{"gene":"PSMB1","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2010,"finding":"PSMB1 was identified as a BCL-3-binding proteasome subunit required for BCL-3 degradation. PSMB1-depleted cells fail to degrade polyubiquitinated BCL-3, and the N-terminal lysines 13 and 26 of BCL-3 (via Lys48-linked polyubiquitination) are required for recruitment to the proteasome via PSMB1. The E3 ligase FBW7 is dispensable for this degradation.","method":"Yeast two-hybrid, co-immunoprecipitation, PSMB1 knockdown cells, ubiquitination assays, mutagenesis of BCL-3 lysine residues","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid identification plus functional knockdown with specific substrate readout and mutagenesis, single lab with multiple orthogonal methods","pmids":["20558726"],"is_preprint":false},{"year":2013,"finding":"PSMB1 functions as a transcriptional activator of the Rbp4 gene in adipocytes. Mutation of a putative tyrosine phosphorylation site to phenylalanine increased nuclear translocation of PSMB1 and enhanced transcriptional activation, indicating that tyrosine phosphorylation status regulates PSMB1 nuclear localization and its transcriptional activator function.","method":"Site-directed mutagenesis of tyrosine phosphorylation site, nuclear translocation assays, transcriptional reporter assays in adipocytes","journal":"Bioscience, biotechnology, and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct mutagenesis with localization and functional transcription readout, single lab, single study","pmids":["23924720"],"is_preprint":false},{"year":2019,"finding":"PSMB1 interacts with IKK-ε and promotes its degradation through the ubiquitin-proteasome system, thereby negatively regulating innate antiviral immune responses. Knockdown of PSMB1 enhanced RNA virus-induced cytokine/chemokine production, while overexpression abolished virus-induced ISRE and IFNβ promoter activation. PSMB1 was found to inhibit both RLR and TLR3 signaling pathways.","method":"Co-immunoprecipitation, PSMB1 knockdown and overexpression, luciferase reporter assays (ISRE, IFNβ promoter), proteasome inhibitor assays, viral infection models","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction plus loss-of-function and gain-of-function with mechanistic pathway readouts, single lab, multiple orthogonal approaches","pmids":["30682859"],"is_preprint":false},{"year":2020,"finding":"A p(Tyr103His) variant in PSMB1/β6 weakens interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits, destabilizing the 20S proteasome complex. This variant impairs both processing of PSMB1/β6 and its incorporation into the proteasome, reducing proteasome activity. CRISPR/Cas9 mutagenesis or morpholino knockdown of psmb1 in zebrafish caused microcephaly, microphthalmia, and reduced brain size.","method":"Structural modeling, biochemical assays in SHSY5Y cells (proteasome activity, processing), CRISPR/Cas9 mutagenesis and morpholino knockdown in zebrafish","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (structural modeling, human cell biochemistry, zebrafish genetic models) across human and zebrafish systems with convergent results","pmids":["32129449"],"is_preprint":false},{"year":2023,"finding":"PSMB1 interacts with PRRSV Nsp12 and recruits the selective autophagy cargo receptor NBR1 to promote autophagic degradation of Nsp12, thereby inhibiting PRRSV replication. The E3 ubiquitin ligase STUB1 interacts with Nsp12, and degradation is dependent on ubiquitination of Nsp12 at lysine 130. PSMB1 expression is downregulated by PRRSV via interaction with transcription factor EBF1.","method":"Co-immunoprecipitation, co-localization in lysosomes, autophagy/proteasome inhibitor assays, cotransfection, site-directed mutagenesis (K130 of Nsp12), knockdown/overexpression experiments","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus mutagenesis plus inhibitor assays, single lab, multiple orthogonal methods","pmids":["36602366"],"is_preprint":false},{"year":2023,"finding":"PSMB1 directly binds to oncoprotein RAB34 and promotes its proteasome-dependent degradation, leading to inactivation of MEK/ERK signaling and inhibition of colorectal cancer progression. Kinetin enhances the interaction between PSMB1 and RAB34, facilitating RAB34 