title: The influenza virus protein PB1-F2 inhibits the induction of type I interferon at the level of the MAVS adaptor protein.
abstract: PB1-F2 is a 90 amino acid protein that is expressed from the +1 open reading frame in the PB1 gene of some influenza A viruses and has been shown to contribute to viral pathogenicity. Notably, a serine at position 66 (66S) in PB1-F2 is known to increase virulence compared to an isogenic virus with an asparagine (66N) at this position. Recently, we found that an influenza virus expressing PB1-F2 N66S suppresses interferon (IFN)-stimulated genes in mice. To characterize this phenomenon, we employed several in vitro assays. Overexpression of the A/Puerto Rico/8/1934 (PR8) PB1-F2 protein in 293T cells decreased RIG-I mediated activation of an IFN-β reporter and secretion of IFN as determined by bioassay. Of note, the PB1-F2 N66S protein showed enhanced IFN antagonism activity compared to PB1-F2 wildtype. Similar observations were found in the context of viral infection with a PR8 PB1-F2 N66S virus. To understand the relationship between NS1, a previously described influenza virus protein involved in suppression of IFN synthesis, and PB1-F2, we investigated the induction of IFN when NS1 and PB1-F2 were co-expressed in an in vitro transfection system. In this assay we found that PB1-F2 N66S further reduced IFN induction in the presence of NS1. By inducing the IFN-β reporter at different levels in the signaling cascade, we found that PB1-F2 inhibited IFN production at the level of the mitochondrial antiviral signaling protein (MAVS). Furthermore, immunofluorescence studies revealed that PB1-F2 co-localizes with MAVS. In summary, we have characterized the anti-interferon function of PB1-F2 and we suggest that this activity contributes to the enhanced pathogenicity seen with PB1-F2 N66S- expressing influenza viruses.
authors.affiliation: Department of Microbiology, Mount Sinai School of Medicine, New York City, New York, United States of America.
authors.forename: Zsuzsanna T
authors.initials: ZT
authors.lastname: Varga
authors.forename: Irene
authors.initials: I
authors.lastname: Ramos
authors.forename: Rong
authors.initials: R
authors.lastname: Hai
authors.forename: Mirco
authors.initials: M
authors.lastname: Schmolke
authors.forename: Adolfo
authors.initials: A
authors.lastname: García-Sastre
authors.forename: Ana
authors.initials: A
authors.lastname: Fernandez-Sesma
authors.forename: Peter
authors.initials: P
authors.lastname: Palese
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000276:immunology*; D000818:Animals; D001854:Bone Marrow Cells; D002478:Cells, Cultured; D003713:Dendritic Cells; D006801:Humans; D009980:Influenza A virus / Q000737:chemistry / Q000276:immunology / Q000472:pathogenicity*; D007370:Interferon Type I / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D020125:Mutation, Missense; D009522:Newcastle disease virus; D015533:Transcriptional Activation; D017361:Viral Nonstructural Proteins / Q000235:genetics; D014764:Viral Proteins / Q000502:physiology*; D014774:Virulence
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D007370:Interferon Type I; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C085820:INS1 protein, influenza virus; C512612:MAVS protein, mouse; C077346:influenza virus polymerase basic protein 1