title: Nonstructural proteins NS1 and NS2 of bovine respiratory syncytial virus block activation of interferon regulatory factor 3.
abstract: We have previously shown that the nonstructural (NS) proteins NS1 and NS2 of bovine respiratory syncytial virus (BRSV) mediate resistance to the alpha/beta interferon (IFN)-mediated antiviral response. Here, we show that they, in addition, are able to prevent the induction of beta IFN (IFN-beta) after virus infection or double-stranded RNA stimulation. In BRSV-infected MDBK cells upregulation of IFN-stimulated genes (ISGs) such as MxA did not occur, although IFN signaling via JAK/STAT was found intact. In contrast, infection with recombinant BRSVs lacking either or both NS genes resulted in efficient upregulation of ISGs. Biological IFN activity and IFN-beta were detected only in supernatants of cells infected with the NS deletion mutants but not with wild-type (wt) BRSV. Subsequent analyses of IFN-beta promoter activity showed that infection of cells with the double deletion mutant BRSV DeltaNS1/2, but not with BRSV wt, resulted in a significant increase in IFN-beta gene promoter activity. Induction of the IFN-beta promoter depends on the activation of three distinct transcription factors, NF-kappaB, ATF-2/c-Jun, and IFN regulatory factor 3 (IRF-3). Whereas NF-kappaB and ATF-2/c-Jun activities were readily detectable and comparable in both wt BRSV- and BRSV DeltaNS1/2-infected cells, phosphorylation and transcriptional activity of IRF-3, however, were observed only after BRSV DeltaNS1/2 infection. NS protein-mediated inhibition of IRF-3 activation and IFN induction should have considerable impact on the pathogenesis and immunogenicity of BRSV.
authors.affiliation: Max von Pettenkofer Institute and Gene Center, Ludwig Maximilians University Munich, D-81377 Munich, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Bossert
authors.forename: Sabrina
authors.initials: S
authors.lastname: Marozin
authors.forename: Karl-Klaus
authors.initials: KK
authors.lastname: Conzelmann
mesh_terms: D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D017353:Gene Deletion; D050835:Interferon Regulatory Factors; D016899:Interferon-beta / Q000235:genetics; D011401:Promoter Regions, Genetic; D018112:Respiratory Syncytial Virus, Bovine / Q000502:physiology*; D015398:Signal Transduction; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000502:physiology; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000502:physiology*; D014764:Viral Proteins; D014775:Virus Activation / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D050835:Interferon Regulatory Factors; D014157:Transcription Factors; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C413486:viral interferon regulatory factors; D016899:Interferon-beta