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

Abstract

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.

Expression of different L1 isoforms of Mastomys natalensis papillomavirus as mechanism to circumvent adaptive immunity

“…However, speculating about the mode of L1 isoform regulation, the following scenario could be envisioned: late PV transcripts are known to be strongly upregulated upon keratinocyte differentiation. However, due to insufficient suppressed late viral promoter activity, late transcripts can already be detected in undifferentiated cells ( Songock et al, 2017 ). Indeed, in contrast to mucosal types (e.g.…”

Mechanisms by which HPV Induces a Replication Competent Environment in Differentiating Keratinocytes

“…However, only the LIP (Liver-enriched Inhibitory Protein) and LAP (Liver-enriched Activator Protein) isoforms of C/EBPα have been shown to regulate late promoter activity [ 41 ]. More recent studies have shown that transcription elongation regulates late promoter activity through the recruitment of elongation mediators (e.g., CDK8, BRD4) to viral genomes upon differentiation [ 42 ]. Late gene expression is also regulated by alternative splicing and changes in polyadenylation site usage [ 16 ].…”

Keratinocyte Differentiation-Dependent Human Papillomavirus Gene Regulation

“…Although RNA polymerase II is bound at the late promoter in undifferentiated keratinocytes, elongation is inefficient and does not progress to the late region. In contrast, in differentiated cells, the enhancer recruits members of the BET family proteins—including Brd4 and its binding partner CDK8—to the Mediator complex to stimulate transcription elongation [ 48 ]. Changes in signaling during keratinocyte differentiation must also regulate the late promoter, for example PKCδ [ 49 ] has been shown to activate it.…”