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Garcin EB, Gon S, Sullivan MR, Brunette GJ, Cian AD, Concordet JP, Giovannangeli C, Dirks WG, Eberth S, Bernstein KA, Prakash R, Jasin M, Modesti M. Differential Requirements for the RAD51 Paralogs in Genome Repair and Maintenance in Human Cells. PLoS Genet 2019; 15:e1008355. [PMID: 31584931 PMCID: PMC6795472 DOI: 10.1371/journal.pgen.1008355] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 10/16/2019] [Accepted: 08/07/2019] [Indexed: 12/16/2022] Open
Abstract
Deficiency in several of the classical human RAD51 paralogs [RAD51B, RAD51C, RAD51D, XRCC2 and XRCC3] is associated with cancer predisposition and Fanconi anemia. To investigate their functions, isogenic disruption mutants for each were generated in non-transformed MCF10A mammary epithelial cells and in transformed U2OS and HEK293 cells. In U2OS and HEK293 cells, viable ablated clones were readily isolated for each RAD51 paralog; in contrast, with the exception of RAD51B, RAD51 paralogs are cell-essential in MCF10A cells. Underlining their importance for genomic stability, mutant cell lines display variable growth defects, impaired sister chromatid recombination, reduced levels of stable RAD51 nuclear foci, and hyper-sensitivity to mitomycin C and olaparib, with the weakest phenotypes observed in RAD51B-deficient cells. Altogether these observations underscore the contributions of RAD51 paralogs in diverse DNA repair processes, and demonstrate essential differences in different cell types. Finally, this study will provide useful reagents to analyze patient-derived mutations and to investigate mechanisms of chemotherapeutic resistance deployed by cancers.
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Affiliation(s)
- Edwige B. Garcin
- Cancer Research Center of Marseille; CNRS; Inserm; Institut Paoli-Calmettes; Aix-Marseille Université, Marseille, France
| | - Stéphanie Gon
- Cancer Research Center of Marseille; CNRS; Inserm; Institut Paoli-Calmettes; Aix-Marseille Université, Marseille, France
| | - Meghan R. Sullivan
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania, United States of America
| | - Gregory J. Brunette
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania, United States of America
| | - Anne De Cian
- Museum National d'Histoire Naturelle, Inserm U1154, CNRS UMR 7196, Sorbonne Universités, Paris, France
| | - Jean-Paul Concordet
- Museum National d'Histoire Naturelle, Inserm U1154, CNRS UMR 7196, Sorbonne Universités, Paris, France
| | - Carine Giovannangeli
- Museum National d'Histoire Naturelle, Inserm U1154, CNRS UMR 7196, Sorbonne Universités, Paris, France
| | - Wilhelm G. Dirks
- Department of Human and Animal Cell Lines, Leibniz-Institute DSMZ-German, Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
| | - Sonja Eberth
- Department of Human and Animal Cell Lines, Leibniz-Institute DSMZ-German, Collection of Microorganisms and Cell Cultures, Braunschweig, Germany
| | - Kara A. Bernstein
- Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania, United States of America
| | - Rohit Prakash
- Developmental Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
| | - Maria Jasin
- Developmental Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
| | - Mauro Modesti
- Cancer Research Center of Marseille; CNRS; Inserm; Institut Paoli-Calmettes; Aix-Marseille Université, Marseille, France
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Kluźniak W, Wokołorczyk D, Rusak B, Huzarski T, Gronwald J, Stempa K, Rudnicka H, Kashyap A, Dębniak T, Jakubowska A, Lener M, Szwiec M, Tomiczek-Szwiec J, Jarkiewicz-Tretyn J, Cechowska M, Domagała P, Szymiczek A, Bagherzadeh M, Lubiński J, Narod SA, Akbari MR, Cybulski C. Inherited variants in XRCC2 and the risk of breast cancer. Breast Cancer Res Treat 2019; 178:657-663. [PMID: 31463769 PMCID: PMC6817746 DOI: 10.1007/s10549-019-05415-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 08/19/2019] [Indexed: 12/19/2022]
Abstract
Background XRCC2 participates in homologous recombination and in DNA repair. XRCC2 has been reported to be a breast cancer susceptibility gene and is now included in several breast cancer susceptibility gene panels. Methods We sequenced XRCC2 in 617 Polish women with familial breast cancer and found a founder mutation. We then genotyped 12,617 women with breast cancer and 4599 controls for the XRCC2 founder mutation. Results We identified a recurrent truncating mutation of XRCC2 (c.96delT, p.Phe32fs) in 3 of 617 patients with familial breast cancer who were sequenced. The c.96delT mutation was then detected in 29 of 12,617 unselected breast cancer cases (0.23%) compared to 11 of 4599 cancer-free women (0.24%) (OR = 0.96; 95% CI 0.48–1.93). The mutation frequency in 1988 women with familial breast cancer was 0.2% (OR = 0.84, 95% CI 0.27–2.65). Breast cancers in XRCC2 mutation carriers and non-carriers were similar with respect to age of diagnosis and clinical characteristics. Loss of the wild-type XRCC2 allele was observed only in one of the eight breast cancers from patients who carried the XRCC2 mutation. No cancer type was more common in first- or second-degree relatives of XRCC2 mutation carriers than in relatives of the non-carriers. Conclusion XRCC2 c.96delT is a protein-truncating founder variant in Poland. There is no evidence that this mutation predisposes to breast cancer (and other cancers). It is premature to consider XRCC2 as a breast cancer-predisposing gene.
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Affiliation(s)
- Wojciech Kluźniak
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Dominika Wokołorczyk
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Bogna Rusak
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Tomasz Huzarski
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland.,Department of Clinical Genetics and Pathology, University of Zielona Góra, Zielona Góra, Poland
| | - Jacek Gronwald
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Klaudia Stempa
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Helena Rudnicka
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Aniruddh Kashyap
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Tadeusz Dębniak
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Anna Jakubowska
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland.,Independent Laboratory of Molecular Biology and Genetic Diagnostics, Pomeranian Medical University in Szczecin, Szczecin, Poland
| | - Marcin Lener
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Marek Szwiec
- Department of Surgery and Oncology, University of Zielona Góra, Zielona Góra, Poland.,Department of Clinical Oncology, University of Zielona Góra, Zielona Góra, Poland
| | - Joanna Tomiczek-Szwiec
- Faculty of Natural Sciences and Technology, University of Opole, Opole, Poland.,Department of Oncological Gynecology, Oncology Center in Opole, Opole, Poland
| | | | - Magdalena Cechowska
- Cancer Genetics Laboratory, Genetic Outpatients Clinic in Toruń, Toruń, Poland
| | - Paweł Domagała
- Department of Pathology, Pomeranian Medical University in Szczecin, Szczecin, Poland
| | - Agata Szymiczek
- Women's College Research Institute, Women's College Hospital, University of Toronto, Toronto, Canada
| | - Maryam Bagherzadeh
- Women's College Research Institute, Women's College Hospital, University of Toronto, Toronto, Canada
| | - Jan Lubiński
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland
| | - Steven A Narod
- Women's College Research Institute, Women's College Hospital, University of Toronto, Toronto, Canada.,Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
| | - Mohammad R Akbari
- Women's College Research Institute, Women's College Hospital, University of Toronto, Toronto, Canada.,Dalla Lana School of Public Health, University of Toronto, Toronto, Canada
| | - Cezary Cybulski
- Department of Genetics and Pathology, International Hereditary Cancer Center, Pomeranian Medical University in Szczecin, Unii Lubelskiej 1, 71-252, Szczecin, Poland.
