{"gene":"BTBD1","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2002,"finding":"BTBD1 physically interacts with the core domain of human topoisomerase I (TOP1); co-precipitation assays confirmed the interaction with 100 kDa TOP1 from HeLa cells, and deletion mapping showed that less than the C-terminal half of BTBD1 is sufficient for binding TOP1.","method":"Yeast two-hybrid screening, co-precipitation assay, GST-pulldown with deletion mapping","journal":"BMC genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal yeast two-hybrid and co-precipitation with deletion mapping in single lab, two orthogonal methods","pmids":["11818025"],"is_preprint":false},{"year":2003,"finding":"BTBD1 and BTBD2 colocalize to punctate or elongated cytoplasmic bodies in mouse and human cells. TRIM5delta (a RING/B-box/coiled-coil TRIM family member) colocalizes with BTBD1/2 and serves as a scaffold for assembly of endogenous BTBD1/2 proteins; deletion of TRIM5delta's coiled-coil region or mutation of its RING domain abolished colocalization with BTBD1/2.","method":"Immunofluorescence colocalization, GFP-fusion expression, deletion/point mutants of TRIM5delta","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct imaging with functional mutants establishing scaffold requirement, single lab","pmids":["12878161"],"is_preprint":false},{"year":2004,"finding":"Stable overexpression of an N-terminally truncated BTBD1 (Delta-BTBD1, lacking 108 N-terminal residues) in C2C12 myoblasts inhibited myogenic differentiation and reduced proliferation, while decreasing nuclear TOP1 content and shifting TOP1 localization from peripheral nuclear to diffuse nuclear, indicating BTBD1 is required for myogenic differentiation and regulates nuclear TOP1 localization.","method":"Stable overexpression of truncated BTBD1 in C2C12 cells, immunofluorescence/subcellular fractionation of TOP1, differentiation assays","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function via dominant-negative truncation with defined phenotypic readout (differentiation block, TOP1 relocalization), single lab","pmids":["15486563"],"is_preprint":false},{"year":2007,"finding":"BTBD1 mRNA is upregulated during myogenesis and downregulated during adipogenesis; BTBD1 expression levels are inversely correlated with TOP1 protein (but not TOP1 mRNA) levels across differentiation conditions, suggesting BTBD1 post-translationally regulates TOP1 protein abundance and controls the balance between myogenic and adipogenic differentiation.","method":"RT-PCR/northern blot across differentiation models (C2C12, 3T3-L1, hMADS), western blot for TOP1 protein, transcriptome analysis","journal":"Experimental cell research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — correlative expression data in differentiation models, single lab, no direct mechanistic manipulation of BTBD1","pmids":["17462629"],"is_preprint":false},{"year":2010,"finding":"The interaction of BTBD1 and BTBD2 with TOP1 requires human TOP1 residues 236 and 237; substitution of these residues with the African Green Monkey counterparts abolished BTBD1/BTBD2 binding. RNAi knockdown of BTBD2 (but not specifically tested for BTBD1 alone) in AGM and human 293T cells increased permissiveness to HIV-1 infection 2–3 fold.","method":"Co-precipitation with TOP1 point mutants, RNAi knockdown, HIV-1 infectivity assay","journal":"Virology journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis of TOP1 residues mapped to BTBD1/2 binding interface, combined with RNAi functional assay, single lab","pmids":["21092135"],"is_preprint":false},{"year":2022,"finding":"BTBD1 (and BTBD2) function as substrate adaptor proteins for the CRL3 (Cullin 3 RING ligase) E3 ubiquitin ligase complex, promoting ubiquitination and proteasomal degradation of TOP1-cleavage complexes (TOP1-ccs). NEDDylation of Cullin 3 activates this pathway; inhibition of NEDDylation or depletion of Cullin 3 sensitizes cancer cells to TOP1 inhibitors.","method":"Protein complex biochemistry (CUL3-BTBD1/2 E3 ligase), ubiquitination assays, NEDD8 pathway inhibition, siRNA depletion, genomic occupancy analysis of TOP1","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro ubiquitination