Activation of cellular tumor suppressor pathways is the cell's major defense against cancer induced by activated oncogenes. The ARF-p53 tumor suppressor pathway, which is one of the most important in mammalian cells, can be activated by a number of viral and cellular oncogenes. Activated ARF induces a p53-mediated block to cell division via a cell cycle arrest or apoptotic cell death. How oncogenic stress activates ARF remains to be elucidated. Polyoma virus middle T-antigen (PyMT) is a potent oncogene able to bind a number of key regulatory cellular proteins and activate a number of important cellular signaling pathways including the ARF-p53 tumor suppressor pathway. We will use PyMT as a model oncogene in order to better understand how ARF is being activated. We hypothesize that PyMT induces ARF by the inappropriate activation of one or more cellular signaling pathways that also mediate the ability of PyMT to transform cells. Our plan is to identify the cellular signaling pathways induced by PyMT that results in activation of ARF. REF52 cells differ from most other established cell lines in containing an intact ARF-p53 tumor suppressor pathway and are distinct in resembling primary cells in their requirement for oncogene cooperation for their transformation. PyMT activates the ARF-p53 pathway, blocking REF52 cell division and will not transform REF52 cells in the absence of a co-operating oncogene. We plan to take advantage of these unique properties of REF52 cells to isolate PyMT and cell mutants that are involved in the activation of ARF. Three interrelated aims will be pursued.
Aim -1 will be to use previously isolated PyMT mutants to identify which domains of PyMT are required to activate ARF.
Aim -2 will be to use mutagenized PyMT to identify sequences in both defined and undefined regions of PyMT that are required for the activation of the ARF-p53 pathway in REF52 cells.
Aim -3 will be to isolate and define REF52 cellular mutants in which PyMT signaling fails to activate the ARF-p53 tumor suppressor surveillance pathway. We believe that such cell mutants will help to differentiate between normal and oncogene activation of important cellular signal transduction pathways. Understanding the mechanism(s) of oncogenic activation of the ARF-p53 tumor pathway will help in designing better drugs and therapies for the treatment of cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Virology Study Section (VR)
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Read-Connole, Elizabeth Lee
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University of California San Francisco
Internal Medicine/Medicine
Schools of Medicine
San Francisco
United States
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Rodriguez-Viciana, P; Collins, C H; Moule, M G et al. (2006) Chromosomal instability at a mutational hotspot in polyoma middle T-antigen affects its ability to activate the ARF-p53 tumor suppressor pathway. Oncogene 25:1454-62
Rodriguez-Viciana, Pablo; Collins, Crista; Fried, Mike (2006) Polyoma and SV40 proteins differentially regulate PP2A to activate distinct cellular signaling pathways involved in growth control. Proc Natl Acad Sci U S A 103:19290-5
Hunt, Abigail E; Moule, Madeleine G; Fried, Mike (2006) The rat ARF protein is translated from two closely spaced ATG start codons and can transcriptionally activate p53 in the absence of p53 protein stabilization. Cell Cycle 5:1324-30
Moule, Madeleine G; Collins, Crista H; McCormick, Frank et al. (2004) Role for PP2A in ARF signaling to p53. Proc Natl Acad Sci U S A 101:14063-6