Induction of SOCS Expression by EV71 Infection Promotes EV71 Replication.

Enterovirus 71 (EV71) is the causative pathogen of hand, foot, and mouth disease (HFMD). However, no effective antiviral therapy is currently available. Some viruses could escape the host's innate immunity by upregulating suppressor of cytokine signaling (SOCS) proteins. Until now, whether EV71 evades the host immune system by regulating the expression of SOCS proteins remains unknown. In this study, we found that EV71 infection promoted SOCS expression at both mRNA and protein levels in vitro and in vivo. Consistently, the infectivity of EV71 was decreased significantly in the SOCS3 or SOCS1 knockdown cells, suggesting that SOCS1 and especially SOCS3 are crucial for EV71 infection. Further investigation showed that SOCS3 promoted virus infection by inhibiting interferon-induced STAT3 phosphorylation. SOCS1 and SOCS3 mRNA expressions were independent on virus-induced type I interferon expression but were blocked by the inhibitor of NF-κB. Therefore, EV71 infection stimulates the expression of SOCS proteins in an interferon-independent way and negatively regulates the JAK/STAT signaling pathway, thus escaping host immunity. All these results may add new information to the mechanism of EV71 in fighting against type I interferon responses.