SARS-CoV-2 Nsp14 activates NF-κB signaling and induces IL-8 upregulation

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection leads to NF-κB activation and induction of pro-inflammatory cytokines, though the underlying mechanism for this activation is not fully understood. Our results reveal that the SARS-CoV-2 Nsp14 protein contributes to the viral activation of NF-κB signaling. Nsp14 caused the nuclear translocation of NF-κB p65. Nsp14 induced the upregulation of IL-6 and IL-8, which also occurred in SARS-CoV-2 infected cells. IL-8 upregulation was further confirmed in lung tissue samples from COVID-19 patients. A previous proteomic screen identified the putative interaction of Nsp14 with host Inosine-5'-monophosphate dehydrogenase 2 (IMPDH2) protein, which is known to regulate NF-κB signaling. We confirmed the Nsp14-IMPDH2 protein interaction and found that IMPDH2 knockdown or chemical inhibition using ribavirin (RIB) and mycophenolic acid (MPA) abolishes Nsp14-mediated NF-κB activation and cytokine induction. Furthermore, IMDPH2 inhibitors (RIB, MPA) efficiently blocked SARS-CoV-2 infection, indicating that IMDPH2, and possibly NF-κB signaling, is beneficial to viral replication. Overall, our results identify a novel role of SARS-CoV-2 Nsp14 in causing the activation of NF-κB.

SARS-CoV-2 Nsp14 mediates the effects of viral infection on the host cell transcriptome

“…In our analysis of the promoters of early upregulated genes, we also detected enrichment for binding sites of transcription factors involved in the interferon response. In support of our findings, recent reports showed that Nsp14 reduces the expression of INFb and ISG luciferase reporters (Yuen et al, 2020), as well as the expression of proteins involved in the NFkB pathway (Hsu et al, 2021;Li et al, 2021).…”

“…Early after transfection with the Nsp14 expression vector, we detected increased CXCL8 expression, which encodes IL8. IL8 is elevated in plasma of COVID-19 patients (Blanco-Melo et al, 2020;Hariharan et al, 2021;Li et al, 2021) and is a marker of acute severe lung distress (Adcock et al, 2015), an inflammatory condition that can lead to severe complications or death. Use of a reporter assay showed that Nsp14 influences transcription of CXCL8.…”

“…We also detected a significant enrichment for NFkB binding sites in the promoters of genes that were differentially expressed at early time points after Nsp14 expression. NFkB is one of the first pathways activated upon SARS-CoV-2 infection (Li et al, 2021;Wyler et al, 2021). One activator of NFkB is PKR (Der and Lau, 1995;Clemens and Elia, 1997).…”

“…The C-terminal region of Nsp14 functions as an S-adenosyl methionine-dependent guanine-N7 methyl transferase that is independent of the ExoN activity (Chen et al, 2009). Recent research suggested that Nsp14 might mediate immune surveillance escape by reducing activity of the interferon pathway and activating the pro-inflammatory response through NFkB transcriptional activity and CXCL8 expression (Yuen et al, 2020;Hsu et al, 2021;Li et al, 2021). However, the biological mechanism behind these events has not fully characterized.…”

“…Guanosine-5'-triphosphate (GTP) is necessary for DNA replication and transcription and is used as energy source for translation and as mediator of signal transduction (Hesketh and Oliver, 2019). How the physical interaction between Nsp14 and IMPDH2 impacts the host pathways is not completely understood (Li et al, 2021). Interestingly, a recent study shows that expression of Nsp14 results in global translation inhibition, but it is not clear if this is a direct effect or a downstream consequence of changes that expression of the protein provoke to the cellular environment (Hsu et al, 2021).…”