{"gene":"KCTD8","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2011,"finding":"KCTD8 was identified as an auxiliary subunit of GABAB receptors, associating with the principal GABAB1/GABAB2 subunits. KCTD8 generates largely non-desensitizing receptor responses. Individual KCTD proteins exhibit distinct axonal or dendritic localizations in neuronal populations, and most brain GABAB receptors incorporate KCTD proteins.","method":"In situ hybridization, immunohistochemistry, and biochemical fractionation in mouse brain","journal":"The Journal of comparative neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with immunohistochemistry and biochemical data, replicated across multiple neuronal populations, single lab","pmids":["21452234"],"is_preprint":false},{"year":2012,"finding":"The H1 domain of KCTD8 lacks the T/NFLEQ motif required for desensitization (present in KCTD12/12b H1 domains), so KCTD8 generates non-desensitizing GABAB receptor responses. KCTD8 also contains a C-terminal H2 homology domain that sterically inhibits desensitization when expressed C-terminal to the H1 domain. The T1 tetramerization domain of KCTD8 binds to GABAB2, while the H1 and H2 domains regulate desensitization properties.","method":"Domain-swap mutagenesis, chimeric protein expression, electrophysiology in transfected cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of specific sequence motifs combined with electrophysiological functional readout, multiple orthogonal constructs in single study","pmids":["23035119"],"is_preprint":false},{"year":2014,"finding":"KCTD8 (along with KCTD16) slightly but significantly increases GABA affinity at recombinant GABAB receptors. KCTD8 reduces tonic G-protein activation when co-expressed with GABABRs, leading to a larger increase in efficacy upon PAM (GS39783) stimulation relative to receptors without KCTD8. KCTD8 binds the G-protein and differentially regulates G-protein signaling.","method":"[35S]GTPγS binding, BRET between G-protein subunits, Kir3 current recordings in transfected CHO cells and cultured hippocampal neurons","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays (BRET, radioligand binding, electrophysiology), single lab","pmids":["25196734"],"is_preprint":false},{"year":2016,"finding":"KCTD8 can hetero-oligomerize with other KCTD subunits (KCTD12, KCTD16) through self-interacting T1 and H1 homology domains. KCTD homo- and hetero-oligomers form at least tetramers that directly interact with both the GABAB receptor and the G-protein. KCTD8 homo-oligomers generate non-desensitizing slowly deactivating K+ currents, distinguishable from KCTD12 homo-oligomers (strongly desensitizing, fast deactivating) and hetero-oligomeric combinations.","method":"Coimmunoprecipitation in mouse hippocampus, BRET in live cells, electrophysiology in heterologous cells and hippocampal neurons of KCTD knock-out mice","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP in native tissue, live-cell BRET, and electrophysiology in KO mice; multiple orthogonal methods","pmids":["28003345"],"is_preprint":false},{"year":2021,"finding":"KCTD8 directly binds to voltage-gated Ca2+ channel Cav2.3 (R-type) in heterologous cells, independent of GABAB receptor activation. KCTD8 potentiates Cav2.3 currents in the absence of GABAB receptors. In the rostral IPN, KCTD8, KCTD12b, and Cav2.3 co-localize at the presynaptic active zone. Genetic deletion experiments indicate bidirectional modulation of Cav2.3-mediated transmitter release by KCTD8 and KCTD12b, with compensatory upregulation of KCTD8 in active zones of KCTD12b-deficient mice.","method":"Co-immunoprecipitation in heterologous cells, electrophysiology (Cav2.3 current recordings), immunofluorescence co-localization, genetic knockout mouse models","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding shown by Co-IP, functional potentiation by electrophysiology, in vivo localization, and KO rescue experiments, multiple orthogonal methods","pmids":["33913808"],"is_preprint":false},{"year":2022,"finding":"KCTD8 (together with KCTD12) facilitates axonal expression of GABAB receptors in habenula cholinergic neurons, thereby enabling presynaptic excitation via GABAB receptors. Genetic knockout of KCTD8/12 (but not other KCTD combinations) substantially reduced GABAB receptor-mediated potentiation of glutamate release and presynaptic Ca2+ entry. The physiological phenotype was associated with a significant decrease in GABAB receptor expression within axonal terminals but not somata. Overexpressing