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Washif M, Kawasumi R, Hirota K. REV3 promotes cellular tolerance to 5-fluorodeoxyuridine by activating translesion DNA synthesis and intra-S checkpoint. PLoS Genet 2024; 20:e1011341. [PMID: 38954736 PMCID: PMC11249241 DOI: 10.1371/journal.pgen.1011341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2024] [Revised: 07/15/2024] [Accepted: 06/13/2024] [Indexed: 07/04/2024] Open
Abstract
The drug floxuridine (5-fluorodeoxyuridine, FUdR) is an active metabolite of 5-Fluorouracil (5-FU). It converts to 5-fluorodeoxyuridine monophosphate (FdUMP) and 5-fluorodeoxyuridine triphosphate (FdUTP), which on incorporation into the genome inhibits DNA replication. Additionally, it inhibits thymidylate synthase, causing dTMP shortage while increasing dUMP availability, which induces uracil incorporation into the genome. However, the mechanisms underlying cellular tolerance to FUdR are yet to be fully elucidated. In this study, we explored the mechanisms underlying cellular resistance to FUdR by screening for FUdR hypersensitive mutants from a collection of DT40 mutants deficient in each genomic maintenance system. We identified REV3, which is involved in translesion DNA synthesis (TLS), to be a critical factor in FUdR tolerance. Replication using a FUdR-damaged template was attenuated in REV3-/- cells, indicating that the TLS function of REV3 is required to maintain replication on the FUdR-damaged template. Notably, FUdR-exposed REV3-/- cells exhibited defective cell cycle arrest in the early S phase, suggesting that REV3 is involved in intra-S checkpoint activation. Furthermore, REV3-/- cells showed defects in Chk1 phosphorylation, which is required for checkpoint activation, but the survival of FUdR-exposed REV3-/- cells was further reduced by the inhibition of Chk1 or ATR. These data indicate that REV3 mediates DNA checkpoint activation at least through Chk1 phosphorylation, but this signal acts in parallel with ATR-Chk1 DNA damage checkpoint pathway. Collectively, we reveal a previously unappreciated role of REV3 in FUdR tolerance.
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Affiliation(s)
- Mubasshir Washif
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Tokyo, Japan
| | - Ryotaro Kawasumi
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Tokyo, Japan
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Tokyo, Japan
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2
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Hosen MB, Kawasumi R, Hirota K. Dominant roles of BRCA1 in cellular tolerance to a chain-terminating nucleoside analog, alovudine. DNA Repair (Amst) 2024; 137:103668. [PMID: 38460389 DOI: 10.1016/j.dnarep.2024.103668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2023] [Revised: 02/28/2024] [Accepted: 03/01/2024] [Indexed: 03/11/2024]
Abstract
Alovudine is a chain-terminating nucleoside analog (CTNA) that is frequently used as an antiviral and anticancer agent. Generally, CTNAs inhibit DNA replication after their incorporation into nascent DNA during DNA synthesis by suppressing subsequent polymerization, which restricts the proliferation of viruses and cancer cells. Alovudine is a thymidine analog used as an antiviral drug. However, the mechanisms underlying the removal of alovudine and DNA damage tolerance pathways involved in cellular resistance to alovudine remain unclear. Here, we explored the DNA damage tolerance pathways responsible for cellular tolerance to alovudine and found that BRCA1-deficient cells exhibited the highest sensitivity to alovudine. Moreover, alovudine interfered with DNA replication in two distinct mechanisms: first: alovudine incorporated at the end of nascent DNA interfered with subsequent DNA synthesis; second: DNA replication stalled on the alovudine-incorporated template strand. Additionally, BRCA1 facilitated the removal of the incorporated alovudine from nascent DNA, and BRCA1-mediated homologous recombination (HR) contributed to the progressive replication on the alovudine-incorporated template. Thus, we have elucidated the previously unappreciated mechanism of alovudine-mediated inhibition of DNA replication and the role of BRCA1 in cellular tolerance to alovudine.
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Affiliation(s)
- Md Bayejid Hosen
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan
| | - Ryotaro Kawasumi
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan.
