1
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Adolph MB, Cortez D. Mechanisms and regulation of replication fork reversal. DNA Repair (Amst) 2024; 141:103731. [PMID: 39089193 DOI: 10.1016/j.dnarep.2024.103731] [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] [Received: 04/24/2024] [Revised: 07/15/2024] [Accepted: 07/17/2024] [Indexed: 08/03/2024]
Abstract
DNA replication is remarkably accurate with estimates of only a handful of mutations per human genome per cell division cycle. Replication stress caused by DNA lesions, transcription-replication conflicts, and other obstacles to the replication machinery must be efficiently overcome in ways that minimize errors and maximize completion of DNA synthesis. Replication fork reversal is one mechanism that helps cells tolerate replication stress. This process involves reannealing of parental template DNA strands and generation of a nascent-nascent DNA duplex. While fork reversal may be beneficial by facilitating DNA repair or template switching, it must be confined to the appropriate contexts to preserve genome stability. Many enzymes have been implicated in this process including ATP-dependent DNA translocases like SMARCAL1, ZRANB3, HLTF, and the helicase FBH1. In addition, the RAD51 recombinase is required. Many additional factors and regulatory activities also act to ensure reversal is beneficial instead of yielding undesirable outcomes. Finally, reversed forks must also be stabilized and often need to be restarted to complete DNA synthesis. Disruption or deregulation of fork reversal causes a variety of human diseases. In this review we will describe the latest models for reversal and key mechanisms of regulation.
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Affiliation(s)
- Madison B Adolph
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States
| | - David Cortez
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, United States.
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2
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Orren DK, Machwe A. Response to Replication Stress and Maintenance of Genome Stability by WRN, the Werner Syndrome Protein. Int J Mol Sci 2024; 25:8300. [PMID: 39125869 PMCID: PMC11311767 DOI: 10.3390/ijms25158300] [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] [Received: 06/17/2024] [Revised: 07/16/2024] [Accepted: 07/25/2024] [Indexed: 08/12/2024] Open
Abstract
Werner syndrome (WS) is an autosomal recessive disease caused by loss of function of WRN. WS is a segmental progeroid disease and shows early onset or increased frequency of many characteristics of normal aging. WRN possesses helicase, annealing, strand exchange, and exonuclease activities and acts on a variety of DNA substrates, even complex replication and recombination intermediates. Here, we review the genetics, biochemistry, and probably physiological functions of the WRN protein. Although its precise role is unclear, evidence suggests WRN plays a role in pathways that respond to replication stress and maintain genome stability particularly in telomeric regions.
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Affiliation(s)
- David K. Orren
- Department of Toxicology and Cancer Biology, University of Kentucky College of Medicine, Lexington, KY 40536, USA;
- Markey Cancer Center, University of Kentucky, Lexington, KY 40506, USA
| | - Amrita Machwe
- Department of Toxicology and Cancer Biology, University of Kentucky College of Medicine, Lexington, KY 40536, USA;
- Markey Cancer Center, University of Kentucky, Lexington, KY 40506, USA
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3
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Shin S, Hyun K, Lee J, Joo D, Kulikowicz T, Bohr V, Kim J, Hohng S. Werner syndrome protein works as a dimer for unwinding and replication fork regression. Nucleic Acids Res 2022; 51:337-348. [PMID: 36583333 PMCID: PMC9841404 DOI: 10.1093/nar/gkac1200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2022] [Revised: 11/28/2022] [Accepted: 12/05/2022] [Indexed: 12/31/2022] Open
Abstract
The determination of the oligomeric state of functional enzymes is essential for the mechanistic understanding of their catalytic activities. RecQ helicases have diverse biochemical activities, but it is still unclear how their activities are related to their oligomeric states. We use single-molecule multi-color fluorescence imaging to determine the oligomeric states of Werner syndrome protein (WRN) during its unwinding and replication fork regression activities. We reveal that WRN binds to a forked DNA as a dimer, and unwinds it without any change of its oligomeric state. In contrast, WRN binds to a replication fork as a tetramer, and is dimerized during activation of replication fork regression. By selectively inhibiting the helicase activity of WRN on specific strands, we reveal how the active dimers of WRN distinctly use the energy of ATP hydrolysis for repetitive unwinding and replication fork regression.
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Affiliation(s)
| | | | - Jinwoo Lee
- Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul, Republic of Korea
| | - Dongwon Joo
- Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul, Republic of Korea
| | - Tomasz Kulikowicz
- Section on DNA repair, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Vilhelm A Bohr
- Section on DNA repair, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Jaehoon Kim
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Sungchul Hohng
- To whom correspondence should be addressed. Tel: +82 2 880 6593;
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4
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Thakkar MK, Lee J, Meyer S, Chang VY. RecQ Helicase Somatic Alterations in Cancer. Front Mol Biosci 2022; 9:887758. [PMID: 35782872 PMCID: PMC9240438 DOI: 10.3389/fmolb.2022.887758] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 05/23/2022] [Indexed: 11/13/2022] Open
Abstract
Named the “caretakers” of the genome, RecQ helicases function in several pathways to maintain genomic stability and repair DNA. This highly conserved family of enzymes consist of five different proteins in humans: RECQL1, BLM, WRN, RECQL4, and RECQL5. Biallelic germline mutations in BLM, WRN, and RECQL4 have been linked to rare cancer-predisposing syndromes. Emerging research has also implicated somatic alterations in RecQ helicases in a variety of cancers, including hematological malignancies, breast cancer, osteosarcoma, amongst others. These alterations in RecQ helicases, particularly overexpression, may lead to increased resistance of cancer cells to conventional chemotherapy. Downregulation of these proteins may allow for increased sensitivity to chemotherapy, and, therefore, may be important therapeutic targets. Here we provide a comprehensive review of our current understanding of the role of RecQ DNA helicases in cancer and discuss the potential therapeutic opportunities in targeting these helicases.
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Affiliation(s)
- Megha K. Thakkar
- Department of Pediatrics, Division of Pediatric Hematology-Oncology, University of California, Los Angeles, Los Angeles, CA, United States
| | - Jamie Lee
- Department of Pediatrics, Division of Pediatric Hematology-Oncology, University of California, Los Angeles, Los Angeles, CA, United States
| | - Stefan Meyer
- Division of Cancer Studies, University of Manchester, Manchester, United Kingdom
- Department of Pediatric Hematology Oncology, Royal Manchester Children’s Hospital and Christie NHS Foundation Trust, Manchester, United Kingdom
| | - Vivian Y. Chang
- Department of Pediatrics, Division of Pediatric Hematology-Oncology, University of California, Los Angeles, Los Angeles, CA, United States
- Childrens Discovery and Innovation Institute, UCLA, Los Angeles, CA, United States
- Jonsson Comprehensive Cancer Center, UCLA, Los Angeles, CA, United States
- *Correspondence: Vivian Y. Chang,
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5
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Shastri VM, Subramanian V, Schmidt KH. A novel cell-cycle-regulated interaction of the Bloom syndrome helicase BLM with Mcm6 controls replication-linked processes. Nucleic Acids Res 2021; 49:8699-8713. [PMID: 34370039 PMCID: PMC8421143 DOI: 10.1093/nar/gkab663] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 07/16/2021] [Accepted: 07/22/2021] [Indexed: 11/13/2022] Open
Abstract
The Bloom syndrome DNA helicase BLM contributes to chromosome stability through its roles in double-strand break repair by homologous recombination and DNA replication fork restart during the replication stress response. Loss of BLM activity leads to Bloom syndrome, which is characterized by extraordinary cancer risk and small stature. Here, we have analyzed the composition of the BLM complex during unperturbed S-phase and identified a direct physical interaction with the Mcm6 subunit of the minichromosome maintenance (MCM) complex. Using distinct binding sites, BLM interacts with the N-terminal domain of Mcm6 in G1 phase and switches to the C-terminal Cdt1-binding domain of Mcm6 in S-phase, with a third site playing a role for Mcm6 binding after DNA damage. Disruption of Mcm6-binding to BLM in S-phase leads to supra-normal DNA replication speed in unperturbed cells, and the helicase activity of BLM is required for this increased replication speed. Upon disruption of BLM/Mcm6 interaction, repair of replication-dependent DNA double-strand breaks is delayed and cells become hypersensitive to DNA damage and replication stress. Our findings reveal that BLM not only plays a role in the response to DNA damage and replication stress, but that its physical interaction with Mcm6 is required in unperturbed cells, most notably in S-phase as a negative regulator of replication speed.
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Affiliation(s)
- Vivek M Shastri
- Department of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620, USA
| | - Veena Subramanian
- Department of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620, USA
| | - Kristina H Schmidt
- Department of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620, USA.,Cancer Biology and Evolution Program, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL 33612, USA
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6
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Conti BA, Smogorzewska A. Mechanisms of direct replication restart at stressed replisomes. DNA Repair (Amst) 2020; 95:102947. [PMID: 32853827 PMCID: PMC7669714 DOI: 10.1016/j.dnarep.2020.102947] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 08/02/2020] [Accepted: 08/04/2020] [Indexed: 02/09/2023]
Affiliation(s)
- Brooke A Conti
- Laboratory of Genome Maintenance, The Rockefeller University, New York 10065, USA
| | - Agata Smogorzewska
- Laboratory of Genome Maintenance, The Rockefeller University, New York 10065, USA.
