{"gene":"KCNH2","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2006,"finding":"The majority (28 of 34) of LQT2 missense mutations in Kv11.1 (hERG) cause loss of function through a trafficking-deficient (class 2) mechanism, trapping channels intracellularly. This trafficking-deficient phenotype could be corrected by incubation at reduced temperature (27°C) or with pore-blocking drugs E4031 or thapsigargin.","method":"Western blot analysis and heterologous expression in HEK293 cells for 34 LQT2 missense mutations","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic study of 34 mutations with biochemical and functional readouts, replicated across multiple mutations and labs","pmids":["16432067"],"is_preprint":false},{"year":1998,"finding":"LQT2 missense mutations (T474I, A614V, V630L) in the S2-S3 linker and outer pore of HERG cause dominant-negative suppression of current. A614V and V630L additionally shift the voltage dependence of steady-state inactivation to negative potentials, enhancing inward rectification — a novel mechanism for HERG current suppression.","method":"Xenopus oocyte heterologous expression, two-electrode voltage clamp, co-injection of WT and mutant cRNA","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct electrophysiological characterization with kinetic analysis, multiple mutations tested in a defined expression system","pmids":["9721698"],"is_preprint":false},{"year":2000,"finding":"The dominant-negative LQT2 mutation A561V reduces wild-type HERG protein abundance by decreasing synthesis and increasing turnover. Co-assembly of wild-type subunits with A561V mutant occurs early in biogenesis, leading to recognition of misfolded channels and targeting for proteolysis via the 26S proteasome. Protein folding facilitation (30°C or glycerol) or proteasome inhibition (ALLN) partially rescues the dominant effect.","method":"Co-expression in mammalian cells, myc-tagged WT HERG tracking, proteasome inhibitor treatment, temperature rescue, Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (pharmacological rescue, temperature rescue, pulse-chase, Western blot) in a single rigorous study","pmids":["10753933"],"is_preprint":false},{"year":2003,"finding":"Thapsigargin (a sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor) rescues surface membrane expression of trafficking-deficient LQT2 mutations G601S and F805C without blocking HERG channel current. Rescue requires an intact Golgi apparatus (blocked by brefeldin A) and produces complex glycosylation. The mechanism of rescue is pharmacologically distinct from the pore-blocker E4031 (which rescues G601S and N470D but not F805C).","method":"Confocal imaging, Western blot, electrophysiology, pharmacological rescue in HEK293 cells expressing LQT2 mutant channels","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (confocal, biochemical, electrophysiological) with mechanistic controls (brefeldin A, multiple mutants)","pmids":["12837749"],"is_preprint":false},{"year":2007,"finding":"FKBP38 (a membrane-integrated co-chaperone) interacts with HERG, co-localizes with it, and promotes its trafficking. siRNA knockdown of FKBP38 reduces HERG trafficking, and FKBP38 overexpression partially rescues the trafficking-deficient LQT2 mutant F805C. FKBP38 functions as part of the Hsc70/Hsp90 chaperone system for HERG.","method":"Proteomics screen, co-immunoprecipitation, confocal co-localization, siRNA knockdown, overexpression rescue in HL-1 and HEK293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, siRNA knockdown with trafficking readout, and rescue experiment in two cell lines","pmids":["17569659"],"is_preprint":false},{"year":2010,"finding":"Hsp70 and Hsc70 reciprocally control hERG stability. Hsp70 suppresses hERG ubiquitination and increases both immature and mature hERG levels and IKr; Hsc70 counteracts these effects. Disease-causing missense mutations in intracellular domains bind Hsc70 more avidly than WT channels. Knockdown of Hsc70 or heat shock (inducing Hsp70) prevents degradation of mutant hERG. Heat shock of HL-1 cardiomyocytes increased IKr and shortened action potential duration.","method":"Co-immunoprecipitation, ubiquitination assays, siRNA knockdown, electrophysiology, immunocytochemistry in HEK293 and HL-1 cells","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ubiquitination assay, electrophysiology, siRNA) in two cell types including native cardiomyocytes","pmids":["21183741"],"is_preprint":false},{"year":2006,"finding":"14-3-3epsilon binds to a PKA phosphorylation site in the HERG C-terminus and amplifies beta-adrenergic stimulation of HERG channel activity (hyperpolarizing shift in voltage dependence). Three LQT2 C-terminal truncation mutations (G965X, R1014PfsX39, V1038AfsX21) remove this PKA phosphorylation site; mutant channels bind 14-3-3epsilon but do not respond with a hyperpolarizing shift. These mutations exert dominant-negative behavior when co-expressed with WT channels.","method":"Co-expression in CHO cells, electrophysiology, dominant-negative co-expression experiments, computational action potential simulation","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology with dominant-negative co-expression and direct mechanistic readout of 14-3-3epsilon binding and signaling","pmids":["16923798"],"is_preprint":false},{"year":2003,"finding":"ERG1 (KCNH2) protein localizes primarily to the transverse tubular system and its entrance in adult rat ventricular and atrial myocytes, as determined by immunoelectron microscopy and confocal immunofluorescence. This restricted T-tubular localization positions ERG1 close to Ca2+ channels for maximal repolarizing effect.","method":"Confocal immunofluorescence microscopy and immunoelectron microscopy of rat heart tissue","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct localization by immunoelectron microscopy in native tissue, single study without functional consequence experiment","pmids":["14670813"],"is_preprint":false},{"year":2003,"finding":"Selective knockout of the ERG1 B isoform in mice eliminates the rapid component of IKr deactivation (biexponential deactivation in WT adult myocytes; no IKr detected in ERG1 B(-/-) adult myocytes). ERG1 B knockout predisposes adult mice to episodic sinus bradycardia, establishing ERG1 B as necessary for IKr expression in the adult ventricular myocyte surface membrane.","method":"Homologous recombination knockout, whole-cell patch clamp of fetal and adult ventricular myocytes, ECG telemetry","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with electrophysiological and in vivo cardiac phenotype, multiple timepoints and controls","pmids":["12612061"],"is_preprint":false},{"year":2014,"finding":"hERG 1b is critical for cardiac IKr and normal repolarization. Specific shRNA knockdown of the 1b subunit in human iPSC-derived cardiomyocytes reduced IKr magnitude by ~50%, increased action potential duration, enhanced AP variability, and caused early afterdepolarizations. Expressing a fragment corresponding to the 1a-specific PAS domain (absent in 1b) to convert heteromers to 1a homomers recapitulated these effects.","method":"shRNA knockdown in human iPSC-derived cardiomyocytes, patch clamp, action potential measurements at physiological temperature","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — loss-of-function in human cardiac cells with electrophysiological readout plus independent corroboration using PAS domain expression strategy","pmids":["25453103"],"is_preprint":false},{"year":2014,"finding":"Multiple interactions between the N-terminal N-Cap/PAS domains and the C-terminal cNBH domain regulate Kv11.1 slow deactivation. Mutant cycle analysis identified a specific charge-charge interaction between Arg56 of the PAS domain and Asp803 of the cNBH domain, and an additional interaction between the N-Cap and cNBH domain. Positively charged N-Cap residues interact with negatively charged C-linker residues to stabilize the open state and slow deactivation.","method":"Mutant cycle analysis by electrophysiology in heterologous expression system","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutant cycle analysis (thermodynamic double-mutant cycles) is a rigorous method for identifying specific residue interactions governing gating kinetics","pmids":["25074935"],"is_preprint":false},{"year":1999,"finding":"Protons and Zn2+ directly interact with HERG channels and preferentially regulate the deactivation mechanism. Extracellular acidification at pHo 6.4 dramatically accelerates tail current deactivation without shifting activation voltage dependence. Kinetics effects occur at lower concentrations than current inhibition (pKa ~7.0 for deactivation kinetics vs 5.8 for tail current inhibition).","method":"Two-electrode voltage clamp in Xenopus oocytes and whole-cell patch clamp in L929 cells","journal":"Biophysical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct electrophysiological characterization in two expression systems with mechanistic kinetic