Prediction of Radiation Sensitivity by Functional Analysis of Reeombinational Repair Genes in Human Cells

在放射治疗前预测放射敏感性是非常重要的，因为放射敏感性与治疗的疗效和副作用密切相关。此外，辐射敏感性也与辐射伤亡者的疾病发生有关。因此，辐射敏感性在放射医学中是非常重要的。然而，辐射敏感性的分子机制在很大程度上是未知的。为了解决这个问题，我们通过产生缺乏DNA双链断裂修复基因的人类细胞，分析了与辐射敏感性相关的遗传多态的生物学意义。我们成功地培育出XRCC3缺失的人类细胞系，XRCC3是一种参与同源重组修复的基因。XRCC3基因缺陷的细胞对DNA损伤剂表现出超敏反应，这是一种同源重组缺陷和染色体断裂。此外，在这些细胞中，内复制的频率显著增加，这表明XRCC3通过阻止DNA重新复制来维持染色体的完整性。T241M变异已被证明与癌症风险有关。通过在XRCC3缺陷细胞中引入这种变异来检验这种变异的生物学意义。令我们惊讶的是，该变体显示了完整的重组修复活动，但失去了防止内复制的能力。这一发现表明，241M通过促进内复制而导致数字染色体异常，从而增加癌症风险。因此，遗传多态经常与DNA代谢网络相关，但不一定与DNA修复活动相关。

It is of great importance that radiation sensitivity can be predicted before radiation therapy because radiation sensitivity is significantly associated with efficacy of therapy and side effects. In addition, radiation sensitivity is also associated with disease occurrence in radiation casualty. Thus, radiation sensitivity is very important in radiation medicine. However, molecular mechanisms of radiation sensitivity are largely unknown. To address this issue, we have analysed biological significance of genetic polymorphisms associated with radiation sensitivity by generating human cells deficient in DNA double-strand break repair genes. We successfully generated human cell lines deficient in XRCC3, a gene involved in homologous recombinational repair. XRCC3-deficient cells show hypersensitivity to DNA-damaging agents, a defect in homologous recombination and chromosome breaks. Furthermore, the frequency of endoreduplication is significantly increased in these cells, suggesting that XRCC3 maintains chromosome integrity by preventing DNA rereplication. The T241M variation has been shown to be associated with cancer risk. The biological significance of this variation was examined by the introduction of this variant in XRCC3-deficient cells. To our surprise, this variant shows intact reoombinational repair activity but loses the ability to prevent endoreduplication. This finding suggests that 241M contributes to cancer risk by inducing numeral chromosome aberrations by promoting endoreduplication. Thus, genetic polymorphisms are often associated with DNA metabolic networks but are not necessarily associated with DNA repair activity.