Determination of Polyomavirus' DNA J's Involvement in Cell Cycle Regulation through Association with Tumor Suppressors of the Retinoblastoma Susceptibility Gene Family
Turenne, Gaetan A.
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Tumor suppressors of the retinoblastoma susceptibility gene family (RB) regulate cell growth and differentiation. RB exists in a complex with the cellular transcription factor E2F that is disrupted by the binding of a viral oncogene such as polyomavirus. Hence in the presence of polyomavirus, E2F is released from the RB-E2F cell regulation complex, which subsequently results in the cell driving into S-phase. A single early gene product of polyoma, large T antigen, can by itself cause this cellular disruption. The binding site for RB on polyoma is obviously a relevant active site of this mechanism, but recent research has demonstrated that another site on the polyoma large T N-terminal also regulates the RB-E2F complex. Those studies have shown that an intact highly conserved HPD (histidine, proline, aspartic acid) region in the polyoma genome is required for large T's association with RB. It was demonstrated that it is the binding of this HPD region with a heat-shock protein (hsp 70) that is the functionally significant determinant of this other regulation site of the RB-E2F complex. In this work, the involvement of the QQA YK (glutamine, glutamine, alanine, tyrosine, lysine) region, which is neighbor to HPD, is assessed. Mutants in the QQA YK sequence were made and transfected into mouse fibroblasts to test for functionality. The mutants were shown to be partly defective in E2F transactivation. The exact mechanism in which the QQA YK mutants reduce the release of E2F from the RBE2F complex is not known but the results contained here, along with the results about the HPD region, link this region of large T to DNA J and attach to it the function of tumor suppressors regulator.With honors.