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7
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Dhar S, Datta A, Brosh RM. DNA helicases and their roles in cancer. DNA Repair (Amst) 2020; 96:102994. [PMID: 33137625 DOI: 10.1016/j.dnarep.2020.102994] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 09/28/2020] [Indexed: 12/15/2022]
Abstract
DNA helicases, known for their fundamentally important roles in genomic stability, are high profile players in cancer. Not only are there monogenic helicase disorders with a strong disposition to cancer, it is well appreciated that helicase variants are associated with specific cancers (e.g., breast cancer). Flipping the coin, DNA helicases are frequently overexpressed in cancerous tissues and reduction in helicase gene expression results in reduced proliferation and growth capacity, as well as DNA damage induction and apoptosis of cancer cells. The seminal roles of helicases in the DNA damage and replication stress responses, as well as DNA repair pathways, validate their vital importance in cancer biology and suggest their potential values as targets in anti-cancer therapy. In recent years, many laboratories have characterized the specialized roles of helicase to resolve transcription-replication conflicts, maintain telomeres, mediate cell cycle checkpoints, remodel stalled replication forks, and regulate transcription. In vivo models, particularly mice, have been used to interrogate helicase function and serve as a bridge for preclinical studies that may lead to novel therapeutic approaches. In this review, we will summarize our current knowledge of DNA helicases and their roles in cancer, emphasizing the latest developments.
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Affiliation(s)
- Srijita Dhar
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Arindam Datta
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA.
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8
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Kafer GR, Cesare AJ. A Survey of Essential Genome Stability Genes Reveals That Replication Stress Mitigation Is Critical for Peri-Implantation Embryogenesis. Front Cell Dev Biol 2020; 8:416. [PMID: 32548123 PMCID: PMC7274024 DOI: 10.3389/fcell.2020.00416] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 05/05/2020] [Indexed: 12/16/2022] Open
Abstract
Murine development demands that pluripotent epiblast stem cells in the peri-implantation embryo increase from approximately 120 to 14,000 cells between embryonic days (E) 4.5 and E7.5. This is possible because epiblast stem cells can complete cell cycles in under 3 h in vivo. To ensure conceptus fitness, epiblast cells must undertake this proliferative feat while maintaining genome integrity. How epiblast cells maintain genome health under such an immense proliferation demand remains unclear. To illuminate the contribution of genome stability pathways to early mammalian development we systematically reviewed knockout mouse data from 347 DDR and repair associated genes. Cumulatively, the data indicate that while many DNA repair functions are dispensable in embryogenesis, genes encoding replication stress response and homology directed repair factors are essential specifically during the peri-implantation stage of early development. We discuss the significance of these findings in the context of the unique proliferative demands placed on pluripotent epiblast stem cells.
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Affiliation(s)
| | - Anthony J. Cesare
- Genome Integrity Unit, Children’s Medical Research Institute, The University of Sydney, Westmead, NSW, Australia
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9
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Jain CK, Mukhopadhyay S, Ganguly A. RecQ Family Helicases in Replication Fork Remodeling and Repair: Opening New Avenues towards the Identification of Potential Targets for Cancer Chemotherapy. Anticancer Agents Med Chem 2020; 20:1311-1326. [PMID: 32418530 DOI: 10.2174/1871520620666200518082433] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 08/08/2019] [Accepted: 12/30/2019] [Indexed: 11/22/2022]
Abstract
Replication fork reversal and restart has gained immense interest as a central response mechanism to replication stress following DNA damage. Although the exact mechanism of fork reversal has not been elucidated precisely, the involvement of diverse pathways and different factors has been demonstrated, which are central to this phenomenon. RecQ helicases known for their vital role in DNA repair and maintaining genome stability has recently been implicated in the restart of regressed replication forks. Through interaction with vital proteins like Poly (ADP) ribose polymerase 1 (PARP1), these helicases participate in the replication fork reversal and restart phenomenon. Most therapeutic agents used for cancer chemotherapy act by causing DNA damage in replicating cells and subsequent cell death. These DNA damages can be repaired by mechanisms involving fork reversal as the key phenomenon eventually reducing the efficacy of the therapeutic agent. Hence the factors contributing to this repair process can be good selective targets for developing more efficient chemotherapeutic agents. In this review, we have discussed in detail the role of various proteins in replication fork reversal and restart with special emphasis on RecQ helicases. Involvement of other proteins like PARP1, recombinase rad51, SWI/SNF complex has also been discussed. Since RecQ helicases play a central role in the DNA damage response following chemotherapeutic treatment, we propose that targeting these helicases can emerge as an alternative to available intervention strategies. We have also summarized the current research status of available RecQ inhibitors and siRNA based therapeutic approaches that targets RecQ helicases. In summary, our review gives an overview of the DNA damage responses involving replication fork reversal and provides new directions for the development of more efficient and sustainable chemotherapeutic approaches.
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Affiliation(s)
- Chetan K Jain
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721302, India
| | - Swagata Mukhopadhyay
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721302, India
| | - Agneyo Ganguly
- Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721302, India
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10
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Brosh RM, Trakselis MA. Fine-tuning of the replisome: Mcm10 regulates fork progression and regression. Cell Cycle 2019; 18:1047-1055. [PMID: 31014174 DOI: 10.1080/15384101.2019.1609833] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Several decades of research have identified Mcm10 hanging around the replisome making several critical contacts with a number of proteins but with no real disclosed function. Recently, the O'Donnell laboratory has been better able to map the interactions of Mcm10 with a larger Cdc45/GINS/MCM (CMG) unwinding complex placing it at the front of the replication fork. They have shown biochemically that Mcm10 has the impressive ability to strip off single-strand binding protein (RPA) and reanneal complementary DNA strands. This has major implications in controlling DNA unwinding speed as well as responding to various situations where fork reversal is needed. This work opens up a number of additional facets discussed here revolving around accessing the DNA junction for different molecular purposes within a crowded replisome. Abbreviations: alt-NHEJ: Alternative Nonhomologous End-Joining; CC: Coli-Coil motif; CMG: Cdc45/GINS/MCM2-7; CMGM: Cdc45/GINS/Mcm2-7/Mcm10; CPT: Camptothecin; CSB: Cockayne Syndrome Group B protein; CTD: C-Terminal Domain; DSB: Double-Strand Break; DSBR: Double-Strand Break Repair; dsDNA: Double-Stranded DNA; GINS: go-ichi-ni-san, Sld5-Psf1-Psf2-Psf3; HJ Dis: Holliday Junction dissolution; HJ Res: Holliday Junction resolution; HR: Homologous Recombination; ICL: Interstrand Cross-Link; ID: Internal Domain; MCM: Minichromosomal Maintenance; ND: Not Determined; NTD: N-Terminal Domain; PCNA: Proliferating Cell Nuclear Antigen; RPA: Replication Protein A; SA: Strand Annealing; SE: Strand Exchange; SEW: Steric Exclusion and Wrapping; ssDNA: Single-Stranded DNA; TCR: Transcription-Coupled Repair; TOP1: Topoisomerase.
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Affiliation(s)
- Robert M Brosh
- a Laboratory of Molecular Gerontology , National Institute on Aging, National Institutes of Health , Baltimore , MD USA
| | - Michael A Trakselis
- b Department of Chemistry and Biochemistry , Baylor University , Waco , TX , USA
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11
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Jalan M, Oehler J, Morrow CA, Osman F, Whitby MC. Factors affecting template switch recombination associated with restarted DNA replication. eLife 2019; 8:41697. [PMID: 30667359 PMCID: PMC6358216 DOI: 10.7554/elife.41697] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Accepted: 01/21/2019] [Indexed: 12/19/2022] Open
Abstract
Homologous recombination helps ensure the timely completion of genome duplication by restarting collapsed replication forks. However, this beneficial function is not without risk as replication restarted by homologous recombination is prone to template switching (TS) that can generate deleterious genome rearrangements associated with diseases such as cancer. Previously we established an assay for studying TS in Schizosaccharomyces pombe (Nguyen et al., 2015). Here, we show that TS is detected up to 75 kb downstream of a collapsed replication fork and can be triggered by head-on collision between the restarted fork and RNA Polymerase III transcription. The Pif1 DNA helicase, Pfh1, promotes efficient restart and also suppresses TS. A further three conserved helicases (Fbh1, Rqh1 and Srs2) strongly suppress TS, but there is no change in TS frequency in cells lacking Fml1 or Mus81. We discuss how these factors likely influence TS.
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Affiliation(s)
- Manisha Jalan
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Judith Oehler
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Carl A Morrow
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Fekret Osman
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Matthew C Whitby
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
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12
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Studying Werner syndrome to elucidate mechanisms and therapeutics of human aging and age-related diseases. Biogerontology 2019; 20:255-269. [PMID: 30666569 DOI: 10.1007/s10522-019-09798-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Accepted: 01/17/2019] [Indexed: 01/22/2023]
Abstract
Aging is a natural and unavoidable part of life. However, aging is also the primary driver of the dominant human diseases, such as cardiovascular disease, cancer, and neurodegenerative diseases, including Alzheimer's disease. Unraveling the sophisticated molecular mechanisms of the human aging process may provide novel strategies to extend 'healthy aging' and the cure of human aging-related diseases. Werner syndrome (WS), is a heritable human premature aging disease caused by mutations in the gene encoding the Werner (WRN) DNA helicase. As a classical premature aging disease, etiological exploration of WS can shed light on the mechanisms of normal human aging and facilitate the development of interventional strategies to improve healthspan. Here, we summarize the latest progress of the molecular understandings of WRN protein, highlight the advantages of using different WS model systems, including Caenorhabditis elegans, Drosophila melanogaster and induced pluripotent stem cell (iPSC) systems. Further studies on WS will propel drug development for WS patients, and possibly also for normal age-related diseases.
