{"gene":"KCTD2","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2017,"finding":"KCTD2 acts as a substrate adaptor (BTB domain protein) for Cullin3 E3 ubiquitin ligase, binding Cullin3 and c-Myc to promote c-Myc ubiquitination and proteasomal degradation, thereby suppressing glioma stem cell self-renewal and aerobic glycolysis.","method":"Yeast two-hybrid screening, co-immunoprecipitation, immunofluorescence, shRNA knockdown, in vivo intracranial tumor growth assay, ubiquitination assay","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, functional KD with defined cellular phenotype, ubiquitination assay, in vivo validation","pmids":["28060381"],"is_preprint":false},{"year":2017,"finding":"KCTD2 (mouse ortholog of Drosophila Insomniac) physically associates with Cullin3 ubiquitin ligase complexes, localizes to synapses in neurons, and can functionally substitute for the Drosophila Inc protein in vivo to restore sleep, indicating conservation of its role as a Cul3 adaptor directing ubiquitination of neuronal/synaptic substrates.","method":"Biochemical co-association assays, in vivo rescue experiments in Drosophila inc mutants, neuronal localization imaging, electrophysiology","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemistry, in vivo rescue, imaging, electrophysiology) with functional validation across species","pmids":["28558011"],"is_preprint":false},{"year":2021,"finding":"KCTD2 forms a hetero-oligomeric complex with KCTD5 that acts as a substrate adaptor for a CUL3-RING E3 ubiquitin ligase; the KCTD2-KCTD5 hetero-oligomer recruits Gβγ (both subunits contribute to Gβγ recognition) in response to G-protein activation, and the complex promotes monoubiquitination of lysine-23 within Gβ1/2, regulating downstream GPCR signaling.","method":"Mass spectrometry interactome, co-immunoprecipitation, in vitro ubiquitination assay, siRNA depletion with downstream signaling readouts in HEK-293 cells","journal":"Journal of proteome research","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro ubiquitination assay with site-specific mapping (K23), MS interactome, reciprocal Co-IP, functional depletion experiments","pmids":["34342229"],"is_preprint":false},{"year":2023,"finding":"KCTD2 interacts with Gβγ in a manner dependent on both its BTB domain and C-terminal region; this interaction is agonist-induced in live cells (BRET assay) and blunts Gβγ-mediated sensitization of adenylyl cyclase 5, shaping cAMP signaling downstream of GPCRs.","method":"Live-cell BRET assay, co-immunoprecipitation, C-terminal deletion/mutation mapping, cAMP pathway functional assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — two orthogonal interaction assays (BRET + Co-IP), domain mapping mutagenesis, and functional cAMP signaling readout","pmids":["36736897"],"is_preprint":false},{"year":2021,"finding":"KCTD2, KCTD5, and KCTD17 were identified as potential E3 ligase adaptors mediating proteasomal degradation of HOXC10 in adipocytes; cold and β-adrenergic exposure induces cAMP/PKA-dependent proteasomal degradation of HOXC10, and KCTD2/5/17 were identified as candidate adaptors by shotgun proteomics.","method":"Shotgun proteomics, proteasome inhibitor experiments, PKA inhibitor experiments in cultured adipocytes","journal":"Diabetes","confidence":"Low","confidence_rationale":"Tier 3 — proteomics identification without direct functional validation specific to KCTD2","pmids":["33990396"],"is_preprint":false},{"year":2024,"finding":"Progressive CRISPR knockout of KCTD2, KCTD5, and KCTD17 in HEK293 cells reveals that all three proteins redundantly control cell growth and proliferation; triple knockout causes the most pervasive growth defects and gene expression changes, and KCTD proteins regulate Gβ1 protein levels, with KCTD KO having opposite transcriptional effects on G protein subunit genes compared to GNB1 KO.","method":"CRISPR/Cas9 sequential knockout, cell growth assays, transcriptomic analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — clean CRISPR KO with defined cellular phenotype, but single lab and limited mechanistic depth for KCTD2 specifically","pmids":["38732215"],"is_preprint":false},{"year":2016,"finding":"Biophysical characterization of the Drosophila Inc protein (ortholog of KCTD2/KCTD5/KCTD17) shows it forms a stable two-domain protein that can simultaneously bind Cul3 and dGRASP, suggesting it acts as a ligase adaptor potentially directing dGRASP ubiquitination; SAXS analysis reveals the Inc-Cul3 complex is highly dynamic.","method":"Heterologous protein expression, SAXS, biophysical binding assays (quantified affinity for Cul3 and dGRASP)","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 1 for structural/biophysical characterization, but data are for Drosophila ortholog; direct relevance to KCTD2 is inferred","pmids":["27678190"],"is_preprint":false}],"current_model":"KCTD2 is a BTB-domain-containing substrate adaptor for CUL3-RING E3 ubiquitin ligase complexes that, alone or as a hetero-oligomer with KCTD5, recruits substrates including c-Myc (promoting its degradation to suppress glioma stem cell identity) and Gβγ (promoting monoubiquitination of Gβ1/2 at K23 to modulate GPCR/cAMP signaling); it also localizes to neuronal synapses and participates in an evolutionarily conserved ubiquitination pathway linking synaptic function and sleep regulation."