Human Papillomavirus integration:\ud The mechanism(s) behind the high-risk associated with this event and cervical disease progression

Cervical cancer is the second most common cancer among women worldwide. Infection with Human Papillomavirus (HPV) is essential but not the only contributing factor in cervical cancer development. HPV integration is reported to be present in over 80% of cervical cancers and disruption of HPV genome through integration leads to high levels of HPV oncogene expression. DNA damage and repair pathways are thought to induce HPV integration since HPV is detected at fragile sites in the human genome. There is controversy as to whether integration is an early or late event in cervical oncogenesis and there are no published studies to date that have investigated HPV integration using sensitive, DNA based, techniques at the nucleotide level in cervical precancers. This study aimed to test the hypothesis that integration is an early event in cervical neoplasia and episomal loss causes malignant transformation through transcription of integrated HPV. Also, this study served to pilot whether HPV integration can predict high-grade cervical disease in women with cytological abnormalities with an aim to improve current cervical screening methods. Assays to detect integration and E2 as a marker of episomal state were developed for HPV16, HPV18 and HPV45 and applied to cervical smears and biopsies from women with varying disease grades. The data presented in this thesis highlight that integration may not be essential for cervical cancer progression and different modes of disease progression may exist between young women and older women. Integration was detected at chromosome fragile sites but was more prevalent at SINE or LINE repeat elements; this implies a role for retroelements in the mechanism of integration. Finally, the data here suggest that integration induces a unique selective process in each individual and clonal selection may arise due to altered HPV oncogene expression and/or disruption to human gene expression.