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Huang RX, Zhou PK. DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer. Signal Transduct Target Ther 2020; 5:60. [PMID: 32355263 PMCID: PMC7192953 DOI: 10.1038/s41392-020-0150-x] [Citation(s) in RCA: 508] [Impact Index Per Article: 127.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Revised: 02/20/2020] [Accepted: 03/16/2020] [Indexed: 12/19/2022] Open
Abstract
Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.
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Affiliation(s)
- Rui-Xue Huang
- Department of Occupational and Environmental Health, Xiangya School of Public Health, Central South University, 410078, Changsha, People's Republic of China
| | - Ping-Kun Zhou
- Department of Radiation Biology, Beijing Key Laboratory for Radiobiology, Beijing Institute of Radiation Medicine, AMMS, 100850, Beijing, People's Republic of China.
- Institute for Chemical Carcinogenesis, State Key Laboratory of Respiratory, Guangzhou Medical University, 511436, Guangzhou, People's Republic of China.
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Mohiuddin IS, Kang MH. DNA-PK as an Emerging Therapeutic Target in Cancer. Front Oncol 2019; 9:635. [PMID: 31380275 PMCID: PMC6650781 DOI: 10.3389/fonc.2019.00635] [Citation(s) in RCA: 122] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 06/27/2019] [Indexed: 12/21/2022] Open
Abstract
The DNA-dependent protein kinase (DNA-PK) plays an instrumental role in the overall survival and proliferation of cells. As a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, DNA-PK is best known as a mediator of the cellular response to DNA damage. In this context, DNA-PK has emerged as an intriguing therapeutic target in the treatment of a variety of cancers, especially when used in conjunction with genotoxic chemotherapy or ionizing radiation. Beyond the DNA damage response, DNA-PK activity is necessary for multiple cellular functions, including the regulation of transcription, progression of the cell cycle, and in the maintenance of telomeres. Here, we review what is currently known about DNA-PK regarding its structure and established roles in DNA repair. We also discuss its lesser-known functions, the pharmacotherapies inhibiting its function in DNA repair, and its potential as a therapeutic target in a broader context.
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Affiliation(s)
- Ismail S Mohiuddin
- Cancer Center, Department of Pediatrics, Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States
| | - Min H Kang
- Cancer Center, Department of Pediatrics, Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, United States
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Cheng L, Brzozowska B, Sollazzo A, Lundholm L, Lisowska H, Haghdoost S, Wojcik A. Simultaneous induction of dispersed and clustered DNA lesions compromises DNA damage response in human peripheral blood lymphocytes. PLoS One 2018; 13:e0204068. [PMID: 30379881 PMCID: PMC6209146 DOI: 10.1371/journal.pone.0204068] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Accepted: 08/31/2018] [Indexed: 11/18/2022] Open
Abstract
Due to its ability to induce DNA damage in a space and time controlled manner, ionising radiation is a unique tool for studying the mechanisms of DNA repair. The biological effectiveness of ionising radiation is related to the ionisation density which is defined by the linear energy transfer (LET). Alpha particles are characterised by high LET, while X-rays by low LET values. An interesting question is how cells react when exposed to a mixed beam of high and low LET radiation. In an earlier study carried out with human peripheral blood lymphocytes (PBL) we could demonstrate that alpha radiation X-rays interact in producing more chromosomal aberrations than expected based on additivity. The aim of the present investigation was to look at the mechanism of the interaction, especially with respect to the question if it is due to an augmented level of initial damage or impaired DNA repair. PBL were exposed to various doses of alpha particles, X-rays and mixed beams. DNA damage and the kinetics of damage repair was quantified by the alkaline comet assay. The levels of phosphorylated, key DNA damage response (DDR) proteins ATM, p53 and DNA-PK were measured by Western blotting and mRNA levels of 6 damage-responsive genes were measured by qPCR. Alpha particles and X-rays interact in inducing DNA damage above the level predicted by assuming additivity and that the repair of damage occurs with a delay. The activation levels of DDR proteins and mRNA levels of the studied genes were highest in cells exposed to mixed beams. The results substantiate the idea that exposure to mixed beams presents a challenge for the cellular DDR system.
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Affiliation(s)
- Lei Cheng
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Beata Brzozowska
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
- Biomedical Physics Division, Faculty of Physics, University of Warsaw, Warszawa, Poland
| | - Alice Sollazzo
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Lovisa Lundholm
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Halina Lisowska
- Institute of Biology, Jan Kochanowski University, Kielce, Poland
| | - Siamak Haghdoost
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Andrzej Wojcik
- Centre for Radiation Protection Research, Department of Molecular Biosciences, the Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
- Institute of Biology, Jan Kochanowski University, Kielce, Poland
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Lisowska H, Cheng L, Sollazzo A, Lundholm L, Wegierek-Ciuk A, Sommer S, Lankoff A, Wojcik A. Hypothermia modulates the DNA damage response to ionizing radiation in human peripheral blood lymphocytes. Int J Radiat Biol 2018; 94:551-557. [PMID: 29668347 DOI: 10.1080/09553002.2018.1466206] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
PURPOSE Low temperature at exposure has been shown to act in a radioprotective manner at the level of cytogenetic damage. It was suggested to be due to an effective transformation of DNA damage to chromosomal damage at low temperature. The purpose of the study was to analyze the kinetics of aberration formation during the first hours after exposing human peripheral blood lymphocytes to ionizing radiation at 0.8 °C and 37 °C. MATERIALS AND METHODS To this end, we applied the technique of premature chromosome condensation. In addition, DNA damage response was analyzed by measuring the levels of phosphorylated DNA damage responsive proteins ATM, DNA-PK and p53 and mRNA levels of the radiation-responsive genes BBC3, FDXR, GADD45A, XPC, MDM2 and CDKN1A. RESULTS A consistently lower frequency of chromosomal breaks was observed in cells exposed at 0.8 °C as compared to 37 °C already after 30 minutes postexposure. This effect was accompanied by elevated levels of phosphorylated ATM and DNA-PK proteins and a reduced immediate level of phosphorylated p53 and of the responsive genes. CONCLUSIONS Low temperature at exposure appears to promote DNA repair leading to reduced transformation of DNA damage to chromosomal aberrations.
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Affiliation(s)
- Halina Lisowska
- a Department of Radiobiology and Immunology , Institute of Biology, Jan Kochanowski University , Kielce , Poland
| | - Lei Cheng
- b Centre for Radiation Protection Research, Department of Molecular Biosciences , The Wenner-Gren Institute, Stockholm University , Stockholm , Sweden
| | - Alice Sollazzo
- b Centre for Radiation Protection Research, Department of Molecular Biosciences , The Wenner-Gren Institute, Stockholm University , Stockholm , Sweden
| | - Lovisa Lundholm
- b Centre for Radiation Protection Research, Department of Molecular Biosciences , The Wenner-Gren Institute, Stockholm University , Stockholm , Sweden
| | - Aneta Wegierek-Ciuk
- a Department of Radiobiology and Immunology , Institute of Biology, Jan Kochanowski University , Kielce , Poland
| | - Sylwester Sommer
- c Institute of Nuclear Chemistry and Technology , Warsaw , Poland
| | - Anna Lankoff
- a Department of Radiobiology and Immunology , Institute of Biology, Jan Kochanowski University , Kielce , Poland.,c Institute of Nuclear Chemistry and Technology , Warsaw , Poland
| | - Andrzej Wojcik
- a Department of Radiobiology and Immunology , Institute of Biology, Jan Kochanowski University , Kielce , Poland.,b Centre for Radiation Protection Research, Department of Molecular Biosciences , The Wenner-Gren Institute, Stockholm University , Stockholm , Sweden
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DNA-dependent protein kinase modulates the anti-cancer properties of silver nanoparticles in human cancer cells. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2017; 824:32-41. [PMID: 29150048 DOI: 10.1016/j.mrgentox.2017.10.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/04/2017] [Accepted: 10/09/2017] [Indexed: 12/19/2022]
Abstract
Silver nanoparticles (Ag-np) were reported to be toxic to eukaryotic cells. These potentially detrimental effects of Ag-np can be advantageous in experimental therapeutics. They are currently being employed to enhance the therapeutic efficacy of cancer drugs. In this study, we demonstrate that Ag-np treatment trigger the activation of DNA-PKcs and JNK pathway at selected doses, presumably as a physiologic response to DNA damage and repair in normal and malignant cells. Ag-np altered the telomere dynamics by disrupting the shelterin complex located at the telomeres and telomere lengths. The genotoxic effect of Ag-np was not restricted to telomeres but the entire genome as Ag-np induced γ-H2AX foci formation, an indicator of global DNA damage. Inhibition of DNA-PKcs activity sensitised the cancer cells towards the cytotoxicity of Ag-np and substantiated the damaging effect of Ag-np at telomeres in human cancer cells. Abrogation of JNK mediated DNA repair and extensive damage of telomeres led to greater cell death following Ag-np treatment in DNA-PKcs inhibited cancer cells. Collectively, this study suggests that improved anti-proliferative and cytotoxic effects of Ag-np treatment in cancer cells can be achieved by the inhibition of DNA-PKcs.
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Szafranski K, Mekhail K. The fine line between lifespan extension and shortening in response to caloric restriction. Nucleus 2014; 5:56-65. [PMID: 24637399 PMCID: PMC4028356 DOI: 10.4161/nucl.27929] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Caloric restriction (CR) is generally linked to lifespan extension in various organisms and may limit age-associated diseases. Processes through which caloric restriction promotes lifespan include obesity-countering weight loss, increased DNA repair, control of ribosomal and telomeric DNA repeats, mitochondrial regulation, activation of antioxidants, and protective autophagy. Several of these protective cellular processes are linked to the suppression of TOR (target of rapamycin) or the activation of sirtuins. In stark contrast, CR fails to extend or even shortens lifespan in certain settings. CR-dependent lifespan shortening is linked to weight loss in the non-obese, mitochondrial hyperactivity, genomic inflexibility, and several other processes. Deciphering the balance between positive and negative effects of CR is critical to understanding its ultimate impact on aging. This knowledge is especially needed in order to fulfil the promise of using CR or its mimetic drugs to counteract age-associated diseases and unhealthy aging.
