{"gene":"ASCC2","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2017,"finding":"The CUE domain of ASCC2 recognizes K63-linked polyubiquitin chains, and this recognition is required for recruitment of the ASCC repair complex to nuclear foci specifically upon alkylation damage. Loss of ASCC2 impedes alkylation adduct repair kinetics and increases sensitivity to alkylating agents but not other DNA damage types. The E3 ligase RNF113A is responsible for upstream ubiquitin signalling in this pathway.","method":"Cell-based foci formation assays, domain-specific binding experiments (CUE domain), alkylation damage sensitivity assays, epistasis with RNF113A","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional assays, domain mutants, genetic epistasis, replicated across cell lines and patient-derived cells in a focused mechanistic study","pmids":["29144457"],"is_preprint":false},{"year":2021,"finding":"The ASCC2 CUE domain selectively binds K63-linked diubiquitin by contacting both the distal and proximal ubiquitin simultaneously. The distal ubiquitin is contacted similarly to other CUE domains, while residues in the N-terminal portion of the ASCC2 α1 helix make unique contacts with the proximal ubiquitin. Mutation of these N-terminal α1 helix residues decreases ASCC2 recruitment to alkylation damage sites.","method":"Structural/biochemical analysis of CUE–diubiquitin interaction, mutagenesis of binding residues, cell-based recruitment assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural and biochemical characterization combined with mutagenesis and functional cell-based validation in a single focused study","pmids":["34971705"],"is_preprint":false},{"year":2020,"finding":"ASCC2 and ASCC3 directly interact; the ASCC3 fragment comprises a central helical domain and terminal extended arms that clasp the compact ASCC2 unit. This interface is evolutionarily conserved, and somatic cancer mutations at the interface reduce ASCC2–ASCC3 binding affinity. ASCC3 shows similar domain organization and regulation to the spliceosomal RNA helicase Brr2.","method":"Structural analysis (crystal structure), interaction mapping, affinity quantification of cancer mutation variants","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of the complex combined with quantitative binding assays and mutagenesis in a focused mechanistic study","pmids":["33139697"],"is_preprint":false},{"year":2020,"finding":"ASCC2 and ASCC3 form the human RQC-trigger (hRQT) complex together with TRIP4, functioning as orthologs of the yeast RQT complex (Slh1/Cue3/yKR023W). The ubiquitin-binding activity of ASCC2 is crucial for triggering ribosome-associated quality control (RQC), specifically recognition of ubiquitinated stalled ribosomes to facilitate subunit dissociation.","method":"Co-immunoprecipitation to define complex composition, functional assays measuring RQC efficiency upon loss of ASCC2 ubiquitin-binding activity, genetic complementation","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP for complex definition, activity mutants tested in cell-based RQC assays, multiple orthogonal readouts in a single focused study","pmids":["32099016"],"is_preprint":false},{"year":2019,"finding":"In a genome-wide CRISPRi screen, ASCC2 and ASCC3 were the two most potent genetic modifiers protecting cells from toxic effects of the ribosome-stalling compound PF8503. Genetic interaction experiments showed ASCC3 acts together with ASCC2 and functions downstream of HBS1L in the ribosome quality control pathway.","method":"Genome-wide CRISPRi screen, genetic interaction (epistasis) experiments","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genome-wide epistasis screen is rigorous but pathway placement relies on a single lab study without orthogonal biochemical validation","pmids":["30875366"],"is_preprint":false},{"year":2018,"finding":"ASCC1 interacts with the ASCC complex through the ASCC3 helicase subunit. Loss of ASCC2 from ASCC3 foci (when ASCC1 is absent) indicates ASCC1 coordinates proper co-recruitment of ASCC2 with ASCC3 during alkylation damage. ASCC1 is present at nuclear speckle foci prior to damage but leaves in response to alkylation.","method":"Co-immunoprecipitation, confocal microscopy of nuclear foci, CRISPR/Cas9 knockout with