title: The RNA- and TRIM25-Binding Domains of Influenza Virus NS1 Protein Are Essential for Suppression of NLRP3 Inflammasome-Mediated Interleukin-1β Secretion.
abstract: Inflammasomes are cytosolic multimolecular protein complexes that stimulate the activation of caspase-1 and the release of mature forms of interleukin-1β (IL-1β) and IL-18. We previously demonstrated that the influenza A virus M2 protein stimulates IL-1β secretion following activation of the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. The nonstructural protein 1 (NS1) of influenza virus inhibits caspase-1 activation and IL-1β secretion. However, the precise mechanism by which NS1 inhibits IL-1β secretion remains unknown. Here, we showed that J774A.1 macrophages stably expressing the NS1 protein inhibited IL-1β secretion after infection with recombinant influenza virus lacking the NS1 gene. Coimmunoprecipitation assay revealed that the NS1 protein interacts with NLRP3. Importantly, the NS1 protein inhibited the NLRP3/ASC-induced single-speck formation required for full activation of inflammasomes. The NS1 protein of other influenza virus strains, including a recent pandemic strain, also inhibited inflammasome-mediated IL-1β secretion. The NS1 RNA-binding domain (basic residues 38 and 41) and TRIM25-binding domain (acidic residues 96 and 97) were required for suppression of NLRP3 inflammasome-mediated IL-1β secretion. These results shed light on a mechanism by which the NS1 protein of influenza virus suppresses NLRP3 inflammasome-mediated IL-1β secretion.
  
  
  OBJECTIVE
  Innate immune sensing of influenza virus via pattern recognition receptors not only plays a key role in generating type I interferons but also triggers inflammatory responses. We previously demonstrated that the influenza A virus M2 protein activates the NLRP3 inflammasome, leading to the secretion of interleukin-1β (IL-1β) and IL-18 following the activation of caspase-1. Although the nonstructural protein 1 (NS1) of influenza virus inhibits IL-1β secretion, the precise mechanism by which it achieves this remains to be defined. Here, we demonstrate that the NS1 protein interacts with NLRP3 to suppress NLRP3 inflammasome activation. J774A.1 macrophages stably expressing the NS1 protein suppressed NLRP3-mediated IL-1β secretion. The NS1 RNA-binding domain (basic residues 38 and 41) and TRIM25-binding domain (acidic residues 96 and 97) are important for suppression of NLRP3 inflammasome-mediated IL-1β secretion. These results will facilitate the development of new anti-inflammatory drugs.
authors: Division of Viral Infection, Department of Infectious Disease Control, International Research Center for Infectious Diseases, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan.|Department of Life Science and Medical Bioscience, Waseda University, Shinjuku-ku, Tokyo, Japan.|Department of Pathology, National Institute of Infectious Diseases, Shinjukuu-ku, Tokyo, Japan.
authors: Miyu
authors: M
authors: Moriyama
authors: Division of Viral Infection, Department of Infectious Disease Control, International Research Center for Infectious Diseases, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan.
authors: I-Yin
authors: IY
authors: Chen
authors: Department of Infection Biology, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors: Atsushi
authors: A
authors: Kawaguchi
authors: Department of Biology, Faculty of Sciences, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors: Takumi
authors: T
authors: Koshiba
authors: Department of Infection Biology, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan.
authors: Kyosuke
authors: K
authors: Nagata
authors: Department of Life Science and Medical Bioscience, Waseda University, Shinjuku-ku, Tokyo, Japan.
authors: Haruko
authors: H
authors: Takeyama
authors: Department of Pathology, National Institute of Infectious Diseases, Shinjukuu-ku, Tokyo, Japan.
authors: Hideki
authors: H
authors: Hasegawa
authors: Division of Viral Infection, Department of Infectious Disease Control, International Research Center for Infectious Diseases, Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, Japan ichinohe@ims.u-tokyo.ac.jp.
authors: Takeshi
authors: T
authors: Ichinohe
mesh_terms: D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D058847:Inflammasomes / Q000276:immunology*; D053583:Interleukin-1beta / Q000378:metabolism*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008810:Mice, Inbred C57BL; D051336:Mitochondrial Membranes / Q000378:metabolism; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D012313:RNA / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C085820:INS1 protein, influenza virus; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D017361:Viral Nonstructural Proteins; D012313:RNA; C084523:TRIM25 protein, human; D044767:Ubiquitin-Protein Ligases