NS1′ protein expression facilitates production of Japanese encephalitis virus in avian cells and embryonated chicken eggs

Japanese encephalitis virus (JEV), which belongs to the genus Flavivirus of the family Flaviviridae, is a leading cause of meningo-encephalitis in Asian countries. The flavivirus non-structural protein 1 (NS1) plays a role in virus replication and in the elicitation of an immune response. The NS1′ protein found among the members of the JEV subgroup is an extended form of NS1 and is generated by a −1 ribosomal frameshift. This protein is known to be involved in viral pathogenicity; however, its specific function is still unknown. Here, we describe an investigation of the molecular function of NS1′ protein through the production of JEV NS1′-expressing and -non-expressing clones and their infection of avian and mammalian cells. Efficient NS1′ protein expression was observed in avian cells and was found to facilitate JEV production in both avian cultured cells and embryonated chicken eggs. NS1′ protein was observed to co-localize with NS5 protein and resulted in increased viral RNA levels in avian cells. These findings clearly indicate that NS1′ enhances the production of JEV in avian cells and may facilitate the amplification/maintenance role of birds in the virus transmission cycle in nature.