{"gene":"UBE2E3","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":1997,"finding":"UBE2E3 (Ubch9) cannot form a thioester with ubiquitin but can form a thioester with SUMO-1, establishing it as a SUMO conjugating enzyme rather than a ubiquitin conjugating enzyme. SUMO conjugation proceeds via a distinct E1 activity separate from the ubiquitin E1.","method":"In vitro thioester formation assay with ubiquitin and SUMO-1","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical assay (thioester formation) replicated and extended in multiple subsequent studies","pmids":["9409737"],"is_preprint":false},{"year":1998,"finding":"In the presence of the SUMO-1 E1 activating enzyme, UBE2E3 (Ubch9) directly conjugates SUMO-1 to IκBα primarily on K21 (also used for ubiquitin modification), thereby protecting IκBα from signal-induced ubiquitination and proteasomal degradation and inhibiting NF-κB activation. Notably, unlike ubiquitination, SUMO-1 modification of IκBα is inhibited by phosphorylation of S32/S36.","method":"In vitro reconstitution with purified recombinant proteins; mutagenesis of IκBα lysine and serine residues","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — fully reconstituted in vitro with defined purified components, mutagenesis confirmation, replicated in follow-up review paper","pmids":["9734360","10582246"],"is_preprint":false},{"year":1999,"finding":"The SUMO-1 E1 activating enzyme (SAE1/SAE2 heterodimer) transfers SUMO-1 thioester to UBE2E3 (Ubch9), which then conjugates SUMO-1 to IκBα in vitro without requiring an E3-equivalent activity, defining UBE2E3 as the E2 enzyme in the minimal SUMO-1 conjugation pathway.","method":"In vitro reconstitution with purified recombinant SAE1/SAE2, UBE2E3, SUMO-1, and IκBα; ATP-dependent thioester assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — fully reconstituted in vitro with all homogeneous recombinant components, mechanistically defines E2 role","pmids":["10187858"],"is_preprint":false},{"year":1999,"finding":"UBE2E3 encodes a functional E2 ubiquitin-conjugating enzyme that forms an E1-dependent thioester bond with ubiquitin through its active-site cysteine (C145); mutation of C145 to serine abolishes thioester formation, confirming the catalytic cysteine.","method":"GST-fusion protein thioester assay; active-site mutagenesis (C145S)","journal":"Cytogenetics and cell genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical thioester assay with active-site mutagenesis in a single study; note this contradicts the earlier Desterro 1997 finding that Ubch9 cannot thioester with Ub — the two papers describe different proteins (UBE2E3 vs UBC9/UBE2I). UBE2E3/UbcM2 CAN thioester with ubiquitin; the alias 'Ubch9' in Desterro refers to the SUMO E2 UBC9 (UBE2I), a different gene. Confidence is high for UBE2E3 forming Ub-thioester.","pmids":["10343118"],"is_preprint":false},{"year":2001,"finding":"UBE2E3 interacts with RING-finger proteins ARA54 and RNF8 via its UBC domain (interaction requires intact RING domain on the E3 partners), and supports E3-dependent autoubiquitination of ARA54 and RNF8 in vitro and in cells, linking UBE2E3 to nuclear protein ubiquitination.","method":"Yeast two-hybrid screen; deletion mutagenesis mapping; in vitro ubiquitination assay with Sf9-expressed proteins; transfection/ubiquitination in COS-7 cells","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus in vitro ubiquitination assay plus cell-based ubiquitination, single lab","pmids":["11322894"],"is_preprint":false},{"year":2004,"finding":"UBE2E3 acts as the E2 enzyme in concert with the E3 ligase Nedd4-2 to ubiquitinate and downregulate ENaC. UBE2E3 and Nedd4-2 co-immunoprecipitate. A catalytically inactive UBE2E3-C145S mutant increases ENaC cell-surface expression in Xenopus oocytes, and this effect depends on intact PY motifs (Nedd4-2 binding sites) and ubiquitination sites on ENaC. No additive effect is seen when UBE2E3-CS is co-expressed with an inactive Nedd4-2 mutant, placing UBE2E3 in the same pathway as Nedd4-2.","method":"Xenopus oocyte electrophysiology; co-immunoprecipitation; catalytic inactive mutant; epistasis with Nedd4-2 mutant; renal mpkCCD cell transepithelial Na+ transport assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional epistasis in two cell systems, co-IP, active-site mutant, pathway placement; multiple orthogonal methods","pmids":["14993279"],"is_preprint":false},{"year":2004,"finding":"UBE2E3 (Ubch9) promotes SUMO modification of Werner helicase (WRN) in a synergistic manner with the tumor suppressor p14 Arf. p14 Arf-driven WRN SUMOylation causes redistribution of WRN within the nucleus, an effect reversed by a SUMO-specific protease, implicating UBE2E3-mediated SUMOylation in WRN nuclear localization.","method":"Cell-based SUMO conjugation assay; co-expression; SUMO-specific protease reversal; fluorescence microscopy of WRN redistribution","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional cell-based assay with protease reversal confirming SUMO dependence, single lab","pmids":["15355988"],"is_preprint":false},{"year":2005,"finding":"Both Nedd4 and Nedd4-2 use UBE2E3 as an E2 partner in in vitro ubiquitination assays, but UBE2E3 supports substrate ubiquitination less efficiently than UbcH5b for these HECT E3 ligases.","method":"In vitro ubiquitination assay comparing multiple E2 enzymes","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro biochemical assay, single lab, single paper","pmids":["16337426"],"is_preprint":false},{"year":2008,"finding":"UBE2E3 localizes to the nucleus of RPE cells and is required for their proliferation; siRNA-mediated depletion causes cell-cycle exit, loss of Ki-67, accumulation of the CDK inhibitor p27Kip1, and doubling of cell area. The mouse ortholog UbcM2 is transcriptionally downregulated during RPE development in vivo.","method":"siRNA knockdown; immunofluorescence (Ki-67, p27Kip1); cell counting; rescue experiment; LacZ reporter mouse for developmental expression","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with specific rescue, defined cell-cycle phenotype, nuclear localization confirmed, single lab","pmids":["18614808"],"is_preprint":false},{"year":2011,"finding":"The N-terminal extension of UBE2E3 prevents it from functioning together with the RING E3 ligase Ro52 (TRIM21), unlike the N-terminal extensions of UBE2E1 and UBE2E2 which allow productive interaction, demonstrating that the class III E2 N-terminal extension uniquely modulates E2/E3 pairing specificity.","method":"E2 panel screening in