1
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Mori H, Noma T, Morine Y, Ishibashi H, Shimada M. Carcinogenic risk in the biliary epithelium of children with congenital biliary dilatation via the DNA damage repair pathway. Surg Today 2023; 53:1126-1131. [PMID: 36828910 DOI: 10.1007/s00595-023-02664-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 02/08/2023] [Indexed: 02/26/2023]
Abstract
PURPOSES Congenital biliary dilatation (CBD) is a high-risk factor for biliary tract cancer (BTC). We previously reported the potential for carcinogenesis in the biliary epithelium of patients with CBD. In this study, we investigated potential carcinogenetic pathways, focusing on the DNA damage repair response, in children with CBD and compared the findings with those in adults. METHODS We enrolled 6 children with CBD and 10 adults with CBD without BTC who underwent extrahepatic bile duct resections, plus 4 control patients who underwent pancreaticoduodenectomy for non-biliary cancer. Levels of phosphorylated histone H2AX (γH2AX), MRE11, and Ku-70 in the biliary tract epithelium were evaluated by immunohistochemistry. RESULTS The levels of γH2AX, MRE11, and Ku-70 were significantly higher in the gallbladder epithelium and bile duct epithelium of both children and adults than in controls. CONCLUSIONS Children and adults with CBD might develop BTC via the DNA damage repair pathway, as evidenced by increased γH2AX, MRE11, and Ku-70 expression.
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Affiliation(s)
- Hiroki Mori
- Department of Surgery, Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-Cho, Tokushima, 770-8503, Japan.
| | - Takayuki Noma
- Department of Surgery, Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-Cho, Tokushima, 770-8503, Japan
| | - Yuji Morine
- Department of Surgery, Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-Cho, Tokushima, 770-8503, Japan
| | - Hiroki Ishibashi
- Department of Surgery, Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-Cho, Tokushima, 770-8503, Japan
| | - Mitsuo Shimada
- Department of Surgery, Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-Cho, Tokushima, 770-8503, Japan
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2
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Tang M, Chen G, Tu B, Hu Z, Huang Y, DuFort CC, Wan X, Mao Z, Liu Y, Zhu WG, Lu W. SMYD2 inhibition-mediated hypomethylation of Ku70 contributes to impaired nonhomologous end joining repair and antitumor immunity. SCIENCE ADVANCES 2023; 9:eade6624. [PMID: 37315132 DOI: 10.1126/sciadv.ade6624] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Accepted: 05/08/2023] [Indexed: 06/16/2023]
Abstract
DNA damage repair (DDR) is a double-edged sword with different roles in cancer susceptibility and drug resistance. Recent studies suggest that DDR inhibitors affect immune surveillance. However, this phenomenon is poorly understood. We report that methyltransferase SMYD2 plays an essential role in nonhomologous end joining repair (NHEJ), driving tumor cells adaptive to radiotherapy. Mechanically, in response to DNA damage, SMYD2 is mobilized onto chromatin and methylates Ku70 at lysine-74, lysine-516, and lysine-539, leading to increased recruitment of Ku70/Ku80/DNA-PKcs complex. Knockdown of SMYD2 or its inhibitor AZ505 results in persistent DNA damage and improper repair, which sequentially leads to accumulation of cytosolic DNA, and activation of cGAS-STING pathway and triggers antitumor immunity via infiltration and activation of cytotoxic CD8+ T cells. Our study reveals an unidentified role of SMYD2 in regulating NHEJ pathway and innate immune responses, suggesting that SMYD2 is a promising therapeutic target for cancer treatment.
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Affiliation(s)
- Ming Tang
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Guofang Chen
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Bo Tu
- Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
| | - Zhiyi Hu
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Yujia Huang
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Christopher C DuFort
- Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
| | - Xiaoping Wan
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Zhiyong Mao
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
| | - Yongzhong Liu
- State Key Laboratory of Oncogenes and Related Genes, Shanghai Cancer Institute, Renji Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200032, China
| | - Wei-Guo Zhu
- Guangdong Key Laboratory of Genome Instability and Human Disease, Shenzhen University International Cancer Center, Department of Biochemistry and Molecular Biology, Shenzhen University Medical School, Shenzhen 518055, China
| | - Wen Lu
- Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai Institute of Maternal-Fetal Medicine and Gynecologic Oncology, Clinical and Translational Research Center, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai 200092, China
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3
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Tang J, Casey PJ, Wang M. Suppression of isoprenylcysteine carboxylmethyltransferase compromises DNA damage repair. Life Sci Alliance 2021; 4:4/12/e202101144. [PMID: 34610973 PMCID: PMC8500237 DOI: 10.26508/lsa.202101144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 09/18/2021] [Accepted: 09/20/2021] [Indexed: 11/24/2022] Open
Abstract
Inhibition of isoprenylcysteine carboxylmethyltransferase reduces cancer cells’ ability to repair DNA damage by suppressing the expression of critical DNA damage repair pathway genes, hence increasing their vulnerability to DNA damaging insults such as PARP inhibitors and other DNA damage agents. DNA damage is a double-edged sword for cancer cells. On the one hand, DNA damage–induced genomic instability contributes to cancer development; on the other hand, accumulating damage compromises proliferation and survival of cancer cells. Understanding the key regulators of DNA damage repair machinery would benefit the development of cancer therapies that induce DNA damage and apoptosis. In this study, we found that isoprenylcysteine carboxylmethyltransferase (ICMT), a posttranslational modification enzyme, plays an important role in DNA damage repair. We found that ICMT suppression consistently reduces the activity of MAPK signaling, which compromises the expression of key proteins in the DNA damage repair machinery. The ensuing accumulation of DNA damage leads to cell cycle arrest and apoptosis in multiple breast cancer cells. Interestingly, these observations are more pronounced in cells grown under anchorage-independent conditions or grown in vivo. Consistent with the negative impact on DNA repair, ICMT inhibition transforms the cancer cells into a “BRCA-like” state, hence sensitizing cancer cells to the treatment of PARP inhibitor and other DNA damage–inducing agents.
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Affiliation(s)
- Jingyi Tang
- Duke-NUS Medical School, Program in Cancer and Stem Cell, Singapore, Singapore
| | - Patrick J Casey
- Duke-NUS Medical School, Program in Cancer and Stem Cell, Singapore, Singapore.,Department of Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, NC, USA
| | - Mei Wang
- Duke-NUS Medical School, Program in Cancer and Stem Cell, Singapore, Singapore .,Department of Biochemistry, National University of Singapore, Singapore 117596
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4
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Degenhardt S, Dreffke K, Schötz U, Petersen C, Engenhart-Cabillic R, Rothkamm K, Dahm-Daphi J, Dikomey E, Mansour WY. Establishment of a Transformation Coupled in vitro End Joining Assay to Estimate Radiosensitivity in Tumor Cells. Front Oncol 2020; 10:1480. [PMID: 32974177 PMCID: PMC7468517 DOI: 10.3389/fonc.2020.01480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 07/10/2020] [Indexed: 11/25/2022] Open
Abstract
Here, we present a modified in vitro end-joining (EJ) assay to quantify EJ capacity, accuracy as well as pathway switch to alternative end-joining (Alt-EJ) or single strand annealing (SSA). A novel transformation assay was established to specifically measure circular repair products, which correlate with classical EJ efficiency. The EJ assay was validated using EJ-deficient mammalian cell lines (Ku80, DNA-PKcs, LigIV, or XRCC4 mutants). A pathway switch to Alt-EJ and SSA was seen exclusively in Ku-deficient cells. Circular EJ product formation correlated with cell survival and DSB repair capacity after X-irradiation. Investigation of 14 HNSCC cell lines revealed differences in the total EJ capacity but a broader variation in the amount of circular repair products. Sequencing of repair junctions in HNSCC cells demonstrated a predominance of high-fidelity EJ and an avoidance of both Alt-EJ and SSA. A significant correlation was observed between the amount of circular repair products, repair of IR-induced DSB and radiosensitivity. Collectively, these data indicate that the presented in vitro-EJ-assay can not only estimate the repair capacity of cancer cells to enable the stratification into radiosensitive or radioresistant, but can also identify repair pathway deregulation such as a switch to Alt-EJ or SSA, which enables tumor targeting.
