Nsp1 proteins of human coronaviruses HCoV-OC43 and SARS-CoV2 inhibit stress granule formation

Abstract

Stress granules (SGs) are cytoplasmic condensates that often form as part of the cellular antiviral response. Despite the growing interest in understanding the interplay between SGs and other biological condensates and viral replication, the role of SG formation during coronavirus infection remains poorly understood. Several proteins from different coronaviruses have been shown to suppress SG formation upon overexpression, but there are only a handful of studies analyzing SG formation in coronavirus-infected cells. To better understand SG inhibition by coronaviruses, we analyzed SG formation during infection with the human common cold coronavirus OC43 (HCoV-OC43) and the pandemic SARS-CoV2. We did not observe SG induction in infected cells and both viruses inhibited eukaryotic translation initiation factor 2α (eIF2α) phosphorylation and SG formation induced by exogenous stress. Furthermore, in SARS-CoV2 infected cells we observed a sharp decrease in the levels of SG-nucleating protein G3BP1. Ectopic overexpression of nucleocapsid (N) and non-structural protein 1 (Nsp1) from both HCoV-OC43 and SARS-CoV2 inhibited SG formation. The Nsp1 proteins of both viruses inhibited arsenite-induced eIF2α phosphorylation, and the Nsp1 of SARS-CoV2 alone was sufficient to cause a decrease in G3BP1 levels. This phenotype was dependent on the depletion of cytoplasmic mRNA mediated by Nsp1 and associated with nuclear accumulation of the SG-nucleating protein TIAR. To test the role of G3BP1 in coronavirus replication, we infected cells overexpressing EGFP-tagged G3BP1 with HCoV-OC43 and observed a significant decrease in virus replication compared to control cells expressing EGFP. The antiviral role of G3BP1 and the existence of multiple SG suppression mechanisms that are conserved between HCoV-OC43 and SARS-CoV2 suggest that SG formation may represent an important antiviral host defense that coronaviruses target to ensure efficient replication.

Influenza A virus NS1 effector domain is required for PA-X mediated host shutoff

“…This model was consistent with the reported mechanism governing nucleocytoplasmic shuttling of PABPC1 [56–58]. It was also informed by our analysis of the SARS-CoV2 host shutoff protein Nsp1 that causes similar nuclear PABPC1 relocalization [59], and a previously proposed model for nuclear PABPC1 accumulation caused by KSHV host shutoff nuclease SOX and its homologue from the murine gammaherpesvirus 68 (MHV68) called muSOX [15]. That work by the Glaunsinger group and their later studies also described how aberrant nuclear accumulation of PABPC1 caused hyperadenylation of mRNAs [15,56].…”

Human Coronavirus OC43 as a Low-Risk Model to Study COVID-19

“…Thus far, only three papers have described the functions of the NS proteins of HCoV-OC43 in the context of HCoV-OC43 biology [ 38 , 44 , 45 ]. Mounir et al characterized the nucleotide and amino acid sequences of NS2 [ 45 ].…”

“…Labonte et al confirmed the expression of the NS2 protein in HCoV-OC43-infected HRT-18 cells. Dolliver et al showed the inhibitory ability of the NS1 protein of HCoV-OC43 against stress granule formation [ 44 ]. Since most of early studies examined the functions of the structural proteins of HCoV-OC43, we focus on the description of characteristics of the structural proteins of HCoV-OC43 in the following section.…”

Multiple functions of stress granules in viral infection at a glance

“…Some studies agree that the N protein could disrupt SG formation by sequestering G3BP1/2 from interacting with other proteins (Stukalov et al, 2021;Kim et al, 2022). The non-structural protein 1 (Nsp1) of the virus can decrease the level of G3BP1, which is associated with nuclear accumulation of the SG-nucleating protein TIAR (Dolliver et al, 2022). Besides, methyltransferases 1 (PRMT1) methylates SARS-CoV-2 N protein at residues R95 and R177.…”