analysis","pmids":["10388757"],"is_preprint":false},{"year":1999,"finding":"The S4 arginine residue R534 of HERG functions as a voltage sensor residue; the LQT2 mutation R534C shifts voltage-dependence of activation to negative potentials, accelerates activation and deactivation, and reduces steady-state inactivation, without causing dominant-negative suppression.","method":"Heterologous expression in Xenopus oocytes, whole-cell voltage clamp, kinetic analysis","journal":"Cardiovascular research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct electrophysiological characterization in Xenopus oocytes, single study identifying S4 as voltage sensor","pmids":["10690305"],"is_preprint":false},{"year":2001,"finding":"TRH modulates erg1, erg2, erg3, and HERG K+ currents in anterior pituitary GH3/B6 cells via a diffusible second messenger, shifting voltage dependence of activation to more positive potentials and reducing maximal current amplitude. Co-injection of rat MiRP1 with HERG did not influence TRH-induced modulation. Cell-attached recording confirmed involvement of a diffusible second messenger.","method":"Perforated-patch whole-cell clamp, cDNA injection in GH3/B6 cells, pharmacological dissection of signaling pathways","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiological characterization in native signaling context with multiple pharmacological controls; mechanism not fully resolved","pmids":["11283231"],"is_preprint":false},{"year":2007,"finding":"Kv11.1 (hERG) protein localizes to cholesterol and sphingolipid-enriched membrane (lipid raft) fractions in both canine ventricular myocytes and HEK293 cells, as well as to the T-tubular sarcolemma. Depletion of membrane cholesterol with methyl-beta-cyclodextrin positively shifts activation voltage dependence and accelerates deactivation; cholesterol loading reduces the voltage dependence of activation and accelerates inactivation. The trafficking-deficient G601S mutant does not localize to lipid raft fractions.","method":"Detergent and non-detergent membrane fractionation, confocal immunocytochemistry, electrophysiology in HEK293 cells and native cardiomyocytes","journal":"Channels (Austin, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fractionation plus functional electrophysiology with pharmacological manipulation of membrane cholesterol, in two cell types","pmids":["18708743"],"is_preprint":false},{"year":2008,"finding":"The KCNH2 polymorphism K897T creates a phosphorylation site for the Akt protein kinase. In cells with K897 (WT), PI3K/PP5 signaling stimulates K897 channels through dephosphorylation. In T897 cells, the same hormonal cascade inhibits T897 channels through Akt-mediated phosphorylation, reversing the direction of hormonal regulation of Kv11.1.","method":"Site-directed mutagenesis, electrophysiology, kinase inhibitor/activator pharmacology in heterologous expression system","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphorylation site identified by mutagenesis with functional electrophysiological readout; single lab","pmids":["18791070"],"is_preprint":false},{"year":2007,"finding":"HERG and KvLQT1 (KCNQ1) directly interact through their C-termini, as shown by co-immunoprecipitation and surface plasmon resonance analysis of isolated C-terminal domains. Expression of pore mutants or WT KvLQT1 in HERG-stable CHO cells reduces IKr by reducing HERG surface expression (~70% reduction); deletion of KvLQT1 NH2-terminus did not abolish downregulation.","method":"Co-immunoprecipitation, surface plasmon resonance, immunostaining, electrophysiology in stable CHO cell lines","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and SPR for direct physical interaction, plus functional electrophysiological consequence; single lab","pmids":["20833965"],"is_preprint":false},{"year":2007,"finding":"HERG co-precipitates more readily with KCNE1 than with KCNE2 during biogenesis. HERG co-localizes with KCNE1 in ER, Golgi, and plasma membrane, whereas KCNE2 is more abundant at the cell surface and in extracellular media. The differential HERG-KCNE association is determined primarily by distinct trafficking rates rather than differences in intrinsic binding affinity.","method":"Co-immunoprecipitation, confocal immunofluorescence, surface labeling, brefeldin A trafficking block, ER-retention signal engineering in heterologous expression system","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods in a single lab to dissect differential trafficking and association","pmids":["17895974"],"is_preprint":false},{"year":2013,"finding":"Pharmacological correction (e.g., E-4031 or ranolazine) of trafficking-deficient LQT2 channel G601S promotes trafficking of channels stored in the transitional ER via a Rab11B-dependent pathway. 30-min drug exposure is sufficient for correction, and increased functional expression persists 4-5 h after washout. Dominant-negative Rab11B expression prevents pharmacological correction.","method":"Confocal analysis, co-expression with dominant-negative Rab11B, cycloheximide chase, pharmacological rescue with E-4031 and ranolazine in HEK293 cells","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic identification of Rab11B-dependent pathway with dominant-negative and pharmacological tools, single lab","pmids":["23864605"],"is_preprint":false},{"year":2002,"finding":"ERG1 (KCNH2) and KCNQ1 alpha-subunits co-immunoprecipitate with KCNE1 in horse heart tissue, providing direct evidence for co-association of these channel subunits in native cardiac tissue.","method":"Immunoblotting, co-immunoprecipitation, immunostaining, and patch-clamp in horse cardiac tissue","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP from native cardiac tissue is technically sound but single lab and limited to co-association without structural detail","pmids":["12063283"],"is_preprint":false},{"year":2012,"finding":"Trafficking-deficient LQT2 mutants G572R-hERG and E637K-hERG interact more strongly with ER chaperones calnexin and calreticulin than WT-hERG, activate the unfolded protein response (UPR) by upregulating active ATF6, and are targeted for proteasomal degradation. Proteasome inhibition increases core-glycosylated forms of mutant hERG and enhances their interaction with calnexin/calreticulin.","method":"Co-immunoprecipitation, confocal microscopy, Western blot, proteasome inhibitor treatment in U2OS and HEK293 cells","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, confocal, Western blot, pharmacological) in two cell lines; single lab","pmids":["22242185"],"is_preprint":false},{"year":2015,"finding":"High glucose reduces hERG channel expression and IKr through inhibition of channel trafficking, mediated by downregulation of Hsp90 and disruption of its interaction with hERG. High-glucose-mediated trafficking inhibition activates the unfolded protein response (ATF-6 and calnexin upregulation). Insulin (100 nM) rescues hERG expression reduced by high glucose.","method":"Western blot, immunoprecipitation, patch clamp, confocal microscopy in hERG-HEK293 cells","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, electrophysiology, confocal) with mechanistic rescue; single lab","pmids":["26303164"],"is_preprint":false},{"year":2012,"finding":"LQT2-associated PAS domain mutations display molecular properties distinct from transmembrane region mutations: many do not cause trafficking deficiency and most trafficking-deficient PAS domain mutants are not rescued by a pore-blocking drug (E4031). PAS domain mutations reduce in vitro folding stability of the isolated PAS domain protein.","method":"Trafficking assay, temperature and drug rescue experiments, thermal and chemical unfolding fluorescence assays of isolated PAS domain proteins","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic characterization of multiple mutations with both cell-based trafficking and in vitro biophysical assays; single lab","pmids":["22396785"],"is_preprint":false},{"year":2012,"finding":"A LQT2 nonsense mutation Q81X escapes nonsense-mediated mRNA decay and generates N-terminally truncated hERG channels by reinitiation of translation at Met124. These truncated channels have increased deactivation rates consistent with disruption of N-terminus-mediated deactivation regulation, and co-assemble with WT hERG to form heteromeric channels with increased deactivation.","method":"RNA analysis of hERG minigenes, Western blot, site-specific mutagenesis, voltage clamp electrophysiology, action potential clamp in HEK293 cells","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — combined RNA, protein, and functional electrophysiological analysis with mutagenesis to identify reinitiation site","pmids":["22964610"],"is_preprint":false},{"year":2005,"finding":"Pentamidine at clinically relevant concentrations (1-10 µM, 48h exposure) reduces hERG membrane expression and current density (36-85% reduction) by decreasing hERG protein levels at the surface membrane, rather than by direct acute channel block (acute IC50 ~252 µM, far