Background Repair of DNA double strand breaks by non-homologous end joining (NHEJ) requires several proteins including Ku, DNA-PKcs, Artemis, XRCC4, Ligase IV and XLF. inhibitor (IC86621) or RNAi and observed their greater sensitivity to telomere dysfunction relative to control cells. Conclusion These results suggest that defective Artemis causes a mild telomere dysfunction phenotype in human cell lines. Background There is increasing evidence that the maintenance of telomeres, physical ends of chromosomes, and DNA damage response mechanisms are interlinked. The first observation of a telomere dysfunction phenotype in a DNA damage response defective environment was reported in the case of Ataxia telangiectasia (AT) cells. The telomere dysfunction phenotype CC 10004 cost in cells from AT patients or ATM (AT mutated) defective mice ranges from accelerated telomere shortening to end-to-end chromosome fusions and extra-chromosomal telomeric fragments [1,2]. Following the observation of telomere dysfunction associated with the ATM defect, a number of DNA damage response factors have been shown to affect telomere maintenance. Most notably, proteins involved in the repair of DNA double strand breaks (DSBs) either by Non-Homologous End Joining (NHEJ) or homologous recombination (HR) including Ku, DNA-PKcs, RAD54, RAD51D and BRCA1 CC 10004 cost if dysfunctional, will cause a severe telomere dysfunction phenotype [3-6]. So far, at least 17 DNA damage response proteins have been shown to affect telomere maintenance . It is not yet clear as to why the interplay between telomere maintenance and DNA damage response is required. However, it is certain that both pathways are essential for chromosome integrity maintenance and perhaps their interaction is important for the stable chromosome segregation. One of the key pathways required for the stable segregation of chromosomes is NHEJ. The key players in this pathway are Ku 70/86 and DNA-PKcs, both shown to be involved in telomere maintenance . Other proteins involved in NHEJ include: Artemis, Ligase IV, XRCC4 and XLF . Previous studies have shown that Ligase IV and XRCC4 do not have effect on telomere length or function . However, it is not clear yet whether the remaining two NHEJ proteins, namely Artemis and XLF, affect telomere maintenance. Artemis has exonuclease and endonuclease activities in the presence of DNA-PKcs and ATP . It is required for V(D)J recombination and people with mutations in the gene coding for Artemis show immunodeficiency and radiosensitivity . Thus, the human disease due to defective Artemis is named RS-SCID (radio-sensitive severe combined immunodeficiency disease). A study of cells from Artemis defective mice  revealed slightly elevated frequencies of end-to-end chromosome fusions, a cytological sign of telomere dysfunction. Furthermore, analysis of a primary fibroblast cell line from an RS-SCID patient showed accelerated shortening of telomeres relative to the normal control cell line . These studies point to the possibility that Artemis, similarly to the other two NHEJ proteins, Ku and DNA-PKcs, may have a role in telomere maintenance. This possibility is further supported by observations that a Rabbit Polyclonal to HEXIM1 close homologue of Artemis, a protein named Apollo, is directly involved in telomere maintenance, most likely true interactions CC 10004 cost with the telomeric protein TRF2 [14,15]. In this study we analyzed spontaneous and radiation induced chromosomal abnormalities and monitored repair kinetics of ionizing radiation (IR) induced DSBs occurring within telomeric sequences in Artemis defective human cells. Furthermore, we either inhibited or knocked-down DNA-PKcs and monitored the effect of this procedure on telomeres. Our results suggest that.