{"gene":"XBP1","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2001,"finding":"XBP1 mRNA is a substrate of the IRE1 endoribonuclease in mammals; IRE1 performs unconventional cytoplasmic splicing of XBP1 mRNA under ER stress, producing a frameshift that generates a highly active transcription factor (spliced XBP1). Additionally, ATF6 induces transcription of XBP1 mRNA upstream of this splicing event.","method":"Molecular cloning, reporter assays, mRNA splicing analysis, and functional UPR activation assays in mammalian cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — foundational biochemical characterization, replicated across many subsequent studies, multiple orthogonal methods in original paper","pmids":["11779464"],"is_preprint":false},{"year":2003,"finding":"IRE1-mediated splicing of XBP1 is required for plasma cell differentiation and immunoglobulin production; only spliced XBP1 rescues immunoglobulin production in XBP1-/- B cells. IL-4 signaling controls XBP1 transcription during B cell differentiation, while immunoglobulin synthesis drives post-transcriptional XBP1 processing. XBP1 also controls IL-6 production, which is essential for plasma cell survival.","method":"Genetic rescue experiments in XBP1-/- mouse B cells, B cell differentiation assays, cytokine measurements","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic rescue with defined cellular phenotype, replicated mechanistic findings across labs","pmids":["12612580"],"is_preprint":false},{"year":2004,"finding":"Hypoxia induces XBP1 at the transcriptional level and activates splicing of its mRNA, resulting in increased activated XBP1 protein. XBP1-deficient cells show increased apoptosis and decreased clonogenic survival under hypoxia, establishing XBP1 as an essential survival factor for hypoxic stress.","method":"Gene expression analysis, XBP1-deficient cell lines, clonogenic survival assays, apoptosis assays, tumor xenograft models","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with defined cellular and in vivo phenotype, multiple orthogonal methods","pmids":["15342372"],"is_preprint":false},{"year":2004,"finding":"Hepatitis C virus suppresses the IRE1-XBP1 pathway; HCV replicons elevate XBP1 expression but repress its trans-activating activity, preventing XBP1-dependent induction of EDEM (required for misfolded protein degradation). IRE1α-null MEFs with defective IRE1-XBP1 signaling show elevated HCV IRES-mediated translation.","method":"HCV replicon cell lines, XBP1 trans-activation assays, IRE1α-null MEFs, EDEM expression analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (null MEFs) and pharmacological approaches, single lab, two orthogonal methods","pmids":["14960590"],"is_preprint":false},{"year":2007,"finding":"Genome-wide mapping revealed that XBP1 regulates distinct target genes in different cell types through different sequence motifs; it controls a core ER-maintenance gene set in all cell types plus tissue-specific targets. XBP1 was found to directly regulate Mist1, a critical regulator of differentiation, explaining developmental defects in XBP1-null mice.","method":"Genome-wide ChIP, microarray expression profiling in skeletal muscle and secretory cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genome-wide ChIP with functional follow-up, multiple cell types, comprehensive transcriptional regulatory mapping","pmids":["17612490"],"is_preprint":false},{"year":2009,"finding":"The IRE1α-XBP1 pathway is indispensable for adipogenesis; C/EBPβ directly binds the Xbp1 proximal promoter to induce its expression, and XBP1 then binds the Cebpa promoter to activate C/EBPα expression. Only the IRE1α-spliced form of XBP1 (XBP1s) rescues adipogenic defects in XBP1-deficient cells.","method":"XBP1-deficient MEFs, 3T3-L1 knockdown, promoter ChIP assays, adipogenic differentiation assays, XBP1s rescue experiments","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — genetic rescue with promoter binding evidence (ChIP), multiple orthogonal methods, defined mechanistic pathway","pmids":["19490910"],"is_preprint":false},{"year":2009,"finding":"XBP1 is required for de novo fatty acid synthesis in the liver; XBP1 protein expression is induced by high-carbohydrate diet and directly controls induction of genes involved in fatty acid synthesis. Liver-specific XBP1 deletion results in profound hypocholesterolemia and hypotriglyceridemia due to diminished hepatic lipid production.","method":"Inducible liver-specific XBP1 knockout mice, gene expression analysis, lipid measurements","journal":"Annals of the New York Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic deletion with defined metabolic phenotype, referenced as primary findings from original research","pmids":["19751410"],"is_preprint":false},{"year":2012,"finding":"miR-30c-2* (miR-30c-2-3p) is induced by the PERK pathway of the UPR and directly suppresses XBP1 expression, limiting the scale of XBP1-mediated gene expression and influencing cell fate in the UPR. This represents a cross-talk mechanism where PERK signaling dampens IRE1/XBP1 output.","method":"miRNA induction assays, miRNA overexpression/inhibition, XBP1 protein/mRNA measurement, PERK pathway genetic approaches","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional miRNA-target relationship established, single lab, multiple orthogonal methods","pmids":["22431749"],"is_preprint":false},{"year":2014,"finding":"XBP1 promotes TNBC tumorigenicity by assembling a transcriptional complex with HIF1α that recruits RNA polymerase II to regulate HIF1α target gene expression. Genome-wide mapping of the XBP1 transcriptional regulatory network confirmed physical interaction of XBP1 with HIF1α.","method":"Genome-wide ChIP-seq, Co-immunoprecipitation, XBP1 depletion (shRNA), tumor xenograft models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP-seq plus Co-IP establishing physical complex, in vitro and in vivo functional validation","pmids":["24670641"],"is_preprint":false},{"year":2014,"finding":"XBP1 regulates epithelial-to-mesenchymal transition (EMT) in breast cancer by upregulating the key EMT regulator Snail, leading to decreased E-cadherin and increased mesenchymal marker expression. XBP1 knockdown restores E-cadherin expression and suppresses cell invasion.","method":"siRNA knockdown, XBP1 overexpression, E-cadherin/mesenchymal marker expression assays, invasion assays","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function experiments with defined molecular phenotype, single lab","pmids":["25280941"],"is_preprint":false},{"year":2015,"finding":"Constitutive XBP1 activation in tumor-associated dendritic cells, fueled by lipid peroxidation byproducts, induces a triglyceride biosynthetic program leading to abnormal lipid accumulation and inhibition of anti-tumor T cell support. DC-specific XBP1 deletion or nanoparticle-mediated XBP1 silencing in tDCs restored immunostimulatory activity.","method":"DC-specific XBP1 conditional knockout mice, nanoparticle-mediated XBP1 silencing, lipid accumulation assays, T cell activation assays, tumor progression models","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific genetic deletion with defined metabolic and immunological phenotype, multiple orthogonal methods","pmids":["26073941"],"is_preprint":false},{"year":2015,"finding":"XBP1 directly binds the promoter of NFATc1 and induces its transcription to drive osteoclastogenesis. IRE1α activation during osteoclastogenesis is partially dependent on Ca2+ oscillation via ITPR2 and ITPR3 in the ER.","method":"Conditional IRE1α knockout mice, osteoclast differentiation assays, ChIP for XBP1 binding to NFATc1 promoter, pharmacological inhibition of ITPR2/3","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vivo genetic model plus direct promoter binding evidence by ChIP, multiple orthogonal approaches","pmids":["26193638"],"is_preprint":false},{"year":2015,"finding":"SEC63 deficiency selectively activates IRE1α-XBP1 in the ER; SEC63 exists in a complex with PC1 (polycystin-1). XBP1 is required for GPS cleavage and maturation of PC1; enforced XBP1s expression enhances GPS cleavage of PC1 and ameliorates polycystic disease.","method":"Murine genetic models (SEC63/XBP1 double knockout), co-immunoprecipitation, GPS cleavage assays, XBP1s overexpression","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reciprocal Co-IP, genetic epistasis, functional rescue, multiple orthogonal methods","pmids":["25844898"],"is_preprint":false},{"year":2015,"finding":"Hepatic XBP1 controls the adaptive UPR response in the liver; liver-specific Xbp1 knockout mice cannot resolve ER stress, leading to sustained UPR activation, progressive liver injury, apoptosis, and fibrosis in response to pharmacological ER stress.","method":"Liver-specific Xbp1 knockout mice, pharmacological ER stress induction, liver injury/apoptosis/fibrosis assessment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo conditional KO with well-defined phenotypic progression, multiple time points","pmids":["26504083"],"is_preprint":false},{"year":2016,"finding":"In addition to ATF6-mediated transcriptional induction of XBP1 mRNA, IRE1α expression is induced by ATF4 downstream of PERK under ER stress; increased IRE1α expression raises the XBP1 mRNA splicing ratio, amplifying and prolonging IRE1α-XBP1 pathway activation.","method":"IRE1α/ATF4 knockdown, XBP1 splicing ratio measurement, ER stress time-course experiments","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway dissection with genetic knockdown, single lab, multiple methods","pmids":["27052593"],"is_preprint":false},{"year":2017,"finding":"Unspliced XBP1 (XBP1-u) negatively regulates the p53/p21 axis by binding and stabilizing MDM2 protein, inhibiting MDM2 self-ubiquitination and thereby enhancing p53 ubiquitination and degradation. The C-terminal domain of XBP1-u (which differs from XBP1-s due to a codon shift) mediates MDM2 binding.","method":"shRNA library screen, Co-immunoprecipitation, ubiquitination assays, domain mapping, cell cycle analysis","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — Co-IP with domain mapping, biochemical ubiquitination assays, functional cell cycle phenotype, multiple orthogonal methods","pmids":["29057323"],"is_preprint":false},{"year":2017,"finding":"XBP1s directly binds the Cyclin D1 promoter to activate its expression, mediating IRE1α-dependent cell proliferation in colorectal cancer cells.","method":"ChIP, luciferase reporter assays, siRNA knockdown of IRE1α/XBP1, proliferation assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding by ChIP with functional proliferation readout, single lab","pmids":["26742428"],"is_preprint":false},{"year":2017,"finding":"XBP1s binds the IL-6 promoter directly and activates its expression in melanoma cells; secreted IL-6 then activates JAK/STAT3 signaling in an autocrine/paracrine manner to promote melanoma cell proliferation. Inhibition of IRE1α RNase activity abolishes this effect.","method":"ChIP experiments, luciferase reporter assays, XBP1s ectopic expression, IRE1α inhibition, western blotting for STAT3","journal":"Journal of translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding by ChIP, pharmacological and genetic validation, single lab","pmids":["28222747"],"is_preprint":false},{"year":2018,"finding":"IRE1α-XBP1 activation in T cells suppresses mitochondrial activity and IFNγ production in ovarian cancer. Mechanistically, XBP1 induction regulates the abundance of glutamine carriers, limiting glutamine influx needed for mitochondrial respiration under glucose-deprived conditions. XBP1-deficient T cells show improved effector capacity.","method":"T cell-specific XBP1 deletion, metabolic assays, glutamine transporter expression analysis, mitochondrial respiration measurement, mouse tumor models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional T cell-specific KO, metabolomics, mechanistic pathway validation, in vivo tumor model","pmids":["30305738"],"is_preprint":false},{"year":2018,"finding":"MYC directly controls IRE1 transcription by binding to its promoter and enhancer. Furthermore, MYC forms a transcriptional complex with XBP1 and enhances XBP1 transcriptional activity. XBP1 is a synthetic lethal partner of MYC in breast cancer.","method":"ChIP for MYC binding to IRE1 promoter/enhancer, Co-immunoprecipitation of MYC-XBP1 complex, XBP1 silencing in MYC-hyperactivated cells, PDX mouse models","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP plus Co-IP establishing physical complex, in vivo PDX validation, multiple orthogonal methods","pmids":["29480818"],"is_preprint":false},{"year":2018,"finding":"IRE1α-XBP1 constitutive activation in pancreatic β cells regulates oxidative folding of proinsulin by controlling expression of five protein disulfide isomerases (PDI, PDIR, P5, ERp44, ERp46). Reconstitution of the IRE1α-XBP1 pathway in Ire1α-deleted insulinoma cells restored proinsulin content, insulin secretion, and PDI expression.","method":"β cell-specific Ire1α conditional knockout mice, Cre-loxP cell lines, insulin secretion assays, PDI expression analysis, IRE1α-XBP1 