The Mechanism of Human Papillomavirus E7 Protein Mediated S-Phase Reentry in the Squamous Epithelium
Advisory Committee Chair
Louise T Chow
Advisory Committee Members
Lawrence J Delucas
Jeffrey A Engler
Weei-Chin Lin
Hengbin Wang
Document Type
Dissertation
Date of Award
2010
Degree Name by School
Doctor of Philosophy (PhD) Heersink School of Medicine
Abstract
Though human papillomavirus infection of the human epidermis is epidemiologically widespread and typically benign, manipulation of the cell cycle within host tissues during infections can predispose the host to malignant neoplastic disease. The frequency of neoplastic progression associated with infection by a particular HPV type is directly related to its risk class; certain virus types are highly prevalent in neoplasia of HPV etiology, whereas other virus types are rarely associated with neoplastic malignancies. Regardless, the gene expression programs of both high-risk and low-risk HPV are sufficient for the production and transmission of viral progeny. In this thesis work we examine the molecular function the E7 protein of both the low-risk and the high-risk HPV E7 in the differentiated squamous epithelium. The E7 protein has direct implications in both cell-cycle dependent replication of the viral genome and deregulation of cellular proliferation associated with cancers through inactivation of E2F co-repressor complexes. By comparative and mutational analysis of both oncogenic and non-oncogenic E7 orthologs, we demonstrated the ubiquitous ability of the E7 gene to promote S-phase reentry in the suprabasal, differentiated strata of organotypic raft cultures. Unique molecular properties of the evaluated E7 orthologs provided further insight into the mode of cell-cycle regulation within the stratified epithelium and furthermore, how the function of the E7 protein is regulated. We demonstrated that E7 dependent destabilization of the retinoblastoma family E2F-corepressor p130 in the stratified epithelium is concomitant with S-phase reentry prerequisite for viral DNA amplification. This ability is shared by both oncogenic and non-oncogenic E7 types capable of inducing unscheduled DNA replication. Furthermore, we showed that this function is greatly enhanced by phosphorylation at the casein kinase II motif, which promotes E7 binding and destabilization of pocket protein repressors. In seminal works that both defined the high-risk E7 protein as an oncogene and characterized nonmutagenic, somatic inactivation of the retinoblastoma protein tumor suppressor, the pRB interaction was largely adopted as the biologically pertinent interaction of E7. These results provide a novel perspective on the archetypal role of E7 in cell-cycle regulation and establish precedence for alternative mechanisms of E7 function during the viral life cycle.
Recommended Citation
Genovese, Nicholas John, "The Mechanism of Human Papillomavirus E7 Protein Mediated S-Phase Reentry in the Squamous Epithelium" (2010). All ETDs from UAB. 1723.
https://digitalcommons.library.uab.edu/etd-collection/1723