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Yue F, Jiang Y, Yu Y, Yang X, Zhang H, Liu R, Wang R. Clinical, cytogenetic, and molecular findings in a fetus with ultrasonic multiple malformations, 4q duplication, and 7q deletion: A case report and literature review. Medicine (Baltimore) 2018; 97:e13094. [PMID: 30407316 PMCID: PMC6250448 DOI: 10.1097/md.0000000000013094] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
RATIONALE Chromosome deletion/duplication has been reported to be associated with mental disability and dysmorphism according to the accumulated research evidence. PATIENT CONCERNS A 25-year-old woman underwent amniocentesis for cytogenetic and single-nucleotide polymorphism (SNP) array analysis at 18 weeks of gestation due to the increased Down syndrome risk of 1/13. DIAGNOSES The fetal chromosomal analysis revealed a seemingly "normal" chromosomal karyotype, but the SNP array results showed a partial duplication of chromosome 4q34.1q35.2 and a deletion of chromosome 7q34q36.3fluorescence in situ hybridization (FISH) analysis showed that the couple had normal chromosome 4 and 7, whereas there was a partial signal fragment of chromosome 4 attached on the long arm of chromosome 7 for the fetus. INTERVENTIONS The couple finally chose to terminate the pregnancy based on the ultrasonic multiple malformations and the abnormal SNP array results. OUTCOMES The duplicated/deleted segments of the fetus were de novo. Meanwhile, we consider SHH and XRCC2 as good candidate genes, which may, in part, explain the observed abnormalities for the fetus. LESSONS The combination of SNP array and FISH analysis can give a molecular chromosomal diagnosis, which will offer more clear cytogenetic diagnosis and genetic counseling.
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Affiliation(s)
- Fagui Yue
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Yuting Jiang
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Yang Yu
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Xiao Yang
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Hongguo Zhang
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Ruizhi Liu
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
| | - Ruixue Wang
- Center for Reproductive Medicine and Center for Prenatal Diagnosis, First Hospital
- Jilin Engineering Research Center for Reproductive Medicine and Genetics, Jilin University, Changchun, China
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Kinetic analysis of DNA double-strand break repair pathways in Arabidopsis. DNA Repair (Amst) 2011; 10:611-9. [PMID: 21530420 DOI: 10.1016/j.dnarep.2011.04.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 03/30/2011] [Accepted: 04/01/2011] [Indexed: 01/19/2023]
Abstract
Double-strand breaks in genomic DNA (DSB) are potentially lethal lesions which separate parts of chromosome arms from their centromeres. Repair of DSB by recombination can generate mutations and further chromosomal rearrangements, making the regulation of recombination and the choice of recombination pathways of the highest importance. Although knowledge of recombination mechanisms has considerably advanced, the complex interrelationships and regulation of pathways are far from being fully understood. We analyse the different pathways of DSB repair acting in G2/M phase nuclei of irradiated plants, through quantitation of the kinetics of appearance and loss of γ-H2AX foci in Arabidopsis mutants. These analyses show the roles for the four major recombination pathways in post-S-phase DSB repair and that non-homologous recombination pathways constitute the major response. The data suggest a hierarchical organisation of DSB repair in these cells: C-NHEJ acts prior to B-NHEJ which can also inhibit MMEJ. Surprisingly the quadruple ku80 xrcc1 xrcc2 xpf mutant can repair DSB, although with severely altered kinetics. This repair leads to massive genetic instability with more than 50% of mitoses showing anaphase bridges following irradiation. This study thus clarifies the relationships between the different pathways of DSB repair in the living plant and points to the existence of novel DSB repair processes.
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5
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The importance of XRCC2 in RAD51-related DNA damage repair. DNA Repair (Amst) 2010; 9:517-25. [DOI: 10.1016/j.dnarep.2010.01.016] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Revised: 12/04/2009] [Accepted: 01/28/2010] [Indexed: 12/11/2022]
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Daboussi F, Courbet S, Benhamou S, Kannouche P, Zdzienicka MZ, Debatisse M, Lopez BS. A homologous recombination defect affects replication-fork progression in mammalian cells. J Cell Sci 2008; 121:162-6. [DOI: 10.1242/jcs.010330] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Faithful genome transmission requires a network of pathways coordinating DNA replication to DNA repair and recombination. Here, we used molecular combing to measure the impact of homologous recombination (HR) on the velocity of DNA replication forks. We used three hamster cell lines defective in HR either by overexpression of a RAD51 dominant-negative form, or by a defect in the RAD51 paralogue XRCC2 or the breast tumor suppressor BRCA2. Irrespectively of the type or extent of HR alteration, all three cell lines exhibited a similar reduction in the rate of replication-fork progression, associated with an increase in the density of replication forks. Importantly, this phenotype was completely reversed in complemented derivatives of Xrcc2 and Brca2 mutants. These data reveal a novel role for HR, different from the reactivation of stalled replication forks, which may play an important role in genome stability and thus in tumor protection.
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Affiliation(s)
- Fayza Daboussi
- UMR 217 CNRS, Institut de Radiobiologie Cellulaire et Moléculaire, 18 route du panorama, 92265, Fontenay aux Roses, Cédex, France
| | - Sylvain Courbet
- UMR 7147 CNRS/Institut Curie, 26 rue d'Ulm, 75 248, Paris Cédex 05, France
| | | | | | - Malgorzata Z. Zdzienicka
- Department of Molecular Cell Genetics, Nicolaus-Copernicus-University in Torun, ul. Sklodowskiej-Curie 9, 85-094 Bydgoszcz, Poland
| | - Michelle Debatisse
- UMR 7147 CNRS/Institut Curie, 26 rue d'Ulm, 75 248, Paris Cédex 05, France
| | - Bernard S. Lopez
- UMR 217 CNRS, Institut de Radiobiologie Cellulaire et Moléculaire, 18 route du panorama, 92265, Fontenay aux Roses, Cédex, France
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Choi VW, McCarty DM, Samulski RJ. Host cell DNA repair pathways in adeno-associated viral genome processing. J Virol 2006; 80:10346-56. [PMID: 17041215 PMCID: PMC1641795 DOI: 10.1128/jvi.00841-06] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Recentstudies have shown that wild-type and recombinant adeno-associated virus (AAV and rAAV) genomes persist in human tissue predominantly as double-stranded (ds) circular episomes derived from input linear single-stranded virion DNA. Using self-complementary recombinant AAV (scAAV) vectors, we generated intermediates that directly transition to ds circular episomes. The scAAV genome ends are palindromic hairpin-structured terminal repeats, resembling a double-stranded break repair intermediate. Utilizing this substrate, we found cellular DNA recombination and repair factors to be essential for generating circular episomal products. To identify the specific cellular proteins involved, the scAAV circularization-dependent vector was used as a reporter in 19 mammalian DNA repair-deficient cell lines. The results show that RecQ helicase family members (BLM and WRN), Mre11 and NBS1 of the Mre11-Rad50-Nbs1 (MRN) complex, and ATM are required for efficient scAAV genome circularization. We further demonstrated that the scAAV genome requires ATM and DNA-PK(CS), but not NBS1, to efficiently convert to a circular form in nondividing cells in vivo using transgenic mice. These studies identify specific pathways involved for further elucidating viral and cellular mechanisms of DNA maintenance important to the viral life cycle and vector utilizations.
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Affiliation(s)
- Vivian W Choi
- Department of Pharmacology, University of North Carolina at Chapel Hill, NC 27599, USA
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8
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Abstract
Meiotic prophase I is a long and complex phase. Homologous recombination is an important process that occurs between homologous chromosomes during meiotic prophase I. Formation of chiasmata, which hold homologous chromosomes together until the metaphase I to anaphase I transition, is critical for proper chromosome segregation. Recent studies have suggested that the SPO11 proteins have conserved functions in a number of organisms in generating sites of double-stranded DNA breaks (DSBs) that are thought to be the starting points of homologous recombination. Processing of these sites of DSBs requires the function of RecA homologs, such as RAD51, DMC1, and others, as suggested by mutant studies; thus the failure to repair these meiotic DSBs results in abnormal chromosomal alternations, leading to disrupted meiosis. Recent discoveries on the functions of these RecA homologs have improved the understanding of the mechanisms underlying meiotic homologous recombination.
