{"gene":"UBB","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2010,"finding":"E2-25K/Hip2 (ubiquitin-conjugating enzyme) binds UBB+1 (frameshift mutant ubiquitin) via its MGF motif and residues in α9; this interaction drives synthesis of UBB+1-anchored polyubiquitin chains that inhibit the 26S proteasome and cause neuronal cell death. Mutagenesis of E2-25K residues disrupting UBB+1 binding markedly diminished synthesis of neurotoxic polyubiquitin.","method":"Crystal structure determination of UBB+1, E2-25K, E2-25K/ubiquitin, and E2-25K/UBB+1 complexes; polyubiquitylation assays with E2-25K mutants; active-site mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures plus in vitro reconstitution of polyubiquitylation plus mutagenesis in a single rigorous study","pmids":["20826778"],"is_preprint":false},{"year":2011,"finding":"The deubiquitinating enzyme UCH-L3 (human ortholog of yeast YUH1) hydrolyzes the C-terminal extension of UBB+1, generating a dysfunctional ubiquitin molecule (UBG76Y). In vitro oxidation of recombinant UCH-L3 impairs its deubiquitinating activity, providing a mechanism for UBB+1 accumulation under oxidative stress.","method":"In vitro deubiquitinating enzyme assay with recombinant UCH-L3/YUH1 and UBB+1 substrate; oxidative inactivation assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro enzymatic assay with defined substrate, single lab, single study","pmids":["21762696"],"is_preprint":false},{"year":2007,"finding":"Targeted disruption of the polyubiquitin gene Ubb in mice causes male and female infertility due to arrest of spermatocytes and oocytes during meiotic prophase I, demonstrating that Ubb-derived ubiquitin is consumed during and required for meiotic progression.","method":"Targeted gene disruption (knockout mouse); histological and cytological analysis of meiotic progression","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype replicated across both sexes, published in peer-reviewed journal","pmids":["18070917"],"is_preprint":false},{"year":2008,"finding":"Loss of Ubb selectively reduces total ubiquitin levels in the hypothalamus, leading to progressive neurodegeneration of arcuate nucleus neurons and adult-onset obesity with impaired hypothalamic energy balance control, demonstrating that adequate cellular ubiquitin supply is essential for neuronal survival.","method":"Ubb knockout mouse; quantitative ubiquitin measurement by immunoblot; histological and metabolic phenotyping","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular and organismal phenotypes, selective reduction of Ub in vulnerable region demonstrated biochemically","pmids":["18299572"],"is_preprint":false},{"year":2003,"finding":"UBB+1 promotes cytokeratin aggresome (Mallory body-like aggregate) formation in vitro: immunoprecipitated cytokeratin-8 incubated with ubiquitin plus UBB+1 (or proteasome inhibitor) formed CK-8/UBB+1/proteasome subunit-positive aggregates, and hepatocytes transfected with UBB+1 protein developed MB-like aggregates co-staining for CK-8 and ubiquitin.","method":"In vitro immunoprecipitation reconstitution assay; cell transfection with Chariot-delivered UBB+1 protein; immunofluorescence co-localization","journal":"Experimental and molecular pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro reconstitution plus cell-based validation, single lab, two orthogonal methods","pmids":["12710947"],"is_preprint":false},{"year":2014,"finding":"Disruption of Ubb in neural stem cells leads to upregulation of Notch intracellular domain (NICD) steady-state levels and consequent elevation of Notch target gene expression, which suppresses proneuronal gene expression, inhibits neurogenesis, and promotes premature gliogenesis.","method":"Ubb knockout mouse; cultured embryonic neural stem cells; immunoblot for NICD; gene expression analysis of Notch target and proneuronal genes","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with defined molecular pathway placement (NICD accumulation → Notch target gene upregulation → gliogenesis), single lab, multiple molecular readouts","pmids":["25391618"],"is_preprint":false},{"year":2014,"finding":"Restoration of free ubiquitin levels (but not ubiquitin conjugates) in Ubb−/− neurons via lentivirus-mediated exogenous ubiquitin delivery abolished increased apoptosis and improved neuronal and glial phenotypes, establishing that free ubiquitin pool maintenance (above a threshold) is the cell-autonomous requirement for neuronal survival.","method":"Lentivirus-mediated ubiquitin rescue in Ubb−/− primary neurons; immunoblot distinguishing free vs. conjugated Ub; apoptosis assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment with defined molecular distinction (free vs. conjugated Ub), single lab","pmids":["25280998"],"is_preprint":false},{"year":2013,"finding":"Knockdown of the polyubiquitin gene Ubb (Ubb-KD) with siRNA reduces cellular ubiquitin levels, attenuates TNFα-induced NF-κB activation, stabilizes tumor suppressor p53, and sensitizes cancer cells to stress, placing Ubb-derived ubiquitin as a required component for oncogenic NF-κB signaling and p53 turnover.","method":"siRNA knockdown; NF-κB reporter assay; p53 immunoblot; cancer cell viability assays; xenograft mouse model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with multiple molecular pathway readouts (NF-κB, p53) using orthogonal assays, single lab","pmids":["24022007"],"is_preprint":false},{"year":2014,"finding":"UBB+1 expression in astrocytes destabilizes mitochondrial fission-specific proteins Drp1, Fis1, and OPA3 (but not fusion proteins Mfn1, Mfn2, OPA1), inducing mitochondrial elongation/fusion and conferring resistance to H2O2-induced cell death. Proteasome inhibitors prevented the reduction in fission proteins, linking UBB+1-mediated proteasome inhibition to mitochondrial dynamics.","method":"Ectopic expression of UBB+1 in astrocytic cells; immunocytochemistry; FRAP; immunoblot with various protease/proteasome inhibitors; cell death assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional overexpression with multiple orthogonal readouts, pharmacological rescue, single lab","pmids":["24941066"],"is_preprint":false},{"year":2017,"finding":"The C-terminal 19-residue extension of UBB+1 is highly flexible (by NMR relaxation) but contains a short less-solvent-exposed stretch; it does not establish long-lived contacts with the globular ubiquitin domain yet alters binding to the UBA2 domain and membrane mimics, demonstrating that the frameshift extension changes biomolecular recognition without grossly perturbing ubiquitin structure.","method":"NMR relaxation and solvent accessibility measurements; thermal stability assay; binding assays with UBA2 domain and membrane mimics","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR structural characterization with functional binding validation, single lab, single study","pmids":["29175520"],"is_preprint":false},{"year":2017,"finding":"Elevated REST levels in Ubb−/− neural stem cells suppress neuronal differentiation; knockdown of REST in Ubb−/− cells restored expression of neuronal markers (βIII-tubulin, α-internexin) and reduced apoptosis, placing REST as a downstream mediator of Ub-deficiency-induced neurogenesis failure.","method":"Ubb knockout cells; siRNA knockdown of REST; immunofluorescence for neuronal markers; apoptosis assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via REST knockdown rescue in Ubb−/− background, single lab, multiple markers","pmids":["28285139"],"is_preprint":false},{"year":2018,"finding":"Lentivirus-mediated Ubb knockdown at DIV1 (early