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RIG-I

Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern recognition receptor (PRR) and RNA helicase that plays a central role in the innate immune system's detection of viral infections by recognizing pathogen-associated molecular patterns (PAMPs) such as 5'-triphosphate (5'ppp) single-stranded RNA and short double-stranded RNA with blunt ends and 5'ppp groups.^[1] Originally identified in 1997 as a gene upregulated by all-trans retinoic acid (ATRA) in human acute promyelocytic leukemia cells, its critical function in antiviral immunity was established in 2004 when it was shown to be essential for double-stranded RNA-induced interferon responses.^[2] ^[3] Structurally, RIG-I consists of two N-terminal caspase activation and recruitment domains (CARDs), a central DExD/H-box helicase domain responsible for ATP-dependent RNA binding and unwinding, and a C-terminal repressor domain (RD) that maintains an autoinhibited state in the absence of ligands.^[1] Upon ligand binding, RIG-I undergoes conformational changes that expose the CARDs, enabling K63-linked ubiquitination by TRIM25 and subsequent oligomerization, which facilitates interaction with the adaptor protein MAVS on mitochondria to activate downstream signaling cascades, including IRF3/7 phosphorylation and robust production of type I interferons (IFN-α/β) as well as proinflammatory cytokines.^[1] This pathway is vital for early defense against a broad spectrum of RNA viruses, including influenza A, hepatitis C, and Sendai virus, while also contributing to responses against some DNA viruses that generate RNA intermediates.^[1] Beyond antiviral roles, RIG-I influences non-infectious processes such as cellular differentiation, apoptosis, and bacterial phagocytosis, and its dysregulation is implicated in autoimmune diseases such as Singleton-Merten syndrome, as well as potential therapeutic applications in cancer immunotherapy. Recent developments as of 2025 include RIG-I-activating nanoparticles and agonists for enhanced antitumor efficacy.^[4]^[2] ^[1] Regulation of RIG-I occurs at multiple levels, including transcriptional upregulation by interferons and lipopolysaccharide (LPS), post-translational modifications like inhibitory phosphorylation at serine 8 that suppresses activity, and negative feedback mechanisms such as deubiquitination by CYLD or sequestration by proteins like NLRX1 to prevent excessive inflammation.^[5]^[2]

Discovery and Nomenclature

Historical Identification

The retinoic acid-inducible gene I (RIG-I), also known as DDX58, was first identified in 1997 through cloning efforts in human acute promyelocytic leukemia cells undergoing differentiation induced by retinoic acid.^[6] This discovery highlighted RIG-I as a homolog of RNA helicases, with its expression upregulated during cellular differentiation, though its functional role remained unclear at the time. In 2004, researchers confirmed RIG-I's role as a key sensor for viral double-stranded RNA (dsRNA), demonstrating that it activates the interferon-beta (IFN-β) promoter in response to dsRNA transfection.^[7] Overexpression of RIG-I in human embryonic kidney 293 cells led to robust induction of IFN-β upon viral infection or synthetic dsRNA stimulation, establishing its essential function in innate antiviral responses.^[7] Parallel studies in 2005 further elucidated RIG-I's signaling network, with one report identifying its interaction with the adaptor protein IPS-1 (later known as MAVS or Cardif), which links RIG-I to downstream interferon induction pathways.^[8] Another study in 2006 using RIG-I knockout mice showed increased susceptibility to RNA viruses, such as vesicular stomatitis virus, underscoring RIG-I's non-redundant role in antiviral defense.^[9] Key experiments supporting these findings included siRNA-mediated knockdown of RIG-I, which significantly reduced IFN-β production and antiviral gene expression in infected cells, confirming its direct involvement in pathogen recognition.^[7]

Naming and Classification

RIG-I, short for retinoic acid-inducible gene I, derives its name from its identification as a gene upregulated by all-trans retinoic acid treatment in human acute promyelocytic leukemia cells.^[2] The designation "I" distinguishes it as the initial member of this class of inducible genes, separate from RIG-G (now known as IFIT3), a concurrently identified gene.^[10] RIG-I belongs to the RIG-I-like receptor (RLR) family of cytoplasmic pattern recognition receptors, alongside melanoma differentiation-associated protein 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2).^[11] Encoded by the DDX58 gene, it functions as a DEXD/H-box RNA helicase that detects viral RNA in the cytosol to initiate innate immune responses.^[12] Phylogenetically, RIG-I-like genes trace their origins to early deuterostomes, with homologs absent in protostomes and non-bilaterian metazoans, reflecting an ancient adaptation in vertebrate immunity.^[13] The core helicase domains of RIG-I exhibit structural homology to bacterial RecA helicases, underscoring a conserved evolutionary mechanism for nucleic acid handling.^[13] In humans, the DDX58 gene resides on chromosome 9p21.1. The orthologous gene in mice is located on chromosome 4.^[14]