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Affiliation(s)
- Wuxing Li
- The Department of Biology, The Intercollege Graduate Degree Program in Plant Physiology, The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802, USA
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Tsaryk R, Fabian K, Thacker J, Kaina B. Xrcc2 deficiency sensitizes cells to apoptosis by MNNG and the alkylating anticancer drugs temozolomide, fotemustine and mafosfamide. Cancer Lett 2006; 239:305-13. [PMID: 16298473 DOI: 10.1016/j.canlet.2005.08.036] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Revised: 08/25/2005] [Accepted: 08/30/2005] [Indexed: 11/23/2022]
Abstract
DNA double-strand breaks (DSBs) are potent killing lesions, and inefficient repair of DSBs does not only lead to cell death but also to genomic instability and tumorigenesis. DSBs are repaired by non-homologous end-joining and homologous recombination (HR). A key player in HR is Xrcc2, a Rad51-like protein. Cells deficient in Xrcc2 are hypersensitive to X-rays and mitomycin C and display increased chromosomal aberration frequencies. In order to elucidate the role of Xrcc2 in resistance to anticancer drugs, we compared Xrcc2 knockout (Xrcc2-/-) mouse embryonic fibroblasts with the corresponding isogenic wild-type and Xrcc2 complemented knockout cells. We show that Xrcc2-/- cells are hypersensitive to the killing effect of the simple methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). They undergo apoptosis after MNNG treatment while necrosis is only marginally enhanced. Complementation of Xrcc2 deficient cells by Xrcc2 cDNA transfection conferred resistance to the cytotoxic and apoptosis-inducing effect of MNNG. The hypersensitivity of Xrcc2-/- cells to MNNG prompted us to investigate their killing and apoptotic response to various methylating, chloroethylating and crosslinking drugs used in anticancer therapy. Xrcc2 deficient cells were found to be hypersensitive to temozolomide, fotemustine and mafosfamide. They were also hypersensitive to cisplatin but not to taxol. The data reveal that Xrcc2 plays a role in the protection against a wide range of anticancer drugs and, therefore, suggest Xrcc2 to be a determinant of anticancer drug resistance. They also indicate that HR is involved in the processing of DNA damage induced by simple alkylating agents.
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Affiliation(s)
- Roman Tsaryk
- Institute of Toxicology, University of Mainz, Obere Zahlbacher Street 67, D-55131 Mainz, Germany
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10
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Bennett BT, Knight KL. Cellular localization of human Rad51C and regulation of ubiquitin-mediated proteolysis of Rad51. J Cell Biochem 2005; 96:1095-109. [PMID: 16215984 DOI: 10.1002/jcb.20640] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Rad51-catalyzed homologous recombination is an important pathway for repair of DNA double strand breaks and maintenance of genome integrity in vertebrate cells. Five proteins referred to as Rad51 paralogs promote Rad51 activity and are proposed to act at various, and in some cases, multiple stages in the recombination pathway. Imaging studies of native Rad51 have revealed its cellular response to DNA damage, yet visualization of the paralog proteins has met with limited success. In this study, we are able to detect endogenous Rad51C and Xrcc3 in human cells. In an effort to determine how Rad51, Rad51C, and Xrcc3 influence the pattern of localization of each other over the time course of DNA damage and repair, we have made the unexpected observation that Rad51 degradation via the ubiquitin-mediated proteasome pathway occurs as a natural part of recombinational DNA repair. Additionally, we find that Rad51C plays an important role in regulating this process. This article contains supplementary material, which may be viewed at the Journal of Cellular Biochemistry website at http://www.interscience.wiley.com/jpages/0730-2312/suppmat/index.html.
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Affiliation(s)
- Brian T Bennett
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Aaron Lazare Medical Research Building, 364 Plantation Street, Worcester, Massachusetts 01605-2324, USA
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11
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Hill MA, Herdman MT, Stevens DL, Jones NJ, Thacker J, Goodhead DT. Relative sensitivities of repair-deficient mammalian cells for clonogenic survival after alpha-particle irradiation. Radiat Res 2004; 162:667-76. [PMID: 15548117 DOI: 10.1667/rr3265] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The clonogenic survival of cells of the radiation-sensitive hamster cell lines irs1, irs2, irs3 and xrs5, representing different DNA repair pathways, was compared to that of their parent lines after alpha-particle irradiation. Measurements of nuclear area were made to calculate the probability of surviving a single alpha-particle traversal, the average number of lethal lesions per track and per unit dose, along with the "intrinsic radiosensitivity" of these cells, allowing for the potential of multiple lethal lesions per traversal. For all cell lines studied, alpha particles were found to be more biologically effective per unit absorbed dose than X rays at inducing cell inactivation. The repair-deficient cells showed an enhanced sensitivity to alpha particles compared to their parent line, but the degree of enhancement was less than for X rays. The reduction in additional sensitivity for alpha-particle irradiation was shown not to be due predominantly to differences in cell geometry limiting the probability of a cell nucleus being traversed. The results suggest that both the nonhomologous end-joining pathway and to a lesser extent the homologous recombination repair pathway play a role in successful repair of alpha-particle-induced damage, although a large proportion of damage is not repaired by either pathway.
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Affiliation(s)
- Mark A Hill
- MRC Radiation and Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, United Kingdom.
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12
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Dudás A, Chovanec M. DNA double-strand break repair by homologous recombination. Mutat Res 2004; 566:131-67. [PMID: 15164978 DOI: 10.1016/j.mrrev.2003.07.001] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2003] [Revised: 07/29/2003] [Accepted: 07/30/2003] [Indexed: 01/06/2023]
Abstract
DNA double-strand breaks (DSB) are presumed to be the most deleterious DNA lesions as they disrupt both DNA strands. Homologous recombination (HR), single-strand annealing, and non-homologous end-joining are considered to be the pathways for repairing DSB. In this review, we focus on DSB repair by HR. The proteins involved in this process as well as the interactions among them are summarized and characterized. The main emphasis is on eukaryotic cells, particularly the budding yeast Saccharomyces cerevisiae and mammals. Only the RAD52 epistasis group proteins are included.
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Affiliation(s)
- Andrej Dudás
- Laboratory of Molecular Genetics, Cancer Research Institute, Slovak Academy of Sciences, Vlárska 7, 833 91 Bratislava 37, Slovak Republic
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13
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Wang H, Boecker W, Wang H, Wang X, Guan J, Thompson LH, Nickoloff JA, Iliakis G. Caffeine inhibits homology-directed repair of I-SceI-induced DNA double-strand breaks. Oncogene 2004; 23:824-34. [PMID: 14737117 DOI: 10.1038/sj.onc.1207168] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We recently reported that two Chinese hamster mutants deficient in the RAD51 paralogs XRCC2 and XRCC3 show reduced radiosensitization after treatment with caffeine, thus implicating homology-directed repair (HDR) of DNA double-strand breaks (DSBs) in the mechanism of caffeine radiosensitization. Here, we investigate directly the effect of caffeine on HDR initiated by DSBs induced by a rare cutting endonuclease (I-SceI) into one of two direct DNA repeats. The results demonstrate a strong inhibition by caffeine of HDR in wild-type cells, and a substantial reduction of this effect in HDR-deficient XRCC3 mutant cells. Inhibition of HDR and cell radiosensitization to killing shows similar dependence on caffeine concentration suggesting a cause-effect relationship between these effects. UCN-01, a kinase inhibitor that effectively abrogates checkpoint activation in irradiated cells, has only a small effect on HDR, indicating that similar to radiosensitization, inhibition of checkpoint signaling is not sufficient for HDR inhibition. Recombination events occurring during treatment with caffeine are characterized by rearrangements reminiscent to those previously reported for the XRCC3 mutant, and immunofluorescence microscopy demonstrates significantly reduced formation of IR-specific RAD51 foci after caffeine treatment. In summary, our results identify inhibition of HDR as a significant contributor to caffeine radiosensitization.
