{"gene":"UBE2L3","run_date":"2026-04-28T21:43:00","timeline":{"discoveries":[{"year":2000,"finding":"Crystal structure of c-Cbl (RING E3) bound to UbcH7 (UBE2L3) reveals that the RING domain recruits the E2 and positions it optimally for ubiquitin transfer; a conserved surface channel leads from the substrate peptide to the E2 active site, suggesting RING E3s act as scaffolds.","method":"X-ray crystallography with functional validation","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mechanistic interpretation, highly cited foundational study","pmids":["10966114"],"is_preprint":false},{"year":1999,"finding":"Crystal structure of the E6AP HECT domain bound to UbcH7 (UBE2L3) reveals determinants of E2-E3 specificity and the mechanism of ubiquitin transfer from E2 to E3 via a thioester intermediate in the catalytic cleft.","method":"X-ray crystallography","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of E2-E3 complex, highly cited foundational paper","pmids":["10558980"],"is_preprint":false},{"year":2011,"finding":"UBE2L3 (UBCH7) lacks intrinsic lysine reactivity (unlike many E2s that function with RING E3s), explaining its preference for HECT-type E3s. RBR E3s (parkin, HHARI) function as RING/HECT hybrids: they bind E2s via RING1 but transfer Ub through an obligate thioester at a conserved RING2 cysteine, and UBE2L3 is the cognate E2 for this class.","method":"In vitro ubiquitination assays, mutagenesis, structural comparisons","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus mutagenesis, highly cited, defines E2 mechanism","pmids":["21532592"],"is_preprint":false},{"year":1999,"finding":"The c-Cbl RING finger domain directly interacts with UbcH7 (UBE2L3), and together they synergistically promote ligand-induced ubiquitination of the EGFR; oncogenic 70Z-Cbl (lacking part of the RING finger) fails to bind UbcH7 and blocks EGFR ubiquitination.","method":"Yeast two-hybrid, in vitro binding assay, in vivo and in vitro ubiquitination assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal binding plus functional ubiquitination assays in vitro and in vivo","pmids":["10531381"],"is_preprint":false},{"year":1996,"finding":"UBE2L3 encodes an E2 ubiquitin-conjugating enzyme (UbcH7) that interacts with the HECT E3 E6-AP and efficiently substitutes for UbcH5 in E6-AP-dependent ubiquitination of p53; UbcH7 can also interact with E6-AP to participate in NF-κB maturation and c-Fos degradation.","method":"Biochemical interaction assays, in vitro ubiquitination assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biochemical assays, replicated across labs","pmids":["8576257"],"is_preprint":false},{"year":1998,"finding":"UBE2L3 (UbcH7) interacts preferentially with a subset of HECT E3s (those sharing E6-AP-like specificity) but not others (e.g., RSP5), demonstrating that different HECT E3s are grouped into at least two classes based on their E2 specificity.","method":"In vitro binding and ubiquitin thioester formation assays with multiple HECT E3s","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — systematic in vitro assays across multiple HECT family members","pmids":["9575161"],"is_preprint":false},{"year":1999,"finding":"UBE2L3 (UbcH7) interacts with RBR-containing proteins HHARI and H7-AP1 through their N-terminal RING finger (HHARI) and IBR domains; this interaction is specific to UbcH7/UbcH8 and not seen with UbcH5 or UbcH1, linking RBR proteins to the ubiquitin pathway via UBE2L3.","method":"Yeast two-hybrid screen, in vitro binding assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid plus pulldown, single study","pmids":["10521492"],"is_preprint":false},{"year":2001,"finding":"HHARI co-localizes with UbcH7 (UBE2L3) in mammalian cells, particularly in the perinuclear region; a minimal interaction region (residues 186-254) was defined, and the distance between RING1 and IBR domains is critical; mutation of RING1 from RING-HC to RING-H2 type abolishes UbcH7 interaction.","method":"Co-immunoprecipitation, co-localization (immunofluorescence), mutagenesis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus live-cell localization plus mutagenesis, single lab","pmids":["11278816"],"is_preprint":false},{"year":2004,"finding":"UbcH7 (UBE2L3) is the specific E2 for ubiquitination of HPV E7 oncoprotein; E7 interacts with the SCF complex (Cul1/Skp2) E3 ligase, and can be ubiquitinated by the Cul1-containing ligase in vitro; E7 half-life is longer in Skp2-/- MEFs.","method":"In vitro ubiquitination assay, co-immunoprecipitation, Skp2 knockout MEFs","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro assay plus genetic KO and Co-IP","pmids":["15113913"],"is_preprint":false},{"year":2004,"finding":"UbcH7 (UBE2L3) acts as a coactivator for steroid hormone receptors (PR, GR, AR, RAR) in a hormone-dependent manner; its ubiquitin conjugation activity is required for coactivation; UbcH7 is recruited to ER- and PR-responsive promoters and cooperates with E6-AP and SRC-1 to potentiate transactivation.","method":"Transient transfection reporter assays, siRNA knockdown, chromatin immunoprecipitation (ChIP), Co-IP","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, siRNA, reporter assay, Co-IP), mechanistic mutagenesis of catalytic residue","pmids":["15367689"],"is_preprint":false},{"year":2006,"finding":"UbcH7 (UBE2L3) physically interacts with the glucocorticoid receptor (GR) and promotes its ubiquitination and proteasome-dependent degradation; a catalytically inactive UbcH7 dominant negative (C89S) fails to repress GR transactivation and stabilizes GR protein, demonstrating that UbcH7 enzymatic activity mediates GR turnover.","method":"Co-immunoprecipitation, dominant-negative mutagenesis, reporter assays, proteasome inhibitor experiments","journal":"The Journal of endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus functional mutagenesis and pharmacological inhibition, single lab","pmids":["17003263"],"is_preprint":false},{"year":2014,"finding":"UbcH7 (UBE2L3) regulates steady-state and replicative stress-induced ubiquitination and proteasomal degradation of 53BP1; depletion of UbcH7 stabilizes 53BP1, inhibits DSB end resection, increases NHEJ, and reduces homologous recombination, making cells sensitive to DNA damage.","method":"shRNA screen, knockdown/depletion, ubiquitination assays, DSB repair pathway assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 — functional KD with defined molecular and cellular phenotype, shRNA screen","pmids":["25422456"],"is_preprint":false},{"year":2014,"finding":"UBE2N, UBE2L3, and UBE2D2/3 are required synergistically for Parkin-dependent mitophagy; UBE2L3 knockdown reduces autophagic clearance of depolarized mitochondria without interfering with PINK1 stabilization or Parkin translocation; combined knockdown reduces mitochondrial polyubiquitylation of substrates including mitofusins, TOM20, TOM70, and VDAC1.","method":"siRNA knockdown, autophagic flux assays, ubiquitination assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — systematic knockdown with defined cellular and molecular phenotype","pmids":["24906799"],"is_preprint":false},{"year":2015,"finding":"UBE2L3 