Molecular Structure

Domain Architecture

RIG-I, or retinoic acid-inducible gene I, is a 925-amino-acid protein in humans that features a modular domain architecture essential for its function as a cytosolic RNA sensor. The protein is divided into an N-terminal region containing two tandem caspase activation and recruitment domains (CARDs), a central DExD/H-box helicase domain composed of two RecA-like subdomains (Helicase 1 [Hel1] and Helicase 2 [Hel2]), and a C-terminal regulatory domain (RD). This arrangement allows RIG-I to integrate RNA recognition, ATP hydrolysis, and downstream signaling. The N-terminal CARD domains, spanning approximately amino acids 1–97 (CARD1) and 98–181 (CARD2), are structurally similar death domains characterized by a six-helix bundle fold. These domains mediate protein-protein interactions critical for signal transduction, and upon activation, they oligomerize into helical filaments to propagate signaling. The central helicase domain, encompassing amino acids 235–761, includes conserved motifs for ATP binding and hydrolysis (such as the Walker A and B motifs) and facilitates RNA duplex unwinding and translocation. Hel1 (residues ~242–456) and Hel2 (residues ~609–745, with an insertion subdomain Hel2i ~458–608) form a clamp-like structure that encases RNA ligands, enabling processive scanning of nucleic acids. This domain binds both ATP and RNA, coupling nucleotide hydrolysis to conformational changes. The C-terminal RD (residues 776–925) is a compact zinc-binding domain that coordinates two Zn²⁺ ions via cysteine and histidine residues, adopting a winged-helix fold similar to those in transcription factors. This domain imparts specificity for viral RNA features and helps regulate overall protein activity. Crystal structures have elucidated these components: the RD was structurally characterized in complex with RNA ligands, revealing its role in 5'-triphosphate recognition, while a near full-length structure (lacking CARDs) bound to double-stranded RNA demonstrated the integrated helicase-RD architecture.

Autoinhibition and Activation

In its autoinhibited state, RIG-I adopts a closed conformation where the regulatory domain (RD) binds to the helicase domain, thereby masking key RNA-binding sites and preventing unintended activation by host RNAs.^[15] The N-terminal caspase activation and recruitment domains (CARDs) are sequestered against the helicase domain through interactions mediated by the intrinsically disordered CARDs-helicase linker (CHL), maintaining RIG-I in a repressed, monomeric form that avoids spontaneous signaling.^[16] This autoinhibition is further reinforced by post-translational modifications, such as Lys-48-linked ubiquitination at Lys-181 by the E3 ligase RNF125, which promotes proteasomal degradation and limits RIG-I availability.^[17] Activation of RIG-I begins with the binding of viral RNA ligands, particularly those bearing a 5'-triphosphate (5'-ppp) end, to the RD, which induces a conformational shift from the closed to an open state.^[18] This ligand engagement triggers ATP binding and hydrolysis at the interface of the helicase subdomains 1 and 2, where the ATP-binding pocket in subdomain 1 facilitates energy-dependent remodeling of the helicase domains around the RNA.^[19] The hydrolysis-driven translocation along the RNA duplex releases the RD from the helicase and disrupts CHL interactions, exposing the CARDs for K63-linked ubiquitination by TRIM25, which promotes CARD dimerization and higher-order oligomerization into signaling-competent filaments.^[20] Recent structural studies using cryo-electron microscopy (cryo-EM), including 2025 analyses, have revealed a two-step RNA clamping mechanism during activation, where initial blunt-end recognition by the RD is followed by helicase domain enclosure to stabilize the complex and amplify signaling, with additional insights into TRIM25-mediated ubiquitination.^[21]^[22]^[23] Proofreading is integrated into this process through ATPase activity, which enables rapid dissociation from non-viral RNAs while throttling translocation at authentic 5'-ppp ends to confirm ligand specificity and prevent erroneous activation.^[24] These CARD filaments then localize to mitochondrial membranes, where they nucleate prion-like polymerization of MAVS CARDs to propagate downstream antiviral responses.^[25]

