Enterovirus 71 Proteins 2A and 3D Antagonize the Antiviral Activity of Gamma Interferon via Signaling Attenuation

Enterovirus 71 (EV71) infection causes severe mortality involving multiple possible mechanisms, including cytokine storm, brain stem encephalitis, and fulminant pulmonary edema. Gamma interferon (IFN-gamma) may confer anti-EV71 activity; however, the claim that disease severity is highly correlated to an increase in IFN-gamma is controversial and would indicate an immune escape initiated by EV71. This study, investigating the role of IFN-gamma in EV71 infection using a murine model, showed that IFN-gamma was elevated. Moreover, IFN-gamma receptor-deficient mice showed higher mortality rates and more severe disease progression with slower viral clearance than wild-type mice. In vitro results showed that IFN-gamma pretreatment reduced EV71 yield, whereas EV71 infection caused IFN-gamma resistance with attenuated IFN-gamma signaling in IFN regulatory factor 1 (IRF1) gene transactivation. To study the immunoediting ability of EV71 proteins in IFN-gamma signaling, 11 viral proteins were stably expressed in cells without cytotoxicity; however, viral proteins 2A and 3D blocked IFN-gamma-induced IRF1 transactivation following a loss of signal transducer and activator of transcription 1 (STAT1) nuclear translocation. Viral 3D attenuated IFN-gamma signaling accompanied by a STAT1 decrease without interfering with IFN-gamma receptor expression. Restoration of STAT1 or blocking 3D activity was able to rescue IFN-gamma signaling. Interestingly, viral 2A attenuated IFN-gamma signaling using another mechanism by reducing the serine phosphorylation of STAT1 following the inactivation of extracellular signal-regulated kinase without affecting STAT1 expression. These results demonstrate the anti-EV71 ability of IFN-gamma and the immunoediting ability by EV71 2A and 3D, which attenuate IFN-gamma signaling through different mechanisms. IMPORTANCE Immunosurveillance by gamma interferon (IFN-gamma) may confer anti-enterovirus 71 (anti-EV71) activity; however, the claim that disease severity is highly correlated to an increase in IFN-gamma is controversial and would indicate an immune escape initiated by EV71. IFN-gamma receptor-deficient mice showed higher mortality and more severe disease progression, indicating the anti-EV71 property of IFN-gamma. However, EV71 infection caused cellular insusceptibility in response to IFN-gamma stimulation. We used an in vitro system with viral protein expression to explore the novel IFN-gamma inhibitory properties of the EV71 2A and 3D proteins through the different mechanisms. According to this study, targeting either 2A or 3D pharmacologically and/or genetically may sustain a cellular susceptibility in response to IFN-gamma, particularly for IFN-gamma-mediated anti-EV71 activity.