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Chan EM, Foster KJ, Bass AJ. WRN Is a Promising Synthetic Lethal Target for Cancers with Microsatellite Instability (MSI). Cancer Treat Res 2023; 186:313-328. [PMID: 37978143 DOI: 10.1007/978-3-031-30065-3_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2023]
Abstract
Microsatellite instability (MSI), a type of genetic hypermutability arising from impaired DNA mismatch repair (MMR), is observed in approximately 3% of all cancers. Preclinical work has identified the RecQ helicase WRN as a promising synthetic lethal target for patients with MSI cancers. WRN depletion substantially impairs the viability of MSI, but not microsatellite stable (MSS), cells. Experimental evidence suggests that this synthetic lethal phenotype is driven by numerous TA dinucleotide repeats that undergo expansion mutations in the setting of long-standing MMR deficiency. The lengthening of TA repeats increases their propensity to form secondary DNA structures that require WRN to resolve. In the absence of WRN helicase activity, these unresolved DNA secondary structures stall DNA replication forks and induce catastrophic DNA damage.
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Affiliation(s)
- Edmond M Chan
- Department of Medicine, Division of Hematology and Oncology, Columbia University, New York, USA.
- Herbert Irving Comprehensive Cancer Center, Columbia University, New York, USA.
- Broad Institute of MIT and Harvard, Cambridge, USA.
- New York Genome Center, New York, USA.
| | | | - Adam J Bass
- Novartis Institutes for BioMedical Research, Cambridge, USA
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2
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Oliver J, Quezada Urban R, Franco Cortés CA, Díaz Velásquez CE, Montealegre Paez AL, Pacheco-Orozco RA, Castro Rojas C, García-Robles R, López Rivera JJ, Gaitán Chaparro S, Gómez AM, Suarez Obando F, Giraldo G, Maya MI, Hurtado-Villa P, Sanchez AI, Serrano N, Orduz Galvis AI, Aruachan S, Nuñez Castillo J, Frecha C, Riggi C, Jauk F, Gómez García EM, Carranza CL, Zamora V, Torres Mejía G, Romieu I, Castañeda CA, Castillo M, Gitler R, Antoniano A, Rojas Jiménez E, Romero Cruz LE, Vallejo Lecuona F, Delgado Enciso I, Martínez Rizo AB, Flores Carranza A, Benites Godinez V, Méndez Catalá CF, Herrera LA, Chirino YI, Terrazas LI, Perdomo S, Vaca Paniagua F. Latin American Study of Hereditary Breast and Ovarian Cancer LACAM: A Genomic Epidemiology Approach. Front Oncol 2019; 9:1429. [PMID: 31921681 PMCID: PMC6933010 DOI: 10.3389/fonc.2019.01429] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 12/02/2019] [Indexed: 12/29/2022] Open
Abstract
Purpose: Hereditary Breast and Ovarian Cancer (HBOC) syndrome is responsible for ~5-10% of all diagnosed breast and ovarian cancers. Breast cancer is the most common malignancy and the leading cause of cancer-related mortality among women in Latin America (LA). The main objective of this study was to develop a comprehensive understanding of the genomic epidemiology of HBOC throughout the establishment of The Latin American consortium for HBOC-LACAM, consisting of specialists from 5 countries in LA and the description of the genomic results from the first phase of the study. Methods: We have recruited 403 individuals that fulfilled the criteria for HBOC from 11 health institutions of Argentina, Colombia, Guatemala, Mexico and Peru. A pilot cohort of 222 individuals was analyzed by NGS gene panels. One hundred forty-three genes were selected on the basis of their putative role in susceptibility to different hereditary cancers. Libraries were sequenced in MiSeq (Illumina, Inc.) and PGM (Ion Torrent-Thermo Fisher Scientific) platforms. Results: The overall prevalence of pathogenic variants was 17% (38/222); the distribution spanned 14 genes and varied by country. The highest relative prevalence of pathogenic variants was found in patients from Argentina (25%, 14/57), followed by Mexico (18%, 12/68), Guatemala (16%, 3/19), and Colombia (13%, 10/78). Pathogenic variants were found in BRCA1 (20%) and BRCA2 (29%) genes. Pathogenic variants were found in other 12 genes, including high and moderate risk genes such as MSH2, MSH6, MUTYH, and PALB2. Additional pathogenic variants were found in HBOC unrelated genes such as DCLRE1C, WRN, PDE11A, and PDGFB. Conclusion: In this first phase of the project, we recruited 403 individuals and evaluated the germline genetic alterations in an initial cohort of 222 patients among 4 countries. Our data show for the first time in LA the distribution of pathogenic variants in a broad set of cancer susceptibility genes in HBOC. Even though we used extended gene panels, there was still a high proportion of patients without any detectable pathogenic variant, which emphasizes the larger, unexplored genetic nature of the disease in these populations.
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Affiliation(s)
- Javier Oliver
- Medical Oncology Service, Hospitales Universitarios Regional y Virgen de la Victoria, Institute of Biomedical Research in Malaga, CIMES, University of Málaga, Málaga, Spain
- Laboratorio de Secuenciación, Instituto de Medicina Traslacional e Ingeniería Biomédica, Hospital Italiano de Buenos Aires, Buenos Aires, Argentina
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
| | - Rosalía Quezada Urban
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | - Claudia Alejandra Franco Cortés
- Laboratorio de Secuenciación, Instituto de Medicina Traslacional e Ingeniería Biomédica, Hospital Italiano de Buenos Aires, Buenos Aires, Argentina
| | - Clara Estela Díaz Velásquez
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
| | - Ana Lorena Montealegre Paez
- Instituto de Nutrición, Genética y Metabolismo, Facultad de Medicina, Universidad El Bosque, Bogota, Colombia
| | | | - Carlos Castro Rojas
- Instituto de Nutrición, Genética y Metabolismo, Facultad de Medicina, Universidad El Bosque, Bogota, Colombia
| | - Reggie García-Robles
- Instituto de Nutrición, Genética y Metabolismo, Facultad de Medicina, Universidad El Bosque, Bogota, Colombia
| | - Juan Javier López Rivera
- Grupo INPAC, Organización Keralty, Departamento de Genética, Clínica Universitaria Colombia, Bogotá, Colombia
| | - Sandra Gaitán Chaparro
- Grupo INPAC, Organización Keralty, Facultad de Medicina, Fundación Universitaria Sanitas, Bogotá, Colombia
| | - Ana Milena Gómez
- Servicio de Genética, Hospital Universitario San Ignacio, Bogotá, Colombia
| | - Fernando Suarez Obando
- Servicio de Genética, Hospital Universitario San Ignacio, Bogotá, Colombia
- Instituto de Genética Humana, Facultad de Medicina, Pontificia Universidad Javeriana, Bogotá, Colombia
| | - Gustavo Giraldo
- Clínica Universitaria Bolivariana, Pontificia Universidad Bolivariana, Medellín, Colombia
| | - Maria Isabel Maya
- Clínica Universitaria Bolivariana, Pontificia Universidad Bolivariana, Medellín, Colombia
| | - Paula Hurtado-Villa
- Departamento Ciencias Básicas de Salud, Facultad de Ciencias de la Salud, Pontificia Universidad Javeriana Cali, Cali, Colombia
- Centro Médico Imbanaco, Cali, Colombia
