title: Identification of a Natural Viral RNA Motif That Optimizes Sensing of Viral RNA by RIG-I.
abstract: Stimulation of the antiviral response depends on the sensing of viral pathogen-associated molecular patterns (PAMPs) by specialized cellular proteins. During infection with RNA viruses, 5'-di- or -triphosphates accompanying specific single or double-stranded RNA motifs trigger signaling of intracellular RIG-I-like receptors (RLRs) and initiate the antiviral response. Although these molecular signatures are present during the replication of many viruses, it is unknown whether they are sufficient for strong activation of RLRs during infection. Immunostimulatory defective viral genomes (iDVGs) from Sendai virus (SeV) are among the most potent natural viral triggers of antiviral immunity. Here we describe an RNA motif (DVG(70-114)) that is essential for the potent immunostimulatory activity of 5'-triphosphate-containing SeV iDVGs. DVG(70-114) enhances viral sensing by the host cell independently of the long stretches of complementary RNA flanking the iDVGs, and it retains its stimulatory potential when transferred to otherwise inert viral RNA. In vitro analysis showed that DVG(70-114) augments the binding of RIG-I to viral RNA and promotes enhanced RIG-I polymerization, thereby facilitating the onset of the antiviral response. Together, our results define a new natural viral PAMP enhancer motif that promotes viral recognition by RLRs and confers potent immunostimulatory activity to viral RNA.
  
  
  OBJECTIVE
  A discrete group of molecular motifs, including 5'-triphosphates associated with double-stranded RNA, have been identified as essential for the triggering of antiviral immunity. Most RNA viruses expose these motifs during their replication; however, successful viruses normally evade immune recognition and replicate to high levels before detection, indicating that unknown factors drive antiviral immunity. DVGs from SeV are among the most potent natural viral stimuli of the antiviral response known to date. These studies define a new natural viral motif present in DVGs that maximizes viral recognition by the intracellular sensor RIG-I, allowing fast and strong antiviral responses even in the presence of viral-encoded immune antagonists. This motif can be harnessed to increase the immunostimulatory potential of otherwise inert viral RNAs and represents a novel immunostimulatory enhancer that could be used in the development of vaccine adjuvants and antivirals.
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Xiomara
authors.initials: X
authors.lastname: Mercado-López
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Jennifer T
authors.initials: JT
authors.lastname: Grier
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Won-keun
authors.initials: WK
authors.lastname: Kim
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Lauren F
authors.initials: LF
authors.lastname: Chun
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Edward B
authors.initials: EB
authors.lastname: Irvine
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Yoandris
authors.initials: Y
authors.lastname: Del Toro Duany
authors.affiliation: Department of Immunology, University of Washington School of Medicine, Seattle, Washington, USA.
authors.forename: Alison
authors.initials: A
authors.lastname: Kell
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Sun
authors.initials: S
authors.lastname: Hur
authors.affiliation: Department of Immunology, University of Washington School of Medicine, Seattle, Washington, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Gale
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Arjun
authors.initials: A
authors.lastname: Raj
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA lopezca@vet.upenn.edu.
authors.forename: Carolina B
authors.initials: CB
authors.lastname: López
mesh_terms: D000818:Animals; D002460:Cell Line; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D006801:Humans; D007113:Immunity, Innate; D008253:Macaca mulatta; D000069452:Pathogen-Associated Molecular Pattern Molecules / Q000378:metabolism*; D011485:Protein Binding; D012367:RNA, Viral / Q000378:metabolism*; D011971:Receptors, Immunologic; D029082:Sendai virus / Q000276:immunology*
chemical_list: D000069452:Pathogen-Associated Molecular Pattern Molecules; D012367:RNA, Viral; D011971:Receptors, Immunologic; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases