Abstract 5338: Transcriptional elongation mediates human papillomavirus type 16 late promoter activation

Abstract

Abstract Human papillomaviruses (HPVs) are small DNA viruses that infect keratinocytes of squamous epithelia and cause benign lesions that can progress to several malignancies, including cervical cancer. Upregulation of viral transcripts by the HPV16 late promoter is dependent on host cellular differentiation. We sought to investigate the main cellular transcription regulators that correlate with differentiation-dependent increase in the late viral transcripts. Here, we show evidence that the step in transcription cycle that is responsible for late promoter activation is transcriptional elongation. We began by establishing that the increase in viral transcripts originating from the late promoter is primarily regulated at the transcript synthesis level rather than post-transcription level. Based on this observation, we investigated whether there is a correlation between late promoter activation and activities that occur during the initiation, pausing or elongation steps of transcription cycle. Using chromatin immunoprecipitation (ChIP), we did not observed a differentiation-dependent increase of RNA Polymerase II (RNAP II) in the late promoter region. However, there was a significant increase of RNAP II at downstream sites of late promoter suggesting elongation is regulated by differentiation. We then sought to investigate the cyclin dependent kinases (CDKs) that are known to regulate transcription elongation. ChIP did not show a significant increase of the elongation factor CDK9 in the late promoter; however, the enrichment of CDK9 at downstream sites of the viral genome significantly increased upon differentiation, suggesting that differentiation induces recruitment of CDK9 to facilitate elongation. Additionally, CDK8, a component of the Mediator complex that recruits CDK9 to the RNAP II, was increased upon differentiation. Kinase inhibitors against CDK8 did not affect late viral transcripts; however, knocking down CDK8 resulted in significant reduction of viral transcripts, suggesting that CDK8 could be involved in protein-protein interactions that are required for the synthesis of late viral transcripts. These findings suggest that HPV has evolved to utilize cellular transcriptional elongation machinery as a way of regulating its late gene expression. This mechanism allows the virus to persistently infect host cells and cause HPV-associated malignancies. Citation Format: William Songock, Jason Bodily. Transcriptional elongation mediates human papillomavirus type 16 late promoter activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5338. doi:10.1158/1538-7445.AM2017-5338