E7-expressing HaCaT keratinocyte cells are resistant to oxidative stress-induced cell death via the induction of catalase.

Cervical carcinoma is one of the most prevalent cancers in women worldwide, and human papillomavirus (HPV) type 16 is the most common agent linked to human cervical carcinoma. In order to identify various relevant factors affected by the E7 oncogene, we established a stable cell line, which constitutively expressed E7 using the HaCaT human keratinocyte cell line. The increased expression and activity of catalase in the E7-expressing HaCaT cells (HaCaT/E7) were verified via matrix-assisted laser desorption/ionization-time of flight, Western blot, and reverse transcription-polymerase chain reaction analyses. The regulation of catalase by E7 was investigated by the detection of catalase promoter activity. E7 enhanced the activities of both the catalase promoter and nuclear factor-kappaB, one of the major transcription factors regulating the expression of the catalase gene. HaCaT/E7 cells produced lower quantities of intracellular reactive oxygen species (ROS), and appeared to be more resistant to H(2)O(2)-induced cell death. Moreover, in order to test the specific effects of E7 on catalase induction, the HaCaT/E7 cells were transiently transfected with E7 antisense vector, resulting in reductions in both the expression and activity of catalase, and a recovery of intracellular ROS levels, thus resulting in recovered sensitivity to H(2)O(2)-induced cell death. These results suggest that the HPV 16 E7 oncogene induces higher resistance to ROS-induced cell injury in the E7-infected cells, probably via the modulation of several anti-oxidant enzymes, including catalase.