{"gene":"PSMB3","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1996,"finding":"PSMB3 is one of the beta-type subunits of the 20S proteasome, a large multicatalytic proteinase complex whose multiple peptidase activities operate through a novel threonine-based proteolytic mechanism; the 20S core assembles into the 26S complex with a 19S regulatory particle to degrade ubiquitinated proteins.","method":"Biochemical purification, structural analysis, and protease activity assays of the 20S and 26S proteasome complexes","journal":"Annual review of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted enzymatic activities, structural characterization, replicated across many labs; foundational review synthesizing extensive biochemical evidence","pmids":["8811196"],"is_preprint":false},{"year":1997,"finding":"The human PSMB3 gene (encoding the beta3 subunit, HsC10-II) was mapped by fluorescence in situ hybridization to chromosome band 2q35; unlike the interferon-inducible PSMB8/PSMB9 subunit genes clustered in the MHC, PSMB3 is independently located, consistent with independent transcriptional regulation of individual proteasome beta subunit genes.","method":"Fluorescence in situ hybridization (FISH) of genomic clones","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 2 — direct cytogenetic localization experiment with clear result","pmids":["9344661"],"is_preprint":false},{"year":1999,"finding":"The mouse ortholog of PSMB3 (C10-II) was cloned by cDNA isolation, and its protein identity was verified by 2D-NEPHGE-PAGE immunoblotting using antisera raised against the subunit, establishing it as one of the 17 subunits forming the mouse 20S proteasome core.","method":"cDNA cloning, two-dimensional NEPHGE-PAGE, immunoblotting with subunit-specific antisera","journal":"Immunogenetics","confidence":"High","confidence_rationale":"Tier 1–2 — direct biochemical verification of protein identity by orthogonal methods (cDNA sequencing plus 2D immunoblot)","pmids":["10436176"],"is_preprint":false},{"year":2002,"finding":"Psmb3 was identified and chromosomally assigned to distal mouse chromosome 11 within a dense gene cluster syntenic to human chromosome 17q12, establishing the mouse genomic locus.","method":"Transgene-induced contig sequencing and cDNA selection","journal":"Cytogenetic and genome research","confidence":"Medium","confidence_rationale":"Tier 2 — direct genomic sequencing and mapping experiment, single study","pmids":["12438746"],"is_preprint":false},{"year":2007,"finding":"siRNA-mediated depletion of PSMB3 (a 20S proteasome subunit) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, demonstrating that proteasome function—specifically involving PSMB3—is required for activation of the Fanconi anemia DNA damage signaling pathway.","method":"siRNA knockdown of PSMB3 in human cells, immunofluorescence for FANCD2 foci, ubiquitination assays","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — specific genetic depletion with defined molecular phenotype (FANCD2 monoubiquitination), single lab","pmids":["17671210"],"is_preprint":false},{"year":2011,"finding":"siRNA knockdown of PSMB3 in human airway epithelial cells increased susceptibility to AAV infection, placing PSMB3/proteasome function as a component of the subcellular barrier that restricts AAV virion trafficking or processing at the level of the secretory/ER-Golgi system.","method":"siRNA knockdown of PSMB3 combined with AAV infection efficiency assays in human airway epithelium models","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2–3 — specific siRNA knockdown with quantified viral transduction phenotype; single lab","pmids":["21625534"],"is_preprint":false},{"year":2011,"finding":"In an RNAi screen of the druggable genome in multiple myeloma cells, silencing of PSMB3 synergistically potentiated growth inhibition by the proteasome inhibitor bortezomib, providing functional evidence that PSMB3 contributes to the proteolytic capacity required for myeloma cell survival under proteasome stress.","method":"Genome-wide siRNA screen (13,984 siRNAs) measuring proliferation in the presence of bortezomib; internal validation by proteasome subunit hits","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — large-scale functional genomic screen with internal validation; phenotypic readout is cell growth, no direct biochemical mechanism elucidated for PSMB3 specifically","pmids":["21289309"],"is_preprint":false},{"year":2011,"finding":"Psmb3 (endopeptidase) shares the same thymic expression profile as Prss16 (Tssp) in mouse cortical thymic epithelial cells, being induced in wild-type and repressed in Prss16-knockout mice, suggesting its participation in self-peptide generation for positive selection of CD4+ T lymphocytes.","method":"Microarray transcriptional profiling comparing wild-type and Prss16-knockout thymic tissue","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 4 — expression profiling only; no direct functional experiment for PSMB3 in thymic selection","pmids":["21773946"],"is_preprint":false},{"year":2013,"finding":"siRNA-mediated knockdown of PSMB3 in a human astrocytic cell line reduced CTG•CAG trinucleotide repeat expansions, demonstrating that the proteolytic activity of the 26S proteasome—specifically requiring PSMB3—drives repeat expansions in human cells.","method":"siRNA knockdown of PSMB3 in human astrocytic cells, quantitative trinucleotide repeat expansion assay; proteasome inhibitor controls confirmed proteolytic (not stress-response) mechanism","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — specific genetic depletion with quantified molecular phenotype; mechanism linked to proteolytic activity via inhibitor controls; single lab","pmids":["23620289"],"is_preprint":false},{"year":2020,"finding":"Double knockdown of transcription factors NFE2L1 and NFE2L3 in cancer cells significantly reduced basal expression of PSMB3 (along with six other proteasome genes), impairing basal proteasome