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Affiliation(s)
- Sarah Degenhardt
- Laboratory of Radiobiology and Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Kristin Dreffke
- Department of Radiotherapy and Radiooncology, Philipps-University Marburg, Marburg, Germany
| | - Urlike Schötz
- Department of Radiotherapy and Radiooncology, Philipps-University Marburg, Marburg, Germany
| | - Cordula Petersen
- Department of Radiotherapy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | | | - Kai Rothkamm
- Laboratory of Radiobiology and Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Jochen Dahm-Daphi
- Laboratory of Radiobiology and Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Department of Radiotherapy and Radiooncology, Philipps-University Marburg, Marburg, Germany
| | - Ekkehard Dikomey
- Laboratory of Radiobiology and Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Department of Radiotherapy and Radiooncology, Philipps-University Marburg, Marburg, Germany
| | - Wael Yassin Mansour
- Laboratory of Radiobiology and Experimental Radiooncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Mildred Scheel Cancer Career Center HaTriCS4, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.,Department of Tumor Biology, National Cancer Institute, Cairo University, Cairo, Egypt
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5
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Pol μ ribonucleotide insertion opposite 8-oxodG facilitates the ligation of premutagenic DNA repair intermediate. Sci Rep 2020; 10:940. [PMID: 31969622 PMCID: PMC6976671 DOI: 10.1038/s41598-020-57886-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 01/07/2020] [Indexed: 01/05/2023] Open
Abstract
DNA polymerase (pol) μ primarily inserts ribonucleotides into a single-nucleotide gapped DNA intermediate, and the ligation step plays a critical role in the joining of noncomplementary DNA ends during nonhomologous end joining (NHEJ) for the repair of double-strand breaks (DSBs) caused by reactive oxygen species. Here, we report that the pol μ insertion products of ribonucleotides (rATP or rCTP), instead of deoxyribonucleotides, opposite 8-oxo-2′-deoxyguanosine (8-oxodG) are efficiently ligated and the presence of Mn2+ stimulates this coupled reaction in vitro. Moreover, our results point to a role of pol μ in mediating ligation during the mutagenic bypass of 8-oxodG, while 3′-preinserted noncanonical base pairs (3′-rA or 3′-rC) on NHEJ repair intermediates compromise the end joining by DNA ligase I or the DNA ligase IV/XRCC4 complex.
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6
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Deycmar S, Faccin E, Kazimova T, Knobel PA, Telarovic I, Tschanz F, Waller V, Winkler R, Yong C, Zingariello D, Pruschy M. The relative biological effectiveness of proton irradiation in dependence of DNA damage repair. Br J Radiol 2019; 93:20190494. [PMID: 31687835 DOI: 10.1259/bjr.20190494] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Clinical parameters and empirical evidence are the primary determinants for current treatment planning in radiation oncology. Personalized medicine in radiation oncology is only at the very beginning to take the genetic background of a tumor entity into consideration to define an individual treatment regimen, the total dose or the combination with a specific anticancer agent. Likewise, stratification of patients towards proton radiotherapy is linked to its physical advantageous energy deposition at the tumor site with minimal healthy tissue being co-irradiated distal to the target volume. Hence, the fact that photon and proton irradiation also induce different qualities of DNA damages, which require differential DNA damage repair mechanisms has been completely neglected so far. These subtle differences could be efficiently exploited in a personalized treatment approach and could be integrated into personalized treatment planning. A differential requirement of the two major DNA double-strand break repair pathways, homologous recombination and non-homologous end joining, was recently identified in response to proton and photon irradiation, respectively, and subsequently influence the mode of ionizing radiation-induced cell death and susceptibility of tumor cells with defects in DNA repair machineries to either quality of ionizing radiation.This review focuses on the differential DNA-damage responses and subsequent biological processes induced by photon and proton irradiation in dependence of the genetic background and discusses their impact on the unicellular level and in the tumor microenvironment and their implications for combined treatment modalities.
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Affiliation(s)
- Simon Deycmar
- Laboratory for Applied Radiobiology Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland
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7
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Ray S, Breuer G, DeVeaux M, Zelterman D, Bindra R, Sweasy JB. DNA polymerase beta participates in DNA End-joining. Nucleic Acids Res 2019; 46:242-255. [PMID: 29161447 PMCID: PMC5758893 DOI: 10.1093/nar/gkx1147] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 10/31/2017] [Indexed: 12/21/2022] Open
Abstract
DNA double strand breaks (DSBs) are one of the most deleterious lesions and if left unrepaired, they lead to cell death, genomic instability and carcinogenesis. Cells combat DSBs by two pathways: homologous recombination (HR) and non-homologous end-joining (NHEJ), wherein the two DNA ends are re-joined. Recently a back-up NHEJ pathway has been reported and is referred to as alternative NHEJ (aNHEJ), which joins ends but results in deletions and insertions. NHEJ requires processing enzymes including nucleases and polymerases, although the roles of these enzymes are poorly understood. Emerging evidence indicates that X family DNA polymerases lambda (Pol λ) and mu (Pol μ) promote DNA end-joining. Here, we show that DNA polymerase beta (Pol β), another member of the X family of DNA polymerases, plays a role in aNHEJ. In the absence of DNA Pol β, fewer small deletions are observed. In addition, depletion of Pol β results in cellular sensitivity to bleomycin and DNA protein kinase catalytic subunit inhibitors due to defective repair of DSBs. In summary, our results indicate that Pol β in functions in aNHEJ and provide mechanistic insight into its role in this process.
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Affiliation(s)
- Sreerupa Ray
- Department of Therapeutic Radiology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
| | - Gregory Breuer
- Department of Therapeutic Radiology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA.,Department of Pathology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
| | - Michelle DeVeaux
- School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
| | - Daniel Zelterman
- School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
| | - Ranjit Bindra
- Department of Therapeutic Radiology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA.,Department of Pathology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
| | - Joann B Sweasy
- Department of Therapeutic Radiology, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA.,Department of Genetics, School of Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA
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8
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Çağlayan M. Interplay between DNA Polymerases and DNA Ligases: Influence on Substrate Channeling and the Fidelity of DNA Ligation. J Mol Biol 2019; 431:2068-2081. [PMID: 31034893 DOI: 10.1016/j.jmb.2019.04.028] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 04/18/2019] [Accepted: 04/18/2019] [Indexed: 02/06/2023]
Abstract
DNA ligases are a highly conserved group of nucleic acid enzymes that play an essential role in DNA repair, replication, and recombination. This review focuses on functional interaction between DNA polymerases and DNA ligases in the repair of single- and double-strand DNA breaks, and discusses the notion that the substrate channeling during DNA polymerase-mediated nucleotide insertion coupled to DNA ligation could be a mechanism to minimize the release of potentially mutagenic repair intermediates. Evidence suggesting that DNA ligases are essential for cell viability includes the fact that defects or insufficiency in DNA ligase are casually linked to genome instability. In the future, it may be possible to develop small molecule inhibitors of mammalian DNA ligases and/or their functional protein partners that potentiate the effects of chemotherapeutic compounds and improve cancer treatment outcomes.
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Affiliation(s)
- Melike Çağlayan
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA.
