{"gene":"UNC93B1","run_date":"2026-04-28T21:43:01","timeline":{"discoveries":[{"year":2006,"finding":"UNC93B1 is required for signaling via intracellular TLR3, TLR7, and TLR9; the 3d missense allele (H412R) of Unc93b1 abolishes all three intracellular TLR pathways, impairs cross-presentation of exogenous antigen, and causes hypersusceptibility to MCMV infection.","method":"ENU mutagenesis screen, positional cloning, genetic complementation, functional TLR signaling assays in dendritic cells","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1-2 — original genetic discovery with positional cloning, multiple TLR functional readouts, replicated across multiple pathogens; foundational paper with >500 citations","pmids":["16415873"],"is_preprint":false},{"year":2006,"finding":"Human UNC93B1 deficiency (autosomal recessive) results in impaired TLR3/7/9-dependent interferon-alpha/beta and -lambda antiviral responses, establishing UNC93B1 as essential for nucleic acid-sensing TLR signaling in humans.","method":"Genetic mapping in patients, functional cellular assays of IFN responses","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — human genetics with functional cellular validation; >500 citations, foundational paper","pmids":["16973841"],"is_preprint":false},{"year":2008,"finding":"UNC93B1 physically interacts with TLR7 and TLR9 in the ER and delivers them to endolysosomes; in 3d (H412R) dendritic cells, neither TLR7 nor TLR9 exits the ER, and this trafficking and signaling defect is rescued by wild-type UNC93B1 expression.","method":"Co-immunoprecipitation, subcellular fractionation, confocal microscopy, complementation in 3d dendritic cells","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding demonstrated by Co-IP, trafficking shown by fractionation/imaging, rescued by complementation; >500 citations","pmids":["18305481"],"is_preprint":false},{"year":2009,"finding":"UNC93B1 residue D34 biases trafficking between TLR7 and TLR9: the D34A mutation increases UNC93B1 association with TLR7 (upregulating TLR7 trafficking and responses) while decreasing association with TLR9 (downregulating TLR9 trafficking and responses), with TLR3 unaffected.","method":"Complementation cloning, Co-IP of endogenous proteins, ligand-induced trafficking assays, TLR signaling assays in DCs","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis of key residue with multiple orthogonal readouts (Co-IP, trafficking, signaling); replicated in subsequent studies","pmids":["19451267"],"is_preprint":false},{"year":2010,"finding":"UNC93B1 directly interacts with TLR11 in the ER, and functional UNC93B1 is required for TLR11-dependent IL-12 secretion by dendritic cells in response to Toxoplasma gondii profilin; loss of UNC93B1 abolishes TLR11-dependent Th1 responses and host resistance.","method":"Co-immunoprecipitation, genetic loss-of-function (3d mice), IL-12 secretion assays, in vivo infection model","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct binding by Co-IP plus clean loss-of-function phenotype with defined cytokine readout","pmids":["21097503"],"is_preprint":false},{"year":2011,"finding":"TLR9 competes with TLR7 for UNC93B1-dependent trafficking and normally predominates; D34A mutation reverses this balance toward TLR7, causing TLR7-dependent systemic lethal inflammation driven by B-cell-dependent CD4+ T cell differentiation into Th1/Th17 subsets.","method":"Knock-in mice with D34A mutation, B-cell depletion experiments, T-cell subset analysis, signaling assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with knock-in mice, depletion rescue, multiple cellular readouts; >185 citations","pmids":["21683627"],"is_preprint":false},{"year":2011,"finding":"UNC93B1 physically associates with human TLR8 and is required for TLR8-mediated signaling; TLR8 localizes to early endosomes/ER in human monocytes, distinct from TLR7/TLR9 late endosomal localization.","method":"Co-immunoprecipitation, subcellular localization by immunofluorescence in human monocytes and HeLa transfectants","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct binding by Co-IP and localization studies; single lab study","pmids":["22164301"],"is_preprint":false},{"year":2013,"finding":"UNC93B1 enters the secretory pathway and controls loading of TLRs into COPII vesicles at the ER exit; UNC93B1 remains associated with TLRs through post-Golgi sorting. TLR9 specifically requires UNC93B1-mediated recruitment of adaptor protein complex 2 (AP-2) for endolysosomal delivery, while TLR7, TLR11, TLR12, and TLR13 use alternative pathways.","method":"COPII vesicle budding assays, subcellular fractionation, AP-2 depletion, Co-IP, trafficking assays in dendritic cells","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted COPII budding assay, multiple orthogonal methods; >215 citations","pmids":["23426999"],"is_preprint":false},{"year":2013,"finding":"Acidic residues (D812, E813) in the juxtamembrane region of TLR9 and (D699, E704) of TLR3 are required for UNC93B1 binding; mutation of these residues prevents UNC93B1 interaction, impairs TLR trafficking from the ER, and abolishes TLR signaling.","method":"Site-directed mutagenesis of TLRs, Co-immunoprecipitation, trafficking assays, TLR signaling assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis of interaction interface with multiple functional readouts in one study","pmids":["23585677"],"is_preprint":false},{"year":2014,"finding":"TLR5, a cell-surface receptor for flagellin, physically interacts with UNC93B1; UNC93B1 is essential for TLR5 plasma membrane localization and flagellin-induced cytokine secretion. 3d or UNC93B1-deficient cells lack TLR5 at the plasma membrane and fail to respond to flagellin.","method":"Co-immunoprecipitation, flow cytometry/surface biotinylation for TLR5 localization, cytokine assays in 3d and UNC93B1-KO mice","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — direct binding plus functional localization and signaling readout in multiple genetic backgrounds","pmids":["24778236"],"is_preprint":false},{"year":2014,"finding":"A C-terminal tyrosine-based sorting motif (YxxΦ) in UNC93B1 differentially regulates TLR7, TLR8, and TLR9 activity in human B cells and monocytes; destruction of YxxΦ abolishes nucleic acid-induced TLR7/8/9 responses but not small-molecule TLR8 responses. YxxΦ influences UNC93B1 subcellular localization via AP1- and AP2-dependent pathways.","method":"Site-directed mutagenesis of UNC93B1 YxxΦ motif, AP knockdown, subcellular localization assays, TLR signaling assays in primary human cells","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis of sorting motif with AP depletion, multiple TLR readouts, primary human cell validation","pmids":["25187660"],"is_preprint":false},{"year":2015,"finding":"LRRC59, an ER membrane protein, associates with UNC93B1 in a ligand-stimulated, TLR-independent manner and promotes UNC93B1-mediated endosomal translocation of nucleic acid-sensing TLRs (TLR3, TLR8, TLR9) upon infection.","method":"Co-immunoprecipitation, LRRC59 knockdown, TLR signaling assays, endosomal localization of TLR3 by imaging","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — binding by Co-IP plus functional knockdown with localization readout; single lab","pmids":["26466955"],"is_preprint":false},{"year":2017,"finding":"UNC93B1 interacts with the ER calcium sensor STIM1, and this interaction is required for STIM1 oligomerization/activation, calcium flux, and antigen cross-presentation in dendritic cells. Expression of constitutively