{"gene":"KCNE4","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":2002,"finding":"KCNE4 functions as an inhibitory subunit to KCNQ1 channels, completely suppressing KCNQ1 current when co-expressed in Xenopus oocytes and CHO-K1 cells. The inhibition occurs at channels already expressed in the plasma membrane (not by reducing surface expression), and is specific to KCNQ1 (not KCNQ2-5 or hERG1).","method":"Two-electrode voltage clamp (Xenopus oocytes), whole-cell patch clamp (CHO-K1), immunocytochemistry, Western blotting, delayed mRNA expression experiments","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods in two heterologous systems, replicated by subsequent studies","pmids":["12096056"],"is_preprint":false},{"year":2003,"finding":"KCNE4 selectively inhibits Kv1.1 and Kv1.3 (but not Kv1.2, Kv1.4, Kv1.5, or Kv4.3) homomeric currents; it also inhibits Kv1.1/Kv1.2 and Kv1.2/Kv1.3 heteromeric complexes. Kv1.1 is present at the cell surface together with KCNE4, shown by confocal microscopy and Western blotting.","method":"Electrophysiology (Xenopus oocytes and HEK293 cells), confocal microscopy, Western blotting","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1-2 — multiple heterologous expression systems with direct electrophysiology and localization, replicated in subsequent papers","pmids":["12944270"],"is_preprint":false},{"year":2008,"finding":"KCNE4 directly associates with KCNQ1 via co-immunoprecipitation, and can co-associate with both KCNE1 and KCNQ1 simultaneously to form a trimeric 'triple subunit' complex (KCNE1-KCNQ1-KCNE4). Cell surface biotinylation showed KCNE4 does not impair plasma membrane expression of KCNQ1 or the triple subunit complex, indicating biophysical (gating) mechanisms underlie inhibition.","method":"Co-immunoprecipitation, immunoblotting, cell surface biotinylation in heterologous expression system","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal biochemical assays with multiple orthogonal methods in a single study","pmids":["18279388"],"is_preprint":false},{"year":2008,"finding":"KCNE4 (MiRP3) co-localizes with the BK (large-conductance Ca2+/voltage-gated) potassium channel at the apical membrane of renal intercalated cells. Co-expression forms detergent-stable complexes; KCNE4 reduces BK current density by shifting the current-voltage relationship ~10 mV to more depolarized voltages in a Ca2+-dependent fashion and by accelerating degradation of MiRP3-BK complexes.","method":"Immunohistochemistry (rabbit kidney), co-immunoprecipitation, electrophysiology in tissue culture cells","journal":"American journal of physiology. Renal physiology","confidence":"High","confidence_rationale":"Tier 2 — in vivo localization combined with biochemical and electrophysiological characterization in same study","pmids":["18463315"],"is_preprint":false},{"year":2008,"finding":"The C-terminus of KCNE4 is the critical domain for inhibition of KCNQ1; replacing the C-termini of KCNE1 or KCNE3 with that of KCNE4 confers strong KCNQ1 inhibition. The KCNE4 transmembrane domain plays a cooperative but not sufficient role; the C-terminus of KCNE4 physically interacts with KCNQ1.","method":"KCNE chimera expression with two-electrode voltage clamp (Xenopus oocytes) and co-immunoprecipitation","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 — systematic chimera mutagenesis plus biochemical interaction assay in a single study","pmids":["19029186"],"is_preprint":false},{"year":2009,"finding":"KCNE4 acts as an inhibitory partner of Kv1.3 in leukocytes: it associates with Kv1.3 in the ER, retains the channel intracellularly, impairs targeting to lipid raft microdomains, decreases current density, slows activation, and accelerates inactivation. KCNE4 and Kv1.3 are differentially regulated by LPS-activation and immunosuppression in macrophages.","method":"Electrophysiology, co-immunoprecipitation, confocal microscopy, lipid raft fractionation, RT-PCR in leukocyte cell lines and macrophages","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (electrophysiology, biochemistry, imaging) in relevant cell type","pmids":["19773357"],"is_preprint":false},{"year":2010,"finding":"KCNE4 biochemically interacts with calmodulin (CaM) in a Ca2+-dependent manner via a tetraleucine motif in the juxtamembrane C-terminal region. Mutagenesis of the tetraleucine motif or acute Ca2+ chelation disrupts the KCNE4-CaM interaction and impairs KCNE4's ability to inhibit KCNQ1. KCNE1 does not interact with CaM.","method":"Co-immunoprecipitation, mutagenesis, Ca2+ chelation, electrophysiology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with biochemical and functional assays in a single rigorous study","pmids":["21118809"],"is_preprint":false},{"year":2010,"finding":"KCNE4 (MiRP3) co-localizes with Kv4.2 in transverse tubules of murine cardiac myocytes. Co-expression of KCNE4 and Kv4.2 in tsA201 cells modulates Kv4.2 gating: shifts V1/2 ~20 mV, slows time to peak ~100%, slows inactivation ~100%, and speeds recovery from inactivation ~30%. A ternary complex of KCNE4, Kv4.2, and KChIP2 can be biochemically isolated with a distinct biophysical profile.","method":"Immunofluorescence microscopy in cardiac myocytes, whole-cell voltage clamp, co-immunoprecipitation in tsA201 cells","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — in vivo localization combined with electrophysiology and biochemistry, ternary complex demonstrated","pmids":["20498229"],"is_preprint":false},{"year":2015,"finding":"KCNE4 co-localizes with Kv7.4 in mesenteric artery myocytes (proximity ligation assay). KCNE4 co-expression in HEK cells increases membrane expression of Kv7.4 and alters its current properties. Morpholino-induced knockdown of KCNE4 in rat mesenteric arteries depolarizes smooth muscle cells, reduces Kv7.4 membrane abundance, increases sensitivity to vasoconstrictors, and impairs Kv7 modulator efficacy.","method":"Proximity ligation assay, patch clamp (HEK cells), morpholino knockdown, myography, Western blot, qPCR","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function in native tissue with multiple functional readouts, protein interaction confirmed by proximity ligation","pmids":["26503181"],"is_preprint":false},{"year":2015,"finding":"KCNE4 transcript is 8-fold higher in male vs. female young adult mouse left ventricle and is regulated by 5α-dihydrotestosterone (DHT): castration reduces male ventricular Kcne4 expression ~2.8-fold and DHT implants restore it. Germline Kcne4 deletion eliminates sex-specific Kv current disparity by reducing fast transient outward current (Ito,f) and IK,slow1. KCNE4 functionally regulates Kv1.5 (which generates IKslow1) in heterologous expression.","method":"Germline knockout, patch clamp of ventricular/atrial myocytes, castration/DHT implant experiments, heterologous expression electrophysiology","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — genetic deletion with defined electrophysiological phenotype plus hormonal regulation experiments","pmids":["26399785"],"is_preprint":false},{"year":2016,"finding":"The C-terminal domain of Kv1.3 is necessary and sufficient for interaction with KCNE4. KCNE4 mediates intracellular retention of Kv1.3 via two additive mechanisms: (1) masking the YMVIEE forward-trafficking motif at the Kv1.3 C-terminus, and (2) an ER retention motif within KCNE4 itself.","method":"Truncation/domain-swap mutagenesis, co-immunoprecipitation, confocal microscopy, electrophysiology in mammalian cells","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — systematic mutagenesis with biochemical and functional validation defining molecular determinants","pmids":["27802162"],"is_preprint":false},{"year":2016,"finding":"Novel N-terminally extended isoforms of hKCNE4 (221 residues, with 