Mouse Norovirus infection arrests host cell translation uncoupled from the stress granule-PKR-eIF2α axis

Abstract

1 8 1 9 ¶ These authors contributed equally to this work. SF and TEA are Joint Authors 2 0 2 1 Abstract 2 5The integrated stress response (ISR) is a cellular response system activated upon different 2 6 types of stresses, including viral infection, to restore cellular homeostasis. However, many viruses 2 7 manipulate this response for their own advantage. In this study we investigated the association 2 8between murine norovirus (MNV) infection and the ISR and demonstrate that MNV regulates the 2 9ISR by activating and recruiting key ISR host factors. We observed that during MNV infection, 3 0there is a progressive increase in phosphorylated eukaryotic initiation factor 2 alpha (p-eIF2α) 3 1 resulting in the suppression of host translation, yet MNV translation still progresses under these 3 2 conditions. Interestingly, the shutoff of host translation also impacts the translation of key signalling 3 3 cytokines such as IFNβ, IL-6 and TNFα. Our subsequent analyses revealed that the phosphorylation 3 4 of eIF2α was mediated via Protein kinase-R (PKR), but further investigation revealed that PKR 3 5 activation, phosphorylation of eIF2α and translational arrest were uncoupled during infection. We 3 6 further observed that stress granules (SGs) are not induced during MNV infection, and MNV has 3 7the capacity to restrict SG nucleation and formation. We observed that MNV recruited the key SG 3 8nucleating protein G3BP1 to its replication sites and intriguingly the silencing of G3BP1 negatively 3 9impacts MNV replication. Thus, it appears, MNV utilises G3BP1 to enhance replication, but 4 0 equally to prevent SG formation, intimating an anti-MNV property of SGs. Overall, thus study 4 1

Noroviruses subvert the core stress granule component G3BP1 to promote viral VPg-dependent translation

“…Recent work confirms that the preferential viral translation is not driven by the GCN2-mediated phosphorylation of eIF2α in MNV infected cells (Brocard et al, 2018). We note however that others have suggested that NS3 may contribute to the translational shut off seen in MNV infected cells (Fritzlar et al, 2019), with the caveat that this observation was made outside of the context of infected cells and used overexpressed tagged viral proteins. We suspect that noroviruses use multiple mechanisms that work cooperatively to enable the control of host gene expression and the subsequent translation of the cellular mRNAs.…”

“…While our data fit with a primary role for G3BP1 in norovirus translation, we are unable to exclude the possibility that G3BP1 plays other roles in the viral life cycle. Recent studies have confirmed that G3BP1 is enriched at sites of viral RNA synthesis (Brocard et al, 2018; Fritzlar et al, 2019) so it is possible that G3BP1 makes multiple contacts between the 40S subunit and viral RNA genome directly. These additional contacts, may further promote viral VPg-dependent translation and/or another aspect of the viral life cycle.…”