differentiation stage) impairs neural stem cell differentiation by activating Notch signaling when it is normally suppressed, whereas Ubb knockdown at DIV7 (after differentiation) has no effect on maturation, demonstrating a stage-specific requirement for Ub in suppressing Notch during NSC differentiation.","method":"Temporal lentiviral Ubb knockdown at defined days in vitro; Notch signaling readouts; neuronal differentiation markers","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — temporal KD epistasis with defined molecular pathway placement, single lab","pmids":["29422555"],"is_preprint":false},{"year":2023,"finding":"UBB+1 is secreted via an unconventional autophagosome-mediated pathway: expression of UBB+1 stimulates LC3B-I to LC3B-II conversion (autophagy induction), and ATG5 deficiency inhibits UBB+1 secretion. UBB+1 associates with secretory autophagosome marker SEC22B (by co-IP and SIM microscopy). UBB+1 is ubiquitinated on K11, K29, and K48 in cells (by LC-MS/MS and mutagenesis), but this ubiquitination does not contribute to its secretion.","method":"Co-immunoprecipitation; 3D structured illumination microscopy; LC-MS/MS; site-directed mutagenesis; ATG5 knockout; LC3B conversion assay","journal":"Biochimica et biophysica acta. Gene regulatory mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, SIM, MS, KO, mutagenesis), single lab","pmids":["37075976"],"is_preprint":false},{"year":2025,"finding":"SQSTM1/p62 functions as a ubiquitin receptor for UBB+1, recognizing its ubiquitin domain and loading it into autophagosomes for secretory autophagy. p62 oligomerization prevents UBB+1 aggregation. Both gain- and loss-of-function of p62 suppress UBB+1 secretion; p62 KO causes UBB+1 accumulation in insoluble aggregates. The R-SNARE SEC22B and Q-SNAREs Syntaxin-4 and SNAP23 mediate fusion of UBB+1-containing autophagosomes with the plasma membrane for exocytosis; SEC22B disruption reduces secretion without affecting intracellular turnover.","method":"Co-immunoprecipitation; p62 knockout and overexpression; SEC22B/STX4/SNAP23 disruption; vesicle secretion assays; immunofluorescence","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain/loss-of-function, multiple SNARE perturbations, Co-IP, multiple orthogonal methods in a single rigorous study","pmids":["41364760"],"is_preprint":false},{"year":2012,"finding":"In the locus coeruleus of Ubb−/− mice, Ubc is significantly upregulated and maintains free ubiquitin levels (though total Ub decreases), preventing neuronal dysfunction and degeneration, whereas in the hypothalamus both free and total Ub are reduced, correlating with neurodegeneration—establishing that free Ub maintenance above a threshold determines neuronal vulnerability.","method":"Ubb knockout mouse; quantitative immunoblot distinguishing free vs. conjugated Ub in dissected brain regions; histological neurodegeneration assessment","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with biochemical distinction of free vs. conjugated Ub pools in defined brain regions, single lab","pmids":["22285186"],"is_preprint":false},{"year":2021,"finding":"Low-level UBB+1 expression in yeast activates the autophagy pathway (increased ATG8p transport to vacuole, enhanced vacuolar activity) and reduces intracellular Aβ42/Aβ40 levels, ameliorating amyloid toxicity in an ATG1-dependent manner, placing UBB+1 upstream of autophagy activation.","method":"Yeast expression system; genome-wide transcriptional analysis; autophagy flux assay (ATG8p-GFP); Aβ toxicity and lifespan assay; atg1Δ epistasis","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with atg1Δ, multiple molecular readouts, single lab using yeast model","pmids":["34751669"],"is_preprint":false},{"year":2024,"finding":"UBB directly interacts with SP1 (specificity protein 1) and thereby controls VEGFA transcription; UBB downregulation in ccRCC releases SP1-dependent VEGFA upregulation. DNMT3A is recruited to the UBB promoter to epigenetically suppress UBB transcription.","method":"Co-immunoprecipitation (UBB–SP1 interaction); VEGFA reporter/expression assays; chromatin immunoprecipitation for DNMT3A at UBB promoter; siRNA/overexpression in ccRCC cells","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ChIP plus functional VEGFA readout, single lab","pmids":["38467852"],"is_preprint":false}],"current_model":"UBB encodes a polyubiquitin precursor whose primary role is to supply the cellular free ubiquitin pool; loss of Ubb selectively depletes free ubiquitin in vulnerable neurons (especially hypothalamic arcuate nucleus), causing meiotic arrest, hypothalamic neurodegeneration, and impaired neural stem cell differentiation via NICD/Notch and REST pathway dysregulation, while the frameshift mutant UBB+1—generated by molecular misreading—caps polyubiquitin chains, inhibits the 26S proteasome through its interaction with E2-25K (structurally defined), is removed by UCH-L3-mediated C-terminal hydrolysis, and is trafficked for secretion via SQSTM1/p62-dependent loading into secretory autophagosomes that fuse with the plasma membrane through SEC22B/Syntaxin-4/SNAP23 SNAREs."},"narrative":{"mechanistic_narrative":"UBB encodes a polyubiquitin precursor whose principal cellular role is to supply the free ubiquitin pool required for cell survival, proliferation, and differentiation [PMID:18299572, PMID:25280998]. Targeted disruption of Ubb in mice selectively depletes ubiquitin in vulnerable tissues, arresting spermatocytes and oocytes in meiotic prophase I [PMID:18070917] and causing progressive degeneration of hypothalamic arcuate nucleus neurons with adult-onset obesity [PMID:18299572]; maintenance of free ubiquitin above a threshold, rather than the conjugated pool, is the cell-autonomous determinant of neuronal vulnerability, as compensatory Ubc upregulation rescues the locus coeruleus but not the hypothalamus, and exogenous free ubiquitin abolishes Ubb-null neuronal apoptosis [PMID:25280998, PMID:22285186]. In neural stem cells, Ubb-derived ubiquitin is required during early differentiation to suppress Notch signaling—loss elevates Notch intracellular domain and REST, blocking neurogenesis and promoting premature gliogenesis [PMID:25391618, PMID:28285139, PMID:29422555]. Ubb-derived ubiquitin also sustains TNFα-induced NF-κB signaling and p53 turnover in cancer cells [PMID:24022007], and UBB binds the transcription factor SP1 to restrain VEGFA transcription in clear cell renal carcinoma, where DNMT3A epigenetically silences the UBB promoter [PMID:38467852]. A distinct branch of UBB biology concerns the frameshift mutant UBB+1: its E2-25K/Hip2-driven incorporation caps polyubiquitin chains and inhibits the 26S proteasome to drive neurotoxicity [PMID:20826778], it is hydrolyzed at its C-terminal extension by UCH-L3 in a manner sensitive to oxidative inactivation [PMID:21762696], and it is cleared by unconventional secretory autophagy in which SQSTM1/p62 recognizes its ubiquitin domain and loads it into autophagosomes that fuse with the plasma membrane via the SEC22B/Syntaxin-4/SNAP23 SNARE machinery [PMID:37075976, PMID:41364760].","teleology":[{"year":2003,"claim":"Established that the frameshift product UBB+1 can act as a pathological seed, driving formation of ubiquitin/cytokeratin protein aggregates resembling Mallory bodies.","evidence":"In vitro immunoprecipitation reconstitution and UBB+1 protein transfection into hepatocytes with immunofluorescence co-localization","pmids":["12710947"],"confidence":"Medium","gaps":["Does not establish whether aggregation occurs at endogenous UBB+1 levels","Mechanism