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Jones CE, Forsburg SL. Monitoring Schizosaccharomyces pombe genome stress by visualizing end-binding protein Ku. Biol Open 2021; 10:bio.054346. [PMID: 33579693 PMCID: PMC7904001 DOI: 10.1242/bio.054346] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Studies of genome stability have exploited visualization of fluorescently tagged proteins in live cells to characterize DNA damage, checkpoint, and repair responses. In this report, we describe a new tool for fission yeast, a tagged version of the end-binding protein Pku70 which is part of the KU protein complex. We compare Pku70 localization to other markers upon treatment to various genotoxins, and identify a unique pattern of distribution. Pku70 provides a new tool to define and characterize DNA lesions and the repair response. Summary: The authors describe a fluorescently tagged Ku70 protein to monitor replication stress in live S. pombe cells.
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Affiliation(s)
- Chance E Jones
- Program in Molecular & Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
| | - Susan L Forsburg
- Program in Molecular & Computational Biology, University of Southern California, Los Angeles, CA 90089, USA
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2
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Yue X, Bai C, Xie D, Ma T, Zhou PK. DNA-PKcs: A Multi-Faceted Player in DNA Damage Response. Front Genet 2020; 11:607428. [PMID: 33424929 PMCID: PMC7786053 DOI: 10.3389/fgene.2020.607428] [Citation(s) in RCA: 88] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 12/01/2020] [Indexed: 12/17/2022] Open
Abstract
DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a member of the phosphatidylinositol 3-kinase related kinase family, which can phosphorylate more than 700 substrates. As the core enzyme, DNA-PKcs forms the active DNA-PK holoenzyme with the Ku80/Ku70 heterodimer to play crucial roles in cellular DNA damage response (DDR). Once DNA double strand breaks (DSBs) occur in the cells, DNA-PKcs is promptly recruited into damage sites and activated. DNA-PKcs is auto-phosphorylated and phosphorylated by Ataxia-Telangiectasia Mutated at multiple sites, and phosphorylates other targets, participating in a series of DDR and repair processes, which determine the cells' fates: DSBs NHEJ repair and pathway choice, replication stress response, cell cycle checkpoints, telomeres length maintenance, senescence, autophagy, etc. Due to the special and multi-faceted roles of DNA-PKcs in the cellular responses to DNA damage, it is important to precisely regulate the formation and dynamic of its functional complex and activities for guarding genomic stability. On the other hand, targeting DNA-PKcs has been considered as a promising strategy of exploring novel radiosensitizers and killing agents of cancer cells. Combining DNA-PKcs inhibitors with radiotherapy can effectively enhance the efficacy of radiotherapy, offering more possibilities for cancer therapy.
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Affiliation(s)
- Xiaoqiao Yue
- School of Public Health, University of South China, Hengyang, China.,Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing, China
| | - Chenjun Bai
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing, China
| | - Dafei Xie
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing, China
| | - Teng Ma
- Department of Cellular and Molecular Biology, Beijing Chest Hospital, Capital Medical University/Beijing Tuberculosis and Thoracic Tumor Research Institute, Beijing, China
| | - Ping-Kun Zhou
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, Beijing, China
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Schizosaccharomyces pombe Assays to Study Mitotic Recombination Outcomes. Genes (Basel) 2020; 11:genes11010079. [PMID: 31936815 PMCID: PMC7016768 DOI: 10.3390/genes11010079] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 01/07/2020] [Accepted: 01/07/2020] [Indexed: 01/16/2023] Open
Abstract
The fission yeast—Schizosaccharomyces pombe—has emerged as a powerful tractable system for studying DNA damage repair. Over the last few decades, several powerful in vivo genetic assays have been developed to study outcomes of mitotic recombination, the major repair mechanism of DNA double strand breaks and stalled or collapsed DNA replication forks. These assays have significantly increased our understanding of the molecular mechanisms underlying the DNA damage response pathways. Here, we review the assays that have been developed in fission yeast to study mitotic recombination.
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Toma M, Sullivan-Reed K, Śliwiński T, Skorski T. RAD52 as a Potential Target for Synthetic Lethality-Based Anticancer Therapies. Cancers (Basel) 2019; 11:E1561. [PMID: 31615159 PMCID: PMC6827130 DOI: 10.3390/cancers11101561] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 10/11/2019] [Accepted: 10/11/2019] [Indexed: 12/15/2022] Open
Abstract
Alterations in DNA repair systems play a key role in the induction and progression of cancer. Tumor-specific defects in DNA repair mechanisms and activation of alternative repair routes create the opportunity to employ a phenomenon called "synthetic lethality" to eliminate cancer cells. Targeting the backup pathways may amplify endogenous and drug-induced DNA damage and lead to specific eradication of cancer cells. So far, the synthetic lethal interaction between BRCA1/2 and PARP1 has been successfully applied as an anticancer treatment. Although PARP1 constitutes a promising target in the treatment of tumors harboring deficiencies in BRCA1/2-mediated homologous recombination (HR), some tumor cells survive, resulting in disease relapse. It has been suggested that alternative RAD52-mediated HR can protect BRCA1/2-deficient cells from the accumulation of DNA damage and the synthetic lethal effect of PARPi. Thus, simultaneous inhibition of RAD52 and PARP1 might result in a robust dual synthetic lethality, effectively eradicating BRCA1/2-deficient tumor cells. In this review, we will discuss the role of RAD52 and its potential application in synthetic lethality-based anticancer therapies.
