c-Myc-dependent transactivation of the telomerase hTERT gene by HPV E6 oncoprotein

The E6 and E7 oncogenes of human papillomavirus (HPV) type 16 are sufficient for the immortalization of human genital keratinocytes in vitro. The products of these viral genes associate with p53 and pRb tumor suppressor proteins, respectively, and interfere with their normal growth-regulatory functions. The HPV-16 E6 protein has also been shown to increase the telomerase enzyme activity in primary epithelial cells independently of p53 degradation. The current dissertation has explored the mechanism by which E6 activates telomerase. We show that E6 upregulates the expression of the telomerase catalytic subunit, hTERT, coordinately with E6-induced telomerase activation. In addition, we demonstrate that E6 is able to transactivate the hTERT promoter, indicating that the mechanism for E6-mediated increases in hTERT expression occurs predominantly at the level of transcriptional regulation. Since the c-Myc protein has been strongly implicated in the control of telomerase activity, we also investigated the possibility that it might have a role in E6-mediated telomerase activation. In transient reporter assays, we demonstrate that expression of a specific antagonist of Myc activity, Mad protein, represses hTERT promoter activation by E6. Furthermore, we show that E6 transactivation of the hTERT promoter is dependent on an intact proximal E-box element for Myc-Max binding. Finally, we demonstrate that E6 and c-Myc can bind in vivo, suggesting that hTERT transcriptional control by E6 may be mediated through its interaction with c-Myc.