The NS3 protease and helicase domains of Japanese encephalitis virus trigger cell death via caspase-dependent and -independent pathways

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, causes acute encephalitis and nervous damage. Previous studies have demonstrated thatJEV induces apoptosis in infected cells. However, to date the mechanisms of JEV-induced apoptosis are unclear. In order to identify the viral proteins associated with JEV-induced apoptosis, pEGFP-non-structural protein 3 (NS3) 1-619 (expressing the JEV NS3 intact protein, including the protease and helicase domains), pEGFP-NS3 1-180 (expressing the protease domain) and pEGFP-NS3 163-619 (expressing the helicase domain) were transfected into target cells to study cell death. Results demonstrate that the JEV NS3 intact protein and protease and helicase domains induce cell death. In addition, cell death was identified to be significantly higher in cells transfected with the NS3 protease domain compared with the intact protein and helicase domain. Caspase activation was also analyzed in the current study. NS3 intact protein and NS3 protease and helicase domains activated caspase-9/-3-dependent and -independent pathways. However, caspase-8 activity was not found to be significantly different in NS3-transfected cells compared with control. In summary, the present study demonstrates that the NS3 helicase and protease domains of JEV activate caspase-9/-3-dependent and -independent cascades and trigger cell death.