reconstitution of CUL3-BTBD1/2 complex, combined with NEDDylation perturbation and depletion experiments providing orthogonal mechanistic validation","pmids":["36490343"],"is_preprint":false}],"current_model":"BTBD1 is a substrate adaptor for the CRL3 (Cullin 3/RING) E3 ubiquitin ligase complex that, upon Cullin 3 NEDDylation, promotes ubiquitination and proteasomal degradation of TOP1-cleavage complexes; it also physically interacts with TOP1 (via its C-terminal half, requiring TOP1 residues 236–237), colocalizes with the TRIM5delta scaffold in cytoplasmic bodies, and is required for myogenic differentiation in part by maintaining proper nuclear TOP1 localization."},"narrative":{"mechanistic_narrative":"BTBD1 is a substrate adaptor for the CRL3 (Cullin 3/RING) E3 ubiquitin ligase complex that controls the abundance of topoisomerase I (TOP1) and its DNA-bound cleavage complexes [PMID:36490343]. BTBD1 physically binds TOP1 through less than the C-terminal half of the protein, an interaction that depends on TOP1 residues 236 and 237 [PMID:11818025, PMID:21092135]. Within the CRL3 complex, BTBD1 promotes ubiquitination and proteasomal degradation of TOP1-cleavage complexes in a manner activated by Cullin 3 NEDDylation, such that blocking NEDDylation or depleting Cullin 3 sensitizes cancer cells to TOP1 inhibitors [PMID:36490343]. Consistent with this post-translational control of TOP1, BTBD1 maintains proper peripheral nuclear TOP1 localization and is required for myogenic differentiation: a dominant-negative N-terminal truncation reduces nuclear TOP1 content and blocks differentiation [PMID:15486563]. BTBD1 also assembles with BTBD2 into cytoplasmic bodies organized by the TRIM5delta scaffold [PMID:12878161].","teleology":[{"year":2002,"claim":"Established the first molecular partner of BTBD1 by showing it binds topoisomerase I, defining the binding determinant within BTBD1.","evidence":"Yeast two-hybrid, co-precipitation, and GST-pulldown deletion mapping with HeLa TOP1","pmids":["11818025"],"confidence":"Medium","gaps":["Functional consequence of the BTBD1-TOP1 interaction not determined","TOP1 residues required for binding not yet mapped"]},{"year":2003,"claim":"Defined the subcellular context of BTBD1 by showing it assembles with BTBD2 into cytoplasmic bodies dependent on a TRIM5delta scaffold.","evidence":"Immunofluorescence colocalization with GFP fusions and TRIM5delta deletion/point mutants in mouse and human cells","pmids":["12878161"],"confidence":"Medium","gaps":["Biochemical function of the cytoplasmic bodies unknown","Relationship between cytoplasmic localization and nuclear TOP1 regulation unresolved"]},{"year":2004,"claim":"Connected BTBD1 to a cellular phenotype, showing it is required for myogenic differentiation and governs nuclear TOP1 localization.","evidence":"Stable dominant-negative truncated BTBD1 overexpression in C2C12 myoblasts with differentiation assays and TOP1 fractionation/imaging","pmids":["15486563"],"confidence":"Medium","gaps":["Mechanism linking BTBD1 to TOP1 relocalization not established","Truncation may act dominant-negatively rather than reflecting loss of function"]},{"year":2007,"claim":"Suggested BTBD1 controls TOP1 at the protein level and balances myogenic versus adipogenic fates.","evidence":"Expression profiling across differentiation models with western blot for TOP1 protein versus mRNA","pmids":["17462629"],"confidence":"Low","gaps":["Correlative only, no direct manipulation of BTBD1","Post-translational mechanism inferred but not demonstrated"]},{"year":2010,"claim":"Mapped the TOP1 binding interface to residues 236-237 and linked the BTBD module to host restriction of HIV-1.","evidence":"Co-precipitation with TOP1 point mutants plus RNAi knockdown and HIV-1 infectivity assays","pmids":["21092135"],"confidence":"Medium","gaps":["HIV-1 phenotype tested for BTBD2 but not specifically BTBD1","Mechanistic basis of altered HIV permissiveness unknown"]},{"year":2022,"claim":"Resolved the biochemical function of BTBD1 as a CRL3 substrate adaptor that targets TOP1-cleavage complexes for NEDDylation-activated ubiquitin-proteasome degradation.","evidence":"In vitro CUL3-BTBD1/2 ubiquitination reconstitution, NEDD8 