Ligand Recognition

Viral PAMPs

RIG-I primarily recognizes viral pathogen-associated molecular patterns (PAMPs) in the form of uncapped single-stranded RNA (ssRNA) bearing a 5'-triphosphate (5'-ppp) group, typically 10-20 nucleotides in length. These short 5'-ppp ssRNAs are potent activators, as demonstrated by their ability to bind the C-terminal domain (CTD) of RIG-I with high affinity and induce conformational changes necessary for signaling. Additionally, RIG-I detects short double-stranded RNA (dsRNA) molecules featuring blunt ends and a 5'-ppp moiety, which exhibit even stronger binding due to the structural complementarity with the receptor's RNA-binding pockets. The minimal length threshold for effective activation is approximately 10 nucleotides, below which ligand recognition and downstream ATPase activity are insufficient to trigger robust immune responses.^[26]30144-5) These viral PAMPs are commonly derived from the genomes or replication intermediates of negative-sense RNA viruses, including paramyxoviruses such as Sendai virus, flaviviruses like hepatitis C virus (HCV), and orthomyxoviruses including influenza A virus. In these pathogens, nascent viral transcripts or genomic RNAs retain the 5'-ppp end due to the absence of host-like capping machinery during cytoplasmic replication. RIG-I also senses uncapped RNAs generated from abortive viral replication attempts, which accumulate as short, triphosphorylated fragments during inefficient infection cycles. The binding affinity of RIG-I is markedly higher for these 5'-ppp viral RNAs compared to capped host mRNAs, primarily because the triphosphate group engages specific positively charged residues in the CTD, enabling discrimination and selective activation despite similar initial binding constants.00021-8)^[27] Representative examples of RIG-I-activating structures include the panhandle formations in influenza A virus genomic RNAs, where complementary sequences at the 5' and 3' ends base-pair to create blunt-ended, 5'-ppp dsRNA segments that directly engage the receptor. Defective interfering (DI) RNAs, which arise in many RNA viruses such as Sendai virus and vesicular stomatitis virus during high-multiplicity infections, similarly serve as potent ligands due to their short, uncapped, and often panhandle-like structures that mimic minimal activation motifs. A recent study revealed that mini-viral RNAs (mvRNAs) produced aberrantly during influenza A virus replication activate RIG-I through a two-step mechanism: initial synthesis of capped complementary RNAs displaces template mvRNAs from the polymerase, forming activating heteroduplexes with exposed 5'-ppp ends.^[28]^[22]

Discrimination from Host RNAs

RIG-I achieves discrimination between viral and host RNAs primarily through its preference for specific structural features at the 5' end of RNA ligands. Unlike host messenger RNAs (mRNAs), which are protected by a 7-methylguanosine (m7G) cap structure added co-transcriptionally, RIG-I strongly favors uncapped 5'-triphosphate (5'-ppp) or 5'-diphosphate (5'-pp) ends typically found on viral RNAs synthesized by RNA-dependent RNA polymerases. This cap structure on host mRNAs sterically hinders RIG-I's C-terminal domain (CTD) from binding, thereby preventing aberrant activation by endogenous transcripts. The m7G cap, combined with subsequent 2'-O-methylation at the first nucleotide (Cap-1), further mimics a "self" signature that evades recognition, ensuring RIG-I remains inactive under steady-state conditions. To enhance specificity, RIG-I employs an ATP-dependent proofreading mechanism involving RNA clamping and translocation. Upon initial binding via the CTD to a potential 5'-ppp ligand, RIG-I's helicase domain undergoes ATP hydrolysis to clamp the RNA and translocate along it in a throttled manner, allowing scrutiny of the RNA's overall features. This kinetic proofreading process discriminates against host RNAs lacking appropriate blunt-ended double-stranded regions or bearing monophosphate (5'-p) ends, which are common in cellular decay intermediates; such RNAs fail to sustain stable clamping and are released without full activation. This ATP-powered mechanism ensures that only high-affinity viral patterns trigger oligomerization and signaling, averting autoimmunity from abundant host RNAs. Host RNA modifications contribute additional layers of discrimination. N6-methyladenosine (m6A) methylation, the most prevalent internal modification on eukaryotic mRNAs, reduces RIG-I binding affinity by altering RNA secondary structure and stability, thereby inhibiting recognition of self transcripts. Similarly, 2'-O-methylation on host mRNAs, particularly in the cap-adjacent region, reinforces evasion by mimicking protective modifications that viruses sometimes co-opt. Recent studies have highlighted roles for RNA-binding proteins like CAPRIN1 in modulating m6A on specific transcripts, including those influencing RIG-I pathway components, to fine-tune immune thresholds during infection. Cellular compartmentalization and expression levels further limit RIG-I's exposure to host RNAs. RIG-I exhibits low basal expression in most cell types, primarily induced upon interferon stimulation, which restricts its availability to engage endogenous RNAs under normal conditions. Additionally, RIG-I localizes to stress granules—cytoplasmic aggregates formed during cellular stress—where it sequesters potential self RNAs and enhances selective scanning of viral patterns without widespread activation. Viruses exploit these discrimination mechanisms for evasion, often by acquiring host-like modifications. For instance, coronaviruses utilize non-structural proteins to cap their genomic and subgenomic RNAs with m7G structures, directly blocking RIG-I engagement and promoting replication. Other viruses employ host polymerases to generate capped transcripts or incorporate 2'-O-methylations, thereby mimicking host mRNA signatures and suppressing innate immune detection. Recent advances have revealed RIG-I's involvement in metabolic sensing of host RNAs. Studies indicate that RIG-I can recognize RNAs capped with metabolites like NAD or FAD, which may serve as damage-associated molecular patterns from stressed cells, linking RNA sensing to broader metabolic regulation of immunity. A 2024 review emphasizes how such non-canonical ligands expand RIG-I's role in distinguishing perturbed host states from true viral threats.

