Antonelli F, Campa A, Esposito G, Giardullo P, Belli M, Dini V, Meschini S, Simone G, Sorrentino E, Gerardi S, Cirrone G A P, Tabocchini M A
a Health and Technology Department, Istituto Superiore di Sanità, Roma, Italy;
Radiat Res. 2015 Apr;183(4):417-31. doi: 10.1667/RR13855.1. Epub 2015 Apr 6.
The spatial distribution of radiation-induced DNA breaks within the cell nucleus depends on radiation quality in terms of energy deposition pattern. It is generally assumed that the higher the radiation linear energy transfer (LET), the greater the DNA damage complexity. Using a combined experimental and theoretical approach, we examined the phosphorylation-dephosphorylation kinetics of radiation-induced γ-H2AX foci, size distribution and 3D focus morphology, and the relationship between DNA damage and cellular end points (i.e., cell killing and lethal mutations) after exposure to gamma rays, protons, carbon ions and alpha particles. Our results showed that the maximum number of foci are reached 30 min postirradiation for all radiation types. However, the number of foci after 0.5 Gy of each radiation type was different with gamma rays, protons, carbon ions and alpha particles inducing 12.64 ± 0.25, 10.11 ± 0.40, 8.84 ± 0.56 and 4.80 ± 0.35 foci, respectively, which indicated a clear influence of the track structure and fluence on the numbers of foci induced after a dose of 0.5 Gy for each radiation type. The γ-H2AX foci persistence was also dependent on radiation quality, i.e., the higher the LET, the longer the foci persisted in the cell nucleus. The γ-H2AX time course was compared with cell killing and lethal mutation and the results highlighted a correlation between cellular end points and the duration of γ-H2AX foci persistence. A model was developed to evaluate the probability that multiple DSBs reside in the same gamma-ray focus and such probability was found to be negligible for doses lower than 1 Gy. Our model provides evidence that the DSBs inside complex foci, such as those induced by alpha particles, are not processed independently or with the same time constant. The combination of experimental, theoretical and simulation data supports the hypothesis of an interdependent processing of closely associated DSBs, possibly associated with a diminished correct repair capability, which affects cell killing and lethal mutation.
细胞核内辐射诱导的DNA断裂的空间分布取决于能量沉积模式方面的辐射质量。一般认为，辐射线性能量传递（LET）越高，DNA损伤的复杂性就越大。我们采用实验与理论相结合的方法，研究了γ-H2AX焦点的磷酸化-去磷酸化动力学、大小分布和三维焦点形态，以及暴露于γ射线、质子、碳离子和α粒子后DNA损伤与细胞终点（即细胞杀伤和致死性突变）之间的关系。我们的结果表明，所有辐射类型在照射后30分钟时达到焦点的最大数量。然而，每种辐射类型在0.5 Gy照射后的焦点数量有所不同，γ射线、质子、碳离子和α粒子分别诱导出12.64±0.25、10.11±0.40、8.84±0.56和4.80±0.35个焦点，这表明径迹结构和注量对每种辐射类型在0.5 Gy剂量后诱导的焦点数量有明显影响。γ-H2AX焦点的持久性也取决于辐射质量，即LET越高，焦点在细胞核中持续的时间越长。将γ-H2AX的时间进程与细胞杀伤和致死性突变进行了比较，结果突出了细胞终点与γ-H2AX焦点持久性持续时间之间的相关性。开发了一个模型来评估多个双链断裂（DSB）存在于同一γ射线焦点中的概率，发现对于低于1 Gy的剂量，这种概率可以忽略不计。我们的模型提供了证据，表明复杂焦点（如由α粒子诱导的焦点）内的DSB不是独立处理的，也不是以相同的时间常数处理的。实验、理论和模拟数据的结合支持了紧密相关的DSB相互依赖处理的假设，这可能与正确修复能力的降低有关，进而影响细胞杀伤和致死性突变。
