In normal cells, the p53 tumour suppressor induces cell cycle arrest or apoptosis in response to a variety of stresses, including DNA damage and ectopic oncogene expression. However, cellular pathways controlled by p53 are compromised in virtually all cancers. Defining the mechanisms regulating p53 activity in normal and tumour cells has therefore been a major priority in cell biology and cancer research. / In this study, we characterized two important regulatory mechanims of p53 activity: (i) Human papillomavirus (HPV) E6 interaction and (ii) alternative splicing. Recognized as the major etiological agents for cervical cancer, the oncogenic potential of HPVs correlates with their ability to target p53 for degradation. This study demonstrates that both p53 and HPV-18 E6 are exported from the nucleus when co-expressed, via a process that involves the C-terminal nuclear export signal (NES) of p53. However, neither nuclear export nor the p53 C-terminal NES is required for HPV-18 E6-mediated ubiquitination or degradation of p53. / This study also demonstrates that both low- and high-risk HPV E6 proteins are degraded by the ubiquitin-proteasome pathway, and thus provides an explanation for the low levels of E6 detected in cervical cancer cells. / Also reported in this study is a novel mechanism of p53 regulation arising through alternative splicing. This novel mRNA encodes a N-terminal deleted isoform of p53, termed p47. As demonstrated within, p47 does not supress cell viability but impairs both p53-mediated transcriptional activity and growth suppression. Interestingly, p47 increases both p53 monoubiquitination and nuclear export. We propose that p47 induces nuclear export of p53 by a mechanism involving monoubiquitination, as supported by recent findings from Li and colleagues (2003). The p47 protein also protects p53 from both Mdm2- and HPV-18 E6-mediated degradation. A number of cancers display abnormal localization of wildtype p53, and it will be important to examine the role of p47 in these tumours. / Taken together, the regulation of p53 activity by both HPV E6 and the alternative splice variant p47 involves alterations in p53 ubiquitination status, protein stability, and cell localization. Insight gained into these negative regulatory mechanisms may aid in the design of therapeutic strategies for reactivating wild-type p53 in HPV-associated and non-associated cancers.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85651 |
| Date | January 2004 |
| Creators | Stewart, Deborah |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Institute of Parasitology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002209067, proquestno: AAINR12950, Theses scanned by UMI/ProQuest. |
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