active STIM1 (not requiring UNC93B1 binding) restores cross-presentation in 3d-mutated DCs.","method":"Co-immunoprecipitation, calcium imaging, antigen cross-presentation assays, rescue by constitutively active STIM1 mutant","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — direct binding, functional rescue with separation-of-function mutant, multiple readouts","pmids":["29158474"],"is_preprint":false},{"year":2018,"finding":"UNC93B1 regulates TLR stability independently of endosomal trafficking: UNC93B1 deficiency causes near-complete loss of TLR3 and TLR7 protein in primary mouse dendritic cells and macrophages. An ER-retained UNC93B1 version is sufficient to stabilize TLRs and largely restore endosomal TLR trafficking and activity.","method":"Western blot of TLR protein levels in UNC93B1-KO primary cells, ER-retained UNC93B1 mutant rescue experiments, TLR signaling assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — clean KO with protein level readout plus separation-of-function (ER-retained) rescue; >113 citations","pmids":["29768176"],"is_preprint":false},{"year":2019,"finding":"UNC93B1 limits TLR7 (but not TLR9) signaling by recruiting syntenin-1 (SDCBP) via phosphorylation-dependent binding, which sorts TLR7 into intralumenal vesicles of multivesicular bodies, terminating signaling. Mutations disrupting syntenin-1 binding cause enhanced TLR7 signaling and TLR7-dependent autoimmunity.","method":"Co-immunoprecipitation, exosome isolation, UNC93B1 phospho-mutants, syntenin-1 KO mice, autoimmunity phenotype analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — direct binding, multivesicular body sorting mechanism, phosphorylation requirement, in vivo autoimmunity validation; >109 citations","pmids":["31546246"],"is_preprint":false},{"year":2019,"finding":"TLR9 is released from UNC93B1 specifically within endosomes, and this release is required for TLR9 ligand binding and signal transduction. Mutations in UNC93B1 that increase TLR9 affinity or artificial tethering of TLR9 to UNC93B1 result in defective signaling. TLR7, unlike TLR9, does not dissociate from UNC93B1 in endosomes and is regulated by distinct mechanisms.","method":"UNC93B1 mutagenesis, artificial tethering constructs, ligand binding assays, TLR signaling assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis plus artificial tether loss-of-function with multiple readouts; mechanistically distinct from other findings; >76 citations","pmids":["31546247"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of human TLR3-UNC93B1, mouse TLR3-UNC93B1, and human TLR7-UNC93B1 complexes reveal that UNC93B1 is structurally similar to major facilitator superfamily transporters and interacts with TLR transmembrane and luminal juxtamembrane regions via its N-terminal six-helix bundle. TLR3 and TLR7 complexes differ in oligomerization state.","method":"Cryo-EM structure determination","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — high-resolution cryo-EM structures of TLR-UNC93B1 complexes with functional context; >73 citations","pmids":["33432245"],"is_preprint":false},{"year":2021,"finding":"UNC93B1 interacts with STING and targets it for autophagy-lysosome degradation, thereby suppressing cGAS-STING-mediated IFN-β signaling. This function depends on UNC93B1 trafficking capability; UNC93B1 knockout leads to STING accumulation and augmented cGAS-STING responses.","method":"Co-immunoprecipitation, lysosome inhibitor treatment, UNC93B1 KO cell lines, in vivo HSV-1 infection, Western blot of STING levels","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct binding plus functional KO phenotype; single lab, limited mechanistic depth","pmids":["33837956"],"is_preprint":false},{"year":2022,"finding":"UNC93B1 interacts with STING and promotes its autophagy-lysosome degradation, reducing STING stability and attenuating IFN-β/IRF3 signaling during DNA virus infection. This interaction requires UNC93B1 trafficking capability and is reversible by lysosome inhibitors.","method":"Co-immunoprecipitation, lysosome inhibitor rescue, UNC93B1 KO (HEK293T), primary macrophages from Unc93b1−/− mice, HSV-1 infection assays","journal":"Journal of medical virology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct binding, KO phenotype with inhibitor rescue; corroborates independent report (PMID 33837956)","pmids":["35577759"],"is_preprint":false},{"year":2022,"finding":"N-glycosylation of UNC93B1 at Asn272 (but not Asn251) is specifically required for TLR9 signaling: the N272Q mutation abolishes MyD88 recruitment to TLR9 and downstream signaling without affecting UNC93B1 expression, localization, or TLR7 signaling.","method":"Site-directed mutagenesis of glycosylation sites, Co-immunoprecipitation of MyD88, TLR signaling assays","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 1 — mutagenesis with mechanistic readout (MyD88 recruitment); single lab study","pmids":["35874766"],"is_preprint":false},{"year":2022,"finding":"UNC93B1 binds STIM1 in the ER lumen near the transmembrane domain and promotes zipping of STIM1 transmembrane and proximal cytosolic helices within resting STIM1 dimers, priming STIM1 for translocation to cortical ER. UNC93B1 deficiency reduces store-operated Ca2+ entry and STIM1-Orai1 interactions.","method":"Cysteine crosslinking in vivo, Co-immunoprecipitation, STIM1 localization imaging, Ca2+ imaging, STIM1-Orai1 interaction assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo crosslinking identifies interaction interface, multiple functional readouts including Ca2+ entry and protein interactions","pmids":["35065962"],"is_preprint":false},{"year":2024,"finding":"Systematic scanning-alanine mutagenesis screen of all cytosolic/luminal UNC93B1 residues identified both negative and positive regulatory regions for TLR3, TLR7, and TLR9 responses, revealing that disruption of specific negative regulatory residues (T93I, R336C) leads to enhanced TLR7/8 responses and systemic autoimmune disease in mice.","method":"Saturation mutagenesis screen, genome-edited knock-in mice, patient genetics, TLR signaling assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1 — comprehensive mutagenesis screen with in vivo validation; strong mechanistic resource","pmids":["38780621"],"is_preprint":false},{"year":2024,"finding":"UNC93B1 variants (E92G, R336L) cause selective TLR7 hyperactivation with constitutive type I IFN signaling. E92G causes UNC93B1 protein instability and reduced interaction with TLR7, paradoxically leading to TLR7 hyperactivation, establishing that UNC93B1 regulates TLR subtype-specific mechanisms of ligand recognition.","method":"Patient genetics, Co-immunoprecipitation (UNC93B1-TLR7 interaction), cytokine assays, TLR-specific agonist stimulation in patient cells and mouse macrophages","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 2 — patient genetics with direct binding measurement and multiple TLR-specific functional readouts","pmids":["38207055"],"is_preprint":false},{"year":2024,"finding":"UNC93B1 missense variants (I317M, G325C causing SLE; L330R, R466S, R525P causing chilblain lupus) differentially enhance TLR7/TLR8 activity. G325C, L330R, and R466S show enhanced interaction with TLR8, revealing that distinct UNC93B1 mutations can selectively gain TLR7 or TLR8 function.","method":"Patient genetics, Co-immunoprecipitation (UNC93B1-TLR8), TLR-specific functional assays in vitro and ex vivo","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — direct binding plus TLR-selective functional assays