{"gene":"PSMB8","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":1993,"finding":"The yeast PRE2 gene (highly homologous to human RING10/PSMB8, 60% identity) encodes a proteasome beta-subunit whose loss abolishes chymotrypsin-like activity of the 20S proteasome and causes accumulation of ubiquitinated proteins, establishing that this subunit is the catalytic component responsible for chymotryptic activity.","method":"Genetic complementation of pre2 mutants, missense mutation identification, biochemical assay of proteasome chymotryptic activity, ubiquitinated protein accumulation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay combined with genetic loss-of-function and rescue, replicated across multiple mutant alleles","pmids":["8383129"],"is_preprint":false},{"year":1992,"finding":"A yeast homolog of RING10 (PSMB8), PRG1, is essential for cell viability, indicating that the proteasome function of this subunit is required for basic cellular processes.","method":"Genomic disruption of PRG1 in yeast showing lethality","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic knockout with defined lethal phenotype, single study","pmids":["1452031"],"is_preprint":false},{"year":1993,"finding":"LMP7 (PSMB8) is synthesized as a proprotein (~30 kDa) and undergoes post-translational N-terminal cleavage to yield the mature 23 kDa subunit that is incorporated into the 20S proteasome complex.","method":"Pulse-chase experiments, Western blot, anti-proteasome and anti-LMP7 immunoprecipitation","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — pulse-chase directly demonstrated processing; independently confirmed by Glynne et al. 1993","pmids":["8365398","8458375"],"is_preprint":false},{"year":1993,"finding":"LMP7 protein undergoes post-translational cleavage of its N-terminus (pro-sequence) before incorporation into the proteasome, reducing from predicted ~30 kDa to 23 kDa; the cleaved form is the active proteasome subunit.","method":"Western blot of anti-proteasome immunoprecipitates, pulse-chase analysis","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical demonstration of proteolytic processing; corroborated by Frentzel et al. 1993","pmids":["8458375"],"is_preprint":false},{"year":1994,"finding":"LMP7 (PSMB8) transfection into lymphoblasts or HeLa cells increases the Vmax of 20S and 26S proteasomes for cleavage after hydrophobic and basic residues (chymotrypsin-like and trypsin-like activities) without affecting hydrolysis after acidic residues; the magnitude of activity change is proportional to the amount of LMP7 incorporated.","method":"Gene transfection, fluorogenic peptide substrate assays of isolated 20S and 26S proteasomes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic reconstitution with dose-response correlation, multiple cell lines","pmids":["7937744"],"is_preprint":false},{"year":1994,"finding":"LMP7 (PSMB8) and LMP2 are assembled into 20S proteasomes via 13-16S precursor complexes; pro-proteins of both subunits are processed within these preproteasome intermediates, and only the processed forms are part of active 20S proteasomes.","method":"Sedimentation analysis, pulse-chase labeling, immunoblotting of precursor and mature proteasome fractions","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical fractionation and pulse-chase showing ordered assembly, single lab with multiple orthogonal methods","pmids":["8120905"],"is_preprint":false},{"year":1995,"finding":"Incorporation of LMP7 (with or without LMP2) into 20S proteasomes alters cleavage site preference and changes the quality of peptide products generated from a defined polypeptide substrate (CMV IE pp89 25-mer), independently of IFN-gamma stimulation; both subunits together induce a drastic increase in positive cooperativity (Hill coefficient) between proteasome subunits.","method":"Stable transfection of LMP subunits, in vitro digestion of defined polypeptide, HPLC and mass spectrometry of cleavage products, fluorogenic substrate kinetics","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro digestion assay with mass spectrometric product identification and kinetic analysis, multiple subunit combinations tested","pmids":["7589133"],"is_preprint":false},{"year":1995,"finding":"The IFN-gamma-inducible 11S regulator (PA28) does not preferentially activate LMP7-containing proteasomes, but binding of PA28 to any proteasome preparation markedly changes the quality and quantity of peptide products; LMP7 content determines the cleavage product profile independently of PA28.","method":"Transfection of LMP subunits, in vitro 25-mer digestion with and without purified PA28, HPLC and electrospray mass spectrometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro assay with mass spectrometric product identification, negative result on PA28 selectivity clearly established","pmids":["7559557"],"is_preprint":false},{"year":1996,"finding":"LMP7 (PSMB8) replaces the constitutive subunit X (epsilon/β5c) upon IFN-gamma treatment; overexpression of X reduces hydrolysis after hydrophobic and basic residues—effects opposite to LMP7 transfection—demonstrating that loss of X contributes to the increased chymotryptic/tryptic activities seen after IFN-gamma induction.","method":"Gene transfection of subunit X into HeLa cells, fluorogenic peptide substrate assays, immunoblot quantification of subunit stoichiometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reciprocal gain/loss-of-function for both constitutive and inducible subunits with enzymatic readout","pmids":["8663318"],"is_preprint":false},{"year":1997,"finding":"LMP7 (PSMB8) is covalently labeled by active-site-directed radiolabeled chloromethane and diazomethane inhibitors of chymotrypsin-like activity, establishing LMP7 as a catalytic subunit that contributes to both trypsin-like and chymotrypsin-like proteasomal activities.","method":"Radiolabeled active-site inhibitor labeling of purified 20S and 26S proteasomes, RP-HPLC, SDS-PAGE, 2D-PAGE, immunoblotting with subunit-specific antibodies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — active-site labeling with blocking controls, two orthogonal separation methods for subunit identification","pmids":["9312091"],"is_preprint":false},{"year":2000,"finding":"The human proteasome maturation protein POMP (Ump1 homolog) is found only in 16S precursor complexes and not in mature 20S proteasomes; LMP7 propeptide deletion reduces incorporation efficiency and causes accumulation of precursor complexes with elevated POMP, indicating the propeptide assists maturation but is not strictly required for incorporation. An active-site threonine mutation does not affect LMP7 incorporation.","method":"2D gel analysis, subcellular fractionation, Northern blot, mutagenesis of LMP7 propeptide and active-site Thr, immunoblotting of precursor fractions in T2 cells","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with biochemical fractionation, multiple LMP7 mutant constructs tested","pmids":["10926487"],"is_preprint":false},{"year":2000,"finding":"Overexpression of LMP2, LMP7, and MECL-1 together (triple transfectants) in cells markedly enhances MHC class I-restricted presentation of the LCMV NP118 epitope; in vitro, immunoproteasomes generate higher amounts of 11- and 12-mer precursor fragments containing NP118 than constitutive proteasomes. PA28 overexpression does not produce a comparable enhancement.","method":"Triple transfection, CTL killing assay for antigen presentation, in vitro peptide digestion with HPLC analysis of products","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of peptide generation combined with functional antigen presentation assay","pmids":["10878350"],"is_preprint":false},{"year":2004,"finding":"HCV NS3 protein directly interacts with the pro-sequence region (amino acids 1-40) of LMP7 via its protease domain (confirmed by yeast two-hybrid and in vitro binding and co-IP); this interaction does not affect NS3 protease activity in vitro, but cells stably replicating HCV subgenomic replicon show markedly reduced LMP7 immunoproteasome peptidase activities.","method":"Yeast two-hybrid screen, in vitro binding assay, co-immunoprecipitation, domain mapping, fluorogenic peptidase activity assay in HCV replicon cell line","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — reciprocal binding confirmed by multiple methods, domain mapping performed, functional consequence measured","pmids":["15303969"],"is_preprint":false},{"year":2005,"finding":"IRF-1 is required for IFN-gamma-dependent LMP7 transcription; a tetracycline-inducible IRF-1 system induces LMP7 expression, a specific IRF-1-binding genomic region in the LMP7 locus was identified, and IRF-1 knockdown by siRNA as well as IRF-1-/- mice confirmed that IRF-1 is the master transcriptional regulator driving concerted immunoproteasome subunit expression.","method":"Tet-inducible IRF-1 expression, siRNA knockdown, IRF-1 knockout mice, genomic footprinting/reporter assay to map IRF-1 binding region","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal approaches (inducible OE, siRNA KD, KO mice) all converge on same conclusion","pmids":["15907481"],"is_preprint":false},{"year":2010,"finding":"LMP7 (PSMB8) deficiency in mice results in significantly attenuated dextran sodium sulfate-induced colitis due to reduced NF-κB signaling; this is mechanistically linked to reduced secretion of proinflammatory cytokines and chemokines, decreased neutrophil infiltration, and diminished Th1/Th17 expansion.","method":"lmp7-/- mouse model, DSS colitis induction, NF-κB pathway analysis, cytokine/chemokine measurement, histological analysis","journal":"Gut","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined mechanistic pathway (NF-κB) and multiple phenotypic readouts, replicated with pharmacological inhibitor bortezomib","pmids":["20581238"],"is_preprint":false},{"year":2010,"finding":"A homozygous missense mutation (Thr75Met) in PSMB8 causes JMP syndrome; the mutation disrupts the tertiary structure of β5i and results in significantly reduced chymotrypsin-like proteolytic activity of immunoproteasomes in patient lymphoblasts compared to normal cells.","method":"Homozygosity mapping, direct sequencing, structural modeling, immunoproteasome chymotryptic activity assay in patient vs. normal lymphoblasts","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — biochemical activity assay in patient cells with structural modeling, causative mutation confirmed by segregation","pmids":["21129723"],"is_preprint":false},{"year":2011,"finding":"A G201V mutation in PSMB8 (β5i) in Nakajo-Nishimura syndrome disrupts the β-sheet structure near the catalytic threonine, prevents efficient incorporation of β5i into immunoproteasome precursors, reduces total proteasome activity, and causes accumulation of ubiquitinated and oxidized proteins; this leads to increased IL-6 and IP-10 secretion and elevated p38 phosphorylation.","method":"Structural analysis (mutation position modeling), immunoproteasome assembly assay, proteasome activity assay, ubiquitinated/oxidized protein accumulation assay, cytokine ELISA, phospho-p38 immunoblot in patient cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal biochemical assays in patient cells with structural context, independent replication across pedigrees","pmids":["21852578"],"is_preprint":false},{"year":2011,"finding":"A G197V mutation in PSMB8 increases assembly intermediates of immunoproteasomes, decreases proteasome function, causes ubiquitin-coupled protein accumulation, and leads to increased IL-6 expression in patient skin and B cells; PSMB8 knockdown inhibits murine and human adipocyte differentiation in vitro, and siRNA injection against Psmb8 in mouse skin reduces adipocyte tissue volume.","method":"Exome sequencing, proteasome activity assay, ubiquitin accumulation immunoblot, siRNA knockdown of Psmb8 in mouse skin/adipocyte differentiation assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biochemical, cell-based, in vivo siRNA), functional consequence of PSMB8 loss on adipogenesis directly demonstrated","pmids":["21881205"],"is_preprint":false},{"year":2011,"finding":"β5i/LMP7 deficiency in mice leads to impaired immunoproteasome function, failure to clear poly-ubiquitinated protein aggregates in cytokine-stressed cardiomyocytes during CVB3 myocarditis, impaired NF-κB activation, and increased apoptotic cell death, resulting in exacerbated acute myocardial damage despite identical viral load.","method":"β5i/LMP7 knockout mice, CVB3 infection model, ubiquitinated aggregate detection, NF-κB activation assay, apoptosis quantification, adoptive T cell transfer","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple mechanistic readouts (protein aggregate clearance, NF-κB, apoptosis) in vivo","pmids":["21909276"],"is_preprint":false},{"year":2012,"finding":"LMP7 propeptide (proLMP7) shows significantly higher chaperone activity than the β5 propeptide (proβ5) in promoting proteasome maturation; proLMP7 promotes integration of both immunosubunits and mixed proteasomes, and increased efficiency of proteasome maturation by proLMP7 is required for optimal MHC class I surface expression. LMP7 induction also increases total proteasome abundance in infected tissue.","method":"LMP7-deficient mouse infection model, IFNγ stimulation experiments, subunit integration assays, proteasome maturation kinetics, MHC class I surface expression by flow cytometry","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple experimental approaches in both cell culture and in vivo, functional MHC class I readout","pmids":["22768135"],"is_preprint":false},{"year":2012,"finding":"LMP7 deficiency or selective inhibition suppresses Th17 and Th1 differentiation while promoting regulatory T cell (Treg) development; mechanistically, LMP7 inhibition blocks STAT3 phosphorylation in developing Th17 cells and enhances SMAD phosphorylation in Tregs, and reduces STAT1 phosphorylation in Th1 cells.","method":"LMP7-/- CD4+ T cells and ONX 0914-treated WT T cells under polarizing conditions, phospho-STAT3/SMAD/STAT1 immunoblot, DSS colitis and T cell transfer colitis models in vivo","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO and pharmacological inhibition converge, mechanistic pathway (STAT3, SMAD, STAT1 phosphorylation) identified, confirmed in vivo","pmids":["22984077"],"is_preprint":false},{"year":2014,"finding":"X-ray crystal structures of murine constitutive and immunoproteasome 20S core particles informed rational design of β5i (LMP7)-selective inhibitors; structural differences in the S1 pocket between β5c and β5i were exploited to achieve cell-permeable inhibitors with high selectivity.","method":"Structure-based drug design using X-ray crystallography of 20S proteasome complexes, selectivity profiling across all proteasome subunits","journal":"Journal of medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with functional inhibitor validation, selectivity profiling across multiple subunits","pmids":["25006746"],"is_preprint":false},{"year":2016,"finding":"miR-451 directly targets LMP7 (PSMB8) 3′UTR to suppress LMP7 expression, thereby inhibiting NF-κB activity and reducing proinflammatory cytokine transcription in mesangial cells; in db/db diabetic mice, increasing miR-451 inhibited LMP7/NF-κB and attenuated glomerular injury.","method":"Deep sequencing, dual-luciferase reporter assay, Western blot, chromatin immunoprecipitation, in vivo miR-451 overexpression in db/db mice","journal":"Molecular and cellular endocrinology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct 3′UTR targeting validated by luciferase reporter, confirmed in vivo, NF-κB pathway link established by ChIP","pmids":["27264074"],"is_preprint":false},{"year":2018,"finding":"Co-inhibition of both LMP7 and LMP2 (but not LMP7 alone) is required to impair MHC class I surface expression, suppress IL-6 secretion, block Th17 differentiation, and strongly ameliorate experimental colitis and EAE; prolonged ONX 0914 exposure inhibits both subunits, explaining its efficacy.","method":"Selective LMP7 inhibitor PRN1126 vs. ONX 0914 comparison, LMP2+LMP7 dual inhibitor combination, DSS colitis, EAE models, IL-6 ELISA, MHC class I flow cytometry","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple pharmacological tools with defined selectivity profiles, in vivo disease models, multiple functional readouts","pmids":["30279279"],"is_preprint":false},{"year":2019,"finding":"β5i (PSMB8) interacts with ATG5, promoting its degradation, thereby inhibiting autophagy and driving pathological cardiac hypertrophy; β5i knockout attenuates hypertrophy, and ATG5 knockdown or autophagy inhibition reverses the β5i-KO protection.","method":"β5i KO and transgenic overexpression mice, Ang II-induced hypertrophy model, Co-IP (β5i–ATG5 interaction), ATG5 degradation assay, autophagic flux assays, genetic epistasis (ATG5 KD + β5i KO)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP for substrate identification, genetic epistasis confirming pathway order, in vivo KO and transgenic models with defined phenotype","pmids":["31086810"],"is_preprint":false},{"year":2019,"finding":"β5i (PSMB8) promotes ATRAP (AT1R-associated protein) degradation in atrial tissue; β5i upregulation by Ang II leads to ATRAP degradation, resulting in AT1R-mediated NF-κB activation, increased NADPH oxidase activity, TGF-β1/Smad signaling, and altered ion channel expression (Kir2.1, CX43), thereby driving atrial fibrillation.","method":"β5i KO and AAV9-β5i overexpression mice, Ang II infusion AF model, ATRAP co-IP and degradation assay, ATRAP overexpression rescue, NF-κB and TGF-β pathway assays","journal":"Hypertension","confidence":"High","confidence_rationale":"Tier 2 / Strong — substrate identified by Co-IP, validated by rescue experiment with ATRAP overexpression, in vivo KO and OE with functional AF readout","pmids":["30571551"],"is_preprint":false},{"year":2019,"finding":"β5i (PSMB8) promotes ATRAP degradation in the retina; β5i KO restores Ang II-induced downregulation of ATRAP and attenuates AT1R-mediated downstream signaling, thereby reducing hypertensive retinopathy, while adenoviral β5i overexpression aggravates the phenotype.","method":"β5i KO and Ad-β5i overexpression mice, Ang II infusion retinopathy model, ATRAP degradation assay, AT1R downstream signaling analysis, ATRAP overexpression rescue","journal":"Molecular therapy","confidence":"High","confidence_rationale":"Tier 2 / Moderate — same ATRAP substrate as parallel cardiac study, confirmed by complementary genetic approaches and rescue experiment","pmids":["31636038"],"is_preprint":false},{"year":2019,"finding":"β5i (PSMB8) promotes PTEN degradation in DOCA-salt hypertensive hearts; β5i KO attenuates cardiac remodeling by restoring PTEN levels, and PTEN blockade reverses the protective effects of β5i KO, placing PTEN as a key substrate whose stability is regulated by β5i-dependent proteasomal degradation.","method":"β5i KO mice and PR-957 pharmacological inhibition, DOCA-salt hypertension model, PTEN degradation assay, AKT/mTOR/TGF-β/NF-κB pathway analysis, VO-OHpic rescue experiment","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO and pharmacological inhibition converge, PTEN substrate confirmed by rescue with PTEN inhibitor","pmids":["31629736"],"is_preprint":false},{"year":2020,"finding":"β5i (PSMB8) promotes atherosclerosis by targeting MERTK for degradation via NF-κB-dependent suppression of Mertk transcription; β5i deletion reduces IκBα degradation, inhibits NF-κB, increases MERTK expression, and enhances efferocytosis of apoptotic cells in atherosclerotic lesions.","method":"β5i/Apoe double KO mice, bone marrow transplantation, ATD-fed mouse atherosclerosis model, efferocytosis assay, MERTK expression, IκBα/NF-κB pathway analysis, PR-957 pharmacological treatment","journal":"The Journal of pathology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic approaches (full KO, bone marrow chimera) plus pharmacological validation, mechanistic pathway (NF-κB→MERTK→efferocytosis) defined","pmids":["31758542"],"is_preprint":false},{"year":2020,"finding":"β5i (PSMB8) promotes macrophage pyroptosis during abdominal aortic aneurysm formation via activation of NF-κB and upregulation of NLRP3; β5i inhibition or knockout decreases macrophage pyroptosis and AAA severity through the IκB/NF-κB pathway.","method":"β5i KO mice, PR-957 treatment, AAA mouse model, pyroptosis markers in tissue and BMDMs, OXLDL stimulation, NF-κB/NLRP3 pathway analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO and pharmacological inhibition, mechanistic pathway identified, single lab","pmids":["33019975"],"is_preprint":false},{"year":2021,"finding":"M3258, an orally bioavailable, reversible, highly selective LMP7 (β5i) inhibitor, was developed through structure-based optimization using X-ray crystal structures; it demonstrates potent suppression of LMP7 activity, ubiquitinated protein turnover, and induces apoptosis in multiple myeloma cells in vitro and in vivo.","method":"Structure-based drug design (X-ray crystallography), selectivity profiling, multiple myeloma xenograft models, ubiquitin turnover assay, apoptosis assay","journal":"Journal of medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus in vivo functional validation in multiple xenograft models","pmids":["34228444"],"is_preprint":false},{"year":2018,"finding":"Lmp7 (PSMB8) levels and activity are significantly increased in a mouse model of α-synuclein aggregation and in post-mortem human PD and dementia with Lewy bodies brains; the immunoproteasome degrades α-synuclein aggregates and generates potentially antigenic peptides from them.","method":"Quantitative proteomics (6215 proteins), immunoproteasome activity assay in mouse model and human post-mortem tissue, α-synuclein aggregate degradation assay","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomic quantification and activity assay both in animal model and human tissue, aggregate degradation directly measured","pmids":["29759483"],"is_preprint":false},{"year":2017,"finding":"LMP7 is required in radioresistant thymic cells (likely mTECs) to prevent excessive negative selection of GP118-125-specific T cell precursors; LMP7-deficient mice completely lack GP118-125-specific CD8+ T cells, which is restored by bone marrow chimeras showing LMP7 requirement in non-hematopoietic cells.","method":"LMP7 KO mice, LCMV infection model, bone marrow chimera generation, adoptive transfer of LMP7-deficient CD8+ T cells into RAG1-/- mice, tetramer staining","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — bone marrow chimeras and adoptive transfer definitively localize LMP7 requirement to radioresistant cells, multiple epistasis experiments","pmids":["29067678"],"is_preprint":false},{"year":2022,"finding":"PSMB8 (β5i) expression is upregulated in manganese-exposed microglia via PERK signaling; selective PSMB8 inhibition reduces neuroinflammation (TNF-α, iNOS, CCL12 production, microglial activation) and inhibition of PSMB8 reduces NF-κB p65 phosphorylation, placing PSMB8 in a PERK/NF-κB signaling axis during Mn neurotoxicity.","method":"In vivo Mn exposure mouse model, BV2 cell culture, selective PSMB8 inhibitor treatment, PERK inhibitor, NF-κB pathway analysis, learning/memory tests, Golgi staining","journal":"Food and chemical toxicology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition of PSMB8 and upstream PERK, in vivo and in vitro, multiple inflammatory readouts; single lab","pmids":["35378207"],"is_preprint":false},{"year":2018,"finding":"Apelin inhibits epithelial-mesenchymal transition (EMT) of podocytes in diabetic mice through downregulation of β5i expression; β5i KO mice confirmed the dependence of apelin's anti-EMT effect on β5i; mechanistically, apelin decreases β5i expression, which reduces degradation of pIκB, promotes IκB nuclear translocation, inhibits NF-κB-driven TGF-β expression, and decreases Smad pathway activation.","method":"β5i KO mice, diabetic mouse model, apelin treatment, pIκB degradation assay, IκB localization, TGF-β/Smad pathway analysis","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO confirms β5i requirement, mechanistic pathway (IκB/NF-κB/TGF-β) established in vivo and in vitro, single lab","pmids":["30301930"],"is_preprint":false}],"current_model":"PSMB8 (LMP7/β5i) is an IFN-γ-inducible catalytic subunit of the 20S immunoproteasome, synthesized as a proprotein that is processed within precursor complexes (its propeptide acting as a chaperone for efficient maturation) and incorporated into the 20S ring where its active-site threonine confers chymotrypsin-like (and contributes to trypsin-like) proteolytic activity; it shifts cleavage specificity toward hydrophobic/basic C-termini to optimize MHC class I antigenic peptide generation, and beyond antigen presentation it targets specific substrates (ATG5, ATRAP, PTEN) for degradation to regulate autophagy, angiotensin signaling, cardiac hypertrophy, atrial fibrillation, and vascular inflammation, while also modulating NF-κB and STAT signaling to control Th1/Th17 differentiation, cytokine production, and tissue homeostasis."},"narrative":{"mechanistic_narrative":"PSMB8 (LMP7/β5i) is the IFN-γ-inducible catalytic subunit of the 20S immunoproteasome, where its active-site threonine confers chymotrypsin-like and contributes to trypsin-like peptide-bond cleavage [PMID:7937744, PMID:9312091]. Its yeast ortholog PRE2 is the proteasomal subunit responsible for chymotryptic activity, loss of which abolishes that activity and causes accumulation of ubiquitinated proteins [PMID:8383129]. PSMB8 is synthesized as a ~30 kDa proprotein whose N-terminal pro-sequence is cleaved within 13–16S precursor complexes to yield the mature 23 kDa subunit incorporated into the 20S ring, with the propeptide acting as a more efficient maturation chaperone than the constitutive β5 propeptide and POMP restricted to precursor intermediates [PMID:8365398, PMID:8458375, PMID:8120905, PMID:10926487, PMID:22768135]. Upon IFN-γ induction—driven transcriptionally by IRF-1—PSMB8 replaces the constitutive subunit X/β5c, shifting cleavage preference toward hydrophobic and basic C-termini and altering the quality of peptide products to optimize generation of MHC class I antigenic peptides [PMID:8663318, PMID:15907481, PMID:7589133, PMID:7559557, PMID:10878350]. This antigen-processing role extends to shaping T cell selection in radioresistant thymic cells [PMID:29067678]. Beyond antigen presentation, PSMB8 controls inflammatory signaling: its activity sustains NF-κB activation and skews CD4 T cell differentiation toward Th1/Th17 over Treg by modulating STAT3, STAT1, and SMAD phosphorylation [PMID:20581238, PMID:22984077]. In cardiovascular and metabolic disease, PSMB8 targets specific substrates for degradation—ATG5 to suppress autophagy and drive cardiac hypertrophy, ATRAP to potentiate AT1R signaling in atrial fibrillation and hypertensive retinopathy, PTEN in hypertensive cardiac remodeling, and MERTK (via NF-κB) to impair efferocytosis in atherosclerosis [PMID:31086810, PMID:30571551, PMID:31636038, PMID:31629736, PMID:31758542]. Causative PSMB8 mutations that disrupt β5i structure and immunoproteasome assembly/activity (Thr75Met in JMP syndrome; G201V in Nakajo-Nishimura syndrome; G197V) produce autoinflammatory syndromes with accumulation of ubiquitinated proteins and elevated proinflammatory cytokines [PMID:21129723, PMID:21852578, PMID:21881205]. Structure-based design exploiting the β5i S1 pocket has yielded selective inhibitors with anti-inflammatory and anti-myeloma activity [PMID:25006746, PMID:34228444, PMID:30279279].","teleology":[{"year":1993,"claim":"Established that this proteasome β-subunit is the catalytic component responsible for chymotrypsin-like activity, defining its core enzymatic identity.","evidence":"Genetic complementation and loss-of-function of the homologous yeast PRE2 gene with proteasome activity and ubiquitin-accumulation assays","pmids":["8383129"],"confidence":"High","gaps":["Inference from yeast ortholog rather than direct human PSMB8 catalysis","Did not address immunoproteasome-specific cleavage preferences"]},{"year":1992,"claim":"Showed the proteasomal function of this subunit is essential for viability in yeast.","evidence":"Genomic disruption of the yeast homolog PRG1 showing lethality","pmids":["1452031"],"confidence":"Medium","gaps":["Essentiality refers to yeast, not the IFN-γ-inducible human subunit","Single study"]},{"year":1993,"claim":"Defined PSMB8 as a proprotein that is N-terminally processed from ~30 kDa to a mature 23 kDa form before incorporation, establishing the maturation logic of the subunit.","evidence":"Pulse-chase, immunoprecipitation, and Western blot of proteasome preparations (two independent reports)","pmids":["8365398","8458375"],"confidence":"High","gaps":["Did not identify the protease/mechanism of propeptide cleavage","Functional role of the propeptide not yet defined"]},{"year":1994,"claim":"Demonstrated that incorporation of PSMB8 raises proteasomal chymotrypsin- and trypsin-like activities in dose-dependent fashion and that assembly proceeds via precursor complexes with intra-precursor processing.","evidence":"Gene transfection with fluorogenic substrate kinetics; sedimentation and pulse-chase fractionation of precursor and mature complexes","pmids":["7937744","8120905"],"confidence":"High","gaps":["Active-site residue not yet directly implicated","Substrate range limited to model fluorogenic peptides"]},{"year":1995,"claim":"Showed PSMB8 incorporation alters cleavage-site specificity and the quality of peptide products from defined polypeptides independent of IFN-γ and of PA28 selectivity, linking the subunit to antigenic peptide repertoire.","evidence":"Stable LMP transfection with in vitro digestion of a defined 25-mer, HPLC/mass spectrometry of products, and PA28 reconstitution","pmids":["7589133","7559557"],"confidence":"High","gaps":["MHC class I presentation not yet directly measured","Cooperativity mechanism between subunits unresolved"]},{"year":1996,"claim":"Established that IFN-γ-induced activity changes arise from PSMB8 replacing the constitutive subunit X/β5c, via reciprocal gain/loss-of-function.","evidence":"Reciprocal transfection of subunit X and PSMB8 in HeLa cells with fluorogenic activity assays and stoichiometry immunoblots","pmids":["8663318"],"confidence":"High","gaps":["Did not map structural basis of differential specificity","Whole-substrate consequences of subunit swap not assessed here"]},{"year":1997,"claim":"Confirmed PSMB8 is itself a catalytic subunit by direct active-site labeling.","evidence":"Radiolabeled active-site-directed inhibitor labeling of purified 20S/26S proteasomes with subunit identification by 2D-PAGE and immunoblot","pmids":["9312091"],"confidence":"High","gaps":["Did not define which residue side-chains shape the S1 pocket","Relative contribution to trypsin- vs chymotrypsin-like activity not quantified"]},{"year":2000,"claim":"Resolved the propeptide's role in maturation—assisting incorporation efficiency but not strictly required—and placed POMP in precursor complexes only.","evidence":"Propeptide and active-site Thr mutagenesis with 2D gel/fractionation and POMP immunoblotting in T2 cells","pmids":["10926487"],"confidence":"High","gaps":["Chaperone strength of the propeptide relative to β5 not yet compared","Active-site Thr role in catalysis vs incorporation only partly separated"]},{"year":2000,"claim":"Linked PSMB8-containing immunoproteasomes to enhanced MHC class I presentation of a defined epitope.","evidence":"Triple LMP transfection with CTL killing assay and in