above clinical exposure). This mechanism of trafficking reduction was established as the major basis for pentamidine-induced QT prolongation.","method":"Whole-cell patch clamp, Western blot, laser-scanning confocal microscopy in hERG-HEK293 cells and guinea pig ventricular myocytes","journal":"British journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (electrophysiology and Western blot/confocal) distinguishing trafficking from acute block mechanisms; single lab","pmids":["15711592"],"is_preprint":false},{"year":2017,"finding":"The transcription factor Tbx20 directly enhances human KCNH2 gene expression and hERG currents (IhERG) and shortens action potential duration in human iPSC-derived cardiomyocytes. The LQT2-associated Tbx20 variant p.R311C fails to increase KCNH2 expression, leading to decreased IhERG and increased APD. Tbx20 does not modify other repolarization channel expression.","method":"Overexpression and variant analysis in hiPSC-CMs, patch clamp electrophysiology, action potential measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology in human iPSC-CMs with loss-of-function variant comparison; single lab","pmids":["28049825"],"is_preprint":false},{"year":2014,"finding":"hERG 1a LQT2 C-terminus truncation mutants (G965X, R1014X) only exert dominant-negative gating and trafficking effects when co-expressed with hERG 1b, not when expressed alone with hERG 1a. Co-immunoprecipitation and FRET assays confirmed association of mutant and WT subunits.","method":"Electrophysiology, co-immunoprecipitation, FRET in HEK293 cells and guinea pig cardiomyocytes","journal":"Heart rhythm","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and FRET for association, plus functional electrophysiology; single lab","pmids":["26775140"],"is_preprint":false},{"year":2017,"finding":"Gating of Kv11.1 (hERG) can be reconstructed from non-covalently linked voltage-sensing and pore modules (split channels), demonstrating that the S4-S5 linker does not function solely as a rigid mechanical lever. Progressive displacement of the split position within the S4-S5 linker modulates activation voltage dependence, deactivation rate, and voltage-sensor structural reorganization. The S4-S5 linker integrates cytoplasmic domain signals as part of the gating machinery.","method":"Split-channel electrophysiology with progressive displacement of split position, MTS accessibility assay of upper S4, voltage clamp in heterologous expression","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — reconstitution of split-channel gating with MTS structural accessibility assay; single lab but mechanistically informative","pmids":["29270671"],"is_preprint":false},{"year":2004,"finding":"The common KCNH2 polymorphism K897T alters channel electrophysiology: K897T channels have lower current density, activate at more negative potentials, and inactivate and recover from inactivation faster than WT channels. P967L and R1047L channels are electrophysiologically indistinguishable from WT. All HERG channel types have similar sensitivity to cisapride block.","method":"Heterologous expression in HEK293 cells, Western blot, voltage-clamp electrophysiology","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — systematic electrophysiological characterization of multiple polymorphisms with biochemical analysis; single lab","pmids":["14975928"],"is_preprint":false},{"year":2004,"finding":"hERG channels physically and functionally interact with beta1 integrin subunits in human neuroblastoma and leukaemia cells. Beta1 integrin activation causes long-lasting hERG channel activation; beta1 integrins and hERG1 co-precipitate, suggesting formation of a macromolecular signaling complex. hERG channel activity modulates integrin downstream signaling.","method":"Co-immunoprecipitation, electrophysiology, integrin activation assays in neuroblastoma and leukaemia cells","journal":"Biochemical Society transactions","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP result reported in a review-type communication with limited mechanistic detail","pmids":["15494025"],"is_preprint":false},{"year":2013,"finding":"Rab11B, a small GTPase, regulates Kv11.1 trafficking; dominant-negative Rab11B prevents pharmacological correction of the trafficking-deficient G601S LQT2 mutant from the transitional ER.","method":"Co-expression with dominant-negative Rab11B in HEK293 cells, confocal analysis, pharmacological rescue assays","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — dominant-negative approach establishing Rab11B in the trafficking pathway; single lab, single method for Rab11B involvement","pmids":["23864605"],"is_preprint":false},{"year":2015,"finding":"Probucol reduces hERG channel membrane expression by decreasing SGK1 expression, leading to decreased phosphorylation of the E3 ubiquitin ligase Nedd4-2. Reduced Nedd4-2 phosphorylation results in enhanced hERG ubiquitination and degradation. Carbachol rescues hERG channels by restoring Nedd4-2 phosphorylation.","method":"Western blot, immunoprecipitation (ubiquitination assays), pharmacological rescue in hERG-HEK293 cells","journal":"Drug design, development and therapy","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP/ubiquitination assays without direct electrophysiological mechanistic confirmation; correlation-based chain of evidence","pmids":["26229434"],"is_preprint":false},{"year":2020,"finding":"KCNH2 (Kcnh2) deficiency in a sepsis model activates the FAK/AKT-FOXO3A pathway: Kcnh2 knockout (Kcnh2+/-) rats show inhibition of FAK/AKT signaling, upregulation of FOXO3A and its downstream pro-apoptotic targets, and worsened cardiac dysfunction. Activation of AKT or siRNA knockdown of FOXO3A rescues the Kcnh2-deficiency phenotype, positioning Kcnh2 upstream of FAK/AKT-FOXO3A in cardiomyocyte survival signaling.","method":"Kcnh2+/- rat model, echocardiography, Western blot, AKT activator pharmacology, FOXO3A siRNA knockdown","journal":"Cell proliferation","confidence":"Low","confidence_rationale":"Tier 3 / Weak — genetic knockout with pathway analysis, but epistasis established primarily by pharmacological rescue without direct molecular interaction data","pmids":["33263944"],"is_preprint":false},{"year":2013,"finding":"PIKfyve, activated by PKB/Akt, upregulates hERG channel activity and increases hERG protein abundance in the cell membrane in Xenopus oocytes. PKB/Akt-resistant PIKfyve (S318A) does not augment hERG when combined with PKB, establishing PKB-mediated PIKfyve activation as upstream of hERG membrane expression.","method":"Xenopus oocyte co-expression, dual electrode voltage clamp, confocal microscopy with antibody-based surface quantification","journal":"Cellular physiology and biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Xenopus oocyte overexpression system without direct molecular mechanism for PIKfyve effect on hERG trafficking","pmids":["23735862"],"is_preprint":false}],"current_model":"KCNH2 (hERG/Kv11.1) encodes the pore-forming alpha-subunit of IKr, the rapid delayed rectifier K+ channel critical for cardiac repolarization; its slow deactivation (regulated by PAS/N-Cap domain interactions with the cNBH and C-linker domains) and rapid voltage-dependent inactivation confer unique gating properties, while protein trafficking to the plasma membrane is governed by a chaperone network (Hsp70/Hsc70/FKBP38), lipid raft localization, and Rab11B-dependent vesicular transport, with most LQT2 mutations causing ER retention and proteasomal degradation rather than intrinsic channel dysfunction, and channel activity regulated by 14-3-3epsilon-mediated PKA phosphorylation, membrane cholesterol, Akt/PI3K signaling, and TRH-dependent second messenger pathways."