{"gene":"KCNMB1","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":2004,"finding":"The E65K (G352A) gain-of-function mutation in KCNMB1 increases Ca2+ sensitivity of BK channels in vascular smooth muscle without changes in channel kinetics, enhancing negative-feedback on vascular smooth muscle contractility.","method":"Heterologous expression and patch-clamp electrophysiology of wild-type vs. E65K mutant BK channels","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 — in vitro electrophysiology with mutagenesis, replicated across multiple studies","pmids":["15057310"],"is_preprint":false},{"year":2006,"finding":"KCNMB1 (β1 subunit) reduces steady-state surface expression of the BK channel α subunit (hSlo) via an endocytic trafficking mechanism dependent on a C-terminal endocytic signal on β1; β1 colocalizes with endosomal markers and switches hSlo from diffuse to punctate intracellular localization upon coexpression.","method":"Site-directed mutagenesis of endocytic signal, colocalization with endosomal markers, surface expression assays in heterologous expression system","journal":"Neuroscience","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with trafficking/localization assays and functional surface expression measurements","pmids":["16908104"],"is_preprint":false},{"year":2008,"finding":"The R140W (C818T) variant of KCNMB1 significantly reduces BK channel openings as measured by patch-clamp electrophysiology, consistent with loss-of-function leading to reduced airway smooth muscle relaxation and worse asthma in African American males.","method":"Patch-clamp electrophysiology of BK channels coexpressed with wild-type or 140Trp β1 variant","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro electrophysiology comparing wild-type and mutant subunit","pmids":["18535015"],"is_preprint":false},{"year":2009,"finding":"KCNMB1 (β1 subunit) is a direct transcriptional target of serum response factor (SRF) and myocardin (MYOCD) via two conserved CArG elements in the proximal promoter and first intron; SRF binds these CArG elements and MYOCD transactivates the KCNMB1 promoter in a CArG-dependent manner in smooth muscle cells.","method":"Gel shift assay, chromatin immunoprecipitation (ChIP), luciferase reporter assay with CArG element mutagenesis, in vivo promoter activity analysis, SRF knockdown, forced MYOCD expression with functional BK current measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including ChIP, mutagenesis, reporter assay, and functional electrophysiology","pmids":["19801679"],"is_preprint":false},{"year":2009,"finding":"KCNMB1 is expressed in the renal connecting tubule (CNT) where it associates with BK channels to facilitate K+ secretion; loss of KCNMB1 (Kcnmb1-/-) causes potassium retention, hyperkalemia, aldosteronism, and volume-expanded hypertension correctable by mineralocorticoid receptor antagonism.","method":"Kcnmb1 knockout mouse model with urinary electrolyte measurements, blood pressure monitoring, eplerenone treatment, and plasma aldosterone measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple physiological readouts and pharmacological rescue","pmids":["19556540"],"is_preprint":false},{"year":2005,"finding":"The E65K polymorphism in KCNMB1 confers protection against diastolic hypertension particularly in aging women, and estrogen modulation of BK channel activity was assessed by heterologous expression and electrophysiology showing the protective effect is independent of acute estrogen modulation of BK channels.","method":"Heterologous expression and electrophysiology of wild-type and E65K channels with estrogen, combined with population genetic analysis","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology with direct channel assessment, but mechanistic conclusion is partially inferential","pmids":["16293791"],"is_preprint":false},{"year":2011,"finding":"HIF-1α directly binds to two adjacent hypoxia response elements (HREs) located between -3,540 and -3,311 bp of the KCNMB1 promoter and recruits the coactivator p300 to drive KCNMB1 transcription in response to hypoxia; KCNMB1 knockdown potentiates hypoxia-induced cytosolic calcium increases in pulmonary artery smooth muscle cells.","method":"ChIP, site-directed mutagenesis of HREs in promoter reporter assays, shRNA knockdown of HIF-1α, HDAC inhibitor treatment, calcium imaging","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP combined with mutagenesis of HREs and functional calcium readout, multiple orthogonal methods","pmids":["22114151"],"is_preprint":false},{"year":2015,"finding":"7-Ketocholesterol (7K) reduces KCNMB1 protein levels in vascular smooth muscle cells through the aryl hydrocarbon receptor (AhR) pathway, linking atherogenic lipids to BK channel downregulation.","method":"Western blotting, immunofluorescence in VSMCs and ApoE-KO mouse vessels, AhR protein level analysis with 7K treatment","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, protein level measurements with pathway identification but limited mechanistic depth","pmids":["25576871"],"is_preprint":false},{"year":2020,"finding":"KCNMB1 knockdown attenuates fibroblast collagen gel contraction and α-smooth muscle actin (α-SMA) expression; pharmacological BK channel activation stimulates α-SMA expression via intracellular calcium elevation, identifying KCNMB1/BK channels as regulators of myofibroblast