in multiple patient families","pmids":["38869500"],"is_preprint":false},{"year":2012,"finding":"UNC93B1 promotes trafficking of differentially glycosylated TLR3 (but not other nucleic acid-sensing TLRs) to the plasma membrane; UNC93B1 is itself transcriptionally up-regulated by TLR3 activation through poly(I:C), creating a positive feedback loop that primes B cells to respond to subsequent TLR9 activation.","method":"siRNA knockdown of UNC93B1, flow cytometry of surface TLR3, TLR signaling assays, reporter assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 — single lab, knockdown with localization and functional readout","pmids":["23166319"],"is_preprint":false},{"year":2003,"finding":"In C. elegans, UNC-93 colocalizes with the two-pore K+ channel SUP-9 and the novel transmembrane protein SUP-10 within muscle cells, and genetic evidence indicates these three proteins form a multi-subunit complex that coordinates muscle contraction.","method":"Genetic epistasis analysis, protein colocalization by immunofluorescence in C. elegans muscle","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2-3 — C. elegans ortholog study; colocalization plus strong genetic epistasis, but the function is not conserved with mammalian UNC93B1","pmids":["14534247"],"is_preprint":false}],"current_model":"UNC93B1 is a 12-transmembrane ER-resident chaperone that binds nucleic acid-sensing TLRs (TLR3, TLR7, TLR8, TLR9, TLR11, TLR12, TLR13) and TLR5 in the ER, stabilizes them, loads them into COPII vesicles for ER exit, and differentially traffics them to endolysosomes or the plasma membrane (TLR5) via distinct post-Golgi sorting mechanisms including AP-2 recruitment (TLR9) and syntenin-1/multivesicular body sorting (TLR7); within endosomes, TLR9 is released from UNC93B1 to enable ligand binding and signaling whereas TLR7 remains bound, and the relative affinity of UNC93B1 for TLR7 versus TLR9 (controlled by residue D34 and N-glycosylation at N272) sets the balance of TLR7/TLR9 activation to prevent autoimmunity; additionally, UNC93B1 interacts with STIM1 to prime store-operated Ca2+ entry and antigen cross-presentation, and negatively regulates cGAS-STING signaling by targeting STING for autophagy-lysosomal degradation."},"narrative":{"teleology":[{"year":2006,"claim":"Before the genetic identification of UNC93B1, the mechanism by which endosomal TLRs reach their signaling compartment was unknown; ENU mutagenesis revealed that the 3d (H412R) mutation in Unc93b1 abolished TLR3, TLR7, and TLR9 signaling and antigen cross-presentation, establishing UNC93B1 as a master regulator of intracellular TLR function.","evidence":"ENU mutagenesis screen with positional cloning and functional TLR assays in mouse dendritic cells; concurrent human genetic study identifying autosomal recessive UNC93B1 deficiency causing impaired antiviral IFN responses","pmids":["16415873","16973841"],"confidence":"High","gaps":["Mechanism of UNC93B1 action (chaperone vs. transport vs. signaling adapter) was not determined","Whether UNC93B1 physically contacts TLRs was not shown"]},{"year":2008,"claim":"The question of whether UNC93B1 directly binds TLRs or acts indirectly was resolved when co-immunoprecipitation and imaging demonstrated physical interaction with TLR7 and TLR9 in the ER and showed that the 3d mutation traps these TLRs in the ER, establishing UNC93B1 as a direct ER-to-endosome trafficking chaperone.","evidence":"Co-immunoprecipitation, subcellular fractionation, confocal microscopy, and complementation in 3d dendritic cells","pmids":["18305481"],"confidence":"High","gaps":["The molecular mechanism of ER exit was not defined","Whether UNC93B1 remains associated with TLRs in endosomes was unclear"]},{"year":2009,"claim":"How UNC93B1 differentially regulates TLR7 versus TLR9 was unclear until the D34A mutation was shown to shift UNC93B1 affinity toward TLR7 and away from TLR9, revealing a competitive binding mechanism that balances TLR7/TLR9 activation and, when disrupted, causes lethal TLR7-dependent inflammation.","evidence":"D34A knock-in mice, co-IP of endogenous proteins, TLR signaling assays, B-cell depletion rescue experiments","pmids":["19451267","21683627"],"confidence":"High","gaps":["Structural basis for D34-mediated selectivity was not resolved","Whether additional residues participate in TLR selectivity was unknown"]},{"year":2013,"claim":"The pathway by which UNC93B1 moves TLRs out of the ER was defined when reconstituted COPII vesicle budding assays showed UNC93B1 loads TLRs into COPII vesicles, and post-Golgi sorting studies revealed that TLR9 requires UNC93B1-mediated AP-2 recruitment for endolysosomal delivery whereas TLR7/11/12/13 use alternative routes; separately, acidic residues in TLR9 and TLR3 juxtamembrane regions were identified as the UNC93B1 binding determinants.","evidence":"COPII vesicle budding reconstitution, AP-2 depletion, site-directed mutagenesis of TLR juxtamembrane residues, co-IP and trafficking assays","pmids":["23426999","23585677"],"confidence":"High","gaps":["Precise post-Golgi sorting machinery for TLR7/11 was not identified","Whether UNC93B1 acts catalytically or stoichiometrically in COPII loading was unclear"]},{"year":2014,"claim":"UNC93B1 was previously thought to regulate only endosomal TLRs; the discovery that UNC93B1 binds TLR5 and is required for its plasma membrane localization and flagellin responses expanded UNC93B1's role to cell-surface TLR trafficking, while identification of a C-terminal YxxΦ sorting motif in UNC93B1 showed that AP-1/AP-2-dependent pathways fine-tune subcellular routing of TLR7/8/9.","evidence":"Co-IP, surface biotinylation, flow cytometry in 3d and UNC93B1-KO mice; mutagenesis of YxxΦ motif with AP knockdown in primary human cells","pmids":["24778236","25187660"],"confidence":"High","gaps":["How TLR5 is sorted to the plasma membrane rather than endosomes via UNC93B1 was not mechanistically resolved"]},{"year":2017,"claim":"The impaired antigen cross-presentation in 3d mice had no mechanistic explanation beyond TLR defects until UNC93B1 was shown to bind STIM1 in the ER, promote STIM1 oligomerization and store-operated Ca²⁺ entry, and thereby enable cross-presentation through a TLR-independent mechanism rescued by constitutively active STIM1.","evidence":"Co-immunoprecipitation, calcium imaging, cross-presentation assays, rescue with constitutively active STIM1","pmids":["29158474"],"confidence":"High","gaps":["The structural basis for UNC93B1-STIM1 interaction was not resolved at this point","Whether STIM1 and TLR binding are mutually exclusive on UNC93B1 was unknown"]},{"year":2018,"claim":"Whether UNC93B1 merely traffics TLRs or also stabilizes them was ambiguous until UNC93B1 knockout was shown to cause near-complete loss of TLR3 and TLR7 protein, and an ER-retained UNC93B1 mutant was sufficient to restore TLR stability and largely rescue signaling, demonstrating a chaperone-like stabilization function independent of forward trafficking.","evidence":"Western blot of TLR protein in UNC93B1-KO primary cells, ER-retained UNC93B1 mutant rescue","pmids":["29768176"],"confidence":"High","gaps":["Whether UNC93B1 prevents proteasomal vs. lysosomal TLR degradation was not determined","The stoichiometry of stabilization was not addressed"]},{"year":2019,"claim":"Two companion studies resolved the endosomal fate of TLR7 versus TLR9: TLR9 is released from UNC93B1 in endosomes to enable ligand binding and signaling, whereas TLR7 remains UNC93B1-bound and is negatively regulated by