High-risk human papillomaviruses (HPVs), such as HPV-16, are the etiological agents of squamous cell carcinomas (SCCs) of the anogenital tract and a subset of oropharyngeal cancers. High-risk HPVs encode two oncoproteins, E6 and E7, which promote unscheduled host cell proliferation by targeting the p53 and pRB tumor suppressor proteins, respectively. HPV-16 E7 has been shown to stimulate structural chromosomal instability and DNA breakage. These findings raise several important questions. First, how does HPV-16 E7 induce DNA damage? Second, what are the precise consequences of HPV-16 E7-induced DNA damage for host cell genomic integrity, and lastly, how do HPV-16 E7-expressing cells maintain proliferation despite activated DNA damage checkpoints? Here, we show that HPV-16 E7 activates the Fanconi Anemia (FA) pathway, a branch of the host cell DNA damage response that primarily responds to stalled DNA replication forks. Importantly, we show that HPV-16 E7 expression in FA-deficient cells accelerates the formation of structural chromosomal alterations, which may help to explain the heightened susceptibility of FA patients to HPV-associated tumors. However, we also provide evidence that HPV-16 E7-induced FA pathway activation in FA-proficient cells may contribute to evasion of anti-proliferative host cell barriers by promoting alternative lengthening of telomeres (ALT). Finally, we demonstrate that HPV-16 E7 circumvents DNA damage checkpoint control and promotes aberrant mitotic entry by increasing the proteolytic turnover of claspin, which plays a role in the ATR/CHK1-mediated replication stress response. Collectively, our results underscore that HPV-16 E7 interferes with host cell genome integrity by inducing DNA replication stress. The detrimental effects of HPV-16 E7 on the genomic integrity of host cells with a deficient FA pathway support the notion that this DNA damage response pathway is crucial to prevent HPV-16 E7-induced genomic instability and malignant progression. However, we also provide evidence that HPV-16 E7 can exploit the FA pathway to promote cellular immortalization. Future experiments to explore these events for cancer therapy and/or prevention are warranted.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08052009-121401 |
| Date | 07 August 2009 |
| Creators | Spardy, Nicole Ann |
| Contributors | James Pipas, Ph.D., Neal DeLuca, Ph.D., Laura Niedernhofer, M.D., Ph.D., Stefan Duensing, M.D., Saleem Khan, Ph.D. |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08052009-121401/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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