Critical Role of IRF-3 in the Direct Regulation of dsRNA-Induced Retinoic Acid-Inducible Gene-I (RIG-I) Expression

Abstract

The cytoplasmic viral sensor retinoic acid-inducible gene-I (RIG-I), which is also known as an IFN-stimulated gene (ISG), senses viral RNA to activate antiviral signaling. It is therefore thought that RIG-I is regulated in a STAT1-dependent manner. Although RIG-I-mediated antiviral signaling is indispensable for the induction of an appropriate adaptive immune response, the mechanism underlying the regulation of RIG-I expression remains elusive. Here, we examined the direct regulation of RIG-I expression by interferon regulatory factor 3 (IRF-3), which is an essential molecule for antiviral innate immunity. We initially found that RIG-I can be induced by dsRNA in both IFN-independent and IRF-3-dependent manners. A sequence analysis revealed that the RIG-I gene has putative IRF-3-binding sites in its promoter region. Using a combination of cellular, molecular biological, and mutational approaches, we first showed that IRF-3 can directly regulate the expression of RIG-I via a single IRF-element (IRF-E) site in the proximal promoter region of the RIG-I gene in response to dsRNA. IRF-3 is considered a master regulator in antiviral signaling for the generation of type I interferons (IFNs). Thus, our findings demonstrate that RIG-I expression induced by the IRF-3-mediated pathway may serve as a crucial antiviral factor for reinforcing a surveillance system against viral invasion through the regulation of the cytoplasmic viral sensor RIG-I.

Cytoplasmic RNA Sensor Pathways and Nitazoxanide Broadly Inhibit Intracellular Mycobacterium tuberculosis Growth

“…MTb glycolipoproteins, lipoproteins, and glycolipids present in the lysate are ligands for TLR4 and TLR2, which can in turn trigger activation of IRF3 and, more broadly, type I IFNs (Falvo et al., 2011, Perkins and Vogel, 2015); thus, the TLR and IRF/IFN pathways may play a complementary role in this context. Indeed, we note that there is evidence that IRF3 can regulate the gene promoters of both RIG-I and MDA5 (Hayakari et al., 2016, Yount et al., 2007) and that interferon-stimulated gene factor 3 (ISGF-3) can regulate the PKR gene promoter (Ward and Samuel, 2003). Furthermore, given that NTZ can promote IRF3-driven IFN-β mRNA expression in addition to its ability to broadly amplify RLR activity (Jasenosky et al., 2019), it is intriguing to speculate that MTb and NTZ directly enhance gene expression of sensor molecules via their effects on upstream transcriptional activators.…”

Role of Mitochondria in Viral Infections

“…TRAF3, along with NF-κB modulator protein NEMO [ 76 ], TRAF family member-associated NF-κB activator (TANK) [ 81 ] and NAK-associated protein 1 (NAP1) [ 82 ], regulates the activity of two noncanonical IKK-related kinases, TANK-binding kinase 1 (TBK1) and inducible IκB kinase (IKKi). The phosphorylation of interferon regulatory factors (IRFs), IRF3 and IRF7, by TBK1 and IKKi leads to the induction of type I IFN genes and a set of IFN-inducible genes that bind to IFN-stimulated response elements (ISREs) in the nucleus [ 83 ]. MAVS activates IRF3 through the ubiquitin-binding domains of NEMO, while NEMO itself activates TBK1 [ 84 ] through TRAF3 [ 85 ].…”

Targeted delivery of immune-stimulating bispecific RNA, inducing apoptosis and anti-tumor immunity in cancer cells

“…RIG-I is described to be overexpressed upon activation, 34 , 35 , 36 to confirm this molecular mechanism, its level of expression was measured by western-blot after 72 h of treatment with either 40 nM of mAb-siPLK1-5′ppp 1 or transfected with 40 nM of siPLK1-5′ppp ( Figure S10 ). In comparison with non-treated cells, a 31-fold increase of RIG-I expression was observed with both treatments ( Figure 4 C), thus confirming the previous RIG-I activation assays.…”