},"narrative":{"teleology":[{"year":2016,"claim":"Structural analysis of the Drosophila ortholog Insomniac established the biophysical framework for understanding how KCTD2-family proteins simultaneously engage Cul3 and substrates such as dGRASP through a two-domain architecture.","evidence":"SAXS, recombinant protein binding assays with quantified affinities for Cul3 and dGRASP using purified Drosophila Inc protein","pmids":["27678190"],"confidence":"Medium","gaps":["Data are from Drosophila ortholog; direct structural characterization of mammalian KCTD2 is lacking","dGRASP ubiquitination was not directly demonstrated","No high-resolution structure of the Inc–Cul3 complex"]},{"year":2017,"claim":"Identification of KCTD2 as a CUL3 adaptor that targets c-Myc for ubiquitin-dependent degradation established its first defined substrate relationship and linked it to glioma stem cell biology.","evidence":"Yeast two-hybrid, reciprocal co-IP, ubiquitination assay, shRNA knockdown phenotypes, and intracranial xenograft tumor growth in mouse models","pmids":["28060381"],"confidence":"High","gaps":["The specific lysine residues on c-Myc targeted for ubiquitination were not mapped","Whether KCTD2-mediated c-Myc degradation operates outside glioma is unknown"]},{"year":2017,"claim":"Cross-species rescue experiments demonstrated that mammalian KCTD2 is a functional ortholog of the Drosophila sleep regulator Insomniac, establishing an evolutionarily conserved role for KCTD2–Cul3 complexes at synapses.","evidence":"In vivo rescue of inc mutant Drosophila sleep phenotype by mouse KCTD2 expression, neuronal synaptic localization imaging, co-association with Cul3","pmids":["28558011"],"confidence":"High","gaps":["The neuronal substrates ubiquitinated by KCTD2 at synapses remain unidentified","Whether KCTD2 regulates sleep in mammals has not been tested"]},{"year":2021,"claim":"Discovery of the KCTD2–KCTD5 hetero-oligomer and its role in monoubiquitinating Gβ1/2 at K23 revealed a second major substrate axis and showed that KCTD2 functions not only as a homo-oligomer but also in mixed assemblies.","evidence":"Mass spectrometry interactome, reciprocal co-IP, in vitro ubiquitination with site-specific K23 mapping, siRNA depletion with downstream cAMP signaling readouts in HEK-293 cells","pmids":["34342229"],"confidence":"High","gaps":["Stoichiometry and structure of the KCTD2–KCTD5 hetero-oligomer are unresolved","In vivo consequences of Gβ1/2 K23 monoubiquitination are not established"]},{"year":2023,"claim":"Domain-mapping and live-cell BRET studies showed that KCTD2 engages Gβγ through both its BTB domain and C-terminal region in an agonist-induced manner, and functionally blunts Gβγ-mediated AC5 sensitization, clarifying how KCTD2 shapes GPCR-cAMP signaling dynamics.","evidence":"Live-cell BRET, co-IP, C-terminal deletion/mutation analysis, cAMP functional assay","pmids":["36736897"],"confidence":"High","gaps":["Whether monoubiquitination is required for the signaling attenuation or whether KCTD2 binding alone suffices is unclear","The role of specific C-terminal residues in substrate discrimination has not been fully defined"]},{"year":2024,"claim":"Sequential CRISPR knockout of KCTD2, KCTD5, and KCTD17 demonstrated functional redundancy among these three paralogs in controlling cell growth and Gβ1 protein levels, explaining why single-gene loss-of-function studies show mild phenotypes.","evidence":"CRISPR/Cas9 sequential KO in HEK293 cells, proliferation assays, transcriptomic profiling","pmids":["38732215"],"confidence":"Medium","gaps":["Individual contributions of KCTD2 versus KCTD5 versus KCTD17 to specific substrates are not deconvoluted","Findings are from a single cell line; in vivo redundancy has not been tested"]},{"year":null,"claim":"The full repertoire of KCTD2 substrates, the structural basis of hetero-oligomer assembly with KCTD5, and whether KCTD2 regulates sleep or synaptic function in mammals remain open questions.