Infection by adeno-associated virus (AAV) is associated with lower cervical cancer rates. We have been investigating the hypothesis that AAV interacts with and inhibits the role of human papillomaviruses (HPV) in cervical cancer. We have been studying the response of bovine papillomavirus type 1 (BPV) oncogenic transformation and DNA replication to AAV as a prototype system. The AAV Rep78 gene product is responsible for this inhibition. Here, it is demonstrated that in two assay systems, focus formation of C127 cells and chloramphenicol acetyl-transferase (CAT, measuring P89 promoter expression) assays, the smaller the time interval between AAV introduction relative to PBV introduction, the higher the level of inhibition resulted. Preinfection with AAV was also effective in inhibiting BPV, but the effectiveness also decreased with increasing time intervals. These differences in inhibition demonstrate that the efficiency of AAV's inhibition of BPV changes dramatically with time (as much as 104 when delaying AAV infection) and possibly reflect temporal changes in viral gene expression by AAV, BPV, or both, which affect the AAV-papillomavirus interaction. It is further found that two different chimeric BPV/AAV genomes, equivalent to a specific simultaneous infection by these viruses at a specific ratio (which can't be duplicated by virus infection), were fully defective for oncogenic transformation and DNA replication. These chimeric BPV/AAV genomes were also able to trans-inhibit the wild-type BPV genome. Finally, and surprisingly, C127 cells with resident AAV Rep78 positive provirus were found to have increased sensitivity to oncogenic transformation by BPV. These data define the conditions under which an inhibitory affect of the AAV Rep78 gene on BPV phentotypes can be expected. However, under certain conditions AAV appears able to stimulate BPV oncogenic transformation. This final observation is not totally unexpected as Rep78 is a transcription factor known to both stimulate or repress AAV's own gene expression depending upon adenovirus coinfection.
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