SARS-CoV nucleocapsid protein antagonizes IFN-β response by targeting initial step of IFN-β induction pathway, and its C-terminal region is critical for the antagonism.
Severe acute respiratory syndrome coronavirus (SARS-CoV) encodes a highly basic nucleocapsid (N) protein which can inhibit the synthesis of type I interferon (IFN), but the molecular mechanism of this antagonism remains to be identified. In this study, we demonstrated that the N protein of SARS-CoV could inhibit IFN-beta (IFN-β) induced by poly(I:C) or Sendai virus. However, we found that N protein could not inhibit IFN-β production induced by overexpression of downstream signaling molecules of two important IFN-β induction pathways, toll-like receptor 3 (TLR3)- and RIG-I-like receptors (RLR)-dependent pathways. These results indicate that SARS-CoV N protein targets the initial step, probably the cellular PRRs (pattern recognition receptors)-RNAs-recognition step in the innate immune pathways, to suppress IFN expression responses. In addition, co-immunoprecipitation assays revealed that N protein did not interact with RIG-I or MDA5. Further, an assay using truncated mutants revealed that the C-terminal domain of N protein was critical for its antagonism of IFN induction, and the N deletion mutant impaired for RNA-binding almost completely lost the IFN-β antagonist activity. These results contribute to our further understanding of the pathogenesis of SARS-CoV.
State Key Laboratory of Virology and Modern Virology Research Center, College of Life Sciences, Wuhan University, Luojia Hill, Wuhan, People's Republic of China.
Xiaolu
X
Lu
Ji'an
J
Pan
Jiali
J
Tao
Deyin
D
Guo
D048868:Adaptor Proteins, Signal Transducing / Q000276:immunology; D002460:Cell Line; D000086462:Coronavirus Nucleocapsid Proteins; D053487:DEAD-box RNA Helicases / Q000276:immunology; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000276:immunology; D016899:Interferon-beta / Q000276:immunology / Q000378:metabolism*; D019590:Nucleocapsid Proteins / Q000276:immunology*; D011070:Poly I-C / Q000276:immunology; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000276:immunology; D012367:RNA, Viral / Q000032:analysis; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology* / Q000472:pathogenicity; D029082:Sendai virus / Q000276:immunology; D017384:Sequence Deletion; D051196:Toll-Like Receptor 3 / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D000086462:Coronavirus Nucleocapsid Proteins; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D019590:Nucleocapsid Proteins; D012367:RNA, Viral; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; D016899:Interferon-beta; D017346:Protein Serine-Threonine Kinases; D053487:DEAD-box RNA Helicases; D011070:Poly I-C