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Affiliation(s)
- Kirk Szafranski
- Department of Laboratory Medicine and Pathobiology; Faculty of Medicine, University of Toronto; Toronto, ON Canada
| | - Karim Mekhail
- Department of Laboratory Medicine and Pathobiology; Faculty of Medicine, University of Toronto; Toronto, ON Canada; Canada Research Chairs Program; Faculty of Medicine, University of Toronto; Toronto, ON Canada
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7
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Liao PH, Yang HW, Huang YF. Genetic expression signatures of oral submucous fibrosis and oral cancer-A preliminary microarray report. J Dent Sci 2013; 11:457-462. [PMID: 30895012 PMCID: PMC6395281 DOI: 10.1016/j.jds.2013.02.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2011] [Revised: 12/21/2011] [Indexed: 11/24/2022] Open
Abstract
Background/purpose Oral submucous fibrosis (OSF) is a potentially malignant disorder of oral squamous cell carcinoma (SCC). In this study, we obtained the genetic expression signatures of OSF and SCC by microarray analysis. Materials and methods Five patients with clinically evident OSF, five patients with SCC who also had existing OSF, and four normal volunteers who did not have a history of chewing betel quids were recruited. Biopsy specimens were obtained with an approved Institutional Review Board protocol. Total RNA from OSF or SCC was isolated and hybridized to a Human Oligo 1A (V2) Microarray (G4110B) chip against normal control RNA that was pooled from the four healthy volunteers. Results We found similar, but distinct genetic expression signatures for OSF and SCC. At the hierarchical clustering analysis, 24 known genes (23 upregulated and 1 downregulated) in OSF were differentially expressed consistently in all participants. Among the genes, XRCC5 was cloned and transfected into oral cancer GNM cells. The results demonstrated that the overexpression of XRCC5 increased the resistance of GNM cells to low-density X-ray irradiation and promoted the cell growth rate. Conclusion The distinct but similar genetic expression signatures seen in OSF and SCC suggested that this expression may be used as a supplemental diagnostic tool in pathology practice. This preliminary study showed that the XRCC5 gene promoted GNM cell growth and conferred resistance to low-density X-ray irradiation. Further studies on the effect of XRCC5 in oral cancer cells are in progress.
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Affiliation(s)
- Pao-Hsin Liao
- Oral Medicine Center, Chung Shan Medical University Hospital, Taichung, Taiwan.,Department of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Hui-Wen Yang
- Oral Medicine Center, Chung Shan Medical University Hospital, Taichung, Taiwan.,Department of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Yu-Feng Huang
- Oral Medicine Center, Chung Shan Medical University Hospital, Taichung, Taiwan.,Department of Dentistry, College of Oral Medicine, Chung Shan Medical University, Taichung, Taiwan
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Grandjean M, Girod PA, Calabrese D, Kostyrko K, Wicht M, Yerly F, Mazza C, Beckmann JS, Martinet D, Mermod N. High-level transgene expression by homologous recombination-mediated gene transfer. Nucleic Acids Res 2011; 39:e104. [PMID: 21652640 PMCID: PMC3159483 DOI: 10.1093/nar/gkr436] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Gene transfer and expression in eukaryotes is often limited by a number of stably maintained gene copies and by epigenetic silencing effects. Silencing may be limited by the use of epigenetic regulatory sequences such as matrix attachment regions (MAR). Here, we show that successive transfections of MAR-containing vectors allow a synergistic increase of transgene expression. This finding is partly explained by an increased entry into the cell nuclei and genomic integration of the DNA, an effect that requires both the MAR element and iterative transfections. Fluorescence in situ hybridization analysis often showed single integration events, indicating that DNAs introduced in successive transfections could recombine. High expression was also linked to the cell division cycle, so that nuclear transport of the DNA occurs when homologous recombination is most active. Use of cells deficient in either non-homologous end-joining or homologous recombination suggested that efficient integration and expression may require homologous recombination-based genomic integration of MAR-containing plasmids and the lack of epigenetic silencing events associated with tandem gene copies. We conclude that MAR elements may promote homologous recombination, and that cells and vectors can be engineered to take advantage of this property to mediate highly efficient gene transfer and expression.
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Affiliation(s)
- Mélanie Grandjean
- Laboratory of Molecular Biotechnology, Center for Biotechnology UNIL-EPFL, University of Lausanne, Lausanne, Switzerland
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Sharma S, Raghavan SC. Nonhomologous DNA end joining in cell-free extracts. J Nucleic Acids 2010; 2010. [PMID: 20936167 PMCID: PMC2945661 DOI: 10.4061/2010/389129] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 07/14/2010] [Accepted: 08/05/2010] [Indexed: 12/19/2022] Open
Abstract
Among various DNA damages, double-strand breaks (DSBs) are considered as most deleterious, as they may lead to chromosomal rearrangements and cancer when unrepaired. Nonhomologous DNA end joining (NHEJ) is one of the major DSB repair pathways in higher organisms. A large number of studies on NHEJ are based on in vitro systems using cell-free extracts. In this paper, we summarize the studies on NHEJ performed by various groups in different cell-free repair systems.
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Affiliation(s)
- Sheetal Sharma
- Department of Biochemistry, Indian Institute of Science, Bangalore 560 012, India
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Gurung RL, Lim SN, Khaw AK, Soon JFF, Shenoy K, Mohamed Ali S, Jayapal M, Sethu S, Baskar R, Hande MP. Thymoquinone induces telomere shortening, DNA damage and apoptosis in human glioblastoma cells. PLoS One 2010; 5:e12124. [PMID: 20711342 PMCID: PMC2920825 DOI: 10.1371/journal.pone.0012124] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Accepted: 06/22/2010] [Indexed: 12/15/2022] Open
Abstract
Background A major concern of cancer chemotherapy is the side effects caused by the non-specific targeting of both normal and cancerous cells by therapeutic drugs. Much emphasis has been placed on discovering new compounds that target tumour cells more efficiently and selectively with minimal toxic effects on normal cells. Methodology/Principal Findings The cytotoxic effect of thymoquinone, a component derived from the plant Nigella sativa, was tested on human glioblastoma and normal cells. Our findings demonstrated that glioblastoma cells were more sensitive to thymoquinone-induced antiproliferative effects. Thymoquinone induced DNA damage, cell cycle arrest and apoptosis in the glioblastoma cells. It was also observed that thymoquinone facilitated telomere attrition by inhibiting the activity of telomerase. In addition to these, we investigated the role of DNA-PKcs on thymoquinone mediated changes in telomere length. Telomeres in glioblastoma cells with DNA-PKcs were more sensitive to thymoquinone mediated effects as compared to those cells deficient in DNA-PKcs. Conclusions/Significance Our results indicate that thymoquinone induces DNA damage, telomere attrition by inhibiting telomerase and cell death in glioblastoma cells. Telomere shortening was found to be dependent on the status of DNA-PKcs. Collectively, these data suggest that thymoquinone could be useful as a potential chemotherapeutic agent in the management for brain tumours.
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Affiliation(s)
- Resham Lal Gurung
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Shi Ni Lim
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Aik Kia Khaw
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Jasmine Fen Fen Soon
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Kirthan Shenoy
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Safiyya Mohamed Ali
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Manikandan Jayapal
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Swaminathan Sethu
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Rajamanickam Baskar
- Division of Cellular and Molecular Research, Department of Radiation Oncology, National Cancer Centre, Singapore, Singapore
| | - M. Prakash Hande
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- * E-mail:
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Frankenberg-Schwager M, Gebauer A, Koppe C, Wolf H, Pralle E, Frankenberg D. Single-strand annealing, conservative homologous recombination, nonhomologous DNA end joining, and the cell cycle-dependent repair of DNA double-strand breaks induced by sparsely or densely ionizing radiation. Radiat Res 2009; 171:265-73. [PMID: 19267553 DOI: 10.1667/rr0784.1] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The cell cycle-dependent relative contributions of error-prone single-strand annealing (SSA), error-free conservative homologous recombination (HR), and potentially error-prone nonhomologous DNA end joining (NHEJ) to repair simple (induced by 200 kV X rays) or complex (induced by (241)Am alpha particles) DNA double-strand breaks (DSBs) in Chinese hamster ovary cells are reported for the first time. Cells of the parental cell line AA8 and its derivatives UV41 (SSA-deficient), irs1SF (HR-deficient) and V3 (NHEJ-deficient) were synchronized in G(1) or in S phase, and survival responses after exposure to either type of radiation were measured. It is demonstrated for the first time that in G(1)-phase SSA is negligible for the repair of DSBs of various complexities. HR-deficient cells exposed to X rays or alpha particles in G(1) phase show enhanced radiosensitivity, but this does not necessarily mean that HR is important in G(1) phase. NHEJ appears to be the most important (if not the only) mechanism in G(1) phase acting efficiently on simple DSBs, but complex DSBs are a less preferred target. In contrast to X rays, NHEJ-deficient cells show no cell cycle-dependent variation in sensitivity to alpha particles. Surprisingly, when these cells are exposed to X rays in G(1) phase, they are even more sensitive compared to alpha particles. It is also shown for the first time that in S phase all three mechanisms play a role in the repair of simple and complex DSBs. A defect in SSA confers radiosensitivity to cells in S phase, suggesting that the error-prone SSA mechanism is important for the repair of specific simple and complex DSBs that are not a substrate for HR or NHEJ. The most important mechanism in S phase for the repair of simple and complex DSBs is HR. This is also emphasized by the finding that irs1SF cells, after complementation of their HR defect by human XRCC3 cDNA, show a greater radioresistance than parental cells, whereas resistance to mitomycin C is only partially restored. Complementation confers a greater resistance to alpha particles than X rays, suggesting an important role of HR, especially for the repair of complex DSBs. In S phase, NHEJ is more important than SSA for the repair of simple DSBs, but SSA is more important than NHEJ for the repair of complex DSBs.