KCTD8 in triple KCTD knockout mice reversed the reduction in axonal GABAB expression and presynaptic excitation.","method":"Multiple KCTD knockout mouse lines, electrophysiology (glutamate release, presynaptic Ca2+ imaging), immunofluorescence quantification of axonal vs. somatic GABAB expression, viral overexpression rescue experiments, behavioral assays","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple KO lines, rescue by overexpression, orthogonal functional and anatomical readouts, specific to KCTD8/12 vs. other isoforms","pmids":["35017224"],"is_preprint":false},{"year":2023,"finding":"KCTD8 forms hetero-oligomeric complexes with KCTD5, as detected by co-immunoprecipitation and live-cell BRET. Different regions of KCTD5 contribute to interactions with different KCTD family members including KCTD8.","method":"Co-immunoprecipitation in lysed cells, live-cell BRET, IP-luminescence domain-mapping","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, co-IP and BRET without functional consequence established for KCTD8 specifically; KCTD5 is the primary focus","pmids":["37762619"],"is_preprint":false},{"year":2024,"finding":"KCTD8 suppresses hepatocellular carcinoma (HCC) cell growth in vitro and in vivo by inhibiting the PI3K/AKT signaling pathway. KCTD8 expression in HCC is regulated by promoter DNA methylation.","method":"Methylation-specific PCR, flow cytometry, immunoprecipitation, xenograft mouse models in HCC cell lines","journal":"Epigenomics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited mechanistic detail on PI3K/AKT interaction in abstract, no direct binding or catalytic assay described","pmids":["39023358"],"is_preprint":false}],"current_model":"KCTD8 is an auxiliary subunit of GABAB receptors that assembles via its T1 domain onto the GABAB2 subunit, directly contacts the G-protein, and—through its H2 domain sterically antagonizing H1-mediated desensitization—generates non-desensitizing, slowly deactivating Kir3 currents; it can also form hetero-oligomers with other KCTD subunits to diversify receptor kinetics, facilitates axonal trafficking of GABAB receptors in habenula cholinergic neurons to enable presynaptic excitation, and independently binds and potentiates Cav2.3 (R-type Ca2+) channels at presynaptic active zones."},"narrative":{"mechanistic_narrative":"KCTD8 is an auxiliary subunit of GABAB receptors that shapes the kinetics of receptor-evoked signaling in neurons [PMID:21452234]. It assembles via its T1 tetramerization domain onto the principal GABAB2 subunit and additionally binds the associated G-protein, while its H1 and H2 homology domains govern desensitization: KCTD8's H1 lacks the T/NFLEQ desensitization motif found in KCTD12-type subunits, and its C-terminal H2 domain sterically inhibits desensitization, so KCTD8-containing receptors generate largely non-desensitizing, slowly deactivating Kir3 currents [PMID:23035119, PMID:25196734]. KCTD8 forms homo- and hetero-oligomers (with KCTD12 and KCTD16) through self-interacting T1 and H1 domains, and these tetrameric assemblies diversify receptor deactivation and desensitization kinetics [PMID:28003345]. Beyond its GABAB role, KCTD8 directly binds and potentiates the voltage-gated Cav2.3 (R-type) Ca2+ channel independently of GABAB receptor activation, co-localizing with Cav2.3 at presynaptic active zones in the interpeduncular nucleus and bidirectionally modulating transmitter release [PMID:33913808]. In habenula cholinergic neurons, KCTD8 (with KCTD12) facilitates axonal expression of GABAB receptors, enabling GABAB-mediated presynaptic excitation of glutamate release and presynaptic Ca2+ entry [PMID:35017224].","teleology":[{"year":2011,"claim":"Establishing that KCTD8 is a bona fide GABAB receptor auxiliary subunit answered whether KCTD proteins are physiological components of native receptors and how they might shape responses.","evidence":"In situ hybridization, immunohistochemistry, and biochemical fractionation in mouse brain","pmids":["21452234"],"confidence":"Medium","gaps":["Did not resolve which domains mediate receptor binding versus kinetic modulation","Mechanism of non-desensitization left undefined","Single-lab localization data"]},{"year":2012,"claim":"Domain dissection answered how KCTD8 produces non-desensitizing responses, mapping receptor binding to T1 and desensitization control to the H1/H2 domains.","evidence":"Domain-swap mutagenesis, chimeric constructs, and electrophysiology in transfected cells","pmids":["23035119"],"confidence":"High","gaps":["Structural