Distinct RIG-I and MDA5 Signaling by RNA Viruses in Innate Immunity

ABSTRACT Alpha/beta interferon immune defenses are essential for resistance to viruses and can be triggered through the actions of the cytoplasmic helicases retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5). Signaling by each is initiated by the recognition of viral products such as RNA and occurs through downstream interaction with the IPS-1 adaptor protein. We directly compared the innate immune signaling requirements of representative viruses of the Flaviviridae, Orthomyxoviridae, Paramyxoviridae, and Reoviridae for RIG-I, MDA5, and interferon promoter-stimulating factor 1 (IPS-1). In cultured fibroblasts, IPS-1 was essential for innate immune signaling of downstream interferon regulatory factor 3 activation and interferon-stimulated gene expression, but the requirements for RIG-I and MDA5 were variable. Each was individually dispensable for signaling triggered by reovirus and dengue virus, whereas RIG-I was essential for signaling by influenza A virus, influenza B virus, and human respiratory syncytial virus. Functional genomics analyses identified cellular genes triggered during influenza A virus infection whose expression was strictly dependent on RIG-I and which are involved in processes of innate or adaptive immunity, apoptosis, cytokine signaling, and inflammation associated with the host response to contemporary and pandemic strains of influenza virus. These results define IPS-1-dependent signaling as an essential feature of host immunity to RNA virus infection. Our observations further demonstrate differential and redundant roles for RIG-I and MDA5 in pathogen recognition and innate immune signaling that may reflect unique and shared biologic properties of RNA viruses whose differential triggering and control of gene expression may impact pathogenesis and infection.

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RIG-I Signaling Is Essential for Influenza B Virus-Induced Rapid Interferon Gene Expression

Journal of Virology ◽

10.1128/jvi.01576-15 ◽

2015 ◽

Vol 89 (23) ◽

pp. 12014-12025 ◽

Cited By ~ 25

Author(s):

Sanna M. Mäkelä ◽

Pamela Österlund ◽

Veera Westenius ◽

Sinikka Latvala ◽

Michael S. Diamond ◽

...

Keyword(s):

Gene Expression ◽

Virus Infection ◽

Influenza A Virus ◽

Influenza A ◽

Innate Immune ◽

Influenza B Virus ◽

Influenza B ◽

Immune Recognition ◽

B Virus ◽

Irf3 Activation

ABSTRACTInfluenza B virus causes annual epidemics and, along with influenza A virus, accounts for substantial disease and economic burden throughout the world. Influenza B virus infects only humans and some marine mammals and is not responsible for pandemics, possibly due to a very low frequency of reassortment and a lower evolutionary rate than that of influenza A virus. Influenza B virus has been less studied than influenza A virus, and thus, a comparison of influenza A and B virus infection mechanisms may provide new insight into virus-host interactions. Here we analyzed the early events in influenza B virus infection and interferon (IFN) gene expression in human monocyte-derived macrophages and dendritic cells. We show that influenza B virus induces IFN regulatory factor 3 (IRF3) activation and IFN-λ1 gene expression with faster kinetics than does influenza A virus, without a requirement for viral protein synthesis or replication. Influenza B virus-induced activation of IRF3 required the fusion of viral and endosomal membranes, and nuclear accumulation of IRF3 and viral NP occurred concurrently. In comparison, immediate early IRF3 activation was not observed in influenza A virus-infected macrophages. Experiments with RIG-I-, MDA5-, and RIG-I/MDA5-deficient mouse fibroblasts showed that RIG-I is the critical pattern recognition receptor needed for the influenza B virus-induced activation of IRF3. Our results show that innate immune mechanisms are activated immediately after influenza B virus entry through the endocytic pathway, whereas influenza A virus avoids early IRF3 activation and IFN gene induction.IMPORTANCERecently, a great deal of interest has been paid to identifying the ligands for RIG-I under conditions of natural infection, as many previous studies have been based on transfection of cells with different types of viral or synthetic RNA structures. We shed light on this question by analyzing the earliest step in innate immune recognition of influenza B virus by human macrophages. We show that influenza B virus induces IRF3 activation, leading to IFN gene expression after viral RNPs (vRNPs) are released into the cytosol and are recognized by RIG-I receptor, meaning that the incoming influenza B virus is already able to activate IFN gene expression. In contrast, influenza A (H3N2) virus failed to activate IRF3 at very early times of infection, suggesting that there are differences in innate immune recognition between influenza A and B viruses.