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Frankenberg-Schwager M, Becker M, Garg I, Pralle E, Wolf H, Frankenberg D. The role of nonhomologous DNA end joining, conservative homologous recombination, and single-strand annealing in the cell cycle-dependent repair of DNA double-strand breaks induced by H(2)O(2) in mammalian cells. Radiat Res 2009; 170:784-93. [PMID: 19138034 DOI: 10.1667/rr1375.1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Accepted: 07/22/2008] [Indexed: 11/03/2022]
Abstract
The purpose of this study was to investigate the cell cycle-dependent role of nonhomologous DNA end joining (NHEJ), conservative homologous recombination (HR), and single-strand annealing (SSA) for the repair of simple DNA double-strand breaks (DSBs) induced by H(2)O(2)-mediated OH radicals in CHO cells. Cells of the cell lines V3 (NHEJ-deficient), irs1SF (HR-deficient) and UV41 (SSA-deficient) and their parental cell line AA8 were exposed to various concentrations of H(2)O(2) in G(1) or S phase of the cell cycle and their colony-forming ability was assayed. In G(1) phase, NHEJ was the most important-if not the only-mechanism to repair H(2)O(2)-mediated DSBs; this was similar to results obtained in a parallel study of more complex DSBs induced by sparsely or densely ionizing radiation. Unlike HR (irs1SF)- and SSA (UV41)-deficient cells, the sensitivity of NHEJ-deficient V3 cells to H(2)O(2) relative to parental AA8 cells in G(1) phase is about 50 times higher compared to 200 kV X rays. This points to a specific role of the catalytic subunit of DNA-PK for efficient NHEJ of H(2)O(2)-mediated DSBs that are located at sites critical for the maintenance of the higher-order structure of cellular DNA, whereas X-ray-induced DSBs are distributed stochastically. Surprisingly, SSA-deficient cells in G(1) phase showed an increased sensitivity to high concentrations of H(2)O(2) relative to the parental wild-type cells and to HR-deficient cells, which may be interpreted in terms of a specific type of H(2)O(2)-induced damage requiring SSA for repair after its transfer into S phase. In S phase, HR is the most important mechanism to repair H(2)O(2)-mediated DSBs, followed by NHEJ. In contrast, the action of error-prone SSA may not be beneficial, since SSA-deficient cells are three times more resistant to H(2)O(2) than wild-type AA8 cells. This is likely due to channeling of DSBs into the error-free HR repair pathway or into the potentially error-prone NHEJ pathway. Cells with or without a defect in DSB repair are considerably more sensitive to H(2)O(2) in S phase compared to G(1) phase. This effect is likely due to the fact that topoisomerase II, which is expressed only in proliferating cells, is a target of H(2)O(2), resulting in enhanced accumulation of DSBs and killing of cells treated in S phase with H(2)O(2). The relative sensitivities to H(2)O(2) differ by orders of magnitude for the four cell lines. This seems to be caused mainly by H(2)O(2)-mediated poisoning of topoisomerase IIalpha rather than by a defect in DSB repair.
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Rübe CE, Grudzenski S, Kühne M, Dong X, Rief N, Löbrich M, Rübe C. DNA double-strand break repair of blood lymphocytes and normal tissues analysed in a preclinical mouse model: implications for radiosensitivity testing. Clin Cancer Res 2008; 14:6546-55. [PMID: 18927295 DOI: 10.1158/1078-0432.ccr-07-5147] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Radiotherapy is an effective cancer treatment, but a few patients suffer severe radiation toxicities in neighboring normal tissues. There is increasing evidence that the variable susceptibility to radiation toxicities is caused by the individual genetic predisposition, by subtle mutations, or polymorphisms in genes involved in cellular responses to ionizing radiation. Double-strand breaks (DSB) are the most deleterious form of radiation-induced DNA damage, and DSB repair deficiencies lead to pronounced radiosensitivity. Using a preclinical mouse model, the highly sensitive gammaH2AX-foci approach was tested to verify even subtle, genetically determined DSB repair deficiencies known to be associated with increased normal tissue radiosensitivity. EXPERIMENTAL DESIGN By enumerating gammaH2AX-foci in blood lymphocytes and normal tissues (brain, lung, heart, and intestine), the induction and repair of DSBs after irradiation with therapeutic doses (0.1-2 Gy) was investigated in repair-proficient and repair-deficient mouse strains in vivo and blood samples irradiated ex vivo. RESULTS gammaH2AX-foci analysis allowed to verify the different DSB repair deficiencies; even slight impairments caused by single polymorphisms were detected similarly in both blood lymphocytes and solid tissues, indicating that DSB repair measured in lymphocytes is valid for different and complex organs. Moreover, gammaH2AX-foci analysis of blood samples irradiated ex vivo was found to reflect repair kinetics measured in vivo and, thus, give reliable information about the individual DSB repair capacity. CONCLUSIONS gammaH2AX analysis of blood and tissue samples allows to detect even minor genetically defined DSB repair deficiencies, affecting normal tissue radiosensitivity. Future studies will have to evaluate the clinical potential to identify patients more susceptible to radiation toxicities before radiotherapy.
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Affiliation(s)
- Claudia E Rübe
- Department of Radiation Oncology, Saarland University, Homburg/Saar, Germany
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14
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Frankenberg D, Greif KD, Beverung W, Langner F, Giesen U. The role of nonhomologous end joining and homologous recombination in the clonogenic bystander effects of mammalian cells after exposure to counted 10 MeV protons and 4.5 MeV alpha-particles of the PTB microbeam. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2008; 47:431-438. [PMID: 18688633 DOI: 10.1007/s00411-008-0187-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 07/15/2008] [Indexed: 05/26/2023]
Abstract
We have studied the dependence of clonogenic bystander effects on defects in the pathways of DNA double-strand break (DSB) repair and on linear energy transfer (LET). The single-ion microbeam of the Physikalisch-Technische Bundesanstalt (PTB) was used to irradiate parental Chinese hamster ovary cells or derivatives deficient in nonhomologous end joining (NHEJ) or homologous recombination (HR) in the G1-phase of the cell cycle. Cell nuclei were targeted with 10 MeV protons (LET = 4.7 keV/microm) or 4.5 MeV alpha-particles (LET = 100 keV/microm). During exposure, the cells were confluent, allowing signal transfer through both gap junctions and diffusion. When all cell nuclei were targeted with 10 MeV protons, approximately exponential survival curves were obtained for all three cell lines. When only 10% of all cell nuclei were targeted, a significant bystander effect was observed for parental and HR-deficient cells, but not for NHEJ-deficient cells. For all three cell lines, the survival data after exposure of all cell nuclei to 4.5 MeV alpha-particles could be fitted by exponential curves. When only 10% of all cell nuclei were targeted, significant bystander effects were obtained for parental and HR-deficient cells, whereas for NHEJ-deficient cells a small, but significant, bystander effect was observed only at higher doses. The data suggest that bystander cell killing is a consequence of un- or misrejoined DSB which occur in bystander cells during the S-phase as a result of the processing of oxidative bistranded DNA lesions. The relative contributions of NHEJ and HR to the repairing of DSB in the late S/G2-phase may affect clonogenic bystander effects.
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Affiliation(s)
- Dieter Frankenberg
- Department 6.4, Ion Accelerators and Reference Radiation Fields, Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
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15
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Kulkarni A, Wilson DM. The involvement of DNA-damage and -repair defects in neurological dysfunction. Am J Hum Genet 2008; 82:539-66. [PMID: 18319069 PMCID: PMC2427185 DOI: 10.1016/j.ajhg.2008.01.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Revised: 12/17/2007] [Accepted: 01/03/2008] [Indexed: 10/22/2022] Open
Abstract
A genetic link between defects in DNA repair and neurological abnormalities has been well established through studies of inherited disorders such as ataxia telangiectasia and xeroderma pigmentosum. In this review, we present a comprehensive summary of the major types of DNA damage, the molecular pathways that function in their repair, and the connection between defective DNA-repair responses and specific neurological disease. Particular attention is given to describing the nature of the repair defect and its relationship to the manifestation of the associated neurological dysfunction. Finally, the review touches upon the role of oxidative stress, a leading precursor to DNA damage, in the development of certain neurodegenerative pathologies, such as Alzheimer's and Parkinson's.
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Affiliation(s)
- Avanti Kulkarni
- Laboratory of Molecular Gerontology, National Institute of Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - David M. Wilson
- Laboratory of Molecular Gerontology, National Institute of Aging, National Institutes of Health, Baltimore, MD 21224, USA
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16
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Agapakis-Caussé C, Boscá F, Castell JV, Hernández D, Marín ML, Marrot L, Miranda MA. Tiaprofenic Acid-photosensitized Damage to Nucleic Acids: A Mechanistic Study Using Complementary in vitro Approaches. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2000)0710499tapdtn2.0.co2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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17
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Chang HW, Kim SY, Yi SL, Son SH, Song DY, Moon SY, Kim JH, Choi EK, Ahn SD, Shin SS, Lee KK, Lee SW. Expression of Ku80 correlates with sensitivities to radiation in cancer cell lines of the head and neck. Oral Oncol 2006; 42:979-86. [PMID: 16472552 DOI: 10.1016/j.oraloncology.2005.12.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Accepted: 12/08/2005] [Indexed: 01/03/2023]
Abstract
The Ku protein is essential for the repair of a majority of DNA double-strand breaks in mammalian cells. The purpose of this study was to investigate the relationship between the expression of Ku70/80 and sensitivity to radiation in cancer cell lines of the head and neck. The sensitivity to radiation in various head and neck cancer cell lines (AMC-HN-1 to -9) was analyzed by colony forming assay. Of the nine cell lines examined, the most radiosensitive cell line (AMC-HN-3) and the most radioresistant cell line (AMC-HN-9) were selected for this experiments. The expression of Ku70/80 was examined after irradiation using real time PCR, Western blotting and immunofluorescence in two different cell lines. Cell cycle distribution after irradiation were analysed. A differential radioresponse was demonstrated by expression of Ku70/80 in AMC-HN-3 and AMC-HN-9 cells. While the expression of Ku70 was slightly increased in the radioresistant AMC-HN-9 cell line, the expression of Ku80 was remarkably increased, suggesting a correlation between Ku80 expression and radiation resistance. Overexpression of Ku80 plays an important role in the repair of DNA damage induced by radiation. Ku80 expression may provide an effective predictive assay of radiosensitivity in head and neck cancers.
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Affiliation(s)
- Hyo Won Chang
- Department of Otolaryngology, University of Ulsan, College of Medicine, Asan Medical Center, Seoul, Republic of Korea
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18
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Zhang Q, Williams ES, Askin KF, Peng Y, Bedford JS, Liber HL, Bailey SM. Suppression of DNA-PK by RNAi has different quantitative effects on telomere dysfunction and mutagenesis in human lymphoblasts treated with gamma rays or HZE particles. Radiat Res 2005; 164:497-504. [PMID: 16187756 DOI: 10.1667/rr3366.1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Basic to virtually all relevant biological effects of ionizing radiation is the underlying damage produced in DNA and the subsequent cellular processing of such damage. The damage can be qualitatively different for different kinds of radiations, and the genetics of the biological systems exposed can greatly affect damage processing and ultimate outcome--the biological effect of concern. The accurate repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity and function. Incorrect repair of such lesions results in chromosomal rearrangements and mutations that can lead to cancer and heritable defects in the progeny of irradiated parents. We have focused on the consequent phenotypic effects of faulty repair by examining connections between cellular radiosensitivity phenotypes relevant for carcinogenesis after exposure to ionizing radiation, and deficiencies in various components of the non-homologous end-joining (NHEJ) system. Here we produced deficiencies of individual components of the DNA-dependent protein kinase (DNA-PK) holoenzyme (Ku86 and the catalytic subunit, DNA-PKcs), both singly and in combination, using RNA interference (RNAi) in human lymphoblastoid cell lines. Exposure of cells exhibiting reduced protein expression to either gamma rays or 1 GeV/nucleon iron particles demonstrated differential effects on telomere dysfunction and mutation frequency as well as differential effects between radiation qualities.