ubiquitination assay; NMR and ELISA mapping of E2/E3 interface","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro ubiquitination assay with panel of E2s and NMR interface mapping, single lab","pmids":["21862588"],"is_preprint":false},{"year":2014,"finding":"UBE2E3 ubiquitinates TDP-43; all three UBE2E family members enhance TDP-43 ubiquitination, but catalytically inactive UBE2E3(C145S) is much less efficient. Silencing UBE2E3 reduces TDP-43 ubiquitination. UBE2E3 was identified as a TDP-43 interactor by yeast two-hybrid and confirmed by co-immunoprecipitation and co-localization in HEK293E cells.","method":"Yeast two-hybrid; co-immunoprecipitation; siRNA knockdown; overexpression with proteasome inhibitor; catalytic mutant (C145S)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, active-site mutant, knockdown, multiple orthogonal methods, single lab","pmids":["24825905"],"is_preprint":false},{"year":2014,"finding":"UBE2E3 (UbcM2) is intrinsically restricted to monoubiquitylation: backside residues of the enzyme (distant from the active site) and K48 of ubiquitin together prevent polyubiquitin chain synthesis. Mutation of backside residues enables K63-linked (and to a lesser extent K6- and K48-linked) chain synthesis, revealing a two-fold non-catalytic restriction mechanism.","method":"Fully recombinant in vitro ubiquitylation assay; backside mutagenesis; ubiquitin K-to-R mutant panel","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with mutagenesis of both enzyme backside and ubiquitin lysines, multiple orthogonal mutants tested in single rigorous study","pmids":["24901938"],"is_preprint":false},{"year":2014,"finding":"UBE2E3 and its nuclear import receptor importin-11 (Imp-11) regulate NRF2 subcellular distribution and transcriptional activity. Knockdown of UBE2E3 reduces nuclear NRF2, decreases NRF2 target gene expression, and relocalizes NRF2 to a perinuclear cluster of mitochondria. Imp-11 restricts KEAP1 from prematurely extracting NRF2 from target gene promoters.","method":"siRNA knockdown; immunofluorescence; gene expression analysis of NRF2 target genes; subcellular fractionation","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown with defined localization and transcriptional phenotype, single lab, multiple readouts","pmids":["25378586"],"is_preprint":false},{"year":2014,"finding":"Mulan (mitochondrial E3 ubiquitin ligase) interacts specifically with UBE2E3 among multiple E2 partners; the Mulan-UBE2E3 complex recruits GABARAP via an LC3-interacting region (LIR) in Mulan's RING domain, and this interaction requires the presence of UBE2E3. This places UBE2E3 in a mitophagy regulatory complex at the outer mitochondrial membrane.","method":"Modified yeast two-hybrid screen (RING-E2 fusion); co-immunoprecipitation; LIR motif mutagenesis","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid plus co-IP with LIR mutagenesis, single lab, interaction confirmed but reconstitution not performed","pmids":["25224329"],"is_preprint":false},{"year":2018,"finding":"UBE2E3 loss induces cellular senescence in the absence of overt DNA damage. Cells depleted of UBE2E3 display a distinct senescence-associated secretory phenotype, increased mitochondrial and lysosomal mass, increased sensitivity to mitochondrial/lysosomal poisons, and elevated basal autophagic flux. The senescence phenotype is partially suppressed by co-depletion of p53, p21CIP1/WAF1, or p16INK4a.","method":"siRNA knockdown; SA-β-galactosidase assay; SASP marker analysis; organelle mass assays; genetic epistasis with p53/p21/p16 co-depletion","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with multiple phenotypic readouts and genetic epistasis placing UBE2E3 upstream of p53/p21/p16 in senescence pathway, single lab","pmids":["29879550"],"is_preprint":false},{"year":2020,"finding":"PJA1 (Praja1 RING-finger E3 ubiquitin ligase) co-immunoprecipitates with both CTF TDP-43 and UBE2E3, identifying UBE2E3 as the E2 partner for PJA1-mediated ubiquitination of TDP-43. PJA1 suppresses phosphorylation and cytoplasmic aggregate formation of TDP-43 in neuronal cells and in vivo in mouse motor neurons.","method":"Co-immunoprecipitation; adenoviral overexpression in neural stem cell-derived neurons; in vivo mouse facial motor neuron model","journal":"Neuropathology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP identifying E2-E3 complex, supported by in vivo functional data, single lab","pmids":["32686212"],"is_preprint":false},{"year":2020,"finding":"OTUB1 inhibits the polyubiquitination activity of UBE2E3 (along with UBE2E1 and UBE2E2) at physiologically relevant concentrations. However, unlike UBE2E1 and UBE2E2, OTUB1 is unable to suppress autoubiquitination by UBE2E3, revealing a unique feature of UBE2E3 within the UBE2E family in its interaction with OTUB1.","method":"In vitro ubiquitination assay; kinetic/thermodynamic characterization of OTUB1:E2 complexes","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct in vitro biochemical assay with quantitative analysis, single lab","pmids":["32049508"],"is_preprint":false},{"year":2021,"finding":"UBE2E3 knockdown accelerates cellular senescence and inhibits osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), while overexpression of UBE2E3 attenuates senescence and enhances osteogenic differentiation of aged BMSCs. Mechanistically, UBE2E3 regulates the NRF2 pathway to control BMSC senescence and differentiation.","method":"siRNA knockdown; lentiviral overexpression; osteogenic differentiation assay; senescence markers; NRF2 pathway readout","journal":"PeerJ","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, knockdown/overexpression with phenotypic readout, NRF2 mechanistic link asserted but not directly demonstrated","pmids":["34820159"],"is_preprint":false},{"year":2023,"finding":"RCBTB1 co-immunoprecipitates with UBE2E3 and with CUL3 from RPE cell protein lysates, placing RCBTB1 in a complex with UBE2E3 and the CUL3 E3 ligase scaffold and suggesting UBE2E3 participates in a CUL3-RCBTB1 ubiquitin ligase complex relevant to oxidative stress response.","method":"Co-immunoprecipitation from iPSC-derived RPE cells using UBE2E3 and CUL3 antibodies","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP experiment, single lab, no functional follow-up on UBE2E3 specifically","pmids":["37408192"],"is_preprint":false}],"current_model":"UBE2E3 (UbcM2/UbcH9) is a metazoan ubiquitin-conjugating enzyme (E2) that forms an E1-dependent thioester with ubiquitin via its active-site C145, is intrinsically restricted to monoubiquitylation through backside surface residues and K48 of ubiquitin, partners with HECT E3 ligases (Nedd4-2, Mulan) and RING E3 ligases (ARA54, RNF8, PJA1) to ubiquitinate substrates including ENaC, TDP-43, ARA54, and RNF8, regulates NRF2 nuclear localization and transcriptional activity, is required for cell proliferation (with depletion inducing p53/p21/p16-dependent senescence), and participates in mitophagy via a Mulan-UBE2E3-GABARAP complex at the outer mitochondrial membrane; the gene also shares its 'Ubch9' alias with UBC9/UBE2I (the primary SUMO E2), so early papers attributing SUMO conjugation to 'Ubch9' reflect UBE2I activity, not UBE2E3."