Radiosensitivity of scid cells for heavy ion particles

缺乏DNA-PK的Scid细胞对低LET辐射高度敏感。用含有DNA-PK结构基因的人类8号染色体片段引入杂交细胞后，放射敏感性恢复到野生亲本细胞水平。scid细胞对高LET辐射的辐射敏感性尚未研究。本研究研究了细胞对重离子的辐射敏感性，以阐明LET辐射对DNA损伤的修复过程。采用x射线（200 kV）和碳离子作为重离子粒子（290MeV/u, 50 keV/μm）。x射线照射下杂交细胞DNA双链断裂（DNA-dsb）的修复呈双相性，而scid细胞DNA双链断裂的修复呈单相性。对碳离子的辐照显示出与x射线相同的结果，表明DNA-dsb的修复是与let无关的。对碳离子进行了RBE分析。scid细胞RBE为1.30，杂交细胞RBE为1.47。scid细胞的放射敏感性值减去杂交细胞的放射敏感性值表明DNA-PK修复损伤，DNA-PK贡献。DNA-PK贡献的RBE为1.02。这些结果表明，在scid细胞和杂交细胞中，不可修复的致死性DNA损伤是依赖于let的，而DNA- pk对DNA损伤的修复是不依赖于let的。

Scid cells deficient in DNA-PK are highly sensitive to low LET radiations. Hybrid cells introduced by a fragment of human chromosome 8 which contains the structural gene of DNA-PK recover radiosensitivity to the level of wild parental cells. Radiosensitivity of scid cells to high LET radiations has not been investigated. In this study radiosensitivity of scid cells to heavy ion particles was investigated in order to elucidate the process how DNA damages induced by LET radiation were repaired.X-rays (200 kV) and carbon ions as heavy ion particles (290MeV/u, 50 keV/μm) were used. Repair of DNA double strand breaks (DNA-dsb) in hybrid cells irradiated to X-rays showed bi-phasic, but mono-phasic in scid cells. Irradiation to carbon ions showed the same result as X-rays, indicating that repair of DNA-dsb was LET-independent. RBE for carbon ions was analyzed. RBE of scid cells was 1.30, and 1.47 for hybrid cells. The value of radiosensitivity of scid cells subtracted that of hybrid cells indicates damages repaired by DNA-PK, DNA-PK contribution. RBE of DNA-PK contribution was 1.02. These results indicate that lethal DNA damages unrepairable in scid cells and hybrid cells are LET-dependent, and that DNA damages repairable by DNA-PK contribution by LET-independent.