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9
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Kohutova A, Raška J, Kruta M, Seneklova M, Barta T, Fojtik P, Jurakova T, Walter CA, Hampl A, Dvorak P, Rotrekl V. Ligase 3–mediated end‐joining maintains genome stability of human embryonic stem cells. FASEB J 2019; 33:6778-6788. [DOI: 10.1096/fj.201801877rr] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Aneta Kohutova
- Department of BiologyMasaryk UniversityBrnoCzech Republic
- International Clinical Research Center (ICRC)St. Anne's University HospitalBrnoCzech Republic
| | - Jan Raška
- Department of BiologyMasaryk UniversityBrnoCzech Republic
| | - Miriama Kruta
- Department of BiologyMasaryk UniversityBrnoCzech Republic
| | | | - Tomas Barta
- Department of BiologyMasaryk UniversityBrnoCzech Republic
| | - Petr Fojtik
- Department of BiologyMasaryk UniversityBrnoCzech Republic
| | | | - Christi A. Walter
- Department of Cell Systems and AnatomyThe University of Texas Health Science Center at San AntonioSan AntonioTexasUSA
| | - Ales Hampl
- Department of Histology and EmbryologyFaculty of MedicineMasaryk UniversityBrnoCzech Republic
- International Clinical Research Center (ICRC)St. Anne's University HospitalBrnoCzech Republic
| | - Petr Dvorak
- Department of BiologyMasaryk UniversityBrnoCzech Republic
- International Clinical Research Center (ICRC)St. Anne's University HospitalBrnoCzech Republic
| | - Vladimir Rotrekl
- Department of BiologyMasaryk UniversityBrnoCzech Republic
- International Clinical Research Center (ICRC)St. Anne's University HospitalBrnoCzech Republic
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10
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Çağlayan M, Wilson SH. Pol μ dGTP mismatch insertion opposite T coupled with ligation reveals promutagenic DNA repair intermediate. Nat Commun 2018; 9:4213. [PMID: 30310068 PMCID: PMC6181931 DOI: 10.1038/s41467-018-06700-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 09/08/2018] [Indexed: 01/01/2023] Open
Abstract
Incorporation of mismatched nucleotides during DNA replication or repair leads to transition or transversion mutations and is considered as a predominant source of base substitution mutagenesis in cancer cells. Watson-Crick like dG:dT base pairing is considered to be an important source of genome instability. Here we show that DNA polymerase (pol) μ insertion of 7,8-dihydro-8′-oxo-dGTP (8-oxodGTP) or deoxyguanosine triphosphate (dGTP) into a model double-strand break DNA repair substrate with template base T results in efficient ligation by DNA ligase. These results indicate that pol μ-mediated dGTP mismatch insertion opposite template base T coupled with ligation could be a feature of mutation prone nonhomologous end joining during double-strand break repair. Incorporation of mismatched nucleotides during DNA replication or repair can lead to mutagenesis. Here the authors reveal that DNA ligase can ligate NHEJ intermediates following incorporation of 8-oxodGTP or dGTP opposite T by DNA Polymerase mu (Pol mu) in vitro, which suggests that Pol mu could cause promutagenic mismatches during DSB repair.
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Affiliation(s)
- Melike Çağlayan
- Genome Integrity and Structural Biology Laboratory, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC, 27709, USA. .,Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, 32610, USA.
| | - Samuel H Wilson
- Genome Integrity and Structural Biology Laboratory, National Institutes of Health, National Institute of Environmental Health Sciences, Research Triangle Park, NC, 27709, USA.
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11
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Deycmar S, Pruschy M. Combined Treatment Modalities for High-Energy Proton Irradiation: Exploiting Specific DNA Repair Dependencies. Int J Part Ther 2018; 5:133-139. [DOI: 10.14338/ijpt-18-00020.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 07/05/2018] [Indexed: 11/21/2022] Open
Affiliation(s)
- Simon Deycmar
- Department of Radiation Oncology, Laboratory for Applied Radiobiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Martin Pruschy
- Department of Radiation Oncology, Laboratory for Applied Radiobiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
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12
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Frick A, Khare V, Paul G, Lang M, Ferk F, Knasmüller S, Beer A, Oberhuber G, Gasche C. Overt Increase of Oxidative Stress and DNA Damage in Murine and Human Colitis and Colitis-Associated Neoplasia. Mol Cancer Res 2018; 16:634-642. [PMID: 29378905 DOI: 10.1158/1541-7786.mcr-17-0451] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 11/17/2017] [Accepted: 01/02/2018] [Indexed: 11/16/2022]
Abstract
Patients with inflammatory bowel disease (IBD) have a higher risk of developing colitis-associated-cancer (CAC); however, the underlying processes of disease progression are not completely understood. Here, the molecular processes of inflammation-driven colon carcinogenesis were investigated using IL10-deficient mice (IL10 KO). IL10 KO mice were euthanized after development of colitis and dysplasia. IHC was performed for markers of colitis-induced DNA damage (CIDD): oxidative DNA lesions (8-oxoG), double-strand breaks (DSB; γH2AX). and DSB repair. MSI, LOH (Trp53, Apc), and global methylation (CIMP) were assessed on microdissected tissue. Comet assay for DNA damage, immunofluorescence, and immunoblotting were performed on intestinal organoids from wild-type (WT) and IL10 KO mice. Sequential biopsies and surgical specimens from IBD and CAC patients were used for IHC analysis. Severity of inflammation correlated with number of dysplasia. 8-oxoG and γH2AX-positive cells were significantly increased in inflamed and dysplastic areas along with activation of DSB repair. The amount of positively stained cells strongly correlated with degree of inflammation (8-oxoG: R = 0.923; γH2AX: R = 0.858). Neither CIMP, MSI nor LOH was observed. Enhanced DSBs in IL10 KO organoids were confirmed by comet assay and increased expression of γH2AX. Human clinical specimens exhibited significantly higher γH2AX and 8-oxoG in IBD, dysplasia, and CAC compared with normal mucosa. These data indicate that inflammation-driven colon carcinogenesis in IL10 KO mice and IBD patients is associated with oxidative DNA damage and overt presence of DSB. Mol Cancer Res; 16(4); 634-42. ©2018 AACR.
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Affiliation(s)
- Adrian Frick
- Department of Internal Medicine III, Division of Gastroenterology and Hepatology, Medical University of Vienna, Vienna, Austria
| | - Vineeta Khare
- Department of Internal Medicine III, Division of Gastroenterology and Hepatology, Medical University of Vienna, Vienna, Austria
| | - Gregor Paul
- Department of Internal Medicine III, Division of Gastroenterology and Hepatology, Medical University of Vienna, Vienna, Austria
| | - Michaela Lang
- Department of Internal Medicine III, Division of Gastroenterology and Hepatology, Medical University of Vienna, Vienna, Austria
| | - Franziska Ferk
- Institute of Cancer Research, Department of Medicine I, Medical University of Vienna, Vienna, Austria
| | - Siegfried Knasmüller
- Institute of Cancer Research, Department of Medicine I, Medical University of Vienna, Vienna, Austria
| | - Andrea Beer
- Clinical Institute of Pathology, Medical University of Vienna, Vienna Austria
| | - Georg Oberhuber
- Pathologie Soleiman, A.ö. Landeskrankenhaus-Universitäts-Kliniken Innsbruck, Innsbruck, Austria
| | - Christoph Gasche
- Department of Internal Medicine III, Division of Gastroenterology and Hepatology, Medical University of Vienna, Vienna, Austria.
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13
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Abstract
Double-strand breaks (DSB) in genomic DNA are induced by ionizing radiation or radiomimetic drugs but also occur spontaneously during the cell cycle at quite significant frequencies. In vertebrate cells, nonhomologous DNA end joining (NHEJ) is considered the major pathway of DSB repair which is able to rejoin two broken DNA termini directly end-to-end irrespective of sequence and structure. Genetic studies in various radiosensitive and DSB repair-deficient cell lines yielded insight into the factors involved in NHEJ. Studies in cell-free systems derived from Xenopus eggs and mammalian cells allowed the dissection of the underlying mechanisms. In the present chapter, we describe a protocol for the preparation of whole cell extracts from mammalian cells and a plasmid-based in vitro assay which permits the easy analysis of the efficiency and fidelity of DSB repair via NHEJ in different cell types.