differentiation.","method":"KCNMB1 siRNA knockdown, collagen gel contraction assay, pharmacological BK channel activation/inhibition, intracellular calcium measurements, patch-clamp electrophysiology","journal":"American journal of respiratory cell and molecular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic KD plus pharmacology with multiple functional readouts and calcium mechanistic link","pmids":["31486669"],"is_preprint":false},{"year":2021,"finding":"Cholesterol (CLR) enrichment activates BK channels in smooth muscle cells by increasing plasmalemmal KCNMB1 protein levels via intracellular trafficking; blocking protein trafficking with brefeldin A (BFA) prevents the CLR-induced increase in membrane KCNMB1 and abolishes BK activation. CLR enrichment fails to activate BK in KCNMB1-/- myocytes.","method":"Inside-out patch-clamp from cerebral artery myocytes, brefeldin A trafficking block, surface protein biotinylation followed by Western blotting, KCNMB1-/- mouse comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including electrophysiology, biochemical surface labeling, trafficking inhibition, and genetic KO","pmids":["33556372"],"is_preprint":false},{"year":2023,"finding":"KCNMB1 proteins regulate BK channel function in cerebral artery smooth muscle and modulate interspecies and regional variability of alcohol-induced arterial constriction; overexpression of KCNMB1 via electroporation confirms its role in vasodilation and alcohol response.","method":"BK channel pharmacological block in de-endothelialized arteries, immunofluorescence, electroporation-mediated KCNMB1 overexpression in mouse arteries","journal":"American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological and gain-of-function overexpression approaches with functional vascular readouts","pmids":["36717168"],"is_preprint":false},{"year":2025,"finding":"KCNMB1 knockdown in rat aortic VSMCs causes a dynamic phenotypic switch: at 24h, cells shift from contractile (long spindle) to proliferative/migratory (polygon) morphology with decreased contractile markers and increased proliferative markers; at 72h, VSMC apoptosis significantly increases.","method":"siRNA knockdown of KCNMB1 in primary rat aortic VSMCs, morphology analysis, scratch assay, TUNEL staining, Western blotting for phenotypic markers","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined time-course phenotypic readouts and marker analysis","pmids":["40653026"],"is_preprint":false}],"current_model":"KCNMB1 encodes the β1 regulatory subunit of large-conductance Ca2+/voltage-activated BK potassium channels, where it increases Ca2+ sensitivity and surface expression of the channel-forming α subunit (via endocytic trafficking), is transcriptionally controlled by the SRF/myocardin axis and HIF-1α in smooth muscle cells, and regulates vascular tone, renal K+ secretion, myofibroblast differentiation, and VSMC phenotypic plasticity—with gain-of-function variants (E65K) conferring protection against hypertension and loss-of-function variants impairing smooth muscle relaxation."},"narrative":{"teleology":[{"year":2004,"claim":"The question of whether human KCNMB1 coding variants alter BK channel function was answered by demonstrating that the E65K gain-of-function polymorphism increases Ca2+ sensitivity without changing kinetics, establishing a molecular basis for genetically variable vascular smooth muscle relaxation.","evidence":"Heterologous expression of wild-type vs. E65K mutant BK channels with patch-clamp electrophysiology","pmids":["15057310"],"confidence":"High","gaps":["Structural basis for how E65K increases Ca2+ sensitivity is unknown","Whether E65K alters trafficking or only gating was not tested"]},{"year":2005,"claim":"Building on the E65K functional characterization, population-level analysis linked this variant to protection against diastolic hypertension in aging women, connecting in vitro BK channel gain-of-function to a cardiovascular phenotype.","evidence":"Electrophysiology of wild-type and E65K channels with estrogen treatment, combined with population genetic analysis","pmids":["16293791"],"confidence":"Medium","gaps":["Mechanistic link between E65K and sex-specific protection is inferential","No in vivo model tested","Population association does not establish causation alone"]},{"year":2006,"claim":"It was unknown how the β1 subunit controls BK channel surface availability; this study showed that KCNMB1 reduces steady-state surface expression of the α subunit via a C-terminal endocytic signal, establishing β1 as a trafficking regulator that directs channels to endosomes.","evidence":"Site-directed mutagenesis of endocytic signal, colocalization with endosomal markers, surface expression assays in heterologous cells","pmids":["16908104"],"confidence":"High","gaps":["The endocytic adaptor that recognizes the C-terminal signal was not identified","Relevance of this mechanism in native smooth muscle was not demonstrated at this time"]},{"year":2008,"claim":"To test whether loss-of-function KCNMB1 variants exist, the R140W variant was shown to significantly reduce BK channel openings, providing a mechanistic explanation for impaired airway smooth muscle relaxation.","evidence":"Patch-clamp electrophysiology of BK channels coexpressed with wild-type or R140W β1","pmids":["18535015"],"confidence":"High","gaps":["Structural mechanism of R140W-induced loss