Ubiquitin accumulation induced by the finger and palm sub-domains of NS5 modulates the replication of West Nile virus.

West Nile virus (WNV) causes encephalitis in human and animals. WNV is phylogenetically classified into at least five distinct genetic lineages with different pathogenicity. The pathogenesis of West Nile encephalitis is affected by ubiquitin accumulation in infected cells, but the mechanism is unknown. In this study, the association between ubiquitin accumulation and WNV pathogenicity was investigated. Ubiquitin accumulation was detected in cells infected with NY99 strain belonging to lineage-1, but not FCG and Zmq16 strains belonging to lineage-2. Substitution of the Finger and Palm sub-domains of NS5 from lineage-1 to -2 decreased ubiquitin accumulation and viral replication. Furthermore, the survival rate was increased, and viral replication and ubiquitin accumulation in the brain were attenuated, in mice inoculated with the substituted WNV compared with lineage-1 WNV. Therefore, the intracellular ubiquitin accumulation induced by the Finger and Palm sub-domains of NS5 is linked to the differences in pathogenicity among WNV lineages.