reconstitution","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — cell-type-specific KO plus pathway reconstitution, multiple molecular targets identified, in vivo and in vitro evidence","pmids":["29507125"],"is_preprint":false},{"year":2018,"finding":"XBP1s directly transactivates the human PTGS2 (COX-2) and PTGES genes to enable optimal prostaglandin E2 production in myeloid cells. IRE1α-XBP1-deficient myeloid cells show compromised induction of Cox-2 and mPGES-1 under ER stress or pattern recognition receptor stimulation.","method":"IRE1α-deficient myeloid cells, XBP1-deficient myeloid cells, ChIP/transactivation assays for PTGS2/PTGES promoters, PGE2 measurements, pain behavior models","journal":"Science","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct promoter transactivation evidence, genetic models, in vivo pain behavior validation","pmids":["31320508"],"is_preprint":false},{"year":2018,"finding":"2',3'-cyclic nucleotide phosphodiesterase (CNP) suppresses RtcB-mediated XBP1 splicing by hydrolyzing 2',3'-cyclic phosphate on cleaved XBP1 exon termini; conversely, RNA 3'-terminal cyclase (RtcA) facilitates XBP1 splicing by converting 2'-phosphate back to 2',3'-cyclic phosphate for RtcB ligation.","method":"In vitro splicing assays, mammalian cell lines, CNP/RtcA overexpression/knockdown, XBP1 splicing measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of splicing mechanism, genetic and biochemical validation, single lab","pmids":["30355738"],"is_preprint":false},{"year":2019,"finding":"Muscle-specific deletion of XBP1 ameliorates cancer cachexia-induced skeletal muscle wasting; overexpression of active XBP1 causes myotube atrophy. XBP1 acts downstream of TLR/MyD88 signaling to mediate muscle wasting, identifying a TLR/MyD88/XBP1 axis in cancer cachexia.","method":"Muscle-specific XBP1 conditional knockout mice, Lewis lung carcinoma tumor-bearing model, myotube atrophy assays, XBP1 overexpression","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with in vivo cancer model, epistasis established with TLR/MyD88","pmids":["31138662"],"is_preprint":false},{"year":2019,"finding":"Constitutive XBP-1s expression in C. elegans increases lysosomal lipase activity and upregulates transcription of Δ9 desaturase FAT-6, increasing oleic acid levels; FAT-6 is required for the full lifespan extension induced by XBP-1s.","method":"C. elegans transgenic expression, metabolomics, fat-6 genetic epistasis, lysosomal lipase activity assays","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in C. elegans model, metabolomic profiling, single lab","pmids":["31315038"],"is_preprint":false},{"year":2020,"finding":"Insulin-activated kinase AKT directly phosphorylates IRE1 at S724, which mediates XBP1u mRNA splicing to generate XBP1s in mouse liver in the fed state, stimulating lipogenic gene expression. In the fasted state, XBP1u (not XBP1s) increases cAMP-stimulated gluconeogenic gene expression (G6pc, Pck1) and glucose production.","method":"AKT phosphorylation site mapping, in vitro kinase assays, hepatocyte-specific XBP1 depletion with re-expression, gluconeogenesis/lipogenesis assays, primary hepatocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct phosphorylation mapping, biochemical and genetic approaches, isoform-specific functional validation","pmids":["35863429"],"is_preprint":false},{"year":2020,"finding":"Hepatocyte-specific XBP1 deletion sensitizes mice to liver injury through hyperactivation of IRE1α (evidenced by XBP1 mRNA splicing, JNK activation, and RIDD). Concomitant deletion of both XBP1 and IRE1α protected mice from fructose-mediated liver injury, demonstrating that deleterious effects of XBP1 deletion are primarily due to IRE1α hyperactivation.","method":"Hepatocyte-specific single and double (XBP1/IRE1α) conditional knockout mice, dietary challenge, liver injury markers, IRE1α activity assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Strong — double conditional KO genetic epistasis with clear mechanistic interpretation, in vivo model","pmids":["33219328"],"is_preprint":false},{"year":2020,"finding":"Liver-specific ablation of XBP1 disrupts the hepatic 12-hour clock and promotes NAFLD; XBP1s directly binds to the hepatic 12-hour cistrome. XBP1 ablation reduces membrane fluidity and impairs lipid homeostasis via fatty acid monounsaturation and phospholipid remodeling pathways.","method":"Liver-specific XBP1 knockout mice, ChIP-seq of 12-hour cistrome, genome-wide transcriptional profiling, lipid/membrane fluidity assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP-seq cistrome mapping plus in vivo conditional KO with comprehensive metabolic phenotyping","pmids":["33277471"],"is_preprint":false},{"year":2021,"finding":"Unspliced XBP1 (XBP1u) directly binds β-catenin via amino acids 205–230 in its C-terminal degradation domain, promoting β-catenin ubiquitin-proteasomal degradation independently of the GSK-3β destruction complex, thereby inhibiting β-catenin/TCF-mediated transcription of Runx2 and Msx2 and suppressing vascular calcification.","method":"Interactome analysis, Co-immunoprecipitation, ubiquitination assays, domain mapping, smooth muscle cell-specific XBP1 knockout mice, vascular calcification models","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — Co-IP with domain mapping, ubiquitination assays, in vivo conditional KO, β-catenin rescue experiment","pmids":["34870453"],"is_preprint":false},{"year":2021,"finding":"XBP1s directly binds the TAp73 promoter and suppresses its transcriptional activity, reducing p53-family tumor suppression and promoting colorectal cancer cell proliferation. TAp73 overexpression cancelled the pro-proliferative effect of XBP1s.","method":"ChIP for XBP1s binding to TAp73 promoter, luciferase reporter assays, XBP1s overexpression, TAp73 rescue experiments","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding by ChIP with functional rescue validation, single lab","pmids":["30473215"],"is_preprint":false},{"year":2021,"finding":"XBP1s genome-wide mRNA profiling identified XBP1 as a transcriptional repressor of PUMA (proapoptotic gene) and IRE1 mRNA expression during UPR, providing a negative feedback mechanism. Elevated XBP1 expression during ER stress had a prosurvival effect with reduced PUMA protein.","method":"XBP1s-inducible human cell line, siRNA silencing, next-generation RNA sequencing, bioinformatic analysis of XBP1-binding motifs","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide transcriptome profiling with inducible system and XBP1 silencing, single lab","pmids":["34636989"],"is_preprint":false},{"year":2022,"finding":"Unspliced XBP1 (XBP1-u) colocalizes with SREBP2 and inhibits its ubiquitination/proteasomal degradation, stabilizing SREBP2 and activating HMGCR transcription, thereby promoting cholesterol biosynthesis and tumorigenesis in hepatocellular carcinoma.","method":"Co-immunoprecipitation, ubiquitination assays, SREBP2 stability assays, HMGCR expression analysis, tumor growth experiments","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with biochemical ubiquitination assays, single lab, multiple methods","pmids":["35933495"],"is_preprint":false},{"year":2022,"finding":"Spliced XBP1 binds directly to the BNIP3 promoter and inhibits BNIP3 transcription in macrophages, thereby suppressing BNIP3-mediated mitophagy. Reduced mitophagy in Xbp1-expressing macrophages promotes cytosolic mtDNA leakage, activating cGAS/STING/NLRP3 signaling to drive liver fibrosis.","method":"Chromatin immunoprecipitation (ChIP) for XBP1 binding to Bnip3 promoter, RNA sequencing, myeloid-specific Xbp1 knockout mice, BNIP3 knockdown, liver fibrosis models","journal":"JHEP reports","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — ChIP demonstrating direct promoter binding, genetic epistasis with conditional KO, RNA-seq pathway analysis","pmids":["36185574"],"is_preprint":false},{"year":2022,"finding":"Cancer cell XBP1 favors synthesis and secretion of cholesterol in small extracellular vesicles; cholesterol is internalized by MDSCs via macropinocytosis, activating MDSCs and causing immunosuppression. XBP1 genetic or pharmacological depletion reduces MDSC abundance and triggers anti-tumor responses.","method":"XBP1 genetic depletion/pharmacological inhibition, extracellular vesicle isolation, cholesterol quantification, MDSC activation assays, tumor models","journal":"Cell metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological XBP1 depletion with defined mechanistic pathway, single lab","pmids":["36351432"],"is_preprint":false},{"year":2022,"finding":"Spliced XBP1 enhances the activity of the NLRP3 promoter (demonstrated by luciferase reporter assay), linking XBP1-mediated ER-mitochondria crosstalk to caspase-1-dependent inflammation in renal ischemia/reperfusion injury.","method":"Luciferase reporter assay for NLRP3 promoter, XBP1 interference in renal tubular cells, in vivo renal IRI model","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter activity assay plus in vivo model, single lab","pmids":["36801911"],"is_preprint":false},{"year":2022,"finding":"In Drosophila, IRE1-mediated phosphorylation of the RNA-binding protein Pumilio enables Pumilio to protect spliced Xbp1 mRNA from regulated Ire1-dependent decay (RIDD). hIRE1 can directly phosphorylate Pumilio, and phosphorylated Pumilio binds and stabilizes Xbp1spliced mRNA.","method":"Drosophila genetics, in vitro IRE1 kinase assays, mRNA stability assays, Pumilio binding site identification in Xbp1 3'UTR","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro kinase assay (direct phosphorylation), Drosophila genetic validation, mRNA stability assays","pmids":["35332141"],"is_preprint":false},{"year":2022,"finding":"ATF6α is required for full activation of XBP1 target genes in pancreatic islet cells; acute ATF6α knockdown reduces induction of XBP1 targets without altering XBP1 mRNA splicing dynamics. XBP1 is not required for activation of ATF6α targets, establishing ATF6α as upstream of XBP1 target expression but not of XBP1 splicing.","method":"Acute ATF6α conditional knockdown in primary mouse islets (adenovirus-Cre), timed ER stressor exposures, transcriptional target gene measurement","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic dissection of pathway hierarchy in primary cells, multiple ER stressors tested, single lab","pmids":["32788214"],"is_preprint":false},{"year":2023,"finding":"XBP1 overexpression increases Hrd1 expression; Hrd1 then interacts with and ubiquitinates Nrf2 under high-glucose conditions (confirmed by Co-IP and ubiquitylation assays), promoting ferroptosis via the XBP1-Hrd1-Nrf2 pathway in diabetic nephropathy.","method":"Co-immunoprecipitation, ubiquitylation assays, XBP1 overexpression, ferroptosis markers, high-glucose cell model","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and ubiquitylation biochemistry establishing pathway, single lab","pmids":["37224754"],"is_preprint":false},{"year":2023,"finding":"XBP1 inhibits SLC38A2 (glutamine transporter) expression by directly binding to its promoter; reduced SLC38A2 decreases glutamine uptake and causes immune dysfunction in cytotoxic T cells in multiple myeloma.","method":"Single-cell RNA sequencing, in vitro XBP1 overexpression/inhibition, ChIP for XBP1 binding to SLC38A2 promoter, glutamine uptake assays, T cell functional assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding by ChIP with functional metabolic and immune phenotype, single lab","pmids":["37054944"],"is_preprint":false},{"year":2023,"finding":"XBP1 in dendritic cells directly promotes TIM4 mRNA and protein expression in response to IL-2. RhoA facilitates binding between XBP1 and GATA3 in CD4+ T cells; XBP1 induces GATA3 phosphorylation to promote Il4 gene transcription and Th2 polarization.","method":"Xbp1-deficient CD4+ T cells and DCs, XBP1-TIM4 promoter binding assays, Co-IP for XBP1-GATA3 interaction, GATA3 phosphorylation assays, in vivo airway allergy models","journal":"Science signaling / Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic conditional KO, Co-IP for protein interaction, functional immune phenotype, single lab","pmids":["37368951","35910793"],"is_preprint":false},{"year":2024,"finding":"XBP1 upregulation promotes ferritinophagy via NCOA4; SeNPs protect against ferroptosis by upregulating XBP1, which in turn suppresses NCOA4-mediated ferritinophagy. XBP1 downregulation promoted ferritinophagy and partially counteracted protective effects on ferroptosis.","method":"In vitro H/R model, in vivo I/R-AKI mouse model, XBP1 knockdown, ferritinophagy and ferroptosis markers, lysosomal Fe2+ measurement","journal":"Cell communication and signaling","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single knockdown approach, indirect pathway inference without direct XBP1-NCOA4 binding evidence","pmids":["39061070"],"is_preprint":false}],"current_model":"XBP1 is a bZIP transcription factor whose activity is controlled by IRE1-mediated unconventional cytoplasmic splicing of its mRNA under ER stress (induced transcriptionally by ATF6), generating a frameshift that produces the potent transcriptional activator XBP1s; the unspliced form (XBP1u) has distinct functions including stabilizing MDM2 to degrade p53 and stabilizing SREBP2 to promote cholesterol biosynthesis, while XBP1s drives a wide transcriptional program encompassing ER expansion, lipid/glucose metabolism (directly transactivating lipogenic and gluconeogenic gene promoters), cell differentiation (plasma cell, adipocyte, osteoclast), and immune regulation (controlling prostaglandin biosynthesis via COX-2/mPGES-1 transactivation, shaping DC and T cell function), with the splicing efficiency itself fine-tuned by CNP/RtcA modulation of RNA termini for RtcB ligation and by IRE1-phosphorylated Pumilio protecting XBP1s mRNA from RIDD."