degradation and decreasing MEK/ERK phosphorylation.","method":"Co-immunoprecipitation, functional assays (proteasome-dependent degradation), western blotting for MEK/ERK signaling, PDX and liver metastasis mouse models, CADD-based drug screening","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding shown by Co-IP plus functional degradation assays plus in vivo models, single lab, multiple orthogonal methods","pmids":["38159835"],"is_preprint":false},{"year":2024,"finding":"In zebrafish, psmb1 is required for craniofacial cartilage, tendon, and muscle differentiation and morphogenesis. psmb1 mutants show failed chondrocyte convergent extension, defective chondrocyte differentiation, absent hyohyal muscles, and disorganized tendons. Overexpression of psmb1 specifically in sox10+ cells rescued cartilage and tendon phenotypes but only partially rescued muscle phenotypes, indicating tissue-autonomous and non-autonomous roles.","method":"Zebrafish psmb1 mutant analysis, cell-type-specific rescue by overexpression (sox10+ cells), histological and live imaging of chondrocyte behavior","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with specific cellular phenotypes plus cell-type-specific rescue experiment, single lab","pmids":["39171526"],"is_preprint":false},{"year":2012,"finding":"Recombinant human PSMB1 protein binds to celastrol in vitro, as demonstrated by BIAcore surface plasmon resonance analysis, with binding affinity exceeding 27 RU at 10 µmol/L celastrol.","method":"Recombinant protein expression/purification, BIAcore surface plasmon resonance binding assay","journal":"Sheng wu gong cheng xue bao = Chinese journal of biotechnology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single in vitro binding assay, no functional follow-up, single lab, single method","pmids":["22667125"],"is_preprint":false}],"current_model":"PSMB1 (proteasome subunit β6/C5) is a structural and catalytic component of the 20S proteasome whose primary role is to promote proteasome-dependent degradation of specific substrates (including BCL-3, IKK-ε, and RAB34) through direct substrate binding, and it also facilitates selective autophagy-mediated degradation of viral proteins (e.g., PRRSV Nsp12) via recruitment of NBR1; additionally, PSMB1 can translocate to the nucleus where it acts as a transcriptional activator, a function regulated by tyrosine phosphorylation status, and loss-of-function in zebrafish demonstrates its essential roles in proteasome assembly, brain development, and craniofacial morphogenesis."},"narrative":{"mechanistic_narrative":"PSMB1 (proteasome subunit β6/C5) is a core component of the 20S proteasome that drives ubiquitin-proteasome-dependent degradation of specific regulatory substrates, and a p(Tyr103His) variant that weakens its interaction with the PSMA5/α5 subunit destabilizes the 20S complex, impairs PSMB1 processing and incorporation, and reduces proteasome activity [PMID:32129449]. Beyond its structural role, PSMB1 selects defined substrates for destruction: it binds BCL-3 to mediate Lys48-polyubiquitin-dependent degradation independently of FBW7 [PMID:20558726], promotes proteasomal degradation of IKK-ε to negatively regulate RLR- and TLR3-driven antiviral signaling [PMID:30682859], and directly binds the oncoprotein RAB34 to promote its degradation and thereby inactivate MEK/ERK signaling and suppress colorectal cancer progression [PMID:38159835]. PSMB1 also routes viral proteins for selective autophagy, recruiting the cargo receptor NBR1 to degrade PRRSV Nsp12 and restrict viral replication [PMID:36602366]. Loss of psmb1 in zebrafish produces microcephaly, microphthalmia, and craniofacial cartilage, tendon, and muscle defects through both tissue-autonomous and non-autonomous mechanisms, establishing essential roles in proteasome assembly and in brain and craniofacial development [PMID:32129449, PMID:39171526]. A distinct nuclear pool of PSMB1, regulated by tyrosine phosphorylation status, acts as a transcriptional activator of the Rbp4 gene in adipocytes [PMID:23924720].","teleology":[{"year":2010,"claim":"Established that PSMB1 is not merely a passive catalytic subunit but a substrate-selective docking point of the proteasome, recruiting a specific polyubiquitinated target