activity; NFE2L3 suppresses NFE2L1 translation via induction of CPEB3, revealing that PSMB3 basal expression in cancer cells is maintained by an NFE2L1/NFE2L3-CPEB3 translational repression axis.","method":"Double siRNA knockdown of NFE2L1/NFE2L3, qRT-PCR and western blot for PSMB3 and other proteasome subunits, proteasome activity assays, polysome profiling for NFE2L1 mRNA","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (knockdown, activity assay, polysome profiling); PSMB3 is one of seven subunits reduced, not the sole focus","pmids":["32366381"],"is_preprint":false},{"year":2023,"finding":"siRNA-mediated silencing of PSMB3 in human hepatocyte cell lines (HuH-7 and HepG2) was sufficient to suppress proteasome function and upregulate TRIB1 mRNA expression, demonstrating that PSMB3 activity is required to maintain basal proteasome function in hepatocytes and that its inhibition triggers transcriptional induction of TRIB1.","method":"siRNA knockdown of PSMB3, RT-qPCR for TRIB1 mRNA, western blot for protein levels and ubiquitylation; comparison with pharmacological proteasome inhibitors","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — genetic silencing with specific molecular readout; multiple methods; single lab","pmids":["37291259"],"is_preprint":false}],"current_model":"PSMB3 encodes the beta3 subunit of the 20S proteasome core, contributing to the complex's threonine-based multicatalytic protease activity; it is required for FANCD2 monoubiquitination in the Fanconi anemia DNA damage response, for restricting AAV virion trafficking at the secretory pathway, for driving trinucleotide repeat expansions via proteolytic activity, and for maintaining basal proteasome activity in cancer cells downstream of an NFE2L1/NFE2L3-CPEB3 transcriptional axis, with its chromosomal locus mapped to human 2q35."},"narrative":{"teleology":[{"year":1996,"claim":"Establishing that PSMB3 is an integral beta-type subunit of the 20S proteasome core resolved its identity as part of the threonine-based multicatalytic protease that forms the catalytic heart of the 26S proteasome.","evidence":"Biochemical purification, structural analysis, and protease activity assays of 20S and 26S proteasome complexes","pmids":["8811196"],"confidence":"High","gaps":["Precise catalytic contribution of beta-3 versus other beta subunits not resolved","No structure of PSMB3 alone or its specific active site"]},{"year":1997,"claim":"Mapping PSMB3 to human chromosome 2q35 established that constitutive proteasome subunit genes are genomically dispersed from MHC-linked inducible subunits, implying distinct transcriptional regulation.","evidence":"FISH of genomic clones to human metaphase chromosomes","pmids":["9344661"],"confidence":"High","gaps":["Cis-regulatory elements controlling PSMB3 transcription were not identified","Relationship between genomic location and tissue-specific expression unexplored"]},{"year":1999,"claim":"Cloning and biochemical verification of the mouse PSMB3 ortholog confirmed cross-species conservation and validated it as one of the 17 subunits of the mammalian 20S core.","evidence":"cDNA cloning, 2D-NEPHGE-PAGE, and immunoblotting with subunit-specific antisera in mouse","pmids":["10436176"],"confidence":"High","gaps":["Functional equivalence between mouse and human PSMB3 assumed but not tested by complementation"]},{"year":2007,"claim":"Demonstrating that PSMB3 knockdown blocks FANCD2 monoubiquitination revealed a specific requirement for proteasome activity in activating the Fanconi anemia DNA damage pathway, moving PSMB3 biology beyond generic proteostasis.","evidence":"siRNA knockdown in human cells with FANCD2 ubiquitination and foci formation assays","pmids":["17671210"],"confidence":"Medium","gaps":["Whether the effect is direct or reflects general proteostasis collapse is unclear","The proteasome substrate whose degradation activates FANCD2 was not identified","Single-lab finding"]},{"year":2011,"claim":"Three independent functional genomic studies linked PSMB3 to diverse biological contexts — AAV restriction at the secretory pathway, bortezomib sensitivity in myeloma, and potential thymic peptide generation — broadening the phenotypic landscape of PSMB3 loss.","evidence":"siRNA knockdown with AAV transduction assays in airway epithelium; genome-wide siRNA screen measuring bortezomib synergy in myeloma; microarray profiling of thymic epithelial cells","pmids":["21625534","21289309","21773946"],"confidence":"Medium","gaps":["AAV restriction mechanism (ER/Golgi trafficking versus capsid degradation) not resolved","Bortezomib synergy screen did not dissect PSMB3-specific mechanism from general proteasome impairment","Thymic expression data lack functional validation for T cell selection"]},{"year":2013,"claim":"Showing that PSMB3 depletion reduces CTG·CAG trinucleotide repeat expansions established that proteasome proteolytic activity — not merely a stress response — drives microsatellite instability in human cells.","evidence":"siRNA knockdown in human astrocytic cells with quantitative repeat expansion assay; proteasome inhibitor controls discriminated proteolytic from stress-response mechanisms","pmids":["23620289"],"confidence":"Medium","gaps":["Identity of the proteasome substrate whose turnover promotes repeat expansion is unknown","Generalizability to other repeat types not tested","Single-lab result"]},{"year":2020,"claim":"Identification of the NFE2L1/NFE2L3–CPEB3 axis as a regulator of basal PSMB3 expression in cancer cells revealed how proteasome subunit transcription is maintained under non-stress conditions, complementing the known stress-induced bounce-back pathway.","evidence":"Double siRNA knockdown of NFE2L1/NFE2L3, qRT-PCR, proteasome activity assays, and polysome profiling in cancer cell lines","pmids":["32366381"],"confidence":"Medium","gaps":["PSMB3 was one of seven coordinately regulated subunits; unique regulatory elements of PSMB3 not dissected","Whether the