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Affiliation(s)
- Monika Toma
- Sol Sherry Thrombosis Research Center and Fels Institute for Cancer Research and Molecular Biology Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.
- Laboratory of Medical Genetics Faculty of Biology and Environmental Protection, University of Lodz, 90-236 Lodz, Poland.
| | - Katherine Sullivan-Reed
- Sol Sherry Thrombosis Research Center and Fels Institute for Cancer Research and Molecular Biology Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.
| | - Tomasz Śliwiński
- Laboratory of Medical Genetics Faculty of Biology and Environmental Protection, University of Lodz, 90-236 Lodz, Poland.
| | - Tomasz Skorski
- Sol Sherry Thrombosis Research Center and Fels Institute for Cancer Research and Molecular Biology Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.
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Hromas R, Kim HS, Sidhu G, Williamson E, Jaiswal A, Totterdale TA, Nole J, Lee SH, Nickoloff JA, Kong KY. The endonuclease EEPD1 mediates synthetic lethality in RAD52-depleted BRCA1 mutant breast cancer cells. Breast Cancer Res 2017; 19:122. [PMID: 29145865 PMCID: PMC5693420 DOI: 10.1186/s13058-017-0912-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2017] [Accepted: 10/30/2017] [Indexed: 02/06/2023] Open
Abstract
Background Proper repair and restart of stressed replication forks requires intact homologous recombination (HR). HR at stressed replication forks can be initiated by the 5′ endonuclease EEPD1, which cleaves the stalled replication fork. Inherited or acquired defects in HR, such as mutations in breast cancer susceptibility protein-1 (BRCA1) or BRCA2, predispose to cancer, including breast and ovarian cancers. In order for these HR-deficient tumor cells to proliferate, they become addicted to a bypass replication fork repair pathway mediated by radiation repair protein 52 (RAD52). Depleting RAD52 can cause synthetic lethality in BRCA1/2 mutant cancers by an unknown molecular mechanism. Methods We hypothesized that cleavage of stressed replication forks by EEPD1 generates a fork repair intermediate that is toxic when HR-deficient cells cannot complete repair with the RAD52 bypass pathway. To test this hypothesis, we applied cell survival assays, immunofluorescence staining, DNA fiber and western blot analyses to look at the correlation between cell survival and genome integrity in control, EEPD1, RAD52 and EEPD1/RAD52 co-depletion BRCA1-deficient breast cancer cells. Results Our data show that depletion of EEPD1 suppresses synthetic lethality, genome instability, mitotic catastrophe, and hypersensitivity to stress of replication of RAD52-depleted, BRCA1 mutant breast cancer cells. Without HR and the RAD52-dependent backup pathway, the BRCA1 mutant cancer cells depleted of EEPD1 skew to the alternative non-homologous end-joining DNA repair pathway for survival. Conclusion This study indicates that the mechanism of synthetic lethality in RAD52-depleted BRCA1 mutant cancer cells depends on the endonuclease EEPD1. The data imply that EEPD1 cleavage of stressed replication forks may result in a toxic intermediate when replication fork repair cannot be completed. Electronic supplementary material The online version of this article (doi:10.1186/s13058-017-0912-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Robert Hromas
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA.
| | - Hyun-Suk Kim
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Gurjit Sidhu
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA
| | - Elizabeth Williamson
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA
| | - Aruna Jaiswal
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA
| | - Taylor A Totterdale
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA
| | - Jocelyn Nole
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA
| | - Suk-Hee Lee
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Jac A Nickoloff
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Kimi Y Kong
- Department of Medicine and the Cancer Center, University of Florida Health, 1600 SW Archer Rd, Gainesville, FL, 32610, USA.
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Multi-BRCT Domain Protein Brc1 Links Rhp18/Rad18 and γH2A To Maintain Genome Stability during S Phase. Mol Cell Biol 2017; 37:MCB.00260-17. [PMID: 28784724 DOI: 10.1128/mcb.00260-17] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 08/04/2017] [Indexed: 12/17/2022] Open
Abstract
DNA replication involves the inherent risk of genome instability, since replisomes invariably encounter DNA lesions or other structures that stall or collapse replication forks during the S phase. In the fission yeast Schizosaccharomyces pombe, the multi-BRCT domain protein Brc1, which is related to budding yeast Rtt107 and mammalian PTIP, plays an important role in maintaining genome integrity and cell viability when cells experience replication stress. The C-terminal pair of BRCT domains in Brc1 were previously shown to bind phosphohistone H2A (γH2A) formed by Rad3/ATR checkpoint kinase at DNA lesions; however, the putative scaffold interactions involving the N-terminal BRCT domains 1 to 4 of Brc1 have remained obscure. Here, we show that these domains bind Rhp18/Rad18, which is an E3 ubiquitin protein ligase that has crucial functions in postreplication repair. A missense allele in BRCT domain 4 of Brc1 disrupts binding to Rhp18 and causes sensitivity to replication stress. Brc1 binding to Rhp18 and γH2A are required for the Brc1 overexpression suppression of smc6-74, a mutation that impairs the Smc5/6 structural maintenance of chromosomes complex required for chromosome integrity and repair of collapsed replication forks. From these findings, we propose that Brc1 provides scaffolding functions linking γH2A, Rhp18, and Smc5/6 complex at damaged replication forks.
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Sanchez A, Gadaleta MC, Limbo O, Russell P. Lingering single-strand breaks trigger Rad51-independent homology-directed repair of collapsed replication forks in the polynucleotide kinase/phosphatase mutant of fission yeast. PLoS Genet 2017; 13:e1007013. [PMID: 28922417 PMCID: PMC5626526 DOI: 10.1371/journal.pgen.1007013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 10/03/2017] [Accepted: 09/08/2017] [Indexed: 11/19/2022] Open
Abstract
The DNA repair enzyme polynucleotide kinase/phosphatase (PNKP) protects genome integrity by restoring ligatable 5'-phosphate and 3'-hydroxyl termini at single-strand breaks (SSBs). In humans, PNKP mutations underlie the neurological disease known as MCSZ, but these individuals are not predisposed for cancer, implying effective alternative repair pathways in dividing cells. Homology-directed repair (HDR) of collapsed replication forks was proposed to repair SSBs in PNKP-deficient cells, but the critical HDR protein Rad51 is not required in PNKP-null (pnk1Δ) cells of Schizosaccharomyces pombe. Here, we report that pnk1Δ cells have enhanced requirements for Rad3 (ATR/Mec1) and Chk1 checkpoint kinases, and the multi-BRCT domain protein Brc1 that binds phospho-histone H2A (γH2A) at damaged replication forks. The viability of pnk1Δ cells depends on Mre11 and Ctp1 (CtIP/Sae2) double-strand break (DSB) resection proteins, Rad52 DNA strand annealing protein, Mus81-Eme1 Holliday junction resolvase, and Rqh1 (BLM/WRN/Sgs1) DNA helicase. Coupled with increased sister chromatid recombination and Rad52 repair foci in pnk1Δ cells, these findings indicate that lingering SSBs in pnk1Δ cells trigger Rad51-independent homology-directed repair of collapsed replication forks. From these data, we propose models for HDR-mediated tolerance of persistent SSBs with 3' phosphate in pnk1Δ cells.
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Affiliation(s)
- Arancha Sanchez
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, United States of America
| | - Mariana C. Gadaleta
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, United States of America
| | - Oliver Limbo
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, United States of America
| | - Paul Russell
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, United States of America
- * E-mail:
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Yadav RK, Jablonowski CM, Fernandez AG, Lowe BR, Henry RA, Finkelstein D, Barnum KJ, Pidoux AL, Kuo YM, Huang J, O’Connell MJ, Andrews AJ, Onar-Thomas A, Allshire RC, Partridge JF. Histone H3G34R mutation causes replication stress, homologous recombination defects and genomic instability in S. pombe. eLife 2017; 6:e27406. [PMID: 28718400 PMCID: PMC5515577 DOI: 10.7554/elife.27406] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2017] [Accepted: 06/20/2017] [Indexed: 12/12/2022] Open
Abstract
Recurrent somatic mutations of H3F3A in aggressive pediatric high-grade gliomas generate K27M or G34R/V mutant histone H3.3. H3.3-G34R/V mutants are common in tumors with mutations in p53 and ATRX, an H3.3-specific chromatin remodeler. To gain insight into the role of H3-G34R, we generated fission yeast that express only the mutant histone H3. H3-G34R specifically reduces H3K36 tri-methylation and H3K36 acetylation, and mutants show partial transcriptional overlap with set2 deletions. H3-G34R mutants exhibit genomic instability and increased replication stress, including slowed replication fork restart, although DNA replication checkpoints are functional. H3-G34R mutants are defective for DNA damage repair by homologous recombination (HR), and have altered HR protein dynamics in both damaged and untreated cells. These data suggest H3-G34R slows resolution of HR-mediated repair and that unresolved replication intermediates impair chromosome segregation. This analysis of H3-G34R mutant fission yeast provides mechanistic insight into how G34R mutation may promote genomic instability in glioma.