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13
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Mukherjee S, Sinha D, Bhattacharya S, Srinivasan K, Abdisalaam S, Asaithamby A. Werner Syndrome Protein and DNA Replication. Int J Mol Sci 2018; 19:ijms19113442. [PMID: 30400178 PMCID: PMC6274846 DOI: 10.3390/ijms19113442] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 10/22/2018] [Accepted: 10/25/2018] [Indexed: 01/07/2023] Open
Abstract
Werner Syndrome (WS) is an autosomal recessive disorder characterized by the premature development of aging features. Individuals with WS also have a greater predisposition to rare cancers that are mesenchymal in origin. Werner Syndrome Protein (WRN), the protein mutated in WS, is unique among RecQ family proteins in that it possesses exonuclease and 3' to 5' helicase activities. WRN forms dynamic sub-complexes with different factors involved in DNA replication, recombination and repair. WRN binding partners either facilitate its DNA metabolic activities or utilize it to execute their specific functions. Furthermore, WRN is phosphorylated by multiple kinases, including Ataxia telangiectasia mutated, Ataxia telangiectasia and Rad3 related, c-Abl, Cyclin-dependent kinase 1 and DNA-dependent protein kinase catalytic subunit, in response to genotoxic stress. These post-translational modifications are critical for WRN to function properly in DNA repair, replication and recombination. Accumulating evidence suggests that WRN plays a crucial role in one or more genome stability maintenance pathways, through which it suppresses cancer and premature aging. Among its many functions, WRN helps in replication fork progression, facilitates the repair of stalled replication forks and DNA double-strand breaks associated with replication forks, and blocks nuclease-mediated excessive processing of replication forks. In this review, we specifically focus on human WRN's contribution to replication fork processing for maintaining genome stability and suppressing premature aging. Understanding WRN's molecular role in timely and faithful DNA replication will further advance our understanding of the pathophysiology of WS.
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Affiliation(s)
- Shibani Mukherjee
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Debapriya Sinha
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Souparno Bhattacharya
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Kalayarasan Srinivasan
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Salim Abdisalaam
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
| | - Aroumougame Asaithamby
- Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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14
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Lee T, Pelletier J. The biology of DHX9 and its potential as a therapeutic target. Oncotarget 2018; 7:42716-42739. [PMID: 27034008 PMCID: PMC5173168 DOI: 10.18632/oncotarget.8446] [Citation(s) in RCA: 120] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 03/16/2016] [Indexed: 12/25/2022] Open
Abstract
DHX9 is member of the DExD/H-box family of helicases with a “DEIH” sequence at its eponymous DExH-box motif. Initially purified from human and bovine cells and identified as a homologue of the Drosophila Maleless (MLE) protein, it is an NTP-dependent helicase consisting of a conserved helicase core domain, two double-stranded RNA-binding domains at the N-terminus, and a nuclear transport domain and a single-stranded DNA-binding RGG-box at the C-terminus. With an ability to unwind DNA and RNA duplexes, as well as more complex nucleic acid structures, DHX9 appears to play a central role in many cellular processes. Its functions include regulation of DNA replication, transcription, translation, microRNA biogenesis, RNA processing and transport, and maintenance of genomic stability. Because of its central role in gene regulation and RNA metabolism, there are growing implications for DHX9 in human diseases and their treatment. This review will provide an overview of the structure, biochemistry, and biology of DHX9, its role in cancer and other human diseases, and the possibility of targeting DHX9 in chemotherapy.
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Affiliation(s)
- Teresa Lee
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
| | - Jerry Pelletier
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada.,Department of Oncology, McGill University, Montreal, Quebec, Canada.,Department of Rosalind and Morris Goodman Cancer Research Center, McGill University, Montreal, Quebec, Canada
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15
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De La Rosa VY, Asfaha J, Fasullo M, Loguinov A, Li P, Moore LE, Rothman N, Nakamura J, Swenberg JA, Scelo G, Zhang L, Smith MT, Vulpe CD. Editor's Highlight: High-Throughput Functional Genomics Identifies Modulators of TCE Metabolite Genotoxicity and Candidate Susceptibility Genes. Toxicol Sci 2017; 160:111-120. [PMID: 28973557 PMCID: PMC5837773 DOI: 10.1093/toxsci/kfx159] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Trichloroethylene (TCE), an industrial chemical and environmental contaminant, is a human carcinogen. Reactive metabolites are implicated in renal carcinogenesis associated with TCE exposure, yet the toxicity mechanisms of these metabolites and their contribution to cancer and other adverse effects remain unclear. We employed an integrated functional genomics approach that combined functional profiling studies in yeast and avian DT40 cell models to provide new insights into the specific mechanisms contributing to toxicity associated with TCE metabolites. Genome-wide profiling studies in yeast identified the error-prone translesion synthesis (TLS) pathway as an import mechanism in response to TCE metabolites. The role of TLS DNA repair was further confirmed by functional profiling in DT40 avian cell lines, but also revealed that TLS and homologous recombination DNA repair likely play competing roles in cellular susceptibility to TCE metabolites in higher eukaryotes. These DNA repair pathways are highly conserved between yeast, DT40, and humans. We propose that in humans, mutagenic TLS is favored over homologous recombination repair in response to TCE metabolites. The results of these studies contribute to the body of evidence supporting a mutagenic mode of action for TCE-induced renal carcinogenesis mediated by reactive metabolites in humans. Our approach illustrates the potential for high-throughput in vitro functional profiling in yeast to elucidate toxicity pathways (molecular initiating events, key events) and candidate susceptibility genes for focused study.
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Affiliation(s)
- Vanessa Y. De La Rosa
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
| | - Jonathan Asfaha
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
| | - Michael Fasullo
- Colleges of Nanoscale Science and Engineering, State University of New York Polytechnic Institute, Albany, New York 12205
| | - Alex Loguinov
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
| | - Peng Li
- International Agency for Research on Cancer (IARC), Lyon, France
| | - Lee E. Moore
- Division of Cancer Epidemiology and Genetics, Department of Health and Human Services, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Nathaniel Rothman
- Division of Cancer Epidemiology and Genetics, Department of Health and Human Services, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Jun Nakamura
- Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, North Carolina
| | | | - Ghislaine Scelo
- International Agency for Research on Cancer (IARC), Lyon, France
| | - Luoping Zhang
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California 94720
| | - Martyn T. Smith
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California 94720
| | - Chris D. Vulpe
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720
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16
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DNA Replication Origins and Fork Progression at Mammalian Telomeres. Genes (Basel) 2017; 8:genes8040112. [PMID: 28350373 PMCID: PMC5406859 DOI: 10.3390/genes8040112] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Revised: 03/23/2017] [Accepted: 03/24/2017] [Indexed: 12/20/2022] Open
Abstract
Telomeres are essential chromosomal regions that prevent critical shortening of linear chromosomes and genomic instability in eukaryotic cells. The bulk of telomeric DNA is replicated by semi-conservative DNA replication in the same way as the rest of the genome. However, recent findings revealed that replication of telomeric repeats is a potential cause of chromosomal instability, because DNA replication through telomeres is challenged by the repetitive telomeric sequences and specific structures that hamper the replication fork. In this review, we summarize current understanding of the mechanisms by which telomeres are faithfully and safely replicated in mammalian cells. Various telomere-associated proteins ensure efficient telomere replication at different steps, such as licensing of replication origins, passage of replication forks, proper fork restart after replication stress, and dissolution of post-replicative structures. In particular, shelterin proteins have central roles in the control of telomere replication. Through physical interactions, accessory proteins are recruited to maintain telomere integrity during DNA replication. Dormant replication origins and/or homology-directed repair may rescue inappropriate fork stalling or collapse that can cause defects in telomere structure and functions.
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17
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The Intra-S Checkpoint Responses to DNA Damage. Genes (Basel) 2017; 8:genes8020074. [PMID: 28218681 PMCID: PMC5333063 DOI: 10.3390/genes8020074] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 02/08/2017] [Accepted: 02/08/2017] [Indexed: 02/03/2023] Open
Abstract
Faithful duplication of the genome is a challenge because DNA is susceptible to damage by a number of intrinsic and extrinsic genotoxins, such as free radicals and UV light. Cells activate the intra-S checkpoint in response to damage during S phase to protect genomic integrity and ensure replication fidelity. The checkpoint prevents genomic instability mainly by regulating origin firing, fork progression, and transcription of G1/S genes in response to DNA damage. Several studies hint that regulation of forks is perhaps the most critical function of the intra-S checkpoint. However, the exact role of the checkpoint at replication forks has remained elusive and controversial. Is the checkpoint required for fork stability, or fork restart, or to prevent fork reversal or fork collapse, or activate repair at replication forks? What are the factors that the checkpoint targets at stalled replication forks? In this review, we will discuss the various pathways activated by the intra-S checkpoint in response to damage to prevent genomic instability.
