Amino Acid at Position 166 of NS2A in Japanese Encephalitis Virus (JEV) Is Associated with In Vitro Growth Characteristics of JEV

We previously showed that the growth ability of the Japanese encephalitis virus (JEV) genotype V (GV) strain Muar is clearly lower than that of the genotype I (GI) JEV strain Mie/41/2002 in murine neuroblastoma cells. Here, we sought to identify the region in GV JEV that is involved in its low growth potential in cultured cells. An intertypic virus containing the NS1-3 region of Muar in the Mie/41/2002 backbone (NS1-3(Muar)) exhibited a markedly diminished growth ability in murine neuroblastoma cells. Moreover, the growth rate of a Muar NS2A-bearing intertypic virus (NS2A(Muar)) was also similar to that of Muar in these cells, indicating that NS2A of Muar is one of the regions responsible for the Muar-specific growth ability in murine neuroblastoma cells. Sequencing analysis of murine neuroblastoma Neuro-2a cell-adapted NS1-3(Muar) virus clones revealed that His-to-Tyr mutation at position 166 of NS2A (NS2A(166)) could rescue the low replication ability of NS1-3(Muar) in Neuro-2a cells. Notably, a virus harboring a Tyr-to-His substitution at NS2A(166) (NS2A(Y166H)) showed a decreased growth ability relative to that of the parental virus Mie/41/2002, whereas an NS2A(Muar)-based mutant virus, NS2A(Muar-H166Y), showed a higher growth ability than NS2A(Muar) in Neuro-2a cells. Thus, these results indicate that the NS2A(166) amino acid in JEV is critical for the growth and tissue tropism of JEV in vitro.