{"gene":"IRF9","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2018,"finding":"Crystal structures of IRF9-IAD alone and in complex with STAT2 coiled-coil domain (CCD) were solved, revealing the molecular interface required for ISGF3 function. The IRF9-IAD surface has diverged from paralogs to enable specific interaction with STAT2-CCD, and mutagenesis of this interface abolished ISGF3 function in cells.","method":"X-ray crystallography, structure-guided mutagenesis, cell-based ISGF3 functional assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional validation by mutagenesis in cells, single rigorous study with multiple orthogonal methods","pmids":["29317535"],"is_preprint":false},{"year":2019,"finding":"Under homeostatic (resting) conditions, preformed STAT2-IRF9 complexes control basal expression of IFN-induced genes. Upon type I IFN or IFN-γ stimulation, a complete ISGF3 complex (STAT1/STAT2/IRF9) assembles on DNA (not in the cytoplasm as previously thought), switching macrophages from resting-state to induced ISG expression.","method":"Integrated transcriptomics, proteomics, ChIP-seq, in vivo proximity-dependent labeling (BioID) in living cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal genome-wide and proteomic methods in a single rigorous study, challenges dogmatic cytoplasmic assembly model","pmids":["31266943"],"is_preprint":false},{"year":2013,"finding":"After IFNβ treatment, elevated IRF9 together with unphosphorylated STAT1 and STAT2 (U-ISGF3) drives a prolonged second-phase antiviral and DNA-damage-resistance response distinct from the initial ISGF3-driven response, acting through distinct ISREs.","method":"IFNβ treatment of cells with manipulated IRF9/STAT expression levels, reporter assays, gene expression analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — defined two mechanistically distinct complexes (ISGF3 vs U-ISGF3) with multiple functional readouts and replicated in multiple cancer/normal cell contexts","pmids":["24065129"],"is_preprint":false},{"year":2018,"finding":"IRF9 (as DNA-binding subunit of ISGF3) and unphosphorylated STAT2 (U-STAT2) cooperate with NF-κB to drive IL6 expression. U-STAT2 binds tightly to IRF9 and also to the p65 subunit of NF-κB, bridging ISRE and κB elements in the IL6 promoter as shown by ChIP.","method":"ChIP analysis, co-immunoprecipitation, reporter assays, exogenous overexpression of U-STAT2 and IRF9","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, ChIP, and functional reporter assays with multiple orthogonal methods in one study","pmids":["29581268"],"is_preprint":false},{"year":2008,"finding":"IFNaR2 intracellular domain (IFNaR2-ICD), STAT2, and IRF9 form a ternary complex. STAT2 serves as an adaptor mediating the interaction between IFNaR2-ICD and IRF9, while the bipartite nuclear localization signal within IRF9 is the primary determinant driving nuclear transit of the complex.","method":"Co-immunoprecipitation, GFP-ICD nuclear localization assays in STAT2- and IRF9-deficient cells","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus nuclear localization functional assay in defined knockdown cells, single lab","pmids":["18456457"],"is_preprint":false},{"year":2015,"finding":"In STAT1-deficient cells, a STAT2/IRF9 complex (requiring STAT2 phosphorylation and the STAT2 transactivation domain) drives expression of ~120 antiviral ISRE-containing ISGs in a prolonged manner compared to ISGF3, and can trigger an antiviral response against EMCV and VSV.","method":"Microarray/genome-wide transcriptomics in STAT1-KO cells stably overexpressing STAT2, antiviral assays, co-immunoprecipitation","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide transcriptomics combined with antiviral functional assay and biochemical characterization of the complex, replicated in human and murine STAT1-deficient systems","pmids":["25564224"],"is_preprint":false},{"year":2013,"finding":"IFNβ + TNFα synergism triggers a non-canonical, STAT1-independent antiviral pathway that requires STAT2 and IRF9 to induce DUOX2 NADPH oxidase expression, which then produces H2O2 as part of an antiviral state in airway epithelial cells.","method":"Knockdown of STAT1, STAT2, IRF9 individually, luciferase reporters, antiviral assays, siRNA-mediated DUOX2 knockdown","journal":"Cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined pathway readout, single lab, multiple gene targets tested","pmids":["23545780"],"is_preprint":false},{"year":2012,"finding":"Cyclophilin A (CypA) binds directly to IRF9 via its PPIase pocket, specifically at the C-terminal IRF-association domain (IAD) but not the DNA-binding or linker domains. CypA also associates with the multimeric ISGF3 complex. CypA inhibitors prevent IRF9-CypA complex formation and enhance IFN-induced transcription. HCV NS5A competes with IRF9 for CypA binding.","method":"Cellular and recombinant pulldown assays, domain deletion mapping, co-immunoprecipitation, transcriptional reporter assays","journal":"Journal of hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal pulldowns with recombinant proteins and domain mapping, functional transcriptional readout, single lab","pmids":["22902549"],"is_preprint":false},{"year":2019,"finding":"PRRSV nonstructural protein nsp11 interacts with the C-terminal IRF-association domain of IRF9 (independently of NendoU endoribonuclease activity), impairing ISGF3 formation and nuclear translocation to antagonize type I IFN signaling.","method":"Co-immunoprecipitation, domain-mapping with nsp11 active-site mutants, nuclear translocation assays, ISRE reporter assays in nsp11-overexpressing and PRRSV-infected cells","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with mutagenesis, nuclear translocation assay, functional reporter, single lab","pmids":["31092569"],"is_preprint":false},{"year":2015,"finding":"Porcine bocavirus NP1 blocks ISGF3 DNA-binding activity by directly interacting with the DNA-binding domain (DBD) of IRF9, without affecting STAT1/STAT2 activation/translocation or ISGF3 complex formation.","method":"Co-immunoprecipitation, domain interaction mapping, ISRE reporter assays, ISG expression analysis","journal":"Virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping plus functional ISRE reporter readout, single lab","pmids":["26342467"],"is_preprint":false},{"year":2020,"finding":"Measles virus V protein displaces IRF9 (IRF-association domain) from preformed STAT2-core/IRF9 complexes, as demonstrated by size-exclusion chromatography with purified recombinant proteins. The MeV V binding site on STAT2 overlaps with that of IRF9, allowing V to inhibit the STAT2/IRF9 interaction and disrupt preassembled ISGF3.","method":"Biophysical binding assays with purified proteins, size exclusion chromatography, quantified dissociation constants","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified proteins, biophysical quantification of binding constants, direct competition assay; single lab but rigorous biochemical methods","pmids":["32581091"],"is_preprint":false},{"year":2002,"finding":"In response to IFNτ, IRF-9 is required for the timely decline of IRF-1 expression after 6 h: cells lacking IRF-9 showed persistent elevated IRF-1 without the normal sharp decline, whereas IRF-1 induction itself required tyrosine-phosphorylated STAT1 (not IRF-9).","method":"Cell lines deficient for specific IFN signaling components (STAT1-deficient, STAT2-deficient, IRF9-deficient), complementation with STAT1 mutants, IRF-1 mRNA/protein time-course analysis","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis using defined cell lines, multiple time points, complementation controls","pmids":["11804954"],"is_preprint":false},{"year":2018,"finding":"Inherited complete loss-of-function IRF9 deficiency in a child abolishes ISGF3 (STAT1/STAT2/IRF9) trimer formation in response to IFN-α2b, greatly narrows the IFN-α2b-induced transcriptome, and prevents control of influenza A, parainfluenza, and RSV in vitro; the phenotype is rescued by wild-type IRF9.","method":"Patient cell studies, IFN stimulation assays, transcriptome analysis, viral replication assays, IRF9 rescue (wild-type re-expression) and knockdown in control cells","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — natural human loss-of-function with rescue by wild-type IRF9, transcriptome plus antiviral