for degradation.","evidence":"Yeast two-hybrid, co-IP, PSMB1 knockdown, and BCL-3 lysine mutagenesis in cultured cells","pmids":["20558726"],"confidence":"High","gaps":["Does not define how PSMB1 distinguishes BCL-3 from other ubiquitinated proteins","Mechanism of recruitment to the catalytic core not structurally resolved","Generality of substrate-specific binding beyond BCL-3 not tested"]},{"year":2012,"claim":"Addressed whether PSMB1 is a direct drug target by testing small-molecule binding to recombinant protein.","evidence":"BIAcore surface plasmon resonance binding of recombinant PSMB1 to celastrol in vitro","pmids":["22667125"],"confidence":"Low","gaps":["Single in vitro binding assay with no functional follow-up","No demonstration that binding affects proteasome activity in cells","Binding site on PSMB1 not mapped"]},{"year":2013,"claim":"Revealed a moonlighting nuclear function for PSMB1 as a transcriptional activator and showed its localization is controlled by tyrosine phosphorylation.","evidence":"Tyrosine-to-phenylalanine mutagenesis, nuclear translocation and transcriptional reporter assays in adipocytes","pmids":["23924720"],"confidence":"Medium","gaps":["Kinase/phosphatase controlling the phosphorylation site not identified","Direct DNA or promoter binding by PSMB1 not demonstrated","Relationship between nuclear PSMB1 and assembled 20S proteasome unclear"]},{"year":2019,"claim":"Connected PSMB1-mediated degradation to immune signaling by identifying IKK-ε as a substrate whose turnover dampens antiviral responses.","evidence":"Reciprocal co-IP, knockdown/overexpression, ISRE/IFNβ luciferase reporters, and proteasome inhibitor assays in viral infection models","pmids":["30682859"],"confidence":"Medium","gaps":["E3 ligase ubiquitinating IKK-ε not identified","Single lab; reciprocal substrate-specificity controls limited","In vivo physiological relevance of antiviral regulation not tested"]},{"year":2020,"claim":"Demonstrated the consequences of disrupting PSMB1 assembly, linking a missense variant to 20S destabilization and to developmental phenotypes in vivo.","evidence":"Structural modeling, proteasome activity/processing assays in SHSY5Y cells, and CRISPR/morpholino knockdown in zebrafish","pmids":["32129449"],"confidence":"High","gaps":["No formal Mendelian disease gene attribution stated in the finding","Mechanism linking reduced proteasome activity to microcephaly not resolved","Whether substrate-specific functions are also impaired by the variant untested"]},{"year":2023,"claim":"Extended PSMB1 substrate selection into autophagy, showing it can recruit a cargo receptor to route a viral protein for autophagic rather than proteasomal degradation.","evidence":"Co-IP, lysosomal co-localization, autophagy/proteasome inhibitor assays, and K130 mutagenesis of PRRSV Nsp12","pmids":["36602366"],"confidence":"Medium","gaps":["How PSMB1 chooses autophagy versus proteasome routing unclear","Direct interaction with NBR1 versus indirect bridging not fully resolved","Single lab; host-protein substrates of this autophagy route not identified"]},{"year":2023,"claim":"Showed PSMB1 substrate selection has tumor-suppressive output by degrading RAB34 to inactivate MEK/ERK signaling, and is pharmacologically enhanceable.","evidence":"Co-IP, proteasome-dependent degradation assays, MEK/ERK western blotting, PDX/liver metastasis mouse models, and kinetin drug screening","pmids":["38159835"],"confidence":"Medium","gaps":["Structural basis of PSMB1–RAB34 binding not defined","Whether kinetin acts directly on PSMB1 not established","Generality across cancer types beyond colorectal not tested"]},{"year":2024,"claim":"Defined the developmental tissue requirements for psmb1, distinguishing autonomous from non-autonomous roles in craniofacial morphogenesis.","evidence":"Zebrafish psmb1 mutant phenotyping with sox10+ cell-type-specific rescue and live imaging of chondrocyte behavior","pmids":["39171526"],"confidence":"Medium","gaps":["Molecular substrates underlying chondrocyte/tendon/muscle defects unknown","Why muscle phenotype is only partially rescued unresolved","Link between proteasome activity and convergent extension mechanistically undefined"]},{"year":null,"claim":"How PSMB1 achieves substrate