},"narrative":{"mechanistic_narrative":"KCNH2 (hERG/Kv11.1) encodes the pore-forming alpha-subunit of the rapid delayed rectifier K+ current (IKr) that governs cardiac repolarization, and most loss-of-function disease alleles act not by disabling the channel pore but by blocking its delivery to the cell surface [PMID:16432067, PMID:12612061]. Its hallmark slow deactivation is built from intramolecular contacts between the N-terminal N-Cap/PAS domain and the C-terminal cyclic-nucleotide-binding homology (cNBH) and C-linker domains, including a specific Arg56–Asp803 charge pair that stabilizes the open state [PMID:25074935], while the S4 arginine R534 serves as a voltage-sensor residue and the S4-S5 linker integrates cytoplasmic signals into gating rather than acting as a rigid lever [PMID:10690305, PMID:29270671]. Native IKr requires co-assembly of the 1a and 1b isoforms: the 1b subunit is necessary for full current and normal action-potential duration, and the 1a-specific PAS domain confers slow deactivation [PMID:12612061, PMID:25453103]. Surface expression depends on a chaperone and trafficking network in which Hsp70 stabilizes the channel and suppresses ubiquitination while Hsc70 promotes degradation, the co-chaperone FKBP38 and Hsp90 promote export, and Rab11B-dependent vesicular transport delivers channels from the ER, with the protein partitioning into cholesterol-rich lipid raft and T-tubular membranes [PMID:21183741, PMID:17569659, PMID:18708743, PMID:23864605]. Trafficking-deficient (class 2) LQT2 mutants are recognized by the ER chaperones calnexin and calreticulin, trigger the unfolded protein response, and are cleared by the 26S proteasome, but can be rescued pharmacologically (E-4031, thapsigargin) or by reduced temperature [PMID:16432067, PMID:10753933, PMID:22242185, PMID:12837749]. Channel activity is further tuned by beta-adrenergic/PKA signaling amplified through 14-3-3epsilon binding to the C-terminus, by extracellular protons that accelerate deactivation, and by Akt/PI3K signaling whose direction is reversed by the common K897T polymorphism [PMID:16923798, PMID:10388757, PMID:18791070]. hERG associates with the KCNQ1/KCNE1 channel subunits in native cardiac tissue, and its expression is transcriptionally driven by Tbx20 [PMID:12063283, PMID:20833965, PMID:28049825].","teleology":[{"year":1998,"claim":"Established that LQT2 missense mutations can suppress IKr through dominant-negative coassembly and, for some alleles, by shifting inactivation voltage dependence, defining distinct biophysical mechanisms of current loss.","evidence":"Two-electrode voltage clamp of WT/mutant co-injected Xenopus oocytes","pmids":["9721698"],"confidence":"High","gaps":["Did not address whether suppression arises from gating versus trafficking defects","Limited to three pore/linker mutations"]},{"year":2000,"claim":"Showed that a dominant-negative LQT2 mutation lowers WT channel abundance by promoting recognition of misfolded heteromers and proteasomal turnover, shifting the disease paradigm toward protein quality control.","evidence":"Co-expression with myc-tagged WT, proteasome inhibition, temperature rescue, pulse-chase in mammalian cells","pmids":["10753933"],"confidence":"High","gaps":["Specific ER recognition machinery not identified","Did not quantify residual surface current"]},{"year":2003,"claim":"Distinguished a trafficking-deficient (class 2) mechanism as correctable through the secretory pathway, showing pharmacological rescue restores surface expression and glycosylation via the Golgi.","evidence":"Confocal imaging, Western blot, electrophysiology with thapsigargin/E4031 and brefeldin A controls in HEK293","pmids":["12837749"],"confidence":"High","gaps":["Molecular targets of thapsigargin/E4031 rescue distinct from acute block unresolved","Mutant-specific rescue differences unexplained"]},{"year":2003,"claim":"Defined the native subcellular localization and isoform requirement of IKr, placing ERG1 at the T-tubular system and showing the ERG1 B isoform is necessary for adult myocyte IKr.","evidence":"Immunoelectron microscopy in rat heart and isoform-selective knockout with patch clamp/ECG in mice","pmids":["14670813","12612061"],"confidence":"Medium","gaps":["Isoform stoichiometry in human myocardium not established","Mechanism linking localization to repolarization efficacy inferred"]},{"year":2006,"claim":"Quantified the dominance of the trafficking-deficient mechanism across LQT2 alleles and identified C-terminal PKA-site/14-3-3epsilon coupling as a beta-adrenergic regulatory axis disrupted by truncation mutations.","evidence":"Systematic Western blot/expression of 34 mutations; CHO electrophysiology with dominant-negative co-expression","pmids":["16432067","16923798"],"confidence":"High","gaps":["In vivo contribution of 14-3-3epsilon regulation to arrhythmia unquantified","Generalizability of rescue across all class-2 alleles incomplete"]},{"year":2007,"claim":"Identified specific chaperone components (FKBP38, Hsc70/Hsp90 system) and lipid raft/T-tubular partitioning as determinants of hERG surface delivery and biophysics.","evidence":"Proteomics, reciprocal Co-IP, siRNA, rescue, and membrane fractionation with cholesterol manipulation in HEK293/HL-1 and cardiomyocytes","pmids":["17569659","18708743"],"confidence":"Medium","gaps":["Hierarchy among co-chaperones not fully ordered","Causal link between raft residence and native IKr gating not proven in vivo"]},{"year":2010,"claim":"Resolved opposing roles of Hsp70 and Hsc70 in hERG ubiquitination and stability and showed mutant channels bind Hsc70 more avidly, linking chaperone choice to degradation and demonstrating heat-shock rescue of IKr in cardiomyocytes.","evidence":"Co-IP, ubiquitination assays, siRNA, electrophysiology in HEK293 and HL-1 cells","pmids":["21183741"],"confidence":"High","gaps":["E3 ligase coupling chaperone state to ubiquitination not identified here","Therapeutic feasibility of heat-shock induction untested in vivo"]},{"year":2012,"claim":"Connected trafficking-deficient mutants to ER chaperone surveillance and the unfolded protein response, and showed PAS-domain mutations form a biophysically distinct class often refractory to pore-blocker rescue.","evidence":"Co-IP with calnexin/calreticulin, ATF6/UPR readouts, in vitro PAS-domain unfolding, and trafficking/rescue assays","pmids":["22242185","22396785"],"confidence":"Medium","gaps":["UPR contribution to arrhythmogenesis in vivo unestablished","Why PAS mutants resist pore-blocker rescue mechanistically unclear"]},{"year":2014,"claim":"Mapped the intramolecular N-Cap/PAS–cNBH/C-linker interactions governing slow deactivation and demonstrated that the 1b isoform and 1a PAS domain set native IKr magnitude and repolarization stability in human cardiomyocytes.","evidence":"Mutant cycle electrophysiology and shRNA/PAS-fragment manipulation in hiPSC-derived cardiomyocytes","pmids":["25074935","25453103","26775140"],"confidence":"High","gaps":["Structural basis of N-Cap/cNBH contacts at atomic resolution not provided","Quantitative 1a:1b ratio in human heart unresolved"]},{"year":2017,"claim":"Defined transcriptional and gating-architecture contributions, showing Tbx20 directly drives KCNH2 expression and that the S4-S5 linker integrates cytoplasmic signals rather than acting as a rigid lever.","evidence":"Tbx20 overexpression/variant analysis in hiPSC-CMs and split-channel/MTS gating experiments","pmids":["28049825","29270671"],"confidence":"Medium","gaps":["Broader transcriptional network controlling KCNH2 not mapped","Physiological signals relayed through the S4-S5 linker not enumerated"]},{"year":2020,"claim":"Extended KCNH2 function beyond ion conduction by placing it upstream of FAK/AKT-FOXO3A cardiomyocyte survival signaling in a sepsis model.","evidence":"Kcnh2+/- rat model with echocardiography, Western blot, AKT activation, and FOXO3A siRNA rescue","pmids":["33263944"],"confidence":"Low","gaps":["Epistasis established by pharmacology without direct molecular interaction data","Whether channel conduction or a non-conducting role drives the effect unresolved","Not confirmed independently"]},{"year":null,"claim":"How the chaperone/quality-control network, lipid environment, transcriptional control, and signaling inputs are integrated to set native IKr and how this can be therapeutically rescued in patient myocardium remains incompletely defined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified in vivo model linking trafficking machinery to arrhythmia outcome","Atomic structures of full-length channel with regulatory domains absent from corpus","Allele-specific rescuability not predictable from sequence"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,8,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,7,14]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,18,20]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[3,17]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[8,9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,5,20]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,18,30]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,15]}],"complexes":["IKr channel (hERG 1a/1b heteromer)","KCNQ1/KCNE1 channel 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Channel properties are modulated by cAMP and subunit assembly (PubMed:10837251). Characterized by unusual gating kinetics by producing relatively small outward currents during membrane depolarization and large inward currents during subsequent repolarization which reflect a rapid inactivation during depolarization and quick recovery from inactivation but slow deactivation (closing) during repolarization (PubMed:10219239, PubMed:10753933, PubMed:10790218, PubMed:10837251, PubMed:11997281, PubMed:12063277, PubMed:18559421, PubMed:22314138, PubMed:22359612, PubMed:26363003, PubMed:27916661, PubMed:9230439, PubMed:9351446, PubMed:9765245). Forms a stable complex with KCNE1 or KCNE2, and that this heteromultimerization regulates inward rectifier potassium channel activity (PubMed:10219239, PubMed:9230439) Has no inward rectifier potassium channel activity by itself, but modulates channel characteristics by forming heterotetramers with other isoforms which are retained intracellularly and undergo ubiquitin-dependent degradation Has no