Increased expression of human DNA repair genes, XRCC1, XRCC3 and RAD51, in radioresistant human KB carcinoma cell line N10.

The radioresistant N10 and parental KB cell lines were examined for the expression of human DNA repair genes which were related to the repair of radiation-induced DNA damage by northern blot analysis using five kinds of DNA probes (XRCC1, XRCC3, XRCC5, RAD51, RAD52). In the unirradiated condition, N10 cells showed higher expression of XRCC1, XRCC3 and RAD51 mRNA than did KB cells. The X-irradiation induced a time-dependent increase in the mRNA levels of XRCC3 and RAD51 in both cell lines with a maximum at 2 h postirradiation. The XRCC1 mRNA in N10 was maintained at the same level even after irradiation, whereas that in KB was decreased after irradiation. There was no difference in the expression of XRCC5 and RAD52 mRNA between N10 and KB cells in both unirradiated and irradiated conditions. From these findings, it was suggested that XRCC1, XRCC3 and RAD51 contribute to the radioresistance in cell line N10.