Sendai virus C protein plays a role in restricting PKR activation by limiting the generation of intracellular double-stranded RNA.
Sendai virus (SeV) C protein is a multifunctional protein that plays important roles in regulating viral genome replication and transcription, antagonizing the host interferon system, suppressing virus-induced apoptosis, and facilitating virus assembly and budding. We here report a novel role of SeV C protein, the limitation of double-stranded RNA (dsRNA) generation for maintaining the rate of protein synthesis in infected cells. It was found that the intracellular protein synthesis rate was maintained even after wild-type (wt) SeV infection, but markedly suppressed following C-knockout SeV infection. This indicates the requirement of C protein for maintaining protein synthesis after infection. In contrast to wt SeV infection, C-knockout SeV infection caused phosphorylation of both the translation initiation factor eIF2alpha and dsRNA-dependent protein kinase (PKR). Phosphorylation of eIF2alpha occurred mainly due to the action of PKR, since knockdown of PKR by small interfering RNA limited eIF2alpha phosphorylation. C protein, however, could inhibit neither poly(I):poly(C)-activated nor Newcastle disease virus-induced phosphorylation of PKR and eIF2alpha, suggesting that C protein does not target common pathways leading to PKR activation. Immunofluorescent staining experiments with a monoclonal antibody specifically recognizing dsRNA revealed generation of a large amount of dsRNA in cells infected with C-knockout SeV but not wt SeV. The dsRNA generation as well as phosphorylation of PKR and eIF2alpha induced by C-knockout SeV was markedly suppressed in cells constitutively expressing C protein. Taken together, these results demonstrate that the SeV C protein limits generation of dsRNA, thereby keeping PKR inactive to maintain intracellular protein synthesis.
Takeuchi
Kenji
K
Division of Microbiology and Infectious Diseases, Department of Pathology, Shiga University of Medical Science, Seta, Otsu, Shiga 520-2192, Japan.
Komatsu
Takayuki
T
Kitagawa
Yoshinori
Y
Sada
Kiyonao
K
Gotoh
Bin
B
D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D016898:Interferon-alpha / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism*; D029082:Sendai virus / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism*
D015852:Eukaryotic Initiation Factor-2; D016898:Interferon-alpha; D012330:RNA, Double-Stranded; D014764:Viral Proteins; C051221:nonstructural C protein, Sendai virus; D019892:eIF-2 Kinase