible for the dissociation of the Ku heterodimer from DNA ends. Ablating phosphorylation of Ku70 leads to the sustained retention of Ku at DSBs, resulting in a significant decrease in DNA end resection and HR, specifically in S phase. This decrease in HR is specific as these phosphorylation sites are not required for NHEJ. Our results demonstrate that the phosphorylation-mediated dissociation of Ku70/80 from DSBs frees DNA ends, allowing the initiation of HR in S phase and providing a mechanism of DSB repair pathway choice in mammalian cells.
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Affiliation(s)
- Kyung-Jong Lee
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Janapriya Saha
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Jingxin Sun
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Kazi R Fattah
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Shu-Chi Wang
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Burkhard Jakob
- Department of Biophysics; GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, Darmstadt, Germany
| | - Linfeng Chi
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Shih-Ya Wang
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - Gisela Taucher-Scholz
- Department of Biophysics; GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, Darmstadt, Germany
| | - Anthony J Davis
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
| | - David J Chen
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, Texas 75390, USA
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20
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Abstract
DNA damage may compromise genome integrity and lead to cell death. Cells have evolved a variety of processes to respond to DNA damage including damage repair and tolerance mechanisms, as well as damage checkpoints. The DNA damage tolerance (DDT) pathway promotes the bypass of single-stranded DNA lesions encountered by DNA polymerases during DNA replication. This prevents the stalling of DNA replication. Two mechanistically distinct DDT branches have been characterized. One is translesion synthesis (TLS) in which a replicative DNA polymerase is temporarily replaced by a specialized TLS polymerase that has the ability to replicate across DNA lesions. TLS is mechanistically simple and straightforward, but it is intrinsically error-prone. The other is the error-free template switching (TS) mechanism in which the stalled nascent strand switches from the damaged template to the undamaged newly synthesized sister strand for extension past the lesion. Error-free TS is a complex but preferable process for bypassing DNA lesions. However, our current understanding of this pathway is sketchy. An increasing number of factors are being found to participate or regulate this important mechanism, which is the focus of this editorial.
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21
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Abstract
The ends of linear chromosomes are capped by nucleoprotein structures called telomeres. A dysfunctional telomere may resemble a DNA double-strand break (DSB), which is a severe form of DNA damage. The presence of one DSB is sufficient to drive cell cycle arrest and cell death. Therefore cells have evolved mechanisms to repair DSBs such as homologous recombination (HR). HR-mediated repair of telomeres can lead to genome instability, a hallmark of cancer cells, which is why such repair is normally inhibited. However, some HR-mediated processes are required for proper telomere function. The need for some recombination activities at telomeres but not others necessitates careful and complex regulation, defects in which can lead to catastrophic consequences. Furthermore, some cell types can maintain telomeres via telomerase-independent, recombination-mediated mechanisms. In humans, these mechanisms are called alternative lengthening of telomeres (ALT) and are used in a subset of human cancer cells. In this review, we summarize the different recombination activities occurring at telomeres and discuss how they are regulated. Much of the current knowledge is derived from work using yeast models, which is the focus of this review, but relevant studies in mammals are also included.
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Affiliation(s)
- Clémence Claussin
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Michael Chang
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
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22
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Fasching CL, Cejka P, Kowalczykowski SC, Heyer WD. Top3-Rmi1 dissolve Rad51-mediated D loops by a topoisomerase-based mechanism. Mol Cell 2015; 57:595-606. [PMID: 25699708 PMCID: PMC4338411 DOI: 10.1016/j.molcel.2015.01.022] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 12/03/2014] [Accepted: 01/02/2015] [Indexed: 11/19/2022]
Abstract
The displacement loop (D loop) is a DNA strand invasion product formed during homologous recombination. Disruption of nascent D loops prevents recombination, and during synthesis-dependent strand annealing (SDSA), disruption of D loops extended by DNA polymerase ensures a non-crossover outcome. The proteins implicated in D loop disruption are DNA motor proteins/helicases that act by moving DNA junctions. Here we report that D loops can also be disrupted by DNA topoisomerase 3 (Top3), and this disruption depends on Top3's catalytic activity. Yeast Top3 specifically disrupts D loops mediated by yeast Rad51/Rad54; protein-free D loops or D loop mediated by bacterial RecA protein or human RAD51/RAD54 resist dissolution. Also, the human Topoisomerase IIIa-RMI1-RMI2 complex is capable of dissolving D loops. Consistent with genetic data, we suggest that the extreme growth defect and hyper-recombination phenotype of Top3-deficient yeast cells is partially a result of unprocessed D loops.
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Affiliation(s)
- Clare L Fasching
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Petr Cejka
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Stephen C Kowalczykowski
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA; Department of Molecular & Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA
| | - Wolf-Dietrich Heyer
- Department of Microbiology & Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA; Department of Molecular & Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA.
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23
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Böhm S, Mihalevic MJ, Casal MA, Bernstein KA. Disruption of SUMO-targeted ubiquitin ligases Slx5-Slx8/RNF4 alters RecQ-like helicase Sgs1/BLM localization in yeast and human cells. DNA Repair (Amst) 2014; 26:1-14. [PMID: 25588990 DOI: 10.1016/j.dnarep.2014.12.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 12/16/2014] [Accepted: 12/17/2014] [Indexed: 10/24/2022]
Abstract
RecQ-like helicases are a highly conserved protein family that functions during DNA repair and, when mutated in humans, is associated with cancer and/or premature aging syndromes. The budding yeast RecQ-like helicase Sgs1 has important functions in double-strand break (DSB) repair of exogenously induced breaks, as well as those that arise endogenously, for example during DNA replication. To further investigate Sgs1's regulation, we analyzed the subcellular localization of a fluorescent fusion of Sgs1 upon DNA damage. Consistent with a role in DSB repair, Sgs1 recruitment into nuclear foci in asynchronous cultures increases after ionizing radiation (IR) and after exposure to the alkylating agent methyl methanesulfonate (MMS). Yet, despite the importance of Sgs1 in replicative damage repair and in contrast to its elevated protein levels during S-phase, we find that the number of Sgs1 foci decreases upon nucleotide pool depletion by hydroxyurea (HU) treatment and that this negative regulation depends on the intra S-phase checkpoint kinase Mec1. Importantly, we identify the SUMO-targeted ubiquitin ligase (STUbL) complex Slx5-Slx8 as a negative regulator of Sgs1 foci, both spontaneously and upon replicative damage. Slx5-Slx8 regulation of Sgs1 foci is likely conserved in eukaryotes, since expression of the mammalian Slx5-Slx8 functional homologue, RNF4, restores Sgs1 focus number in slx8 cells and furthermore, knockdown of RNF4 leads to more BLM foci in U-2 OS cells. Our results point to a model where RecQ-like helicase subcellular localization is regulated by STUbLs in response to DNA damage, presumably to prevent illegitimate recombination events.