pathway inhibition, siRNA depletion, and TOP1 genomic occupancy analysis","pmids":["36490343"],"confidence":"High","gaps":["Relative contributions of BTBD1 versus BTBD2 not dissected","Link between this degradation pathway and the myogenic differentiation phenotype not directly tested"]},{"year":null,"claim":"How the cytoplasmic TRIM5delta-organized BTBD1 bodies relate to its nuclear CRL3-mediated TOP1 degradation function remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No mechanism connecting cytoplasmic localization to nuclear TOP1 control","Substrate repertoire of CRL3-BTBD1 beyond TOP1-cc unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5]}],"complexes":["CRL3 (Cullin 3 RING ligase)"],"partners":["TOP1","CUL3","BTBD2","TRIM5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H0C5","full_name":"BTB/POZ domain-containing protein 1","aliases":["Hepatitis C virus NS5A-transactivated protein 8","HCV NS5A-transactivated protein 8"],"length_aa":482,"mass_kda":52.8,"function":"Probable substrate-specific adapter of an E3 ubiquitin-protein ligase complex which mediates the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:14528312). Seems to regulate expression levels and/or subnuclear distribution of TOP1, via an unknown mechanism (By similarity). May play a role in mesenchymal differentiation where it promotes myogenic differentiation and suppresses adipogenesis (By similarity)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9H0C5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/BTBD1","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/BTBD1","total_profiled":1310},"omim":[{"mim_id":"608531","title":"BTB/POZ DOMAIN-CONTAINING PROTEIN 2; BTBD2","url":"https://www.omim.org/entry/608531"},{"mim_id":"608530","title":"BTB/POZ DOMAIN-CONTAINING PROTEIN 1; BTBD1","url":"https://www.omim.org/entry/608530"},{"mim_id":"608487","title":"TRIPARTITE MOTIF-CONTAINING PROTEIN 5; TRIM5","url":"https://www.omim.org/entry/608487"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytoplasmic bodies","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":304.4},{"tissue":"tongue","ntpm":215.5}],"url":"https://www.proteinatlas.org/search/BTBD1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9H0C5","domains":[{"cath_id":"3.30.710.10","chopping":"52-173","consensus_level":"high","plddt":89.8261,"start":52,"end":173},{"cath_id":"1.25.40","chopping":"178-307","consensus_level":"medium","plddt":93.2588,"start":178,"end":307},{"cath_id":"2.60.120.820","chopping":"329-480","consensus_level":"high","plddt":93.1637,"start":329,"end":480}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H0C5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H0C5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H0C5-F1-predicted_aligned_error_v6.png","plddt_mean":86.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=BTBD1","jax_strain_url":"https://www.jax.org/strain/search?query=BTBD1"},"sequence":{"accession":"Q9H0C5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H0C5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H0C5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H0C5"}},"corpus_meta":[{"pmid":"33643817","id":"PMC_33643817","title":"Development of small-molecule tropomyosin receptor kinase (TRK) inhibitors for NTRK fusion cancers.","date":"2020","source":"Acta pharmaceutica Sinica. B","url":"https://pubmed.ncbi.nlm.nih.gov/33643817","citation_count":118,"is_preprint":false},{"pmid":"12878161","id":"PMC_12878161","title":"BTBD1 and BTBD2 colocalize to cytoplasmic bodies with the RBCC/tripartite motif protein, TRIM5delta.","date":"2003","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/12878161","citation_count":89,"is_preprint":false},{"pmid":"11818025","id":"PMC_11818025","title":"Characterization of BTBD1 and BTBD2, two similar BTB-domain-containing Kelch-like proteins that interact with Topoisomerase I.","date":"2002","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/11818025","citation_count":43,"is_preprint":false},{"pmid":"15486563","id":"PMC_15486563","title":"The topoisomerase 1-interacting protein BTBD1 is essential for muscle cell