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14
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Ahlberg S, Antonopulos A, Diendorf J, Dringen R, Epple M, Flöck R, Goedecke W, Graf C, Haberl N, Helmlinger J, Herzog F, Heuer F, Hirn S, Johannes C, Kittler S, Köller M, Korn K, Kreyling WG, Krombach F, Lademann J, Loza K, Luther EM, Malissek M, Meinke MC, Nordmeyer D, Pailliart A, Raabe J, Rancan F, Rothen-Rutishauser B, Rühl E, Schleh C, Seibel A, Sengstock C, Treuel L, Vogt A, Weber K, Zellner R. PVP-coated, negatively charged silver nanoparticles: A multi-center study of their physicochemical characteristics, cell culture and in vivo experiments. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2014; 5:1944-65. [PMID: 25383306 PMCID: PMC4222445 DOI: 10.3762/bjnano.5.205] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 10/07/2014] [Indexed: 04/14/2023]
Abstract
PVP-capped silver nanoparticles with a diameter of the metallic core of 70 nm, a hydrodynamic diameter of 120 nm and a zeta potential of -20 mV were prepared and investigated with regard to their biological activity. This review summarizes the physicochemical properties (dissolution, protein adsorption, dispersability) of these nanoparticles and the cellular consequences of the exposure of a broad range of biological test systems to this defined type of silver nanoparticles. Silver nanoparticles dissolve in water in the presence of oxygen. In addition, in biological media (i.e., in the presence of proteins) the surface of silver nanoparticles is rapidly coated by a protein corona that influences their physicochemical and biological properties including cellular uptake. Silver nanoparticles are taken up by cell-type specific endocytosis pathways as demonstrated for hMSC, primary T-cells, primary monocytes, and astrocytes. A visualization of particles inside cells is possible by X-ray microscopy, fluorescence microscopy, and combined FIB/SEM analysis. By staining organelles, their localization inside the cell can be additionally determined. While primary brain astrocytes are shown to be fairly tolerant toward silver nanoparticles, silver nanoparticles induce the formation of DNA double-strand-breaks (DSB) and lead to chromosomal aberrations and sister-chromatid exchanges in Chinese hamster fibroblast cell lines (CHO9, K1, V79B). An exposure of rats to silver nanoparticles in vivo induced a moderate pulmonary toxicity, however, only at rather high concentrations. The same was found in precision-cut lung slices of rats in which silver nanoparticles remained mainly at the tissue surface. In a human 3D triple-cell culture model consisting of three cell types (alveolar epithelial cells, macrophages, and dendritic cells), adverse effects were also only found at high silver concentrations. The silver ions that are released from silver nanoparticles may be harmful to skin with disrupted barrier (e.g., wounds) and induce oxidative stress in skin cells (HaCaT). In conclusion, the data obtained on the effects of this well-defined type of silver nanoparticles on various biological systems clearly demonstrate that cell-type specific properties as well as experimental conditions determine the biocompatibility of and the cellular responses to an exposure with silver nanoparticles.
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Abstract
BACKGROUND The benefits of radiotherapy for cancer have been well documented for many years, but many patients treated with radiation develop adverse effects. This study analyzed the current research into the biological basis of radiotherapy-induced normal tissue damage. METHODS Using the PubMed and EMBASE databases, articles on adverse effects of radiotherapy on normal tissue published from January of 2005 through May of 2012 were identified. Their abstracts were reviewed for information relevant to radiotherapy-induced DNA damage and DNA repair. Articles in the reference lists that seemed relevant were reviewed with no limitations on publication date. RESULTS Of 1751 publications, 1729 were eliminated because they did not address fundamental biology or were duplicates. The 22 included articles revealed that many adverse effects are driven by chronic oxidative stress affecting the nuclear function of DNA repair mechanisms. Among normal cells undergoing replication, cells in S phase are most radioresistant because of overexpression of DNA repair enzymes, while cells in M phase are especially radiosensitive. Cancer cells exhibit increased radiosensitivity, leading to accumulation of irreparable DNA lesions and cell death. Irradiated cells have an indirect effect on the cell cycle and survival of cocultured nonirradiated cells. Method of irradiation and linear energy transfer to cancer cells versus bystander cells are shown to have an effect on cell survival. CONCLUSIONS Radiotherapy-induced increases in reactive oxygen species in irradiated cells may signal healthy cells by increasing metabolic stress and creating DNA lesions. The side effects of radiotherapy and bystander cell signaling may have a larger impact than previously acknowledged.
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Grosse N, Fontana AO, Hug EB, Lomax A, Coray A, Augsburger M, Paganetti H, Sartori AA, Pruschy M. Deficiency in Homologous Recombination Renders Mammalian Cells More Sensitive to Proton Versus Photon Irradiation. Int J Radiat Oncol Biol Phys 2014; 88:175-81. [DOI: 10.1016/j.ijrobp.2013.09.041] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 09/12/2013] [Accepted: 09/16/2013] [Indexed: 11/17/2022]
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17
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Jia Q, den Dulk-Ras A, Shen H, Hooykaas PJJ, de Pater S. Poly(ADP-ribose)polymerases are involved in microhomology mediated back-up non-homologous end joining in Arabidopsis thaliana. PLANT MOLECULAR BIOLOGY 2013; 82:339-51. [PMID: 23625359 DOI: 10.1007/s11103-013-0065-9] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 04/20/2013] [Indexed: 05/25/2023]
Abstract
Besides the KU-dependent classical non-homologous end-joining (C-NHEJ) pathway, an alternative NHEJ pathway first identified in mammalian systems, which is often called the back-up NHEJ (B-NHEJ) pathway, was also found in plants. In mammalian systems PARP was found to be one of the essential components in B-NHEJ. Here we investigated whether PARP1 and PARP2 were also involved in B-NHEJ in Arabidopsis. To this end Arabidopsis parp1, parp2 and parp1parp2 (p1p2) mutants were isolated and functionally characterized. The p1p2 double mutant was crossed with the C-NHEJ ku80 mutant resulting in the parp1parp2ku80 (p1p2k80) triple mutant. As expected, because of their role in single strand break repair (SSBR) and base excision repair (BER), the p1p2 and p1p2k80 mutants were shown to be sensitive to treatment with the DNA damaging agent MMS. End-joining assays in cell-free leaf protein extracts of the different mutants using linear DNA substrates with different ends reflecting a variety of double strand breaks were performed. The results showed that compatible 5'-overhangs were accurately joined in all mutants, that KU80 protected the ends preventing the formation of large deletions and that PARP proteins were involved in microhomology mediated end joining (MMEJ), one of the characteristics of B-NHEJ.
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Affiliation(s)
- Qi Jia
- Department of Molecular and Developmental Genetics, Institute of Biology, Leiden University, Leiden, The Netherlands
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18
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Elguero ME, de Campos-Nebel M, González-Cid M. DNA-PKcs-dependent NHEJ pathway supports the progression of topoisomerase II poison-induced chromosome aberrant cells. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2012; 53:608-618. [PMID: 22987276 DOI: 10.1002/em.21729] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 07/18/2012] [Accepted: 07/30/2012] [Indexed: 06/01/2023]
Abstract
The role of DNA double strand break (DSB) repair pathways, non-homologous end joining (NHEJ), and homologous recombination (HR) was evaluated to prevent the chromosome instability induced by the topoisomerase II (Top2) poisons, idarubicin, and etoposide in Chinese hamster cell lines. XR-C1 (DNA-PKcs deficient) and V-C8 (BRCA2 deficient) showed higher sensitivity to increased concentrations of Top2 poisons compared with their normal counterparts, CHO9 and V79. Both proficient and deficient cells exhibited a marked DSB induction in all phases of the cell cycle. Additionally, deficient cells showed persistent DNA damage 24 hr post-treatment. Chromosomal aberrations increased in the first mitosis following Top2 poison-treatments in G1 or G2 in proficient and deficient cells. CHO9 and V79 demonstrated chromosome and chromatid exchanges following treatments in G1 and G2 phases, respectively. Deficient cells showed high frequencies of chromatid exchanges following treatments in G1 and G2. Simultaneously, we analyzed the micronuclei (MN) induction in interphase cells after treatments in G1, S, or G2 of the previous cell cycle. Both Top2 poisons induced an important increase in MN in CHO9, V79, and V-C8 cells. XR-C1 exhibited an increased MN frequency when cells were treated in G1 phase but not in S or G2. This MN reduction was due to a cell accumulation at G2/M and death in G2-treated cells. Our data suggest that NHEJ and HR operate differentially throughout the cell cycle to protect from Top2 poison-induced chromosome instability, and that DNA-PKcs-dependent NHEJ pathway allows the survival of chromosome damaged cells during S/G2 to the next interphase.
