Abstract
Previous studies have indicated that the survival of Chinese hamster ovary cells (CHO-K1) after ultraviolet C irradiation (25 J/m2) is greatly reduced if cells are treated with colcemid (50 ng/ml) after irradiation. This inhibitory effect of colcemid was also detected in my study with EM9 cells but not with UV24 cells. EM9 and UV24 cells are both the derivatives of CHO cells except that EM9 and UV24 cells have defect in base-excision repair (BER) and nucleotide excision repair (NER), respectively. This observation suggests that the colcemid’s effect was NER dependent. Further study with enzyme-linked immunosorbent assay using specific antibodies to two major UVC-induced DNA damages, i.e. cyclobutane pyrimidine dimer (CPD) and 6-4 photoproduct (6-4 PP) shows that colcemid did not affect the excision of CPD or 6-4PP. However, study with the comet assay indicates that colcemid increased the DNA breaks in UVC-irradiated cells. Further analysis reveals that colcemid did not inhibit the unscheduled DNA synthesis. Taking together, I hypothesize that colcemid might inhibit the step of ligation of NER pathway.