The RNA Helicase DDX6 Associates with RIG-I to Augment Induction of Antiviral Signaling.

Rocío Núñez,Thorsten Wolff,Sandra Saenger,Anne Sadewasser,Ulrike Arnold,Katharina Paki,Matthias Budt

doi:10.3390/ijms19071877

Rocío Núñez, Thorsten Wolff + Show 5 more

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https://doi.org/10.3390/ijms19071877

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Abstract

Virus infections induce sensitive antiviral responses within the host cell. The RNA helicase retinoic acid-inducible gene I (RIG-I) is a key sensor of influenza virus RNA that induces the expression of antiviral type I interferons. Recent evidence suggests a complex pattern of RIG-I regulation involving multiple interactions and cellular sites. In an approach employing affinity purification and quantitative mass spectrometry, we identified proteins with increased binding to RIG-I in response to influenza B virus infection. Among them was the RIG-I related RNA helicase DEAD box helicase 6 (DDX6), a known component of cytoplasmic mRNA-ribonucleoprotein (mRNP) granules like P-bodies and stress granules (SGs). RIG-I and DDX6 both localized to the cytosol and were detected in virus-induced SGs. Coimmunoprecipitation assays detected a basal level of complexes harboring RIG-I and DDX6 that increased after infection. Functionally, DDX6 augmented RIG-I mediated induction of interferon (IFN)-β expression. Notably, DDX6 was found to bind viral RNA capable to stimulate RIG-I. These findings imply a novel function for DDX6 as an RNA co-sensor and signaling enhancer for RIG-I.

Highlights

Influenza viruses (IVs) cause annual epidemics and occasional pandemics in the human population with severe impact on global health
The infected cells presented stress granules (SGs) in which G3BP colocalized with retinoic acid-inducible gene I (RIG-I) (Figure 2b) as well as with DDX6 (Figure 2c). These results show that RIG-I and DDX6 presented a diffuse distribution throughout the cytosol in wild type virus infected cells and colocalized in SGs, when cells were infected with the mutant influenza B virus
Our data argue against an RNA-bridged interaction of RIG-I and DDX6, since DDX6 directly binds to the RIG-I caspase recruitment domains (CARDs) domains

Summary

Introduction

Influenza viruses (IVs) cause annual epidemics and occasional pandemics in the human population with severe impact on global health. Oligomerization of RIG-I on RNA ligands drives the formation of helical CARD domain filaments which recruits and organizes the downstream adapter MAVS ( known as IPS-1, VISA, or Cardif) into similar filamentous aggregates [14] This mediates activation of the transcription factors IRF3 and IRF7 through the phosphorylation by Iκ-B kinase family members TBK1 and IKKε. Stalled translation machinery is accumulated in stress granules (SGs), which are dynamic cytosolic aggregates that contain translationally arrested mRNAs, 40S ribosomes, and various RNA-binding proteins like TIA-1, TIAR, and G3BP1 [31,32] It has been recently suggested, that SGs serve as assembly platforms for the shaping of an antiviral host response and their presence correlates with reduced virus replication [33,34]. Virus ribonucleoprotein complexes are present in SGs, yet how this contributes to the host antiviral response is not well established [35,36]

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