epistasis analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP, live-cell imaging, and genetic epistasis used but findings are from a single lab","pmids":["29997253"],"is_preprint":false},{"year":2026,"finding":"ASCC2 recruits ASCC3 to stalled replication forks; this recruitment requires both ASCC2 ubiquitin-binding activity and polyubiquitylation of PCNA at K164 catalyzed by SHPRH, HLTF, and RFWD3. At stalled forks, ASCC3 unwinds DNA in a manner required for SMARCAL1 recruitment, restrained fork progression, and fork degradation in BRCA1/BRCA2-deficient cells.","method":"Protein recruitment assays at stalled forks, ubiquitin-binding mutants of ASCC2, in vitro DNA unwinding assays, genetic epistasis with PCNA ubiquitin E3 ligases","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple functional assays and in vitro reconstitution but single lab, peer-reviewed publication","pmids":["41785087"],"is_preprint":false},{"year":2026,"finding":"lncRNA DLEU1 promotes ASCC2 nuclear translocation and its interaction with ALKBH3 in gastric cancer cells, thereby facilitating alkylation DNA repair and stabilizing E2F1 mRNA. Co-targeting DLEU1 and ASCC2 synergizes with G6PD inhibition to impair cancer cell viability.","method":"RNA-protein interaction assays, western blotting for localization, functional co-targeting experiments in organoids and xenograft models","journal":"Biomarker research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, mechanistic details on ASCC2 nuclear translocation rely on co-localization and interaction assays without deep mechanistic dissection of ASCC2 itself","pmids":["41484982"],"is_preprint":false}],"current_model":"ASCC2 is a ubiquitin-binding subunit of the ASCC (Activating Signal Cointegrator Complex) that uses its CUE domain to selectively recognize K63-linked polyubiquitin chains by contacting both distal and proximal ubiquitins, thereby recruiting the ASCC3–ALKBH3 dealkylase-helicase complex to alkylation DNA damage sites in the nucleus; the same ubiquitin-binding activity also mediates ASCC2/ASCC3 recruitment to stalled replication forks (dependent on PCNA-K164 polyubiquitylation) and is essential for ribosome-associated quality control by enabling the human RQT complex (ASCC2/ASCC3/TRIP4) to recognize ubiquitinated stalled ribosomes and trigger subunit dissociation."},"narrative":{"mechanistic_narrative":"ASCC2 is the ubiquitin-sensing subunit of the Activating Signal Cointegrator Complex (ASCC) that couples K63-linked polyubiquitin signals to the recruitment of the ASCC3 helicase across DNA repair, replication-stress, and ribosome quality-control pathways [PMID:29144457, PMID:32099016]. Its CUE domain selectively recognizes K63-linked diubiquitin by simultaneously contacting both the distal and proximal ubiquitin moieties, with unique contacts made by residues in the N-terminal portion of its α1 helix; mutation of these residues abolishes recruitment to damage sites [PMID:34971705]. In the nucleus, this ubiquitin-binding activity—downstream of the E3 ligase RNF113A—directs the ASCC repair complex specifically to alkylation DNA damage, and ASCC2 loss slows alkylation adduct repair and sensitizes cells to alkylating agents [PMID:29144457]. ASCC2 binds ASCC3 directly through a conserved interface clasped by ASCC3's extended arms, an interaction weakened by somatic cancer mutations [PMID:33139697]. Beyond DNA repair, ASCC2/ASCC3 together with TRIP4 constitute the human RQC-trigger (hRQT) complex, where ASCC2 ubiquitin recognition of stalled ribosomes is essential to trigger ribosomal subunit dissociation [PMID:32099016], and the same activity recruits ASCC3 to stalled replication forks in a PCNA-K164-polyubiquitylation-dependent manner to enable fork unwinding and SMARCAL1 recruitment [PMID:41785087].","teleology":[{"year":2017,"claim":"Established that ASCC2 acts as a ubiquitin reader linking a specific ubiquitin signal to targeted DNA repair, answering how the ASCC complex is recruited selectively to alkylation lesions.","evidence":"Cell-based foci assays, CUE domain binding experiments, alkylation sensitivity assays, and RNF113A epistasis","pmids":["29144457"],"confidence":"High","gaps":["Did not resolve atomic basis of K63-linkage selectivity","Did not address ASCC2 roles