title: PACT- and RIG-I-Dependent Activation of Type I Interferon Production by a Defective Interfering RNA Derived from Measles Virus Vaccine.
abstract: The live attenuated measles virus vaccine is highly immunostimulatory. Identification and characterization of its components that activate the innate immune response might provide new strategies and agents for the rational design and development of chemically defined adjuvants. In this study, we report on the activation of type I interferon (IFN) production by a defective interfering (DI) RNA isolated from the Hu-191 vaccine strain of measles virus. We found that the Hu-191 virus induced IFN-β much more potently than the Edmonston strain. In the search for IFN-inducing species in Hu-191, we identified a DI RNA specifically expressed by this strain. This DI RNA, which was of the copy-back type, was predicted to fold into a hairpin structure with a long double-stranded stem region of 206 bp, and it potently induced the expression of IFN-β. Its IFN-β-inducing activity was further enhanced when both cytoplasmic RNA sensor RIG-I and its partner, PACT, were overexpressed. On the contrary, this activity was abrogated in cells deficient in PACT or RIG-I. The DI RNA was found to be associated with PACT in infected cells. In addition, both the 5'-di/triphosphate end and the double-stranded stem region on the DI RNA were essential for its activation of PACT and RIG-I. Taken together, our findings support a model in which a viral DI RNA is sensed by PACT and RIG-I to initiate an innate antiviral response. Our work might also provide a foundation for identifying physiological PACT ligands and developing novel adjuvants or antivirals.
  
  
  OBJECTIVE
  The live attenuated measles virus vaccine is one of the most successful human vaccines and has largely contained the devastating impact of a highly contagious virus. Identifying the components in this vaccine that stimulate the host immune response and understanding their mechanism of action might help to design and develop better adjuvants, vaccines, antivirals, and immunotherapeutic agents. We identified and characterized a defective interfering RNA from the Hu-191 vaccine strain of measles virus which has safely been used in millions of people for many years. We further demonstrated that this RNA potently induces an antiviral immune response through cellular sensors of viral RNA known as PACT and RIG-I. Similar types of viral RNA that bind with and activate PACT and RIG-I might retain the immunostimulatory property of measles virus vaccines but would not induce adaptive immunity. They are potentially useful as chemically defined vaccine adjuvants, antivirals, and immunostimulatory agents.
authors.affiliation: School of Biomedical Sciences, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Ting-Hin
authors.initials: TH
authors.lastname: Ho
authors.affiliation: School of Biomedical Sciences, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Chun
authors.initials: C
authors.lastname: Kew
authors.affiliation: School of Biomedical Sciences, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Pak-Yin
authors.initials: PY
authors.lastname: Lui
authors.affiliation: School of Biomedical Sciences, The University of Hong Kong, Pokfulam, Hong Kong.
authors.forename: Chi-Ping
authors.initials: CP
authors.lastname: Chan
authors.affiliation: Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Satoh
authors.affiliation: Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Shizuo
authors.initials: S
authors.lastname: Akira
authors.affiliation: School of Biomedical Sciences, The University of Hong Kong, Pokfulam, Hong Kong dyjin@hku.hk khkok@hku.hk.
authors.forename: Dong-Yan
authors.identifier: http://orcid.org/0000-0002-2778-3530
authors.initials: DY
authors.lastname: Jin
authors.affiliation: Department of Microbiology, The University of Hong Kong, Pokfulam, Hong Kong dyjin@hku.hk khkok@hku.hk.
authors.forename: Kin-Hang
authors.initials: KH
authors.lastname: Kok
mesh_terms: D002460:Cell Line; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D003673:Defective Viruses / Q000235:genetics / Q000276:immunology*; D006801:Humans; D016899:Interferon-beta / Q000096:biosynthesis*; D008458:Measles Vaccine / Q000235:genetics / Q000276:immunology*; D008459:Measles virus / Q000235:genetics / Q000276:immunology*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D012367:RNA, Viral / Q000737:chemistry / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011971:Receptors, Immunologic
chemical_list: D008458:Measles Vaccine; C104647:PRKRA protein, human; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D011971:Receptors, Immunologic; D016899:Interferon-beta; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases