Early upregulation of cyclooxygenase-2 in human papillomavirus type 16 and telomerase-induced immortalization of human esophageal epithelial cells

Background and Aim:  Cyclooxygenase-2 (COX-2) plays an important role in the carcinogenesis of esophageal squamous cell carcinoma (ESCC). However, it is not clear whether COX-2 is involved in the early or late stage of the development of ESCC. The aim of this study was to investigate the role of COX-2 in the carcinogenesis of ESCC by an immortalized esophageal epithelial cell line. Methods:  Human papillomavirus type 16 (HPV16)–E6/E7 and human telomerase reverse transcriptase (hTERT) transfection were used for immortalization of esophageal epithelial cells. COX-2-specific RNA interference was used for the inhibition of COX-2 expression. Results:  An immortalized esophageal epithelial cell line, NE6-E6E7/hTERT, was established, which had high proliferation activity but failed to induce colony formation in soft agar. COX-2 expression was upregulated in the early process of immortalization, while COX-2 small interfering RNA (siRNA) decreased the Bcl-2 expression, increased the expression of Bax, and induced cell-cycle arrest at the G0/G1 phase in NE6-E6E7/hTERT cells. Expressions of p53, cyclinD1, and the ratio of hyperphosphorylated-RB/hypophosphorylated-RB were progressively increased after E6E7 and the subsequent hTERT transfections. These changes were accompanied by the alteration of COX-2 expression, but could be reversed by COX-2 siRNA (P < 0.05). P16 expression was significantly downregulated in NE6-E6E7 or NE6-E6E7/hTERT cells (P < 0.05), and was not affected by COX-2 siRNA. Conclusions:  Our results suggest that induction of cyclooxygenase-2 is essential in the human papillomavirus type 16 and hTERT-induced immortalization of human esophageal epithelial cells, and that COX-2 inhibition may be a potential target to block the carcinogenesis of ESCC at the precancerous stage.