title: Double-stranded RNA induces biphasic STAT1 phosphorylation by both type I interferon (IFN)-dependent and type I IFN-independent pathways.
abstract: Upon viral infection, pattern recognition receptors sense viral nucleic acids, leading to the production of type I interferons (IFNs), which initiate antiviral activities. Type I IFNs bind to their cognate receptor, IFNAR, resulting in the activation of signal-transducing activators of transcription 1 (STAT1). Thus, it has long been thought that double-stranded RNA (dsRNA)-induced STAT1 phosphorylation is mediated by the transactivation of type I IFN signaling. Foreign RNA, such as viral RNA, in cells is sensed by the cytoplasmic sensors retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5). In this study, we explored the molecular mechanism responsible for STAT1 phosphorylation in response to the sensing of dsRNA by cytosolic RNA sensors. Polyinosinic-poly(C) [poly(I:C)], a synthetic dsRNA that is sensed by both RIG-I and MDA-5, induces STAT1 phosphorylation. We found that the poly(I:C)-induced initial phosphorylation of STAT1 is dependent on the RIG-I pathway and that MDA-5 is not involved in STAT1 phosphorylation. Furthermore, pretreatment of the cells with neutralizing antibody targeting the IFN receptor suppressed the initial STAT1 phosphorylation in response to poly(I:C), suggesting that this initial phosphorylation event is predominantly type I IFN dependent. In contrast, neither the known RIG-I pathway nor type I IFN is involved in the late phosphorylation of STAT1. In addition, poly(I:C) stimulated STAT1 phosphorylation in type I IFN receptor-deficient U5A cells with delayed kinetics. Collectively, our study provides evidence of a comprehensive regulatory mechanism in which dsRNA induces STAT1 phosphorylation, indicating the importance of STAT1 in maintaining very tight regulation of the innate immune system.
authors.affiliation: Department of Cardiology, Respiratory Medicine and Nephrology, Hirosaki University Graduate School of Medicine, Hirosaki, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Dempoya
authors.forename: Tomoh
authors.initials: T
authors.lastname: Matsumiya
authors.forename: Tadaatsu
authors.initials: T
authors.lastname: Imaizumi
authors.forename: Ryo
authors.initials: R
authors.lastname: Hayakari
authors.forename: Fei
authors.initials: F
authors.lastname: Xing
authors.forename: Hidemi
authors.initials: H
authors.lastname: Yoshida
authors.forename: Ken
authors.initials: K
authors.lastname: Okumura
authors.forename: Kei
authors.initials: K
authors.lastname: Satoh
mesh_terms: D045744:Cell Line, Tumor; D004797:Enzyme-Linked Immunosorbent Assay; D005455:Fluorescent Antibody Technique; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D015151:Immunoblotting; D007370:Interferon Type I / Q000378:metabolism*; D016899:Interferon-beta / Q000276:immunology; D035683:MicroRNAs / Q000235:genetics; D009841:Oligonucleotides / Q000235:genetics; D010766:Phosphorylation; D011070:Poly I-C / Q000276:immunology; D034622:RNA Interference; D012327:RNA Virus Infections / Q000276:immunology*; D012330:RNA, Double-Stranded / Q000276:immunology* / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000276:immunology*
chemical_list: D007370:Interferon Type I; D035683:MicroRNAs; D009841:Oligonucleotides; D012330:RNA, Double-Stranded; D050794:STAT1 Transcription Factor; D016899:Interferon-beta; D011070:Poly I-C