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. These cells were also instrumental in the discovery that E1/E2 complex binding at the origin of DNA replication represses transcription from the E6/E7 promoter. Currently, this laboratory is using the BEF cells to further characterize the E6/E7 promoter. These studies have identified 3 critical SP1 sites upstream of the promoter and a region which is inhibitory to basal promoter activity. Mapping studies within this inhibitory region indicate that a consensus E2F site may be involved. As E2F/Rb complex bound at E2F sites have been shown to be transcriptional inhibitors, this finding raises the possibility that regulation of this promoter is influenced by the cell cycle. The other approach this laboratory has undertaken to identify host facts 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. This method has identified at least 20 mRNA species on Northern blots which are specifically expressed in the wart tissue as compared to uninfected bovine basal keratinocytes or BEF cells. Further characterization of the role these genes play in BPV-1 transcriptional regulation is underway.