| | - Ana Isabel Sanchez
- Centro Médico Imbanaco, Cali, Colombia
- Departamento Materno Infantil, Facultad de Ciencias de la Salud, Pontificia Universidad Javeriana Cali, Cali, Colombia
| | - Norma Serrano
- Fundación Cardiovascular de Colombia, Centro de Investigaciones, Floridablanca, Colombia
| | | | - Sandra Aruachan
- Departamento de Investigación y Estudios Clínicos, IMAT - Oncomédica S.A., Montería, Colombia
| | - Johanna Nuñez Castillo
- Departamento de Investigación y Estudios Clínicos, IMAT - Oncomédica S.A., Montería, Colombia
| | - Cecilia Frecha
- Instituto de Medicina Traslacional e Ingeniería Biomédica, CONICET-Instituto Universitario del Hospital Italiano-Hospital Italiano de Buenos Aires, Buenos Aires, Argentina
| | - Cecilia Riggi
- Servicio de Ginecología, Hospital Italiano de Buenos Aires, Buenos Aires, Argentina
| | - Federico Jauk
- Laboratorio de Secuenciación, Instituto de Medicina Traslacional e Ingeniería Biomédica, Hospital Italiano de Buenos Aires, Buenos Aires, Argentina
| | | | | | | | | | - Isabelle Romieu
- Instituto Nacional de Salud Pública, Cuernavaca, Mexico
- Hubert Department of Global Health, Emory University, Atlanta, GA, United States
| | - Carlos Arturo Castañeda
- Departamento de Oncología Médica, Instituto Nacional de Enfermedades Neoplásicas, Lima, Peru
| | - Miluska Castillo
- Departamento de Investigación, Instituto Nacional de Enfermedades Neoplásicas, Lima, Peru
| | | | | | - Ernesto Rojas Jiménez
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | - Luis Enrique Romero Cruz
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | - Fernando Vallejo Lecuona
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | | | | | | | | | - Claudia Fabiola Méndez Catalá
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
| | - Luis Alonso Herrera
- Unidad de Investigación Biomédica en Cáncer, Instituto de Investigaciones Biomédicas-Instituto Nacional de Cancerología, Ciudad de México, Mexico
| | - Yolanda Irasema Chirino
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | - Luis Ignacio Terrazas
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
| | - Sandra Perdomo
- Instituto de Nutrición, Genética y Metabolismo, Facultad de Medicina, Universidad El Bosque, Bogota, Colombia
- Departamento de Patología, Hospital Universitario Fundación Santa Fe de Bogotá, Bogota, Colombia
| | - Felipe Vaca Paniagua
- Laboratorio Nacional en Salud, Diagnóstico Molecular y Efecto Ambiental en Enfermedades Crónico-Degenerativas, Facultad de Estudios Superiores Iztacala, Tlalnepantla de Baz, Mexico
- Unidad de Biomedicina, Facultad de Estudios Superiores Iztacala, UNAM, Tlalnepantla de Baz, Mexico
- Instituto Nacional de Cancerología, Ciudad de México, Mexico
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3
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Li B, Reddy S, Comai L. The Werner Syndrome Helicase Coordinates Sequential Strand Displacement and FEN1-Mediated Flap Cleavage during Polymerase δ Elongation. Mol Cell Biol 2017; 37:e00560-16. [PMID: 27849570 DOI: 10.1128/MCB.00560-16] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 11/08/2016] [Indexed: 02/01/2023] Open
Abstract
The Werner syndrome protein (WRN) suppresses the loss of telomeres replicated by lagging-strand synthesis by a yet to be defined mechanism. Here, we show that whereas either WRN or the Bloom syndrome helicase (BLM) stimulates DNA polymerase δ progression across telomeric G-rich repeats, only WRN promotes sequential strand displacement synthesis and FEN1 cleavage, a critical step in Okazaki fragment maturation, at these sequences. Helicase activity, as well as the conserved winged-helix (WH) motif and the helicase and RNase D C-terminal (HRDC) domain play important but distinct roles in this process. Remarkably, WRN also influences the formation of FEN1 cleavage products during strand displacement on a nontelomeric substrate, suggesting that WRN recruitment and cooperative interaction with FEN1 during lagging-strand synthesis may serve to regulate sequential strand displacement and flap cleavage at other genomic sites. These findings define a biochemical context for the physiological role of WRN in maintaining genetic stability.
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4
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Grundy GJ, Moulding HA, Caldecott KW, Rulten SL. One ring to bring them all--the role of Ku in mammalian non-homologous end joining. DNA Repair (Amst) 2014; 17:30-8. [PMID: 24680220 DOI: 10.1016/j.dnarep.2014.02.019] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 02/25/2014] [Indexed: 12/26/2022]
Abstract
The repair of DNA double strand breaks is essential for cell survival and several conserved pathways have evolved to ensure their rapid and efficient repair. The non-homologous end joining pathway is initiated when Ku binds to the DNA break site. Ku is an abundant nuclear heterodimer of Ku70 and Ku80 with a toroidal structure that allows the protein to slide over the broken DNA end and bind with high affinity. Once locked into placed, Ku acts as a tool-belt to recruit multiple interacting proteins, forming one or more non-homologous end joining complexes that act in a regulated manner to ensure efficient repair of DNA ends. Here we review the structure and functions of Ku and the proteins with which it interacts during non-homologous end joining.
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Affiliation(s)
- Gabrielle J Grundy
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Hayley A Moulding
- School of Biochemistry, Medical Sciences, University Walk, Bristol BS8 1TD, UK
| | - Keith W Caldecott
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Stuart L Rulten
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
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5
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Liu D, Deng X, Yuan C, Chen L, Cong Y, Xu X. Werner syndrome protein positively regulates XRCC4-like factor transcription. Mol Med Rep 2014; 9:1648-52. [PMID: 24626809 PMCID: PMC4020486 DOI: 10.3892/mmr.2014.2030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2013] [Accepted: 02/24/2014] [Indexed: 01/20/2023] Open
Abstract
XRCC4-like factor (XLF) is involved in non-homologous end joining-mediated repair of DNA double-strand breaks (DSBs). Mutations in the WRN gene results in the development of Werner syndrome (WS), a rare autosomal recessive disorder characterized by premature ageing and genome instability. In the present study, it was identified that XLF protein levels were lower in WRN-deficient fibroblasts, compared with normal fibroblasts. Depletion of WRN in HeLa cells led to a decrease of XLF mRNA and its promoter activity. Chromatin immunoprecipitation assays demonstrated that WRN was associated with the XLF promoter. Depletion of XLF in normal human fibroblasts increased the percentage of β-galactosidase (β-gal) staining-positive cells, indicating acceleration in cellular senescence. Taken together, the results suggest that XLF is a transcriptional target of WRN and may be involved in the regulation of cellular senescence.
