{"gene":"ABRAXAS1","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2007,"finding":"Abraxas directly binds the BRCA1 BRCT repeats through a phospho-Ser-X-X-Phe (pSXXF) motif, forming a distinct BRCA1 complex (BRCA1-A complex) that excludes BACH1 and CtIP binding","method":"Phosphopeptide affinity proteomics, Co-IP, reciprocal pulldown","journal":"Science","confidence":"High","confidence_rationale":"Tier 1-2 — phosphopeptide affinity proteomics plus reciprocal Co-IP, replicated across multiple labs","pmids":["17525340"],"is_preprint":false},{"year":2007,"finding":"Abraxas recruits RAP80 to the BRCA1-A complex via a RAP80 Abraxas-interacting region (AIR domain), and RAP80 UIM domains recognize K63-linked polyubiquitin chains at DNA damage sites to recruit the entire BRCA1-A complex","method":"Co-IP, domain mapping, immunofluorescence (foci formation assay)","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with domain mapping, replicated in multiple papers","pmids":["17525340","18077395"],"is_preprint":false},{"year":2007,"finding":"Abraxas and BRCC36 associate through coiled-coil domains on each protein as part of the BRCA1-A complex assembly","method":"Co-IP, domain mapping (coiled-coil deletion mutants)","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with domain mapping, single lab","pmids":["18077395"],"is_preprint":false},{"year":2007,"finding":"RNF8 (E3 ubiquitin ligase) and Ubc13 (E2 conjugating enzyme) generate K63-linked polyubiquitin chains at DNA damage sites that are recognized by RAP80 UIM domains, enabling recruitment of Abraxas and the entire BRCA1-A complex to damage foci","method":"siRNA knockdown, Co-IP, immunofluorescence foci assay","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with KD plus foci assay, replicated","pmids":["18077395"],"is_preprint":false},{"year":2007,"finding":"Abraxas and RAP80 are required for DNA damage resistance, G2/M checkpoint control, and DNA repair (loss-of-function knockdown phenotype)","method":"siRNA knockdown, clonogenic survival, G2/M checkpoint assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined cellular phenotypes, replicated","pmids":["17525340"],"is_preprint":false},{"year":2007,"finding":"CCDC98 (Abraxas) mediates the interaction between BRCA1 and RAP80, and is required for BRCA1 foci formation and G2/M checkpoint activation in response to ionizing radiation","method":"Co-IP, siRNA knockdown, immunofluorescence foci assay, checkpoint assay","journal":"Nature Structural & Molecular Biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional KD, independently replicated in two concurrent papers","pmids":["17643121","17643122"],"is_preprint":false},{"year":2016,"finding":"ATM-dependent phosphorylation of Abraxas serine 404 (adjacent to its pSPxF motif) induces dimerization of the BRCT/Abraxas complex, which is required for BRCA1 accumulation at DNA damage sites; crystal structure of BRCT/Abraxas complex revealed the molecular basis of this phosphorylation-dependent dimerization","method":"Crystal structure determination, mutagenesis (S404A), IR-induced phosphorylation assay, immunofluorescence foci assay, clonogenic survival","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis plus functional cellular validation in one study","pmids":["26778126"],"is_preprint":false},{"year":2012,"finding":"The Abraxas Arg361Gln mutation abrogates nuclear localization of Abraxas and disrupts BRCA1-dependent DNA damage response functions (G2/M checkpoint, foci formation)","method":"Patient-derived cells, immunofluorescence, checkpoint assays, IR sensitivity","journal":"Science Translational Medicine","confidence":"Medium","confidence_rationale":"Tier 2 — patient-derived cells with multiple functional assays, single lab","pmids":["22357538"],"is_preprint":false},{"year":2014,"finding":"Homozygous and heterozygous Abraxas knockout in mice leads to decreased survival, increased tumor incidence, and impaired DNA repair, demonstrating a tumor suppressor role that depends on BRCA1 BRCT domain interaction","method":"Conditional knockout mouse model, tumor incidence analysis, DNA repair assays","journal":"Cell Reports","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO model with defined phenotype","pmids":["25066119"],"is_preprint":false},{"year":2019,"finding":"The Finnish ABRAXAS1 founder mutation (Arg361Gln), even in heterozygous state, causes decreased BRCA1 protein levels, reduced nuclear localization and foci formation of BRCA1 and