selectivity across distinct degradation routes (proteasomal versus autophagic) and how its catalytic/structural role integrates with its nuclear transcriptional and developmental functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of PSMB1 substrate-binding interface","Unifying mechanism connecting proteasome assembly, substrate selection, and nuclear function absent","E3 ligases pairing with PSMB1 for most substrates unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,5]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,6]}],"complexes":["20S proteasome"],"partners":["BCL3","IKBKE","RAB34","PSMA5","NBR1","EBF1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P20618","full_name":"Proteasome subunit beta type-1","aliases":["Macropain subunit C5","Multicatalytic endopeptidase complex subunit C5","Proteasome component C5","Proteasome gamma chain","Proteasome subunit beta-6","beta-6"],"length_aa":241,"mass_kda":26.5,"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/P20618/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PSMB1","classification":"Common Essential","n_dependent_lines":1195,"n_total_lines":1208,"dependency_fraction":0.9892384105960265},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000008018","cell_line_id":"CID000099","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"PSMA1","stoichiometry":10.0},{"gene":"PSMA2","stoichiometry":10.0},{"gene":"PSMA3","stoichiometry":10.0},{"gene":"PSMA4","stoichiometry":10.0},{"gene":"PSMA5","stoichiometry":10.0},{"gene":"PSMA6","stoichiometry":10.0},{"gene":"PSME3","stoichiometry":10.0},{"gene":"PSMD12","stoichiometry":10.0},{"gene":"PSMD11","stoichiometry":10.0},{"gene":"PSMD3","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000099","total_profiled":1310},"omim":[{"mim_id":"620038","title":"NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, HYPOTONIA, AND ABSENT LANGUAGE; NEDMHAL","url":"https://www.omim.org/entry/620038"},{"mim_id":"613386","title":"PROTEASOME MATURATION PROTEIN; POMP","url":"https://www.omim.org/entry/613386"},{"mim_id":"604726","title":"SERINE/THREONINE PROTEIN KINASE 17A; STK17A","url":"https://www.omim.org/entry/604726"},{"mim_id":"602017","title":"PROTEASOME SUBUNIT, BETA-TYPE, 1; PSMB1","url":"https://www.omim.org/entry/602017"},{"mim_id":"176843","title":"PROTEASOME SUBUNIT, ALPHA-TYPE, 3; PSMA3","url":"https://www.omim.org/entry/176843"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PSMB1"},"hgnc":{"alias_symbol":["PMSB1","HC5"],"prev_symbol":[]},"alphafold":{"accession":"P20618","domains":[{"cath_id":"3.60.20.10","chopping":"38-237","consensus_level":"high","plddt":97.4206,"start":38,"end":237}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P20618","model_url":"https://alphafold.ebi.ac.uk/files/AF-P20618-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P20618-F1-predicted_aligned_error_v6.png","plddt_mean":91.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PSMB1","jax_strain_url":"https://www.jax.org/strain/search?query=PSMB1"},"sequence":{"accession":"P20618","fasta_url":"https://rest.uniprot.org/uniprotkb/P20618.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P20618/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P20618"}},"corpus_meta":[{"pmid":"32129449","id":"PMC_32129449","title":"Biallelic variants in PSMB1 encoding the proteasome subunit β6 cause impairment of proteasome function, microcephaly, intellectual disability, developmental delay and short stature.","date":"2020","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32129449","citation_count":39,"is_preprint":false},{"pmid":"36602366","id":"PMC_36602366","title":"PSMB1 Inhibits the Replication of Porcine Reproductive and Respiratory Syndrome Virus by Recruiting NBR1 To Degrade Nonstructural Protein 12 by Autophagy.","date":"2023","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/36602366","citation_count":23,"is_preprint":false},{"pmid":"20558726","id":"PMC_20558726","title":"BCL-3 degradation involves its polyubiquitination through a FBW7-independent pathway and its binding to the proteasome subunit PSMB1.