Abstract
The failure of G1 arrest in CHO.K1 cells is widely observed following X-ray or other DNA-damaging treatments. Recent research in our laboratory has found that the expression of p21 (Waf1/Cip1) gene is deficient in CHO.K1 cells. In addition, cells were sensitive to UV irradiation (25 J/m2) and underwent apoptosis in colcemid-containing medium. In this study, the role of p21 (Waf1/Cip1) protein in CHO.K1 cells following environmental assaults was investigated. After constructing a tetracycline-regulated human p21 expression system, we ectopically expressed human p21 (Waf1/Cip1) prior to treatment with DNA damaging agents and diagnosed the cell cycle distribution by flow cytometric analysis. Intriguingly, we observed recovery of G1 checkpoint in CHO.K1 cells with overexpression of human p21 following UV or X-ray irradiation. Furthermore, the survival analysis of CHO.K1 cells indicated that cells with overexpression of human p21 (Waf1/Cip1) protein were significantly resistant to UV than those without p21 expression, which seemed to block the massive apoptotic death exacerbated by UV irradiation in the presence of colcemid. These results demonstrate that overexpression of human p21 (Waf1/Cip1) in CHO.K1 cells can complement the G1 checkpoint defect and promote cell survival ability to against from DNA damaging agents.