linking UBB+1 to proteasome subunit recruitment not resolved"]},{"year":2007,"claim":"Demonstrated that Ubb-derived ubiquitin is consumed during and indispensable for meiotic progression, defining a non-redundant developmental requirement for this polyubiquitin gene.","evidence":"Ubb knockout mouse with histological and cytological analysis of meiosis in both sexes","pmids":["18070917"],"confidence":"High","gaps":["Which ubiquitin-dependent meiotic substrates are limiting is not identified","Does not address why meiotic cells are particularly ubiquitin-sensitive"]},{"year":2008,"claim":"Showed that adequate ubiquitin supply is essential for neuronal survival, linking Ubb loss to region-selective hypothalamic neurodegeneration and metabolic disease.","evidence":"Ubb knockout mouse with quantitative ubiquitin immunoblot and metabolic/histological phenotyping","pmids":["18299572"],"confidence":"High","gaps":["Molecular basis of arcuate nucleus selectivity not defined","Does not separate free vs conjugated ubiquitin contributions"]},{"year":2010,"claim":"Provided the structural and biochemical mechanism by which UBB+1 becomes neurotoxic: E2-25K/Hip2 binds UBB+1 to synthesize chain-capping polyubiquitin that inhibits the proteasome.","evidence":"Crystal structures of UBB+1, E2-25K, and their complexes plus polyubiquitylation assays with binding-disrupting mutants","pmids":["20826778"],"confidence":"High","gaps":["In vivo contribution of E2-25K to disease-associated UBB+1 toxicity not established","Does not quantify proteasome inhibition thresholds in neurons"]},{"year":2011,"claim":"Identified UCH-L3 as the deubiquitinase that processes the UBB+1 C-terminal extension and showed oxidative inactivation as a route to UBB+1 accumulation under stress.","evidence":"In vitro deubiquitinating assay with recombinant UCH-L3/YUH1 and oxidative inactivation assay","pmids":["21762696"],"confidence":"Medium","gaps":["Single in vitro study without cellular confirmation","Physiological relevance of oxidative UCH-L3 inhibition in disease not shown"]},{"year":2012,"claim":"Resolved why neuronal populations differ in vulnerability: free ubiquitin maintenance above a threshold, supported by compensatory Ubc upregulation, determines survival.","evidence":"Ubb knockout mouse with region-resolved immunoblot distinguishing free vs conjugated ubiquitin and histology","pmids":["22285186"],"confidence":"Medium","gaps":["Mechanism controlling region-specific Ubc compensation unknown","Quantitative free-ubiquitin threshold not defined"]},{"year":2013,"claim":"Placed Ubb-derived ubiquitin as a required component of oncogenic NF-κB signaling and p53 turnover, suggesting therapeutic relevance in cancer.","evidence":"siRNA knockdown with NF-κB reporter, p53 immunoblot, viability assays and xenograft model","pmids":["24022007"],"confidence":"Medium","gaps":["Does not distinguish direct vs general ubiquitin-pool effects on these pathways","Specificity to UBB versus other ubiquitin genes not fully isolated"]},{"year":2014,"claim":"Mapped how ubiquitin deficiency disrupts neural stem cell fate by elevating NICD/Notch signaling and impairing free-ubiquitin-dependent neuronal survival.","evidence":"Ubb knockout NSC cultures with NICD immunoblot, Notch/proneuronal gene analysis, and lentiviral free-ubiquitin rescue of apoptosis","pmids":["25391618","25280998"],"confidence":"Medium","gaps":["Direct ubiquitin-dependent NICD degradation step not biochemically defined","Does not establish in vivo developmental consequences"]},{"year":2014,"claim":"Extended UBB+1 pathology to organelle dynamics, linking its proteasome inhibition to destabilization of mitochondrial fission proteins and altered cell death sensitivity.","evidence":"Ectopic UBB+1 expression in astrocytes with immunoblot, FRAP, proteasome-inhibitor rescue and cell-death assays","pmids":["24941066"],"confidence":"Medium","gaps":["Direct mechanism of fission-protein loss not resolved","Overexpression system may not reflect endogenous UBB+1 levels"]},{"year":2017,"claim":"Defined the structural consequences of the frameshift extension and identified REST as a downstream mediator of ubiquitin-deficiency-induced neurogenesis failure.","evidence":"NMR relaxation/binding studies of the UBB+1 extension; siRNA REST knockdown rescue in Ubb-null NSCs","pmids":["29175520","28285139"],"confidence":"Medium","gaps":["How elevated REST mechanistically connects to ubiquitin shortage not defined","Functional relevance of altered UBA2/membrane binding by the extension not established in cells"]},{"year":2018,"claim":"Demonstrated a stage-specific requirement for Ubb in suppressing Notch during early NSC differentiation, refining when ubiquitin is critical for neurogenesis.","evidence":"Temporal lentiviral Ubb knockdown at defined days in vitro with Notch and differentiation readouts","pmids":["29422555"],"confidence":"Medium","gaps":["Molecular timer governing the stage-specific dependence unknown","Direct ubiquitin substrate within the Notch axis not identified"]},{"year":2021,"claim":"Showed UBB+1 can act upstream of autophagy activation, reducing amyloid-beta toxicity in an ATG1-dependent manner, indicating context-dependent protective signaling.","evidence":"Yeast expression with transcriptomics, autophagy flux assay, Aβ toxicity/lifespan, and atg1Δ epistasis","pmids":["34751669"],"confidence":"Medium","gaps":["Yeast model relevance to mammalian neurons uncertain","Mechanism by which UBB+1 triggers autophagy not defined"]},{"year":2023,"claim":"Established that UBB+1 is exported by unconventional secretory autophagy, identifying ATG5-dependent autophagosome routing and SEC22B association as the clearance pathway.","evidence":"Co-IP, 3D-SIM, LC-MS/MS ubiquitination mapping, ATG5 knockout and LC3B conversion assays","pmids":["37075976"],"confidence":"Medium","gaps":["Whether secretion is protective or pathological in vivo not shown","K11/K29/K48 ubiquitination role beyond secretion not resolved"]},{"year":2024,"claim":"Identified a transcription-factor-binding role for UBB, showing it interacts with SP1 to restrain VEGFA, with DNMT3A epigenetically silencing UBB in renal carcinoma.","evidence":"Co-IP for UBB–SP1, VEGFA reporter/expression assays, ChIP for DNMT3A at the UBB promoter, perturbation in ccRCC cells","pmids":["38467852"],"confidence":"Medium","gaps":["Whether free ubiquitin or the precursor mediates SP1 binding unclear","Single cancer-context study without broader validation"]},{"year":2025,"claim":"Completed the secretory route for UBB+1 by defining SQSTM1/p62 as its ubiquitin receptor and the SEC22B/Syntaxin-4/SNAP23 SNARE complex as the fusion machinery for plasma-membrane exocytosis.","evidence":"Reciprocal p62 gain/loss-of-function, SNARE disruptions, Co-IP, vesicle secretion assays and imaging","pmids":["41364760"],"confidence":"High","gaps":["Physiological consequence of secreted UBB+1 on neighboring cells not determined","Trigger that diverts UBB+1 to secretion versus degradation unknown"]},{"year":null,"claim":"How free ubiquitin scarcity is mechanistically translated into selective NICD/REST dysregulation and region-specific neurodegeneration, and whether UBB+1 secretion is protective or disease-propagating in vivo, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No identified rate-limiting ubiquitin substrate in the Notch/REST axis","In vivo fate and effect of secreted UBB+1 not established","Link between transcriptional UBB regulation and the free-ubiquitin pool not quantified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0031386","term_label":"protein tag activity","supporting_discovery_ids":[2,3,6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,8]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6,14]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12,13]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,3,6]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[12,13,15]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,11]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[13]}],"complexes":[],"partners":["UBE2K","UCHL3","SQSTM1","SEC22B","STX4","SNAP23","SP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P0CG47","full_name":"Polyubiquitin-B","aliases":[],"length_aa":229,"mass_kda":25.8,"function":"Exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in proteotoxic stress response and cell cycle; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling","subcellular_location":"Cytoplasm; Nucleus; Mitochondrion outer membrane","url":"https://www.uniprot.org/uniprotkb/P0CG47/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBB","classification":"Not Classified","n_dependent_lines":201,"n_total_lines":1090,"dependency_fraction":0.18440366972477065},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000170315","cell_line_id":"CID000332","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"UBB;UBC;RPS27A;UBA52","stoichiometry":10.0},{"gene":"HDAC6","stoichiometry":0.2},{"gene":"CLMN","stoichiometry":0.2},{"gene":"UBE3B","stoichiometry":0.2},{"gene":"NUB1","stoichiometry":0.2},{"gene":"RNF40","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000332","total_profiled":1310},"omim":[{"mim_id":"618866","title":"TREMOR, HEREDITARY ESSENTIAL, 6; ETM6","url":"https://www.omim.org/entry/618866"},{"mim_id":"616840","title":"PARKINSON DISEASE 23, AUTOSOMAL RECESSIVE EARLY-ONSET; PARK23","url":"https://www.omim.org/entry/616840"},{"mim_id":"616199","title":"POLYGLUCOSAN BODY MYOPATHY 2; PGBM2","url":"https://www.omim.org/entry/616199"},{"mim_id":"615708","title":"ZINC FINGER PROTEIN 451; ZNF451","url":"https://www.omim.org/entry/615708"},{"mim_id":"614534","title":"ANAPHASE-PROMOTING COMPLEX SUBUNIT 11; ANAPC11","url":"https://www.omim.org/entry/614534"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Cytosol","reliability":"Uncertain"},{"location":"Acrosome","reliability":"Additional"},{"location":"Equatorial segment","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UBB"},"hgnc":{"alias_symbol":["MGC8385","FLJ25987"],"prev_symbol":[]},"alphafold":{"accession":"P0CG47","domains":[{"cath_id":"3.10.20.90","chopping":"1-70","consensus_level":"high","plddt":95.695,"start":1,"end":70},{"cath_id":"3.10.20.90","chopping":"77-146","consensus_level":"high","plddt":95.169,"start":77,"end":146},{"cath_id":"3.10.20.90","chopping":"153-222","consensus_level":"high","plddt":95.2311,"start":153,"end":222}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P0CG47","model_url":"https://alphafold.ebi.ac.uk/files/AF-P0CG47-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P0CG47-F1-predicted_aligned_error_v6.png","plddt_mean":93.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBB","jax_strain_url":"https://www.jax.org/strain/search?query=UBB"},"sequence":{"accession":"P0CG47","fasta_url":"https://rest.uniprot.org/uniprotkb/P0CG47.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P0CG47/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P0CG47"}},"corpus_meta":[{"pmid":"18070917","id":"PMC_18070917","title":"The mouse polyubiquitin gene Ubb is essential for meiotic progression.","date":"2007","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18070917","citation_count":89,"is_preprint":false},{"pmid":"18299572","id":"PMC_18299572","title":"Hypothalamic neurodegeneration and adult-onset obesity in mice lacking the Ubb polyubiquitin gene.","date":"2008","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18299572","citation_count":82,"is_preprint":false},{"pmid":"20826778","id":"PMC_20826778","title":"Structural basis of E2-25K/UBB+1 interaction leading to proteasome inhibition and neurotoxicity.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20826778","citation_count":48,"is_preprint":false},{"pmid":"32161257","id":"PMC_32161257","title":"UBB pseudogene 4 encodes functional ubiquitin variants.","date":"2020","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/32161257","citation_count":47,"is_preprint":false},{"pmid":"24022007","id":"PMC_24022007","title":"Downregulation of ubiquitin level via knockdown of polyubiquitin gene Ubb as potential cancer therapeutic intervention.","date":"2013","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/24022007","citation_count":44,"is_preprint":false},{"pmid":"17931355","id":"PMC_17931355","title":"Expression of mutant ubiquitin (UBB+1) and p62 in myotilinopathies and desminopathies.","date":"2007","source":"Neuropathology and applied neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/17931355","citation_count":41,"is_preprint":false},{"pmid":"21762696","id":"PMC_21762696","title":"Mutant ubiquitin (UBB+1) associated with neurodegenerative disorders is hydrolyzed by ubiquitin C-terminal hydrolase L3 (UCH-L3).","date":"2011","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/21762696","citation_count":40,"is_preprint":false},{"pmid":"25391618","id":"PMC_25391618","title":"Disruption of polyubiquitin gene Ubb causes dysregulation of neural stem cell differentiation with premature gliogenesis.","date":"2014","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/25391618","citation_count":29,"is_preprint":false},{"pmid":"12710947","id":"PMC_12710947","title":"The mechanism of cytokeratin aggresome formation: the role of mutant ubiquitin (UBB+1).","date":"2003","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/12710947","citation_count":29,"is_preprint":false},{"pmid":"22730000","id":"PMC_22730000","title":"Long-term proteasomal inhibition in transgenic mice by UBB(+1) expression results in dysfunction of central respiration control reminiscent of brainstem neuropathology in Alzheimer patients.","date":"2012","source":"Acta neuropathologica","url":"https://pubmed.ncbi.nlm.nih.gov/22730000","citation_count":25,"is_preprint":false},{"pmid":"38467852","id":"PMC_38467852","title":"Downregulation of UBB potentiates SP1/VEGFA-dependent angiogenesis in clear cell renal cell carcinoma.","date":"2024","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/38467852","citation_count":22,"is_preprint":false},{"pmid":"2154095","id":"PMC_2154095","title":"Localization of the human UbB polyubiquitin gene to chromosome band 17p11.1-17p12.","date":"1990","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/2154095","citation_count":20,"is_preprint":false},{"pmid":"20002312","id":"PMC_20002312","title":"Loss of polyubiquitin gene Ubb leads to metabolic and sleep abnormalities in mice.","date":"2009","source":"Neuropathology and applied neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/20002312","citation_count":17,"is_preprint":false},{"pmid":"22082077","id":"PMC_22082077","title":"Review: unchained maladie - a reassessment of the role of Ubb(+1) -capped polyubiquitin chains in Alzheimer's disease.","date":"2012","source":"Neuropathology and applied neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/22082077","citation_count":17,"is_preprint":false},{"pmid":"25280998","id":"PMC_25280998","title":"Restoration of cellular ubiquitin reverses impairments in neuronal development caused by disruption of the polyubiquitin gene Ubb.","date":"2014","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/25280998","citation_count":17,"is_preprint":false},{"pmid":"34312369","id":"PMC_34312369","title":"Polyubiquitin gene Ubb is required for upregulation of Piwi protein level during mouse testis development.","date":"2021","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/34312369","citation_count":16,"is_preprint":false},{"pmid":"31654319","id":"PMC_31654319","title":"The Molecular Misreading of APP and UBB Induces a Humoral Immune Response in Alzheimer's Disease Patients with Diagnostic Ability.","date":"2019","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/31654319","citation_count":16,"is_preprint":false},{"pmid":"29422555","id":"PMC_29422555","title":"Temporal downregulation of the polyubiquitin gene Ubb affects neuronal differentiation, but not maturation, in cells cultured in vitro.