Although the human papillomaviruses have been implicated in malignant disease, research on these viruses have been hampered because of the lack of a suitable tissue culture system. To understand the role of the papillomavirus genome in cell transformation, experiments have been designed to assign function to specific open reading frames in the transforming region of the genomes of two animal viruses active in culture; bovine papillomavirus type 1 (BPV-1) and deer papillomavirus (DPV). Studies will involve (i) perturbation of open reading frames within the transforming region and assaying the effect by cell transformation and (ii) synthesis by bacterial expression vectors of putative polypeptides encoded within the transforming region to determine if they are expressed in tumor cells. BPV-1 and DPV differentially transform mouse cells. BPV-1 transforms C127 and NIH/3T3 but not Balb/3T3 cells whereas DPV is unable to transform C127 cells. Experiments have been proposed to create chimeric genomes between these two viruses by recombination in vitro and in vivo and determine the transforming ability on the three cell lines. These studies may provide information into papillomavirus control mechanisms since chimeras will represent replicating and transforming domains derived from these two viruses. Three new BPV isolates molecularly cloned from DNA obtained from morphologically distinct teat papillomas will be further characterized. These virus genomes will be assayed for transformation in cell culture and their genomes analyzed by DNA sequencing. Sodium butyrate inhibits the growth of BPV-1-transformed mouse cells and decreases the BPV-1 genome copy number. Clones obtained from treated cultures have a flat phenotype. To study this further, BPV-1 DNAs obtained from flat revertants will be characterized to determine if they have been mutated and studies have also been proposed to determine kinetics of decay of the viral sequences and whether tumor promoters can reestablish the transformed phenotype in flat revertants. These studies should yield insights into the mechanism of transformation by papillomaviruses.
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