51 extra extracellular residues) are expressed in human tissues. The longer full-length hKCNE4 shows altered channel regulatory properties: inhibition of KCNQ1 is reduced to ~40% vs. ~80% for the shorter form, KCNQ4 augmentation is abolished, while slowing of Kv4.2 inactivation is preserved.","method":"Molecular cloning, two-electrode voltage clamp in Xenopus oocytes, Western blot, RT-PCR in human tissues","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology in heterologous system for novel isoform; single study","pmids":["27162025"],"is_preprint":false},{"year":2016,"finding":"Germline Kcne4 deletion increases mesenteric artery contractility to α-adrenoceptor agonist methoxamine and decreases responses to Kv7.2-7.5 activator ML213 in male but not female mice. Kcne4 deletion reduces Kv7.4 protein expression in mesenteric artery in both sexes. Female mice have 2-fold lower Kcne4 expression and 2-fold higher Kv7.4 protein than males.","method":"Germline knockout mouse, myography, Western blot, qPCR","journal":"Journal of vascular research","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with multiple functional readouts in native vascular tissue, sex-specific analysis","pmids":["27710966"],"is_preprint":false},{"year":2007,"finding":"The KCNE4 E145D polymorphism (associated with atrial fibrillation) converts KCNE4 from an inhibitor to an activator of KCNQ1: wild-type KCNE4 inhibits KCNQ1 current while KCNE4(145D) augments it and shifts V1/2 of activation toward depolarized potentials, representing a gain-of-function.","method":"Site-directed mutagenesis, whole-cell patch clamp in CHO-K1 cells","journal":"Chinese medical journal","confidence":"Medium","confidence_rationale":"Tier 2 — patch clamp with defined mutagenesis, single study","pmids":["17335661"],"is_preprint":false},{"year":2019,"finding":"The tetraleucine motif in the KCNE4 C-terminal juxtamembrane domain mediates direct association with Kv1.3, and Kv1.3 and Ca2+/calmodulin compete for binding to this same motif on KCNE4. A structural model of the Kv1.3-KCNE4 complex was proposed consistent with KCNE4 hiding the forward-trafficking YMVIEE motif and adding an ER retention signature.","method":"Mutagenesis, co-immunoprecipitation, FRET, in silico structural modelling, electrophysiology","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis with multiple biochemical/biophysical methods and structural modelling confirming mechanism","pmids":["30969795"],"is_preprint":false},{"year":2020,"finding":"Up to four KCNE4 subunits can associate with a single Kv1.3 channel (variable stoichiometry). A single KCNE4 subunit is sufficient to cooperatively enhance Kv1.3 inactivation, while increasing KCNE4 number progressively slows activation and decreases Kv1.3 surface abundance.","method":"Tandem-linked concatemer constructs, electrophysiology, flow cytometry surface expression assays in mammalian cells","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — defined stoichiometry using concatemer strategy with electrophysiology and surface expression readouts; single study","pmids":["32370164"],"is_preprint":false},{"year":2021,"finding":"KCNE4 dimerizes via its tetraleucine juxtamembrane C-terminal domain, making it unique among KCNE family members. Ca2+/calmodulin-dependent KCNE4 dimerization controls KCNE4 membrane targeting: KCNE4 is highly retained in the ER and escapes in a CaM-dependent, COP-II-dependent manner. The tetraleucine motif is a competitive interaction platform for Kv1.3, Ca2+/CaM, and dimerizing KCNE4.","method":"FRET, co-immunoprecipitation, Ca2+ chelation experiments, confocal microscopy, trafficking inhibitor experiments in leukocyte/mammalian cells","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods demonstrating dimerization and CaM-dependent trafficking mechanism","pmids":["34234241"],"is_preprint":false},{"year":2021,"finding":"KCNE4 overexpression in Jurkat T cells (which normally have low KCNE4) inhibits Kv1.3 rearrangement at the immunological synapse, decreases cell growth, promotes apoptosis, and reduces IL-2 production. KCNE4 ablation in CY15 dendritic cells augments proliferation. LPS activation increases Kv1.3 without increasing KCNE4, raising the free Kv1.3:Kv1.3-KCNE4 ratio.","method":"Overexpression and knockdown/ablation in leukocyte cell lines, electrophysiology, flow cytometry, ELISA, confocal microscopy","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function and gain-of-function in relevant cell types with defined immune functional readouts","pmids":["34272451"],"is_preprint":false},{"year":2018,"finding":"Kcne4 deletion causes sex-independent QT prolongation in aged mice but preferentially predisposes aged males to ischemia/reperfusion-induced ventricular tachyarrhythmias. This sex specificity is due to testosterone-dependent impairment of RISK/SAFE pathway induction in Kcne4-/- males; castration of Kcne4-/- males restores normal RISK/SAFE pathway responses and eliminates sex-specific arrhythmia predisposition.","method":"Germline Kcne4 knockout, ECG telemetry, ischemia/reperfusion surgery, phospho-protein western blot (RISK/SAFE pathway), castration/pharmacological inhibition experiments","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with surgical and pharmacological epistasis experiments defining molecular pathway","pmids":["29844497"],"is_preprint":false},{"year":2024,"finding":"Purified KCNE4 reconstituted in lipid bilayers adopts a topology with distinct extracellular, transmembrane, and intracellular regions, confirmed by CW-EPR power saturation experiments. CD spectroscopy confirms proper secondary structure folding of the purified protein.","method":"Recombinant E. coli expression and purification, SDS-PAGE, CD spectroscopy, CW-EPR, EPR power saturation","journal":"The journal of physical chemistry. B","confidence":"Medium","confidence_rationale":"Tier 1 — structural characterization in lipid bilayer environment with EPR; single study, in vitro reconstitution","pmids":["39780724"],"is_preprint":false},{"year":2016,"finding":"Full-length hKCNE4L (long isoform) co-localizes with Kv4.3 in human atrium and potently inhibits Kv4.2 and Kv4.3 currents in Xenopus oocytes; co-expression of KChIP2 partially relieves Kv4.3 but not Kv4.2 inhibition. KCNE3L and KCNE4L also modulate Kv4 inactivation kinetics, voltage dependence, and recovery.","method":"Two-electrode voltage clamp in Xenopus oocytes, immunofluorescence in human atrial tissue","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology in heterologous system validated by human tissue co-localization; single study","pmids":["27922120"],"is_preprint":false},{"year":2020,"finding":"KCNE4 co-immunoprecipitates with Kv7.4 and Kv7.5, and FRET confirms direct interaction. Co-expression of KCNE4 highly attenuates the agonistic effect of URO-K10 on Kv7.4 and Kv7.5 channels in HEK293 cells.","method":"Co-immunoprecipitation, FRET, whole-cell patch clamp in HEK293 cells","journal":"The Korean journal of physiology & pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 — direct biochemical interaction confirmed by FRET and Co-IP with functional electrophysiology; single study","pmids":["33093272"],"is_preprint":false}],"current_model":"KCNE4 is a single-transmembrane ancillary (β) subunit that inhibits multiple voltage-gated K+ channels (KCNQ1, Kv1.1, Kv1.3, Kv4.2, Kv7.4, BK) through biophysical gating mechanisms and/or intracellular retention rather than reduced surface trafficking of the α subunit; its inhibitory activity on KCNQ1 requires its C-terminal domain and cooperative input from its transmembrane domain, while its regulation of Kv1.3 in leukocytes is mediated by a juxtamembrane tetraleucine motif that competitively binds Kv1.3, Ca²⁺/calmodulin, and dimerizing KCNE4, controlling ER retention and COP-II-dependent forward trafficking in a Ca²⁺/CaM-dependent fashion."