UNC93B1-mediated recruitment of syntenin-1, which sorts TLR7 into multivesicular body intralumenal vesicles; disruption of either mechanism causes autoimmunity.","evidence":"UNC93B1 mutagenesis, artificial TLR9-UNC93B1 tethering, syntenin-1 KO mice, exosome isolation, phospho-mutant analysis","pmids":["31546246","31546247"],"confidence":"High","gaps":["The signal triggering TLR9 release from UNC93B1 was not identified","Whether syntenin-1-dependent sorting applies to TLR8 was not tested"]},{"year":2021,"claim":"Cryo-EM structures of TLR3–UNC93B1 and TLR7–UNC93B1 complexes revealed that UNC93B1 adopts a major facilitator superfamily fold and contacts TLR transmembrane and juxtamembrane regions via its N-terminal six-helix bundle, providing the first structural framework for understanding TLR-selective binding.","evidence":"Cryo-EM structure determination of human and mouse complexes","pmids":["33432245"],"confidence":"High","gaps":["No TLR9–UNC93B1 structure was solved","How D34 or glycosylation sites modulate the interface was not structurally resolved"]},{"year":2021,"claim":"UNC93B1 was found to negatively regulate cGAS-STING signaling by binding STING and directing it to autophagy-lysosomal degradation, extending UNC93B1's function beyond TLR regulation to cytosolic DNA sensing pathway control.","evidence":"Co-immunoprecipitation, lysosome inhibitor rescue, UNC93B1-KO cell lines and Unc93b1−/− mice with HSV-1 infection","pmids":["33837956","35577759"],"confidence":"Medium","gaps":["The domain of UNC93B1 mediating STING interaction was not mapped","Whether STING degradation requires UNC93B1 trafficking or only ER interaction was not fully resolved","Independent replication beyond two related studies is limited"]},{"year":2022,"claim":"The UNC93B1-STIM1 interaction was mechanistically refined: UNC93B1 binds near the STIM1 transmembrane domain and promotes zipping of transmembrane and proximal cytosolic helices within resting STIM1 dimers, priming STIM1 for cortical ER translocation and Orai1 coupling; separately, N-glycosylation at N272 was shown to be specifically required for TLR9 signaling via MyD88 recruitment.","evidence":"In vivo cysteine crosslinking, Ca²⁺ imaging, STIM1-Orai1 interaction assays; glycosylation-site mutagenesis with MyD88 co-IP","pmids":["35065962","35874766"],"confidence":"High","gaps":["Whether N272 glycosylation affects TLR9 release from UNC93B1 in endosomes was not tested","Structural view of UNC93B1-STIM1 complex is lacking"]},{"year":2024,"claim":"Systematic mutagenesis of all UNC93B1 cytosolic/luminal residues combined with patient genetics identified both negative and positive regulatory regions for TLR3/7/8/9, establishing that specific gain-of-function UNC93B1 variants (T93I, R336C, E92G, R336L, G325C, I317M) cause selective TLR7 or TLR8 hyperactivation leading to SLE and chilblain lupus, mechanistically linking UNC93B1 to monogenic autoimmune disease.","evidence":"Saturation alanine-scanning mutagenesis screen, genome-edited knock-in mice, patient family genetics, co-IP of UNC93B1-TLR interactions, TLR-specific agonist assays","pmids":["38780621","38207055","38869500"],"confidence":"High","gaps":["Structural mapping of newly identified regulatory surfaces onto the cryo-EM structure is incomplete","Whether therapeutic targeting of UNC93B1-TLR7/8 interface can ameliorate lupus is untested"]},{"year":null,"claim":"Key unresolved questions include the signal that triggers TLR9 dissociation from UNC93B1 in endosomes, the structural basis for TLR9-selective glycosylation-dependent regulation, how UNC93B1 simultaneously coordinates TLR chaperoning with STIM1 priming and STING degradation, and whether UNC93B1's regulatory surfaces can be pharmacologically targeted to treat autoimmune disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["No endosomal release signal for TLR9 identified","No structure of UNC93B1-STIM1 or UNC93B1-STING complexes","Therapeutic tractability of UNC93B1 is unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,2,13]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[7,10,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,5,14,15,17]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,7,12,13,16]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[7,14,15]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,2,3,5,7,9,14,15]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[17,18]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[7,9,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[12,20]}],"complexes":[],"partners":["TLR3","TLR7","TLR9","TLR5","TLR8","STIM1","SDCBP","STING1"],"other_free_text":[]},"mechanistic_narrative":"UNC93B1 is a 12-transmembrane ER-resident chaperone that controls the stability, trafficking, and signaling of nucleic acid-sensing Toll-like receptors (TLR3, TLR7, TLR8, TLR9, TLR11, TLR12, TLR13) and the cell-surface receptor TLR5. UNC93B1 stabilizes TLR proteins in the ER, loads them into COPII vesicles for ER exit, and directs post-Golgi sorting to endolysosomes via AP-2-dependent (TLR9) or alternative pathways, while TLR5 is routed to the plasma membrane [PMID:18305481, PMID:23426999, PMID:24778236, PMID:29768176]. Within endosomes, UNC93B1 releases TLR9 to permit ligand binding while retaining TLR7, and it terminates TLR7 signaling by recruiting syntenin-1 to sort TLR7 into multivesicular bodies; the balance of TLR7 versus TLR9 activation—governed by residue D34, N-glycosylation at N272, and negative regulatory residues—prevents autoimmunity, as loss-of-function mutations cause susceptibility to herpes simplex encephalitis while gain-of-function variants cause systemic lupus erythematosus and chilblain lupus [PMID:16973841, PMID:31546246, PMID:31546247, PMID:38780621, PMID:38869500]. UNC93B1 also interacts with STIM1 to prime store-operated Ca²⁺ entry for antigen cross-presentation and negatively regulates cGAS-STING signaling by directing STING to autophagy-lysosomal degradation [PMID:29158474, PMID:35065962, PMID:33837956]."},"prefetch_data":{"uniprot":{"accession":"Q9H1C4","full_name":"Protein unc-93 homolog B1","aliases":[],"length_aa":597,"mass_kda":66.6,"function":"Plays an important role in innate and adaptive immunity by regulating nucleotide-sensing Toll-like receptor (TLR) signaling. Required for the transport of a subset of TLRs (including TLR3, TLR7 and TLR9) from the endoplasmic reticulum to endolysosomes where they can engage pathogen nucleotides and activate signaling cascades. May play a role in autoreactive B-cells removal","subcellular_location":"Endoplasmic reticulum membrane; Endosome; Lysosome; Cytoplasmic vesicle, phagosome","url":"https://www.uniprot.org/uniprotkb/Q9H1C4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UNC93B1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":74,"dependency_fraction":0.013513513513513514},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UNC93B1","total_profiled":1310},"omim":[{"mim_id":"614850","title":"ENCEPHALOPATHY, ACUTE, INFECTION-INDUCED (HERPES-SPECIFIC), SUSCEPTIBILITY TO, 6; IIAE6","url":"https://www.omim.org/entry/614850"},{"mim_id":"610551","title":"ENCEPHALOPATHY, ACUTE, INFECTION-INDUCED (HERPES-SPECIFIC), SUSCEPTIBILITY TO, 1; IIAE1","url":"https://www.omim.org/entry/610551"},{"mim_id":"608204","title":"UNC93 HOMOLOG B1, TLR SIGNALING REGULATOR; UNC93B1","url":"https://www.omim.org/entry/608204"},{"mim_id":"601896","title":"TNF RECEPTOR-ASSOCIATED FACTOR 3; TRAF3","url":"https://www.omim.org/entry/601896"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid 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missense allele (H412R) of Unc93b1 abolishes all three intracellular TLR pathways, impairs cross-presentation of exogenous antigen, and causes hypersusceptibility to MCMV infection.\",\n      \"method\": \"ENU mutagenesis screen, positional cloning, genetic complementation, functional TLR signaling assays in dendritic cells\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — original genetic discovery with positional cloning, multiple TLR functional readouts, replicated across multiple pathogens; foundational paper with >500 citations\",\n      \"pmids\": [\"16415873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human UNC93B1 deficiency (autosomal recessive) results in impaired TLR3/7/9-dependent interferon-alpha/beta and -lambda antiviral responses, establishing UNC93B1 as essential for nucleic acid-sensing TLR signaling in humans.\",\n      \"method\": \"Genetic mapping in patients, functional cellular assays of IFN responses\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human genetics with functional cellular validation; >500 citations, foundational paper\",\n      \"pmids\": [\"16973841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UNC93B1 physically interacts with TLR7 and TLR9 in the ER and delivers them to endolysosomes; in 3d (H412R) dendritic cells, neither TLR7 nor TLR9 exits the ER, and this trafficking and signaling defect is rescued by wild-type UNC93B1 expression.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, confocal microscopy, complementation in 3d dendritic cells\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding demonstrated by Co-IP, trafficking shown by fractionation/imaging, rescued by complementation; >500 citations\",\n      \"pmids\": [\"18305481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"UNC93B1 residue D34 biases trafficking between TLR7 and TLR9: the D34A mutation increases UNC93B1 association with TLR7 (upregulating TLR7 trafficking and responses) while decreasing association with TLR9 (downregulating TLR9 trafficking and responses), with TLR3 unaffected.\",\n      \"method\": \"Complementation cloning, Co-IP of endogenous proteins, ligand-induced trafficking assays, TLR signaling assays in DCs\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis of key residue with multiple orthogonal readouts (Co-IP, trafficking, signaling); replicated in subsequent studies\",\n      \"pmids\": [\"19451267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"UNC93B1 directly interacts with TLR11 in the ER, and functional UNC93B1 is required for TLR11-dependent IL-12 secretion by dendritic cells in response to Toxoplasma gondii profilin; loss of UNC93B1 abolishes TLR11-dependent Th1 responses and host resistance.\",\n      \"method\": \"Co-immunoprecipitation, genetic loss-of-function (3d mice), IL-12 secretion assays, in vivo infection model\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding by Co-IP plus clean loss-of-function phenotype with defined cytokine readout\",\n      \"pmids\": [\"21097503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TLR9 competes with TLR7 for UNC93B1-dependent trafficking and normally predominates; D34A mutation reverses this balance toward TLR7, causing TLR7-dependent systemic lethal inflammation driven by B-cell-dependent CD4+ T cell differentiation into Th1/Th17 subsets.\",\n      \"method\": \"Knock-in mice with D34A mutation, B-cell depletion experiments, T-cell subset analysis, signaling assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with knock-in mice, depletion rescue, multiple cellular readouts; >185 citations\",\n      \"pmids\": [\"21683627\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"UNC93B1 physically associates with human TLR8 and is required for TLR8-mediated signaling; TLR8 localizes to early endosomes/ER in human monocytes, distinct from TLR7/TLR9 late endosomal localization.\",\n      \"method\": \"Co-immunoprecipitation, subcellular localization by immunofluorescence in human monocytes and HeLa transfectants\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct binding by Co-IP and localization studies; single lab study\",\n      \"pmids\": [\"22164301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"UNC93B1 enters the secretory pathway and controls loading of TLRs into COPII vesicles at the ER exit; UNC93B1 remains associated with TLRs through post-Golgi sorting. TLR9 specifically requires UNC93B1-mediated recruitment of adaptor protein complex 2 (AP-2) for endolysosomal delivery, while TLR7, TLR11, TLR12, and TLR13 use alternative pathways.\",\n      \"method\": \"COPII vesicle budding assays, subcellular fractionation, AP-2 depletion, Co-IP, trafficking assays in dendritic cells\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted COPII budding assay, multiple orthogonal methods; >215 citations\",\n      \"pmids\": [\"23426999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Acidic residues (D812, E813) in the juxtamembrane region of TLR9 and (D699, E704) of TLR3 are required for UNC93B1 binding; mutation of these residues prevents UNC93B1 interaction, impairs TLR trafficking from the ER, and abolishes TLR signaling.\",\n      \"method\": \"Site-directed mutagenesis of TLRs, Co-immunoprecipitation, trafficking assays, TLR signaling assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis of interaction interface with multiple functional readouts in one study\",\n      \"pmids\": [\"23585677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TLR5, a cell-surface receptor for flagellin, physically interacts with UNC93B1; UNC93B1 is essential for TLR5 plasma membrane localization and flagellin-induced cytokine secretion. 3d or UNC93B1-deficient cells lack TLR5 at the plasma membrane and fail to respond to flagellin.\",\n      \"method\": \"Co-immunoprecipitation, flow cytometry/surface biotinylation for TLR5 localization, cytokine assays in 3d and UNC93B1-KO mice\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding plus functional localization and signaling readout in multiple genetic backgrounds\",\n      \"pmids\": [\"24778236\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A C-terminal tyrosine-based sorting motif (YxxΦ) in UNC93B1 differentially regulates TLR7, TLR8, and TLR9 activity in human B cells and monocytes; destruction of YxxΦ abolishes nucleic acid-induced TLR7/8/9 responses but not small-molecule TLR8 responses. YxxΦ influences UNC93B1 subcellular localization via AP1- and AP2-dependent pathways.\",\n      \"method\": \"Site-directed mutagenesis of UNC93B1 YxxΦ motif, AP knockdown, subcellular localization assays, TLR signaling assays in primary human cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis of sorting motif with AP depletion, multiple TLR readouts, primary human cell validation\",\n      \"pmids\": [\"25187660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LRRC59, an ER membrane protein, associates with UNC93B1 in a ligand-stimulated, TLR-independent manner and promotes UNC93B1-mediated endosomal translocation of nucleic acid-sensing TLRs (TLR3, TLR8, TLR9) upon infection.\",\n      \"method\": \"Co-immunoprecipitation, LRRC59 knockdown, TLR signaling assays, endosomal localization of TLR3 by imaging\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — binding by Co-IP plus functional knockdown with localization readout; single lab\",\n      \"pmids\": [\"26466955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"UNC93B1 interacts with the ER calcium sensor STIM1, and this interaction is required for STIM1 oligomerization/activation, calcium flux, and antigen cross-presentation in dendritic cells. Expression of constitutively active STIM1 (not requiring UNC93B1 binding) restores cross-presentation in 3d-mutated DCs.\",\n      \"method\": \"Co-immunoprecipitation, calcium imaging, antigen cross-presentation assays, rescue by constitutively active STIM1 mutant\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding, functional rescue with separation-of-function mutant, multiple readouts\",\n      \"pmids\": [\"29158474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"UNC93B1 regulates TLR stability independently of endosomal trafficking: UNC93B1 deficiency causes near-complete loss of TLR3 and TLR7 protein in primary mouse dendritic cells and macrophages. An ER-retained UNC93B1 version is sufficient to stabilize TLRs and largely restore endosomal TLR trafficking and activity.\",\n      \"method\": \"Western blot of TLR protein levels in UNC93B1-KO primary cells, ER-retained UNC93B1 mutant rescue experiments, TLR signaling assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with protein level readout plus separation-of-function (ER-retained) rescue; >113 citations\",\n      \"pmids\": [\"29768176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UNC93B1 limits TLR7 (but not TLR9) signaling by recruiting syntenin-1 (SDCBP) via phosphorylation-dependent binding, which sorts TLR7 into intralumenal vesicles of multivesicular bodies, terminating signaling. Mutations disrupting syntenin-1 binding cause enhanced TLR7 signaling and TLR7-dependent autoimmunity.\",\n      \"method\": \"Co-immunoprecipitation, exosome isolation, UNC93B1 phospho-mutants, syntenin-1 KO mice, autoimmunity phenotype analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding, multivesicular body sorting mechanism, phosphorylation requirement, in vivo autoimmunity validation; >109 citations\",\n      \"pmids\": [\"31546246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TLR9 is released from UNC93B1 specifically within endosomes, and this release is required for TLR9 ligand binding and signal transduction. Mutations in UNC93B1 that increase TLR9 affinity or artificial tethering of TLR9 to UNC93B1 result in defective signaling. TLR7, unlike TLR9, does not dissociate from UNC93B1 in endosomes and is regulated by distinct mechanisms.\",\n      \"method\": \"UNC93B1 mutagenesis, artificial tethering constructs, ligand binding assays, TLR signaling assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis plus artificial tether loss-of-function with multiple readouts; mechanistically distinct from other findings; >76 citations\",\n      \"pmids\": [\"31546247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of human TLR3-UNC93B1, mouse TLR3-UNC93B1, and human TLR7-UNC93B1 complexes reveal that UNC93B1 is structurally similar to major facilitator superfamily transporters and interacts with TLR transmembrane and luminal juxtamembrane regions via its N-terminal six-helix bundle. TLR3 and TLR7 complexes differ in oligomerization state.\",\n      \"method\": \"Cryo-EM structure determination\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution cryo-EM structures of TLR-UNC93B1 complexes with functional context; >73 citations\",\n      \"pmids\": [\"33432245\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"UNC93B1 interacts with STING and targets it for autophagy-lysosome degradation, thereby suppressing cGAS-STING-mediated IFN-β signaling. This function depends on UNC93B1 trafficking capability; UNC93B1 knockout leads to STING accumulation and augmented cGAS-STING responses.\",\n      \"method\": \"Co-immunoprecipitation, lysosome inhibitor treatment, UNC93B1 KO cell lines, in vivo HSV-1 infection, Western blot of STING levels\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct binding plus functional KO phenotype; single lab, limited mechanistic depth\",\n      \"pmids\": [\"33837956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UNC93B1 interacts with STING and promotes its autophagy-lysosome degradation, reducing STING stability and attenuating IFN-β/IRF3 signaling during DNA virus infection. This interaction requires UNC93B1 trafficking capability and is reversible by lysosome inhibitors.\",\n      \"method\": \"Co-immunoprecipitation, lysosome inhibitor rescue, UNC93B1 KO (HEK293T), primary macrophages from Unc93b1−/− mice, HSV-1 infection assays\",\n      \"journal\": \"Journal of medical virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct binding, KO phenotype with inhibitor rescue; corroborates independent report (PMID 33837956)\",\n      \"pmids\": [\"35577759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"N-glycosylation of UNC93B1 at Asn272 (but not Asn251) is specifically required for TLR9 signaling: the N272Q mutation abolishes MyD88 recruitment to TLR9 and downstream signaling without affecting UNC93B1 expression, localization, or TLR7 signaling.\",\n      \"method\": \"Site-directed mutagenesis of glycosylation sites, Co-immunoprecipitation of MyD88, TLR signaling assays\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with mechanistic readout (MyD88 recruitment); single lab study\",\n      \"pmids\": [\"35874766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UNC93B1 binds STIM1 in the ER lumen near the transmembrane domain and promotes zipping of STIM1 transmembrane and proximal cytosolic helices within resting STIM1 dimers, priming STIM1 for translocation to cortical ER. UNC93B1 deficiency reduces store-operated Ca2+ entry and STIM1-Orai1 interactions.\",\n      \"method\": \"Cysteine crosslinking in vivo, Co-immunoprecipitation, STIM1 localization imaging, Ca2+ imaging, STIM1-Orai1 interaction assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo crosslinking identifies interaction interface, multiple functional readouts including Ca2+ entry and protein interactions\",\n      \"pmids\": [\"35065962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Systematic scanning-alanine mutagenesis screen of all cytosolic/luminal UNC93B1 residues identified both negative and positive regulatory regions for TLR3, TLR7, and TLR9 responses, revealing that disruption of specific negative regulatory residues (T93I, R336C) leads to enhanced TLR7/8 responses and systemic autoimmune disease in mice.\",\n      \"method\": \"Saturation mutagenesis screen, genome-edited knock-in mice, patient genetics, TLR signaling assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — comprehensive mutagenesis screen with in vivo validation; strong mechanistic resource\",\n      \"pmids\": [\"38780621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UNC93B1 variants (E92G, R336L) cause selective TLR7 hyperactivation with constitutive type I IFN signaling. E92G causes UNC93B1 protein instability and reduced interaction with TLR7, paradoxically leading to TLR7 hyperactivation, establishing that UNC93B1 regulates TLR subtype-specific mechanisms of ligand recognition.\",\n      \"method\": \"Patient genetics, Co-immunoprecipitation (UNC93B1-TLR7 interaction), cytokine assays, TLR-specific agonist stimulation in patient cells and mouse macrophages\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — patient genetics with direct binding measurement and multiple TLR-specific functional readouts\",\n      \"pmids\": [\"38207055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UNC93B1 missense variants (I317M, G325C causing SLE; L330R, R466S, R525P causing chilblain lupus) differentially enhance TLR7/TLR8 activity. G325C, L330R, and R466S show enhanced interaction with TLR8, revealing that distinct UNC93B1 mutations can selectively gain TLR7 or TLR8 function.