Virological characteristics of cervical cancers carrying pure episomal form of HPV16 genome

- Integration of the HPV16 viral genome is not a necessary step and that an alternative mechanism exists.
- Virological characteristics which included viral lineage, E2 and LCR sequence variations are correlated to viral genome physical status.
- The alternate pathway is possibly by methylation within the E2 binding sites that are located in the HPV16 promoter.

ObjectiveMany studies on integration have reported conflicting results regarding the role of HPV integration in cervical cancer. We hypothesized that high viral load and disruption of E2 gene associated with integration of HPV were not the only pathway leading to cancer development.MethodsThis study analysed the viral load and integration status of HPV16, measured the HPV16 E6/E7 mRNA transcript levels, delineated the E2 and LCR sequence variation, and determined the methylation status of two E2 binding sites.ResultsThe results showed that viral load was not associated with the physical status of HPV genome. Levels of the three E6/E7 mRNA transcripts in invasive cervical cancers containing purely episomal viral genome were found to be similar to those containing integrated viral genome, suggesting that cancers containing episomal viral genome were also mediated by an up-regulated E6/E7 mRNA expression, and more importantly, did not depend on integration and disruption of the E2 gene.ConclusionsThe alternative mechanism that up-regulated the expression of E6 and E7 in invasive cancers harbouring episomal viral genome was likely to be a consequence of methylation of the two E2 binding sites located at the promoter region of HPV16. These observations are in line with the hypothesis that HPV integration was not the only mechanism leading to the development of cervical cancer.