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20558726","citation_count":23,"is_preprint":false},{"pmid":"30682859","id":"PMC_30682859","title":"PSMB1 Negatively Regulates the Innate Antiviral Immunity by Facilitating Degradation of IKK-ε.","date":"2019","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/30682859","citation_count":15,"is_preprint":false},{"pmid":"9887308","id":"PMC_9887308","title":"Characterization of cryptic plasmids pDP1 and pSMB1 of Streptococcus pneumoniae.","date":"1999","source":"Plasmid","url":"https://pubmed.ncbi.nlm.nih.gov/9887308","citation_count":13,"is_preprint":false},{"pmid":"38159835","id":"PMC_38159835","title":"Discovery of Kinetin in inhibiting colorectal cancer progression via enhancing PSMB1-mediated RAB34 degradation.","date":"2023","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/38159835","citation_count":7,"is_preprint":false},{"pmid":"15194198","id":"PMC_15194198","title":"Comparative analysis of the PDCD2-TBP-PSMB1 region in vertebrates.","date":"2004","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/15194198","citation_count":5,"is_preprint":false},{"pmid":"23924720","id":"PMC_23924720","title":"Role of nuclear localization of PSMB1 in transcriptional activation.","date":"2013","source":"Bioscience, biotechnology, and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23924720","citation_count":5,"is_preprint":false},{"pmid":"39171526","id":"PMC_39171526","title":"The proteasome subunit psmb1 is essential for craniofacial cartilage maturation and morphogenesis.","date":"2024","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/39171526","citation_count":1,"is_preprint":false},{"pmid":"40317040","id":"PMC_40317040","title":"Circ-PSMB1 knockdown inhibits the pyroptosis of ox-LDL treated human aortic cells via the miR-624-3p/ASC axis.","date":"2025","source":"Journal of cardiothoracic surgery","url":"https://pubmed.ncbi.nlm.nih.gov/40317040","citation_count":1,"is_preprint":false},{"pmid":"22667125","id":"PMC_22667125","title":"[Expression, purification of proteasome subunit PSMB1 and application in screening of possible proteasome inhibitors].","date":"2012","source":"Sheng wu gong cheng xue bao = Chinese journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/22667125","citation_count":0,"is_preprint":false},{"pmid":"42177737","id":"PMC_42177737","title":"PSMB1 screened by CRISPR-CAS9 promoted breast cancer progression via PI3K-AKT-mTOR signaling.","date":"2026","source":"Discover oncology","url":"https://pubmed.ncbi.nlm.nih.gov/42177737","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7576,"output_tokens":2334,"usd":0.028869,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9388,"output_tokens":3246,"usd":0.064045,"stage2_stop_reason":"end_turn"},"total_usd":0.092914,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"PSMB1 was identified as a BCL-3-binding proteasome subunit required for BCL-3 degradation. PSMB1-depleted cells fail to degrade polyubiquitinated BCL-3, and the N-terminal lysines 13 and 26 of BCL-3 (via Lys48-linked polyubiquitination) are required for recruitment to the proteasome via PSMB1. The E3 ligase FBW7 is dispensable for this degradation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, PSMB1 knockdown cells, ubiquitination assays, mutagenesis of BCL-3 lysine residues\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid identification plus functional knockdown with specific substrate readout and mutagenesis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20558726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PSMB1 functions as a transcriptional activator of the Rbp4 gene in adipocytes. Mutation of a putative tyrosine phosphorylation site to phenylalanine increased nuclear translocation of PSMB1 and enhanced transcriptional activation, indicating that tyrosine phosphorylation status regulates PSMB1 nuclear localization and its transcriptional activator function.\",\n      \"method\": \"Site-directed mutagenesis of tyrosine phosphorylation site, nuclear translocation assays, transcriptional reporter assays in adipocytes\",\n      \"journal\": \"Bioscience, biotechnology, and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct mutagenesis with localization and functional transcription readout, single lab, single study\",\n      \"pmids\": [\"23924720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PSMB1 interacts with IKK-ε and promotes its degradation through the ubiquitin-proteasome system, thereby negatively regulating innate antiviral immune responses. Knockdown of PSMB1 enhanced RNA virus-induced cytokine/chemokine production, while overexpression abolished virus-induced ISRE and IFNβ promoter activation. PSMB1 was found to inhibit both RLR and TLR3 signaling pathways.