\",\n      \"method\": \"Patient genetics, Co-immunoprecipitation (UNC93B1-TLR8), TLR-specific functional assays in vitro and ex vivo\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding plus TLR-selective functional assays in multiple patient families\",\n      \"pmids\": [\"38869500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"UNC93B1 promotes trafficking of differentially glycosylated TLR3 (but not other nucleic acid-sensing TLRs) to the plasma membrane; UNC93B1 is itself transcriptionally up-regulated by TLR3 activation through poly(I:C), creating a positive feedback loop that primes B cells to respond to subsequent TLR9 activation.\",\n      \"method\": \"siRNA knockdown of UNC93B1, flow cytometry of surface TLR3, TLR signaling assays, reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — single lab, knockdown with localization and functional readout\",\n      \"pmids\": [\"23166319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In C. elegans, UNC-93 colocalizes with the two-pore K+ channel SUP-9 and the novel transmembrane protein SUP-10 within muscle cells, and genetic evidence indicates these three proteins form a multi-subunit complex that coordinates muscle contraction.\",\n      \"method\": \"Genetic epistasis analysis, protein colocalization by immunofluorescence in C. elegans muscle\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — C. elegans ortholog study; colocalization plus strong genetic epistasis, but the function is not conserved with mammalian UNC93B1\",\n      \"pmids\": [\"14534247\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UNC93B1 is a 12-transmembrane ER-resident chaperone that binds nucleic acid-sensing TLRs (TLR3, TLR7, TLR8, TLR9, TLR11, TLR12, TLR13) and TLR5 in the ER, stabilizes them, loads them into COPII vesicles for ER exit, and differentially traffics them to endolysosomes or the plasma membrane (TLR5) via distinct post-Golgi sorting mechanisms including AP-2 recruitment (TLR9) and syntenin-1/multivesicular body sorting (TLR7); within endosomes, TLR9 is released from UNC93B1 to enable ligand binding and signaling whereas TLR7 remains bound, and the relative affinity of UNC93B1 for TLR7 versus TLR9 (controlled by residue D34 and N-glycosylation at N272) sets the balance of TLR7/TLR9 activation to prevent autoimmunity; additionally, UNC93B1 interacts with STIM1 to prime store-operated Ca2+ entry and antigen cross-presentation, and negatively regulates cGAS-STING signaling by targeting STING for autophagy-lysosomal degradation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"UNC93B1 is a 12-transmembrane ER-resident chaperone that controls the stability, trafficking, and signaling of nucleic acid-sensing Toll-like receptors (TLR3, TLR7, TLR8, TLR9, TLR11, TLR12, TLR13) and the cell-surface receptor TLR5. UNC93B1 stabilizes TLR proteins in the ER, loads them into COPII vesicles for ER exit, and directs post-Golgi sorting to endolysosomes via AP-2-dependent (TLR9) or alternative pathways, while TLR5 is routed to the plasma membrane [PMID:18305481, PMID:23426999, PMID:24778236, PMID:29768176]. Within endosomes, UNC93B1 releases TLR9 to permit ligand binding while retaining TLR7, and it terminates TLR7 signaling by recruiting syntenin-1 to sort TLR7 into multivesicular bodies; the balance of TLR7 versus TLR9 activation—governed by residue D34, N-glycosylation at N272, and negative regulatory residues—prevents autoimmunity, as loss-of-function mutations cause susceptibility to herpes simplex encephalitis while gain-of-function variants cause systemic lupus erythematosus and chilblain lupus [PMID:16973841, PMID:31546246, PMID:31546247, PMID:38780621, PMID:38869500]. UNC93B1 also interacts with STIM1 to prime store-operated Ca²⁺ entry for antigen cross-presentation and negatively regulates cGAS-STING signaling by directing STING to autophagy-lysosomal degradation [PMID:29158474, PMID:35065962, PMID:33837956].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Before the genetic identification of UNC93B1, the mechanism by which endosomal TLRs reach their signaling compartment was unknown; ENU mutagenesis revealed that the 3d (H412R) mutation in Unc93b1 abolished TLR3, TLR7, and TLR9 signaling and antigen cross-presentation, establishing UNC93B1 as a master regulator of intracellular TLR function.\",\n      \"evidence\": \"ENU mutagenesis screen with positional cloning and functional TLR assays in mouse dendritic cells; concurrent human genetic study identifying autosomal recessive UNC93B1 deficiency causing impaired antiviral IFN responses\",\n      \"pmids\": [\"16415873\", \"16973841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of UNC93B1 action (chaperone vs. transport vs. signaling adapter) was not determined\", \"Whether UNC93B1 physically contacts TLRs was not shown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The question of whether UNC93B1 directly binds TLRs or acts indirectly was resolved when co-immunoprecipitation and imaging demonstrated physical interaction with TLR7 and TLR9 in the ER and showed that the 3d mutation traps these TLRs in the ER, establishing UNC93B1 as a direct ER-to-endosome trafficking chaperone.\",\n      \"evidence\": \"Co-immunoprecipitation, subcellular fractionation, confocal microscopy, and complementation in 3d dendritic cells\",\n      \"pmids\": [\"18305481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular mechanism of ER exit was not defined\", \"Whether UNC93B1 remains associated with TLRs in endosomes was unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"How UNC93B1 differentially regulates TLR7 versus TLR9 was unclear until the D34A mutation was shown to shift UNC93B1 affinity toward TLR7 and away from TLR9, revealing a competitive binding mechanism that balances TLR7/TLR9 activation and, when disrupted, causes lethal TLR7-dependent inflammation.\",\n      \"evidence\": \"D34A knock-in mice, co-IP of endogenous proteins, TLR signaling assays, B-cell depletion rescue experiments\",\n      \"pmids\": [\"19451267\", \"21683627\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for D34-mediated selectivity was not resolved\", \"Whether additional residues participate in TLR selectivity was unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The pathway by which UNC93B1 moves TLRs out of the ER was defined when reconstituted COPII vesicle budding assays showed UNC93B1 loads TLRs into COPII vesicles, and post-Golgi sorting studies revealed that TLR9 requires UNC93B1-mediated AP-2 recruitment for endolysosomal delivery whereas TLR7/11/12/13 use alternative routes; separately, acidic residues in TLR9 and TLR3 juxtamembrane regions were identified as the UNC93B1 binding determinants.\",\n      \"evidence\": \"COPII vesicle budding reconstitution, AP-2 depletion, site-directed mutagenesis of TLR juxtamembrane residues, co-IP and trafficking assays\",\n      \"pmids\": [\"23426999\", \"23585677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise post-Golgi sorting machinery for TLR7/11 was not identified\", \"Whether UNC93B1 acts catalytically or stoichiometrically in COPII loading was unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"UNC93B1 was previously thought to regulate only endosomal TLRs; the discovery that UNC93B1 binds TLR5 and is required for its plasma membrane localization and flagellin responses expanded UNC93B1's role to cell-surface TLR trafficking, while identification of a C-terminal YxxΦ sorting motif in UNC93B1 showed that AP-1/AP-2-dependent pathways fine-tune subcellular routing of TLR7/8/9.