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Affiliation(s)
- Maria Eugenia Elguero
- Laboratorio de Mutagenesis, Instituto de Medicina Experimental, IMEX-CONICET, Academia Nacional de Medicina, Buenos Aires, Argentina
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Wang JL, Wang PC. The effect of aging on the DNA damage and repair capacity in 2BS cells undergoing oxidative stress. Mol Biol Rep 2012; 39:233-41. [PMID: 21556771 DOI: 10.1007/s11033-011-0731-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Accepted: 04/23/2011] [Indexed: 01/15/2023]
Abstract
Aging is associated with a reduction in the DNA repair capacity under oxidative stress. However, whether the DNA damage and repair capacity can be a biomarker of aging remains controversial. In this study, we demonstrated two cause-and-effect relationships, the one is between the DNA damage and repair capacity and the cellular age, another is between DNA damage and repair capacity and the level of oxidative stress in human embryonic lung fibroblasts (2BS) exposed to different doses of hydrogen peroxide (H2O2). To clarify the mechanisms of the age-related reduction in DNA damage and repair capacity, we preliminarily evaluated the expressions of six kinds of pivotal enzymes involved in the two classical DNA repair pathways. The DNA repair capacity was observed in human fibroblasts cells using the comet assay; the age-related DNA repair enzymes were selected by RT-PCR and then verified by Western blot in vitro. Results showed that the DNA repair capacity was negatively and linearly correlated with (i) cumulative population doubling (PD) levels only in the group of low concentration of hydrogen peroxide treatment, (ii) with the level of oxidative stress only in the group of young PD cells. The mRNA expression of DNA polymerase δ1 decreased substantially in senescent cells and showed negative linear-correlation with PD levels; the protein expression level was well consistent with the mRNA level. Taken together, DNA damage and repair capacity can be a biomarker of aging. Reduced expression of DNA polymerase δ1 may be responsible for the decrease of DNA repair capacity in senescent cells.
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Affiliation(s)
- Jin-Ling Wang
- Department of Clinical Laboratory, Xuanwu Hospital, Capital Medical University, Beijing, 100053, People's Republic of China.
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20
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Cheng Q, Barboule N, Frit P, Gomez D, Bombarde O, Couderc B, Ren GS, Salles B, Calsou P. Ku counteracts mobilization of PARP1 and MRN in chromatin damaged with DNA double-strand breaks. Nucleic Acids Res 2011; 39:9605-19. [PMID: 21880593 PMCID: PMC3239177 DOI: 10.1093/nar/gkr656] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In mammalian cells, the main pathway for DNA double-strand breaks (DSBs) repair is classical non-homologous end joining (C-NHEJ). An alternative or back-up NHEJ (B-NHEJ) pathway has emerged which operates preferentially under C-NHEJ defective conditions. Although B-NHEJ appears particularly relevant to genomic instability associated with cancer, its components and regulation are still largely unknown. To get insights into this pathway, we have knocked-down Ku, the main contributor to C-NHEJ. Thus, models of human cell lines have been engineered in which the expression of Ku70/80 heterodimer can be significantly lowered by the conditional induction of a shRNA against Ku70. On Ku reduction in cells, resulting NHEJ competent protein extracts showed a shift from C- to B-NHEJ that could be reversed by addition of purified Ku protein. Using a cellular fractionation protocol after treatment with a strong DSBs inducer followed by western blotting or immunostaining, we established that, among C-NHEJ factors, Ku is the main counteracting factor against mobilization of PARP1 and the MRN complex to damaged chromatin. In addition, Ku limits PAR synthesis and single-stranded DNA production in response to DSBs. These data support the involvement of PARP1 and the MRN proteins in the B-NHEJ route for the repair of DNA DSBs.
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Affiliation(s)
- Qiao Cheng
- CNRS, Institut de Pharmacologie et de Biologie Structurale, F-31077 Toulouse, France
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21
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Different DNA-PKcs functions in the repair of radiation-induced and spontaneous DSBs within interstitial telomeric sequences. Chromosoma 2011; 120:309-19. [PMID: 21359527 DOI: 10.1007/s00412-011-0313-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Revised: 02/03/2011] [Accepted: 02/03/2011] [Indexed: 10/18/2022]
Abstract
Interstitial telomeric sequences (ITSs) in hamster cells are hot spots for spontaneous and induced chromosome aberrations (CAs). Most data on ITS instability to date have been obtained in DNA repair-proficient cells. The classical non-homologous end joining repair pathway (C-NHEJ), which is the principal double strand break (DSB) repair mechanism in mammalian cells, is thought to restore the morphologically correct chromosome structure. The production of CAs thus involves DNA-PKcs-independent repair pathways. In our current study, we investigated the participation of DNA-PKcs from the C-NHEJ pathway in the repair of spontaneous or radiation-induced DSBs in ITSs using wild-type and DNA-PKcs mutant Chinese hamster ovary cells. Our data demonstrate that DNA-PKcs stabilizes spontaneous DSBs within ITSs from the chromosome 9 long arm, leading to the formation of terminal deletions. In addition, we show that DNA-PKcs-dependent C-NHEJ is employed following radiation-induced DSBs in other ITSs and restores morphologically correct chromosomes, whereas DNA-PKcs independent mechanisms co-exist in DNA-PKcs proficient cells leading to an excess of CAs within ITSs.
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Adams BR, Hawkins AJ, Povirk LF, Valerie K. ATM-independent, high-fidelity nonhomologous end joining predominates in human embryonic stem cells. Aging (Albany NY) 2010; 2:582-596. [PMID: 20844317 PMCID: PMC2984607 DOI: 10.18632/aging.100197] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Accepted: 09/10/2010] [Indexed: 05/28/2023]
Abstract
We recently demonstrated that human embryonic stem cells (hESCs) utilize homologous recombination repair (HRR) as primary means of double-strand break (DSB) repair. We now show that hESCs also use nonhomologous end joining (NHEJ). NHEJ kinetics were several-fold slower in hESCs and neural progenitors (NPs) than in astrocytes derived from hESCs. ATM and DNA-PKcs inhibitors were ineffective or partially effective, respectively, at inhibiting NHEJ in hESCs, whereas progressively more inhibition was seen in NPs and astrocytes. The lack of any major involvement of DNA-PKcs in NHEJ in hESCs was supported by siRNA-mediated DNA-PKcs knockdown. Expression of a truncated XRCC4 decoy or XRCC4 knock-down reduced NHEJ by more than half suggesting that repair is primarily canonical NHEJ. Poly(ADP-ribose) polymerase (PARP) was dispensable for NHEJ suggesting that repair is largely independent of backup NHEJ. Furthermore, as hESCs differentiated a progressive decrease in the accuracy of NHEJ was observed. Altogether, we conclude that NHEJ in hESCs is largely independent of ATM, DNA-PKcs, and PARP but dependent on XRCC4 with repair fidelity several-fold greater than in astrocytes.
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Affiliation(s)
- Bret R. Adams
- Departments of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA
- Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA
| | - Amy J. Hawkins
- Departments of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA
| | - Lawrence F. Povirk
- Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA 23298, USA
- the Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA
| | - Kristoffer Valerie
- Departments of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA
- Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA
- the Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA
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Mansour WY, Rhein T, Dahm-Daphi J. The alternative end-joining pathway for repair of DNA double-strand breaks requires PARP1 but is not dependent upon microhomologies. Nucleic Acids Res 2010; 38:6065-77. [PMID: 20483915 PMCID: PMC2952854 DOI: 10.1093/nar/gkq387] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Non-homologous end-joining (NHEJ), the major repair pathway for DNA double-strand breaks (DSB) in mammalian cells, employs a repertoire of core proteins, the recruitment of which to DSB-ends is Ku-dependent. Lack of either of the core components invariably leads to a repair deficiency. There has been evidence that an alternative end-joining operates in the absence of the core components. We used chromosomal reporter substrates to specifically monitor NHEJ of single I-SceI-induced-DSB for detailed comparison of classical and alternative end-joining. We show that rapid repair of both compatible and non-compatible ends require Ku-protein. In the absence of Ku, cells use a slow but efficient repair mode which experiences increasing sequence-loss with time after DSB induction. Chemical inhibition and PARP1-depletion demonstrated that the alternative end-joining in vivo is completely dependent upon functional PARP1. Furthermore, we show that the requirement for PARP1 depends on the absence of Ku but not on DNA-dependent protein kinase (DNA-PKcs). Extensive sequencing of repair junctions revealed that the alternative rejoining does not require long microhomologies. Together, we show that mammalian cells need Ku for rapid and conservative NHEJ. PARP1-dependent alternative route may partially rescue the deficient repair phenotype presumably at the expense of an enhanced mutation rate.
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Affiliation(s)
- Wael Y Mansour
- Laboratory of Radiobiology & Experimental Radiation Oncology, Department of Radiotherapy and Radiation Oncology, University Medical School Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
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24
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Taylor EM, Cecillon SM, Bonis A, Chapman JR, Povirk LF, Lindsay HD. The Mre11/Rad50/Nbs1 complex functions in resection-based DNA end joining in Xenopus laevis. Nucleic Acids Res 2009; 38:441-54. [PMID: 19892829 PMCID: PMC2811014 DOI: 10.1093/nar/gkp905] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The repair of DNA double-strand breaks (DSBs) is essential to maintain genomic integrity. In higher eukaryotes, DNA DSBs are predominantly repaired by non-homologous end joining (NHEJ), but DNA ends can also be joined by an alternative error-prone mechanism termed microhomology-mediated end joining (MMEJ). In MMEJ, the repair of DNA breaks is mediated by annealing at regions of microhomology and is always associated with deletions at the break site. In budding yeast, the Mre11/Rad5/Xrs2 complex has been demonstrated to play a role in both classical NHEJ and MMEJ, but the involvement of the analogous MRE11/RAD50/NBS1 (MRN) complex in end joining in higher eukaryotes is less certain. Here we demonstrate that in Xenopus laevis egg extracts, the MRN complex is not required for classical DNA-PK-dependent NHEJ. However, the XMRN complex is necessary for resection-based end joining of mismatched DNA ends. This XMRN-dependent end joining process is independent of the core NHEJ components Ku70 and DNA-PK, occurs with delayed kinetics relative to classical NHEJ and brings about repair at sites of microhomology. These data indicate a role for the X. laevis MRN complex in MMEJ.
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Affiliation(s)
- Elaine M Taylor
- Divisions of Medicine and Biomedical and Life Sciences, School of Health and Medicine, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK
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25
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de Pater S, Neuteboom LW, Pinas JE, Hooykaas PJJ, van der Zaal BJ. ZFN-induced mutagenesis and gene-targeting in Arabidopsis through Agrobacterium-mediated floral dip transformation. PLANT BIOTECHNOLOGY JOURNAL 2009; 7:821-35. [PMID: 19754840 DOI: 10.1111/j.1467-7652.2009.00446.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Zinc-finger nucleases (ZFNs) are artificial restriction enzymes, custom designed for induction of double-strand breaks (DSBs) at a specific locus. These DSBs may result in site-specific mutagenesis or homologous recombination at the repair site, depending on the DNA repair pathway that is used. These promising techniques for genome engineering were evaluated in Arabidopsis plants using Agrobacterium-mediated floral dip transformation. A T-DNA containing the target site for a ZFN pair, that was shown to be active in yeast, was integrated in the Arabidopsis genome. Subsequently, the corresponding pair of ZFN genes was stably integrated in the Arabidopsis genome and ZFN activity was determined by PCR and sequence analysis of the target site. Footprints were obtained in up to 2% of the PCR products, consisting of deletions ranging between 1 and 200 bp and insertions ranging between 1 and 14 bp. We did not observe any toxicity from expression of the ZFNs. In order to obtain ZFN-induced gene-targeting (GT), Arabidopsis plants containing the target site and expressing the ZFN pair were transformed with a T-DNA GT construct. Three GT plants were obtained from approximately 3000 transformants. Two of these represent heritable true GT events, as determined by PCR, Southern blot analysis and sequencing of the resulting recombined locus. The third plant showed an ectopic GT event. No GT plants were obtained in a comparable number of transformants that did not contain the ZFNs. Our results demonstrate that ZFNs enhance site-specific mutagenesis and gene-targeting of Agrobacterium T-DNA constructs delivered through floral dip transformation.
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Affiliation(s)
- Sylvia de Pater
- Department of Molecular and Developmental Genetics, Institute of Biology Leiden, Leiden University, 2333 BE Leiden, The Netherlands.
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26
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Singh SK, Wu W, Wu W, Wang M, Iliakis G. Extensive Repair of DNA Double-Strand Breaks in Cells Deficient in the DNA-PK-Dependent Pathway of NHEJ after Exclusion of Heat-Labile Sites. Radiat Res 2009; 172:152-64. [DOI: 10.1667/rr1745.1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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27
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Sasaki MS. Advances in the biophysical and molecular bases of radiation cytogenetics. Int J Radiat Biol 2009; 85:26-47. [PMID: 19205983 DOI: 10.1080/09553000802641185] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE For more than 70 years radiation cytogenetics has continued to be a topic of major concern in relation to the action of radiation on living cells. To date, diverse cytogenetic findings have developed into orderly, quantitative interpretations and have stimulated numerous biophysical models. However, it is generally agreed that any one of the models used alone is still unable to explain all aspects of the observed chromosomal effects. In this review, a large number of radiation-induced chromosome aberration findings from the literature are reassessed with special attention given to the reaction kinetics and the relevant molecular processes. CONCLUSION It is now clear that DNA double-strand breaks (DSB) are an integral component of radiation-induced chromosome aberration. At the nexus of the maintenance of genome integrity, cells are equipped with excellent systems to repair DSB, notably non-homologous end-joining (NHEJ) and homologous recombination repair (HRR). These repair mechanisms are strictly regulated along with the DNA turnover cycle. NHEJ functions in all phases of the cell cycle, whereas HRR has a supplementary role specifically in S/G2 phase, where homologous DNA sequences are available in close proximity. The repair pathways are further regulated by a complex nuclear dynamism, where DSB are sensed and large numbers of repair proteins are recruited and assembled to form a repair complex involving multiple DSB. Considering such DSB repair dynamism, radiation-induced chromosome aberrations could be well understood as DSB-DSB pairwise interactions associated with the NHEJ pathway in all phases of the cell cycle and misrepair of a single DSB associated with the complementary HRR pathway in late S/G2 phase.
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Affiliation(s)
- M S Sasaki
- Radiation Biology Center, Kyoto University, Yoshida-konoecho, Sakyo-ku, Kyoto, Japan.
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Bentley J, L'Hôte C, Platt F, Hurst CD, Lowery J, Taylor C, Sak SC, Harnden P, Knowles MA, Kiltie AE. Papillary and muscle invasive bladder tumors with distinct genomic stability profiles have different DNA repair fidelity and KU DNA-binding activities. Genes Chromosomes Cancer 2009; 48:310-21. [PMID: 19105236 DOI: 10.1002/gcc.20641] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Low-grade noninvasive papillary bladder tumors are genetically stable whereas muscle invasive bladder tumors display high levels of chromosomal aberrations. As cells deficient for nonhomologous end-joining (NHEJ) pathway components display increased genomic instability, we sought to determine the NHEJ repair characteristics of bladder tumors and correlate this with tumor stage and grade. A panel of 13 human bladder tumors of defined stage and grade were investigated for chromosomal aberrations by comparative genomic hybridization and for NHEJ repair fidelity and function. Repair assays were conducted with extracts made directly from bladder tumor specimens to avoid culture-induced phenotypic alterations and selection bias as only a minority of bladder tumors grow in culture. Four noninvasive bladder tumors (pTaG2), which were genetically stable, repaired a partially incompatible double-strand break (DSB) by NHEJ-dependent annealing of termini and fill-in of overhangs with minimal loss of nucleotides. In contrast, four muscle invasive bladder cancers (pT2-3G3), which displayed gross chromosomal rearrangements, repaired DSBs in an error-prone manner involving extensive resection and microhomology association. Four minimally invasive bladder cancers (pT1G3) had characteristics of both repair types. Error-prone repair in bladder tumors correlated with reduced KU DNA-binding and loss of TP53 function. In conclusion, there were distinct differences in DSB repair between noninvasive papillary tumors and higher stage/grade invasive cancers. End-joining fidelity correlated with stage and was increasingly error-prone as tumors became more invasive and KU binding activity reduced; these changes may underlie the different genomic profiles of these tumors.