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Affiliation(s)
- Stefanie Böhm
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA
| | - Michael Joseph Mihalevic
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA
| | - Morgan Alexandra Casal
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA
| | - Kara Anne Bernstein
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA.
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24
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Sgs1 and Sae2 promote telomere replication by limiting accumulation of ssDNA. Nat Commun 2014; 5:5004. [DOI: 10.1038/ncomms6004] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 08/15/2014] [Indexed: 02/02/2023] Open
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25
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Davis AJ, Chi L, So S, Lee KJ, Mori E, Fattah K, Yang J, Chen DJ. BRCA1 modulates the autophosphorylation status of DNA-PKcs in S phase of the cell cycle. Nucleic Acids Res 2014; 42:11487-501. [PMID: 25223785 PMCID: PMC4191403 DOI: 10.1093/nar/gku824] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Non-homologous end-joining (NHEJ) and homologous recombination (HR) are the two prominent pathways responsible for the repair of DNA double-strand breaks (DSBs). NHEJ is not restricted to a cell-cycle stage, whereas HR is active primarily in the S/G2 phases suggesting there are cell cycle-specific mechanisms that play a role in the choice between NHEJ and HR. Here we show NHEJ is attenuated in S phase via modulation of the autophosphorylation status of the NHEJ factor DNA-PKcs at serine 2056 by the pro-HR factor BRCA1. BRCA1 interacts with DNA-PKcs in a cell cycle-regulated manner and this interaction is mediated by the tandem BRCT domain of BRCA1, but surprisingly in a phospho-independent manner. BRCA1 attenuates DNA-PKcs autophosphorylation via directly blocking the ability of DNA-PKcs to autophosphorylate. Subsequently, blocking autophosphorylation of DNA-PKcs at the serine 2056 phosphorylation cluster promotes HR-required DNA end processing and loading of HR factors to DSBs and is a possible mechanism by which BRCA1 promotes HR.
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Affiliation(s)
- Anthony J Davis
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
| | - Linfeng Chi
- The First Affiliated Hospital, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Zhejiang University, Hangzhou, Zhejiang, China
| | - Sairei So
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
| | - Kyung-Jong Lee
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
| | - Eiichiro Mori
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
| | - Kazi Fattah
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
| | - Jun Yang
- The First Affiliated Hospital, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Zhejiang University, Hangzhou, Zhejiang, China Department of Toxicology, Hangzhou Normal University School of Public Health, 16 Xue Lin Street, Hangzhou, Zhejiang, China
| | - David J Chen
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
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26
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Chen CF, Brill SJ. Multimerization domains are associated with apparent strand exchange activity in BLM and WRN DNA helicases. DNA Repair (Amst) 2014; 22:137-46. [PMID: 25198671 DOI: 10.1016/j.dnarep.2014.07.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 07/10/2014] [Accepted: 07/22/2014] [Indexed: 12/11/2022]
Abstract
BLM and WRN are members of the RecQ family of DNA helicases that act to suppress genome instability and cancer predisposition. In addition to a RecQ helicase domain, each of these proteins contains an N-terminal domain of approximately 500 amino acids (aa) that is incompletely characterized. Previously, we showed that the N-terminus of Sgs1, the yeast ortholog of BLM, contains a physiologically important 200 aa domain (Sgs1103-322) that displays single-stranded DNA (ssDNA) binding, strand annealing (SA), and apparent strand-exchange (SE) activities in vitro. Here we used a genetic assay to search for heterologous proteins that could functionally replace this domain of Sgs1 in vivo. In contrast to Rad59, the oligomeric Rad52 protein provided in vivo complementation, suggesting that multimerization is functionally important. An N-terminal domain of WRN was also identified that could replace Sgs1103-322 in yeast. This domain, WRN235-526, contains a known coiled coil and displays the same SA and SE activities as Sgs1103-322. The coiled coil domain of WRN235-526 is required for both its in vivo activity and its in vitro SE activity. Based on this result, a potential coiled coil was identified within Sgs1103-322. This 25 amino acid region was similarly essential for wt Sgs1 activity in vivo and was replaceable by a heterologous coiled coil. Taken together, the results indicate that a coiled coil and a closely linked apparent SE activity are conserved features of the BLM and WRN DNA helicases.
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Affiliation(s)
- Chi-Fu Chen
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ, United States
| | - Steven J Brill
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ, United States.
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27
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Böhm S, Bernstein KA. The role of post-translational modifications in fine-tuning BLM helicase function during DNA repair. DNA Repair (Amst) 2014; 22:123-32. [PMID: 25150915 DOI: 10.1016/j.dnarep.2014.07.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Accepted: 07/14/2014] [Indexed: 12/12/2022]
Abstract
RecQ-like helicases are a highly conserved family of proteins which are critical for preserving genome integrity. Genome instability is considered a hallmark of cancer and mutations within three of the five human RECQ genes cause hereditary syndromes that are associated with cancer predisposition. The human RecQ-like helicase BLM has a central role in DNA damage signaling, repair, replication, and telomere maintenance. BLM and its budding yeast orthologue Sgs1 unwind double-stranded DNA intermediates. Intriguingly, BLM functions in both a pro- and anti-recombinogenic manner upon replicative damage, acting on similar substrates. Thus, BLM activity must be intricately controlled to prevent illegitimate recombination events that could have detrimental effects on genome integrity. In recent years it has become evident that post-translational modifications (PTMs) of BLM allow a fine-tuning of its function. To date, BLM phosphorylation, ubiquitination, and SUMOylation have been identified, in turn regulating its subcellular localization, protein-protein interactions, and protein stability. In this review, we will discuss the cellular context of when and how these different modifications of BLM occur. We will reflect on the current model of how PTMs control BLM function during DNA damage repair and compare this to what is known about post-translational regulation of the budding yeast orthologue Sgs1. Finally, we will provide an outlook toward future research, in particular to dissect the cross-talk between the individual PTMs on BLM.
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Affiliation(s)
- Stefanie Böhm
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, United States
| | - Kara Anne Bernstein
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, United States.
