Analysis of intracellular localization of viral RNA sensor, RLR

Abstract

Type I interferons (IFNs) play a pivotal role for antiviral innate immunity and subsequent modulation of adaptive immunity. Normally IFN genes are not expressed, however upon viral infection, the genes are transiently activated, and the secreted IFNs inhibit viral replications through induction of a series of IFN stimulated genes.Viral RNA appearing in cells as a result of viral infection is detected by cytoplasmic sensors, retinoic acid inducible gene‐I (RIG‐I)‐like receptors (RLRs). RLRs, which are DExD/H ‐ box containing RNA helicases, consist of RIG‐I, melanoma differentiation‐associated gene 5 (MDA5), and laboratory of genetics and physiology 2 (LGP2). All RLRs contain a conserved C‐terminal domain, which is responsible for specific recognition of the viral RNAs. Although the domain structure of RLRs for detection of non‐self RNA has been elucidated, it has been unclear how RLRs encounter viral RNA and trigger signaling.To address this issue, we made specific antibodies against RLRs and examined their intracellular localization in virus‐infected cells by immunostaining using confocal fluorescence microscope. When cells were infected with Influenza A virus (IAV) deficient for its Non‐structural protein 1 (NS1), RIG‐I accumulated as granular‐like pattern in the cyotosol and colocalized with viral Nucleocapsid protein. Moreover, RIG‐I colocalized with MDA5, LGP2 and several antiviral proteins such as PKR and OAS. We also detected similar localization patterns of RIG‐I in cells‐infected with various RNA viruses such as HCV and NDV. We are going to discuss relationship between the subcellular localization of RLRs and viral detection in detail.