Flavivirus prM interacts with MDA5 and MAVS to inhibit RLR antiviral signaling

Vector-borne flaviviruses, including tick-borne encephalitis virus (TBEV), Zika virus (ZIKA), West Nile virus (WNV), yellow fever virus (YFV), dengue virus (DENV), and Japanese encephalitis virus (JEV), pose a growing threat to public health worldwide, and have evolved complex mechanisms to overcome host antiviral innate immunity. However, the underlying mechanisms of flavivirus structural proteins to evade host immune response remain elusive. Here we show that TBEV structural proteins, including pre-membrane (prM), envelope, and capsid proteins, could inhibit type I interferon (IFN-I) production. Mechanically, TBEV prM interacted with both MDA5 and MAVS and interfered with the formation of MDA5-MAVS complex, thereby impeded the nuclear translocation and dimerization of IRF3 to inhibit RLR antiviral signaling. ZIKA and WNV prM was also demonstrated to interact with both MDA5 and MAVS, while dengue virus serotype 2 (DENV2) and YFV prM associated only with MDA5 or MAVS to suppress IFN-I production. In contrast, JEV prM could not suppress IFN-I production. Overexpression of TBEV and ZIKA prM significantly promoted the replication of Sendai virus. Our findings reveal the immune evasion mechanisms of flavivirus prM, which may contribute to understanding flavivirus pathogenicity, therapeutic intervention and vaccine development. Author SummaryAll flaviviruses must overcome the antiviral innate immunity to infect vertebrate host. The non-structural proteins of flaviviruses are mainly responsible for viral replication and host innate immune escape, and the structural proteins are involved in the virus assembly, which are potential targets for prevention and treatment of flaviviral infections. Whether flavivirus structural proteins participate in host innate immune escape remains to be determined. Here, we found that tick-borne encephalitis virus structural proteins precursor membrane (prM), capsid, and envelope proteins can antagonize type I interferon production, in which prM interacts with both MDA5 and MAVS to inhibit RLR antiviral signaling. Additionally, Zika virus and West Nile virus prMs also interact with both MDA5 and MAVS, while dengue virus serotype 2 and yellow fever virus prMs associate only with MDA5 or MAVS to suppress type I interferon production. In contrast, Japanese encephalitis virus prM cannot antagonize type I interferon production. Our findings reveal that flavivirus prM inhibits type I interferon production via interacting with MDA5 and/or MAVS in a species-dependent manner, which may contribute to understanding flavivirus pathogenicity, therapeutic intervention, and vaccine development.