Signaling Mechanisms

MAVS-Mediated Pathway

Upon activation by viral RNA ligands, RIG-I undergoes a conformational change that exposes its N-terminal CARD domains, leading to their oligomerization into a tetrameric structure that binds to the CARD domain of MAVS localized on the outer membranes of mitochondria and peroxisomes. Recent studies have shown that RIG-I oligomerization can also involve liquid-liquid phase separation (LLPS) driven by disulfide bond formation between Cys864 and Cys869, forming stable condensates that enhance signaling efficiency and resistance to degradation.^[29] This interaction nucleates the assembly of MAVS into prion-like aggregates, which propagate through CARD-CARD interactions and amplify the signaling cascade in a manner analogous to prion conversion. These MAVS aggregates serve as scaffolds to recruit downstream effectors, including the E3 ubiquitin ligases TRAF3 and TRAF6, as well as the kinase complexes IKK and TBK1.^[1] Critical to this process is K63-linked ubiquitination, primarily mediated by the E3 ligases TRIM25 and Riplet, which target specific lysine residues on RIG-I's CARD domains (e.g., Lys172) and MAVS, stabilizing the oligomeric states and enhancing affinity for MAVS.^[30] TRIM25 initiates ubiquitination of RIG-I, promoting its interaction with MAVS, while Riplet further ubiquitinates RIG-I's C-terminal domain and CARDs, ensuring robust signal transmission to MAVS aggregates. Additionally, UFMylation of the adaptor protein 14-3-3ε at lysines K50 and K215 stabilizes the MAVS signaling complex, facilitating RIG-I recruitment and downstream activation as of October 2025.^[31] These modifications facilitate the recruitment of TRAF3/6 to MAVS, which in turn activate two parallel branches: TBK1 phosphorylates IRF3 at Ser396 and Ser398, inducing its dimerization and nuclear translocation; concurrently, the IKK complex (including IKKα, IKKβ, and NEMO) phosphorylates IκB, leading to its degradation and subsequent NF-κB activation.^[1]^[18] A 2023 study revealed that Riplet can promote RIG-I signaling even with short double-stranded RNAs that do not induce RIG-I oligomerization, by directly facilitating CARD ubiquitination and MAVS engagement independently of mitochondrial aggregation requirements in certain contexts.^[32] This highlights Riplet's versatile role in initiating the MAVS-mediated pathway beyond canonical long-RNA-induced filaments.

Downstream Immune Responses

Upon activation of the RIG-I signaling pathway, phosphorylated IRF3 and IRF7 undergo dimerization and translocate to the nucleus, where they bind to interferon-stimulated response elements (ISREs) to induce transcription of type I interferons, primarily IFN-α and IFN-β.^[12] Concurrently, NF-κB activation leads to the expression of proinflammatory cytokines such as TNF-α and IL-6, which amplify the inflammatory response and recruit additional immune cells to the site of infection.^[33] These transcriptional events establish a robust antiviral state within infected cells and neighboring tissues. The induced type I IFNs bind to their cognate receptors, triggering a JAK-STAT signaling cascade that upregulates the expression of RIG-I and MDA5 through interferon-stimulated response elements in their promoter regions, thereby creating a positive feedback loop that enhances detection and response to ongoing viral replication.^[34] This amplification mechanism ensures sustained innate immune activation, with IFN-β particularly effective in priming cells for heightened sensitivity to viral RNA patterns. Downstream of IFN signaling, interferon-stimulated genes (ISGs) such as PKR and OAS are transcriptionally induced to directly inhibit viral replication; PKR phosphorylates eIF2α to halt protein synthesis, while OAS activates RNase L to degrade viral and host RNAs.^[35] In certain contexts, RIG-I activation promotes apoptosis through mitochondrial outer membrane permeabilization and caspase activation, limiting viral spread by sacrificing infected cells.^[36] RIG-I signaling integrates with Toll-like receptor (TLR) pathways to coordinate broader innate immunity, where shared downstream effectors like IRF3 and NF-κB allow synergistic cytokine production in response to diverse pathogens.^[33] Additionally, RIG-I responses influence metabolic reprogramming, shifting cellular glucose metabolism toward the pentose phosphate pathway and hexosamine biosynthesis to support sustained antiviral signaling, while metabolites like lactate and itaconate in turn modulate RLR activity.^[37] RIG-I exhibits high sensitivity, with activation detectable upon recognition of small quantities (on the order of tens to hundreds) of viral RNA molecules, sufficient to initiate measurable IFN production.^[38]

