published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Cervical cancer is a major cause of death in women and is strongly associated with infection by human papillomavirus (HPV). Integration of HPV is thought to form a key step in the formation of cancer, and is thought to involve the upregulation of HPV E6 and E7 due to the loss of E2 transcriptional control. Leptomycin B (LMB), a nuclear export inhibitor, has previously been shown to induce apoptosis in HPV-containing cancer cell lines and HPV 16 E7 or E6/E7 transduced primary keratinocytes, but not in normal cells. This thesis shows that LMB can induce apoptosis and a reduction in the colony survival of derivatives of the W12 cell line that contain HPV 16 in either episomal or integrated form. The HPV genome status, including variations in viral integration type, appears to influence the cumulative and temporal pattern of LMB-induced apoptosis. The effects of LMB were also apparent in cells grown in organotypic raft culture, with differences in behaviour again apparent between cells containing episomal and integrated HPV. As previously noted, treatment with LMB was associated with increased expression of the cell regulators p53 and p21; however, the induction of apoptosis was not dependent upon transcriptionally active p53. It is therefore likely that induction and mediation of LMB-induced apoptosis occurs via alternative, currently unidentified, pathways. These findings suggest that LMB can induce apoptosis in keratinocytes containing HPV 16 in either episomal or integrated form, with genome status and potentially lesion grade likely to influence the response of HPV-associated anogenital lesions to LMB treatment.

Indiana University-Purdue University Indianapolis (IUPUI) / Papillomaviruses (PVs) are small, double-stranded DNA viruses. Hundreds of species have evolved to replicate in mammals, birds, and reptiles. Approximately two hundred species are estimated to infect humans alone, and these human papillomaviruses (HPVs) cause diseases ranging from benign warts to anogenital and oropharyngeal cancers. While vaccination is effective at preventing the majority of these infections and their disease outcomes, there are no successful treatments for existing infections; thus, exploration of novel therapeutic targets is warranted. PVs control expression and function of their gene products through alternative splicing, alternate start codons, and post-translational modification (PTM). The viral E2 protein regulates transcription, replication, and genome maintenance in infected cells, and PTMs have been demonstrated for E2 proteins from multiple papillomavirus types. Serine phosphorylation events were reported to influence E2 stability, and our laboratory was the first to describe in vitro acetylation events with implications for E2 transcription function. Here we report confirmation of these acetylation events in vivo and additional data elucidating the role of these PTMs in viral transcription. Moreover, we present a novel phosphorylation site for bovine papillomavirus type 1 (BPV-1) E2 at tyrosine 102 (Y102). Using phospho-deficient and phospho-mimetic point mutants, we found that this site influences E2-mediated transcription and replication, and we hypothesize that phosphorylation at Y102 regulates these activities by interrupting the association of E2 with its binding partners. We also report interaction of BPV-1 E2 and HPV-31 E2 with different receptor tyrosine kinases (TKs), most notably members of the fibroblast growth factor receptor family. We hypothesize that Y102 phosphorylation by these receptors occurs early in infection to limit viral replication and gene expression. Further studies will cement the role of RTKs in PV biology and could reveal novel therapeutic strategies.