vitro epitope-precursor digestion analysis","pmids":["10878350"],"confidence":"High","gaps":["Contribution of PSMB8 alone vs the triplet not isolated","Did not address presentation breadth genome-wide"]},{"year":2004,"claim":"Identified a viral strategy targeting PSMB8 maturation, showing HCV NS3 binds the propeptide region and reduces immunoproteasome peptidase activity.","evidence":"Yeast two-hybrid, in vitro binding, co-IP, domain mapping, and peptidase assays in HCV replicon cells","pmids":["15303969"],"confidence":"High","gaps":["Mechanism by which propeptide binding lowers activity not defined","In vivo immune-evasion consequence not tested"]},{"year":2005,"claim":"Identified IRF-1 as the master transcriptional driver of IFN-γ-dependent PSMB8 and coordinate immunoproteasome subunit expression.","evidence":"Tet-inducible IRF-1, siRNA knockdown, IRF-1 knockout mice, and genomic binding-site mapping","pmids":["15907481"],"confidence":"High","gaps":["Other cooperating transcription factors not delineated","Cell-type-specific regulation not addressed"]},{"year":2010,"claim":"Connected PSMB8 to NF-κB-driven mucosal inflammation, establishing an immune-effector role beyond antigen processing.","evidence":"lmp7-/- mice in DSS colitis with NF-κB, cytokine, and Th1/Th17 analyses, plus bortezomib replication","pmids":["20581238"],"confidence":"High","gaps":["Direct molecular substrate linking PSMB8 to NF-κB not identified here","Bortezomib is non-selective"]},{"year":2010,"claim":"Identified PSMB8 mutations as causative for human autoinflammatory syndromes (JMP, Nakajo-Nishimura) by disrupting β5i structure, assembly, and proteolytic activity.","evidence":"Homozygosity/exome mapping, structural modeling, immunoproteasome activity and assembly assays, and cytokine measurements in patient cells; in vivo siRNA adipocyte studies","pmids":["21129723","21852578","21881205"],"confidence":"High","gaps":["Precise substrate(s) whose mishandling drives cytokine elevation not defined","Adipocyte differentiation mechanism partly correlative"]},{"year":2011,"claim":"Demonstrated PSMB8 is protective in stressed tissue, clearing ubiquitinated aggregates and supporting NF-κB-dependent survival during viral myocarditis.","evidence":"β5i knockout mice in CVB3 myocarditis with aggregate, NF-κB, and apoptosis readouts and adoptive T cell transfer","pmids":["21909276"],"confidence":"High","gaps":["Context-dependence of NF-κB outcomes (protective vs pathogenic) unresolved","Substrate underlying aggregate clearance not specified"]},{"year":2012,"claim":"Showed the PSMB8 propeptide is a superior maturation chaperone required for optimal MHC class I surface expression, mechanistically linking maturation efficiency to immune function.","evidence":"LMP7-deficient mouse infection, subunit integration assays, maturation kinetics, and MHC class I flow cytometry","pmids":["22768135"],"confidence":"High","gaps":["Structural basis of enhanced chaperone activity not resolved","Quantitative contribution to total proteasome pool tissue-dependent"]},{"year":2012,"claim":"Defined a mechanism for PSMB8 control of T helper fate via STAT3/STAT1/SMAD phosphorylation balancing Th17/Th1 versus Treg.","evidence":"LMP7-/- and ONX 0914-treated CD4+ T cells under polarizing conditions with phospho-immunoblots and in vivo colitis models","pmids":["22984077"],"confidence":"High","gaps":["Direct proteasomal substrate controlling STAT phosphorylation not identified","ONX 0914 selectivity caveat (see 2018 finding)"]},{"year":2014,"claim":"Provided the structural basis for selective β5i inhibition by exploiting S1-pocket differences between β5c and β5i.","evidence":"X-ray crystallography of constitutive and immunoproteasome 20S cores with inhibitor selectivity profiling","pmids":["25006746"],"confidence":"High","gaps":["Did not address in vivo target engagement or off-subunit effects at higher exposure","Structure of human β5i not the species crystallized"]},{"year":2018,"claim":"Localized a non-hematopoietic PSMB8 requirement in thymic stromal cells preventing excessive negative selection, refining its role in T cell repertoire shaping.","evidence":"LMP7 KO mice with LCMV infection, bone marrow chimeras, adoptive transfer, and tetramer staining","pmids":["29067678"],"confidence":"High","gaps":["Specific self-peptides altered by PSMB8 loss not identified","mTEC identity inferred"]},{"year":2018,"claim":"Implicated PSMB8 in neurodegenerative protein aggregation, showing increased immunoproteasome activity that degrades α-synuclein aggregates.","evidence":"Quantitative proteomics and activity assays in α-synuclein mouse model and human PD/DLB brain with aggregate degradation assay","pmids":["29759483"],"confidence":"Medium","gaps":["Causal versus reactive role of PSMB8 upregulation unresolved","Single-lab observation"]},{"year":2018,"claim":"Linked PSMB8 to podocyte EMT via IκB/NF-κB/TGF-β signaling in diabetic kidney, downstream of apelin.","evidence":"β5i KO mice with apelin treatment and IκB/NF-κB/TGF-β/Smad pathway analyses","pmids":["30301930"],"confidence":"Medium","gaps":["Direct PSMB8 substrate in this axis not identified","Single lab"]},{"year":2019,"claim":"Identified specific PSMB8 degradation substrates (ATG5, ATRAP, PTEN) explaining its role in autophagy suppression, AT1R signaling, and cardiovascular remodeling.","evidence":"β5i KO and overexpression mice across hypertrophy/AF/retinopathy/hypertension models with Co-IP, degradation assays, and substrate-rescue epistasis","pmids":["31086810","30571551","31636038","31629736"],"confidence":"High","gaps":["How an immunoproteasome subunit acquires substrate specificity for these targets mechanistically unclear","Co-IP-based interactions without structural detail"]},{"year":2020,"claim":"Extended PSMB8's NF-κB-coupled disease role to atherosclerosis (MERTK/efferocytosis) and aortic aneurysm (NLRP3 pyroptosis).","evidence":"β5i/Apoe double KO, bone marrow chimeras, and PR-957 in atherosclerosis and AAA models with efferocytosis and pyroptosis readouts","pmids":["31758542","33019975"],"confidence":"Medium","gaps":["MERTK regulation is transcriptional (via NF-κB) rather than direct degradation","AAA finding single lab"]},{"year":2021,"claim":"Advanced selective PSMB8 inhibitors as therapeutics, including an oral agent active against multiple myeloma, and clarified that dual β5i/β2i inhibition underlies some immunomodulatory efficacy.","evidence":"Structure-based inhibitor design (M3258) with myeloma xenografts; comparison of selective PRN1126 vs ONX 0914 in colitis/EAE","pmids":["34228444","30279279"],"confidence":"High","gaps":["Therapeutic window of pure β5i inhibition in autoinflammation uncertain","Long-term safety of immunoproteasome inhibition not addressed"]},{"year":2022,"claim":"Placed PSMB8 in a PERK/NF-κB neuroinflammatory axis in manganese-exposed microglia.","evidence":"In vivo Mn exposure and BV2 cells with selective PSMB8 and PERK inhibitors and NF-κB analysis","pmids":["35378207"],"confidence":"Medium","gaps":["Direct substrate connecting PERK to PSMB8 to NF-κB not identified","Single lab"]},{"year":null,"claim":"It remains unresolved how an immunoproteasome catalytic subunit achieves selective targeting of individual substrates (ATG5, ATRAP, PTEN) and tilts NF-κB outcomes in a tissue-specific, sometimes opposing (protective vs pathogenic), manner.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Structural/biochemical basis of substrate selectivity beyond bulk proteolysis unknown","Mechanism switching PSMB8 between protective aggregate-clearance and pathogenic substrate degradation undefined","Direct degradation versus indirect transcriptional effects not always distinguished"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,4,6,9]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[4,9,15]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[10,19]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,4,5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[11,14,20,32]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,20,24,25,28]}],"complexes":["20S immunoproteasome","20S proteasome core particle","16S immunoproteasome precursor complex"],"partners":["POMP","PSMB9","ATG5","ATRAP","PTEN","IRF1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P28062","full_name":"Proteasome subunit beta type-8","aliases":["Low molecular mass protein 7","Macropain subunit C13","Multicatalytic endopeptidase complex subunit C13","Proteasome component C13","Proteasome subunit beta-5i","Really interesting new gene 10 protein"],"length_aa":276,"mass_kda":30.4,"function":"The proteasome is a multicatalytic proteinase complex which is characterized by its ability to cleave peptides with Arg, Phe, Tyr, Leu, and Glu adjacent to the leaving group at neutral or slightly basic pH. The proteasome has an ATP-dependent proteolytic activity. This subunit is involved in antigen processing to generate class I binding peptides. Replacement of PSMB5 by PSMB8 increases the capacity of the immunoproteasome to cleave model peptides after hydrophobic and basic residues. Involved in the generation of spliced peptides resulting from the ligation of two separate proteasomal cleavage products that are not contiguous in the parental protein (PubMed:27049119). Acts as a major component of interferon gamma-induced sensitivity. Plays a key role in apoptosis via the degradation of the apoptotic inhibitor MCL1. May be involved in the inflammatory response pathway. In cancer cells, substitution of isoform 1 (E2) by isoform 2 (E1) results in immunoproteasome deficiency. Required for the differentiation of preadipocytes into adipocytes","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P28062/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PSMB8","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PSMB8","total_profiled":1310},"omim":[{"mim_id":"618048","title":"PROTEASOME-ASSOCIATED AUTOINFLAMMATORY SYNDROME 2; PRAAS2","url":"https://www.omim.org/entry/618048"},{"mim_id":"611137","title":"PROTEASOME SUBUNIT, BETA-TYPE, 11; PSMB11","url":"https://www.omim.org/entry/611137"},{"mim_id":"609648","title":"NLR FAMILY, PYRIN DOMAIN-CONTAINING 12; NLRP12","url":"https://www.omim.org/entry/609648"},{"mim_id":"607319","title":"SCM-LIKE PROTEIN WITH 4 MBT DOMAINS 1; SFMBT1","url":"https://www.omim.org/entry/607319"},{"mim_id":"602177","title":"PROTEASOME SUBUNIT, BETA-TYPE, 4; PSMB4","url":"https://www.omim.org/entry/602177"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Cytokinetic bridge","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PSMB8"},"hgnc":{"alias_symbol":["RING10","D6S216E","PSMB5i","beta5i"],"prev_symbol":["LMP7"]},"alphafold":{"accession":"P28062","domains":[{"cath_id":"3.60.20.10","chopping":"74-274","consensus_level":"high","plddt":95.4069,"start":74,"end":274}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P28062","model_url":"https://alphafold.ebi.ac.uk/files/AF-P28062-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P28062-F1-predicted_aligned_error_v6.png","plddt_mean":83.