{"gene":"UBE2H","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2004,"finding":"UBE2H (Ubc8) functions as an ISG15-conjugating E2 enzyme, mediating protein ISGylation upon interferon stimulation. siRNA knockdown of Ubc8 in HeLa cells reduces ISGylation after interferon treatment. Neither the closest homologue UbcH7/UbcM4 nor Ubc9 can substitute for Ubc8 in this activity.","method":"siRNA knockdown, transfection assays, in-cell ISGylation assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA loss-of-function with defined biochemical readout (ISGylation) plus specificity demonstrated by testing closely related E2s; single lab","pmids":["15485925"],"is_preprint":false},{"year":1994,"finding":"Human UBE2H (UbcH2) is a ubiquitin-conjugating enzyme that catalyzes ubiquitination of histones in vitro, similar to its yeast ortholog UBC8. The first 12 N-terminal residues of UBC8 are required for histone ubiquitination but not for thiolester formation with ubiquitin, suggesting the N-terminus is needed for substrate recognition or ubiquitin transfer onto substrates.","method":"In vitro ubiquitination assay, N-terminal truncation mutagenesis, thiolester formation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of enzymatic activity with mutagenesis (truncation), ortholog comparison; single lab but multiple orthogonal biochemical methods","pmids":["8132613"],"is_preprint":false},{"year":2022,"finding":"UBE2H is the cognate E2 ubiquitin-conjugating enzyme for the CTLH E3 ubiquitin ligase complex during erythropoiesis. UBE2H protein abundance increases during terminal erythroid differentiation and its expression depends on catalytically active CTLH E3 complexes. CRISPR-Cas9 inactivation of CTLH E3 assemblies or UBE2H in erythroid progenitors causes defects in erythroid maturation progression and inefficient enucleation.","method":"CRISPR-Cas9 loss-of-function, proteomics, in vitro human erythropoiesis model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with defined cellular phenotype (maturation and enucleation defects), proteomics, identification of E2-E3 partnership; single lab with multiple orthogonal methods","pmids":["36459484"],"is_preprint":false},{"year":2023,"finding":"The specific E3-E2 pairing between GID/CTLH and Ubc8/UBE2H is established through an unconventional catalytic assembly and auxiliary interactions 70–100 Å away from the active site, mediated by multisite phosphorylation of E2 CK2-targeted acidic sequences that anchor the E2 C-terminus to basic patches on the E3. Phosphorylation-dependent multivalency rigidifies the catalytic centers and facilitates substrate ubiquitylation; dephosphorylation is antagonistic to this interaction.","method":"Cryo-EM structure determination, biochemical assays, cell biology experiments, mutagenesis of phosphorylation sites","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure plus biochemistry plus mutagenesis plus cell biology in a single rigorous study establishing the molecular mechanism of E2-E3 pairing","pmids":["38113892"],"is_preprint":false},{"year":2022,"finding":"Yeast Ubc8 (ortholog of UBE2H) promotes assembly of the translocase of the outer mitochondrial membrane (TOM complex) and increases levels of Tom22, a cytosol-exposed receptor subunit. Ubc8 deficiency results in compromised mitochondrial protein import and reduced steady-state levels of mitochondrial proteins during the transition from respiratory to fermentative conditions.","method":"Yeast genetic deletion, mitochondrial protein import assay, TOM complex assembly analysis, quantitative proteomics","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in yeast with defined biochemical phenotype (import assay, TOM assembly), single lab; yeast ortholog study","pmids":["36253107"],"is_preprint":false},{"year":2023,"finding":"Zebrafish Ube2h is required for normal brain development. Knockdown of ube2h activates the ATM-p53 signaling pathway and induces apoptosis specifically in differentiated neural cells. A missense mutation mimicking the human patient variant (c.449C>T; p.Thr150Met) causes aberrant Ube2h function in zebrafish embryos.","method":"Zebrafish gene knockdown (morpholino), transcriptomic analysis, apoptosis assays, functional validation of patient variant","journal":"Human genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — zebrafish KD with defined cellular phenotype (neural apoptosis) and pathway