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18
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Sekelsky J. DNA Repair in Drosophila: Mutagens, Models, and Missing Genes. Genetics 2017; 205:471-490. [PMID: 28154196 PMCID: PMC5289830 DOI: 10.1534/genetics.116.186759] [Citation(s) in RCA: 80] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 10/18/2016] [Indexed: 12/22/2022] Open
Abstract
The numerous processes that damage DNA are counterbalanced by a complex network of repair pathways that, collectively, can mend diverse types of damage. Insights into these pathways have come from studies in many different organisms, including Drosophila melanogaster Indeed, the first ideas about chromosome and gene repair grew out of Drosophila research on the properties of mutations produced by ionizing radiation and mustard gas. Numerous methods have been developed to take advantage of Drosophila genetic tools to elucidate repair processes in whole animals, organs, tissues, and cells. These studies have led to the discovery of key DNA repair pathways, including synthesis-dependent strand annealing, and DNA polymerase theta-mediated end joining. Drosophila appear to utilize other major repair pathways as well, such as base excision repair, nucleotide excision repair, mismatch repair, and interstrand crosslink repair. In a surprising number of cases, however, DNA repair genes whose products play important roles in these pathways in other organisms are missing from the Drosophila genome, raising interesting questions for continued investigations.
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Affiliation(s)
- Jeff Sekelsky
- Department of Biology and Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, North Carolina 27599
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19
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Bloom's syndrome: Why not premature aging?: A comparison of the BLM and WRN helicases. Ageing Res Rev 2017; 33:36-51. [PMID: 27238185 DOI: 10.1016/j.arr.2016.05.010] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 05/17/2016] [Accepted: 05/19/2016] [Indexed: 01/19/2023]
Abstract
Genomic instability is a hallmark of cancer and aging. Premature aging (progeroid) syndromes are often caused by mutations in genes whose function is to ensure genomic integrity. The RecQ family of DNA helicases is highly conserved and plays crucial roles as genome caretakers. In humans, mutations in three RecQ genes - BLM, WRN, and RECQL4 - give rise to Bloom's syndrome (BS), Werner syndrome (WS), and Rothmund-Thomson syndrome (RTS), respectively. WS is a prototypic premature aging disorder; however, the clinical features present in BS and RTS do not indicate accelerated aging. The BLM helicase has pivotal functions at the crossroads of DNA replication, recombination, and repair. BS cells exhibit a characteristic form of genomic instability that includes excessive homologous recombination. The excessive homologous recombination drives the development in BS of the many types of cancers that affect persons in the normal population. Replication delay and slower cell turnover rates have been proposed to explain many features of BS, such as short stature. More recently, aberrant transcriptional regulation of growth and survival genes has been proposed as a hypothesis to explain features of BS.
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20
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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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21
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Active Control of Repetitive Structural Transitions between Replication Forks and Holliday Junctions by Werner Syndrome Helicase. Structure 2016; 24:1292-1300. [PMID: 27427477 DOI: 10.1016/j.str.2016.06.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Revised: 05/11/2016] [Accepted: 06/05/2016] [Indexed: 11/20/2022]
Abstract
The reactivation of stalled DNA replication via fork regression invokes Holliday junction formation, branch migration, and the recovery of the replication fork after DNA repair or error-free DNA synthesis. The coordination mechanism for these DNA structural transitions by molecular motors, however, remains unclear. Here we perform single-molecule fluorescence experiments with Werner syndrome protein (WRN) and model replication forks. The Holliday junction is readily formed once the lagging arm is unwound, and migrated unidirectionally with 3.2 ± 0.03 bases/s velocity. The recovery of the replication fork was controlled by branch migration reversal of WRN, resulting in repetitive fork regression. The Holliday junction formation, branch migration, and migration direction reversal are all ATP dependent, revealing that WRN uses the energy of ATP hydrolysis to actively coordinate the structural transitions of DNA.
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22
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Wu Y, Qian Y, Zhou G, Lv J, Yan Q, Dong X. Effect of GEN1 interference on the chemosensitivity of the breast cancer MCF-7 and SKBR3 cell lines. Oncol Lett 2016; 11:3597-3604. [PMID: 27284361 PMCID: PMC4887781 DOI: 10.3892/ol.2016.4489] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 03/01/2016] [Indexed: 12/20/2022] Open
Abstract
Chemotherapy is a notable method for the treatment of breast cancer. Numerous genes associated with the sensitivity of cancer to chemotherapy have been found. In recent years, evidence has suggested that a particular structure termed Holliday junction (HJ) plays a crucial role in cancer chemosensitivity. Targeting HJ resolvases, such as structure-specific endonuclease subunit SLX4 (Slx4) and MUS81 structure-specific endonuclease subunit (Mus81), significantly increases the chemosensitivity of tumor cells. Flap endonuclease GEN homolog 1 (GEN1) is a HJ resolvase that belongs to the Rad2/xeroderma pigmentosum complementation group G nuclease family. Whether GEN1 affects the chemosensitivity of tumor cells in a similar manner to Slx4 and Mus81 remains unknown. The aim of the present study was to determine the effect of GEN1 interference on the chemosensitivity of breast cancer cell lines. The investigation of the function of GEN1 was performed using MCF-7 and SKBR3 cells. Short hairpin RNA was used to suppress the expression of GEN1, and western blot analysis and reverse transcription-quantitative polymerase chain reaction were used to detect gene expression. In addition, a cell counting kit-8 assay was performed to detect the viability of cells and flow cytometry was performed to test apoptosis levels. Suppression of GEN1 in SKBR3 cells effectively increased the sensitivity to the chemotherapeutic drug 5-fluorouracil (5-FU), while MCF-7 cells showed no significant change in sensitivity following GEN1 suppression. However, when GEN1 was targeted in addition to Mus81, the MCF-7 cells also demonstrated a significantly increased sensitivity to 5-FU. In addition, when the level of Mus81 was low, GEN1 expression was increased under a low concentration of 5-FU. The present results suggest that GEN1 may play different roles in different breast cancer cell lines. The function of GEN1 may be affected by the level of Mus81 in the cell line. In addition, GEN1 interference may improve the sensitivity to chemotherapy induced by targeting Mus81 alone.
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Affiliation(s)
- Yunlu Wu
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China; The Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang 325000, P.R. China
| | - Ying Qian
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China
| | - Guozhong Zhou
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China
| | - Juan Lv
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China
| | - Qiuyue Yan
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China; The Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang 325000, P.R. China
| | - Xuejun Dong
- Clinical Laboratory Center, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing, Zhejiang 312000, P.R. China; The Key Laboratory of Laboratory Medicine, Ministry of Education of China, School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang 325000, P.R. China
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23
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Drosopoulos WC, Kosiyatrakul ST, Schildkraut CL. BLM helicase facilitates telomere replication during leading strand synthesis of telomeres. J Cell Biol 2016. [PMID: 26195664 PMCID: PMC4508891 DOI: 10.1083/jcb.201410061] [Citation(s) in RCA: 110] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
BLM helicase facilitates telomere replication by resolving G-quadruplex structures that can form in the G-rich repeats during leading strand synthesis. Based on its in vitro unwinding activity on G-quadruplex (G4) DNA, the Bloom syndrome–associated helicase BLM is proposed to participate in telomere replication by aiding fork progression through G-rich telomeric DNA. Single molecule analysis of replicated DNA (SMARD) was used to determine the contribution of BLM helicase to telomere replication. In BLM-deficient cells, replication forks initiating from origins within the telomere, which copy the G-rich strand by leading strand synthesis, moved slower through the telomere compared with the adjacent subtelomere. Fork progression through the telomere was further slowed in the presence of a G4 stabilizer. Using a G4-specific antibody, we found that deficiency of BLM, or another G4-unwinding helicase, the Werner syndrome-associated helicase WRN, resulted in increased G4 structures in cells. Importantly, deficiency of either helicase led to greater increases in G4 DNA detected in the telomere compared with G4 seen genome-wide. Collectively, our findings are consistent with BLM helicase facilitating telomere replication by resolving G4 structures formed during copying of the G-rich strand by leading strand synthesis.
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Affiliation(s)
| | | | - Carl L Schildkraut
- Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461
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24
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Hisama FM, Oshima J, Martin GM. How Research on Human Progeroid and Antigeroid Syndromes Can Contribute to the Longevity Dividend Initiative. Cold Spring Harb Perspect Med 2016; 6:a025882. [PMID: 26931459 DOI: 10.1101/cshperspect.a025882] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Although translational applications derived from research on basic mechanisms of aging are likely to enhance health spans and life spans for most of us (the longevity dividend), there will remain subsets of individuals with special vulnerabilities. Medical genetics is a discipline that describes such "private" patterns of aging and can reveal underlying mechanisms, many of which support genomic instability as a major mechanism of aging. We review examples of three classes of informative disorders: "segmental progeroid syndromes" (those that appear to accelerate multiple features of aging), "unimodal progeroid syndromes" (those that impact on a single disorder of aging), and "unimodal antigeroid syndromes," variants that provide enhanced protection against specific disorders of aging; we urge our colleagues to expand our meager research efforts on the latter, including ancillary somatic cell genetic approaches.