outside alkylation repair"]},{"year":2020,"claim":"Defined the structural architecture of the ASCC2–ASCC3 interaction, showing how the two subunits assemble and that cancer mutations destabilize the complex.","evidence":"Crystal structure of the ASCC2–ASCC3 interface with affinity quantification of cancer-mutation variants","pmids":["33139697"],"confidence":"High","gaps":["Did not capture full-length complex or ubiquitin-bound state","Functional consequence of weakened binding in cells not measured"]},{"year":2020,"claim":"Extended ASCC2 function beyond DNA repair by showing it forms the hRQT complex with ASCC3 and TRIP4, using ubiquitin recognition to trigger dissociation of stalled ribosomes.","evidence":"Reciprocal Co-IP for complex composition, ubiquitin-binding mutants tested in cell-based RQC assays, genetic complementation","pmids":["32099016"],"confidence":"High","gaps":["Did not define the ribosomal ubiquitin substrate recognized by ASCC2","Mechanism of subunit dissociation by ASCC3 not resolved"]},{"year":2019,"claim":"Genetically placed ASCC2/ASCC3 as the most potent modifiers of ribosome-stalling toxicity acting downstream of HBS1L, independently corroborating the RQC role.","evidence":"Genome-wide CRISPRi screen and epistasis experiments with PF8503 stalling compound","pmids":["30875366"],"confidence":"Medium","gaps":["Pathway placement lacked orthogonal biochemical validation","Did not distinguish ASCC2 vs ASCC3 specific contributions"]},{"year":2018,"claim":"Identified ASCC1 as a coordinator of ASCC2 co-recruitment with ASCC3 to alkylation damage, refining the assembly logic of the nuclear repair complex.","evidence":"Co-IP, confocal foci imaging, and CRISPR knockout epistasis","pmids":["29997253"],"confidence":"Medium","gaps":["Single-lab study","Molecular basis of ASCC1-dependent co-recruitment not defined"]},{"year":2021,"claim":"Resolved the structural basis of K63-linkage selectivity, explaining how the CUE domain discriminates K63 chains by contacting both distal and proximal ubiquitins.","evidence":"Structural/biochemical analysis of CUE–diubiquitin, mutagenesis, and cell-based recruitment assays","pmids":["34971705"],"confidence":"High","gaps":["Did not test selectivity in the context of full ASCC complex","In vivo chain-type specificity at damage sites not directly imaged"]},{"year":2026,"claim":"Demonstrated a distinct ASCC2 role at stalled replication forks, where ubiquitin-binding and PCNA-K164 polyubiquitylation recruit ASCC3 to drive fork unwinding and SMARCAL1 loading.","evidence":"Fork recruitment assays, ASCC2 ubiquitin-binding mutants, in vitro DNA unwinding, and epistasis with PCNA E3 ligases","pmids":["41785087"],"confidence":"Medium","gaps":["Single-lab study","Relationship between fork and alkylation-repair functions of ASCC2 unresolved"]},{"year":2026,"claim":"Implicated ASCC2 nuclear translocation in cancer, with lncRNA DLEU1 promoting ASCC2–ALKBH3 interaction to support alkylation repair.","evidence":"RNA-protein interaction assays, localization western blots, and co-targeting in organoid/xenograft models","pmids":["41484982"],"confidence":"Low","gaps":["Mechanism of ASCC2 translocation relies on co-localization without deep dissection","Direct ASCC2–ALKBH3 contact not structurally defined","Single-lab cancer-context study"]},{"year":null,"claim":"How ASCC2 ubiquitin recognition is partitioned and regulated across its nuclear DNA-repair, replication-fork, and cytoplasmic ribosome-quality-control functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model for context-specific deployment of one ubiquitin reader","Cytoplasmic vs nuclear ASCC2 pools not delineated","Regulation of CUE-domain accessibility unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,5]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[6]}],"complexes":["ASCC (Activating Signal Cointegrator Complex)","human RQC-trigger (hRQT) complex"],"partners":["ASCC3","TRIP4","ASCC1","RNF113A","ALKBH3","PCNA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H1I8","full_name":"Activating signal cointegrator 1 complex subunit 2","aliases":["ASC-1 complex subunit p100","Trip4 complex subunit p100"],"length_aa":757,"mass_kda":86.4,"function":"Ubiquitin-binding protein involved in DNA repair and rescue of stalled