identification (ATM-p53 activation), functional validation of patient variant; single lab","pmids":["37208785"],"is_preprint":false},{"year":2026,"finding":"CDK- and mTOR-dependent phosphorylation of UBE2H at N-terminal serine residues S3/S5 reduces UBE2H charging with ubiquitin, limiting the pool of active E2 available to the CTLH E3 complex. Mitotic CDK activity inactivates UBE2H during mitosis; mTOR restrains UBE2H charging in interphase to couple CTLH-dependent ubiquitylation to nutrient status. Preventing this phosphorylation enhances CTLH-mediated substrate degradation, promotes CTLH subunit turnover, and causes proliferation and mitotic defects. Two additional CTLH substrates were identified using hyperactive UBE2H: the mitotic kinase NEK9 and AAMP, with a DR-like C-degron recognized by CTLH subunit MKLN1.","method":"Phospho-site mutagenesis (S3/S5), ubiquitin-charging assay, substrate degradation assay, mass spectrometry, cell proliferation and mitosis assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro charging assay with mutagenesis, identification of kinase writers (CDK, mTOR), substrate identification by MS; preprint, single lab, not yet peer-reviewed","pmids":["41959163"],"is_preprint":true},{"year":2026,"finding":"UBE2H is an aneuploid-specific genetic dependency in human cancer cell lines. Mechanistic analyses link UBE2H to mitochondrial protein abundance, suggesting a role in maintaining mitochondrial proteostasis under aneuploid stress.","method":"Paired CRISPR loss-of-function screens (genome-wide and focused druggable genome library), functional validation in isogenic aneuploid/near-euploid cell lines, proteomics","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — paired CRISPR screens with functional validation and proteomic mechanistic link to mitochondria; preprint, single lab","pmids":["42094535"],"is_preprint":true}],"current_model":"UBE2H is a ubiquitin-conjugating E2 enzyme that acts as the dedicated E2 for the CTLH/GID E3 ubiquitin ligase complex, with their interaction governed by CK2-mediated multisite phosphorylation of UBE2H's C-terminal acidic sequences that anchor it to the E3; UBE2H charging with ubiquitin is further tuned by CDK (during mitosis) and mTOR (in interphase) phosphorylation of N-terminal residues S3/S5, coupling CTLH ubiquitylation activity to cell cycle state and nutrient status; UBE2H-CTLH modules control erythroid maturation and enucleation, support mitochondrial proteostasis, and are required for normal neurogenesis through ATM-p53 pathway regulation; additionally, UBE2H can act as an ISG15-conjugating E2 enzyme for protein ISGylation upon interferon stimulation."},"narrative":{"mechanistic_narrative":"UBE2H is a ubiquitin-conjugating (E2) enzyme that catalyzes substrate ubiquitination, originally characterized through its ability to ubiquitinate histones in vitro, with its first 12 N-terminal residues required for substrate modification but dispensable for thiolester formation with ubiquitin [PMID:8132613]. Its principal physiological role is as the cognate E2 for the CTLH/GID E3 ubiquitin ligase complex [PMID:36459484, PMID:38113892]. This E2–E3 pairing is achieved through an unconventional catalytic assembly in which CK2-mediated multisite phosphorylation of acidic sequences in the UBE2H C-terminus anchors the enzyme to basic patches on the E3, with phosphorylation-dependent multivalency rigidifying the catalytic center to drive substrate ubiquitylation [PMID:38113892]. UBE2H charging with ubiquitin is independently tuned by CDK and mTOR phosphorylation of N-terminal serines S3/S5, coupling CTLH ubiquitylation activity to mitotic state and nutrient status; preventing this phosphorylation enhances CTLH-mediated degradation of substrates including NEK9 and AAMP and produces proliferation and mitotic defects [PMID:41959163]. Through the CTLH module, UBE2H is required for terminal erythroid maturation and enucleation [PMID:36459484] and supports mitochondrial proteostasis, a role conserved in yeast Ubc8 where it promotes TOM complex assembly and mitochondrial protein import [PMID:36253107]. UBE2H is also required for normal neurogenesis, where its loss activates ATM-p53 signaling and induces apoptosis in differentiated neural cells [PMID:37208785], and it can act as an ISG15-conjugating E2 for protein ISGylation upon interferon stimulation [PMID:15485925].","teleology":[{"year":1994,"claim":"Establishing that human UBE2H is a catalytically active ubiquitin-conjugating enzyme answered whether it could transfer ubiquitin to substrates and localized substrate-recognition function to its N-terminus.","evidence":"in vitro ubiquitination and thiolester assays with N-terminal truncation mutagenesis, ortholog comparison to yeast UBC8","pmids":["8132613"],"confidence":"High","gaps":["Physiological substrates beyond in vitro histones not defined","No cognate E3 partner identified at this stage"]},{"year":2004,"claim":"Demonstrating UBE2H as an ISG15-conjugating E2 extended its activity beyond ubiquitin to a ubiquitin-like modifier in the interferon response.","evidence":"siRNA knockdown in HeLa cells with in-cell ISGylation readout and specificity testing against related E2s","pmids":["15485925"],"confidence":"Medium","gaps":["ISG15 E3 partner for UBE2H not defined","Substrate specificity of ISGylation by UBE2H unresolved"]},{"year":2022,"claim":"Identifying UBE2H as the cognate E2 for the CTLH E3 complex during erythropoiesis placed it in a defined physiological ubiquitylation pathway with a cellular phenotype.","evidence":"CRISPR-Cas9 loss-of-function and proteomics in an in vitro human erythropoiesis model","pmids":["36459484"],"confidence":"High","gaps":["Erythroid CTLH substrates driving maturation/enucleation not enumerated","Molecular basis of the E2-E3 pairing not yet resolved"]},{"year":2022,"claim":"Yeast Ubc8 work linked this E2 to mitochondrial proteostasis by showing it promotes TOM complex assembly and protein import.","evidence":"yeast genetic deletion with mitochondrial import assays, TOM assembly analysis, and quantitative proteomics","pmids":["36253107"],"confidence":"Medium","gaps":["Direct E3 partner and substrates in the mitochondrial pathway not defined","Conservation of this role to human UBE2H not established in this study"]},{"year":2023,"claim":"Cryo-EM and biochemistry resolved how UBE2H is selected by CTLH/GID, revealing phosphorylation-dependent anchoring of its C-terminus to the E3 distant from the active site.","evidence":"cryo-EM structure determination plus biochemistry, phospho-site mutagenesis, and cell biology","pmids":["38113892"],"confidence":"High","gaps":["In vivo dynamics of CK2 phosphorylation/dephosphorylation cycling not fully resolved","Whether other E2s engage CTLH via similar mechanisms unaddressed"]},{"year":2023,"claim":"Zebrafish loss-of-function tied UBE2H to neurogenesis and connected a human patient variant to disease-relevant neural apoptosis via ATM-p53 signaling.","evidence":"morpholino knockdown, transcriptomics, apoptosis assays, and functional validation of the p.Thr150Met patient variant in embryos","pmids":["37208785"],"confidence":"Medium","gaps":["Mechanistic link between UBE2H loss and ATM-p53 activation unresolved","Relevant CTLH substrates in neural cells not identified"]},{"year":2026,"claim":"Identifying CDK/mTOR phosphorylation of N-terminal S3/S5 as a brake on UBE2H ubiquitin-charging showed how CTLH activity is coupled to cell cycle and nutrient state, and uncovered new substrates.","evidence":"phospho-site mutagenesis, ubiquitin-charging and degradation assays, and mass spectrometry identifying NEK9 and AAMP (preprint)","pmids":["41959163"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Relative contribution of N-terminal vs C-terminal phospho-regulation in vivo unclear","C-degron recognition of NEK9 not fully mapped"]},{"year":2026,"claim":"CRISPR screens defined UBE2H as an aneuploidy-specific dependency, linking its function to mitochondrial proteostasis under aneuploid stress.","evidence":"paired CRISPR loss-of-function screens with isogenic aneuploid/near-euploid validation and proteomics (preprint)","pmids":["42094535"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Direct mechanistic chain from UBE2H to mitochondrial protein abundance not established","Whether dependency is CTLH-dependent not resolved"]},{"year":null,"claim":"The full substrate repertoire of UBE2H-CTLH across tissues and the mechanistic basis connecting its activity to ATM-p53 signaling and mitochondrial proteostasis remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Comprehensive substrate map of UBE2H-CTLH lacking","Integration of N-terminal and C-terminal phospho-regulation in vivo undefined","Direct ISG15 vs ubiquitin partitioning of UBE2H activity unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,3]},{"term_id":"GO:0031386","term_label":"protein tag activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0]}],"complexes":["CTLH/GID E3 ubiquitin ligase complex"],"partners":["MKLN1","NEK9","AAMP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P62256","full_name":"Ubiquitin-conjugating enzyme E2 H","aliases":["(E3-independent) E2 ubiquitin-conjugating enzyme H","E2 ubiquitin-conjugating enzyme H","UbcH2","Ubiquitin carrier protein H","Ubiquitin-conjugating enzyme E2-20K","Ubiquitin-protein ligase H"],"length_aa":183,"mass_kda":20.7,"function":"Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins (PubMed:17588522, PubMed:20061386, PubMed:8132613). E2 ubiquitin conjugating enzyme that transfers ubiquitin to MAEA, a core component of the CTLH E3 ubiquitin-protein ligase complex (PubMed:29911972). In vitro catalyzes 'Lys-11'- and 'Lys-48'-linked polyubiquitination (PubMed:20061386). Capable, in vitro, to ubiquitinate histone H2A (PubMed:8132613)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P62256/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBE2H","classification":"Not Classified","n_dependent_lines":559,"n_total_lines":1208,"dependency_fraction":0.46274834437086093},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UBE2H","total_profiled":1310},"omim":[{"mim_id":"616017","title":"TRIPARTITE MOTIF-CONTAINING PROTEIN 69; TRIM69","url":"https://www.omim.org/entry/616017"},{"mim_id":"613336","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 9; MARCHF9","url":"https://www.omim.org/entry/613336"},{"mim_id":"613335","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 8; MARCHF8","url":"https://www.omim.org/entry/613335"},{"mim_id":"613332","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 2; MARCHF2","url":"https://www.omim.org/entry/613332"},{"mim_id":"613331","title":"MEMBRANE-ASSOCIATED RING-CH FINGER PROTEIN 1; MARCHF1","url":"https://www.omim.org/entry/613331"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UBE2H"},"hgnc":{"alias_symbol":["UBCH","UBC8","GID3"],"prev_symbol":[]},"alphafold":{"accession":"P62256","domains":[{"cath_id":"3.10.110.10","chopping":"5-153","consensus_level":"high","plddt":96.0084,"start":5,"end":153}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P62256","model_url":"https://alphafold.ebi.ac.uk/files/AF-P62256-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P62256-F1-predicted_aligned_error_v6.png","plddt_mean":89.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBE2H","jax_strain_url":"https://www.jax.org/strain/search?query=UBE2H"},"sequence":{"accession":"P62256","fasta_url":"https://rest.uniprot.org/uniprotkb/P62256.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P62256/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P62256"}},"corpus_meta":[{"pmid":"15485925","id":"PMC_15485925","title":"Interferon-inducible ubiquitin E2, Ubc8, is a conjugating enzyme for protein ISGylation.","date":"2004","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15485925","citation_count":195,"is_preprint":false},{"pmid":"8132613","id":"PMC_8132613","title":"A human ubiquitin-conjugating enzyme homologous to yeast UBC8.","date":"1994","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8132613","citation_count":52,"is_preprint":false},{"pmid":"36459484","id":"PMC_36459484","title":"Modular UBE2H-CTLH E2-E3 complexes regulate erythroid maturation.","date":"2022","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/36459484","citation_count":25,"is_preprint":false},{"pmid":"38113892","id":"PMC_38113892","title":"Multisite phosphorylation dictates selective E2-E3 pairing as revealed by Ubc8/UBE2H-GID/CTLH assemblies.","date":"2023","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/38113892","citation_count":21,"is_preprint":false},{"pmid":"14639049","id":"PMC_14639049","title":"Mutation screening and association study of the UBE2H gene on chromosome 7q32 in autistic disorder.","date":"2003","source":"Psychiatric genetics","url":"https://pubmed.ncbi.nlm.nih.gov/14639049","citation_count":21,"is_preprint":false},{"pmid":"32403399","id":"PMC_32403399","title":"Predictive Potential of Circulating Ube2h mRNA as an E2 Ubiquitin-Conjugating Enzyme for Diagnosis or Treatment of Alzheimer's Disease.","date":"2020","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32403399","citation_count":19,"is_preprint":false},{"pmid":"33924823","id":"PMC_33924823","title":"Ubiquitin Conjugating Enzyme E2 H (UBE2H) Is Linked to Poor Outcomes and Metastasis in Lung Adenocarcinoma.","date":"2021","source":"Biology","url":"https://pubmed.ncbi.nlm.nih.gov/33924823","citation_count":11,"is_preprint":false},{"pmid":"36253107","id":"PMC_36253107","title":"The metabolite-controlled ubiquitin conjugase Ubc8 promotes mitochondrial protein import.","date":"2022","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/36253107","citation_count":9,"is_preprint":false},{"pmid":"19922136","id":"PMC_19922136","title":"Association study of the ubiquitin conjugating enzyme gene UBE2H in sporadic ALS.","date":"2009","source":"Amyotrophic lateral sclerosis : official publication of the World Federation of Neurology Research Group on Motor Neuron Diseases","url":"https://pubmed.ncbi.nlm.nih.gov/19922136","citation_count":9,"is_preprint":false},{"pmid":"24811676","id":"PMC_24811676","title":"RING-type ubiquitin ligase McCPN1 catalyzes UBC8-dependent protein ubiquitination and interacts with Argonaute 4 in halophyte ice plant.","date":"2014","source":"Plant physiology and biochemistry : PPB","url":"https://pubmed.ncbi.nlm.nih.gov/24811676","citation_count":5,"is_preprint":false},{"pmid":"37208785","id":"PMC_37208785","title":"A heterozygous mutation in UBE2H in a patient with developmental delay leads to an aberrant brain development in zebrafish.","date":"2023","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/37208785","citation_count":4,"is_preprint":false},{"pmid":"41174727","id":"PMC_41174727","title":"An integrative analysis of transcriptome, methylome and single-cell RNA sequencing data identifies UBE2H as a marker of oxaliplatin resistance in colorectal cancer.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/41174727","citation_count":3,"is_preprint":false},{"pmid":"34420605","id":"PMC_34420605","title":"Molecular characterization of ubiquitin-conjugating enzyme gene ube2h and siRNA-mediated regulation on targeting p53 in turbot, Scophthalmus maximus.","date":"2021","source":"Journal of thermal biology","url":"https://pubmed.ncbi.nlm.nih.gov/34420605","citation_count":3,"is_preprint":false},{"pmid":"41286881","id":"PMC_41286881","title":"Integrated scRNA-seq and transcriptome analyses uncover the effects of UBE2H on the immune microenvironment regulation in pancreatic cancer.","date":"2025","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/41286881","citation_count":0,"is_preprint":false},{"pmid":"42094535","id":"PMC_42094535","title":"Paired CRISPR screens identify mitochondrial metabolism and UBE2H as aneuploid-specific dependencies in human cancer cell lines.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/42094535","citation_count":0,"is_preprint":false},{"pmid":"41959163","id":"PMC_41959163","title":"CDK/mTOR-dependent phosphorylation of UBE2H restrains its charging with ubiquitin and regulates CTLH-dependent degradation.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41959163","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.04.07.25325355","title":"Hierarchical representation learning of preeclampsia interactome connecting endometrial maturation, placentation, chorioamnionitis, and HELLP syndrome","date":"2025-04-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.07.25325355","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10755,"output_tokens":2394,"usd":0.034087,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9474,"output_tokens":3021,"usd":0.061448,"stage2_stop_reason":"end_turn"},"total_usd":0.095535,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"UBE2H (Ubc8) functions as an ISG15-conjugating E2 enzyme, mediating protein ISGylation upon interferon stimulation. siRNA knockdown of Ubc8 in HeLa cells reduces ISGylation after interferon treatment. Neither the closest homologue UbcH7/UbcM4 nor Ubc9 can substitute for Ubc8 in this activity.\",\n      \"method\": \"siRNA knockdown, transfection assays, in-cell ISGylation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA loss-of-function with defined biochemical readout (ISGylation) plus specificity demonstrated by testing closely related E2s; single lab\",\n      \"pmids\": [\"15485925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Human UBE2H (UbcH2) is a ubiquitin-conjugating enzyme that catalyzes ubiquitination of histones in vitro, similar to its yeast ortholog UBC8. The first 12 N-terminal residues of UBC8 are required for histone ubiquitination but not for thiolester formation with ubiquitin, suggesting the N-terminus is needed for substrate recognition or ubiquitin transfer onto substrates.