Regulation of antiviral innate immune signaling by stress-induced RNA granules.

Activation of antiviral innate immunity is triggered by cellular pattern recognition receptors. Retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs) detect viral non-self RNA in cytoplasm of virus-infected cells and play a critical role in the clearance of the invaded viruses through production of antiviral cytokines. Among the three known RLRs, RIG-I and melanoma differentiation-associated gene 5 recognize distinct non-self signatures of viral RNA and activate antiviral signaling.

Viral RNA detection by RIG-I-like receptors.

In higher vertebrates, recognition of the non-self signature of invading viruses by genome-encoded pattern recognition receptors initiates antiviral innate immunity. Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) detect viral RNA as a non-self pattern in the cytoplasm and activate downstream signaling. Detection of viral RNA also activates stress responses resulting in stress granule-like aggregates, which facilitate RLR-mediated antiviral immunity.

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.

Critical role of an antiviral stress granule containing RIG-I and PKR in viral detection and innate immunity.

Retinoic acid inducible gene I (RIG-I)-like receptors (RLRs) function as cytoplasmic sensors for viral RNA to initiate antiviral responses including type I interferon (IFN) production. It has been unclear how RIG-I encounters and senses viral RNA. To address this issue, we examined intracellular localization of RIG-I in response to viral infection using newly generated anti-RIG-I antibody.

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-beta 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.