},"narrative":{"teleology":[{"year":2002,"claim":"The first functional identity of KCNE4 was established: it is an inhibitory β-subunit of KCNQ1, resolving whether this orphan KCNE family member modulates any known K⁺ channel.","evidence":"Two-electrode voltage clamp in Xenopus oocytes and patch clamp in CHO-K1 cells with delayed mRNA expression and immunocytochemistry","pmids":["12096056"],"confidence":"High","gaps":["Mechanism of inhibition (gating vs. trafficking) not fully resolved","No native tissue context established","No structural information"]},{"year":2003,"claim":"KCNE4's partner range was expanded beyond KCNQ1 to Kv1.1 and Kv1.3 (but not Kv1.2, Kv1.4, Kv1.5, Kv4.3), establishing subunit selectivity among Shaker-family channels.","evidence":"Electrophysiology in Xenopus oocytes and HEK293 cells with confocal microscopy and Western blotting","pmids":["12944270"],"confidence":"High","gaps":["Molecular determinants of selectivity among Kv1 subtypes unknown","No loss-of-function data in native tissues"]},{"year":2007,"claim":"A disease-relevant polymorphism (E145D) was shown to convert KCNE4 from a KCNQ1 inhibitor to an activator, linking KCNE4 to atrial fibrillation susceptibility.","evidence":"Site-directed mutagenesis with patch clamp in CHO-K1 cells","pmids":["17335661"],"confidence":"Medium","gaps":["Single heterologous system study","No patient functional data or animal model confirmation","Structural basis of gain-of-function unknown"]},{"year":2008,"claim":"Three advances defined the molecular architecture and domain requirements of KCNE4 inhibition: KCNE4 forms trimeric complexes with KCNE1/KCNQ1 without reducing surface expression, the C-terminal domain is necessary and sufficient for KCNQ1 inhibition, and KCNE4 associates with BK channels in renal cells to modulate Ca²⁺-dependent gating.","evidence":"Co-immunoprecipitation, cell surface biotinylation, chimera mutagenesis, immunohistochemistry in kidney, and electrophysiology","pmids":["18279388","19029186","18463315"],"confidence":"High","gaps":["Atomic-level structure of any KCNE4–channel complex not determined","BK modulation not confirmed by genetic loss-of-function","Whether trimeric stoichiometry is obligatory in vivo unknown"]},{"year":2009,"claim":"KCNE4 was established as the physiologically relevant inhibitor of Kv1.3 in leukocytes, acting through ER retention and lipid raft exclusion rather than purely gating modulation, and its expression is dynamically regulated by immune activation.","evidence":"Electrophysiology, co-immunoprecipitation, confocal microscopy, lipid raft fractionation, and RT-PCR in macrophages and leukocyte cell lines","pmids":["19773357"],"confidence":"High","gaps":["Molecular determinants of ER retention not yet mapped","In vivo immune phenotype of KCNE4 deletion not tested"]},{"year":2010,"claim":"A Ca²⁺/calmodulin-dependent mechanism was identified for KCNE4's inhibitory activity: CaM binds the juxtamembrane tetraleucine motif in KCNE4's C-terminus, and disruption of this interaction impairs KCNQ1 inhibition. Separately, KCNE4 was shown to co-localize with Kv4.2 in cardiac transverse tubules and form ternary complexes with KChIP2.","evidence":"Co-immunoprecipitation, mutagenesis, Ca²⁺ chelation, electrophysiology; immunofluorescence in cardiac myocytes with patch clamp and co-IP in tsA201 cells","pmids":["21118809","20498229"],"confidence":"High","gaps":["Whether CaM is bound constitutively or recruited dynamically in native cells unknown","Physiological role of KCNE4-Kv4.2-KChIP2 ternary complex not tested by loss-of-function"]},{"year":2015,"claim":"Genetic loss-of-function studies in mice established that KCNE4 is required for sex-specific cardiac K⁺ current magnitude (Ito,f and IK,slow1) under testosterone control, and for Kv7.4-dependent vascular tone in mesenteric arteries.","evidence":"Germline Kcne4 knockout with patch clamp in cardiomyocytes, castration/DHT implants; morpholino knockdown in mesenteric arteries with myography and proximity ligation assay","pmids":["26399785","26503181"],"confidence":"High","gaps":["Whether KCNE4 regulation of Kv1.5 underlies IK,slow1 change was shown only in heterologous expression","How testosterone regulates Kcne4 transcription is undefined"]},{"year":2016,"claim":"The molecular mechanism of Kv1.3 retention was dissected: KCNE4 masks the Kv1.3 YMVIEE forward-trafficking motif and contributes its own ER retention signal, operating through dual additive mechanisms. Concurrently, novel N-terminally extended KCNE4 isoforms with altered regulatory properties were identified in human tissues, and Kv4.3 was added as a target in human atrium.","evidence":"Truncation/domain-swap mutagenesis with electrophysiology and confocal microscopy; molecular cloning with oocyte electrophysiology; germline knockout myography","pmids":["27802162","27162025","27922120","27710966"],"confidence":"High","gaps":["Whether the long isoform predominates in vivo is unresolved","How dual retention signals are coordinated with COP-II trafficking unknown"]},{"year":2018,"claim":"KCNE4 deletion was linked to sex-specific cardiac arrhythmia: aged Kcne4⁻/⁻ males show QT prolongation and ischemia/reperfusion-induced ventricular tachyarrhythmias due to testosterone-dependent impairment of RISK/SAFE cardioprotective pathways.","evidence":"Germline knockout, ECG telemetry, ischemia/reperfusion surgery, phospho-protein Western blot, castration experiments","pmids":["29844497"],"confidence":"High","gaps":["How KCNE4 influences RISK/SAFE signaling mechanistically is unclear","Human translational data for arrhythmia link absent"]},{"year":2019,"claim":"The tetraleucine motif was shown to be the direct binding site for Kv1.3 and Ca²⁺/CaM in a competitive manner, unifying the trafficking-control and CaM-dependent regulatory mechanisms into a single molecular switch.","evidence":"Mutagenesis, co-immunoprecipitation, FRET, in silico structural modelling, electrophysiology","pmids":["30969795"],"confidence":"High","gaps":["No experimentally determined high-resolution structure of the KCNE4-Kv1.3 complex","In vivo relevance of competitive CaM/Kv1.3 binding not tested"]},{"year":2020,"claim":"Variable stoichiometry of KCNE4 association with Kv1.3 (up to 4:4) was demonstrated, with distinct functional consequences at each occupancy level, and KCNE4 was confirmed to interact with Kv7.4 and Kv7.5 by FRET.","evidence":"Tandem-linked concatemer constructs with electrophysiology and flow cytometry; co-immunoprecipitation and FRET with patch clamp in HEK293 cells","pmids":["32370164","33093272"],"confidence":"Medium","gaps":["Native stoichiometry in leukocytes or cardiac cells not determined","Kv7.5 regulation not confirmed in native tissue"]},{"year":2021,"claim":"KCNE4 was found to uniquely dimerize among KCNE family members via its tetraleucine motif in a CaM/Ca²⁺-dependent manner, controlling its own ER-to-surface trafficking via COP-II; this established the tetraleucine motif as a three-way competitive platform (Kv1.3, CaM, and KCNE4 dimerization). Functionally, KCNE4 was shown to control T cell activation and dendritic cell proliferation through Kv1.3 regulation at the immunological synapse.","evidence":"FRET, co-immunoprecipitation, Ca²⁺ chelation, confocal microscopy, COP-II inhibitor experiments; overexpression/ablation in Jurkat T cells and CY15 dendritic cells with functional immune readouts","pmids":["34234241","34272451"],"confidence":"High","gaps":["Crystal or cryo-EM structure of KCNE4 dimer not available","In vivo immune phenotype of KCNE4 knockout not reported","Whether dimerization also regulates KCNE4 association with