Biological Roles

Antiviral Immunity

RIG-I plays a pivotal role in the innate immune defense against RNA viruses in vivo, serving as a cytosolic sensor that detects viral pathogen-associated molecular patterns (PAMPs) and initiates protective responses. Studies using RIG-I-deficient (RIG-I^{-/-}) mice have demonstrated their heightened susceptibility to infections by flaviviruses, such as dengue virus and West Nile virus, and paramyxoviruses, including Sendai virus and Newcastle disease virus, due to impaired type I interferon (IFN) production and antiviral state induction.^[12]^[27] RIG-I-deficient mice show specificity primarily for RNA viruses, with limited direct involvement in DNA virus sensing, though some DNA viruses may be detected indirectly via RNA intermediates.^[39] RIG-I's antiviral activity is prominent against certain RNA viruses, including hepatitis C virus (HCV), where it recognizes 5'-triphosphate RNA structures to suppress replication, and influenza A virus (IAV), which it detects to limit viral spread in the respiratory tract.^[40]^[12] For SARS-CoV-2, RIG-I contributes partially to restraint of replication in lung cells through type I/III IFN signaling, though its efficacy is modulated by viral evasion strategies.^[41] Conversely, picornaviruses, such as encephalomyocarditis virus, are primarily sensed by MDA5, rendering RIG-I less dominant in these infections.^[42] By triggering the MAVS-dependent pathway, RIG-I induces type I IFNs that promote dendritic cell (DC) maturation, enhancing antigen presentation and migration to lymph nodes.^[43] This IFN-mediated process facilitates cross-priming of CD8^{+} T cells and polyfunctional T-cell responses, bridging innate detection to adaptive antiviral immunity during infections like IAV.^[44]^[45] The therapeutic potential of RIG-I activation has been explored through synthetic agonists, such as 5'-triphosphate RNA mimics, which emulate viral PAMPs to elicit broad antiviral states and serve as adjuvants in vaccines against RNA viruses.^[46] These agonists enhance IFN responses and adaptive immunity without requiring live virus, showing promise in preclinical models for preventing infections like influenza.^[47] A recent 2024 study identified DDX11 as a helicase that enhances RIG-I signaling by facilitating its interaction with MAVS and viral dsRNA, thereby boosting antiviral defenses against RNA viruses in vitro and in vivo.^[48]

Roles in Cancer and Autoimmunity

RIG-I functions as a tumor suppressor in various cancers by inducing type I interferon (IFN) responses that promote apoptosis and inhibit cell proliferation. In melanoma, RIG-I activation triggers G1 phase cell cycle arrest and apoptosis through regulation of the MKK/p38 MAPK signaling pathway, thereby suppressing tumor growth.^[49]^[50] This IFN-mediated antitumor effect is also evident in hepatocellular carcinoma (HCC), where RIG-I signaling restricts tumor progression by enhancing M1 macrophage polarization and cell death pathways.^[51] However, RIG-I exhibits context-dependent pro-tumorigenic roles, particularly in settings of chronic inflammation. In chronic hepatitis C virus (HCV) infection, dysregulated RIG-I signaling contributes to persistent inflammation that fosters hepatocarcinogenesis, as HCV evasion mechanisms suppress RIG-I while low-level activation sustains fibrogenic responses leading to HCC development.^[52]^[53] RIG-I deficiency exacerbates cancer-related inflammation in HCC by impairing STAT1 activation, correlating with poor patient outcomes and therapy resistance, while certain mutant forms enhance inflammation through alternative pathways like circRIG-I signaling.^[54] In autoimmunity, gain-of-function mutations in the DDX58 gene encoding RIG-I lead to constitutive activation and excessive type I IFN production, driving inflammatory disorders such as Singleton-Merten syndrome (SMS). These mutations, including those disrupting autoinhibition (e.g., p.Glu373Ala and p.Cys268Phe), cause atypical SMS features like aortic calcification, glaucoma, and dental dysplasia through aberrant sensing of self-RNA.^[55]^[56] RIG-I hyperactivity also contributes to type I interferonopathies resembling Aicardi-Goutières syndrome (AGS), where elevated IFN signatures result in neuroinflammation and developmental abnormalities, though primary AGS mutations more commonly affect related sensors like MDA5.^[57]^[58] Mechanistically, RIG-I influences T-cell dynamics in the tumor microenvironment by acting as an intracellular checkpoint that promotes CD8+ T-cell exhaustion and limits antitumor activity. In tumor-infiltrating CD8+ T cells, upregulated RIG-I restrains effector functions, reducing cytokine production and proliferation; its inhibition enhances antitumor responses, particularly in PD-1-resistant tumors.^[59] Additionally, RIG-I regulates programmed cell death (PCD) pathways, including apoptosis via BH3-only proteins like Noxa and Puma, as well as pyroptosis and necroptosis through MAVS-dependent inflammasome activation, balancing antitumor immunity and inflammatory damage in cancer and autoimmunity.^[60]^[61] Clinically, RIG-I agonists show promise in cancer immunotherapy by inducing immunogenic cell death and synergizing with checkpoint inhibitors. Synthetic ligands like 3pRNA activate RIG-I to enhance tumor control in melanoma and HCC models, improving responses when combined with PD-1 blockade to overcome resistance and boost CD8+ T-cell efficacy.^[62]^[63] In autoimmunity, targeting hyperactive RIG-I with antagonists, such as in SMS treatment trials using IFN inhibitors like anifrolumab, aims to mitigate excessive IFN-driven inflammation.^[64]

