Bovine papillomavirus type 1 (BPV-1) has served as the prototype for studying the molecular biology of papillomaviruses. The papillomavirus life cycle has been refractory to study because of its link to the terminal differentiation of epithelium. Previous studies have utilized the ability of BPV-1 to transform rodent cells in culture to elucidate mechanisms of papillomavirus gene regulation. However, in order to investigate viral functions or interactions which may be specific to the natural host, this laboratory has recently begun to examine papillomavirus transcriptional control in the context of the natural host. The first approach employed toward this goal has been to perform transcriptional characterization studies in primary bovine embryo fibroblasts (BEF). In these cells, transcription from the viral promoters, expression of the viral genes, and replication of the viral genome all occur. Recently, this laboratory has been using the BEF cells to further characterize the P89 (E6/E7) promoter. Reporter constructs have been used to demonstrate that three SP1 sites upstream of this promoter are required for both basal promoter activity as well as E2-transactivated expression. The functional importance NF-1, AP1, E2F, and YY1 transcription factor binding sites are currently being investigated. The other approach this laboratory has undertaken to identify host factors involved in the control of papillomavirus transcription is to """"""""differentially display"""""""" (Liang and Pardee, Science 257:967) genes specifically expressed in BPV- 1 infected wart tissue. The PCR amplified cDNAs have been used to screen a bovine wart cDNA library. Approximately 50 genes have been identified using this approach and are currently being characterized by Northern blotting, DNA sequencing, and in situ hybridization. Among these genes are a number of genes, particularly the keratin genes, known to be differentially expressed in squamous epithelia, verifying the validity of this approach. An expression library is also being screened for proteins which bind to papillomavirus posttranscriptional regulatory elements.