CtIP, attenuated DNA damage response, and deregulated G2/M checkpoint in a dominant-negative manner","method":"Patient-derived heterozygous cells, Western blot, immunofluorescence, checkpoint assays, DNA repair pathway assays","journal":"Human Molecular Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — patient-derived cells with multiple orthogonal assays, single lab","pmids":["31630195"],"is_preprint":false},{"year":2021,"finding":"Abraxas suppresses break-induced replication (BIR) by counteracting K63-linked ubiquitin modification to restrict SLX4/MUS81 recruitment to CPT-induced DNA damage sites, thereby limiting MRE11/CtIP/DNA2/BLM-mediated end resection and RAD52/POLD3-dependent, RAD51-independent mitotic DNA synthesis","method":"siRNA/CRISPR knockdown/KO, proximity ligation assay, chromatin fractionation, mitotic DNA synthesis assay (EdU/FANCD2 co-staining), chromosome aberration analysis","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 — multiple KD/KO experiments with defined molecular pathway and multiple orthogonal readouts","pmids":["34272385"],"is_preprint":false},{"year":2023,"finding":"Truncating ABRAXAS1 mutations lacking the C-terminal BRCA1-binding site retain N-terminal interaction with RAP80, channeling BRCA1 from the BRCA1-A complex to the BRCA1-C complex and inducing single-strand annealing (SSA); further truncation deleting the coiled-coil region de-represses multiple low-fidelity DSB repair pathways including SSA and NHEJ","method":"Patient-derived lymphoblastoid cells, HR reporter assay, RAD51-foci, PARP-inhibitor sensitivity, SSA reporter assay, NHEJ assay, dominant-negative mutant expression","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 — patient-derived cells plus genetically manipulated cells with multiple orthogonal assays, single lab","pmids":["37198153"],"is_preprint":false}],"current_model":"ABRAXAS1 is a scaffold protein of the BRCA1-A complex that directly binds the BRCA1 BRCT repeats via a phospho-SPxF motif (further stabilized by ATM-induced phosphorylation of S404 promoting BRCT/Abraxas dimerization), recruits RAP80 (which binds K63-polyubiquitin chains generated by RNF8/Ubc13 at damage sites) and BRCC36 (via coiled-coil interactions) to localize BRCA1 to DNA double-strand breaks, and actively suppresses mutagenic repair pathways including break-induced replication by restraining SLX4/MUS81-dependent end resection, thereby maintaining genome stability and acting as a tumor suppressor."},"narrative":{"teleology":[{"year":2007,"claim":"Identification of Abraxas as the direct BRCA1 BRCT-binding partner that nucleates a distinct BRCA1-A complex resolved the long-standing question of how BRCA1 is recruited to DNA damage sites independently of BACH1 and CtIP.","evidence":"Phosphopeptide affinity proteomics, reciprocal Co-IP, domain mapping, and siRNA knockdown with checkpoint/survival assays in human cells","pmids":["17525340","17643121","17643122"],"confidence":"High","gaps":["Structural basis of the pSXXF–BRCT interaction not yet resolved","Stoichiometry and assembly order of the full BRCA1-A complex not determined","In vivo physiological significance not tested"]},{"year":2007,"claim":"Establishing the recruitment chain—RNF8/Ubc13-generated K63-polyubiquitin recognized by RAP80 UIMs, RAP80 bound to Abraxas, and BRCC36 associated via coiled-coil domains—defined the molecular logic by which the BRCA1-A complex localizes to damage-induced chromatin.","evidence":"Co-IP with domain deletion mutants, siRNA epistasis, and immunofluorescence foci assays","pmids":["18077395"],"confidence":"High","gaps":["Mechanism by which BRCC36 deubiquitinase activity feeds back on K63-ubiquitin recognition was not addressed","Coiled-coil interaction between Abraxas and BRCC36 characterized only by deletion mutant Co-IP, no structural detail"]},{"year":2012,"claim":"Discovery that the patient-derived Arg361Gln mutation abolishes Abraxas nuclear localization and disrupts BRCA1-dependent checkpoint functions provided the first link between ABRAXAS1 dysfunction and human cancer predisposition.","evidence":"Patient-derived cells with immunofluorescence, checkpoint assays, and IR sensitivity","pmids":["22357538"],"confidence":"Medium","gaps":["Single-lab study on one kindred; independent replication in additional families needed","Mechanism by which R361Q disrupts nuclear import not molecularly defined"]},{"year":2014,"claim":"Mouse knockout studies demonstrated that Abraxas is a bona fide tumor