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PSMB8","jax_strain_url":"https://www.jax.org/strain/search?query=PSMB8"},"sequence":{"accession":"P28062","fasta_url":"https://rest.uniprot.org/uniprotkb/P28062.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P28062/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P28062"}},"corpus_meta":[{"pmid":"7937744","id":"PMC_7937744","title":"Peptidase 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indicating that the proteasome function of this subunit is required for basic cellular processes.\",\n      \"method\": \"Genomic disruption of PRG1 in yeast showing lethality\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic knockout with defined lethal phenotype, single study\",\n      \"pmids\": [\"1452031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"LMP7 (PSMB8) is synthesized as a proprotein (~30 kDa) and undergoes post-translational N-terminal cleavage to yield the mature 23 kDa subunit that is incorporated into the 20S proteasome complex.\",\n      \"method\": \"Pulse-chase experiments, Western blot, anti-proteasome and anti-LMP7 immunoprecipitation\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — pulse-chase directly demonstrated processing; independently confirmed by Glynne et al. 1993\",\n      \"pmids\": [\"8365398\", \"8458375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"LMP7 protein undergoes post-translational cleavage of its N-terminus (pro-sequence) before incorporation into the proteasome, reducing from predicted ~30 kDa to 23 kDa; the cleaved form is the active proteasome subunit.\",\n      \"method\": \"Western blot of anti-proteasome immunoprecipitates, pulse-chase analysis\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical demonstration of proteolytic processing; corroborated by Frentzel et al. 1993\",\n      \"pmids\": [\"8458375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"LMP7 (PSMB8) transfection into lymphoblasts or HeLa cells increases the Vmax of 20S and 26S proteasomes for cleavage after hydrophobic and basic residues (chymotrypsin-like and trypsin-like activities) without affecting hydrolysis after acidic residues; the magnitude of activity change is proportional to the amount of LMP7 incorporated.\",\n      \"method\": \"Gene transfection, fluorogenic peptide substrate assays of isolated 20S and 26S proteasomes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic reconstitution with dose-response correlation, multiple cell lines\",\n      \"pmids\": [\"7937744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"LMP7 (PSMB8) and LMP2 are assembled into 20S proteasomes via 13-16S precursor complexes; pro-proteins of both subunits are processed within these preproteasome intermediates, and only the processed forms are part of active 20S proteasomes.\",\n      \"method\": \"Sedimentation analysis, pulse-chase labeling, immunoblotting of precursor and mature proteasome fractions\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical fractionation and pulse-chase showing ordered assembly, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"8120905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Incorporation of LMP7 (with or without LMP2) into 20S proteasomes alters cleavage site preference and changes the quality of peptide products generated from a defined polypeptide substrate (CMV IE pp89 25-mer), independently of IFN-gamma stimulation; both subunits together induce a drastic increase in positive cooperativity (Hill coefficient) between proteasome subunits.\",\n      \"method\": \"Stable transfection of LMP subunits, in vitro digestion of defined polypeptide, HPLC and mass spectrometry of cleavage products, fluorogenic substrate kinetics\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro digestion assay with mass spectrometric product identification and kinetic analysis, multiple subunit combinations tested\",\n      \"pmids\": [\"7589133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The IFN-gamma-inducible 11S regulator (PA28) does not preferentially activate LMP7-containing proteasomes, but binding of PA28 to any proteasome preparation markedly changes the quality and quantity of peptide products; LMP7 content determines the cleavage product profile independently of PA28.\",\n      \"method\": \"Transfection of LMP subunits, in vitro 25-mer digestion with and without purified PA28, HPLC and electrospray mass spectrometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro assay with mass spectrometric product identification, negative result on PA28 selectivity clearly established\",\n      \"pmids\": [\"7559557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"LMP7 (PSMB8) replaces the constitutive subunit X (epsilon/β5c) upon IFN-gamma treatment; overexpression of X reduces hydrolysis after hydrophobic and basic residues—effects opposite to LMP7 transfection—demonstrating that loss of X contributes to the increased chymotryptic/tryptic activities seen after IFN-gamma induction.\",\n      \"method\": \"Gene transfection of subunit X into HeLa cells, fluorogenic peptide substrate assays, immunoblot quantification of subunit stoichiometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reciprocal gain/loss-of-function for both constitutive and inducible subunits with enzymatic readout\",\n      \"pmids\": [\"8663318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"LMP7 (PSMB8) is covalently labeled by active-site-directed radiolabeled chloromethane and diazomethane inhibitors of chymotrypsin-like activity, establishing LMP7 as a catalytic subunit that contributes to both trypsin-like and chymotrypsin-like proteasomal activities.\",\n      \"method\": \"Radiolabeled active-site inhibitor labeling of purified 20S and 26S proteasomes, RP-HPLC, SDS-PAGE, 2D-PAGE, immunoblotting with subunit-specific antibodies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — active-site labeling with blocking controls, two orthogonal separation methods for subunit identification\",\n      \"pmids\": [\"9312091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The human proteasome maturation protein POMP (Ump1 homolog) is found only in 16S precursor complexes and not in mature 20S proteasomes; LMP7 propeptide deletion reduces incorporation efficiency and causes accumulation of precursor complexes with elevated POMP, indicating the propeptide assists maturation but is not strictly required for incorporation. An active-site threonine mutation does not affect LMP7 incorporation.\",\n      \"method\": \"2D gel analysis, subcellular fractionation, Northern blot, mutagenesis of LMP7 propeptide and active-site Thr, immunoblotting of precursor fractions in T2 cells\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with biochemical fractionation, multiple LMP7 mutant constructs tested\",\n      \"pmids\": [\"10926487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Overexpression of LMP2, LMP7, and MECL-1 together (triple transfectants) in cells markedly enhances MHC class I-restricted presentation of the LCMV NP118 epitope; in vitro, immunoproteasomes generate higher amounts of 11- and 12-mer precursor fragments containing NP118 than constitutive proteasomes. PA28 overexpression does not produce a comparable enhancement.\",\n      \"method\": \"Triple transfection, CTL killing assay for antigen presentation, in vitro peptide digestion with HPLC analysis of products\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of peptide generation combined with functional antigen presentation assay\",\n      \"pmids\": [\"10878350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"HCV NS3 protein directly interacts with the pro-sequence region (amino acids 1-40) of LMP7 via its protease domain (confirmed by yeast two-hybrid and in vitro binding and co-IP); this interaction does not affect NS3 protease activity in vitro, but cells stably replicating HCV subgenomic replicon show markedly reduced LMP7 immunoproteasome peptidase activities.\",\n      \"method\": \"Yeast two-hybrid screen, in vitro binding assay, co-immunoprecipitation, domain mapping, fluorogenic peptidase activity assay in HCV replicon cell line\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — reciprocal binding confirmed by multiple methods, domain mapping performed, functional consequence measured\",\n      \"pmids\": [\"15303969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"IRF-1 is required for IFN-gamma-dependent LMP7 transcription; a tetracycline-inducible IRF-1 system induces LMP7 expression, a specific IRF-1-binding genomic region in the LMP7 locus was identified, and IRF-1 knockdown by siRNA as well as IRF-1-/- mice confirmed that IRF-1 is the master transcriptional regulator driving concerted immunoproteasome subunit expression.\",\n      \"method\": \"Tet-inducible IRF-1 expression, siRNA knockdown, IRF-1 knockout mice, genomic footprinting/reporter assay to map IRF-1 binding region\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal approaches (inducible OE, siRNA KD, KO mice) all converge on same conclusion\",\n      \"pmids\": [\"15907481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"LMP7 (PSMB8) deficiency in mice results in significantly attenuated dextran sodium sulfate-induced colitis due to reduced NF-κB signaling; this is mechanistically linked to reduced secretion of proinflammatory cytokines and chemokines, decreased neutrophil infiltration, and diminished Th1/Th17 expansion.\",\n      \"method\": \"lmp7-/- mouse model, DSS colitis induction, NF-κB pathway analysis, cytokine/chemokine measurement, histological analysis\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined mechanistic pathway (NF-κB) and multiple phenotypic readouts, replicated with pharmacological inhibitor bortezomib\",\n      \"pmids\": [\"20581238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A homozygous missense mutation (Thr75Met) in PSMB8 causes JMP syndrome; the mutation disrupts the tertiary structure of β5i and results in significantly reduced chymotrypsin-like proteolytic activity of immunoproteasomes in patient lymphoblasts compared to normal cells.