title: Synoviocyte innate immune responses: II. Pivotal role of IFN regulatory factor 3.
abstract: Innate immune responses contribute to synovial inflammation in rheumatoid arthritis. The present study was designed to investigate the contribution of IFN regulatory factor (IRF)3 and IRF7 to type I IFN-regulated gene expression in synoviocytes. Fibroblast-like synoviocytes were stimulated with polyinosinic-polycytidylic acid (poly [I-C]) after transfection with IRF3 or IRF7 small interfering RNA to knockdown transcription factor expression. Western blots, luciferase assay after transfection with reporter constructs, quantitative PCR, and AP-1 DNA binding ELISA were performed to evaluate the role of IRF3 and IRF7 in poly (I-C)-induced signaling and synoviocyte gene expression. IRF3 regulates IFN-stimulated response element (ISRE) promoter activity as well as IFN-beta, IRF5, IRF7, RANTES, IFN-inducible protein-10, MCP-1, and MIP1alpha gene expression in response to poly (I-C). IRF7 knockdown modestly decreased a subset of genes and ISRE activity, although the results were not statistically significant. Surprisingly, IRF3 knockdown almost completely blocked expression of additional genes in which the ISRE is not traditionally considered a dominant promoter site in fibroblast-like synoviocytes, including matrix metalloproteinase (MMP)3, MMP9, IL-6, and IL-8. Transcription factor activation studies demonstrated a role for IRF3 in regulation of c-Jun phosphorylation and AP-1 binding. IRF3 rather than IRF7 regulates poly (I-C)-induced type I IFN responses in human synoviocytes by increasing ISRE promoter activity. IRF3 also partially regulates expression of other cytokines and MMP through activation of c-Jun and the AP-1 promoter site. Targeting synoviocyte IRF3 represents a potential approach to suppress diverse mediators while limiting suppression of IRF7-mediated immune responses.
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, University of California San Diego School of Medicine, La Jolla, CA 92093, USA. ssweeney@ucsd.edu
authors.forename: Susan E
authors.initials: SE
authors.lastname: Sweeney
authors.forename: Trevor B
authors.initials: TB
authors.lastname: Kimbler
authors.forename: Gary S
authors.initials: GS
authors.lastname: Firestein
mesh_terms: D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000276:immunology*; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression; D005786:Gene Expression Regulation / Q000276:immunology*; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics*; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000276:immunology*; D050839:Interferon Regulatory Factor-7 / Q000235:genetics / Q000276:immunology*; D011070:Poly I-C / Q000276:immunology; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000276:immunology; D034622:RNA Interference; D034741:RNA, Small Interfering; D020218:Response Elements / Q000235:genetics / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D013583:Synovial Membrane / Q000166:cytology / Q000276:immunology*; D014162:Transfection
chemical_list: C494232:IRF3 protein, human; C494234:IRF7 protein, human; D050838:Interferon Regulatory Factor-3; D050839:Interferon Regulatory Factor-7; D034741:RNA, Small Interfering; D011070:Poly I-C