ribosomes (PubMed:29144457, PubMed:32099016, PubMed:32579943, PubMed:36302773). Plays a role in DNA damage repair as component of the ASCC complex (PubMed:29144457). Recruits ASCC3 and ALKBH3 to sites of DNA damage by binding to polyubiquitinated proteins that have 'Lys-63'-linked polyubiquitin chains (PubMed:29144457). Part of the ASC-1 complex that enhances NF-kappa-B, SRF and AP1 transactivation (PubMed:12077347). Involved in activation of the ribosome quality control (RQC) pathway, a pathway that degrades nascent peptide chains during problematic translation (PubMed:32099016, PubMed:32579943, PubMed:36302773). Specifically recognizes and binds RPS20/uS10 ubiquitinated by ZNF598, promoting recruitment of the RQT (ribosome quality control trigger) complex on stalled ribosomes, followed by disassembly of stalled ribosomes (PubMed:36302773)","subcellular_location":"Nucleus; Nucleus speckle","url":"https://www.uniprot.org/uniprotkb/Q9H1I8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ASCC2","classification":"Not Classified","n_dependent_lines":8,"n_total_lines":1208,"dependency_fraction":0.006622516556291391},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"DDX6","stoichiometry":0.2},{"gene":"DRG1","stoichiometry":0.2},{"gene":"NPM1","stoichiometry":0.2},{"gene":"RACK1","stoichiometry":0.2},{"gene":"RIOK3","stoichiometry":0.2},{"gene":"SRP68","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/ASCC2","total_profiled":1310},"omim":[{"mim_id":"614217","title":"ACTIVATING SIGNAL COINTEGRATOR 1 COMPLEX, SUBUNIT 3; ASCC3","url":"https://www.omim.org/entry/614217"},{"mim_id":"614216","title":"ACTIVATING SIGNAL COINTEGRATOR 1 COMPLEX, SUBUNIT 2; ASCC2","url":"https://www.omim.org/entry/614216"},{"mim_id":"614215","title":"ACTIVATING SIGNAL COINTEGRATOR 1 COMPLEX, SUBUNIT 1; ASCC1","url":"https://www.omim.org/entry/614215"},{"mim_id":"604501","title":"THYROID HORMONE RECEPTOR INTERACTOR 4; TRIP4","url":"https://www.omim.org/entry/604501"},{"mim_id":"300951","title":"RING FINGER PROTEIN 113A; RNF113A","url":"https://www.omim.org/entry/300951"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Focal adhesion sites","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ASCC2"},"hgnc":{"alias_symbol":["ASC1p100","FLJ21588","DKFZp586O0223"],"prev_symbol":[]},"alphafold":{"accession":"Q9H1I8","domains":[{"cath_id":"-","chopping":"27-186","consensus_level":"high","plddt":94.968,"start":27,"end":186},{"cath_id":"-","chopping":"193-216_231-404","consensus_level":"high","plddt":93.5429,"start":193,"end":404},{"cath_id":"1.10.8.10","chopping":"466-524","consensus_level":"medium","plddt":81.6692,"start":466,"end":524}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H1I8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H1I8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H1I8-F1-predicted_aligned_error_v6.png","plddt_mean":77.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ASCC2","jax_strain_url":"https://www.jax.org/strain/search?query=ASCC2"},"sequence":{"accession":"Q9H1I8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H1I8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H1I8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H1I8"}},"corpus_meta":[{"pmid":"29144457","id":"PMC_29144457","title":"A ubiquitin-dependent signalling axis specific for ALKBH-mediated DNA dealkylation repair.","date":"2017","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/29144457","citation_count":87,"is_preprint":false},{"pmid":"32099016","id":"PMC_32099016","title":"Identification of a novel trigger complex that facilitates ribosome-associated quality control in mammalian cells.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/32099016","citation_count":84,"is_preprint":false},{"pmid":"30875366","id":"PMC_30875366","title":"Cellular response to small molecules that selectively stall protein synthesis by the ribosome.","date":"2019","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30875366","citation_count":28,"is_preprint":false},{"pmid":"30327447","id":"PMC_30327447","title":"Novel ASCC1 mutations causing prenatal-onset muscle weakness with arthrogryposis and congenital bone fractures.","date":"2018","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30327447","citation_count":27,"is_preprint":false},{"pmid":"29997253","id":"PMC_29997253","title":"RNA ligase-like domain in activating signal cointegrator 1 complex subunit 1 (ASCC1) regulates ASCC complex function during alkylation damage.