\",\n      \"method\": \"Co-immunoprecipitation, PSMB1 knockdown and overexpression, luciferase reporter assays (ISRE, IFNβ promoter), proteasome inhibitor assays, viral infection models\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction plus loss-of-function and gain-of-function with mechanistic pathway readouts, single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"30682859\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A p(Tyr103His) variant in PSMB1/β6 weakens interactions between PSMB1/β6 and PSMA5/α5 proteasome subunits, destabilizing the 20S proteasome complex. This variant impairs both processing of PSMB1/β6 and its incorporation into the proteasome, reducing proteasome activity. CRISPR/Cas9 mutagenesis or morpholino knockdown of psmb1 in zebrafish caused microcephaly, microphthalmia, and reduced brain size.\",\n      \"method\": \"Structural modeling, biochemical assays in SHSY5Y cells (proteasome activity, processing), CRISPR/Cas9 mutagenesis and morpholino knockdown in zebrafish\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (structural modeling, human cell biochemistry, zebrafish genetic models) across human and zebrafish systems with convergent results\",\n      \"pmids\": [\"32129449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PSMB1 interacts with PRRSV Nsp12 and recruits the selective autophagy cargo receptor NBR1 to promote autophagic degradation of Nsp12, thereby inhibiting PRRSV replication. The E3 ubiquitin ligase STUB1 interacts with Nsp12, and degradation is dependent on ubiquitination of Nsp12 at lysine 130. PSMB1 expression is downregulated by PRRSV via interaction with transcription factor EBF1.\",\n      \"method\": \"Co-immunoprecipitation, co-localization in lysosomes, autophagy/proteasome inhibitor assays, cotransfection, site-directed mutagenesis (K130 of Nsp12), knockdown/overexpression experiments\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus mutagenesis plus inhibitor assays, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36602366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PSMB1 directly binds to oncoprotein RAB34 and promotes its proteasome-dependent degradation, leading to inactivation of MEK/ERK signaling and inhibition of colorectal cancer progression. Kinetin enhances the interaction between PSMB1 and RAB34, facilitating RAB34 degradation and decreasing MEK/ERK phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, functional assays (proteasome-dependent degradation), western blotting for MEK/ERK signaling, PDX and liver metastasis mouse models, CADD-based drug screening\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding shown by Co-IP plus functional degradation assays plus in vivo models, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38159835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In zebrafish, psmb1 is required for craniofacial cartilage, tendon, and muscle differentiation and morphogenesis. psmb1 mutants show failed chondrocyte convergent extension, defective chondrocyte differentiation, absent hyohyal muscles, and disorganized tendons. Overexpression of psmb1 specifically in sox10+ cells rescued cartilage and tendon phenotypes but only partially rescued muscle phenotypes, indicating tissue-autonomous and non-autonomous roles.\",\n      \"method\": \"Zebrafish psmb1 mutant analysis, cell-type-specific rescue by overexpression (sox10+ cells), histological and live imaging of chondrocyte behavior\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with specific cellular phenotypes plus cell-type-specific rescue experiment, single lab\",\n      \"pmids\": [\"39171526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Recombinant human PSMB1 protein binds to celastrol in vitro, as demonstrated by BIAcore surface plasmon resonance analysis, with binding affinity exceeding 27 RU at 10 µmol/L celastrol.