title: Induction of interferon-stimulated genes by IRF3 promotes replication of Toxoplasma gondii.
abstract: Innate immunity is the first line of defense against microbial insult. The transcription factor, IRF3, is needed by mammalian cells to mount innate immune responses against many microbes, especially viruses. IRF3 remains inactive in the cytoplasm of uninfected cells; upon virus infection, it gets phosphorylated and then translocates to the nucleus, where it binds to the promoters of antiviral genes and induces their expression. Such genes include type I interferons (IFNs) as well as Interferon Stimulated Genes (ISGs). IRF3-/- cells support enhanced replication of many viruses and therefore, the corresponding mice are highly susceptible to viral pathogenesis. Here, we provide evidence for an unexpected pro-microbial role of IRF3: the replication of the protozoan parasite, Toxoplasma gondii, was significantly impaired in IRF3-/- cells. In exploring whether the transcriptional activity of IRF3 was important for its pro-parasitic function, we found that ISGs induced by parasite-activated IRF3 were indeed essential, whereas type I interferons were not important. To delineate the signaling pathway that activates IRF3 in response to parasite infection, we used genetically modified human and mouse cells. The pro-parasitic signaling pathway, which we termed PISA (Parasite-IRF3 Signaling Activation), activated IRF3 without any involvement of the Toll-like receptor or RIG-I-like receptor pathways, thereby ruling out a role of parasite-derived RNA species in activating PISA. Instead, PISA needed the presence of cGAS, STING, TBK1 and IRF3, indicating the necessity of DNA-triggered signaling. To evaluate the physiological significance of our in vitro findings, IRF3-/- mice were challenged with parasite infection and their morbidity and mortality were measured. Unlike WT mice, the IRF3-/- mice did not support replication of the parasite and were resistant to pathogenesis caused by it. Our results revealed a new paradigm in which the antiviral host factor, IRF3, plays a cell-intrinsic pro-parasitic role.
authors: Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio, United States of America.
authors: Tanmay
authors: T
authors: Majumdar
authors: Department of Molecular Genetics, Lerner Research Institute of the Cleveland Clinic, Cleveland, Ohio, United States of America.
authors: Saurabh
authors: S
authors: Chattopadhyay
authors: Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio, United States of America.
authors: Evgeny
authors: E
authors: Ozhegov
authors: Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio, United States of America.
authors: Jayeeta
authors: J
authors: Dhar
authors: Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio, United States of America.
authors: Ramansu
authors: R
authors: Goswami
authors: Department of Molecular Genetics, Lerner Research Institute of the Cleveland Clinic, Cleveland, Ohio, United States of America.
authors: Ganes C
authors: GC
authors: Sen
authors: Center for Gene Regulation in Health and Disease, and Department of Biological, Geological and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio, United States of America.
authors: Sailen
authors: S
authors: Barik
mesh_terms: D000818:Animals; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000276:immunology; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000276:immunology*; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000276:immunology; D011971:Receptors, Immunologic; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014122:Toxoplasma / Q000276:immunology*; D014123:Toxoplasmosis / Q000235:genetics / Q000276:immunology*; D000099197:STING Protein
chemical_list: D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D050838:Interferon Regulatory Factor-3; D008565:Membrane Proteins; D017346:Protein Serine-Threonine Kinases; D011971:Receptors, Immunologic; C494232:IRF3 protein, human; C494233:Irf3 protein, mouse; C532857:STING1 protein, human; D000099197:STING Protein; C530855:Sting1 protein, mouse; C498588:Tbk1 protein, mouse; C403191:TBK1 protein, human; C452820:RIGI protein, human; C503356:Ddx58 protein, mouse