suppressor whose protective function depends on its BRCA1 BRCT interaction, establishing in vivo relevance beyond cell-based assays.","evidence":"Conditional knockout mouse model with tumor incidence monitoring and DNA repair assays","pmids":["25066119"],"confidence":"High","gaps":["Tumor spectrum and tissue specificity of Abraxas loss not fully characterized","Whether haploinsufficiency alone drives tumorigenesis in mice was not fully resolved"]},{"year":2016,"claim":"Crystallographic resolution of the BRCT/Abraxas complex revealed that ATM-dependent phosphorylation of S404 induces dimerization of the BRCT/Abraxas unit, explaining how damage signaling amplifies BRCA1 accumulation at break sites.","evidence":"Crystal structure determination, S404A mutagenesis, IR-induced phosphorylation assay, foci and survival assays","pmids":["26778126"],"confidence":"High","gaps":["Whether BRCT/Abraxas dimerization influences the stoichiometry or activity of other BRCA1-A subunits is unknown","Full-length complex structure not available"]},{"year":2019,"claim":"Characterization of heterozygous R361Q patient cells revealed a dominant-negative mechanism—reduced BRCA1 protein levels, impaired CtIP foci, and deregulated G2/M checkpoint—explaining how a monoallelic ABRAXAS1 mutation confers cancer risk.","evidence":"Patient-derived heterozygous lymphoblastoid cells with Western blot, immunofluorescence, checkpoint and DNA repair pathway assays","pmids":["31630195"],"confidence":"Medium","gaps":["Single-lab study; mechanism of dominant-negative action (e.g., poisonous heterodimer) not structurally resolved","Penetrance and genotype–phenotype correlation in larger cohorts not established"]},{"year":2021,"claim":"Demonstration that Abraxas suppresses break-induced replication by restricting K63-ubiquitin-dependent SLX4/MUS81 recruitment and downstream end resection shifted understanding of Abraxas from a passive scaffold to an active suppressor of mutagenic repair.","evidence":"siRNA/CRISPR KO, proximity ligation assay, chromatin fractionation, mitotic DNA synthesis (EdU/FANCD2), chromosome aberration analysis","pmids":["34272385"],"confidence":"High","gaps":["Whether Abraxas directly modulates K63-ubiquitin levels or acts indirectly through BRCC36 DUB activity is not fully delineated","Relative contribution of BIR suppression versus HR promotion to tumor suppression is unknown"]},{"year":2023,"claim":"Analysis of truncating ABRAXAS1 mutations showed that loss of the C-terminal BRCA1-binding site redirects BRCA1 to the BRCA1-C complex to activate SSA, while further loss of the coiled-coil region de-represses both SSA and NHEJ, revealing allele-specific pathway rewiring.","evidence":"Patient-derived lymphoblastoid cells, HR/SSA/NHEJ reporter assays, RAD51 foci, PARP-inhibitor sensitivity","pmids":["37198153"],"confidence":"Medium","gaps":["Single-lab study; allele-specific repair pathway effects not validated in independent systems","How residual N-terminal Abraxas–RAP80 interaction channels BRCA1 to alternative complexes is mechanistically unclear","Clinical significance of SSA activation for therapeutic response is not addressed"]},{"year":null,"claim":"A full-length structure of the assembled BRCA1-A complex, the precise mechanism by which Abraxas coordinates BRCC36 DUB activity with BIR suppression, and the genotype–phenotype relationship for diverse ABRAXAS1 mutations in human cancer remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length or cryo-EM structure of the complete BRCA1-A complex","Functional interdependence of Abraxas scaffold role and BRCC36 catalytic activity at damage sites not dissected","Systematic clinical studies correlating specific ABRAXAS1 mutations with repair pathway outcomes and cancer risk are lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2,5,11]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5,7,9]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[3,6,10]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,4,6,8,10,11]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[4,5,9]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,9]}],"complexes":["BRCA1-A complex"],"partners":["BRCA1","RAP80","BRCC36","RNF8","SLX4","MUS81","CTIP"],"other_free_text":[]},"mechanistic_narrative":"ABRAXAS1 is a scaffold protein central to the BRCA1-A complex that orchestrates BRCA1 recruitment to DNA double-strand breaks and suppresses mutagenic repair pathways to maintain genome stability. It directly