Role of p53 in antioxidant defense of HPV-positive cervical carcinoma cells following H₂O₂ exposure

In HPV-positive cervical carcinoma cells, p53 protein is functionally antagonized by the E6 oncoprotein. We investigated a possible role of p53 in antioxidant defense of HPV-positive cervical cancer cell lines. We found that SiHa cells containing integrated HPV 16 had higher expression of p53 and exhibited the greatest resistant to H₂O₂-induced oxidative damage, compared with HeLa, CaSki and ME180 cell lines. Downregulation of p53 resulted in the inhibition of p53-regulated antioxidant enzymes and elevated intracellular ROS in SiHa cells. By contrast, the ROS level was not affected in HeLa, CaSki and ME180 cell lines after inhibition of the p53 protein. Under mild or severe H₂O₂-induced stress, p53-deficient SiHa cells exhibited much higher ROS levels than control SiHa cells. Furthermore, we analyzed cell viability and apoptosis after H₂O₂ treatment and found that p53 deficiency sensitized SiHa cells to H₂O₂ damage. Inhibition of p53 resulted in excessive oxidation of DNA; control SiHa cells exhibited a more rapid removal of 8-oxo-7,8-dihydro-2'-deoxyguanosine from DNA compared with p53-deficient SiHa cells exposed to the same level of H₂O₂ challenge. These data collectively show that endogenous p53 in SiHa cells has an antioxidant function and involves in the reinforcement of the antioxidant defense.