Abstract
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.