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Affiliation(s)
- Huichen Wang
- Department of Radiation Oncology of Kimmel Cancer Center, Jefferson Medical College, Philadelphia, PA 19107, USA
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14
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Miller KA, Sawicka D, Barsky D, Albala JS. Domain mapping of the Rad51 paralog protein complexes. Nucleic Acids Res 2004; 32:169-78. [PMID: 14704354 PMCID: PMC373258 DOI: 10.1093/nar/gkg925] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The five human Rad51 paralogs are suggested to play an important role in the maintenance of genome stability through their function in DNA double-strand break repair. These proteins have been found to form two distinct complexes in vivo, Rad51B-Rad51C-Rad51D-Xrcc2 (BCDX2) and Rad51C-Xrcc3 (CX3). Based on the recent Pyrococcus furiosus Rad51 structure, we have used homology modeling to design deletion mutants of the Rad51 paralogs. The models of the human Rad51B, Rad51C, Xrcc3 and murine Rad51D (mRad51D) proteins reveal distinct N-terminal and C-terminal domains connected by a linker region. Using yeast two-hybrid and co-immunoprecipitation techniques, we have demonstrated that a fragment of Rad51B containing amino acid residues 1-75 interacts with the C-terminus and linker of Rad51C, residues 79-376, and this region of Rad51C also interacts with mRad51D and Xrcc3. We have also determined that the N-terminal domain of mRad51D, residues 4-77, binds to Xrcc2 while the C-terminal domain of mRad51D, residues 77-328, binds Rad51C. By this, we have identified the binding domains of the BCDX2 and CX3 complexes to further characterize the interaction of these proteins and propose a scheme for the three-dimensional architecture of the BCDX2 and CX3 paralog complexes.
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Affiliation(s)
- Kristi A Miller
- Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, 7000 East Avenue, L-448, Livermore, CA 94550, USA
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15
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Wachters FM, van Putten JWG, Maring JG, Zdzienicka MZ, Groen HJM, Kampinga HH. Selective targeting of homologous DNA recombination repair by gemcitabine. Int J Radiat Oncol Biol Phys 2003; 57:553-62. [PMID: 12957269 DOI: 10.1016/s0360-3016(03)00503-0] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
PURPOSE Gemcitabine (2',2'-difluoro-2'-deoxycytidine, dFdC) is a potent radiosensitizer. The mechanism of dFdC-mediated radiosensitization is yet poorly understood. We recently excluded inhibition of DNA double-strand break (DSB) repair by nonhomologous end-joining (NHEJ) as a means of radiosensitization. In the current study, we addressed the possibility that dFdC might affect homologous recombination (HR)-mediated DSB repair or base excision repair (BER). METHODS AND MATERIALS DFdC-mediated radiosensitization in cell lines deficient in BER and in HR was compared with that in their BER-proficient and HR-proficient parental counterparts. Sensitization to mitomycin C (MMC) was also investigated in cell lines deficient and proficient in HR. Additionally, the effect of dFdC on Rad51 foci formation after irradiation was studied. RESULTS DFdC did induce radiosensitization in BER-deficient cells; however, the respective mutant cells deficient in HR did not show dFdC-mediated radiosensitization. In HR-proficient, but not in HR-deficient, cells dFdC also induced substantial enhancement of the cytotoxic effect of MMC. Finally, we found that dFdC interferes with Rad51 foci formation after irradiation. CONCLUSION DFdC causes radiosensitization by specific interference with HR.
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Affiliation(s)
- Floris M Wachters
- Department of Pulmonary Diseases, University Hospital Groningen, Groningen, The Netherlands.
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16
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Thacker J, Zdzienicka MZ. The mammalian XRCC genes: their roles in DNA repair and genetic stability. DNA Repair (Amst) 2003; 2:655-72. [PMID: 12767346 DOI: 10.1016/s1568-7864(03)00062-4] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Analysis of the XRCC genes has played an important part in understanding mammalian DNA repair processes, especially those involved in double-strand break (DSB) repair. Most of these genes were identified through their ability to correct DNA damage hypersensitivity in rodent cell lines, and they represent components of several different repair pathways including base-excision repair, non-homologous end joining, and homologous recombination. We document the phenotypic effects of mutation of the XRCC genes, and the current state of our knowledge of their functions. In addition to their continuing importance in discovering mechanisms of DNA repair, analysis of the XRCC genes is making a substantial contribution to the understanding of specific human disorders, including cancer.
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Affiliation(s)
- John Thacker
- Medical Research Council, Radiation and Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, UK.
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17
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Schwientek T, Bennett EP, Flores C, Thacker J, Hollmann M, Reis CA, Behrens J, Mandel U, Keck B, Schäfer MA, Haselmann K, Zubarev R, Roepstorff P, Burchell JM, Taylor-Papadimitriou J, Hollingsworth MA, Clausen H. Functional conservation of subfamilies of putative UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferases in Drosophila, Caenorhabditis elegans, and mammals. One subfamily composed of l(2)35Aa is essential in Drosophila. J Biol Chem 2002; 277:22623-38. [PMID: 11925450 DOI: 10.1074/jbc.m202684200] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The completed fruit fly genome was found to contain up to 15 putative UDP-N-acetyl-alpha-d-galactosamine:polypeptide N-acetylgalactosaminyltransferase (GalNAc-transferase) genes. Phylogenetic analysis of the putative catalytic domains of the large GalNAc-transferase enzyme families of Drosophila melanogaster (13 available), Caenorhabditis elegans (9 genes), and mammals (12 genes) indicated that distinct subfamilies of orthologous genes are conserved in each species. In support of this hypothesis, we provide evidence that distinctive functional properties of Drosophila and human GalNAc-transferase isoforms were exhibited by evolutionarily conserved members of two subfamilies (dGalNAc-T1 (l(2)35Aa) and GalNAc-T11; dGalNAc-T2 (CG6394) and GalNAc-T7). dGalNAc-T1 and novel human GalNAc-T11 were shown to encode functional GalNAc-transferases with the same polypeptide acceptor substrate specificity, and dGalNAc-T2 was shown to encode a GalNAc-transferase with similar GalNAc glycopeptide substrate specificity as GalNAc-T7. Previous data suggested that the putative GalNAc-transferase encoded by l(2)35Aa had a lethal phenotype (Flores, C., and Engels, W. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 2964-2969), and this was substantiated by sequencing of three lethal alleles l(2)35Aa(HG8), l(2)35Aa(SF12), and l(2)35Aa(SF32). The finding that subfamilies of GalNAc-transferases with distinct catalytic functions are evolutionarily conserved stresses that GalNAc-transferase isoforms may serve unique biological functions rather than providing functional redundancy, and this is further supported by the lethal phenotype of l(2)35Aa.
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Affiliation(s)
- Tilo Schwientek
- School of Dentistry, University of Copenhagen, Nørre Alle 20, 2200 Copenhagen N, Denmark.
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18
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French CA, Masson JY, Griffin CS, O'Regan P, West SC, Thacker J. Role of mammalian RAD51L2 (RAD51C) in recombination and genetic stability. J Biol Chem 2002; 277:19322-30. [PMID: 11912211 DOI: 10.1074/jbc.m201402200] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The highly conserved RAD51 protein has a central role in homologous recombination. Five novel RAD51-like genes have been identified in mammalian cells, but little is known about their functions. A DNA damage-sensitive hamster cell line, irs3, was found to have a mutation in the RAD51L2 gene and an undetectable level of RAD51L2 protein. Resistance of irs3 to DNA-damaging agents was significantly increased by expression of the human RAD51L2 gene, but not by other RAD51-like genes or RAD51 itself. Consistent with a role for RAD51L2 in homologous recombination, irs3 cells show a reduction in sister chromatid exchange, an increase in isochromatid breaks, and a decrease in damage-dependent RAD51 focus formation compared with wild type cells. As recently demonstrated for human cells, we show that RAD51L2 forms part of two separate complexes of hamster RAD51-like proteins. Strikingly, neither complex of RAD51-like proteins is formed in irs3 cells. Our results demonstrate that RAD51L2 has a key role in mammalian RAD51-dependent processes, contingent on the formation of protein complexes involved in homologous recombination repair.