inward rectifier potassium channel activity by itself, but modulates channel characteristics by forming heterotetramers with other isoforms which are retained intracellularly and undergo ubiquitin-dependent degradation","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q12809/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNH2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNH2","total_profiled":1310},"omim":[{"mim_id":"616923","title":"RING FINGER PROTEIN 207; RNF207","url":"https://www.omim.org/entry/616923"},{"mim_id":"616249","title":"LONG QT SYNDROME 15; LQT15","url":"https://www.omim.org/entry/616249"},{"mim_id":"616247","title":"LONG QT SYNDROME 14; LQT14","url":"https://www.omim.org/entry/616247"},{"mim_id":"613695","title":"LONG QT SYNDROME 5; LQT5","url":"https://www.omim.org/entry/613695"},{"mim_id":"613693","title":"LONG QT SYNDROME 6; LQT6","url":"https://www.omim.org/entry/613693"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":39.0},{"tissue":"pituitary gland","ntpm":41.5}],"url":"https://www.proteinatlas.org/search/KCNH2"},"hgnc":{"alias_symbol":["Kv11.1","HERG","erg1"],"prev_symbol":["LQT2"]},"alphafold":{"accession":"Q12809","domains":[{"cath_id":"3.30.450.20","chopping":"11-130","consensus_level":"high","plddt":87.6188,"start":11,"end":130},{"cath_id":"-","chopping":"394-438_446-544","consensus_level":"medium","plddt":80.811,"start":394,"end":544},{"cath_id":"1.10.287.70","chopping":"545-690","consensus_level":"medium","plddt":87.8998,"start":545,"end":690},{"cath_id":"2.60.120.10","chopping":"722-860","consensus_level":"high","plddt":90.9719,"start":722,"end":860}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q12809","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q12809-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q12809-F1-predicted_aligned_error_v6.png","plddt_mean":62.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNH2","jax_strain_url":"https://www.jax.org/strain/search?query=KCNH2"},"sequence":{"accession":"Q12809","fasta_url":"https://rest.uniprot.org/uniprotkb/Q12809.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q12809/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q12809"}},"corpus_meta":[{"pmid":"16554806","id":"PMC_16554806","title":"hERG potassium channels and cardiac arrhythmia.","date":"2006","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/16554806","citation_count":1205,"is_preprint":false},{"pmid":"22988594","id":"PMC_22988594","title":"hERG K(+) channels: structure, function, and clinical significance.","date":"2012","source":"Physiological reviews","url":"https://pubmed.ncbi.nlm.nih.gov/22988594","citation_count":564,"is_preprint":false},{"pmid":"16432067","id":"PMC_16432067","title":"Most LQT2 mutations reduce Kv11.1 (hERG) current by a class 2 (trafficking-deficient) mechanism.","date":"2006","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/16432067","citation_count":343,"is_preprint":false},{"pmid":"15750627","id":"PMC_15750627","title":"Frequent overexpression of ETS-related gene-1 (ERG1) in prostate cancer transcriptome.","date":"2005","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/15750627","citation_count":277,"is_preprint":false},{"pmid":"18616963","id":"PMC_18616963","title":"The hERG potassium channel and hERG screening for drug-induced torsades de pointes.","date":"2008","source":"Pharmacology & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/18616963","citation_count":236,"is_preprint":false},{"pmid":"32283295","id":"PMC_32283295","title":"hERG toxicity assessment: Useful guidelines for drug design.","date":"2020","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32283295","citation_count":235,"is_preprint":false},{"pmid":"11339975","id":"PMC_11339975","title":"HERG K+ channels: friend and foe.","date":"2001","source":"Trends in pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/11339975","citation_count":222,"is_preprint":false},{"pmid":"18329284","id":"PMC_18329284","title":"The hERG K+ channel: target and antitarget strategies in drug development.","date":"2008","source":"Pharmacological research","url":"https://pubmed.ncbi.nlm.nih.gov/18329284","citation_count":122,"is_preprint":false},{"pmid":"28467598","id":"PMC_28467598","title":"Development of Safe Drugs: The hERG Challenge.","date":"2017","source":"Medicinal research reviews","url":"https://pubmed.ncbi.nlm.nih.gov/28467598","citation_count":120,"is_preprint":false},{"pmid":"14975928","id":"PMC_14975928","title":"Molecular and functional characterization of common polymorphisms in HERG (KCNH2) potassium channels.","date":"2004","source":"American journal of physiology. 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This trafficking-deficient phenotype could be corrected by incubation at reduced temperature (27°C) or with pore-blocking drugs E4031 or thapsigargin.\",\n      \"method\": \"Western blot analysis and heterologous expression in HEK293 cells for 34 LQT2 missense mutations\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic study of 34 mutations with biochemical and functional readouts, replicated across multiple mutations and labs\",\n      \"pmids\": [\"16432067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"LQT2 missense mutations (T474I, A614V, V630L) in the S2-S3 linker and outer pore of HERG cause dominant-negative suppression of current. A614V and V630L additionally shift the voltage dependence of steady-state inactivation to negative potentials, enhancing inward rectification — a novel mechanism for HERG current suppression.\",\n      \"method\": \"Xenopus oocyte heterologous expression, two-electrode voltage clamp, co-injection of WT and mutant cRNA\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct electrophysiological characterization with kinetic analysis, multiple mutations tested in a defined expression system\",\n      \"pmids\": [\"9721698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The dominant-negative LQT2 mutation A561V reduces wild-type HERG protein abundance by decreasing synthesis and increasing turnover. Co-assembly of wild-type subunits with A561V mutant occurs early in biogenesis, leading to recognition of misfolded channels and targeting for proteolysis via the 26S proteasome. Protein folding facilitation (30°C or glycerol) or proteasome inhibition (ALLN) partially rescues the dominant effect.\",\n      \"method\": \"Co-expression in mammalian cells, myc-tagged WT HERG tracking, proteasome inhibitor treatment, temperature rescue, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (pharmacological rescue, temperature rescue, pulse-chase, Western blot) in a single rigorous study\",\n      \"pmids\": [\"10753933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Thapsigargin (a sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor) rescues surface membrane expression of trafficking-deficient LQT2 mutations G601S and F805C without blocking HERG channel current. Rescue requires an intact Golgi apparatus (blocked by brefeldin A) and produces complex glycosylation. The mechanism of rescue is pharmacologically distinct from the pore-blocker E4031 (which rescues G601S and N470D but not F805C).\",\n      \"method\": \"Confocal imaging, Western blot, electrophysiology, pharmacological rescue in HEK293 cells expressing LQT2 mutant channels\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (confocal, biochemical, electrophysiological) with mechanistic controls (brefeldin A, multiple mutants)\",\n      \"pmids\": [\"12837749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"FKBP38 (a membrane-integrated co-chaperone) interacts with HERG, co-localizes with it, and promotes its trafficking. siRNA knockdown of FKBP38 reduces HERG trafficking, and FKBP38 overexpression partially rescues the trafficking-deficient LQT2 mutant F805C. FKBP38 functions as part of the Hsc70/Hsp90 chaperone system for HERG.\",\n      \"method\": \"Proteomics screen, co-immunoprecipitation, confocal co-localization, siRNA knockdown, overexpression rescue in HL-1 and HEK293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, siRNA knockdown with trafficking readout, and rescue experiment in two cell lines\",\n      \"pmids\": [\"17569659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Hsp70 and Hsc70 reciprocally control hERG stability. Hsp70 suppresses hERG ubiquitination and increases both immature and mature hERG levels and IKr; Hsc70 counteracts these effects. Disease-causing missense mutations in intracellular domains bind Hsc70 more avidly than WT channels. Knockdown of Hsc70 or heat shock (inducing Hsp70) prevents degradation of mutant hERG. Heat shock of HL-1 cardiomyocytes increased IKr and shortened action potential duration.