Regulation

Positive Regulators

Positive regulators of RIG-I function include E3 ubiquitin ligases that modify the receptor post-translationally to enhance its activation and signaling capacity. TRIM25 catalyzes K63-linked polyubiquitination on the CARD domains of RIG-I, which is essential for the oligomerization of RIG-I and its interaction with MAVS to initiate antiviral signaling. Similarly, Riplet (also known as RNF135) promotes K63-linked ubiquitination specifically on lysine residues in the helicase domain of RIG-I, facilitating viral RNA binding and subsequent activation independent of TRIM25 activity. At the transcriptional level, RIG-I expression is upregulated by type I interferons (IFN-α and IFN-β) through an IFN-inducible promoter, creating a positive feedback loop that amplifies antiviral responses in various cell types such as epithelial cells and dendritic cells.^[65] Additionally, all-trans retinoic acid (ATRA) induces RIG-I transcription via retinoic acid receptor (RAR) signaling, as observed in acute promyelocytic leukemia cells and epidermal keratinocytes, thereby enhancing innate immune readiness.^[65] RIG-I activity is further potentiated by interacting protein partners, including the DEAD-box helicase DDX11, which directly binds RIG-I and MAVS to stabilize their interaction and promote IFN signaling in response to double-stranded RNA ligands. Metabolic sensors also link glycolytic pathways to RIG-I regulation; for instance, RIG-I activation via MAVS redirects glucose flux away from glycolysis toward the pentose phosphate pathway, supporting nucleotide synthesis and enhancing sustained antiviral signaling during infection. Recent studies have shown that Riplet promotes RIG-I signaling through pathways independent of oligomerization, such as enhancing ATPase activity and RNA binding without relying on CARD ubiquitination, as demonstrated in structural and functional analyses of viral infections.^[32]

Negative Regulators

Negative regulators of RIG-I signaling play crucial roles in attenuating antiviral responses to prevent excessive inflammation and maintain immune homeostasis. These mechanisms include deubiquitination, suppression by host proteins, intrinsic autoregulation, viral interference, and post-transcriptional modifications that collectively dampen RIG-I activation, ubiquitination, or downstream signaling through MAVS.^[66] Deubiquitinases such as CYLD and DUBA counteract the K63-linked ubiquitination essential for RIG-I activation. CYLD, a tumor suppressor deubiquitinase, removes K63-polyubiquitin chains from RIG-I and the downstream kinase TBK1, thereby inhibiting IRF3 phosphorylation and type I IFN production during viral infection.^[67] Similarly, DUBA (also known as OTUD5) deubiquitinates TRAF3, a key adaptor in the RIG-I pathway, by cleaving K63-linked ubiquitin chains, which disrupts TRAF3 oligomerization and attenuates IFN-β induction in response to RNA viruses. Host suppressors like NLRX1 and PCBP2 further inhibit RIG-I signaling at multiple levels. NLRX1, a mitochondrial Nod-like receptor, interacts with the CARD domain of MAVS to sequester it and prevent RIG-I-MAVS complex formation, thereby suppressing antiviral cytokine production during RNA virus infections such as vesicular stomatitis virus.00226-3) PCBP2, an RNA-binding protein, promotes K48-linked ubiquitination and proteasomal degradation of MAVS by recruiting the E3 ligase AIP4, indirectly blocking RIG-I-mediated signaling and reducing IFN responses to viruses like Sendai virus. Intrinsic autoregulation of RIG-I ensures basal repression in the absence of ligands. The C-terminal repressor domain (RD) of RIG-I maintains an autoinhibited conformation by binding to the CARD domains and helicase region, preventing premature activation and ATP hydrolysis until viral RNA with 5'-triphosphate ends displaces it.^[1] Additionally, LGP2, a CARD-less RIG-I family member, acts as a competitive inhibitor by binding diverse viral dsRNAs with high affinity, sequestering potential RIG-I ligands and suppressing RIG-I-dependent IFN production during infections like encephalomyocarditis virus, although its role can vary by context. Viral antagonists exploit these regulatory nodes to evade detection. The hepatitis C virus (HCV) NS3/4A protease cleaves MAVS at cysteine 508, dislocating its N-terminal fragment from mitochondria and abolishing RIG-I signal transmission to IRF3, thereby enabling persistent HCV replication.^[68] Paramyxovirus V proteins, such as those from Sendai virus, bind the RIG-I-TRIM25 complex to inhibit TRIM25-mediated K63 ubiquitination of RIG-I, disrupting CARD oligomerization and downstream IFN-β expression. Recent insights highlight post-transcriptional control via RNA modifications. In 2025, CAPRIN1 was identified as a mediator of N6-methyladenosine (m6A) modification on RIG-I mRNA by interacting with the methyltransferase METTL3, promoting m6A deposition that enhances mRNA decay and reduces RIG-I protein levels, thereby silencing RIG-I signaling to modulate immune responses during Mycobacterium tuberculosis infection.^[69]

