Conserved charged amino acids within Sendai virus C protein play multiple roles in the evasion of innate immune responses.
One of the accessory proteins of Sendai virus (SeV), C, translated from an alternate reading frame of P/V mRNA has been shown to function at multiple stages of infection in cell cultures as well as in mice. C protein has been reported to counteract signal transduction by interferon (IFN), inhibit apoptosis induced by the infection, enhance the efficiency of budding of viral particles, and regulate the polarity of viral genome-length RNA synthesis to maximize production of infectious particles. In this study, we have generated a series of SeV recombinants containing substitutions of highly conserved, charged residues within the C protein, and characterized them together with previously-reported C'/C(-), 4C(-), and F170S recombinant viruses in infected cell cultures in terms of viral replication, cytopathogenicity, and antagonizing effects on host innate immunity. Unexpectedly, the amino acid substitutions had no or minimal effect on viral growth and viral RNA synthesis. However, all the substitutions of charged amino acids resulted in the loss of a counteracting effect against the establishment of an IFN-alpha-mediated anti-viral state. Infection by the virus (Cm2') containing mutations at K77 and D80 induced significant IFN-beta production, severe cytopathic effects, and detectable amounts of viral dsRNA production. In addition to the Cm2' virus, the virus containing mutations at E114 and E115 did not inhibit the poly(I:C)-triggered translocation of cellular IRF-3 to the nucleus. These results suggest that the C protein play important roles in viral escape from induction of IFN-beta and cell death triggered by infection by means of counteracting the pathway leading to activation of IRF-3 as well as of minimizing viral dsRNA production.
Irie
Takashi
T
Department of Virology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan. tirie@hiroshima-u.ac.jp
Nagata
Natsuko
N
Igarashi
Tomoki
T
Okamoto
Isao
I
Sakaguchi
Takemasa
T
D000596:Amino Acids / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D017124:Conserved Sequence; D003588:Cytopathogenic Effect, Viral / Q000187:drug effects; D016679:Genome, Viral / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D057131:Immune Evasion / Q000187:drug effects / Q000276:immunology*; D007113:Immunity, Innate / Q000187:drug effects / Q000276:immunology*; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D016899:Interferon-beta / Q000096:biosynthesis; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D011070:Poly I-C / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D012330:RNA, Double-Stranded / Q000096:biosynthesis; D011995:Recombination, Genetic / Q000187:drug effects / Q000235:genetics; D010253:Respirovirus Infections / Q000276:immunology / Q000821:virology; D029082:Sendai virus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism*; D014771:Virion / Q000235:genetics
D000596:Amino Acids; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D012330:RNA, Double-Stranded; D014764:Viral Proteins; C051221:nonstructural C protein, Sendai virus; D016899:Interferon-beta; D011070:Poly I-C