\",\n      \"method\": \"Recombinant protein expression/purification, BIAcore surface plasmon resonance binding assay\",\n      \"journal\": \"Sheng wu gong cheng xue bao = Chinese journal of biotechnology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single in vitro binding assay, no functional follow-up, single lab, single method\",\n      \"pmids\": [\"22667125\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PSMB1 (proteasome subunit β6/C5) is a structural and catalytic component of the 20S proteasome whose primary role is to promote proteasome-dependent degradation of specific substrates (including BCL-3, IKK-ε, and RAB34) through direct substrate binding, and it also facilitates selective autophagy-mediated degradation of viral proteins (e.g., PRRSV Nsp12) via recruitment of NBR1; additionally, PSMB1 can translocate to the nucleus where it acts as a transcriptional activator, a function regulated by tyrosine phosphorylation status, and loss-of-function in zebrafish demonstrates its essential roles in proteasome assembly, brain development, and craniofacial morphogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PSMB1 (proteasome subunit β6/C5) is a core component of the 20S proteasome that drives ubiquitin-proteasome-dependent degradation of specific regulatory substrates, and a p(Tyr103His) variant that weakens its interaction with the PSMA5/α5 subunit destabilizes the 20S complex, impairs PSMB1 processing and incorporation, and reduces proteasome activity [#3]. Beyond its structural role, PSMB1 selects defined substrates for destruction: it binds BCL-3 to mediate Lys48-polyubiquitin-dependent degradation independently of FBW7 [#0], promotes proteasomal degradation of IKK-ε to negatively regulate RLR- and TLR3-driven antiviral signaling [#2], and directly binds the oncoprotein RAB34 to promote its degradation and thereby inactivate MEK/ERK signaling and suppress colorectal cancer progression [#5]. PSMB1 also routes viral proteins for selective autophagy, recruiting the cargo receptor NBR1 to degrade PRRSV Nsp12 and restrict viral replication [#4]. Loss of psmb1 in zebrafish produces microcephaly, microphthalmia, and craniofacial cartilage, tendon, and muscle defects through both tissue-autonomous and non-autonomous mechanisms, establishing essential roles in proteasome assembly and in brain and craniofacial development [#3, #6]. A distinct nuclear pool of PSMB1, regulated by tyrosine phosphorylation status, acts as a transcriptional activator of the Rbp4 gene in adipocytes [#1].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that PSMB1 is not merely a passive catalytic subunit but a substrate-selective docking point of the proteasome, recruiting a specific polyubiquitinated target for degradation.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, PSMB1 knockdown, and BCL-3 lysine mutagenesis in cultured cells\",\n      \"pmids\": [\"20558726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Does not define how PSMB1 distinguishes BCL-3 from other ubiquitinated proteins\",\n        \"Mechanism of recruitment to the catalytic core not structurally resolved\",\n        \"Generality of substrate-specific binding beyond BCL-3 not tested\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Addressed whether PSMB1 is a direct drug target by testing small-molecule binding to recombinant protein.\",\n      \"evidence\": \"BIAcore surface plasmon resonance binding of recombinant PSMB1 to celastrol in vitro\",\n      \"pmids\": [\"22667125\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Single in vitro binding assay with no functional follow-up\",\n        \"No demonstration that binding affects proteasome activity in cells\",\n        \"Binding site on PSMB1 not mapped\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed a moonlighting nuclear function for PSMB1 as a transcriptional activator and showed its localization is controlled by tyrosine phosphorylation.\",\n      \"evidence\": \"Tyrosine-to-phenylalanine mutagenesis, nuclear translocation and transcriptional reporter assays in adipocytes\",\n      \"pmids\": [\"23924720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Kinase/phosphatase controlling the phosphorylation site not identified\",\n        \"Direct DNA or promoter binding by PSMB1 not demonstrated\",\n        \"Relationship between nuclear PSMB1 and assembled 20S proteasome unclear\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected PSMB1-mediated degradation to immune signaling by identifying IKK-ε as a substrate whose turnover dampens antiviral responses.