},"narrative":{"mechanistic_narrative":"XBP1 is a bZIP transcription factor central to the IRE1α arm of the unfolded protein response, whose activity is gated by an unconventional cytoplasmic splicing event: under ER stress IRE1 cleaves XBP1 mRNA to remove a short intron, producing a frameshift that converts the inert unspliced product into the potent transcriptional activator XBP1s, with ATF6 supplying the upstream transcriptional induction of XBP1 mRNA [PMID:11779464, PMID:32788214]. This pathway is amplified and tuned at multiple levels—ATF4 downstream of PERK raises IRE1α to increase the splicing ratio [PMID:27052593], PERK-induced miR-30c-2* dampens XBP1 output [PMID:22431749], and the splicing reaction itself is set by CNP/RtcA remodeling of cleaved exon termini for RtcB ligation [PMID:30355738] and by IRE1-phosphorylated Pumilio that shields spliced XBP1 mRNA from regulated IRE1-dependent decay [PMID:35332141]. XBP1s executes a broad, cell-type-specific transcriptional program: it maintains a core ER-folding/secretory gene set in all cells while directing tissue-specific targets, including direct control of the differentiation regulator Mist1 [PMID:17612490], and it is required for plasma cell differentiation and immunoglobulin/IL-6 production [PMID:12612580], adipogenesis via a C/EBPβ→XBP1→C/EBPα circuit [PMID:19490910], and osteoclastogenesis through direct transactivation of NFATc1 [PMID:26193638]. In metabolism, XBP1s drives hepatic de novo lipogenesis and lipid homeostasis, governs a hepatic 12-hour clock cistrome, and controls oxidative proinsulin folding by inducing protein disulfide isomerases [PMID:19751410, PMID:33277471, PMID:29507125], while the unspliced isoform XBP1u carries out distinct, splicing-independent functions—stabilizing MDM2 to degrade p53 [PMID:29057323], stabilizing SREBP2 to drive cholesterol synthesis [PMID:35933495], and targeting β-catenin for degradation [PMID:34870453]. XBP1 also acts as a survival and pro-tumorigenic factor: it supports survival under hypoxia [PMID:15342372], forms transcriptional complexes with HIF1α and MYC to potentiate their programs [PMID:24670641, PMID:29480818], and reshapes the tumor microenvironment by reprogramming dendritic-cell lipid metabolism and constraining T-cell effector function through glutamine-transporter regulation [PMID:26073941, PMID:30305738]. In innate immunity it directly transactivates PTGS2/PTGES to enable prostaglandin E2 production [PMID:31320508].","teleology":[{"year":2001,"claim":"Established the defining regulatory logic of XBP1: that its mRNA is the substrate of IRE1 cytoplasmic splicing, converting it by frameshift into an active transcription factor, with ATF6 inducing the message upstream.","evidence":"Molecular cloning, reporter and splicing assays in mammalian cells","pmids":["11779464"],"confidence":"High","gaps":["Did not enumerate the downstream transcriptional program","Splicing machinery components (ligase, terminal processing) not resolved"]},{"year":2003,"claim":"Showed the IRE1-XBP1 splicing event is physiologically essential for a defined differentiation program, linking the UPR to plasma cell development and antibody secretion.","evidence":"Genetic rescue in XBP1-/- mouse B cells with differentiation and cytokine readouts","pmids":["12612580"],"confidence":"High","gaps":["Direct target genes mediating the differentiation block not mapped here","How IL-4 controls XBP1 transcription mechanistically unresolved"]},{"year":2004,"claim":"Extended XBP1 beyond classical ER stress to hypoxia, defining it as a survival factor whose loss increases apoptosis—relevant to tumor biology.","evidence":"XBP1-deficient cells, clonogenic/apoptosis assays and xenografts","pmids":["15342372"],"confidence":"High","gaps":["Survival-mediating target genes not identified","Spliced vs unspliced contribution under hypoxia not dissected"]},{"year":2007,"claim":"Resolved how one factor produces diverse outputs by mapping cell-type-specific cistromes, distinguishing a universal ER-maintenance set from tissue-specific targets such as Mist1.","evidence":"Genome-wide ChIP and expression profiling in muscle and secretory cells","pmids":["17612490"],"confidence":"High","gaps":["Determinants of cell-type-specific motif selection not defined","Cofactors directing context-specific binding unknown at this stage"]},{"year":2009,"claim":"Defined XBP1 as a required node in metabolic differentiation and lipid synthesis, establishing direct promoter circuits in adipogenesis and hepatic lipogenesis.","evidence":"XBP1-deficient MEFs/3T3-L1, promoter ChIP, liver-specific knockout with lipid phenotyping","pmids":["19490910","19751410"],"confidence":"High","gaps":["Whether lipogenic control is purely XBP1s-dependent left open here","Relationship between metabolic and ER-folding programs unresolved"]},{"year":2012,"claim":"Revealed inter-arm UPR cross-talk in which PERK-induced miR-30c-2* caps XBP1 output, showing XBP1 levels are set not just by splicing but by miRNA control.","evidence":"miRNA gain/loss-of-function with XBP1 measurement and PERK genetics","pmids":["22431749"],"confidence":"Medium","gaps":["Single-lab finding","Quantitative contribution relative to splicing not established"]},{"year":2014,"claim":"Identified XBP1 as a partner that physically assembles with HIF1α to potentiate hypoxic transcription and drive TNBC tumorigenicity, beyond its canonical UPR role.","evidence":"ChIP-seq, Co-IP, shRNA depletion and xenografts","pmids":["24670641"],"confidence":"High","gaps":["Interaction interface not mapped","Whether complex requires XBP1s splicing not formally isolated"]},{"year":2014,"claim":"Linked XBP1 to invasion programs by showing it upregulates Snail to drive EMT in breast cancer.","evidence":"siRNA/overexpression with marker and invasion assays","pmids":["25280941"],"confidence":"Medium","gaps":["Direct vs indirect regulation of Snail not resolved","Single lab"]},{"year":2015,"claim":"Broadened the cell-fate program of XBP1s to osteoclast differentiation via direct NFATc1 transactivation, with IRE1 activation tied to ER Ca2+ oscillation.","evidence":"Conditional IRE1α KO mice, osteoclast assays, NFATc1-promoter ChIP","pmids":["26193638"],"confidence":"High","gaps":["How Ca2+ oscillation feeds IRE1 mechanistically incomplete"]},{"year":2015,"claim":"Connected selective IRE1α-XBP1 activation to secretory protein maturation and disease, showing XBP1 is required for polycystin-1 GPS cleavage and ameliorates polycystic disease.","evidence":"SEC63/XBP1 double-KO mice, reciprocal Co-IP, GPS cleavage and XBP1s overexpression","pmids":["25844898"],"confidence":"High","gaps":["Direct targets mediating PC1 maturation not fully enumerated"]},{"year":2015,"claim":"Established XBP1 as the adaptive resolver of hepatic ER stress, with its loss causing maladaptive UPR, injury and fibrosis.","evidence":"Liver-specific XBP1 KO with pharmacological ER stress","pmids":["26504083"],"confidence":"High","gaps":["Did not separate loss-of-XBP1 effects from secondary IRE1α hyperactivation (resolved later)"]},{"year":2015,"claim":"Uncovered a pathogenic role in tumor immunity, showing constitutive XBP1 in tumor dendritic cells drives a lipid program that disables anti-tumor T-cell support.","evidence":"DC-specific XBP1 KO, nanoparticle silencing, lipid and T-cell assays, tumor models","pmids":["26073941"],"confidence":"High","gaps":["Direct lipogenic target genes in tDCs not fully mapped"]},{"year":2016,"claim":"Showed feed-forward amplification of the pathway, with PERK/ATF4-driven IRE1α induction raising the XBP1 splicing ratio to prolong signaling.","evidence":"IRE1α/ATF4 knockdown with splicing-ratio time courses","pmids":["27052593"],"confidence":"Medium","gaps":["Single lab","Quantitative impact on target output not measured"]},{"year":2017,"claim":"Distinguished a splicing-independent function: unspliced XBP1u stabilizes MDM2 via its unique C-terminus to promote p53 degradation, redefining the 'inactive' isoform as a functional regulator.","evidence":"shRNA screen, Co-IP, domain mapping, ubiquitination and cell-cycle assays","pmids":["29057323"],"confidence":"High","gaps":["Cellular contexts where XBP1u-MDM2 axis dominates not delineated"]},{"year":2017,"claim":"Added direct proliferation- and inflammation-promoting target circuits, showing XBP1s transactivates Cyclin D1 and IL-6 in cancer.","evidence":"ChIP, luciferase, siRNA/ectopic expression and proliferation/STAT3 readouts","pmids":["26742428","28222747"],"confidence":"Medium","gaps":["Single-lab findings per target","Cell-type generality not tested"]},{"year":2018,"claim":"Defined XBP1 as a metabolic brake on T-cell function in cancer, limiting glutamine influx and mitochondrial respiration to suppress IFNγ.","evidence":"T-cell-specific XBP1 KO, metabolomics, transporter and respiration assays, tumor models","pmids":["30305738"],"confidence":"High","gaps":["Direct transporter-gene targets not all confirmed in this study"]},{"year":2018,"claim":"Showed reciprocal transcription-factor coupling, with MYC controlling IRE1 and forming a complex with XBP1, establishing XBP1 as a synthetic-lethal MYC partner.","evidence":"ChIP, Co-IP, XBP1 silencing in MYC-driven cells, PDX models","pmids":["29480818"],"confidence":"High","gaps":["Structural basis of MYC-XBP1 complex unknown"]},{"year":2018,"claim":"Linked constitutive IRE1α-XBP1 to secretory cell physiology by showing it controls proinsulin oxidative folding via induction of multiple PDIs.","evidence":"β-cell-specific Ire1α KO and pathway reconstitution with insulin/PDI readouts","pmids":["29507125"],"confidence":"High","gaps":["Direct XBP1 binding at all five PDI promoters not individually demonstrated"]},{"year":2018,"claim":"Connected XBP1 to inflammatory lipid mediator production, showing XBP1s directly transactivates PTGS2/PTGES for prostaglandin E2 synthesis in myeloid cells.","evidence":"IRE1α/XBP1-deficient myeloid cells, promoter transactivation, PGE2 and pain models","pmids":["31320508"],"confidence":"High","gaps":["Stimulus-specific control of the COX-2/mPGES-1 module not fully parsed"]},{"year":2018,"claim":"Mechanistically defined splicing fidelity, showing CNP and RtcA antagonistically set XBP1 exon-terminus chemistry for RtcB ligation.","evidence":"In vitro splicing assays with CNP/RtcA manipulation","pmids":["30355738"],"confidence":"High","gaps":["Physiological conditions modulating CNP/RtcA balance not defined"]},{"year":2019,"claim":"Extended XBP1 to muscle pathology, identifying a TLR/MyD88/XBP1 axis driving cancer cachexia-associated muscle wasting.","evidence":"Muscle-specific XBP1 KO, tumor-bearing model, myotube atrophy and overexpression","pmids":["31138662"],"confidence":"High","gaps":["Atrophy-effector target genes downstream of XBP1 not mapped"]},{"year":2019,"claim":"Showed evolutionary conservation of XBP1s as a lipid-metabolism and longevity effector, acting via lysosomal lipase and FAT-6 desaturase in C. elegans.","evidence":"C. elegans transgenics, metabolomics and fat-6 epistasis","pmids":["31315038"],"confidence":"Medium","gaps":["Direct transcriptional targets in the worm not mapped","Single-organism inference"]},{"year":2020,"claim":"Integrated XBP1 isoforms into nutrient signaling, showing AKT phosphorylates IRE1 to generate XBP1s for fed-state lipogenesis while XBP1u drives fasting gluconeogenesis.","evidence":"AKT/IRE1 phosphosite mapping, kinase assays, hepatocyte depletion/re-expression with isoform-specific readouts","pmids":["35863429"],"confidence":"High","gaps":["Mechanism by which XBP1u potentiates cAMP-driven gluconeogenic genes unresolved"]},{"year":2020,"claim":"Resolved a long-standing ambiguity by genetic epistasis: XBP1-loss liver injury arises mainly from secondary IRE1α hyperactivation rather than loss of XBP1 transcriptional output.","evidence":"Hepatocyte XBP1/IRE1α single and double conditional KO with dietary challenge","pmids":["33219328"],"confidence":"High","gaps":["RIDD substrate spectrum driving injury not enumerated"]},{"year":2020,"claim":"Linked XBP1 to circadian and membrane lipid homeostasis, defining a hepatic 12-hour cistrome whose loss promotes NAFLD.","evidence":"Liver-specific KO, 12-hour cistrome ChIP-seq, lipid/membrane fluidity assays","pmids":["33277471"],"confidence":"High","gaps":["Relationship between 12-hour clock and canonical UPR targets unresolved"]},{"year":2021,"claim":"Expanded XBP1u's degradation-targeting role beyond MDM2, showing it directly binds