non-Kv1.3 partners is untested"]},{"year":2024,"claim":"Purified KCNE4 was reconstituted in lipid bilayers, confirming its predicted single-transmembrane topology by EPR, representing the first biophysical characterization of KCNE4 protein structure outside a channel complex.","evidence":"Recombinant expression and purification from E. coli, CD spectroscopy, CW-EPR power saturation in lipid bilayers","pmids":["39780724"],"confidence":"Medium","gaps":["No high-resolution structure yet","Reconstitution with a channel partner not performed","Only topology confirmed, not tertiary fold details"]},{"year":null,"claim":"Major unresolved questions include the high-resolution structure of KCNE4 alone and in complex with any channel partner, the in vivo immune phenotype of KCNE4 genetic deletion, the mechanism by which KCNE4 influences RISK/SAFE cardioprotective signaling, and whether the long N-terminal isoform is the predominant functional form in human tissues.","evidence":"","pmids":[],"confidence":"Low","gaps":["No experimentally determined atomic structure","No KCNE4 knockout immune phenotype reported in vivo","Human genetic validation for cardiac arrhythmia remains limited"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,4,5,6,14,15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,3,8]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[5,10,16]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,5,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,17]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[7,9]}],"complexes":["KCNQ1-KCNE4","Kv1.3-KCNE4","Kv4.2-KCNE4-KChIP2","KCNE4 homodimer"],"partners":["KCNQ1","KCNA3","KCNA1","KCNQ4","KCND2","KCNMA1","CALM1","KCNQ5"],"other_free_text":[]},"mechanistic_narrative":"KCNE4 is a single-transmembrane ancillary (β) subunit that broadly inhibits voltage-gated potassium channels, shaping K⁺ current properties in cardiac, vascular, renal, and immune cells. It suppresses KCNQ1 current through biophysical gating modulation at the plasma membrane—not by reducing surface expression—with its C-terminal domain necessary and sufficient for inhibition and its transmembrane domain playing a cooperative role [PMID:12096056, PMID:19029186]. KCNE4 also inhibits Kv1.3 in leukocytes by retaining the channel in the ER through a juxtamembrane tetraleucine motif that masks Kv1.3's forward-trafficking signal and provides an intrinsic ER retention signal; this motif serves as a competitive binding platform for Kv1.3, Ca²⁺/calmodulin, and KCNE4 dimers, coupling CaM-dependent COP-II trafficking to channel surface abundance [PMID:27802162, PMID:30969795, PMID:34234241]. Germline Kcne4 deletion in mice reveals testosterone-dependent roles in cardiac repolarization and arrhythmia susceptibility as well as vascular smooth muscle tone via regulation of Kv7.4 surface expression [PMID:29844497, PMID:26503181, PMID:27710966]."},"prefetch_data":{"uniprot":{"accession":"Q8WWG9","full_name":"Potassium voltage-gated channel subfamily E member 4","aliases":["MinK-related peptide 3","MiRP3","Minimum potassium ion channel-related peptide 3","Potassium channel subunit beta MiRP3"],"length_aa":221,"mass_kda":23.8,"function":"Ancillary protein that functions as a regulatory subunit of the voltage-gated potassium (Kv) channel complex composed of pore-forming and potassium-conducting alpha subunits and of regulatory beta subunits. KCNE4 beta subunit modulates the gating kinetics and enhances stability of the channel complex (PubMed:12096056, PubMed:19687231, PubMed:20533308, PubMed:27162025). Associates with KCNQ1/KVLTQ1 alpha subunit to inhibit potassium currents (PubMed:12096056, PubMed:19687231, PubMed:20533308, PubMed:27162025) May inhibit KCNQ4-mediated potassium currents","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q8WWG9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNE4","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":381,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNE4","total_profiled":1310},"omim":[{"mim_id":"614280","title":"EPILEPSY, JUVENILE MYOCLONIC, SUSCEPTIBILITY TO, 9; EJM9","url":"https://www.omim.org/entry/614280"},{"mim_id":"609153","title":"PSEUDOHYPERKALEMIA, FAMILIAL, 2, DUE TO RED CELL LEAK; PSHK2","url":"https://www.omim.org/entry/609153"},{"mim_id":"607775","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, ISK-RELATED SUBFAMILY, MEMBER 4; KCNE4","url":"https://www.omim.org/entry/607775"},{"mim_id":"604433","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, ISK-RELATED SUBFAMILY, MEMBER 3; KCNE3","url":"https://www.omim.org/entry/604433"},{"mim_id":"601144","title":"BRUGADA SYNDROME 1; BRGDA1","url":"https://www.omim.org/entry/601144"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Microtubules","reliability":"Approved"},{"location":"Nuclear bodies","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"smooth muscle","ntpm":39.9}],"url":"https://www.proteinatlas.org/search/KCNE4"},"hgnc":{"alias_symbol":["MiRP3"],"prev_symbol":[]},"alphafold":{"accession":"Q8WWG9","domains":[{"cath_id":"1.20.5","chopping":"85-134","consensus_level":"medium","plddt":77.1466,"start":85,"end":134}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WWG9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WWG9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8WWG9-F1-predicted_aligned_error_v6.png","plddt_mean":56.97},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNE4","jax_strain_url":"https://www.jax.org/strain/search?query=KCNE4"},"sequence":{"accession":"Q8WWG9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8WWG9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8WWG9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8WWG9"}},"corpus_meta":[{"pmid":"12096056","id":"PMC_12096056","title":"KCNE4 is an inhibitory subunit to the KCNQ1 channel.","date":"2002","source":"The Journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/12096056","citation_count":135,"is_preprint":false},{"pmid":"19773357","id":"PMC_19773357","title":"KCNE4 suppresses Kv1.3 currents by modulating trafficking, surface expression and channel gating.","date":"2009","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/19773357","citation_count":67,"is_preprint":false},{"pmid":"12944270","id":"PMC_12944270","title":"KCNE4 is an inhibitory subunit to Kv1.1 and Kv1.3 potassium channels.","date":"2003","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/12944270","citation_count":64,"is_preprint":false},{"pmid":"26503181","id":"PMC_26503181","title":"Fundamental role for the KCNE4 ancillary subunit in Kv7.4 regulation of arterial tone.","date":"2015","source":"The Journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/26503181","citation_count":61,"is_preprint":false},{"pmid":"18279388","id":"PMC_18279388","title":"KCNE4 can co-associate with the I(Ks) (KCNQ1-KCNE1) channel complex.","date":"2008","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/18279388","citation_count":40,"is_preprint":false},{"pmid":"27484720","id":"PMC_27484720","title":"KCNE4 and KCNE5: K(+) channel regulation and cardiac arrhythmogenesis.","date":"2016","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/27484720","citation_count":39,"is_preprint":false},{"pmid":"27710966","id":"PMC_27710966","title":"Kcne4 Deletion Sex-Dependently Alters Vascular Reactivity.","date":"2016","source":"Journal of vascular research","url":"https://pubmed.ncbi.nlm.nih.gov/27710966","citation_count":36,"is_preprint":false},{"pmid":"21118809","id":"PMC_21118809","title":"KCNE4 juxtamembrane region is required for interaction with calmodulin and for functional suppression of KCNQ1.