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, siRNA knockdown, electrophysiology, immunocytochemistry in HEK293 and HL-1 cells\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ubiquitination assay, electrophysiology, siRNA) in two cell types including native cardiomyocytes\",\n      \"pmids\": [\"21183741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"14-3-3epsilon binds to a PKA phosphorylation site in the HERG C-terminus and amplifies beta-adrenergic stimulation of HERG channel activity (hyperpolarizing shift in voltage dependence). Three LQT2 C-terminal truncation mutations (G965X, R1014PfsX39, V1038AfsX21) remove this PKA phosphorylation site; mutant channels bind 14-3-3epsilon but do not respond with a hyperpolarizing shift. These mutations exert dominant-negative behavior when co-expressed with WT channels.\",\n      \"method\": \"Co-expression in CHO cells, electrophysiology, dominant-negative co-expression experiments, computational action potential simulation\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology with dominant-negative co-expression and direct mechanistic readout of 14-3-3epsilon binding and signaling\",\n      \"pmids\": [\"16923798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ERG1 (KCNH2) protein localizes primarily to the transverse tubular system and its entrance in adult rat ventricular and atrial myocytes, as determined by immunoelectron microscopy and confocal immunofluorescence. This restricted T-tubular localization positions ERG1 close to Ca2+ channels for maximal repolarizing effect.\",\n      \"method\": \"Confocal immunofluorescence microscopy and immunoelectron microscopy of rat heart tissue\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct localization by immunoelectron microscopy in native tissue, single study without functional consequence experiment\",\n      \"pmids\": [\"14670813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Selective knockout of the ERG1 B isoform in mice eliminates the rapid component of IKr deactivation (biexponential deactivation in WT adult myocytes; no IKr detected in ERG1 B(-/-) adult myocytes). ERG1 B knockout predisposes adult mice to episodic sinus bradycardia, establishing ERG1 B as necessary for IKr expression in the adult ventricular myocyte surface membrane.\",\n      \"method\": \"Homologous recombination knockout, whole-cell patch clamp of fetal and adult ventricular myocytes, ECG telemetry\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with electrophysiological and in vivo cardiac phenotype, multiple timepoints and controls\",\n      \"pmids\": [\"12612061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"hERG 1b is critical for cardiac IKr and normal repolarization. Specific shRNA knockdown of the 1b subunit in human iPSC-derived cardiomyocytes reduced IKr magnitude by ~50%, increased action potential duration, enhanced AP variability, and caused early afterdepolarizations. Expressing a fragment corresponding to the 1a-specific PAS domain (absent in 1b) to convert heteromers to 1a homomers recapitulated these effects.\",\n      \"method\": \"shRNA knockdown in human iPSC-derived cardiomyocytes, patch clamp, action potential measurements at physiological temperature\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in human cardiac cells with electrophysiological readout plus independent corroboration using PAS domain expression strategy\",\n      \"pmids\": [\"25453103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Multiple interactions between the N-terminal N-Cap/PAS domains and the C-terminal cNBH domain regulate Kv11.1 slow deactivation. Mutant cycle analysis identified a specific charge-charge interaction between Arg56 of the PAS domain and Asp803 of the cNBH domain, and an additional interaction between the N-Cap and cNBH domain. Positively charged N-Cap residues interact with negatively charged C-linker residues to stabilize the open state and slow deactivation.\",\n      \"method\": \"Mutant cycle analysis by electrophysiology in heterologous expression system\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutant cycle analysis (thermodynamic double-mutant cycles) is a rigorous method for identifying specific residue interactions governing gating kinetics\",\n      \"pmids\": [\"25074935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Protons and Zn2+ directly interact with HERG channels and preferentially regulate the deactivation mechanism. Extracellular acidification at pHo 6.4 dramatically accelerates tail current deactivation without shifting activation voltage dependence. Kinetics effects occur at lower concentrations than current inhibition (pKa ~7.0 for deactivation kinetics vs 5.8 for tail current inhibition).\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes and whole-cell patch clamp in L929 cells\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct electrophysiological characterization in two expression systems with mechanistic kinetic analysis\",\n      \"pmids\": [\"10388757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The S4 arginine residue R534 of HERG functions as a voltage sensor residue; the LQT2 mutation R534C shifts voltage-dependence of activation to negative potentials, accelerates activation and deactivation, and reduces steady-state inactivation, without causing dominant-negative suppression.\",\n      \"method\": \"Heterologous expression in Xenopus oocytes, whole-cell voltage clamp, kinetic analysis\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct electrophysiological characterization in Xenopus oocytes, single study identifying S4 as voltage sensor\",\n      \"pmids\": [\"10690305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"TRH modulates erg1, erg2, erg3, and HERG K+ currents in anterior pituitary GH3/B6 cells via a diffusible second messenger, shifting voltage dependence of activation to more positive potentials and reducing maximal current amplitude. Co-injection of rat MiRP1 with HERG did not influence TRH-induced modulation. Cell-attached recording confirmed involvement of a diffusible second messenger.\",\n      \"method\": \"Perforated-patch whole-cell clamp, cDNA injection in GH3/B6 cells, pharmacological dissection of signaling pathways\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiological characterization in native signaling context with multiple pharmacological controls; mechanism not fully resolved\",\n      \"pmids\": [\"11283231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Kv11.1 (hERG) protein localizes to cholesterol and sphingolipid-enriched membrane (lipid raft) fractions in both canine ventricular myocytes and HEK293 cells, as well as to the T-tubular sarcolemma. Depletion of membrane cholesterol with methyl-beta-cyclodextrin positively shifts activation voltage dependence and accelerates deactivation; cholesterol loading reduces the voltage dependence of activation and accelerates inactivation. The trafficking-deficient G601S mutant does not localize to lipid raft fractions.\",\n      \"method\": \"Detergent and non-detergent membrane fractionation, confocal immunocytochemistry, electrophysiology in HEK293 cells and native cardiomyocytes\",\n      \"journal\": \"Channels (Austin, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fractionation plus functional electrophysiology with pharmacological manipulation of membrane cholesterol, in two cell types\",\n      \"pmids\": [\"18708743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The KCNH2 polymorphism K897T creates a phosphorylation site for the Akt protein kinase. In cells with K897 (WT), PI3K/PP5 signaling stimulates K897 channels through dephosphorylation. In T897 cells, the same hormonal cascade inhibits T897 channels through Akt-mediated phosphorylation, reversing the direction of hormonal regulation of Kv11.1.\",\n      \"method\": \"Site-directed mutagenesis, electrophysiology, kinase inhibitor/activator pharmacology in heterologous expression system\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphorylation site identified by mutagenesis with functional electrophysiological readout; single lab\",\n      \"pmids\": [\"18791070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HERG and KvLQT1 (KCNQ1) directly interact through their C-termini, as shown by co-immunoprecipitation and surface plasmon resonance analysis of isolated C-terminal domains. Expression of pore mutants or WT KvLQT1 in HERG-stable CHO cells reduces IKr by reducing HERG surface expression (~70% reduction); deletion of KvLQT1 NH2-terminus did not abolish downregulation.\",\n      \"method\": \"Co-immunoprecipitation, surface plasmon resonance, immunostaining, electrophysiology in stable CHO cell lines\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and SPR for direct physical interaction, plus functional electrophysiological consequence; single lab\",\n      \"pmids\": [\"20833965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HERG co-precipitates more readily with KCNE1 than with KCNE2 during biogenesis. HERG co-localizes with KCNE1 in ER, Golgi, and plasma membrane, whereas KCNE2 is more abundant at the cell surface and in extracellular media. The differential HERG-KCNE association is determined primarily by distinct trafficking rates rather than differences in intrinsic binding affinity.