A non-structural protein 1 substitution of dengue virus enhances viral replication by interfering with the antiviral signaling pathway.

Background: The largest dengue virus 2 (DENV2) outbreak occurred in Taiwan in 2015, resulting in many fatalities. We therefore aim to identify crucial genetic variations which determine the virulence of the 2015 Taiwan outbreak strains.

Methods: We compared the 2015 Taiwan DENV2 sequences to the pre-2015 sequences. Reverse genetics (rg) viruses with substitutions were produced and the viral growth kinetics were investigated. We treated A549 cells with interferon (IFN) to determine the interferon-stimulated genes (ISGs) expression and STAT1 phosphorylation in the rg viral infection and plasmid transfection systems. IFN and pro-inflammatory cytokines levels were measured upon DENV infection using ELISA.

Results: The rgNS1-K272R mutant showed faster replication in IFN-I producing cells compared to wildtype (WT) virus. Results revealed that NS1-K272R substitution contributed to higher soluble NS1 secretion and evade the antiviral response by suppressing the expression of ISGs and STAT1 phosphorylation compared to NS1-WT. Infection with rgNS1-K272R induced higher secretion of pro-inflammatory cytokines through the activation of canonical nuclear factor-kappa B (NF-κB) signaling pathway.

Conclusions: Our results revealed that the DENV NS1 amino acid substitution affects the NS1 ability in immune evasion, which may contribute to the largest dengue outbreak in Taiwan since the 1990s.