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28
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Kramarz K, Litwin I, Cal-Bąkowska M, Szakal B, Branzei D, Wysocki R, Dziadkowiec D. Swi2/Snf2-like protein Uls1 functions in the Sgs1-dependent pathway of maintenance of rDNA stability and alleviation of replication stress. DNA Repair (Amst) 2014; 21:24-35. [PMID: 25091157 DOI: 10.1016/j.dnarep.2014.05.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Revised: 05/05/2014] [Accepted: 05/25/2014] [Indexed: 10/25/2022]
Abstract
The Saccharomyces cerevisiae Uls1 belongs to the Swi2/Snf2 family of DNA-dependent ATPases and a new protein family of SUMO-targeted ubiquitin ligases. Here we show that Uls1 is implicated in DNA repair independently of the replication stress response pathways mediated by the endonucleases Mus81 and Yen1 and the helicases Mph1 and Srs2. Uls1 works together with Sgs1 and we demonstrate that the attenuation of replication stress-related defects in sgs1Δ by deletion of ULS1 depends on a functional of Rad51 recombinase and post-replication repair pathway mediated by Rad18 and Rad5, but not on the translesion polymerase, Rev3. The higher resistance of sgs1Δ uls1Δ mutants to genotoxic stress compared to single sgs1Δ cells is not the result of decreased formation or accelerated resolution of recombination-dependent DNA structures. Instead, deletion of ULS1 restores stability of the rDNA region in sgs1Δ cells. Our data suggest that Uls1 may contribute to genomic stability during DNA synthesis and channel the repair of replication lesions into the Sgs1-dependent pathway, with DNA translocase and SUMO binding activities of Uls1 as well as a RING domain being essential for its functions in replication stress response.
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Affiliation(s)
- Karol Kramarz
- Institute of Experimental Biology, Faculty of Biological Sciences, University of Wrocław, 50-328 Wrocław, Poland
| | - Ireneusz Litwin
- Institute of Experimental Biology, Faculty of Biological Sciences, University of Wrocław, 50-328 Wrocław, Poland
| | - Magdalena Cal-Bąkowska
- Institute of Experimental Biology, Faculty of Biological Sciences, University of Wrocław, 50-328 Wrocław, Poland
| | - Barnabas Szakal
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan 20139, Italy
| | - Dana Branzei
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan 20139, Italy
| | - Robert Wysocki
- Institute of Experimental Biology, Faculty of Biological Sciences, University of Wrocław, 50-328 Wrocław, Poland
| | - Dorota Dziadkowiec
- Faculty of Biotechnology, University of Wrocław, 50-383 Wrocław, Poland.
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Eissler CL, Mazón G, Powers BL, Savinov SN, Symington LS, Hall MC. The Cdk/cDc14 module controls activation of the Yen1 holliday junction resolvase to promote genome stability. Mol Cell 2014; 54:80-93. [PMID: 24631283 DOI: 10.1016/j.molcel.2014.02.012] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 01/17/2014] [Accepted: 02/03/2014] [Indexed: 10/25/2022]
Abstract
Faithful genome transmission during cell division requires precise, coordinated action of DNA metabolic enzymes, including proteins responsible for DNA damage detection and repair. Dynamic phosphorylation plays an important role in controlling repair enzymes during the DNA damage response (DDR). Cdc14 phosphatases oppose cyclin-dependent kinase (Cdk) phosphorylation and have been implicated in the DDR in several model systems. Here, we have refined the substrate specificity of budding yeast Cdc14 and, using this insight, identified the Holliday junction resolvase Yen1 as a DNA repair target of Cdc14. Cdc14 activation at anaphase triggers nuclear accumulation and enzymatic activation of Yen1, likely to resolve persistent recombinational repair intermediates. Consistent with this, expression of a phosphomimetic Yen1 mutant increased sister chromatid nondisjunction. In contrast, lack of Cdk phosphorylation resulted in constitutive activity and elevated crossover-associated repair. The precise timing of Yen1 activation, governed by core cell-cycle regulators, helps coordinate DNA repair with chromosome segregation and safeguards against genome destabilization.
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Affiliation(s)
- Christie L Eissler
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA; Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA
| | - Gerard Mazón
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY 10032, USA
| | - Brendan L Powers
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA; Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA
| | - Sergey N Savinov
- Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA
| | - Lorraine S Symington
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY 10032, USA
| | - Mark C Hall
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA; Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA.
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30
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Burgess RC, Sebesta M, Sisakova A, Marini VP, Lisby M, Damborsky J, Klein H, Rothstein R, Krejci L. The PCNA interaction protein box sequence in Rad54 is an integral part of its ATPase domain and is required for efficient DNA repair and recombination. PLoS One 2013; 8:e82630. [PMID: 24376557 PMCID: PMC3869717 DOI: 10.1371/journal.pone.0082630] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Accepted: 10/25/2013] [Indexed: 11/19/2022] Open
Abstract
Rad54 is an ATP-driven translocase involved in the genome maintenance pathway of homologous recombination (HR). Although its activity has been implicated in several steps of HR, its exact role(s) at each step are still not fully understood. We have identified a new interaction between Rad54 and the replicative DNA clamp, proliferating cell nuclear antigen (PCNA). This interaction was only mildly weakened by the mutation of two key hydrophobic residues in the highly-conserved PCNA interaction motif (PIP-box) of Rad54 (Rad54-AA). Intriguingly, the rad54-AA mutant cells displayed sensitivity to DNA damage and showed HR defects similar to the null mutant, despite retaining its ability to interact with HR proteins and to be recruited to HR foci in vivo. We therefore surmised that the PCNA interaction might be impaired in vivo and was unable to promote repair synthesis during HR. Indeed, the Rad54-AA mutant was defective in primer extension at the MAT locus as well as in vitro, but additional biochemical analysis revealed that this mutant also had diminished ATPase activity and an inability to promote D-loop formation. Further mutational analysis of the putative PIP-box uncovered that other phenotypically relevant mutants in this domain also resulted in a loss of ATPase activity. Therefore, we have found that although Rad54 interacts with PCNA, the PIP-box motif likely plays only a minor role in stabilizing the PCNA interaction, and rather, this conserved domain is probably an extension of the ATPase domain III.