of function not determined","In vivo airway phenotype not directly demonstrated in animal model"]},{"year":2009,"claim":"Two key questions—what transcription factors drive smooth-muscle-specific KCNMB1 expression and what renal function β1 serves—were resolved: SRF/myocardin transactivates KCNMB1 via CArG elements, and renal β1 facilitates K⁺ secretion, with its loss causing hyperkalemia and hypertension.","evidence":"ChIP, luciferase reporter mutagenesis, and SRF knockdown in smooth muscle cells (transcriptional regulation); Kcnmb1 knockout mouse with electrolyte, blood pressure, and aldosterone measurements plus eplerenone rescue (renal function)","pmids":["19801679","19556540"],"confidence":"High","gaps":["Whether SRF/myocardin regulation operates in renal connecting tubule specifically was not tested","Compensation by other β subunits in the knockout was not assessed"]},{"year":2011,"claim":"It was unknown how hypoxia regulates KCNMB1; HIF-1α was shown to directly bind HREs in the KCNMB1 promoter and recruit p300 to drive transcription in pulmonary artery smooth muscle cells, with KCNMB1 knockdown potentiating hypoxia-induced calcium overload.","evidence":"ChIP for HIF-1α and p300, HRE mutagenesis in reporter assays, shRNA knockdown of HIF-1α, calcium imaging in pulmonary artery smooth muscle cells","pmids":["22114151"],"confidence":"High","gaps":["Whether HIF-1α-driven KCNMB1 upregulation is protective or pathogenic in pulmonary hypertension was not resolved","Interplay between HIF-1α and SRF/myocardin pathways at the KCNMB1 locus was not examined"]},{"year":2020,"claim":"Whether KCNMB1/BK channels influence fibroblast-to-myofibroblast differentiation was unknown; KCNMB1 knockdown attenuated collagen gel contraction and α-SMA expression, while pharmacological BK activation promoted differentiation via intracellular calcium elevation, establishing a non-vascular role for β1.","evidence":"siRNA knockdown, collagen gel contraction assay, pharmacological BK activation/inhibition, intracellular calcium measurements, patch-clamp electrophysiology in fibroblasts","pmids":["31486669"],"confidence":"High","gaps":["In vivo fibrosis relevance not tested","Which specific calcium signaling pathway downstream of BK drives α-SMA expression was not identified"]},{"year":2021,"claim":"The mechanism by which cholesterol modulates BK channels was clarified: cholesterol enrichment promotes intracellular-to-plasma-membrane trafficking of KCNMB1, and blocking trafficking with brefeldin A or deleting KCNMB1 abolishes cholesterol-induced BK activation, establishing β1 trafficking as the lipid-sensitive step.","evidence":"Inside-out patch-clamp from cerebral artery myocytes, brefeldin A trafficking block, surface biotinylation, KCNMB1-/- mouse comparison","pmids":["33556372"],"confidence":"High","gaps":["The cholesterol-sensing element on β1 or its trafficking machinery is unknown","Whether this mechanism operates in non-cerebral vascular beds was not tested"]},{"year":2025,"claim":"KCNMB1 knockdown was shown to trigger a time-dependent phenotypic switch in VSMCs—from contractile to proliferative/migratory at 24h, progressing to apoptosis at 72h—establishing β1 as a gatekeeper of smooth muscle cell identity and survival.","evidence":"siRNA knockdown in primary rat aortic VSMCs with morphology analysis, scratch assay, TUNEL staining, and Western blotting for phenotypic markers at defined time points","pmids":["40653026"],"confidence":"Medium","gaps":["Whether the phenotypic switch is mediated by altered BK channel activity or a channel-independent β1 function is not distinguished","In vivo vascular remodeling phenotype upon KCNMB1 loss in adult animals not demonstrated","Single study without independent replication"]},{"year":null,"claim":"Major open questions include the structural basis for β1-mediated Ca2+ sensitivity enhancement, the identity of the endocytic adaptor recognizing the β1 C-terminal signal, and whether β1 has channel-independent signaling roles in VSMC phenotypic switching and fibrosis.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of α/β1 complex showing Ca2+-sensitivity mechanism","Endocytic adaptor and cholesterol-sensing mechanism unidentified","Channel-independent versus channel-dependent effects in VSMC phenotype switching not resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2,9]},{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2,4]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,9,10]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,9]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,2,4,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,8,9]}],"complexes":["BK channel (Slo1/β1 complex)"],"partners":["KCNMA1","SRF","MYOCD","HIF1A"],"other_free_text":[]},"mechanistic_narrative":"KCNMB1 encodes the β1 regulatory subunit of large-conductance calcium- and voltage-activated BK potassium channels, functioning as a critical modulator of channel calcium sensitivity, surface trafficking, and smooth muscle physiology. The β1 subunit increases BK channel Ca2+ sensitivity in vascular smooth muscle, thereby enhancing negative feedback on contractility, and regulates channel surface density through an endocytic trafficking mechanism dependent on a C-terminal signal; cholesterol enrichment activates BK channels by promoting β1 translocation to the plasma membrane [PMID:15057310, PMID:16908104, PMID:33556372]. KCNMB1 transcription is driven by the SRF/myocardin axis via CArG elements and by HIF-1α via hypoxia response elements, coupling channel expression to smooth muscle differentiation programs and oxygen sensing [PMID:19801679, PMID:22114151]. Beyond vascular tone, KCNMB1 facilitates renal K⁺ secretion in the connecting tubule—its deletion causes hyperkalemia and volume-expanded hypertension—and regulates myofibroblast differentiation and VSMC phenotypic switching [PMID:19556540, PMID:31486669, PMID:40653026]."