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FUNCTION Key transcriptional regulator of type I interferon (IFN)-dependent immune responses which plays a critical role in the innate immune response against DNA and RNA viruses (PubMed:22394562, PubMed:24049179, PubMed:25636800, PubMed:27302953, PubMed:31340999, PubMed:36603579, PubMed:8524823, PubMed:39362857). Regulates the transcription of type I IFN genes (IFN-alpha and IFN-beta) and IFN-stimulated genes (ISG) by binding to an interferon-stimulated response element (ISRE) in their promoters (PubMed:11846977, PubMed:16846591, PubMed:16979567, PubMed:20049431, PubMed:32972995, PubMed:36603579, PubMed:8524823). Acts as a more potent activator of the IFN-beta (IFNB) gene than the IFN-alpha (IFNA) gene and plays a critical role in both the early and late phases of the IFNA/B gene induction (PubMed:16846591, PubMed:16979567, PubMed:20049431, PubMed:36603579). Found in an inactive form in the cytoplasm of uninfected cells and following viral infection, double-stranded RNA (dsRNA), or toll-like receptor (TLR) signaling, is phosphorylated by IKBKE and TBK1 kinases (PubMed:22394562, PubMed:25636800, PubMed:27302953, PubMed:36603579). This induces a conformational change, leading to its dimerization and nuclear localization and association with CREB binding protein (CREBBP) to form dsRNA-activated factor 1 (DRAF1), a complex which activates the transcription of the type I IFN and ISG genes (PubMed:16154084, PubMed:27302953, PubMed:33440148, PubMed:36603579). Can activate distinct gene expression programs in macrophages and can induce significant apoptosis in primary macrophages (PubMed:16846591). In response to Sendai virus infection, is recruited by TOMM70:HSP90AA1 to mitochondrion and forms an apoptosis complex TOMM70:HSP90AA1:IRF3:BAX inducing apoptosis (PubMed:25609812). Key transcription factor regulating the IFN response during SARS-CoV-2 infection (PubMed:33440148).ACTIVITY REGULATION In the absence of viral infection, maintained as a monomer in an autoinhibited state (PubMed:16846591, PubMed:16979567, PubMed:20049431). Phosphorylation by TBK1 and IKBKE disrupts this autoinhibition leading to the liberation of the DNA-binding and dimerization activities and its nuclear localization where it can activate type I IFN and ISG genes (PubMed:25636800). Phosphorylation and activation follow the following steps: innate adapter proteins, such as MAVS, STING1 or TICAM1, are first activated by viral RNA, cytosolic DNA and bacterial lipopolysaccharide (LPS), respectively, leading to activation of the kinases TBK1 and IKBKE (PubMed:25636800, PubMed:36603579). These kinases then phosphorylate the adapter proteins on their pLxIS motif, leading to recruitment of IRF3, thereby licensing IRF3 for phosphorylation by TBK1 (PubMed:25636800, PubMed:36603579). Phosphorylated IRF3 dissociates from the adapter proteins, dimerizes, and then enters the nucleus to induce IFNs (PubMed:25636800, PubMed:27302953).ACTIVITY REGULATION (Microbial infection) Activated upon coronavirus SARS-CoV-2 infection.SUBUNIT Monomer (PubMed:16846591, PubMed:16979567, PubMed:20049431, PubMed:36603579). Homodimer; phosphorylation-induced (PubMed:22394562, PubMed:25636800, PubMed:26347139, PubMed:36603579). Interacts (when phosphorylated) with CREBBP (PubMed:16154084, PubMed:27302953). Interacts with MAVS (via phosphorylated pLxIS motif) (PubMed:16153868, PubMed:25636800, PubMed:27302953). Interacts with TICAM1 (via phosphorylated pLxIS motif) (PubMed:12471095, PubMed:14739303, PubMed:25636800, PubMed:27302953). Interacts with STING1 (via phosphorylated pLxIS motif) (PubMed:22394562, PubMed:25636800, PubMed:27302953, PubMed:28331227). Interacts with IKBKE and TBK1 (PubMed:16281057, PubMed:23478265, PubMed:25636800). Interacts with TICAM2 (PubMed:14517278). Interacts with RBCK1 (PubMed:18711448). Interacts with HERC5 (PubMed:20308324). Interacts with DDX3X (phosphorylated at 'Ser-102'); the interaction allows the phosphorylation and activation of IRF3 by IKBKE (PubMed:23478265, PubMed:27980081). Interacts with TRIM21 and ULK1, in the presence of TRIM21; this interaction leads to IRF3 degradation by autophagy (PubMed:18641315, PubMed:26347139). Interacts with RIOK3; RIOK3 probably mediates the interaction of TBK1 with IRF3 (PubMed:19557502). Interacts with ILRUN; the interaction inhibits IRF3 binding to its DNA consensus sequence (PubMed:29802199). Interacts with LYAR; this interaction impairs IRF3 DNA-binding activity (PubMed:31413131). Interacts with TRAF3 (PubMed:27980081). Interacts with ZDHHC11; ZDHHC11 recruits IRF3 to STING1 upon DNA virus infection and thereby promotes IRF3 activation (PubMed:28331227). Interacts with HSP90AA1; the interaction mediates IRF3 