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Affiliation(s)
- Rebecca C. Burgess
- Department of Genetics & Development, Columbia University Medical Center, New York, New York, United States of America
| | - Marek Sebesta
- National Centre for Biomolecular Research, Masaryk University, Brno, Czech Republic
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
- International Clinical Research Centre, Centre for Biomolecular and Cellular Engineering, Saint Anne's University Hospital, Brno, Czech Republic
| | - Alexandra Sisakova
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
- International Clinical Research Centre, Centre for Biomolecular and Cellular Engineering, Saint Anne's University Hospital, Brno, Czech Republic
| | - Victoria P. Marini
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Michael Lisby
- Department of Molecular Biology, University of Copenhagen, Copenhagen N, Denmark
| | - Jiri Damborsky
- International Clinical Research Centre, Centre for Biomolecular and Cellular Engineering, Saint Anne's University Hospital, Brno, Czech Republic
- Department of Experimental Biology, Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Hannah Klein
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York, United States of America
| | - Rodney Rothstein
- Department of Genetics & Development, Columbia University Medical Center, New York, New York, United States of America
| | - Lumir Krejci
- National Centre for Biomolecular Research, Masaryk University, Brno, Czech Republic
- Department of Biology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
- International Clinical Research Centre, Centre for Biomolecular and Cellular Engineering, Saint Anne's University Hospital, Brno, Czech Republic
- * E-mail:
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Schröpfer S, Kobbe D, Hartung F, Knoll A, Puchta H. Defining the roles of the N-terminal region and the helicase activity of RECQ4A in DNA repair and homologous recombination in Arabidopsis. Nucleic Acids Res 2013; 42:1684-97. [PMID: 24174542 PMCID: PMC3919593 DOI: 10.1093/nar/gkt1004] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
RecQ helicases are critical for the maintenance of genomic stability. The Arabidopsis RecQ helicase RECQ4A is the functional counterpart of human BLM, which is mutated in the genetic disorder Bloom’s syndrome. RECQ4A performs critical roles in regulation of homologous recombination (HR) and DNA repair. Loss of RECQ4A leads to elevated HR frequencies and hypersensitivity to genotoxic agents. Through complementation studies, we were now able to demonstrate that the N-terminal region and the helicase activity of RECQ4A are both essential for the cellular response to replicative stress induced by methyl methanesulfonate and cisplatin. In contrast, loss of helicase activity or deletion of the N-terminus only partially complemented the mutant hyper-recombination phenotype. Furthermore, the helicase-deficient protein lacking its N-terminus did not complement the hyper-recombination phenotype at all. Therefore, RECQ4A seems to possess at least two different and independent sub-functions involved in the suppression of HR. By in vitro analysis, we showed that the helicase core was able to regress an artificial replication fork. Swapping of the terminal regions of RECQ4A with the closely related but functionally distinct helicase RECQ4B indicated that in contrast to the C-terminus, the N-terminus of RECQ4A was required for its specific functions in DNA repair and recombination.
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Affiliation(s)
- Susan Schröpfer
- Botanical Institute II, Karlsruhe Institute of Technology, Hertzstrasse 16, Karlsruhe 76187, Germany and Institute for Biosafety in Plant Biotechnology, Julius Kühn Institute (JKI), Erwin-Baur-Strasse 27, Quedlinburg 06484, Germany
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Resection activity of the Sgs1 helicase alters the affinity of DNA ends for homologous recombination proteins in Saccharomyces cerevisiae. Genetics 2013; 195:1241-51. [PMID: 24097410 DOI: 10.1534/genetics.113.157370] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The RecQ helicase family is critical during DNA damage repair, and mutations in these proteins are associated with Bloom, Werner, or Rothmund-Thompson syndromes in humans, leading to cancer predisposition and/or premature aging. In the budding yeast Saccharomyces cerevisiae, mutations in the RecQ homolog, SGS1, phenocopy many of the defects observed in the human syndromes. One challenge to studying RecQ helicases is that their disruption leads to a pleiotropic phenotype. Using yeast, we show that the separation-of-function allele of SGS1, sgs1-D664Δ, has impaired activity at DNA ends, resulting in a resection processivity defect. Compromising Sgs1 resection function in the absence of the Sae2 nuclease causes slow growth, which is alleviated by making the DNA ends accessible to Exo1 nuclease. Furthermore, fluorescent microscopy studies reveal that, when Sgs1 resection activity is compromised in sae2Δ cells, Mre11 repair foci persist. We suggest a model where the role of Sgs1 in end resection along with Sae2 is important for removing Mre11 from DNA ends during repair.
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Szakal B, Branzei D. Premature Cdk1/Cdc5/Mus81 pathway activation induces aberrant replication and deleterious crossover. EMBO J 2013; 32:1155-67. [PMID: 23531881 PMCID: PMC3630363 DOI: 10.1038/emboj.2013.67] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Accepted: 03/04/2013] [Indexed: 12/31/2022] Open
Abstract
The error-free DNA damage tolerance (DDT) pathway is crucial for replication completion and genome integrity. Mechanistically, this process is driven by a switch of templates accompanied by sister chromatid junction (SCJ) formation. Here, we asked if DDT intermediate processing is temporarily regulated, and what impact such regulation may have on genome stability. We find that persistent DDT recombination intermediates are largely resolved before anaphase through a G2/M damage checkpoint-independent, but Cdk1/Cdc5-dependent pathway that proceeds via a previously described Mus81-Mms4-activating phosphorylation. The Sgs1-Top3- and Mus81-Mms4-dependent resolution pathways occupy different temporal windows in relation to replication, with the Mus81-Mms4 pathway being restricted to late G2/M. Premature activation of the Cdk1/Cdc5/Mus81 pathway, achieved here with phosphomimetic Mms4 variants as well as in S-phase checkpoint-deficient genetic backgrounds, induces crossover-associated chromosome translocations and precocious processing of damage-bypass SCJ intermediates. Taken together, our results underscore the importance of uncoupling error-free versus erroneous recombination intermediate processing pathways during replication, and establish a new paradigm for the role of the DNA damage response in regulating genome integrity by controlling crossover timing.
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Affiliation(s)
- Barnabas Szakal
- Department of Molecular Oncology, Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan 20139, Italy
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34
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Chon H, Sparks JL, Rychlik M, Nowotny M, Burgers PM, Crouch RJ, Cerritelli SM. RNase H2 roles in genome integrity revealed by unlinking its activities. Nucleic Acids Res 2013; 41:3130-43. [PMID: 23355612 PMCID: PMC3597693 DOI: 10.1093/nar/gkt027] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ribonuclease H2 (RNase H2) protects genome integrity by its dual roles of resolving transcription-related R-loops and ribonucleotides incorporated in DNA during replication. To unlink these two functions, we generated a Saccharomyces cerevisiae RNase H2 mutant that can resolve R-loops but cannot cleave single ribonucleotides in DNA. This mutant definitively correlates the 2-5 bp deletions observed in rnh201Δ strains with single rNMPs in DNA. It also establishes a connection between R-loops and Sgs1-mediated replication reinitiation at stalled forks and identifies R-loops uniquely processed by RNase H2. In mouse, deletion of any of the genes coding for RNase H2 results in embryonic lethality, and in humans, RNase H2 hypomorphic mutations cause Aicardi-Goutières syndrome (AGS), a neuroinflammatory disorder. To determine the contribution of R-loops and rNMP in DNA to the defects observed in AGS, we characterized in yeast an AGS-related mutation, which is impaired in processing both substrates, but has sufficient R-loop degradation activity to complement the defects of rnh201Δ sgs1Δ strains. However, this AGS-related mutation accumulates 2-5 bp deletions at a very similar rate as the deletion strain.