binds the BRCA1 BRCT repeats through a phospho-SPxF motif—further stabilized by ATM-dependent phosphorylation of S404, which induces BRCT/Abraxas dimerization required for efficient BRCA1 accumulation at damage sites—while simultaneously recruiting RAP80 (which recognizes RNF8/Ubc13-generated K63-polyubiquitin chains) and BRCC36 (via coiled-coil interactions) to assemble the damage-site signaling platform [PMID:17525340, PMID:18077395, PMID:26778126]. Beyond recruiting BRCA1, ABRAXAS1 actively suppresses break-induced replication by counteracting K63-ubiquitin-dependent SLX4/MUS81 recruitment and restraining end resection, and its loss de-represses multiple low-fidelity DSB repair pathways including single-strand annealing and NHEJ [PMID:34272385, PMID:37198153]. ABRAXAS1 functions as a tumor suppressor: knockout mice display increased tumor incidence and impaired DNA repair, and the Finnish founder mutation Arg361Gln acts in a dominant-negative manner to disrupt BRCA1 nuclear localization, DNA damage response, and G2/M checkpoint control, conferring cancer predisposition [PMID:25066119, PMID:22357538, PMID:31630195]."},"prefetch_data":{"uniprot":{"accession":"Q6UWZ7","full_name":"BRCA1-A complex subunit Abraxas 1","aliases":["Coiled-coil domain-containing protein 98","Protein FAM175A"],"length_aa":409,"mass_kda":46.7,"function":"Involved in DNA damage response and double-strand break (DSB) repair. Component of the BRCA1-A complex, acting as a central scaffold protein that assembles the various components of the complex and mediates the recruitment of BRCA1. The BRCA1-A complex specifically recognizes 'Lys-63'-linked ubiquitinated histones H2A and H2AX at DNA lesion sites, leading to target the BRCA1-BARD1 heterodimer to sites of DNA damage at DSBs. This complex also possesses deubiquitinase activity that specifically removes 'Lys-63'-linked ubiquitin on histones H2A and H2AX","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q6UWZ7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ABRAXAS1","classification":"Not Classified","n_dependent_lines":155,"n_total_lines":1208,"dependency_fraction":0.12831125827814568},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ABRAXAS1","total_profiled":1310},"omim":[{"mim_id":"611143","title":"ABRAXAS 1, BRCA1 A COMPLEX SUBUNIT; ABRAXAS1","url":"https://www.omim.org/entry/611143"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear bodies","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ABRAXAS1"},"hgnc":{"alias_symbol":["FLJ13614","ABRA1","ABRAXAS"],"prev_symbol":["CCDC98","FAM175A"]},"alphafold":{"accession":"Q6UWZ7","domains":[{"cath_id":"3.40.140.10","chopping":"4-170","consensus_level":"high","plddt":91.1839,"start":4,"end":170},{"cath_id":"-","chopping":"275-319","consensus_level":"medium","plddt":73.2182,"start":275,"end":319},{"cath_id":"1.20.5","chopping":"219-272","consensus_level":"medium","plddt":90.0311,"start":219,"end":272}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UWZ7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UWZ7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UWZ7-F1-predicted_aligned_error_v6.png","plddt_mean":77.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ABRAXAS1","jax_strain_url":"https://www.jax.org/strain/search?query=ABRAXAS1"},"sequence":{"accession":"Q6UWZ7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UWZ7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UWZ7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UWZ7"}},"corpus_meta":[{"pmid":"17525340","id":"PMC_17525340","title":"Abraxas and RAP80 form a BRCA1 protein complex required for the DNA damage response.","date":"2007","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/17525340","citation_count":577,"is_preprint":false},{"pmid":"18077395","id":"PMC_18077395","title":"Ubc13/Rnf8 ubiquitin ligases control foci formation of the Rap80/Abraxas/Brca1/Brcc36 complex in response to DNA damage.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18077395","citation_count":357,"is_preprint":false},{"pmid":"17643122","id":"PMC_17643122","title":"CCDC98 is a BRCA1-BRCT domain-binding protein involved in the DNA damage response.","date":"2007","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17643122","citation_count":170,"is_preprint":false},{"pmid":"17643121","id":"PMC_17643121","title":"CCDC98 targets BRCA1 to DNA damage sites.","date":"2007","source":"Nature 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ABRAXAS1 mutation carrier cells.","date":"2019","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31630195","citation_count":6,"is_preprint":false},{"pmid":"27270457","id":"PMC_27270457","title":"ABRAXAS (FAM175A) and Breast Cancer Susceptibility: No Evidence of Association in the Breast Cancer Family Registry.