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Differential recognition of viral RNA by RIG-I - PMC - NIH
By examining endogenous RIG-I/RNA complexes in influenza virus- and Sendai virus-infected cells we were able to identify viral RNA molecules that specifically ...Missing: sources flaviviruses
[22]
A two-step mechanism for RIG-I activation by influenza virus mvRNAs
Aug 8, 2025 · Transient RNA structures cause aberrant influenza virus replication and innate immune activation. Hollie French, Sci Adv, 2022. RIGorous ...
[23]
https://www.jbc.org/article/S0021-9258%2825%2900836-7/fulltext
[24]
Patterning of sodium ions and the control of electrons in sodium cobaltate - Nature
The provided content from https://www.nature.com/articles/nature05531 is a Nature article titled "Patterning of sodium ions and the control of electrons in sodium cobaltate," published on February 8, 2007. It is not the TRIM25 paper related to RIG-I ubiquitination for MAVS signaling. Instead, it focuses on the structural and electronic properties of sodium cobaltate (NaₓCoO₂), using neutron diffraction and simulations to study sodium ion ordering and its impact on electron behavior.
[25]
https://pmc.ncbi.nlm.nih.gov/articles/PMC4470786/
[26]
The E3 ligase Riplet promotes RIG-I signaling independent ... - Nature
Nov 11, 2023 · Here we show that Riplet is required for RIG-I signaling in the presence of both short and long dsRNAs, establishing that Riplet activation does not depend ...
[27]
RIG-I like receptors and their signaling crosstalk in the regulation of ...
The RIG-I-like receptor (RLR) family of pattern recognition receptors (PRRs) is a group of cytosolic RNA helicase proteins that can identify viral RNA as ...Missing: classification | Show results with:classification
[28]
Expression and Functional Characterization of the RIG-I-Like ...
In mammals, activation of RIG-I/MDA5 by viral RNA PAMPs induces IFN expression, and these surveillance mechanisms are enhanced by the synthesized IFNs via a ...
[29]
interferon-independent induction of interferon-stimulated genes and ...
Sep 20, 2024 · For instance, dsRNA-induced RIG-I triggers two distinct sets of ISGs by independent pathways, both of which contribute co-ordinately to the ...
[30]
DHX15 and Rig-I Coordinate Apoptosis and Innate Immune ... - NIH
In this study, we found that DEAH-box polypeptide 15 (DHX15) and retinoic acid-inducible gene I (Rig-I) are essential for apoptosis induced by RL RNAs.
[31]
https://www.biorxiv.org/content/10.1101/2025.10.21.683613v1
[32]
Regulation of RIG-I-like receptor signaling by host and viral proteins
In addition to RIG-I's function as a sensor of RNA viruses, there is new evidence that RIG-I also detects various DNA viruses by sensing small viral RNA species ...
[33]
RIG-I Like Receptors in Antiviral Immunity and Therapeutic ... - MDPI
The RLR family of PRRs is comprised of three members: Retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA5), and laboratory ...Missing: classification | Show results with:classification<|separator|>
[34]
RIG-I triggers a signaling-abortive anti-SARS-CoV-2 defense in ...
May 11, 2021 · Here we show that retinoic acid–inducible gene-I (RIG-I) sufficiently restrains SARS-CoV-2 replication in human lung cells in a type I/III interferon (IFN)- ...Missing: HCV picornaviruses
[35]
Physiological functions of RIG-I-like receptors: Immunity - Cell Press
RIG-I-like receptors (RLRs) are crucial for pathogen detection and triggering immune responses and have immense physiological importance.
[36]
Human Plasmacytoid and Monocyte-Derived Dendritic Cells Display ...
Interestingly, human monocyte-derived DCs (moDC) triggered via RIG-I show a commitment to glycolysis to promote type I IFN production and T cell priming in ...
[37]
RIG-I Signaling Is Critical for Efficient Polyfunctional T Cell ...
Here, we demonstrate that RIG-I signaling plays a crucial role in restricting IAV tropism and regulating host immune responses. Mice deficient in the RIG-I-MAVS ...
[38]
RIG-I activating immunostimulatory RNA boosts the efficacy of ...
RIG-I-induced cross-priming of cytotoxic T cells as well as antitumor immunity were dependent on the host adapter protein MAVS and type I interferon (IFN-I) ...
[39]
A Sendai Virus-Derived RNA Agonist of RIG-I as a Virus Vaccine ...
RIG-I activation leads to the production of an appropriate cytokine and chemokine cocktail that stimulates an antiviral state and drives the adaptive immune ...
[40]
RIG-I-Like Receptors as Novel Targets for Pan-Antivirals ... - Frontiers
The antiviral effect of 5′pppRNA was also detected against HIV in CD4+ T cells and HCV in Huh 7.5 cells (53). Besides that, 5′pppRNA was also an effective ...Missing: mimics | Show results with:mimics