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21118809","citation_count":29,"is_preprint":false},{"pmid":"26399785","id":"PMC_26399785","title":"Kcne4 deletion sex- and age-specifically impairs cardiac repolarization in mice.","date":"2015","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/26399785","citation_count":25,"is_preprint":false},{"pmid":"27802162","id":"PMC_27802162","title":"The C-terminal domain of Kv1.3 regulates functional interactions with the KCNE4 subunit.","date":"2016","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/27802162","citation_count":22,"is_preprint":false},{"pmid":"17335661","id":"PMC_17335661","title":"Modulation of KCNQ1 current by atrial fibrillation-associated KCNE4 (145E/D) gene polymorphism.","date":"2007","source":"Chinese medical journal","url":"https://pubmed.ncbi.nlm.nih.gov/17335661","citation_count":20,"is_preprint":false},{"pmid":"18463315","id":"PMC_18463315","title":"MiRP3 acts as an accessory subunit with the BK potassium channel.","date":"2008","source":"American journal of physiology. 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Regulatory, integrative and comparative physiology","url":"https://pubmed.ncbi.nlm.nih.gov/30758982","citation_count":7,"is_preprint":false},{"pmid":"38462626","id":"PMC_38462626","title":"Influential upregulation of KCNE4: Propelling cancer associated fibroblasts-driven colorectal cancer progression.","date":"2024","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/38462626","citation_count":6,"is_preprint":false},{"pmid":"37295249","id":"PMC_37295249","title":"The novel KV7 channel activator URO-K10 exerts enhanced pulmonary vascular effects independent of the KCNE4 regulatory subunit.","date":"2023","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/37295249","citation_count":4,"is_preprint":false},{"pmid":"39118175","id":"PMC_39118175","title":"KCNE4 is a crucial host factor for Orf virus infection by mediating viral entry.","date":"2024","source":"Virology journal","url":"https://pubmed.ncbi.nlm.nih.gov/39118175","citation_count":4,"is_preprint":false},{"pmid":"28981946","id":"PMC_28981946","title":"[Association of KCNE1 and KCNE4 gene polymorphisms with atrial fibrillation among Uygur and Han Chinese populations in Xinjiang].","date":"2017","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28981946","citation_count":4,"is_preprint":false},{"pmid":"33093272","id":"PMC_33093272","title":"The agonistic action of URO-K10 on Kv7.4 and 7.5 channels is attenuated by co-expression of KCNE4 ancillary subunit.","date":"2020","source":"The Korean journal of physiology & pharmacology : official journal of the Korean Physiological Society and the Korean Society of Pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/33093272","citation_count":3,"is_preprint":false},{"pmid":"23866632","id":"PMC_23866632","title":"[Effect of additional disease (comorbidity) on association of allergic rhinitis with KCNE4 gene rs12621643 variant].","date":"2013","source":"Genetika","url":"https://pubmed.ncbi.nlm.nih.gov/23866632","citation_count":3,"is_preprint":false},{"pmid":"35915077","id":"PMC_35915077","title":"Induction of potassium channel regulator KCNE4 in a submandibular lymph node metastasis model.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/35915077","citation_count":2,"is_preprint":false},{"pmid":"39780724","id":"PMC_39780724","title":"The Expression, Purification, Spectroscopic Characterization, and Membrane Topology Classification of KCNE4 from Recombinant E. coli.","date":"2024","source":"The journal of physical chemistry. 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The inhibition occurs at channels already expressed in the plasma membrane (not by reducing surface expression), and is specific to KCNQ1 (not KCNQ2-5 or hERG1).\",\n      \"method\": \"Two-electrode voltage clamp (Xenopus oocytes), whole-cell patch clamp (CHO-K1), immunocytochemistry, Western blotting, delayed mRNA expression experiments\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods in two heterologous systems, replicated by subsequent studies\",\n      \"pmids\": [\"12096056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"KCNE4 selectively inhibits Kv1.1 and Kv1.3 (but not Kv1.2, Kv1.4, Kv1.5, or Kv4.3) homomeric currents; it also inhibits Kv1.1/Kv1.2 and Kv1.2/Kv1.3 heteromeric complexes. Kv1.1 is present at the cell surface together with KCNE4, shown by confocal microscopy and Western blotting.\",\n      \"method\": \"Electrophysiology (Xenopus oocytes and HEK293 cells), confocal microscopy, Western blotting\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple heterologous expression systems with direct electrophysiology and localization, replicated in subsequent papers\",\n      \"pmids\": [\"12944270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KCNE4 directly associates with KCNQ1 via co-immunoprecipitation, and can co-associate with both KCNE1 and KCNQ1 simultaneously to form a trimeric 'triple subunit' complex (KCNE1-KCNQ1-KCNE4). Cell surface biotinylation showed KCNE4 does not impair plasma membrane expression of KCNQ1 or the triple subunit complex, indicating biophysical (gating) mechanisms underlie inhibition.\",\n      \"method\": \"Co-immunoprecipitation, immunoblotting, cell surface biotinylation in heterologous expression system\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal biochemical assays with multiple orthogonal methods in a single study\",\n      \"pmids\": [\"18279388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KCNE4 (MiRP3) co-localizes with the BK (large-conductance Ca2+/voltage-gated) potassium channel at the apical membrane of renal intercalated cells. Co-expression forms detergent-stable complexes; KCNE4 reduces BK current density by shifting the current-voltage relationship ~10 mV to more depolarized voltages in a Ca2+-dependent fashion and by accelerating degradation of MiRP3-BK complexes.\",\n      \"method\": \"Immunohistochemistry (rabbit kidney), co-immunoprecipitation, electrophysiology in tissue culture cells\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo localization combined with biochemical and electrophysiological characterization in same study\",\n      \"pmids\": [\"18463315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The C-terminus of KCNE4 is the critical domain for inhibition of KCNQ1; replacing the C-termini of KCNE1 or KCNE3 with that of KCNE4 confers strong KCNQ1 inhibition. The KCNE4 transmembrane domain plays a cooperative but not sufficient role; the C-terminus of KCNE4 physically interacts with KCNQ1.\",\n      \"method\": \"KCNE chimera expression with two-electrode voltage clamp (Xenopus oocytes) and co-immunoprecipitation\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic chimera mutagenesis plus biochemical interaction assay in a single study\",\n      \"pmids\": [\"19029186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KCNE4 acts as an inhibitory partner of Kv1.3 in leukocytes: it associates with Kv1.3 in the ER, retains the channel intracellularly, impairs targeting to lipid raft microdomains, decreases current density, slows activation, and accelerates inactivation. KCNE4 and Kv1.3 are differentially regulated by LPS-activation and immunosuppression in macrophages.\",\n      \"method\": \"Electrophysiology, co-immunoprecipitation, confocal microscopy, lipid raft fractionation, RT-PCR in leukocyte cell lines and macrophages\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (electrophysiology, biochemistry, imaging) in relevant cell type\",\n      \"pmids\": [\"19773357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KCNE4 biochemically interacts with calmodulin (CaM) in a Ca2+-dependent manner via a tetraleucine motif in the juxtamembrane C-terminal region. Mutagenesis of the tetraleucine motif or acute Ca2+ chelation disrupts the KCNE4-CaM interaction and impairs KCNE4's ability to inhibit KCNQ1. KCNE1 does not interact with CaM.