The E6 oncoprotein of bovine papillomavirus type 1 (BPV-1) can transform cells independently of p53 degradation. The precise mechanisms underlying this transformation are not yet completely understood. Here it is shown that BPV-1 E6 interacts with CBP/p300 in the same way as described for the E6 proteins of oncogenic human papillomaviruses. This interaction results in an inhibition of the transcriptional coactivator function of CBP/p300 required by p53 and probably by other transcription factors. The comparison of the CBP/p300-binding properties of BPV-1 E6 mutants previously characterized in transcription and transformation studies suggests (i) that the E6-CBP/p300 interaction may be necessary, but not sufficient, for cell transformation, and (ii) that the transcriptional activator function, inherent to the E6 protein, is not derived from forming a complex with CBP/p300.Bovine papillomavirus type 1 (BPV-1) causes fibropapillomas in its natural host (cattle), sarcoids in horses, nonproductive fibromas in rodents after experimental infection and foci in cell cultures like mouse c127 fibroblasts (Howley, 1996). As there is great interest in human papillomaviruses (HPVs) as a cause of genital cancer (International Agency for

The life cycles of human papillomaviruses (HPVs) are intimately linked to the differentiation program of infected stratified epithelia, with both viral gene expression and replication being maintained at low levels in undifferentiated basal cells and increased upon host cell differentiation. We recently identified, in HPV-16, a negative regulatory element between the epithelial-cell-specific enhancer and the E6 promoter that is capable of silencing E6 promoter activity, and we termed this element a papillomavirus silencing motif (PSM) and the unknown cellular factor that bound to it PSM binding protein (PSM-BP). Here we show that the homologous genomic segments of six other distantly related genital HPV types contain a PSM that binds PSM-BP and is capable of repressing transcription. Conservation of the PSM suggests that it is indispensable for the HPV life cycle. Purification, electrophoretic mobility shift assay experiments, and the use of specific antibodies proved that the cellular factor PSM-BP is identical to a previously described transcriptional repressor, the CCAAT displacement protein ( Human papillomaviruses (HPVs) infect mucosal and cutaneous epithelia and cause benign and malignant lesions, such as common warts, genital warts, and cervical cancer (29,67). Transcription of HPVs is regulated in a complex manner in response to the identity of the infected epithelial cell type, the differentiation state of the stratified epithelium, the physiological state of the host, and the episomal or chromosomally integrated state of the viral genome. Most of the cis-responsive elements that mediate the activity of cellular and viral factors on HPV gene regulation are located in the long control region (LCR), which lies between the 3Ј terminus of the L1 capsid gene and the start of the E6 oncogene. With a size of 850 bp in HPV-16 and a similar length in other genital HPVs, the LCR takes up about 11% of the 7.9-kb circular DNA genome. When one compares remotely related HPV types, one finds that their genes are clearly homologous but their LCRs have diverged so much that they cannot be unequivocally aligned and their nucleotide sequences lack long, similar segments. However, when one compares the LCRs of more closely related HPV types, such as the large group of genital HPVs, one finds many short similar cis-responsive elements, which are activated by a defined subset of the cellular transcription factors of the infected cell. This conservation of sequence and function suggests that these particular mechanisms are so appropriate for the biology of these HPV types that they could not undergo evolutionary changes (13, 44). Here we study such an element that is conserved among genital HPVs, and for the first time we describe an element that represses both transcription and replication, most probably in response to the differentiation of stratified epithelia.The central part of the LCR of genital HPVs functions as an epithelial-cell-specific transcriptional enhancer (14,23,50), and the 3Ј part contains the replication or...

Regulation of the human papillomavirus type 16 (HPV-16) E6 promoter is a complex process in which transcriptional repression as well as activation plays an important role. Here, we identify a negative regulatory element that in the context of a continuous long control region fragment overcomes the activation of the HPV-16 enhancer. This silencing element, which we have termed a PSM (papillomavirus silencing motif), consists of two copies of the sequence 5′-TAYAATAAT-3′ that overlap the origin of replication. Each copy of this 9-bp sequence binds the same unknown cellular factor, which we refer to as PSM-BP (PSM binding protein). Both copies of the binding sequence are required for transcriptional repression, and we provide evidence that suggests that this particular organization results in the stabilization of a PSM-BP dimer. The silencing motif, while functioning in either orientation, showed a positional requirement between the enhancer and the promoter. Experiments with both a heterologous enhancer and a promoter also demonstrated a general ability of this element to function as a transcriptional silencer in non-HPV systems. Our findings provide an important addition to our understanding of HPV-16 gene regulation and an interesting model for the study of transcriptional repression.