\",\n      \"method\": \"Homozygosity mapping, direct sequencing, structural modeling, immunoproteasome chymotryptic activity assay in patient vs. normal lymphoblasts\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — biochemical activity assay in patient cells with structural modeling, causative mutation confirmed by segregation\",\n      \"pmids\": [\"21129723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A G201V mutation in PSMB8 (β5i) in Nakajo-Nishimura syndrome disrupts the β-sheet structure near the catalytic threonine, prevents efficient incorporation of β5i into immunoproteasome precursors, reduces total proteasome activity, and causes accumulation of ubiquitinated and oxidized proteins; this leads to increased IL-6 and IP-10 secretion and elevated p38 phosphorylation.\",\n      \"method\": \"Structural analysis (mutation position modeling), immunoproteasome assembly assay, proteasome activity assay, ubiquitinated/oxidized protein accumulation assay, cytokine ELISA, phospho-p38 immunoblot in patient cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal biochemical assays in patient cells with structural context, independent replication across pedigrees\",\n      \"pmids\": [\"21852578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A G197V mutation in PSMB8 increases assembly intermediates of immunoproteasomes, decreases proteasome function, causes ubiquitin-coupled protein accumulation, and leads to increased IL-6 expression in patient skin and B cells; PSMB8 knockdown inhibits murine and human adipocyte differentiation in vitro, and siRNA injection against Psmb8 in mouse skin reduces adipocyte tissue volume.\",\n      \"method\": \"Exome sequencing, proteasome activity assay, ubiquitin accumulation immunoblot, siRNA knockdown of Psmb8 in mouse skin/adipocyte differentiation assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biochemical, cell-based, in vivo siRNA), functional consequence of PSMB8 loss on adipogenesis directly demonstrated\",\n      \"pmids\": [\"21881205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"β5i/LMP7 deficiency in mice leads to impaired immunoproteasome function, failure to clear poly-ubiquitinated protein aggregates in cytokine-stressed cardiomyocytes during CVB3 myocarditis, impaired NF-κB activation, and increased apoptotic cell death, resulting in exacerbated acute myocardial damage despite identical viral load.\",\n      \"method\": \"β5i/LMP7 knockout mice, CVB3 infection model, ubiquitinated aggregate detection, NF-κB activation assay, apoptosis quantification, adoptive T cell transfer\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple mechanistic readouts (protein aggregate clearance, NF-κB, apoptosis) in vivo\",\n      \"pmids\": [\"21909276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LMP7 propeptide (proLMP7) shows significantly higher chaperone activity than the β5 propeptide (proβ5) in promoting proteasome maturation; proLMP7 promotes integration of both immunosubunits and mixed proteasomes, and increased efficiency of proteasome maturation by proLMP7 is required for optimal MHC class I surface expression. LMP7 induction also increases total proteasome abundance in infected tissue.\",\n      \"method\": \"LMP7-deficient mouse infection model, IFNγ stimulation experiments, subunit integration assays, proteasome maturation kinetics, MHC class I surface expression by flow cytometry\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple experimental approaches in both cell culture and in vivo, functional MHC class I readout\",\n      \"pmids\": [\"22768135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LMP7 deficiency or selective inhibition suppresses Th17 and Th1 differentiation while promoting regulatory T cell (Treg) development; mechanistically, LMP7 inhibition blocks STAT3 phosphorylation in developing Th17 cells and enhances SMAD phosphorylation in Tregs, and reduces STAT1 phosphorylation in Th1 cells.\",\n      \"method\": \"LMP7-/- CD4+ T cells and ONX 0914-treated WT T cells under polarizing conditions, phospho-STAT3/SMAD/STAT1 immunoblot, DSS colitis and T cell transfer colitis models in vivo\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO and pharmacological inhibition converge, mechanistic pathway (STAT3, SMAD, STAT1 phosphorylation) identified, confirmed in vivo\",\n      \"pmids\": [\"22984077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"X-ray crystal structures of murine constitutive and immunoproteasome 20S core particles informed rational design of β5i (LMP7)-selective inhibitors; structural differences in the S1 pocket between β5c and β5i were exploited to achieve cell-permeable inhibitors with high selectivity.\",\n      \"method\": \"Structure-based drug design using X-ray crystallography of 20S proteasome complexes, selectivity profiling across all proteasome subunits\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with functional inhibitor validation, selectivity profiling across multiple subunits\",\n      \"pmids\": [\"25006746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"miR-451 directly targets LMP7 (PSMB8) 3′UTR to suppress LMP7 expression, thereby inhibiting NF-κB activity and reducing proinflammatory cytokine transcription in mesangial cells; in db/db diabetic mice, increasing miR-451 inhibited LMP7/NF-κB and attenuated glomerular injury.\",\n      \"method\": \"Deep sequencing, dual-luciferase reporter assay, Western blot, chromatin immunoprecipitation, in vivo miR-451 overexpression in db/db mice\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3′UTR targeting validated by luciferase reporter, confirmed in vivo, NF-κB pathway link established by ChIP\",\n      \"pmids\": [\"27264074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Co-inhibition of both LMP7 and LMP2 (but not LMP7 alone) is required to impair MHC class I surface expression, suppress IL-6 secretion, block Th17 differentiation, and strongly ameliorate experimental colitis and EAE; prolonged ONX 0914 exposure inhibits both subunits, explaining its efficacy.\",\n      \"method\": \"Selective LMP7 inhibitor PRN1126 vs. ONX 0914 comparison, LMP2+LMP7 dual inhibitor combination, DSS colitis, EAE models, IL-6 ELISA, MHC class I flow cytometry\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple pharmacological tools with defined selectivity profiles, in vivo disease models, multiple functional readouts\",\n      \"pmids\": [\"30279279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"β5i (PSMB8) interacts with ATG5, promoting its degradation, thereby inhibiting autophagy and driving pathological cardiac hypertrophy; β5i knockout attenuates hypertrophy, and ATG5 knockdown or autophagy inhibition reverses the β5i-KO protection.\",\n      \"method\": \"β5i KO and transgenic overexpression mice, Ang II-induced hypertrophy model, Co-IP (β5i–ATG5 interaction), ATG5 degradation assay, autophagic flux assays, genetic epistasis (ATG5 KD + β5i KO)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP for substrate identification, genetic epistasis confirming pathway order, in vivo KO and transgenic models with defined phenotype\",\n      \"pmids\": [\"31086810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"β5i (PSMB8) promotes ATRAP (AT1R-associated protein) degradation in atrial tissue; β5i upregulation by Ang II leads to ATRAP degradation, resulting in AT1R-mediated NF-κB activation, increased NADPH oxidase activity, TGF-β1/Smad signaling, and altered ion channel expression (Kir2.1, CX43), thereby driving atrial fibrillation.\",\n      \"method\": \"β5i KO and AAV9-β5i overexpression mice, Ang II infusion AF model, ATRAP co-IP and degradation assay, ATRAP overexpression rescue, NF-κB and TGF-β pathway assays\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — substrate identified by Co-IP, validated by rescue experiment with ATRAP overexpression, in vivo KO and OE with functional AF readout\",\n      \"pmids\": [\"30571551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"β5i (PSMB8) promotes ATRAP degradation in the retina; β5i KO restores Ang II-induced downregulation of ATRAP and attenuates AT1R-mediated downstream signaling, thereby reducing hypertensive retinopathy, while adenoviral β5i overexpression aggravates the phenotype.\",\n      \"method\": \"β5i KO and Ad-β5i overexpression mice, Ang II infusion retinopathy model, ATRAP degradation assay, AT1R downstream signaling analysis, ATRAP overexpression rescue\",\n      \"journal\": \"Molecular therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — same ATRAP substrate as parallel cardiac study, confirmed by complementary genetic approaches and rescue experiment\",\n      \"pmids\": [\"31636038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"β5i (PSMB8) promotes PTEN degradation in DOCA-salt hypertensive hearts; β5i KO attenuates cardiac remodeling by restoring PTEN levels, and PTEN blockade reverses the protective effects of β5i KO, placing PTEN as a key substrate whose stability is regulated by β5i-dependent proteasomal degradation.\",\n      \"method\": \"β5i KO mice and PR-957 pharmacological inhibition, DOCA-salt hypertension model, PTEN degradation assay, AKT/mTOR/TGF-β/NF-κB pathway analysis, VO-OHpic rescue experiment\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO and pharmacological inhibition converge, PTEN substrate confirmed by rescue with PTEN inhibitor\",\n      \"pmids\": [\"31629736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"β5i (PSMB8) promotes atherosclerosis by targeting MERTK for degradation via NF-κB-dependent suppression of Mertk transcription; β5i deletion reduces IκBα degradation, inhibits NF-κB, increases MERTK expression, and enhances efferocytosis of apoptotic cells in atherosclerotic lesions.\",\n      \"method\": \"β5i/Apoe double KO mice, bone marrow transplantation, ATD-fed mouse atherosclerosis model, efferocytosis assay, MERTK expression, IκBα/NF-κB pathway analysis, PR-957 pharmacological treatment\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic approaches (full KO, bone marrow chimera) plus pharmacological validation, mechanistic pathway (NF-κB→MERTK→efferocytosis) defined\",\n      \"pmids\": [\"31758542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"β5i (PSMB8) promotes macrophage pyroptosis during abdominal aortic aneurysm formation via activation of NF-κB and upregulation of NLRP3; β5i inhibition or knockout decreases macrophage pyroptosis and AAA severity through the IκB/NF-κB pathway.