Regulation of the human papillomavirus type 16 late promoter by transcriptional elongation

- The HPV16 late promoter is upregulated by transcriptional rather than posttranscriptional mechanisms.
- Promoter upregulation upon differentiation is associated with increased Pol II occupancy at the 3′ end of the early region.
- Elongation factor CDK9 associates with HPV16 genomes upon differentiation; late promoter upregulation requires CDK9 activity.
- CDK8 and Brd4 are recruited to the viral genome upon differentiation and contribute to promoter activity.

Transcripts from the late promoter of human papillomavirus type 16 (HPV16) are upregulated upon host cell differentiation. Differentiation-dependent transcript regulation is thought to sequester viral antigens in the uppermost epithelial layers, facilitating immune evasion. The mechanisms regulating late promoter upregulation during differentiation are poorly characterized. We show that the late promoter is upregulated at the transcriptional level and that the viral enhancer stimulates promoter activity. Using kinase inhibition and chromatin immunoprecipitation analysis, we show evidence for differentiation-dependent enhancement of transcript elongation. Three factors that promote transcript elongation, cyclin dependent kinase 9 (CDK9), CDK8 (a subunit of the Mediator complex), and bromodomain containing protein 4 (Brd4) are recruited to viral genomes upon differentiation, and each plays a role in promoter activity. These results shed light on the transcriptional processes utilized by HPV16 for proper regulation of gene expression during the viral life cycle.