differentiation.","date":"2004","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/15486563","citation_count":17,"is_preprint":false},{"pmid":"36490343","id":"PMC_36490343","title":"NEDDylated Cullin 3 mediates the adaptive response to topoisomerase 1 inhibitors.","date":"2022","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/36490343","citation_count":17,"is_preprint":false},{"pmid":"11179693","id":"PMC_11179693","title":"Identification and characterization of BTBD1, a novel BTB domain containing gene on human chromosome 15q24.","date":"2001","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/11179693","citation_count":15,"is_preprint":false},{"pmid":"17462629","id":"PMC_17462629","title":"Involvement of BTBD1 in mesenchymal differentiation.","date":"2007","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/17462629","citation_count":11,"is_preprint":false},{"pmid":"33995494","id":"PMC_33995494","title":"Identification of Hub Genes and MicroRNAs Associated With Idiopathic Pulmonary Arterial Hypertension by Integrated Bioinformatics Analyses.","date":"2021","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33995494","citation_count":11,"is_preprint":false},{"pmid":"35655479","id":"PMC_35655479","title":"Establishment and Verification of a Gene Signature for Diagnosing Type 2 Diabetics by WGCNA, LASSO Analysis, and In Vitro Experiments.","date":"2022","source":"BioMed research international","url":"https://pubmed.ncbi.nlm.nih.gov/35655479","citation_count":6,"is_preprint":false},{"pmid":"32894148","id":"PMC_32894148","title":"A 15q25.2 microdeletion phenotype for premature ovarian failure in a Chinese girl: a case report and review of literature.","date":"2020","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/32894148","citation_count":3,"is_preprint":false},{"pmid":"37290676","id":"PMC_37290676","title":"MiR-200b-5p inhibits tumor progression in salivary adenoid cystic carcinoma via targeting BTBD1.","date":"2023","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/37290676","citation_count":2,"is_preprint":false},{"pmid":"21092135","id":"PMC_21092135","title":"Human TOP1 residues implicated in species specificity of HIV-1 infection are required for interaction with BTBD2, and RNAi of BTBD2 in old world monkey and human cells increases permissiveness to HIV-1 infection.","date":"2010","source":"Virology journal","url":"https://pubmed.ncbi.nlm.nih.gov/21092135","citation_count":2,"is_preprint":false},{"pmid":"16936789","id":"PMC_16936789","title":"Identification and isolation of a BTB-POZ-containing gene expressed in oocytes and early embryos of the zebrafish Danio rerio.","date":"2006","source":"Genome","url":"https://pubmed.ncbi.nlm.nih.gov/16936789","citation_count":2,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8320,"output_tokens":1676,"usd":0.02505,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8500,"output_tokens":2202,"usd":0.048775,"stage2_stop_reason":"end_turn"},"total_usd":0.073825,"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\": 2002,\n      \"finding\": \"BTBD1 physically interacts with the core domain of human topoisomerase I (TOP1); co-precipitation assays confirmed the interaction with 100 kDa TOP1 from HeLa cells, and deletion mapping showed that less than the C-terminal half of BTBD1 is sufficient for binding TOP1.\",\n      \"method\": \"Yeast two-hybrid screening, co-precipitation assay, GST-pulldown with deletion mapping\",\n      \"journal\": \"BMC genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal yeast two-hybrid and co-precipitation with deletion mapping in single lab, two orthogonal methods\",\n      \"pmids\": [\"11818025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"BTBD1 and BTBD2 colocalize to punctate or elongated cytoplasmic bodies in mouse and human cells. TRIM5delta (a RING/B-box/coiled-coil TRIM family member) colocalizes with BTBD1/2 and serves as a scaffold for assembly of endogenous BTBD1/2 proteins; deletion of TRIM5delta's coiled-coil region or mutation of its RING domain abolished colocalization with BTBD1/2.