Mechanisms of human papillomavirus type 16 E7 (HPV-16 E7)-induced disruption of centriole duplication control
by Korzeniewski, Nina M., Ph.D., UNIVERSITY OF PITTSBURGH, 2010, 120 pages; 3435424

Abstract:

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.

 
AdviserStefan Duensing
SchoolUNIVERSITY OF PITTSBURGH
SourceDAI/B 72-01, p. , Dec 2010
Source TypeDissertation
SubjectsGenetics; Virology
Publication Number3435424
Adobe PDF Access the complete dissertation:
 

» Find an electronic copy at your library.
  Use the link below to access a full citation record of this graduate work:
  http://gateway.proquest.com/openurl%3furl_ver=Z39.88-2004%26res_dat=xri:pqdiss%26rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation%26rft_dat=xri:pqdiss:3435424
  If your library subscribes to the ProQuest Dissertations & Theses (PQDT) database, you may be entitled to a free electronic version of this graduate work. If not, you will have the option to purchase one, and access a 24 page preview for free (if available).

About ProQuest Dissertations & Theses
With over 2.3 million records, the ProQuest Dissertations & Theses (PQDT) database is the most comprehensive collection of dissertations and theses in the world. It is the database of record for graduate research.

The database includes citations of graduate works ranging from the first U.S. dissertation, accepted in 1861, to those accepted as recently as last semester. Of the 2.3 million graduate works included in the database, ProQuest offers more than 1.9 million in full text formats. Of those, over 860,000 are available in PDF format. More than 60,000 dissertations and theses are added to the database each year.

If you have questions, please feel free to visit the ProQuest Web site - http://www.proquest.com - or call ProQuest Hotline Customer Support at 1-800-521-3042.