},"narrative":{"mechanistic_narrative":"UBE2E3 (UbcM2) is a metazoan ubiquitin-conjugating (E2) enzyme that forms an E1-dependent thioester with ubiquitin through its active-site cysteine C145, supporting E3-dependent substrate ubiquitination [PMID:10343118]. A defining feature of UBE2E3 is its intrinsic restriction to monoubiquitylation: backside surface residues of the enzyme acting together with K48 of ubiquitin block polyubiquitin chain synthesis, and mutation of these backside residues unlocks K63-, K6-, and K48-linked chain formation [PMID:24901938]. UBE2E3 cooperates with diverse E3 ligases to ubiquitinate distinct substrates: it partners with the HECT ligases Nedd4/Nedd4-2 to ubiquitinate and downregulate the epithelial sodium channel ENaC [PMID:14993279, PMID:16337426], with the RING ligases ARA54 and RNF8 to support their autoubiquitination [PMID:11322894], and with the RING ligases PJA1 to drive ubiquitination of TDP-43, suppressing TDP-43 phosphorylation and cytoplasmic aggregation [PMID:24825905, PMID:32686212]. Its E2/E3 pairing is selectively gated by its class III N-terminal extension, which prevents productive pairing with Ro52/TRIM21 [PMID:21862588], and its polyubiquitination output is constrained by the deubiquitinase OTUB1 [PMID:32049508]. Beyond proteostasis, UBE2E3 controls the redox transcription factor NRF2 by promoting its nuclear localization and target-gene expression together with importin-11 [PMID:25378586], and it operates at the outer mitochondrial membrane within a Mulan-UBE2E3-GABARAP complex implicated in mitophagy [PMID:25224329]. Functionally, UBE2E3 is required for cell proliferation, and its depletion induces cellular senescence with a senescence-associated secretory phenotype that is partially suppressed by co-depletion of p53, p21, or p16 [PMID:18614808, PMID:29879550]. Several early reports attributing SUMO-1 conjugation to 'Ubch9' [PMID:9409737, PMID:9734360, PMID:10582246, PMID:10187858, PMID:15355988] reflect the activity of the distinct SUMO E2 UBC9/UBE2I sharing the alias, not UBE2E3.","teleology":[{"year":1999,"claim":"Established that UBE2E3 is a genuine ubiquitin-conjugating E2, resolving its identity against the SUMO-pathway 'Ubch9' alias by directly demonstrating ubiquitin thioester formation through its catalytic cysteine.","evidence":"GST-fusion thioester assay with active-site C145S mutagenesis","pmids":["10343118"],"confidence":"High","gaps":["Did not identify cognate E3 partners or substrates","Alias collision with UBC9/UBE2I leaves earlier SUMO-conjugation reports (idx 0,1,2,6) attributable to a different gene"]},{"year":2001,"claim":"Connected UBE2E3 to nuclear protein ubiquitination by showing it pairs with RING E3 ligases through its UBC domain and supports their autoubiquitination, defining a class of physiological E3 partners.","evidence":"Yeast two-hybrid, deletion mapping, in vitro and cell-based ubiquitination of ARA54 and RNF8","pmids":["11322894"],"confidence":"Medium","gaps":["Physiological substrates beyond E3 autoubiquitination not defined","Chain type and processivity not characterized"]},{"year":2004,"claim":"Placed UBE2E3 in a defined physiological pathway by showing it serves as the E2 for Nedd4-2-mediated ubiquitination and downregulation of the ENaC channel via reciprocal epistasis.","evidence":"Xenopus oocyte electrophysiology, co-IP, catalytic-dead mutant, epistasis with inactive Nedd4-2, renal cell transport assay","pmids":["14993279"],"confidence":"High","gaps":["Relative in vivo contribution versus other E2s not quantified","Did not establish chain linkage on ENaC"]},{"year":2005,"claim":"Tested the efficiency of UBE2E3 as a HECT-ligase partner, showing it works with Nedd4/Nedd4-2 but less efficiently than UbcH5b, framing UBE2E3 as a context-selective rather than dominant E2.","evidence":"In vitro ubiquitination assay comparing multiple E2 enzymes","pmids":["16337426"],"confidence":"Medium","gaps":["Does not explain which substrates require UBE2E3 specifically","No cellular validation of efficiency differences"]},{"year":2008,"claim":"Linked UBE2E3 to a cellular phenotype by demonstrating it is nuclear and required for RPE cell proliferation, with depletion causing cell-cycle exit and p27Kip1 accumulation.","evidence":"siRNA knockdown with rescue, Ki-67/p27 immunofluorescence, developmental reporter mouse","pmids":["18614808"],"confidence":"Medium","gaps":["Ubiquitination substrate driving proliferation not identified","Mechanistic link from E2 activity to cell-cycle arrest unresolved"]},{"year":2011,"claim":"Explained E2/E3 pairing specificity by showing the class III N-terminal extension of UBE2E3 uniquely blocks productive pairing with Ro52/TRIM21, distinguishing it from UBE2E1/UBE2E2.","evidence":"E2 panel ubiquitination assay, NMR and ELISA interface mapping","pmids":["21862588"],"confidence":"Medium","gaps":["Generality of N-terminal gating across other E3s not mapped","Structural basis at residue level incomplete"]},{"year":2014,"claim":"Defined the intrinsic catalytic restriction of UBE2E3 to monoubiquitylation, attributing it to enzyme backside residues plus K48 of ubiquitin and showing backside mutation unlocks chain synthesis.","evidence":"Fully recombinant in vitro ubiquitylation with backside and ubiquitin K-to-R mutagenesis","pmids":["24901938"],"confidence":"High","gaps":["Whether E3 partners can override the restriction in cells not determined","Physiological consequence of mono- versus poly-output on substrates untested"]},{"year":2014,"claim":"Expanded UBE2E3 substrate range to TDP-43 and to redox signaling, showing it ubiquitinates TDP-43 and controls NRF2 nuclear localization and target-gene activity with importin-11.","evidence":"Yeast two-hybrid, reciprocal co-IP, catalytic mutant and knockdown for TDP-43; siRNA, immunofluorescence, fractionation and target-gene readouts for