basis of H2-mediated steric inhibition not directly visualized","Behavior in native neuronal contexts not addressed"]},{"year":2014,"claim":"Direct G-protein engagement studies answered how KCTD8 tunes receptor efficacy and agonist affinity beyond desensitization.","evidence":"[35S]GTPγS binding, BRET between G-protein subunits, and Kir3 recordings in CHO cells and hippocampal neurons","pmids":["25196734"],"confidence":"Medium","gaps":["Binding interface on the G-protein not mapped","Single-lab functional data"]},{"year":2016,"claim":"Demonstrating KCTD8 hetero-oligomerization answered how a limited set of KCTD subunits generates a continuum of receptor kinetics.","evidence":"Native co-IP in mouse hippocampus, live-cell BRET, and electrophysiology in KCTD-knockout mice","pmids":["28003345"],"confidence":"High","gaps":["Stoichiometry of mixed oligomers in vivo not quantified","Functional impact of each combination on specific synapses incompletely defined"]},{"year":2021,"claim":"Identifying Cav2.3 as a GABAB-independent partner answered whether KCTD8 has functions outside the GABAB receptor, revealing a presynaptic Ca2+ channel modulatory role.","evidence":"Co-IP in heterologous cells, Cav2.3 current recordings, immunofluorescence co-localization, and knockout mouse models","pmids":["33913808"],"confidence":"High","gaps":["Domain of KCTD8 mediating Cav2.3 binding not mapped","Mechanism of compensatory upregulation unresolved"]},{"year":2022,"claim":"Knockout and rescue experiments answered how KCTD8 contributes to receptor trafficking, showing it drives axonal GABAB expression underlying presynaptic excitation.","evidence":"Multiple KCTD knockout lines, electrophysiology, axonal vs. somatic GABAB quantification, and viral overexpression rescue","pmids":["35017224"],"confidence":"High","gaps":["Molecular machinery linking KCTD8 to axonal trafficking not identified","Whether trafficking role generalizes beyond habenula neurons unknown"]},{"year":2023,"claim":"Interaction mapping tested whether KCTD8 partners with KCTD5, extending the hetero-oligomer network.","evidence":"Co-IP in cell lysates, live-cell BRET, and IP-luminescence domain mapping","pmids":["37762619"],"confidence":"Low","gaps":["No functional consequence established for the KCTD8–KCTD5 interaction","KCTD5 was the primary focus; KCTD8 specificity secondary","Single-lab data"]},{"year":2024,"claim":"A tumor-biology study raised a candidate role for KCTD8 in suppressing hepatocellular carcinoma growth via PI3K/AKT.","evidence":"Methylation-specific PCR, flow cytometry, immunoprecipitation, and xenograft models in HCC cell lines","pmids":["39023358"],"confidence":"Low","gaps":["No direct binding or catalytic mechanism on the PI3K/AKT axis demonstrated","Single-lab finding outside the neuronal context","Connection to KCTD8's auxiliary-subunit biology unclear"]},{"year":null,"claim":"How KCTD8 oligomer stoichiometry, G-protein contacts, and Cav2.3 binding are structurally integrated to encode synapse-specific signaling kinetics remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of KCTD8-containing receptor complexes","Cav2.3-binding interface unmapped","Trafficking mechanism for axonal GABAB delivery undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2,4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,5]}],"complexes":["GABAB receptor auxiliary complex"],"partners":["GABBR2","KCTD12","KCTD16","KCTD5","CACNA1E"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6ZWB6","full_name":"BTB/POZ domain-containing protein KCTD8","aliases":[],"length_aa":473,"mass_kda":52.4,"function":"Auxiliary subunit of GABA-B receptors that determine the pharmacology and kinetics of the receptor response. Increases agonist potency and markedly alter the G-protein signaling of the receptors by accelerating onset and promoting desensitization (By similarity)","subcellular_location":"Presynaptic cell membrane; Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q6ZWB6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCTD8","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCTD8","total_profiled":1310},"omim":[{"mim_id":"618442","title":"POTASSIUM CHANNEL TETRAMERIZATION DOMAIN-CONTAINING PROTEIN 8; KCTD8","url":"https://www.omim.org/entry/618442"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytoplasmic bodies","reliability":"Approved"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":16.9},{"tissue":"retina","ntpm":6.3}],"url":"https://www.proteinatlas.org/search/KCTD8"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q6ZWB6","domains":[{"cath_id":"3.30.710.10","chopping":"44-76_88-145","consensus_level":"high","plddt":89.8984,"start":44,"end":145},{"cath_id":"-","chopping":"206-220_228-320","consensus_level":"high","plddt":90.0219,"start":206,"end":320}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZWB6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZWB6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6ZWB6-F1-predicted_aligned_error_v6.png","plddt_mean":66.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCTD8","jax_strain_url":"https://www.jax.org/strain/search?query=KCTD8"},"sequence":{"accession":"Q6ZWB6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6ZWB6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6ZWB6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6ZWB6"}},"corpus_meta":[{"pmid":"22930747","id":"PMC_22930747","title":"Genome-wide methylation screen in low-grade breast cancer identifies novel epigenetically altered genes as potential biomarkers for tumor diagnosis.","date":"2012","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/22930747","citation_count":77,"is_preprint":false},{"pmid":"21452234","id":"PMC_21452234","title":"Distribution of the auxiliary GABAB receptor subunits KCTD8, 12, 12b, and 16 in the mouse brain.","date":"2011","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/21452234","citation_count":73,"is_preprint":false},{"pmid":"28003345","id":"PMC_28003345","title":"KCTD Hetero-oligomers Confer Unique Kinetic Properties on Hippocampal GABAB Receptor-Induced K+ Currents.","date":"2016","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/28003345","citation_count":48,"is_preprint":false},{"pmid":"23035119","id":"PMC_23035119","title":"Opposite effects of KCTD subunit domains on GABA(B) receptor-mediated desensitization.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23035119","citation_count":47,"is_preprint":false},{"pmid":"25689571","id":"PMC_25689571","title":"Altered emotionality and neuronal excitability in mice lacking KCTD12, an auxiliary subunit of GABAB receptors associated with mood disorders.","date":"2015","source":"Translational psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/25689571","citation_count":43,"is_preprint":false},{"pmid":"23843457","id":"PMC_23843457","title":"Up-regulation of GABA(B) receptor signaling by constitutive assembly with the K+ channel tetramerization domain-containing protein 12 (KCTD12).","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23843457","citation_count":36,"is_preprint":false},{"pmid":"25196734","id":"PMC_25196734","title":"Pharmacological characterization of GABAB receptor subtypes assembled with auxiliary KCTD subunits.","date":"2014","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/25196734","citation_count":31,"is_preprint":false},{"pmid":"22156575","id":"PMC_22156575","title":"KCTD8 gene and brain growth in adverse intrauterine environment: a genome-wide association study.","date":"2011","source":"Cerebral cortex (New York, N.Y. : 1991)","url":"https://pubmed.ncbi.nlm.nih.gov/22156575","citation_count":30,"is_preprint":false},{"pmid":"23937595","id":"PMC_23937595","title":"A genome-wide search for type 2 diabetes susceptibility genes in an extended Arab family.","date":"2013","source":"Annals of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23937595","citation_count":27,"is_preprint":false},{"pmid":"33913808","id":"PMC_33913808","title":"GABAB receptor auxiliary subunits modulate Cav2.3-mediated release from medial habenula terminals.","date":"2021","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/33913808","citation_count":21,"is_preprint":false},{"pmid":"35017224","id":"PMC_35017224","title":"KCTD8 and KCTD12 Facilitate Axonal Expression of GABAB Receptors in Habenula Cholinergic Neurons.","date":"2022","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/35017224","citation_count":12,"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":"37799139","id":"PMC_37799139","title":"Uncovering structural variants associated with body weight and obesity risk in labrador retrievers: a genome-wide study.