Frankenberg-Schwager Marlis, Gebauer Anja, Koppe Cordula, Wolf Hartmut, Pralle Elke, Frankenberg Dieter
University of Goettingen, Radiology Center, Department of Nuclear Medicine, 37075 Goettingen, Germany.
Radiat Res. 2009 Mar;171(3):265-73. doi: 10.1667/RR0784.1.
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.
首次报道了中国仓鼠卵巢细胞中易错单链退火（SSA）、无错保守同源重组（HR）以及可能易错的非同源DNA末端连接（NHEJ）在细胞周期依赖性方面对修复简单（由200 kV X射线诱导）或复杂（由（241）Amα粒子诱导）DNA双链断裂（DSB）的相对贡献。亲本细胞系AA8及其衍生物UV41（缺乏SSA）、irs1SF（缺乏HR）和V3（缺乏NHEJ）的细胞在G1期或S期同步化，然后测量暴露于两种辐射后的存活反应。首次证明，在G1期，SSA对于各种复杂性DSB的修复可忽略不计。在G1期暴露于X射线或α粒子的HR缺陷细胞显示出更高的放射敏感性，但这不一定意味着HR在G1期很重要。NHEJ似乎是G1期作用于简单DSB的最重要（如果不是唯一）机制，但复杂DSB是较不受青睐的靶点。与X射线不同，缺乏NHEJ的细胞对α粒子的敏感性没有细胞周期依赖性变化。令人惊讶的是，当这些细胞在G1期暴露于X射线时，它们甚至比暴露于α粒子时更敏感。还首次表明，在S期，所有三种机制在简单和复杂DSB的修复中都起作用。SSA缺陷使S期细胞具有放射敏感性，这表明易错的SSA机制对于修复不是HR或NHEJ底物的特定简单和复杂DSB很重要。S期修复简单和复杂DSB的最重要机制是HR。这也通过以下发现得到强调：irs1SF细胞在用人XRCC3 cDNA补充其HR缺陷后，显示出比亲本细胞更高的抗辐射性，而对丝裂霉素C的抗性仅部分恢复。补充赋予对α粒子的抗性比对X射线的抗性更大，这表明HR的重要作用，特别是对于复杂DSB的修复。在S期，NHEJ对于简单DSB的修复比SSA更重要，但SSA对于复杂DSB的修复比NHEJ更重要。