β-catenin for proteasomal degradation independent of GSK-3β, suppressing vascular calcification.","evidence":"Interactome, Co-IP, domain mapping, ubiquitination, SMC-specific KO and rescue","pmids":["34870453"],"confidence":"High","gaps":["E3 ligase used by XBP1u for β-catenin not identified"]},{"year":2021,"claim":"Showed XBP1s can act as a transcriptional repressor of tumor-suppressive and pro-apoptotic programs, suppressing TAp73 and PUMA to favor proliferation/survival.","evidence":"ChIP/luciferase with rescue (TAp73); inducible XBP1s RNA-seq with motif analysis (PUMA/IRE1)","pmids":["30473215","34636989"],"confidence":"Medium","gaps":["Repressive cofactors enabling XBP1s repression not defined","Single-lab findings"]},{"year":2022,"claim":"Defined XBP1u as a driver of cholesterol biosynthesis by stabilizing SREBP2 to induce HMGCR, promoting hepatocellular carcinoma.","evidence":"Co-IP, ubiquitination/stability assays, HMGCR analysis and tumor growth","pmids":["35933495"],"confidence":"Medium","gaps":["Single lab","Direct vs indirect SREBP2 stabilization mechanism partial"]},{"year":2022,"claim":"Connected XBP1s to innate immune signaling via mitophagy control, showing it represses BNIP3 to enhance cGAS/STING/NLRP3 activation and liver fibrosis.","evidence":"BNIP3-promoter ChIP, RNA-seq, myeloid XBP1 KO and BNIP3 knockdown in fibrosis models","pmids":["36185574"],"confidence":"High","gaps":["Generality across macrophage subsets not tested"]},{"year":2022,"claim":"Added a paracrine immunosuppressive mechanism whereby cancer-cell XBP1 promotes cholesterol-laden extracellular vesicles that activate MDSCs.","evidence":"XBP1 depletion/inhibition, EV cholesterol quantification, MDSC and tumor assays","pmids":["36351432"],"confidence":"Medium","gaps":["Which XBP1 isoform drives EV cholesterol secretion not specified","Single lab"]},{"year":2022,"claim":"Linked XBP1s to inflammasome priming by enhancing NLRP3 promoter activity in renal ischemia/reperfusion injury.","evidence":"NLRP3 promoter luciferase, XBP1 interference and in vivo renal IRI","pmids":["36801911"],"confidence":"Medium","gaps":["Direct XBP1 occupancy at NLRP3 promoter not shown by ChIP","Single lab"]},{"year":2022,"claim":"Demonstrated metazoan conservation of post-transcriptional protection of spliced XBP1, with IRE1-phosphorylated Pumilio shielding it from RIDD.","evidence":"Drosophila genetics, in vitro IRE1 kinase assays, mRNA stability and 3'UTR binding","pmids":["35332141"],"confidence":"High","gaps":["Whether the mammalian Pumilio orthologs perform the same role in vivo not established"]},{"year":2022,"claim":"Clarified pathway hierarchy, showing ATF6α is required for full XBP1 target induction but not for XBP1 splicing, and is itself independent of XBP1.","evidence":"Acute ATF6α knockdown in primary islets with timed ER stressors and target measurement","pmids":["32788214"],"confidence":"Medium","gaps":["Molecular basis of ATF6α/XBP1 cooperativity at promoters not defined","Single lab"]},{"year":2023,"claim":"Extended XBP1 control to redox/cell-death pathways, defining an XBP1-Hrd1-Nrf2 axis promoting ferroptosis under high glucose.","evidence":"Co-IP, ubiquitylation assays and ferroptosis markers in high-glucose models","pmids":["37224754"],"confidence":"Medium","gaps":["Whether Hrd1 is a direct XBP1 transcriptional target not shown by ChIP here","Single lab"]},{"year":2023,"claim":"Showed XBP1 represses a glutamine transporter (SLC38A2) to impair cytotoxic T cells in myeloma, paralleling its glutamine-limiting role in ovarian-cancer T cells.","evidence":"scRNA-seq, XBP1 gain/loss, SLC38A2-promoter ChIP and glutamine/T-cell assays","pmids":["37054944"],"confidence":"Medium","gaps":["Single lab","Direct vs indirect repression mechanism not fully resolved"]},{"year":2023,"claim":"Defined XBP1's role in shaping adaptive immune polarization, promoting TIM4 in DCs and partnering with GATA3 (via RhoA) to drive Th2 IL-4 transcription.","evidence":"Xbp1-deficient T cells/DCs, promoter binding, XBP1-GATA3 Co-IP, GATA3 phosphorylation and airway allergy models","pmids":["37368951","35910793"],"confidence":"Medium","gaps":["Mechanism of XBP1-induced GATA3 phosphorylation unresolved","Single lab"]},{"year":2024,"claim":"Proposed XBP1 as a regulator of ferritinophagy via NCOA4, protecting against ferroptosis in ischemic kidney injury.","evidence":"XBP1 knockdown in H/R and I/R-AKI models with ferritinophagy/ferroptosis markers","pmids":["39061070"],"confidence":"Low","gaps":["No direct XBP1-NCOA4 binding evidence; pathway inferred indirectly","Single knockdown approach, single lab"]},{"year":null,"claim":"How the choice between XBP1s and XBP1u functions—and which isoform dominates in a given tissue or disease—is integrated with upstream kinase, splicing-fidelity, and cofactor inputs remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Structural basis of XBP1 partnerships with HIF1α, MYC and GATA3 unknown","E3 ligases and degradation machinery used by XBP1u not identified","Quantitative rules governing cell-type-specific cistromes undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,4,5,11,21,27]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[4,11,21,27,32,38]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[15,28,31]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4,8,11,27]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[15,28,31]}],"pathway":[{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[0,13,20]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[4,8,11,21,27]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,20,22]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[6,18,27,31]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[1,10,18,21,39]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,5,11]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,22,35]}],"complexes":[],"partners":["IRE1","HIF1A","MYC","MDM2","SREBP2","CTNNB1","GATA3","PUM"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P17861","full_name":"X-box-binding protein 1","aliases":["Tax-responsive element-binding protein 5","TREB-5"],"length_aa":261,"mass_kda":28.7,"function":"Functions as a transcription factor during endoplasmic reticulum (ER) stress by regulating the unfolded protein response (UPR). Required for cardiac myogenesis and hepatogenesis during embryonic development, and the development of secretory tissues such as exocrine pancreas and salivary gland (By similarity). Involved in terminal differentiation of B lymphocytes to plasma cells and production of immunoglobulins (PubMed:11460154). Modulates the cellular response to ER stress in a PIK3R-dependent manner (PubMed:20348923). Binds to the cis-acting X box present in the promoter regions of major histocompatibility complex class II genes (PubMed:8349596). Involved in VEGF-induced endothelial cell (EC) proliferation and retinal blood vessel formation during embryonic development but also for angiogenesis in adult tissues under ischemic conditions. Also functions as a major regulator of the UPR in obesity-induced insulin resistance and type 2 diabetes for the management of obesity and diabetes prevention (By similarity) Plays a role in the unconventional cytoplasmic splicing processing of its own mRNA triggered by the endoplasmic reticulum (ER) transmembrane endoribonuclease ERN1: upon ER stress, the emerging XBP1 polypeptide chain, as part of a mRNA-ribosome-nascent chain (R-RNC) complex, cotranslationally recruits its own unprocessed mRNA through transient docking to the ER membrane and translational pausing, therefore facilitating efficient IRE1-mediated XBP1 mRNA isoform 2 production (PubMed:19394296, PubMed:21233347). In endothelial cells (EC), associated with KDR, promotes IRE1-mediated XBP1 mRNA isoform 2 productions in a vascular endothelial growth factor (VEGF)-dependent manner, leading to EC proliferation and angiogenesis (PubMed:23529610). Functions as a negative feed-back regulator of the potent transcription factor XBP1 isoform 2 protein levels through proteasome-mediated degradation, thus preventing the constitutive activation of the ER stress response signaling pathway (PubMed:16461360, PubMed:25239945). Inhibits the transactivation activity of XBP1 isoform 2 in myeloma cells (By similarity). Acts as a weak transcriptional factor (PubMed:8657566). Together with HDAC3, contributes to the activation of NFE2L2-mediated HMOX1 transcription factor gene expression in a PI(3)K/mTORC2/Akt-dependent signaling pathway leading to EC survival under disturbed flow/oxidative stress (PubMed:25190803). Binds to the ER stress response element (ERSE) upon ER stress (PubMed:11779464). Binds to the consensus 5'-GATGACGTG[TG]N(3)[AT]T-3' sequence related to cAMP responsive element (CRE)-like sequences (PubMed:8657566). Binds the Tax-responsive element (TRE) present in the long terminal repeat (LTR) of T-cell leukemia virus type 1 (HTLV-I) and to the TPA response elements (TRE) (PubMed:1903538, PubMed:2196176, PubMed:2321018, PubMed:8657566). Associates preferentially to the HDAC3 gene promoter region in a static flow-dependent manner (PubMed:25190803). Binds to the CDH5/VE-cadherin gene promoter region (PubMed:19416856) Functions as a stress-inducible potent transcriptional activator during endoplasmic reticulum (ER) stress by inducing unfolded protein response (UPR) target genes via binding to the UPR element (UPRE). Up-regulates target genes encoding ER chaperones and ER-associated degradation (ERAD) components to enhance the capacity of productive folding and degradation mechanism, respectively, in order to maintain the homeostasis of the ER under ER stress (PubMed:11779464, PubMed:25239945). Plays a role in the production of immunoglobulins and interleukin-6 in the presence of stimuli required for plasma cell differentiation (By similarity). Induces phospholipid biosynthesis and ER expansion (PubMed:15466483). Contributes to the VEGF-induced endothelial cell (EC) growth and proliferation in a Akt/GSK-dependent and/or -independent signaling pathway, respectively, leading to beta-catenin nuclear translocation and E2F2 gene expression (PubMed:23529610). Promotes umbilical vein EC apoptosis and atherosclerotisis development in a caspase-dependent signaling pathway, and contributes to VEGF-induced EC proliferation and angiogenesis in adult tissues under ischemic conditions (PubMed:19416856, PubMed:23529610). Involved in the regulation of endostatin-induced autophagy in EC through BECN1 transcriptional activation (PubMed:23184933). Plays a role as an oncogene by promoting tumor progression: stimulates zinc finger protein SNAI1 transcription to induce epithelial-to-mesenchymal (EMT) transition, cell migration and invasion of breast cancer cells (PubMed:25280941). Involved in adipocyte differentiation by regulating lipogenic gene expression during lactation. Plays a role in the survival of both dopaminergic neurons of the substantia nigra pars compacta (SNpc), by maintaining protein homeostasis and of myeloma cells. Increases insulin sensitivity in the liver as a response to a high carbohydrate diet, resulting in improved glucose tolerance. Also improves glucose homeostasis in an ER stress- and/or insulin-independent manner through both binding and proteasome-induced degradation of the transcription factor FOXO1, hence resulting in suppression of gluconeogenic genes expression and in a reduction of blood glucose levels. Controls the induction of de novo fatty acid synthesis in hepatocytes by regulating the expression of a subset of lipogenic genes in an ER stress- and UPR-independent manner (By similarity). Associates preferentially to the HDAC3 gene promoter region in a disturbed flow-dependent manner (PubMed:25190803). Binds to the BECN1 gene promoter region (PubMed:23184933). Binds to the CDH5/VE-cadherin gene promoter region (PubMed:19416856). Binds to the ER stress response element (ERSE) upon ER stress (PubMed:11779464). Binds to the 5'-CCACG-3' motif in the PPARG promoter (By similarity). Binds to the HEPN1 gene promoter region and activates transcription (PubMed:25448679)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P17861/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/XBP1","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/XBP1","total_profiled":1310},"omim":[{"mim_id":"621097","title":"IMMUNODEFICIENCY 131; IMD131","url":"https://www.omim.org/entry/621097"},{"mim_id":"621029","title":"RING FINGER PROTEIN 183; RNF183","url":"https://www.omim.org/entry/621029"},{"mim_id":"620714","title":"DEAFNESS, AUTOSOMAL RECESSIVE 122; DFNB122","url":"https://www.omim.org/entry/620714"},{"mim_id":"620670","title":"IMMUNODEFICIENCY, COMMON VARIABLE, 15; CVID15","url":"https://www.omim.org/entry/620670"},{"mim_id":"620534","title":"NEUTROPENIA, SEVERE CONGENITAL, 10, AUTOSOMAL RECESSIVE; SCN10","url":"https://www.omim.org/entry/620534"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"pancreas","ntpm":1102.3},{"tissue":"salivary gland","ntpm":792.7}],"url":"https://www.proteinatlas.org/search/XBP1"},"hgnc":{"alias_symbol":[],"prev_symbol":["XBP2"]},"alphafold":{"accession":"P17861","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P17861","model_url":"https://alphafold.ebi.ac.uk/files/AF-P17861-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P17861-F1-predicted_aligned_error_v6.png","plddt_mean":68.