\",\n      \"method\": \"Immunofluorescence colocalization, GFP-fusion expression, deletion/point mutants of TRIM5delta\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct imaging with functional mutants establishing scaffold requirement, single lab\",\n      \"pmids\": [\"12878161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Stable overexpression of an N-terminally truncated BTBD1 (Delta-BTBD1, lacking 108 N-terminal residues) in C2C12 myoblasts inhibited myogenic differentiation and reduced proliferation, while decreasing nuclear TOP1 content and shifting TOP1 localization from peripheral nuclear to diffuse nuclear, indicating BTBD1 is required for myogenic differentiation and regulates nuclear TOP1 localization.\",\n      \"method\": \"Stable overexpression of truncated BTBD1 in C2C12 cells, immunofluorescence/subcellular fractionation of TOP1, differentiation assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function via dominant-negative truncation with defined phenotypic readout (differentiation block, TOP1 relocalization), single lab\",\n      \"pmids\": [\"15486563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"BTBD1 mRNA is upregulated during myogenesis and downregulated during adipogenesis; BTBD1 expression levels are inversely correlated with TOP1 protein (but not TOP1 mRNA) levels across differentiation conditions, suggesting BTBD1 post-translationally regulates TOP1 protein abundance and controls the balance between myogenic and adipogenic differentiation.\",\n      \"method\": \"RT-PCR/northern blot across differentiation models (C2C12, 3T3-L1, hMADS), western blot for TOP1 protein, transcriptome analysis\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — correlative expression data in differentiation models, single lab, no direct mechanistic manipulation of BTBD1\",\n      \"pmids\": [\"17462629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The interaction of BTBD1 and BTBD2 with TOP1 requires human TOP1 residues 236 and 237; substitution of these residues with the African Green Monkey counterparts abolished BTBD1/BTBD2 binding. RNAi knockdown of BTBD2 (but not specifically tested for BTBD1 alone) in AGM and human 293T cells increased permissiveness to HIV-1 infection 2–3 fold.\",\n      \"method\": \"Co-precipitation with TOP1 point mutants, RNAi knockdown, HIV-1 infectivity assay\",\n      \"journal\": \"Virology journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis of TOP1 residues mapped to BTBD1/2 binding interface, combined with RNAi functional assay, single lab\",\n      \"pmids\": [\"21092135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"BTBD1 (and BTBD2) function as substrate adaptor proteins for the CRL3 (Cullin 3 RING ligase) E3 ubiquitin ligase complex, promoting ubiquitination and proteasomal degradation of TOP1-cleavage complexes (TOP1-ccs). NEDDylation of Cullin 3 activates this pathway; inhibition of NEDDylation or depletion of Cullin 3 sensitizes cancer cells to TOP1 inhibitors.\",\n      \"method\": \"Protein complex biochemistry (CUL3-BTBD1/2 E3 ligase), ubiquitination assays, NEDD8 pathway inhibition, siRNA depletion, genomic occupancy analysis of TOP1\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro ubiquitination reconstitution of CUL3-BTBD1/2 complex, combined with NEDDylation perturbation and depletion experiments providing orthogonal mechanistic validation\",\n      \"pmids\": [\"36490343\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"BTBD1 is a substrate adaptor for the CRL3 (Cullin 3/RING) E3 ubiquitin ligase complex that, upon Cullin 3 NEDDylation, promotes ubiquitination and proteasomal degradation of TOP1-cleavage complexes; it also physically interacts with TOP1 (via its C-terminal half, requiring TOP1 residues 236–237), colocalizes with the TRIM5delta scaffold in cytoplasmic bodies, and is required for myogenic differentiation in part by maintaining proper nuclear TOP1 localization.