title: Middle East Respiratory Syndrome Coronavirus NS4b Protein Inhibits Host RNase L Activation.
abstract: Middle East respiratory syndrome coronavirus (MERS-CoV) is the first highly pathogenic human coronavirus to emerge since severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002. Like many coronaviruses, MERS-CoV carries genes that encode multiple accessory proteins that are not required for replication of the genome but are likely involved in pathogenesis. Evasion of host innate immunity through interferon (IFN) antagonism is a critical component of viral pathogenesis. The IFN-inducible oligoadenylate synthetase (OAS)-RNase L pathway activates upon sensing of viral double-stranded RNA (dsRNA). Activated RNase L cleaves viral and host single-stranded RNA (ssRNA), which leads to translational arrest and subsequent cell death, preventing viral replication and spread. Here we report that MERS-CoV, a lineage CBetacoronavirus, and related bat CoV NS4b accessory proteins have phosphodiesterase (PDE) activity and antagonize OAS-RNase L by enzymatically degrading 2',5'-oligoadenylate (2-5A), activators of RNase L. This is a novel function for NS4b, which has previously been reported to antagonize IFN signaling. NS4b proteins are distinct from lineage ABetacoronavirusPDEs and rotavirus gene-encoded PDEs, in having an amino-terminal nuclear localization signal (NLS) and are localized mostly to the nucleus. However, the expression level of cytoplasmic MERS-CoV NS4b protein is sufficient to prevent activation of RNase L. Finally, this is the first report of an RNase L antagonist expressed by a human or bat coronavirus and provides a specific mechanism by which this occurs. Our findings provide a potential mechanism for evasion of innate immunity by MERS-CoV while also identifying a potential target for therapeutic intervention.
  
  
  OBJECTIVE
  Middle East respiratory syndrome coronavirus (MERS-CoV) is the first highly pathogenic human coronavirus to emerge since severe acute respiratory syndrome coronavirus (SARS-CoV). MERS-CoV, like other coronaviruses, carries genes that encode accessory proteins that antagonize the host antiviral response, often the type I interferon response, and contribute to virulence. We found that MERS-CoV NS4b and homologs from related lineage C bat betacoronaviruses BtCoV-SC2013 (SC2013) and BtCoV-HKU5 (HKU5) are members of the 2H-phosphoesterase (2H-PE) enzyme family with phosphodiesterase (PDE) activity. Like murine coronavirus NS2, a previously characterized PDE, MERS NS4b, can antagonize activation of the OAS-RNase L pathway, an interferon-induced potent antiviral activity. Furthermore, MERS-CoV mutants with deletion of genes encoding accessory proteins NS3 to NS5 or NS4b alone or inactivation of the PDE can activate RNase L during infection of Calu-3 cells. Our report may offer a potential target for therapeutic intervention if NS4b proves to be critical to pathogenesis inin vivomodels of MERS-CoV infection.
authors.affiliation: Department of Microbiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Thornbrough
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.
authors.forename: Babal K
authors.initials: BK
authors.lastname: Jha
authors.affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Boyd
authors.initials: B
authors.lastname: Yount
authors.affiliation: Department of Microbiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Goldstein
authors.affiliation: Department of Microbiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Yize
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Microbiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Ruth
authors.initials: R
authors.lastname: Elliott
authors.affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Sims
authors.affiliation: Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Ralph S
authors.initials: RS
authors.lastname: Baric
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Silverman
authors.affiliation: Department of Microbiology, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA weisssr@upenn.edu.
authors.forename: Susan R
authors.identifier: http://orcid.org/0000-0002-8155-4528
authors.initials: SR
authors.lastname: Weiss
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism*; D000818:Animals; D006224:Cricetinae; D004722:Endoribonucleases / Q000037:antagonists & inhibitors*; D054884:Host-Pathogen Interactions; D006801:Humans; D057131:Immune Evasion; D051379:Mice; D065207:Middle East Respiratory Syndrome Coronavirus / Q000502:physiology*; D019913:Nuclear Localization Signals; D009843:Oligoribonucleotides / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000227:Adenine Nucleotides; D019913:Nuclear Localization Signals; D009843:Oligoribonucleotides; D017361:Viral Nonstructural Proteins; C023505:2',5'-oligoadenylate; D004722:Endoribonucleases; C031956:2-5A-dependent ribonuclease