functional assays, human clinical validation","pmids":["30143481"],"is_preprint":false},{"year":2010,"finding":"IRF9 concentration is a key rate-limiting determinant of IFNα signaling dynamics: mathematical modeling and IRF9 overexpression experiments demonstrated that increasing IRF9 reduces time-to-peak, increases amplitude, and enhances termination of JAK-STAT pathway activation, forming a positive feedback loop that accelerates early antiviral gene expression.","method":"Mathematical modeling combined with IRF9 overexpression studies, quantitative gene expression analysis","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — model predictions experimentally verified by overexpression, single lab","pmids":["20964804"],"is_preprint":false},{"year":2009,"finding":"IRF9 is required for the antiproliferative activity of IFN-α: IRF9 RNAi completely abolished IFN-α antiproliferative effects in OVCAR3 cells (unlike STAT1 RNAi), and IRF9 RNAi specifically inhibited IFN-α-induced TRAIL transcription. ISGF3 binds ISRE-like motifs in the TRAIL promoter after IFN-α treatment. IRF9 overexpression facilitated IFN-α-induced apoptosis in IFN-α-resistant T98G cells.","method":"RNAi knockdown, ISRE/TRAIL promoter binding (ChIP/EMSA), overexpression rescue, cell proliferation assays","journal":"Journal of immunotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function RNAi with specific phenotypic readout, promoter binding evidence, gain-of-function in resistant cells, single lab","pmids":["19752753"],"is_preprint":false},{"year":2001,"finding":"Transcriptional activation of IRF9 (independent of IFN) corresponds with resistance to antimicrotubule agents in breast adenocarcinoma cells. Transient overexpression of IRF9 alone reproduced the drug-resistance phenotype and induced expression of IFN-responsive genes, whereas overexpression of STAT1 or STAT2 did not.","method":"Differential display, single-gene overexpression, drug resistance assays, gene expression analysis","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain-of-function with defined phenotypic readout, specificity shown by STAT1/STAT2 overexpression controls, single lab","pmids":["11522652"],"is_preprint":false},{"year":2015,"finding":"IRF9 functions in a noncanonical proinflammatory complex with STAT1 (apart from IFN-I and IFN-III signaling) in intestinal epithelial cells. IRF9 deficiency protects mice from DSS-induced colitis, while combined loss of type I and III IFN receptors worsens colitis. The CXCL10 chemokine gene is an important mediator of this IRF9/STAT1 proinflammatory activity.","method":"DSS colitis mouse model, IRF9-KO and IFNAR/IL28R double-KO mice, gene expression analysis, genetic epistasis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple knockout combinations, defined in vivo phenotype, single lab","pmids":["25918247"],"is_preprint":false},{"year":2018,"finding":"IRF9 and STAT1 are required for IFN-α-mediated upregulation of TLR7 in B cells and for IgG (but not IgM) autoantibody production in pristane-induced murine lupus. IRF9-KO B cells are incapable of activation through TLR7.","method":"IRF9-KO and STAT1-KO mouse model (pristane-induced SLE), B cell stimulation assays through TLR7/TLR9, autoantibody measurement","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with defined immune phenotype and B cell functional readouts, single lab","pmids":["18340381"],"is_preprint":false},{"year":2008,"finding":"IFN-β-mediated inhibition of IL-8 expression requires all three ISGF3 components (STAT1, STAT2, and IRF9); however, the transactivation domains of STAT1 and STAT2 are not essential for this inhibitory signaling, distinguishing it from positive ISGF3-driven gene activation.","method":"Cell lines deficient for STAT1, STAT2, or IRF9, ISRE reporter assays, IL-8 expression analysis, transactivation domain mutants","journal":"Journal of interferon & cytokine research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cell-line genetic epistasis with domain mutant analysis, single lab","pmids":["18370868"],"is_preprint":false},{"year":2010,"finding":"Expression of IRF9 fused to the transactivation domain of STAT1 (IRF9-S1C) or STAT2 (IRF9-S2C) in IFN-α-resistant HCV replicon cells restored ISRE promoter activity, induced HLA-1 surface expression, and significantly inhibited HCV RNA replication and viral protein expression independently of IFN-α, demonstrating that the IRF9 nuclear translocation is intact in these resistant cells while STAT phosphorylation is defective.","method":"Fusion protein expression, ISRE luciferase reporter, HCV replication assays, flow cytometry for HLA-1","journal":"Virology journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional rescue with engineered fusion proteins in defined deficient cells, antiviral assay, single lab","pmids":["20939906"],"is_preprint":false},{"year":2021,"finding":"SARS-CoV-2 Spike-transfected cells release exosomes loaded with miR-148a and miR-590; these miRNAs are internalized by human microglia and suppress USP33 expression. USP33 regulates IRF9 turnover via deubiquitylation, so its suppression reduces IRF9 protein levels and alters innate immune gene expression.","method":"Exosome isolation, miRNA transfection, knockdown assays, Western blot for IRF9/USP33, inflammatory gene expression","journal":"Frontiers in immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic link between USP33 deubiquitylation and IRF9 stability inferred but not directly demonstrated with ubiquitylation assays","pmids":["33936086"],"is_preprint":false},{"year":2023,"finding":"IRF9 is phosphorylated at S252 and S253 under IFNβ-induced conditions and at R242 under non-induced conditions. Site-directed mutagenesis of S252/S253 to alanine or aspartic acid modestly affects USP18 gene expression (a negative regulator of type I IFN) but not Mx1 gene expression.","method":"Phosphoprotein enrichment, Phos-tag assay, tandem mass spectrometry on immunoprecipitated IRF9, site-directed mutagenesis, qPCR for ISG expression","journal":"Molecular biology reports","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — mass spectrometry identification of phosphosites combined with mutagenesis, but functional effects are modest and single lab","pmids":["36662450"],"is_preprint":false},{"year":2018,"finding":"IRF9 binds the SIRT1 promoter and represses SIRT1 expression in AML cells; IRF9 knockdown promotes proliferation and survival while overexpression inhibits growth. This IRF9-SIRT1 repression increases p53 acetylation (a SIRT1 deacetylation substrate) and promotes expression of p53 target genes.","method":"ChIP for IRF9 on SIRT1 promoter, IRF9 knockdown/overexpression, cell proliferation/colony assays, Western blot for acetylated p53","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus gain/loss-of-function with functional readouts, single lab; note a related FEBS Letters paper [PMID:28213966] was retracted, but the Experimental cell research paper is distinct","pmids":["29501566"],"is_preprint":false},{"year":2023,"finding":"In renal fibroblasts, the MRTF-A/TEAD1 complex activates ZEB1 transcription; ZEB1 in turn represses IRF9 transcription. IRF9 knockdown promotes fibroblast-myofibroblast transition (FMyT), whereas IRF9 overexpression antagonizes TGF-β-induced FMyT, placing IRF9 downstream of the MRTF-A–ZEB1 axis as an anti-fibrotic factor.","method":"RNA-seq, ChIP for MRTF-A/TEAD1 on Zeb1 promoter, IRF9 knockdown/overexpression, myofibroblast differentiation assays, myofibroblast-specific MRTF-A KO mice","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with in vivo mouse model and in vitro functional assays, single lab","pmids":["37121967"],"is_preprint":false},{"year":2021,"finding":"IRF9 promotes PASMC proliferation by directly interacting with AKT to inhibit AKT phosphorylation at Thr308, leading to mitochondrial dysfunction. IRF9 also directly restrains PHB1 (Prohibitin 1) expression. Both mechanisms contribute to PASMC proliferation in pulmonary arterial hypertension models.","method":"IRF9 overexpression/knockdown, co-immunoprecipitation for IRF9-AKT interaction, AKT inhibitor (MK2206) rescue, EdU proliferation assays, PHB1 expression analysis, PAH rat models","journal":"Frontiers in pharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP for interaction, pharmacological rescue, but