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Affiliation(s)
- Dongyun Liu
- Beijing Key Laboratory of DNA Damage Response, College of Life Science, Capital Normal University, Beijing 100048, P.R. China
| | - Xiaoli Deng
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou, Zhejiang 310036, P.R. China
| | - Chongzhen Yuan
- Beijing Key Laboratory of DNA Damage Response, College of Life Science, Capital Normal University, Beijing 100048, P.R. China
| | - Lin Chen
- Beijing Key Laboratory of DNA Damage Response, College of Life Science, Capital Normal University, Beijing 100048, P.R. China
| | - Yusheng Cong
- Institute of Aging Research, Hangzhou Normal University School of Medicine, Hangzhou, Zhejiang 310036, P.R. China
| | - Xingzhi Xu
- Beijing Key Laboratory of DNA Damage Response, College of Life Science, Capital Normal University, Beijing 100048, P.R. China
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6
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Shirodkar P, Fenton AL, Meng L, Koch CA. Identification and functional characterization of a Ku-binding motif in aprataxin polynucleotide kinase/phosphatase-like factor (APLF). J Biol Chem 2013; 288:19604-13. [PMID: 23689425 DOI: 10.1074/jbc.m112.440388] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Aprataxin polynucleotide kinase/phosphatase-like factor (APLF) facilitates nonhomologous end joining (NHEJ) and associates with the core NHEJ components XRCC4-DNA ligase IV and Ku. The APLF forkhead-associated (FHA) domain directs interactions with XRCC4, but the APLF-Ku interaction has not been well characterized. Here we describe an evolutionarily conserved amino acid motif within APLF that is required for mediating the physical interaction between APLF and Ku. This APLF Ku-binding motif possesses a similarity to regions identified in other NHEJ factors, WRN and XLF, which also direct interactions with Ku. Indeed, peptides derived from the Ku-binding region of APLF, WRN, or XLF were sufficient to reconstitute the interaction with Ku in vitro. Although APLF is localized predominantly to the nucleus, it does not possess a nuclear localization signal (NLS). Interestingly, the disruption of the APLF-Ku interaction by substituting key residues in the APLF Ku-binding motif was associated with increased relocalization of APLF to the cytoplasm and reduced association with XRCC4, which was rescued by the introduction of an NLS onto APLF. When human cells stably depleted of APLF were reconstituted with APLF Ku-binding mutants, or with an APLF FHA mutant that is known to disrupt interactions with XRCC4, APLF-dependent NHEJ and the retention of APLF at sites of laser-generated DNA damage were impaired. These data suggest functional requirements for Ku and XRCC4 in APLF-dependent NHEJ and a unique role for Ku as a factor required to facilitate the nuclear retention of APLF.
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Affiliation(s)
- Purnata Shirodkar
- Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada
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Mason PA, Cox LS. The role of DNA exonucleases in protecting genome stability and their impact on ageing. Age (Dordr) 2012; 34:1317-1340. [PMID: 21948156 PMCID: PMC3528374 DOI: 10.1007/s11357-011-9306-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Accepted: 08/19/2011] [Indexed: 05/30/2023]
Abstract
Exonucleases are key enzymes involved in many aspects of cellular metabolism and maintenance and are essential to genome stability, acting to cleave DNA from free ends. Exonucleases can act as proof-readers during DNA polymerisation in DNA replication, to remove unusual DNA structures that arise from problems with DNA replication fork progression, and they can be directly involved in repairing damaged DNA. Several exonucleases have been recently discovered, with potentially critical roles in genome stability and ageing. Here we discuss how both intrinsic and extrinsic exonuclease activities contribute to the fidelity of DNA polymerases in DNA replication. The action of exonucleases in processing DNA intermediates during normal and aberrant DNA replication is then assessed, as is the importance of exonucleases in repair of double-strand breaks and interstrand crosslinks. Finally we examine how exonucleases are involved in maintenance of mitochondrial genome stability. Throughout the review, we assess how nuclease mutation or loss predisposes to a range of clinical diseases and particularly ageing.
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Affiliation(s)
- Penelope A. Mason
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Lynne S. Cox
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
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Kobayashi J, Okui M, Komatsu K, Chen DJ. Possible Role of WRN Protein in Cellular Response Induced by a Little DNA Damage. Fusion Science and Technology 2011. [DOI: 10.13182/fst11-a12627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Junya Kobayashi
- Radiation Biology Center, Kyoto University, Kyoto 606-0025 Japan
| | - Michiyo Okui
- Biomedical Engineering Center, Toin University of Yokohama, Yokohama 225-8502, Japan
| | - Kenshi Komatsu
- Radiation Biology Center, Kyoto University, Kyoto 606-0025 Japan
| | - David J. Chen
- University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390-9187, USs
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Rezazadeh S. RecQ helicases; at the crossroad of genome replication, repair, and recombination. Mol Biol Rep 2012; 39:4527-43. [PMID: 21947842 DOI: 10.1007/s11033-011-1243-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Accepted: 09/14/2011] [Indexed: 01/07/2023]
Abstract
DNA helicases are ubiquitous enzymes that unwind double-stranded DNA in an ATP-dependent and directionally specific manner. Such an action is essential for the processes of DNA repair, recombination, transcription, and DNA replication. Here, I focus on a subgroup of DNA helicases, the RecQ family, which is highly conserved in evolution. Members of this conserved family of proteins have a key role in protecting and stabilizing the genome against deleterious changes. Deficiencies in RecQ helicases can lead to high levels of genomic instability and, in humans, to premature aging and increased susceptibility to cancer. Their diverse roles in DNA metabolism, which include a role in telomere maintenance, reflect interactions with multiple cellular proteins, some of which are multifunctional and also have very diverse functions. In this review, protein structural motifs and the roles of different domains will be discussed first. The Review moves on to speculate about the different models to explain why RecQ helicases are required to protect against genome instability.
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10
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Jog SP, Reddy S, Comai L. Cell cycle-regulated association between the Werner syndrome protein and its molecular partners. Cell Cycle 2011; 10:2038-40. [PMID: 21558813 DOI: 10.4161/cc.10.12.16044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Singh DK, Ghosh AK, Croteau DL, Bohr VA. RecQ helicases in DNA double strand break repair and telomere maintenance. Mutat Res 2012; 736:15-24. [PMID: 21689668 DOI: 10.1016/j.mrfmmm.2011.06.002] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 04/19/2011] [Accepted: 06/02/2011] [Indexed: 10/24/2022]
Abstract
Organisms are constantly exposed to various environmental insults which could adversely affect the stability of their genome. To protect their genomes against the harmful effect of these environmental insults, organisms have evolved highly diverse and efficient repair mechanisms. Defective DNA repair processes can lead to various kinds of chromosomal and developmental abnormalities. RecQ helicases are a family of evolutionarily conserved, DNA unwinding proteins which are actively engaged in various DNA metabolic processes, telomere maintenance and genome stability. Bacteria and lower eukaryotes, like yeast, have only one RecQ homolog, whereas higher eukaryotes including humans possess multiple RecQ helicases. These multiple RecQ helicases have redundant and/or non-redundant functions depending on the types of DNA damage and DNA repair pathways. Humans have five different RecQ helicases and defects in three of them cause autosomal recessive diseases leading to various kinds of cancer predisposition and/or aging phenotypes. Emerging evidence also suggests that the RecQ helicases have important roles in telomere maintenance. This review mainly focuses on recent knowledge about the roles of RecQ helicases in DNA double strand break repair and telomere maintenance which are important in preserving genome integrity.