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/29997253","citation_count":27,"is_preprint":false},{"pmid":"33139697","id":"PMC_33139697","title":"The interaction of DNA repair factors ASCC2 and ASCC3 is affected by somatic cancer mutations.","date":"2020","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/33139697","citation_count":21,"is_preprint":false},{"pmid":"33777101","id":"PMC_33777101","title":"A Dual Systems Genetics Approach Identifies Common Genes, Networks, and Pathways for Type 1 and 2 Diabetes in Human Islets.","date":"2021","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33777101","citation_count":19,"is_preprint":false},{"pmid":"36819725","id":"PMC_36819725","title":"Sensogenomics of music and Alzheimer's disease: An interdisciplinary view from neuroscience, transcriptomics, and epigenomics.","date":"2023","source":"Frontiers in aging neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/36819725","citation_count":15,"is_preprint":false},{"pmid":"36577525","id":"PMC_36577525","title":"Whole-genome characterization of myoepithelial carcinomas of the soft tissue.","date":"2022","source":"Cold Spring Harbor molecular case studies","url":"https://pubmed.ncbi.nlm.nih.gov/36577525","citation_count":9,"is_preprint":false},{"pmid":"35047834","id":"PMC_35047834","title":"Discovery of a neuromuscular syndrome caused by biallelic variants in ASCC3.","date":"2021","source":"HGG advances","url":"https://pubmed.ncbi.nlm.nih.gov/35047834","citation_count":9,"is_preprint":false},{"pmid":"34971705","id":"PMC_34971705","title":"The ASCC2 CUE domain in the ALKBH3-ASCC DNA repair complex recognizes adjacent ubiquitins in K63-linked polyubiquitin.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34971705","citation_count":8,"is_preprint":false},{"pmid":"40881169","id":"PMC_40881169","title":"Integrative multi-omics analysis and machine learning reveal the unique role of ASCC3 in combination with various immune-related genes in rectal adenocarcinoma.","date":"2025","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40881169","citation_count":2,"is_preprint":false},{"pmid":"40594069","id":"PMC_40594069","title":"Pan-cancer analysis reveals ASCC family promotes the cancer progression of lung adenocarcinoma.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40594069","citation_count":1,"is_preprint":false},{"pmid":"41785087","id":"PMC_41785087","title":"Ski2-like helicase ASCC3 unwinds DNA upon fork stalling to control replication stress responses.","date":"2026","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/41785087","citation_count":1,"is_preprint":false},{"pmid":"41484982","id":"PMC_41484982","title":"Histone modification-regulated LncRNA DLEU1 interacts with ASCC2/ALKBH3 complex to drive DNA repair, antioxidant homeostasis and glucose metabolism in gastric cancer.","date":"2026","source":"Biomarker research","url":"https://pubmed.ncbi.nlm.nih.gov/41484982","citation_count":0,"is_preprint":false},{"pmid":"40777259","id":"PMC_40777259","title":"The Ski2 helicase ASCC3 unwinds DNA upon fork stalling to control replication stress responses.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40777259","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.19.629410","title":"Genome-wide association analyses in dairy heifers highlight genes overlapping with mouse and human fertility and human health traits","date":"2024-12-21","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.19.629410","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11277,"output_tokens":2218,"usd":0.03355,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9284,"output_tokens":2950,"usd":0.060085,"stage2_stop_reason":"end_turn"},"total_usd":0.093635,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"The CUE domain of ASCC2 recognizes K63-linked polyubiquitin chains, and this recognition is required for recruitment of the ASCC repair complex to nuclear foci specifically upon alkylation damage. Loss of ASCC2 impedes alkylation adduct repair kinetics and increases sensitivity to alkylating agents but not other DNA damage types. The E3 ligase RNF113A is responsible for upstream ubiquitin signalling in this pathway.