New role of gramicidin A in RIG‐I‐like receptors‐mediated IFN signalling

• Published in: Immunology Vol. 169; no. 2; pp. 219 - 228
• Main Authors: Li, Xiao, Sun, Xinyuan, Yan, Zhongyi, Zhao, Zhenxiang, Pang, Zhaojun, Yang, Han, Ji, Xiaoxin, Lei, Yi, Zhu, Zixiang, Guo, Xiangqian, Mu, Xin
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.06.2023
• Subjects: Assaying; Chemical properties; Cytoplasm; Cytotoxicity; DEAD Box Protein 58 - genetics; DEAD Box Protein 58 - metabolism; Double-stranded RNA; GOF; Gramicidin; gramicidin A; IFN; Immunity, Innate; Innate immunity; Interferon; Interferon-Induced Helicase, IFIH1 - genetics; Interferon-Induced Helicase, IFIH1 - metabolism; Interferons - genetics; Lipids; MAVS; MDA5; Melanoma; Oligomerization; Pattern recognition; Pattern recognition receptors; Reagents; Receptors; Retinoic acid; RIG‐I; RNA, Double-Stranded; Signal Transduction; Signaling; Stimulators; Sucrose; Ultracentrifugation; IFN; RIG-I; gramicidin A; MAVS; GOF; MDA5
• ISSN: 0019-2805; 1365-2567
• DOI: 10.1111/imm.13626

The pattern recognition receptors (PRRs) sense exogenous molecular patterns most commonly derived from invading pathogens, to active the interferon (IFN) signalling. In the cytoplasm, the viral double‐stranded RNAs (dsRNAs) are sensed by retinoic acid‐inducible gene I (RIG‐I) or melanoma differentiation‐associated protein 5 (MDA5), depending on the length and chemical properties. Through the binding and oligomerizing onto the RNAs, they form filament to initiate the signalling cascade. Regulation of these receptors' activities are essential for manipulating the strength of IFN signalling. Here, through the virtual screening of chemical reagents using the published MDA5‐dsRNA complex structure (PDB: 4GL2), we identified an antibiotic, gramicidin A as a stimulator that enhanced MDA5‐mediated IFN signalling. Cytotoxic assay and IFN signalling assay suggested that disruption of lipid membrane, which is a well‐defined mechanism of gramicidin A to perform its action, was dispensable in this process. Sucrose gradient ultracentrifugation assay showed that the gramicidin A treatment enhanced MDA5 oligomerization status in the presence of dsRNA. Our work implicated a new role of gramicidin A in innate immunity and presented a new tool to manipulate MDA5 activity. Li et al found that gramicidin A, a commonly used antimicrobial drug, can enhance MDA5 (or RIG‐I)‐mediated interferon (IFN) signalling. This activity is not due to its lipid membrane attacking capacity, but via the specifically targeting of dsRNA‐MDA5 complex and thus the enhance of the proportion of filamentous MDA5. More filamentous MDA5 then, activate MAVS more efficiently to initiate IFN expression. This study uncovered a new role of gramicidin A in host's antiviral defence and may expand the application of gramicidin A.