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Ducu RI, Dayaram T, Marriott SJ. The HTLV-1 Tax oncoprotein represses Ku80 gene expression. Virology 2011; 416:1-8. [PMID: 21571351 DOI: 10.1016/j.virol.2011.04.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Revised: 02/13/2011] [Accepted: 04/24/2011] [Indexed: 12/20/2022]
Abstract
The HTLV-I oncoprotein Tax interferes with DNA double strand break repair. Since non-homologous end joining (NHEJ) is a major pathway used to repair DNA double strand breaks we examined the effect of Tax on this pathway, with particular interest in the expression and function of Ku80, a critical component of the NHEJ pathway. Tax expression decreased Ku80 mRNA and protein levels, and repressed transcription from the Ku80 promoter. Conversely, Ku80 mRNA increased following siRNA knockdown of Tax in HTLV-I infected cells. Tax expression was associated with an elevated number of micronuclei and nucleoplasmic bridges, hallmarks of improper DNA double strand break repair. Our studies identified Tax as a transcriptional repressor of Ku80 that correlates with decreased DNA repair function. The reduction of Ku80 transcription by Tax may deplete the cell of an essential DNA break binding protein, resulting in reduced repair of DNA double strand breaks and accumulation genomic mutations.
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Affiliation(s)
- Razvan I Ducu
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
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Abstract
Telomeres are ends of chromosomes that play an important part in the biology of eukaryotic cells. Through the coordinated action of the telomerase and networks of other proteins and factors, the length and integrity of telomeres are maintained to prevent telomere dysfunction that has been linked to senescence, aging, diseases, and cancer. The tools and assays being used to study telomeres are being broadened, which has allowed us to derive a more detailed, high-resolution picture of the various players and pathways at work at the telomeres.
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Affiliation(s)
- Zhou Songyang
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, USA.
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Abstract
Werner syndrome
is an inherited human progeriod syndrome caused by mutations in the gene
encoding the Werner Syndrome protein, WRN. It has both 3'-5' DNA
helicase and exonuclease activities, and is
suggested to have roles in many aspects of DNA metabolism, including DNA
repair and telomere maintenance. The DNA-PK complex also functions in both
DNA double strand break repair and telomere maintenance. Interaction
between WRN and the DNA-PK complex has been reported in DNA double strand
break repair, but their possible cooperation at telomeres has not been
reported. This study analyzes thein vitro and in vivo
interaction at the telomere between WRN and DNA-PKcs, the catalytic subunit
of DNA-PK. The results show that DNA-PKcs selectively stimulates WRN
helicase but not WRN exonuclease in vitro, affecting that WRN
helicase unwinds and promotes the release of the full-length invading strand
of a telomere D-loop model substrate. In addition, the length of telomeric
G-tails decreases in DNA-PKcs knockdown cells, and this phenotype is
reversed by overexpression of WRN helicase. These results suggest that WRN
and DNA-PKcs may cooperatively prevent G-tail shortening in vivo.
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Affiliation(s)
- Rika Kusumoto-Matsuo
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
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15
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Rahn JJ, Lowery MP, Della-Coletta L, Adair GM, Nairn RS. Depletion of Werner helicase results in mitotic hyperrecombination and pleiotropic homologous and nonhomologous recombination phenotypes. Mech Ageing Dev 2010; 131:562-73. [PMID: 20708636 DOI: 10.1016/j.mad.2010.08.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 07/22/2010] [Accepted: 08/03/2010] [Indexed: 11/30/2022]
Abstract
Werner syndrome (WS) is a rare, segmental progeroid syndrome caused by defects in the WRN gene, which encodes a RecQ helicase. WRN has roles in many aspects of DNA metabolism including DNA repair and recombination. In this study, we exploited two different recombination assays previously used to describe a role for the structure-specific endonuclease ERCC1-XPF in mitotic and targeted homologous recombination. We constructed Chinese hamster ovary (CHO) cell lines isogenic with the cell lines used in these previous studies by depleting WRN using shRNA vectors. When intrachromosomal, mitotic recombination was assayed in WRN-depleted CHO cells, a hyperrecombination phenotype was observed, and a small number of aberrant recombinants were generated. Targeted homologous recombination was also examined in WRN-depleted CHO cells using a plasmid-chromosome targeting assay. In these experiments, loss of WRN resulted in a significant decrease in nonhomologous integration events and ablation of recombinants that required random integration of the corrected targeting vector. Aberrant recombinants were also recovered, but only from WRN-depleted cells. The pleiotropic recombination phenotypes conferred by WRN depletion, reflected in distinct homologous and nonhomologous recombination pathways, suggest a role for WRN in processing specific types of homologous recombination intermediates as well as an important function in nonhomologous recombination.
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Affiliation(s)
- Jennifer J Rahn
- University of Texas M.D. Anderson Cancer Center, Department of Carcinogenesis, Science Park Research Division, P.O. Box 389, Smithville, TX 78597, United States
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16
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Abstract
Double-strand DNA breaks are common events in eukaryotic cells, and there are two major pathways for repairing them: homologous recombination (HR) and nonhomologous DNA end joining (NHEJ). The various causes of double-strand breaks (DSBs) result in a diverse chemistry of DNA ends that must be repaired. Across NHEJ evolution, the enzymes of the NHEJ pathway exhibit a remarkable degree of structural tolerance in the range of DNA end substrate configurations upon which they can act. In vertebrate cells, the nuclease, DNA polymerases, and ligase of NHEJ are the most mechanistically flexible and multifunctional enzymes in each of their classes. Unlike repair pathways for more defined lesions, NHEJ repair enzymes act iteratively, act in any order, and can function independently of one another at each of the two DNA ends being joined. NHEJ is critical not only for the repair of pathologic DSBs as in chromosomal translocations, but also for the repair of physiologic DSBs created during variable (diversity) joining [V(D)J] recombination and class switch recombination (CSR). Therefore, patients lacking normal NHEJ are not only sensitive to ionizing radiation (IR), but also severely immunodeficient.
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Affiliation(s)
- Michael R Lieber
- Norris Comprehensive Cancer Center, Department of Pathology, University of Southern California Keck School of Medicine, Los Angeles, California 90089, USA.
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17
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Abstract
A critical link exists between DNA mutation and chromosomal rearrangements (genomic instability) and cancer development. This genomic instability can manifest itself as small changes at the nucleotide level or as gross chromosomal alterations. Mutations in the genes that encode DNA damage response proteins are responsible for a variety of genomic instability syndromes including hereditary non-polyposis colorectal carcinoma, Bloom's syndrome, ataxia-telangiectasia, BRCA-associated breast and ovarian cancers and Fanconi anaemia. Similarly, epigenetic silencing of genes associated with the maintenance of genomic stability have also been implicated in the pathogenesis of cancer. Here, we discuss how different tumours may be classified not only by tumour site but also by the type of underlying genetic instability. This type of classification may assist in the optimization of existing treatment regimens as well as informing the development of new therapeutic approaches.