mechanistic detail limited and non-canonical role; single lab","pmids":["34925032"],"is_preprint":false},{"year":2023,"finding":"SVV 3Cpro antagonizes type I IFN signaling by degrading STAT1, STAT2, and IRF9, and by cleaving STAT2. SVV 3Cpro also degrades karyopherin α1 (KPNA1) to block ISGF3 nuclear translocation.","method":"Overexpression assays, Western blot for protein degradation/cleavage, nuclear translocation assays, IFN signaling reporter assays","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic dissection of multiple targets with defined molecular readouts, single lab","pmids":["37819133"],"is_preprint":false},{"year":2017,"finding":"Kobuvirus VP3 protein associates with STAT2 and IRF9, interfering with STAT2-IRF9 and STAT2-STAT2 complex formation, thereby impairing nuclear translocation of both STAT2 and IRF9 and suppressing downstream antiviral gene expression.","method":"Co-immunoprecipitation, nuclear translocation assays, IFN-β luciferase reporter, qPCR for ISG expression","journal":"Virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus nuclear translocation and functional reporter assays, single lab","pmids":["28441586"],"is_preprint":false},{"year":2022,"finding":"STAT3 is activated upstream of IRF9 in multicellular spheroids of colon carcinoma cells and binds the IRF9 promoter, driving IRF9 expression and subsequent IRDS gene upregulation. This occurs via gp130/JAK signaling from a soluble factor in conditioned media.","method":"STAT3 ChIP on IRF9 promoter, conditioned media transfer experiments, STAT3 inhibition, IRF9 knockdown, gene expression analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for direct promoter binding, conditioned media functional assay, defined pathway inhibitors, single lab","pmids":["30679726"],"is_preprint":false},{"year":2023,"finding":"IRF9 interacts with Twist1 in human trophoblast cells; this interaction is required for IRF9 binding to the IFN-stimulated response element (ISRE) and constitutive ISG expression. Twist1 also acts as an upstream regulator controlling basal IRF9 protein levels. Absence of Twist1 renders trophoblasts susceptible to ZIKV infection.","method":"Co-immunoprecipitation for IRF9-Twist1 interaction, ISRE reporter assays, knockdown experiments, antiviral (ZIKV) assays","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ISRE functional assay plus antiviral phenotype, single lab","pmids":["37144865"],"is_preprint":false},{"year":2025,"finding":"IRF8 promotes IRF9 degradation through the ubiquitin-proteasome pathway by upregulating the E3 ubiquitin ligase NEDD4L, thereby suppressing type I IFN signaling and facilitating BEFV replication. Knockdown of NEDD4L reduced IRF8-driven IRF9 degradation.","method":"Knockdown/overexpression of IRF8 and NEDD4L, Western blot for IRF9 protein levels, proteasome inhibitor experiments, viral replication assays","journal":"Veterinary microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with knockdown rescue, proteasomal pathway mechanistic link, single lab","pmids":["40513519"],"is_preprint":false},{"year":2026,"finding":"L-lactic acid induces IRF9 L-lactylation mediated by AARS1. IRF9 L-lactylation promotes IRF9-STAT2 interaction, potentiating type I IFN signaling and boosting antiviral immune response. Viruses achieve immune evasion by promoting SIRT1-mediated delactylation of IRF9. Metformin enhances IRF9 L-lactylation by accumulating lactic acid and disrupting virus-induced IRF9-SIRT1 interaction.","method":"L-lactylation modification identification, AARS1 knockdown, Co-IP for IRF9-STAT2 interaction, SIRT1 delactylation assay, antiviral assays, metformin treatment","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — novel PTM identification with writer (AARS1) and eraser (SIRT1) identified, functional consequence on IRF9-STAT2 interaction shown, single lab","pmids":["41481472"],"is_preprint":false},{"year":2012,"finding":"Fish IRF9 (CaIRF9) is constitutively present in the nucleus driven by two nuclear localization signals (NLS): one within the DNA-binding domain and one immediately behind the DBD (mammalian IRF9 has only the first NLS). CaIRF9 together with CaSTAT2 activates ISRE-containing promoters, upregulates ISGs, and also activates the IFN promoter itself.","method":"GFP-fusion subcellular localization, NLS deletion mutants, co-transfection reporter assays, ISG expression analysis","journal":"Fish & shellfish immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with domain mutants plus functional reporter assays; ortholog study in fish","pmids":["22626811"],"is_preprint":false},{"year":2022,"finding":"In STAT2- or IRF9-deficient cells, deficiency of any ISGF3 component suppresses induction of negative regulators such as USP18, leading to abnormally prolonged IFN-I receptor signaling. In cells lacking STAT2 or IRF9, this aberrant late transcriptional response to IFN-α mimics the effect of IFN-γ (GAF-like response), suggesting a negative feedback failure mechanism.","method":"IFN stimulation kinetics in patient-derived primary cells and iPSC-derived macrophages from STAT1-, STAT2-, or IRF9-deficient patients, transcriptome analysis, USP18 expression assays","journal":"The Journal of allergy and clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined human genetic deficiency models with transcriptome readouts, mechanistic negative-feedback model supported, single study","pmids":["35182547"],"is_preprint":false}],"current_model":"IRF9 is the DNA-binding subunit of the ISGF3 transcription factor complex (STAT1/STAT2/IRF9), where it recognizes ISRE elements to drive IFN-stimulated gene expression; ISGF3 assembly now appears to occur on DNA rather than in the cytoplasm, while unphosphorylated IRF9 with U-STAT1/U-STAT2 (U-ISGF3) sustains a prolonged second-phase antiviral response; preformed STAT2-IRF9 dimers maintain basal ISG expression under homeostatic conditions; IRF9 interacts with the STAT2 coiled-coil domain via its IAD (structurally defined by crystallography), with CypA, Twist1, and AKT as additional binding partners, and its activity is regulated by phosphorylation (at S252/S253) and by L-lactylation (written by AARS1, erased by SIRT1) that enhances STAT2 interaction, as well as by ubiquitin-proteasome degradation promoted by the IRF8-NEDD4L axis; beyond canonical interferon signaling, IRF9 represses SIRT1 transcription (modulating the SIRT1-p53 axis), cooperates with NF-κB via U-STAT2 bridging to drive IL-6, and participates in non-canonical STAT1-independent antiviral and proinflammatory pathways."},"narrative":{"mechanistic_narrative":"IRF9 is the DNA-binding subunit of the interferon-stimulated gene factor 3 (ISGF3) transcription factor, which it forms with STAT1 and STAT2 to recognize ISRE elements and drive type I and type III interferon-stimulated gene (ISG) expression [PMID:31266943, PMID:30143481]. Its IRF-association domain (IAD) engages a divergent surface that specifically binds the STAT2 coiled-coil domain, an interface defined by crystallography and required for ISGF3 function [PMID:29317535], while its bipartite nuclear localization signal drives nuclear transit of the STAT2-bridged complex [PMID:18456457]. Rather than assembling in the cytoplasm, the complete ISGF3 trimer assembles on DNA, switching cells from a basal state—maintained by preformed STAT2-IRF9 complexes—to induced ISG expression [PMID:31266943]. IRF9 dosage is rate-limiting for the amplitude, timing, and termination of IFNα signaling, including induction of the negative regulator USP18, whose loss in IRF9-deficient cells causes aberrantly prolonged receptor signaling [PMID:20964804, PMID:35182547]. Beyond the canonical trimer, IRF9 supports a prolonged second-phase response through unphosphorylated U-ISGF3 acting on distinct ISREs [PMID:24065129], drives a STAT1-independent STAT2/IRF9 antiviral program [PMID:25564224], and cooperates with NF-κB through U-STAT2 bridging to induce IL6 [PMID:29581268]. Inherited complete IRF9 deficiency abolishes ISGF3 formation, narrows the IFN-induced transcriptome, and impairs control of influenza A, parainfluenza, and RSV, with the phenotype rescued by wild-type IRF9 [PMID:30143481]. IRF9 is targeted by numerous viral antagonists that bind its IAD or DNA-binding domain to block ISGF3 assembly, DNA binding, or nuclear translocation [PMID:31092569, PMID:26342467, PMID:32581091, PMID:28441586], and its activity is tuned by post-translational regulation including S252/S253 phosphorylation [PMID:36662450], AARS1-written L-lactylation that enhances STAT2 interaction [PMID:41481472], and IRF8-NEDD4L-driven proteasomal degradation [PMID:40513519]. IRF9 also acts as a sequence-specific transcriptional regulator outside interferon signaling, repressing SIRT1 to modulate p53 acetylation [PMID:29501566] and acting as an anti-fibrotic factor downstream of an MRTF-A–ZEB1 axis [PMID:37121967].","teleology":[{"year":2002,"claim":"Established that IRF9 has a regulatory role in interferon responses distinct from initiating STAT1 phosphorylation, controlling the timely decline of IRF-1.","evidence":"Genetic epistasis in STAT1/STAT2/IRF9-deficient cells with IRF-1 time-course analysis after IFNτ","pmids":["11804954"],"confidence":"Medium","gaps":["Mechanism by which IRF9 drives IRF-1 decline not defined","Direct target genes not mapped"]},{"year":2008,"claim":"Defined how the ISGF3 components are physically coupled and routed to the nucleus, showing STAT2 adapts IFNaR2 to IRF9 while IRF9's NLS drives nuclear entry.","evidence":"Co-IP and GFP-ICD nuclear localization assays in STAT2- and IRF9-deficient cells","pmids":["18456457"],"confidence":"Medium","gaps":["Stoichiometry of the ternary complex unresolved","Whether assembly is cytoplasmic vs DNA-templated not addressed here"]},{"year":2010,"claim":"Showed IRF9 abundance is a rate-limiting determinant of IFNα signaling dynamics, framing IRF9 as a quantitative tuner of the antiviral response.","evidence":"Mathematical modeling with IRF9 overexpression and quantitative gene expression","pmids":["20964804"],"confidence":"Medium","gaps":["Endogenous IRF9 fluctuations not measured","Single cell context"]},{"year":2013,"claim":"Revealed non-canonical IRF9 functions: unphosphorylated U-ISGF3 sustains a prolonged second-phase antiviral/DNA-damage-resistance response, and a STAT1-independent STAT2/IRF9 pathway induces DUOX2-driven antiviral H2O2.","evidence":"Manipulated IRF9/STAT expression with reporter and gene-expression analysis; knockdown plus antiviral assays for the DUOX2 pathway","pmids":["24065129","23545780"],"confidence":"High","gaps":["Distinct ISRE recognition rules for U-ISGF3 vs ISGF3 not defined","DUOX2 induction mechanism single-lab"]},{"year":2015,"claim":"Demonstrated that STAT2/IRF9 alone can drive a broad, prolonged antiviral ISG program independent of STAT1, and that IRF9/STAT1 mediates a non-IFN proinflammatory program in vivo.","evidence":"Genome-wide transcriptomics and antiviral assays in STAT1-KO cells; DSS colitis with IRF9-KO and IFNAR/IL28R-KO mice","pmids":["25564224","25918247"],"confidence":"High","gaps":["Determinants selecting STAT2/IRF9 vs full ISGF3 unclear","CXCL10 sufficiency not tested in isolation"]},{"year":2018,"claim":"Resolved the molecular interface underlying ISGF3 specificity and provided human genetic proof that IRF9 is essential for antiviral immunity.","evidence":"Crystal structures of IRF9-IAD alone and with STAT2-CCD plus mutagenesis; patient with inherited complete IRF9 loss-of-function, transcriptome/viral assays and wild-type rescue","pmids":["29317535","30143481"],"confidence":"High","gaps":["Structure of full ISGF3 on DNA not solved","Spectrum of viruses controlled by IRF9 in patients limited"]},{"year":2019,"claim":"Overturned the cytoplasmic-assembly dogma by showing ISGF3 assembles on DNA, with preformed STAT2-IRF9 maintaining basal ISG expression.","evidence":"Integrated transcriptomics, proteomics, ChIP-seq and in vivo BioID proximity labeling in macrophages","pmids":["31266943"],"confidence":"High","gaps":["Kinetics of on-DNA assembly not directly timed","Whether all cell types follow this model unknown"]},{"year":2018,"claim":"Identified IRF9 as a direct transcriptional repressor outside interferon signaling, linking it to the SIRT1-p53 axis in leukemia.","evidence":"ChIP on the SIRT1 promoter with IRF9 knockdown/overexpression and acetyl-p53 readout","pmids":["29501566"],"confidence":"Medium","gaps":["DNA motif for IRF9 at SIRT1 promoter not defined","Cofactor requirements unknown"]},{"year":2018,"claim":"Showed IRF9/STAT1 is required for IFN-driven TLR7 upregulation and autoantibody production, implicating IRF9 in autoimmunity.","evidence":"Pristane-induced lupus in IRF9-KO and STAT1-KO mice with B cell stimulation assays","pmids":["18340381"],"confidence":"Medium","gaps":["Direct IRF9 binding at TLR7 locus not shown","Human relevance untested"]},{"year":2022,"claim":"Explained why ISGF3 deficiency causes prolonged IFN signaling, identifying failed induction of the negative regulator USP18.","evidence":"IFN stimulation kinetics and transcriptomics in patient-derived and iPSC-macrophage STAT1/STAT2/IRF9-deficient cells","pmids":["35182547"],"confidence":"Medium","gaps":["Direct IRF9 occupancy at USP18 not mapped here","Therapeutic implications untested"]},{"year":2023,"claim":"Extended IRF9 regulatory biology with phosphosite mapping, a Twist1-dependent constitutive ISG mechanism, and an anti-fibrotic role downstream of MRTF-A–ZEB1.","evidence":"MS phosphosite identification with S252/S253 mutagenesis; Twist1 Co-IP with ISRE and ZIKV assays; RNA-seq/ChIP and MRTF-A KO mice for fibrosis","pmids":["36662450","37144865","37121967"],"confidence":"Medium","gaps":["Functional effect of S252/S253 modest and target-selective","Kinase for IRF9 phosphorylation unknown","Twist1-IRF9 interface not structurally defined"]},{"year":2026,"claim":"Defined post-translational control of IRF9-STAT2 binding by a lactylation-delactylation cycle, opening a metabolic input into antiviral signaling.","evidence":"L-lactylation identification with AARS1 (writer) knockdown, SIRT1 (eraser) delactylation, Co-IP and antiviral/metformin assays","pmids":["41481472"],"confidence":"Medium","gaps":["Lactylation site(s) on IRF9 not pinpointed","In vivo relevance single-lab"]},{"year":null,"claim":"How distinct IRF9-containing complexes (ISGF3, U-ISGF3, STAT2/IRF9, IRF9/STAT1, IRF9-NF-κB) are selected, targeted to specific genomic elements, and integrated with IRF9's PTM state remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of any full complex on DNA","Rules distinguishing ISRE subclasses not defined","PTM-to-complex-choice logic uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,9,14,22]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1,22,23]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,4]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,4,31]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,4]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,5,12]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,22,23]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,13,32]}],"complexes":["ISGF3 (STAT1/STAT2/IRF9)","U-ISGF3","STAT2/IRF9"],"partners":["STAT2","STAT1","IFNAR2","PPIA","TWIST1","AKT1","RELA","NEDD4L"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q00978","full_name":"Interferon regulatory factor 9","aliases":["IFN-alpha-responsive transcription factor subunit","ISGF3 p48 subunit","Interferon-stimulated gene factor 3 gamma","ISGF-3 gamma","Transcriptional regulator ISGF3 subunit gamma"],"length_aa":393,"mass_kda":43.7,"function":"Transcription factor that plays an essential role in anti-viral immunity. It mediates signaling by type I IFNs (IFN-alpha and IFN-beta). Following type I IFN binding to cell surface receptors, Jak kinases (TYK2 and JAK1) are activated, leading to tyrosine phosphorylation of STAT1 and STAT2. IRF9/ISGF3G associates with the phosphorylated STAT1:STAT2 dimer to form a complex termed ISGF3 transcription factor, that enters the nucleus. ISGF3 binds to the IFN stimulated response element (ISRE) to activate the transcription of interferon stimulated genes, which drive the cell in an antiviral state","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q00978/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IRF9","classification":"Not Classified","n_dependent_lines":11,"n_total_lines":1208,"dependency_fraction":0.009105960264900662},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IRF9","total_profiled":1310},"omim":[{"mim_id":"618648","title":"IMMUNODEFICIENCY 65, SUSCEPTIBILITY TO VIRAL INFECTIONS; IMD65","url":"https://www.omim.org/entry/618648"},{"mim_id":"615332","title":"INTERFERON REGULATORY FACTOR 2-BINDING PROTEIN 2; 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The IRF9-IAD surface has diverged from paralogs to enable specific interaction with STAT2-CCD, and mutagenesis of this interface abolished ISGF3 function in cells.