is the preferred E2 conjugating enzyme for LUBAC (linear ubiquitin chain assembly complex, containing HOIL-1 and HOIP) in vivo, and is essential for LUBAC-mediated NF-κB activation; dominant-negative UBE2L3 (C86S) or UBE2L3 silencing abolishes NF-κB upregulation by LUBAC; the autoimmune risk haplotype increases UBE2L3 expression, correlating with enhanced NF-κB activation and plasma cell development.","method":"Reporter assays, dominant-negative mutant (C86S), siRNA knockdown, imaging flow cytometry for NF-κB translocation, flow cytometry for B cell subsets","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, dominant-negative and knockdown, primary human cells","pmids":["25640675"],"is_preprint":false},{"year":2017,"finding":"Structural analysis of HHARI RING1 in complex with UbcH7~Ub shows that a Zn2+-loop II extension unique to RBR RING1 (absent in canonical RING E3s) acts as a steric wedge to disrupt closed E2~Ub conformation, favoring open conformation required for Ub transfer to the E3 active-site cysteine rather than directly to substrate.","method":"Structural biology (crystal structure), biochemical assays","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional mechanistic explanation","pmids":["28552575"],"is_preprint":false},{"year":2018,"finding":"NMR and mass spectrometry show that UbcH7~Ub binds to parkin in the open conformation, with conjugated Ub binding at the RING1/IBR interface; recruitment of UbcH7~Ub and phosphorylation of parkin's Ubl domain act synergistically to rearrange the RING2 catalytic cysteine and enhance ubiquitin transfer activity.","method":"NMR chemical shift perturbation, mass spectrometry, in vitro ubiquitination assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — NMR structure plus mass spectrometry plus functional assays","pmids":["30446597"],"is_preprint":false},{"year":2005,"finding":"HIV Nef mediates exclusion of UbcH7 (UBE2L3) from lipid rafts via a p85Cool-1/βPix–c-Cbl ternary complex, preventing ubiquitination of activated Vav by c-Cbl/UbcH7 and thereby enhancing T cell signaling to promote HIV replication.","method":"Lipid raft fractionation, siRNA knockdown of p85Cool-1/βPix, ubiquitination assays, Co-IP","journal":"Immunity","confidence":"Medium","confidence_rationale":"Tier 2 — subcellular fractionation plus knockdown plus ubiquitination assay, mechanistically linked","pmids":["16356860"],"is_preprint":false},{"year":2009,"finding":"The RBR E3 ligase Triad1 inhibits myeloid cell proliferation through differential interactions of its two RING domains with UbcH7 (UBE2L3) and Ubc13, catalyzing distinct ubiquitin chain types; deletion of either RING domain abrogates the inhibitory effect on myeloid colony formation.","method":"In vitro binding assays, myeloid clonogenic assays, domain deletion mutagenesis","journal":"Leukemia","confidence":"Medium","confidence_rationale":"Tier 2 — domain mutagenesis plus functional cell assays","pmids":["19340006"],"is_preprint":false},{"year":2015,"finding":"Ndfip1 acts as an adaptor protein that facilitates recruitment of UbcH7 (UBE2L3) to the HECT E3 Itch, enhancing Itch ligase activity and Tak1 ubiquitination; the N-terminal region of Ndfip1 binds UbcH7 while the PY motif binds Itch, and reconstitution with full-length Ndfip1 (but not interaction-dead mutants) restores defective Tak1 ubiquitination.","method":"Co-immunoprecipitation, in vitro reconstitution, Ndfip1-/- and Itch-/- mouse models, mutagenesis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — reconstitution plus mutagenesis plus KO mouse model","pmids":["25632008"],"is_preprint":false},{"year":2014,"finding":"MAP1B light chain 1 (LC1) interacts with both CaV2.2 (N-type Ca2+ channel) and UBE2L3 via Co-IP; the LC1/UBE2L3 complex promotes ubiquitination and proteasomal degradation of CaV2.2, reducing channel surface expression and current density; MG132 prevents LC1-induced channel degradation.","method":"Co-immunoprecipitation, yeast two-hybrid, patch-clamp, proteasome inhibition","journal":"Pflugers Archiv","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP plus functional electrophysiology and pharmacological inhibition","pmids":["24566975"],"is_preprint":false},{"year":2018,"finding":"UBE2L3 (UBCH7) specifically stabilizes p27Kip1 by catalyzing the conjugation of heterotypic ubiquitin chains on p27 that are proteolytically incompetent; overexpression of UBE2L3 stabilizes p27 and delays G1-to-S transition, while depletion increases p27 turnover, without affecting p21, p57, cyclin A, or cyclin E levels.","method":"Overexpression, siRNA knockdown, cell cycle analysis, in vitro ubiquitination assays","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro ubiquitination plus KD/OE with defined cell-cycle phenotype","pmids":["30113882"],"is_preprint":false},{"year":2023,"finding":"UBE2L3 promotes pro-IL-1β ubiquitylation and proteasomal disposal; deletion of Ube2l3 in mice reduces pro-IL-1β turnover in macrophages, leading to excessive mature IL-1β production, neutrophilic inflammation after inflammasome activation; RNAi screen identified TRIP12 and AREL1 (HECT E3s) as the partner E3 ligases that add destabilizing K27-, K29-, and K33-linked poly-ubiquitin chains on pro-IL-1β.","method":"Ube2l3 conditional knockout mouse, RNAi screen, in vitro ubiquitination assays, inflammasome activation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — KO mouse plus unbiased RNAi screen plus in vitro ubiquitination with chain-type specificity","pmids":["37474493"],"is_preprint":false},{"year":2023,"finding":"UBE2L3 is critical for NF-κB activation downstream of TLR7 stimulation via interaction with LUBAC; dimethyl fumarate (DMF) directly inhibits UBE2L3 and significantly reduces TLR7-induced NF-κB activation, plasmablast/memory B cell differentiation, and autoantibody secretion in SLE.","method":"Knockdown, overexpression, reporter assays, flow cytometry, DMF pharmacological inhibition","journal":"Journal of autoimmunity","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic knockdown plus pharmacological inhibition with defined cellular outcome","pmids":["37001433"],"is_preprint":false},{"year":2024,"finding":"SMURF1 acts as the E3 ligase partner of UBE2L3 (UbcH7) to ubiquitinate p27Kip1 with K29-linked chains, stabilizing p27 and promoting cell migration; SMURF1, UbcH7, and p27 co-localize at the leading edge of migrating cells; knockdown of SMURF1 or UbcH7 reduces cell migration.","method":"In vitro ubiquitination screen, K29 chain-type mutagenesis, co-localization imaging, knockdown assays, migration assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro ubiquitination with chain-type specificity plus co-localization plus functional KD","pmids":["38301893"],"is_preprint":false},{"year":2024,"finding":"MARCHF8 (a membrane RING E3 ligase) binds to and ubiquitinates UBE2L3 and CUL1, promoting their degradation and thereby stabilizing HPV16 E7; MARCHF8 knockdown increases UBE2L3 and CUL1 levels and enhances E7 ubiquitination; overexpression of CUL1 or UBE2L3 decreases E7 levels and suppresses tumor growth in