\",\n      \"method\": \"Co-immunoprecipitation, confocal immunofluorescence, surface labeling, brefeldin A trafficking block, ER-retention signal engineering in heterologous expression system\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods in a single lab to dissect differential trafficking and association\",\n      \"pmids\": [\"17895974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Pharmacological correction (e.g., E-4031 or ranolazine) of trafficking-deficient LQT2 channel G601S promotes trafficking of channels stored in the transitional ER via a Rab11B-dependent pathway. 30-min drug exposure is sufficient for correction, and increased functional expression persists 4-5 h after washout. Dominant-negative Rab11B expression prevents pharmacological correction.\",\n      \"method\": \"Confocal analysis, co-expression with dominant-negative Rab11B, cycloheximide chase, pharmacological rescue with E-4031 and ranolazine in HEK293 cells\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic identification of Rab11B-dependent pathway with dominant-negative and pharmacological tools, single lab\",\n      \"pmids\": [\"23864605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ERG1 (KCNH2) and KCNQ1 alpha-subunits co-immunoprecipitate with KCNE1 in horse heart tissue, providing direct evidence for co-association of these channel subunits in native cardiac tissue.\",\n      \"method\": \"Immunoblotting, co-immunoprecipitation, immunostaining, and patch-clamp in horse cardiac tissue\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP from native cardiac tissue is technically sound but single lab and limited to co-association without structural detail\",\n      \"pmids\": [\"12063283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Trafficking-deficient LQT2 mutants G572R-hERG and E637K-hERG interact more strongly with ER chaperones calnexin and calreticulin than WT-hERG, activate the unfolded protein response (UPR) by upregulating active ATF6, and are targeted for proteasomal degradation. Proteasome inhibition increases core-glycosylated forms of mutant hERG and enhances their interaction with calnexin/calreticulin.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy, Western blot, proteasome inhibitor treatment in U2OS and HEK293 cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, confocal, Western blot, pharmacological) in two cell lines; single lab\",\n      \"pmids\": [\"22242185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"High glucose reduces hERG channel expression and IKr through inhibition of channel trafficking, mediated by downregulation of Hsp90 and disruption of its interaction with hERG. High-glucose-mediated trafficking inhibition activates the unfolded protein response (ATF-6 and calnexin upregulation). Insulin (100 nM) rescues hERG expression reduced by high glucose.\",\n      \"method\": \"Western blot, immunoprecipitation, patch clamp, confocal microscopy in hERG-HEK293 cells\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, electrophysiology, confocal) with mechanistic rescue; single lab\",\n      \"pmids\": [\"26303164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LQT2-associated PAS domain mutations display molecular properties distinct from transmembrane region mutations: many do not cause trafficking deficiency and most trafficking-deficient PAS domain mutants are not rescued by a pore-blocking drug (E4031). PAS domain mutations reduce in vitro folding stability of the isolated PAS domain protein.\",\n      \"method\": \"Trafficking assay, temperature and drug rescue experiments, thermal and chemical unfolding fluorescence assays of isolated PAS domain proteins\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic characterization of multiple mutations with both cell-based trafficking and in vitro biophysical assays; single lab\",\n      \"pmids\": [\"22396785\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A LQT2 nonsense mutation Q81X escapes nonsense-mediated mRNA decay and generates N-terminally truncated hERG channels by reinitiation of translation at Met124. These truncated channels have increased deactivation rates consistent with disruption of N-terminus-mediated deactivation regulation, and co-assemble with WT hERG to form heteromeric channels with increased deactivation.\",\n      \"method\": \"RNA analysis of hERG minigenes, Western blot, site-specific mutagenesis, voltage clamp electrophysiology, action potential clamp in HEK293 cells\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — combined RNA, protein, and functional electrophysiological analysis with mutagenesis to identify reinitiation site\",\n      \"pmids\": [\"22964610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Pentamidine at clinically relevant concentrations (1-10 µM, 48h exposure) reduces hERG membrane expression and current density (36-85% reduction) by decreasing hERG protein levels at the surface membrane, rather than by direct acute channel block (acute IC50 ~252 µM, far above clinical exposure). This mechanism of trafficking reduction was established as the major basis for pentamidine-induced QT prolongation.\",\n      \"method\": \"Whole-cell patch clamp, Western blot, laser-scanning confocal microscopy in hERG-HEK293 cells and guinea pig ventricular myocytes\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (electrophysiology and Western blot/confocal) distinguishing trafficking from acute block mechanisms; single lab\",\n      \"pmids\": [\"15711592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The transcription factor Tbx20 directly enhances human KCNH2 gene expression and hERG currents (IhERG) and shortens action potential duration in human iPSC-derived cardiomyocytes. The LQT2-associated Tbx20 variant p.R311C fails to increase KCNH2 expression, leading to decreased IhERG and increased APD. Tbx20 does not modify other repolarization channel expression.\",\n      \"method\": \"Overexpression and variant analysis in hiPSC-CMs, patch clamp electrophysiology, action potential measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology in human iPSC-CMs with loss-of-function variant comparison; single lab\",\n      \"pmids\": [\"28049825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"hERG 1a LQT2 C-terminus truncation mutants (G965X, R1014X) only exert dominant-negative gating and trafficking effects when co-expressed with hERG 1b, not when expressed alone with hERG 1a. Co-immunoprecipitation and FRET assays confirmed association of mutant and WT subunits.\",\n      \"method\": \"Electrophysiology, co-immunoprecipitation, FRET in HEK293 cells and guinea pig cardiomyocytes\",\n      \"journal\": \"Heart rhythm\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and FRET for association, plus functional electrophysiology; single lab\",\n      \"pmids\": [\"26775140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Gating of Kv11.1 (hERG) can be reconstructed from non-covalently linked voltage-sensing and pore modules (split channels), demonstrating that the S4-S5 linker does not function solely as a rigid mechanical lever. Progressive displacement of the split position within the S4-S5 linker modulates activation voltage dependence, deactivation rate, and voltage-sensor structural reorganization. The S4-S5 linker integrates cytoplasmic domain signals as part of the gating machinery.\",\n      \"method\": \"Split-channel electrophysiology with progressive displacement of split position, MTS accessibility assay of upper S4, voltage clamp in heterologous expression\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution of split-channel gating with MTS structural accessibility assay; single lab but mechanistically informative\",\n      \"pmids\": [\"29270671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The common KCNH2 polymorphism K897T alters channel electrophysiology: K897T channels have lower current density, activate at more negative potentials, and inactivate and recover from inactivation faster than WT channels. P967L and R1047L channels are electrophysiologically indistinguishable from WT. All HERG channel types have similar sensitivity to cisapride block.\",\n      \"method\": \"Heterologous expression in HEK293 cells, Western blot, voltage-clamp electrophysiology\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic electrophysiological characterization of multiple polymorphisms with biochemical analysis; single lab\",\n      \"pmids\": [\"14975928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"hERG channels physically and functionally interact with beta1 integrin subunits in human neuroblastoma and leukaemia cells. Beta1 integrin activation causes long-lasting hERG channel activation; beta1 integrins and hERG1 co-precipitate, suggesting formation of a macromolecular signaling complex. hERG channel activity modulates integrin downstream signaling.