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Affiliation(s)
- Johanne Bentley
- Cancer Research UK Clinical Centre, Section of Experimental Oncology, Leeds Institute of Molecular Medicine, St James's University Hospital, Leeds, UK
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29
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Arlt MF, Mulle JG, Schaibley VM, Ragland RL, Durkin SG, Warren ST, Glover TW. Replication stress induces genome-wide copy number changes in human cells that resemble polymorphic and pathogenic variants. Am J Hum Genet 2009; 84:339-50. [PMID: 19232554 PMCID: PMC2667984 DOI: 10.1016/j.ajhg.2009.01.024] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Revised: 01/23/2009] [Accepted: 01/30/2009] [Indexed: 11/28/2022] Open
Abstract
Copy number variants (CNVs) are an important component of genomic variation in humans and other mammals. Similar de novo deletions and duplications, or copy number changes (CNCs), are now known to be a major cause of genetic and developmental disorders and to arise somatically in many cancers. A major mechanism leading to both CNVs and disease-associated CNCs is meiotic unequal crossing over, or nonallelic homologous recombination (NAHR), mediated by flanking repeated sequences or segmental duplications. Others appear to involve nonhomologous end joining (NHEJ) or aberrant replication suggesting a mitotic cell origin. Here we show that aphidicolin-induced replication stress in normal human cells leads to a high frequency of CNCs of tens to thousands of kilobases across the human genome that closely resemble CNVs and disease-associated CNCs. Most deletion and duplication breakpoint junctions were characterized by short (<6 bp) microhomologies, consistent with the hypothesis that these rearrangements were formed by NHEJ or a replication-coupled process, such as template switching. This is a previously unrecognized consequence of replication stress and suggests that replication fork stalling and subsequent error-prone repair are important mechanisms in the formation of CNVs and pathogenic CNCs in humans.
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Affiliation(s)
- Martin F. Arlt
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jennifer G. Mulle
- Department of Human Genetics, Emory University, Atlanta, GA 30322, USA
| | | | - Ryan L. Ragland
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Sandra G. Durkin
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Stephen T. Warren
- Department of Human Genetics, Emory University, Atlanta, GA 30322, USA
| | - Thomas W. Glover
- Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA
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30
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Kasten-Pisula U, Menegakis A, Brammer I, Borgmann K, Mansour WY, Degenhardt S, Krause M, Schreiber A, Dahm-Daphi J, Petersen C, Dikomey E, Baumann M. The extreme radiosensitivity of the squamous cell carcinoma SKX is due to a defect in double-strand break repair. Radiother Oncol 2008; 90:257-64. [PMID: 19038467 DOI: 10.1016/j.radonc.2008.10.019] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Revised: 10/15/2008] [Accepted: 10/22/2008] [Indexed: 11/17/2022]
Abstract
PURPOSE Squamous cell carcinomas (SCCs) are characterized by moderate radiosensitivity. We have established the human head & neck SCC cell line SKX, which shows an exceptionally high radiosensitivity. It was the aim of this study to understand the underlying mechanisms. MATERIALS & METHODS Experiments were performed with SKX and FaDu, the latter taken as a control of moderate radiosensitivity. Cell lines were grown as xenografts as well as cell cultures. For xenografts, radiosensitivity was determined via local tumour control assay, and for cell cultures using colony assay. For cell cultures, apoptosis was determined by Annexin V staining and G1-arrest by BrdU labelling. Double-strand breaks (DSBs) were detected by both constant-field gel electrophoresis (CFGE) and gammaH2AX-foci technique; DSB rejoining was also assessed by in vitro rejoining assay; chromosomal damage was determined by G01-assay. RESULTS Compared to FaDu, SKX cells are extremely radiosensitive as found for both xenografts (TCD(50) for 10 fractions 46.0Gy [95% C.I.: 39; 54 Gy] vs. 18.9 Gy [95% C.I.: 13; 25Gy]) and cell cultures (D(0.01); 7.1 vs. 3.5Gy). Both cell lines showed neither radiation-induced apoptosis nor radiation-induced permanent G1-arrest. For DSBs, there was no difference in the induction but for repair with SKX cells showing a higher level of both, slowly repaired DSBs and residual DSBs. The in vitro DSB repair assay revealed that SKX cells are defective in nonhomologous endjoining (NHEJ), and that more than 40% of DSBs are rejoined by single-strand annealing (SSA). SKX cells also depicted a two-fold higher number of lethal chromosomal aberrations when compared to FaDu cells. CONCLUSIONS The extreme radiosensitivity of the SCC SKX seen both in vivo and in vitro can be ascribed to a reduced DNA double-strand break repair, resulting from a defect in NHEJ. This defect might be due to preferred usage of other pathways, such as SSA, which prevents efficient endjoining.
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Affiliation(s)
- Ulla Kasten-Pisula
- Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg - Eppendorf, Hamburg, Germany
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31
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McVey M, Lee SE. MMEJ repair of double-strand breaks (director's cut): deleted sequences and alternative endings. Trends Genet 2008; 24:529-38. [PMID: 18809224 DOI: 10.1016/j.tig.2008.08.007] [Citation(s) in RCA: 702] [Impact Index Per Article: 43.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 08/21/2008] [Accepted: 08/22/2008] [Indexed: 11/28/2022]
Abstract
DNA double-strand breaks are normal consequences of cell division and differentiation and must be repaired faithfully to maintain genome stability. Two mechanistically distinct pathways are known to efficiently repair double-strand breaks: homologous recombination and Ku-dependent non-homologous end joining. Recently, a third, less characterized repair mechanism, named microhomology-mediated end joining (MMEJ), has received increasing attention. MMEJ repairs DNA breaks via the use of substantial microhomology and always results in deletions. Furthermore, it probably contributes to oncogenic chromosome rearrangements and genetic variation in humans. Here, we summarize the genetic attributes of MMEJ from several model systems and discuss the relationship between MMEJ and 'alternative end joining'. We propose a mechanistic model for MMEJ and highlight important questions for future research.
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Affiliation(s)
- Mitch McVey
- Department of Biology, Tufts University, 165 Packard Avenue, Medford, MA 02155, USA.
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32
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Abstract
ERCC1-XPF endonuclease is required for nucleotide excision repair (NER) of helix-distorting DNA lesions. However, mutations in ERCC1 or XPF in humans or mice cause a more severe phenotype than absence of NER, prompting a search for novel repair activities of the nuclease. In Saccharomyces cerevisiae, orthologs of ERCC1-XPF (Rad10-Rad1) participate in the repair of double-strand breaks (DSBs). Rad10-Rad1 contributes to two error-prone DSB repair pathways: microhomology-mediated end joining (a Ku86-independent mechanism) and single-strand annealing. To determine if ERCC1-XPF participates in DSB repair in mammals, mutant cells and mice were screened for sensitivity to gamma irradiation. ERCC1-XPF-deficient fibroblasts were hypersensitive to gamma irradiation, and gammaH2AX foci, a marker of DSBs, persisted in irradiated mutant cells, consistent with a defect in DSB repair. Mutant mice were also hypersensitive to irradiation, establishing an essential role for ERCC1-XPF in protecting against DSBs in vivo. Mice defective in both ERCC1-XPF and Ku86 were not viable. However, Ercc1(-/-) Ku86(-/-) fibroblasts were hypersensitive to gamma irradiation compared to single mutants and accumulated significantly greater chromosomal aberrations. Finally, in vitro repair of DSBs with 3' overhangs led to large deletions in the absence of ERCC1-XPF. These data support the conclusion that, as in yeast, ERCC1-XPF facilitates DSB repair via an end-joining mechanism that is Ku86 independent.
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Mansour WY, Schumacher S, Rosskopf R, Rhein T, Schmidt-Petersen F, Gatzemeier F, Haag F, Borgmann K, Willers H, Dahm-Daphi J. Hierarchy of nonhomologous end-joining, single-strand annealing and gene conversion at site-directed DNA double-strand breaks. Nucleic Acids Res 2008; 36:4088-98. [PMID: 18539610 PMCID: PMC2475611 DOI: 10.1093/nar/gkn347] [Citation(s) in RCA: 128] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
In mammalian cells, DNA double-strand breaks (DSBs) are repaired by three pathways, nonhomologous end-joining (NHEJ), gene conversion (GC) and single-strand annealing (SSA). These pathways are distinct with regard to repair efficiency and mutagenic potential and must be tightly controlled to preserve viability and genomic stability. Here, we employed chromosomal reporter constructs to characterize the hierarchy of NHEJ, GC and SSA at a single I-SceI-induced DSB in Chinese hamster ovary cells. We discovered that the use of GC and SSA was increased by 6- to 8-fold upon loss of Ku80 function, suggesting that NHEJ is dominant over the other two pathways. However, NHEJ efficiency was not altered if GC was impaired by Rad51 knockdown. Interestingly, when SSA was made available as an alternative mode for DSB repair, loss of Rad51 function led to an increase in SSA activity at the expense of NHEJ, implying that Rad51 may indirectly promote NHEJ by limiting SSA. We conclude that a repair hierarchy exists to limit the access of the most mutagenic mechanism, SSA, to the break site. Furthermore, the cellular choice of repair pathways is reversible and can be influenced at the level of effector proteins such as Ku80 or Rad51.
