Session topic

18:05–18:10

Title: Antagonism of IFN induction and signaling by SARS-CoV-2
ID: PS 27
Type: Poster session
Talk time: 3 + 2 min
Session: Poster session 1
Innate immunity

Speaker: Maximilian Hirschenberger (Ulm/DE)


Abstract - Text

Abstract text (incl. references and figure legends)

Introduction
Upon infection, RNA viruses including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are rapidly detected by host immune sensors such as retinoic acid-inducible gene I (RIG-I). Activation of these sensors triggers signaling cascades eventually leading to the induction of different types of interferons (IFNs) and pro-inflammatory cytokines. Released IFNs in turn induce an antiviral state in cells in an autocrine or paracrine fashion. Current research indicates that SARS-CoV-2 perturbs the IFN response, but we lack knowledge about the responsible viral proteins.


Objectives
Our goal was to systematically analyze the impact of all SARS-CoV-2 proteins on IFN induction and signaling to gain insight into the interplay between the virus and the IFN system.


Materials & Methods
The impact of all SARS-CoV-2 proteins on activation and signaling of the IFN response was systematically analyzed using reporter gene assays. For mechanistic analyses, we employed western blotting, quantitative confocal microscopy and proteomics. The effect of cytokines on SARS-CoV-2 was analyzed using viral infections and qPCR.


Results
We revealed that RLR signaling is potently inhibited by Nsp1, Nsp5, Nsp15, ORF3a, E, M, ORF6 and ORF7b. Moreover, Nsp1, Nsp5, Nsp13, Nsp14, ORF6 and ORF7b antagonize type I IFN signaling (IFN-α2 and -β), and to a weaker extent type II (IFN-γ) and III (IFN-λ1) signaling. Mechanistic analysis showed, that the respective signaling pathways are targeted at various steps. For example, Nsp14 decreases the endogenous levels of the type I IFN receptor IFNAR and consequently activation of the transcription factors STAT1 and STAT2. Although signaling by all different types of IFNs is antagonized by SARS-CoV-2 proteins, the overall inhibition of individual signaling cascades differs. Notably, the anti-SARS-CoV-2 effect of IFNs correlates with the average inhibition of the respective pathway. Our studies identified IFN-γ and -λ1 as most potent inhibitors and revealed that they act synergistically.


Conclusion
We identified several SARS-CoV-2 proteins as key inhibitors of IFN induction and signaling. Furthermore, our analysis revealed that type II and III IFN signaling is overall less antagonized than type I signaling. Consequently, treatment with IFN-y and -λ1 potently inhibits viral replication. Thus, analysis of the interplay between SARS-CoV-2 and host provides clues towards targeted immune activation as a therapeutic approach.