A comparison of the roles of XRCC4 and Artemis in the cellular response to DNA-damaging agents in human cells

DNA double-strand breaks (DSBs) represent the most serious threat among the cellular effects of ionizing radiation (IR). XRCC4 and Artemis play key roles in non-homologous end-joining (NHEJ), the predominant repair pathway of DSBs, in multicellular eukaryotes. XRCC4 is an essential component of DNA ligase IV complex, which rejoins broken DNA ends. On the other hand, Artemis is a nuclease required for trimming of some, but not all, types of broken DNA ends prior to rejoining by the DNA ligase IV/XRCC4 complex. To better understand the roles of these factors on risks related to radiation-induced events in human, we inactivated the XRCC4 and Artemis loci by gene targeting in the human colon adenocarcinoma cell line HCT116, and assessed their cellular responses to various DNA-damaging agents including X-rays. As anticipated, kinetic analyses of gamma-H2AX foci and chromosomal aberrations after IR demonstrated a serious incompetence of DSB repair in the XRCC4-deficient cells, and relatively moderate impairment in the Artemis-deficient cells. The XRCC4-deficient cells were highly sensitive to etoposide and 5-fluoro-2\u27-deoxyuridine as well as IR, and showed moderate sensitivities to camptothecin, methyl methanesulfonate, cisplatin, mitomycin C, aphidicolin and hydroxyurea, compared to the parental HCT116 cells. Meanwhile, consistent with the restricted role of Artemis in NHEJ repair system, the Artemis-deficient cells were not as sensitive to most of these DNA-damaging agents as the XRCC4-deficient cells. Nevertheless, the Artemis-deficient cells were unexpectedly more sensitive to DNA cross-linking agents, such as mitomycin C and cisplatin, than the XRCC4-deficient cells. By contrast, the Artemis-deficient cells were significantly more resistant to hydroxyurea than the parental cells. These observations suggest that Artemis also functions in some DNA damage response pathways other than NHEJ in human cells.14th International Congress of Radiation Researc