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

放射敏感性与放射治疗的疗效和副作用密切相关，因此在放射治疗前预测放射敏感性具有重要意义。此外，辐射敏感性也与辐射损伤后疾病的发生有关。因此，辐射敏感性在放射医学中非常重要。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，我们分析了与辐射敏感性相关的遗传多态性的生物学意义，通过产生缺乏DNA双链断裂修复基因的人类细胞。我们成功地产生了缺乏XRCC3的人类细胞系，XRCC3是一种参与同源重组修复的基因。XRCC 3缺陷细胞对DNA损伤剂表现出超敏反应，这是一种同源重组和染色体断裂缺陷。此外，在这些细胞中核内复制的频率显著增加，表明XRCC3通过阻止DNA再复制来维持染色体完整性。T241M变异已被证明与癌症风险相关。通过在XRCC 3缺陷细胞中引入该变体来检查该变异的生物学意义。令我们惊讶的是，这种变异显示出完整的重组修复活性，但失去了阻止核内复制的能力。这一发现表明，241 M通过促进核内复制诱导染色体数目畸变而导致癌症风险。因此，遗传多态性通常与DNA代谢网络相关，但不一定与DNA修复活性相关。

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.