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Affiliation(s)
- Sarah A Martin
- CRUK Gene Function Laboratory, Institute of Cancer Research, Fulham Road, London SW3 6JB, UK
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18
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Abstract
Werner syndrome protein (WRN) is one of a family of five human RecQ helicases implicated in the maintenance of genome stability. The conserved RecQ family also includes RecQ1, Bloom syndrome protein (BLM), RecQ4, and RecQ5 in humans, as well as Sgs1 in Saccharomyces cerevisiae, Rqh1 in Schizosaccharomyces pombe, and homologs in Caenorhabditis elegans, Xenopus laevis, and Drosophila melanogaster. Defects in three of the RecQ helicases, RecQ4, BLM, and WRN, cause human pathologies linked with cancer predisposition and premature aging. Mutations in the WRN gene are the causative factor of Werner syndrome (WS). WRN is one of the best characterized of the RecQ helicases and is known to have roles in DNA replication and repair, transcription, and telomere maintenance. Studies both in vitro and in vivo indicate that the roles of WRN in a variety of DNA processes are mediated by post-translational modifications, as well as several important protein-protein interactions. In this work, we will summarize some of the early studies on the cellular roles of WRN and highlight the recent findings that shed some light on the link between the protein with its cellular functions and the disease pathology.
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Affiliation(s)
- Marie L Rossi
- Laboratory of Molecular Gerontology, National Institute on Aging, Baltimore, MD 21224, USA
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19
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Abstract
Syndromes of accelerated aging could provide an entry point for identifying and dissecting the cellular pathways that are involved in the development of age-related pathologies in the general population. However, their usefulness for aging research has been controversial, as it has been argued that these diseases do not faithfully reflect the process of natural aging. Here we review recent findings on the molecular basis of two progeroid diseases, Werner syndrome (WS) and Hutchinson-Gilford progeria syndrome (HGPS), and highlight functional connections to cellular processes that may contribute to normal aging.
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Affiliation(s)
- Baomin Li
- Department of Molecular Microbiology and Immunology, Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, USA
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20
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Dhillon KK, Sidorova JM, Albertson TM, Anderson JB, Ladiges WC, Rabinovitch PS, Preston BD, Monnat RJ Jr. Divergent cellular phenotypes of human and mouse cells lacking the Werner syndrome RecQ helicase. DNA Repair (Amst) 2010; 9:11-22. [PMID: 19896421 DOI: 10.1016/j.dnarep.2009.09.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Revised: 09/13/2009] [Accepted: 09/25/2009] [Indexed: 01/06/2023]
Abstract
Werner syndrome (WS) is a human autosomal recessive genetic instability and cancer predisposition syndrome with features of premature aging. Several genetically determined mouse models of WS have been generated, however, none develops features of premature aging or an elevated risk of neoplasia unless additional genetic perturbations are introduced. In order to determine whether differences in cellular phenotype could explain the discrepant phenotypes of Wrn-/- mice and WRN-deficient humans, we compared the cellular phenotype of newly derived Wrn-/- mouse primary fibroblasts with previous analyses of primary and transformed fibroblasts from WS patients and with newly derived, WRN-depleted human primary fibroblasts. These analyses confirmed previously reported cellular phenotypes of WRN-mutant and WRN-deficient human fibroblasts, and demonstrated that the human WRN-deficient cellular phenotype can be detected in cells grown in 5% or in 20% oxygen. In contrast, we did not identify prominent cellular phenotypes present in WRN-deficient human cells in Wrn-/- mouse fibroblasts. Our results indicate that human and mouse fibroblasts have different functional requirements for WRN protein, and that the absence of a strong cellular phenotype may in part explain the failure of Wrn-/- mice to develop an organismal phenotype resembling Werner syndrome.
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21
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Abstract
The molecular mechanisms involved in human aging are complicated. Two progeria syndromes, Werner's syndrome (WS) and Hutchinson-Gilford progeria syndrome (HGPS), characterized by clinical features mimicking physiological aging at an early age, provide insights into the mechanisms of natural aging. Based on recent findings on WS and HGPS, we suggest a model of human aging. Human aging can be triggered by two main mechanisms, telomere shortening and DNA damage. In telomere-dependent aging, telomere shortening and dysfunction may lead to DNA damage responses which induce cellular senescence. In DNA damage-initiated aging, DNA damage accumulates, along with DNA repair deficiencies, resulting in genomic instability and accelerated cellular senescence. In addition, aging due to both mechanisms (DNA damage and telomere shortening) is strongly dependent on p53 status. These two mechanisms can also act cooperatively to increase the overall level ofgenomic instability, triggering the onset of human aging phenotypes.
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Affiliation(s)
- Shian-Ling Ding
- Department of Nursing, Kang-Ning Junior College of Medical Care and Management,Taipei,Taiwan.
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22
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Ren X, Lim S, Smith MT, Zhang L. Werner syndrome protein, WRN, protects cells from DNA damage induced by the benzene metabolite hydroquinone. Toxicol Sci 2008; 107:367-75. [PMID: 19064679 DOI: 10.1093/toxsci/kfn254] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Werner syndrome (WS) is a rare autosomal progeroid disorder caused by a mutation in the gene encoding the WRN (Werner syndrome protein), a member of the RecQ family of helicases with a role in maintaining genomic stability. Genetic association studies have previously suggested a link between WRN and susceptibility to benzene-induced hematotoxicity. To further explore the role of WRN in benzene-induced hematotoxicity, we used short hairpin RNA to silence endogenous levels of WRN in the human HL60 acute promyelocytic cell line and subsequently exposed the cells to hydroquinone (HQ). Suppression of WRN led to an accelerated cell growth rate, increased susceptibility to hydroquinone-induced cytotoxicity and genotoxicity as measured by the single-cell gel electrophoresis assay, and an enhanced DNA damage response. More specifically, loss of WRN resulted in higher levels of early apoptosis, marked by increases in relative levels of cleaved caspase-7 and cleaved poly (ADP-ribose) polymerase 1, in cells treated with HQ compared with control cells. Our data suggests that WRN plays an important role in the surveillance of and protection against DNA damage induced by HQ. This provides mechanistic support for the link between WRN and benzene-induced hematotoxicity.