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Affiliation(s)
- Rajesh K Yadav
- Department of Pathology, St. Jude Children’s Research Hospital, Memphis, United States
| | - Carolyn M Jablonowski
- Department of Pathology, St. Jude Children’s Research Hospital, Memphis, United States
| | - Alfonso G Fernandez
- Department of Pathology, St. Jude Children’s Research Hospital, Memphis, United States
| | - Brandon R Lowe
- Department of Pathology, St. Jude Children’s Research Hospital, Memphis, United States
| | - Ryan A Henry
- Department of Cancer Biology, Fox Chase Cancer Center, Philadelphia, United States
| | - David Finkelstein
- Department of Bioinformatics, St. Jude Children’s Research Hospital, Memphis, United States
| | - Kevin J Barnum
- Department of Oncological Sciences and Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, United States
| | - Alison L Pidoux
- Wellcome Trust School for Biological Sciences, University of Edinburgh, Edinburgh, Scotland
| | - Yin-Ming Kuo
- Department of Cancer Biology, Fox Chase Cancer Center, Philadelphia, United States
| | - Jie Huang
- Department of Biostatistics, St. Jude Children’s Research Hospital, Memphis, United States
| | - Matthew J O’Connell
- Department of Oncological Sciences and Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, United States
| | - Andrew J Andrews
- Department of Cancer Biology, Fox Chase Cancer Center, Philadelphia, United States
| | - Arzu Onar-Thomas
- Department of Biostatistics, St. Jude Children’s Research Hospital, Memphis, United States
| | - Robin C Allshire
- Wellcome Trust School for Biological Sciences, University of Edinburgh, Edinburgh, Scotland
| | - Janet F Partridge
- Department of Pathology, St. Jude Children’s Research Hospital, Memphis, United States
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Zabrady K, Adamus M, Vondrova L, Liao C, Skoupilova H, Novakova M, Jurcisinova L, Alt A, Oliver AW, Lehmann AR, Palecek JJ. Chromatin association of the SMC5/6 complex is dependent on binding of its NSE3 subunit to DNA. Nucleic Acids Res 2016; 44:1064-79. [PMID: 26446992 PMCID: PMC4756808 DOI: 10.1093/nar/gkv1021] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 09/23/2015] [Accepted: 09/26/2015] [Indexed: 11/13/2022] Open
Abstract
SMC5/6 is a highly conserved protein complex related to cohesin and condensin, which are the key components of higher-order chromatin structures. The SMC5/6 complex is essential for proliferation in yeast and is involved in replication fork stability and processing. However, the precise mechanism of action of SMC5/6 is not known. Here we present evidence that the NSE1/NSE3/NSE4 sub-complex of SMC5/6 binds to double-stranded DNA without any preference for DNA-replication/recombination intermediates. Mutations of key basic residues within the NSE1/NSE3/NSE4 DNA-binding surface reduce binding to DNA in vitro. Their introduction into the Schizosaccharomyces pombe genome results in cell death or hypersensitivity to DNA damaging agents. Chromatin immunoprecipitation analysis of the hypomorphic nse3 DNA-binding mutant shows a reduced association of fission yeast SMC5/6 with chromatin. Based on our results, we propose a model for loading of the SMC5/6 complex onto the chromatin.
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Affiliation(s)
- Katerina Zabrady
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, Brno, 62500, Czech Republic Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
| | - Marek Adamus
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, Brno, 62500, Czech Republic
| | - Lucie Vondrova
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, Brno, 62500, Czech Republic Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
| | - Chunyan Liao
- Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton BN1 9RQ, United Kingdom
| | - Hana Skoupilova
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
| | - Marketa Novakova
- Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
| | - Lenka Jurcisinova
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, Brno, 62500, Czech Republic Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
| | - Aaron Alt
- Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton BN1 9RQ, United Kingdom
| | - Antony W Oliver
- Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton BN1 9RQ, United Kingdom
| | - Alan R Lehmann
- Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton BN1 9RQ, United Kingdom
| | - Jan J Palecek
- Mendel Centre for Plant Genomics and Proteomics, Central European Institute of Technology, Masaryk University, Kamenice 5, Brno, 62500, Czech Republic Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlarska 2, Brno, 61137, Czech Republic
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Wu Y, Lee SH, Williamson EA, Reinert BL, Cho JH, Xia F, Jaiswal AS, Srinivasan G, Patel B, Brantley A, Zhou D, Shao L, Pathak R, Hauer-Jensen M, Singh S, Kong K, Wu X, Kim HS, Beissbarth T, Gaedcke J, Burma S, Nickoloff JA, Hromas RA. EEPD1 Rescues Stressed Replication Forks and Maintains Genome Stability by Promoting End Resection and Homologous Recombination Repair. PLoS Genet 2015; 11:e1005675. [PMID: 26684013 PMCID: PMC4684289 DOI: 10.1371/journal.pgen.1005675] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 10/26/2015] [Indexed: 12/13/2022] Open
Abstract
Replication fork stalling and collapse is a major source of genome instability leading to neoplastic transformation or cell death. Such stressed replication forks can be conservatively repaired and restarted using homologous recombination (HR) or non-conservatively repaired using micro-homology mediated end joining (MMEJ). HR repair of stressed forks is initiated by 5’ end resection near the fork junction, which permits 3’ single strand invasion of a homologous template for fork restart. This 5’ end resection also prevents classical non-homologous end-joining (cNHEJ), a competing pathway for DNA double-strand break (DSB) repair. Unopposed NHEJ can cause genome instability during replication stress by abnormally fusing free double strand ends that occur as unstable replication fork repair intermediates. We show here that the previously uncharacterized Exonuclease/Endonuclease/Phosphatase Domain-1 (EEPD1) protein is required for initiating repair and restart of stalled forks. EEPD1 is recruited to stalled forks, enhances 5’ DNA end resection, and promotes restart of stalled forks. Interestingly, EEPD1 directs DSB repair away from cNHEJ, and also away from MMEJ, which requires limited end resection for initiation. EEPD1 is also required for proper ATR and CHK1 phosphorylation, and formation of gamma-H2AX, RAD51 and phospho-RPA32 foci. Consistent with a direct role in stalled replication fork cleavage, EEPD1 is a 5’ overhang nuclease in an obligate complex with the end resection nuclease Exo1 and BLM. EEPD1 depletion causes nuclear and cytogenetic defects, which are made worse by replication stress. Depleting 53BP1, which slows cNHEJ, fully rescues the nuclear and cytogenetic abnormalities seen with EEPD1 depletion. These data demonstrate that genome stability during replication stress is maintained by EEPD1, which initiates HR and inhibits cNHEJ and MMEJ. The cell itself damages its own DNA throughout the cell cycle as a result of oxidative metabolism, and this damage creates barriers for replication fork progression. Thus, DNA replication is not a smooth and continuous process, but rather one of stalls and restarts. Therefore, proper replication fork restart is crucial to maintain the integrity of the cell’s genome, and preventing its own death or immortalization. To restart after stalling, the replication fork subverts a DNA repair pathway termed homologous recombination. Using any other pathway for fork repair will result in an unstable genome. How the homologous recombination repair pathway is initiated at the replication fork is not well defined. In this study we demonstrate the previously uncharacterized EEPD1 protein is a novel gatekeeper for the initiation of this fork repair pathway. EEPD1 promotes 5’ end resection, the initial step of homologous recombination, which also prevents alternative fork repair pathways that lead to unstable chromosomes. Thus, EEPD1 protects the integrity of the cell genome by promoting the safe homologous recombination fork repair pathway.