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Affiliation(s)
- Hyongi Chon
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
| | - Justin L. Sparks
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
| | - Monika Rychlik
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
| | - Marcin Nowotny
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
| | - Peter M. Burgers
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
| | - Robert J. Crouch
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland,*To whom correspondence should be addressed. Tel: +1 301 496 4082; Fax: +1 301 496 0243;
| | - Susana M. Cerritelli
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA, Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA and Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, 4 Trojdena Street, 02-109 Warsaw, Poland
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Cejka P, Plank JL, Dombrowski CC, Kowalczykowski SC. Decatenation of DNA by the S. cerevisiae Sgs1-Top3-Rmi1 and RPA complex: a mechanism for disentangling chromosomes. Mol Cell 2012; 47:886-96. [PMID: 22885009 DOI: 10.1016/j.molcel.2012.06.032] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Revised: 06/11/2012] [Accepted: 06/30/2012] [Indexed: 01/27/2023]
Abstract
Genetic evidence indicates that Saccharomyces cerevisiae Sgs1, Top3, and Rmi1 resolve topologically linked intermediates arising from DNA replication and recombination. Using purified proteins, we show that Sgs1, Top3, Rmi1, and replication protein A (RPA) coordinate catenation and decatenation of dsDNA through sequential passage of single strands of DNA, establishing a unique pathway for dsDNA decatenation in eukaryotic cells. Sgs1 is required for dsDNA unwinding and, unexpectedly, also has a structural role in DNA strand passage. RPA promotes DNA unwinding by Sgs1 by trapping ssDNA, and it stimulates DNA strand passage by Top3. Paradoxically, Rmi1 has a unique regulatory capacity that slows DNA relaxation by Top3 but stimulates DNA decatenation. We establish that Rmi1 stabilizes the "open" Top3-DNA covalent complex formed as a transient intermediate of strand passage. This concerted activity of the Sgs1-Top3-Rmi1-RPA represents an important mechanism for disentangling structures resulting from the topological features of duplex DNA.
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Affiliation(s)
- Petr Cejka
- Departments of Microbiology and Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA
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36
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An N-terminal acidic region of Sgs1 interacts with Rpa70 and recruits Rad53 kinase to stalled forks. EMBO J 2012; 31:3768-83. [PMID: 22820947 DOI: 10.1038/emboj.2012.195] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Accepted: 06/28/2012] [Indexed: 11/08/2022] Open
Abstract
DNA replication fork stalling poses a major threat to genome stability. This is counteracted in part by the intra-S phase checkpoint, which stabilizes arrested replication machinery, prevents cell-cycle progression and promotes DNA repair. The checkpoint kinase Mec1/ATR and RecQ helicase Sgs1/BLM contribute synergistically to fork maintenance on hydroxyurea (HU). Both enzymes interact with replication protein A (RPA). We identified and deleted the major interaction sites on Sgs1 for Rpa70, generating a mutant called sgs1-r1. In contrast to a helicase-dead mutant of Sgs1, sgs1-r1 did not significantly reduce recovery of DNA polymerase α at HU-arrested replication forks. However, the Sgs1 R1 domain is a target of Mec1 kinase, deletion of which compromises Rad53 activation on HU. Full activation of Rad53 is achieved through phosphorylation of the Sgs1 R1 domain by Mec1, which promotes Sgs1 binding to the FHA1 domain of Rad53 with high affinity. We propose that the recruitment of Rad53 by phosphorylated Sgs1 promotes the replication checkpoint response on HU. Loss of the R1 domain increases lethality selectively in cells lacking Mus81, Slx4, Slx5 or Slx8.
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Stead BE, Brandl CJ, Sandre MK, Davey MJ. Mcm2 phosphorylation and the response to replicative stress. BMC Genet 2012; 13:36. [PMID: 22564307 PMCID: PMC3517340 DOI: 10.1186/1471-2156-13-36] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2012] [Accepted: 05/07/2012] [Indexed: 12/30/2022] Open
Abstract
Background The replicative helicase in eukaryotic cells is comprised of minichromosome maintenance (Mcm) proteins 2 through 7 (Mcm2-7) and is a key target for regulation of cell proliferation. In addition, it is regulated in response to replicative stress. One of the protein kinases that targets Mcm2-7 is the Dbf4-dependent kinase Cdc7 (DDK). In a previous study, we showed that alanine mutations of the DDK phosphorylation sites at S164 and S170 in Saccharomyces cerevisiae Mcm2 result in sensitivity to caffeine and methyl methanesulfonate (MMS) leading us to suggest that DDK phosphorylation of Mcm2 is required in response to replicative stress. Results We show here that a strain with the mcm2 allele lacking DDK phosphorylation sites (mcm2AA) is also sensitive to the ribonucleotide reductase inhibitor, hydroxyurea (HU) and to the base analogue 5-fluorouracil (5-FU) but not the radiomimetic drug, phleomycin. We screened the budding yeast non-essential deletion collection for synthetic lethal interactions with mcm2AA and isolated deletions that include genes involved in the control of genome integrity and oxidative stress. In addition, the spontaneous mutation rate, as measured by mutations in CAN1, was increased in the mcm2AA strain compared to wild type, whereas with a phosphomimetic allele (mcm2EE) the mutation rate was decreased. These results led to the idea that the mcm2AA strain is unable to respond properly to DNA damage. We examined this by screening the deletion collection for suppressors of the caffeine sensitivity of mcm2AA. Deletions that decrease spontaneous DNA damage, increase homologous recombination or slow replication forks were isolated. Many of the suppressors of caffeine sensitivity suppressed other phenotypes of mcm2AA including sensitivity to genotoxic drugs, the increased frequency of cells with RPA foci and the increased mutation rate. Conclusions Together these observations point to a role for DDK-mediated phosphorylation of Mcm2 in the response to replicative stress, including some forms of DNA damage. We suggest that phosphorylation of Mcm2 modulates Mcm2-7 activity resulting in the stabilization of replication forks in response to replicative stress.
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Affiliation(s)
- Brent E Stead
- Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada
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Shao Z, Davis AJ, Fattah KR, So S, Sun J, Lee KJ, Harrison L, Yang J, Chen DJ. Persistently bound Ku at DNA ends attenuates DNA end resection and homologous recombination. DNA Repair (Amst) 2012; 11:310-6. [PMID: 22265216 DOI: 10.1016/j.dnarep.2011.12.007] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Revised: 12/19/2011] [Accepted: 12/21/2011] [Indexed: 10/24/2022]
Abstract
DNA double strand breaks (DSBs) are repaired by non-homologous end joining (NHEJ) or homologous recombination (HR). The DNA cell cycle stage and resection of the DSB ends are two key mechanisms which are believed to push DSB repair to the HR pathway. Here, we show that the NHEJ factor Ku80 associates with DSBs in S phase, when HR is thought to be the preferred repair pathway, and its dynamics/kinetics at DSBs is similar to those observed for Ku80 in non-S phase in mammalian cells. A Ku homolog from Mycobacterium tuberculosis binds to and is retained at DSBs in S phase and was used as a tool to determine if blocking DNA ends affects end resection and HR in mammalian cells. A decrease in DNA end resection, as marked by IR-induced RPA, BrdU, and Rad51 focus formation, and HR are observed when Ku deficient rodent cells are complemented with Mt-Ku. Together, this data suggests that Ku70/80 binds to DSBs in all cell cycle stages and is likely actively displaced from DSB ends to free the DNA ends for DNA end resection and thus HR to occur.