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of mammalian KCTD2 alone or in complex with CUL3/substrates","Neuronal substrates at synapses are unidentified","Mammalian sleep regulation by KCTD2 has not been directly tested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,3]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,2]},{"term_id":"GO:0043226","term_label":"organelle","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,2,5]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[1]}],"complexes":["CUL3-KCTD2 E3 ubiquitin ligase complex","KCTD2-KCTD5 hetero-oligomer"],"partners":["CUL3","KCTD5","MYC","GNB1","GNB2","KCTD17"],"other_free_text":[]},"mechanistic_narrative":"KCTD2 is a BTB-domain-containing substrate adaptor for Cullin3-RING E3 ubiquitin ligase complexes that directs ubiquitination of diverse substrates to regulate cell proliferation, GPCR signaling, and neuronal function. It recruits c-Myc for polyubiquitination and proteasomal degradation, thereby suppressing glioma stem cell self-renewal and aerobic glycolysis [PMID:28060381]. KCTD2 also forms hetero-oligomers with KCTD5 to recruit Gβγ subunits in an agonist-dependent manner, promoting monoubiquitination of Gβ1/2 at K23 and attenuating Gβγ-mediated sensitization of adenylyl cyclase 5, thus shaping cAMP signaling downstream of GPCRs [PMID:34342229, PMID:36736897]. KCTD2 localizes to neuronal synapses, functionally substitutes for the Drosophila sleep regulator Insomniac in vivo, and acts redundantly with KCTD5 and KCTD17 to control cell growth and Gβ1 protein levels [PMID:28558011, PMID:38732215]."},"prefetch_data":{"uniprot":{"accession":"Q14681","full_name":"BTB/POZ domain-containing protein KCTD2","aliases":["Potassium channel tetramerization domain-containing protein 2"],"length_aa":263,"mass_kda":28.5,"function":"","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q14681/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCTD2","classification":"Not Classified","n_dependent_lines":47,"n_total_lines":1208,"dependency_fraction":0.03890728476821192},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCTD2","total_profiled":1310},"omim":[{"mim_id":"613422","title":"POTASSIUM CHANNEL TETRAMERIZATION DOMAIN-CONTAINING PROTEIN 2; KCTD2","url":"https://www.omim.org/entry/613422"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":10.0}],"url":"https://www.proteinatlas.org/search/KCTD2"},"hgnc":{"alias_symbol":["KIAA0176"],"prev_symbol":[]},"alphafold":{"accession":"Q14681","domains":[{"cath_id":"3.30.710.10","chopping":"72-178","consensus_level":"high","plddt":89.2339,"start":72,"end":178},{"cath_id":"3.30.70.2000","chopping":"182-218_228-239","consensus_level":"medium","plddt":88.9688,"start":182,"end":239}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14681","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q14681-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q14681-F1-predicted_aligned_error_v6.png","plddt_mean":73.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCTD2","jax_strain_url":"https://www.jax.org/strain/search?query=KCTD2"},"sequence":{"accession":"Q14681","fasta_url":"https://rest.uniprot.org/uniprotkb/Q14681.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q14681/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q14681"}},"corpus_meta":[{"pmid":"23857120","id":"PMC_23857120","title":"ATP5H/KCTD2 locus is associated with Alzheimer's disease risk.","date":"2013","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/23857120","citation_count":57,"is_preprint":false},{"pmid":"26913989","id":"PMC_26913989","title":"Shared genetic contribution to Ischaemic Stroke and Alzheimer's Disease.","date":"2016","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/26913989","citation_count":54,"is_preprint":false},{"pmid":"22011044","id":"PMC_22011044","title":"Overexpression of S100B, TM4SF4, and OLFM4 genes is correlated with liver metastasis in Taiwanese colorectal cancer patients.","date":"2011","source":"DNA and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22011044","citation_count":41,"is_preprint":false},{"pmid":"28558011","id":"PMC_28558011","title":"Conserved properties of Drosophila Insomniac link sleep regulation and synaptic function.","date":"2017","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28558011","citation_count":31,"is_preprint":false},{"pmid":"28060381","id":"PMC_28060381","title":"KCTD2, an adaptor of Cullin3 E3 ubiquitin ligase, suppresses gliomagenesis by destabilizing c-Myc.","date":"2017","source":"Cell death and differentiation","url":"https://pubmed.ncbi.nlm.nih.gov/28060381","citation_count":30,"is_preprint":false},{"pmid":"34342229","id":"PMC_34342229","title":"Human Multisubunit E3 Ubiquitin Ligase Required for Heterotrimeric G-Protein β-Subunit Ubiquitination and Downstream