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3
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Tsuda M, Shimizu N, Tomikawa H, Morozumi R, Ide H. Repair pathways for radiation DNA damage under normoxic and hypoxic conditions: Assessment with a panel of repair-deficient human TK6 cells. JOURNAL OF RADIATION RESEARCH 2021:rrab084. [PMID: 34562004 DOI: 10.1093/jrr/rrab084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Revised: 08/16/2021] [Accepted: 08/21/2021] [Indexed: 06/13/2023]
Abstract
Various types of DNA lesions are produced when cells are exposed to ionizing radiation (IR). The type and yield of IR-induced DNA damage is influenced by the oxygen concentration. Thus, different DNA repair mechanisms may be involved in the response of normoxic and hypoxic cells to irradiation with IR. However, differences between the repair mechanisms of IR-induced DNA damage under normoxic versus hypoxic conditions have not been clarified. Elucidating the relative contribution of individual repair factors to cell survival would give insight into the repair mechanisms operating in irradiated normoxic and hypoxic cells. In the present study, we used a panel of repair-deficient human TK6 cell lines that covered seven repair pathways. Cells were irradiated with X-rays under normoxic and hypoxic conditions, and the sensitivities of each mutant relative to the wild-type (i.e. relative sensitivity) were determined for normoxic and hypoxic conditions. The sensitivity of cells varied depending on the type of repair defects. However, for each repair mutant, the relative sensitivity under normoxic conditions was comparable to that under hypoxic conditions. This result indicates that the relative contribution of individual repair pathways to cell survival is comparable in normoxic and hypoxic cells, although the spectrum of IR-induced DNA damage in hypoxic cells differs from that of normoxic cells.
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Affiliation(s)
- Masataka Tsuda
- Program of Mathematical and Life Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
| | - Naoto Shimizu
- Program of Mathematical and Life Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
| | - Hinako Tomikawa
- Program of Mathematical and Life Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
| | - Ryosuke Morozumi
- Program of Mathematical and Life Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
| | - Hiroshi Ide
- Program of Mathematical and Life Sciences, Graduate School of Integrated Sciences for Life, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan
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4
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Chen Y, Cui J, Gong Y, Wei S, Wei Y, Yi L. MicroRNA: a novel implication for damage and protection against ionizing radiation. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2021; 28:15584-15596. [PMID: 33533004 PMCID: PMC7854028 DOI: 10.1007/s11356-021-12509-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 01/12/2021] [Indexed: 04/16/2023]
Abstract
Ionizing radiation (IR) is a form of high energy. It poses a serious threat to organisms, but radiotherapy is a key therapeutic strategy for various cancers. It is significant to reduce radiation injury but maximize the effect of radiotherapy. MicroRNAs (miRNAs) are posttranscriptionally regulatory factors involved in cellular radioresponse. In this review, we show how miRNAs regulate important genes on cellular response to IR-induced damage and how miRNAs participate in IR-induced carcinogenesis. Additionally, we summarize the experimental and clinical evidence for miRNA involvement in radiotherapy and discuss their potential for improvement of radiotherapy. Finally, we highlight the role that miRNAs play in accident exposure to IR or radiotherapy as predictive biomarker. miRNA therapeutics have shown great perspective in radiobiology; miRNA may become a novel strategy for damage and protection against IR.
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Affiliation(s)
- Yonglin Chen
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China
| | - Jian Cui
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China
| | - Yaqi Gong
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China
| | - Shuang Wei
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China
| | - Yuanyun Wei
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China
| | - Lan Yi
- Hengyang Medical College, Institute of Cytology and Genetics, The Hengyang Key Laboratory of Cellular Stress Biology, University of South China, Hengyang, 421001, Hunan Province, People's Republic of China.
- Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, Hengyang, 421001, Hunan Province, People's Republic of China.
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5
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Kaplan AR, Glazer PM. Impact of hypoxia on DNA repair and genome integrity. Mutagenesis 2021; 35:61-68. [PMID: 31282537 DOI: 10.1093/mutage/gez019] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 06/24/2019] [Indexed: 12/12/2022] Open
Abstract
Hypoxia is a hallmark of the tumour microenvironment with profound effects on tumour biology, influencing cancer progression, the development of metastasis and patient outcome. Hypoxia also contributes to genomic instability and mutation frequency by inhibiting DNA repair pathways. This review summarises the diverse mechanisms by which hypoxia affects DNA repair, including suppression of homology-directed repair, mismatch repair and base excision repair. We also discuss the effects of hypoxia mimetics and agents that induce hypoxia on DNA repair, and we highlight areas of potential clinical relevance as well as future directions.
