Yap Seow Fong, Boo Cynthia Sk, Loong Susan LE, Baskar Rajamanickam
Department of Radiation Oncology, Division of Cellular and Molecular Research, National Cancer Centre, Singapore.
J Cancer. 2013 Sep 7;4(8):606-13. doi: 10.7150/jca.6453.
Non-homologous end joining (NHEJ) is the main repair pathway for DNA double strand breaks (DSBs) induced by ionizing radiation in mammalian cells. Subsets of cancer patients are hypersensitive to radiotherapy after standard doses. We sought to determine the radiosensitivity of human lymphoblastic cells (LB0005) for the abnormality in NHEJ components.
Lymphoblastic (LB0005) cells are derived from an adult cancer patient with late radionecrosis. A low magnesium in vitro DNA-end joining assay was performed to examine for any defect in NHEJ activity. Single-nucleotide polymorphism (SNP) and sequence analysis were performed to examine for abnormality if any, in the genetic sequence of known NHEJ components.
LB0005 cells showed a gain of functional abnormality in the NHEJ pathway. While genetic sequence analysis showed no apparent mutational variations in the known classical NHEJ components, DNA-PKcs (DNA-dependent protein kinase catalytic subunit) protein is reduced in quantity compared to normal control, in spite of higher transcript levels.
Taken together cells derived from a radiosensitive patient showed an abnormality in NHEJ activity. Proteins other than the classical NHEJ factors may regulate the NHEJ activity. Furthermore, the defect in theses regulatory proteins may have an impact on the stability of DNA-PKcs.
非同源末端连接（NHEJ）是哺乳动物细胞中电离辐射诱导的DNA双链断裂（DSB）的主要修复途径。部分癌症患者在接受标准剂量放疗后对放疗高度敏感。我们试图确定人类淋巴细胞（LB0005）因NHEJ组分异常而产生的放射敏感性。
淋巴细胞（LB0005）来源于一名患有晚期放射性坏死的成年癌症患者。进行低镁体外DNA末端连接试验以检测NHEJ活性是否存在缺陷。进行单核苷酸多态性（SNP）和序列分析以检测已知NHEJ组分的基因序列中是否存在异常。
LB0005细胞在NHEJ途径中出现功能异常。虽然基因序列分析显示已知经典NHEJ组分中没有明显的突变变异，但与正常对照相比，DNA-PKcs（DNA依赖性蛋白激酶催化亚基）蛋白的量减少，尽管转录水平较高。
总体而言，来自放射敏感患者的细胞显示出NHEJ活性异常。除经典NHEJ因子外的其他蛋白质可能调节NHEJ活性。此外，这些调节蛋白的缺陷可能会影响DNA-PKcs的稳定性。