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37799139","citation_count":4,"is_preprint":false},{"pmid":"39023358","id":"PMC_39023358","title":"Epigenetic silencing of KCTD8 promotes hepatocellular carcinoma growth by activating PI3K/AKT signaling.","date":"2024","source":"Epigenomics","url":"https://pubmed.ncbi.nlm.nih.gov/39023358","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10141,"output_tokens":2411,"usd":0.033294,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9401,"output_tokens":2827,"usd":0.05884,"stage2_stop_reason":"end_turn"},"total_usd":0.092134,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2011,\n      \"finding\": \"KCTD8 was identified as an auxiliary subunit of GABAB receptors, associating with the principal GABAB1/GABAB2 subunits. KCTD8 generates largely non-desensitizing receptor responses. Individual KCTD proteins exhibit distinct axonal or dendritic localizations in neuronal populations, and most brain GABAB receptors incorporate KCTD proteins.\",\n      \"method\": \"In situ hybridization, immunohistochemistry, and biochemical fractionation in mouse brain\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with immunohistochemistry and biochemical data, replicated across multiple neuronal populations, single lab\",\n      \"pmids\": [\"21452234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The H1 domain of KCTD8 lacks the T/NFLEQ motif required for desensitization (present in KCTD12/12b H1 domains), so KCTD8 generates non-desensitizing GABAB receptor responses. KCTD8 also contains a C-terminal H2 homology domain that sterically inhibits desensitization when expressed C-terminal to the H1 domain. The T1 tetramerization domain of KCTD8 binds to GABAB2, while the H1 and H2 domains regulate desensitization properties.\",\n      \"method\": \"Domain-swap mutagenesis, chimeric protein expression, electrophysiology in transfected cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of specific sequence motifs combined with electrophysiological functional readout, multiple orthogonal constructs in single study\",\n      \"pmids\": [\"23035119\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"KCTD8 (along with KCTD16) slightly but significantly increases GABA affinity at recombinant GABAB receptors. KCTD8 reduces tonic G-protein activation when co-expressed with GABABRs, leading to a larger increase in efficacy upon PAM (GS39783) stimulation relative to receptors without KCTD8. KCTD8 binds the G-protein and differentially regulates G-protein signaling.\",\n      \"method\": \"[35S]GTPγS binding, BRET between G-protein subunits, Kir3 current recordings in transfected CHO cells and cultured hippocampal neurons\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays (BRET, radioligand binding, electrophysiology), single lab\",\n      \"pmids\": [\"25196734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KCTD8 can hetero-oligomerize with other KCTD subunits (KCTD12, KCTD16) through self-interacting T1 and H1 homology domains. KCTD homo- and hetero-oligomers form at least tetramers that directly interact with both the GABAB receptor and the G-protein. KCTD8 homo-oligomers generate non-desensitizing slowly deactivating K+ currents, distinguishable from KCTD12 homo-oligomers (strongly desensitizing, fast deactivating) and hetero-oligomeric combinations.\",\n      \"method\": \"Coimmunoprecipitation in mouse hippocampus, BRET in live cells, electrophysiology in heterologous cells and hippocampal neurons of KCTD knock-out mice\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP in native tissue, live-cell BRET, and electrophysiology in KO mice; multiple orthogonal methods\",\n      \"pmids\": [\"28003345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KCTD8 directly binds to voltage-gated Ca2+ channel Cav2.3 (R-type) in heterologous cells, independent of GABAB receptor activation. KCTD8 potentiates Cav2.3 currents in the absence of GABAB receptors. In the rostral IPN, KCTD8, KCTD12b, and Cav2.3 co-localize at the presynaptic active zone. Genetic deletion experiments indicate bidirectional modulation of Cav2.3-mediated transmitter release by KCTD8 and KCTD12b, with compensatory upregulation of KCTD8 in active zones of KCTD12b-deficient mice.\",\n      \"method\": \"Co-immunoprecipitation in heterologous cells, electrophysiology (Cav2.3 current recordings), immunofluorescence co-localization, genetic knockout mouse models\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding shown by Co-IP, functional potentiation by electrophysiology, in vivo localization, and KO rescue experiments, multiple orthogonal methods\",\n      \"pmids\": [\"33913808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KCTD8 (together with KCTD12) facilitates axonal expression of GABAB receptors in habenula cholinergic neurons, thereby enabling presynaptic excitation via GABAB receptors. Genetic knockout of KCTD8/12 (but not other KCTD combinations) substantially reduced GABAB receptor-mediated potentiation of glutamate release and presynaptic Ca2+ entry. The physiological phenotype was associated with a significant decrease in GABAB receptor expression within axonal terminals but not somata. Overexpressing KCTD8 in triple KCTD knockout mice reversed the reduction in axonal GABAB expression and presynaptic excitation.