NS5-V372A and NS5-H386Y variations are responsible for differences in interferon α/β induction and co-contribute to the replication advantage of Japanese encephalitis virus genotype I over genotype III in ducklings.

Chenxi Li,Xin Wang,Zongjie Li,Jianchao Wei,Hui Huang,Qiqi Xia,Xiaochun Ma,Donghua Shao,Beibei Li,Zhiyong Ma,Di Di,Ke Liu,Yafeng Qiu,Sonja Best

doi:10.1371/journal.ppat.1008773

Abstract

Japanese encephalitis virus (JEV) genotype I (GI) replicates more efficiently than genotype III (GIII) in birds, and this difference is considered to be one of the reasons for the JEV genotype shift. In this study, we utilized duck embryo fibroblasts and domestic ducklings as in vitro and in vivo models of a JEV amplifying avian host to identify the viral determinants of the differing replication efficiency between the GI and GIII strains in birds. GI strains induced significantly lower levels of interferon (IFN)-α and β production than GIII strains, an effect orrelated with the enhanced replication efficiency of GI strains over GIII strains. By using a series of chimeric viruses with exchange of viral structural and non-structural (NS) proteins, we identified NS5 as the viral determinant of the differences in IFN-α and β induction and replication efficiency between the GI and III strains. NS5 inhibited IFN-α and β production induced by poly(I:C) stimulation and harbored 11 amino acid variations, of which the NS5-V372A and NS5-H386Y variations were identified to co-contribute to the differences in IFN-α and β induction and replication efficiency between the strains. The NS5-V372A and NS5-H386Y variations resulted in alterations in the number of hydrogen bonds formed with neighboring residues, which were associated with the different ability of the GI and GIII strains to inhibit IFN-α and β production. Our findings indicated that the NS5-V372A and NS5-H386Y variations enabled GI strains to inhibit IFN-α and β production more efficiently than GIII strains for antagonism of the IFN-I mediated antiviral response, thereby leading to the replication and host adaption advantages of GI strains over GIII strains in birds. These findings provide new insight into the molecular basis of the JEV genotype shift.

Highlights

Japanese encephalitis virus (JEV) belongs to the genus Flavivirus of the family Flaviviridae, which comprises more than 70 species—including West Nile virus (WNV), dengue virus (DENV), Zika virus (ZIKV), yellow fever virus, and tick-borne encephalitis virus—and causes Japanese encephalitis in humans and reproductive disorders in pigs[1, 2]
Our findings indicated that the NS5-V372A and NS5-H386Y variations enabled genotype I (GI) strains to inhibit IFN-α and β production more efficiently than genotype III (GIII) strains for antagonism of the IFN-I mediated antiviral response, thereby leading to the replication and host adaption advantages of GI strains over GIII strains in birds
No significant differences in IFN-α and β induction at both the mRNA and protein levels between the GI and GIII strains were observed in either (Fig 1A and 1B) or bEnd.3 cells (Fig 1C and 1D); significant differences were observed in duck embryo fibroblasts (DEF) (Fig 1E and 1F)

Summary

Introduction

Japanese encephalitis virus (JEV) belongs to the genus Flavivirus of the family Flaviviridae, which comprises more than 70 species—including West Nile virus (WNV), dengue virus (DENV), Zika virus (ZIKV), yellow fever virus, and tick-borne encephalitis virus—and causes Japanese encephalitis in humans and reproductive disorders in pigs[1, 2]. JEV was first isolated in Japan in 1935 and is currently prevalent mainly in East and Southeast Asia[3,4,5]. The JEV genome is a single-stranded, positive-sense RNA approximately 11 kb in length that encodes a single polyprotein. According to the nucleotide sequence of the E gene, JEV is phylogenetically classified into five genotypes (genotype I to V), and most isolates belong to genotype I (GI) or genotype III (GIII)[9]. The number of GI isolates has increased in the past 20 years, resulting in a JEV genotype shift from GIII to GI; the re-emergent GI has become the dominant genotype instead of GIII in most countries in Asia[14]

Methods

Results

Discussion

Conclusion