@misc{oai:repo.qst.go.jp:00069011,
 author = {Mori, Masahiko and Katsube, Takanori and Shiomi, Naoko and Shiomi, Tadahiro and Onoda, Makoto and 森 雅彦 and 勝部 孝則 and 塩見 尚子 and 塩見 忠博 and 小野田 眞},
 month = {Jul},
 note = {DNA double strand breaks (DSBs) can arise from multiple sources including ionizing radiation (IR), and is the most serious DNA damage. Non-homologous end joining (NHEJ), which simply pieces together the broken DNA ends, can function in all phases of the cell cycle and is the predominant repair pathway in mammalian cells. In the current study, we carried out the generation and characterization of the NHEJ-related gene deficient human cell lines to clarify the biological role of NHEJ-related genes on DNA damage induced by IR. 
 We have produced cells that bearing a disrupted NHEJ-related gene, such as XRCC4, Artemis and MDC1, by using gene-targeting technique in human colon tumor cell line (HCT116). For clonogenic survival experiments, cells were exposed to X-rays (~ 5 Gy), plated for colony formation assay immediately after irradiation, and processed for a visualization and count of colonies 2 weeks after plating. Enumerating discrete nuclear foci of g-H2AX visible by immunofluorescence was performed to evaluate the ability for repairing DSBs induced by IR (~ 2 Gy) in both wild and deficient cells.
 Proliferation rates were slightly slower in all deficient cell lines than that in wild type cells, although any morphological difference was not observed between the cell lines. The highest survival rate was exhibited in the wild type cells (D10 = 3.9 Gy) and the lowest was in XRCC4-/- cells (D10 = 1.2 Gy). Artemis-/- cells (D10 = 2.2 Gy) took a middle position between wild and XRCC4-/- cells. Formation of g-H2AX foci increased in a dose dependent manner of X-rays and peaked at 30 min after X-ray-exposure in all cell lines. A remarkable recovery from the DNA damage was observed in wild type cells and the number of g-H2AX foci returned to the basal level within 4 hr, whereas a slower disappearance of g-H2AX was shown in NHEJ-related gene deficient cells such as XRCC4-/- and MDC1-/- cells, indicating a delay of repairing DSBs induced by IR. These results suggest that deficient of NHEJ-related gene causes a deterioration of DNA DSB repair function and DNA repair deficient underlies a significant component of the radiosensitivity of these cells. NHEJ-related gene deficient human cell lines generated in this study could contribute to further development and understanding of basic research of DNA damage and repair in radiation-biology., The 13th International Congress of Radiation Research},
 title = {Generation and characterization of DNA double-strand break repair gene deficient human cell lines},
 year = {2007}
}