\",\n      \"method\": \"Multiple KCTD knockout mouse lines, electrophysiology (glutamate release, presynaptic Ca2+ imaging), immunofluorescence quantification of axonal vs. somatic GABAB expression, viral overexpression rescue experiments, behavioral assays\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple KO lines, rescue by overexpression, orthogonal functional and anatomical readouts, specific to KCTD8/12 vs. other isoforms\",\n      \"pmids\": [\"35017224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KCTD8 forms hetero-oligomeric complexes with KCTD5, as detected by co-immunoprecipitation and live-cell BRET. Different regions of KCTD5 contribute to interactions with different KCTD family members including KCTD8.\",\n      \"method\": \"Co-immunoprecipitation in lysed cells, live-cell BRET, IP-luminescence domain-mapping\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, co-IP and BRET without functional consequence established for KCTD8 specifically; KCTD5 is the primary focus\",\n      \"pmids\": [\"37762619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KCTD8 suppresses hepatocellular carcinoma (HCC) cell growth in vitro and in vivo by inhibiting the PI3K/AKT signaling pathway. KCTD8 expression in HCC is regulated by promoter DNA methylation.\",\n      \"method\": \"Methylation-specific PCR, flow cytometry, immunoprecipitation, xenograft mouse models in HCC cell lines\",\n      \"journal\": \"Epigenomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited mechanistic detail on PI3K/AKT interaction in abstract, no direct binding or catalytic assay described\",\n      \"pmids\": [\"39023358\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCTD8 is an auxiliary subunit of GABAB receptors that assembles via its T1 domain onto the GABAB2 subunit, directly contacts the G-protein, and—through its H2 domain sterically antagonizing H1-mediated desensitization—generates non-desensitizing, slowly deactivating Kir3 currents; it can also form hetero-oligomers with other KCTD subunits to diversify receptor kinetics, facilitates axonal trafficking of GABAB receptors in habenula cholinergic neurons to enable presynaptic excitation, and independently binds and potentiates Cav2.3 (R-type Ca2+) channels at presynaptic active zones.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCTD8 is an auxiliary subunit of GABAB receptors that shapes the kinetics of receptor-evoked signaling in neurons [#0]. It assembles via its T1 tetramerization domain onto the principal GABAB2 subunit and additionally binds the associated G-protein, while its H1 and H2 homology domains govern desensitization: KCTD8's H1 lacks the T/NFLEQ desensitization motif found in KCTD12-type subunits, and its C-terminal H2 domain sterically inhibits desensitization, so KCTD8-containing receptors generate largely non-desensitizing, slowly deactivating Kir3 currents [#1, #2]. KCTD8 forms homo- and hetero-oligomers (with KCTD12 and KCTD16) through self-interacting T1 and H1 domains, and these tetrameric assemblies diversify receptor deactivation and desensitization kinetics [#3]. Beyond its GABAB role, KCTD8 directly binds and potentiates the voltage-gated Cav2.3 (R-type) Ca2+ channel independently of GABAB receptor activation, co-localizing with Cav2.3 at presynaptic active zones in the interpeduncular nucleus and bidirectionally modulating transmitter release [#4]. In habenula cholinergic neurons, KCTD8 (with KCTD12) facilitates axonal expression of GABAB receptors, enabling GABAB-mediated presynaptic excitation of glutamate release and presynaptic Ca2+ entry [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing that KCTD8 is a bona fide GABAB receptor auxiliary subunit answered whether KCTD proteins are physiological components of native receptors and how they might shape responses.