\",\n      \"method\": \"In vitro ubiquitination assay, N-terminal truncation mutagenesis, thiolester formation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of enzymatic activity with mutagenesis (truncation), ortholog comparison; single lab but multiple orthogonal biochemical methods\",\n      \"pmids\": [\"8132613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UBE2H is the cognate E2 ubiquitin-conjugating enzyme for the CTLH E3 ubiquitin ligase complex during erythropoiesis. UBE2H protein abundance increases during terminal erythroid differentiation and its expression depends on catalytically active CTLH E3 complexes. CRISPR-Cas9 inactivation of CTLH E3 assemblies or UBE2H in erythroid progenitors causes defects in erythroid maturation progression and inefficient enucleation.\",\n      \"method\": \"CRISPR-Cas9 loss-of-function, proteomics, in vitro human erythropoiesis model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with defined cellular phenotype (maturation and enucleation defects), proteomics, identification of E2-E3 partnership; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"36459484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The specific E3-E2 pairing between GID/CTLH and Ubc8/UBE2H is established through an unconventional catalytic assembly and auxiliary interactions 70–100 Å away from the active site, mediated by multisite phosphorylation of E2 CK2-targeted acidic sequences that anchor the E2 C-terminus to basic patches on the E3. Phosphorylation-dependent multivalency rigidifies the catalytic centers and facilitates substrate ubiquitylation; dephosphorylation is antagonistic to this interaction.\",\n      \"method\": \"Cryo-EM structure determination, biochemical assays, cell biology experiments, mutagenesis of phosphorylation sites\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure plus biochemistry plus mutagenesis plus cell biology in a single rigorous study establishing the molecular mechanism of E2-E3 pairing\",\n      \"pmids\": [\"38113892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Yeast Ubc8 (ortholog of UBE2H) promotes assembly of the translocase of the outer mitochondrial membrane (TOM complex) and increases levels of Tom22, a cytosol-exposed receptor subunit. Ubc8 deficiency results in compromised mitochondrial protein import and reduced steady-state levels of mitochondrial proteins during the transition from respiratory to fermentative conditions.\",\n      \"method\": \"Yeast genetic deletion, mitochondrial protein import assay, TOM complex assembly analysis, quantitative proteomics\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in yeast with defined biochemical phenotype (import assay, TOM assembly), single lab; yeast ortholog study\",\n      \"pmids\": [\"36253107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Zebrafish Ube2h is required for normal brain development. Knockdown of ube2h activates the ATM-p53 signaling pathway and induces apoptosis specifically in differentiated neural cells. A missense mutation mimicking the human patient variant (c.449C>T; p.Thr150Met) causes aberrant Ube2h function in zebrafish embryos.\",\n      \"method\": \"Zebrafish gene knockdown (morpholino), transcriptomic analysis, apoptosis assays, functional validation of patient variant\",\n      \"journal\": \"Human genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — zebrafish KD with defined cellular phenotype (neural apoptosis) and pathway identification (ATM-p53 activation), functional validation of patient variant; single lab\",\n      \"pmids\": [\"37208785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"CDK- and mTOR-dependent phosphorylation of UBE2H at N-terminal serine residues S3/S5 reduces UBE2H charging with ubiquitin, limiting the pool of active E2 available to the CTLH E3 complex. Mitotic CDK activity inactivates UBE2H during mitosis; mTOR restrains UBE2H charging in interphase to couple CTLH-dependent ubiquitylation to nutrient status. Preventing this phosphorylation enhances CTLH-mediated substrate degradation, promotes CTLH subunit turnover, and causes proliferation and mitotic defects. Two additional CTLH substrates were identified using hyperactive UBE2H: the mitotic kinase NEK9 and AAMP, with a DR-like C-degron recognized by CTLH subunit MKLN1.