vivo.","method":"Co-immunoprecipitation, ubiquitination assays, MARCHF8 knockdown, in vivo xenograft","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP, ubiquitination assays, and in vivo model","pmids":["38226814"],"is_preprint":false},{"year":2024,"finding":"UBE2L3 interacts with the E3 ligase ZNF598 (confirmed by LC-MS/MS and Co-IP) and disrupts ZNF598-mediated ubiquitination of the autophagy protein LAMP-2, thereby reducing GPX4 expression and activating an autophagy-dependent ferroptosis pathway in benzene-exposed cells.","method":"Co-immunoprecipitation, LC-MS/MS, overexpression/knockdown, immunofluorescence, TEM","journal":"Ecotoxicology and environmental safety","confidence":"Low","confidence_rationale":"Tier 3 — Co-IP and knockdown/OE, single study, indirect mechanism","pmids":["39059346"],"is_preprint":false},{"year":2025,"finding":"UBE2L3 specifically binds to and ubiquitinates MLKL (necroptosis effector), promoting its degradation; UBE2L3 knockdown increases phospho-MLKL and phospho-RIP1 levels and promotes necroptosis in osteosarcoma cells and in vivo xenograft tumors.","method":"Co-immunoprecipitation, ubiquitination assays, in vivo xenograft model","journal":"World journal of surgical oncology","confidence":"Low","confidence_rationale":"Tier 3 — Co-IP and in vivo model, single study, limited mechanistic detail","pmids":["39988669"],"is_preprint":false},{"year":2026,"finding":"UBE2L3 interacts with the E3 ligase SMURF2 to control TSC2 protein ubiquitination and degradation; UBE2L3 downregulation increases TSC2, suppresses mTOR activity, and alters autophagy in TNBC cells, sensitizing tumors to anti-PD-1 therapy.","method":"In vivo CRISPR/Cas9 library screen, Co-IP, knockdown, in vivo tumor models","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR screen plus Co-IP plus functional assays in vitro and in vivo","pmids":["41943836"],"is_preprint":false},{"year":2009,"finding":"UbcH7 (UBE2L3) overexpression delays entry into S phase while its depletion increases S phase length and decreases cell proliferation; UbcH7 depletion increases Chk1 levels and decreases phospho-PTEN, placing UbcH7 in a PTEN/Akt/Chk1 pathway that regulates S phase length.","method":"Overexpression, siRNA knockdown, FACS cell cycle analysis, protein level analysis","journal":"Cell division","confidence":"Low","confidence_rationale":"Tier 3 — KD/OE with phenotype but pathway placement indirect, single lab, single study","pmids":["19664228"],"is_preprint":false},{"year":2017,"finding":"TCDD (an AhR ligand) promotes AhR binding to the UBE2L3 (Ubch7) gene promoter and induces UbcH7 expression in the mouse brain; increased UbcH7 promotes ubiquitination and degradation of synphilin-1 via the UbcH7-parkin complex.","method":"ChIP, promoter assay, protein stability/half-life analysis in mouse brain","journal":"Journal of biochemical and molecular toxicology","confidence":"Low","confidence_rationale":"Tier 3 — ChIP and protein stability assay, single study, indirect mechanism","pmids":["28621812"],"is_preprint":false}],"current_model":"UBE2L3 (UbcH7) is an E2 ubiquitin-conjugating enzyme that lacks intrinsic lysine reactivity and therefore functions selectively with HECT-type E3s (e.g., E6-AP, Itch, TRIP12, AREL1) and RBR-type E3s (e.g., parkin, HHARI, LUBAC components HOIL-1/HOIP), which use obligate thioester intermediates for ubiquitin transfer; it interacts with RING E3s like c-Cbl to ubiquitinate substrates including EGFR, steroid receptors, 53BP1, pro-IL-1β, p27Kip1, and HPV oncoproteins, regulating NF-κB signaling (via LUBAC-mediated linear ubiquitination), DNA double-strand break repair pathway choice, mitophagy, and inflammatory cytokine homeostasis."},"narrative":{"teleology":[{"year":1996,"claim":"Identification of UBE2L3 as a functional E2 conjugating enzyme for the HECT E3 E6-AP established its entry point into the ubiquitin pathway and demonstrated it could support ubiquitination of p53 and NF-κB precursors.","evidence":"Biochemical interaction and in vitro ubiquitination assays","pmids":["8576257"],"confidence":"High","gaps":["No structural basis for E2–E3 selectivity","Range of E3 partners unknown"]},{"year":1998,"claim":"Systematic testing against multiple HECT E3s revealed that UBE2L3 is selective for an E6-AP-like subclass of HECT ligases, establishing the principle of E2–HECT specificity classes.","evidence":"In vitro binding and ubiquitin thioester formation assays across HECT family members","pmids":["9575161"],"confidence":"High","gaps":["Structural determinants of selectivity unresolved","In vivo relevance of specificity not tested"]},{"year":1999,"claim":"Crystal structures of UBE2L3 bound to E6-AP (HECT) and c-Cbl (RING) defined the two principal modes of E2 recruitment and revealed how RING E3s scaffold the E2 active site for ubiquitin transfer, while HECT E3s accept ubiquitin via transthiolation.","evidence":"X-ray crystallography of E6-AP HECT–UbcH7 and c-Cbl RING–UbcH7 complexes with functional validation","pmids":["10558980","10966114","10531381"],"confidence":"High","gaps":["Why UBE2L3 pairs with RING E3s like c-Cbl despite lacking lysine reactivity was unexplained","RBR class not yet recognized"]},{"year":1999,"claim":"Discovery that UBE2L3 interacts with RBR-containing proteins HHARI and H7-AP1 through their RING1 domain linked the then-uncharacterized RBR family to the ubiquitin pathway.","evidence":"Yeast two-hybrid and in vitro binding assays","pmids":["10521492"],"confidence":"Medium","gaps":["RBR catalytic mechanism unknown","Whether RBR proteins function as E3 ligases unproven at this time"]},{"year":2004,"claim":"UBE2L3 was shown to function as a transcriptional coactivator for steroid hormone receptors and to target HPV E7 for proteasomal degradation via SCF, broadening its substrate repertoire beyond canonical ubiquitin pathway roles.","evidence":"ChIP, siRNA knockdown, reporter assays for steroid receptors; in vitro ubiquitination and Skp2-knockout MEFs for E7","pmids":["15367689","15113913"],"confidence":"High","gaps":["How UBE2L3 is recruited to chromatin mechanistically unclear","Whether UBE2L3 catalytic activity at promoters involves substrate ubiquitination or non-degradative modification unknown"]},{"year":2011,"claim":"The landmark discovery that UBE2L3 lacks intrinsic lysine reactivity resolved the paradox of its E3 selectivity: it functions exclusively with E3s that form a covalent thioester with ubiquitin (HECT and RBR types), and RBR E3s were reclassified as RING/HECT hybrids.","evidence":"In vitro ubiquitination assays with mutagenesis and structural comparisons","pmids":["21532592"],"confidence":"High","gaps":["How UBE2L3 is prevented from functioning with canonical RING E3s in cells not fully addressed","Structural basis for open vs. closed E2~Ub conformations with RBR E3s unresolved"]},{"year":2014,"claim":"Functional studies established UBE2L3 in two new cellular processes: regulation of DNA double-strand break repair pathway choice (via 53BP1 ubiquitination) and Parkin-dependent mitophagy (cooperating with UBE2N and UBE2D).","evidence":"shRNA screen and knockdown with DSB repair assays; siRNA knockdown with mitophagy flux assays","pmids":["25422456","24906799"],"confidence":"Medium","gaps":["Identity of E3 ligase partnering with UBE2L3 for 53BP1 ubiquitination unknown","Relative contribution of UBE2L3 vs. UBE2D in Parkin-mediated ubiquitination unclear"]},{"year":2015,"claim":"UBE2L3 was identified as the preferred E2 for the LUBAC complex in vivo, directly linking it to linear ubiquitin chain assembly and NF-κB activation; the autoimmune risk haplotype at the UBE2L3 locus increases its expression and enhances NF-κB-driven plasma cell development.","evidence":"Reporter assays, dominant-negative C86S, siRNA, imaging flow cytometry in primary human B cells","pmids":["25640675"],"confidence":"High","gaps":["Whether UBE2L3 directly charges HOIP or acts through HOIL-1 within LUBAC not resolved","Mechanism by which expression-level variation drives autoimmune risk incompletely defined"]},{"year":2017,"claim":"Structural analysis of the HHARI RING1–UbcH7~Ub complex revealed how a Zn²⁺-loop extension unique to RBR RING1 domains acts as a steric wedge to enforce the open E2~Ub conformation, explaining why UBE2L3 delivers ubiquitin exclusively via transthiolation with RBR E3s.","evidence":"Crystal structure with biochemical assays","pmids":["28552575"],"confidence":"High","gaps":["Generalizability to all RBR E3s not formally tested","Whether the open conformation is dynamically regulated in cells unknown"]},{"year":2018,"claim":"NMR studies of UbcH7~Ub with Parkin showed that conjugated ubiquitin binds at the RING1/IBR interface in the open conformation, and that E2 binding synergizes with Ubl phosphorylation to activate Parkin's RING2 catalytic cysteine.","evidence":"NMR chemical shift perturbation, mass spectrometry, in vitro ubiquitination assays","pmids":["30446597"],"confidence":"High","gaps":["Full-length activated Parkin–UbcH7~Ub structure not available","How substrate selection occurs after E2~Ub docking unclear"]},{"year":2023,"claim":"Conditional Ube2l3 knockout in mice revealed its role in disposing of pro-IL-1β via TRIP12- and AREL1-catalyzed K27/K29/K33 polyubiquitin chains, establishing UBE2L3 as a gatekeeper of inflammasome-driven inflammation.","evidence":"Conditional KO mouse, RNAi screen for E3 partners, in vitro ubiquitination with chain-type specificity","pmids":["37474493"],"confidence":"High","gaps":["Whether TRIP12 and AREL1 act redundantly or sequentially on pro-IL-1β unclear","Chain-type decoding mechanism downstream not identified"]},{"year":2024,"claim":"SMURF1 was identified as the E3 ligase that cooperates with UBE2L3 to conjugate K29-linked chains on p27Kip1, stabilizing rather than degrading p27 and promoting cell migration, demonstrating that UBE2L3 can generate non-degradative ubiquitin signals.","evidence":"In vitro ubiquitination screen, K29 chain-type mutagenesis, co-localization imaging, knockdown migration assays","pmids":["38301893"],"confidence":"High","gaps":["How K29 chains on p27 are read by downstream effectors unknown","Whether other non-K48/K63 chain types built by UBE2L3 have distinct signaling roles untested"]},{"year":null,"claim":"Key unresolved questions include: how UBE2L3 is directed to specific E3 partners in a context-dependent manner in vivo; the full spectrum of non-canonical ubiquitin chain types it generates and their downstream readers; and whether its roles in necroptosis and ferroptosis represent direct or indirect functions.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No global proteomics of UBE2L3-dependent ubiquitinome","Structural basis for UBE2L3 selectivity among different HECT E3 subclasses incomplete","In vivo relevance of UBE2L3 in necroptosis regulation based on single low-confidence study"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,4,11,12,13,21,23]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[2,4,21,23]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7,16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,11]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[16,23]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,4,11,21,23]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[13,21,22]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[13,22]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[11]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[12]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[20,23]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[12]}],"complexes":["LUBAC (as cognate E2)"],"partners":["E6AP","HOIP","HOIL1","PRKN","HHARI","CBL","SMURF1","TRIP12"],"other_free_text":[]},"mechanistic_narrative":"UBE2L3 (UbcH7) is an E2 ubiquitin-conjugating enzyme that lacks intrinsic lysine reactivity and therefore functions selectively with HECT-type and RBR-type E3 ligases, which transfer ubiquitin through an obligate thioester intermediate on their own catalytic cysteine [PMID:21532592]. Structural studies reveal that UBE2L3 is recruited by RING domains of E3 ligases such as c-Cbl and HHARI, with RBR E3s employing a unique steric mechanism to maintain the E2~Ub conjugate in an open conformation that favors transthiolation to the E3 active site rather than direct substrate lysine discharge [PMID:10966114, PMID:28552575, PMID:30446597]. UBE2L3 partners with diverse E3 ligases—including LUBAC (HOIL-1/HOIP), E6-AP, Itch/Ndfip1, TRIP12, AREL1, SMURF1, and parkin—to ubiquitinate substrates such as pro-IL-1β, 53BP1, p27Kip1, steroid receptors, and mitochondrial proteins, thereby regulating NF-κB signaling, DNA double-strand break repair pathway choice, cell cycle progression, inflammatory cytokine homeostasis, and mitophagy [PMID:25640675, PMID:25422456, PMID:37474493, PMID:38301893, PMID:24906799, PMID:15367689]. Notably, UBE2L3 catalyzes non-canonical (K27-, K29-, K33-linked) ubiquitin chains on pro-IL-1β and p27Kip1, generating proteolytically competent or incompetent modifications depending on the E3 partner and chain type [PMID:37474493, PMID:38301893]."},"prefetch_data":{"uniprot":{"accession":"P68036","full_name":"Ubiquitin-conjugating enzyme E2 L3","aliases":["E2 ubiquitin-conjugating enzyme L3","L-UBC","UbcH7","Ubiquitin carrier protein L3","Ubiquitin-conjugating enzyme E2-F1","Ubiquitin-protein ligase L3"],"length_aa":154,"mass_kda":17.9,"function":"Ubiquitin-conjugating enzyme E2 that specifically acts with HECT-type and RBR family E3 ubiquitin-protein ligases. Does not function with most RING-containing E3 ubiquitin-protein ligases because it lacks intrinsic E3-independent reactivity with lysine; in contrast, it has activity with the RBR family E3 enzymes, such as PRKN, RNF31 and ARIH1, that function like RING-HECT hybrids. Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. Mediates ubiquitination by the CUL9-RBX1 complex (PubMed:38605244). In vitro catalyzes 'Lys-11'-linked polyubiquitination. Involved in the selective degradation of short-lived and abnormal proteins. Down-regulated during the S-phase it is involved in progression through the cell cycle. Regulates nuclear hormone receptors transcriptional activity. 