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29422555","citation_count":16,"is_preprint":false},{"pmid":"22285186","id":"PMC_22285186","title":"Locus coeruleus neurons are resistant to dysfunction and degeneration by maintaining free ubiquitin levels although total ubiquitin levels decrease upon disruption of polyubiquitin gene Ubb.","date":"2012","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/22285186","citation_count":14,"is_preprint":false},{"pmid":"29175520","id":"PMC_29175520","title":"Alzheimer's disease-associated ubiquitin mutant Ubb+1: Properties of the carboxy-terminal domain and its influence on biomolecular interactions.","date":"2017","source":"International journal of biological macromolecules","url":"https://pubmed.ncbi.nlm.nih.gov/29175520","citation_count":11,"is_preprint":false},{"pmid":"30935687","id":"PMC_30935687","title":"Disruption of the polyubiquitin gene Ubb causes retinal degeneration in mice.","date":"2019","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/30935687","citation_count":10,"is_preprint":false},{"pmid":"24941066","id":"PMC_24941066","title":"Mutant ubiquitin UBB+1 induces mitochondrial fusion by destabilizing mitochondrial fission-specific proteins and confers resistance to oxidative stress-induced cell death in astrocytic cells.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24941066","citation_count":10,"is_preprint":false},{"pmid":"2834222","id":"PMC_2834222","title":"Human ubiquitin genes: one member of the UbB gene subfamily is a tetrameric non-processed pseudogene.","date":"1988","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/2834222","citation_count":10,"is_preprint":false},{"pmid":"32321641","id":"PMC_32321641","title":"Disruption of the polyubiquitin gene Ubb reduces the self-renewal capacity of neural stem cells.","date":"2020","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/32321641","citation_count":8,"is_preprint":false},{"pmid":"37075976","id":"PMC_37075976","title":"Alzheimer's disease-associated mutant ubiquitin (UBB+1) is secreted through an autophagosome-like vesicle-mediated unconventional pathway.","date":"2023","source":"Biochimica et biophysica acta. Gene regulatory mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/37075976","citation_count":6,"is_preprint":false},{"pmid":"33842548","id":"PMC_33842548","title":"The Dose-Dependent Pleiotropic Effects of the UBB+1 Ubiquitin Mutant.","date":"2021","source":"Frontiers in molecular biosciences","url":"https://pubmed.ncbi.nlm.nih.gov/33842548","citation_count":5,"is_preprint":false},{"pmid":"34751669","id":"PMC_34751669","title":"UBB+1 reduces amyloid-β cytotoxicity by activation of autophagy in yeast.","date":"2021","source":"Aging","url":"https://pubmed.ncbi.nlm.nih.gov/34751669","citation_count":5,"is_preprint":false},{"pmid":"41364760","id":"PMC_41364760","title":"Molecular mechanisms underlying p62-dependent secretion of the Alzheimer-associated ubiquitin variant UBB+1.","date":"2025","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41364760","citation_count":2,"is_preprint":false},{"pmid":"28285139","id":"PMC_28285139","title":"Regulation of REST levels overcomes dysregulation of neural stem cell differentiation caused by disruption of polyubiquitin gene Ubb.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28285139","citation_count":1,"is_preprint":false},{"pmid":"40287809","id":"PMC_40287809","title":"A Potential Link Between Early Onset Reactive Astrogliosis and Adult-Onset Dysfunction of Leptin Signaling in Polyubiquitin Gene Ubb Knockout Mice.","date":"2025","source":"Discovery medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40287809","citation_count":0,"is_preprint":false},{"pmid":"42120939","id":"PMC_42120939","title":"UBB as an early-stage potential biomarker for breast cancer via modulation of the ubiquitination pathway.","date":"2026","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/42120939","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.31.630908","title":"Molecular mechanisms underlying p62-dependent secretion of the Alzheimer-associated ubiquitin variant, UBB  <sup>+1</sup>","date":"2025-01-02","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.31.630908","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.19.24317595","title":"c-Triadem: A constrained, explainable deep learning model to identify novel biomarkers in Alzheimer’s disease","date":"2024-11-20","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.19.24317595","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.07.30.605947","title":"IDENTIFICATION OF IMMUNE RESPONSE AND RNA NETWORK OF RHEUMATOID ARTHRITIS AND MOLECULAR DOCKING OF  <i>CELASTRUS PANICULATUS</i>  AS POTENTIAL THERAPEUTIC AGENT","date":"2024-08-01","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.30.605947","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18333,"output_tokens":4486,"usd":0.061144,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12638,"output_tokens":4889,"usd":0.092707,"stage2_stop_reason":"end_turn"},"total_usd":0.153851,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"E2-25K/Hip2 (ubiquitin-conjugating enzyme) binds UBB+1 (frameshift mutant ubiquitin) via its MGF motif and residues in α9; this interaction drives synthesis of UBB+1-anchored polyubiquitin chains that inhibit the 26S proteasome and cause neuronal cell death. Mutagenesis of E2-25K residues disrupting UBB+1 binding markedly diminished synthesis of neurotoxic polyubiquitin.\",\n      \"method\": \"Crystal structure determination of UBB+1, E2-25K, E2-25K/ubiquitin, and E2-25K/UBB+1 complexes; polyubiquitylation assays with E2-25K mutants; active-site mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures plus in vitro reconstitution of polyubiquitylation plus mutagenesis in a single rigorous study\",\n      \"pmids\": [\"20826778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The deubiquitinating enzyme UCH-L3 (human ortholog of yeast YUH1) hydrolyzes the C-terminal extension of UBB+1, generating a dysfunctional ubiquitin molecule (UBG76Y). In vitro oxidation of recombinant UCH-L3 impairs its deubiquitinating activity, providing a mechanism for UBB+1 accumulation under oxidative stress.\",\n      \"method\": \"In vitro deubiquitinating enzyme assay with recombinant UCH-L3/YUH1 and UBB+1 substrate; oxidative inactivation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro enzymatic assay with defined substrate, single lab, single study\",\n      \"pmids\": [\"21762696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Targeted disruption of the polyubiquitin gene Ubb in mice causes male and female infertility due to arrest of spermatocytes and oocytes during meiotic prophase I, demonstrating that Ubb-derived ubiquitin is consumed during and required for meiotic progression.