\",\n      \"method\": \"Co-immunoprecipitation, mutagenesis, Ca2+ chelation, electrophysiology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with biochemical and functional assays in a single rigorous study\",\n      \"pmids\": [\"21118809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KCNE4 (MiRP3) co-localizes with Kv4.2 in transverse tubules of murine cardiac myocytes. Co-expression of KCNE4 and Kv4.2 in tsA201 cells modulates Kv4.2 gating: shifts V1/2 ~20 mV, slows time to peak ~100%, slows inactivation ~100%, and speeds recovery from inactivation ~30%. A ternary complex of KCNE4, Kv4.2, and KChIP2 can be biochemically isolated with a distinct biophysical profile.\",\n      \"method\": \"Immunofluorescence microscopy in cardiac myocytes, whole-cell voltage clamp, co-immunoprecipitation in tsA201 cells\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo localization combined with electrophysiology and biochemistry, ternary complex demonstrated\",\n      \"pmids\": [\"20498229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"KCNE4 co-localizes with Kv7.4 in mesenteric artery myocytes (proximity ligation assay). KCNE4 co-expression in HEK cells increases membrane expression of Kv7.4 and alters its current properties. Morpholino-induced knockdown of KCNE4 in rat mesenteric arteries depolarizes smooth muscle cells, reduces Kv7.4 membrane abundance, increases sensitivity to vasoconstrictors, and impairs Kv7 modulator efficacy.\",\n      \"method\": \"Proximity ligation assay, patch clamp (HEK cells), morpholino knockdown, myography, Western blot, qPCR\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function in native tissue with multiple functional readouts, protein interaction confirmed by proximity ligation\",\n      \"pmids\": [\"26503181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"KCNE4 transcript is 8-fold higher in male vs. female young adult mouse left ventricle and is regulated by 5α-dihydrotestosterone (DHT): castration reduces male ventricular Kcne4 expression ~2.8-fold and DHT implants restore it. Germline Kcne4 deletion eliminates sex-specific Kv current disparity by reducing fast transient outward current (Ito,f) and IK,slow1. KCNE4 functionally regulates Kv1.5 (which generates IKslow1) in heterologous expression.\",\n      \"method\": \"Germline knockout, patch clamp of ventricular/atrial myocytes, castration/DHT implant experiments, heterologous expression electrophysiology\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic deletion with defined electrophysiological phenotype plus hormonal regulation experiments\",\n      \"pmids\": [\"26399785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The C-terminal domain of Kv1.3 is necessary and sufficient for interaction with KCNE4. KCNE4 mediates intracellular retention of Kv1.3 via two additive mechanisms: (1) masking the YMVIEE forward-trafficking motif at the Kv1.3 C-terminus, and (2) an ER retention motif within KCNE4 itself.\",\n      \"method\": \"Truncation/domain-swap mutagenesis, co-immunoprecipitation, confocal microscopy, electrophysiology in mammalian cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — systematic mutagenesis with biochemical and functional validation defining molecular determinants\",\n      \"pmids\": [\"27802162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Novel N-terminally extended isoforms of hKCNE4 (221 residues, with 51 extra extracellular residues) are expressed in human tissues. The longer full-length hKCNE4 shows altered channel regulatory properties: inhibition of KCNQ1 is reduced to ~40% vs. ~80% for the shorter form, KCNQ4 augmentation is abolished, while slowing of Kv4.2 inactivation is preserved.\",\n      \"method\": \"Molecular cloning, two-electrode voltage clamp in Xenopus oocytes, Western blot, RT-PCR in human tissues\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology in heterologous system for novel isoform; single study\",\n      \"pmids\": [\"27162025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Germline Kcne4 deletion increases mesenteric artery contractility to α-adrenoceptor agonist methoxamine and decreases responses to Kv7.2-7.5 activator ML213 in male but not female mice. Kcne4 deletion reduces Kv7.4 protein expression in mesenteric artery in both sexes. Female mice have 2-fold lower Kcne4 expression and 2-fold higher Kv7.4 protein than males.\",\n      \"method\": \"Germline knockout mouse, myography, Western blot, qPCR\",\n      \"journal\": \"Journal of vascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with multiple functional readouts in native vascular tissue, sex-specific analysis\",\n      \"pmids\": [\"27710966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The KCNE4 E145D polymorphism (associated with atrial fibrillation) converts KCNE4 from an inhibitor to an activator of KCNQ1: wild-type KCNE4 inhibits KCNQ1 current while KCNE4(145D) augments it and shifts V1/2 of activation toward depolarized potentials, representing a gain-of-function.\",\n      \"method\": \"Site-directed mutagenesis, whole-cell patch clamp in CHO-K1 cells\",\n      \"journal\": \"Chinese medical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patch clamp with defined mutagenesis, single study\",\n      \"pmids\": [\"17335661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The tetraleucine motif in the KCNE4 C-terminal juxtamembrane domain mediates direct association with Kv1.3, and Kv1.3 and Ca2+/calmodulin compete for binding to this same motif on KCNE4. A structural model of the Kv1.3-KCNE4 complex was proposed consistent with KCNE4 hiding the forward-trafficking YMVIEE motif and adding an ER retention signature.\",\n      \"method\": \"Mutagenesis, co-immunoprecipitation, FRET, in silico structural modelling, electrophysiology\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis with multiple biochemical/biophysical methods and structural modelling confirming mechanism\",\n      \"pmids\": [\"30969795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Up to four KCNE4 subunits can associate with a single Kv1.3 channel (variable stoichiometry). A single KCNE4 subunit is sufficient to cooperatively enhance Kv1.3 inactivation, while increasing KCNE4 number progressively slows activation and decreases Kv1.3 surface abundance.\",\n      \"method\": \"Tandem-linked concatemer constructs, electrophysiology, flow cytometry surface expression assays in mammalian cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined stoichiometry using concatemer strategy with electrophysiology and surface expression readouts; single study\",\n      \"pmids\": [\"32370164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KCNE4 dimerizes via its tetraleucine juxtamembrane C-terminal domain, making it unique among KCNE family members. Ca2+/calmodulin-dependent KCNE4 dimerization controls KCNE4 membrane targeting: KCNE4 is highly retained in the ER and escapes in a CaM-dependent, COP-II-dependent manner. The tetraleucine motif is a competitive interaction platform for Kv1.3, Ca2+/CaM, and dimerizing KCNE4.\",\n      \"method\": \"FRET, co-immunoprecipitation, Ca2+ chelation experiments, confocal microscopy, trafficking inhibitor experiments in leukocyte/mammalian cells\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods demonstrating dimerization and CaM-dependent trafficking mechanism\",\n      \"pmids\": [\"34234241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"KCNE4 overexpression in Jurkat T cells (which normally have low KCNE4) inhibits Kv1.3 rearrangement at the immunological synapse, decreases cell growth, promotes apoptosis, and reduces IL-2 production. KCNE4 ablation in CY15 dendritic cells augments proliferation. LPS activation increases Kv1.3 without increasing KCNE4, raising the free Kv1.3:Kv1.3-KCNE4 ratio.