Nonstructural protein p39 of feline calicivirus suppresses host innate immune response by preventing IRF-3 activation

• Nonstructural protein p39 of FCV suppresses type 1 IFN and ISG15 mRNA production.
• p39 suppresses phosphorylation and dimerization of IRF-3.
• First report showing that a nonstructural protein of FCV suppresses IFN signaling.
• Our finding will be important to understand the pathogenesis and virulence of FCV.

Feline calicivirus (FCV) is an important veterinary pathogen that causes acute upper respiratory tract diseases and, occasionally, highly contagious febrile hemorrhagic syndrome in cats. Many viruses have adopted mechanisms for evading IFN-α/β signaling, particularly by directly or indirectly suppressing activation of IRF-3. In this study, we investigated whether nonstructural proteins of FCV possess these mechanisms. When p39, a nonstructural protein of FCV, was transiently expressed in 293T cells, it suppressed IFN-β and ISG15 mRNA production induced by dsRNA. Expression of p39 also suppressed phosphorylation and dimerization of IRF-3 induced by dsRNA. These results suggest that p39 suppresses type 1 IFN production by preventing IRF-3 activation. This may become an important factor in understanding the pathogenesis and virulence of FCV.