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Affiliation(s)
- Xuefeng Ren
- Division of Environmental Health Sciences, School of Public Health, University of California, Berkeley, California 94720, USA
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23
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Sallmyr A, Tomkinson AE, Rassool FV. Up-regulation of WRN and DNA ligase IIIalpha in chronic myeloid leukemia: consequences for the repair of DNA double-strand breaks. Blood 2008; 112:1413-23. [PMID: 18524993 DOI: 10.1182/blood-2007-07-104257] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of oncogenic BCR-ABL in chronic myeloid leukemia (CML) results in increased reactive oxygen species (ROS) that in turn cause increased DNA damage, including DNA double-strand breaks (DSBs). We have previously shown increased error-prone repair of DSBs by nonhomologous end-joining (NHEJ) in CML cells. Recent reports have identified alternative NHEJ pathways that are highly error prone, prompting us to examine the role of the alternative NHEJ pathways in BCR-ABL-positive CML. Importantly, we show that key proteins in the major NHEJ pathway, Artemis and DNA ligase IV, are down-regulated, whereas DNA ligase IIIalpha, and the protein deleted in Werner syndrome, WRN, are up-regulated. DNA ligase IIIalpha and WRN form a complex that is recruited to DSBs in CML cells. Furthermore, "knockdown" of either DNA ligase IIIalpha or WRN leads to increased accumulation of unrepaired DSBs, demonstrating that they contribute to the repair of DSBs. These results indicate that altered DSB repair in CML cells is caused by the increased activity of an alternative NHEJ repair pathway, involving DNA ligase IIIalpha and WRN. We suggest that, although the repair of ROS-induced DSBs by this pathway contributes to the survival of CML cells, the resultant genomic instability drives disease progression.
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24
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Sinha KM, Stephanou NC, Gao F, Glickman MS, Shuman S. Mycobacterial UvrD1 is a Ku-dependent DNA helicase that plays a role in multiple DNA repair events, including double-strand break repair. J Biol Chem 2007; 282:15114-25. [PMID: 17376770 DOI: 10.1074/jbc.m701167200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Mycobacterium tuberculosis and other bacterial pathogens have a Ku-dependent nonhomologous end joining pathway of DNA double-strand break repair. Here we identify mycobacterial UvrD1 as a novel interaction partner for Ku in a genome-wide yeast two-hybrid screen. UvrD1 per se is a vigorous DNA-dependent ATPase but a feeble DNA helicase. Ku stimulates UvrD1 to catalyze ATP-dependent unwinding of 3'-tailed DNAs. UvrD1, Ku, and DNA form a stable ternary complex in the absence of ATP. The Ku binding determinants are located in the distinctive C-terminal segment of UvrD1. A second mycobacterial paralog, UvrD2, is a vigorous Ku-independent DNA helicase. Ablation of UvrD1 sensitizes Mycobacterium smegmatis to killing by ultraviolet and ionizing radiation and to a single chromosomal break generated by I-SceI endonuclease. The physical and functional interactions of bacterial Ku and UvrD1 highlight the potential for cross-talk between components of nonhomologous end joining and nucleotide excision repair pathways.
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Affiliation(s)
- Krishna Murari Sinha
- Molecular Biology, Sloan-Kettering Institute, Memorial-Sloan Kettering Cancer Center, New York, New York 10021, USA
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25
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Abstract
Double-strand breaks are a cataclysmic threat to genome integrity. In higher eukaryotes the predominant recourse is the nonhomologous end-joining (NHEJ) double-strand break repair pathway. NHEJ is a versatile mechanism employing the Ku heterodimer, ligase IV/XRCC4 and a host of other proteins that juxtapose two free DNA ends for ligation. A critical function of telomeres is their ability to distinguish the ends of linear chromosomes from double-strand breaks, and avoid NHEJ. Telomeres accomplish this feat by forming a unique higher order nucleoprotein structure. Paradoxically, key components of NHEJ associate with normal telomeres and are required for proper length regulation and end protection. Here we review the biochemical mechanism of NHEJ in double-strand break repair, and in the response to dysfunctional telomeres. We discuss the ways in which NHEJ proteins contribute to telomere biology, and highlight how the NHEJ machinery and the telomere complex are evolving to maintain genome stability.
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Affiliation(s)
- Karel Riha
- Gregor Mendel Institute of Plant Molecular Biology, Austrian Academy of Sciences, A-1030 Vienna, Austria.
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26
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Abstract
Werner syndrome (WS) is an autosomal recessive progeroid disease characterized by genomic instability. WRN gene encodes one of the RecQ helicase family proteins, WRN, which has ATPase, helicase, exonuclease and single stranded DNA annealing activities. There is accumulating evidence suggesting that WRN contributes to the maintenance of genomic integrity through its involvement in DNA repair, replication and recombination. The role of WRN in these pathways can be modulated by its post-translational modifications in response to DNA damage. Here, we review the functional consequences of post-translational modifications on WRN as well as specific DNA repair pathways where WRN is involved and discuss how these modifications affect DNA repair pathways.
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Affiliation(s)
- Rika Kusumoto
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA
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27
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Perry JJP, Fan L, Tainer JA. Developing master keys to brain pathology, cancer and aging from the structural biology of proteins controlling reactive oxygen species and DNA repair. Neuroscience 2006; 145:1280-99. [PMID: 17174478 PMCID: PMC1904427 DOI: 10.1016/j.neuroscience.2006.10.045] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2006] [Revised: 10/15/2006] [Accepted: 10/17/2006] [Indexed: 12/11/2022]
Abstract
This review is focused on proteins with key roles in pathways controlling either reactive oxygen species or DNA damage responses, both of which are essential for preserving the nervous system. An imbalance of reactive oxygen species or inappropriate DNA damage response likely causes mutational or cytotoxic outcomes, which may lead to cancer and/or aging phenotypes. Moreover, individuals with hereditary disorders in proteins of these cellular pathways have significant neurological abnormalities. Mutations in a superoxide dismutase, which removes oxygen free radicals, may cause the neurodegenerative disease amyotrophic lateral sclerosis. Additionally, DNA repair disorders that affect the brain to various extents include ataxia-telangiectasia-like disorder, Cockayne syndrome or Werner syndrome. Here, we highlight recent advances gained through structural biochemistry studies on enzymes linked to these disorders and other related enzymes acting within the same cellular pathways. We describe the current understanding of how these vital proteins coordinate chemical steps and integrate cellular signaling and response events. Significantly, these structural studies may provide a set of master keys to developing a unified understanding of the survival mechanisms utilized after insults by reactive oxygen species and genotoxic agents, and also provide a basis for developing an informed intervention in brain tumor and neurodegenerative disease progression.
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Affiliation(s)
- J J P Perry
- Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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28
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Sasakawa N, Fukui T, Waga S. Accumulation of FFA-1, the Xenopus homolog of Werner helicase, and DNA polymerase delta on chromatin in response to replication fork arrest. J Biochem 2006; 140:95-103. [PMID: 16798775 DOI: 10.1093/jb/mvj130] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Werner syndrome is a genetic disorder characterized by premature aging and cancer-prone symptoms, and is caused by mutation of the WRN gene. WRN is a member of the RecQ helicase family and is thought to function in processes implicated in DNA replication and repair to maintain genome stability; however, its precise function is still unclear. We found that replication fork arrest markedly enhances chromatin binding of focus-forming activity 1 (FFA-1), a Xenopus WRN homolog, in Xenopus egg extracts. In addition to FFA-1, DNA polymerase delta (Poldelta) and replication protein A, but not DNA polymerase epsilon and proliferating cell nuclear antigen, accumulated increasingly on replication-arrested chromatin. Elevated accumulation of these proteins was dependent on formation of pre-replicative complexes (pre-RCs). Double-strand break (DSB) formation also enhanced chromatin binding of FFA-1, but not Poldelta, independently of pre-RC formation. In contrast to FFA-1, chromatin binding of Xenopus Bloom syndrome helicase (xBLM) only slightly increased after replication arrest or DSB formation. Thus, WRN-specific, distinct processes can be reproduced in the in vitro system in egg extracts, and this system is useful for biochemical analysis of WRN functions during DNA metabolism.