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Affiliation(s)
- Fuki M Hisama
- Division of Medical Genetics, Department of Medicine, University of Washington School of Medicine, Seattle, Washington 98195 International Registry of Werner Syndrome, University of Washington School of Medicine, Seattle, Washington 98195
| | - Junko Oshima
- Department of Pathology, University of Washington School of Medicine, Seattle, Washington 98195 International Registry of Werner Syndrome, University of Washington School of Medicine, Seattle, Washington 98195 Department of Medicine, Chiba University, Chiba 260-8670, Japan
| | - George M Martin
- Department of Pathology, University of Washington School of Medicine, Seattle, Washington 98195 International Registry of Werner Syndrome, University of Washington School of Medicine, Seattle, Washington 98195
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25
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The DNA structure and sequence preferences of WRN underlie its function in telomeric recombination events. Nat Commun 2015; 6:8331. [PMID: 26420422 PMCID: PMC4589872 DOI: 10.1038/ncomms9331] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 08/11/2015] [Indexed: 12/27/2022] Open
Abstract
Telomeric abnormalities caused by loss of function of the RecQ helicase WRN are linked to the multiple premature ageing phenotypes that characterize Werner syndrome. Here we examine WRN's role in telomeric maintenance, by comparing its action on a variety of DNA structures without or with telomeric sequences. Our results show that WRN clearly prefers to act on strand invasion intermediates in a manner that favours strand invasion and exchange. Moreover, WRN unwinding of these recombination structures is further enhanced when the invading strand contains at least three G-rich single-stranded telomeric repeats. These selectivities are most pronounced at NaCl concentrations within the reported intranuclear monovalent cation concentration range, and are partly conferred by WRN's C-terminal region. Importantly, WRN's specificity for the G-rich telomeric sequence within this precise structural context is particularly relevant to telomere metabolism and strongly suggests a physiological role in telomeric recombination processes, including T-loop dynamics.
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26
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Iannascoli C, Palermo V, Murfuni I, Franchitto A, Pichierri P. The WRN exonuclease domain protects nascent strands from pathological MRE11/EXO1-dependent degradation. Nucleic Acids Res 2015; 43:9788-803. [PMID: 26275776 PMCID: PMC4787784 DOI: 10.1093/nar/gkv836] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 08/06/2015] [Indexed: 11/17/2022] Open
Abstract
The WRN helicase/exonuclease protein is required for proper replication fork recovery and maintenance of genome stability. However, whether the different catalytic activities of WRN cooperate to recover replication forks in vivo is unknown. Here, we show that, in response to replication perturbation induced by low doses of the TOP1 inhibitor camptothecin, loss of the WRN exonuclease resulted in enhanced degradation and ssDNA formation at nascent strands by the combined action of MRE11 and EXO1, as opposed to the limited processing of nascent strands performed by DNA2 in wild-type cells. Nascent strand degradation by MRE11/EXO1 took place downstream of RAD51 and affected the ability to resume replication, which correlated with slow replication rates in WRN exonuclease-deficient cells. In contrast, loss of the WRN helicase reduced exonucleolytic processing at nascent strands and led to severe genome instability. Our findings identify a novel role of the WRN exonuclease at perturbed forks, thus providing the first in vivo evidence for a distinct action of the two WRN enzymatic activities upon fork stalling and providing insights into the pathological mechanisms underlying the processing of perturbed forks.
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Affiliation(s)
- Chiara Iannascoli
- Section of Experimental and Computational Carcinogenesis, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Valentina Palermo
- Section of Experimental and Computational Carcinogenesis, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Ivana Murfuni
- Section of Experimental and Computational Carcinogenesis, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Annapaola Franchitto
- Section of Molecular Epidemiology, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Pietro Pichierri
- Section of Experimental and Computational Carcinogenesis, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
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27
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Abstract
Billions of base pairs of DNA must be replicated trillions of times in a human lifetime. Complete and accurate replication once and only once per cell division cycle is essential to maintain genome integrity and prevent disease. Impediments to replication fork progression including difficult to replicate DNA sequences, conflicts with transcription, and DNA damage further add to the genome maintenance challenge. These obstacles frequently cause fork stalling, but only rarely cause a failure to complete replication. Robust mechanisms ensure that stalled forks remain stable and capable of either resuming DNA synthesis or being rescued by converging forks. However, when failures do happen the fork collapses leading to genome rearrangements, cell death and disease. Despite intense interest, the mechanisms to repair damaged replication forks, stabilize them, and ensure successful replication remain only partly understood. Different models of fork collapse have been proposed with varying descriptions of what happens to the DNA and replisome. Here, I will define fork collapse and describe what is known about how the replication checkpoint prevents it to maintain genome stability.
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28
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Abstract
Genome instability is a hallmark of cancer, and DNA replication is the most vulnerable cellular process that can lead to it. Any condition leading to high levels of DNA damage will result in replication stress, which is a source of genome instability and a feature of pre-cancerous and cancerous cells. Therefore, understanding the molecular basis of replication stress is crucial to the understanding of tumorigenesis. Although a negative aspect of replication stress is its prominent role in tumorigenesis, a positive aspect is that it provides a potential target for cancer therapy. In this Review, we discuss the link between persistent replication stress and tumorigenesis, with the goal of shedding light on the mechanisms underlying the initiation of an oncogenic process, which should open up new possibilities for cancer diagnostics and treatment.
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Affiliation(s)
- Hélène Gaillard
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Av. Américo Vespucio s/n, Sevilla 41092, Spain
| | - Tatiana García-Muse
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Av. Américo Vespucio s/n, Sevilla 41092, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla, Av. Américo Vespucio s/n, Sevilla 41092, Spain
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29
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Thangavel S, Berti M, Levikova M, Pinto C, Gomathinayagam S, Vujanovic M, Zellweger R, Moore H, Lee EH, Hendrickson EA, Cejka P, Stewart S, Lopes M, Vindigni A. DNA2 drives processing and restart of reversed replication forks in human cells. ACTA ACUST UNITED AC 2015; 208:545-62. [PMID: 25733713 PMCID: PMC4347643 DOI: 10.1083/jcb.201406100] [Citation(s) in RCA: 264] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Following prolonged genotoxic stress, DNA2 and WRN functionally interact to degrade reversed replication forks and promote replication restart, thereby preventing aberrant processing of unresolved replication intermediates Accurate processing of stalled or damaged DNA replication forks is paramount to genomic integrity and recent work points to replication fork reversal and restart as a central mechanism to ensuring high-fidelity DNA replication. Here, we identify a novel DNA2- and WRN-dependent mechanism of reversed replication fork processing and restart after prolonged genotoxic stress. The human DNA2 nuclease and WRN ATPase activities functionally interact to degrade reversed replication forks with a 5′-to-3′ polarity and promote replication restart, thus preventing aberrant processing of unresolved replication intermediates. Unexpectedly, EXO1, MRE11, and CtIP are not involved in the same mechanism of reversed fork processing, whereas human RECQ1 limits DNA2 activity by preventing extensive nascent strand degradation. RAD51 depletion antagonizes this mechanism, presumably by preventing reversed fork formation. These studies define a new mechanism for maintaining genome integrity tightly controlled by specific nucleolytic activities and central homologous recombination factors.
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Affiliation(s)
- Saravanabhavan Thangavel
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104
| | - Matteo Berti
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104
| | - Maryna Levikova
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Cosimo Pinto
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Shivasankari Gomathinayagam
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104
| | - Marko Vujanovic
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Ralph Zellweger
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Hayley Moore
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Eu Han Lee
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Eric A Hendrickson
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Petr Cejka
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Sheila Stewart
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110
| | - Massimo Lopes
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Alessandro Vindigni
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104
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30
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Neelsen KJ, Lopes M. Replication fork reversal in eukaryotes: from dead end to dynamic response. Nat Rev Mol Cell Biol 2015; 16:207-20. [PMID: 25714681 DOI: 10.1038/nrm3935] [Citation(s) in RCA: 366] [Impact Index Per Article: 40.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The remodelling of replication forks into four-way junctions following replication perturbation, known as fork reversal, was hypothesized to promote DNA damage tolerance and repair during replication. Albeit conceptually attractive, for a long time fork reversal in vivo was found only in prokaryotes and specific yeast mutants, calling its evolutionary conservation and physiological relevance into question. Based on the recent visualization of replication forks in metazoans, fork reversal has emerged as a global, reversible and regulated process, with intriguing implications for replication completion, chromosome integrity and the DNA damage response. The study of the putative in vivo roles of recently identified eukaryotic factors in fork remodelling promises to shed new light on mechanisms of genome maintenance and to provide novel attractive targets for cancer therapy.
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Affiliation(s)
- Kai J Neelsen
- 1] Institute of Molecular Cancer Research, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland. [2] The Novo Nordisk Foundation Center for Protein Research, 2200 Copenhagen, Denmark
| | - Massimo Lopes
- Institute of Molecular Cancer Research, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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31
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Kotsantis P, Jones RM, Higgs MR, Petermann E. Cancer therapy and replication stress: forks on the road to perdition. Adv Clin Chem 2015; 69:91-138. [PMID: 25934360 DOI: 10.1016/bs.acc.2014.12.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Deregulated DNA replication occurs in cancer where it contributes to genomic instability. This process is a target of cytotoxic therapies. Chemotherapies exploit high DNA replication in cancer cells by modifying the DNA template or by inhibiting vital enzymatic activities that lead to slowing or stalling replication fork progression. Stalled replication forks can be converted into toxic DNA double-strand breaks resulting in cell death, i.e., replication stress. While likely crucial for many cancer treatments, replication stress is poorly understood due to its complexity. While we still know relatively little about the role of replication stress in cancer therapy, technical advances in recent years have shed new light on the effect that cancer therapeutics have on replication forks and the molecular mechanisms that lead from obstructed fork progression to cell death. This chapter will give an overview of our current understanding of replication stress in the context of cancer therapy.