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Affiliation(s)
- Qinming Zhang
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523, USA
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19
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Jones KR, Gewirtz DA, Yannone SM, Zhou S, Schatz DG, Valerie K, Povirk LF. Radiosensitization of MDA-MB-231 breast tumor cells by adenovirus-mediated overexpression of a fragment of the XRCC4 protein. Mol Cancer Ther 2005; 4:1541-7. [PMID: 16227403 DOI: 10.1158/1535-7163.mct-05-0193] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Incomplete DNA repair or misrepair can contribute to the cytotoxicity of DNA double-strand breaks. Consequently, interference with double-strand break repair, by pharmacologic or genetic means, is likely to sensitize tumor cells to ionizing radiation. The current studies were designed to inhibit the nonhomologous end joining repair pathway by interfering with the function of the XRCC4/ligase IV complex. A PCR-generated fragment of the XRCC4 gene, encompassing the homodimerization and ligase IV-binding domains, was inserted into a plasmid vector (pFLAG-CMV-2) expressing the FLAG peptide and the cassette encoding FLAG-tagged XRCC4 fragment was cloned into an adenoviral vector. Both the plasmid and the corresponding adenovirus elicited robust expression of a truncated XRCC4 protein designed to compete in a dominant-negative fashion with full-length XRCC4 for binding to ligase IV. Binding of the XRCC4 fragment to ligase IV in vivo was confirmed by immunoprecipitation. Clonogenic survival assays showed that the adenovirus expressing the truncated XRCC4 protein sensitizes MDA-MB-231 breast tumor cells to ionizing radiation, presumably through interference with the functional activity of ligase IV, leading to inhibition of the final ligation step in end joining. These studies support the potential clinical utility of combining radiation therapy with agents that inhibit DNA double-strand break repair.
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Affiliation(s)
- Kara R Jones
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, P.O. Box 980230, Richmond, VA 23298, USA
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20
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Lee SW, Cho KJ, Park JH, Kim SY, Nam SY, Lee BJ, Kim SB, Choi SH, Kim JH, Ahn SD, Shin SS, Choi EK, Yu E. Expressions of Ku70 and DNA-PKcs as prognostic indicators of local control in nasopharyngeal carcinoma. Int J Radiat Oncol Biol Phys 2005; 62:1451-7. [PMID: 16029807 DOI: 10.1016/j.ijrobp.2004.12.049] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2004] [Revised: 12/10/2004] [Accepted: 12/17/2004] [Indexed: 11/29/2022]
Abstract
PURPOSE The objective of this study was to determine whether the expressions of the two components of DNA-dependent protein kinase, Ku70 and DNA-protein kinase catalytic subunit (DNA-PKcs), influence the response to radiotherapy (RT) and outcome of treatment of nondisseminated nasopharyngeal carcinoma (NPC) in patients who received definitive RT. METHODS AND MATERIALS Sixty-six patients with NPC who were treated with radiotherapy alone or with concurrent chemotherapy between June 1995 and December 2001 were divided into groups based on the levels of immunoreactivity for Ku70 and DNA-PKcs in pretreatment biopsy specimens. The overexpression of Ku70 or DNA-PKcs groups included patients whose biopsy specimens showed at least 50% immunopositive tumor cells; patients in which less than 50% of the tumor cells in the biopsy tissues were immunopositive were placed in the low Ku70 and DNA-PKcs groups. The immunoreactivities for Ku70 and DNA-PKcs were retrospectively compared with the sensitivity of the tumor to radiation and the patterns of therapy failure. Univariate analyses were performed to determine the prognostic factors that influenced locoregional control of NPC. RESULTS The 5-year locoregional control rate was significantly higher in the low Ku70 group (Ku-) (85%) than in the high Ku70 group (Ku+) (42%) (p = 0.0042). However, there were no differences in the metastases-free survival rates between the 2 groups (Ku70+, 82%; Ku70- 78%; p = 0.8672). Univariate analysis indicated that the overexpression of Ku70 surpassed other well-known predictive clinicopathologic parameters as an independent prognostic factor for locoregional control. Eighteen of 22 patients who had locoregional recurrences of the tumor displayed an overexpression of Ku70. No significant association was found between the level of DNA-PKcs expression and the clinical outcome. CONCLUSIONS Our data suggest that the level of Ku70 expression can be used as a molecular marker to predict the response to RT and the locoregional control after RT and concurrent chemotherapy in patients with nondisseminated NPC.
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Affiliation(s)
- Sang-Wook Lee
- Department of Radiation Oncology, University of Ulsan, College of Medicine, Asan Medical Center, Seoul, South Korea
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21
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Hinz JM, Yamada NA, Salazar EP, Tebbs RS, Thompson LH. Influence of double-strand-break repair pathways on radiosensitivity throughout the cell cycle in CHO cells. DNA Repair (Amst) 2005; 4:782-92. [PMID: 15951249 DOI: 10.1016/j.dnarep.2005.03.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2005] [Revised: 03/17/2005] [Accepted: 03/22/2005] [Indexed: 11/17/2022]
Abstract
Unrepaired DNA double-strand breaks (DSBs) produced by ionizing radiation (IR) are a major determinant of cell killing. To determine the contribution of DNA repair pathways to the well-established cell cycle variation in IR sensitivity, we compared the radiosensitivity of wild-type CHO cells to mutant lines defective in nonhomologous end joining (NHEJ), homologous recombination repair (HRR), and the Fanconi anemia pathway. Cells were irradiated with IR doses that killed approximately 90% of each asynchronous population, separated into synchronous fractions by centrifugal elutriation, and assayed for survival (colony formation). Wild-type cells had lowest resistance in early G1 and highest resistance in S phase, followed by declining resistance as cells move into G2/M. In contrast, HR-defective cells (xrcc3 mutation) were most resistant in early G1 and became progressively less resistant in S and G2/M, indicating that the S-phase resistance in wild-type cells requires HRR. Cells defective in NHEJ (dna-pk(cs) mutation) were exquisitely sensitive in early G1, most resistant in S phase, and then somewhat less resistant in G2/M. Fancg mutant cells had almost normal IR sensitivity and normal cell cycle dependence, suggesting that Fancg contributes modestly to survival and in a manner that is independent of cell cycle position.
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Affiliation(s)
- John M Hinz
- Biosciences Directorate, L441 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, USA
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22
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Chen GG, Sin FLF, Leung BCS, Ng HK, Poon WS. Glioblastoma cells deficient in DNA-dependent protein kinase are resistant to cell death. J Cell Physiol 2005; 203:127-32. [PMID: 15493013 DOI: 10.1002/jcp.20230] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
DNA-dependent protein kinase (DNA-PK), a nuclear serine/threonine kinase, is responsible for the DNA double-strand break repair. Cells lacking or with dysfunctional DNA-PK are often associated with mis-repair, chromosome aberrations, and complex exchanges, all of which are known to contribute to the development of human cancers including glioblastoma. Two human glioblastoma cell lines were used in the experiment, M059J cells lacking the catalytic subunit of DNA-PK, and their isogenic but DNA-PK proficient counterpart, M059K. We found that M059K cells were much more sensitive to staurosporine (STS) treatment than M059J cells, as demonstrated by MTT assay, TUNEL detection, and annexin-V and propidium iodide (PI) staining. A possible mechanism responsible for the different sensitivity in these two cell lines was explored by the examination of Bcl-2, Bax, Bak, and Fas. The cell death stimulus increased anti-apoptotic Bcl-2 and decreased pro-apoptotic Bcl-2 members (Bak and Bax) and Fas in glioblastoma cells deficient in DNA-PK. Activation of DNA-PK is known to promote cell death of human tumor cells via modulation of p53, which can down-regulate the anti-apoptotic Bcl-2 member proteins, induce pro-apoptotic Bcl-2 family members and promote a Bax-Bak interaction. Our experiment also demonstrated that the mode of glioblastoma cell death induced by STS consisted of both apoptosis and necrosis and the percentage of cell death in both modes was similar in glioblastoma cell lines either lacking DNA-PK or containing intact DNA-PK. Taken together, our findings suggest that DNA-PK has a positive role in the regulation of apoptosis in human glioblastomas. The aberrant expression of Bcl-2 family members and Fas was, at least in part, responsible for decreased sensitivity of DNA-PK deficient glioblastoma cells to cell death stimuli.
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Affiliation(s)
- George G Chen
- Department of Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, N.T., Hong Kong.
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23
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Yamaguchi S, Hasegawa M, Aizawa S, Tanaka K, Yoshida K, Noda Y, Tatsumi K, Hirokawa K, Kitagawa M. DNA-dependent protein kinase enhances DNA damage-induced apoptosis in association with Friend gp70. Leuk Res 2005; 29:307-16. [PMID: 15661267 DOI: 10.1016/j.leukres.2004.07.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2004] [Accepted: 07/24/2004] [Indexed: 01/01/2023]
Abstract
Friend leukemia virus (FLV) infection strongly enhances gamma-irradiation-induced apoptosis of hematopoietic cells of C3H hosts leading to a lethal anemia. Experiments using p53 knockout mice with the C3H background have clarified that the apoptosis is p53-dependent and would not be associated with changes of cell populations caused by the infection with FLV. In bone marrow cells of FLV + total body irradiation (TBI)-treated C3H mice, the p53 protein was prominently activated to overexpress p21 and bax suggesting that apoptosis-enhancing mechanisms lay upstream of p53 protein in the signaling pathway. Neither of DNA-dependent protein kinase (DNA-PK)-deficient SCID mice nor ataxia telangiectasia mutated (ATM) gene knockout mice with the C3H background exhibited a remarkable enhancement of apoptosis or p53 activation on FLV + TBI-treatment indicating that DNA-PK and ATM were both essential. ATM appeared necessary for introducing DNA damage-induced apoptosis, while DNA-PK enhanced p53-dependent apoptosis under FLV-infection. Surprisingly, viral envelope protein, gp70, was co-precipitated with DNA-PK but not with ATM in FLV + TBI-treated C3H mice. These results indicated that FLV-infection enhances DNA damage-induced apoptosis via p53 activation and that DNA-PK, in association with gp70, might play critical roles in modulating the signaling pathway.