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Interplay between influenza A virus and the innate immune signaling

Microbes and Infection ◽

10.1016/j.micinf.2009.09.007 ◽

2010 ◽

Vol 12 (1) ◽

pp. 81-87 ◽

Cited By ~ 90

Author(s):

Christina Ehrhardt ◽

Roman Seyer ◽

Eike R. Hrincius ◽

Thorsten Eierhoff ◽

Thorsten Wolff ◽

...

Keyword(s):

Influenza A Virus ◽

Influenza A ◽

Innate Immune ◽

Immune Signaling ◽

Innate Immune Signaling

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The adaptor protein FHL2 enhances the cellular innate immune response to influenza A virus infection

Cellular Microbiology ◽

10.1111/j.1462-5822.2012.01787.x ◽

2012 ◽

Vol 14 (7) ◽

pp. 1135-1147 ◽

Cited By ~ 9

Author(s):

Carolin Nordhoff ◽

Andrea Hillesheim ◽

Beate M. Walter ◽

Emanuel Haasbach ◽

Oliver Planz ◽

...

Keyword(s):

Immune Response ◽

Virus Infection ◽

Influenza A Virus ◽

Innate Immune Response ◽

Influenza A ◽

Adaptor Protein ◽

Innate Immune ◽

Influenza A Virus Infection

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Spatiotemporal dynamics of innate immune signaling via RIG-I–like receptors

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1921861117 ◽

2020 ◽

Vol 117 (27) ◽

pp. 15778-15788 ◽

Cited By ~ 3

Author(s):

Katharina Esser-Nobis ◽

Lauren D. Hatfield ◽

Michael Gale

Keyword(s):

Innate Immunity ◽

Virus Infection ◽

Rna Virus ◽

Adaptor Protein ◽

Innate Immune ◽

Negative Regulator ◽

Resting Cells ◽

Immune Signaling ◽

Innate Immune Signaling ◽

Irf3 Activation

RIG-I, MDA5, and LGP2 comprise the RIG-I–like receptors (RLRs). RIG-I and MDA5 are essential pathogen recognition receptors sensing viral infections while LGP2 has been described as both RLR cofactor and negative regulator. After sensing and binding to viral RNA, including double-stranded RNA (dsRNA), RIG-I and MDA5 undergo cytosol-to-membrane relocalization to bind and signal through the MAVS adaptor protein on intracellular membranes, thus directing downstream activation of IRF3 and innate immunity. Here, we report examination of the dynamic subcellular localization of all three RLRs within the intracellular response to dsRNA and RNA virus infection. Observations from high resolution biochemical fractionation and electron microscopy, coupled with analysis of protein interactions and IRF3 activation, show that, in resting cells, microsome but not mitochondrial fractions harbor the central components to initiate innate immune signaling. LGP2 interacts with MAVS in microsomes, blocking the RIG-I/MAVS interaction. Remarkably, in response to dsRNA treatment or RNA virus infection, LGP2 is rapidly released from MAVS and redistributed to mitochondria, temporally correlating with IRF3 activation. We reveal that IRF3 activation does not take place on mitochondria but instead occurs at endoplasmic reticulum (ER)-derived membranes. Our observations suggest ER-derived membranes as key RLR signaling platforms controlled through inhibitory actions of LGP2 binding to MAVS wherein LGP2 translocation to mitochondria releases MAVS inhibition to facilitate RLR-mediated signaling of innate immunity.

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