\",\n      \"method\": \"Cell-based foci formation assays, domain-specific binding experiments (CUE domain), alkylation damage sensitivity assays, epistasis with RNF113A\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional assays, domain mutants, genetic epistasis, replicated across cell lines and patient-derived cells in a focused mechanistic study\",\n      \"pmids\": [\"29144457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The ASCC2 CUE domain selectively binds K63-linked diubiquitin by contacting both the distal and proximal ubiquitin simultaneously. The distal ubiquitin is contacted similarly to other CUE domains, while residues in the N-terminal portion of the ASCC2 α1 helix make unique contacts with the proximal ubiquitin. Mutation of these N-terminal α1 helix residues decreases ASCC2 recruitment to alkylation damage sites.\",\n      \"method\": \"Structural/biochemical analysis of CUE–diubiquitin interaction, mutagenesis of binding residues, cell-based recruitment assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural and biochemical characterization combined with mutagenesis and functional cell-based validation in a single focused study\",\n      \"pmids\": [\"34971705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ASCC2 and ASCC3 directly interact; the ASCC3 fragment comprises a central helical domain and terminal extended arms that clasp the compact ASCC2 unit. This interface is evolutionarily conserved, and somatic cancer mutations at the interface reduce ASCC2–ASCC3 binding affinity. ASCC3 shows similar domain organization and regulation to the spliceosomal RNA helicase Brr2.\",\n      \"method\": \"Structural analysis (crystal structure), interaction mapping, affinity quantification of cancer mutation variants\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of the complex combined with quantitative binding assays and mutagenesis in a focused mechanistic study\",\n      \"pmids\": [\"33139697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ASCC2 and ASCC3 form the human RQC-trigger (hRQT) complex together with TRIP4, functioning as orthologs of the yeast RQT complex (Slh1/Cue3/yKR023W). The ubiquitin-binding activity of ASCC2 is crucial for triggering ribosome-associated quality control (RQC), specifically recognition of ubiquitinated stalled ribosomes to facilitate subunit dissociation.\",\n      \"method\": \"Co-immunoprecipitation to define complex composition, functional assays measuring RQC efficiency upon loss of ASCC2 ubiquitin-binding activity, genetic complementation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP for complex definition, activity mutants tested in cell-based RQC assays, multiple orthogonal readouts in a single focused study\",\n      \"pmids\": [\"32099016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In a genome-wide CRISPRi screen, ASCC2 and ASCC3 were the two most potent genetic modifiers protecting cells from toxic effects of the ribosome-stalling compound PF8503. Genetic interaction experiments showed ASCC3 acts together with ASCC2 and functions downstream of HBS1L in the ribosome quality control pathway.\",\n      \"method\": \"Genome-wide CRISPRi screen, genetic interaction (epistasis) experiments\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genome-wide epistasis screen is rigorous but pathway placement relies on a single lab study without orthogonal biochemical validation\",\n      \"pmids\": [\"30875366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ASCC1 interacts with the ASCC complex through the ASCC3 helicase subunit. Loss of ASCC2 from ASCC3 foci (when ASCC1 is absent) indicates ASCC1 coordinates proper co-recruitment of ASCC2 with ASCC3 during alkylation damage. ASCC1 is present at nuclear speckle foci prior to damage but leaves in response to alkylation.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy of nuclear foci, CRISPR/Cas9 knockout with epistasis analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP, live-cell imaging, and genetic epistasis used but findings are from a single lab\",\n      \"pmids\": [\"29997253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ASCC2 recruits ASCC3 to stalled replication forks; this recruitment requires both ASCC2 ubiquitin-binding activity and polyubiquitylation of PCNA at K164 catalyzed by SHPRH, HLTF, and RFWD3. At stalled forks, ASCC3 unwinds DNA in a manner required for SMARCAL1 recruitment, restrained fork progression, and fork degradation in BRCA1/BRCA2-deficient cells.