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Affiliation(s)
- Zhengping Shao
- Division of Molecular Radiation Biology, Department of Radiation Oncology, The University of Texas Southwestern Medical Center, 2201 Inwood Rd, Dallas, TX 75390, USA
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Patro BS, Frøhlich R, Bohr VA, Stevnsner T. WRN helicase regulates the ATR-CHK1-induced S-phase checkpoint pathway in response to topoisomerase-I-DNA covalent complexes. J Cell Sci 2011; 124:3967-79. [PMID: 22159421 DOI: 10.1242/jcs.081372] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Checkpoints are cellular surveillance and signaling pathways that coordinate the response to DNA damage and replicative stress. Consequently, failure of cellular checkpoints increases susceptibility to DNA damage and can lead to profound genome instability. This study examines the role of a human RECQ helicase, WRN, in checkpoint activation in response to DNA damage. Mutations in WRN lead to genomic instability and the premature aging condition Werner syndrome. Here, the role of WRN in a DNA-damage-induced checkpoint was analyzed in U-2 OS (WRN wild type) and isogenic cells stably expressing WRN-targeted shRNA (WRN knockdown). The results of our studies suggest that WRN has a crucial role in inducing an S-phase checkpoint in cells exposed to the topoisomerase I inhibitor campthothecin (CPT), but not in cells exposed to hydroxyurea. Intriguingly, WRN decreases the rate of replication fork elongation, increases the accumulation of ssDNA and stimulates phosphorylation of CHK1, which releases CHK1 from chromatin in CPT-treated cells. Importantly, knockdown of WRN expression abolished or delayed all these processes in response to CPT. Together, our results strongly suggest an essential regulatory role for WRN in controlling the ATR-CHK1-mediated S-phase checkpoint in CPT-treated cells.
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Affiliation(s)
- Birija Sankar Patro
- Department of Molecular Biology, University of Aarhus, C. F. Mollers Alle 3, DK-8000 Aarhus C, Denmark
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40
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Histone H3 lysine 56 acetylation and the response to DNA replication fork damage. Mol Cell Biol 2011; 32:154-72. [PMID: 22025679 DOI: 10.1128/mcb.05415-11] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Saccharomyces cerevisiae, histone H3 lysine 56 acetylation (H3K56ac) occurs in newly synthesized histones that are deposited throughout the genome during DNA replication. Defects in H3K56ac sensitize cells to genotoxic agents, suggesting that this modification plays an important role in the DNA damage response. However, the links between histone acetylation, the nascent chromatin structure, and the DNA damage response are poorly understood. Here we report that cells devoid of H3K56ac are sensitive to DNA damage sustained during transient exposure to methyl methanesulfonate (MMS) or camptothecin but are only mildly affected by hydroxyurea. We demonstrate that, after exposure to MMS, H3K56ac-deficient cells cannot complete DNA replication and eventually segregate chromosomes with intranuclear foci containing the recombination protein Rad52. In addition, we provide evidence that these phenotypes are not due to defects in base excision repair, defects in DNA damage tolerance, or a lack of Rad51 loading at sites of DNA damage. Our results argue that the acute sensitivity of H3K56ac-deficient cells to MMS and camptothecin stems from a failure to complete the repair of specific types of DNA lesions by recombination and/or from defects in the completion of DNA replication.
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41
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Identification of Trypanosoma brucei RMI1/BLAP75 homologue and its roles in antigenic variation. PLoS One 2011; 6:e25313. [PMID: 21980422 PMCID: PMC3182221 DOI: 10.1371/journal.pone.0025313] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Accepted: 08/31/2011] [Indexed: 11/30/2022] Open
Abstract
At any time, each cell of the protozoan parasite Trypanosoma brucei expresses a single species of its major antigenic protein, the variant surface glycoprotein (VSG), from a repertoire of >2,000 VSG genes and pseudogenes. The potential to express different VSGs by transcription and recombination allows the parasite to escape the antibody-mediated host immune response, a mechanism known as antigenic variation. The active VSG is transcribed from a sub-telomeric polycistronic unit called the expression site (ES), whose promoter is 40–60 kb upstream of the VSG. While the mechanisms that initiate recombination remain unclear, the resolution phase of these reactions results in the recombinational replacement of the expressed VSG with a donor from one of three distinct chromosomal locations; sub-telomeric loci on the 11 essential chromosomes, on minichromosomes, or at telomere-distal loci. Depending on the type of recombinational replacement (single or double crossover, duplicative gene conversion, etc), several DNA-repair pathways have been thought to play a role. Here we show that VSG recombination relies on at least two distinct DNA-repair pathways, one of which requires RMI1-TOPO3α to suppress recombination and one that is dependent on RAD51 and RMI1. These genetic interactions suggest that both RAD51-dependent and RAD51-independent recombination pathways operate in antigenic switching and that trypanosomes differentially utilize recombination factors for VSG switching, depending on currently unknown parameters within the ES.
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Cal-Bakowska M, Litwin I, Bocer T, Wysocki R, Dziadkowiec D. The Swi2-Snf2-like protein Uls1 is involved in replication stress response. Nucleic Acids Res 2011; 39:8765-77. [PMID: 21764775 PMCID: PMC3203583 DOI: 10.1093/nar/gkr587] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The Saccharomyces cerevisiae Uls1 belongs to the Swi2–Snf2 family of DNA-dependent ATPases and a new protein family of SUMO-targeted ubiquitin ligases. Here, we examine a physiological role of Uls1 and report for the first time its involvement in response to replication stress. We found that deletion of ULS1 in cells lacking RAD52 caused a synthetic growth defect accompanied by prolonged S phase and aberrant cell morphology. uls1Δ also progressed slower through S phase upon MMS treatment and took longer to resolve replication intermediates during recovery. This suggests an important function for Uls1 during replication stress. Consistently, cells lacking Uls1 and endonuclease Mus81 were more sensitive to HU, MMS and CPT than single mus81Δ. Interestingly, deletion of ULS1 attenuated replication stress-related defects in sgs1Δ, such as sensitivity to HU and MMS while increasing the level of PCNA ubiquitination and Rad53 phosphorylation. Importantly, Uls1 interactions with Mus81 and Sgs1 were dependent on its helicase domain. We propose that Uls1 directs a subset of DNA structures arising during replication into the Sgs1-dependent pathway facilitating S phase progression. Thus, in the absence of Uls1 other modes of replication fork processing and repair are employed.