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Affiliation(s)
- Noriko Sasakawa
- Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
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29
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Perry JJP, Yannone SM, Holden LG, Hitomi C, Asaithamby A, Han S, Cooper PK, Chen DJ, Tainer JA. WRN exonuclease structure and molecular mechanism imply an editing role in DNA end processing. Nat Struct Mol Biol 2006; 13:414-22. [PMID: 16622405 DOI: 10.1038/nsmb1088] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 03/17/2006] [Indexed: 01/24/2023]
Abstract
WRN is unique among the five human RecQ DNA helicases in having a functional exonuclease domain (WRN-exo) and being defective in the premature aging and cancer-related disorder Werner syndrome. Here, we characterize WRN-exo crystal structures, biochemical activity and participation in DNA end joining. Metal-ion complex structures, active site mutations and activity assays reveal a nuclease mechanism mediated by two metal ions. The DNA end-binding Ku70/80 complex specifically stimulates WRN-exo activity, and structure-based mutational inactivation of WRN-exo alters DNA end joining in human cells. We furthermore establish structural and biochemical similarities of WRN-exo to DnaQ-family replicative proofreading exonucleases, describing WRN-specific adaptations consistent with double-stranded DNA specificity and functionally important conformational changes. These results indicate WRN-exo is a human DnaQ family member and support DnaQ-like proofreading activities stimulated by Ku70/80, with implications for WRN functions in age-related pathologies and maintenance of genomic integrity.
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Affiliation(s)
- J Jefferson P Perry
- Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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30
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Lan L, Nakajima S, Komatsu K, Nussenzweig A, Shimamoto A, Oshima J, Yasui A. Accumulation of Werner protein at DNA double-strand breaks in human cells. J Cell Sci 2005; 118:4153-62. [PMID: 16141234 DOI: 10.1242/jcs.02544] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Werner syndrome is an autosomal recessive accelerated-aging disorder caused by a defect in the WRN gene, which encodes a member of the RecQ family of DNA helicases with an exonuclease activity. In vitro experiments have suggested that WRN functions in several DNA repair processes, but the actual functions of WRN in living cells remain unknown. Here, we analyzed the kinetics of the intranuclear mobilization of WRN protein in response to a variety of types of DNA damage produced locally in the nucleus of human cells. A striking accumulation of WRN was observed at laser-induced double-strand breaks, but not at single-strand breaks or oxidative base damage. The accumulation of WRN at double-strand breaks was rapid, persisted for many hours, and occurred in the absence of several known interacting proteins including polymerase β, poly(ADP-ribose) polymerase 1 (PARP1), Ku80, DNA-dependent protein kinase (DNA-PKcs), NBS1 and histone H2AX. Abolition of helicase activity or deletion of the exonuclease domain had no effect on accumulation, whereas the presence of the HRDC (helicase and RNaseD C-terminal) domain was necessary and sufficient for the accumulation. Our data suggest that WRN functions mainly at DNA double-strand breaks and structures resembling double-strand breaks in living cells, and that an autonomous accumulation through the HRDC domain is the initial response of WRN to the double-strand breaks.
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Affiliation(s)
- Li Lan
- Department of Molecular Genetics, Institute of Development, Aging and Cancer, Tohoku University, Seiryomachi 4-1, Sendai 980-8575, Japan
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31
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Abstract
Double-strand breaks (DSBs) arise endogenously during normal cellular processes and exogenously by genotoxic agents such as ionizing radiation (IR). DSBs are one of the most severe types of DNA damage, which if left unrepaired are lethal to the cell. Several different DNA repair pathways combat DSBs, with nonhomologous end-joining (NHEJ) being one of the most important in mammalian cells. Competent NHEJ catalyses repair of DSBs by joining together and ligating two free DNA ends of little homology (microhomology) or DNA ends of no homology. The core components of mammalian NHEJ are the catalytic subunit of DNA protein kinase (DNA-PK(cs)), Ku subunits Ku70 and Ku80, Artemis, XRCC4 and DNA ligase IV. DNA-PK is a nuclear serine/threonine protein kinase that comprises a catalytic subunit (DNA-PK(cs)), with the Ku subunits acting as the regulatory element. It has been proposed that DNA-PK is a molecular sensor for DNA damage that enhances the signal via phosphorylation of many downstream targets. The crucial role of DNA-PK in the repair of DSBs is highlighted by the hypersensitivity of DNA-PK(-/-) mice to IR and the high levels of unrepaired DSBs after genotoxic insult. Recently, DNA-PK has emerged as a suitable genetic target for molecular therapeutics such as siRNA, antisense and novel inhibitory small molecules. This review encompasses the recent literature regarding the role of DNA-PK in the protection of genomic stability and focuses on how this knowledge has aided the development of specific DNA-PK inhibitors, via both small molecule and directed molecular targeting techniques. This review promotes the inhibition of DNA-PK as a valid approach to enhance the tumor-cell-killing effects of treatments such as IR.
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Affiliation(s)
- Spencer J Collis
- Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, School of Medicine, Baltimore, MD 21231, USA.
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32
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Comai L, Li B. The Werner syndrome protein at the crossroads of DNA repair and apoptosis. Mech Ageing Dev 2005; 125:521-8. [PMID: 15336909 DOI: 10.1016/j.mad.2004.06.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2004] [Revised: 06/10/2004] [Accepted: 06/11/2004] [Indexed: 01/08/2023]
Abstract
Werner syndrome (WS) is a premature aging disease characterized by genetic instability. WS is caused by mutations in a gene encoding for a 160 kDa nuclear protein, the Werner syndrome protein (WRN), which has exonuclease and helicase activities. The mechanism whereby WRN controls genome stability and life span is not known. Over the last few years, WRN has become the focus of intense investigation by a growing number of scientists. The studies carried out by many laboratories have provided a wealth of new information about the functional properties of WRN and its cellular partners. This review focuses on recent findings that demonstrate a functional interaction between WRN and two factors that bind to DNA breaks, Ku and poly(ADP-ribose) polymerase 1, and discuss how these interactions can influence fundamental cellular processes such as DNA repair, apoptosis and possibly regulate cell senescence and organismal aging.
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Affiliation(s)
- Lucio Comai
- Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
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33
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Abstract
Repair of DNA double-strand breaks (DSBs) by non-homologous end-joining (NHEJ) is required for resistance to genotoxic agents, such as ionizing radiation, but also for proper development of the vertebrate immune system. Much progress has been made in identifying the factors that are involved in this repair pathway. We are now entering the phase in which we begin to understand basic concepts of the reaction mechanism and regulation of non-homologous end-joining. This review concentrates on novel insights into damage recognition and subsequent tethering, processing and joining of DNA ends.