},"prefetch_data":{"uniprot":{"accession":"Q16558","full_name":"Calcium-activated potassium channel subunit beta-1","aliases":["BK channel subunit beta-1","BKbeta","BKbeta1","Hbeta1","Calcium-activated potassium channel, subfamily M subunit beta-1","Calcium-activated potassium channel subunit beta","Charybdotoxin receptor subunit beta-1","K(VCA)beta-1","Maxi K channel subunit beta-1","Slo-beta-1","Slo-beta"],"length_aa":191,"mass_kda":21.8,"function":"Regulatory subunit of the calcium activated potassium KCNMA1 (maxiK) channel. Modulates the calcium sensitivity and gating kinetics of KCNMA1, thereby contributing to KCNMA1 channel diversity. Increases the apparent Ca(2+)/voltage sensitivity of the KCNMA1 channel. It also modifies KCNMA1 channel kinetics and alters its pharmacological properties. It slows down the activation and the deactivation kinetics of the channel. Acts as a negative regulator of smooth muscle contraction by enhancing the calcium sensitivity to KCNMA1. Its presence is also a requirement for internal binding of the KCNMA1 channel opener dehydrosoyasaponin I (DHS-1) triterpene glycoside and for external binding of the agonist hormone 17-beta-estradiol (E2). Increases the binding activity of charybdotoxin (CTX) toxin to KCNMA1 peptide blocker by increasing the CTX association rate and decreasing the dissociation rate","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q16558/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNMB1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNMB1","total_profiled":1310},"omim":[{"mim_id":"613505","title":"LEUCINE-RICH REPEAT-CONTAINING PROTEIN 26; LRRC26","url":"https://www.omim.org/entry/613505"},{"mim_id":"608622","title":"HYPERTENSION, DIASTOLIC, RESISTANCE TO","url":"https://www.omim.org/entry/608622"},{"mim_id":"605223","title":"POTASSIUM CHANNEL, CALCIUM-ACTIVATED, LARGE CONDUCTANCE, SUBFAMILY M, BETA MEMBER 4; KCNMB4","url":"https://www.omim.org/entry/605223"},{"mim_id":"605222","title":"POTASSIUM CHANNEL, CALCIUM-ACTIVATED, LARGE CONDUCTANCE, SUBFAMILY M, BETA MEMBER 3; KCNMB3","url":"https://www.omim.org/entry/605222"},{"mim_id":"605214","title":"POTASSIUM CHANNEL, CALCIUM-ACTIVATED, LARGE CONDUCTANCE, SUBFAMILY M, BETA MEMBER 2; KCNMB2","url":"https://www.omim.org/entry/605214"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"blood vessel","ntpm":70.3},{"tissue":"intestine","ntpm":76.1}],"url":"https://www.proteinatlas.org/search/KCNMB1"},"hgnc":{"alias_symbol":["hslo-beta"],"prev_symbol":[]},"alphafold":{"accession":"Q16558","domains":[{"cath_id":"-","chopping":"50-152","consensus_level":"high","plddt":79.7689,"start":50,"end":152}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16558","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16558-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16558-F1-predicted_aligned_error_v6.png","plddt_mean":84.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNMB1","jax_strain_url":"https://www.jax.org/strain/search?query=KCNMB1"},"sequence":{"accession":"Q16558","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16558.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16558/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16558"}},"corpus_meta":[{"pmid":"15057310","id":"PMC_15057310","title":"Gain-of-function mutation in the KCNMB1 potassium channel subunit is associated with low prevalence of diastolic hypertension.","date":"2004","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/15057310","citation_count":154,"is_preprint":false},{"pmid":"19556540","id":"PMC_19556540","title":"Hypertension of Kcnmb1-/- is linked to deficient K secretion and aldosteronism.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19556540","citation_count":88,"is_preprint":false},{"pmid":"16293791","id":"PMC_16293791","title":"Protective effect of the KCNMB1 E65K genetic polymorphism against diastolic hypertension in aging women and its relevance to cardiovascular risk.","date":"2005","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/16293791","citation_count":65,"is_preprint":false},{"pmid":"19801679","id":"PMC_19801679","title":"The smooth muscle cell-restricted KCNMB1 ion channel subunit is a direct transcriptional target of serum response factor and myocardin.