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Affiliation(s)
- Yuehan Wu
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Suk-Hee Lee
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Elizabeth A. Williamson
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Brian L. Reinert
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Ju Hwan Cho
- Department of Radiation Oncology, Comprehensive Cancer Center, The Ohio State University, Columbus, Ohio, United States of America
| | - Fen Xia
- Department of Radiation Oncology, Comprehensive Cancer Center, The Ohio State University, Columbus, Ohio, United States of America
| | - Aruna Shanker Jaiswal
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Gayathri Srinivasan
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Bhavita Patel
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Alexis Brantley
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Daohong Zhou
- Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - Lijian Shao
- Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - Rupak Pathak
- Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - Martin Hauer-Jensen
- Department of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - Sudha Singh
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
| | - Kimi Kong
- Department of Craniofacial Regeneration, College of Dental Medicine, Columbia University, New York, New York, United States of America
| | - Xaiohua Wu
- Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California, United States of America
| | - Hyun-Suk Kim
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Timothy Beissbarth
- Department of Medical Statistics, and General, Visceral, and Pediatric Surgery, University Medical Center Göttingen, Göttingen, Germany
| | - Jochen Gaedcke
- Department of Medical Statistics, and General, Visceral, and Pediatric Surgery, University Medical Center Göttingen, Göttingen, Germany
| | - Sandeep Burma
- Department of Radiation Oncology, University of Texas Southwestern, Dallas, Texas, United States of America
| | - Jac A. Nickoloff
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- * E-mail: (JAN); (RAH)
| | - Robert A. Hromas
- Department of Medicine and the Cancer Center, University of Florida Health, Gainesville, Florida, United States of America
- * E-mail: (JAN); (RAH)
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Rtt107 BRCT domains act as a targeting module in the DNA damage response. DNA Repair (Amst) 2015; 37:22-32. [PMID: 26641499 DOI: 10.1016/j.dnarep.2015.10.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 01/11/2023]
Abstract
Cells are constantly exposed to assaults that cause DNA damage, which must be detected and repaired to prevent genome instability. The DNA damage response is mediated by key kinases that activate various signaling pathways. In Saccharomyces cerevisiae, one of these kinases is Mec1, which phosphorylates numerous targets, including H2A and the DNA damage protein Rtt107. In addition to being phosphorylated, Rtt107 contains six BRCA1 C-terminal (BRCT) domains, which typically recognize phospho-peptides. Thus Rtt107 represented an opportunity to study complementary aspects of the phosphorylation cascades within one protein. Here we sought to describe the functional roles of the multiple BRCT domains in Rtt107. Rtt107 BRCT5/6 facilitated recruitment to sites of DNA lesions via its interaction with phosphorylated H2A. Rtt107 BRCT3/4 also contributed to Rtt107 recruitment, but BRCT3/4 was not sufficient for recruitment when BRCT5/6 was absent. Intriguingly, both mutations that affected Rtt107 recruitment also abrogated its phosphorylation. Pointing to its modular nature, replacing Rtt107 BRCT5/6 with the BRCT domains from the checkpoint protein Rad9 was able to sustain Rtt107 function. Although Rtt107 physically interacts with both the endonuclease Slx4 and the DNA replication and repair protein Dpb11, only Slx4 was dependent on Rtt107 for its recruitment to DNA lesions. Fusing Rtt107 BRCT5/6 to Slx4, which presumably allows artificial recruitment of Slx4 to DNA lesions, alleviated some phenotypes of rtt107Δ mutants, indicating the functional importance of Slx4 recruitment. Together this data revealed a key function of the Rtt107 BRCT domains for targeting of both itself and its interaction partners to DNA lesions.
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12
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Managing Single-Stranded DNA during Replication Stress in Fission Yeast. Biomolecules 2015; 5:2123-39. [PMID: 26393661 PMCID: PMC4598791 DOI: 10.3390/biom5032123] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Revised: 08/28/2015] [Accepted: 09/01/2015] [Indexed: 01/27/2023] Open
Abstract
Replication fork stalling generates a variety of responses, most of which cause an increase in single-stranded DNA. ssDNA is a primary signal of replication distress that activates cellular checkpoints. It is also a potential source of genome instability and a substrate for mutation and recombination. Therefore, managing ssDNA levels is crucial to chromosome integrity. Limited ssDNA accumulation occurs in wild-type cells under stress. In contrast, cells lacking the replication checkpoint cannot arrest forks properly and accumulate large amounts of ssDNA. This likely occurs when the replication fork polymerase and helicase units are uncoupled. Some cells with mutations in the replication helicase (mcm-ts) mimic checkpoint-deficient cells, and accumulate extensive areas of ssDNA to trigger the G2-checkpoint. Another category of helicase mutant (mcm4-degron) causes fork stalling in early S-phase due to immediate loss of helicase function. Intriguingly, cells realize that ssDNA is present, but fail to detect that they accumulate ssDNA, and continue to divide. Thus, the cellular response to replication stalling depends on checkpoint activity and the time that replication stress occurs in S-phase. In this review we describe the signs, signals, and symptoms of replication arrest from an ssDNA perspective. We explore the possible mechanisms for these effects. We also advise the need for caution when detecting and interpreting data related to the accumulation of ssDNA.