axis operates in non-transformed cells is unknown"]},{"year":2023,"claim":"Demonstrating that PSMB3 silencing in hepatocytes induces TRIB1 transcription provided the first link between proteasome capacity and the TRIB1 regulatory network, suggesting a feedback loop connecting proteostasis and lipid/metabolic gene regulation.","evidence":"siRNA knockdown of PSMB3 in HuH-7 and HepG2 cells with RT-qPCR for TRIB1 and western blot for ubiquitylation","pmids":["37291259"],"confidence":"Medium","gaps":["Mechanism connecting proteasome inhibition to TRIB1 transcription not identified","Whether TRIB1 induction is specific to PSMB3 loss or a generic proteasome impairment response is unclear","In vivo relevance not established"]},{"year":null,"claim":"The specific catalytic or structural contribution of the beta-3 subunit to 20S proteasome activity — as distinct from other constitutive beta subunits — remains undefined, and no disease-causing mutations in PSMB3 have been reported.","evidence":"","pmids":[],"confidence":"High","gaps":["No active-site mutagenesis distinguishing PSMB3's catalytic role from assembly function","No loss-of-function animal model","No Mendelian disease association established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,8]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,8]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,5]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,6,9,10]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[4,8]}],"complexes":["20S proteasome","26S proteasome"],"partners":["NFE2L1","NFE2L3","FANCD2"],"other_free_text":[]},"mechanistic_narrative":"PSMB3 encodes the beta-3 subunit of the 20S proteasome core particle, which assembles with other alpha and beta subunits to form the multicatalytic threonine protease complex that, together with the 19S regulatory particle, constitutes the 26S proteasome responsible for ubiquitin-dependent protein degradation [PMID:8811196, PMID:10436176]. Beyond its general housekeeping role in proteostasis, PSMB3-dependent proteasome activity is specifically required for FANCD2 monoubiquitination in the Fanconi anemia DNA damage response [PMID:17671210], for CTG·CAG trinucleotide repeat expansion in human cells [PMID:23620289], and for restricting adeno-associated virus trafficking through the secretory pathway [PMID:21625534]. Basal PSMB3 transcription in cancer cells is maintained by an NFE2L1/NFE2L3–CPEB3 regulatory axis, and its depletion impairs overall proteasome capacity, sensitizing myeloma cells to bortezomib and triggering compensatory transcriptional responses such as TRIB1 induction in hepatocytes [PMID:32366381, PMID:21289309, PMID:37291259]. The human PSMB3 locus maps to chromosome 2q35, independently of the MHC-linked inducible proteasome subunit genes [PMID:9344661]."},"prefetch_data":{"uniprot":{"accession":"P49720","full_name":"Proteasome subunit beta type-3","aliases":["Proteasome chain 13","Proteasome component C10-II","Proteasome subunit beta-3","beta-3","Proteasome theta chain"],"length_aa":205,"mass_kda":22.9,"function":"Non-catalytic component of the 20S core proteasome complex involved in the proteolytic degradation of most intracellular proteins. This complex plays numerous essential roles within the cell by associating with different regulatory particles. Associated with two 19S regulatory particles, forms the 26S proteasome and thus participates in the ATP-dependent degradation of ubiquitinated proteins. The 26S proteasome plays a key role in the maintenance of protein homeostasis by removing misfolded or damaged proteins that could impair cellular functions, and by removing proteins whose functions are no longer required. Associated with the PA200 or PA28, the 20S proteasome mediates ubiquitin-independent protein degradation. This type of proteolysis is required in several pathways including spermatogenesis (20S-PA200 complex) or generation of a subset of MHC class I-presented antigenic peptides (20S-PA28 complex)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P49720/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PSMB3","classification":"Common Essential","n_dependent_lines":1208,"n_total_lines":1208,"dependency_fraction":1.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000277791","cell_line_id":"CID000100","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"PSMD4","stoichiometry":10.0},{"gene":"PSMC1","stoichiometry":10.0},{"gene":"PSMC5","stoichiometry":10.0},{"gene":"PSMD6","stoichiometry":10.0},{"gene":"PSME1","stoichiometry":10.0},{"gene":"PSMD2","stoichiometry":10.0},{"gene":"POMP","stoichiometry":10.0},{"gene":"PSMB7","stoichiometry":10.0},{"gene":"PSMC3","stoichiometry":10.0},{"gene":"PSMA4","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000100","total_profiled":1310},"omim":[{"mim_id":"617872","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 34; COXPD34","url":"https://www.omim.org/entry/617872"},{"mim_id":"611974","title":"MITOCHONDRIAL RIBOSOMAL PROTEIN S7; MRPS7","url":"https://www.omim.org/entry/611974"},{"mim_id":"602177","title":"PROTEASOME SUBUNIT, BETA-TYPE, 4; PSMB4","url":"https://www.omim.org/entry/602177"},{"mim_id":"602176","title":"PROTEASOME SUBUNIT, BETA-TYPE, 3; PSMB3","url":"https://www.omim.org/entry/602176"},{"mim_id":"602175","title":"PROTEASOME SUBUNIT, BETA-TYPE, 2; PSMB2","url":"https://www.omim.org/entry/602175"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PSMB3"},"hgnc":{"alias_symbol":["HC10-II","MGC4147"],"prev_symbol":[]},"alphafold":{"accession":"P49720","domains":[{"cath_id":"3.60.20.10","chopping":"2-199","consensus_level":"high","plddt":97.6087,"start":2,"end":199}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P49720","model_url":"https://alphafold.ebi.ac.uk/files/AF-P49720-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P49720-F1-predicted_aligned_error_v6.png","plddt_mean":97.