\",\n      \"evidence\": \"In situ hybridization, immunohistochemistry, and biochemical fractionation in mouse brain\",\n      \"pmids\": [\"21452234\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Did not resolve which domains mediate receptor binding versus kinetic modulation\",\n        \"Mechanism of non-desensitization left undefined\",\n        \"Single-lab localization data\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Domain dissection answered how KCTD8 produces non-desensitizing responses, mapping receptor binding to T1 and desensitization control to the H1/H2 domains.\",\n      \"evidence\": \"Domain-swap mutagenesis, chimeric constructs, and electrophysiology in transfected cells\",\n      \"pmids\": [\"23035119\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of H2-mediated steric inhibition not directly visualized\",\n        \"Behavior in native neuronal contexts not addressed\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Direct G-protein engagement studies answered how KCTD8 tunes receptor efficacy and agonist affinity beyond desensitization.\",\n      \"evidence\": \"[35S]GTPγS binding, BRET between G-protein subunits, and Kir3 recordings in CHO cells and hippocampal neurons\",\n      \"pmids\": [\"25196734\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Binding interface on the G-protein not mapped\",\n        \"Single-lab functional data\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating KCTD8 hetero-oligomerization answered how a limited set of KCTD subunits generates a continuum of receptor kinetics.\",\n      \"evidence\": \"Native co-IP in mouse hippocampus, live-cell BRET, and electrophysiology in KCTD-knockout mice\",\n      \"pmids\": [\"28003345\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Stoichiometry of mixed oligomers in vivo not quantified\",\n        \"Functional impact of each combination on specific synapses incompletely defined\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying Cav2.3 as a GABAB-independent partner answered whether KCTD8 has functions outside the GABAB receptor, revealing a presynaptic Ca2+ channel modulatory role.\",\n      \"evidence\": \"Co-IP in heterologous cells, Cav2.3 current recordings, immunofluorescence co-localization, and knockout mouse models\",\n      \"pmids\": [\"33913808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Domain of KCTD8 mediating Cav2.3 binding not mapped\",\n        \"Mechanism of compensatory upregulation unresolved\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Knockout and rescue experiments answered how KCTD8 contributes to receptor trafficking, showing it drives axonal GABAB expression underlying presynaptic excitation.\",\n      \"evidence\": \"Multiple KCTD knockout lines, electrophysiology, axonal vs. somatic GABAB quantification, and viral overexpression rescue\",\n      \"pmids\": [\"35017224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular machinery linking KCTD8 to axonal trafficking not identified\",\n        \"Whether trafficking role generalizes beyond habenula neurons unknown\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Interaction mapping tested whether KCTD8 partners with KCTD5, extending the hetero-oligomer network.\",\n      \"evidence\": \"Co-IP in cell lysates, live-cell BRET, and IP-luminescence domain mapping\",\n      \"pmids\": [\"37762619\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional consequence established for the KCTD8–KCTD5 interaction\",\n        \"KCTD5 was the primary focus; KCTD8 specificity secondary\",\n        \"Single-lab data\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A tumor-biology study raised a candidate role for KCTD8 in suppressing hepatocellular carcinoma growth via PI3K/AKT.\",\n      \"evidence\": \"Methylation-specific PCR, flow cytometry, immunoprecipitation, and xenograft models in HCC cell lines\",\n      \"pmids\": [\"39023358\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct binding or catalytic mechanism on the PI3K/AKT axis demonstrated\",\n        \"Single-lab finding outside the neuronal context\",\n        \"Connection to KCTD8's auxiliary-subunit biology unclear\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How KCTD8 oligomer stoichiometry, G-protein contacts, and Cav2.3 binding are structurally integrated to encode synapse-specific signaling kinetics remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of KCTD8-containing receptor complexes\",\n        \"Cav2.3-binding interface unmapped\",\n        \"Trafficking mechanism for axonal GABAB delivery undefined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"complexes\": [\"GABAB receptor auxiliary complex\"],\n    \"partners\": [\"GABBR2\", \"KCTD12\", \"KCTD16\", \"KCTD5\", \"CACNA1E\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}