ABSTRACT
Human papillomavirus type 16 (HPV16) and other oncoviruses have been shown to block innate immune responses and to persist in the host. However, to avoid viral persistence, the immune response attempts to clear the infection. IL-1ß is a powerful cytokine produced when viral motifs are sensed by innate receptors that are members of the inflammasome family. Whether oncoviruses such as HPV16 can activate the inflammasome pathway remains unknown. Here, we show that infection of human keratinocytes with HPV16 induced the secretion of IL-1ß. Yet, upon expression of the viral early genes, IL-1ß transcription was blocked. We went on to show that expression of the viral oncoprotein E6 in human keratinocytes inhibited IRF6 transcription which we revealed regulated IL-1ß promoter activity. Preventing E6 expression using siRNA, or using E6 mutants that prevented degradation of p53, showed that p53 regulated IRF6 transcription. HPV16 abrogation of p53 binding to the IRF6 promoter was shown by ChIP in tissues from patients with cervical cancer. Thus E6 inhibition of IRF6 is an escape strategy used by HPV16 to block the production IL-1ß. Our findings reveal a struggle between oncoviral persistence and host immunity; which is centered on IL-1ß regulation.
Subject(s)
Gene Expression Regulation/immunology , Immune Evasion/immunology , Interferon Regulatory Factors/metabolism , Interleukin-1beta/biosynthesis , Papillomavirus Infections/immunology , Human papillomavirus 16/immunology , Humans , Interferon Regulatory Factors/immunology , Interleukin-1beta/immunology , Keratinocytes/immunology , Keratinocytes/metabolism , Keratinocytes/virology , Oncogene Proteins, Viral/metabolism , Papillomavirus Infections/metabolism , Repressor Proteins/metabolismABSTRACT
The stimulation of TLRs by pathogen-derived molecules leads to the production of proinflammatory cytokines. Because uncontrolled inflammation can be life threatening, TLR regulation is important; however, few studies have identified the signaling pathways that contribute to the modulation of TLR expression. In this study, we examined the relationship between activation and the transcriptional regulation of TLR9. We demonstrate that infection of primary human epithelial cells, B cells, and plasmacytoid dendritic cells with dsDNA viruses induces a regulatory temporary negative-feedback loop that blocks TLR9 transcription and function. TLR9 transcriptional downregulation was dependent on TLR9 signaling and was not induced by TLR5 or other NF-κB activators, such as TNF-α. Engagement of the TLR9 receptor induced the recruitment of a suppressive complex, consisting of NF-κBp65 and HDAC3, to an NF-κB cis element on the TLR9 promoter. Knockdown of HDAC3 blocked the transient suppression in which TLR9 function was restored. These results provide a framework for understanding the complex pathways involved in transcriptional regulation of TLR9, immune induction, and inflammation against viruses.