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Affiliation(s)
- Shuichi Yamaguchi
- Department of Comprehensive Pathology, Aging and Developmental Sciences, Tokyo Medical and Dental University, Graduate School, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
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24
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Milano M. Le récepteur à l'EGF et les cancers des voies aérodigestives supérieures. Cancer Radiother 2005; 9:51-4. [PMID: 15804620 DOI: 10.1016/j.canrad.2005.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/05/2005] [Indexed: 11/16/2022]
Abstract
EGFR is overexpressed and is associated with a poor prognosis in head and neck cancer. Among the biological and cellular effects resulting from EGFR targeting in head and neck cancer there is the capacity to restore apoptotic capacities. Other experimental results put into evidence that DNA-repair activity was reduced by the application of EGFR targeting agents. This context was in favor of a research oriented towards combination between anti-EGFR drugs and cytotoxic agents, particularly irradiation. Supra-additive cytotoxic effects have been observed at the experimental level when combining anti-EGFR drugs with irradiation in head and neck cancer. These experimental data were recently confirmed at the clinical level in locally advanced head and neck cancer.
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Affiliation(s)
- M Milano
- Service pharmacie du CHU de Nice, hôpital de Tende, 06430 Tende, France.
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25
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Dudásová Z, Dudás A, Chovanec M. Non-homologous end-joining factors of Saccharomyces cerevisiae. FEMS Microbiol Rev 2005; 28:581-601. [PMID: 15539075 DOI: 10.1016/j.femsre.2004.06.001] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2004] [Revised: 06/02/2004] [Accepted: 06/02/2004] [Indexed: 01/09/2023] Open
Abstract
DNA double-strand breaks (DSB) are considered to be a severe form of DNA damage, because if left unrepaired, they can cause a cell death and, if misrepaired, they can lead to genomic instability and, ultimately, the development of cancer in multicellular organisms. The budding yeast Saccharomyces cerevisiae repairs DSB primarily by homologous recombination (HR), despite the presence of the KU70, KU80, DNA ligase IV and XRCC4 homologues, essential factors of the mammalian non-homologous end-joining (NHEJ) machinery. S. cerevisiae, however, lacks clear DNA-PKcs and ARTEMIS homologues, two important additional components of mammalian NHEJ. On the other hand, S. cerevisiae is endowed with a regulatory NHEJ component, Nej1, which has not yet been found in other organisms. Furthermore, there is evidence in budding yeast for a requirement for the Mre11/Rad50/Xrs2 complex for NHEJ, which does not appear to be the case either in Schizosaccharomyces pombe or in mammals. Here, we comprehensively describe the functions of all the S. cerevisiae NHEJ components identified so far and present current knowledge about the NHEJ process in this organism. In addition, this review depicts S. cerevisiae as a powerful model system for investigating the utilization of either NHEJ or HR in DSB repair.
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Affiliation(s)
- Zuzana Dudásová
- Laboratory of Molecular Genetics, Cancer Research Institute, Slovak Academy of Sciences, Vlárska 7, 833 91 Bratislava 37, Slovak Republic
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26
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Bourguignon MH, Gisone PA, Perez MR, Michelin S, Dubner D, Giorgio MD, Carosella ED. Genetic and epigenetic features in radiation sensitivity. Eur J Nucl Med Mol Imaging 2005; 32:229-46. [PMID: 15657757 DOI: 10.1007/s00259-004-1730-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Recent progress especially in the field of gene identification and expression has attracted greater attention to genetic and epigenetic susceptibility to cancer, possibly enhanced by ionising radiation. It has been proposed that the occurrence and severity of the adverse reactions to radiation therapy are also influenced by such genetic susceptibility. This issue is especially important for radiation therapists since hypersensitive patients may suffer from adverse effects in normal tissues following standard radiation therapy, while normally sensitive patients could receive higher doses of radiation offering a better likelihood of cure for malignant tumours. This paper, the first of two parts, reviews the main mechanisms involved in cell response to ionising radiation. DNA repair machinery and cell signalling pathways are considered and their role in radiosensitivity is analysed. The implication of non-targeted and delayed effects in radiosensitivity is also discussed.
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Affiliation(s)
- Michel H Bourguignon
- Direction Générale de la Sûreté Nucléaire et de la Radioprotection (DGSNR), 6 Place du Colonel Bourgoin, 75572, Paris Cedex 12, France.
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27
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Zhou T, Lee JW, Tatavarthi H, Lupski JR, Valerie K, Povirk LF. Deficiency in 3'-phosphoglycolate processing in human cells with a hereditary mutation in tyrosyl-DNA phosphodiesterase (TDP1). Nucleic Acids Res 2005; 33:289-97. [PMID: 15647511 PMCID: PMC546157 DOI: 10.1093/nar/gki170] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Tyrosyl-DNA phosphodiesterase (TDP1) is a DNA repair enzyme that removes peptide fragments linked through tyrosine to the 3′ end of DNA, and can also remove 3′-phosphoglycolates (PGs) formed by free radical-mediated DNA cleavage. To assess whether TDP1 is primarily responsible for PG removal during in vitro end joining of DNA double-strand breaks (DSBs), whole-cell extracts were prepared from lymphoblastoid cells derived either from spinocerebellar ataxia with axonal neuropathy (SCAN1) patients, who have an inactivating mutation in the active site of TDP1, or from closely matched normal controls. Whereas extracts from normal cells catalyzed conversion of 3′-PG termini, both on single-strand oligomers and on 3′ overhangs of DSBs, to 3′-phosphate termini, extracts of SCAN1 cells did not process either substrate. Addition of recombinant TDP1 to SCAN1 extracts restored 3′-PG removal, allowing subsequent gap filling on the aligned DSB ends. Two of three SCAN1 lines examined were slightly more radiosensitive than normal cells, but only for fractionated radiation in plateau phase. The results suggest that the TDP1 mutation in SCAN1 abolishes the 3′-PG processing activity of the enzyme, and that there are no other enzymes in cell extracts capable of processing protruding 3′-PG termini. However, the lack of severe radiosensitivity suggests that there must be alternative, TDP1-independent pathways for repair of 3′-PG DSBs.
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Affiliation(s)
| | | | | | - James R. Lupski
- Department of Molecular and Human Genetics, Baylor College of MedicineHouston, TX 77030, USA
| | - Kristoffer Valerie
- Department of Radiation Oncology, Virginia Commonwealth UniversityRichmond, VA 23298, USA
| | - Lawrence F. Povirk
- To whom correspondence should be addressed at Virginia Commonwealth University, PO Box 980230, Richmond, VA 23298-0230, USA. Tel: +1 804 828 9640; Fax: +1 804 828 8079;
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Abstract
EGF-receptor (EGFR) is a transmembrane protein, which was implicated in the progression of many epithelial cancer types. Its activation induce some transduction pathways inside the cell, and contribute to many cellular processes as cell proliferation, inhibition of apoptosis and angiogenesis. Monoclonal antibodies directed against EGFR or small molecules inhibiting its tyrosine-kinase function could block all these pathways. By modulating these cellular functions, these molecules enhance the antitumor activity of ionizing radiation. Several mechanisms have been discussed (alteration od DNA damage repair, facilitation of apoptosis, inhibition of tumour repopulation) and justify the current clinical trials combining these drugs and radiotherapy.
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Affiliation(s)
- G Milano
- Laboratoire d'oncopharmacologie, centre Antoine-Lacassagne, 33, avenue de Valombrose, 06189 Nice 2, France.
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29
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Weterings E, van Gent DC. The mechanism of non-homologous end-joining: a synopsis of synapsis. DNA Repair (Amst) 2004; 3:1425-35. [PMID: 15380098 DOI: 10.1016/j.dnarep.2004.06.003] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2004] [Indexed: 11/18/2022]
Abstract
Repair of DNA double-strand breaks (DSBs) by non-homologous end-joining (NHEJ) is required for resistance to genotoxic agents, such as ionizing radiation, but also for proper development of the vertebrate immune system. Much progress has been made in identifying the factors that are involved in this repair pathway. We are now entering the phase in which we begin to understand basic concepts of the reaction mechanism and regulation of non-homologous end-joining. This review concentrates on novel insights into damage recognition and subsequent tethering, processing and joining of DNA ends.
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Affiliation(s)
- Eric Weterings
- Department of Cell Biology and Genetics, Erasmus Medical Center, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
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30
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Kampinga HH, Dynlacht JR, Dikomey E. Mechanism of radiosensitization by hyperthermia (> or = 43 degrees C) as derived from studies with DNA repair defective mutant cell lines. Int J Hyperthermia 2004; 20:131-9. [PMID: 15195507 DOI: 10.1080/02656730310001627713] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
All biochemical and cytogenetic data on radiosensitization by heat treatment at and above 43 degrees C indicate that inhibition of DNA repair plays a central role. There are several DNA repair pathways involved in restoration of damage after ionising irradiation and the kinetics of all of them are affected by heat shock. This, however, does not imply that the inhibition of each of these pathways is relevant to the effect of heat on cellular radiosensitivity. The current review evaluates the available data on heat radiosensitization in mutant or knockout cell lines defective in various DNA repair proteins and/or pathways. The data show that thermal inhibition of the non-homologous end-joining pathway (NHEJ) plays no role in heat radiosensitization. Furthermore, limited data suggest that the homologous recombination pathway may also not be a major heat target. By deduction, it is suggested that inhibition of base damage repair (BER) could be the crucial step in radiosensitization by heat. While a lack of mutant cell lines and redundancy of the BER pathway have hampered efforts toward a conclusive study, biochemical and correlative evidence support this hypothesis.
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Affiliation(s)
- H H Kampinga
- Department of Radiation and Stress Cell Biology, University of Groningen, A Deusinglaan 1, 9713 AV, Groningen, The Netherlands.
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Callén E, Surrallés J. Telomere dysfunction in genome instability syndromes. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2004; 567:85-104. [PMID: 15341904 DOI: 10.1016/j.mrrev.2004.06.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2004] [Revised: 06/22/2004] [Accepted: 06/22/2004] [Indexed: 12/28/2022]
Abstract
Telomeres are nucleoprotein complexes located at the end of eukaryotic chromosomes. They have essential roles in preventing terminal fusions, protecting chromosome ends from degradation, and in chromosome positioning in the nucleus. These terminal structures consist of a tandemly repeated DNA sequence (TTAGGG in vertebrates) that varies in length from 5 to 15 kb in humans. Several proteins are attached to this telomeric DNA, some of which are also involved in different DNA damage response pathways, including Ku80, Mre11, NBS and BLM, among others. Mutations in the genes encoding these proteins cause a number of rare genetic syndromes characterized by chromosome and/or genetic instability and cancer predisposition. Deletions or mutations in any of these genes may also cause a telomere defect resulting in accelerated telomere shortening, lack of end-capping function, and/or end-to-end chromosome fusions. This telomere phenotype is also known to promote chromosomal instability and carcinogenesis. Therefore, it is essential to understand the interplay between telomere biology and genome stability. This review is focused in the dual role of chromosome fragility proteins in telomere maintenance.