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Affiliation(s)
- Wael Y Mansour
- Laboratory of Radiobiology & Experimental Radiation Oncology, Department of Radiotherapy and Radiation Oncology, University Medical School Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany
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Forkhead-associated domain of yeast Xrs2, a homolog of human Nbs1, promotes nonhomologous end joining through interaction with a ligase IV partner protein, Lif1. Genetics 2008; 179:213-25. [PMID: 18458108 DOI: 10.1534/genetics.107.079236] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
DNA double-strand breaks (DSB) are repaired through two different pathways, homologous recombination (HR) and nonhomologous end joining (NHEJ). Yeast Xrs2, a homolog of human Nbs1, is a component of the Mre11-Rad50-Xrs2 (MRX) complex required for both HR and NHEJ. Previous studies showed that the N-terminal forkhead-associated (FHA) domain of Xrs2/Nbs1 in yeast is not involved in HR, but is likely to be in NHEJ. In this study, we showed that the FHA domain of Xrs2 plays a critical role in efficient DSB repair by NHEJ. The FHA domain of Xrs2 specifically interacts with Lif1, a component of the ligase IV complex, Dnl4-Nej1-Lif1 (DNL). Lif1, which is phosphorylated in vivo, contains two Xrs2-binding regions. Serine 383 of Lif1 plays an important role in the interaction with Xrs2 as well as in NHEJ. Interestingly, the phospho-mimetic substitutions of serine 383 enhance the NHEJ activity of Lif1. Our results suggest that the phosphorylation of Lif1 at serine 383 is recognized by the Xrs2 FHA domain, which in turn may promote recruitment of the DNL complex to DSB for NHEJ. The interaction between Xrs2 and Lif1 through the FHA domain is conserved in humans; the FHA domain Nbs1 interacts with Xrcc4, a Lif1 homolog of human.
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Schulte-Uentrop L, El-Awady RA, Schliecker L, Willers H, Dahm-Daphi J. Distinct roles of XRCC4 and Ku80 in non-homologous end-joining of endonuclease- and ionizing radiation-induced DNA double-strand breaks. Nucleic Acids Res 2008; 36:2561-9. [PMID: 18332040 PMCID: PMC2377445 DOI: 10.1093/nar/gkn094] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Non-homologous end-joining (NHEJ) of DNA double-strand breaks (DSBs) is mediated by two protein complexes comprising Ku80/Ku70/DNA-PKcs/Artemis and XRCC4/LigaseIV/XLF. Loss of Ku or XRCC4/LigaseIV function compromises the rejoining of radiation-induced DSBs and leads to defective V(D)J recombination. In this study, we sought to define how XRCC4 and Ku80 affect NHEJ of site-directed chromosomal DSBs in murine fibroblasts. We employed a recently developed reporter system based on the rejoining of I-SceI endonuclease-induced DSBs. We found that the frequency of NHEJ was reduced by more than 20-fold in XRCC4-/- compared to XRCC4+/+ cells, while a Ku80 knock-out reduced the rejoining efficiency by only 1.4-fold. In contrast, lack of either XRCC4 or Ku80 increased end degradation and shifted repair towards a mode that used longer terminal microhomologies for rejoining. However, both proteins proved to be essential for the repair of radiation-induced DSBs. The remarkably different phenotype of XRCC4- and Ku80-deficient cells with regard to the repair of enzyme-induced DSBs mirrors the embryonic lethality of XRCC4 knock-out mice as opposed to the viability of the Ku80 knock-out. Thus, I-SceI-induced breaks may resemble DSBs arising during normal DNA metabolism and mouse development. The removal of these breaks likely has different genetic requirements than the repair of radiation-induced DSBs.
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Affiliation(s)
- Leonie Schulte-Uentrop
- Laboratory of Radiobiology & Experimental Radiation Oncology, Department of Radiotherapy and Radiation Oncology, University Medical School Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany
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36
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Distinctive differences in DNA double-strand break repair between normal urothelial and urothelial carcinoma cells. Mutat Res 2007; 638:56-65. [PMID: 17928011 DOI: 10.1016/j.mrfmmm.2007.08.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2007] [Revised: 08/24/2007] [Accepted: 08/29/2007] [Indexed: 01/10/2023]
Abstract
Several lines of evidence suggest that defective repair of DNA double-strand breaks (DSB) contributes to genomic instability in human cancers, including urothelial carcinoma. In particular, extracts from urothelial cancers have been reported to repair DSBs preferentially by microhomology-mediated end-joining (MMEJ), considered as more error-prone than canonical non-homologous end-joining (NHEJ) predominating in normal urothelial cell extracts. However, it is not clear whether such differences are relevant to intact cells. We therefore transfected plasmids digested with different restriction enzymes to yield incompatible ends (blunt, 5'-protruding or 3'-protruding) into urothelial carcinoma cell lines or normal urothelial cells and characterized the recovered circular plasmids. All cells competently repaired DSBs in a standard cloning vector plasmid, processing 5'- as well as 3'-protruding ends. No significant differences in the extent of processing were detected and the junctions presented short microhomologies indicative of canonical NHEJ. However, dramatic and distinctive differences between normal and cancerous urothelial cells were seen in two different experiments. First, cancer cell lines processed a significantly higher fraction of plasmids cut with a single restriction enzyme that could have been repaired by direct ligation than normal cells. Secondly, for the repair of a large plasmid with incompatible ends containing a large fragment of human genomic DNA, normal cells used almost exclusively MMEJ exploiting a microhomology with the 3'-end of the break, whereas cancer cell lines often processed DNA despite suitable microhomologies. DNA repair of the small or large plasmid was almost abolished by siRNA knockdown of Ku70. These findings strongly suggest that urothelial carcinoma cells lack control mechanisms preventing overprocessing during NHEJ repair. This may account for previous findings that urothelial cancers contain unusually large chromosomal deletions. Moreover, in contrast to prevailing interpretations, our observations suggest that MMEJ, despite its error-proneness, in some instances may act as a failsafe mechanism against overprocessing during NHEJ.
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Povirk LF, Zhou RZ, Ramsden DA, Lees-Miller SP, Valerie K. Phosphorylation in the serine/threonine 2609-2647 cluster promotes but is not essential for DNA-dependent protein kinase-mediated nonhomologous end joining in human whole-cell extracts. Nucleic Acids Res 2007; 35:3869-78. [PMID: 17526517 PMCID: PMC1919499 DOI: 10.1093/nar/gkm339] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Previous work suggested that phosphorylation of DNA-PKcs at several serine/threonine (S/T) residues at positions 2609–2647 promotes DNA-PK-dependent end joining. In an attempt to clarify the role of such phosphorylation, end joining was examined in extracts of DNA-PKcs-deficient M059J cells. Joining of ends requiring gap filling prior to ligation was completely dependent on complementation of these extracts with exogenous DNA-PKcs. DNA-PKcs with either S/T → A or S/T → D substitutions at all six sites in the 2609–2647 cluster also supported end joining, but with markedly lower efficiency than wild-type protein. The residual end joining was greater with the S/T → D-substituted than with the S/T → A-substituted protein. A specific inhibitor of the kinase activity of DNA-PK, KU57788, completely blocked end joining promoted by wild type as well as both mutant forms of DNA-PK, while inhibition of ATM kinase did not. The fidelity of end joining was not affected by the mutant DNA-PKcs alleles or the inhibitors. Overall, the results support a role for autophosphorylation of the 2609–2647 cluster in promoting end joining and controlling the accessibility of DNA ends, but suggest that DNA-PK-mediated phosphorylation at other sites, on either DNA-PKcs or other proteins, is at least as important as the 2609–2647 cluster in regulating end joining.
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Affiliation(s)
- Lawrence F Povirk
- Department of Pharmacology and Toxicology, Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA.
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