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19801679","citation_count":63,"is_preprint":false},{"pmid":"16908104","id":"PMC_16908104","title":"KCNMB1 regulates surface expression of a voltage and Ca2+-activated K+ channel via endocytic trafficking signals.","date":"2006","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/16908104","citation_count":60,"is_preprint":false},{"pmid":"18535015","id":"PMC_18535015","title":"An african-specific functional polymorphism in KCNMB1 shows sex-specific association with asthma severity.","date":"2008","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18535015","citation_count":59,"is_preprint":false},{"pmid":"17700361","id":"PMC_17700361","title":"KCNMB1 genotype influences response to verapamil SR and adverse outcomes in the INternational VErapamil SR/Trandolapril STudy (INVEST).","date":"2007","source":"Pharmacogenetics and genomics","url":"https://pubmed.ncbi.nlm.nih.gov/17700361","citation_count":53,"is_preprint":false},{"pmid":"31486669","id":"PMC_31486669","title":"The Role of KCNMB1 and BK Channels in Myofibroblast Differentiation and Pulmonary Fibrosis.","date":"2020","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/31486669","citation_count":33,"is_preprint":false},{"pmid":"22114151","id":"PMC_22114151","title":"Hypoxia-inducible factor-1α regulates KCNMB1 expression in human pulmonary artery smooth muscle cells.","date":"2011","source":"American journal of physiology. Lung cellular and molecular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/22114151","citation_count":30,"is_preprint":false},{"pmid":"18418400","id":"PMC_18418400","title":"The protective effect of KCNMB1 E65K against hypertension is restricted to blood pressure treatment with beta-blockade.","date":"2008","source":"Journal of human hypertension","url":"https://pubmed.ncbi.nlm.nih.gov/18418400","citation_count":20,"is_preprint":false},{"pmid":"33556372","id":"PMC_33556372","title":"Cholesterol activates BK channels by increasing KCNMB1 protein levels in the plasmalemma.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/33556372","citation_count":16,"is_preprint":false},{"pmid":"25576871","id":"PMC_25576871","title":"7-Ketocholesterol induces the reduction of KCNMB1 in atherosclerotic blood vessels.","date":"2015","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/25576871","citation_count":11,"is_preprint":false},{"pmid":"20861615","id":"PMC_20861615","title":"Common charge-shift mutation Glu65Lys in K+ channel β₁-Subunit KCNMB1: pleiotropic consequences for glomerular filtration rate and progressive renal disease.","date":"2010","source":"American journal of nephrology","url":"https://pubmed.ncbi.nlm.nih.gov/20861615","citation_count":11,"is_preprint":false},{"pmid":"36717168","id":"PMC_36717168","title":"Interspecies and regional variability of alcohol action on large cerebral arteries: regulation by KCNMB1 proteins.","date":"2023","source":"American journal of physiology. Regulatory, integrative and comparative physiology","url":"https://pubmed.ncbi.nlm.nih.gov/36717168","citation_count":8,"is_preprint":false},{"pmid":"34447465","id":"PMC_34447465","title":"Fumaric acid and succinic acid treat gestational hypertension by downregulating the expression of KCNMB1 and TET1.","date":"2021","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34447465","citation_count":7,"is_preprint":false},{"pmid":"16155733","id":"PMC_16155733","title":"E65 K polymorphism in KCNMB1 gene is not associated with ischaemic heart disease in Spanish patients.","date":"2005","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16155733","citation_count":3,"is_preprint":false},{"pmid":"40653026","id":"PMC_40653026","title":"Reduced expression of KCNMB1 leads to vascular smooth muscle cell phenotypic switch and apoptosis.","date":"2025","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/40653026","citation_count":2,"is_preprint":false},{"pmid":"41648137","id":"PMC_41648137","title":"Ionic Regulation of Mechanosurveillance and Metastasis via the MRTFA/KCNMB1 Axis.","date":"2026","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41648137","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.01.673553","title":"β2 and β3a regulatory subunits can coassemble in the same BK channels","date":"2025-09-04","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.01.673553","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11376,"output_tokens":2892,"usd":0.038754},"stage2":{"model":"claude-opus-4-6","input_tokens":6295,"output_tokens":2675,"usd":0.147525},"total_usd":0.186279,"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\": 2004,\n      \"finding\": \"The E65K (G352A) gain-of-function mutation in KCNMB1 increases Ca2+ sensitivity of BK channels in vascular smooth muscle without changes in channel kinetics, enhancing negative-feedback on vascular smooth muscle contractility.\",\n      \"method\": \"Heterologous expression and patch-clamp electrophysiology of wild-type vs. E65K mutant BK channels\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro electrophysiology with mutagenesis, replicated across multiple studies\",\n      \"pmids\": [\"15057310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"KCNMB1 (β1 subunit) reduces steady-state surface expression of the BK channel α subunit (hSlo) via an endocytic trafficking mechanism dependent on a C-terminal endocytic signal on β1; β1 colocalizes with endosomal markers and switches hSlo from diffuse to punctate intracellular localization upon coexpression.\",\n      \"method\": \"Site-directed mutagenesis of endocytic signal, colocalization with endosomal markers, surface expression assays in heterologous expression system\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with trafficking/localization assays and functional surface expression measurements\",\n      \"pmids\": [\"16908104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The R140W (C818T) variant of KCNMB1 significantly reduces BK channel openings as measured by patch-clamp electrophysiology, consistent with loss-of-function leading to reduced airway smooth muscle relaxation and worse asthma in African American males.