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Scientist: London Regional Cancer Program, London Health Sciences Centre, London, Ontario
Associate Editor: Molecular Cancer
London Regional Cancer Program
Room A4-837, Cancer Research Laboratory Program
790 Commissioners Rd. E.
Canada N6A 4L6
Tel: 519.685.8600, ext. 53012
Lab: 519-685-8600 ext. 53016
It is estimated that viruses are responsible for about 15% of human cancers. In this respect, viruses are a risk factor for cancer second only to tobacco. Human papillomavirus (HPV) infection is thought to account for about two-thirds of these cancers, and nearly all cervical cancers in particular. Infection with HPV forces quiescent cells to enter the cell division cycle. This abnormal cell proliferation initiates progression to the cancer phenotype in combination with virally induced chromosomal instability, evasion of the host immune response and suppression of programmed cell death. E6 and E7 are the two key viral proteins that are required for these activities. E7 binds pRB, the product of the retinoblastoma tumor susceptibility locus, which is an important regulator of cell growth. This interaction is not sufficient for the effects of E7 on cell growth, indicating that E7 targets additional cellular proteins.
Human adenovirus differs from HPV in that it they are not known to be associated with human cancers. However, they can oncogenically transform cells in culture, providing an important model for cancer research. The adenoviral E1A and E1B oncogenes encode two key viral proteins required for transformation. Like E7, E1A binds pRB and many other cellular regulatory proteins.
We are interested in discovering new targets of the E1A and E7 oncoproteins and learning more about their effects on cellular functions. We use genetic and biochemical approaches to study their effect on cell growth. Our goal is to use these viral oncogenes as tools to identify and characterize cellular regulatory pathways that, when altered, contribute to cancer formation and its spread throughout the body. Surprisingly, the E1A proteins also possess anti-oncogenic properties and can suppress oncogenic transformation, tumorigenicity and metastasis. For this reason, studies of E1A function will help us identify events that can contribute to tumour formation as well as allow us to identify mechanisms that can inhibit the spread of cancer in an afflicted individual.
Cancer is the direct result of alterations in gene expression that lead to unrestricted cell growth. For this reason, an understanding of the molecular basis of cancer demands an in-depth understanding of the regulation of gene expression. The proteins encoded by Early Region 1A (E1A) of human adenovirus and the E7 proteins of human papillomavirus are powerful tools for investigating the relationship between gene regulation and aberrant cell growth because of the large number of gene and growth regulatory activities they perform.
Although studied extensively, much remains to be learned about the mechanisms by which these viral oncogenes reprogram cell growth and differentiation, largely because of the technical difficulties associated with genetic analysis in mammalian cells. In contrast, powerful molecular genetic tools are available for these types of studies in the simple eukaryote Saccharomyces cerevisiae. The conservation of many important biological processes between yeast and higher eukaryotes makes yeast a particularly useful model organism. Importantly, E1A and E7 have been shown to interact with multiple regulatory pathways in yeast to deregulate growth and transcription. Our analysis of E1A and E7 function in S. cerevisiae will identify new protein targets of these viral oncoproteins and increase our understanding of the mechanisms by which they and their interacting proteins modulate cell growth and differentiation. We will then pursue these studies in relevant mammalian cell models. The information obtained regarding the mechanisms regulating cell growth and development may help define novel targets for cancer therapies or suggest strategies to prevent cancer.
Molecular genetic analysis of adenovirus E1A function (CIHR funded)
The E1A proteins target multiple cellular regulatory proteins and these interactions form the molecular basis by which E1A alters cell growth and gene expression. Our studies have demonstrated that at least some of these targets are conserved in the yeast S. cerevisiae. We propose to perform a molecular genetic analysis of E1A function that will identify new targets of E1A and the protein binding motifs mediating these interactions. We are also investigating the mechanisms by which these proteins, as well as other known E1A taargets, regulate conserved biological processes.
We are seeking to:
Molecular genetic analysis of human papillomavirus (HPV) 16 E7 function (CIHR funded)
The E7 proteins of HPV target multiple cellular regulatory proteins and these interactions alter cell growth and gene expression. We are undertaking a detailed struncture-function analysis of HPV16 E7 function.
We are seeking to:
1: Systematically mutate all solvent exposed residues in HPV16 E7
2: Assess the dimerization properties of E7
3: Assess the ability of E7 mutants to bind pRb and induce its degradation
Identification and analysis of non-conventional nuclear import signals (NSERC funded)
Proper protein function often requires targeting to particular sub-cellular compartments via specific localization signals. Nuclear import of cellular and viral proteins is typically mediated by their physical interaction with soluble cytosolic receptor proteins via nuclear localization signals (NLS). The proteins encoded by the early region 1A (E1A) gene human of adenovirus type 5 (Ad5) influence a variety of transcriptional and cell cycle events by interacting with a number of cellular regulatory factors in the nucleus. The Ad5 E1A proteins contain a well characterized monopartite NLS located near the C-terminus. However, this signal is not conserved in the E1A proteins of many other human adenoviruses, which also lack any other canonical NLSs. Additional regions of Ad5 E1A can also mediate nuclear import, suggesting that E1A contains multiple non-canonical NLSs that function via unknown pathways. As such, the E1A proteins provide an excellent model system to identify and characterize novel mechanisms that contribute to nuclear localization.
Our objective is to use the E1A proteins to identify and elucidate mechanisms by which nuclear import of cellular proteins is regulated. We are using several different approaches in both the yeast S. cerevisiae and mammalian cells to pursue these studies.
Post Doctorates:Dr.Peter Pelka, Department of Microbiology & Immunology
Graduate Students:Jai Ablack, PhD Student, Department of Microbiology & Immunology
Biljana Todorovic, PhD Student, Department of Microbiology and Immunology
Project: Cell cycle deregulation by HPV16 E7
Email Biljana Todorovic
Kathy Hung, MSc
Email Kathy Hung