Telomerase activation in cervical keratinocytes containing stably replicating human papillomavirus type 16 episomes

Retroviral transduction and expression of the human papillomavirus type 16 (HPV-16) E6 gene has been shown to activate telomerase in human cervical and foreskin keratinocytes. There still remains some controversy, however, as to whether expression of E6 in the context of the whole HPV-16 genome can activate telomerase. In this study, we have generated human cervical keratinocyte clones that contain stably replicating HPV-16 episomes. Interestingly, the majority of the clones exhibited low or no telomerase activity at early passage and this was associated with low transcript levels of the reverse transcriptase component of telomerase, hTERT. The HPV-16-containing clones became immortal without a crisis and, at later passage, exhibited elevated levels of telomerase and higher levels of hTERT without any apparent increase in HPV-16 copy number, E6 transcript levels, or ability to degrade p53. These results indicate that HPV-16 by itself does not necessarily cause telomerase activation in cervical keratinocytes, but rather, supports a model in which HPV-16 facilitates telomerase activation in conjunction with other viral or cellular changes over time.