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Affiliation(s)
- Catherine A French
- Medical Research Council, Radiation & Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, United Kingdom
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19
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Masson JY, Tarsounas MC, Stasiak AZ, Stasiak A, Shah R, McIlwraith MJ, Benson FE, West SC. Identification and purification of two distinct complexes containing the five RAD51 paralogs. Genes Dev 2001; 15:3296-307. [PMID: 11751635 PMCID: PMC312846 DOI: 10.1101/gad.947001] [Citation(s) in RCA: 282] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2001] [Accepted: 10/31/2001] [Indexed: 12/29/2022]
Abstract
Cells defective in any of the RAD51 paralogs (RAD51B, RAD51C, RAD51D, XRCC2, and XRCC3) are sensitive to DNA cross-linking agents and to ionizing radiation. Because the paralogs are required for the assembly of DNA damage-induced RAD51 foci, and mutant cell lines are defective in homologous recombination and show genomic instability, their defect is thought to be caused by an inability to promote efficient recombinational repair. Here, we show that the five paralogs exist in two distinct complexes in human cells: one contains RAD51B, RAD51C, RAD51D, and XRCC2 (defined as BCDX2), whereas the other consists of RAD51C with XRCC3. Both protein complexes have been purified to homogeneity and their biochemical properties investigated. BCDX2 binds single-stranded DNA and single-stranded gaps in duplex DNA, in accord with the proposal that the paralogs play an early (pre-RAD51) role in recombinational repair. Moreover, BCDX2 complex binds specifically to nicks in duplex DNA. We suggest that the extreme sensitivity of paralog-defective cell lines to cross-linking agents is owing to defects in the processing of incised cross links and the consequential failure to initiate recombinational repair at these sites.
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Affiliation(s)
- J Y Masson
- Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK
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20
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Abstract
DNA interstrand cross-links (ICLs) are very toxic to dividing cells, because they induce mutations, chromosomal rearrangements and cell death. Inducers of ICLs are important drugs in cancer treatment. We discuss the main properties of several classes of ICL agents and the types of damage they induce. The current insights in ICL repair in bacteria, yeast and mammalian cells are reviewed. An intriguing aspect of ICLs is that a number of multi-step DNA repair pathways including nucleotide excision repair, homologous recombination and post-replication/translesion repair all impinge on their repair. Furthermore, the breast cancer-associated proteins Brca1 and Brca2, the Fanconi anemia-associated FANC proteins, and cell cycle checkpoint proteins are involved in regulating the cellular response to ICLs. We depict several models that describe possible pathways for the repair or replicational bypass of ICLs.
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Affiliation(s)
- M L Dronkert
- Department of Cell Biology and Genetics, Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
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21
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O'Regan P, Wilson C, Townsend S, Thacker J. XRCC2 is a nuclear RAD51-like protein required for damage-dependent RAD51 focus formation without the need for ATP binding. J Biol Chem 2001; 276:22148-53. [PMID: 11301337 DOI: 10.1074/jbc.m102396200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human XRCC2 gene was recently identified by its ability to complement a hamster cell line, irs1, which is sensitive to DNA-damaging agents and shows genetic instability. The XRCC2 protein is highly conserved in mammalian species and has structural features, including a putative ATP-binding domain (P-loop), consistent with membership of the RecA/RAD51 family of recombination-repair proteins. We show that a hybrid XRCC2-green fluorescent protein, which was found to be functional by complementation, localizes to the nucleus. We have established a functional link between XRCC2 and RAD51 by looking at damage-dependent RAD51 focus formation in the irs1 cell line. Little or no formation of RAD51 foci occurred in irs1. This effect was specific to the loss of XRCC2 because transfection of the gene into irs1 restored normal levels of focus formation. Surprisingly, XRCC2 genes carrying site-specific mutations in P-loop residues were found to be able to complement the XRCC2-deficient irs1 line for a number of different end points. We conclude that XRCC2 is important in the early stages of homologous recombination in mammalian cells to facilitate RAD51-dependent recombination repair but that it does not make use of ATP binding to promote this function.
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Affiliation(s)
- P O'Regan
- Radiation and Genome Stability Unit, Medical Research Council, Harwell, Oxfordshire OX11 0RD, United Kingdom
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22
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Little MP. Cancer after exposure to radiation in the course of treatment for benign and malignant disease. Lancet Oncol 2001; 2:212-20. [PMID: 11905766 DOI: 10.1016/s1470-2045(00)00291-6] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
This review assesses the patterns of radiation-associated relative risks of cancer incidence and mortality in groups exposed to ionising radiation in the course of treatment for various malignant and non-malignant conditions. In general, the relative risks among Japanese survivors of atomic-bomb explosions are greater than those among comparable subsets in studies of medically exposed individuals. Cell sterilisation largely accounts for the discrepancy in the relative risks between these two populations, although other factors may contribute, such as the generally higher underlying cancer risks in the medical series than in the Japanese atomic-bomb survivors, and dose-fractionation effects. The higher underlying cancer risk in some of the medically exposed populations, in particular for those with cancer-prone conditions, implies that the absolute excess risk is sometimes higher than in the Japanese data. For these cancer-prone individuals, the increase in absolute risk for those receiving the large doses of radiation associated with radiotherapy may be quite significant. This increase in risk has to be balanced against the generally high spontaneous cancer risk in these individuals and the benefits accruing from radiotherapy.
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Affiliation(s)
- M P Little
- Department of Epidemiology and Public Health, Imperial College School of Medicine, London, UK.
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23
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Deans B, Griffin CS, Maconochie M, Thacker J. Xrcc2 is required for genetic stability, embryonic neurogenesis and viability in mice. EMBO J 2000; 19:6675-85. [PMID: 11118202 PMCID: PMC305908 DOI: 10.1093/emboj/19.24.6675] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Repair of DNA damage by homologous recombination has only recently been established as an important mechanism in maintaining genetic stability in mammalian cells. The recently cloned Xrcc2 gene is a member of the mammalian Rad51 gene family, thought to be central to homologous recombination repair. To understand its function in mammals, we have disrupted Xrcc2 in mice. No Xrcc2(-/-) animals were found alive, with embryonic lethality occurring from mid-gestation. Xrcc2(-/-) embryos surviving until later stages of embryogenesis commonly showed developmental abnormalities and died at birth. Neonatal lethality, apparently due to respiratory failure, was associated with a high frequency of apoptotic death of post- mitotic neurons in the developing brain, leading to abnormal cortical structure. Embryonic cells showed genetic instability, revealed by a high level of chromosomal aberrations, and were sensitive to gamma-rays. Our findings demonstrate that homologous recombination has an important role in endogenous damage repair in the developing embryo. Xrcc2 disruption identifies a range of defects that arise from malfunction of this repair pathway, and establishes a previously unidentified role for homologous recombination repair in correct neuronal development.
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Affiliation(s)
- B Deans
- Medical Research Council, Radiation and Genome Stability Unit and Mammalian Genetics Unit, Harwell, Oxfordshire OX11 0RD, UK
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24
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Asaad NA, Zeng ZC, Guan J, Thacker J, Iliakis G. Homologous recombination as a potential target for caffeine radiosensitization in mammalian cells: reduced caffeine radiosensitization in XRCC2 and XRCC3 mutants. Oncogene 2000; 19:5788-800. [PMID: 11126366 DOI: 10.1038/sj.onc.1203953] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The radiosensitizing effect of caffeine has been associated with the disruption of multiple DNA damage-responsive cell cycle checkpoints, but several lines of evidence also implicate inhibition of DNA repair. The role of DNA repair inhibition in caffeine radiosensitization remains uncharacterized, and it is unknown which repair process, or lesion, is affected. We show that a radiosensitive cell line, mutant for the RAD51 homolog XRCC2 and defective in homologous recombination repair (HRR), displays significantly diminished caffeine radiosensitization that can be restored by expression of XRCC2. Despite the reduced radiosensitization, caffeine effectively abrogates checkpoints in S and G2 phases in XRCC2 mutant cells indicating that checkpoint abrogation is not sufficient for radiosensitization. Another radiosensitive line, mutant for XRCC3 and defective in HRR, similarly shows reduced caffeine radiosensitization. On the other hand, a radiosensitive mutant (irs-20) of DNA-PKcs with a defect in non-homologous end-joining (NHEJ) is radiosensitized by caffeine to an extent comparable to wild-type cells. In addition, rejoining of radiation-induced DNA DSBs, that mainly reflects NHEJ, remains unaffected by caffeine in XRCC2 and XRCC3 mutants, or their wild-type counterparts. These observations suggest that caffeine targets steps in HRR but not in NHEJ and that abrogation of checkpoint response is not sufficient to explain radiosensitization. Indeed, immortalized fibroblasts from AT patients show caffeine radiosensitization despite the checkpoint defects associated with ATM mutation. We propose that caffeine radiosensitization is mediated by inhibition of stages in DNA DSB repair requiring HRR and that checkpoint disruption contributes by allowing these DSBs to transit into irreparable states. Thus, checkpoints may contribute to genomic stability by promoting error-free HRR.
