RIG-I-like receptors에 의한 인터페론 발현 시스템에서 신호 조절과 세포의 이상성 반응에 대한 연구

Abstract

We are constantly exposed to various pathogens, such as fungi, parasites, bacteria and viruses. Infection by pathogens could be a severe threat

therefore, we have developed defense mechanisms against unwanted biological invasion, known as immunity. During the innate immune response, pattern recognition receptors (PRRs) discriminate between self and non-self through their recognition of pathogen-associated molecular patterns (PAMPs) that activate signal cascades and elimination of foreign molecules.In RNA virus-infected cells, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) sense cytosolic foreign RNAs and activate downstream signals to produce IFNα and IFNβ (IFNα/β). Due to the protective and destructive effects of IFNα/β, fine-tuned regulation of the IFNα/β response during viral infection is required. To investigate the dynamics of IFNβ expression, I constructed an IFNβ1p-GFP-IFNβ1UTR reporter cell. Using this experimental system, I observed a bimodal distribution of IFNβ-expressing cells upon stimulation with intracellular non-self RNA. Feedback loops mediated by secreted IFNα/β were critical for the bimodality of the IFNβ-producing cells, as the bimodal distribution of IFNβ production was disturbed by the blockage of IFNα/β secretion, or by the silencing of the IFNα/β receptor. Interestingly, IFNα/β production positively correlated with the amount of RLR and cellular apoptosis. These data suggest that biphasic cellular responses may act to restrict the total amount of IFNα/β and the number of cells undergoing apoptosis in the infected population.As a ligand of RLRs, the RIG-I protein is a good target for controlling IFNα/β production. In an attempt to identify a novel tool for modulating IFNα/β expression, I screened RNA aptamers using SELEX technology, which specifically targets RIG-I protein. Most of the selected RIG-I aptamers contained polyU motifs in the second half region that played a critical role in the activation of RIG-I-mediated IFNβ production. Unlike other known ligands, RIG-I aptamers bound and activated RIG-I in a 5’-triphosphate-independent manner. The helicase and RD domain of RIG-I were used for aptamer binding, but intact RIG-I protein was required to exert aptamer-mediated signaling activation. Furthermore, replication of NDV, VSV, and influenza virus in infected host cells was efficiently blocked by pre- or post-treatment with RIG-I aptamer. Based on these data, I propose that RIG-I aptamers have strong potential for use as antiviral agents that specifically boost the RIG-I-dependent signaling cascade.