NRF2","pmids":["24825905","25378586"],"confidence":"Medium","gaps":["Direct E3 ligase for NRF2 regulation not defined in this work","Whether NRF2 effect requires UBE2E3 catalytic activity not resolved"]},{"year":2014,"claim":"Positioned UBE2E3 at the outer mitochondrial membrane in a mitophagy context by showing the mitochondrial E3 Mulan recruits GABARAP via a LIR motif in a UBE2E3-dependent manner.","evidence":"RING-E2 fusion yeast two-hybrid, co-IP, LIR mutagenesis","pmids":["25224329"],"confidence":"Medium","gaps":["Mitophagy outcome not reconstituted or assayed functionally","Substrate ubiquitinated within the Mulan-UBE2E3-GABARAP complex unknown"]},{"year":2018,"claim":"Established UBE2E3 as a guardian against senescence, showing its loss triggers p53/p21/p16-dependent senescence with a SASP and altered organelle mass independent of overt DNA damage.","evidence":"siRNA knockdown, SA-β-gal, SASP and organelle assays, genetic epistasis with p53/p21/p16","pmids":["29879550"],"confidence":"Medium","gaps":["Direct ubiquitination substrate upstream of the senescence program not identified","Connection between NRF2/mitochondrial roles and senescence not mechanistically bridged"]},{"year":2020,"claim":"Refined regulation of UBE2E3 output by showing OTUB1 inhibits its polyubiquitination but uniquely cannot suppress its autoubiquitination, distinguishing it within the UBE2E family.","evidence":"In vitro ubiquitination assay with kinetic/thermodynamic characterization of OTUB1:E2 complexes","pmids":["32049508"],"confidence":"Medium","gaps":["Cellular consequence of OTUB1 regulation of UBE2E3 untested","Substrate context of OTUB1 inhibition unknown"]},{"year":2020,"claim":"Extended the TDP-43 axis in vivo by identifying PJA1 as the E3 partner for UBE2E3-mediated TDP-43 ubiquitination, with PJA1 suppressing TDP-43 aggregation in motor neurons.","evidence":"Co-IP, adenoviral overexpression in neurons, in vivo mouse facial motor neuron model","pmids":["32686212"],"confidence":"Medium","gaps":["Requirement for UBE2E3 catalytic activity in the in vivo phenotype not isolated","Chain type on TDP-43 and proteostatic fate not defined"]},{"year":2021,"claim":"Linked UBE2E3 to stem-cell aging, indicating its level controls BMSC senescence and osteogenic differentiation via the NRF2 pathway.","evidence":"siRNA knockdown and lentiviral overexpression with senescence and osteogenic readouts","pmids":["34820159"],"confidence":"Low","gaps":["NRF2 mechanistic link asserted but not directly demonstrated","No ubiquitination substrate identified in this context"]},{"year":2023,"claim":"Suggested UBE2E3 participates in a CUL3-based ligase assembly relevant to RPE oxidative stress by detecting it in a complex with RCBTB1 and CUL3.","evidence":"Co-immunoprecipitation from iPSC-derived RPE cells","pmids":["37408192"],"confidence":"Low","gaps":["Single co-IP without reciprocal or functional validation for UBE2E3","Substrate and biological output of the CUL3-RCBTB1-UBE2E3 complex unknown"]},{"year":null,"claim":"It remains unresolved which direct ubiquitination substrate(s) of UBE2E3 mediate its NRF2-regulatory, proliferative, and anti-senescence functions, and how its enforced monoubiquitylation output is reconciled with substrate fates across its distinct E3 partners.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No substrate causally linking UBE2E3 catalytic activity to senescence","Mechanism connecting monoubiquitylation restriction to physiological signaling outcomes undefined","In vivo roles beyond neuronal TDP-43 model not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3,5,10,11]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[3,11]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,5,11]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[12,14]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[8,14]}],"complexes":["Mulan-UBE2E3-GABARAP complex","CUL3-RCBTB1-UBE2E3 complex"],"partners":["NEDD4L","NEDD4","RNF8","PJA1","MUL1","OTUB1","CUL3","IPO11"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q969T4","full_name":"Ubiquitin-conjugating enzyme E2 E3","aliases":["E2 ubiquitin-conjugating enzyme E3","UbcH9","Ubiquitin carrier protein E3","Ubiquitin-conjugating enzyme E2-23 kDa","Ubiquitin-protein ligase E3"],"length_aa":207,"mass_kda":22.9,"function":"Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. In vitro catalyzes 'Lys-11'- and 'Lys-48'-, as well as 'Lys-63'-linked polyubiquitination. Participates in the regulation of transepithelial sodium transport in renal cells","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q969T4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBE2E3","classification":"Not Classified","n_dependent_lines":22,"n_total_lines":1208,"dependency_fraction":0.018211920529801324},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UBE2E3","total_profiled":1310},"omim":[{"mim_id":"616014","title":"RING FINGER PROTEIN 25; RNF25","url":"https://www.omim.org/entry/616014"},{"mim_id":"612548","title":"TRIPARTITE MOTIF-CONTAINING PROTEIN 50; TRIM50","url":"https://www.omim.org/entry/612548"},{"mim_id":"610889","title":"IMPORTIN 11; IPO11","url":"https://www.omim.org/entry/610889"},{"mim_id":"610637","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 5; MARCHF5","url":"https://www.omim.org/entry/610637"},{"mim_id":"607867","title":"RCC1 DOMAIN- AND BTB DOMAIN-CONTAINING PROTEIN 1; RCBTB1","url":"https://www.omim.org/entry/607867"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UBE2E3"},"hgnc":{"alias_symbol":["UbcH9"],"prev_symbol":[]},"alphafold":{"accession":"Q969T4","domains":[{"cath_id":"3.10.110.10","chopping":"60-205","consensus_level":"high","plddt":97.6604,"start":60,"end":205}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969T4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q969T4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q969T4-F1-predicted_aligned_error_v6.png","plddt_mean":85.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBE2E3","jax_strain_url":"https://www.jax.org/strain/search?query=UBE2E3"},"sequence":{"accession":"Q969T4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q969T4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q969T4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969T4"}},"corpus_meta":[{"pmid":"9734360","id":"PMC_9734360","title":"SUMO-1 modification of IkappaBalpha inhibits NF-kappaB activation.","date":"1998","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/9734360","citation_count":930,"is_preprint":false},{"pmid":"9409737","id":"PMC_9409737","title":"Ubch9 conjugates SUMO but not ubiquitin.","date":"1997","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/9409737","citation_count":314,"is_preprint":false},{"pmid":"10187858","id":"PMC_10187858","title":"Identification of the enzyme required for activation of the small ubiquitin-like protein SUMO-1.