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PSMB3","jax_strain_url":"https://www.jax.org/strain/search?query=PSMB3"},"sequence":{"accession":"P49720","fasta_url":"https://rest.uniprot.org/uniprotkb/P49720.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P49720/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P49720"}},"corpus_meta":[{"pmid":"18281682","id":"PMC_18281682","title":"Identification of proteomic 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depolarization.","date":"2013","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/23503661","citation_count":870,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"32296183","id":"PMC_32296183","title":"A reference map of the human binary protein interactome.","date":"2020","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/32296183","citation_count":849,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"29507755","id":"PMC_29507755","title":"VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation.","date":"2018","source":"Cell discovery","url":"https://pubmed.ncbi.nlm.nih.gov/29507755","citation_count":829,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"14528300","id":"PMC_14528300","title":"The antiretroviral enzyme APOBEC3G is degraded by the proteasome in response to HIV-1 Vif.","date":"2003","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/14528300","citation_count":798,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12859895","id":"PMC_12859895","title":"Species-specific exclusion of APOBEC3G from HIV-1 virions by Vif.","date":"2003","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/12859895","citation_count":763,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"17353931","id":"PMC_17353931","title":"Large-scale mapping of human protein-protein interactions by mass spectrometry.","date":"2007","source":"Molecular systems biology","url":"https://pubmed.ncbi.nlm.nih.gov/17353931","citation_count":733,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"33961781","id":"PMC_33961781","title":"Dual proteome-scale networks reveal cell-specific remodeling of the human 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bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/21873635","citation_count":656,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"14527406","id":"PMC_14527406","title":"HIV-1 Vif blocks the antiviral activity of APOBEC3G by impairing both its translation and intracellular stability.","date":"2003","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/14527406","citation_count":607,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"19056867","id":"PMC_19056867","title":"Large-scale proteomics and phosphoproteomics of urinary exosomes.","date":"2008","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/19056867","citation_count":607,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"12750511","id":"PMC_12750511","title":"Hypermutation of HIV-1 DNA in the absence of the Vif protein.","date":"2003","source":"Science (New York, 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pathways.","date":"2011","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/21565611","citation_count":507,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"15489334","id":"PMC_15489334","title":"The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).","date":"2004","source":"Genome research","url":"https://pubmed.ncbi.nlm.nih.gov/15489334","citation_count":438,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16003,"output_tokens":1366,"usd":0.03425},"stage2":{"model":"claude-opus-4-6","input_tokens":4605,"output_tokens":1683,"usd":0.09765},"total_usd":0.335271,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of 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\"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PSMB3 (C10-II) was identified as one of the 17 subunits of the mouse 20S proteasome core, verified by 2D NEPHGE-PAGE using antisera raised against the subunit, establishing it as a bona fide component of the mammalian 20S proteolytic core.\",\n      \"method\": \"cDNA cloning, two-dimensional NEPHGE-PAGE, immunological verification with antisera\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical identification with immunological validation; single study\",\n      \"pmids\": [\"10436176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Depletion of PSMB3 (a 20S proteasome subunit) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, demonstrating that PSMB3-containing proteasome activity is required for Fanconi anemia pathway activation and DNA damage signaling (including IR-induced foci of 53BP1, phospho-ATM, NBS1, BRCA1, FANCD2, and RAD51).\",\n      \"method\": \"siRNA-mediated knockdown of PSMB3 in human cells, FANCD2 monoubiquitination assay, nuclear foci formation assay by immunofluorescence\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined molecular phenotype; single lab, multiple readouts\",\n      \"pmids\": [\"17671210\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"siRNA-mediated knockdown of PSMB3 in a human astrocytic cell line reduced CTG•CAG trinucleotide repeat expansions, establishing that PSMB3-containing 26S proteasome proteolytic activity drives trinucleotide repeat expansions in human cells.\",\n      \"method\": \"siRNA knockdown of PSMB3 in human cells, trinucleotide repeat expansion assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with specific molecular phenotype readout; single lab\",\n      \"pmids\": [\"23620289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Double knockdown of NFE2L1 and NFE2L3 significantly reduced basal expression of PSMB3 (among six other proteasome-related genes) and impaired basal proteasome activity in cancer cells, placing PSMB3 expression under transcriptional control of the NFE2L1/NFE2L3 axis.\",\n      \"method\": \"Double siRNA knockdown of NFE2L1 and NFE2L3, RT-qPCR for PSMB3 mRNA, proteasome activity assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with gene expression and functional proteasome activity readouts; single lab, multiple methods\",\n      \"pmids\": [\"32366381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PSMB3 silencing by siRNA was sufficient to increase TRIB1 mRNA expression in human hepatocyte cell lines, demonstrating that PSMB3-dependent proteasome function suppresses TRIB1 transcription under basal conditions.\",\n      \"method\": \"siRNA knockdown of PSMB3, RT-qPCR for TRIB1 mRNA in HuH-7 and HepG2 cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method, indirect mechanistic link\",\n      \"pmids\": [\"37291259\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PSMB3 is a catalytic beta-subunit of the 20S core of the 26S proteasome whose proteolytic activity is required for Fanconi anemia pathway activation (FANCD2 monoubiquitination), DNA damage response signaling, and trinucleotide repeat expansions, while its expression is maintained at baseline by the transcription factors NFE2L1 and NFE2L3.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEEP papers.\n\n**Classification:**\n\nKEEP papers (canonical PSMB3 protein):\n- [1] PMID:18281682 - PSMB3 protein identified in sperm proteomics\n- [2] PMID:17671210 - PSMB3 subunit depletion experiments\n- [3] PMID:21289309 - PSMB3 siRNA sensitization screen\n- [4] PMID:32366381 - PSMB3 expression regulated by NFE2L1/NFE2L3\n- [7] PMID:21625534 - PSMB3 siRNA knockdown affects AAV trafficking\n- [8] PMID:10436176 - Mouse PSMB3 cDNA cloning and characterization\n- [13] PMID:9344661 - PSMB3 chromosomal mapping\n- [16] PMID:37172766 - Insect PSMB3 ortholog (Bactrocera - insect, NOT mammalian ortholog; incompatible function - ecdysteroid production in insect gonads) → EXCLUDE (symbol collision / incompatible biology)\n- [18] PMID:23620289 - PSMB3 knockdown drives trinucleotide repeat expansions\n- [19] PMID:12438746 - Psmb3 chromosomal assignment in mouse\n- [21] PMID:21773946 - Psmb3 expression in thymus\n- [23] PMID:37291259 - PSMB3 silencing increases TRIB1 mRNA\n\nAdditional gene2pubmed papers:\n- [1] PMID:8811196 - General proteasome review (KEEP as foundational mechanism)\n- [4] PMID:19489727 - General proteasome review (KEEP)\n\nEXCLUDE (alias collision - these are APOBEC3G/CEM15 papers):\n- gene2pubmed [2] PMID:12167863, [6] PMID:12808466, [7] PMID:12809610, [11] PMID:14564014, [13] PMID:12808465, [14] PMID:23503661 (PARKIN), [17] PMID:14528300, [18] PMID:12859895, [22] PMID:14528301, [24] PMID:14527406, [26] PMID:12750511 — all APOBEC3G papers, not PSMB3\n\nEXCLUDE (no direct PSMB3 mechanism, expression/biomarker only):\n- [5] PMID:23637351, [6] PMID:36759259, [9] PMID:29457374, [10] PMID:34239933, [11] PMID:34938809, [12] PMID:28848558, [14] PMID:24464829, [15] PMID:33919822, [17] PMID:34689859, [20] PMID:37875878, [24] PMID:40766308, [25] PMID:40899950, [26] PMID:40923709, [27] PMID:41760790, [22] PMID:39342401\n\nEXCLUDE (large interactome/proteome screens with no specific PSMB3 mechanism):\n- gene2pubmed [5] PMID:19615732, [8] PMID:26186194, [9] PMID:28514442, [10] PMID:26496610, [12] PMID:25416956, [15] PMID:32296183, [19] PMID:17353931, [20] PMID:33961781, [21] PMID:22939629, [25] PMID:19056867, [27] PMID:28302793, [28] PMID:17110338, [29] PMID:21565611\n\nEXCLUDE (MGC cDNA projects, general):\n- gene2pubmed [3] PMID:12477932, [30] PMID:15489334\n\nEXCLUDE (VIRMA/m6A):\n- gene2pubmed [16] PMID:29507755\n\nEXCLUDE (GO phylogenetic):\n- gene2pubmed [23] PMID:21873635\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"PSMB3 is one of the beta-type subunits of the 20S proteasome, a large multicatalytic proteinase complex whose multiple peptidase activities operate through a novel threonine-based proteolytic mechanism; the 20S core assembles into the 26S complex with a 19S regulatory particle to degrade ubiquitinated proteins.\",\n      \"method\": \"Biochemical purification, structural analysis, and protease activity assays of the 20S and 26S proteasome complexes\",\n      \"journal\": \"Annual review of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted enzymatic activities, structural characterization, replicated across many labs; foundational review synthesizing extensive biochemical evidence\",\n      \"pmids\": [\"8811196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The human PSMB3 gene (encoding the beta3 subunit, HsC10-II) was mapped by fluorescence in situ hybridization to chromosome band 2q35; unlike the interferon-inducible PSMB8/PSMB9 subunit genes clustered in the MHC, PSMB3 is independently located, consistent with independent transcriptional regulation of individual proteasome beta subunit genes.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH) of genomic clones\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct cytogenetic localization experiment with clear result\",\n      \"pmids\": [\"9344661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The mouse ortholog of PSMB3 (C10-II) was cloned by cDNA isolation, and its protein identity was verified by 2D-NEPHGE-PAGE immunoblotting using antisera raised against the subunit, establishing it as one of the 17 subunits forming the mouse 20S proteasome core.\",\n      \"method\": \"cDNA cloning, two-dimensional NEPHGE-PAGE, immunoblotting with subunit-specific antisera\",\n      \"journal\": \"Immunogenetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct biochemical verification of protein identity by orthogonal methods (cDNA sequencing plus 2D immunoblot)\",\n      \"pmids\": [\"10436176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Psmb3 was identified and chromosomally assigned to distal mouse chromosome 11 within a dense gene cluster syntenic to human chromosome 17q12, establishing the mouse genomic locus.\",\n      \"method\": \"Transgene-induced contig sequencing and cDNA selection\",\n      \"journal\": \"Cytogenetic and genome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct genomic sequencing and mapping experiment, single study\",\n      \"pmids\": [\"12438746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"siRNA-mediated depletion of PSMB3 (a 20S proteasome subunit) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, demonstrating that proteasome function—specifically involving PSMB3—is required for activation of the Fanconi anemia DNA damage signaling pathway.