trans activation by the full-length E2 proteins of human papillomavirus type 16 and bovine papillomavirus type 1 in vitro and in vivo: cooperation with activation domains of cellular transcription factors.

Papillomaviral E2 genes encode proteins that regulate viral transcription. While the full-length bovine papillomavirus type 1 (BPV-1) E2 peptide is a strong trans activator, the homologous full-length E2 product of human papillomavirus type 16 (HPV-16) appeared to vary in function in previous studies. Here we show that when expressed from comparable constructs, the full-length E2 products of HPV-16 and BPV-1 trans activate a simple E2- and Sp1-dependent promoter up to approximately 100-fold in human keratinocytes and other epithelial cells as well as human and animal fibroblasts. Vaccinia virus-expressed, purified full-length HPV-16 and BPV-1 E2 proteins bound a consensus E2 site with high specific affinities (Kd = approximately 10(-9) M) and stimulated in vitro transcription up to six- to eightfold. In vivo and in vitro trans activation by either E2 protein required cooperation with another activator, such as Sp1, or other factors that interact with papillomavirus promoters, such as AP-1, Oct-1, nuclear factor 1/CTF, transcriptional enhancer factor 1, or USF. The glutamine-rich domain B of Sp1 or the mutually unrelated activation domains of other transcription factors were necessary and sufficient for cooperation with either E2 factor. We conclude that like BPV-1 E2, the HPV-16 E2 protein has the potential to function as a strong activator of viral gene expression in cooperation with cellular transcription factors.

Transcriptional enhancer factor (TEF)-1 and its cell-specific co-activator activate human papillomavirus-16 E6 and E7 oncogene transcription in keratinocytes and cervical carcinoma cells.

The human papillomavirus (HPV)-16 oncogenes, E6 and E7, are transcribed preferentially in keratinocytes and cervical carcinoma cells due to a 5' enhancer. An abundant peptide binding to a 37 nt enhancer element was purified from human keratinocytes by sequence-specific DNA chromatography. This protein was identified as transcriptional enhancer factor (TEF)-1 by complex mobility, binding to wild-type and mutant SV40 and HPV-16 enhansons and antigenic reactivity with two anti-TEF-1 antibodies. TEF-1 is cell-specific, but its transactivation also depends on a limiting, cell-specific TEF-1 'co-activator'. We show that both TEF-1 and the TEF-1 co-activator are active in human keratinocytes and essential for HPV-16 transcription. TEF-1 binding in vivo was necessary for HPV-16 P97 promoter activity. Excess TEF-1 and chimeric GAL4-TEF-1 specifically inhibited the P97 promoter by 'squelching', indicating that HPV-16 transcription also requires a limiting TEF-1 co-activator. TEF-1 and the TEF-1 co-activator functions mirrored HPV-16 transcription by their presence in keratinocytes and cervical carcinoma cells and their absence from lymphoid B-cells, but also functioned in liver cells where the HPV-16 promoter is inactive. TEF-1 and its associated co-activator are thus part of a complex mechanism which determines the restricted cell range of the HPV-16 E6 and E7 oncogene promoter.