The autophagy‐related degradation of MDA5 by Tembusu virus nonstructural 2B disrupts IFNβ production

Abstract

Duck Tembusu virus (TMUV) is a serious avian pathogen causing a decline in egg production, but the mechanism of the virus that breaks through the innate immune system is poorly understood. Here, we show that TMUV inhibits poly(I:C)‐induced interferon (IFN) production. Because poly(I:C) transfection can specifically activate the MDA5 pathway in duck primary cells, we found that infection with TMUV can specifically target MDA5 and lead to its degradation. MDA5 downregulation could be blocked by the autophagy inhibitor 3‐methyladenine (3‐MA) but not a proteasome inhibitor, strongly implicating MDA5 degradation as an autophagy‐related degradation pathway. Pretreatment with 3‐MA enhanced the expression of MDA5 and inhibited TMUV replication. To screen TMUV proteins that degraded MDA5, the TMUV replicon and MDA5‐Flag were cotransfected into cells, and the western blot analysis showed that nonstructural 2B (NS2B) can degrade MDA5 in a dose‐dependent manner. Dual‐luciferase assays indicate that NS2B alone inhibits MDA5‐ or poly(I:C)‐mediated IFN production. NS2B binds MDA5 in the presence of 3‐MA. The deletion of the amino acids of NS2B from residues 51 to 92 (hydrophilic area) restored the expression of MDA5 and relieved the MDA5‐mediated IFNβ production inhibition by NS2B, indicating that the hydrophilic area of NS2B is important for its interaction with host innate immunity.

Avian IRF1 and IRF7 Play Overlapping and Distinct Roles in Regulating IFN-Dependent and -Independent Antiviral Responses to Duck Tembusu Virus Infection

“…NS2A and TBK1 compete with STING to inhibit IFN production and subsequent stages of IFN signaling [ 25 ]. NS2B cuts and combines duck STING to subvert the induction of IFNβ [ 23 ] and can also target MDA5 for rapid degradation [ 48 ]. NS4B significantly inhibits IFN-β and the ISRE promoter activity by competitively binding to TBK1 and STING, resulting in a decrease in TBK1 phosphorylation.…”

Advancements in Research on Duck Tembusu Virus Infections

“…TMUV NS2B specifically interacts with mitochondrial antiviral signaling protein (duMAVS) to mediate ubiquitination and proteasomal degradation, thereby inhibiting the production of IFN [142]. NS2B is capable of inhibiting MDA5-or poly (I:C)-mediated IFN-β production, and this inhibitory effect is weakened when amino acid residues 51 to 92 (hydrophilic region) are deleted, indicating the importance of the hydrophilic region of NS2B for its interaction with the host innate immune system [143].…”

REPLICAID: replicon vaccines to combat avian infectious diseases

“…Similar to alphaviruses, TMUV is primarily detected by MDA-5 (Z. Wu et al, 2022), making it less likely that the lack of RIG-I is the primary reason why the VEEV replicon system only partially protects chickens (Schultz-Cherry et al, 2000). The slower onset of heterologous protein expression (Chapter 3) and most likely delayed production of dsRNA intermediates, however, might lower the innate immune reaction elicited in chickens in response to TMUV replicon vaccination (Näslund et al, 2011).…”