INMI1 Zika Virus NS4B Antagonizes the Interferon Signaling by Suppressing STAT1 Phosphorylation.

Elisa Fanunza,Jessica Milia,Giuseppe Ippolito,Angela Corona,Laura Ermellino,Enzo Tramontano,Fabrizio Carletti,Maria Rosaria Capobianchi,Nicole Grandi,Marina Quartu

doi:10.3390/v13122448

Abstract

The evasion of the Interferon response has important implications in Zika virus (ZIKV) disease. Mutations in ZIKV viral protein NS4B, associated with modulation of the interferon (IFN) system, have been linked to increased pathogenicity in animal models. In this study, we unravel ZIKV NS4B as antagonist of the IFN signaling cascade. Firstly, we reported the genomic characterization of NS4B isolated from a strain of the 2016 outbreak, ZIKV Brazil/2016/INMI1, and we predicted its membrane topology. Secondly, we analyzed its phylogenetic correlation with other flaviviruses, finding a high similarity with dengue virus 2 (DEN2) strains; in particular, the highest conservation was found when NS4B was aligned with the IFN inhibitory domain of DEN2 NS4B. Hence, we asked whether ZIKV NS4B was also able to inhibit the IFN signaling cascade, as reported for DEN2 NS4B. Our results showed that ZIKV NS4B was able to strongly inhibit the IFN stimulated response element and the IFN-γ-activated site transcription, blocking IFN-I/-II responses. mRNA expression levels of the IFN stimulated genes ISG15 and OAS1 were also strongly reduced in presence of NS4B. We found that the viral protein was acting by suppressing the STAT1 phosphorylation and consequently blocking the nuclear transport of both STAT1 and STAT2.

Highlights

Zika virus (ZIKV) is a mosquito-borne virus, belonging to the family of Flaviviridae, causing a flu-like illness associated with neurological complications [1]
ZIKV is characterized by a positivesense, single-stranded RNA genome, encoding a polyprotein that is processed into three structural proteins, the capsid (C), membrane and envelope (E) and seven non-structural (NS) proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5) [3]
[34].isBased on on our a 69 nt regionstrains upstream start site which conserved our alignment, we found a nt region upstream the start site which is conserved between ZIKV INMI1 and other flaviviruses and that corresponds to a 2-kDa signal pepbetween other and2K-NS4B

Summary

Introduction

ZIKV is a mosquito-borne virus, belonging to the family of Flaviviridae, causing a flu-like illness associated with neurological complications [1]. ZIKV is characterized by a positivesense, single-stranded RNA genome (ssRNA+), encoding a polyprotein that is processed into three structural proteins, the capsid (C), membrane (prM) and envelope (E) and seven non-structural (NS) proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5) [3]. The viral protein NS4B is a highly hydrophobic protein with a molecular weight of about 27 kDa, integrated into the endoplasmic reticulum membrane. NS4B is a component of the viral replication complex [4,5]. It mediates virus–host interactions by suppressing the host RNA interference [6] and evading the innate interferon (IFN)

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Conclusion