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Affiliation(s)
- Magdalena Cal-Bakowska
- Institute of Plant Biology, Faculty of Biological Sciences, University of Wrocław, 50-328 Wrocław, Poland
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Stead BE, Brandl CJ, Davey MJ. Phosphorylation of Mcm2 modulates Mcm2-7 activity and affects the cell's response to DNA damage. Nucleic Acids Res 2011; 39:6998-7008. [PMID: 21596784 PMCID: PMC3167627 DOI: 10.1093/nar/gkr371] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The S-phase kinase, DDK controls DNA replication through phosphorylation of the replicative helicase, Mcm2–7. We show that phosphorylation of Mcm2 at S164 and S170 is not essential for viability. However, the relevance of Mcm2 phosphorylation is demonstrated by the sensitivity of a strain containing alanine at these positions (mcm2AA) to methyl methanesulfonate (MMS) and caffeine. Consistent with a role for Mcm2 phosphorylation in response to DNA damage, the mcm2AA strain accumulates more RPA foci than wild type. An allele with the phosphomimetic mutations S164E and S170E (mcm2EE) suppresses the MMS and caffeine sensitivity caused by deficiencies in DDK function. In vitro, phosphorylation of Mcm2 or Mcm2EE reduces the helicase activity of Mcm2–7 while increasing DNA binding. The reduced helicase activity likely results from the increased DNA binding since relaxing DNA binding with salt restores helicase activity. The finding that the ATP site mutant mcm2K549R has higher DNA binding and less ATPase than mcm2EE, but like mcm2AA results in drug sensitivity, supports a model whereby a specific range of Mcm2–7 activity is required in response to MMS and caffeine. We propose that phosphorylation of Mcm2 fine-tunes the activity of Mcm2–7, which in turn modulates DNA replication in response to DNA damage.
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Affiliation(s)
- Brent E Stead
- Department of Biochemistry, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada, N6A 5C1
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Abstract
The RecQ helicases are conserved from bacteria to humans and play a critical role in genome stability. In humans, loss of RecQ gene function is associated with cancer predisposition and/or premature aging. Recent experiments have shown that the RecQ helicases function during distinct steps during DNA repair; DNA end resection, displacement-loop (D-loop) processing, branch migration, and resolution of double Holliday junctions (dHJs). RecQ function in these different processing steps has important implications for its role in repair of double-strand breaks (DSBs) that occur during DNA replication and meiosis, as well as at specific genomic loci such as telomeres.
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Affiliation(s)
- Kara A Bernstein
- Columbia University Medical Center, Department of Genetics & Development, New York, New York 10032, USA.
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Chavez A, Agrawal V, Johnson FB. Homologous recombination-dependent rescue of deficiency in the structural maintenance of chromosomes (Smc) 5/6 complex. J Biol Chem 2010; 286:5119-25. [PMID: 21138837 DOI: 10.1074/jbc.m110.201608] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The essential and evolutionarily conserved Smc5-Smc6 complex (Smc5/6) is critical for the maintenance of genome stability. Partial loss of Smc5/6 function yields several defects in DNA repair, which are rescued by inactivation of the homologous recombination (HR) machinery. Thus HR is thought to be toxic to cells with defective Smc5/6. Recent work has highlighted a role for Smc5/6 and the Sgs1 DNA helicase in preventing the accumulation of unresolved HR intermediates. Here we investigate how deletion of MPH1, encoding the orthologue of the human FANCM DNA helicase, rescues the DNA damage sensitivity of smc5/6 but not sgs1Δ mutants. We find that MPH1 deletion diminishes accumulation of HR intermediates within both smc5/6 and sgs1Δ cells, suggesting that MPH1 deletion is sufficient to decrease the use of template switch recombination (TSR) to bypass DNA lesions. We further explain how avoidance of TSR is nonetheless insufficient to rescue defects in sgs1Δ mutants, by demonstrating a requirement for Sgs1, along with the post-replicative repair (PRR) and HR machinery, in a pathway that operates in mph1Δ mutants. In addition, we map the region of Mph1 that binds Smc5, and describe a novel allele of MPH1 encoding a protein unable to bind Smc5 (mph1-Δ60). Remarkably, mph1-Δ60 supports normal growth and responses to DNA damaging agents, indicating that Smc5/6 does not simply restrain the recombinogenic activity of Mph1 via direct binding. These data as a whole highlight a role for Smc5/6 and Sgs1 in the resolution of Mph1-dependent HR intermediates.
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Affiliation(s)
- Alejandro Chavez
- Department of Pathology and Laboratory Medicine., University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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Sgs1 truncations induce genome rearrangements but suppress detrimental effects of BLM overexpression in Saccharomyces cerevisiae. J Mol Biol 2010; 405:877-91. [PMID: 21111748 DOI: 10.1016/j.jmb.2010.11.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Revised: 11/09/2010] [Accepted: 11/16/2010] [Indexed: 11/23/2022]
Abstract
RecQ-like DNA helicases are conserved from bacteria to humans. They perform functions in the maintenance of genome stability, and their mutation is associated with cancer predisposition and premature aging syndromes in humans. Here, a series of C-terminal deletions and point mutations of Sgs1, the only RecQ-like helicase in yeast, show that the Helicase/RNase D C-terminal domain and the Rad51 interaction domain are dispensable for Sgs1's role in suppressing genome instability, whereas the zinc-binding domain and the helicase domain are required. BLM expression from the native SGS1 promoter had no adverse effects on cell growth and was unable to complement any sgs1Δ defects. BLM overexpression, however, significantly increased the rate of accumulating gross-chromosomal rearrangements in a dosage-dependent manner and greatly exacerbated sensitivity to DNA-damaging agents. Co-expressing sgs1 truncations of up to 900 residues, lacking all known functional domains of Sgs1, suppressed the hydroxyurea sensitivity of BLM-overexpressing cells, suggesting a functional relationship between Sgs1 and BLM. Protein disorder prediction analysis of Sgs1 and BLM was used to produce a functional Sgs1-BLM chimera by replacing the N-terminus of BLM with the disordered N-terminus of Sgs1. The functionality of this chimera suggests that it is the disordered N-terminus, a site of protein binding and posttranslational modification, that confers species specificity to these two RecQ-like proteins.
