Summary auto-generated
This study examines how the transcription factor YY1 regulates the E6 promoter of human papillomavirus type 8 (HPV-8), a cutaneous virus associated with skin cancers in epidermodysplasia verruciformis patients. Using DNase I footprinting and gel retardation assays, researchers identified three functional YY1 binding sites (BS1, BS2, and BS3) clustered around the HPV-8 E6 transcription start site. Functional analysis in human keratinocytes revealed that YY1 exerts bidirectional control: binding to the upstream site (BS1) activates transcription, while binding to downstream site BS2 represses it, with BS3 enhancing the repressive effect of BS2. This dual regulation mechanism appears unique among papillomaviruses, providing fine-tuned control of the E6 oncogene. The findings establish YY1 as an important cellular regulator of skin-specific HPV-8 oncogene expression and highlight the previously unrecognized regulatory role of sequences downstream of the transcription start site in papillomavirus promoters.
Key findings
- HPV-8 E6 promoter contains three functional YY1 binding sites with dual regulatory functions: upstream BS1 activates transcription while downstream BS2 and BS3 repress it
- YY1 binding to site 2 alone increases promoter activity 3.2-fold, while combined mutations of sites 2 and 3 enhance activity 4.8-fold
- Downstream YY1 binding sites in the HPV-8 E6 promoter represent an unusual arrangement not previously described in papillomavirus promoters
- The balance between positive and negative YY1 effects provides fine-tuned regulation of HPV-8 E6 oncogene expression in a single cell line under identical conditions
- BS2 location corresponds to the translational start codon of E6, suggesting that YY1 binding sites may be conserved features near translation initiation sites in many genes
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Abstract
Human papillomavirus type 8 (HPV-8) is a strictly cutaneous oncogenic virus known to induce malignant skin lesions in epidermodysplasia verruciformis patients. Our study shows that sequences surrounding transcription start sites of the HPV-8 oncogene E6 (nt 175-179) and comprising the presumable CCAAC and TATA boxes of the E6 promoter P175 contain a cluster of four motifs similar to the DNA recognition site of the multifunctional cellular transcription factor yin-yang 1 (YY1). Using DNase I footprinting and gel retardation tests it could be demonstrated that three of these motifs indeed act as YY1 binding sites. To test their functional relevance for P175 activity, engineered YY1 binding site mutants were analysed in the context of a P175 test vector using transient expression assays with human keratinocytes. YY1 turned out to exert both positive and negative effects upon the activity of the HPV-8 E6 promoter; binding of YY1 to a site upstream of the promoter's cap-position (BS1) activated transcription, whereas the downstream site (BS2) mediated repression. The second downstream YY1 binding site (BS3) seemed to play an auxiliary role, enhancing the negative effect of YY1 BS2. These observations define YY1 as an important cellular protein involved in the control of E6 oncogene expression of the skin-specific 'high risk' HPV-8 and emphasize the potential regulatory role of sequences located downstream of the transcription start site.