\",\n      \"method\": \"X-ray crystallography, structure-guided mutagenesis, cell-based ISGF3 functional assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional validation by mutagenesis in cells, single rigorous study with multiple orthogonal methods\",\n      \"pmids\": [\"29317535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Under homeostatic (resting) conditions, preformed STAT2-IRF9 complexes control basal expression of IFN-induced genes. Upon type I IFN or IFN-γ stimulation, a complete ISGF3 complex (STAT1/STAT2/IRF9) assembles on DNA (not in the cytoplasm as previously thought), switching macrophages from resting-state to induced ISG expression.\",\n      \"method\": \"Integrated transcriptomics, proteomics, ChIP-seq, in vivo proximity-dependent labeling (BioID) in living cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal genome-wide and proteomic methods in a single rigorous study, challenges dogmatic cytoplasmic assembly model\",\n      \"pmids\": [\"31266943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"After IFNβ treatment, elevated IRF9 together with unphosphorylated STAT1 and STAT2 (U-ISGF3) drives a prolonged second-phase antiviral and DNA-damage-resistance response distinct from the initial ISGF3-driven response, acting through distinct ISREs.\",\n      \"method\": \"IFNβ treatment of cells with manipulated IRF9/STAT expression levels, reporter assays, gene expression analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — defined two mechanistically distinct complexes (ISGF3 vs U-ISGF3) with multiple functional readouts and replicated in multiple cancer/normal cell contexts\",\n      \"pmids\": [\"24065129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRF9 (as DNA-binding subunit of ISGF3) and unphosphorylated STAT2 (U-STAT2) cooperate with NF-κB to drive IL6 expression. U-STAT2 binds tightly to IRF9 and also to the p65 subunit of NF-κB, bridging ISRE and κB elements in the IL6 promoter as shown by ChIP.\",\n      \"method\": \"ChIP analysis, co-immunoprecipitation, reporter assays, exogenous overexpression of U-STAT2 and IRF9\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, ChIP, and functional reporter assays with multiple orthogonal methods in one study\",\n      \"pmids\": [\"29581268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IFNaR2 intracellular domain (IFNaR2-ICD), STAT2, and IRF9 form a ternary complex. STAT2 serves as an adaptor mediating the interaction between IFNaR2-ICD and IRF9, while the bipartite nuclear localization signal within IRF9 is the primary determinant driving nuclear transit of the complex.\",\n      \"method\": \"Co-immunoprecipitation, GFP-ICD nuclear localization assays in STAT2- and IRF9-deficient cells\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus nuclear localization functional assay in defined knockdown cells, single lab\",\n      \"pmids\": [\"18456457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In STAT1-deficient cells, a STAT2/IRF9 complex (requiring STAT2 phosphorylation and the STAT2 transactivation domain) drives expression of ~120 antiviral ISRE-containing ISGs in a prolonged manner compared to ISGF3, and can trigger an antiviral response against EMCV and VSV.\",\n      \"method\": \"Microarray/genome-wide transcriptomics in STAT1-KO cells stably overexpressing STAT2, antiviral assays, co-immunoprecipitation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide transcriptomics combined with antiviral functional assay and biochemical characterization of the complex, replicated in human and murine STAT1-deficient systems\",\n      \"pmids\": [\"25564224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IFNβ + TNFα synergism triggers a non-canonical, STAT1-independent antiviral pathway that requires STAT2 and IRF9 to induce DUOX2 NADPH oxidase expression, which then produces H2O2 as part of an antiviral state in airway epithelial cells.\",\n      \"method\": \"Knockdown of STAT1, STAT2, IRF9 individually, luciferase reporters, antiviral assays, siRNA-mediated DUOX2 knockdown\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined pathway readout, single lab, multiple gene targets tested\",\n      \"pmids\": [\"23545780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Cyclophilin A (CypA) binds directly to IRF9 via its PPIase pocket, specifically at the C-terminal IRF-association domain (IAD) but not the DNA-binding or linker domains. CypA also associates with the multimeric ISGF3 complex. CypA inhibitors prevent IRF9-CypA complex formation and enhance IFN-induced transcription. HCV NS5A competes with IRF9 for CypA binding.\",\n      \"method\": \"Cellular and recombinant pulldown assays, domain deletion mapping, co-immunoprecipitation, transcriptional reporter assays\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pulldowns with recombinant proteins and domain mapping, functional transcriptional readout, single lab\",\n      \"pmids\": [\"22902549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PRRSV nonstructural protein nsp11 interacts with the C-terminal IRF-association domain of IRF9 (independently of NendoU endoribonuclease activity), impairing ISGF3 formation and nuclear translocation to antagonize type I IFN signaling.\",\n      \"method\": \"Co-immunoprecipitation, domain-mapping with nsp11 active-site mutants, nuclear translocation assays, ISRE reporter assays in nsp11-overexpressing and PRRSV-infected cells\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with mutagenesis, nuclear translocation assay, functional reporter, single lab\",\n      \"pmids\": [\"31092569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Porcine bocavirus NP1 blocks ISGF3 DNA-binding activity by directly interacting with the DNA-binding domain (DBD) of IRF9, without affecting STAT1/STAT2 activation/translocation or ISGF3 complex formation.\",\n      \"method\": \"Co-immunoprecipitation, domain interaction mapping, ISRE reporter assays, ISG expression analysis\",\n      \"journal\": \"Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping plus functional ISRE reporter readout, single lab\",\n      \"pmids\": [\"26342467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Measles virus V protein displaces IRF9 (IRF-association domain) from preformed STAT2-core/IRF9 complexes, as demonstrated by size-exclusion chromatography with purified recombinant proteins. The MeV V binding site on STAT2 overlaps with that of IRF9, allowing V to inhibit the STAT2/IRF9 interaction and disrupt preassembled ISGF3.\",\n      \"method\": \"Biophysical binding assays with purified proteins, size exclusion chromatography, quantified dissociation constants\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified proteins, biophysical quantification of binding constants, direct competition assay; single lab but rigorous biochemical methods\",\n      \"pmids\": [\"32581091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"In response to IFNτ, IRF-9 is required for the timely decline of IRF-1 expression after 6 h: cells lacking IRF-9 showed persistent elevated IRF-1 without the normal sharp decline, whereas IRF-1 induction itself required tyrosine-phosphorylated STAT1 (not IRF-9).\",\n      \"method\": \"Cell lines deficient for specific IFN signaling components (STAT1-deficient, STAT2-deficient, IRF9-deficient), complementation with STAT1 mutants, IRF-1 mRNA/protein time-course analysis\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis using defined cell lines, multiple time points, complementation controls\",\n      \"pmids\": [\"11804954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Inherited complete loss-of-function IRF9 deficiency in a child abolishes ISGF3 (STAT1/STAT2/IRF9) trimer formation in response to IFN-α2b, greatly narrows the IFN-α2b-induced transcriptome, and prevents control of influenza A, parainfluenza, and RSV in vitro; the phenotype is rescued by wild-type IRF9.