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27270457","citation_count":6,"is_preprint":false},{"pmid":"37198153","id":"PMC_37198153","title":"ABRAXAS1 orchestrates BRCA1 activities to counter genome destabilizing repair pathways-lessons from breast cancer patients.","date":"2023","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/37198153","citation_count":4,"is_preprint":false},{"pmid":"24316840","id":"PMC_24316840","title":"Preliminary crystallographic studies of BRCA1 BRCT-ABRAXAS complex.","date":"2013","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/24316840","citation_count":3,"is_preprint":false},{"pmid":"25105795","id":"PMC_25105795","title":"Mislocalization of BRCA1-complex due to ABRAXAS Arg361Gln mutation.","date":"2014","source":"Journal of biomolecular structure & dynamics","url":"https://pubmed.ncbi.nlm.nih.gov/25105795","citation_count":1,"is_preprint":false},{"pmid":"32845162","id":"PMC_32845162","title":"Transcriptional regulation of human abraxas brother protein 1 expression by yin yang 1.","date":"2020","source":"Biochemistry and cell biology = Biochimie et biologie cellulaire","url":"https://pubmed.ncbi.nlm.nih.gov/32845162","citation_count":0,"is_preprint":false},{"pmid":"41746808","id":"PMC_41746808","title":"Streptococcus anginosus-generated succinate promotes the progression of gastric cancer via the succinate/SUCNR1/ABRAXAS1 axis.","date":"2026","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/41746808","citation_count":0,"is_preprint":false},{"pmid":"30786683","id":"PMC_30786683","title":"Searching for new breast cancer-associated genes. ABRAXAS1 gene mutations in the group of BRCA1-negative patients.","date":"2018","source":"Polish journal of pathology : official journal of the Polish Society of Pathologists","url":"https://pubmed.ncbi.nlm.nih.gov/30786683","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11610,"output_tokens":2517,"usd":0.036292},"stage2":{"model":"claude-opus-4-6","input_tokens":5865,"output_tokens":2603,"usd":0.1416},"total_usd":0.177892,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"Abraxas directly binds the BRCA1 BRCT repeats through a phospho-Ser-X-X-Phe (pSXXF) motif, forming a distinct BRCA1 complex (BRCA1-A complex) that excludes BACH1 and CtIP binding\",\n      \"method\": \"Phosphopeptide affinity proteomics, Co-IP, reciprocal pulldown\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphopeptide affinity proteomics plus reciprocal Co-IP, replicated across multiple labs\",\n      \"pmids\": [\"17525340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Abraxas recruits RAP80 to the BRCA1-A complex via a RAP80 Abraxas-interacting region (AIR domain), and RAP80 UIM domains recognize K63-linked polyubiquitin chains at DNA damage sites to recruit the entire BRCA1-A complex\",\n      \"method\": \"Co-IP, domain mapping, immunofluorescence (foci formation assay)\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with domain mapping, replicated in multiple papers\",\n      \"pmids\": [\"17525340\", \"18077395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Abraxas and BRCC36 associate through coiled-coil domains on each protein as part of the BRCA1-A complex assembly\",\n      \"method\": \"Co-IP, domain mapping (coiled-coil deletion mutants)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with domain mapping, single lab\",\n      \"pmids\": [\"18077395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RNF8 (E3 ubiquitin ligase) and Ubc13 (E2 conjugating enzyme) generate K63-linked polyubiquitin chains at DNA damage sites that are recognized by RAP80 UIM domains, enabling recruitment of Abraxas and the entire BRCA1-A complex to damage foci\",\n      \"method\": \"siRNA knockdown, Co-IP, immunofluorescence foci assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with KD plus foci assay, replicated\",\n      \"pmids\": [\"18077395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Abraxas and RAP80 are required for DNA damage resistance, G2/M checkpoint control, and DNA repair (loss-of-function knockdown phenotype)\",\n      \"method\": \"siRNA knockdown, clonogenic survival, G2/M checkpoint assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotypes, replicated\",\n      \"pmids\": [\"17525340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CCDC98 (Abraxas) mediates the interaction between BRCA1 and RAP80, and is required for BRCA1 foci formation and G2/M checkpoint activation in response to ionizing radiation\",\n      \"method\": \"Co-IP, siRNA knockdown, immunofluorescence foci assay, checkpoint assay\",\n      \"journal\": \"Nature Structural & Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional KD, independently replicated in two concurrent papers\",\n      \"pmids\": [\"17643121\", \"17643122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ATM-dependent phosphorylation of Abraxas serine 404 (adjacent to its pSPxF motif) induces dimerization of the BRCT/Abraxas complex, which is required for BRCA1 accumulation at DNA damage sites; crystal structure of BRCT/Abraxas complex revealed the molecular basis of this phosphorylation-dependent dimerization\",\n      \"method\": \"Crystal structure determination, mutagenesis (S404A), IR-induced phosphorylation assay, immunofluorescence foci assay, clonogenic survival\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis plus functional cellular validation in one study\",\n      \"pmids\": [\"26778126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Abraxas Arg361Gln mutation abrogates nuclear localization of Abraxas and disrupts BRCA1-dependent DNA damage response functions (G2/M checkpoint, foci formation)\",\n      \"method\": \"Patient-derived cells, immunofluorescence, checkpoint assays, IR sensitivity\",\n      \"journal\": \"Science Translational Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells with multiple functional assays, single lab\",\n      \"pmids\": [\"22357538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Homozygous and heterozygous Abraxas knockout in mice leads to decreased survival, increased tumor incidence, and impaired DNA repair, demonstrating a tumor suppressor role that depends on BRCA1 BRCT domain interaction\",\n      \"method\": \"Conditional knockout mouse model, tumor incidence analysis, DNA repair assays\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO model with defined phenotype\",\n      \"pmids\": [\"25066119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The Finnish ABRAXAS1 founder mutation (Arg361Gln), even in heterozygous state, causes decreased BRCA1 protein levels, reduced nuclear localization and foci formation of BRCA1 and CtIP, attenuated DNA damage response, and deregulated G2/M checkpoint in a dominant-negative manner\",\n      \"method\": \"Patient-derived heterozygous cells, Western blot, immunofluorescence, checkpoint assays, DNA repair pathway assays\",\n      \"journal\": \"Human Molecular Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells with multiple orthogonal assays, single lab\",\n      \"pmids\": [\"31630195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Abraxas suppresses break-induced replication (BIR) by counteracting K63-linked ubiquitin modification to restrict SLX4/MUS81 recruitment to CPT-induced DNA damage sites, thereby limiting MRE11/CtIP/DNA2/BLM-mediated end resection and RAD52/POLD3-dependent, RAD51-independent mitotic DNA synthesis\",\n      \"method\": \"siRNA/CRISPR knockdown/KO, proximity ligation assay, chromatin fractionation, mitotic DNA synthesis assay (EdU/FANCD2 co-staining), chromosome aberration analysis\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple KD/KO experiments with defined molecular pathway and multiple orthogonal readouts\",\n      \"pmids\": [\"34272385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Truncating ABRAXAS1 mutations lacking the C-terminal BRCA1-binding site retain N-terminal interaction with RAP80, channeling BRCA1 from the BRCA1-A complex to the BRCA1-C complex and inducing single-strand annealing (SSA); further truncation deleting the coiled-coil region de-represses multiple low-fidelity DSB repair pathways including SSA and NHEJ\",\n      \"method\": \"Patient-derived lymphoblastoid cells, HR reporter assay, RAD51-foci, PARP-inhibitor sensitivity, SSA reporter assay, NHEJ assay, dominant-negative mutant expression\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells plus genetically manipulated cells with multiple orthogonal assays, single lab\",\n      \"pmids\": [\"37198153\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ABRAXAS1 is a scaffold protein of the BRCA1-A complex that directly binds the BRCA1 BRCT repeats via a phospho-SPxF motif (further stabilized by ATM-induced phosphorylation of S404 promoting BRCT/Abraxas dimerization), recruits RAP80 (which binds K63-polyubiquitin chains generated by RNF8/Ubc13 at damage sites) and BRCC36 (via coiled-coil interactions) to localize BRCA1 to DNA double-strand breaks, and actively suppresses mutagenic repair pathways including break-induced replication by restraining SLX4/MUS81-dependent end resection, thereby maintaining genome stability and acting as a tumor suppressor.