\",\n      \"method\": \"Targeted gene disruption (knockout mouse); histological and cytological analysis of meiotic progression\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype replicated across both sexes, published in peer-reviewed journal\",\n      \"pmids\": [\"18070917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Loss of Ubb selectively reduces total ubiquitin levels in the hypothalamus, leading to progressive neurodegeneration of arcuate nucleus neurons and adult-onset obesity with impaired hypothalamic energy balance control, demonstrating that adequate cellular ubiquitin supply is essential for neuronal survival.\",\n      \"method\": \"Ubb knockout mouse; quantitative ubiquitin measurement by immunoblot; histological and metabolic phenotyping\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular and organismal phenotypes, selective reduction of Ub in vulnerable region demonstrated biochemically\",\n      \"pmids\": [\"18299572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"UBB+1 promotes cytokeratin aggresome (Mallory body-like aggregate) formation in vitro: immunoprecipitated cytokeratin-8 incubated with ubiquitin plus UBB+1 (or proteasome inhibitor) formed CK-8/UBB+1/proteasome subunit-positive aggregates, and hepatocytes transfected with UBB+1 protein developed MB-like aggregates co-staining for CK-8 and ubiquitin.\",\n      \"method\": \"In vitro immunoprecipitation reconstitution assay; cell transfection with Chariot-delivered UBB+1 protein; immunofluorescence co-localization\",\n      \"journal\": \"Experimental and molecular pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro reconstitution plus cell-based validation, single lab, two orthogonal methods\",\n      \"pmids\": [\"12710947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Disruption of Ubb in neural stem cells leads to upregulation of Notch intracellular domain (NICD) steady-state levels and consequent elevation of Notch target gene expression, which suppresses proneuronal gene expression, inhibits neurogenesis, and promotes premature gliogenesis.\",\n      \"method\": \"Ubb knockout mouse; cultured embryonic neural stem cells; immunoblot for NICD; gene expression analysis of Notch target and proneuronal genes\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with defined molecular pathway placement (NICD accumulation → Notch target gene upregulation → gliogenesis), single lab, multiple molecular readouts\",\n      \"pmids\": [\"25391618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Restoration of free ubiquitin levels (but not ubiquitin conjugates) in Ubb−/− neurons via lentivirus-mediated exogenous ubiquitin delivery abolished increased apoptosis and improved neuronal and glial phenotypes, establishing that free ubiquitin pool maintenance (above a threshold) is the cell-autonomous requirement for neuronal survival.\",\n      \"method\": \"Lentivirus-mediated ubiquitin rescue in Ubb−/− primary neurons; immunoblot distinguishing free vs. conjugated Ub; apoptosis assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment with defined molecular distinction (free vs. conjugated Ub), single lab\",\n      \"pmids\": [\"25280998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Knockdown of the polyubiquitin gene Ubb (Ubb-KD) with siRNA reduces cellular ubiquitin levels, attenuates TNFα-induced NF-κB activation, stabilizes tumor suppressor p53, and sensitizes cancer cells to stress, placing Ubb-derived ubiquitin as a required component for oncogenic NF-κB signaling and p53 turnover.\",\n      \"method\": \"siRNA knockdown; NF-κB reporter assay; p53 immunoblot; cancer cell viability assays; xenograft mouse model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with multiple molecular pathway readouts (NF-κB, p53) using orthogonal assays, single lab\",\n      \"pmids\": [\"24022007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UBB+1 expression in astrocytes destabilizes mitochondrial fission-specific proteins Drp1, Fis1, and OPA3 (but not fusion proteins Mfn1, Mfn2, OPA1), inducing mitochondrial elongation/fusion and conferring resistance to H2O2-induced cell death. Proteasome inhibitors prevented the reduction in fission proteins, linking UBB+1-mediated proteasome inhibition to mitochondrial dynamics.\",\n      \"method\": \"Ectopic expression of UBB+1 in astrocytic cells; immunocytochemistry; FRAP; immunoblot with various protease/proteasome inhibitors; cell death assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional overexpression with multiple orthogonal readouts, pharmacological rescue, single lab\",\n      \"pmids\": [\"24941066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The C-terminal 19-residue extension of UBB+1 is highly flexible (by NMR relaxation) but contains a short less-solvent-exposed stretch; it does not establish long-lived contacts with the globular ubiquitin domain yet alters binding to the UBA2 domain and membrane mimics, demonstrating that the frameshift extension changes biomolecular recognition without grossly perturbing ubiquitin structure.\",\n      \"method\": \"NMR relaxation and solvent accessibility measurements; thermal stability assay; binding assays with UBA2 domain and membrane mimics\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR structural characterization with functional binding validation, single lab, single study\",\n      \"pmids\": [\"29175520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Elevated REST levels in Ubb−/− neural stem cells suppress neuronal differentiation; knockdown of REST in Ubb−/− cells restored expression of neuronal markers (βIII-tubulin, α-internexin) and reduced apoptosis, placing REST as a downstream mediator of Ub-deficiency-induced neurogenesis failure.\",\n      \"method\": \"Ubb knockout cells; siRNA knockdown of REST; immunofluorescence for neuronal markers; apoptosis assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via REST knockdown rescue in Ubb−/− background, single lab, multiple markers\",\n      \"pmids\": [\"28285139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Lentivirus-mediated Ubb knockdown at DIV1 (early differentiation stage) impairs neural stem cell differentiation by activating Notch signaling when it is normally suppressed, whereas Ubb knockdown at DIV7 (after differentiation) has no effect on maturation, demonstrating a stage-specific requirement for Ub in suppressing Notch during NSC differentiation.\",\n      \"method\": \"Temporal lentiviral Ubb knockdown at defined days in vitro; Notch signaling readouts; neuronal differentiation markers\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — temporal KD epistasis with defined molecular pathway placement, single lab\",\n      \"pmids\": [\"29422555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"UBB+1 is secreted via an unconventional autophagosome-mediated pathway: expression of UBB+1 stimulates LC3B-I to LC3B-II conversion (autophagy induction), and ATG5 deficiency inhibits UBB+1 secretion. UBB+1 associates with secretory autophagosome marker SEC22B (by co-IP and SIM microscopy). UBB+1 is ubiquitinated on K11, K29, and K48 in cells (by LC-MS/MS and mutagenesis), but this ubiquitination does not contribute to its secretion.