\",\n      \"method\": \"Overexpression and knockdown/ablation in leukocyte cell lines, electrophysiology, flow cytometry, ELISA, confocal microscopy\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function and gain-of-function in relevant cell types with defined immune functional readouts\",\n      \"pmids\": [\"34272451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Kcne4 deletion causes sex-independent QT prolongation in aged mice but preferentially predisposes aged males to ischemia/reperfusion-induced ventricular tachyarrhythmias. This sex specificity is due to testosterone-dependent impairment of RISK/SAFE pathway induction in Kcne4-/- males; castration of Kcne4-/- males restores normal RISK/SAFE pathway responses and eliminates sex-specific arrhythmia predisposition.\",\n      \"method\": \"Germline Kcne4 knockout, ECG telemetry, ischemia/reperfusion surgery, phospho-protein western blot (RISK/SAFE pathway), castration/pharmacological inhibition experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with surgical and pharmacological epistasis experiments defining molecular pathway\",\n      \"pmids\": [\"29844497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Purified KCNE4 reconstituted in lipid bilayers adopts a topology with distinct extracellular, transmembrane, and intracellular regions, confirmed by CW-EPR power saturation experiments. CD spectroscopy confirms proper secondary structure folding of the purified protein.\",\n      \"method\": \"Recombinant E. coli expression and purification, SDS-PAGE, CD spectroscopy, CW-EPR, EPR power saturation\",\n      \"journal\": \"The journal of physical chemistry. B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — structural characterization in lipid bilayer environment with EPR; single study, in vitro reconstitution\",\n      \"pmids\": [\"39780724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Full-length hKCNE4L (long isoform) co-localizes with Kv4.3 in human atrium and potently inhibits Kv4.2 and Kv4.3 currents in Xenopus oocytes; co-expression of KChIP2 partially relieves Kv4.3 but not Kv4.2 inhibition. KCNE3L and KCNE4L also modulate Kv4 inactivation kinetics, voltage dependence, and recovery.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, immunofluorescence in human atrial tissue\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology in heterologous system validated by human tissue co-localization; single study\",\n      \"pmids\": [\"27922120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KCNE4 co-immunoprecipitates with Kv7.4 and Kv7.5, and FRET confirms direct interaction. Co-expression of KCNE4 highly attenuates the agonistic effect of URO-K10 on Kv7.4 and Kv7.5 channels in HEK293 cells.\",\n      \"method\": \"Co-immunoprecipitation, FRET, whole-cell patch clamp in HEK293 cells\",\n      \"journal\": \"The Korean journal of physiology & pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct biochemical interaction confirmed by FRET and Co-IP with functional electrophysiology; single study\",\n      \"pmids\": [\"33093272\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCNE4 is a single-transmembrane ancillary (β) subunit that inhibits multiple voltage-gated K+ channels (KCNQ1, Kv1.1, Kv1.3, Kv4.2, Kv7.4, BK) through biophysical gating mechanisms and/or intracellular retention rather than reduced surface trafficking of the α subunit; its inhibitory activity on KCNQ1 requires its C-terminal domain and cooperative input from its transmembrane domain, while its regulation of Kv1.3 in leukocytes is mediated by a juxtamembrane tetraleucine motif that competitively binds Kv1.3, Ca²⁺/calmodulin, and dimerizing KCNE4, controlling ER retention and COP-II-dependent forward trafficking in a Ca²⁺/CaM-dependent fashion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KCNE4 is a single-transmembrane ancillary (β) subunit that broadly inhibits voltage-gated potassium channels, shaping K⁺ current properties in cardiac, vascular, renal, and immune cells. It suppresses KCNQ1 current through biophysical gating modulation at the plasma membrane—not by reducing surface expression—with its C-terminal domain necessary and sufficient for inhibition and its transmembrane domain playing a cooperative role [PMID:12096056, PMID:19029186]. KCNE4 also inhibits Kv1.3 in leukocytes by retaining the channel in the ER through a juxtamembrane tetraleucine motif that masks Kv1.3's forward-trafficking signal and provides an intrinsic ER retention signal; this motif serves as a competitive binding platform for Kv1.3, Ca²⁺/calmodulin, and KCNE4 dimers, coupling CaM-dependent COP-II trafficking to channel surface abundance [PMID:27802162, PMID:30969795, PMID:34234241]. Germline Kcne4 deletion in mice reveals testosterone-dependent roles in cardiac repolarization and arrhythmia susceptibility as well as vascular smooth muscle tone via regulation of Kv7.4 surface expression [PMID:29844497, PMID:26503181, PMID:27710966].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"The first functional identity of KCNE4 was established: it is an inhibitory β-subunit of KCNQ1, resolving whether this orphan KCNE family member modulates any known K⁺ channel.\",\n      \"evidence\": \"Two-electrode voltage clamp in Xenopus oocytes and patch clamp in CHO-K1 cells with delayed mRNA expression and immunocytochemistry\",\n      \"pmids\": [\"12096056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of inhibition (gating vs. trafficking) not fully resolved\", \"No native tissue context established\", \"No structural information\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"KCNE4's partner range was expanded beyond KCNQ1 to Kv1.1 and Kv1.3 (but not Kv1.2, Kv1.4, Kv1.5, Kv4.3), establishing subunit selectivity among Shaker-family channels.\",\n      \"evidence\": \"Electrophysiology in Xenopus oocytes and HEK293 cells with confocal microscopy and Western blotting\",\n      \"pmids\": [\"12944270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinants of selectivity among Kv1 subtypes unknown\", \"No loss-of-function data in native tissues\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"A disease-relevant polymorphism (E145D) was shown to convert KCNE4 from a KCNQ1 inhibitor to an activator, linking KCNE4 to atrial fibrillation susceptibility.\",\n      \"evidence\": \"Site-directed mutagenesis with patch clamp in CHO-K1 cells\",\n      \"pmids\": [\"17335661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single heterologous system study\", \"No patient functional data or animal model confirmation\", \"Structural basis of gain-of-function unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Three advances defined the molecular architecture and domain requirements of KCNE4 inhibition: KCNE4 forms trimeric complexes with KCNE1/KCNQ1 without reducing surface expression, the C-terminal domain is necessary and sufficient for KCNQ1 inhibition, and KCNE4 associates with BK channels in renal cells to modulate Ca²⁺-dependent gating.\",\n      \"evidence\": \"Co-immunoprecipitation, cell surface biotinylation, chimera mutagenesis, immunohistochemistry in kidney, and electrophysiology\",\n      \"pmids\": [\"18279388\", \"19029186\", \"18463315\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level structure of any KCNE4–channel complex not determined\", \"BK modulation not confirmed by genetic loss-of-function\", \"Whether trimeric stoichiometry is obligatory in vivo unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"KCNE4 was established as the physiologically relevant inhibitor of Kv1.3 in leukocytes, acting through ER retention and lipid raft exclusion rather than purely gating modulation, and its expression is dynamically regulated by immune activation.