\",\n      \"method\": \"Patch-clamp electrophysiology of BK channels coexpressed with wild-type or 140Trp β1 variant\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro electrophysiology comparing wild-type and mutant subunit\",\n      \"pmids\": [\"18535015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KCNMB1 (β1 subunit) is a direct transcriptional target of serum response factor (SRF) and myocardin (MYOCD) via two conserved CArG elements in the proximal promoter and first intron; SRF binds these CArG elements and MYOCD transactivates the KCNMB1 promoter in a CArG-dependent manner in smooth muscle cells.\",\n      \"method\": \"Gel shift assay, chromatin immunoprecipitation (ChIP), luciferase reporter assay with CArG element mutagenesis, in vivo promoter activity analysis, SRF knockdown, forced MYOCD expression with functional BK current measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including ChIP, mutagenesis, reporter assay, and functional electrophysiology\",\n      \"pmids\": [\"19801679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KCNMB1 is expressed in the renal connecting tubule (CNT) where it associates with BK channels to facilitate K+ secretion; loss of KCNMB1 (Kcnmb1-/-) causes potassium retention, hyperkalemia, aldosteronism, and volume-expanded hypertension correctable by mineralocorticoid receptor antagonism.\",\n      \"method\": \"Kcnmb1 knockout mouse model with urinary electrolyte measurements, blood pressure monitoring, eplerenone treatment, and plasma aldosterone measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple physiological readouts and pharmacological rescue\",\n      \"pmids\": [\"19556540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The E65K polymorphism in KCNMB1 confers protection against diastolic hypertension particularly in aging women, and estrogen modulation of BK channel activity was assessed by heterologous expression and electrophysiology showing the protective effect is independent of acute estrogen modulation of BK channels.\",\n      \"method\": \"Heterologous expression and electrophysiology of wild-type and E65K channels with estrogen, combined with population genetic analysis\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology with direct channel assessment, but mechanistic conclusion is partially inferential\",\n      \"pmids\": [\"16293791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"HIF-1α directly binds to two adjacent hypoxia response elements (HREs) located between -3,540 and -3,311 bp of the KCNMB1 promoter and recruits the coactivator p300 to drive KCNMB1 transcription in response to hypoxia; KCNMB1 knockdown potentiates hypoxia-induced cytosolic calcium increases in pulmonary artery smooth muscle cells.\",\n      \"method\": \"ChIP, site-directed mutagenesis of HREs in promoter reporter assays, shRNA knockdown of HIF-1α, HDAC inhibitor treatment, calcium imaging\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP combined with mutagenesis of HREs and functional calcium readout, multiple orthogonal methods\",\n      \"pmids\": [\"22114151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"7-Ketocholesterol (7K) reduces KCNMB1 protein levels in vascular smooth muscle cells through the aryl hydrocarbon receptor (AhR) pathway, linking atherogenic lipids to BK channel downregulation.\",\n      \"method\": \"Western blotting, immunofluorescence in VSMCs and ApoE-KO mouse vessels, AhR protein level analysis with 7K treatment\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, protein level measurements with pathway identification but limited mechanistic depth\",\n      \"pmids\": [\"25576871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KCNMB1 knockdown attenuates fibroblast collagen gel contraction and α-smooth muscle actin (α-SMA) expression; pharmacological BK channel activation stimulates α-SMA expression via intracellular calcium elevation, identifying KCNMB1/BK channels as regulators of myofibroblast differentiation.\",\n      \"method\": \"KCNMB1 siRNA knockdown, collagen gel contraction assay, pharmacological BK channel activation/inhibition, intracellular calcium measurements, patch-clamp electrophysiology\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD plus pharmacology with multiple functional readouts and calcium mechanistic link\",\n      \"pmids\": [\"31486669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cholesterol (CLR) enrichment activates BK channels in smooth muscle cells by increasing plasmalemmal KCNMB1 protein levels via intracellular trafficking; blocking protein trafficking with brefeldin A (BFA) prevents the CLR-induced increase in membrane KCNMB1 and abolishes BK activation. CLR enrichment fails to activate BK in KCNMB1-/- myocytes.\",\n      \"method\": \"Inside-out patch-clamp from cerebral artery myocytes, brefeldin A trafficking block, surface protein biotinylation followed by Western blotting, KCNMB1-/- mouse comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including electrophysiology, biochemical surface labeling, trafficking inhibition, and genetic KO\",\n      \"pmids\": [\"33556372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KCNMB1 proteins regulate BK channel function in cerebral artery smooth muscle and modulate interspecies and regional variability of alcohol-induced arterial constriction; overexpression of KCNMB1 via electroporation confirms its role in vasodilation and alcohol response.