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13
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Mejia-Ramirez E, Limbo O, Langerak P, Russell P. Critical Function of γH2A in S-Phase. PLoS Genet 2015; 11:e1005517. [PMID: 26368543 PMCID: PMC4569340 DOI: 10.1371/journal.pgen.1005517] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 08/20/2015] [Indexed: 11/24/2022] Open
Abstract
Phosphorylation of histone H2AX by ATM and ATR establishes a chromatin recruitment platform for DNA damage response proteins. Phospho-H2AX (γH2AX) has been most intensively studied in the context of DNA double-strand breaks caused by exogenous clastogens, but recent studies suggest that DNA replication stress also triggers formation of γH2A (ortholog of γH2AX) in Schizosaccharomyces pombe. Here, a focused genetic screen in fission yeast reveals that γH2A is critical when there are defects in Replication Factor C (RFC), which loads proliferating cell nuclear antigen (PCNA) clamp onto duplex DNA. Surprisingly Chk1, Cds1/Chk2 and the Rad9-Hus1-Rad1 checkpoint clamp, which are crucial for surviving many genotoxins, are fully dispensable in RFC-defective cells. Immunoblot analysis confirms that Rad9-Hus1-Rad1 is not required for formation of γH2A by Rad3/ATR in S-phase. Defects in DNA polymerase epsilon, which binds PCNA in the replisome, also create an acute need for γH2A. These requirements for γH2A were traced to its role in docking with Brc1, which is a 6-BRCT-domain protein that is structurally related to budding yeast Rtt107 and mammalian PTIP. Brc1, which localizes at stalled replication forks by binding γH2A, prevents aberrant formation of Replication Protein A (RPA) foci in RFC-impaired cells, suggesting that Brc1-coated chromatin stabilizes replisomes when PCNA or DNA polymerase availability limits DNA synthesis. ATM (ataxia telangiectasia mutated) and ATR (ATM and Rad3 related) are evolutionary conserved protein kinases that phosphorylate the carboxyl-tail of histone H2AX in chromatin flanking DNA lesions. Phosphorylated histone H2AX (aka γH2AX) tethers important DNA damage response (DDR) proteins to DNA double-strand breaks but its function during DNA replication is unclear. A novel genetic screen reveals that a partial defect in Replication Factor C (RFC) creates a critical requirement for γH2AX in fission yeast. These studies indicate that γH2AX stabilizes replication forks by recruiting Brc1 when RFC is unable to load the DNA clamp known as proliferating cell nuclear antigen (PCNA) onto duplex DNA. Surprisingly, this activity of γH2AX is more critical than ATM/ATR-mediated activation of the checkpoint kinase Chk1 and Chk2.
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Affiliation(s)
- Eva Mejia-Ramirez
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Oliver Limbo
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Petra Langerak
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Paul Russell
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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14
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Sabatinos SA, Ranatunga NS, Yuan JP, Green MD, Forsburg SL. Replication stress in early S phase generates apparent micronuclei and chromosome rearrangement in fission yeast. Mol Biol Cell 2015; 26:3439-50. [PMID: 26246602 PMCID: PMC4591689 DOI: 10.1091/mbc.e15-05-0318] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 07/24/2015] [Indexed: 12/21/2022] Open
Abstract
Unable to complete S phase, a fission yeast MCM mutant evades the mitotic checkpoint, causing aneuploidy, chromosome fragments, and bridges. The formation of apparent yeast micronuclei that are membrane bound is shown in real time; they develop DNA damage signals and may rejoin the parent nucleus. DNA replication stress causes genome mutations, rearrangements, and chromosome missegregation, which are implicated in cancer. We analyze a fission yeast mutant that is unable to complete S phase due to a defective subunit of the MCM helicase. Despite underreplicated and damaged DNA, these cells evade the G2 damage checkpoint to form ultrafine bridges, fragmented centromeres, and uneven chromosome segregations that resembles micronuclei. These micronuclei retain DNA damage markers and frequently rejoin with the parent nucleus. Surviving cells show an increased rate of mutation and chromosome rearrangement. This first report of micronucleus-like segregation in a yeast replication mutant establishes underreplication as an important factor contributing to checkpoint escape, abnormal chromosome segregation, and chromosome instability.