\",\n      \"method\": \"Phospho-site mutagenesis (S3/S5), ubiquitin-charging assay, substrate degradation assay, mass spectrometry, cell proliferation and mitosis assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro charging assay with mutagenesis, identification of kinase writers (CDK, mTOR), substrate identification by MS; preprint, single lab, not yet peer-reviewed\",\n      \"pmids\": [\"41959163\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"UBE2H is an aneuploid-specific genetic dependency in human cancer cell lines. Mechanistic analyses link UBE2H to mitochondrial protein abundance, suggesting a role in maintaining mitochondrial proteostasis under aneuploid stress.\",\n      \"method\": \"Paired CRISPR loss-of-function screens (genome-wide and focused druggable genome library), functional validation in isogenic aneuploid/near-euploid cell lines, proteomics\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — paired CRISPR screens with functional validation and proteomic mechanistic link to mitochondria; preprint, single lab\",\n      \"pmids\": [\"42094535\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"UBE2H is a ubiquitin-conjugating E2 enzyme that acts as the dedicated E2 for the CTLH/GID E3 ubiquitin ligase complex, with their interaction governed by CK2-mediated multisite phosphorylation of UBE2H's C-terminal acidic sequences that anchor it to the E3; UBE2H charging with ubiquitin is further tuned by CDK (during mitosis) and mTOR (in interphase) phosphorylation of N-terminal residues S3/S5, coupling CTLH ubiquitylation activity to cell cycle state and nutrient status; UBE2H-CTLH modules control erythroid maturation and enucleation, support mitochondrial proteostasis, and are required for normal neurogenesis through ATM-p53 pathway regulation; additionally, UBE2H can act as an ISG15-conjugating E2 enzyme for protein ISGylation upon interferon stimulation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBE2H is a ubiquitin-conjugating (E2) enzyme that catalyzes substrate ubiquitination, originally characterized through its ability to ubiquitinate histones in vitro, with its first 12 N-terminal residues required for substrate modification but dispensable for thiolester formation with ubiquitin [#1]. Its principal physiological role is as the cognate E2 for the CTLH/GID E3 ubiquitin ligase complex [#2, #3]. This E2–E3 pairing is achieved through an unconventional catalytic assembly in which CK2-mediated multisite phosphorylation of acidic sequences in the UBE2H C-terminus anchors the enzyme to basic patches on the E3, with phosphorylation-dependent multivalency rigidifying the catalytic center to drive substrate ubiquitylation [#3]. UBE2H charging with ubiquitin is independently tuned by CDK and mTOR phosphorylation of N-terminal serines S3/S5, coupling CTLH ubiquitylation activity to mitotic state and nutrient status; preventing this phosphorylation enhances CTLH-mediated degradation of substrates including NEK9 and AAMP and produces proliferation and mitotic defects [#6]. Through the CTLH module, UBE2H is required for terminal erythroid maturation and enucleation [#2] and supports mitochondrial proteostasis, a role conserved in yeast Ubc8 where it promotes TOM complex assembly and mitochondrial protein import [#4]. UBE2H is also required for normal neurogenesis, where its loss activates ATM-p53 signaling and induces apoptosis in differentiated neural cells [#5], and it can act as an ISG15-conjugating E2 for protein ISGylation upon interferon stimulation [#0].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing that human UBE2H is a catalytically active ubiquitin-conjugating enzyme answered whether it could transfer ubiquitin to substrates and localized substrate-recognition function to its N-terminus.\",\n      \"evidence\": \"in vitro ubiquitination and thiolester assays with N-terminal truncation mutagenesis, ortholog comparison to yeast UBC8\",\n      \"pmids\": [\"8132613\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates beyond in vitro histones not defined\", \"No cognate E3 partner identified at this stage\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating UBE2H as an ISG15-conjugating E2 extended its activity beyond ubiquitin to a ubiquitin-like modifier in the interferon response.