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XBP1","jax_strain_url":"https://www.jax.org/strain/search?query=XBP1"},"sequence":{"accession":"P17861","fasta_url":"https://rest.uniprot.org/uniprotkb/P17861.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P17861/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P17861"}},"corpus_meta":[{"pmid":"11779464","id":"PMC_11779464","title":"XBP1 mRNA is induced by ATF6 and spliced by IRE1 in response to ER stress to produce a highly active transcription factor.","date":"2001","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/11779464","citation_count":3335,"is_preprint":false},{"pmid":"26073941","id":"PMC_26073941","title":"ER Stress Sensor XBP1 Controls Anti-tumor Immunity by Disrupting Dendritic Cell Homeostasis.","date":"2015","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/26073941","citation_count":752,"is_preprint":false},{"pmid":"12612580","id":"PMC_12612580","title":"Plasma cell differentiation and the unfolded protein response intersect at the transcription factor XBP-1.","date":"2003","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/12612580","citation_count":719,"is_preprint":false},{"pmid":"24670641","id":"PMC_24670641","title":"XBP1 promotes triple-negative breast cancer by controlling the HIF1α pathway.","date":"2014","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/24670641","citation_count":704,"is_preprint":false},{"pmid":"17612490","id":"PMC_17612490","title":"XBP1 controls diverse cell type- and condition-specific transcriptional regulatory networks.","date":"2007","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/17612490","citation_count":688,"is_preprint":false},{"pmid":"15342372","id":"PMC_15342372","title":"XBP1 is essential for survival under hypoxic conditions and is required for tumor growth.","date":"2004","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/15342372","citation_count":458,"is_preprint":false},{"pmid":"30305738","id":"PMC_30305738","title":"IRE1α-XBP1 controls T cell function in ovarian cancer by regulating mitochondrial activity.","date":"2018","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/30305738","citation_count":354,"is_preprint":false},{"pmid":"19490910","id":"PMC_19490910","title":"The IRE1alpha-XBP1 pathway of the unfolded protein response is required for adipogenesis.","date":"2009","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/19490910","citation_count":241,"is_preprint":false},{"pmid":"14960590","id":"PMC_14960590","title":"Hepatitis C virus suppresses the IRE1-XBP1 pathway of the unfolded protein response.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14960590","citation_count":194,"is_preprint":false},{"pmid":"29480818","id":"PMC_29480818","title":"Pharmacological targeting of MYC-regulated IRE1/XBP1 pathway suppresses MYC-driven breast cancer.","date":"2018","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/29480818","citation_count":193,"is_preprint":false},{"pmid":"25986851","id":"PMC_25986851","title":"Targeting the IRE1α-XBP1 branch of the unfolded protein response in human diseases.","date":"2015","source":"Seminars in cancer biology","url":"https://pubmed.ncbi.nlm.nih.gov/25986851","citation_count":149,"is_preprint":false},{"pmid":"36351432","id":"PMC_36351432","title":"Cancer cell-intrinsic XBP1 drives immunosuppressive reprogramming of intratumoral myeloid cells by promoting cholesterol production.","date":"2022","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/36351432","citation_count":142,"is_preprint":false},{"pmid":"35292349","id":"PMC_35292349","title":"Role of XBP1 in regulating the progression of non-alcoholic steatohepatitis.","date":"2022","source":"Journal of hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/35292349","citation_count":120,"is_preprint":false},{"pmid":"31320508","id":"PMC_31320508","title":"IRE1α-XBP1 signaling in leukocytes controls prostaglandin biosynthesis and pain.","date":"2019","source":"Science (New York, 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cytoplasmic splicing of XBP1 mRNA under ER stress, producing a frameshift that generates a highly active transcription factor (spliced XBP1). Additionally, ATF6 induces transcription of XBP1 mRNA upstream of this splicing event.\",\n      \"method\": \"Molecular cloning, reporter assays, mRNA splicing analysis, and functional UPR activation assays in mammalian cells\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — foundational biochemical characterization, replicated across many subsequent studies, multiple orthogonal methods in original paper\",\n      \"pmids\": [\"11779464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IRE1-mediated splicing of XBP1 is required for plasma cell differentiation and immunoglobulin production; only spliced XBP1 rescues immunoglobulin production in XBP1-/- B cells. IL-4 signaling controls XBP1 transcription during B cell differentiation, while immunoglobulin synthesis drives post-transcriptional XBP1 processing. XBP1 also controls IL-6 production, which is essential for plasma cell survival.\",\n      \"method\": \"Genetic rescue experiments in XBP1-/- mouse B cells, B cell differentiation assays, cytokine measurements\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic rescue with defined cellular phenotype, replicated mechanistic findings across labs\",\n      \"pmids\": [\"12612580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hypoxia induces XBP1 at the transcriptional level and activates splicing of its mRNA, resulting in increased activated XBP1 protein. XBP1-deficient cells show increased apoptosis and decreased clonogenic survival under hypoxia, establishing XBP1 as an essential survival factor for hypoxic stress.\",\n      \"method\": \"Gene expression analysis, XBP1-deficient cell lines, clonogenic survival assays, apoptosis assays, tumor xenograft models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with defined cellular and in vivo phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"15342372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hepatitis C virus suppresses the IRE1-XBP1 pathway; HCV replicons elevate XBP1 expression but repress its trans-activating activity, preventing XBP1-dependent induction of EDEM (required for misfolded protein degradation). IRE1α-null MEFs with defective IRE1-XBP1 signaling show elevated HCV IRES-mediated translation.\",\n      \"method\": \"HCV replicon cell lines, XBP1 trans-activation assays, IRE1α-null MEFs, EDEM expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (null MEFs) and pharmacological approaches, single lab, two orthogonal methods\",\n      \"pmids\": [\"14960590\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Genome-wide mapping revealed that XBP1 regulates distinct target genes in different cell types through different sequence motifs; it controls a core ER-maintenance gene set in all cell types plus tissue-specific targets. XBP1 was found to directly regulate Mist1, a critical regulator of differentiation, explaining developmental defects in XBP1-null mice.\",\n      \"method\": \"Genome-wide ChIP, microarray expression profiling in skeletal muscle and secretory cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genome-wide ChIP with functional follow-up, multiple cell types, comprehensive transcriptional regulatory mapping\",\n      \"pmids\": [\"17612490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The IRE1α-XBP1 pathway is indispensable for adipogenesis; C/EBPβ directly binds the Xbp1 proximal promoter to induce its expression, and XBP1 then binds the Cebpa promoter to activate C/EBPα expression. Only the IRE1α-spliced form of XBP1 (XBP1s) rescues adipogenic defects in XBP1-deficient cells.\",\n      \"method\": \"XBP1-deficient MEFs, 3T3-L1 knockdown, promoter ChIP assays, adipogenic differentiation assays, XBP1s rescue experiments\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — genetic rescue with promoter binding evidence (ChIP), multiple orthogonal methods, defined mechanistic pathway\",\n      \"pmids\": [\"19490910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"XBP1 is required for de novo fatty acid synthesis in the liver; XBP1 protein expression is induced by high-carbohydrate diet and directly controls induction of genes involved in fatty acid synthesis. Liver-specific XBP1 deletion results in profound hypocholesterolemia and hypotriglyceridemia due to diminished hepatic lipid production.\",\n      \"method\": \"Inducible liver-specific XBP1 knockout mice, gene expression analysis, lipid measurements\",\n      \"journal\": \"Annals of the New York Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic deletion with defined metabolic phenotype, referenced as primary findings from original research\",\n      \"pmids\": [\"19751410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"miR-30c-2* (miR-30c-2-3p) is induced by the PERK pathway of the UPR and directly suppresses XBP1 expression, limiting the scale of XBP1-mediated gene expression and influencing cell fate in the UPR. This represents a cross-talk mechanism where PERK signaling dampens IRE1/XBP1 output.\",\n      \"method\": \"miRNA induction assays, miRNA overexpression/inhibition, XBP1 protein/mRNA measurement, PERK pathway genetic approaches\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional miRNA-target relationship established, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"22431749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"XBP1 promotes TNBC tumorigenicity by assembling a transcriptional complex with HIF1α that recruits RNA polymerase II to regulate HIF1α target gene expression. Genome-wide mapping of the XBP1 transcriptional regulatory network confirmed physical interaction of XBP1 with HIF1α.\",\n      \"method\": \"Genome-wide ChIP-seq, Co-immunoprecipitation, XBP1 depletion (shRNA), tumor xenograft models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP-seq plus Co-IP establishing physical complex, in vitro and in vivo functional validation\",\n      \"pmids\": [\"24670641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"XBP1 regulates epithelial-to-mesenchymal transition (EMT) in breast cancer by upregulating the key EMT regulator Snail, leading to decreased E-cadherin and increased mesenchymal marker expression. XBP1 knockdown restores E-cadherin expression and suppresses cell invasion.\",\n      \"method\": \"siRNA knockdown, XBP1 overexpression, E-cadherin/mesenchymal marker expression assays, invasion assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function experiments with defined molecular phenotype, single lab\",\n      \"pmids\": [\"25280941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Constitutive XBP1 activation in tumor-associated dendritic cells, fueled by lipid peroxidation byproducts, induces a triglyceride biosynthetic program leading to abnormal lipid accumulation and inhibition of anti-tumor T cell support. DC-specific XBP1 deletion or nanoparticle-mediated XBP1 silencing in tDCs restored immunostimulatory activity.\",\n      \"method\": \"DC-specific XBP1 conditional knockout mice, nanoparticle-mediated XBP1 silencing, lipid accumulation assays, T cell activation assays, tumor progression models\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific genetic deletion with defined metabolic and immunological phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"26073941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"XBP1 directly binds the promoter of NFATc1 and induces its transcription to drive osteoclastogenesis. IRE1α activation during osteoclastogenesis is partially dependent on Ca2+ oscillation via ITPR2 and ITPR3 in the ER.\",\n      \"method\": \"Conditional IRE1α knockout mice, osteoclast differentiation assays, ChIP for XBP1 binding to NFATc1 promoter, pharmacological inhibition of ITPR2/3\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vivo genetic model plus direct promoter binding evidence by ChIP, multiple orthogonal approaches\",\n      \"pmids\": [\"26193638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SEC63 deficiency selectively activates IRE1α-XBP1 in the ER; SEC63 exists in a complex with PC1 (polycystin-1). XBP1 is required for GPS cleavage and maturation of PC1; enforced XBP1s expression enhances GPS cleavage of PC1 and ameliorates polycystic disease.\",\n      \"method\": \"Murine genetic models (SEC63/XBP1 double knockout), co-immunoprecipitation, GPS cleavage assays, XBP1s overexpression\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reciprocal Co-IP, genetic epistasis, functional rescue, multiple orthogonal methods\",\n      \"pmids\": [\"25844898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hepatic XBP1 controls the adaptive UPR response in the liver; liver-specific Xbp1 knockout mice cannot resolve ER stress, leading to sustained UPR activation, progressive liver injury, apoptosis, and fibrosis in response to pharmacological ER stress.