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10187858","citation_count":304,"is_preprint":false},{"pmid":"22526258","id":"PMC_22526258","title":"The circadian protein period 1 contributes to blood pressure control and coordinately regulates renal sodium transport genes.","date":"2012","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/22526258","citation_count":123,"is_preprint":false},{"pmid":"22965876","id":"PMC_22965876","title":"Selective histone deacetylase (HDAC) inhibition imparts beneficial effects in Huntington's disease mice: implications for the ubiquitin-proteasomal and autophagy systems.","date":"2012","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22965876","citation_count":100,"is_preprint":false},{"pmid":"10582246","id":"PMC_10582246","title":"Control of NF-kappa B transcriptional activation by signal induced proteolysis of I kappa B alpha.","date":"1999","source":"Philosophical transactions of the Royal Society of London. 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SUMO conjugation proceeds via a distinct E1 activity separate from the ubiquitin E1.\",\n      \"method\": \"In vitro thioester formation assay with ubiquitin and SUMO-1\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical assay (thioester formation) replicated and extended in multiple subsequent studies\",\n      \"pmids\": [\"9409737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"In the presence of the SUMO-1 E1 activating enzyme, UBE2E3 (Ubch9) directly conjugates SUMO-1 to IκBα primarily on K21 (also used for ubiquitin modification), thereby protecting IκBα from signal-induced ubiquitination and proteasomal degradation and inhibiting NF-κB activation. Notably, unlike ubiquitination, SUMO-1 modification of IκBα is inhibited by phosphorylation of S32/S36.\",\n      \"method\": \"In vitro reconstitution with purified recombinant proteins; mutagenesis of IκBα lysine and serine residues\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — fully reconstituted in vitro with defined purified components, mutagenesis confirmation, replicated in follow-up review paper\",\n      \"pmids\": [\"9734360\", \"10582246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The SUMO-1 E1 activating enzyme (SAE1/SAE2 heterodimer) transfers SUMO-1 thioester to UBE2E3 (Ubch9), which then conjugates SUMO-1 to IκBα in vitro without requiring an E3-equivalent activity, defining UBE2E3 as the E2 enzyme in the minimal SUMO-1 conjugation pathway.\",\n      \"method\": \"In vitro reconstitution with purified recombinant SAE1/SAE2, UBE2E3, SUMO-1, and IκBα; ATP-dependent thioester assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — fully reconstituted in vitro with all homogeneous recombinant components, mechanistically defines E2 role\",\n      \"pmids\": [\"10187858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UBE2E3 encodes a functional E2 ubiquitin-conjugating enzyme that forms an E1-dependent thioester bond with ubiquitin through its active-site cysteine (C145); mutation of C145 to serine abolishes thioester formation, confirming the catalytic cysteine.\",\n      \"method\": \"GST-fusion protein thioester assay; active-site mutagenesis (C145S)\",\n      \"journal\": \"Cytogenetics and cell genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical thioester assay with active-site mutagenesis in a single study; note this contradicts the earlier Desterro 1997 finding that Ubch9 cannot thioester with Ub — the two papers describe different proteins (UBE2E3 vs UBC9/UBE2I). UBE2E3/UbcM2 CAN thioester with ubiquitin; the alias 'Ubch9' in Desterro refers to the SUMO E2 UBC9 (UBE2I), a different gene. Confidence is high for UBE2E3 forming Ub-thioester.\",\n      \"pmids\": [\"10343118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"UBE2E3 interacts with RING-finger proteins ARA54 and RNF8 via its UBC domain (interaction requires intact RING domain on the E3 partners), and supports E3-dependent autoubiquitination of ARA54 and RNF8 in vitro and in cells, linking UBE2E3 to nuclear protein ubiquitination.\",\n      \"method\": \"Yeast two-hybrid screen; deletion mutagenesis mapping; in vitro ubiquitination assay with Sf9-expressed proteins; transfection/ubiquitination in COS-7 cells\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus in vitro ubiquitination assay plus cell-based ubiquitination, single lab\",\n      \"pmids\": [\"11322894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"UBE2E3 acts as the E2 enzyme in concert with the E3 ligase Nedd4-2 to ubiquitinate and downregulate ENaC. UBE2E3 and Nedd4-2 co-immunoprecipitate. A catalytically inactive UBE2E3-C145S mutant increases ENaC cell-surface expression in Xenopus oocytes, and this effect depends on intact PY motifs (Nedd4-2 binding sites) and ubiquitination sites on ENaC. No additive effect is seen when UBE2E3-CS is co-expressed with an inactive Nedd4-2 mutant, placing UBE2E3 in the same pathway as Nedd4-2.\",\n      \"method\": \"Xenopus oocyte electrophysiology; co-immunoprecipitation; catalytic inactive mutant; epistasis with Nedd4-2 mutant; renal mpkCCD cell transepithelial Na+ transport assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional epistasis in two cell systems, co-IP, active-site mutant, pathway placement; multiple orthogonal methods\",\n      \"pmids\": [\"14993279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"UBE2E3 (Ubch9) promotes SUMO modification of Werner helicase (WRN) in a synergistic manner with the tumor suppressor p14 Arf. p14 Arf-driven WRN SUMOylation causes redistribution of WRN within the nucleus, an effect reversed by a SUMO-specific protease, implicating UBE2E3-mediated SUMOylation in WRN nuclear localization.\",\n      \"method\": \"Cell-based SUMO conjugation assay; co-expression; SUMO-specific protease reversal; fluorescence microscopy of WRN redistribution\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cell-based assay with protease reversal confirming SUMO dependence, single lab\",\n      \"pmids\": [\"15355988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Both Nedd4 and Nedd4-2 use UBE2E3 as an E2 partner in in vitro ubiquitination assays, but UBE2E3 supports substrate ubiquitination less efficiently than UbcH5b for these HECT E3 ligases.\",\n      \"method\": \"In vitro ubiquitination assay comparing multiple E2 enzymes\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro biochemical assay, single lab, single paper\",\n      \"pmids\": [\"16337426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UBE2E3 localizes to the nucleus of RPE cells and is required for their proliferation; siRNA-mediated depletion causes cell-cycle exit, loss of Ki-67, accumulation of the CDK inhibitor p27Kip1, and doubling of cell area. The mouse ortholog UbcM2 is transcriptionally downregulated during RPE development in vivo.\",\n      \"method\": \"siRNA knockdown; immunofluorescence (Ki-67, p27Kip1); cell counting; rescue experiment; LacZ reporter mouse for developmental expression\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with specific rescue, defined cell-cycle phenotype, nuclear localization confirmed, single lab\",\n      \"pmids\": [\"18614808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The N-terminal extension of UBE2E3 prevents it from functioning together with the RING E3 ligase Ro52 (TRIM21), unlike the N-terminal extensions of UBE2E1 and UBE2E2 which allow productive interaction, demonstrating that the class III E2 N-terminal extension uniquely modulates E2/E3 pairing specificity.\",\n      \"method\": \"E2 panel screening in ubiquitination assay; NMR and ELISA mapping of E2/E3 interface\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro ubiquitination assay with panel of E2s and NMR interface mapping, single lab\",\n      \"pmids\": [\"21862588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UBE2E3 ubiquitinates TDP-43; all three UBE2E family members enhance TDP-43 ubiquitination, but catalytically inactive UBE2E3(C145S) is much less efficient. Silencing UBE2E3 reduces TDP-43 ubiquitination. UBE2E3 was identified as a TDP-43 interactor by yeast two-hybrid and confirmed by co-immunoprecipitation and co-localization in HEK293E cells.\",\n      \"method\": \"Yeast two-hybrid; co-immunoprecipitation; siRNA knockdown; overexpression with proteasome inhibitor; catalytic mutant (C145S)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, active-site mutant, knockdown, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"24825905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UBE2E3 (UbcM2) is intrinsically restricted to monoubiquitylation: backside residues of the enzyme (distant from the active site) and K48 of ubiquitin together prevent polyubiquitin chain synthesis. Mutation of backside residues enables K63-linked (and to a lesser extent K6- and K48-linked) chain synthesis, revealing a two-fold non-catalytic restriction mechanism.\",\n      \"method\": \"Fully recombinant in vitro ubiquitylation assay; backside mutagenesis; ubiquitin K-to-R mutant panel\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with mutagenesis of both enzyme backside and ubiquitin lysines, multiple orthogonal mutants tested in single rigorous study\",\n      \"pmids\": [\"24901938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UBE2E3 and its nuclear import receptor importin-11 (Imp-11) regulate NRF2 subcellular distribution and transcriptional activity. Knockdown of UBE2E3 reduces nuclear NRF2, decreases NRF2 target gene expression, and relocalizes NRF2 to a perinuclear cluster of mitochondria. Imp-11 restricts KEAP1 from prematurely extracting NRF2 from target gene promoters.\",\n      \"method\": \"siRNA knockdown; immunofluorescence; gene expression analysis of NRF2 target genes; subcellular fractionation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown with defined localization and transcriptional phenotype, single lab, multiple readouts\",\n      \"pmids\": [\"25378586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mulan (mitochondrial E3 ubiquitin ligase) interacts specifically with UBE2E3 among multiple E2 partners; the Mulan-UBE2E3 complex recruits GABARAP via an LC3-interacting region (LIR) in Mulan's RING domain, and this interaction requires the presence of UBE2E3. This places UBE2E3 in a mitophagy regulatory complex at the outer mitochondrial membrane.\",\n      \"method\": \"Modified yeast two-hybrid screen (RING-E2 fusion); co-immunoprecipitation; LIR motif mutagenesis\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid plus co-IP with LIR mutagenesis, single lab, interaction confirmed but reconstitution not performed\",\n      \"pmids\": [\"25224329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"UBE2E3 loss induces cellular senescence in the absence of overt DNA damage. Cells depleted of UBE2E3 display a distinct senescence-associated secretory phenotype, increased mitochondrial and lysosomal mass, increased sensitivity to mitochondrial/lysosomal poisons, and elevated basal autophagic flux. The senescence phenotype is partially suppressed by co-depletion of p53, p21CIP1/WAF1, or p16INK4a.\",\n      \"method\": \"siRNA knockdown; SA-β-galactosidase assay; SASP marker analysis; organelle mass assays; genetic epistasis with p53/p21/p16 co-depletion\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with multiple phenotypic readouts and genetic epistasis placing UBE2E3 upstream of p53/p21/p16 in senescence pathway, single lab\",\n      \"pmids\": [\"29879550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PJA1 (Praja1 RING-finger E3 ubiquitin ligase) co-immunoprecipitates with both CTF TDP-43 and UBE2E3, identifying UBE2E3 as the E2 partner for PJA1-mediated ubiquitination of TDP-43. PJA1 suppresses phosphorylation and cytoplasmic aggregate formation of TDP-43 in neuronal cells and in vivo in mouse motor neurons.\",\n      \"method\": \"Co-immunoprecipitation; adenoviral overexpression in neural stem cell-derived neurons; in vivo mouse facial motor neuron model\",\n      \"journal\": \"Neuropathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP identifying E2-E3 complex, supported by in vivo functional data, single lab\",\n      \"pmids\": [\"32686212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"OTUB1 inhibits the polyubiquitination activity of UBE2E3 (along with UBE2E1 and UBE2E2) at physiologically relevant concentrations. However, unlike UBE2E1 and UBE2E2, OTUB1 is unable to suppress autoubiquitination by UBE2E3, revealing a unique feature of UBE2E3 within the UBE2E family in its interaction with OTUB1.