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\"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mechanistic interpretation, highly cited foundational study\",\n      \"pmids\": [\"10966114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Crystal structure of the E6AP HECT domain bound to UbcH7 (UBE2L3) reveals determinants of E2-E3 specificity and the mechanism of ubiquitin transfer from E2 to E3 via a thioester intermediate in the catalytic cleft.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of E2-E3 complex, highly cited foundational paper\",\n      \"pmids\": [\"10558980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"UBE2L3 (UBCH7) lacks intrinsic lysine reactivity (unlike many E2s that function with RING E3s), explaining its preference for HECT-type E3s. RBR E3s (parkin, HHARI) function as RING/HECT hybrids: they bind E2s via RING1 but transfer Ub through an obligate thioester at a conserved RING2 cysteine, and UBE2L3 is the cognate E2 for this class.\",\n      \"method\": \"In vitro ubiquitination assays, mutagenesis, structural comparisons\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus mutagenesis, highly cited, defines E2 mechanism\",\n      \"pmids\": [\"21532592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The c-Cbl RING finger domain directly interacts with UbcH7 (UBE2L3), and together they synergistically promote ligand-induced ubiquitination of the EGFR; oncogenic 70Z-Cbl (lacking part of the RING finger) fails to bind UbcH7 and blocks EGFR ubiquitination.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, in vivo and in vitro ubiquitination assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding plus functional ubiquitination assays in vitro and in vivo\",\n      \"pmids\": [\"10531381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"UBE2L3 encodes an E2 ubiquitin-conjugating enzyme (UbcH7) that interacts with the HECT E3 E6-AP and efficiently substitutes for UbcH5 in E6-AP-dependent ubiquitination of p53; UbcH7 can also interact with E6-AP to participate in NF-κB maturation and c-Fos degradation.\",\n      \"method\": \"Biochemical interaction assays, in vitro ubiquitination assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical assays, replicated across labs\",\n      \"pmids\": [\"8576257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"UBE2L3 (UbcH7) interacts preferentially with a subset of HECT E3s (those sharing E6-AP-like specificity) but not others (e.g., RSP5), demonstrating that different HECT E3s are grouped into at least two classes based on their E2 specificity.\",\n      \"method\": \"In vitro binding and ubiquitin thioester formation assays with multiple HECT E3s\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic in vitro assays across multiple HECT family members\",\n      \"pmids\": [\"9575161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"UBE2L3 (UbcH7) interacts with RBR-containing proteins HHARI and H7-AP1 through their N-terminal RING finger (HHARI) and IBR domains; this interaction is specific to UbcH7/UbcH8 and not seen with UbcH5 or UbcH1, linking RBR proteins to the ubiquitin pathway via UBE2L3.\",\n      \"method\": \"Yeast two-hybrid screen, in vitro binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid plus pulldown, single study\",\n      \"pmids\": [\"10521492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"HHARI co-localizes with UbcH7 (UBE2L3) in mammalian cells, particularly in the perinuclear region; a minimal interaction region (residues 186-254) was defined, and the distance between RING1 and IBR domains is critical; mutation of RING1 from RING-HC to RING-H2 type abolishes UbcH7 interaction.\",\n      \"method\": \"Co-immunoprecipitation, co-localization (immunofluorescence), mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus live-cell localization plus mutagenesis, single lab\",\n      \"pmids\": [\"11278816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"UbcH7 (UBE2L3) is the specific E2 for ubiquitination of HPV E7 oncoprotein; E7 interacts with the SCF complex (Cul1/Skp2) E3 ligase, and can be ubiquitinated by the Cul1-containing ligase in vitro; E7 half-life is longer in Skp2-/- MEFs.\",\n      \"method\": \"In vitro ubiquitination assay, co-immunoprecipitation, Skp2 knockout MEFs\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro assay plus genetic KO and Co-IP\",\n      \"pmids\": [\"15113913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"UbcH7 (UBE2L3) acts as a coactivator for steroid hormone receptors (PR, GR, AR, RAR) in a hormone-dependent manner; its ubiquitin conjugation activity is required for coactivation; UbcH7 is recruited to ER- and PR-responsive promoters and cooperates with E6-AP and SRC-1 to potentiate transactivation.\",\n      \"method\": \"Transient transfection reporter assays, siRNA knockdown, chromatin immunoprecipitation (ChIP), Co-IP\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, siRNA, reporter assay, Co-IP), mechanistic mutagenesis of catalytic residue\",\n      \"pmids\": [\"15367689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"UbcH7 (UBE2L3) physically interacts with the glucocorticoid receptor (GR) and promotes its ubiquitination and proteasome-dependent degradation; a catalytically inactive UbcH7 dominant negative (C89S) fails to repress GR transactivation and stabilizes GR protein, demonstrating that UbcH7 enzymatic activity mediates GR turnover.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative mutagenesis, reporter assays, proteasome inhibitor experiments\",\n      \"journal\": \"The Journal of endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional mutagenesis and pharmacological inhibition, single lab\",\n      \"pmids\": [\"17003263\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UbcH7 (UBE2L3) regulates steady-state and replicative stress-induced ubiquitination and proteasomal degradation of 53BP1; depletion of UbcH7 stabilizes 53BP1, inhibits DSB end resection, increases NHEJ, and reduces homologous recombination, making cells sensitive to DNA damage.\",\n      \"method\": \"shRNA screen, knockdown/depletion, ubiquitination assays, DSB repair pathway assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional KD with defined molecular and cellular phenotype, shRNA screen\",\n      \"pmids\": [\"25422456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"UBE2N, UBE2L3, and UBE2D2/3 are required synergistically for Parkin-dependent mitophagy; UBE2L3 knockdown reduces autophagic clearance of depolarized mitochondria without interfering with PINK1 stabilization or Parkin translocation; combined knockdown reduces mitochondrial polyubiquitylation of substrates including mitofusins, TOM20, TOM70, and VDAC1.\",\n      \"method\": \"siRNA knockdown, autophagic flux assays, ubiquitination assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic knockdown with defined cellular and molecular phenotype\",\n      \"pmids\": [\"24906799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"UBE2L3 is the preferred E2 conjugating enzyme for LUBAC (linear ubiquitin chain assembly complex, containing HOIL-1 and HOIP) in vivo, and is essential for LUBAC-mediated NF-κB activation; dominant-negative UBE2L3 (C86S) or UBE2L3 silencing abolishes NF-κB upregulation by LUBAC; the autoimmune risk haplotype increases UBE2L3 expression, correlating with enhanced NF-κB activation and plasma cell development.