\",\n      \"method\": \"Patient cell studies, IFN stimulation assays, transcriptome analysis, viral replication assays, IRF9 rescue (wild-type re-expression) and knockdown in control cells\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — natural human loss-of-function with rescue by wild-type IRF9, transcriptome plus antiviral functional assays, human clinical validation\",\n      \"pmids\": [\"30143481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IRF9 concentration is a key rate-limiting determinant of IFNα signaling dynamics: mathematical modeling and IRF9 overexpression experiments demonstrated that increasing IRF9 reduces time-to-peak, increases amplitude, and enhances termination of JAK-STAT pathway activation, forming a positive feedback loop that accelerates early antiviral gene expression.\",\n      \"method\": \"Mathematical modeling combined with IRF9 overexpression studies, quantitative gene expression analysis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — model predictions experimentally verified by overexpression, single lab\",\n      \"pmids\": [\"20964804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IRF9 is required for the antiproliferative activity of IFN-α: IRF9 RNAi completely abolished IFN-α antiproliferative effects in OVCAR3 cells (unlike STAT1 RNAi), and IRF9 RNAi specifically inhibited IFN-α-induced TRAIL transcription. ISGF3 binds ISRE-like motifs in the TRAIL promoter after IFN-α treatment. IRF9 overexpression facilitated IFN-α-induced apoptosis in IFN-α-resistant T98G cells.\",\n      \"method\": \"RNAi knockdown, ISRE/TRAIL promoter binding (ChIP/EMSA), overexpression rescue, cell proliferation assays\",\n      \"journal\": \"Journal of immunotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function RNAi with specific phenotypic readout, promoter binding evidence, gain-of-function in resistant cells, single lab\",\n      \"pmids\": [\"19752753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Transcriptional activation of IRF9 (independent of IFN) corresponds with resistance to antimicrotubule agents in breast adenocarcinoma cells. Transient overexpression of IRF9 alone reproduced the drug-resistance phenotype and induced expression of IFN-responsive genes, whereas overexpression of STAT1 or STAT2 did not.\",\n      \"method\": \"Differential display, single-gene overexpression, drug resistance assays, gene expression analysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain-of-function with defined phenotypic readout, specificity shown by STAT1/STAT2 overexpression controls, single lab\",\n      \"pmids\": [\"11522652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"IRF9 functions in a noncanonical proinflammatory complex with STAT1 (apart from IFN-I and IFN-III signaling) in intestinal epithelial cells. IRF9 deficiency protects mice from DSS-induced colitis, while combined loss of type I and III IFN receptors worsens colitis. The CXCL10 chemokine gene is an important mediator of this IRF9/STAT1 proinflammatory activity.\",\n      \"method\": \"DSS colitis mouse model, IRF9-KO and IFNAR/IL28R double-KO mice, gene expression analysis, genetic epistasis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple knockout combinations, defined in vivo phenotype, single lab\",\n      \"pmids\": [\"25918247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRF9 and STAT1 are required for IFN-α-mediated upregulation of TLR7 in B cells and for IgG (but not IgM) autoantibody production in pristane-induced murine lupus. IRF9-KO B cells are incapable of activation through TLR7.\",\n      \"method\": \"IRF9-KO and STAT1-KO mouse model (pristane-induced SLE), B cell stimulation assays through TLR7/TLR9, autoantibody measurement\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with defined immune phenotype and B cell functional readouts, single lab\",\n      \"pmids\": [\"18340381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IFN-β-mediated inhibition of IL-8 expression requires all three ISGF3 components (STAT1, STAT2, and IRF9); however, the transactivation domains of STAT1 and STAT2 are not essential for this inhibitory signaling, distinguishing it from positive ISGF3-driven gene activation.\",\n      \"method\": \"Cell lines deficient for STAT1, STAT2, or IRF9, ISRE reporter assays, IL-8 expression analysis, transactivation domain mutants\",\n      \"journal\": \"Journal of interferon & cytokine research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cell-line genetic epistasis with domain mutant analysis, single lab\",\n      \"pmids\": [\"18370868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Expression of IRF9 fused to the transactivation domain of STAT1 (IRF9-S1C) or STAT2 (IRF9-S2C) in IFN-α-resistant HCV replicon cells restored ISRE promoter activity, induced HLA-1 surface expression, and significantly inhibited HCV RNA replication and viral protein expression independently of IFN-α, demonstrating that the IRF9 nuclear translocation is intact in these resistant cells while STAT phosphorylation is defective.\",\n      \"method\": \"Fusion protein expression, ISRE luciferase reporter, HCV replication assays, flow cytometry for HLA-1\",\n      \"journal\": \"Virology journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional rescue with engineered fusion proteins in defined deficient cells, antiviral assay, single lab\",\n      \"pmids\": [\"20939906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SARS-CoV-2 Spike-transfected cells release exosomes loaded with miR-148a and miR-590; these miRNAs are internalized by human microglia and suppress USP33 expression. USP33 regulates IRF9 turnover via deubiquitylation, so its suppression reduces IRF9 protein levels and alters innate immune gene expression.\",\n      \"method\": \"Exosome isolation, miRNA transfection, knockdown assays, Western blot for IRF9/USP33, inflammatory gene expression\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic link between USP33 deubiquitylation and IRF9 stability inferred but not directly demonstrated with ubiquitylation assays\",\n      \"pmids\": [\"33936086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IRF9 is phosphorylated at S252 and S253 under IFNβ-induced conditions and at R242 under non-induced conditions. Site-directed mutagenesis of S252/S253 to alanine or aspartic acid modestly affects USP18 gene expression (a negative regulator of type I IFN) but not Mx1 gene expression.\",\n      \"method\": \"Phosphoprotein enrichment, Phos-tag assay, tandem mass spectrometry on immunoprecipitated IRF9, site-directed mutagenesis, qPCR for ISG expression\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — mass spectrometry identification of phosphosites combined with mutagenesis, but functional effects are modest and single lab\",\n      \"pmids\": [\"36662450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRF9 binds the SIRT1 promoter and represses SIRT1 expression in AML cells; IRF9 knockdown promotes proliferation and survival while overexpression inhibits growth. This IRF9-SIRT1 repression increases p53 acetylation (a SIRT1 deacetylation substrate) and promotes expression of p53 target genes.\",\n      \"method\": \"ChIP for IRF9 on SIRT1 promoter, IRF9 knockdown/overexpression, cell proliferation/colony assays, Western blot for acetylated p53\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus gain/loss-of-function with functional readouts, single lab; note a related FEBS Letters paper [PMID:28213966] was retracted, but the Experimental cell research paper is distinct\",\n      \"pmids\": [\"29501566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In renal fibroblasts, the MRTF-A/TEAD1 complex activates ZEB1 transcription; ZEB1 in turn represses IRF9 transcription. IRF9 knockdown promotes fibroblast-myofibroblast transition (FMyT), whereas IRF9 overexpression antagonizes TGF-β-induced FMyT, placing IRF9 downstream of the MRTF-A–ZEB1 axis as an anti-fibrotic factor.\",\n      \"method\": \"RNA-seq, ChIP for MRTF-A/TEAD1 on Zeb1 promoter, IRF9 knockdown/overexpression, myofibroblast differentiation assays, myofibroblast-specific MRTF-A KO mice\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with in vivo mouse model and in vitro functional assays, single lab\",\n      \"pmids\": [\"37121967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IRF9 promotes PASMC proliferation by directly interacting with AKT to inhibit AKT phosphorylation at Thr308, leading to mitochondrial dysfunction. IRF9 also directly restrains PHB1 (Prohibitin 1) expression. Both mechanisms contribute to PASMC proliferation in pulmonary arterial hypertension models.