\",\n      \"evidence\": \"Reciprocal co-IP, knockdown/overexpression, ISRE/IFNβ luciferase reporters, and proteasome inhibitor assays in viral infection models\",\n      \"pmids\": [\"30682859\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"E3 ligase ubiquitinating IKK-ε not identified\",\n        \"Single lab; reciprocal substrate-specificity controls limited\",\n        \"In vivo physiological relevance of antiviral regulation not tested\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated the consequences of disrupting PSMB1 assembly, linking a missense variant to 20S destabilization and to developmental phenotypes in vivo.\",\n      \"evidence\": \"Structural modeling, proteasome activity/processing assays in SHSY5Y cells, and CRISPR/morpholino knockdown in zebrafish\",\n      \"pmids\": [\"32129449\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No formal Mendelian disease gene attribution stated in the finding\",\n        \"Mechanism linking reduced proteasome activity to microcephaly not resolved\",\n        \"Whether substrate-specific functions are also impaired by the variant untested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended PSMB1 substrate selection into autophagy, showing it can recruit a cargo receptor to route a viral protein for autophagic rather than proteasomal degradation.\",\n      \"evidence\": \"Co-IP, lysosomal co-localization, autophagy/proteasome inhibitor assays, and K130 mutagenesis of PRRSV Nsp12\",\n      \"pmids\": [\"36602366\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How PSMB1 chooses autophagy versus proteasome routing unclear\",\n        \"Direct interaction with NBR1 versus indirect bridging not fully resolved\",\n        \"Single lab; host-protein substrates of this autophagy route not identified\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed PSMB1 substrate selection has tumor-suppressive output by degrading RAB34 to inactivate MEK/ERK signaling, and is pharmacologically enhanceable.\",\n      \"evidence\": \"Co-IP, proteasome-dependent degradation assays, MEK/ERK western blotting, PDX/liver metastasis mouse models, and kinetin drug screening\",\n      \"pmids\": [\"38159835\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural basis of PSMB1–RAB34 binding not defined\",\n        \"Whether kinetin acts directly on PSMB1 not established\",\n        \"Generality across cancer types beyond colorectal not tested\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the developmental tissue requirements for psmb1, distinguishing autonomous from non-autonomous roles in craniofacial morphogenesis.\",\n      \"evidence\": \"Zebrafish psmb1 mutant phenotyping with sox10+ cell-type-specific rescue and live imaging of chondrocyte behavior\",\n      \"pmids\": [\"39171526\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular substrates underlying chondrocyte/tendon/muscle defects unknown\",\n        \"Why muscle phenotype is only partially rescued unresolved\",\n        \"Link between proteasome activity and convergent extension mechanistically undefined\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PSMB1 achieves substrate selectivity across distinct degradation routes (proteasomal versus autophagic) and how its catalytic/structural role integrates with its nuclear transcriptional and developmental functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No structural model of PSMB1 substrate-binding interface\",\n        \"Unifying mechanism connecting proteasome assembly, substrate selection, and nuclear function absent\",\n        \"E3 ligases pairing with PSMB1 for most substrates unidentified\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 6]}\n    ],\n    \"complexes\": [\n      \"20S proteasome\"\n    ],\n    \"partners\": [\n      \"BCL3\",\n      \"IKBKE\",\n      \"RAB34\",\n      \"PSMA5\",\n      \"NBR1\",\n      \"EBF1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":4,"faith_total":5,"faith_pct":80.0}}