\",\n      \"method\": \"Protein recruitment assays at stalled forks, ubiquitin-binding mutants of ASCC2, in vitro DNA unwinding assays, genetic epistasis with PCNA ubiquitin E3 ligases\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple functional assays and in vitro reconstitution but single lab, peer-reviewed publication\",\n      \"pmids\": [\"41785087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"lncRNA DLEU1 promotes ASCC2 nuclear translocation and its interaction with ALKBH3 in gastric cancer cells, thereby facilitating alkylation DNA repair and stabilizing E2F1 mRNA. Co-targeting DLEU1 and ASCC2 synergizes with G6PD inhibition to impair cancer cell viability.\",\n      \"method\": \"RNA-protein interaction assays, western blotting for localization, functional co-targeting experiments in organoids and xenograft models\",\n      \"journal\": \"Biomarker research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, mechanistic details on ASCC2 nuclear translocation rely on co-localization and interaction assays without deep mechanistic dissection of ASCC2 itself\",\n      \"pmids\": [\"41484982\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ASCC2 is a ubiquitin-binding subunit of the ASCC (Activating Signal Cointegrator Complex) that uses its CUE domain to selectively recognize K63-linked polyubiquitin chains by contacting both distal and proximal ubiquitins, thereby recruiting the ASCC3–ALKBH3 dealkylase-helicase complex to alkylation DNA damage sites in the nucleus; the same ubiquitin-binding activity also mediates ASCC2/ASCC3 recruitment to stalled replication forks (dependent on PCNA-K164 polyubiquitylation) and is essential for ribosome-associated quality control by enabling the human RQT complex (ASCC2/ASCC3/TRIP4) to recognize ubiquitinated stalled ribosomes and trigger subunit dissociation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ASCC2 is the ubiquitin-sensing subunit of the Activating Signal Cointegrator Complex (ASCC) that couples K63-linked polyubiquitin signals to the recruitment of the ASCC3 helicase across DNA repair, replication-stress, and ribosome quality-control pathways [#0, #3]. Its CUE domain selectively recognizes K63-linked diubiquitin by simultaneously contacting both the distal and proximal ubiquitin moieties, with unique contacts made by residues in the N-terminal portion of its α1 helix; mutation of these residues abolishes recruitment to damage sites [#1]. In the nucleus, this ubiquitin-binding activity—downstream of the E3 ligase RNF113A—directs the ASCC repair complex specifically to alkylation DNA damage, and ASCC2 loss slows alkylation adduct repair and sensitizes cells to alkylating agents [#0]. ASCC2 binds ASCC3 directly through a conserved interface clasped by ASCC3's extended arms, an interaction weakened by somatic cancer mutations [#2]. Beyond DNA repair, ASCC2/ASCC3 together with TRIP4 constitute the human RQC-trigger (hRQT) complex, where ASCC2 ubiquitin recognition of stalled ribosomes is essential to trigger ribosomal subunit dissociation [#3], and the same activity recruits ASCC3 to stalled replication forks in a PCNA-K164-polyubiquitylation-dependent manner to enable fork unwinding and SMARCAL1 recruitment [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Established that ASCC2 acts as a ubiquitin reader linking a specific ubiquitin signal to targeted DNA repair, answering how the ASCC complex is recruited selectively to alkylation lesions.\",\n      \"evidence\": \"Cell-based foci assays, CUE domain binding experiments, alkylation sensitivity assays, and RNF113A epistasis\",\n      \"pmids\": [\"29144457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve atomic basis of K63-linkage selectivity\", \"Did not address ASCC2 roles outside alkylation repair\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined the structural architecture of the ASCC2–ASCC3 interaction, showing how the two subunits assemble and that cancer mutations destabilize the complex.