Abstract
It has been generally believed that biological significance of DNA damage checkpoint is time-sparing for DNA damage repair. However, some lines of evidence, which is obtained from radiation biology, casts doubt on the well-known paradigm. The first evidence is: there is no significant difference in the repair kinetics of DNA double-strand breaks within 2 h after X-irradiation between normal human cells and ataxia-telangiectasia (AT) cells, which cannot induce DNA damage checkpoint, and approximately 90% of initial DNA double-strand breaks are rejoined in AT cells in the end (Kühne, et al., Cancer Res. 64, 500-508, 2004). The second evidence is: seventy to eighty percent of DNA double-strand breaks produced in G0/G1 phase is rejoined within 2 h after X-irradiation, while G1 checkpoint is induced much more slowly, and its induction requires at least 6-8 h after irradiation (Riballo, et al., Mol. Cell 16, 715-724, 2004; Kastan, et al., Cancer Res. 51, 6304-6311, 1991; Di Leonardo, et al., Genes Dev. 8, 2540-2551, 1994). In this workshop, it will be discussed whether the "time-sparing theory" of DNA damage checkpoint is right or not by distinguished speakers.