\",\n      \"method\": \"BK channel pharmacological block in de-endothelialized arteries, immunofluorescence, electroporation-mediated KCNMB1 overexpression in mouse arteries\",\n      \"journal\": \"American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological and gain-of-function overexpression approaches with functional vascular readouts\",\n      \"pmids\": [\"36717168\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KCNMB1 knockdown in rat aortic VSMCs causes a dynamic phenotypic switch: at 24h, cells shift from contractile (long spindle) to proliferative/migratory (polygon) morphology with decreased contractile markers and increased proliferative markers; at 72h, VSMC apoptosis significantly increases.\",\n      \"method\": \"siRNA knockdown of KCNMB1 in primary rat aortic VSMCs, morphology analysis, scratch assay, TUNEL staining, Western blotting for phenotypic markers\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined time-course phenotypic readouts and marker analysis\",\n      \"pmids\": [\"40653026\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCNMB1 encodes the β1 regulatory subunit of large-conductance Ca2+/voltage-activated BK potassium channels, where it increases Ca2+ sensitivity and surface expression of the channel-forming α subunit (via endocytic trafficking), is transcriptionally controlled by the SRF/myocardin axis and HIF-1α in smooth muscle cells, and regulates vascular tone, renal K+ secretion, myofibroblast differentiation, and VSMC phenotypic plasticity—with gain-of-function variants (E65K) conferring protection against hypertension and loss-of-function variants impairing smooth muscle relaxation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KCNMB1 encodes the β1 regulatory subunit of large-conductance calcium- and voltage-activated BK potassium channels, functioning as a critical modulator of channel calcium sensitivity, surface trafficking, and smooth muscle physiology. The β1 subunit increases BK channel Ca2+ sensitivity in vascular smooth muscle, thereby enhancing negative feedback on contractility, and regulates channel surface density through an endocytic trafficking mechanism dependent on a C-terminal signal; cholesterol enrichment activates BK channels by promoting β1 translocation to the plasma membrane [PMID:15057310, PMID:16908104, PMID:33556372]. KCNMB1 transcription is driven by the SRF/myocardin axis via CArG elements and by HIF-1α via hypoxia response elements, coupling channel expression to smooth muscle differentiation programs and oxygen sensing [PMID:19801679, PMID:22114151]. Beyond vascular tone, KCNMB1 facilitates renal K⁺ secretion in the connecting tubule—its deletion causes hyperkalemia and volume-expanded hypertension—and regulates myofibroblast differentiation and VSMC phenotypic switching [PMID:19556540, PMID:31486669, PMID:40653026].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"The question of whether human KCNMB1 coding variants alter BK channel function was answered by demonstrating that the E65K gain-of-function polymorphism increases Ca2+ sensitivity without changing kinetics, establishing a molecular basis for genetically variable vascular smooth muscle relaxation.\",\n      \"evidence\": \"Heterologous expression of wild-type vs. E65K mutant BK channels with patch-clamp electrophysiology\",\n      \"pmids\": [\"15057310\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how E65K increases Ca2+ sensitivity is unknown\", \"Whether E65K alters trafficking or only gating was not tested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Building on the E65K functional characterization, population-level analysis linked this variant to protection against diastolic hypertension in aging women, connecting in vitro BK channel gain-of-function to a cardiovascular phenotype.\",\n      \"evidence\": \"Electrophysiology of wild-type and E65K channels with estrogen treatment, combined with population genetic analysis\",\n      \"pmids\": [\"16293791\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between E65K and sex-specific protection is inferential\", \"No in vivo model tested\", \"Population association does not establish causation alone\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"It was unknown how the β1 subunit controls BK channel surface availability; this study showed that KCNMB1 reduces steady-state surface expression of the α subunit via a C-terminal endocytic signal, establishing β1 as a trafficking regulator that directs channels to endosomes.\",\n      \"evidence\": \"Site-directed mutagenesis of endocytic signal, colocalization with endosomal markers, surface expression assays in heterologous cells\",\n      \"pmids\": [\"16908104\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The endocytic adaptor that recognizes the C-terminal signal was not identified\", \"Relevance of this mechanism in native smooth muscle was not demonstrated at this time\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"To test whether loss-of-function KCNMB1 variants exist, the R140W variant was shown to significantly reduce BK channel openings, providing a mechanistic explanation for impaired airway smooth muscle relaxation.