\",\n      \"method\": \"IRF9 overexpression/knockdown, co-immunoprecipitation for IRF9-AKT interaction, AKT inhibitor (MK2206) rescue, EdU proliferation assays, PHB1 expression analysis, PAH rat models\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP for interaction, pharmacological rescue, but mechanistic detail limited and non-canonical role; single lab\",\n      \"pmids\": [\"34925032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SVV 3Cpro antagonizes type I IFN signaling by degrading STAT1, STAT2, and IRF9, and by cleaving STAT2. SVV 3Cpro also degrades karyopherin α1 (KPNA1) to block ISGF3 nuclear translocation.\",\n      \"method\": \"Overexpression assays, Western blot for protein degradation/cleavage, nuclear translocation assays, IFN signaling reporter assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic dissection of multiple targets with defined molecular readouts, single lab\",\n      \"pmids\": [\"37819133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Kobuvirus VP3 protein associates with STAT2 and IRF9, interfering with STAT2-IRF9 and STAT2-STAT2 complex formation, thereby impairing nuclear translocation of both STAT2 and IRF9 and suppressing downstream antiviral gene expression.\",\n      \"method\": \"Co-immunoprecipitation, nuclear translocation assays, IFN-β luciferase reporter, qPCR for ISG expression\",\n      \"journal\": \"Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus nuclear translocation and functional reporter assays, single lab\",\n      \"pmids\": [\"28441586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"STAT3 is activated upstream of IRF9 in multicellular spheroids of colon carcinoma cells and binds the IRF9 promoter, driving IRF9 expression and subsequent IRDS gene upregulation. This occurs via gp130/JAK signaling from a soluble factor in conditioned media.\",\n      \"method\": \"STAT3 ChIP on IRF9 promoter, conditioned media transfer experiments, STAT3 inhibition, IRF9 knockdown, gene expression analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for direct promoter binding, conditioned media functional assay, defined pathway inhibitors, single lab\",\n      \"pmids\": [\"30679726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IRF9 interacts with Twist1 in human trophoblast cells; this interaction is required for IRF9 binding to the IFN-stimulated response element (ISRE) and constitutive ISG expression. Twist1 also acts as an upstream regulator controlling basal IRF9 protein levels. Absence of Twist1 renders trophoblasts susceptible to ZIKV infection.\",\n      \"method\": \"Co-immunoprecipitation for IRF9-Twist1 interaction, ISRE reporter assays, knockdown experiments, antiviral (ZIKV) assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ISRE functional assay plus antiviral phenotype, single lab\",\n      \"pmids\": [\"37144865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"IRF8 promotes IRF9 degradation through the ubiquitin-proteasome pathway by upregulating the E3 ubiquitin ligase NEDD4L, thereby suppressing type I IFN signaling and facilitating BEFV replication. Knockdown of NEDD4L reduced IRF8-driven IRF9 degradation.\",\n      \"method\": \"Knockdown/overexpression of IRF8 and NEDD4L, Western blot for IRF9 protein levels, proteasome inhibitor experiments, viral replication assays\",\n      \"journal\": \"Veterinary microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with knockdown rescue, proteasomal pathway mechanistic link, single lab\",\n      \"pmids\": [\"40513519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"L-lactic acid induces IRF9 L-lactylation mediated by AARS1. IRF9 L-lactylation promotes IRF9-STAT2 interaction, potentiating type I IFN signaling and boosting antiviral immune response. Viruses achieve immune evasion by promoting SIRT1-mediated delactylation of IRF9. Metformin enhances IRF9 L-lactylation by accumulating lactic acid and disrupting virus-induced IRF9-SIRT1 interaction.\",\n      \"method\": \"L-lactylation modification identification, AARS1 knockdown, Co-IP for IRF9-STAT2 interaction, SIRT1 delactylation assay, antiviral assays, metformin treatment\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — novel PTM identification with writer (AARS1) and eraser (SIRT1) identified, functional consequence on IRF9-STAT2 interaction shown, single lab\",\n      \"pmids\": [\"41481472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Fish IRF9 (CaIRF9) is constitutively present in the nucleus driven by two nuclear localization signals (NLS): one within the DNA-binding domain and one immediately behind the DBD (mammalian IRF9 has only the first NLS). CaIRF9 together with CaSTAT2 activates ISRE-containing promoters, upregulates ISGs, and also activates the IFN promoter itself.\",\n      \"method\": \"GFP-fusion subcellular localization, NLS deletion mutants, co-transfection reporter assays, ISG expression analysis\",\n      \"journal\": \"Fish & shellfish immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with domain mutants plus functional reporter assays; ortholog study in fish\",\n      \"pmids\": [\"22626811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In STAT2- or IRF9-deficient cells, deficiency of any ISGF3 component suppresses induction of negative regulators such as USP18, leading to abnormally prolonged IFN-I receptor signaling. In cells lacking STAT2 or IRF9, this aberrant late transcriptional response to IFN-α mimics the effect of IFN-γ (GAF-like response), suggesting a negative feedback failure mechanism.\",\n      \"method\": \"IFN stimulation kinetics in patient-derived primary cells and iPSC-derived macrophages from STAT1-, STAT2-, or IRF9-deficient patients, transcriptome analysis, USP18 expression assays\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined human genetic deficiency models with transcriptome readouts, mechanistic negative-feedback model supported, single study\",\n      \"pmids\": [\"35182547\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IRF9 is the DNA-binding subunit of the ISGF3 transcription factor complex (STAT1/STAT2/IRF9), where it recognizes ISRE elements to drive IFN-stimulated gene expression; ISGF3 assembly now appears to occur on DNA rather than in the cytoplasm, while unphosphorylated IRF9 with U-STAT1/U-STAT2 (U-ISGF3) sustains a prolonged second-phase antiviral response; preformed STAT2-IRF9 dimers maintain basal ISG expression under homeostatic conditions; IRF9 interacts with the STAT2 coiled-coil domain via its IAD (structurally defined by crystallography), with CypA, Twist1, and AKT as additional binding partners, and its activity is regulated by phosphorylation (at S252/S253) and by L-lactylation (written by AARS1, erased by SIRT1) that enhances STAT2 interaction, as well as by ubiquitin-proteasome degradation promoted by the IRF8-NEDD4L axis; beyond canonical interferon signaling, IRF9 represses SIRT1 transcription (modulating the SIRT1-p53 axis), cooperates with NF-κB via U-STAT2 bridging to drive IL-6, and participates in non-canonical STAT1-independent antiviral and proinflammatory pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IRF9 is the DNA-binding subunit of the interferon-stimulated gene factor 3 (ISGF3) transcription factor, which it forms with STAT1 and STAT2 to recognize ISRE elements and drive type I and type III interferon-stimulated gene (ISG) expression [#1, #12]. Its IRF-association domain (IAD) engages a divergent surface that specifically binds the STAT2 coiled-coil domain, an interface defined by crystallography and required for ISGF3 function [#0], while its bipartite nuclear localization signal drives nuclear transit of the STAT2-bridged complex [#4]. Rather than assembling in the cytoplasm, the complete ISGF3 trimer assembles on DNA, switching cells from a basal state—maintained by preformed STAT2-IRF9 complexes—to induced ISG expression [#1]. IRF9 dosage is rate-limiting for the amplitude, timing, and termination of IFNα signaling, including induction of the negative regulator USP18, whose loss in IRF9-deficient cells causes aberrantly prolonged receptor signaling [#13, #32]. Beyond the canonical trimer, IRF9 supports a prolonged second-phase response through unphosphorylated U-ISGF3 acting on distinct ISREs [#2], drives a STAT1-independent STAT2/IRF9 antiviral program [#5], and cooperates with NF-κB through U-STAT2 bridging to induce IL6 [#3]. Inherited complete IRF9 deficiency abolishes ISGF3 formation, narrows the IFN-induced transcriptome, and impairs control of influenza A, parainfluenza, and RSV, with the phenotype rescued by wild-type IRF9 [#12]. IRF9 is targeted by numerous viral antagonists that bind its IAD or DNA-binding domain to block ISGF3 assembly, DNA binding, or nuclear translocation [#8, #9, #10, #26], and its activity is tuned by post-translational regulation including S252/S253 phosphorylation [#21], AARS1-written L-lactylation that enhances STAT2 interaction [#30], and IRF8-NEDD4L-driven proteasomal degradation [#29]. IRF9 also acts as a sequence-specific transcriptional regulator outside interferon signaling, repressing SIRT1 to modulate p53 acetylation [#22] and acting as an anti-fibrotic factor downstream of an MRTF-A–ZEB1 axis [#23].