Abstract
DNA double-strand breaks (DSBs) represent the most serious threat among the cellular effects of ionizing radiation. XRCC4 and Artemis play key roles in non-homologous end-joining (NHEJ), the predominant repair pathway of DSBs, in multicellular eukaryotes. XRCC4, a component of DNA ligase IV complex, is an essential factor for activation and stabilization of the ligase itself in the process of NHEJ. On the other hand, Artemis may not be required for whole NHEJ system, but rather functions in processing of a subset of complex DNA ends prior to ligation. To elucidate roles of these proteins on risks related to radiation-induced events in human, we established XRCC4 and Artemis gene deficient cells in human colon carcinoma cell line HCT116 by gene targeting. In this current study, we compared sensitivities of the mutant human cells, XRCC4-/- and Artemis-/-, to various DNA damaging agents by clonogenic survival assay. XRCC4-/- cells exhibited serious sensitivities to X-rays, etoposide and 5-fluorodeoxyuridine, and modest sensitivities to camptothecin, methyl methanesulfonate, cisplatin, mitomycin C, hydroxyurea and aphidicolin as compared to parental HCT116 cells. Consistent with the above-mentioned functions of these proteins in NHEJ, sensitivities of Artemis-/- cells to most of those DNA damaging agents were equivalent to or lower than those of XRCC4-/- cells. Nevertheless, Artemis-/- cells were more sensitive to DNA cross-linking agents, mitomycin C or cisplatin, than XRCC4-/- cells. By contrast, Artemis-/- cells were significantly resistant to hydroxyurea than parental cells. These results suggest that Artemis also function in some DNA damage response pathways other than NHEJ.