\",\n      \"evidence\": \"Co-IP, surface biotinylation, flow cytometry in 3d and UNC93B1-KO mice; mutagenesis of YxxΦ motif with AP knockdown in primary human cells\",\n      \"pmids\": [\"24778236\", \"25187660\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TLR5 is sorted to the plasma membrane rather than endosomes via UNC93B1 was not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The impaired antigen cross-presentation in 3d mice had no mechanistic explanation beyond TLR defects until UNC93B1 was shown to bind STIM1 in the ER, promote STIM1 oligomerization and store-operated Ca²⁺ entry, and thereby enable cross-presentation through a TLR-independent mechanism rescued by constitutively active STIM1.\",\n      \"evidence\": \"Co-immunoprecipitation, calcium imaging, cross-presentation assays, rescue with constitutively active STIM1\",\n      \"pmids\": [\"29158474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The structural basis for UNC93B1-STIM1 interaction was not resolved at this point\", \"Whether STIM1 and TLR binding are mutually exclusive on UNC93B1 was unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Whether UNC93B1 merely traffics TLRs or also stabilizes them was ambiguous until UNC93B1 knockout was shown to cause near-complete loss of TLR3 and TLR7 protein, and an ER-retained UNC93B1 mutant was sufficient to restore TLR stability and largely rescue signaling, demonstrating a chaperone-like stabilization function independent of forward trafficking.\",\n      \"evidence\": \"Western blot of TLR protein in UNC93B1-KO primary cells, ER-retained UNC93B1 mutant rescue\",\n      \"pmids\": [\"29768176\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether UNC93B1 prevents proteasomal vs. lysosomal TLR degradation was not determined\", \"The stoichiometry of stabilization was not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Two companion studies resolved the endosomal fate of TLR7 versus TLR9: TLR9 is released from UNC93B1 in endosomes to enable ligand binding and signaling, whereas TLR7 remains UNC93B1-bound and is negatively regulated by UNC93B1-mediated recruitment of syntenin-1, which sorts TLR7 into multivesicular body intralumenal vesicles; disruption of either mechanism causes autoimmunity.\",\n      \"evidence\": \"UNC93B1 mutagenesis, artificial TLR9-UNC93B1 tethering, syntenin-1 KO mice, exosome isolation, phospho-mutant analysis\",\n      \"pmids\": [\"31546246\", \"31546247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The signal triggering TLR9 release from UNC93B1 was not identified\", \"Whether syntenin-1-dependent sorting applies to TLR8 was not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cryo-EM structures of TLR3–UNC93B1 and TLR7–UNC93B1 complexes revealed that UNC93B1 adopts a major facilitator superfamily fold and contacts TLR transmembrane and juxtamembrane regions via its N-terminal six-helix bundle, providing the first structural framework for understanding TLR-selective binding.\",\n      \"evidence\": \"Cryo-EM structure determination of human and mouse complexes\",\n      \"pmids\": [\"33432245\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No TLR9–UNC93B1 structure was solved\", \"How D34 or glycosylation sites modulate the interface was not structurally resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"UNC93B1 was found to negatively regulate cGAS-STING signaling by binding STING and directing it to autophagy-lysosomal degradation, extending UNC93B1's function beyond TLR regulation to cytosolic DNA sensing pathway control.\",\n      \"evidence\": \"Co-immunoprecipitation, lysosome inhibitor rescue, UNC93B1-KO cell lines and Unc93b1−/− mice with HSV-1 infection\",\n      \"pmids\": [\"33837956\", \"35577759\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The domain of UNC93B1 mediating STING interaction was not mapped\", \"Whether STING degradation requires UNC93B1 trafficking or only ER interaction was not fully resolved\", \"Independent replication beyond two related studies is limited\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The UNC93B1-STIM1 interaction was mechanistically refined: UNC93B1 binds near the STIM1 transmembrane domain and promotes zipping of transmembrane and proximal cytosolic helices within resting STIM1 dimers, priming STIM1 for cortical ER translocation and Orai1 coupling; separately, N-glycosylation at N272 was shown to be specifically required for TLR9 signaling via MyD88 recruitment.\",\n      \"evidence\": \"In vivo cysteine crosslinking, Ca²⁺ imaging, STIM1-Orai1 interaction assays; glycosylation-site mutagenesis with MyD88 co-IP\",\n      \"pmids\": [\"35065962\", \"35874766\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether N272 glycosylation affects TLR9 release from UNC93B1 in endosomes was not tested\", \"Structural view of UNC93B1-STIM1 complex is lacking\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Systematic mutagenesis of all UNC93B1 cytosolic/luminal residues combined with patient genetics identified both negative and positive regulatory regions for TLR3/7/8/9, establishing that specific gain-of-function UNC93B1 variants (T93I, R336C, E92G, R336L, G325C, I317M) cause selective TLR7 or TLR8 hyperactivation leading to SLE and chilblain lupus, mechanistically linking UNC93B1 to monogenic autoimmune disease.\",\n      \"evidence\": \"Saturation alanine-scanning mutagenesis screen, genome-edited knock-in mice, patient family genetics, co-IP of UNC93B1-TLR interactions, TLR-specific agonist assays\",\n      \"pmids\": [\"38780621\", \"38207055\", \"38869500\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mapping of newly identified regulatory surfaces onto the cryo-EM structure is incomplete\", \"Whether therapeutic targeting of UNC93B1-TLR7/8 interface can ameliorate lupus is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the signal that triggers TLR9 dissociation from UNC93B1 in endosomes, the structural basis for TLR9-selective glycosylation-dependent regulation, how UNC93B1 simultaneously coordinates TLR chaperoning with STIM1 priming and STING degradation, and whether UNC93B1's regulatory surfaces can be pharmacologically targeted to treat autoimmune disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No endosomal release signal for TLR9 identified\", \"No structure of UNC93B1-STIM1 or UNC93B1-STING complexes\", \"Therapeutic tractability of UNC93B1 is unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 2, 13]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [7, 10, 14]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 5, 14, 15, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 7, 12, 13, 16]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [7, 14, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 2, 3, 5, 7, 9, 14, 15]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [17, 18]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [7, 9, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [12, 20]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"TLR3\",\n      \"TLR7\",\n      \"TLR9\",\n      \"TLR5\",\n      \"TLR8\",\n      \"STIM1\",\n      \"SDCBP\",\n      \"STING1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}