High-risk human papillomaviruses (HPVs) are associated with almost all cases of cervical carcinoma and also contribute to other anogenital tract carcinomas as well as oral carcinomas. During carcinogenic progression, the viral genome often integrates into a host chromosome, resulting in the deregulated expression of the viral E6 and E7 oncoproteins. High-risk HPV E6 and E7 promote the degradation of the p53 and pRB tumor suppressor proteins, respectively. Accordingly, the persistent expression of the E6 and E7 oncoproteins is necessary for the initiation and maintenance of the transformed phenotype of HPV-associated cancers. Nevertheless, the malignant progression of HPV-associated neoplasias is a slow and rather rare event and further mutations to the host genome are required for carcinogenic progression. Importantly, high-risk HPV E6 and E7 oncoproteins each subvert genomic integrity, likely through different mechanisms, and thereby create a cellular environment conducive to acquiring as well as perpetuating genomic mutations. We are particularly interested in understanding the mechanisms by which high-risk HPV type 16 (HPV16) E7 destabilizes the host genome to understand the contributions of this viral oncoprotein to malignant progression.
Our lab has previously shown that HPV16 E7 uncouples centrosome duplication from the cell division cycle. Because centrosomes play critical roles during mitosis and are essential for proper chromosome segregation, supernumerary centrosomes have been linked to the establishment of aneuploidy in many cancer cells. Therefore, we believe that HPV16 E7-induced centrosome overduplication contributes to genomic destabilization. In this dissertation, we describe a previously unknown interaction between HPV16 E7 and the centrosomal component γ-tubulin that contributes, in part, to HPV16 E7-mediated centrosome overduplication. Furthermore, in addition to centrosomal aberrations, mitotic errors, such as lagging chromosomes, are detected in HPV16 E7-expressing cells. In this dissertation, we also present a newly discovered function of HPV16 E7 that is associated with mitotic abnormalities and, hence, genomic instability. We show that HPV16 E7 associates with the microtubule stabilizing protein, nuclear mitotic apparatus protein 1 (NuMA), and delocalizes the microtubule motor dynein from mitotic spindles. Furthermore, cells expressing HPV16 E7 exhibit a prometaphase delay that we hypothesize may be a result of defects in chromosome alignment, a process that NuMA has been implicated in. These studies lend mechanistic insights into HPV16 E7-associated genomic destabilization and carcinogenic progression and provide information that is valuable in the understanding the origins of numerous cancer types.