\",\n      \"evidence\": \"Crystal structure of the ASCC2–ASCC3 interface with affinity quantification of cancer-mutation variants\",\n      \"pmids\": [\"33139697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not capture full-length complex or ubiquitin-bound state\", \"Functional consequence of weakened binding in cells not measured\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended ASCC2 function beyond DNA repair by showing it forms the hRQT complex with ASCC3 and TRIP4, using ubiquitin recognition to trigger dissociation of stalled ribosomes.\",\n      \"evidence\": \"Reciprocal Co-IP for complex composition, ubiquitin-binding mutants tested in cell-based RQC assays, genetic complementation\",\n      \"pmids\": [\"32099016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the ribosomal ubiquitin substrate recognized by ASCC2\", \"Mechanism of subunit dissociation by ASCC3 not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genetically placed ASCC2/ASCC3 as the most potent modifiers of ribosome-stalling toxicity acting downstream of HBS1L, independently corroborating the RQC role.\",\n      \"evidence\": \"Genome-wide CRISPRi screen and epistasis experiments with PF8503 stalling compound\",\n      \"pmids\": [\"30875366\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pathway placement lacked orthogonal biochemical validation\", \"Did not distinguish ASCC2 vs ASCC3 specific contributions\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified ASCC1 as a coordinator of ASCC2 co-recruitment with ASCC3 to alkylation damage, refining the assembly logic of the nuclear repair complex.\",\n      \"evidence\": \"Co-IP, confocal foci imaging, and CRISPR knockout epistasis\",\n      \"pmids\": [\"29997253\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Molecular basis of ASCC1-dependent co-recruitment not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Resolved the structural basis of K63-linkage selectivity, explaining how the CUE domain discriminates K63 chains by contacting both distal and proximal ubiquitins.\",\n      \"evidence\": \"Structural/biochemical analysis of CUE–diubiquitin, mutagenesis, and cell-based recruitment assays\",\n      \"pmids\": [\"34971705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test selectivity in the context of full ASCC complex\", \"In vivo chain-type specificity at damage sites not directly imaged\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Demonstrated a distinct ASCC2 role at stalled replication forks, where ubiquitin-binding and PCNA-K164 polyubiquitylation recruit ASCC3 to drive fork unwinding and SMARCAL1 loading.\",\n      \"evidence\": \"Fork recruitment assays, ASCC2 ubiquitin-binding mutants, in vitro DNA unwinding, and epistasis with PCNA E3 ligases\",\n      \"pmids\": [\"41785087\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Relationship between fork and alkylation-repair functions of ASCC2 unresolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Implicated ASCC2 nuclear translocation in cancer, with lncRNA DLEU1 promoting ASCC2–ALKBH3 interaction to support alkylation repair.\",\n      \"evidence\": \"RNA-protein interaction assays, localization western blots, and co-targeting in organoid/xenograft models\",\n      \"pmids\": [\"41484982\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Mechanism of ASCC2 translocation relies on co-localization without deep dissection\", \"Direct ASCC2–ALKBH3 contact not structurally defined\", \"Single-lab cancer-context study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ASCC2 ubiquitin recognition is partitioned and regulated across its nuclear DNA-repair, replication-fork, and cytoplasmic ribosome-quality-control functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model for context-specific deployment of one ubiquitin reader\", \"Cytoplasmic vs nuclear ASCC2 pools not delineated\", \"Regulation of CUE-domain accessibility unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\"ASCC (Activating Signal Cointegrator Complex)\", \"human RQC-trigger (hRQT) complex\"],\n    \"partners\": [\"ASCC3\", \"TRIP4\", \"ASCC1\", \"RNF113A\", \"ALKBH3\", \"PCNA\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}