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Affiliation(s)
- Eric Weterings
- Department of Cell Biology and Genetics, Erasmus Medical Center, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
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34
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Block WD, Yu Y, Merkle D, Gifford JL, Ding Q, Meek K, Lees-Miller SP. Autophosphorylation-dependent remodeling of the DNA-dependent protein kinase catalytic subunit regulates ligation of DNA ends. Nucleic Acids Res 2004; 32:4351-7. [PMID: 15314205 PMCID: PMC514382 DOI: 10.1093/nar/gkh761] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Non-homologous end joining (NHEJ) is one of the primary pathways for the repair of ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) in mammalian cells. Proteins required for NHEJ include the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), Ku, XRCC4 and DNA ligase IV. Current models predict that DNA-PKcs, Ku, XRCC4 and DNA ligase IV assemble at DSBs and that the protein kinase activity of DNA-PKcs is essential for NHEJ-mediated repair of DSBs in vivo. We previously identified a cluster of autophosphorylation sites between amino acids 2609 and 2647 of DNA-PKcs. Cells expressing DNA-PKcs in which these autophosphorylation sites have been mutated to alanine are highly radiosensitive and defective in their ability to repair DSBs in the context of extrachromosomal assays. Here, we show that cells expressing DNA-PKcs with mutated autophosphorylation sites are also defective in the repair of IR-induced DSBs in the context of chromatin. Purified DNA-PKcs proteins containing serine/threonine to alanine or aspartate mutations at this cluster of autophosphorylation sites were indistinguishable from wild-type (wt) protein with respect to protein kinase activity. However, mutant DNA-PKcs proteins were defective relative to wt DNA-PKcs with respect to their ability to support T4 DNA ligase-mediated intermolecular ligation of DNA ends. We propose that autophosphorylation of DNA-PKcs at this cluster of sites is important for remodeling of DNA-PK complexes at DNA ends prior to DNA end joining.
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Affiliation(s)
- Wesley D Block
- Cancer Biology Research Group and Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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Abstract
The ability to sense DNA damage and activate response pathways that coordinate cell cycle progression and DNA repair is essential for the maintenance of genomic integrity and the viability of organisms. During the last couple of years, several proteins have been identified that participate very early in the DNA damage response. Here we review the current understanding of the mechanisms by which mammalian cells detect DNA lesions, especially double-strand breaks, and mediate the signal to downstream transducers.
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Affiliation(s)
- Irene Ward
- Division of Oncology Research, Mayo Clinic, Rochester, Minnesota 55905, USA
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Plchova H, Hartung F, Puchta H. Biochemical characterization of an exonuclease from Arabidopsis thaliana reveals similarities to the DNA exonuclease of the human Werner syndrome protein. J Biol Chem 2003; 278:44128-38. [PMID: 12937173 DOI: 10.1074/jbc.m303891200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human Werner syndrome protein (hWRN-p) possessing DNA helicase and exonuclease activities is essential for genome stability. Plants have no homologue of this bifunctional protein, but surprisingly the Arabidopsis genome contains a small open reading frame (ORF) (AtWRNexo) with homology to the exonuclease domain of hWRN-p. Expression of this ORF in Escherichia coli revealed an exonuclease activity for AtWRN-exo-p with similarities but also some significant differences to hWRN-p. The protein digests recessed strands of DNA duplexes in the 3' --> 5' direction but hardly single-stranded DNA or blunt-ended duplexes. In contrast to the Werner exonuclease, AtWRNexo-p is also able to digest 3'-protruding strands. DNA with recessed 3'-PO4 and 3'-OH termini is degraded to a similar extent. AtWRNexo-p hydrolyzes the 3'-recessed strand termini of duplexes containing mismatched bases. AtWRNexo-p needs the divalent cation Mg2+ for activity, which can be replaced by Mn2+. Apurinic sites, cholesterol adducts, and oxidative DNA damage (such as 8-oxoadenine and 8-oxoguanine) inhibit or block the enzyme. Other DNA modifications, including uracil, hypoxanthine and ethenoadenine, did not inhibit AtWRNexo-p. A mutation of a conserved residue within the exonuclease domain (E135A) completely abolished the exonucleolytic activity. Our results indicate that a type of WRN-like exonuclease activity seems to be a common feature of the DNA metabolism of animals and plants.
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Affiliation(s)
- Helena Plchova
- Institute of Plant Genetics and Crop Plant Research, Corrensstrasse 3, D-06466 Gatersleben, Germany
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Bachrati CZ, Hickson ID. RecQ helicases: suppressors of tumorigenesis and premature aging. Biochem J 2003; 374:577-606. [PMID: 12803543 PMCID: PMC1223634 DOI: 10.1042/bj20030491] [Citation(s) in RCA: 302] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2003] [Revised: 06/10/2003] [Accepted: 06/12/2003] [Indexed: 02/04/2023]
Abstract
The RecQ helicases represent a subfamily of DNA helicases that are highly conserved in evolution. Loss of RecQ helicase function leads to a breakdown in the maintenance of genome integrity, in particular hyper-recombination. Germ-line defects in three of the five known human RecQ helicases give rise to defined genetic disorders associated with cancer predisposition and/or premature aging. These are Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome, which are caused by defects in the genes BLM, WRN and RECQ4 respectively. Here we review the properties of RecQ helicases in organisms from bacteria to humans, with an emphasis on the biochemical functions of these enzymes and the range of protein partners that they operate with. We will discuss models in which RecQ helicases are required to protect against replication fork demise, either through prevention of fork breakdown or restoration of productive DNA synthesis.
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Affiliation(s)
- Csanád Z Bachrati
- Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
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Abstract
The double-strand break (DSB) is believed to be one of the most severe types of DNA damage, and if left unrepaired is lethal to the cell. Several different types of repair act on the DSB. The most important in mammalian cells are nonhomologous end-joining (NHEJ) and homologous recombination repair (HRR). NHEJ is the predominant type of DSB repair in mammalian cells, as opposed to lower eucaryotes, but HRR has recently been implicated in critical cell signaling and regulatory functions that are essential for cell viability. Whereas NHEJ repair appears constitutive, HRR is regulated by the cell cycle and inducible signal transduction pathways. More is known about the molecular details of NHEJ than HRR in mammalian cells. This review focuses on the mechanisms and regulation of DSB repair in mammalian cells, the signaling pathways that regulate these processes and the potential crosstalk between NHEJ and HRR, and between repair and other stress-induced pathways with emphasis on the regulatory circuitry associated with the ataxia telangiectasia mutated (ATM) protein.
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Affiliation(s)
- Kristoffer Valerie
- Department of Radiation Oncology, Medical College of Virginia Commonwealth University, Richmond, VA 23298-0058, USA.
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Abstract
RecQ helicases are highly conserved from bacteria to man. Germline mutations in three of the five known family members in humans give rise to debilitating disorders that are characterized by, amongst other things, a predisposition to the development of cancer. One of these disorders--Bloom's syndrome--is uniquely associated with a predisposition to cancers of all types. So how do RecQ helicases protect against cancer? They seem to maintain genomic stability by functioning at the interface between DNA replication and DNA repair.
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Affiliation(s)
- Ian D Hickson
- Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK.
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