\",\n      \"method\": \"Reporter assays, dominant-negative mutant (C86S), siRNA knockdown, imaging flow cytometry for NF-κB translocation, flow cytometry for B cell subsets\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, dominant-negative and knockdown, primary human cells\",\n      \"pmids\": [\"25640675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Structural analysis of HHARI RING1 in complex with UbcH7~Ub shows that a Zn2+-loop II extension unique to RBR RING1 (absent in canonical RING E3s) acts as a steric wedge to disrupt closed E2~Ub conformation, favoring open conformation required for Ub transfer to the E3 active-site cysteine rather than directly to substrate.\",\n      \"method\": \"Structural biology (crystal structure), biochemical assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional mechanistic explanation\",\n      \"pmids\": [\"28552575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NMR and mass spectrometry show that UbcH7~Ub binds to parkin in the open conformation, with conjugated Ub binding at the RING1/IBR interface; recruitment of UbcH7~Ub and phosphorylation of parkin's Ubl domain act synergistically to rearrange the RING2 catalytic cysteine and enhance ubiquitin transfer activity.\",\n      \"method\": \"NMR chemical shift perturbation, mass spectrometry, in vitro ubiquitination assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure plus mass spectrometry plus functional assays\",\n      \"pmids\": [\"30446597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HIV Nef mediates exclusion of UbcH7 (UBE2L3) from lipid rafts via a p85Cool-1/βPix–c-Cbl ternary complex, preventing ubiquitination of activated Vav by c-Cbl/UbcH7 and thereby enhancing T cell signaling to promote HIV replication.\",\n      \"method\": \"Lipid raft fractionation, siRNA knockdown of p85Cool-1/βPix, ubiquitination assays, Co-IP\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — subcellular fractionation plus knockdown plus ubiquitination assay, mechanistically linked\",\n      \"pmids\": [\"16356860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The RBR E3 ligase Triad1 inhibits myeloid cell proliferation through differential interactions of its two RING domains with UbcH7 (UBE2L3) and Ubc13, catalyzing distinct ubiquitin chain types; deletion of either RING domain abrogates the inhibitory effect on myeloid colony formation.\",\n      \"method\": \"In vitro binding assays, myeloid clonogenic assays, domain deletion mutagenesis\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain mutagenesis plus functional cell assays\",\n      \"pmids\": [\"19340006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ndfip1 acts as an adaptor protein that facilitates recruitment of UbcH7 (UBE2L3) to the HECT E3 Itch, enhancing Itch ligase activity and Tak1 ubiquitination; the N-terminal region of Ndfip1 binds UbcH7 while the PY motif binds Itch, and reconstitution with full-length Ndfip1 (but not interaction-dead mutants) restores defective Tak1 ubiquitination.\",\n      \"method\": \"Co-immunoprecipitation, in vitro reconstitution, Ndfip1-/- and Itch-/- mouse models, mutagenesis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstitution plus mutagenesis plus KO mouse model\",\n      \"pmids\": [\"25632008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MAP1B light chain 1 (LC1) interacts with both CaV2.2 (N-type Ca2+ channel) and UBE2L3 via Co-IP; the LC1/UBE2L3 complex promotes ubiquitination and proteasomal degradation of CaV2.2, reducing channel surface expression and current density; MG132 prevents LC1-induced channel degradation.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, patch-clamp, proteasome inhibition\",\n      \"journal\": \"Pflugers Archiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP plus functional electrophysiology and pharmacological inhibition\",\n      \"pmids\": [\"24566975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"UBE2L3 (UBCH7) specifically stabilizes p27Kip1 by catalyzing the conjugation of heterotypic ubiquitin chains on p27 that are proteolytically incompetent; overexpression of UBE2L3 stabilizes p27 and delays G1-to-S transition, while depletion increases p27 turnover, without affecting p21, p57, cyclin A, or cyclin E levels.\",\n      \"method\": \"Overexpression, siRNA knockdown, cell cycle analysis, in vitro ubiquitination assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro ubiquitination plus KD/OE with defined cell-cycle phenotype\",\n      \"pmids\": [\"30113882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"UBE2L3 promotes pro-IL-1β ubiquitylation and proteasomal disposal; deletion of Ube2l3 in mice reduces pro-IL-1β turnover in macrophages, leading to excessive mature IL-1β production, neutrophilic inflammation after inflammasome activation; RNAi screen identified TRIP12 and AREL1 (HECT E3s) as the partner E3 ligases that add destabilizing K27-, K29-, and K33-linked poly-ubiquitin chains on pro-IL-1β.\",\n      \"method\": \"Ube2l3 conditional knockout mouse, RNAi screen, in vitro ubiquitination assays, inflammasome activation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — KO mouse plus unbiased RNAi screen plus in vitro ubiquitination with chain-type specificity\",\n      \"pmids\": [\"37474493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"UBE2L3 is critical for NF-κB activation downstream of TLR7 stimulation via interaction with LUBAC; dimethyl fumarate (DMF) directly inhibits UBE2L3 and significantly reduces TLR7-induced NF-κB activation, plasmablast/memory B cell differentiation, and autoantibody secretion in SLE.\",\n      \"method\": \"Knockdown, overexpression, reporter assays, flow cytometry, DMF pharmacological inhibition\",\n      \"journal\": \"Journal of autoimmunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic knockdown plus pharmacological inhibition with defined cellular outcome\",\n      \"pmids\": [\"37001433\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SMURF1 acts as the E3 ligase partner of UBE2L3 (UbcH7) to ubiquitinate p27Kip1 with K29-linked chains, stabilizing p27 and promoting cell migration; SMURF1, UbcH7, and p27 co-localize at the leading edge of migrating cells; knockdown of SMURF1 or UbcH7 reduces cell migration.\",\n      \"method\": \"In vitro ubiquitination screen, K29 chain-type mutagenesis, co-localization imaging, knockdown assays, migration assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro ubiquitination with chain-type specificity plus co-localization plus functional KD\",\n      \"pmids\": [\"38301893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MARCHF8 (a membrane RING E3 ligase) binds to and ubiquitinates UBE2L3 and CUL1, promoting their degradation and thereby stabilizing HPV16 E7; MARCHF8 knockdown increases UBE2L3 and CUL1 levels and enhances E7 ubiquitination; overexpression of CUL1 or UBE2L3 decreases E7 levels and suppresses tumor growth in vivo.