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Affiliation(s)
- N A Asaad
- Department of Radiation Oncology of Kimmel Cancer Center, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA
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25
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Griffin CS, Simpson PJ, Wilson CR, Thacker J. Mammalian recombination-repair genes XRCC2 and XRCC3 promote correct chromosome segregation. Nat Cell Biol 2000; 2:757-61. [PMID: 11025669 DOI: 10.1038/35036399] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Growth and development are dependent on the faithful duplication of cells. Duplication requires accurate genome replication, the repair of any DNA damage, and the precise segregation of chromosomes at mitosis; molecular checkpoints ensure the proper progression and fidelity of each stage. Loss of any of these highly conserved functions may result in genetic instability and proneness to cancer. Here we show that highly significant increases in chromosome missegregation occur in cell lines lacking the RAD51-like genes XRCC2 and XRCC3. This increased missegregation is associated with fragmentation of the centrosome, a component of the mitotic spindle, and not with loss of the spindle checkpoint. Our results show that unresolved DNA damage triggers this instability, and that XRCC2 and XRCC3 are potential tumour-suppressor genes in mammals.
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Affiliation(s)
- C S Griffin
- MRC Radiation & Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, England
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26
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Braybrooke JP, Spink KG, Thacker J, Hickson ID. The RAD51 family member, RAD51L3, is a DNA-stimulated ATPase that forms a complex with XRCC2. J Biol Chem 2000; 275:29100-6. [PMID: 10871607 DOI: 10.1074/jbc.m002075200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Rad51 protein in eukaryotic cells is a structural and functional homolog of Escherichia coli RecA with a role in DNA repair and genetic recombination. Several proteins showing sequence similarity to Rad51 have previously been identified in both yeast and human cells. In Saccharomyces cerevisiae, two of these proteins, Rad55p and Rad57p, form a heterodimer that can stimulate Rad51-mediated DNA strand exchange. Here, we report the purification of one of the representatives of the RAD51 family in human cells. We demonstrate that the purified RAD51L3 protein possesses single-stranded DNA binding activity and DNA-stimulated ATPase activity, consistent with the presence of "Walker box" motifs in the deduced RAD51L3 sequence. We have identified a protein complex in human cells containing RAD51L3 and a second RAD51 family member, XRCC2. By using purified proteins, we demonstrate that the interaction between RAD51L3 and XRCC2 is direct. Given the requirements for XRCC2 in genetic recombination and protection against DNA-damaging agents, we suggest that the complex of RAD51L3 and XRCC2 is likely to be important for these functions in human cells.
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Affiliation(s)
- J P Braybrooke
- Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, Oxfordshire OX11 ORD, United Kingdom
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27
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Wheldon TE. Radiation physics and genetic targeting: new directions for radiotherapy. The Douglas Lea Lecture 1999. Phys Med Biol 2000; 45:R77-95. [PMID: 10943913 DOI: 10.1088/0031-9155/45/7/201] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Radiation as a cancer treatment modality is of high physical precision but limited biological specificity. Targeted radiotherapy, the delivery of radiation to cancer cells by radioisotopes conjugated to tumour-seeking targeting agents, is a biologically attractive option but is currently effective for just a few tumour types (neuroblastoma, lymphoma) for which efficacious targeting agents are available. Radiobiological modelling and radiation microdosimetry have provided useful guidelines in choosing treatment strategies for targeted radiotherapy. These considerations generally favour the incorporation of targeted radiotherapy as one component of a multimodal treatment regimen. Very recently, gene therapy techniques have been developed which should enhance the clinical efficacy of both external beam radiation and targeted radiotherapy. Typically, non-harmful viruses are modified to incorporate therapeutic genes which cause altered cellular radiosensitivity or which facilitate the cellular uptake of targeting agents. To achieve specificity, therapeutic genes would be co-transfected with tissue-specific promoter genes causing the therapeutic genes to be expressed in cells of particular types. In laboratory models, our research group are exploring the transfection-mediated uptake of the targeting agents MIBG and sodium iodide. These approaches do not require transfection of every cell in order to cure a tumour-cells which have escaped transfection may be sterilized by radiation cross-fire from transfected neighbours. A new task for radiation microdosimetry is to quantify the cross-fire effect and to compute the efficacies of gene transfection which will be required for tumour cure. In the spirit of Douglas Lea, the analytic approach of physics can be used to illuminate and enhance developments in genetics, to the benefit of medicine.
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Affiliation(s)
- T E Wheldon
- Department of Clinical Physics, Glasgow University and Beatson Oncology Centre, CRC Beatson Laboratories, UK
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28
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Corcoran MM, Mould SJ, Orchard JA, Ibbotson RE, Chapman RM, Boright AP, Platt C, Tsui LC, Scherer SW, Oscier DG. Dysregulation of cyclin dependent kinase 6 expression in splenic marginal zone lymphoma through chromosome 7q translocations. Oncogene 1999; 18:6271-7. [PMID: 10597225 DOI: 10.1038/sj.onc.1203033] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The increased or inappropriate expression of genes with oncogenic properties through specific chromosome translocations is an important event in the pathogenesis of B-cell lymphoproliferative diseases. Recent studies have found deletions or translocations of chromosome 7q to be the most common cytogenetic abnormality observed in SLVL, a leukemic variant of SMZL, with the q21-q22 region being most frequently affected. In three patients with translocations between chromosomes 2 and 7, the cloning of the breakpoints at 7q21 revealed that each was located within a small region of DNA 3.6 kb upstream of the transcription start site of cyclin dependent kinase 6 (CDK6). In each case the translocation event was consistent with aberrant VJ recombination between the immunoglobulin light chain region (Ig kappa) on chromosome 2p12 and DNA sequences at 7q21, resembling the heptamer recombination site. The t(7;21) breakpoint in an additional patient with splenic marginal zone lymphoma (SMZL), resided 66 kb telomeric to the t(2;7) breakpoints juxtaposing CDK6 to an uncharacterized transcript. In two of the SLVL patient samples, the CDK6 protein was found to be markedly over expressed. These results suggest that dysregulation of CDK6 gene expression contributes to the pathogenesis of SLVL and SMZL.
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MESH Headings
- Aged
- Chromosomes, Human, Pair 2/genetics
- Chromosomes, Human, Pair 2/ultrastructure
- Chromosomes, Human, Pair 21/genetics
- Chromosomes, Human, Pair 21/ultrastructure
- Chromosomes, Human, Pair 7/genetics
- Chromosomes, Human, Pair 7/ultrastructure
- Cyclin-Dependent Kinase 6
- Cyclin-Dependent Kinases
- DNA, Neoplasm/genetics
- Enzyme Induction
- Female
- Gene Expression Regulation, Neoplastic
- Genes, Immunoglobulin
- Humans
- Immunoglobulin kappa-Chains/genetics
- Lymphoma, B-Cell/enzymology
- Lymphoma, B-Cell/genetics
- Male
- Middle Aged
- Protein Serine-Threonine Kinases/biosynthesis
- Protein Serine-Threonine Kinases/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Sequence Deletion
- Splenic Neoplasms/enzymology
- Splenic Neoplasms/genetics
- Translocation, Genetic
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Affiliation(s)
- M M Corcoran
- Department of Haematology, Royal Bournemouth Hospital, Bournemouth, UK
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29
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Abstract
The process of homologous recombination appears enigmatic: it creates genetic diversity but also provides an important way of repairing DNA damage without errors. The recent cloning and functional analysis of eukaryotic recombination genes suggests that at least part of the intricate mechanism involved is conserved from bacteria to humans, but is also yielding some surprises.