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Vanoli F, Fumasoni M, Szakal B, Maloisel L, Branzei D. Replication and recombination factors contributing to recombination-dependent bypass of DNA lesions by template switch. PLoS Genet 2010; 6:e1001205. [PMID: 21085632 PMCID: PMC2978687 DOI: 10.1371/journal.pgen.1001205] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Accepted: 10/13/2010] [Indexed: 02/06/2023] Open
Abstract
Damage tolerance mechanisms mediating damage-bypass and gap-filling are crucial for genome integrity. A major damage tolerance pathway involves recombination and is referred to as template switch. Template switch intermediates were visualized by 2D gel electrophoresis in the proximity of replication forks as X-shaped structures involving sister chromatid junctions. The homologous recombination factor Rad51 is required for the formation/stabilization of these intermediates, but its mode of action remains to be investigated. By using a combination of genetic and physical approaches, we show that the homologous recombination factors Rad55 and Rad57, but not Rad59, are required for the formation of template switch intermediates. The replication-proficient but recombination-defective rfa1-t11 mutant is normal in triggering a checkpoint response following DNA damage but is impaired in X-structure formation. The Exo1 nuclease also has stimulatory roles in this process. The checkpoint kinase, Rad53, is required for X-molecule formation and phosphorylates Rad55 robustly in response to DNA damage. Although Rad55 phosphorylation is thought to activate recombinational repair under conditions of genotoxic stress, we find that Rad55 phosphomutants do not affect the efficiency of X-molecule formation. We also examined the DNA polymerase implicated in the DNA synthesis step of template switch. Deficiencies in translesion synthesis polymerases do not affect X-molecule formation, whereas DNA polymerase δ, required also for bulk DNA synthesis, plays an important role. Our data indicate that a subset of homologous recombination factors, together with DNA polymerase δ, promote the formation of template switch intermediates that are then preferentially dissolved by the action of the Sgs1 helicase in association with the Top3 topoisomerase rather than resolved by Holliday Junction nucleases. Our results allow us to propose the choreography through which different players contribute to template switch in response to DNA damage and to distinguish this process from other recombination-mediated processes promoting DNA repair. Completion of DNA replication is essential for cellular survival. Both endogenous processes and exogenous DNA damage can lead to lesions that impede DNA replication or result in an accumulation of DNA gaps. Recombination plays an important role in facilitating replication completion under conditions of replication stress or DNA damage. One DNA damage tolerance mechanism involving recombination factors, template switch, uses the information on the newly synthesized sister chromatid to fill in the gaps arising during replication under damaging conditions. This process leads to the formation of repair structures involving sister chromatid junctions in the proximity of replication forks. The template switch structures can be detected by 2D gel electrophoresis of replication intermediates as cruciform, X-shaped intermediates. Additional factors and regulatory pathways are required for the resolution of such structures to prevent their toxic effects. In this work, we have dissected the recombination/replication factors required for the formation of template switch intermediates. Another recombination mechanism, which has been implicated in the restart of collapsed forks, is break-induced replication (BIR). This study allows us to identify the core factors required for template switch and to distinguish this process from other recombination-mediated processes promoting DNA repair.
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Affiliation(s)
- Fabio Vanoli
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan, Italy
| | - Marco Fumasoni
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan, Italy
- Università degli Studi di Milano, Milan, Italy
| | - Barnabas Szakal
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan, Italy
| | - Laurent Maloisel
- CEA, DSV, iRCM, SIGRR, LRGM, and CNRS, UMR 217, Fontenay-aux-Roses, France
| | - Dana Branzei
- Fondazione IFOM, Istituto FIRC di Oncologia Molecolare, Milan, Italy
- * E-mail:
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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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Marrero VA, Symington LS. Extensive DNA end processing by exo1 and sgs1 inhibits break-induced replication. PLoS Genet 2010; 6:e1001007. [PMID: 20628570 PMCID: PMC2900301 DOI: 10.1371/journal.pgen.1001007] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Accepted: 05/27/2010] [Indexed: 11/18/2022] Open
Abstract
Homology-dependent repair of DNA double-strand breaks (DSBs) by gene conversion involves short tracts of DNA synthesis and limited loss of heterozygosity (LOH). For DSBs that present only one end, repair occurs by invasion into a homologous sequence followed by replication to the end of the chromosome resulting in extensive LOH, a process called break-induced replication (BIR). We developed a BIR assay in Saccharomyces cerevisiae consisting of a plasmid with a telomere seeding sequence separated from sequence homologous to chromosome III by an I-SceI endonuclease recognition site. Following cleavage of the plasmid by I-SceI in vivo, de novo telomere synthesis occurs at one end of the vector, and the other end invades at the homologous sequence on chromosome III and initiates replication to the end of the chromosome to generate a stable chromosome fragment (CF). BIR was infrequent in wild-type cells due to degradation of the linearized vector. However, in the exo1Δ sgs1Δ mutant, which is defective in the 5′-3′ resection of DSBs, the frequency of BIR was increased by 39-fold. Extension of the invading end of the plasmid was detected by physical analysis two hours after induction of the I-SceI endonuclease in the wild-type exo1Δ, sgs1Δ, and exo1Δ sgs1Δ mutants, but fully repaired products were only visible in the exo1Δ sgs1Δ mutant. The inhibitory effect of resection was less in a plasmid-chromosome gene conversion assay, compared to BIR, and products were detected by physical assay in the wild-type strain. The rare chromosome rearrangements due to BIR template switching at repeated sequences were increased in the exo1Δ sgs1Δ mutant, suggesting that reduced resection can decrease the fidelity of homologous recombination. DNA double-strand breaks (DSBs) can occur spontaneously in cells by defective DNA replication or are induced by various types of DNA damaging agents, such as those used in chemo- or radiation therapy. Failure to repair DSBs, or inappropriate repair, can result in chromosome loss or chromosome rearrangements, events associated with development of cancer cells. Typically, DNA DSBs have two ends that are reunited faithfully by copying from a homologous donor chromosome. For DSBs that present only one end, repair occurs by invasion into a homologous sequence followed by replication to the end of the chromosome, a process called break-induced replication (BIR). This repair pathway is thought to be suppressed at two-ended DSBs to prevent extensive loss of heterozygosity. Here, we describe a new assay to physically monitor BIR to see how this repair pathway differs from the repair of two-ended DSBs. We show this pathway is infrequent, but can be detected by eliminating factors (Exo1 and Sgs1) that degrade linear DNA. However, increased chromosome rearrangements were found in the resection-defective strain. We found the kinetics of strand invasion in two-ended and one-ended DSB repair were the same, suggesting that the distinction between these pathways occurs after initial repair steps have begun.
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Affiliation(s)
- Vanessa A. Marrero
- Department of Genetics and Development, Columbia University Medical Center, New York, New York, United States of America
| | - Lorraine S. Symington
- Department of Microbiology and Immunology, Columbia University Medical Center New York, New York, United States of America
- * E-mail:
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50
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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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