Signaling.","date":"2021","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/34342229","citation_count":22,"is_preprint":false},{"pmid":"36736897","id":"PMC_36736897","title":"Multiple potassium channel tetramerization domain (KCTD) family members interact with Gβγ, with effects on cAMP signaling.","date":"2023","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/36736897","citation_count":20,"is_preprint":false},{"pmid":"33990396","id":"PMC_33990396","title":"HOXC10 Suppresses Browning to Maintain White Adipocyte Identity.","date":"2021","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/33990396","citation_count":11,"is_preprint":false},{"pmid":"37762619","id":"PMC_37762619","title":"KCTD5 Forms Hetero-Oligomeric Complexes with Various Members of the KCTD Protein Family.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37762619","citation_count":11,"is_preprint":false},{"pmid":"20188772","id":"PMC_20188772","title":"Identification of cellular genes critical to recombinant protein production using a Gaussia luciferase-based siRNA screening system.","date":"2010","source":"Journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/20188772","citation_count":10,"is_preprint":false},{"pmid":"27678190","id":"PMC_27678190","title":"Proteins involved in sleep homeostasis: Biophysical characterization of INC and its partners.","date":"2016","source":"Biochimie","url":"https://pubmed.ncbi.nlm.nih.gov/27678190","citation_count":7,"is_preprint":false},{"pmid":"28758108","id":"PMC_28758108","title":"Blood Transcriptional Signatures for Disease Progression in a Rat Model of Osteoarthritis.","date":"2017","source":"International journal of genomics","url":"https://pubmed.ncbi.nlm.nih.gov/28758108","citation_count":5,"is_preprint":false},{"pmid":"40832836","id":"PMC_40832836","title":"Mechanistic Insights Into the Tumor-Driving and Diagnostic Roles of KCTD Family Genes in Ovarian Cancer: An Integrated In Silico and In Vitro Analysis.","date":"2025","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40832836","citation_count":1,"is_preprint":false},{"pmid":"38732215","id":"PMC_38732215","title":"KCTD Proteins Have Redundant Functions in Controlling Cellular Growth.","date":"2024","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38732215","citation_count":1,"is_preprint":false},{"pmid":"41756822","id":"PMC_41756822","title":"EchoVisuALL: From Echocardiography to Gene Discovery.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41756822","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8577,"output_tokens":1912,"usd":0.027206},"stage2":{"model":"claude-opus-4-6","input_tokens":5205,"output_tokens":2197,"usd":0.121425},"total_usd":0.148631,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"KCTD2 acts as a substrate adaptor (BTB domain protein) for Cullin3 E3 ubiquitin ligase, binding Cullin3 and c-Myc to promote c-Myc ubiquitination and proteasomal degradation, thereby suppressing glioma stem cell self-renewal and aerobic glycolysis.\",\n      \"method\": \"Yeast two-hybrid screening, co-immunoprecipitation, immunofluorescence, shRNA knockdown, in vivo intracranial tumor growth assay, ubiquitination assay\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, functional KD with defined cellular phenotype, ubiquitination assay, in vivo validation\",\n      \"pmids\": [\"28060381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"KCTD2 (mouse ortholog of Drosophila Insomniac) physically associates with Cullin3 ubiquitin ligase complexes, localizes to synapses in neurons, and can functionally substitute for the Drosophila Inc protein in vivo to restore sleep, indicating conservation of its role as a Cul3 adaptor directing ubiquitination of neuronal/synaptic substrates.\",\n      \"method\": \"Biochemical co-association assays, in vivo rescue experiments in Drosophila inc mutants, neuronal localization imaging, electrophysiology\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemistry, in vivo rescue, imaging, electrophysiology) with functional validation across species\",\n      \"pmids\": [\"28558011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KCTD2 forms a hetero-oligomeric complex with KCTD5 that acts as a substrate adaptor for a CUL3-RING E3 ubiquitin ligase; the KCTD2-KCTD5 hetero-oligomer recruits Gβγ (both subunits contribute to Gβγ recognition) in response to G-protein activation, and the complex promotes monoubiquitination of lysine-23 within Gβ1/2, regulating downstream GPCR signaling.