Laboratory for Molecular Radiobiology, University Hospital Zurich, Zurich, Switzerland.
Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland.
Int J Radiat Oncol Biol Phys. 2014 Jan 1;88(1):175-81. doi: 10.1016/j.ijrobp.2013.09.041. Epub 2013 Nov 13.
To investigate the impact of the 2 major DNA repair machineries on cellular survival in response to irradiation with the 2 types of ionizing radiation.
The DNA repair and cell survival endpoints in wild-type, homologous recombination (HR)-deficient, and nonhomologous end-joining-deficient cells were analyzed after irradiation with clinically relevant, low-linear energy transfer (LET) protons and 200-keV photons.
All cell lines were more sensitive to proton irradiation compared with photon irradiation, despite no differences in the induction of DNA breaks. Interestingly, HR-deficient cells and wild-type cells with small interfering RNA-down-regulated Rad51 were markedly hypersensitive to proton irradiation, resulting in an increased relative biological effectiveness in comparison with the relative biological effectiveness determined in wild-type cells. In contrast, lack of nonhomologous end-joining did not result in hypersensitivity toward proton irradiation. Repair kinetics of DNA damage in wild-type cells were equal after both types of irradiation, although proton irradiation resulted in more lethal chromosomal aberrations. Finally, repair kinetics in HR-deficient cells were significantly delayed after proton irradiation, with elevated amounts of residual γH2AX foci after irradiation.
Our data indicate a differential quality of DNA damage by proton versus photon irradiation, with a specific requirement for homologous recombination for DNA repair and enhanced cell survival. This has potential relevance for clinical stratification of patients carrying mutations in the DNA damage response pathways.
研究两种主要的 DNA 修复机制在细胞对两种类型电离辐射（辐射）的反应中对细胞存活的影响。
在对临床相关的低线性能量转移（LET）质子和 200keV 光子进行照射后，分析野生型、同源重组（HR）缺陷型和非同源末端连接缺陷型细胞中的 DNA 修复和细胞存活终点。
与光子照射相比，所有细胞系对质子照射都更为敏感，尽管 DNA 断裂的诱导没有差异。有趣的是，HR 缺陷细胞和经小干扰 RNA 下调 Rad51 的野生型细胞对质子照射明显敏感，导致与野生型细胞确定的相对生物学效应相比，相对生物学效应增加。相比之下，非同源末端连接的缺乏不会导致对质子照射的敏感性增加。两种照射后，野生型细胞的 DNA 损伤修复动力学相同，尽管质子照射导致更多的致死性染色体畸变。最后，质子照射后 HR 缺陷细胞的修复动力学明显延迟，照射后γH2AX 焦点的残留量增加。
我们的数据表明，质子与光子照射导致的 DNA 损伤质量不同，同源重组对 DNA 修复和增强细胞存活有特定要求。这对于携带 DNA 损伤反应途径突变的患者的临床分层具有潜在意义。