\",\n      \"method\": \"siRNA knockdown of PSMB3 in human cells, immunofluorescence for FANCD2 foci, ubiquitination assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific genetic depletion with defined molecular phenotype (FANCD2 monoubiquitination), single lab\",\n      \"pmids\": [\"17671210\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"siRNA knockdown of PSMB3 in human airway epithelial cells increased susceptibility to AAV infection, placing PSMB3/proteasome function as a component of the subcellular barrier that restricts AAV virion trafficking or processing at the level of the secretory/ER-Golgi system.\",\n      \"method\": \"siRNA knockdown of PSMB3 combined with AAV infection efficiency assays in human airway epithelium models\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — specific siRNA knockdown with quantified viral transduction phenotype; single lab\",\n      \"pmids\": [\"21625534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In an RNAi screen of the druggable genome in multiple myeloma cells, silencing of PSMB3 synergistically potentiated growth inhibition by the proteasome inhibitor bortezomib, providing functional evidence that PSMB3 contributes to the proteolytic capacity required for myeloma cell survival under proteasome stress.\",\n      \"method\": \"Genome-wide siRNA screen (13,984 siRNAs) measuring proliferation in the presence of bortezomib; internal validation by proteasome subunit hits\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — large-scale functional genomic screen with internal validation; phenotypic readout is cell growth, no direct biochemical mechanism elucidated for PSMB3 specifically\",\n      \"pmids\": [\"21289309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Psmb3 (endopeptidase) shares the same thymic expression profile as Prss16 (Tssp) in mouse cortical thymic epithelial cells, being induced in wild-type and repressed in Prss16-knockout mice, suggesting its participation in self-peptide generation for positive selection of CD4+ T lymphocytes.\",\n      \"method\": \"Microarray transcriptional profiling comparing wild-type and Prss16-knockout thymic tissue\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — expression profiling only; no direct functional experiment for PSMB3 in thymic selection\",\n      \"pmids\": [\"21773946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"siRNA-mediated knockdown of PSMB3 in a human astrocytic cell line reduced CTG•CAG trinucleotide repeat expansions, demonstrating that the proteolytic activity of the 26S proteasome—specifically requiring PSMB3—drives repeat expansions in human cells.\",\n      \"method\": \"siRNA knockdown of PSMB3 in human astrocytic cells, quantitative trinucleotide repeat expansion assay; proteasome inhibitor controls confirmed proteolytic (not stress-response) mechanism\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific genetic depletion with quantified molecular phenotype; mechanism linked to proteolytic activity via inhibitor controls; single lab\",\n      \"pmids\": [\"23620289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Double knockdown of transcription factors NFE2L1 and NFE2L3 in cancer cells significantly reduced basal expression of PSMB3 (along with six other proteasome genes), impairing basal proteasome activity; NFE2L3 suppresses NFE2L1 translation via induction of CPEB3, revealing that PSMB3 basal expression in cancer cells is maintained by an NFE2L1/NFE2L3-CPEB3 translational repression axis.\",\n      \"method\": \"Double siRNA knockdown of NFE2L1/NFE2L3, qRT-PCR and western blot for PSMB3 and other proteasome subunits, proteasome activity assays, polysome profiling for NFE2L1 mRNA\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (knockdown, activity assay, polysome profiling); PSMB3 is one of seven subunits reduced, not the sole focus\",\n      \"pmids\": [\"32366381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"siRNA-mediated silencing of PSMB3 in human hepatocyte cell lines (HuH-7 and HepG2) was sufficient to suppress proteasome function and upregulate TRIB1 mRNA expression, demonstrating that PSMB3 activity is required to maintain basal proteasome function in hepatocytes and that its inhibition triggers transcriptional induction of TRIB1.\",\n      \"method\": \"siRNA knockdown of PSMB3, RT-qPCR for TRIB1 mRNA, western blot for protein levels and ubiquitylation; comparison with pharmacological proteasome inhibitors\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic silencing with specific molecular readout; multiple methods; single lab\",\n      \"pmids\": [\"37291259\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PSMB3 encodes the beta3 subunit of the 20S proteasome core, contributing to the complex's threonine-based multicatalytic protease activity; it is required for FANCD2 monoubiquitination in the Fanconi anemia DNA damage response, for restricting AAV virion trafficking at the secretory pathway, for driving trinucleotide repeat expansions via proteolytic activity, and for maintaining basal proteasome activity in cancer cells downstream of an NFE2L1/NFE2L3-CPEB3 transcriptional axis, with its chromosomal locus mapped to human 2q35.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PSMB3 is a constitutive beta-type subunit of the 20S proteasome core particle that contributes to ubiquitin-dependent proteolysis [PMID:10436176]. Its proteolytic activity is required for activation of the Fanconi anemia DNA damage response pathway, including FANCD2 monoubiquitination and formation of DNA repair foci for 53BP1, phospho-ATM, NBS1, BRCA1, and RAD51 [PMID:17671210], and also promotes CTG·CAG trinucleotide repeat expansions in human cells [PMID:23620289]. Basal transcription of PSMB3 is maintained by the NFE2L1/NFE2L3 transcription factor axis, coupling proteasome gene expression to cellular proteasome activity [PMID:32366381].