Molecular Biology of SV40.
Simian virus 40 (SV40) belongs to a small collection of viruses that induce tumors. We utilize SV40 as a model system for understanding the molecular events that drive tumorigenesis. Our studies focus on the virus-encoded master regulatory protein, large T antigen. Large T antigen controls several aspects of viral infection including DNA replication, transcription and virion assembly. In addition, T antigen is necessary and, in most cases, sufficient for SV40-mediated tumorigenesis. T antigen induces tumors in rodents and the neoplastic transformation of cells in culture (Figure 1) by binding to key cellular proteins that regulate proliferation and survival, and altering their activities. Our basic strategy is to use a combination of genetics and proteomics to identify cellular targets of T antigen and then to use molecular biology and mouse model approaches to understand how these actions contribute to tumorigenesis.
Currently we are studying the biochemical mechanisms by which T antigen acts on complexes containing p130 or pRb with the E2F family of transcription factors, and how these actions contribute to neoplasia. Our studies are focused on understanding how the molecular chaperone function of T antigen through its J domain disrupts the p130/E2F4 repressive complex, and on how T antigen blocks the ability of pRb to repress E2F-dependent transcription.
We employ mouse model systems to study the effects of T antigen actions on Rb-E2F complexes in tumorigenesis. We have generated a series of transgenic mouse lines that express wild-type or various T antigen mutants in the intestinal epithelium (Figure 2). We have also generated gene knockout mice in which pRb or various E2Fs have been ablated (Chong et al. Nature 2009). We plan to use this combination of transgenic and gene knockout technologies coupled with molecular studies such as gene microarrays and ChIP experiments to explore differences in cell-cycle control exhibited by progenitor and differentiated cells.