[41]
Helicase protein DDX11 as a novel antiviral factor promoting RIG-I ...
Oct 29, 2024 · We also prepared truncated versions of DDX11 involving amino acids (aa) 1–445, 1–665, 445–665, 445–945, and 665–945. Deletion analysis indicated ...<|separator|>
[42]
RIG-I acts as a tumor suppressor in melanoma via ... - PubMed
Apr 13, 2022 · Our data showed that RIG-I promotes apoptosis and inhibits proliferation by G1 phase cell cycle arrest in the melanoma cell lines.
[43]
[PDF] RIG-I acts as a tumor suppressor in melanoma via regulating the ...
Jul 30, 2021 · The current study demonstrated that RIG-I suppressed the development of melanoma via regulating the activity of MKK/p38 MAPK signaling pathway, ...
[44]
RIG-I Promotes Cell Death in Hepatocellular Carcinoma by Inducing ...
Sep 3, 2020 · RIG-I Promotes Cell Death in Hepatocellular Carcinoma by Inducing M1 Polarization of Perineal Macrophages Through the RIG-I/MAVS/NF-κB Pathway.
[45]
Hepatitis C Virus and Hepatocellular Carcinoma: When the Host ...
Chronic infection with hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC). Novel treatments with direct-acting antivirals achieve ...
[46]
Hepatocellular Carcinoma Mechanisms Associated with Chronic ...
Apr 15, 2020 · This review describes the multifaceted mechanisms that create a tumorigenic environment during chronic HCV infection.
[47]
Mutant RIG-I enhances cancer-related inflammation through ...
Nov 19, 2022 · Through impairing STAT1 activation, RIG-I deficiency predicts poor outcome of HCC patients and resistance to immunotherapy. It is conceivable ...
[48]
Mutations in DDX58, which Encodes RIG-I, Cause Atypical ...
Our results demonstrate that DDX58 mutations cause atypical SMS manifesting with variable expression of glaucoma, aortic calcification, and skeletal ...
[49]
Unified mechanisms for self-RNA recognition by RIG-I Singleton ...
Jul 26, 2018 · Intriguingly, despite an overall high structural similarity to wtRIG-I Δ2CARD bound to dsRNA (Jiang et al., 2011), the SMS mutant shows crucial ...
[50]
RIG-I-Like Receptors and Type I Interferonopathies - PubMed Central
Aicardi–Goutieres Syndrome. Patients with the neuroinflammatory autoimmune disease AGS exhibit profound intellectual disabilities, dystonia and IFN signatures, ...
[51]
Aicardi-Goutières Syndrome Is Caused by IFIH1 Mutations - PMC
This study suggests that the IFIH1 mutations are responsible for the AGS phenotype due to an excessive production of type I interferon.
[52]
RIG-I is an intracellular checkpoint that limits CD8+ T-cell antitumour ...
Sep 25, 2024 · This study revealed another role of RIG-I as an intracellular immune checkpoint that negatively regulates the antitumour function of CD8+ T ...
[53]
Beyond Immunity: RIG-I as a Bifunctional Regulator of Cell Fate in ...
Sep 19, 2025 · RIG-I promotes apoptosis, immunogenic cell death, pyroptosis, and necroptosis. · RIG-I regulates autophagy to maintain homeostasis to promote ...
[54]
Harnessing RIG-I and intrinsic immunity in the tumor ... - Oncotarget
Jun 22, 2018 · Cellular mechanisms by which RIG-I induces PCD include activation of the intrinsic apoptosis pathway, the extrinsic apoptosis pathway, and a ...
[55]
Synthetic RIG-I agonist-mediated cancer immunotherapy synergizes ...
Jul 19, 2024 · Our study suggests that agonist-induced activation of RIG-I with its synthetic ligand 3pRNA could vastly improve tumor control in a substantial fraction of ...
[56]
RIG-I-based immunotherapy enhances survival in preclinical AML ...
Nov 18, 2019 · Here, we explore the responsiveness of AML to ppp-RNA treatment alone and in combination with anti-PD-1 blocking antibodies in the murine ...
[57]
Anifrolumab treatment of Singleton-Merten syndrome 2 due to a ...
Sep 5, 2025 · SMS2 is associated with gain-of-function (GOF) variants in retinoic acid-inducible gene 1 (RIGI [previously known as DDX58]), an intracellular ...
[58]
https://pmc.ncbi.nlm.nih.gov/articles/PMC4085581/
[59]
Negative regulators of the RIG-I-like receptor signaling pathway - PMC
This review highlights contemporary findings on negative regulators of the RLR signaling pathway, with specific focus on the proteins and biological processes
[60]
The tumour suppressor CYLD is a negative regulator of RIG‐I ...
Here, we report that CYLD interacts with components of the RIG‐I pathway to inhibit IRF3 signalling and subsequent IFNβ production.
[61]
Hepatitis C virus protease NS3/4A cleaves mitochondrial antiviral ...
NS3/4A cleaves MAVS at Cys-508, resulting in the dislocation of the N-terminal fragment of MAVS from the mitochondria. Remarkably, a point mutation of MAVS at ...
[62]
https://www.cell.com/molecular-therapy-family/nucleic-acids/fulltext/S2162-2531%2824%2900170-7