\",\n      \"method\": \"Co-immunoprecipitation; 3D structured illumination microscopy; LC-MS/MS; site-directed mutagenesis; ATG5 knockout; LC3B conversion assay\",\n      \"journal\": \"Biochimica et biophysica acta. Gene regulatory mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, SIM, MS, KO, mutagenesis), single lab\",\n      \"pmids\": [\"37075976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SQSTM1/p62 functions as a ubiquitin receptor for UBB+1, recognizing its ubiquitin domain and loading it into autophagosomes for secretory autophagy. p62 oligomerization prevents UBB+1 aggregation. Both gain- and loss-of-function of p62 suppress UBB+1 secretion; p62 KO causes UBB+1 accumulation in insoluble aggregates. The R-SNARE SEC22B and Q-SNAREs Syntaxin-4 and SNAP23 mediate fusion of UBB+1-containing autophagosomes with the plasma membrane for exocytosis; SEC22B disruption reduces secretion without affecting intracellular turnover.\",\n      \"method\": \"Co-immunoprecipitation; p62 knockout and overexpression; SEC22B/STX4/SNAP23 disruption; vesicle secretion assays; immunofluorescence\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain/loss-of-function, multiple SNARE perturbations, Co-IP, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"41364760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In the locus coeruleus of Ubb−/− mice, Ubc is significantly upregulated and maintains free ubiquitin levels (though total Ub decreases), preventing neuronal dysfunction and degeneration, whereas in the hypothalamus both free and total Ub are reduced, correlating with neurodegeneration—establishing that free Ub maintenance above a threshold determines neuronal vulnerability.\",\n      \"method\": \"Ubb knockout mouse; quantitative immunoblot distinguishing free vs. conjugated Ub in dissected brain regions; histological neurodegeneration assessment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with biochemical distinction of free vs. conjugated Ub pools in defined brain regions, single lab\",\n      \"pmids\": [\"22285186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Low-level UBB+1 expression in yeast activates the autophagy pathway (increased ATG8p transport to vacuole, enhanced vacuolar activity) and reduces intracellular Aβ42/Aβ40 levels, ameliorating amyloid toxicity in an ATG1-dependent manner, placing UBB+1 upstream of autophagy activation.\",\n      \"method\": \"Yeast expression system; genome-wide transcriptional analysis; autophagy flux assay (ATG8p-GFP); Aβ toxicity and lifespan assay; atg1Δ epistasis\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with atg1Δ, multiple molecular readouts, single lab using yeast model\",\n      \"pmids\": [\"34751669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBB directly interacts with SP1 (specificity protein 1) and thereby controls VEGFA transcription; UBB downregulation in ccRCC releases SP1-dependent VEGFA upregulation. DNMT3A is recruited to the UBB promoter to epigenetically suppress UBB transcription.\",\n      \"method\": \"Co-immunoprecipitation (UBB–SP1 interaction); VEGFA reporter/expression assays; chromatin immunoprecipitation for DNMT3A at UBB promoter; siRNA/overexpression in ccRCC cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ChIP plus functional VEGFA readout, single lab\",\n      \"pmids\": [\"38467852\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBB encodes a polyubiquitin precursor whose primary role is to supply the cellular free ubiquitin pool; loss of Ubb selectively depletes free ubiquitin in vulnerable neurons (especially hypothalamic arcuate nucleus), causing meiotic arrest, hypothalamic neurodegeneration, and impaired neural stem cell differentiation via NICD/Notch and REST pathway dysregulation, while the frameshift mutant UBB+1—generated by molecular misreading—caps polyubiquitin chains, inhibits the 26S proteasome through its interaction with E2-25K (structurally defined), is removed by UCH-L3-mediated C-terminal hydrolysis, and is trafficked for secretion via SQSTM1/p62-dependent loading into secretory autophagosomes that fuse with the plasma membrane through SEC22B/Syntaxin-4/SNAP23 SNAREs.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBB encodes a polyubiquitin precursor whose principal cellular role is to supply the free ubiquitin pool required for cell survival, proliferation, and differentiation [#3, #6]. Targeted disruption of Ubb in mice selectively depletes ubiquitin in vulnerable tissues, arresting spermatocytes and oocytes in meiotic prophase I [#2] and causing progressive degeneration of hypothalamic arcuate nucleus neurons with adult-onset obesity [#3]; maintenance of free ubiquitin above a threshold, rather than the conjugated pool, is the cell-autonomous determinant of neuronal vulnerability, as compensatory Ubc upregulation rescues the locus coeruleus but not the hypothalamus, and exogenous free ubiquitin abolishes Ubb-null neuronal apoptosis [#6, #14]. In neural stem cells, Ubb-derived ubiquitin is required during early differentiation to suppress Notch signaling—loss elevates Notch intracellular domain and REST, blocking neurogenesis and promoting premature gliogenesis [#5, #10, #11]. Ubb-derived ubiquitin also sustains TNF\\u03b1-induced NF-\\u03baB signaling and p53 turnover in cancer cells [#7], and UBB binds the transcription factor SP1 to restrain VEGFA transcription in clear cell renal carcinoma, where DNMT3A epigenetically silences the UBB promoter [#16]. A distinct branch of UBB biology concerns the frameshift mutant UBB+1: its E2-25K/Hip2-driven incorporation caps polyubiquitin chains and inhibits the 26S proteasome to drive neurotoxicity [#0], it is hydrolyzed at its C-terminal extension by UCH-L3 in a manner sensitive to oxidative inactivation [#1], and it is cleared by unconventional secretory autophagy in which SQSTM1/p62 recognizes its ubiquitin domain and loads it into autophagosomes that fuse with the plasma membrane via the SEC22B/Syntaxin-4/SNAP23 SNARE machinery [#12, #13].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established that the frameshift product UBB+1 can act as a pathological seed, driving formation of ubiquitin/cytokeratin protein aggregates resembling Mallory bodies.\",\n      \"evidence\": \"In vitro immunoprecipitation reconstitution and UBB+1 protein transfection into hepatocytes with immunofluorescence co-localization\",\n      \"pmids\": [\"12710947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish whether aggregation occurs at endogenous UBB+1 levels\", \"Mechanism linking UBB+1 to proteasome subunit recruitment not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrated that Ubb-derived ubiquitin is consumed during and indispensable for meiotic progression, defining a non-redundant developmental requirement for this polyubiquitin gene.\",\n      \"evidence\": \"Ubb knockout mouse with histological and cytological analysis of meiosis in both sexes\",\n      \"pmids\": [\"18070917\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which ubiquitin-dependent meiotic substrates are limiting is not identified\", \"Does not address why meiotic cells are particularly ubiquitin-sensitive\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed that adequate ubiquitin supply is essential for neuronal survival, linking Ubb loss to region-selective hypothalamic neurodegeneration and metabolic disease.\",\n      \"evidence\": \"Ubb knockout mouse with quantitative ubiquitin immunoblot and metabolic/histological phenotyping\",\n      \"pmids\": [\"18299572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of arcuate nucleus selectivity not defined\", \"Does not separate free vs conjugated ubiquitin contributions\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided the structural and biochemical mechanism by which UBB+1 becomes neurotoxic: E2-25K/Hip2 binds UBB+1 to synthesize chain-capping polyubiquitin that inhibits the proteasome.