Abstract: BACKGROUND ＆ AIM: There are now many reports that telomerase activity can be upregulated in some cells following exposure to low doses radiation, and that the enzyme may be involved in the repair of radiation damage. We studied the effect of telomerase inhibitor Azidothymidine (AZT) on repair of DNA damage induced by irradiation in human HeLa cells. MATERIALS AND METHODS: There were four groups：control group, azidothymidine group(HeLa cells were pretreated by 400 μmol/L Azidothymidine for 24 h),radiation group(HeLa cells were irradiated with 2 Gy 60Co γ rays), azidothymidine/radiation group(HeLa cells were irradiated with 2 Gy 60Co γ rays,with pretreatment by 400 μmol/L Azidothymidine for 24 h). Telomerase activity was measured by a PCR_based telomeric repeat amplification protocol (TRAP) coupled with ELISA and DNA single_stranded breaks was evaluated by single cell gel electrophoresis assay (SCGE). RESULTS: Telomerase activity of HeLa cells began increasing at 10 minutes,more at 60 min,and peaked at 360 min after irradiation with 2 Gy 60Co γ rays,and decreased about 50％ after pretreatment with Azidothymidine. Azidothymidine could inhibit telomerase activity increase after irradiation (P<0.05).In SCGE tests,0－10 min after irradiation with 2 Gy 60Co γ rays, there was no difference in percentage of DNA in the tail between Radiation group and Azidothymidine /Radiation group(P>0.05), but percentage of DNA in the tail of Azidothymidine /Radiation group was more than Radiation group(P<0.05)30－60 min after irradiation. CONCLUSION: Azidothymidine could reduce the repair of single_stranded DNA breaks 30－360 min after irradiation. These results suggested that telomerase could play an important role in irradiation_induced DNA damage repair.

Key words: azidothymidine, HeLa cells, telomerase, DNA repair