\",\n      \"method\": \"Liver-specific Xbp1 knockout mice, pharmacological ER stress induction, liver injury/apoptosis/fibrosis assessment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo conditional KO with well-defined phenotypic progression, multiple time points\",\n      \"pmids\": [\"26504083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In addition to ATF6-mediated transcriptional induction of XBP1 mRNA, IRE1α expression is induced by ATF4 downstream of PERK under ER stress; increased IRE1α expression raises the XBP1 mRNA splicing ratio, amplifying and prolonging IRE1α-XBP1 pathway activation.\",\n      \"method\": \"IRE1α/ATF4 knockdown, XBP1 splicing ratio measurement, ER stress time-course experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway dissection with genetic knockdown, single lab, multiple methods\",\n      \"pmids\": [\"27052593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Unspliced XBP1 (XBP1-u) negatively regulates the p53/p21 axis by binding and stabilizing MDM2 protein, inhibiting MDM2 self-ubiquitination and thereby enhancing p53 ubiquitination and degradation. The C-terminal domain of XBP1-u (which differs from XBP1-s due to a codon shift) mediates MDM2 binding.\",\n      \"method\": \"shRNA library screen, Co-immunoprecipitation, ubiquitination assays, domain mapping, cell cycle analysis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — Co-IP with domain mapping, biochemical ubiquitination assays, functional cell cycle phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"29057323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"XBP1s directly binds the Cyclin D1 promoter to activate its expression, mediating IRE1α-dependent cell proliferation in colorectal cancer cells.\",\n      \"method\": \"ChIP, luciferase reporter assays, siRNA knockdown of IRE1α/XBP1, proliferation assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding by ChIP with functional proliferation readout, single lab\",\n      \"pmids\": [\"26742428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"XBP1s binds the IL-6 promoter directly and activates its expression in melanoma cells; secreted IL-6 then activates JAK/STAT3 signaling in an autocrine/paracrine manner to promote melanoma cell proliferation. Inhibition of IRE1α RNase activity abolishes this effect.\",\n      \"method\": \"ChIP experiments, luciferase reporter assays, XBP1s ectopic expression, IRE1α inhibition, western blotting for STAT3\",\n      \"journal\": \"Journal of translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding by ChIP, pharmacological and genetic validation, single lab\",\n      \"pmids\": [\"28222747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRE1α-XBP1 activation in T cells suppresses mitochondrial activity and IFNγ production in ovarian cancer. Mechanistically, XBP1 induction regulates the abundance of glutamine carriers, limiting glutamine influx needed for mitochondrial respiration under glucose-deprived conditions. XBP1-deficient T cells show improved effector capacity.\",\n      \"method\": \"T cell-specific XBP1 deletion, metabolic assays, glutamine transporter expression analysis, mitochondrial respiration measurement, mouse tumor models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional T cell-specific KO, metabolomics, mechanistic pathway validation, in vivo tumor model\",\n      \"pmids\": [\"30305738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MYC directly controls IRE1 transcription by binding to its promoter and enhancer. Furthermore, MYC forms a transcriptional complex with XBP1 and enhances XBP1 transcriptional activity. XBP1 is a synthetic lethal partner of MYC in breast cancer.\",\n      \"method\": \"ChIP for MYC binding to IRE1 promoter/enhancer, Co-immunoprecipitation of MYC-XBP1 complex, XBP1 silencing in MYC-hyperactivated cells, PDX mouse models\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP plus Co-IP establishing physical complex, in vivo PDX validation, multiple orthogonal methods\",\n      \"pmids\": [\"29480818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRE1α-XBP1 constitutive activation in pancreatic β cells regulates oxidative folding of proinsulin by controlling expression of five protein disulfide isomerases (PDI, PDIR, P5, ERp44, ERp46). Reconstitution of the IRE1α-XBP1 pathway in Ire1α-deleted insulinoma cells restored proinsulin content, insulin secretion, and PDI expression.\",\n      \"method\": \"β cell-specific Ire1α conditional knockout mice, Cre-loxP cell lines, insulin secretion assays, PDI expression analysis, IRE1α-XBP1 reconstitution\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — cell-type-specific KO plus pathway reconstitution, multiple molecular targets identified, in vivo and in vitro evidence\",\n      \"pmids\": [\"29507125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"XBP1s directly transactivates the human PTGS2 (COX-2) and PTGES genes to enable optimal prostaglandin E2 production in myeloid cells. IRE1α-XBP1-deficient myeloid cells show compromised induction of Cox-2 and mPGES-1 under ER stress or pattern recognition receptor stimulation.\",\n      \"method\": \"IRE1α-deficient myeloid cells, XBP1-deficient myeloid cells, ChIP/transactivation assays for PTGS2/PTGES promoters, PGE2 measurements, pain behavior models\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct promoter transactivation evidence, genetic models, in vivo pain behavior validation\",\n      \"pmids\": [\"31320508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"2',3'-cyclic nucleotide phosphodiesterase (CNP) suppresses RtcB-mediated XBP1 splicing by hydrolyzing 2',3'-cyclic phosphate on cleaved XBP1 exon termini; conversely, RNA 3'-terminal cyclase (RtcA) facilitates XBP1 splicing by converting 2'-phosphate back to 2',3'-cyclic phosphate for RtcB ligation.\",\n      \"method\": \"In vitro splicing assays, mammalian cell lines, CNP/RtcA overexpression/knockdown, XBP1 splicing measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of splicing mechanism, genetic and biochemical validation, single lab\",\n      \"pmids\": [\"30355738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Muscle-specific deletion of XBP1 ameliorates cancer cachexia-induced skeletal muscle wasting; overexpression of active XBP1 causes myotube atrophy. XBP1 acts downstream of TLR/MyD88 signaling to mediate muscle wasting, identifying a TLR/MyD88/XBP1 axis in cancer cachexia.\",\n      \"method\": \"Muscle-specific XBP1 conditional knockout mice, Lewis lung carcinoma tumor-bearing model, myotube atrophy assays, XBP1 overexpression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with in vivo cancer model, epistasis established with TLR/MyD88\",\n      \"pmids\": [\"31138662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Constitutive XBP-1s expression in C. elegans increases lysosomal lipase activity and upregulates transcription of Δ9 desaturase FAT-6, increasing oleic acid levels; FAT-6 is required for the full lifespan extension induced by XBP-1s.\",\n      \"method\": \"C. elegans transgenic expression, metabolomics, fat-6 genetic epistasis, lysosomal lipase activity assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in C. elegans model, metabolomic profiling, single lab\",\n      \"pmids\": [\"31315038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Insulin-activated kinase AKT directly phosphorylates IRE1 at S724, which mediates XBP1u mRNA splicing to generate XBP1s in mouse liver in the fed state, stimulating lipogenic gene expression. In the fasted state, XBP1u (not XBP1s) increases cAMP-stimulated gluconeogenic gene expression (G6pc, Pck1) and glucose production.\",\n      \"method\": \"AKT phosphorylation site mapping, in vitro kinase assays, hepatocyte-specific XBP1 depletion with re-expression, gluconeogenesis/lipogenesis assays, primary hepatocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct phosphorylation mapping, biochemical and genetic approaches, isoform-specific functional validation\",\n      \"pmids\": [\"35863429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Hepatocyte-specific XBP1 deletion sensitizes mice to liver injury through hyperactivation of IRE1α (evidenced by XBP1 mRNA splicing, JNK activation, and RIDD). Concomitant deletion of both XBP1 and IRE1α protected mice from fructose-mediated liver injury, demonstrating that deleterious effects of XBP1 deletion are primarily due to IRE1α hyperactivation.\",\n      \"method\": \"Hepatocyte-specific single and double (XBP1/IRE1α) conditional knockout mice, dietary challenge, liver injury markers, IRE1α activity assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double conditional KO genetic epistasis with clear mechanistic interpretation, in vivo model\",\n      \"pmids\": [\"33219328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Liver-specific ablation of XBP1 disrupts the hepatic 12-hour clock and promotes NAFLD; XBP1s directly binds to the hepatic 12-hour cistrome. XBP1 ablation reduces membrane fluidity and impairs lipid homeostasis via fatty acid monounsaturation and phospholipid remodeling pathways.\",\n      \"method\": \"Liver-specific XBP1 knockout mice, ChIP-seq of 12-hour cistrome, genome-wide transcriptional profiling, lipid/membrane fluidity assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP-seq cistrome mapping plus in vivo conditional KO with comprehensive metabolic phenotyping\",\n      \"pmids\": [\"33277471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Unspliced XBP1 (XBP1u) directly binds β-catenin via amino acids 205–230 in its C-terminal degradation domain, promoting β-catenin ubiquitin-proteasomal degradation independently of the GSK-3β destruction complex, thereby inhibiting β-catenin/TCF-mediated transcription of Runx2 and Msx2 and suppressing vascular calcification.\",\n      \"method\": \"Interactome analysis, Co-immunoprecipitation, ubiquitination assays, domain mapping, smooth muscle cell-specific XBP1 knockout mice, vascular calcification models\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — Co-IP with domain mapping, ubiquitination assays, in vivo conditional KO, β-catenin rescue experiment\",\n      \"pmids\": [\"34870453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XBP1s directly binds the TAp73 promoter and suppresses its transcriptional activity, reducing p53-family tumor suppression and promoting colorectal cancer cell proliferation. TAp73 overexpression cancelled the pro-proliferative effect of XBP1s.\",\n      \"method\": \"ChIP for XBP1s binding to TAp73 promoter, luciferase reporter assays, XBP1s overexpression, TAp73 rescue experiments\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding by ChIP with functional rescue validation, single lab\",\n      \"pmids\": [\"30473215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XBP1s genome-wide mRNA profiling identified XBP1 as a transcriptional repressor of PUMA (proapoptotic gene) and IRE1 mRNA expression during UPR, providing a negative feedback mechanism. Elevated XBP1 expression during ER stress had a prosurvival effect with reduced PUMA protein.\",\n      \"method\": \"XBP1s-inducible human cell line, siRNA silencing, next-generation RNA sequencing, bioinformatic analysis of XBP1-binding motifs\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide transcriptome profiling with inducible system and XBP1 silencing, single lab\",\n      \"pmids\": [\"34636989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Unspliced XBP1 (XBP1-u) colocalizes with SREBP2 and inhibits its ubiquitination/proteasomal degradation, stabilizing SREBP2 and activating HMGCR transcription, thereby promoting cholesterol biosynthesis and tumorigenesis in hepatocellular carcinoma.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, SREBP2 stability assays, HMGCR expression analysis, tumor growth experiments\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with biochemical ubiquitination assays, single lab, multiple methods\",\n      \"pmids\": [\"35933495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Spliced XBP1 binds directly to the BNIP3 promoter and inhibits BNIP3 transcription in macrophages, thereby suppressing BNIP3-mediated mitophagy. Reduced mitophagy in Xbp1-expressing macrophages promotes cytosolic mtDNA leakage, activating cGAS/STING/NLRP3 signaling to drive liver fibrosis.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for XBP1 binding to Bnip3 promoter, RNA sequencing, myeloid-specific Xbp1 knockout mice, BNIP3 knockdown, liver fibrosis models\",\n      \"journal\": \"JHEP reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — ChIP demonstrating direct promoter binding, genetic epistasis with conditional KO, RNA-seq pathway analysis\",\n      \"pmids\": [\"36185574\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cancer cell XBP1 favors synthesis and secretion of cholesterol in small extracellular vesicles; cholesterol is internalized by MDSCs via macropinocytosis, activating MDSCs and causing immunosuppression. XBP1 genetic or pharmacological depletion reduces MDSC abundance and triggers anti-tumor responses.\",\n      \"method\": \"XBP1 genetic depletion/pharmacological inhibition, extracellular vesicle isolation, cholesterol quantification, MDSC activation assays, tumor models\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological XBP1 depletion with defined mechanistic pathway, single lab\",\n      \"pmids\": [\"36351432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Spliced XBP1 enhances the activity of the NLRP3 promoter (demonstrated by luciferase reporter assay), linking XBP1-mediated ER-mitochondria crosstalk to caspase-1-dependent inflammation in renal ischemia/reperfusion injury.\",\n      \"method\": \"Luciferase reporter assay for NLRP3 promoter, XBP1 interference in renal tubular cells, in vivo renal IRI model\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter activity assay plus in vivo model, single lab\",\n      \"pmids\": [\"36801911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Drosophila, IRE1-mediated phosphorylation of the RNA-binding protein Pumilio enables Pumilio to protect spliced Xbp1 mRNA from regulated Ire1-dependent decay (RIDD). hIRE1 can directly phosphorylate Pumilio, and phosphorylated Pumilio binds and stabilizes Xbp1spliced mRNA.\",\n      \"method\": \"Drosophila genetics, in vitro IRE1 kinase assays, mRNA stability assays, Pumilio binding site identification in Xbp1 3'UTR\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro kinase assay (direct phosphorylation), Drosophila genetic validation, mRNA stability assays\",\n      \"pmids\": [\"35332141\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ATF6α is required for full activation of XBP1 target genes in pancreatic islet cells; acute ATF6α knockdown reduces induction of XBP1 targets without altering XBP1 mRNA splicing dynamics. XBP1 is not required for activation of ATF6α targets, establishing ATF6α as upstream of XBP1 target expression but not of XBP1 splicing.\",\n      \"method\": \"Acute ATF6α conditional knockdown in primary mouse islets (adenovirus-Cre), timed ER stressor exposures, transcriptional target gene measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic dissection of pathway hierarchy in primary cells, multiple ER stressors tested, single lab\",\n      \"pmids\": [\"32788214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XBP1 overexpression increases Hrd1 expression; Hrd1 then interacts with and ubiquitinates Nrf2 under high-glucose conditions (confirmed by Co-IP and ubiquitylation assays), promoting ferroptosis via the XBP1-Hrd1-Nrf2 pathway in diabetic nephropathy.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitylation assays, XBP1 overexpression, ferroptosis markers, high-glucose cell model\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and ubiquitylation biochemistry establishing pathway, single lab\",\n      \"pmids\": [\"37224754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XBP1 inhibits SLC38A2 (glutamine transporter) expression by directly binding to its promoter; reduced SLC38A2 decreases glutamine uptake and causes immune dysfunction in cytotoxic T cells in multiple myeloma.\",\n      \"method\": \"Single-cell RNA sequencing, in vitro XBP1 overexpression/inhibition, ChIP for XBP1 binding to SLC38A2 promoter, glutamine uptake assays, T cell functional assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding by ChIP with functional metabolic and immune phenotype, single lab\",\n      \"pmids\": [\"37054944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XBP1 in dendritic cells directly promotes TIM4 mRNA and protein expression in response to IL-2. RhoA facilitates binding between XBP1 and GATA3 in CD4+ T cells; XBP1 induces GATA3 phosphorylation to promote Il4 gene transcription and Th2 polarization.\",\n      \"method\": \"Xbp1-deficient CD4+ T cells and DCs, XBP1-TIM4 promoter binding assays, Co-IP for XBP1-GATA3 interaction, GATA3 phosphorylation assays, in vivo airway allergy models\",\n      \"journal\": \"Science signaling / Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic conditional KO, Co-IP for protein interaction, functional immune phenotype, single lab\",\n      \"pmids\": [\"37368951\", \"35910793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XBP1 upregulation promotes ferritinophagy via NCOA4; SeNPs protect against ferroptosis by upregulating XBP1, which in turn suppresses NCOA4-mediated ferritinophagy. XBP1 downregulation promoted ferritinophagy and partially counteracted protective effects on ferroptosis.\",\n      \"method\": \"In vitro H/R model, in vivo I/R-AKI mouse model, XBP1 knockdown, ferritinophagy and ferroptosis markers, lysosomal Fe2+ measurement\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single knockdown approach, indirect pathway inference without direct XBP1-NCOA4 binding evidence\",\n      \"pmids\": [\"39061070\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XBP1 is a bZIP transcription factor whose activity is controlled by IRE1-mediated unconventional cytoplasmic splicing of its mRNA under ER stress (induced transcriptionally by ATF6), generating a frameshift that produces the potent transcriptional activator XBP1s; the unspliced form (XBP1u) has distinct functions including stabilizing MDM2 to degrade p53 and stabilizing SREBP2 to promote cholesterol biosynthesis, while XBP1s drives a wide transcriptional program encompassing ER expansion, lipid/glucose metabolism (directly transactivating lipogenic and gluconeogenic gene promoters), cell differentiation (plasma cell, adipocyte, osteoclast), and immune regulation (controlling prostaglandin biosynthesis via COX-2/mPGES-1 transactivation, shaping DC and T cell function), with the splicing efficiency itself fine-tuned by CNP/RtcA modulation of RNA termini for RtcB ligation and by IRE1-phosphorylated Pumilio protecting XBP1s mRNA from RIDD.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XBP1 is a bZIP transcription factor central to the IRE1α arm of the unfolded protein response, whose activity is gated by an unconventional cytoplasmic splicing event: under ER stress IRE1 cleaves XBP1 mRNA to remove a short intron, producing a frameshift that converts the inert unspliced product into the potent transcriptional activator XBP1s, with ATF6 supplying the upstream transcriptional induction of XBP1 mRNA [#0, #36]. This pathway is amplified and tuned at multiple levels—ATF4 downstream of PERK raises IRE1α to increase the splicing ratio [#14], PERK-induced miR-30c-2* dampens XBP1 output [#7], and the splicing reaction itself is set by CNP/RtcA remodeling of cleaved exon termini for RtcB ligation [#22] and by IRE1-phosphorylated Pumilio that shields spliced XBP1 mRNA from regulated IRE1-dependent decay [#35]. XBP1s executes a broad, cell-type-specific transcriptional program: it maintains a core ER-folding/secretory gene set in all cells while directing tissue-specific targets, including direct control of the differentiation regulator Mist1 [#4], and it is required for plasma cell differentiation and immunoglobulin/IL-6 production [#1], adipogenesis via a C/EBPβ→XBP1→C/EBPα circuit [#5], and osteoclastogenesis through direct transactivation of NFATc1 [#11]. In metabolism, XBP1s drives hepatic de novo lipogenesis and lipid homeostasis, governs a hepatic 12-hour clock cistrome, and controls oxidative proinsulin folding by inducing protein disulfide isomerases [#6, #27, #20], while the unspliced isoform XBP1u carries out distinct, splicing-independent functions—stabilizing MDM2 to degrade p53 [#15], stabilizing SREBP2 to drive cholesterol synthesis [#31], and targeting β-catenin for degradation [#28]. XBP1 also acts as a survival and pro-tumorigenic factor: it supports survival under hypoxia [#2], forms transcriptional complexes with HIF1α and MYC to potentiate their programs [#8, #19], and reshapes the tumor microenvironment by reprogramming dendritic-cell lipid metabolism and constraining T-cell effector function through glutamine-transporter regulation [#10, #18]. In innate immunity it directly transactivates PTGS2/PTGES to enable prostaglandin E2 production [#21].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established the defining regulatory logic of XBP1: that its mRNA is the substrate of IRE1 cytoplasmic splicing, converting it by frameshift into an active transcription factor, with ATF6 inducing the message upstream.\",\n      \"evidence\": \"Molecular cloning, reporter and splicing assays in mammalian cells\",\n      \"pmids\": [\"11779464\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not enumerate the downstream transcriptional program\", \"Splicing machinery components (ligase, terminal processing) not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showed the IRE1-XBP1 splicing event is physiologically essential for a defined differentiation program, linking the UPR to plasma cell development and antibody secretion.\",\n      \"evidence\": \"Genetic rescue in XBP1-/- mouse B cells with differentiation and cytokine readouts\",\n      \"pmids\": [\"12612580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct target genes mediating the differentiation block not mapped here\", \"How IL-4 controls XBP1 transcription mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Extended XBP1 beyond classical ER stress to hypoxia, defining it as a survival factor whose loss increases apoptosis—relevant to tumor biology.\",\n      \"evidence\": \"XBP1-deficient cells, clonogenic/apoptosis assays and xenografts\",\n      \"pmids\": [\"15342372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Survival-mediating target genes not identified\", \"Spliced vs unspliced contribution under hypoxia not dissected\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Resolved how one factor produces diverse outputs by mapping cell-type-specific cistromes, distinguishing a universal ER-maintenance set from tissue-specific targets such as Mist1.\",\n      \"evidence\": \"Genome-wide ChIP and expression profiling in muscle and secretory cells\",\n      \"pmids\": [\"17612490\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of cell-type-specific motif selection not defined\", \"Cofactors directing context-specific binding unknown at this stage\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined XBP1 as a required node in metabolic differentiation and lipid synthesis, establishing direct promoter circuits in adipogenesis and hepatic lipogenesis.\",\n      \"evidence\": \"XBP1-deficient MEFs/3T3-L1, promoter ChIP, liver-specific knockout with lipid phenotyping\",\n      \"pmids\": [\"19490910\", \"19751410\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether lipogenic control is purely XBP1s-dependent left open here\", \"Relationship between metabolic and ER-folding programs unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Revealed inter-arm UPR cross-talk in which PERK-induced miR-30c-2* caps XBP1 output, showing XBP1 levels are set not just by splicing but by miRNA control.\",\n      \"evidence\": \"miRNA gain/loss-of-function with XBP1 measurement and PERK genetics\",\n      \"pmids\": [\"22431749\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"Quantitative contribution relative to splicing not established\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified XBP1 as a partner that physically assembles with HIF1α to potentiate hypoxic transcription and drive TNBC tumorigenicity, beyond its canonical UPR role.\",\n      \"evidence\": \"ChIP-seq, Co-IP, shRNA depletion and xenografts\",\n      \"pmids\": [\"24670641\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interaction interface not mapped\", \"Whether complex requires XBP1s splicing not formally isolated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked XBP1 to invasion programs by showing it upregulates Snail to drive EMT in breast cancer.\",\n      \"evidence\": \"siRNA/overexpression with marker and invasion assays\",\n      \"pmids\": [\"25280941\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect regulation of Snail not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Broadened the cell-fate program of XBP1s to osteoclast differentiation via direct NFATc1 transactivation, with IRE1 activation tied to ER Ca2+ oscillation.\",\n      \"evidence\": \"Conditional IRE1α KO mice, osteoclast assays, NFATc1-promoter ChIP\",\n      \"pmids\": [\"26193638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Ca2+ oscillation feeds IRE1 mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected selective IRE1α-XBP1 activation to secretory protein maturation and disease, showing XBP1 is required for polycystin-1 GPS cleavage and ameliorates polycystic disease.\",\n      \"evidence\": \"SEC63/XBP1 double-KO mice, reciprocal Co-IP, GPS cleavage and XBP1s overexpression\",\n      \"pmids\": [\"25844898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct targets mediating PC1 maturation not fully enumerated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established XBP1 as the adaptive resolver of hepatic ER stress, with its loss causing maladaptive UPR, injury and fibrosis.