\",\n      \"evidence\": \"siRNA knockdown in HeLa cells with in-cell ISGylation readout and specificity testing against related E2s\",\n      \"pmids\": [\"15485925\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"ISG15 E3 partner for UBE2H not defined\", \"Substrate specificity of ISGylation by UBE2H unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying UBE2H as the cognate E2 for the CTLH E3 complex during erythropoiesis placed it in a defined physiological ubiquitylation pathway with a cellular phenotype.\",\n      \"evidence\": \"CRISPR-Cas9 loss-of-function and proteomics in an in vitro human erythropoiesis model\",\n      \"pmids\": [\"36459484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Erythroid CTLH substrates driving maturation/enucleation not enumerated\", \"Molecular basis of the E2-E3 pairing not yet resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Yeast Ubc8 work linked this E2 to mitochondrial proteostasis by showing it promotes TOM complex assembly and protein import.\",\n      \"evidence\": \"yeast genetic deletion with mitochondrial import assays, TOM assembly analysis, and quantitative proteomics\",\n      \"pmids\": [\"36253107\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct E3 partner and substrates in the mitochondrial pathway not defined\", \"Conservation of this role to human UBE2H not established in this study\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM and biochemistry resolved how UBE2H is selected by CTLH/GID, revealing phosphorylation-dependent anchoring of its C-terminus to the E3 distant from the active site.\",\n      \"evidence\": \"cryo-EM structure determination plus biochemistry, phospho-site mutagenesis, and cell biology\",\n      \"pmids\": [\"38113892\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo dynamics of CK2 phosphorylation/dephosphorylation cycling not fully resolved\", \"Whether other E2s engage CTLH via similar mechanisms unaddressed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Zebrafish loss-of-function tied UBE2H to neurogenesis and connected a human patient variant to disease-relevant neural apoptosis via ATM-p53 signaling.\",\n      \"evidence\": \"morpholino knockdown, transcriptomics, apoptosis assays, and functional validation of the p.Thr150Met patient variant in embryos\",\n      \"pmids\": [\"37208785\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between UBE2H loss and ATM-p53 activation unresolved\", \"Relevant CTLH substrates in neural cells not identified\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identifying CDK/mTOR phosphorylation of N-terminal S3/S5 as a brake on UBE2H ubiquitin-charging showed how CTLH activity is coupled to cell cycle and nutrient state, and uncovered new substrates.\",\n      \"evidence\": \"phospho-site mutagenesis, ubiquitin-charging and degradation assays, and mass spectrometry identifying NEK9 and AAMP (preprint)\",\n      \"pmids\": [\"41959163\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Relative contribution of N-terminal vs C-terminal phospho-regulation in vivo unclear\", \"C-degron recognition of NEK9 not fully mapped\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"CRISPR screens defined UBE2H as an aneuploidy-specific dependency, linking its function to mitochondrial proteostasis under aneuploid stress.\",\n      \"evidence\": \"paired CRISPR loss-of-function screens with isogenic aneuploid/near-euploid validation and proteomics (preprint)\",\n      \"pmids\": [\"42094535\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Direct mechanistic chain from UBE2H to mitochondrial protein abundance not established\", \"Whether dependency is CTLH-dependent not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full substrate repertoire of UBE2H-CTLH across tissues and the mechanistic basis connecting its activity to ATM-p53 signaling and mitochondrial proteostasis remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Comprehensive substrate map of UBE2H-CTLH lacking\", \"Integration of N-terminal and C-terminal phospho-regulation in vivo undefined\", \"Direct ISG15 vs ubiquitin partitioning of UBE2H activity unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0031386\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"CTLH/GID E3 ubiquitin ligase complex\"],\n    \"partners\": [\"MKLN1\", \"NEK9\", \"AAMP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}