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Affiliation(s)
- Elsa Callén
- Group of Mutagenesis, Department of Genetics and Microbiology, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
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Kampinga HH, Van Waarde-Verhagen MAWH, Van Assen-Bolt AJ, Nieuwenhuis B, Rodemann HP, Prowse KR, Linskens MHK. Reconstitution of active telomerase in primary human foreskin fibroblasts: effects on proliferative characteristics and response to ionizing radiation. Int J Radiat Biol 2004; 80:377-88. [PMID: 15223771 DOI: 10.1080/09553000410001692735] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
PURPOSE Telomere shortening has been proposed to trigger senescence, and since most primary cells do not express active telomerase, reactivation of telomerase activity was proposed as a safe and non-transforming way of immortalizing cells. However, to study radiation responses, it is as yet unclear whether cells immortalized by telomerase reactivation behave in a similar manner as their parental primary cells. MATERIALS AND METHODS Primary human foreskin fibroblasts were transfected with the human catalytic subunit of telomerase, the reverse transcriptase (hTERT), and their growth characteristics and response to DNA damage were characterized. RESULTS The sole expression of the human hTERT was sufficient to immortalize the human foreskin fibroblasts. With time in culture, the immortalized cells almost doubled their average telomeric length and the clonal population contained almost no post-mitotic fibroblasts anymore. Up to 300 population doublings, no alterations compared with the parental primary cells were seen in terms of clonogenic radiosensitivity, DNA double-strand break repair, radiation-induced increases in p53 and p21(WAF-1,CIP-1) expression, and the G1/S and G2/M cell cycle checkpoints. Moreover, mitogen-induced mitotic arrest of fibroblasts was still possible in the hTERT-immortalized clones. CONCLUSIONS Immortalizing fibroblasts by reconstitution of active telomerase seems a good, reliable manner to generate a large source of cells with a radiation damage response similar to the primary cells.
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Affiliation(s)
- H H Kampinga
- Department of Radiation and Stress Cell Biology, DCB, Faculty of Medical Sciences, University of Groningen, Groningen 9713 AV, The Netherlands.
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Veuger SJ, Curtin NJ, Smith GCM, Durkacz BW. Effects of novel inhibitors of poly(ADP-ribose) polymerase-1 and the DNA-dependent protein kinase on enzyme activities and DNA repair. Oncogene 2004; 23:7322-9. [PMID: 15286704 DOI: 10.1038/sj.onc.1207984] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
DNA-dependent protein kinase (DNA-PK) and poly (ADP-ribose) polymerase-1 (PARP-1) participate in nonhomologous end joining and base excision repair, respectively, and are key determinants of radio- and chemo-resistance. Both PARP-1 and DNA-PK have been identified as therapeutic targets for anticancer drug development. Here we investigate the effects of specific inhibitors on enzyme activities and DNA double-strand break (DSB) repair. The enzyme activities were investigated using purified enzymes and in permeabilized cells. Inhibition, or loss of activity, was compared using potent inhibitors of DNA-PK (NU7026) and PARP-1 (AG14361), and cell lines proficient or deficient for DNA-PK or PARP-1. Inactive DNA-PK suppressed the activity of PARP-1 and vice versa. This was not the consequence of simple substrate competition, since DNA ends were provided in excess. The inhibitory effect of DNA-PK on PARP activity was confirmed in permeabilized cells. Both inhibitors prevented ionizing radiation-induced DSB repair, but only AG14361 prevented single-strand break repair. An increase in DSB levels caused by inhibition of PARP-1 was shown to be caused by a decrease in DSB repair, and not by the formation of additional DSBs. These data point to combined inhibition of PARP-1 and DNA-PK as a powerful strategy for tumor radiosensitization.
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Affiliation(s)
- Stephany J Veuger
- Northern Institute for Cancer Research, University of Newcastle, Newcastle upon Tyne, NE2 4HH, UK
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Um JH, Kim SJ, Kim DW, Ha MY, Jang JH, Kim DW, Chung BS, Kang CD, Kim SH. Tissue-specific changes of DNA repair protein Ku and mtHSP70 in aging rats and their retardation by caloric restriction. Mech Ageing Dev 2004; 124:967-75. [PMID: 14499502 DOI: 10.1016/s0047-6374(03)00169-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
To provide an improved understanding of the molecular basis of the aging process, it is necessary to measure biological age on a tissue-specific basis. The role of DNA damage has emerged as a significant mechanism for determination of life span, and DNA repair genes and stress-response genes are also implicated in the aging process. In the present study, we investigated the changes of DNA-PK activity, especially Ku activity, in the various tissues including kidney, lung, testis and liver during aging and its correlation with mtHSP70 expression. We showed that the modulation of Ku activity during the aging process was highly tissue-specific as shown with highly impaired Ku activity in testis and unaffected Ku activity in liver with age, and the level of Ku70 or Ku80 was differentially expressed in each aging tissue. We found also that age-associated alteration of Ku70/80 was prevented or not prevented by caloric restriction (CR) in a tissue-specific manner. Age-related decline in Ku70 during the aging process was associated with the increase of mtHSP70, which could play a role as a predictive marker for aging related to Ku regulation, and CR retarded aging-induced mtHSP70.
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Affiliation(s)
- Jee Hyun Um
- Department of Biochemistry, College of Medicine, Pusan National University, Pusan 602-739, South Korea
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35
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Kühne C, Tjörnhammar ML, Pongor S, Banks L, Simoncsits A. Repair of a minimal DNA double-strand break by NHEJ requires DNA-PKcs and is controlled by the ATM/ATR checkpoint. Nucleic Acids Res 2004; 31:7227-37. [PMID: 14654698 PMCID: PMC291875 DOI: 10.1093/nar/gkg937] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Mammalian cells primarily rejoin DNA double-strand breaks (DSBs) by the non-homologous end-joining (NHEJ) pathway. The joining of the broken DNA ends appears directly without template and accuracy is ensured by the NHEJ factors that are under ATM/ATR regulated checkpoint control. In the current study we report the engineering of a mono-specific DNA damaging agent. This was used to study the molecular requirements for the repair of the least complex DSB in vivo. Single-chain PvuII restriction enzymes fused to protein delivery sequences transduce cells efficiently and induce blunt end DSBs in vivo. We demonstrate that beside XRCC4/LigaseIV and KU, the DNA-PK catalytic subunit (DNA-PKcs) is also essential for the joining of this low complex DSB in vivo. The appearance of blunt end 3'-hydroxyl and 5'-phosphate DNA DSBs induces a significantly higher frequency of anaphase bridges in cells that do not contain functional DNA-PKcs, suggesting an absolute requirement for DNA-PKcs in the control of chromosomal stability during end joining. Moreover, these minimal blunt end DSBs are sufficient to induce a p53 and ATM/ATR checkpoint function.
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Affiliation(s)
- Christian Kühne
- International Center for Genetic Engineering and Biotechnology (ICGEB), Area Science Park, Padriciano 99, I-34000 Trieste, Italy.
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36
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Boldogh I, Roy G, Lee MS, Bacsi A, Hazra TK, Bhakat KK, Das GC, Mitra S. Reduced DNA double strand breaks in chlorambucil resistant cells are related to high DNA-PKcs activity and low oxidative stress. Toxicology 2003; 193:137-52. [PMID: 14599773 DOI: 10.1016/j.tox.2003.08.013] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Modulation of DNA repair represents a strategy to overcome acquired drug resistance of cells to genotoxic chemotherapeutic agents, including nitrogen mustards (NM). These agents induce DNA inter-strand cross-links, which in turn produce double strand breaks (dsbs). These breaks are primarily repaired via the nonhomologous end-joining (NHEJ) pathway. A DNA-dependent protein kinase (DNA-PK) complex plays an important role in NHEJ, and its increased level/activity is associated with acquired drug resistance of human tumors. We show in this report that the DNA-PK complex has comparable levels and kinase activity of DNA-PK catalytic subunit (DNA-PKcs) in a nearly isogenic pair of drug-sensitive (A2780) and resistant (A2780/100) cells; however, treatment with chlorambucil (Cbl), a NM-type of drug, induced differential effects in these cells. The kinase activity of DNA-PKcs was increased up to 2h after Cbl treatment in both cell types; however, it subsequently decreased only in sensitive cells, which is consistent with increased levels of DNA dsbs. The decreased kinase activity of DNA-PKcs was not due to a change in its amount or the levels of Ku70 and Ku86, their subcellular distribution, cell cycle progression or caspase-mediated degradation of DNA-PK. In addition to DNA cross-links, Cbl treatment of cells causes a 2.2-fold increase in the level of reactive oxygen species (ROS) in both cell types. However, the ROS in A2780/100 cells were reduced to the basal level after 3-4h, while sensitive cells continued to produce ROS and undergo apoptosis. Pre-treatment of A2780 cells with the glutathione (GSH) precursor, N-acetyl-L-cysteine prevented Cbl-induced increase in ROS, augmented the kinase activity of DNA-PKcs, decreased the levels of DNA dsbs and increased cell survival. Depletion in GSH from A2780/100 cells by L-buthionine sulfoximine (BSO) resulted in sustained production of ROS, lowered DNA-PKcs kinase activity, enhanced levels of DNA dsbs, and increased cell killing by Cbl. We propose that oxidative stress decreases repair of DNA dsbs via lowering kinase activity of DNA-PKcs and that induction of ROS could be the basis for adjuvant therapies for sensitizing tumor cells to nitrogen mustards and other DNA cross-linking drugs.
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Affiliation(s)
- Istvan Boldogh
- Department of Microbiology and Immunology, Sealy Center for Molecular Sciences, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA.