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, MARCHF8 knockdown, in vivo xenograft\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, ubiquitination assays, and in vivo model\",\n      \"pmids\": [\"38226814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBE2L3 interacts with the E3 ligase ZNF598 (confirmed by LC-MS/MS and Co-IP) and disrupts ZNF598-mediated ubiquitination of the autophagy protein LAMP-2, thereby reducing GPX4 expression and activating an autophagy-dependent ferroptosis pathway in benzene-exposed cells.\",\n      \"method\": \"Co-immunoprecipitation, LC-MS/MS, overexpression/knockdown, immunofluorescence, TEM\",\n      \"journal\": \"Ecotoxicology and environmental safety\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and knockdown/OE, single study, indirect mechanism\",\n      \"pmids\": [\"39059346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"UBE2L3 specifically binds to and ubiquitinates MLKL (necroptosis effector), promoting its degradation; UBE2L3 knockdown increases phospho-MLKL and phospho-RIP1 levels and promotes necroptosis in osteosarcoma cells and in vivo xenograft tumors.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, in vivo xenograft model\",\n      \"journal\": \"World journal of surgical oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and in vivo model, single study, limited mechanistic detail\",\n      \"pmids\": [\"39988669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"UBE2L3 interacts with the E3 ligase SMURF2 to control TSC2 protein ubiquitination and degradation; UBE2L3 downregulation increases TSC2, suppresses mTOR activity, and alters autophagy in TNBC cells, sensitizing tumors to anti-PD-1 therapy.\",\n      \"method\": \"In vivo CRISPR/Cas9 library screen, Co-IP, knockdown, in vivo tumor models\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR screen plus Co-IP plus functional assays in vitro and in vivo\",\n      \"pmids\": [\"41943836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"UbcH7 (UBE2L3) overexpression delays entry into S phase while its depletion increases S phase length and decreases cell proliferation; UbcH7 depletion increases Chk1 levels and decreases phospho-PTEN, placing UbcH7 in a PTEN/Akt/Chk1 pathway that regulates S phase length.\",\n      \"method\": \"Overexpression, siRNA knockdown, FACS cell cycle analysis, protein level analysis\",\n      \"journal\": \"Cell division\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — KD/OE with phenotype but pathway placement indirect, single lab, single study\",\n      \"pmids\": [\"19664228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TCDD (an AhR ligand) promotes AhR binding to the UBE2L3 (Ubch7) gene promoter and induces UbcH7 expression in the mouse brain; increased UbcH7 promotes ubiquitination and degradation of synphilin-1 via the UbcH7-parkin complex.\",\n      \"method\": \"ChIP, promoter assay, protein stability/half-life analysis in mouse brain\",\n      \"journal\": \"Journal of biochemical and molecular toxicology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — ChIP and protein stability assay, single study, indirect mechanism\",\n      \"pmids\": [\"28621812\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBE2L3 (UbcH7) is an E2 ubiquitin-conjugating enzyme that lacks intrinsic lysine reactivity and therefore functions selectively with HECT-type E3s (e.g., E6-AP, Itch, TRIP12, AREL1) and RBR-type E3s (e.g., parkin, HHARI, LUBAC components HOIL-1/HOIP), which use obligate thioester intermediates for ubiquitin transfer; it interacts with RING E3s like c-Cbl to ubiquitinate substrates including EGFR, steroid receptors, 53BP1, pro-IL-1β, p27Kip1, and HPV oncoproteins, regulating NF-κB signaling (via LUBAC-mediated linear ubiquitination), DNA double-strand break repair pathway choice, mitophagy, and inflammatory cytokine homeostasis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"UBE2L3 (UbcH7) is an E2 ubiquitin-conjugating enzyme that lacks intrinsic lysine reactivity and therefore functions selectively with HECT-type and RBR-type E3 ligases, which transfer ubiquitin through an obligate thioester intermediate on their own catalytic cysteine [PMID:21532592]. Structural studies reveal that UBE2L3 is recruited by RING domains of E3 ligases such as c-Cbl and HHARI, with RBR E3s employing a unique steric mechanism to maintain the E2~Ub conjugate in an open conformation that favors transthiolation to the E3 active site rather than direct substrate lysine discharge [PMID:10966114, PMID:28552575, PMID:30446597]. UBE2L3 partners with diverse E3 ligases—including LUBAC (HOIL-1/HOIP), E6-AP, Itch/Ndfip1, TRIP12, AREL1, SMURF1, and parkin—to ubiquitinate substrates such as pro-IL-1β, 53BP1, p27Kip1, steroid receptors, and mitochondrial proteins, thereby regulating NF-κB signaling, DNA double-strand break repair pathway choice, cell cycle progression, inflammatory cytokine homeostasis, and mitophagy [PMID:25640675, PMID:25422456, PMID:37474493, PMID:38301893, PMID:24906799, PMID:15367689]. Notably, UBE2L3 catalyzes non-canonical (K27-, K29-, K33-linked) ubiquitin chains on pro-IL-1β and p27Kip1, generating proteolytically competent or incompetent modifications depending on the E3 partner and chain type [PMID:37474493, PMID:38301893].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of UBE2L3 as a functional E2 conjugating enzyme for the HECT E3 E6-AP established its entry point into the ubiquitin pathway and demonstrated it could support ubiquitination of p53 and NF-κB precursors.\",\n      \"evidence\": \"Biochemical interaction and in vitro ubiquitination assays\",\n      \"pmids\": [\"8576257\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural basis for E2–E3 selectivity\", \"Range of E3 partners unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Systematic testing against multiple HECT E3s revealed that UBE2L3 is selective for an E6-AP-like subclass of HECT ligases, establishing the principle of E2–HECT specificity classes.\",\n      \"evidence\": \"In vitro binding and ubiquitin thioester formation assays across HECT family members\",\n      \"pmids\": [\"9575161\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural determinants of selectivity unresolved\", \"In vivo relevance of specificity not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Crystal structures of UBE2L3 bound to E6-AP (HECT) and c-Cbl (RING) defined the two principal modes of E2 recruitment and revealed how RING E3s scaffold the E2 active site for ubiquitin transfer, while HECT E3s accept ubiquitin via transthiolation.\",\n      \"evidence\": \"X-ray crystallography of E6-AP HECT–UbcH7 and c-Cbl RING–UbcH7 complexes with functional validation\",\n      \"pmids\": [\"10558980\", \"10966114\", \"10531381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why UBE2L3 pairs with RING E3s like c-Cbl despite lacking lysine reactivity was unexplained\", \"RBR class not yet recognized\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that UBE2L3 interacts with RBR-containing proteins HHARI and H7-AP1 through their RING1 domain linked the then-uncharacterized RBR family to the ubiquitin pathway.