\",\n      \"method\": \"β5i KO mice, PR-957 treatment, AAA mouse model, pyroptosis markers in tissue and BMDMs, OXLDL stimulation, NF-κB/NLRP3 pathway analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO and pharmacological inhibition, mechanistic pathway identified, single lab\",\n      \"pmids\": [\"33019975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"M3258, an orally bioavailable, reversible, highly selective LMP7 (β5i) inhibitor, was developed through structure-based optimization using X-ray crystal structures; it demonstrates potent suppression of LMP7 activity, ubiquitinated protein turnover, and induces apoptosis in multiple myeloma cells in vitro and in vivo.\",\n      \"method\": \"Structure-based drug design (X-ray crystallography), selectivity profiling, multiple myeloma xenograft models, ubiquitin turnover assay, apoptosis assay\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus in vivo functional validation in multiple xenograft models\",\n      \"pmids\": [\"34228444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Lmp7 (PSMB8) levels and activity are significantly increased in a mouse model of α-synuclein aggregation and in post-mortem human PD and dementia with Lewy bodies brains; the immunoproteasome degrades α-synuclein aggregates and generates potentially antigenic peptides from them.\",\n      \"method\": \"Quantitative proteomics (6215 proteins), immunoproteasome activity assay in mouse model and human post-mortem tissue, α-synuclein aggregate degradation assay\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic quantification and activity assay both in animal model and human tissue, aggregate degradation directly measured\",\n      \"pmids\": [\"29759483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"LMP7 is required in radioresistant thymic cells (likely mTECs) to prevent excessive negative selection of GP118-125-specific T cell precursors; LMP7-deficient mice completely lack GP118-125-specific CD8+ T cells, which is restored by bone marrow chimeras showing LMP7 requirement in non-hematopoietic cells.\",\n      \"method\": \"LMP7 KO mice, LCMV infection model, bone marrow chimera generation, adoptive transfer of LMP7-deficient CD8+ T cells into RAG1-/- mice, tetramer staining\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — bone marrow chimeras and adoptive transfer definitively localize LMP7 requirement to radioresistant cells, multiple epistasis experiments\",\n      \"pmids\": [\"29067678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PSMB8 (β5i) expression is upregulated in manganese-exposed microglia via PERK signaling; selective PSMB8 inhibition reduces neuroinflammation (TNF-α, iNOS, CCL12 production, microglial activation) and inhibition of PSMB8 reduces NF-κB p65 phosphorylation, placing PSMB8 in a PERK/NF-κB signaling axis during Mn neurotoxicity.\",\n      \"method\": \"In vivo Mn exposure mouse model, BV2 cell culture, selective PSMB8 inhibitor treatment, PERK inhibitor, NF-κB pathway analysis, learning/memory tests, Golgi staining\",\n      \"journal\": \"Food and chemical toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition of PSMB8 and upstream PERK, in vivo and in vitro, multiple inflammatory readouts; single lab\",\n      \"pmids\": [\"35378207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Apelin inhibits epithelial-mesenchymal transition (EMT) of podocytes in diabetic mice through downregulation of β5i expression; β5i KO mice confirmed the dependence of apelin's anti-EMT effect on β5i; mechanistically, apelin decreases β5i expression, which reduces degradation of pIκB, promotes IκB nuclear translocation, inhibits NF-κB-driven TGF-β expression, and decreases Smad pathway activation.\",\n      \"method\": \"β5i KO mice, diabetic mouse model, apelin treatment, pIκB degradation assay, IκB localization, TGF-β/Smad pathway analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO confirms β5i requirement, mechanistic pathway (IκB/NF-κB/TGF-β) established in vivo and in vitro, single lab\",\n      \"pmids\": [\"30301930\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PSMB8 (LMP7/β5i) is an IFN-γ-inducible catalytic subunit of the 20S immunoproteasome, synthesized as a proprotein that is processed within precursor complexes (its propeptide acting as a chaperone for efficient maturation) and incorporated into the 20S ring where its active-site threonine confers chymotrypsin-like (and contributes to trypsin-like) proteolytic activity; it shifts cleavage specificity toward hydrophobic/basic C-termini to optimize MHC class I antigenic peptide generation, and beyond antigen presentation it targets specific substrates (ATG5, ATRAP, PTEN) for degradation to regulate autophagy, angiotensin signaling, cardiac hypertrophy, atrial fibrillation, and vascular inflammation, while also modulating NF-κB and STAT signaling to control Th1/Th17 differentiation, cytokine production, and tissue homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PSMB8 (LMP7/β5i) is the IFN-γ-inducible catalytic subunit of the 20S immunoproteasome, where its active-site threonine confers chymotrypsin-like and contributes to trypsin-like peptide-bond cleavage [#4, #9]. Its yeast ortholog PRE2 is the proteasomal subunit responsible for chymotryptic activity, loss of which abolishes that activity and causes accumulation of ubiquitinated proteins [#0]. PSMB8 is synthesized as a ~30 kDa proprotein whose N-terminal pro-sequence is cleaved within 13–16S precursor complexes to yield the mature 23 kDa subunit incorporated into the 20S ring, with the propeptide acting as a more efficient maturation chaperone than the constitutive β5 propeptide and POMP restricted to precursor intermediates [#2, #5, #10, #19]. Upon IFN-γ induction—driven transcriptionally by IRF-1—PSMB8 replaces the constitutive subunit X/β5c, shifting cleavage preference toward hydrophobic and basic C-termini and altering the quality of peptide products to optimize generation of MHC class I antigenic peptides [#8, #13, #6, #7, #11]. This antigen-processing role extends to shaping T cell selection in radioresistant thymic cells [#32]. Beyond antigen presentation, PSMB8 controls inflammatory signaling: its activity sustains NF-κB activation and skews CD4 T cell differentiation toward Th1/Th17 over Treg by modulating STAT3, STAT1, and SMAD phosphorylation [#14, #20]. In cardiovascular and metabolic disease, PSMB8 targets specific substrates for degradation—ATG5 to suppress autophagy and drive cardiac hypertrophy, ATRAP to potentiate AT1R signaling in atrial fibrillation and hypertensive retinopathy, PTEN in hypertensive cardiac remodeling, and MERTK (via NF-κB) to impair efferocytosis in atherosclerosis [#24, #25, #26, #27, #28]. Causative PSMB8 mutations that disrupt β5i structure and immunoproteasome assembly/activity (Thr75Met in JMP syndrome; G201V in Nakajo-Nishimura syndrome; G197V) produce autoinflammatory syndromes with accumulation of ubiquitinated proteins and elevated proinflammatory cytokines [#15, #16, #17]. Structure-based design exploiting the β5i S1 pocket has yielded selective inhibitors with anti-inflammatory and anti-myeloma activity [#21, #30, #23].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established that this proteasome β-subunit is the catalytic component responsible for chymotrypsin-like activity, defining its core enzymatic identity.\",\n      \"evidence\": \"Genetic complementation and loss-of-function of the homologous yeast PRE2 gene with proteasome activity and ubiquitin-accumulation assays\",\n      \"pmids\": [\"8383129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Inference from yeast ortholog rather than direct human PSMB8 catalysis\", \"Did not address immunoproteasome-specific cleavage preferences\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Showed the proteasomal function of this subunit is essential for viability in yeast.\",\n      \"evidence\": \"Genomic disruption of the yeast homolog PRG1 showing lethality\",\n      \"pmids\": [\"1452031\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Essentiality refers to yeast, not the IFN-γ-inducible human subunit\", \"Single study\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Defined PSMB8 as a proprotein that is N-terminally processed from ~30 kDa to a mature 23 kDa form before incorporation, establishing the maturation logic of the subunit.\",\n      \"evidence\": \"Pulse-chase, immunoprecipitation, and Western blot of proteasome preparations (two independent reports)\",\n      \"pmids\": [\"8365398\", \"8458375\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the protease/mechanism of propeptide cleavage\", \"Functional role of the propeptide not yet defined\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrated that incorporation of PSMB8 raises proteasomal chymotrypsin- and trypsin-like activities in dose-dependent fashion and that assembly proceeds via precursor complexes with intra-precursor processing.\",\n      \"evidence\": \"Gene transfection with fluorogenic substrate kinetics; sedimentation and pulse-chase fractionation of precursor and mature complexes\",\n      \"pmids\": [\"7937744\", \"8120905\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Active-site residue not yet directly implicated\", \"Substrate range limited to model fluorogenic peptides\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showed PSMB8 incorporation alters cleavage-site specificity and the quality of peptide products from defined polypeptides independent of IFN-γ and of PA28 selectivity, linking the subunit to antigenic peptide repertoire.\",\n      \"evidence\": \"Stable LMP transfection with in vitro digestion of a defined 25-mer, HPLC/mass spectrometry of products, and PA28 reconstitution\",\n      \"pmids\": [\"7589133\", \"7559557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MHC class I presentation not yet directly measured\", \"Cooperativity mechanism between subunits unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that IFN-γ-induced activity changes arise from PSMB8 replacing the constitutive subunit X/β5c, via reciprocal gain/loss-of-function.\",\n      \"evidence\": \"Reciprocal transfection of subunit X and PSMB8 in HeLa cells with fluorogenic activity assays and stoichiometry immunoblots\",\n      \"pmids\": [\"8663318\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not map structural basis of differential specificity\", \"Whole-substrate consequences of subunit swap not assessed here\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Confirmed PSMB8 is itself a catalytic subunit by direct active-site labeling.