Infection with high-risk human papillomaviruses (HPVs) is the main cause of cervical cancer, the second most common cause of cancer-related mortality in women worldwide. High-risk HPV types, such as HPV-16, express two oncoproteins, E6 and E7, which function to subvert critical host cell cycle control mechanisms in order to promote viral genome amplification. Disruption of the pRB signaling axis and the p53-mediated stress response by the HPV E7 and E6 oncoproteins, respectively, results not only in aberrant proliferation but also in host cellular changes that can promote genomic instability. The high-risk HPV-16 E7 oncoprotein was found to induce centrosome abnormalities thereby disrupting mitotic fidelity and increasing the risk for chromosome missegregation and aneuploidy. Aneuploidy is frequently found in pre-malignant high-risk HPV-associated lesions and is a critical factor for malignant progression. This thesis was designed to determine the molecular mechanisms behind the ability of HPV-16 E7 to rapidly induce centriole overduplication. This rapid induction was found to be possible through the simultaneous formation of more than one daughter centriole at single maternal centrioles (centriole multiplication). It was previously discovered that the centriole multiplication pathway relied on cyclin E, CDK2 and PLK4. However, it was not known before how these molecular players cooperate in the centriole multiplication pathway or how HPV-16 E7 expression promotes the activation of this pathway. Here, we report that cyclin E/CDK2 mediates the aberrant recruitment of PLK4 to maternal centrioles. This initial recruitment step was not sufficient to induce centriole multiplication unless PLK4 protein levels were increased. We found that PLK4 protein levels were controlled by proteolysis, specifically by CUL1-based E3 ubiquitin ligase complexes localized at maternal centrioles. SCF activity was found to control not only baseline PLK4 protein stability but its activity-dependent degradation following cyclin E/CDK2 overexpression. High-risk HPV-16 E7 is known to deregulate cyclin E/CDK2 complexes and we found that ectopic expression of HPV-16 E7 promoted the aberrant recruitment of PLK4 to maternal centrioles. Since our previous experiments have shown that aberrant recruitment of PLK4 is not sufficient to drive centriole overduplication, we determined whether HPV-16 E7 may also disrupt PLK4 expression. We found that HPV-16 E7, but not low-risk HPV proteins or mutants of HPV-16 E7 that lack the ability to induce centriole overduplication, causes a moderate but significant upregulation of PLK4 mRNA. Besides centriole duplication control, we discovered that proteolysis also regulates other aspects of centriole synthesis such as regulation of daughter centriole length. Defining the precise molecular circuitry of centriole biogenesis will aid not only in deepening the current understanding of centriole biogenesis but also aid in identification of novel targets, such as CDK2 or PLK4, for small molecules to prevent centriole abnormalities, mitotic infidelity and malignant progression in pre-invasive high-risk HPV-associated lesions.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-05182010-163549 |
| Date | 26 May 2010 |
| Creators | Korzeniewski, Nina |
| Contributors | Stefan Duensing, M.D., Saleem Khan, Ph.D., Ole Gjoerup, Ph.D., Laura Niedernhofer, M.D., Ph.D., Martin Schmidt, 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-05182010-163549/ |
| 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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