Dr. Philip Branton
Rosalind and Morris Goodman Cancer Research Centre
Department of Oncology and Biochemistry
1. Named inaugural Scientific Director of the Institute of Cancer Research of the Canadian Institutes of Health Research, 2000
2. Fellow of the Royal Society of Canada, 2002
3. R.M. Taylor Medal, Canadian Cancer Society and the National Cancer Institute of Canada, 2005
4. Canadian Cancer Research Alliance (CCRA) Award for Exceptional Leadership in Cancer Research, 2011
5. Queen Elizabeth II Diamond Jubilee Medal, 2013
Dr. Branton’s laboratory studies the mode of action of two human adenovirus early region 4 products during infection and in normal and cancer cells.
Early viral products typically have evolved to modify cellular pathways to optimize the yield of progeny virions during productive infection. Those encoded by early region 4 of human adenoviruses are no exception. The E4orf4 protein alters both viral transcription and splicing patterns during infection, but more interestingly, when expressed alone at high levels, it induces the death of human cancer cells.
Cell toxicity is characterized by a significant mitotic delay followed by slow death due to mitotic catastrophe. At least in yeast, the defect in mitosis seems to be induced by the inappropriate activation of the E3 ubiquitin ligase, anaphase promotin complex (APC). A major target involved in E4orf4 killing is protein phosphatase 2A (PP2A). E4orf4 binds to the B55 class of regulatory subunits and inhibits phosphatase activity of this class of PP2A enzymes. Current work in Dr. Branton’s laboratory concerns the detailed analysis of the E4orf4 death pathway in human cells and yeast, and the mechanism of regulation of PP2A by E4orf4.
The E4orf6 protein, in cooperation with another early adenovirus product, E1B55K, regulates, among other things, the selective transport and stabilization of late viral mRNAs during lytic infection. E4orf6 forms a Cullin 2 or 5-based E3 ubiquitin ligase involving elongins B and C. E1B55K binds to this complex and introduces a variety of substrates for degradation. At present, it is still not known how this degradation complex regulates mRNA transport and metabolism. The best-known substrate of this complex is p53; however, Dr. Branton’s team and others have identified three additional substrates whose degradation promotes viral replication, and other substrates, perhaps many, clearly exist. Their work focuses on the mechanism of action of this complex and the identification of additional substrates, including those involved in mRNA regulation.