\",\n      \"evidence\": \"Radiolabeled active-site-directed inhibitor labeling of purified 20S/26S proteasomes with subunit identification by 2D-PAGE and immunoblot\",\n      \"pmids\": [\"9312091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which residue side-chains shape the S1 pocket\", \"Relative contribution to trypsin- vs chymotrypsin-like activity not quantified\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Resolved the propeptide's role in maturation—assisting incorporation efficiency but not strictly required—and placed POMP in precursor complexes only.\",\n      \"evidence\": \"Propeptide and active-site Thr mutagenesis with 2D gel/fractionation and POMP immunoblotting in T2 cells\",\n      \"pmids\": [\"10926487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chaperone strength of the propeptide relative to β5 not yet compared\", \"Active-site Thr role in catalysis vs incorporation only partly separated\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Linked PSMB8-containing immunoproteasomes to enhanced MHC class I presentation of a defined epitope.\",\n      \"evidence\": \"Triple LMP transfection with CTL killing assay and in vitro epitope-precursor digestion analysis\",\n      \"pmids\": [\"10878350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Contribution of PSMB8 alone vs the triplet not isolated\", \"Did not address presentation breadth genome-wide\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified a viral strategy targeting PSMB8 maturation, showing HCV NS3 binds the propeptide region and reduces immunoproteasome peptidase activity.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding, co-IP, domain mapping, and peptidase assays in HCV replicon cells\",\n      \"pmids\": [\"15303969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which propeptide binding lowers activity not defined\", \"In vivo immune-evasion consequence not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified IRF-1 as the master transcriptional driver of IFN-γ-dependent PSMB8 and coordinate immunoproteasome subunit expression.\",\n      \"evidence\": \"Tet-inducible IRF-1, siRNA knockdown, IRF-1 knockout mice, and genomic binding-site mapping\",\n      \"pmids\": [\"15907481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Other cooperating transcription factors not delineated\", \"Cell-type-specific regulation not addressed\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected PSMB8 to NF-κB-driven mucosal inflammation, establishing an immune-effector role beyond antigen processing.\",\n      \"evidence\": \"lmp7-/- mice in DSS colitis with NF-κB, cytokine, and Th1/Th17 analyses, plus bortezomib replication\",\n      \"pmids\": [\"20581238\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular substrate linking PSMB8 to NF-κB not identified here\", \"Bortezomib is non-selective\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified PSMB8 mutations as causative for human autoinflammatory syndromes (JMP, Nakajo-Nishimura) by disrupting β5i structure, assembly, and proteolytic activity.\",\n      \"evidence\": \"Homozygosity/exome mapping, structural modeling, immunoproteasome activity and assembly assays, and cytokine measurements in patient cells; in vivo siRNA adipocyte studies\",\n      \"pmids\": [\"21129723\", \"21852578\", \"21881205\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise substrate(s) whose mishandling drives cytokine elevation not defined\", \"Adipocyte differentiation mechanism partly correlative\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated PSMB8 is protective in stressed tissue, clearing ubiquitinated aggregates and supporting NF-κB-dependent survival during viral myocarditis.\",\n      \"evidence\": \"β5i knockout mice in CVB3 myocarditis with aggregate, NF-κB, and apoptosis readouts and adoptive T cell transfer\",\n      \"pmids\": [\"21909276\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Context-dependence of NF-κB outcomes (protective vs pathogenic) unresolved\", \"Substrate underlying aggregate clearance not specified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed the PSMB8 propeptide is a superior maturation chaperone required for optimal MHC class I surface expression, mechanistically linking maturation efficiency to immune function.\",\n      \"evidence\": \"LMP7-deficient mouse infection, subunit integration assays, maturation kinetics, and MHC class I flow cytometry\",\n      \"pmids\": [\"22768135\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of enhanced chaperone activity not resolved\", \"Quantitative contribution to total proteasome pool tissue-dependent\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined a mechanism for PSMB8 control of T helper fate via STAT3/STAT1/SMAD phosphorylation balancing Th17/Th1 versus Treg.\",\n      \"evidence\": \"LMP7-/- and ONX 0914-treated CD4+ T cells under polarizing conditions with phospho-immunoblots and in vivo colitis models\",\n      \"pmids\": [\"22984077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct proteasomal substrate controlling STAT phosphorylation not identified\", \"ONX 0914 selectivity caveat (see 2018 finding)\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided the structural basis for selective β5i inhibition by exploiting S1-pocket differences between β5c and β5i.\",\n      \"evidence\": \"X-ray crystallography of constitutive and immunoproteasome 20S cores with inhibitor selectivity profiling\",\n      \"pmids\": [\"25006746\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address in vivo target engagement or off-subunit effects at higher exposure\", \"Structure of human β5i not the species crystallized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Localized a non-hematopoietic PSMB8 requirement in thymic stromal cells preventing excessive negative selection, refining its role in T cell repertoire shaping.\",\n      \"evidence\": \"LMP7 KO mice with LCMV infection, bone marrow chimeras, adoptive transfer, and tetramer staining\",\n      \"pmids\": [\"29067678\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific self-peptides altered by PSMB8 loss not identified\", \"mTEC identity inferred\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Implicated PSMB8 in neurodegenerative protein aggregation, showing increased immunoproteasome activity that degrades α-synuclein aggregates.\",\n      \"evidence\": \"Quantitative proteomics and activity assays in α-synuclein mouse model and human PD/DLB brain with aggregate degradation assay\",\n      \"pmids\": [\"29759483\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal versus reactive role of PSMB8 upregulation unresolved\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked PSMB8 to podocyte EMT via IκB/NF-κB/TGF-β signaling in diabetic kidney, downstream of apelin.\",\n      \"evidence\": \"β5i KO mice with apelin treatment and IκB/NF-κB/TGF-β/Smad pathway analyses\",\n      \"pmids\": [\"30301930\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PSMB8 substrate in this axis not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified specific PSMB8 degradation substrates (ATG5, ATRAP, PTEN) explaining its role in autophagy suppression, AT1R signaling, and cardiovascular remodeling.\",\n      \"evidence\": \"β5i KO and overexpression mice across hypertrophy/AF/retinopathy/hypertension models with Co-IP, degradation assays, and substrate-rescue epistasis\",\n      \"pmids\": [\"31086810\", \"30571551\", \"31636038\", \"31629736\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How an immunoproteasome subunit acquires substrate specificity for these targets mechanistically unclear\", \"Co-IP-based interactions without structural detail\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended PSMB8's NF-κB-coupled disease role to atherosclerosis (MERTK/efferocytosis) and aortic aneurysm (NLRP3 pyroptosis).\",\n      \"evidence\": \"β5i/Apoe double KO, bone marrow chimeras, and PR-957 in atherosclerosis and AAA models with efferocytosis and pyroptosis readouts\",\n      \"pmids\": [\"31758542\", \"33019975\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MERTK regulation is transcriptional (via NF-κB) rather than direct degradation\", \"AAA finding single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Advanced selective PSMB8 inhibitors as therapeutics, including an oral agent active against multiple myeloma, and clarified that dual β5i/β2i inhibition underlies some immunomodulatory efficacy.\",\n      \"evidence\": \"Structure-based inhibitor design (M3258) with myeloma xenografts; comparison of selective PRN1126 vs ONX 0914 in colitis/EAE\",\n      \"pmids\": [\"34228444\", \"30279279\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Therapeutic window of pure β5i inhibition in autoinflammation uncertain\", \"Long-term safety of immunoproteasome inhibition not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placed PSMB8 in a PERK/NF-κB neuroinflammatory axis in manganese-exposed microglia.\",\n      \"evidence\": \"In vivo Mn exposure and BV2 cells with selective PSMB8 and PERK inhibitors and NF-κB analysis\",\n      \"pmids\": [\"35378207\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct substrate connecting PERK to PSMB8 to NF-κB not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how an immunoproteasome catalytic subunit achieves selective targeting of individual substrates (ATG5, ATRAP, PTEN) and tilts NF-κB outcomes in a tissue-specific, sometimes opposing (protective vs pathogenic), manner.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural/biochemical basis of substrate selectivity beyond bulk proteolysis unknown\", \"Mechanism switching PSMB8 between protective aggregate-clearance and pathogenic substrate degradation undefined\", \"Direct degradation versus indirect transcriptional effects not always distinguished\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 4, 6, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [4, 9, 15]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [10, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 4, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [11, 14, 20, 32]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 20, 24, 25, 28]}\n    ],\n    \"complexes\": [\"20S immunoproteasome\", \"20S proteasome core particle\", \"16S immunoproteasome precursor complex\"],\n    \"partners\": [\"POMP\", \"PSMB9\", \"ATG5\", \"ATRAP\", \"PTEN\", \"IRF1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}