\",\n      \"evidence\": \"Crystal structures of UBB+1, E2-25K, and their complexes plus polyubiquitylation assays with binding-disrupting mutants\",\n      \"pmids\": [\"20826778\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of E2-25K to disease-associated UBB+1 toxicity not established\", \"Does not quantify proteasome inhibition thresholds in neurons\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified UCH-L3 as the deubiquitinase that processes the UBB+1 C-terminal extension and showed oxidative inactivation as a route to UBB+1 accumulation under stress.\",\n      \"evidence\": \"In vitro deubiquitinating assay with recombinant UCH-L3/YUH1 and oxidative inactivation assay\",\n      \"pmids\": [\"21762696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single in vitro study without cellular confirmation\", \"Physiological relevance of oxidative UCH-L3 inhibition in disease not shown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolved why neuronal populations differ in vulnerability: free ubiquitin maintenance above a threshold, supported by compensatory Ubc upregulation, determines survival.\",\n      \"evidence\": \"Ubb knockout mouse with region-resolved immunoblot distinguishing free vs conjugated ubiquitin and histology\",\n      \"pmids\": [\"22285186\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism controlling region-specific Ubc compensation unknown\", \"Quantitative free-ubiquitin threshold not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed Ubb-derived ubiquitin as a required component of oncogenic NF-\\u03baB signaling and p53 turnover, suggesting therapeutic relevance in cancer.\",\n      \"evidence\": \"siRNA knockdown with NF-\\u03baB reporter, p53 immunoblot, viability assays and xenograft model\",\n      \"pmids\": [\"24022007\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not distinguish direct vs general ubiquitin-pool effects on these pathways\", \"Specificity to UBB versus other ubiquitin genes not fully isolated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped how ubiquitin deficiency disrupts neural stem cell fate by elevating NICD/Notch signaling and impairing free-ubiquitin-dependent neuronal survival.\",\n      \"evidence\": \"Ubb knockout NSC cultures with NICD immunoblot, Notch/proneuronal gene analysis, and lentiviral free-ubiquitin rescue of apoptosis\",\n      \"pmids\": [\"25391618\", \"25280998\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitin-dependent NICD degradation step not biochemically defined\", \"Does not establish in vivo developmental consequences\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended UBB+1 pathology to organelle dynamics, linking its proteasome inhibition to destabilization of mitochondrial fission proteins and altered cell death sensitivity.\",\n      \"evidence\": \"Ectopic UBB+1 expression in astrocytes with immunoblot, FRAP, proteasome-inhibitor rescue and cell-death assays\",\n      \"pmids\": [\"24941066\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism of fission-protein loss not resolved\", \"Overexpression system may not reflect endogenous UBB+1 levels\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the structural consequences of the frameshift extension and identified REST as a downstream mediator of ubiquitin-deficiency-induced neurogenesis failure.\",\n      \"evidence\": \"NMR relaxation/binding studies of the UBB+1 extension; siRNA REST knockdown rescue in Ubb-null NSCs\",\n      \"pmids\": [\"29175520\", \"28285139\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How elevated REST mechanistically connects to ubiquitin shortage not defined\", \"Functional relevance of altered UBA2/membrane binding by the extension not established in cells\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated a stage-specific requirement for Ubb in suppressing Notch during early NSC differentiation, refining when ubiquitin is critical for neurogenesis.\",\n      \"evidence\": \"Temporal lentiviral Ubb knockdown at defined days in vitro with Notch and differentiation readouts\",\n      \"pmids\": [\"29422555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular timer governing the stage-specific dependence unknown\", \"Direct ubiquitin substrate within the Notch axis not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed UBB+1 can act upstream of autophagy activation, reducing amyloid-beta toxicity in an ATG1-dependent manner, indicating context-dependent protective signaling.\",\n      \"evidence\": \"Yeast expression with transcriptomics, autophagy flux assay, A\\u03b2 toxicity/lifespan, and atg1\\u0394 epistasis\",\n      \"pmids\": [\"34751669\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Yeast model relevance to mammalian neurons uncertain\", \"Mechanism by which UBB+1 triggers autophagy not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established that UBB+1 is exported by unconventional secretory autophagy, identifying ATG5-dependent autophagosome routing and SEC22B association as the clearance pathway.\",\n      \"evidence\": \"Co-IP, 3D-SIM, LC-MS/MS ubiquitination mapping, ATG5 knockout and LC3B conversion assays\",\n      \"pmids\": [\"37075976\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether secretion is protective or pathological in vivo not shown\", \"K11/K29/K48 ubiquitination role beyond secretion not resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a transcription-factor-binding role for UBB, showing it interacts with SP1 to restrain VEGFA, with DNMT3A epigenetically silencing UBB in renal carcinoma.\",\n      \"evidence\": \"Co-IP for UBB\\u2013SP1, VEGFA reporter/expression assays, ChIP for DNMT3A at the UBB promoter, perturbation in ccRCC cells\",\n      \"pmids\": [\"38467852\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether free ubiquitin or the precursor mediates SP1 binding unclear\", \"Single cancer-context study without broader validation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Completed the secretory route for UBB+1 by defining SQSTM1/p62 as its ubiquitin receptor and the SEC22B/Syntaxin-4/SNAP23 SNARE complex as the fusion machinery for plasma-membrane exocytosis.\",\n      \"evidence\": \"Reciprocal p62 gain/loss-of-function, SNARE disruptions, Co-IP, vesicle secretion assays and imaging\",\n      \"pmids\": [\"41364760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of secreted UBB+1 on neighboring cells not determined\", \"Trigger that diverts UBB+1 to secretion versus degradation unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How free ubiquitin scarcity is mechanistically translated into selective NICD/REST dysregulation and region-specific neurodegeneration, and whether UBB+1 secretion is protective or disease-propagating in vivo, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified rate-limiting ubiquitin substrate in the Notch/REST axis\", \"In vivo fate and effect of secreted UBB+1 not established\", \"Link between transcriptional UBB regulation and the free-ubiquitin pool not quantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0031386\", \"supporting_discovery_ids\": [2, 3, 6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6, 14]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 3, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [12, 13, 15]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 11]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"UBE2K\", \"UCHL3\", \"SQSTM1\", \"SEC22B\", \"STX4\", \"SNAP23\", \"SP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}