\",\n      \"method\": \"Mass spectrometry interactome, co-immunoprecipitation, in vitro ubiquitination assay, siRNA depletion with downstream signaling readouts in HEK-293 cells\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro ubiquitination assay with site-specific mapping (K23), MS interactome, reciprocal Co-IP, functional depletion experiments\",\n      \"pmids\": [\"34342229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KCTD2 interacts with Gβγ in a manner dependent on both its BTB domain and C-terminal region; this interaction is agonist-induced in live cells (BRET assay) and blunts Gβγ-mediated sensitization of adenylyl cyclase 5, shaping cAMP signaling downstream of GPCRs.\",\n      \"method\": \"Live-cell BRET assay, co-immunoprecipitation, C-terminal deletion/mutation mapping, cAMP pathway functional assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two orthogonal interaction assays (BRET + Co-IP), domain mapping mutagenesis, and functional cAMP signaling readout\",\n      \"pmids\": [\"36736897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KCTD2, KCTD5, and KCTD17 were identified as potential E3 ligase adaptors mediating proteasomal degradation of HOXC10 in adipocytes; cold and β-adrenergic exposure induces cAMP/PKA-dependent proteasomal degradation of HOXC10, and KCTD2/5/17 were identified as candidate adaptors by shotgun proteomics.\",\n      \"method\": \"Shotgun proteomics, proteasome inhibitor experiments, PKA inhibitor experiments in cultured adipocytes\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — proteomics identification without direct functional validation specific to KCTD2\",\n      \"pmids\": [\"33990396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Progressive CRISPR knockout of KCTD2, KCTD5, and KCTD17 in HEK293 cells reveals that all three proteins redundantly control cell growth and proliferation; triple knockout causes the most pervasive growth defects and gene expression changes, and KCTD proteins regulate Gβ1 protein levels, with KCTD KO having opposite transcriptional effects on G protein subunit genes compared to GNB1 KO.\",\n      \"method\": \"CRISPR/Cas9 sequential knockout, cell growth assays, transcriptomic analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean CRISPR KO with defined cellular phenotype, but single lab and limited mechanistic depth for KCTD2 specifically\",\n      \"pmids\": [\"38732215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Biophysical characterization of the Drosophila Inc protein (ortholog of KCTD2/KCTD5/KCTD17) shows it forms a stable two-domain protein that can simultaneously bind Cul3 and dGRASP, suggesting it acts as a ligase adaptor potentially directing dGRASP ubiquitination; SAXS analysis reveals the Inc-Cul3 complex is highly dynamic.\",\n      \"method\": \"Heterologous protein expression, SAXS, biophysical binding assays (quantified affinity for Cul3 and dGRASP)\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 for structural/biophysical characterization, but data are for Drosophila ortholog; direct relevance to KCTD2 is inferred\",\n      \"pmids\": [\"27678190\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCTD2 is a BTB-domain-containing substrate adaptor for CUL3-RING E3 ubiquitin ligase complexes that, alone or as a hetero-oligomer with KCTD5, recruits substrates including c-Myc (promoting its degradation to suppress glioma stem cell identity) and Gβγ (promoting monoubiquitination of Gβ1/2 at K23 to modulate GPCR/cAMP signaling); it also localizes to neuronal synapses and participates in an evolutionarily conserved ubiquitination pathway linking synaptic function and sleep regulation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KCTD2 is a BTB-domain-containing substrate adaptor for Cullin3-RING E3 ubiquitin ligase complexes that directs ubiquitination of diverse substrates to regulate cell proliferation, GPCR signaling, and neuronal function. It recruits c-Myc for polyubiquitination and proteasomal degradation, thereby suppressing glioma stem cell self-renewal and aerobic glycolysis [PMID:28060381]. KCTD2 also forms hetero-oligomers with KCTD5 to recruit Gβγ subunits in an agonist-dependent manner, promoting monoubiquitination of Gβ1/2 at K23 and attenuating Gβγ-mediated sensitization of adenylyl cyclase 5, thus shaping cAMP signaling downstream of GPCRs [PMID:34342229, PMID:36736897]. KCTD2 localizes to neuronal synapses, functionally substitutes for the Drosophila sleep regulator Insomniac in vivo, and acts redundantly with KCTD5 and KCTD17 to control cell growth and Gβ1 protein levels [PMID:28558011, PMID:38732215].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Structural analysis of the Drosophila ortholog Insomniac established the biophysical framework for understanding how KCTD2-family proteins simultaneously engage Cul3 and substrates such as dGRASP through a two-domain architecture.