Date Published: August 8, 2018
Publisher: Public Library of Science
Author(s): Michelle Ainouze, Pauline Rochefort, Peggy Parroche, Guillaume Roblot, Issam Tout, François Briat, Claudia Zannetti, Marie Marotel, Nadege Goutagny, Philip Auron, Alexandra Traverse-Glehen, Aude Lunel-Potencier, Francois Golfier, Murielle Masson, Alexis Robitaille, Massimo Tommasino, Christine Carreira, Thierry Walzer, Thomas Henry, Katia Zanier, Gilles Trave, Uzma Ayesha Hasan, Paul Francis Lambert.
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-1β 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-1β. Yet, upon expression of the viral early genes, IL-1β 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-1β 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-1β. Our findings reveal a struggle between oncoviral persistence and host immunity; which is centered on IL-1β regulation.
The innate immune system is the first line of defense in response to danger signals from microbial invasion or tissue injury. Viruses are sensed by several immune receptors that activate signaling pathways leading to cytokine production. Many oncogenic viruses can deregulate several immune-related pathways which guarantee a persistent infection. High-Risk Human Papilloma Viruses (HR HPV) are the etiological factor of cervical as well as certain head and neck cancers and is responsible for 20% of all human cancers linked to infection . Persistence and progression of the disease are achieved by deregulating both cellular and immune defense mechanisms. Among the HR types, HPV16 is the most prevalent type in premalignant and malignant cervical lesions . HPV16 viral oncoproteins E6 and E7 can target many cellular proteins such as binding and degrading the tumor suppressors’ p53, and pRb, respectively. In parallel E6 and E7 are able to deregulate several innate immune-related pathways that block cytokine and chemokine production, antigen presentation, and adherence molecules . Recently Lau et al., showed that E7 from HPV18 suppresses the cGAS pathway by inhibiting the adapter protein STING . Similarly, some antiviral genes induced by interferons such as IFIT1, MX1 and the innate sensors RIG-I, TLR3 and TLR9 are also inhibited by HPV [5,6]. Indeed, Niebler et al., and Karim et al., have shown that HPV is capable of blocking IL-1β [7,8]. On the flip side, host cells have strategies to thwart viral immune escape.
We showed that human keratinocytes produce IL-1β when exposed to 16QsV. Furthermore, addition of recombinant IL-1β on 16QsV infected keratinocytes led to a block in viral gene transcription. Viral gene transcription was restored in the presence of an antagonist for the IL-1 receptor. More importantly we delineated that IL-1β gene transcription increased when exposed to 16QsV. These data show that HPV16 stimulates IL-1β secretion that has an anti-viral effect on infected cells. IL-1β depends on inflammasome activation; we have data showing that 16QsV was not sensed by NLPR3 or AIM2 (S5A Fig). Bone marrow derived macrophages from NLRP3 and AIM2 knock out mice were still able to produce IL-1β in the presence of 16QsV (S5A Fig). Therefore we still need to elucidate which innate-inflammasome sensor can detect 16QsV. However IL-1β gene expression began to decrease post 8h infection with 16QsV. These data implicate that HPV16 has developed an escape mechanism to block IL-1β production. Our findings are summarised in Fig 10.