\",\n      \"evidence\": \"Patch-clamp electrophysiology of BK channels coexpressed with wild-type or R140W β1\",\n      \"pmids\": [\"18535015\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of R140W-induced loss of function not determined\", \"In vivo airway phenotype not directly demonstrated in animal model\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Two key questions—what transcription factors drive smooth-muscle-specific KCNMB1 expression and what renal function β1 serves—were resolved: SRF/myocardin transactivates KCNMB1 via CArG elements, and renal β1 facilitates K⁺ secretion, with its loss causing hyperkalemia and hypertension.\",\n      \"evidence\": \"ChIP, luciferase reporter mutagenesis, and SRF knockdown in smooth muscle cells (transcriptional regulation); Kcnmb1 knockout mouse with electrolyte, blood pressure, and aldosterone measurements plus eplerenone rescue (renal function)\",\n      \"pmids\": [\"19801679\", \"19556540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SRF/myocardin regulation operates in renal connecting tubule specifically was not tested\", \"Compensation by other β subunits in the knockout was not assessed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"It was unknown how hypoxia regulates KCNMB1; HIF-1α was shown to directly bind HREs in the KCNMB1 promoter and recruit p300 to drive transcription in pulmonary artery smooth muscle cells, with KCNMB1 knockdown potentiating hypoxia-induced calcium overload.\",\n      \"evidence\": \"ChIP for HIF-1α and p300, HRE mutagenesis in reporter assays, shRNA knockdown of HIF-1α, calcium imaging in pulmonary artery smooth muscle cells\",\n      \"pmids\": [\"22114151\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HIF-1α-driven KCNMB1 upregulation is protective or pathogenic in pulmonary hypertension was not resolved\", \"Interplay between HIF-1α and SRF/myocardin pathways at the KCNMB1 locus was not examined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Whether KCNMB1/BK channels influence fibroblast-to-myofibroblast differentiation was unknown; KCNMB1 knockdown attenuated collagen gel contraction and α-SMA expression, while pharmacological BK activation promoted differentiation via intracellular calcium elevation, establishing a non-vascular role for β1.\",\n      \"evidence\": \"siRNA knockdown, collagen gel contraction assay, pharmacological BK activation/inhibition, intracellular calcium measurements, patch-clamp electrophysiology in fibroblasts\",\n      \"pmids\": [\"31486669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo fibrosis relevance not tested\", \"Which specific calcium signaling pathway downstream of BK drives α-SMA expression was not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The mechanism by which cholesterol modulates BK channels was clarified: cholesterol enrichment promotes intracellular-to-plasma-membrane trafficking of KCNMB1, and blocking trafficking with brefeldin A or deleting KCNMB1 abolishes cholesterol-induced BK activation, establishing β1 trafficking as the lipid-sensitive step.\",\n      \"evidence\": \"Inside-out patch-clamp from cerebral artery myocytes, brefeldin A trafficking block, surface biotinylation, KCNMB1-/- mouse comparison\",\n      \"pmids\": [\"33556372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The cholesterol-sensing element on β1 or its trafficking machinery is unknown\", \"Whether this mechanism operates in non-cerebral vascular beds was not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"KCNMB1 knockdown was shown to trigger a time-dependent phenotypic switch in VSMCs—from contractile to proliferative/migratory at 24h, progressing to apoptosis at 72h—establishing β1 as a gatekeeper of smooth muscle cell identity and survival.\",\n      \"evidence\": \"siRNA knockdown in primary rat aortic VSMCs with morphology analysis, scratch assay, TUNEL staining, and Western blotting for phenotypic markers at defined time points\",\n      \"pmids\": [\"40653026\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the phenotypic switch is mediated by altered BK channel activity or a channel-independent β1 function is not distinguished\", \"In vivo vascular remodeling phenotype upon KCNMB1 loss in adult animals not demonstrated\", \"Single study without independent replication\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the structural basis for β1-mediated Ca2+ sensitivity enhancement, the identity of the endocytic adaptor recognizing the β1 C-terminal signal, and whether β1 has channel-independent signaling roles in VSMC phenotypic switching and fibrosis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of α/β1 complex showing Ca2+-sensitivity mechanism\", \"Endocytic adaptor and cholesterol-sensing mechanism unidentified\", \"Channel-independent versus channel-dependent effects in VSMC phenotype switching not resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2, 9]},\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 9, 10]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 2, 4, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 8, 9]}\n    ],\n    \"complexes\": [\n      \"BK channel (Slo1/β1 complex)\"\n    ],\n    \"partners\": [\n      \"KCNMA1\",\n      \"SRF\",\n      \"MYOCD\",\n      \"HIF1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}