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Affiliation(s)
- J Thacker
- Medical Research Council, Radiation and Genome Stability Unit, Harwell, Oxfordshire, UK OX11 0RD.
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30
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Calléja F, Jansen JG, Vrieling H, Laval F, van Zeeland AA. Modulation of the toxic and mutagenic effects induced by methyl methanesulfonate in Chinese hamster ovary cells by overexpression of the rat N-alkylpurine-DNA glycosylase. Mutat Res 1999; 425:185-94. [PMID: 10216211 DOI: 10.1016/s0027-5107(99)00034-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Exposure of mammalian cells to alkylating agents causes transfer of alkyl groups to N- as well as O-atoms of DNA bases. Especially the O-alkylated G and T bases have strong mutagenic properties, since they are capable of mispairing during replication. The mutagenic potential of N-alkylbases is less clear although specific base excision repair (BER) pathways exist which remove those lesions from the DNA. We investigated the relative contribution of N-alkylations to mutation induction at the Hprt gene in cultured Chinese hamster ovary cells (CHO). To this end BER activity in CHO cells was modulated by introduction of an expression vector carrying the rat N-alkylpurine-DNA glycosylase (APDG) gene, which codes for a glycosylase that is able to remove 3-methyladenine and 7-methylguanine from DNA thereby generating apurinic sites. Upon selection of a CHO clone which 10 times overproduced APDG compared to control CHO cells, mutation induction, the mutational spectrum, and cell survival were determined in both cell lines following treatment with methyl methanesulfonate (MMS). The results show that over-expression of APDG renders CHO cells more sensitive for mutation induction as well as cytotoxicity induced by MMS. The involvement of apurinic sites in induction of base pair changes at positions where 3-methyladenine was induced is inferred from the observation that the mutational spectrum of MMS-induced mutations in APDG-CHO cells showed twice as much base pair changes at AT base pairs (33.3%) compared to the spectrum of MMS-induced mutations in CHO-control cells (15.8%).
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Affiliation(s)
- F Calléja
- MGC-Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Centre, Wassenaarseweg 72, 2333 AL Leiden, Netherlands
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31
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Thacker J. Repair of ionizing radiation damage in mammalian cells. Alternative pathways and their fidelity. COMPTES RENDUS DE L'ACADEMIE DES SCIENCES. SERIE III, SCIENCES DE LA VIE 1999; 322:103-8. [PMID: 10196659 DOI: 10.1016/s0764-4469(99)80030-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Ionizing radiation causes a variety of types of damage to DNA in cells, requiring the concerted action of a number of DNA repair enzymes to restore genomic integrity. The DNA base-excision repair and DNA double-strand break repair pathways are particularly important. While single base damages are rapidly excised and repaired using the opposite (undamaged) strand as a template, the correct repair of DNA double-strand breaks may present more difficulties to cellular enzymes owing to the loss of template. In the last few years evidence in support of several enzymatic pathways for the repair of such double-stranded damage has been found. At present we may distinguish at least three pathways: homologous recombination repair, non-homologous (DNA-PK-dependent) end joining, and repeat-driven end joining. This paper focuses on evidence for the first and third of these pathways, and considers in particular their relative importance in mammalian cells and implications for the fidelity of repair.
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Affiliation(s)
- J Thacker
- Medical Research Council, Radiation & Genome Stability Unit, Harwell, Oxfordshire, UK.
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32
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Zdzienicka MZ. Mammalian X-ray-sensitive mutants which are defective in non-homologous (illegitimate) DNA double-strand break repair. Biochimie 1999; 81:107-16. [PMID: 10214915 DOI: 10.1016/s0300-9084(99)80043-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In all organisms multiple pathways to repair DNA double-strand breaks (DSB) have been identified. In mammalian cells DSB are repaired by two distinct pathways, homologous and non-homologous (illegitimate) recombination. X-ray-sensitive mutants have provided a tool for the identification and understanding of the illegitimate recombination pathway in mammalian cells. Two (sub-)pathways can be distinguished, the first mediated by DNA-PK-dependent protein kinase (DNA-PK), and the second directed by the hMre11/hRad50 complex. A variety of mutants impaired in DSB repair by illegitimate recombination, with mutations in Ku, DNA-PKcs, XRCC4 or nibrin, have been described. Herein, the characterization of these mutants with respect to the impaired cellular function and the molecular defect is provided. Further studies on these mutants, as well as on new mutants impaired in as-of-yet unidentified pathways, should be helpful to a better understanding of DSB repair and of the processes leading to genome instability and cancer.
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Affiliation(s)
- M Z Zdzienicka
- MGC, Department of Radiation Genetics and Chemical Mutagenesis, Leiden University-LUMC, The Netherlands
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33
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Thacker J. The role of homologous recombination processes in the repair of severe forms of DNA damage in mammalian cells. Biochimie 1999; 81:77-85. [PMID: 10214913 DOI: 10.1016/s0300-9084(99)80041-8] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The role of homologous recombination processes in the repair of severe forms of DNA damage is reviewed, with particular attention to the functions of members of the recA/RAD51 family of genes. In the yeast Saccharomyces cerevisiae, several of the gene products involved in homologous recombination repair (HRR) have been studied in detail, and a picture is beginning to emerge of the repair mechanism for DNA double-strand breaks. Knowledge is fragmentary for other eukaryotic organisms and for other types of DNA damage. In mammalian cells, while it has been known for some years that HRR occurs, the relative importance of the process in repairing DNA damage is unknown and very few of the gene products involved have been identified. Very recently, a number of RAD51-like genes have been identified in mammals, either through cloning genes complementing cell lines sensitive to DNA-damaging agents (XRCC2, XRCC3), or through homology searches (RAD51L1, RAD51L2, RAD51L3). As yet the role of these genes and their possible functions are speculative, although the combination of sequence conservation and gene expression patterns suggest that they function in HRR pathways.
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Affiliation(s)
- J Thacker
- Medical Research Council, Radiation & Genome Stability Unit, Harwell, Oxfordshire, UK
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34
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Cartwright R, Tambini CE, Simpson PJ, Thacker J. The XRCC2 DNA repair gene from human and mouse encodes a novel member of the recA/RAD51 family. Nucleic Acids Res 1998; 26:3084-9. [PMID: 9628903 PMCID: PMC147676 DOI: 10.1093/nar/26.13.3084] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We recently identified a positional candidate for the XRCC2 DNA repair gene at human chromosome 7q36.1. We have now cloned the cDNA for this gene from both human and mouse and show that it is a highly conserved novel member of the recA / RAD51 recombination repair gene family. The cDNA is able to complement significantly the phenotype of a unique cell line, irs1 , which shows extreme sensitivity to DNA cross-linking agents and genetic instability. Thisphenotype is consistent with a role for the XRCC2 gene in recombination repair in somatic cells, suggesting that in addition to RAD51 , other members of this gene family have an important function in high fidelity repair processes in mammals. Despite this function, the XRCC2 gene transcript is expressed at a very low level in somatic tissue, but is elevated in mouse testis, suggesting an additional role in meiosis.