\",\n      \"evidence\": \"Electrophysiology, co-immunoprecipitation, confocal microscopy, lipid raft fractionation, and RT-PCR in macrophages and leukocyte cell lines\",\n      \"pmids\": [\"19773357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular determinants of ER retention not yet mapped\", \"In vivo immune phenotype of KCNE4 deletion not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"A Ca²⁺/calmodulin-dependent mechanism was identified for KCNE4's inhibitory activity: CaM binds the juxtamembrane tetraleucine motif in KCNE4's C-terminus, and disruption of this interaction impairs KCNQ1 inhibition. Separately, KCNE4 was shown to co-localize with Kv4.2 in cardiac transverse tubules and form ternary complexes with KChIP2.\",\n      \"evidence\": \"Co-immunoprecipitation, mutagenesis, Ca²⁺ chelation, electrophysiology; immunofluorescence in cardiac myocytes with patch clamp and co-IP in tsA201 cells\",\n      \"pmids\": [\"21118809\", \"20498229\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CaM is bound constitutively or recruited dynamically in native cells unknown\", \"Physiological role of KCNE4-Kv4.2-KChIP2 ternary complex not tested by loss-of-function\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Genetic loss-of-function studies in mice established that KCNE4 is required for sex-specific cardiac K⁺ current magnitude (Ito,f and IK,slow1) under testosterone control, and for Kv7.4-dependent vascular tone in mesenteric arteries.\",\n      \"evidence\": \"Germline Kcne4 knockout with patch clamp in cardiomyocytes, castration/DHT implants; morpholino knockdown in mesenteric arteries with myography and proximity ligation assay\",\n      \"pmids\": [\"26399785\", \"26503181\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KCNE4 regulation of Kv1.5 underlies IK,slow1 change was shown only in heterologous expression\", \"How testosterone regulates Kcne4 transcription is undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The molecular mechanism of Kv1.3 retention was dissected: KCNE4 masks the Kv1.3 YMVIEE forward-trafficking motif and contributes its own ER retention signal, operating through dual additive mechanisms. Concurrently, novel N-terminally extended KCNE4 isoforms with altered regulatory properties were identified in human tissues, and Kv4.3 was added as a target in human atrium.\",\n      \"evidence\": \"Truncation/domain-swap mutagenesis with electrophysiology and confocal microscopy; molecular cloning with oocyte electrophysiology; germline knockout myography\",\n      \"pmids\": [\"27802162\", \"27162025\", \"27922120\", \"27710966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the long isoform predominates in vivo is unresolved\", \"How dual retention signals are coordinated with COP-II trafficking unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"KCNE4 deletion was linked to sex-specific cardiac arrhythmia: aged Kcne4⁻/⁻ males show QT prolongation and ischemia/reperfusion-induced ventricular tachyarrhythmias due to testosterone-dependent impairment of RISK/SAFE cardioprotective pathways.\",\n      \"evidence\": \"Germline knockout, ECG telemetry, ischemia/reperfusion surgery, phospho-protein Western blot, castration experiments\",\n      \"pmids\": [\"29844497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How KCNE4 influences RISK/SAFE signaling mechanistically is unclear\", \"Human translational data for arrhythmia link absent\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The tetraleucine motif was shown to be the direct binding site for Kv1.3 and Ca²⁺/CaM in a competitive manner, unifying the trafficking-control and CaM-dependent regulatory mechanisms into a single molecular switch.\",\n      \"evidence\": \"Mutagenesis, co-immunoprecipitation, FRET, in silico structural modelling, electrophysiology\",\n      \"pmids\": [\"30969795\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimentally determined high-resolution structure of the KCNE4-Kv1.3 complex\", \"In vivo relevance of competitive CaM/Kv1.3 binding not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Variable stoichiometry of KCNE4 association with Kv1.3 (up to 4:4) was demonstrated, with distinct functional consequences at each occupancy level, and KCNE4 was confirmed to interact with Kv7.4 and Kv7.5 by FRET.\",\n      \"evidence\": \"Tandem-linked concatemer constructs with electrophysiology and flow cytometry; co-immunoprecipitation and FRET with patch clamp in HEK293 cells\",\n      \"pmids\": [\"32370164\", \"33093272\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Native stoichiometry in leukocytes or cardiac cells not determined\", \"Kv7.5 regulation not confirmed in native tissue\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"KCNE4 was found to uniquely dimerize among KCNE family members via its tetraleucine motif in a CaM/Ca²⁺-dependent manner, controlling its own ER-to-surface trafficking via COP-II; this established the tetraleucine motif as a three-way competitive platform (Kv1.3, CaM, and KCNE4 dimerization). Functionally, KCNE4 was shown to control T cell activation and dendritic cell proliferation through Kv1.3 regulation at the immunological synapse.\",\n      \"evidence\": \"FRET, co-immunoprecipitation, Ca²⁺ chelation, confocal microscopy, COP-II inhibitor experiments; overexpression/ablation in Jurkat T cells and CY15 dendritic cells with functional immune readouts\",\n      \"pmids\": [\"34234241\", \"34272451\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal or cryo-EM structure of KCNE4 dimer not available\", \"In vivo immune phenotype of KCNE4 knockout not reported\", \"Whether dimerization also regulates KCNE4 association with non-Kv1.3 partners is untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Purified KCNE4 was reconstituted in lipid bilayers, confirming its predicted single-transmembrane topology by EPR, representing the first biophysical characterization of KCNE4 protein structure outside a channel complex.\",\n      \"evidence\": \"Recombinant expression and purification from E. coli, CD spectroscopy, CW-EPR power saturation in lipid bilayers\",\n      \"pmids\": [\"39780724\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure yet\", \"Reconstitution with a channel partner not performed\", \"Only topology confirmed, not tertiary fold details\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the high-resolution structure of KCNE4 alone and in complex with any channel partner, the in vivo immune phenotype of KCNE4 genetic deletion, the mechanism by which KCNE4 influences RISK/SAFE cardioprotective signaling, and whether the long N-terminal isoform is the predominant functional form in human tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No experimentally determined atomic structure\", \"No KCNE4 knockout immune phenotype reported in vivo\", \"Human genetic validation for cardiac arrhythmia remains limited\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 4, 5, 6, 14, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 3, 8]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [5, 10, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 5, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 17]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [7, 9]}\n    ],\n    \"complexes\": [\n      \"KCNQ1-KCNE4\",\n      \"Kv1.3-KCNE4\",\n      \"Kv4.2-KCNE4-KChIP2\",\n      \"KCNE4 homodimer\"\n    ],\n    \"partners\": [\n      \"KCNQ1\",\n      \"KCNA3\",\n      \"KCNA1\",\n      \"KCNQ4\",\n      \"KCND2\",\n      \"KCNMA1\",\n      \"CALM1\",\n      \"KCNQ5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}