\",\n      \"evidence\": \"Yeast two-hybrid and in vitro binding assays\",\n      \"pmids\": [\"10521492\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"RBR catalytic mechanism unknown\", \"Whether RBR proteins function as E3 ligases unproven at this time\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"UBE2L3 was shown to function as a transcriptional coactivator for steroid hormone receptors and to target HPV E7 for proteasomal degradation via SCF, broadening its substrate repertoire beyond canonical ubiquitin pathway roles.\",\n      \"evidence\": \"ChIP, siRNA knockdown, reporter assays for steroid receptors; in vitro ubiquitination and Skp2-knockout MEFs for E7\",\n      \"pmids\": [\"15367689\", \"15113913\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How UBE2L3 is recruited to chromatin mechanistically unclear\", \"Whether UBE2L3 catalytic activity at promoters involves substrate ubiquitination or non-degradative modification unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The landmark discovery that UBE2L3 lacks intrinsic lysine reactivity resolved the paradox of its E3 selectivity: it functions exclusively with E3s that form a covalent thioester with ubiquitin (HECT and RBR types), and RBR E3s were reclassified as RING/HECT hybrids.\",\n      \"evidence\": \"In vitro ubiquitination assays with mutagenesis and structural comparisons\",\n      \"pmids\": [\"21532592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How UBE2L3 is prevented from functioning with canonical RING E3s in cells not fully addressed\", \"Structural basis for open vs. closed E2~Ub conformations with RBR E3s unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Functional studies established UBE2L3 in two new cellular processes: regulation of DNA double-strand break repair pathway choice (via 53BP1 ubiquitination) and Parkin-dependent mitophagy (cooperating with UBE2N and UBE2D).\",\n      \"evidence\": \"shRNA screen and knockdown with DSB repair assays; siRNA knockdown with mitophagy flux assays\",\n      \"pmids\": [\"25422456\", \"24906799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of E3 ligase partnering with UBE2L3 for 53BP1 ubiquitination unknown\", \"Relative contribution of UBE2L3 vs. UBE2D in Parkin-mediated ubiquitination unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"UBE2L3 was identified as the preferred E2 for the LUBAC complex in vivo, directly linking it to linear ubiquitin chain assembly and NF-κB activation; the autoimmune risk haplotype at the UBE2L3 locus increases its expression and enhances NF-κB-driven plasma cell development.\",\n      \"evidence\": \"Reporter assays, dominant-negative C86S, siRNA, imaging flow cytometry in primary human B cells\",\n      \"pmids\": [\"25640675\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether UBE2L3 directly charges HOIP or acts through HOIL-1 within LUBAC not resolved\", \"Mechanism by which expression-level variation drives autoimmune risk incompletely defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Structural analysis of the HHARI RING1–UbcH7~Ub complex revealed how a Zn²⁺-loop extension unique to RBR RING1 domains acts as a steric wedge to enforce the open E2~Ub conformation, explaining why UBE2L3 delivers ubiquitin exclusively via transthiolation with RBR E3s.\",\n      \"evidence\": \"Crystal structure with biochemical assays\",\n      \"pmids\": [\"28552575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generalizability to all RBR E3s not formally tested\", \"Whether the open conformation is dynamically regulated in cells unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"NMR studies of UbcH7~Ub with Parkin showed that conjugated ubiquitin binds at the RING1/IBR interface in the open conformation, and that E2 binding synergizes with Ubl phosphorylation to activate Parkin's RING2 catalytic cysteine.\",\n      \"evidence\": \"NMR chemical shift perturbation, mass spectrometry, in vitro ubiquitination assays\",\n      \"pmids\": [\"30446597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length activated Parkin–UbcH7~Ub structure not available\", \"How substrate selection occurs after E2~Ub docking unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Conditional Ube2l3 knockout in mice revealed its role in disposing of pro-IL-1β via TRIP12- and AREL1-catalyzed K27/K29/K33 polyubiquitin chains, establishing UBE2L3 as a gatekeeper of inflammasome-driven inflammation.\",\n      \"evidence\": \"Conditional KO mouse, RNAi screen for E3 partners, in vitro ubiquitination with chain-type specificity\",\n      \"pmids\": [\"37474493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRIP12 and AREL1 act redundantly or sequentially on pro-IL-1β unclear\", \"Chain-type decoding mechanism downstream not identified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"SMURF1 was identified as the E3 ligase that cooperates with UBE2L3 to conjugate K29-linked chains on p27Kip1, stabilizing rather than degrading p27 and promoting cell migration, demonstrating that UBE2L3 can generate non-degradative ubiquitin signals.\",\n      \"evidence\": \"In vitro ubiquitination screen, K29 chain-type mutagenesis, co-localization imaging, knockdown migration assays\",\n      \"pmids\": [\"38301893\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How K29 chains on p27 are read by downstream effectors unknown\", \"Whether other non-K48/K63 chain types built by UBE2L3 have distinct signaling roles untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how UBE2L3 is directed to specific E3 partners in a context-dependent manner in vivo; the full spectrum of non-canonical ubiquitin chain types it generates and their downstream readers; and whether its roles in necroptosis and ferroptosis represent direct or indirect functions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No global proteomics of UBE2L3-dependent ubiquitinome\", \"Structural basis for UBE2L3 selectivity among different HECT E3 subclasses incomplete\", \"In vivo relevance of UBE2L3 in necroptosis regulation based on single low-confidence study\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 4, 11, 12, 13, 21, 23]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [2, 4, 21, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 11]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [16, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 4, 11, 21, 23]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13, 21, 22]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [13, 22]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [20, 23]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [\n      \"LUBAC (as cognate E2)\"\n    ],\n    \"partners\": [\n      \"E6AP\",\n      \"HOIP\",\n      \"HOIL1\",\n      \"PRKN\",\n      \"HHARI\",\n      \"CBL\",\n      \"SMURF1\",\n      \"TRIP12\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}