Integration of the full-length HPV16 genome in cervical cancer and Caski and Siha cell lines and the possible ways of HPV integration

Integration of high-risk human papillomavirus (HPV) into the host genome is a key event for cervical carcinogenesis. Different methods have been used to explore the physical states of the HPV genome to reveal the mechanisms for malignant transformation of the infected cells. Consensus has been reached that, although variable portions of the HPV genome are deleted in the integrated HPV sequences, common disruption of the viral E2 gene has been demonstrated in different studies. The head-to-tail concatemers of the full-length HPV16 genome is another typical integration pattern of HPV16, typically found in Caski cell lines, but its prevalence in cervical cancer has never been tested. Here, by introducing a modified PCR, we identified this head-to-tail concatemers of full-length HPV genomes in advanced cervical cancer with HPV16 single positive. Our results show that more than half of the cases contain this integrated head-to-tail concatemers of full-length HPV16 genomes. Further studies in two cervical cell lines, Caski cells and Siha cells, revealed a correlation between the prevalence of the spliced variants of integrated HPV16 sequences and the full-length transcription of the integrated head-to-tail concatemers of the full-length HPV16 genome. Based on these results, we propose that HPV16 integrated into host cells by two mechanisms: one mechanism is shared by other DNA virus and cause integration of the head-to-tail concatemers of the viral genome; another is related to the reverse transcription process, which the integrated HPV sequence is generated by the reverse transcription of the viral mRNA.