Displacement of YY1 by Differentiation-Specific Transcription Factor hSkn-1a Activates the P670Promoter of Human Papillomavirus Type 16

ABSTRACTTranscription from human papillomavirus type 16 (HPV16) P670, a promoter in the E7 open reading frame, is repressed in undifferentiated keratinocytes but becomes activated upon differentiation. We showed that the transient luciferase expression driven by P670was markedly enhanced in HeLa cells cotransfected with an expression plasmid for human Skn-1a (hSkn-1a), a transcription factor specific to differentiating keratinocytes. The hSkn-1a POU domain alone, which mediates sequence-specific DNA binding, was sufficient to activate the expression of luciferase. Electrophoretic mobility shift assay revealed the presence of two binding sites, sites 1 and 2, upstream of P670, which were shared by hSkn-1a and YY1. Site 1 bound more strongly to hSkn-1a than site 2 did. YY1 complexing with a short DNA fragment having site 1 was displaced by hSkn-1a, indicating that hSkn-1a's affinity with site 1 was stronger than YY1's. Disrupting the binding sites by nucleotide substitutions raised the basal expression level of luciferase and decreased the enhancing effect of hSkn-1a. In HeLa cells transfected with circular HPV16 DNA along with the expression plasmid for hSkn-1a, the transcript from P670was detectable, which indicates that the results obtained with the reporter plasmids are likely to have mimicked the regulation of P670in authentic HPV16 DNA. The data strongly suggest that the transcription from P670is repressed primarily by YY1 binding to the two sites, and the displacement of YY1 by hSkn-1a releases P670from the repression.