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Mapping PSMB3 to chromosome 2q35 established it as an independently regulated proteasome subunit gene, resolving its genomic position relative to other beta subunit loci.\",\n      \"evidence\": \"FISH of genomic clones on human metaphase chromosomes\",\n      \"pmids\": [\"9344661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional data at this stage\", \"Transcriptional regulation uncharacterized\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Biochemical identification of PSMB3 as one of 17 subunits of the mammalian 20S proteasome core confirmed it is a bona fide structural component of the proteolytic particle.\",\n      \"evidence\": \"cDNA cloning, 2D NEPHGE-PAGE, and subunit-specific antisera in mouse 20S proteasome\",\n      \"pmids\": [\"10436176\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Catalytic versus structural role within the 20S core not distinguished\", \"No loss-of-function data\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that PSMB3 depletion blocks FANCD2 monoubiquitination and DNA repair foci formation revealed that proteasome activity is an upstream requirement for Fanconi anemia pathway activation and the broader DNA damage response.\",\n      \"evidence\": \"siRNA knockdown of PSMB3 in human cells with FANCD2 monoubiquitination and immunofluorescence foci assays\",\n      \"pmids\": [\"17671210\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the effect is PSMB3-specific or reflects general proteasome inhibition not resolved\", \"Substrate(s) degraded by the proteasome to license FA pathway activation not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing that PSMB3 knockdown reduces CTG·CAG trinucleotide repeat expansions extended proteasome function to genome instability mechanisms distinct from classical DNA repair, linking protein turnover to repeat expansion dynamics.\",\n      \"evidence\": \"siRNA knockdown of PSMB3 in human astrocytic cells with trinucleotide repeat expansion assay\",\n      \"pmids\": [\"23620289\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of proteasome substrate(s) whose degradation promotes repeat expansion unknown\", \"Whether other proteasome subunits phenocopy PSMB3 knockdown not shown in this study\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of the NFE2L1/NFE2L3 transcription factor axis as a driver of basal PSMB3 expression connected proteasome subunit gene regulation to the cellular proteasome homeostasis circuit.\",\n      \"evidence\": \"Double siRNA knockdown of NFE2L1 and NFE2L3 in cancer cells with RT-qPCR and proteasome activity assays\",\n      \"pmids\": [\"32366381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter binding by NFE2L1/NFE2L3 at the PSMB3 locus not demonstrated\", \"Relative contributions of NFE2L1 versus NFE2L3 to PSMB3 expression not separated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Observation that PSMB3 silencing upregulates TRIB1 mRNA suggested proteasome-dependent turnover of a transcriptional regulator suppresses TRIB1 expression, though the intermediate target is unknown.\",\n      \"evidence\": \"siRNA knockdown of PSMB3 with RT-qPCR in HuH-7 and HepG2 hepatocyte lines\",\n      \"pmids\": [\"37291259\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single-method, single-lab finding not independently confirmed\", \"Mechanism linking proteasome activity to TRIB1 transcription not identified\", \"Whether this is a PSMB3-specific or general proteasome effect is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A central unresolved question is whether any phenotype attributed to PSMB3 knockdown reflects a unique role of PSMB3 versus general proteasome inhibition; the specific substrates whose degradation licenses FA pathway activation and trinucleotide repeat expansion remain unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No PSMB3-specific catalytic activity distinct from the 20S core has been demonstrated\", \"No structural model of PSMB3 within the human 20S proteasome at atomic resolution reported in the timeline\", \"No disease-causing mutations in PSMB3 reported\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\"20S proteasome core\", \"26S proteasome\"],\n    \"partners\": [\"NFE2L1\", \"NFE2L3\", \"FANCD2\"],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"PSMB3 encodes the beta-3 subunit of the 20S proteasome core particle, which assembles with other alpha and beta subunits to form the multicatalytic threonine protease complex that, together with the 19S regulatory particle, constitutes the 26S proteasome responsible for ubiquitin-dependent protein degradation [PMID:8811196, PMID:10436176]. Beyond its general housekeeping role in proteostasis, PSMB3-dependent proteasome activity is specifically required for FANCD2 monoubiquitination in the Fanconi anemia DNA damage response [PMID:17671210], for CTG·CAG trinucleotide repeat expansion in human cells [PMID:23620289], and for restricting adeno-associated virus trafficking through the secretory pathway [PMID:21625534]. Basal PSMB3 transcription in cancer cells is maintained by an NFE2L1/NFE2L3–CPEB3 regulatory axis, and its depletion impairs overall proteasome capacity, sensitizing myeloma cells to bortezomib and triggering compensatory transcriptional responses such as TRIB1 induction in hepatocytes [PMID:32366381, PMID:21289309, PMID:37291259]. The human PSMB3 locus maps to chromosome 2q35, independently of the MHC-linked inducible proteasome subunit genes [PMID:9344661].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Establishing that PSMB3 is an integral beta-type subunit of the 20S proteasome core resolved its identity as part of the threonine-based multicatalytic protease that forms the catalytic heart of the 26S proteasome.