\",\n      \"evidence\": \"SAXS, recombinant protein binding assays with quantified affinities for Cul3 and dGRASP using purified Drosophila Inc protein\",\n      \"pmids\": [\"27678190\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Data are from Drosophila ortholog; direct structural characterization of mammalian KCTD2 is lacking\",\n        \"dGRASP ubiquitination was not directly demonstrated\",\n        \"No high-resolution structure of the Inc–Cul3 complex\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of KCTD2 as a CUL3 adaptor that targets c-Myc for ubiquitin-dependent degradation established its first defined substrate relationship and linked it to glioma stem cell biology.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal co-IP, ubiquitination assay, shRNA knockdown phenotypes, and intracranial xenograft tumor growth in mouse models\",\n      \"pmids\": [\"28060381\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The specific lysine residues on c-Myc targeted for ubiquitination were not mapped\",\n        \"Whether KCTD2-mediated c-Myc degradation operates outside glioma is unknown\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Cross-species rescue experiments demonstrated that mammalian KCTD2 is a functional ortholog of the Drosophila sleep regulator Insomniac, establishing an evolutionarily conserved role for KCTD2–Cul3 complexes at synapses.\",\n      \"evidence\": \"In vivo rescue of inc mutant Drosophila sleep phenotype by mouse KCTD2 expression, neuronal synaptic localization imaging, co-association with Cul3\",\n      \"pmids\": [\"28558011\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The neuronal substrates ubiquitinated by KCTD2 at synapses remain unidentified\",\n        \"Whether KCTD2 regulates sleep in mammals has not been tested\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery of the KCTD2–KCTD5 hetero-oligomer and its role in monoubiquitinating Gβ1/2 at K23 revealed a second major substrate axis and showed that KCTD2 functions not only as a homo-oligomer but also in mixed assemblies.\",\n      \"evidence\": \"Mass spectrometry interactome, reciprocal co-IP, in vitro ubiquitination with site-specific K23 mapping, siRNA depletion with downstream cAMP signaling readouts in HEK-293 cells\",\n      \"pmids\": [\"34342229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Stoichiometry and structure of the KCTD2–KCTD5 hetero-oligomer are unresolved\",\n        \"In vivo consequences of Gβ1/2 K23 monoubiquitination are not established\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Domain-mapping and live-cell BRET studies showed that KCTD2 engages Gβγ through both its BTB domain and C-terminal region in an agonist-induced manner, and functionally blunts Gβγ-mediated AC5 sensitization, clarifying how KCTD2 shapes GPCR-cAMP signaling dynamics.\",\n      \"evidence\": \"Live-cell BRET, co-IP, C-terminal deletion/mutation analysis, cAMP functional assay\",\n      \"pmids\": [\"36736897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether monoubiquitination is required for the signaling attenuation or whether KCTD2 binding alone suffices is unclear\",\n        \"The role of specific C-terminal residues in substrate discrimination has not been fully defined\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Sequential CRISPR knockout of KCTD2, KCTD5, and KCTD17 demonstrated functional redundancy among these three paralogs in controlling cell growth and Gβ1 protein levels, explaining why single-gene loss-of-function studies show mild phenotypes.\",\n      \"evidence\": \"CRISPR/Cas9 sequential KO in HEK293 cells, proliferation assays, transcriptomic profiling\",\n      \"pmids\": [\"38732215\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Individual contributions of KCTD2 versus KCTD5 versus KCTD17 to specific substrates are not deconvoluted\",\n        \"Findings are from a single cell line; in vivo redundancy has not been tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full repertoire of KCTD2 substrates, the structural basis of hetero-oligomer assembly with KCTD5, and whether KCTD2 regulates sleep or synaptic function in mammals remain open questions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of mammalian KCTD2 alone or in complex with CUL3/substrates\",\n        \"Neuronal substrates at synapses are unidentified\",\n        \"Mammalian sleep regulation by KCTD2 has not been directly tested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0043226\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\n      \"CUL3-KCTD2 E3 ubiquitin ligase complex\",\n      \"KCTD2-KCTD5 hetero-oligomer\"\n    ],\n    \"partners\": [\n      \"CUL3\",\n      \"KCTD5\",\n      \"MYC\",\n      \"GNB1\",\n      \"GNB2\",\n      \"KCTD17\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}