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Sendai Virus C Protein Plays a Role in Restricting PKR Activation by Limiting the Generation of Intracellular Double-Stranded RNA

2008; American Society for Microbiology; Volume: 82; Issue: 20 Linguagem: Inglês

10.1128/jvi.00599-08

1098-5514

Kenji Takeuchi, Takayuki Komatsu, Yoshinori Kitagawa, Kiyonao Sada, Bin Gotoh,

interferon and immune responses

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.