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ABRAXAS1 is a scaffold protein central to the BRCA1-A complex that orchestrates BRCA1 recruitment to DNA double-strand breaks and suppresses mutagenic repair pathways to maintain genome stability. It directly binds the BRCA1 BRCT repeats through a phospho-SPxF motif—further stabilized by ATM-dependent phosphorylation of S404, which induces BRCT/Abraxas dimerization required for efficient BRCA1 accumulation at damage sites—while simultaneously recruiting RAP80 (which recognizes RNF8/Ubc13-generated K63-polyubiquitin chains) and BRCC36 (via coiled-coil interactions) to assemble the damage-site signaling platform [PMID:17525340, PMID:18077395, PMID:26778126]. Beyond recruiting BRCA1, ABRAXAS1 actively suppresses break-induced replication by counteracting K63-ubiquitin-dependent SLX4/MUS81 recruitment and restraining end resection, and its loss de-represses multiple low-fidelity DSB repair pathways including single-strand annealing and NHEJ [PMID:34272385, PMID:37198153]. ABRAXAS1 functions as a tumor suppressor: knockout mice display increased tumor incidence and impaired DNA repair, and the Finnish founder mutation Arg361Gln acts in a dominant-negative manner to disrupt BRCA1 nuclear localization, DNA damage response, and G2/M checkpoint control, conferring cancer predisposition [PMID:25066119, PMID:22357538, PMID:31630195].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of Abraxas as the direct BRCA1 BRCT-binding partner that nucleates a distinct BRCA1-A complex resolved the long-standing question of how BRCA1 is recruited to DNA damage sites independently of BACH1 and CtIP.\",\n      \"evidence\": \"Phosphopeptide affinity proteomics, reciprocal Co-IP, domain mapping, and siRNA knockdown with checkpoint/survival assays in human cells\",\n      \"pmids\": [\"17525340\", \"17643121\", \"17643122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the pSXXF–BRCT interaction not yet resolved\",\n        \"Stoichiometry and assembly order of the full BRCA1-A complex not determined\",\n        \"In vivo physiological significance not tested\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Establishing the recruitment chain—RNF8/Ubc13-generated K63-polyubiquitin recognized by RAP80 UIMs, RAP80 bound to Abraxas, and BRCC36 associated via coiled-coil domains—defined the molecular logic by which the BRCA1-A complex localizes to damage-induced chromatin.\",\n      \"evidence\": \"Co-IP with domain deletion mutants, siRNA epistasis, and immunofluorescence foci assays\",\n      \"pmids\": [\"18077395\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which BRCC36 deubiquitinase activity feeds back on K63-ubiquitin recognition was not addressed\",\n        \"Coiled-coil interaction between Abraxas and BRCC36 characterized only by deletion mutant Co-IP, no structural detail\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery that the patient-derived Arg361Gln mutation abolishes Abraxas nuclear localization and disrupts BRCA1-dependent checkpoint functions provided the first link between ABRAXAS1 dysfunction and human cancer predisposition.\",\n      \"evidence\": \"Patient-derived cells with immunofluorescence, checkpoint assays, and IR sensitivity\",\n      \"pmids\": [\"22357538\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study on one kindred; independent replication in additional families needed\",\n        \"Mechanism by which R361Q disrupts nuclear import not molecularly defined\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mouse knockout studies demonstrated that Abraxas is a bona fide tumor suppressor whose protective function depends on its BRCA1 BRCT interaction, establishing in vivo relevance beyond cell-based assays.