association with TOMM70 (PubMed:20628368, PubMed:25609812). Interacts with BCL2; the interaction decreases upon Sendai virus infection (PubMed:25609812). Interacts with BAX; the interaction is direct, increases upon Sendai virus infection and mediates the formation of the apoptosis complex TOMM70:HSP90AA1:IRF3:BAX (PubMed:25609812). Interacts with DDX56 (PubMed:31340999). Interacts with NBR1 (PubMed:35914352).SUBUNIT (Microbial infection) Interacts with rotavirus A NSP1 (via pLxIS motif); this interaction leads to the proteasome-dependent degradation of IRF3.SUBUNIT (Microbial infection) Interacts with herpes virus 8/HHV-8 protein VIRF1 (PubMed:11314014).SUBUNIT (Microbial infection) Interacts with Seneca Valley virus protease 3C; this interaction is involved in the suppression of IRF3 expression and phosphorylation by the virus.SUBUNIT (Microbial infection) Interacts with herpes virus 2/HHV-2 protein ICP27; this interaction inhibits IRF3 phosphorylation and nuclear translocation.SUBUNIT (Microbial infection) Interacts with human cytomegalovirus protein UL44; this interaction prevents IRF3 binding to its promoters.SUBUNIT (Microbial infection) Interacts with the two fragments of MERS-COV protein N produced by CASP6 through proteolytic cleavage; both interactions inhibit IRF3 nuclear translocation after activation and IFN signaling.INTERACTION Shuttles between cytoplasmic and nuclear compartments, with export being the prevailing effect (PubMed:10805757, PubMed:35922005). When activated, IRF3 interaction with CREBBP prevents its export to the cytoplasm (PubMed:10805757). Recruited to mitochondria via TOMM70:HSP90AA1 upon Sendai virus infection (PubMed:25609812).ALTERNATIVE PRODUCTS Expressed constitutively in a variety of tissues.PTM Constitutively phosphorylated on many Ser/Thr residues (PubMed:22394562, PubMed:23478265, PubMed:23746807). Activated following phosphorylation by TBK1 and IKBKE (PubMed:23478265, PubMed:23746807, PubMed:25636800, PubMed:36603579). Innate adapter proteins, such as MAVS, STING1 or TICAM1, are first activated by viral RNA, cytosolic DNA, and bacterial lipopolysaccharide (LPS), respectively, leading to activation of the kinases TBK1 and IKBKE (PubMed:25636800). These kinases then phosphorylate the adapter proteins on the pLxIS motif, leading to recruitment of IRF3, thereby licensing IRF3 for phosphorylation by TBK1 (PubMed:25636800). Phosphorylation at Ser-386 is followed by pyrophosphorylation at the same residue, promoting phosphorylation at Ser-396 (PubMed:36603579). Phosphorylated IRF3 dissociates from the adapter proteins, dimerizes, and then enters the nucleus to induce IFNs (PubMed:25636800, PubMed:36603579). Phosphorylation of IRF3 at Ser-385 and Ser-386 plays an important role in the PBLD-triggered IFN-I cascade (PubMed:39362857).PTM Pyrophosphorylated by UAP1 following phosphorylation at Ser-386 by TBK1 (PubMed:36603579). Pyrophosphorylation promotes subsequent phosphorylation at Ser-396, leading to homodimerization of IRF3 (PubMed:36603579).PTM Acetylation at Lys-366 by KAT8 inhibits recruimtent to promoters and transcription factor activity. Acetylation by KAT8 is promoted by phosphorylation at Ser-396.PTM Deamidation of Asn-85 by CTPS1 prevents IRF3 from binding DNA, thereby inhibiting the transcription factor activity.PTM Ubiquitinated; ubiquitination involves RBCK1 leading to proteasomal degradation (PubMed:18711448). Polyubiquitinated; ubiquitination involves TRIM21 leading to proteasomal degradation (PubMed:18641315). Ubiquitinated by UBE3C, leading to its degradation (PubMed:21167755). Deubiquitinated by USP5 on both 'Lys-48'-linked unanchored and 'Lys-63'-linked anchored polyubiquitin, leading to inhibition of anti-RNA viral innate immunity (PubMed:39761299).PTM ISGylated by HERC5 resulting in sustained IRF3 activation and in the inhibition of IRF3 ubiquitination by disrupting PIN1 binding. The phosphorylation state of IRF3 does not alter ISGylation.PTM Proteolytically cleaved by apoptotic caspases during apoptosis, leading to its inactivation (PubMed:30878284). Cleavage by CASP3 during virus-induced apoptosis inactivates it, preventing cytokine overproduction (PubMed:30878284).PTM (Microbial infection) ISGylated. ISGylation is cleaved and removed by SARS-COV-2 nsp3 which attenuates type I interferon responses.PTM (Microbial infection) Phosphorylation and subsequent activation of IRF3 is inhibited by vaccinia virus protein E3.PTM (Microbial infection) Phosphorylated by herpes simplex virus 1/HHV-1 US3 at Ser-175 to prevent IRF3 activation.DISEASE Disease susceptibility is associated with variants affecting the gene represented in this entry.SIMILARITY Belongs to the IRF family.
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