Norovirus infection results in eIF2α independent host translation shut-off and remodels the G3BP1 interactome evading stress granule formation.

Michèle Brocard,Ian G Goodfellow,Glenys Lewis,Philipp Klein,Belinda Hall,Roy Parker,James Burke,Valentina Iadevaia,Alessia Ruggieri,Jia Lu,Nicolas Locker,Margaret M Willcocks

doi:10.1371/journal.ppat.1008250

Abstract

Viral infections impose major stress on the host cell. In response, stress pathways can rapidly deploy defence mechanisms by shutting off the protein synthesis machinery and triggering the accumulation of mRNAs into stress granules to limit the use of energy and nutrients. Because this threatens viral gene expression, viruses need to evade these pathways to propagate. Human norovirus is responsible for gastroenteritis outbreaks worldwide. Here we examined how norovirus interacts with the eIF2α signaling axis controlling translation and stress granules. While norovirus infection represses host cell translation, our mechanistic analyses revealed that eIF2α signaling mediated by the stress kinase GCN2 is uncoupled from translational stalling. Moreover, infection results in a redistribution of the RNA-binding protein G3BP1 to replication complexes and remodelling of its interacting partners, allowing the avoidance from canonical stress granules. These results define novel strategies by which norovirus undergo efficient replication whilst avoiding the host stress response and manipulating the G3BP1 interactome.

Highlights

The synthesis of viral proteins, whose functions are essential to viral replication and propagation, is wholly dependent on gaining control of the host cell translation machinery
Viruses have evolved elegant strategies to evade host responses that restrict viral propagation by targeting the protein synthesis machinery and stress granules, which are membrane-less RNA granules with antiviral properties
To account for different cellular models used to study murine norovirus (MNV) replication, we chose to address this event in the murine macrophages cell lines RAW264.7 and primary murine bone marrow derived macrophages (BMDMs)

Summary

Introduction

The synthesis of viral proteins, whose functions are essential to viral replication and propagation, is wholly dependent on gaining control of the host cell translation machinery. The accumulation of double-stranded (ds) RNA replication intermediates or viral proteins imposes major stress on the host [1] In response to this stress, infected cells can induce several defence mechanisms to promote cell survival and limit the use of energy and nutrients, which can culminate in a global reduction of protein synthesis, while paradoxically allowing the rapid synthesis of antiviral proteins [1,2,3]. Most translational arrest strategies target translation initiation This can be achieved by interfering with the initial cap-binding step mediated by eukaryotic initiation factor (eIF) 4F, targeting its integrity with viral proteases or its activity by modulating the mTOR or MAPK signaling pathways, or by altering the availability of the eIF2-GTP-tRNAiMet ternary complex by phosphorylating eIF2α [3, 4]. Among the four eIF2α kinases, protein kinase R (PKR) is activated by viral dsRNA sensing in the cytoplasm, the other kinases: heme regulated eIF2α kinase (HRI), general control nonderepressible 2 (GCN2) and PKR-like ER localised kinase (PERK) can be activated by infection cues such as oxidative stress, amino acid starvation and ER stress, respectively

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Conclusion