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37
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Dikomey E, Borgmann K, Brammer I, Kasten-Pisula U. Molecular mechanisms of individual radiosensitivity studied in normal diploid human fibroblasts. Toxicology 2003; 193:125-35. [PMID: 14599772 DOI: 10.1016/s0300-483x(03)00293-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The molecular mechanisms of individual radiosensitivity were studied in normal diploid human fibroblasts. For fibroblasts irradiated with X-rays in G1-phase the individual radiosensitivity was shown to be correlated with the extent of double-strand break (dsb) repair. The number of residual dsbs (including both non- and mis-rejoined dsbs) varied between 2 and 5% of the initial number induced and was low for resistant and high for sensitive strains. In the G1-phase dsbs are considered to be mostly repaired via the non-homologous end-joining pathway (NHEJ). However, so far none of the parameters tested for this pathway was found to be correlated with the number of residual dsbs. The parameters tested were mRNA expression, protein level and localisation and activity of the DNA-PK, which is the central complex of NHEJ. The dsb-repair capacity is also not regulated by the differentiation status, which varies substantially among fibroblast strains, whereas there is some indication that dsb repair might depend on the chromatin structure, with more efficient repair in cells with condensed DNA. Residual dsbs are converted into lethal chromosome aberrations finally leading to the loss of clonogenic activity, when cells pass through mitosis. Beside this so-called mitotic death, X-irradiated human fibroblasts are also inactivated via the TP53-dependent permanent G1-arrest, while apoptosis appears to be not important. On average, mitotic death and G1-arrest are equally effective, but there is a broad variation from one strain to the other, with a negative correlation between these two pathways. Fibroblast strains exhibiting only a moderate G1-arrest showed a high number of lethal aberrations and vice versa. This result points to a common regulator of both G1-arrest and dsb repair, which is presently under investigation.
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Affiliation(s)
- Ekkehard Dikomey
- Institute of Biophysics and Radiobiology, University-Hospital Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
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Shintani S, Mihara M, Li C, Nakahara Y, Hino S, Nakashiro KI, Hamakawa H. Up-regulation of DNA-dependent protein kinase correlates with radiation resistance in oral squamous cell carcinoma. Cancer Sci 2003; 94:894-900. [PMID: 14556663 PMCID: PMC11160163 DOI: 10.1111/j.1349-7006.2003.tb01372.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2003] [Revised: 08/18/2003] [Accepted: 08/25/2003] [Indexed: 11/30/2022] Open
Abstract
DNA-PK is a nuclear protein with serine/threonine kinase activity and forms a complex consisting of the DNA-PKcs and a heterodimer of Ku70 and Ku80 proteins. Recent laboratory experiments have demonstrated that the DNA-PK complex formation is one of the major pathways by which mammalian cells respond to DNA double-strand breaks induced by ionizing radiation. In this study, we evaluated the relationship between expression levels of DNA-PKcs, Ku70 and Ku80 proteins and radiation sensitivity in oral squamous cell carcinoma (OSCC) cell lines and in OSCC patients treated with preoperative radiation therapy. The OSCC cell lines greatly differed in their response to irradiation, as assessed by a standard colony formation assay. However, the expression levels of the DNA-PK complex proteins were all similar, and there was no association between the magnitude of their expression and the tumor radiation sensitivity. Expression of DNA-PK complex proteins increased after radiation treatment, and the increased values correlated with the tumor radiation resistance. Expression of DNA-PKcs and Ku70 after irradiation was increased in the surviving cells of OSCC tissues irradiated preoperatively. These results suggest that up-regulation of DNA-PK complex protein, especially DNA-PKcs, after radiation treatment correlates to radiation resistance. DNA-PKcs might be a molecular target for a novel radiation sensitization therapy of OSCC.
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Affiliation(s)
- Satoru Shintani
- Department of Oral and Maxillofacial Surgery, Ehime University School of Medicine, Shigenobu-cho, Onsen-gun, Ehime, 791-0295, Japan.
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39
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Abstract
Damage induced in the DNA after exposure of cells to ionizing radiation activates checkpoint pathways that inhibit progression of cells through the G1 and G2 phases and induce a transient delay in the progression through S phase. Checkpoints together with repair and apoptosis are integrated in a circuitry that determines the ultimate response of a cell to DNA damage. Checkpoint activation typically requires sensors and mediators of DNA damage, signal transducers and effectors. Here, we review the current state of knowledge regarding mechanisms of checkpoint activation and proteins involved in the different steps of the process. Emphasis is placed on the role of ATM and ATR, as well on CHK1 and CHK2 kinases in checkpoint response. The roles of downstream effectors, such as P53 and the CDC25 family of proteins, are also described, and connections between repair and checkpoint activation are attempted. The role of checkpoints in genomic stability and the potential of improving the treatment of cancer by DNA damage inducing agents through checkpoint abrogation are also briefly outlined.
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Affiliation(s)
- George Iliakis
- Institute of Medical Radiation Biology, University of Essen Medical School, Hufelanstrasse 55, 45122 Essen, Germany.
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40
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Jeffries AR, Mungall AJ, Dawson E, Halls K, Langford CF, Murray RM, Dunham I, Powell JF. beta-1,3-Glucuronyltransferase-1 gene implicated as a candidate for a schizophrenia-like psychosis through molecular analysis of a balanced translocation. Mol Psychiatry 2003; 8:654-63. [PMID: 12874601 DOI: 10.1038/sj.mp.4001382] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have mapped and sequenced both chromosome breakpoints of a balanced t(6;11)(q14.2;q25) chromosome translocation that segregates with a schizophrenia-like psychosis. Bioinformatics analysis of the regions revealed a number of confirmed and predicted transcripts. No confirmed transcripts are disrupted by either breakpoint. The chromosome 6 breakpoint region is gene poor, the closest transcript being the serotonin receptor 1E (HTR1E) at 625 kb telomeric to the breakpoint. The chromosome 11 breakpoint is situated close to the telomere. The closest gene, beta-1,3-glucuronyltransferase (B3GAT1 or GlcAT-P), is 299 kb centromeric to the breakpoint. B3GAT1 is the key enzyme during the biosynthesis of the carbohydrate epitope HNK-1, which is present on a number of cell adhesion molecules important in neurodevelopment. Mice deleted for the B3GAT1 gene show defects in hippocampal long-term potentiation and in spatial memory formation. We propose that the translocation causes a positional effect on B3GAT1, affecting expression levels and making it a plausible candidate for the psychosis found in this family. More generally, regions close to telomeres are highly polymorphic in both sequence and length in the general population and several studies have implicated subtelomeric deletions as a common cause of idiopathic mental retardation. This leads us to the hypothesis that polymorphic or other variation of the 11q telomere may affect the activity of B3GAT1 and be a risk factor for schizophrenia and related psychoses in the general population.
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MESH Headings
- Base Sequence
- Chromosome Breakage
- Chromosome Mapping/methods
- Chromosomes, Human, Pair 11/genetics
- Chromosomes, Human, Pair 11/ultrastructure
- Chromosomes, Human, Pair 6/genetics
- Chromosomes, Human, Pair 6/ultrastructure
- Depression/genetics
- Expressed Sequence Tags
- Female
- Glucuronosyltransferase/genetics
- Glucuronosyltransferase/physiology
- Humans
- Male
- Molecular Sequence Data
- Pedigree
- Psychotic Disorders/epidemiology
- Psychotic Disorders/genetics
- Risk Factors
- Sequence Deletion
- Suicide
- Suicide, Attempted
- Telomere/ultrastructure
- Translocation, Genetic
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Affiliation(s)
- A R Jeffries
- Department of Neuroscience, Institute of Psychiatry, King's College London, Denmark Hill, London, UK.
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41
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Hashimoto M, Rao S, Tokuno O, Yamamoto KI, Takata M, Takeda S, Utsumi H. DNA-PK: the major target for wortmannin-mediated radiosensitization by the inhibition of DSB repair via NHEJ pathway. JOURNAL OF RADIATION RESEARCH 2003; 44:151-159. [PMID: 13678345 DOI: 10.1269/jrr.44.151] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The effect of wortmannin posttreatment was studied in cells derived from different species (hamster, mouse, chicken, and human) with normal and defective DNA-dependent protein kinase (DNA-PK) activity, cells with and without the ataxia telangiectasia (ATM) gene, and cells lacking other regulatory proteins involved in the DNA double-strand break (DSB) repair pathways. Clonogenic assays were used to obtain all results. Wortmannin radiosensitization was observed in Chinese hamster cells (V79-B310H , CHO-K1), mouse mammary carcinoma cells (SR-1), transformed human fibroblast (N2KYSV), chicken B lymphocyte wild-type cells (DT40), and chicken Rad54 knockout cells (Rad54-/-). However, mouse mammary carcinoma cells (SX9) with defects in the DNA-PK and chicken DNA-PK catalytic subunit (DNA-PKcs) knockout cells (DNA-PKcs-/-/-) failed to exhibit wortmannin radiosensitization. On the other hand, SCID mouse cells (SC3VA2) exposed to wortmannin exhibited significant increases in radiosensitivity, possibly because of some residual function of DNA-PKcs. Moreover, the transformed human cells derived from AT patients (AT2KYSV) and chicken ATM knockout cells (ATM-/-) showed pronounced wortmannin radiosensitization. These studies demonstrate confirm that the mechanism underlying wortmannin radiosensitization is the inhibition of DNA-PK, but not of ATM, thereby resulting in the inhibition of DSB repair via nonhomologous endjoining (NHEJ).
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Affiliation(s)
- Mitsumasa Hashimoto
- Research Reactor Institute, Kyoto University, Kumatori, Sennan-gun, Osaka 590-0494, Japan
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42
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Um JH, Kang CD, Hwang BW, Ha MY, Hur JG, Kim DW, Chung BS, Kim SH. Involvement of DNA-dependent protein kinase in regulation of the mitochondrial heat shock proteins. Leuk Res 2003; 27:509-16. [PMID: 12648511 DOI: 10.1016/s0145-2126(02)00264-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Since DNA-dependent protein kinase (DNA-PK) has been known to play a protective role against drug-induced apoptosis, the role of DNA-PK in the regulation of mitochondrial heat shock proteins by anticancer drugs was examined. The levels of basal and drug-induced mitochondrial heat shock proteins of drug-sensitive parental cells were higher than those of multidrug-resistant (MDR) cells. We also demonstrated that the development of MDR might be correlated with the increased expression of Ku-subunit of DNA-PK and concurrent down-regulation of mitochondrial heat shock proteins. The basal mtHsp70 and Hsp60 levels of Ku70(-/-) cells, which were known to be sensitive to anticancer drugs, were higher than those of parental MEF cells, but conversely these mitochondrial heat shock proteins of R7080-6 cells over-expressing both Ku70 and Ku80 were lower than those of parental Rat-1 cells. Also, the mtHsp70 and Hsp60 levels of DNA-PKcs-deficient SCID cells were higher than those of parental CB-17 cells. Our results suggest the possibility that mitochondrial heat shock protein may be one of determinants of drug sensitivity and could be regulated by DNA-PK activity.