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Affiliation(s)
- Sarah A Sabatinos
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089 Department of Chemistry and Biology, Ryerson University, Toronto, ON M5B 2K3, Canada
| | - Nimna S Ranatunga
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089
| | - Ji-Ping Yuan
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089
| | - Marc D Green
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089
| | - Susan L Forsburg
- Program in Molecular and Computational Biology, University of Southern California, Los Angeles, CA 90089
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15
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Sánchez A, Russell P. Ku stabilizes replication forks in the absence of Brc1. PLoS One 2015; 10:e0126598. [PMID: 25965521 PMCID: PMC4428774 DOI: 10.1371/journal.pone.0126598] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 04/05/2015] [Indexed: 11/21/2022] Open
Abstract
DNA replication errors are a major source of genome instability in all organisms. In the fission yeast Schizosaccharomyces pombe, the DNA damage response protein Brc1 binds phospho-histone H2A (γH2A)-marked chromatin during S-phase, but how Brc1 protects genome integrity remains unclear. Here we report that the non-homologous end-joining (NHEJ) protein Ku becomes critical for survival of replication stress in brc1∆ cells. Ku’s protective activity in brc1∆ cells does not involve its canonical NHEJ function or its roles in protecting telomeres or shielding DNA ends from Exo1 exonuclease. In brc1∆ pku80∆ cells, nuclear foci of Rad52 homologous recombination (HR) protein increase and Mus81-Eme1 Holliday junction resolvase becomes critical, indicating increased replication fork instability. Ku’s localization at a ribosomal DNA replication fork barrier associated with frequent replisome-transcriptosome collisions increases in brc1∆ cells and increased collisions correlate with an enhanced requirement for Brc1. These data indicate that Ku stabilizes replication forks in the absence of Brc1.
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Affiliation(s)
- Arancha Sánchez
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Paul Russell
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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16
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Genetic Interaction Landscape Reveals Critical Requirements for Schizosaccharomyces pombe Brc1 in DNA Damage Response Mutants. G3-GENES GENOMES GENETICS 2015; 5:953-62. [PMID: 25795664 PMCID: PMC4426379 DOI: 10.1534/g3.115.017251] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Brc1, which was first identified as a high-copy, allele-specific suppressor of a mutation impairing the Smc5-Smc6 holocomplex in Schizosaccharomyces pombe, protects genome integrity during normal DNA replication and when cells are exposed to toxic compounds that stall or collapse replication forks. The C-terminal tandem BRCT (BRCA1 C-terminus) domain of fission yeast Brc1 docks with phosphorylated histone H2A (γH2A)-marked chromatin formed by ATR/Rad3 checkpoint kinase at arrested and damaged replication forks; however, how Brc1 functions in relation to other genome protection modules remains unclear. Here, an epistatic mini-array profile reveals critical requirements for Brc1 in mutants that are defective in multiple DNA damage response pathways, including checkpoint signaling by Rad3-Rad26/ATR-ATRIP kinase, DNA repair by Smc5-Smc6 holocomplex, replication fork stabilization by Mrc1/claspin and Swi1-Swi3/Timeless-Tipin, and control of ubiquitin-regulated proteolysis by the COP9 signalosome (CSN). Exogenous genotoxins enhance these negative genetic interactions. Rad52 and RPA foci are increased in CSN-defective cells, and loss of γH2A increases genotoxin sensitivity, indicating a critical role for the γH2A-Brc1 module in stabilizing replication forks in CSN-defective cells. A negative genetic interaction with the Nse6 subunit of Smc5-Smc6 holocomplex indicates that the DNA repair functions of Brc1 and Smc5-Smc6 holocomplex are at least partially independent. Rtt107, the Brc1 homolog in Saccharomyces cerevisiae, has a very different pattern of genetic interactions, indicating evolutionary divergence of functions and DNA damage responses.
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Abstract
The inhibition of the central growth regulatory kinase TOR, which participates in two complexes, TORC1 and TORC2, has been a focus of metabolic and cancer studies for many years. Most studies have dealt with TORC1, the canonical target of rapamycin, and the role of this complex in autophagy, protein synthesis, and cell growth control. Recent work on TORC2 in budding and fission yeast species points to a conserved role of this lesser-known TOR complex in the survival of DNA damage. In budding yeast, TORC2 controls lipid biosynthesis and actin cytoskeleton through downstream AGC kinases, which are now, surprisingly, implicated in the survival of oxidative DNA damage. Preliminary data from mTORC2 modulation in cancer cells suggest that an extension to human chemotherapy is worth exploring.
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Affiliation(s)
- Ronit Weisman
- Department of Natural and Life Sciences, The Open University of Israel, Raanana, Israel
| | - Adiel Cohen
- Department of Natural and Life Sciences, The Open University of Israel, Raanana, Israel
| | - Susan M Gasser
- Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
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18
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Tapia-Alveal C, Lin SJ, Yeoh A, Jabado OJ, O'Connell MJ. H2A.Z-dependent regulation of cohesin dynamics on chromosome arms. Mol Cell Biol 2014; 34:2092-104. [PMID: 24687850 PMCID: PMC4019066 DOI: 10.1128/mcb.00193-14] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 02/25/2014] [Accepted: 03/21/2014] [Indexed: 11/20/2022] Open
Abstract
Structural maintenance of chromosomes (SMC) complexes and DNA topoisomerases are major determinants of chromosome structure and dynamics. The cohesin complex embraces sister chromatids throughout interphase, but during mitosis most cohesin is stripped from chromosome arms by early prophase, while the remaining cohesin at kinetochores is cleaved at anaphase. This two-step removal of cohesin is required for sister chromatids to separate. The cohesin-related Smc5/6 complex has been studied mostly as a determinant of DNA repair via homologous recombination. However, chromosome segregation fails in Smc5/6 null mutants or cells treated with small interfering RNAs. This also occurs in Smc5/6 hypomorphs in the fission yeast Schizosaccharomyces pombe following genotoxic and replication stress, or topoisomerase II dysfunction, and these mitotic defects are due to the postanaphase retention of cohesin on chromosome arms. Here we show that mitotic and repair roles for Smc5/6 are genetically separable in S. pombe. Further, we identified the histone variant H2A.Z as a critical factor to modulate cohesin dynamics, and cells lacking H2A.Z suppress the mitotic defects conferred by Smc5/6 dysfunction. Together, H2A.Z and the SMC complexes ensure genome integrity through accurate chromosome segregation.
