RESUMEN
Host pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs) detect viruses and other pathogens, inducing production of cytokines that cause inflammation and mobilize cells to control infection. Vaccinia virus (VACV) encodes proteins that antagonize these host innate immune responses, and elucidating the mechanisms of action of these viral proteins helped shed light on PRR signaling mechanisms. The VACV virulence factor E3 is one of the most intensely studied VACV proteins and has multiple effects on host cells, many of which cannot be explained by the currently known cellular targets of E3. Here, we report that E3 expression in human monocytes alters TLR2- and TLR8-dependent cytokine induction, and particularly inhibits interleukin (IL)-6. Using MS, we identified DExD/H-box helicase 9 (DHX9) as an E3 target. Although DHX9 has previously been implicated as a PRR for sensing nucleic acid in dendritic cells, we found no role for DHX9 as a nucleic acid-sensing PRR in monocytes. Rather, DHX9 suppression in these cells phenocopied the effects of E3 expression on TLR2- and TLR8-dependent cytokine induction, in that DHX9 was required for all TLR8-dependent cytokines measured, and for TLR2-dependent IL-6. Furthermore, DHX9 also had a cell- and stimulus-independent role in IL-6 promoter induction. DHX9 enhanced NF-κB-dependent IL-6 promoter activation, which was directly antagonized by E3. These results indicate new roles for DHX9 in regulating cytokines in innate immunity and reveal that VACV E3 disrupts innate immune responses by targeting of DHX9.
Asunto(s)
ARN Helicasas DEAD-box/genética , Interacciones Huésped-Patógeno/genética , Inmunidad Innata/genética , Proteínas de Neoplasias/genética , Proteínas de Unión al ARN/genética , Receptor Toll-Like 2/genética , Proteínas Virales/genética , Regulación Viral de la Expresión Génica , Interacciones Huésped-Patógeno/inmunología , Humanos , Interleucina-6/genética , Monocitos/virología , Regiones Promotoras Genéticas , Receptores de Reconocimiento de Patrones/genética , Receptor Toll-Like 8/genética , Vaccinia/genética , Vaccinia/virología , Virus Vaccinia/genética , Virus Vaccinia/patogenicidadRESUMEN
Innate immune DNA sensing underpins many physiological and pathological responses to DNA, including anti-viral immunity to DNA viruses. Although it has been appreciated for many years that cytosolic DNA can evoke a type I interferon response, it is only within the past decade that the cellular mechanisms responsible for such a response have been defined. Here we review the discoveries that led to an appreciation of the existence of cytosolic DNA sensor proteins, and discuss two key such sensors, cGAS and IFI16, in detail. DNA sensors operate via STING, a protein shown to have a central role in controlling altered gene induction in response to DNA in vivo, and as such to be central to a rapidly expanding list of both protective and harmful responses to DNA. We also discuss recent insights into how and when DNA stimulates innate immunity, and highlight current outstanding questions in the DNA sensing field.