\",\n      \"method\": \"In vitro ubiquitination assay; kinetic/thermodynamic characterization of OTUB1:E2 complexes\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro biochemical assay with quantitative analysis, single lab\",\n      \"pmids\": [\"32049508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"UBE2E3 knockdown accelerates cellular senescence and inhibits osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), while overexpression of UBE2E3 attenuates senescence and enhances osteogenic differentiation of aged BMSCs. Mechanistically, UBE2E3 regulates the NRF2 pathway to control BMSC senescence and differentiation.\",\n      \"method\": \"siRNA knockdown; lentiviral overexpression; osteogenic differentiation assay; senescence markers; NRF2 pathway readout\",\n      \"journal\": \"PeerJ\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, knockdown/overexpression with phenotypic readout, NRF2 mechanistic link asserted but not directly demonstrated\",\n      \"pmids\": [\"34820159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RCBTB1 co-immunoprecipitates with UBE2E3 and with CUL3 from RPE cell protein lysates, placing RCBTB1 in a complex with UBE2E3 and the CUL3 E3 ligase scaffold and suggesting UBE2E3 participates in a CUL3-RCBTB1 ubiquitin ligase complex relevant to oxidative stress response.\",\n      \"method\": \"Co-immunoprecipitation from iPSC-derived RPE cells using UBE2E3 and CUL3 antibodies\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP experiment, single lab, no functional follow-up on UBE2E3 specifically\",\n      \"pmids\": [\"37408192\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBE2E3 (UbcM2/UbcH9) is a metazoan ubiquitin-conjugating enzyme (E2) that forms an E1-dependent thioester with ubiquitin via its active-site C145, is intrinsically restricted to monoubiquitylation through backside surface residues and K48 of ubiquitin, partners with HECT E3 ligases (Nedd4-2, Mulan) and RING E3 ligases (ARA54, RNF8, PJA1) to ubiquitinate substrates including ENaC, TDP-43, ARA54, and RNF8, regulates NRF2 nuclear localization and transcriptional activity, is required for cell proliferation (with depletion inducing p53/p21/p16-dependent senescence), and participates in mitophagy via a Mulan-UBE2E3-GABARAP complex at the outer mitochondrial membrane; the gene also shares its 'Ubch9' alias with UBC9/UBE2I (the primary SUMO E2), so early papers attributing SUMO conjugation to 'Ubch9' reflect UBE2I activity, not UBE2E3.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBE2E3 (UbcM2) is a metazoan ubiquitin-conjugating (E2) enzyme that forms an E1-dependent thioester with ubiquitin through its active-site cysteine C145, supporting E3-dependent substrate ubiquitination [#3]. A defining feature of UBE2E3 is its intrinsic restriction to monoubiquitylation: backside surface residues of the enzyme acting together with K48 of ubiquitin block polyubiquitin chain synthesis, and mutation of these backside residues unlocks K63-, K6-, and K48-linked chain formation [#11]. UBE2E3 cooperates with diverse E3 ligases to ubiquitinate distinct substrates: it partners with the HECT ligases Nedd4/Nedd4-2 to ubiquitinate and downregulate the epithelial sodium channel ENaC [#5, #7], with the RING ligases ARA54 and RNF8 to support their autoubiquitination [#4], and with the RING ligases PJA1 to drive ubiquitination of TDP-43, suppressing TDP-43 phosphorylation and cytoplasmic aggregation [#10, #15]. Its E2/E3 pairing is selectively gated by its class III N-terminal extension, which prevents productive pairing with Ro52/TRIM21 [#9], and its polyubiquitination output is constrained by the deubiquitinase OTUB1 [#16]. Beyond proteostasis, UBE2E3 controls the redox transcription factor NRF2 by promoting its nuclear localization and target-gene expression together with importin-11 [#12], and it operates at the outer mitochondrial membrane within a Mulan-UBE2E3-GABARAP complex implicated in mitophagy [#13]. Functionally, UBE2E3 is required for cell proliferation, and its depletion induces cellular senescence with a senescence-associated secretory phenotype that is partially suppressed by co-depletion of p53, p21, or p16 [#8, #14]. Several early reports attributing SUMO-1 conjugation to 'Ubch9' [#0, #1, #2, #6] reflect the activity of the distinct SUMO E2 UBC9/UBE2I sharing the alias, not UBE2E3.\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that UBE2E3 is a genuine ubiquitin-conjugating E2, resolving its identity against the SUMO-pathway 'Ubch9' alias by directly demonstrating ubiquitin thioester formation through its catalytic cysteine.\",\n      \"evidence\": \"GST-fusion thioester assay with active-site C145S mutagenesis\",\n      \"pmids\": [\"10343118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify cognate E3 partners or substrates\", \"Alias collision with UBC9/UBE2I leaves earlier SUMO-conjugation reports (idx 0,1,2,6) attributable to a different gene\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Connected UBE2E3 to nuclear protein ubiquitination by showing it pairs with RING E3 ligases through its UBC domain and supports their autoubiquitination, defining a class of physiological E3 partners.\",\n      \"evidence\": \"Yeast two-hybrid, deletion mapping, in vitro and cell-based ubiquitination of ARA54 and RNF8\",\n      \"pmids\": [\"11322894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological substrates beyond E3 autoubiquitination not defined\", \"Chain type and processivity not characterized\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Placed UBE2E3 in a defined physiological pathway by showing it serves as the E2 for Nedd4-2-mediated ubiquitination and downregulation of the ENaC channel via reciprocal epistasis.\",\n      \"evidence\": \"Xenopus oocyte electrophysiology, co-IP, catalytic-dead mutant, epistasis with inactive Nedd4-2, renal cell transport assay\",\n      \"pmids\": [\"14993279\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo contribution versus other E2s not quantified\", \"Did not establish chain linkage on ENaC\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Tested the efficiency of UBE2E3 as a HECT-ligase partner, showing it works with Nedd4/Nedd4-2 but less efficiently than UbcH5b, framing UBE2E3 as a context-selective rather than dominant E2.\",\n      \"evidence\": \"In vitro ubiquitination assay comparing multiple E2 enzymes\",\n      \"pmids\": [\"16337426\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not explain which substrates require UBE2E3 specifically\", \"No cellular validation of efficiency differences\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked UBE2E3 to a cellular phenotype by demonstrating it is nuclear and required for RPE cell proliferation, with depletion causing cell-cycle exit and p27Kip1 accumulation.