We analyzed the phenotype of cells derived from SCID patients with different mutations in the Artemis gene. Using clonogenic survival assay an increased sensitivity was found to X-rays (2-3-fold) and bleomycin (2-fold), as well as to etoposide, camptothecin and methylmethane sulphonate (up to 1.5-fold). In contrast, we did not find increased sensitivity to cross-linking agents mitomycin C and cis-platinum. The kinetics of DSB repair assessed by pulsed-field gel electrophoresis and γH2AX foci formation after ionizing irradiation, indicate that 15-20% of DSB are not repaired in Artemis-deficient cells. In order to get a better understanding of the repair defect in Artemis-deficient cells, we studied chromosomal damage at different stages of the cell cycle. In contrast to AT cells, Artemis-deficient cells appear to have a normal G1/S-block that resulted in a similar frequency of dicentrics and translocations, however, frequency of acentrics fragments was found to be 2-4-fold higher compared to normal fibroblasts. Irradiation in G2resulted in a higher frequency of chromatid-type aberrations (1.5-3-fold) than in normal cells, indicating that a fraction of DSB requires Artemis for proper repair. Our data are consistent with a function of Artemis protein in processing of a subset of complex DSB, without G1cell cycle checkpoint defects. This type of DSB can be induced in high proportion and persist through S-phase and in part might be responsible for the formation of chromatid-type exchanges in G1-irradiated Artemis-deficient cells. Among different human radiosensitive fibroblasts studied for endogenous (in untreated samples) as well as X-ray-induced DNA damage, the ranking order on the basis of higher incidence of spontaneously occurring chromosomal alterations and induced ones was: ligase 4 ≥ AT > Artemis. This observation implicates that in human fibroblasts following exposure to ionizing radiation a lower risk might be created when cells are devoid of endogenous damage.

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doi.org/10.1016/j.mrfmmm.2006.11.029, hdl.handle.net/1765/35577
Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
Erasmus MC: University Medical Center Rotterdam

Darroudi, F., Wiegant, W., Meijers, M., Friedl, A., van der Burg, M., Fomina, J., … Zdzienicka, M. (2007). Role of Artemis in DSB repair and guarding chromosomal stability following exposure to ionizing radiation at different stages of cell cycle. Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis, 615(1-2), 111–124. doi:10.1016/j.mrfmmm.2006.11.029