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Affiliation(s)
- Panagiotis Kotsantis
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Rebecca M Jones
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Martin R Higgs
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Eva Petermann
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom.
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32
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Franchitto A, Pichierri P. Replication fork recovery and regulation of common fragile sites stability. Cell Mol Life Sci 2014; 71:4507-17. [PMID: 25216703 PMCID: PMC11113654 DOI: 10.1007/s00018-014-1718-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 08/28/2014] [Indexed: 10/24/2022]
Abstract
The acquisition of genomic instability is a triggering factor in cancer development, and common fragile sites (CFS) are the preferential target of chromosomal instability under conditions of replicative stress in the human genome. Although the mechanisms leading to CFS expression and the cellular factors required to suppress CFS instability remain largely undefined, it is clear that DNA becomes more susceptible to breakage when replication is impaired. The models proposed so far to explain how CFS instability arises imply that replication fork progression along these regions is perturbed due to intrinsic features of fragile sites and events that directly affect DNA replication. The observation that proteins implicated in the safe recovery of stalled forks or in engaging recombination at collapsed forks increase CFS expression when downregulated or mutated suggests that the stabilization and recovery of perturbed replication forks are crucial to guarantee CFS integrity.
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Affiliation(s)
- Annapaola Franchitto
- Section of Molecular Epidemiology, Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena, 299, 00161, Rome, Italy,
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33
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Chatterjee S, Zagelbaum J, Savitsky P, Sturzenegger A, Huttner D, Janscak P, Hickson ID, Gileadi O, Rothenberg E. Mechanistic insight into the interaction of BLM helicase with intra-strand G-quadruplex structures. Nat Commun 2014; 5:5556. [PMID: 25418155 PMCID: PMC4243535 DOI: 10.1038/ncomms6556] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Accepted: 10/14/2014] [Indexed: 01/15/2023] Open
Abstract
Bloom syndrome is an autosomal recessive disorder caused by mutations in the RecQ family helicase BLM that is associated with growth retardation and predisposition to cancer. BLM helicase has a high specificity for non-canonical G-quadruplex (G4) DNA structures, which are formed by G-rich DNA strands and play an important role in the maintenance of genomic integrity. Here, we used single-molecule FRET to define the mechanism of interaction of BLM helicase with intra-stranded G4 structures. We show that the activity of BLM is substrate dependent, and highly regulated by a short ssDNA segment that separates the G4 motif from dsDNA. We demonstrate cooperativity between the RQC and HRDC domains of BLM during binding and unfolding of the G4 structure, where the RQC domain interaction with G4 is stabilized by HRDC binding to ssDNA. We present a model that proposes a unique role for G4 structures in modulating the activity of DNA processing enzymes.
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Affiliation(s)
- Sujoy Chatterjee
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, MSB 394, 550 First Avenue, New York, New York 10016, USA
| | - Jennifer Zagelbaum
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, MSB 394, 550 First Avenue, New York, New York 10016, USA
| | - Pavel Savitsky
- Genome Integrity group, Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, UK
| | - Andreas Sturzenegger
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Diana Huttner
- 1] NovoNordisk Foundation Center for Protein Research, University of Copenhagen, 2200 Copenhagen, Denmark [2] Department of Cellular and Molecular Medicine, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Pavel Janscak
- Institute of Molecular Cancer Research, University of Zurich, CH-8057 Zurich, Switzerland
| | - Ian D Hickson
- Department of Cellular and Molecular Medicine, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Opher Gileadi
- Genome Integrity group, Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, UK
| | - Eli Rothenberg
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, MSB 394, 550 First Avenue, New York, New York 10016, USA
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Zimmermann M, Kibe T, Kabir S, de Lange T. TRF1 negotiates TTAGGG repeat-associated replication problems by recruiting the BLM helicase and the TPP1/POT1 repressor of ATR signaling. Genes Dev 2014; 28:2477-91. [PMID: 25344324 PMCID: PMC4233241 DOI: 10.1101/gad.251611.114] [Citation(s) in RCA: 140] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The semiconservative replication of telomeres is facilitated by the shelterin component TRF1. Without TRF1, replication forks stall in the telomeric repeats, leading to ATR kinase signaling upon S-phase progression, fragile metaphase telomeres that resemble the common fragile sites (CFSs), and the association of sister telomeres. In contrast, TRF1 does not contribute significantly to the end protection functions of shelterin. We addressed the mechanism of TRF1 action using mouse conditional knockouts of BLM, TRF1, TPP1, and Rap1 in combination with expression of TRF1 and TIN2 mutants. The data establish that TRF1 binds BLM to facilitate lagging but not leading strand telomeric DNA synthesis. As the template for lagging strand telomeric DNA synthesis is the TTAGGG repeat strand, TRF1-bound BLM is likely required to remove secondary structures formed by these sequences. In addition, the data establish that TRF1 deploys TIN2 and the TPP1/POT1 heterodimers in shelterin to prevent ATR during telomere replication and repress the accompanying sister telomere associations. Thus, TRF1 uses two distinct mechanisms to promote replication of telomeric DNA and circumvent the consequences of replication stress. These data are relevant to the expression of CFSs and provide insights into TIN2, which is compromised in dyskeratosis congenita (DC) and related disorders.
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Affiliation(s)
- Michal Zimmermann
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA; Central European Institute of Technology, Masaryk University, Brno 625 00, Czech Republic
| | - Tatsuya Kibe
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
| | - Shaheen Kabir
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA;
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35
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Ben Salah G, Hadj Salem I, Masmoudi A, Kallabi F, Turki H, Fakhfakh F, Ayadi H, Kamoun H. A novel frameshift mutation in BLM gene associated with high sister chromatid exchanges (SCE) in heterozygous family members. Mol Biol Rep 2014; 41:7373-80. [PMID: 25129257 DOI: 10.1007/s11033-014-3624-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 07/19/2014] [Indexed: 12/01/2022]
Abstract
The Bloom syndrome (BS) is an autosomic recessive disorder comprising a wide range of abnormalities, including stunted growth, immunodeficiency, sun sensitivity and increased frequency of various types of cancer. Bloom syndrome cells display a high level of genetic instability, including a 10-fold increase in the sister chromatid exchanges (SCE) level. Bloom syndrome arises through mutations in both alleles of the BLM gene, which was identified as a member of the RecQ helicase family. In this study, we screened a Tunisian family with three BS patients. Cytogenetic analysis showed several chromosomal aberrations, and an approximately 14-fold elevated SCE frequency in BS cells. A significant increase in SCE frequency was observed in some family members but not reaching the BS patients values, leading to suggest that this could be due to the heterozygous profile. Microsatellite genotyping using four fluorescent dye-labeled microsatellite markers revealed evidence of linkage to BLM locus and the healthy members, sharing higher SCE frequency, showed heterozygous haplotypes as expected. Additionally, the direct BLM gene sequencing identified a novel homozygous frameshift mutation c.3617-3619delAA (p.K1207fsX9) in BS patients and a heterozygous BLM mutation in the family members with higher SCE frequency. Our findings suggest that this latter mutation likely leads to a reduced BLM activity explaining the homologous recombination repair defect and, therefore, the increase in SCE. Based on the present data, the screening of this mutation could contribute to the rapid diagnosis of BS. The genetic confirmation of the mutation in BLM gene provides crucial information for genetic counseling and prenatal diagnosis.
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Affiliation(s)
- Ghada Ben Salah
- Laboratory of Human Molecular Genetics, Faculty of Medicine, University of Sfax, Av. Majida Boulila, 3029, Sfax, Tunisia,
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36
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León-Ortiz AM, Svendsen J, Boulton SJ. Metabolism of DNA secondary structures at the eukaryotic replication fork. DNA Repair (Amst) 2014; 19:152-62. [PMID: 24815912 DOI: 10.1016/j.dnarep.2014.03.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
DNA secondary structures are largely advantageous for numerous cellular processes but can pose specific threats to the progression of the replication machinery and therefore genome duplication and cell division. A number of specialized enzymes dismantle these structures to allow replication fork progression to proceed faithfully. In this review, we discuss the in vitro and in vivo data that has lead to the identification of these enzymes in eukaryotes, and the evidence that suggests that they act specifically at replication forks to resolve secondary structures. We focus on the role of helicases, which catalyze the dissociation of nucleotide complexes, and on the role of nucleases, which cleave secondary structures to allow replication fork progression at the expense of local rearrangements. Finally, we discuss outstanding questions in terms of dismantling DNA secondary structures, as well as the interplay between diverse enzymes that act upon specific types of structures.