\",\n      \"evidence\": \"Liver-specific XBP1 KO with pharmacological ER stress\",\n      \"pmids\": [\"26504083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not separate loss-of-XBP1 effects from secondary IRE1α hyperactivation (resolved later)\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Uncovered a pathogenic role in tumor immunity, showing constitutive XBP1 in tumor dendritic cells drives a lipid program that disables anti-tumor T-cell support.\",\n      \"evidence\": \"DC-specific XBP1 KO, nanoparticle silencing, lipid and T-cell assays, tumor models\",\n      \"pmids\": [\"26073941\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct lipogenic target genes in tDCs not fully mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed feed-forward amplification of the pathway, with PERK/ATF4-driven IRE1α induction raising the XBP1 splicing ratio to prolong signaling.\",\n      \"evidence\": \"IRE1α/ATF4 knockdown with splicing-ratio time courses\",\n      \"pmids\": [\"27052593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Quantitative impact on target output not measured\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Distinguished a splicing-independent function: unspliced XBP1u stabilizes MDM2 via its unique C-terminus to promote p53 degradation, redefining the 'inactive' isoform as a functional regulator.\",\n      \"evidence\": \"shRNA screen, Co-IP, domain mapping, ubiquitination and cell-cycle assays\",\n      \"pmids\": [\"29057323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular contexts where XBP1u-MDM2 axis dominates not delineated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Added direct proliferation- and inflammation-promoting target circuits, showing XBP1s transactivates Cyclin D1 and IL-6 in cancer.\",\n      \"evidence\": \"ChIP, luciferase, siRNA/ectopic expression and proliferation/STAT3 readouts\",\n      \"pmids\": [\"26742428\", \"28222747\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab findings per target\", \"Cell-type generality not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined XBP1 as a metabolic brake on T-cell function in cancer, limiting glutamine influx and mitochondrial respiration to suppress IFNγ.\",\n      \"evidence\": \"T-cell-specific XBP1 KO, metabolomics, transporter and respiration assays, tumor models\",\n      \"pmids\": [\"30305738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transporter-gene targets not all confirmed in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed reciprocal transcription-factor coupling, with MYC controlling IRE1 and forming a complex with XBP1, establishing XBP1 as a synthetic-lethal MYC partner.\",\n      \"evidence\": \"ChIP, Co-IP, XBP1 silencing in MYC-driven cells, PDX models\",\n      \"pmids\": [\"29480818\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of MYC-XBP1 complex unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked constitutive IRE1α-XBP1 to secretory cell physiology by showing it controls proinsulin oxidative folding via induction of multiple PDIs.\",\n      \"evidence\": \"β-cell-specific Ire1α KO and pathway reconstitution with insulin/PDI readouts\",\n      \"pmids\": [\"29507125\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct XBP1 binding at all five PDI promoters not individually demonstrated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected XBP1 to inflammatory lipid mediator production, showing XBP1s directly transactivates PTGS2/PTGES for prostaglandin E2 synthesis in myeloid cells.\",\n      \"evidence\": \"IRE1α/XBP1-deficient myeloid cells, promoter transactivation, PGE2 and pain models\",\n      \"pmids\": [\"31320508\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stimulus-specific control of the COX-2/mPGES-1 module not fully parsed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Mechanistically defined splicing fidelity, showing CNP and RtcA antagonistically set XBP1 exon-terminus chemistry for RtcB ligation.\",\n      \"evidence\": \"In vitro splicing assays with CNP/RtcA manipulation\",\n      \"pmids\": [\"30355738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological conditions modulating CNP/RtcA balance not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended XBP1 to muscle pathology, identifying a TLR/MyD88/XBP1 axis driving cancer cachexia-associated muscle wasting.\",\n      \"evidence\": \"Muscle-specific XBP1 KO, tumor-bearing model, myotube atrophy and overexpression\",\n      \"pmids\": [\"31138662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atrophy-effector target genes downstream of XBP1 not mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed evolutionary conservation of XBP1s as a lipid-metabolism and longevity effector, acting via lysosomal lipase and FAT-6 desaturase in C. elegans.\",\n      \"evidence\": \"C. elegans transgenics, metabolomics and fat-6 epistasis\",\n      \"pmids\": [\"31315038\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional targets in the worm not mapped\", \"Single-organism inference\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Integrated XBP1 isoforms into nutrient signaling, showing AKT phosphorylates IRE1 to generate XBP1s for fed-state lipogenesis while XBP1u drives fasting gluconeogenesis.\",\n      \"evidence\": \"AKT/IRE1 phosphosite mapping, kinase assays, hepatocyte depletion/re-expression with isoform-specific readouts\",\n      \"pmids\": [\"35863429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which XBP1u potentiates cAMP-driven gluconeogenic genes unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved a long-standing ambiguity by genetic epistasis: XBP1-loss liver injury arises mainly from secondary IRE1α hyperactivation rather than loss of XBP1 transcriptional output.\",\n      \"evidence\": \"Hepatocyte XBP1/IRE1α single and double conditional KO with dietary challenge\",\n      \"pmids\": [\"33219328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RIDD substrate spectrum driving injury not enumerated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linked XBP1 to circadian and membrane lipid homeostasis, defining a hepatic 12-hour cistrome whose loss promotes NAFLD.\",\n      \"evidence\": \"Liver-specific KO, 12-hour cistrome ChIP-seq, lipid/membrane fluidity assays\",\n      \"pmids\": [\"33277471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between 12-hour clock and canonical UPR targets unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Expanded XBP1u's degradation-targeting role beyond MDM2, showing it directly binds β-catenin for proteasomal degradation independent of GSK-3β, suppressing vascular calcification.\",\n      \"evidence\": \"Interactome, Co-IP, domain mapping, ubiquitination, SMC-specific KO and rescue\",\n      \"pmids\": [\"34870453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase used by XBP1u for β-catenin not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed XBP1s can act as a transcriptional repressor of tumor-suppressive and pro-apoptotic programs, suppressing TAp73 and PUMA to favor proliferation/survival.\",\n      \"evidence\": \"ChIP/luciferase with rescue (TAp73); inducible XBP1s RNA-seq with motif analysis (PUMA/IRE1)\",\n      \"pmids\": [\"30473215\", \"34636989\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Repressive cofactors enabling XBP1s repression not defined\", \"Single-lab findings\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined XBP1u as a driver of cholesterol biosynthesis by stabilizing SREBP2 to induce HMGCR, promoting hepatocellular carcinoma.\",\n      \"evidence\": \"Co-IP, ubiquitination/stability assays, HMGCR analysis and tumor growth\",\n      \"pmids\": [\"35933495\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct vs indirect SREBP2 stabilization mechanism partial\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Connected XBP1s to innate immune signaling via mitophagy control, showing it represses BNIP3 to enhance cGAS/STING/NLRP3 activation and liver fibrosis.\",\n      \"evidence\": \"BNIP3-promoter ChIP, RNA-seq, myeloid XBP1 KO and BNIP3 knockdown in fibrosis models\",\n      \"pmids\": [\"36185574\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across macrophage subsets not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Added a paracrine immunosuppressive mechanism whereby cancer-cell XBP1 promotes cholesterol-laden extracellular vesicles that activate MDSCs.\",\n      \"evidence\": \"XBP1 depletion/inhibition, EV cholesterol quantification, MDSC and tumor assays\",\n      \"pmids\": [\"36351432\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Which XBP1 isoform drives EV cholesterol secretion not specified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked XBP1s to inflammasome priming by enhancing NLRP3 promoter activity in renal ischemia/reperfusion injury.\",\n      \"evidence\": \"NLRP3 promoter luciferase, XBP1 interference and in vivo renal IRI\",\n      \"pmids\": [\"36801911\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct XBP1 occupancy at NLRP3 promoter not shown by ChIP\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated metazoan conservation of post-transcriptional protection of spliced XBP1, with IRE1-phosphorylated Pumilio shielding it from RIDD.\",\n      \"evidence\": \"Drosophila genetics, in vitro IRE1 kinase assays, mRNA stability and 3'UTR binding\",\n      \"pmids\": [\"35332141\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the mammalian Pumilio orthologs perform the same role in vivo not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Clarified pathway hierarchy, showing ATF6α is required for full XBP1 target induction but not for XBP1 splicing, and is itself independent of XBP1.\",\n      \"evidence\": \"Acute ATF6α knockdown in primary islets with timed ER stressors and target measurement\",\n      \"pmids\": [\"32788214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of ATF6α/XBP1 cooperativity at promoters not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended XBP1 control to redox/cell-death pathways, defining an XBP1-Hrd1-Nrf2 axis promoting ferroptosis under high glucose.\",\n      \"evidence\": \"Co-IP, ubiquitylation assays and ferroptosis markers in high-glucose models\",\n      \"pmids\": [\"37224754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Hrd1 is a direct XBP1 transcriptional target not shown by ChIP here\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed XBP1 represses a glutamine transporter (SLC38A2) to impair cytotoxic T cells in myeloma, paralleling its glutamine-limiting role in ovarian-cancer T cells.\",\n      \"evidence\": \"scRNA-seq, XBP1 gain/loss, SLC38A2-promoter ChIP and glutamine/T-cell assays\",\n      \"pmids\": [\"37054944\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct vs indirect repression mechanism not fully resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined XBP1's role in shaping adaptive immune polarization, promoting TIM4 in DCs and partnering with GATA3 (via RhoA) to drive Th2 IL-4 transcription.\",\n      \"evidence\": \"Xbp1-deficient T cells/DCs, promoter binding, XBP1-GATA3 Co-IP, GATA3 phosphorylation and airway allergy models\",\n      \"pmids\": [\"37368951\", \"35910793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of XBP1-induced GATA3 phosphorylation unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Proposed XBP1 as a regulator of ferritinophagy via NCOA4, protecting against ferroptosis in ischemic kidney injury.\",\n      \"evidence\": \"XBP1 knockdown in H/R and I/R-AKI models with ferritinophagy/ferroptosis markers\",\n      \"pmids\": [\"39061070\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct XBP1-NCOA4 binding evidence; pathway inferred indirectly\", \"Single knockdown approach, single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the choice between XBP1s and XBP1u functions—and which isoform dominates in a given tissue or disease—is integrated with upstream kinase, splicing-fidelity, and cofactor inputs remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Structural basis of XBP1 partnerships with HIF1α, MYC and GATA3 unknown\", \"E3 ligases and degradation machinery used by XBP1u not identified\", \"Quantitative rules governing cell-type-specific cistromes undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 4, 5, 11, 21, 27]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [4, 11, 21, 27, 32, 38]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [15, 28, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4, 8, 11, 27]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [15, 28, 31]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 13, 20]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 8, 11, 21, 27]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 20, 22]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 18, 27, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [1, 10, 18, 21, 39]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 5, 11]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 22, 35]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IRE1\", \"HIF1A\", \"MYC\", \"MDM2\", \"SREBP2\", \"CTNNB1\", \"GATA3\", \"PUM\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}