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Affiliation(s)
- Jee Hyun Um
- Department of Biochemistry, College of Medicine, Pusan National University, Pusan 602-739, South Korea
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43
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Do E, Taira E, Irie Y, Gan Y, Tanaka H, Kuo CH, Miki N. Molecular cloning and characterization of rKAB1, which interacts with KARP-1, localizes in the nucleus and protects cells against oxidative death. Mol Cell Biochem 2003; 248:77-83. [PMID: 12870657 DOI: 10.1023/a:1024157515342] [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: 11/12/2022]
Abstract
The Ku autoantigen/KARP-1 (Ku86 autoantigen related protein-1) plays an important role in the double-strand break repair of mammalian DNA as a DNA-binding component of DNA-dependent protein kinase (DNA-PK) complex. KARP-1 is differently transcribed from the human Ku86 autoantigen gene locus and it is implicated in the control of DNA-dependent protein kinase activity. We cloned rKAB1, a rat homolog of KAB1 (KARP-1 binding protein 1 of human) from a rat hippocampal cDNA library. rKAB1 mRNA was specifically expressed in the brain and the thymus. EGFP-tagged rKAB1 protein localized in cell nucleus and in the condensed chromosome during the mitotic cell division. We found that rKAB1 works as a protective protein against cell damage by oxidative stress.
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Affiliation(s)
- Eunju Do
- Department of Pharmacology, Osaka University Medical School, Suita, Osaka, Japan
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44
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Ko L, Chin WW. Nuclear receptor coactivator thyroid hormone receptor-binding protein (TRBP) interacts with and stimulates its associated DNA-dependent protein kinase. J Biol Chem 2003; 278:11471-9. [PMID: 12519782 DOI: 10.1074/jbc.m209723200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nuclear receptors mediate gene activation through ligand-dependent interaction with coactivators. We previously cloned and characterized thyroid hormone receptor-binding protein, TRBP (NcoA6: AIB3/ASC-2/RAP250/PRIP/TRBP/NRC), as an LXXLL-containing coactivator that associates with coactivator complexes through its C terminus. To search for protein factors involved in TRBP action, we identified a distinct set of proteins from HeLa nuclear extract that interacts with the C terminus of TRBP. Analysis by mass spectrometric protein sequencing revealed a DNA-dependent protein kinase (DNA-PK) complex including its catalytic subunit and regulatory subunits, Ku70 and Ku86. DNA-PK is a heterotrimeric nuclear phosphatidylinositol 3-kinase that functions in DNA repair, recombination, and transcriptional regulation. DNA-PK phosphorylates TRBP at its C-terminal region, which directly interacts with Ku70 but not Ku86 in vitro. In addition, in the absence of DNA, TRBP itself activates DNA-PK, and the TRBP-stimulated DNA-PK activity has an altered phosphorylation pattern from DNA-stimulated activity. An anti-TRBP antibody inhibits TRBP-induced kinase activity, suggesting that protein content of TRBP is responsible for the stimulation of DNA-independent kinase activity. Furthermore, in DNA-PK-deficient scid cells, TRBP-mediated transactivation is significantly impaired, and nuclear localization of TRBP is altered. The activation of DNA-PK in the absence of DNA ends by the coactivator TRBP suggests a novel mechanism of coactivator-stimulated DNA-PK phosphorylation in transcriptional regulation.
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Affiliation(s)
- Lan Ko
- Department of Gene Regulation, Bone and Inflammation Research, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA.
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45
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Yang J, Yu Y, Duerksen-Hughes PJ. Protein kinases and their involvement in the cellular responses to genotoxic stress. Mutat Res 2003; 543:31-58. [PMID: 12510016 DOI: 10.1016/s1383-5742(02)00069-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cells are constantly subjected to genotoxic stress, and much has been learned regarding their response to this type of stress during the past year. In general, the cellular genotoxic response can be thought to occur in three stages: (1) damage sensing; (2) activation of signal transduction pathways; (3) biological consequences and attenuation of the response. The biological consequences, in particular, include cell cycle arrest and cell death. Although our understanding of the molecular mechanisms underlying cellular genotoxic stress responses remains incomplete, many cellular components have been identified over the years, including a group of protein kinases that appears to play a major role. Various DNA-damaging agents can activate these protein kinases, triggering a protein phosphorylation cascade that leads to the activation of transcription factors, and altering gene expression. In this review, the involvement of protein kinases, particularly the mitogen-activated protein kinases (MAPKs), at different stages of the genotoxic response is discussed.
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Affiliation(s)
- Jun Yang
- Department of Pathophysiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310031, China
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Belli M, Sapora O, Tabocchini MA. Molecular targets in cellular response to ionizing radiation and implications in space radiation protection. JOURNAL OF RADIATION RESEARCH 2002; 43 Suppl:S13-S19. [PMID: 12793724 DOI: 10.1269/jrr.43.s13] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
DNA repair systems and cell cycle checkpoints closely co-operate in the attempt of maintaining the genomic integrity of cells damaged by ionizing radiation. DNA double-strand breaks (DSB) are considered as the most biologically important radiation-induced damage. Their spatial distribution and association with other types of damage depend on radiation quality. It is believed these features affect damage reparability, thus explaining the higher efficiency for cellular effects of densely ionizing radiation with respect to gamma-rays. DSB repair systems identified in mammalian cells are homologous recombination (HR), single-strand annealing (SSA) and non-homologous end-joining (NHEJ). Some enzymes may participate in more than one of these repair systems. DNA damage also triggers biochemical signals activating checkpoints responsible for delay in cell cycle progression that allows more time for repair. Those at G1/S and S phases prevent replication of damaged DNA and those at G2/M phase prevent segregation of changed chromosomes. Individuals with lack or alterations of genes involved in DNA DSB repair and cell cycle checkpoints exhibit syndromes characterized by genome instability and predisposition to cancer. Information reviewed in this paper on the basic mechanisms of cellular response to ionizing radiation indicates their importance for a number of issues relevant to protection of astronauts from space radiation.
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Affiliation(s)
- Mauro Belli
- Physics Laboratory, Istituto Superiore di Sanità, 00161 Rome, Italy.
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Koike M. Dimerization, translocation and localization of Ku70 and Ku80 proteins. JOURNAL OF RADIATION RESEARCH 2002; 43:223-236. [PMID: 12518983 DOI: 10.1269/jrr.43.223] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The Ku protein is a complex of two subunits, Ku70 and Ku80, and was originally identified as an autoantigen recognized by the sera of patients with autoimmune diseases. The Ku protein plays a key role in multiple nuclear processes, e.g., DNA repair, chromosome maintenance, transcription regulation, and V(D)J recombination. The mechanism underlying the regulation of all the diverse functions of Ku is still unclear, although it seems that Ku is a multifunctional protein that works in nuclei. On the other hand, several studies have reported cytoplasmic or cell surface localization of Ku in various cell types. To clarify the fundamental characteristics of Ku, we have examined the expression, heterodimerization, subcellular localization, chromosome location, and molecular mechanisms of the nuclear transport of Ku70 and Ku80. The mechanism that regulates for nuclear localization of Ku70 and Ku80 appears to play, at least in part, a key role in regulating the physiological function of Ku in vivo.
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Affiliation(s)
- Manabu Koike
- Radiation Hazards Research Group, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
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Choi EK, Lee YH, Choi YS, Kwon HM, Choi MS, Ro JY, Park SK, Yu E. Heterogeneous expression of Ku70 in human tissues is associated with morphological and functional alterations of the nucleus. J Pathol 2002; 198:121-30. [PMID: 12210072 DOI: 10.1002/path.1164] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Ku70 is a subunit of DNA-protein kinase complex and involved in diverse intranuclear events including the repair of double-stranded DNA breaks. Ku70 is rich in the interphase nucleus of cultured cells. In human tissues, however, the distribution of Ku70 has not yet been systematically examined. To characterize the difference of Ku70 distribution between cells of human tissues and cultured cells, the expression of Ku70 was examined in various normal and neoplastic human tissues by immunohistochemistry and immunoblot. In addition, the role of Ku70 in the cellular response against ionizing radiation (IR) was analysed in fibroblasts after exposure to 5 Gy IR and apoptotic indices were examined in Ku70-overexpressed fibroblasts from an ataxia telangiectasia patient and in normal fibroblasts, before and after irradiation. In contrast to cultured cells, Ku70 was not detected in some interphase cells of human tissues and was distributed heterogeneously, even in the same nucleus. Ku70 expression was strikingly low in terminally differentiated cells such as neutrophils, eosinophils, glomerular capillary endothelial cells and fibroblasts, and was absent in spermatids. In spermatocytes, Ku70 was tightly integrated with chromosome filaments, unlike other somatic cells under mitosis. After exposure to IR, Ku70 expression was not increased in ataxia telangiectasia fibroblasts, but was significantly increased in normal fibroblasts. Most of the increased Ku70 was of soluble nuclear protein fraction. Furthermore, overexpression of Ku70 increased radiation resistance both in ataxia telangiectasia fibroblasts and normal fibroblasts. The presented data indicate that the distribution of Ku70 in cells of human tissues is closely associated with the cell cycle, cellular differentiation, nuclear shape and the process of repair of DNA damage caused by IR.
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Affiliation(s)
- Eun Kyung Choi
- Department of Radiation Oncology, University of Ulsan College of Medicine Asan Medical Centre, Seoul, Korea
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West CE, Waterworth WM, Story GW, Sunderland PA, Jiang Q, Bray CM. Disruption of the Arabidopsis AtKu80 gene demonstrates an essential role for AtKu80 protein in efficient repair of DNA double-strand breaks in vivo. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 31:517-528. [PMID: 12182708 DOI: 10.1046/j.1365-313x.2002.01370.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Double-strand breaks (DSBs) in DNA may occur spontaneously in the cell or be induced experimentally by gamma-irradiation, and represent one of the most serious threats to genomic integrity. Non-homologous end joining (NHEJ) rather than homologous recombination appears to be the major pathway for DSB repair in humans and plants, and it may also be the major route whereby T-DNA integrates into the plant genome during cell transformation. In yeast and mammals, the exposed ends of damaged DNA are bound with high affinity by a dimer of Ku70 and Ku80 proteins, which protects the ends from exonucleases and juxtaposes the two ends of the DSB, independent of sequence homology. Here we report the functional characterization of Ku70 and Ku80 from Arabidopsis thaliana, and demonstrate that AtKu80 and AtKu70 form a heterodimer with DNA binding activity that is specific for DNA ends. An atku80 knockout mutant shows hypersensitivity to the DNA-damaging agents menadione and bleomycin, consistent with a role for AtKu80 in the repair of DSBs in vivo in Arabidopsis.
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Affiliation(s)
- Christopher E West
- School of Biological Sciences, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
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Shiloh Y. ATM: from phenotype to functional genomics--and back. ERNST SCHERING RESEARCH FOUNDATION WORKSHOP 2002:51-70. [PMID: 11859564 DOI: 10.1007/978-3-662-04667-8_4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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