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that IRF9 has a regulatory role in interferon responses distinct from initiating STAT1 phosphorylation, controlling the timely decline of IRF-1.\",\n      \"evidence\": \"Genetic epistasis in STAT1/STAT2/IRF9-deficient cells with IRF-1 time-course analysis after IFNτ\",\n      \"pmids\": [\"11804954\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which IRF9 drives IRF-1 decline not defined\", \"Direct target genes not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined how the ISGF3 components are physically coupled and routed to the nucleus, showing STAT2 adapts IFNaR2 to IRF9 while IRF9's NLS drives nuclear entry.\",\n      \"evidence\": \"Co-IP and GFP-ICD nuclear localization assays in STAT2- and IRF9-deficient cells\",\n      \"pmids\": [\"18456457\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry of the ternary complex unresolved\", \"Whether assembly is cytoplasmic vs DNA-templated not addressed here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed IRF9 abundance is a rate-limiting determinant of IFNα signaling dynamics, framing IRF9 as a quantitative tuner of the antiviral response.\",\n      \"evidence\": \"Mathematical modeling with IRF9 overexpression and quantitative gene expression\",\n      \"pmids\": [\"20964804\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous IRF9 fluctuations not measured\", \"Single cell context\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed non-canonical IRF9 functions: unphosphorylated U-ISGF3 sustains a prolonged second-phase antiviral/DNA-damage-resistance response, and a STAT1-independent STAT2/IRF9 pathway induces DUOX2-driven antiviral H2O2.\",\n      \"evidence\": \"Manipulated IRF9/STAT expression with reporter and gene-expression analysis; knockdown plus antiviral assays for the DUOX2 pathway\",\n      \"pmids\": [\"24065129\", \"23545780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Distinct ISRE recognition rules for U-ISGF3 vs ISGF3 not defined\", \"DUOX2 induction mechanism single-lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated that STAT2/IRF9 alone can drive a broad, prolonged antiviral ISG program independent of STAT1, and that IRF9/STAT1 mediates a non-IFN proinflammatory program in vivo.\",\n      \"evidence\": \"Genome-wide transcriptomics and antiviral assays in STAT1-KO cells; DSS colitis with IRF9-KO and IFNAR/IL28R-KO mice\",\n      \"pmids\": [\"25564224\", \"25918247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants selecting STAT2/IRF9 vs full ISGF3 unclear\", \"CXCL10 sufficiency not tested in isolation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the molecular interface underlying ISGF3 specificity and provided human genetic proof that IRF9 is essential for antiviral immunity.\",\n      \"evidence\": \"Crystal structures of IRF9-IAD alone and with STAT2-CCD plus mutagenesis; patient with inherited complete IRF9 loss-of-function, transcriptome/viral assays and wild-type rescue\",\n      \"pmids\": [\"29317535\", \"30143481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full ISGF3 on DNA not solved\", \"Spectrum of viruses controlled by IRF9 in patients limited\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Overturned the cytoplasmic-assembly dogma by showing ISGF3 assembles on DNA, with preformed STAT2-IRF9 maintaining basal ISG expression.\",\n      \"evidence\": \"Integrated transcriptomics, proteomics, ChIP-seq and in vivo BioID proximity labeling in macrophages\",\n      \"pmids\": [\"31266943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetics of on-DNA assembly not directly timed\", \"Whether all cell types follow this model unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified IRF9 as a direct transcriptional repressor outside interferon signaling, linking it to the SIRT1-p53 axis in leukemia.\",\n      \"evidence\": \"ChIP on the SIRT1 promoter with IRF9 knockdown/overexpression and acetyl-p53 readout\",\n      \"pmids\": [\"29501566\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"DNA motif for IRF9 at SIRT1 promoter not defined\", \"Cofactor requirements unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed IRF9/STAT1 is required for IFN-driven TLR7 upregulation and autoantibody production, implicating IRF9 in autoimmunity.\",\n      \"evidence\": \"Pristane-induced lupus in IRF9-KO and STAT1-KO mice with B cell stimulation assays\",\n      \"pmids\": [\"18340381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct IRF9 binding at TLR7 locus not shown\", \"Human relevance untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Explained why ISGF3 deficiency causes prolonged IFN signaling, identifying failed induction of the negative regulator USP18.\",\n      \"evidence\": \"IFN stimulation kinetics and transcriptomics in patient-derived and iPSC-macrophage STAT1/STAT2/IRF9-deficient cells\",\n      \"pmids\": [\"35182547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct IRF9 occupancy at USP18 not mapped here\", \"Therapeutic implications untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended IRF9 regulatory biology with phosphosite mapping, a Twist1-dependent constitutive ISG mechanism, and an anti-fibrotic role downstream of MRTF-A–ZEB1.\",\n      \"evidence\": \"MS phosphosite identification with S252/S253 mutagenesis; Twist1 Co-IP with ISRE and ZIKV assays; RNA-seq/ChIP and MRTF-A KO mice for fibrosis\",\n      \"pmids\": [\"36662450\", \"37144865\", \"37121967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional effect of S252/S253 modest and target-selective\", \"Kinase for IRF9 phosphorylation unknown\", \"Twist1-IRF9 interface not structurally defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined post-translational control of IRF9-STAT2 binding by a lactylation-delactylation cycle, opening a metabolic input into antiviral signaling.\",\n      \"evidence\": \"L-lactylation identification with AARS1 (writer) knockdown, SIRT1 (eraser) delactylation, Co-IP and antiviral/metformin assays\",\n      \"pmids\": [\"41481472\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Lactylation site(s) on IRF9 not pinpointed\", \"In vivo relevance single-lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct IRF9-containing complexes (ISGF3, U-ISGF3, STAT2/IRF9, IRF9/STAT1, IRF9-NF-κB) are selected, targeted to specific genomic elements, and integrated with IRF9's PTM state remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of any full complex on DNA\", \"Rules distinguishing ISRE subclasses not defined\", \"PTM-to-complex-choice logic uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 9, 14, 22]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1, 22, 23]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 4, 31]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 5, 12]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 22, 23]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 13, 32]}\n    ],\n    \"complexes\": [\"ISGF3 (STAT1/STAT2/IRF9)\", \"U-ISGF3\", \"STAT2/IRF9\"],\n    \"partners\": [\"STAT2\", \"STAT1\", \"IFNAR2\", \"PPIA\", \"TWIST1\", \"AKT1\", \"RELA\", \"NEDD4L\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}