Abstract
N-acetyl-L-cysteine (NAC), a well-known antioxidant is a scavenger of free radicals that can remove excess free radicals from cells and protect cells from damage by oxidants. In cycling CHO-K1 cells, NAC can inhibit the proliferation of cells, delay the procession of cell cycle and change the morphology of cells. When the cells are treated by NAC, the morphology of cells changes from normal spindle to abnormal round gradually. But we can't find the morphology change on quiescent cells. When the medium containing NAC is removed, cell cycle will go ahead and the change of cell morphology will reverse. Proliferating cell nuclear antigen (PCNA), an auxiliary factor of DNA polymerase δ□andε, is required for eukaryotic cell DNA synthesis and excision repair. Expression of PCNA is growth regulated but can be induced by variable extracellular stimuli including exposure to UV irradiation. We have found that UV-C irradiation can induce PCNA gene expression in CHO.K1 cells, no matter recovering in serum or in serum-free medium. To exclude the effect of serum stimulation, we have treated quiescent cells with NAC before and after UV-C irradiation under serum free condition. We find that NAC can inhibit UV-C induction of PCNA mRNA and protein. Although NAC is a GSH precursor, the inhibitory effect of UV induction of PCNA seems to GSH independent. The results suggest that NAC involves in anti-proliferation of CHO.K1 cells and regulation of UV-C response of PCNA.