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Affiliation(s)
- R Cartwright
- Medical Research Council, Radiation and Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, UK
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35
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Wheldon TE, Mairs RJ, Rampling RP, Barrett A. Modelling the enhancement of fractionated radiotherapy by gene transfer to sensitize tumour cells to radiation. Radiother Oncol 1998; 48:5-13. [PMID: 9756166 DOI: 10.1016/s0167-8140(98)00022-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND AND PURPOSE Several strategies now exist for the use of gene transfer methodologies to sensitize tumour cells to radiation. These include the transfection of genes synthesizing cytokines, p53 gene replacement and methods based on the use of HSV-tk and gancyclovir. Very recently, the sequencing of radioprotector or repair genes, such as ATM, Ku80 and XRCC2, has made it possible to consider the design of gene transfer strategies resulting in protector gene knock-out. Selectivity of transfected gene expression might be achieved by use of tissue-specific promoters or by the trophism of viral vectors. The purpose of this study was to evaluate the probable efficacy of such strategies. METHODS We have modelled gene transfer-mediated radiosensitization of tumour cells during radiotherapy, focusing on anti-protector gene strategies, to explore the role of transfection frequency, sensitizing efficacy, transfection stability, untransfectable subpopulations, the timing of gene therapy and the treatment schedule structure. RESULTS We predict a substantial therapeutic benefit of gene transfer treatment (with at least weekly transfection) which modifies cellular radiosensitivity by a factor of 1.5 or more, despite modest efficiency of cellular transfection (e.g. 50%), transient retention of the transfected gene (e.g. 2-day half-life) and the existence of a small minority (e.g. 1%) of untransfectable cells. CONCLUSIONS The analysis shows repeated administration of gene transfer treatment to be obligatory and implies that the existence of untransfectable minority subpopulations (i.e. cells inaccessible to the vector) will be the major limiting factor in therapy. Experimental work is needed to confirm these predictions before clinical studies begin.
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Affiliation(s)
- T E Wheldon
- Department of Radiation Oncology, University of Glasgow, CRC Beatson Laboratories, UK
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36
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Fukumura R, Araki R, Fujimori A, Mori M, Saito T, Watanabe F, Sarashi M, Itsukaichi H, Eguchi-Kasai K, Sato K, Tatsumi K, Abe M. Murine cell line SX9 bearing a mutation in the dna-pkcs gene exhibits aberrant V(D)J recombination not only in the coding joint but also in the signal joint. J Biol Chem 1998; 273:13058-64. [PMID: 9582343 DOI: 10.1074/jbc.273.21.13058] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We established the radiosensitive cell line SX9 from mammary carcinoma cell line FM3A. In SX9 cells a defect of DNA-dependent protein kinase (DNA-PK) activity was suggested. Additionally, a complementation test suggested that the SX9 cell line belongs to a x-ray cross-complementing group (XRCC) 7. Isolation and sequence analyses of DNA-dependent protein kinase catalytic subunit (dna-pkcs) cDNA in SX9 cells disclosed nucleotide "T" (9572) to "C" transition causing substitution of amino acid residue leucine (3191) to proline. Interestingly, the mutation occurs in one allele, and transcripts of the dna-pkcs expressed exclusively from mutated allele. V(D)J recombination assay using extrachromosomal vector revealed the defects of not only coding but also signal joint formation. The frequency of the signal joint decreased to approximately one-tenth and the fidelity drastically decreased to 12. 2% as compared with the normal cell line. To confirm the responsibility of the dna-pkcs gene for abnormal V(D)J recombination in SX9, the full-length dna-pkcs gene was introduced into SX9. As a result, restoration of V(D)J recombination by wild type dna-pkcs cDNA was observed. SX9 is a novel dna-pkcs-deficient cell line.
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Affiliation(s)
- R Fukumura
- National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba-shi, Chiba 263-8555, Japan
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37
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Verrelle P, Bourhis J. [Modulation of cellular response to ionizing radiation: towards new molecular targets?]. Cancer Radiother 1998; 1:484-93. [PMID: 9587381 DOI: 10.1016/s1278-3218(97)89592-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Recent advances have been made in the understanding of molecular events following cellular exposure to ionizing radiations, suggesting that new molecular targets could be used to modulate radio-induced cellular response, including genes and their encoded protein involved in DNA repair, signal transduction, apoptosis and cell cycle regulation. These potential molecular targets include some radio-induced cytokines and growth factors that could modulate radiation response in irradiated normal tissues (TGF beta). In addition, in order to increase tumor cell lethality after irradiation exposure, two promising approaches have been recently explored, including firstly the modulation of radiation-induced apoptosis via the transfer of genes involved in the regulation of apoptosis (p53), and secondly the modulation of double strand break DNA repair.
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Affiliation(s)
- P Verrelle
- Département de radiothérapie, centre Jean-Perrin, Clermont-Ferrand, France
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38
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Liu N, Lamerdin JE, Tebbs RS, Schild D, Tucker JD, Shen MR, Brookman KW, Siciliano MJ, Walter CA, Fan W, Narayana LS, Zhou ZQ, Adamson AW, Sorensen KJ, Chen DJ, Jones NJ, Thompson LH. XRCC2 and XRCC3, new human Rad51-family members, promote chromosome stability and protect against DNA cross-links and other damages. Mol Cell 1998; 1:783-93. [PMID: 9660962 DOI: 10.1016/s1097-2765(00)80078-7] [Citation(s) in RCA: 405] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The phenotypically similar hamster mutants irs1 and irs1SF exhibit high spontaneous chromosome instability and broad-spectrum mutagen sensitivity, including extreme sensitivity to DNA cross-linking agents. The human XRCC2 and XRCC3 genes, which functionally complement irs1 and irs1SF, respectively, were previously mapped in somatic cell hybrids. Characterization of these genes and sequence alignments reveal that XRCC2 and XRCC3 are members of an emerging family of Rad51-related proteins that likely participate in homologous recombination to maintain chromosome stability and repair DNA damage. XRCC3 is shown to interact directly with HsRad51, and like Rad55 and Rad57 in yeast, may cooperate with HsRad51 during recombinational repair. Analysis of the XRCC2 mutation in irs1 implies that XRCC2's function is not essential for viability in cultured hamster cells.
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Affiliation(s)
- N Liu
- Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, Livermore, California 94551, USA
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39
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Cartwright R, Dunn AM, Simpson PJ, Tambini CE, Thacker J. Isolation of novel human and mouse genes of the recA/RAD51 recombination-repair gene family. Nucleic Acids Res 1998; 26:1653-9. [PMID: 9512535 PMCID: PMC147465 DOI: 10.1093/nar/26.7.1653] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Genes from the recA/RAD51 family play essential roles in homologous recombination in all organisms. Using sequence homologies from eukaryotic members of this family we have identified fragments of two additional mammalian genes with homology to RAD51. Cloning the full-length cDNAs for both human and mouse genes showed that the sequences are highly conserved, and that the predicted proteins have characteristic features of this gene family. One of the novel genes (R51H2) occurs in two forms in human cDNA, differing extensively at the 3' end, probably due to an unusual form of alternative splicing. The new genes (R51H2 and R51H3) were mapped to human chromosomes 14q23-24 and 17q1.2, respectively. Expression studies showed that R51H2 is expressed at lower levels than R51H3 , but that expression of both genes occurs at elevated levels in the testis compared with other tissues. The combination of gene structure conservation and the transcript expression patterns suggests that these new members of the recA/RAD51 family may also function in homologous recombination-repair pathways.
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Affiliation(s)
- R Cartwright
- Medical Research Council, Radiation and Genome Stability Unit, Harwell, Oxfordshire OX11 0RD, UK
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40
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Albala JS, Thelen MP, Prange C, Fan W, Christensen M, Thompson LH, Lennon GG. Identification of a novel human RAD51 homolog, RAD51B. Genomics 1997; 46:476-9. [PMID: 9441753 DOI: 10.1006/geno.1997.5062] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The highly conserved Saccharomyces cerevisiae RAD51 protein functions in both mitotic and meiotic homologous recombination and in double-strand break repair. Screening of the public cDNA sequence database for RAD51-like genes led to the identification of a partial sequence from a breast tissue library present in the I.M.A.G.E. (Integrated Molecular Analysis of Genes and their Expression) collection. An extended 1764-bp cDNA clone encoding an open reading frame of 350 amino acids was isolated. This clone showed significant amino acid identity with other human RAD51 homologs. The new homolog, named RAD51B, was mapped to human chromosome 14q23-q24.2 using a panel of human-hamster somatic cell hybrids and fluorescence in situ hybridization. Northern blot analysis demonstrated that RAD51B mRNA is widely expressed and most abundant in tissues active in recombination. Functions associated with known RAD51 homologs suggest a role for RAD51B in meiotic recombination and/or recombinational repair.
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Affiliation(s)
- J S Albala
- Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, California 95441-0808, USA.
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