\",\n      \"evidence\": \"Conditional knockout mouse model with tumor incidence monitoring and DNA repair assays\",\n      \"pmids\": [\"25066119\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Tumor spectrum and tissue specificity of Abraxas loss not fully characterized\",\n        \"Whether haploinsufficiency alone drives tumorigenesis in mice was not fully resolved\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Crystallographic resolution of the BRCT/Abraxas complex revealed that ATM-dependent phosphorylation of S404 induces dimerization of the BRCT/Abraxas unit, explaining how damage signaling amplifies BRCA1 accumulation at break sites.\",\n      \"evidence\": \"Crystal structure determination, S404A mutagenesis, IR-induced phosphorylation assay, foci and survival assays\",\n      \"pmids\": [\"26778126\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether BRCT/Abraxas dimerization influences the stoichiometry or activity of other BRCA1-A subunits is unknown\",\n        \"Full-length complex structure not available\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Characterization of heterozygous R361Q patient cells revealed a dominant-negative mechanism—reduced BRCA1 protein levels, impaired CtIP foci, and deregulated G2/M checkpoint—explaining how a monoallelic ABRAXAS1 mutation confers cancer risk.\",\n      \"evidence\": \"Patient-derived heterozygous lymphoblastoid cells with Western blot, immunofluorescence, checkpoint and DNA repair pathway assays\",\n      \"pmids\": [\"31630195\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study; mechanism of dominant-negative action (e.g., poisonous heterodimer) not structurally resolved\",\n        \"Penetrance and genotype–phenotype correlation in larger cohorts not established\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstration that Abraxas suppresses break-induced replication by restricting K63-ubiquitin-dependent SLX4/MUS81 recruitment and downstream end resection shifted understanding of Abraxas from a passive scaffold to an active suppressor of mutagenic repair.\",\n      \"evidence\": \"siRNA/CRISPR KO, proximity ligation assay, chromatin fractionation, mitotic DNA synthesis (EdU/FANCD2), chromosome aberration analysis\",\n      \"pmids\": [\"34272385\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether Abraxas directly modulates K63-ubiquitin levels or acts indirectly through BRCC36 DUB activity is not fully delineated\",\n        \"Relative contribution of BIR suppression versus HR promotion to tumor suppression is unknown\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Analysis of truncating ABRAXAS1 mutations showed that loss of the C-terminal BRCA1-binding site redirects BRCA1 to the BRCA1-C complex to activate SSA, while further loss of the coiled-coil region de-represses both SSA and NHEJ, revealing allele-specific pathway rewiring.\",\n      \"evidence\": \"Patient-derived lymphoblastoid cells, HR/SSA/NHEJ reporter assays, RAD51 foci, PARP-inhibitor sensitivity\",\n      \"pmids\": [\"37198153\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-lab study; allele-specific repair pathway effects not validated in independent systems\",\n        \"How residual N-terminal Abraxas–RAP80 interaction channels BRCA1 to alternative complexes is mechanistically unclear\",\n        \"Clinical significance of SSA activation for therapeutic response is not addressed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length structure of the assembled BRCA1-A complex, the precise mechanism by which Abraxas coordinates BRCC36 DUB activity with BIR suppression, and the genotype–phenotype relationship for diverse ABRAXAS1 mutations in human cancer remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No full-length or cryo-EM structure of the complete BRCA1-A complex\",\n        \"Functional interdependence of Abraxas scaffold role and BRCC36 catalytic activity at damage sites not dissected\",\n        \"Systematic clinical studies correlating specific ABRAXAS1 mutations with repair pathway outcomes and cancer risk are lacking\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2, 5, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5, 7, 9]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [3, 6, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 4, 6, 8, 10, 11]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [4, 5, 9]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"complexes\": [\n      \"BRCA1-A complex\"\n    ],\n    \"partners\": [\n      \"BRCA1\",\n      \"RAP80\",\n      \"BRCC36\",\n      \"RNF8\",\n      \"SLX4\",\n      \"MUS81\",\n      \"CtIP\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}