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Affiliation(s)
- Ana María León-Ortiz
- DNA Damage Response Laboratory, London Research Institute, Cancer Research UK, Clare Hall, South Mimms EN6 3LD, UK
| | - Jennifer Svendsen
- DNA Damage Response Laboratory, London Research Institute, Cancer Research UK, Clare Hall, South Mimms EN6 3LD, UK
| | - Simon J Boulton
- DNA Damage Response Laboratory, London Research Institute, Cancer Research UK, Clare Hall, South Mimms EN6 3LD, UK.
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37
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The Drosophila Werner exonuclease participates in an exonuclease-independent response to replication stress. Genetics 2014; 197:643-52. [PMID: 24709634 DOI: 10.1534/genetics.114.164228] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Members of the RecQ family of helicases are known for their roles in DNA repair, replication, and recombination. Mutations in the human RecQ helicases, WRN and BLM, cause Werner and Bloom syndromes, which are diseases characterized by genome instability and an increased risk of cancer. While WRN contains both a helicase and an exonuclease domain, the Drosophila melanogaster homolog, WRNexo, contains only the exonuclease domain. Therefore the Drosophila model system provides a unique opportunity to study the exonuclease functions of WRN separate from the helicase. We created a null allele of WRNexo via imprecise P-element excision. The null WRNexo mutants are not sensitive to double-strand break-inducing reagents, suggesting that the exonuclease does not play a key role in homologous recombination-mediated repair of DSBs. However, WRNexo mutant embryos have a reduced hatching frequency and larvae are sensitive to the replication fork-stalling reagent, hydroxyurea (HU), suggesting that WRNexo is important in responding to replication stress. The role of WRNexo in the HU-induced stress response is independent of Rad51. Interestingly, the hatching defect and HU sensitivity of WRNexo mutants do not occur in flies containing an exonuclease-dead copy of WRNexo, suggesting that the role of WRNexo in replication is independent of exonuclease activity. Additionally, WRNexo and Blm mutants exhibit similar sensitivity to HU and synthetic lethality in combination with mutations in structure-selective endonucleases. We propose that WRNexo and BLM interact to promote fork reversal following replication fork stalling and in their absence regressed forks are restarted through a Rad51-mediated process.
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38
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Croteau DL, Popuri V, Opresko PL, Bohr VA. Human RecQ helicases in DNA repair, recombination, and replication. Annu Rev Biochem 2014; 83:519-52. [PMID: 24606147 DOI: 10.1146/annurev-biochem-060713-035428] [Citation(s) in RCA: 404] [Impact Index Per Article: 40.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
RecQ helicases are an important family of genome surveillance proteins conserved from bacteria to humans. Each of the five human RecQ helicases plays critical roles in genome maintenance and stability, and the RecQ protein family members are often referred to as guardians of the genome. The importance of these proteins in cellular homeostasis is underscored by the fact that defects in BLM, WRN, and RECQL4 are linked to distinct heritable human disease syndromes. Each human RecQ helicase has a unique set of protein-interacting partners, and these interactions dictate its specialized functions in genome maintenance, including DNA repair, recombination, replication, and transcription. Human RecQ helicases also interact with each other, and these interactions have significant impact on enzyme function. Future research goals in this field include a better understanding of the division of labor among the human RecQ helicases and learning how human RecQ helicases collaborate and cooperate to enhance genome stability.
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Affiliation(s)
- Deborah L Croteau
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, Maryland 21224;
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39
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Rass U. Resolving branched DNA intermediates with structure-specific nucleases during replication in eukaryotes. Chromosoma 2013; 122:499-515. [PMID: 24008669 PMCID: PMC3827899 DOI: 10.1007/s00412-013-0431-z] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 08/03/2013] [Accepted: 08/08/2013] [Indexed: 11/29/2022]
Abstract
Genome duplication requires that replication forks track the entire length of every chromosome. When complications occur, homologous recombination-mediated repair supports replication fork movement and recovery. This leads to physical connections between the nascent sister chromatids in the form of Holliday junctions and other branched DNA intermediates. A key role in the removal of these recombination intermediates falls to structure-specific nucleases such as the Holliday junction resolvase RuvC in Escherichia coli. RuvC is also known to cut branched DNA intermediates that originate directly from blocked replication forks, targeting them for origin-independent replication restart. In eukaryotes, multiple structure-specific nucleases, including Mus81-Mms4/MUS81-EME1, Yen1/GEN1, and Slx1-Slx4/SLX1-SLX4 (FANCP) have been implicated in the resolution of branched DNA intermediates. It is becoming increasingly clear that, as a group, they reflect the dual function of RuvC in cleaving recombination intermediates and failing replication forks to assist the DNA replication process.
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Affiliation(s)
- Ulrich Rass
- Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, 4058, Basel, Switzerland,
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40
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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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41
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Carroll C, Badu-Nkansah A, Hunley T, Baradaran-Heravi A, Cortez D, Frangoul H. Schimke Immunoosseous Dysplasia associated with undifferentiated carcinoma and a novel SMARCAL1 mutation in a child. Pediatr Blood Cancer 2013; 60:E88-90. [PMID: 23630135 PMCID: PMC3713188 DOI: 10.1002/pbc.24542] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 03/01/2013] [Indexed: 12/25/2022]
Abstract
Schimke Immunoosseous Dysplasia (SIOD) is a rare, autosomal recessive disorder of childhood with classical features of spondyloepiphyseal dysplasia, renal failure, and T cell immunodeficiency. SIOD has been associated with several malignancies, including non-Hodgkin lymphoma and osteosarcoma. About half of SIOD patients have biallelic mutations in SMARCAL1 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily a-like 1). This gene encodes an annealing helicase and replication stress response protein that localizes to damage-stalled DNA replication forks. We report a child with SIOD and a novel S859P missense mutation in SMARCAL1 who developed undifferentiated carcinoma of the sinus.
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Affiliation(s)
- Clinton Carroll
- Division of Pediatric Hematology/Oncology, Monroe Carell Jr. Children's Hospital, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6310, USA.
| | - Akosua Badu-Nkansah
- Biochemistry, Monroe Carell Jr. Children’s Hospital, Vanderbilt University School of Medicine, Nashville, TN, United States, 37232
| | - Tracy Hunley
- Pediatric Nephrology, Monroe Carell Jr. Children’s Hospital, Vanderbilt University School of Medicine, Nashville, TN, United States, 37232
| | - Alireza Baradaran-Heravi
- Department of Medical Genetics, University of British Columbia, Child & Family Research Institute, Vancouver, British Columbia, Canada V5Z4H4
| | - David Cortez
- Biochemistry, Monroe Carell Jr. Children’s Hospital, Vanderbilt University School of Medicine, Nashville, TN, United States, 37232
| | - Haydar Frangoul
- Pediatric Hematology/Oncology, Monroe Carell Jr. Children’s Hospital, Vanderbilt University School of Medicine, Nashville, TN, United States, 37232
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42
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Yamanishi A, Yusa K, Horie K, Tokunaga M, Kusano K, Kokubu C, Takeda J. Enhancement of microhomology-mediated genomic rearrangements by transient loss of mouse Bloom syndrome helicase. Genome Res 2013; 23:1462-73. [PMID: 23908384 PMCID: PMC3759722 DOI: 10.1101/gr.152744.112] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Bloom syndrome, an autosomal recessive disorder of the BLM gene, confers predisposition to a broad spectrum of early-onset cancers in multiple tissue types. Loss of genomic integrity is a primary hallmark of such human malignancies, but many studies using disease-affected specimens are limited in that they are retrospective and devoid of an appropriate experimental control. To overcome this, we devised an experimental system to recapitulate the early molecular events in genetically engineered mouse embryonic stem cells, in which cells undergoing loss of heterozygosity (LOH) can be enriched after inducible down-regulation of Blm expression, with or without site-directed DNA double-strand break (DSB) induction. Transient loss of BLM increased the rate of LOH, whose breakpoints were distributed along the chromosome. Combined with site-directed DSB induction, loss of BLM synergistically increased the rate of LOH and concentrated the breakpoints around the targeted chromosomal region. We characterized the LOH events using specifically tailored genomic tools, such as high-resolution array comparative genomic hybridization and high-density single nucleotide polymorphism genotyping, revealing that the combination of BLM suppression and DSB induction enhanced genomic rearrangements, including deletions and insertions, whose breakpoints were clustered in genomic inverted repeats and associated with junctional microhomologies. Our experimental approach successfully uncovered the detailed molecular mechanisms of as-yet-uncharacterized loss of heterozygosities and reveals the significant contribution of microhomology-mediated genomic rearrangements, which could be widely applicable to the early steps of cancer formation in general.
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Affiliation(s)
- Ayako Yamanishi
- Department of Social and Environmental Medicine, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
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43
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Abstract
Helicases have major roles in genome maintenance by unwinding structured nucleic acids. Their prominence is marked by various cancers and genetic disorders that are linked to helicase defects. Although considerable effort has been made to understand the functions of DNA helicases that are important for genomic stability and cellular homeostasis, the complexity of the DNA damage response leaves us with unanswered questions regarding how helicase-dependent DNA repair pathways are regulated and coordinated with cell cycle checkpoints. Further studies may open the door to targeting helicases in order to improve cancer treatments based on DNA-damaging chemotherapy or radiation.
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Affiliation(s)
- Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA.