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Affiliation(s)
- Claudia Tapia-Alveal
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Su-Jiun Lin
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Aaron Yeoh
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Omar J. Jabado
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Matthew J. O'Connell
- Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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19
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Schonbrun M, Kolesnikov M, Kupiec M, Weisman R. TORC2 is required to maintain genome stability during S phase in fission yeast. J Biol Chem 2013; 288:19649-60. [PMID: 23703609 DOI: 10.1074/jbc.m113.464974] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA damage can occur due to environmental insults or intrinsic metabolic processes and is a major threat to genome stability. The DNA damage response is composed of a series of well coordinated cellular processes that include activation of the DNA damage checkpoint, transient cell cycle arrest, DNA damage repair, and reentry into the cell cycle. Here we demonstrate that mutant cells defective for TOR complex 2 (TORC2) or the downstream AGC-like kinase, Gad8, are highly sensitive to chronic replication stress but are insensitive to ionizing radiation. We show that in response to replication stress, TORC2 is dispensable for Chk1-mediated cell cycle arrest but is required for the return to cell cycle progression. Rad52 is a DNA repair and recombination protein that forms foci at DNA damage sites and stalled replication forks. TORC2 mutant cells show increased spontaneous nuclear Rad52 foci, particularly during S phase, suggesting that TORC2 protects cells from DNA damage that occurs during normal DNA replication. Consistently, the viability of TORC2-Gad8 mutant cells is dependent on the presence of the homologous recombination pathway and other proteins that are required for replication restart following fork replication stalling. Our findings indicate that TORC2 is required for genome integrity. This may be relevant for the growing amount of evidence implicating TORC2 in cancer development.
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Affiliation(s)
- Miriam Schonbrun
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Israel
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20
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Lee SY, Russell P. Brc1 links replication stress response and centromere function. Cell Cycle 2013; 12:1665-71. [PMID: 23656778 DOI: 10.4161/cc.24900] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Protection of genome integrity depends on the coordinated activities of DNA replication, DNA repair, chromatin assembly and chromosome segregation mechanisms. DNA lesions are detected by the master checkpoint kinases ATM (Tel1) and ATR (Rad3/Mec1), which phosphorylate multiple substrates, including a C-terminal SQ motif in histone H2A or H2AX. The 6-BRCT domain protein Brc1, which is required for efficient recovery from replication fork arrest and collapse in fission yeast, binds phospho-histone H2A (γH2A)-coated chromatin at stalled and damaged replication forks. We recently found that Brc1 co-localizes with γH2A that appears in pericentromeric heterochromatin during S-phase. Our studies indicate that Brc1 contributes to the maintenance of pericentromeric heterochromatin, which is required for efficient chromosome segregation during mitosis. Here, we review these studies and present additional results that establish the functional requirements for the N-terminal BRCT domains of Brc1 in the replication stress response and resistance to the microtubule destabilizing drug thiabendazole (TBZ). We also identify the nuclear localization signal (NLS) in Brc1, which closely abuts the C-terminal pair of BRCT domains that form the γH2A-binding pocket. This compact arrangement of localization domains may be a shared feature of other γH2A-binding proteins, including Rtt107, PTIP and Mdc1.
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Affiliation(s)
- Si Young Lee
- Cell and Molecular Biology Department, The Scripps Research Institute, La Jolla, CA USA
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21
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Replication fork collapse and genome instability in a deoxycytidylate deaminase mutant. Mol Cell Biol 2012; 32:4445-54. [PMID: 22927644 DOI: 10.1128/mcb.01062-12] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Ribonucleotide reductase (RNR) and deoxycytidylate deaminase (dCMP deaminase) are pivotal allosteric enzymes required to maintain adequate pools of deoxyribonucleoside triphosphates (dNTPs) for DNA synthesis and repair. Whereas RNR inhibition slows DNA replication and activates checkpoint responses, the effect of dCMP deaminase deficiency is largely unknown. Here, we report that deleting the Schizosaccharomyces pombe dcd1(+) dCMP deaminase gene (SPBC2G2.13c) increases dCTP ∼30-fold and decreases dTTP ∼4-fold. In contrast to the robust growth of a Saccharomyces cerevisiae dcd1Δ mutant, fission yeast dcd1Δ cells delay cell cycle progression in early S phase and are sensitive to multiple DNA-damaging agents, indicating impaired DNA replication and repair. DNA content profiling of dcd1Δ cells differs from an RNR-deficient mutant. Dcd1 deficiency activates genome integrity checkpoints enforced by Rad3 (ATR), Cds1 (Chk2), and Chk1 and creates critical requirements for proteins involved in recovery from replication fork collapse, including the γH2AX-binding protein Brc1 and Mus81 Holliday junction resolvase. These effects correlate with increased nuclear foci of the single-stranded DNA binding protein RPA and the homologous recombination repair protein Rad52. Moreover, Brc1 suppresses spontaneous mutagenesis in dcd1Δ cells. We propose that replication forks stall and collapse in dcd1Δ cells, burdening DNA damage and checkpoint responses to maintain genome integrity.
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