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"BTBD1 is a substrate adaptor for the CRL3 (Cullin 3/RING) E3 ubiquitin ligase complex that controls the abundance of topoisomerase I (TOP1) and its DNA-bound cleavage complexes [#5]. BTBD1 physically binds TOP1 through less than the C-terminal half of the protein, an interaction that depends on TOP1 residues 236 and 237 [#0, #4]. Within the CRL3 complex, BTBD1 promotes ubiquitination and proteasomal degradation of TOP1-cleavage complexes in a manner activated by Cullin 3 NEDDylation, such that blocking NEDDylation or depleting Cullin 3 sensitizes cancer cells to TOP1 inhibitors [#5]. Consistent with this post-translational control of TOP1, BTBD1 maintains proper peripheral nuclear TOP1 localization and is required for myogenic differentiation: a dominant-negative N-terminal truncation reduces nuclear TOP1 content and blocks differentiation [#2]. BTBD1 also assembles with BTBD2 into cytoplasmic bodies organized by the TRIM5delta scaffold [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established the first molecular partner of BTBD1 by showing it binds topoisomerase I, defining the binding determinant within BTBD1.\",\n      \"evidence\": \"Yeast two-hybrid, co-precipitation, and GST-pulldown deletion mapping with HeLa TOP1\",\n      \"pmids\": [\"11818025\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the BTBD1-TOP1 interaction not determined\", \"TOP1 residues required for binding not yet mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the subcellular context of BTBD1 by showing it assembles with BTBD2 into cytoplasmic bodies dependent on a TRIM5delta scaffold.\",\n      \"evidence\": \"Immunofluorescence colocalization with GFP fusions and TRIM5delta deletion/point mutants in mouse and human cells\",\n      \"pmids\": [\"12878161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Biochemical function of the cytoplasmic bodies unknown\", \"Relationship between cytoplasmic localization and nuclear TOP1 regulation unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Connected BTBD1 to a cellular phenotype, showing it is required for myogenic differentiation and governs nuclear TOP1 localization.\",\n      \"evidence\": \"Stable dominant-negative truncated BTBD1 overexpression in C2C12 myoblasts with differentiation assays and TOP1 fractionation/imaging\",\n      \"pmids\": [\"15486563\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking BTBD1 to TOP1 relocalization not established\", \"Truncation may act dominant-negatively rather than reflecting loss of function\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Suggested BTBD1 controls TOP1 at the protein level and balances myogenic versus adipogenic fates.\",\n      \"evidence\": \"Expression profiling across differentiation models with western blot for TOP1 protein versus mRNA\",\n      \"pmids\": [\"17462629\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Correlative only, no direct manipulation of BTBD1\", \"Post-translational mechanism inferred but not demonstrated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapped the TOP1 binding interface to residues 236-237 and linked the BTBD module to host restriction of HIV-1.\",\n      \"evidence\": \"Co-precipitation with TOP1 point mutants plus RNAi knockdown and HIV-1 infectivity assays\",\n      \"pmids\": [\"21092135\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"HIV-1 phenotype tested for BTBD2 but not specifically BTBD1\", \"Mechanistic basis of altered HIV permissiveness unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the biochemical function of BTBD1 as a CRL3 substrate adaptor that targets TOP1-cleavage complexes for NEDDylation-activated ubiquitin-proteasome degradation.\",\n      \"evidence\": \"In vitro CUL3-BTBD1/2 ubiquitination reconstitution, NEDD8 pathway inhibition, siRNA depletion, and TOP1 genomic occupancy analysis\",\n      \"pmids\": [\"36490343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of BTBD1 versus BTBD2 not dissected\", \"Link between this degradation pathway and the myogenic differentiation phenotype not directly tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the cytoplasmic TRIM5delta-organized BTBD1 bodies relate to its nuclear CRL3-mediated TOP1 degradation function remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mechanism connecting cytoplasmic localization to nuclear TOP1 control\", \"Substrate repertoire of CRL3-BTBD1 beyond TOP1-cc unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"CRL3 (Cullin 3 RING ligase)\"],\n    \"partners\": [\"TOP1\", \"CUL3\", \"BTBD2\", \"TRIM5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}