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Sakamoto Y, Kokuta T, Teshigahara A, Iijima K, Kitao H, Takata M, Tauchi H. Mitotic cells can repair DNA double-strand breaks via a homology-directed pathway. JOURNAL OF RADIATION RESEARCH 2021; 62:25-33. [PMID: 33009557 PMCID: PMC7779344 DOI: 10.1093/jrr/rraa095] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 08/21/2020] [Indexed: 05/04/2023]
Abstract
The choice of repair pathways of DNA double-strand breaks (DSBs) is dependent upon the cell cycle phases. While homologous recombination repair (HRR) is active between the S and G2 phases, its involvement in mitotic DSB repair has not been examined in detail. In the present study, we developed a new reporter assay system to detect homology-directed repair (HDR), a major pathway used for HRR, in combination with an inducible DSB-generation system. As expected, the maximal HDR activity was observed in the late S phase, along with minimal activity in the G1 phase and at the G1/S boundary. Surprisingly, significant HDR activity was observed in M phase, and the repair efficiency was similar to that observed in late S phase. HDR was also confirmed in metaphase cells collected with continuous colcemid exposure. ChIP assays revealed the recruitment of RAD51 to the vicinity of DSBs in M phase. In addition, the ChIP assay for gamma-H2AX and phosphorylated DNA-PKcs indicated that a part of M-phase cells with DSBs could proceed into the next G1 phase. These results provide evidence showing that a portion of mitotic cell DSBs are undoubtedly repaired through action of the HDR repair pathway.
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Affiliation(s)
- Yuki Sakamoto
- Department of Biological Sciences, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan
| | - Tetsuya Kokuta
- Department of Biological Sciences, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan
| | - Ai Teshigahara
- Department of Biological Sciences, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan
| | - Kenta Iijima
- Department of Biological Sciences, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan
- Department of Cancer Biology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan
| | - Hiroyuki Kitao
- Department of Molecular Cancer Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan
| | - Minoru Takata
- Radiation Biology Center, Kyoto University, Yoshida-Konoe Cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Hiroshi Tauchi
- Corresponding author. Department of Biological Sciences, Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512, Japan. Tel: +81-29-228-8383; Fax: +81-29-228-8403;
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Tauchi H, Waku H, Matsumoto E, Yara S, Okumura S, Iwata Y, Komatsu K, Furusawa Y, Eguchi-Kasai K, Tachibana A. Two major factors involved in the reverse dose-rate effect for somatic mutation induction are the cell cycle position and LET value. JOURNAL OF RADIATION RESEARCH 2009; 50:441-448. [PMID: 19506344 DOI: 10.1269/jrr.09033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
To study mechanisms which could be involved in the reverse dose rate effect observed during mutation induction after exposure to high LET radiation, synchronized mouse L5178Y cells were exposed to carbon 290 MeV/n beams with different LET values at the G2/M, G1, G1/S or S phases in the cell cycle. The frequency of Hprt-deficient (6-thioguanine-resistant) mutant induction was subsequently determined. The results showed that after exposure to high LET value radiation (50.8 and 76.5 keV/microm), maximum mutation frequencies were seen at the G2/M phase, but after exposure to lower LET radiation (13.3 keV/microm), the highest mutation frequencies were observed at the G1 phase. The higher LET beam always produced higher mutation frequencies in the G2/M phase than in the G1 phase, regardless of radiation dose. These results suggest that cells in the G2/M phase is hyper-sensitive for mutation induction from high LET radiation, but not to mutation induction from low LET radiation. Molecular analysis of mutation spectra showed that large deletions (which could include almost entire exons) of the mouse Hprt gene were most efficiently induced in G2/M cells irradiated with high LET radiation. These entire exon deletions were not as frequent in cells exposed to lower LET radiation. This suggests that inappropriate recombination repair might have occurred in response to condensed damage in condensed chromatin in the G2/M phase. In addition, by using a hyper-sensitive mutation detection system (GM06318-10 cells), a reverse dose-rate effect was clearly observed after exposure to carbon beams with higher LET values (66 keV/microm), but not after exposure to beams with lower LET values (13.3 keV/microm). Thus, G2/M sensitivity towards mutation induction, and the dependence on radiation LET values could both be major factors involved in the reverse dose rate effect produced by high LET radiation.
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Affiliation(s)
- Hiroshi Tauchi
- Department of Biological Science, Faculty of Science, Ibaraki University, Ibaraki.
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Tauchi H, Endo S, Eguchi-Kasai K, Furusawa Y, Suzuki M, Matsuura S, Ando K, Nakamura N, Sawada S, Komatsu K. Cell cycle and LET dependence for radiation-induced mutation: a possible mechanism for reversed dose-rate effect. JOURNAL OF RADIATION RESEARCH 1999; 40 Suppl:45-52. [PMID: 10804993 DOI: 10.1269/jrr.40.s45] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A previous study of the mutagenic action of 252Cf radiation in mouse L5178Y cells showed that the mutation frequency was higher when the dose was chronic rather than acute, which was in sharp contrast to the effects reported for gamma-rays (Nakamura and Sawada, 1988). A subsequent study using synchronized cells revealed that the cells at the G2/M stage were uniquely sensitive to mutation induction by 252Cf radiation but not to gamma-rays (Tauchi et al., 1993). A long phase cell population was first subjected to conditioning gamma or 252Cf radiation doses at different dose-rates. The cell cycle distribution of these cells was then observed, and they were then exposed to 252Cf radiation, and the mutation rate was determined. The G2/M fraction increased by 3- to 4-fold when the conditioning doses (2 Gy of gamma or 1 Gy of 252Cf radiation) were delivered chronically over 10 h, but only slightly when the same doses were delivered over a 1 h period or less. Subsequent 252Cf irradiation gave higher mutation frequencies in the cells pre-irradiated with gamma-rays over a protracted period of time than in those exposed with the higher dose-rate gamma-rays. These results suggest that the radiation-induced G2 block could be at least partly (but not totally) responsible for this reverse dose-rate effect (Tauchi et al. 1996). Possible factors which cause the hyper-sensitivity of G2/M cells to mutation induction by neutrons will be discussed.
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Affiliation(s)
- H Tauchi
- Department of Radiation Biology, Hiroshima University, Japan
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