SARS-CoV-2 Membrane Protein Inhibits Type I Interferon Production Through Ubiquitin-Mediated Degradation of TBK1.

Liyan Sui,Ping Wu,Zedong Wang,Yinghua Zhao,Yang Yu,Zhijun Hou,Guangyun Tan,Wenfang Wang,Quan Liu

doi:10.3389/fimmu.2021.662989

Abstract

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is the causative pathogen of current COVID-19 pandemic, and insufficient production of type I interferon (IFN-I) is associated with the severe forms of the disease. Membrane (M) protein of SARS-CoV-2 has been reported to suppress host IFN-I production, but the underlying mechanism is not completely understood. In this study, SARS-CoV-2 M protein was confirmed to suppress the expression of IFNβ and interferon-stimulated genes induced by RIG-I, MDA5, IKKϵ, and TBK1, and to inhibit IRF3 phosphorylation and dimerization caused by TBK1. SARS-CoV-2 M could interact with MDA5, TRAF3, IKKϵ, and TBK1, and induce TBK1 degradation via K48-linked ubiquitination. The reduced TBK1 further impaired the formation of TRAF3–TANK–TBK1-IKKε complex that leads to inhibition of IFN-I production. Our study revealed a novel mechanism of SARS-CoV-2 M for negative regulation of IFN-I production, which would provide deeper insight into the innate immunosuppression and pathogenicity of SARS-CoV-2.

Highlights

The newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the coronavirus disease 2019 (COVID-19) pandemic is a novel viral member in the genus Betacoronavirus of the family Coronaviridae [1, 2], which is the third coronavirus associated with severe respiratory diseases, following SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) [3, 4]
QPCR results showed that M protein significantly inhibited IFNa, IFNb and ISG15 mRNA expression induced by retinoic acid-inducible gene-I (RIG-I), melanoma differentiation associated gene 5 (MDA5), TANK-binding kinase 1 (TBK1) and IKKε (Figures 1I–K)
ELISA results showed that IFNb induced by MDA5, TBK1 and IKKε was significantly inhibited by M protein (Figure 1L).These results indicate that SARS-CoV-2 M inhibits RIG-I/MDA5/IKKε/TBK1-mediated IFN-b and interferon-stimulated genes (ISGs) production

Summary

Introduction

The newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the coronavirus disease 2019 (COVID-19) pandemic is a novel viral member in the genus Betacoronavirus of the family Coronaviridae [1, 2], which is the third coronavirus associated with severe respiratory diseases, following SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) [3, 4]. Innate immune response is considered as the first host defense against viral infections, which initiates antiviral responses through the pattern recognition receptors (PRRs) of hosts. The double-strand RNA, resulting from coronavirus genome replication and transcription, is first recognized by host PRRs, including the retinoic acid-inducible gene-I (RIG-I) like receptors (RLRs), such as RIG-I and melanoma differentiation associated gene 5 (MDA5) [6, 7]. Activated RLRs trigger TANK-binding kinase 1 (TBK1) activation through the key adaptor mitochondrial antiviral signaling (MAVS) [8], further activating the transcription factor interferon regulation factor 3 (IRF3) to induce production of type I interferon (IFN-I) and downstream interferon-stimulated genes (ISGs), the critical host antiviral factors [9, 10]

Methods

Results

Conclusion