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44
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Sirbu BM, Cortez D. DNA damage response: three levels of DNA repair regulation. Cold Spring Harb Perspect Biol 2013; 5:a012724. [PMID: 23813586 DOI: 10.1101/cshperspect.a012724] [Citation(s) in RCA: 174] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Genome integrity is challenged by DNA damage from both endogenous and environmental sources. This damage must be repaired to allow both RNA and DNA polymerases to accurately read and duplicate the information in the genome. Multiple repair enzymes scan the DNA for problems, remove the offending damage, and restore the DNA duplex. These repair mechanisms are regulated by DNA damage response kinases including DNA-PKcs, ATM, and ATR that are activated at DNA lesions. These kinases improve the efficiency of DNA repair by phosphorylating repair proteins to modify their activities, by initiating a complex series of changes in the local chromatin structure near the damage site, and by altering the overall cellular environment to make it more conducive to repair. In this review, we focus on these three levels of regulation to illustrate how the DNA damage kinases promote efficient repair to maintain genome integrity and prevent disease.
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Affiliation(s)
- Bianca M Sirbu
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37027, USA
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45
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Human RECQ1 promotes restart of replication forks reversed by DNA topoisomerase I inhibition. Nat Struct Mol Biol 2013; 20:347-54. [PMID: 23396353 PMCID: PMC3897332 DOI: 10.1038/nsmb.2501] [Citation(s) in RCA: 368] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 12/26/2012] [Indexed: 12/31/2022]
Abstract
Topoisomerase I (TOP1) inhibitors are an important class of anticancer drugs. The cytotoxicity of TOP1 inhibitors can be modulated by replication fork reversal, in a process that requires PARP activity. Whether regressed forks can efficiently restart and the factors required to restart fork progression after fork reversal are still unknown. Here we combined biochemical and electron microscopy approaches with single-molecule DNA fiber analysis, to identify a key role for human RECQ1 helicase in replication fork restart after TOP1 inhibition, not shared by other human RecQ proteins. We show that the poly(ADPribosyl)ation activity of PARP1 stabilizes forks in their regressed state by limiting their restart by RECQ1. These studies provide new mechanistic insights into the roles of RECQ1 and PARP in DNA replication and offer molecular perspectives to potentiate chemotherapeutic regimens based on TOP1 inhibition.
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46
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Sidorova JM, Kehrli K, Mao F, Monnat R. Distinct functions of human RECQ helicases WRN and BLM in replication fork recovery and progression after hydroxyurea-induced stalling. DNA Repair (Amst) 2012; 12:128-39. [PMID: 23253856 DOI: 10.1016/j.dnarep.2012.11.005] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 10/15/2012] [Accepted: 11/18/2012] [Indexed: 12/21/2022]
Abstract
Human WRN and BLM genes are members of the conserved RECQ helicase family. Mutations in these genes are associated with Werner and Bloom syndromes. WRN and BLM proteins are implicated in DNA replication, recombination, repair, telomere maintenance, and transcription. Using microfluidics-assisted display of DNA for replication track analysis (ma-RTA), we show that WRN and BLM contribute additively to normal replication fork progression, and non-additively, in a RAD51-dependent pathway, to resumption of replication after arrest by hydroxyurea (HU), a replication-stalling drug. WRN but not BLM is required to support fork progression after HU. Resumption of replication by forks may be necessary but is not sufficient for timely completion of the cell cycle after HU arrest, as depletion of WRN or BLM compromises fork recovery to a similar degree, but only BLM depletion leads to extensive delay of cell division after HU, as well as more pronounced chromatin bridging. Finally, we show that recovery from HU includes apparent removal of some of the DNA that was synthesized immediately after release from HU, a novel phenomenon that we refer to as nascent strand processing, NSP.
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Affiliation(s)
- Julia M Sidorova
- Department of Pathology, University of Washington, Seattle, WA 98195-7705, United States.
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47
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Maddukuri L, Ketkar A, Eddy S, Zafar MK, Griffin WC, Eoff RL. Enhancement of human DNA polymerase η activity and fidelity is dependent upon a bipartite interaction with the Werner syndrome protein. J Biol Chem 2012; 287:42312-23. [PMID: 23045531 DOI: 10.1074/jbc.m112.410332] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We have investigated the interaction between human DNA polymerase η (hpol η) and the Werner syndrome protein (WRN). Functional assays revealed that the WRN exonuclease and RecQ C-terminal (RQC) domains are necessary for full stimulation of hpol η-catalyzed formation of correct base pairs. We find that WRN does not stimulate hpol η-catalyzed formation of mispairs. Moreover, the exonuclease activity of WRN prevents stable mispair formation by hpol η. These results are consistent with a proofreading activity for WRN during single-nucleotide additions. ATP hydrolysis by WRN appears to attenuate stimulation of hpol η. Pre-steady-state kinetic results show that k(pol) is increased 4-fold by WRN. Finally, pulldown assays reveal a bipartite physical interaction between hpol η and WRN that is mediated by the exonuclease and RQC domains. Taken together, these results are consistent with alteration of the rate-limiting step in polymerase catalysis by direct protein-protein interactions between WRN and hpol η. In summary, WRN improves the efficiency and fidelity of hpol η to promote more effective replication of DNA.
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Affiliation(s)
- Leena Maddukuri
- Department of Biochemistry and Molecular Biology, The University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205-7199, USA
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48
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Unwinding and rewinding: double faces of helicase? J Nucleic Acids 2012; 2012:140601. [PMID: 22888405 PMCID: PMC3409536 DOI: 10.1155/2012/140601] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Accepted: 05/28/2012] [Indexed: 12/29/2022] Open
Abstract
Helicases are enzymes that use ATP-driven motor force to unwind double-stranded DNA or RNA. Recently, increasing evidence demonstrates that some helicases also possess rewinding activity—in other words, they can anneal two complementary single-stranded nucleic acids. All five members of the human RecQ helicase family, helicase PIF1, mitochondrial helicase TWINKLE, and helicase/nuclease Dna2 have been shown to possess strand-annealing activity. Moreover, two recently identified helicases—HARP and AH2 have only ATP-dependent rewinding activity. These findings not only enhance our understanding of helicase enzymes but also establish the presence of a new type of protein: annealing helicases. This paper discusses what is known about these helicases, focusing on their biochemical activity to zip and unzip double-stranded DNA and/or RNA, their possible regulation mechanisms, and biological functions.
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Mazina OM, Rossi MJ, Deakyne JS, Huang F, Mazin AV. Polarity and bypass of DNA heterology during branch migration of Holliday junctions by human RAD54, BLM, and RECQ1 proteins. J Biol Chem 2012; 287:11820-32. [PMID: 22356911 DOI: 10.1074/jbc.m112.341347] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Several proteins have been shown to catalyze branch migration (BM) of the Holliday junction, a key intermediate in DNA repair and recombination. Here, using joint molecules made by human RAD51 or Escherichia coli RecA, we find that the polarity of the displaced ssDNA strand of the joint molecules defines the polarity of BM of RAD54, BLM, RECQ1, and RuvAB. Our results demonstrate that RAD54, BLM, and RECQ1 promote BM preferentially in the 3'→5' direction, whereas RuvAB drives it in the 5'→3' direction relative to the displaced ssDNA strand. Our data indicate that the helicase activity of BM proteins does not play a role in the heterology bypass. Thus, RAD54 that lacks helicase activity is more efficient in DNA heterology bypass than BLM or REQ1 helicases. Furthermore, we demonstrate that the BLM helicase and BM activities require different protein stoichiometries, indicating that different complexes, monomers and multimers, respectively, are responsible for these two activities. These results define BM as a mechanistically distinct activity of DNA translocating proteins, which may serve an important function in DNA repair and recombination.
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Affiliation(s)
- Olga M Mazina
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102-1192, USA
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Kamath-Loeb AS, Shen JC, Schmitt MW, Loeb LA. The Werner syndrome exonuclease facilitates DNA degradation and high fidelity DNA polymerization by human DNA polymerase δ. J Biol Chem 2012; 287:12480-90. [PMID: 22351772 DOI: 10.1074/jbc.m111.332577] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA Polymerase δ (Pol δ) and the Werner syndrome protein, WRN, are involved in maintaining cellular genomic stability. Pol δ synthesizes the lagging strand during replication of genomic DNA and also functions in the synthesis steps of DNA repair and recombination. WRN is a member of the RecQ helicase family, loss of which results in the premature aging and cancer-prone disorder, Werner syndrome. Both Pol δ and WRN encode 3' → 5' DNA exonuclease activities. Pol δ exonuclease removes 3'-terminal mismatched nucleotides incorporated during replication to ensure high fidelity DNA synthesis. WRN exonuclease degrades DNA containing alternate secondary structures to prevent formation and enable resolution of stalled replication forks. We now observe that similarly to WRN, Pol δ degrades alternate DNA structures including bubbles, four-way junctions, and D-loops. Moreover, WRN and Pol δ form a complex with enhanced ability to hydrolyze these structures. We also present evidence that WRN can proofread for Pol δ; WRN excises 3'-terminal mismatches to enable primer extension by Pol δ. Consistent with our in vitro observations, we show that WRN contributes to the maintenance of DNA synthesis fidelity in vivo. Cells expressing limiting amounts (∼10% of normal) of WRN have elevated mutation frequencies compared with wild-type cells. Together, our data highlight the importance of WRN exonuclease activity and its cooperativity with Pol δ in preserving genome stability, which is compromised by the loss of WRN in Werner syndrome.
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