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Affiliation(s)
- Alanna R Kaplan
- Department of Therapeutic Radiology, New Haven, CT, USA.,Department of Experimental Pathology, New Haven, CT, USA
| | - Peter M Glazer
- Department of Therapeutic Radiology, New Haven, CT, USA.,Department of Genetics, Yale University, New Haven, CT, USA
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Nakazato A, Kajita K, Ooka M, Akagawa R, Abe T, Takeda S, Branzei D, Hirota K. SPARTAN promotes genetic diversification of the immunoglobulin-variable gene locus in avian DT40 cells. DNA Repair (Amst) 2018; 68:50-57. [PMID: 29935364 DOI: 10.1016/j.dnarep.2018.06.003] [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] [Received: 03/09/2018] [Revised: 06/12/2018] [Accepted: 06/13/2018] [Indexed: 11/17/2022]
Abstract
Prolonged replication arrest on damaged templates is a cause of fork collapse, potentially resulting in genome instability. Arrested replication is rescued by translesion DNA synthesis (TLS) and homologous recombination (HR)-mediated template switching. SPARTAN, a ubiquitin-PCNA-interacting regulator, regulates TLS via mechanisms incompletely understood. Here we show that SPARTAN promotes diversification of the chicken DT40 immunoglobulin-variable λ gene by facilitating TLS-mediated hypermutation and template switch-mediated gene-conversion, both induced by replication blocks at abasic sites. SPARTAN-/- and SPARTAN-/-/Polη-/-/Polζ-/- cells showed defective and similar decrease in hypermutation rates, as well as alterations in the mutation spectra, with decreased dG-to-dC transversions and increased dG-to-dA transitions. Strikingly, SPARTAN-/- cells also showed reduced template switch-mediated gene-conversion at the immunoglobulin locus, while being proficient in HR-mediated double strand break repair, and sister chromatid recombination. Notably, SPARTAN's ubiquitin-binding zinc-finger 4 domain, but not the PCNA interacting peptide domain or its DNA-binding domain, was specifically required for the promotion of immunoglobulin gene-conversion, while all these three domains were shown to contribute similarly to TLS. In all, our results suggest that SPARTAN mediates TLS in concert with the Polη-Polζ pathway and that it facilitates HR-mediated template switching at a subset of stalled replication forks, potentially by interacting with unknown ubiquitinated proteins.
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Affiliation(s)
- Arisa Nakazato
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Kinumi Kajita
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Masato Ooka
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Remi Akagawa
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Takuya Abe
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan; IFOM, The FIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milan, Italy
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Dana Branzei
- IFOM, The FIRC Institute of Molecular Oncology, Via Adamello 16, 20139 Milan, Italy; Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Via Abbiategrasso 207, 27100, Pavia, Italy.
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan.
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7
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Ooka M, Kobayashi K, Abe T, Akiyama K, Hada M, Takeda S, Hirota K. Determination of genotoxic potential by comparison of structurally related azo dyes using DNA repair-deficient DT40 mutant panels. CHEMOSPHERE 2016; 164:106-112. [PMID: 27580264 DOI: 10.1016/j.chemosphere.2016.08.092] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 07/15/2016] [Accepted: 08/20/2016] [Indexed: 06/06/2023]
Abstract
Azo dyes, including Sudan I, Orange II and Orange G, are industrial dyes that are assumed to have genotoxic potential. However, neither the type of DNA damage induced nor the structural features responsible for toxicity have been determined. We used a panel of DNA-repair-pathway-deficient mutants generated from chicken DT40 cells to evaluate the ability of these azo dyes to induce DNA damage and to identify the type of DNA damage induced. We compared the structurally related azo dyes Sudan I, Orange II and Orange G to identify the structural features responsible for genotoxicity. Compared with wild type cells, the double-strand break repair defective RAD54-/-/KU70-/- cells were significantly more sensitive to Sudan I, but not to Orange II or Orange G. The quantum-chemical calculations revealed that Sudan I, but not Orange II or Orange G, has a complete planar aromatic ring structure. These suggest that the planar feature of Sudan I is critical to the inducing of double-strand breaks. In summary, we used a DNA-repair mutant panel in combination with quantum-chemical calculations to provide a clue to the chemical structure responsible for genotoxicity.
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Affiliation(s)
- Masato Ooka
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Koji Kobayashi
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Takuya Abe
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Kazuhiko Akiyama
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Masahiko Hada
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan.
