Virus-Infection or 5′ppp-RNA Activates Antiviral Signal through Redistribution of IPS-1 Mediated by MFN1

In virus-infected cells, RIG-I-like receptor (RLR) recognizes cytoplasmic viral RNA and triggers innate immune responses including production of type I and III interferon (IFN) and the subsequent expression of IFN-inducible genes. Interferon-β promoter stimulator 1 (IPS-1, also known as MAVS, VISA and Cardif) is a downstream molecule of RLR and is expressed on the outer membrane of mitochondria. While it is known that the location of IPS-1 is essential to its function, its underlying mechanism is unknown. Our aim in this study was to delineate the function of mitochondria so as to identify more precisely its role in innate immunity. In doing so we discovered that viral infection as well as transfection with 5′ppp-RNA resulted in the redistribution of IPS-1 to form speckle-like aggregates in cells. We further found that Mitofusin 1 (MFN1), a key regulator of mitochondrial fusion and a protein associated with IPS-1 on the outer membrane of mitochondria, positively regulates RLR-mediated innate antiviral responses. Conversely, specific knockdown of MFN1 abrogates both the virus-induced redistribution of IPS-1 and IFN production. Our study suggests that mitochondria participate in the segregation of IPS-1 through their fusion processes

Dysregulation of IFN System Can Lead to Poor Response to Pegylated Interferon and Ribavirin Therapy in Chronic Hepatitis C

Despite being expensive, the standard combination of pegylated interferon (Peg-IFN)- α and ribavirin used to treat chronic hepatitis C (CH) results in a moderate clearance rate and a plethora of side effects. This makes it necessary to predict patient outcome so as to improve the accuracy of treatment. Although the antiviral mechanism of genetically altered IL28B is unknown, IL28B polymorphism is considered a good predictor of IFN combination treatment outcome

Virus Sensor RIG-I Represses RNA Interference by Interacting with TRBP through LGP2 in Mammalian Cells

Exogenous double-stranded RNAs (dsRNAs) similar to viral RNAs induce antiviral RNA silencing or RNA interference (RNAi) in plants or invertebrates, whereas interferon (IFN) response is induced through activation of virus sensor proteins including Toll like receptor 3 (TLR3) or retinoic acid-inducible gene I (RIG-I) like receptors (RLRs) in mammalian cells. Both RNA silencing and IFN response are triggered by dsRNAs. However, the relationship between these two pathways has remained unclear. Laboratory of genetics and physiology 2 (LGP2) is one of the RLRs, but its function has remained unclear. Recently, we reported that LGP2 regulates endogenous microRNA-mediated RNA silencing by interacting with an RNA silencing enhancer, TAR-RNA binding protein (TRBP). Here, we investigated the contribution of other RLRs, RIG-I and melanoma-differentiation-associated gene 5 (MDA5), in the regulation of RNA silencing. We found that RIG-I, but not MDA5, also represses short hairpin RNA (shRNA)-induced RNAi by type-I IFN. Our finding suggests that RIG-I, but not MDA5, interacts with TRBP indirectly through LGP2 to function as an RNAi modulator in mammalian cells

Encephalomyocarditis virus disrupts stress granules, the critical platform for triggering antiviral innate immune responses.

In response to stress, cells induce ribonucleoprotein aggregates, termed stress granules (SGs). SGs are transient loci containing translation-stalled mRNA, which is eventually degraded or recycled for translation. Infection of some viruses, including influenza A virus with a deletion of nonstructural protein 1 (IAVΔNS1), induces SG-like protein aggregates. Previously, we showed that IAVΔNS1-induced SGs are required for efficient induction of type I interferon (IFN). Here, we investigated SG formation by different viruses using green fluorescent protein (GFP)-tagged Ras-Gap SH3 domain binding protein 1 (GFP-G3BP1) as an SG probe. HeLa cells stably expressing GFP-G3BP1 were infected with different viruses, and GFP fluorescence was monitored live with time-lapse microscopy. SG formations by different viruses was classified into 4 different patterns: no SG formation, stable SG formation, transient SG formation, and alternate SG formation. We focused on encephalomyocarditis virus (EMCV) infection, which exhibited transient SG formation. We found that EMCV disrupts SGs by cleavage of G3BP1 at late stages of infection (>8 h) through a mechanism similar to that used by poliovirus. Expression of a G3BP1 mutant that is resistant to the cleavage conferred persistent formation of SGs as well as an enhanced induction of IFN and other cytokines at late stages of infection. Additionally, knockdown of endogenous G3BP1 blocked SG formation with an attenuated induction of IFN and potentiated viral replication. Taken together, our findings suggest a critical role of SGs as an antiviral platform and shed light on one of the mechanisms by which a virus interferes with host stress and subsequent antiviral responses

Mechanisms of length-dependent recognition of viral double-stranded RNA by RIG-I

Abstract Retinoic acid-inducible gene I (RIG-I) is the most front-line cytoplasmic viral RNA sensor and induces antiviral immune responses. RIG-I recognizes short double-stranded (dsRNA) ( 500 bp) to trigger antiviral signaling. Since RIG-I is capable of binding with dsRNA irrespective of size, length-dependent RIG-I signaling remains elusive. Here, we demonstrated that RIG-I bound to long dsRNA with slow kinetics. Remarkably, RIG-I/short dsRNA complex efficiently dissociated in an ATP hydrolysis-dependent manner, whereas RIG-I/long dsRNA was stable and did not dissociate. Our study suggests that the dissociation of RIG-I from RIG-I/dsRNA complex could be a step for efficient antiviral signaling. Dissociated RIG-I exhibited homo-oligomerization, acquiring ability to physically associate with MAVS, and biological activity upon introduction into living cells. We herein discuss common and unique mechanisms of viral dsRNA recognition by RIG-I and MDA5

Virus-induced expression of retinoic acid inducible gene-I and melanoma differentiation-associated gene 5 in the cochlear sensory epithelium.

The inner ear has been regarded as an immunoprivileged site because of isolation by the blood-labyrinthine barrier. Several reports have indicated the existence of immune cells in the inner ear, but there are no reports showing immunocompetence of the cochlear tissue. In this report, we examined the potential involvement of retinoic acid inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5), which are critical for initiating antiviral innate immune responses. We found that RIG-I and MDA5 are expressed in the mouse cochlear sensory epithelium, including Hensen's and Claudius' cells. Ex vivo viral infection using Theiler's murine encephalomyelitis virus revealed that the virus replicates in these cells and that protein levels of RIG-I and MDA5 are up-regulated. Furthermore, the critical antiviral transcription factor, interferon (IFN) regulatory factor-3, is activated in the infected cells as judged by its nuclear translocation and the accumulation of type I IFN transcripts. These results strongly suggest that RIG-I and MDA5 participate in innate antiviral responses in cochlear tissue

Nerezi, Sveti Panteleimon

Diabeschriftung Hallensleben: "Nerezi, Nordarm / Nordwand/ [Bild] / Zone I-III"Bestand Hallensleben Digitales Forschungsarchiv Byzan