\",\n      \"evidence\": \"siRNA knockdown with rescue, Ki-67/p27 immunofluorescence, developmental reporter mouse\",\n      \"pmids\": [\"18614808\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitination substrate driving proliferation not identified\", \"Mechanistic link from E2 activity to cell-cycle arrest unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Explained E2/E3 pairing specificity by showing the class III N-terminal extension of UBE2E3 uniquely blocks productive pairing with Ro52/TRIM21, distinguishing it from UBE2E1/UBE2E2.\",\n      \"evidence\": \"E2 panel ubiquitination assay, NMR and ELISA interface mapping\",\n      \"pmids\": [\"21862588\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality of N-terminal gating across other E3s not mapped\", \"Structural basis at residue level incomplete\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the intrinsic catalytic restriction of UBE2E3 to monoubiquitylation, attributing it to enzyme backside residues plus K48 of ubiquitin and showing backside mutation unlocks chain synthesis.\",\n      \"evidence\": \"Fully recombinant in vitro ubiquitylation with backside and ubiquitin K-to-R mutagenesis\",\n      \"pmids\": [\"24901938\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether E3 partners can override the restriction in cells not determined\", \"Physiological consequence of mono- versus poly-output on substrates untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Expanded UBE2E3 substrate range to TDP-43 and to redox signaling, showing it ubiquitinates TDP-43 and controls NRF2 nuclear localization and target-gene activity with importin-11.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal co-IP, catalytic mutant and knockdown for TDP-43; siRNA, immunofluorescence, fractionation and target-gene readouts for NRF2\",\n      \"pmids\": [\"24825905\", \"25378586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct E3 ligase for NRF2 regulation not defined in this work\", \"Whether NRF2 effect requires UBE2E3 catalytic activity not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Positioned UBE2E3 at the outer mitochondrial membrane in a mitophagy context by showing the mitochondrial E3 Mulan recruits GABARAP via a LIR motif in a UBE2E3-dependent manner.\",\n      \"evidence\": \"RING-E2 fusion yeast two-hybrid, co-IP, LIR mutagenesis\",\n      \"pmids\": [\"25224329\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mitophagy outcome not reconstituted or assayed functionally\", \"Substrate ubiquitinated within the Mulan-UBE2E3-GABARAP complex unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established UBE2E3 as a guardian against senescence, showing its loss triggers p53/p21/p16-dependent senescence with a SASP and altered organelle mass independent of overt DNA damage.\",\n      \"evidence\": \"siRNA knockdown, SA-β-gal, SASP and organelle assays, genetic epistasis with p53/p21/p16\",\n      \"pmids\": [\"29879550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination substrate upstream of the senescence program not identified\", \"Connection between NRF2/mitochondrial roles and senescence not mechanistically bridged\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Refined regulation of UBE2E3 output by showing OTUB1 inhibits its polyubiquitination but uniquely cannot suppress its autoubiquitination, distinguishing it within the UBE2E family.\",\n      \"evidence\": \"In vitro ubiquitination assay with kinetic/thermodynamic characterization of OTUB1:E2 complexes\",\n      \"pmids\": [\"32049508\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cellular consequence of OTUB1 regulation of UBE2E3 untested\", \"Substrate context of OTUB1 inhibition unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended the TDP-43 axis in vivo by identifying PJA1 as the E3 partner for UBE2E3-mediated TDP-43 ubiquitination, with PJA1 suppressing TDP-43 aggregation in motor neurons.\",\n      \"evidence\": \"Co-IP, adenoviral overexpression in neurons, in vivo mouse facial motor neuron model\",\n      \"pmids\": [\"32686212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Requirement for UBE2E3 catalytic activity in the in vivo phenotype not isolated\", \"Chain type on TDP-43 and proteostatic fate not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked UBE2E3 to stem-cell aging, indicating its level controls BMSC senescence and osteogenic differentiation via the NRF2 pathway.\",\n      \"evidence\": \"siRNA knockdown and lentiviral overexpression with senescence and osteogenic readouts\",\n      \"pmids\": [\"34820159\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"NRF2 mechanistic link asserted but not directly demonstrated\", \"No ubiquitination substrate identified in this context\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Suggested UBE2E3 participates in a CUL3-based ligase assembly relevant to RPE oxidative stress by detecting it in a complex with RCBTB1 and CUL3.\",\n      \"evidence\": \"Co-immunoprecipitation from iPSC-derived RPE cells\",\n      \"pmids\": [\"37408192\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single co-IP without reciprocal or functional validation for UBE2E3\", \"Substrate and biological output of the CUL3-RCBTB1-UBE2E3 complex unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved which direct ubiquitination substrate(s) of UBE2E3 mediate its NRF2-regulatory, proliferative, and anti-senescence functions, and how its enforced monoubiquitylation output is reconciled with substrate fates across its distinct E3 partners.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No substrate causally linking UBE2E3 catalytic activity to senescence\", \"Mechanism connecting monoubiquitylation restriction to physiological signaling outcomes undefined\", \"In vivo roles beyond neuronal TDP-43 model not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3, 5, 10, 11]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [3, 11]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 5, 11]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [12, 14]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [8, 14]}\n    ],\n    \"complexes\": [\n      \"Mulan-UBE2E3-GABARAP complex\",\n      \"CUL3-RCBTB1-UBE2E3 complex\"\n    ],\n    \"partners\": [\n      \"NEDD4L\",\n      \"NEDD4\",\n      \"RNF8\",\n      \"PJA1\",\n      \"MUL1\",\n      \"OTUB1\",\n      \"CUL3\",\n      \"IPO11\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}