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8
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Kobayashi K, Guilliam TA, Tsuda M, Yamamoto J, Bailey LJ, Iwai S, Takeda S, Doherty AJ, Hirota K. Repriming by PrimPol is critical for DNA replication restart downstream of lesions and chain-terminating nucleosides. Cell Cycle 2016; 15:1997-2008. [PMID: 27230014 PMCID: PMC4968974 DOI: 10.1080/15384101.2016.1191711] [Citation(s) in RCA: 75] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 05/12/2016] [Accepted: 05/14/2016] [Indexed: 01/28/2023] Open
Abstract
PrimPol is a DNA damage tolerance enzyme possessing both translesion synthesis (TLS) and primase activities. To uncover its potential role in TLS-mediated IgVλ hypermutation and define its interplay with other TLS polymerases, PrimPol(-/-) and PrimPol(-/-)/Polη(-/-)/Polζ (-/-) gene knockouts were generated in avian cells. Loss of PrimPol had no significant impact on the rate of hypermutation or the mutation spectrum of IgVλ. However, PrimPol(-/-) cells were sensitive to methylmethane sulfonate, suggesting that it may bypass abasic sites at the IgVλ segment by repriming DNA synthesis downstream of these sites. PrimPol(-/-) cells were also sensitive to cisplatin and hydroxyurea, indicating that it assists in maintaining / restarting replication at a variety of lesions. To accurately measure the relative contribution of the TLS and primase activities, we examined DNA damage sensitivity in PrimPol(-/-) cells complemented with polymerase or primase-deficient PrimPol. Polymerase-defective, but not primase-deficient, PrimPol suppresses the hypersensitivity of PrimPol(-/-) cells. This indicates that its primase, rather than TLS activity, is pivotal for DNA damage tolerance. Loss of TLS polymerases, Polη and Polζ has an additive effect on the sensitivity of PrimPol(-/-) cells. Moreover, we found that PrimPol and Polη-Polζ redundantly prevented cell death and facilitated unperturbed cell cycle progression. PrimPol(-/-) cells also exhibited increased sensitivity to a wide variety of chain-terminating nucleoside analogs (CTNAs). PrimPol could perform close-coupled repriming downstream of CTNAs and oxidative damage in vitro. Together, these results indicate that PrimPol's repriming activity plays a central role in reinitiating replication downstream from CTNAs and other specific DNA lesions.
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Affiliation(s)
- Kaori Kobayashi
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan
| | - Thomas A. Guilliam
- Genome Damage and Stability Center, School of Life Sciences, University of Sussex, Brighton, UK
| | - Masataka Tsuda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, Japan
| | - Junpei Yamamoto
- Division of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Laura J. Bailey
- Genome Damage and Stability Center, School of Life Sciences, University of Sussex, Brighton, UK
| | - Shigenori Iwai
- Division of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto, Japan
| | - Aidan J. Doherty
- Genome Damage and Stability Center, School of Life Sciences, University of Sussex, Brighton, UK
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji-shi, Tokyo, Japan
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Ooka M, Takazawa H, Takeda S, Hirota K. Cytotoxic and genotoxic profiles of benzo[a]pyrene and N-nitrosodimethylamine demonstrated using DNA repair deficient DT40 cells with metabolic activation. CHEMOSPHERE 2016; 144:1901-1907. [PMID: 26547024 DOI: 10.1016/j.chemosphere.2015.10.085] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 10/19/2015] [Accepted: 10/21/2015] [Indexed: 06/05/2023]
Abstract
Benzo[a]pyrene and N-nitrosodimethylamine are major genotoxic compounds present in cigarette smoke, food and oil. To examine the type(s) of DNA damage induced by these compounds, we used a panel of DNA-repair-pathway-deficient mutants generated from chicken DT40 cells and achieved metabolic activation of the test compounds by including rat liver S9 mix. Consistent with expections, benzo[a]pyrene and N-nitrosodimethylamine require metabolicactivation to become genotoxic. The REV3(-/-) mutant cell line exhibited the highest sensitivity, in terms of increased cytotoxicity, to the both compounds after metabolic activation consistent with the known ability of these two compounds to induce DNA adducts. Strikingly, we found that the RAD54(-/-)/KU70(-/-) cell line, a mutant defective in the repair of double-strand breaks, is sensitive to benzo[a]pyrene, suggesting that this compound also induces strand breaks in these cells. In this study we combined a previously employed method, metabolic activation by S9 mix, with the use of a DNA-repair mutant panel, thereby broadening the range of compounds that can be screened for potential genotoxicity.
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Affiliation(s)
- Masato Ooka
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan
| | - Hironori Takazawa
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan
| | - Shunichi Takeda
- Department of Radiation Genetics, Graduate School of Medicine, Kyoto University, Yoshidakonoe, Sakyo-ku, Kyoto 606-8501, Japan
| | - Kouji Hirota
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji-shi, Tokyo 192-0397, Japan.
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