\",\n      \"evidence\": \"Biochemical purification, structural analysis, and protease activity assays of 20S and 26S proteasome complexes\",\n      \"pmids\": [\"8811196\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise catalytic contribution of beta-3 versus other beta subunits not resolved\", \"No structure of PSMB3 alone or its specific active site\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Mapping PSMB3 to human chromosome 2q35 established that constitutive proteasome subunit genes are genomically dispersed from MHC-linked inducible subunits, implying distinct transcriptional regulation.\",\n      \"evidence\": \"FISH of genomic clones to human metaphase chromosomes\",\n      \"pmids\": [\"9344661\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cis-regulatory elements controlling PSMB3 transcription were not identified\", \"Relationship between genomic location and tissue-specific expression unexplored\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Cloning and biochemical verification of the mouse PSMB3 ortholog confirmed cross-species conservation and validated it as one of the 17 subunits of the mammalian 20S core.\",\n      \"evidence\": \"cDNA cloning, 2D-NEPHGE-PAGE, and immunoblotting with subunit-specific antisera in mouse\",\n      \"pmids\": [\"10436176\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional equivalence between mouse and human PSMB3 assumed but not tested by complementation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that PSMB3 knockdown blocks FANCD2 monoubiquitination revealed a specific requirement for proteasome activity in activating the Fanconi anemia DNA damage pathway, moving PSMB3 biology beyond generic proteostasis.\",\n      \"evidence\": \"siRNA knockdown in human cells with FANCD2 ubiquitination and foci formation assays\",\n      \"pmids\": [\"17671210\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the effect is direct or reflects general proteostasis collapse is unclear\", \"The proteasome substrate whose degradation activates FANCD2 was not identified\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Three independent functional genomic studies linked PSMB3 to diverse biological contexts — AAV restriction at the secretory pathway, bortezomib sensitivity in myeloma, and potential thymic peptide generation — broadening the phenotypic landscape of PSMB3 loss.\",\n      \"evidence\": \"siRNA knockdown with AAV transduction assays in airway epithelium; genome-wide siRNA screen measuring bortezomib synergy in myeloma; microarray profiling of thymic epithelial cells\",\n      \"pmids\": [\"21625534\", \"21289309\", \"21773946\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"AAV restriction mechanism (ER/Golgi trafficking versus capsid degradation) not resolved\", \"Bortezomib synergy screen did not dissect PSMB3-specific mechanism from general proteasome impairment\", \"Thymic expression data lack functional validation for T cell selection\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing that PSMB3 depletion reduces CTG·CAG trinucleotide repeat expansions established that proteasome proteolytic activity — not merely a stress response — drives microsatellite instability in human cells.\",\n      \"evidence\": \"siRNA knockdown in human astrocytic cells with quantitative repeat expansion assay; proteasome inhibitor controls discriminated proteolytic from stress-response mechanisms\",\n      \"pmids\": [\"23620289\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the proteasome substrate whose turnover promotes repeat expansion is unknown\", \"Generalizability to other repeat types not tested\", \"Single-lab result\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of the NFE2L1/NFE2L3–CPEB3 axis as a regulator of basal PSMB3 expression in cancer cells revealed how proteasome subunit transcription is maintained under non-stress conditions, complementing the known stress-induced bounce-back pathway.\",\n      \"evidence\": \"Double siRNA knockdown of NFE2L1/NFE2L3, qRT-PCR, proteasome activity assays, and polysome profiling in cancer cell lines\",\n      \"pmids\": [\"32366381\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PSMB3 was one of seven coordinately regulated subunits; unique regulatory elements of PSMB3 not dissected\", \"Whether the axis operates in non-transformed cells is unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrating that PSMB3 silencing in hepatocytes induces TRIB1 transcription provided the first link between proteasome capacity and the TRIB1 regulatory network, suggesting a feedback loop connecting proteostasis and lipid/metabolic gene regulation.\",\n      \"evidence\": \"siRNA knockdown of PSMB3 in HuH-7 and HepG2 cells with RT-qPCR for TRIB1 and western blot for ubiquitylation\",\n      \"pmids\": [\"37291259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting proteasome inhibition to TRIB1 transcription not identified\", \"Whether TRIB1 induction is specific to PSMB3 loss or a generic proteasome impairment response is unclear\", \"In vivo relevance not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The specific catalytic or structural contribution of the beta-3 subunit to 20S proteasome activity — as distinct from other constitutive beta subunits — remains undefined, and no disease-causing mutations in PSMB3 have been reported.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No active-site mutagenesis distinguishing PSMB3's catalytic role from assembly function\", \"No loss-of-function animal model\", \"No Mendelian disease association established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 6, 9, 10]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [4, 8]}\n    ],\n    \"complexes\": [\n      \"20S proteasome\",\n      \"26S proteasome\"\n    ],\n    \"partners\": [\n      \"NFE2L1\",\n      \"NFE2L3\",\n      \"FANCD2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}