\",\n      \"method\": \"Co-immunoprecipitation, electrophysiology, integrin activation assays in neuroblastoma and leukaemia cells\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP result reported in a review-type communication with limited mechanistic detail\",\n      \"pmids\": [\"15494025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rab11B, a small GTPase, regulates Kv11.1 trafficking; dominant-negative Rab11B prevents pharmacological correction of the trafficking-deficient G601S LQT2 mutant from the transitional ER.\",\n      \"method\": \"Co-expression with dominant-negative Rab11B in HEK293 cells, confocal analysis, pharmacological rescue assays\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — dominant-negative approach establishing Rab11B in the trafficking pathway; single lab, single method for Rab11B involvement\",\n      \"pmids\": [\"23864605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Probucol reduces hERG channel membrane expression by decreasing SGK1 expression, leading to decreased phosphorylation of the E3 ubiquitin ligase Nedd4-2. Reduced Nedd4-2 phosphorylation results in enhanced hERG ubiquitination and degradation. Carbachol rescues hERG channels by restoring Nedd4-2 phosphorylation.\",\n      \"method\": \"Western blot, immunoprecipitation (ubiquitination assays), pharmacological rescue in hERG-HEK293 cells\",\n      \"journal\": \"Drug design, development and therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP/ubiquitination assays without direct electrophysiological mechanistic confirmation; correlation-based chain of evidence\",\n      \"pmids\": [\"26229434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"KCNH2 (Kcnh2) deficiency in a sepsis model activates the FAK/AKT-FOXO3A pathway: Kcnh2 knockout (Kcnh2+/-) rats show inhibition of FAK/AKT signaling, upregulation of FOXO3A and its downstream pro-apoptotic targets, and worsened cardiac dysfunction. Activation of AKT or siRNA knockdown of FOXO3A rescues the Kcnh2-deficiency phenotype, positioning Kcnh2 upstream of FAK/AKT-FOXO3A in cardiomyocyte survival signaling.\",\n      \"method\": \"Kcnh2+/- rat model, echocardiography, Western blot, AKT activator pharmacology, FOXO3A siRNA knockdown\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — genetic knockout with pathway analysis, but epistasis established primarily by pharmacological rescue without direct molecular interaction data\",\n      \"pmids\": [\"33263944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PIKfyve, activated by PKB/Akt, upregulates hERG channel activity and increases hERG protein abundance in the cell membrane in Xenopus oocytes. PKB/Akt-resistant PIKfyve (S318A) does not augment hERG when combined with PKB, establishing PKB-mediated PIKfyve activation as upstream of hERG membrane expression.\",\n      \"method\": \"Xenopus oocyte co-expression, dual electrode voltage clamp, confocal microscopy with antibody-based surface quantification\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Xenopus oocyte overexpression system without direct molecular mechanism for PIKfyve effect on hERG trafficking\",\n      \"pmids\": [\"23735862\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCNH2 (hERG/Kv11.1) encodes the pore-forming alpha-subunit of IKr, the rapid delayed rectifier K+ channel critical for cardiac repolarization; its slow deactivation (regulated by PAS/N-Cap domain interactions with the cNBH and C-linker domains) and rapid voltage-dependent inactivation confer unique gating properties, while protein trafficking to the plasma membrane is governed by a chaperone network (Hsp70/Hsc70/FKBP38), lipid raft localization, and Rab11B-dependent vesicular transport, with most LQT2 mutations causing ER retention and proteasomal degradation rather than intrinsic channel dysfunction, and channel activity regulated by 14-3-3epsilon-mediated PKA phosphorylation, membrane cholesterol, Akt/PI3K signaling, and TRH-dependent second messenger pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCNH2 (hERG/Kv11.1) encodes the pore-forming alpha-subunit of the rapid delayed rectifier K+ current (IKr) that governs cardiac repolarization, and most loss-of-function disease alleles act not by disabling the channel pore but by blocking its delivery to the cell surface [#0, #8]. Its hallmark slow deactivation is built from intramolecular contacts between the N-terminal N-Cap/PAS domain and the C-terminal cyclic-nucleotide-binding homology (cNBH) and C-linker domains, including a specific Arg56–Asp803 charge pair that stabilizes the open state [#10], while the S4 arginine R534 serves as a voltage-sensor residue and the S4-S5 linker integrates cytoplasmic signals into gating rather than acting as a rigid lever [#12, #27]. Native IKr requires co-assembly of the 1a and 1b isoforms: the 1b subunit is necessary for full current and normal action-potential duration, and the 1a-specific PAS domain confers slow deactivation [#8, #9]. Surface expression depends on a chaperone and trafficking network in which Hsp70 stabilizes the channel and suppresses ubiquitination while Hsc70 promotes degradation, the co-chaperone FKBP38 and Hsp90 promote export, and Rab11B-dependent vesicular transport delivers channels from the ER, with the protein partitioning into cholesterol-rich lipid raft and T-tubular membranes [#5, #4, #14, #18]. Trafficking-deficient (class 2) LQT2 mutants are recognized by the ER chaperones calnexin and calreticulin, trigger the unfolded protein response, and are cleared by the 26S proteasome, but can be rescued pharmacologically (E-4031, thapsigargin) or by reduced temperature [#0, #2, #20, #3]. Channel activity is further tuned by beta-adrenergic/PKA signaling amplified through 14-3-3epsilon binding to the C-terminus, by extracellular protons that accelerate deactivation, and by Akt/PI3K signaling whose direction is reversed by the common K897T polymorphism [#6, #11, #15]. hERG associates with the KCNQ1/KCNE1 channel subunits in native cardiac tissue, and its expression is transcriptionally driven by Tbx20 [#19, #16, #25].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that LQT2 missense mutations can suppress IKr through dominant-negative coassembly and, for some alleles, by shifting inactivation voltage dependence, defining distinct biophysical mechanisms of current loss.\",\n      \"evidence\": \"Two-electrode voltage clamp of WT/mutant co-injected Xenopus oocytes\",\n      \"pmids\": [\"9721698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether suppression arises from gating versus trafficking defects\", \"Limited to three pore/linker mutations\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Showed that a dominant-negative LQT2 mutation lowers WT channel abundance by promoting recognition of misfolded heteromers and proteasomal turnover, shifting the disease paradigm toward protein quality control.\",\n      \"evidence\": \"Co-expression with myc-tagged WT, proteasome inhibition, temperature rescue, pulse-chase in mammalian cells\",\n      \"pmids\": [\"10753933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific ER recognition machinery not identified\", \"Did not quantify residual surface current\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Distinguished a trafficking-deficient (class 2) mechanism as correctable through the secretory pathway, showing pharmacological rescue restores surface expression and glycosylation via the Golgi.\",\n      \"evidence\": \"Confocal imaging, Western blot, electrophysiology with thapsigargin/E4031 and brefeldin A controls in HEK293\",\n      \"pmids\": [\"12837749\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular targets of thapsigargin/E4031 rescue distinct from acute block unresolved\", \"Mutant-specific rescue differences unexplained\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the native subcellular localization and isoform requirement of IKr, placing ERG1 at the T-tubular system and showing the ERG1 B isoform is necessary for adult myocyte IKr.\",\n      \"evidence\": \"Immunoelectron microscopy in rat heart and isoform-selective knockout with patch clamp/ECG in mice\",\n      \"pmids\": [\"14670813\", \"12612061\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Isoform stoichiometry in human myocardium not established\", \"Mechanism linking localization to repolarization efficacy inferred\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Quantified the dominance of the trafficking-deficient mechanism across LQT2 alleles and identified C-terminal PKA-site/14-3-3epsilon coupling as a beta-adrenergic regulatory axis disrupted by truncation mutations.\",\n      \"evidence\": \"Systematic Western blot/expression of 34 mutations; CHO electrophysiology with dominant-negative co-expression\",\n      \"pmids\": [\"16432067\", \"16923798\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of 14-3-3epsilon regulation to arrhythmia unquantified\", \"Generalizability of rescue across all class-2 alleles incomplete\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified specific chaperone components (FKBP38, Hsc70/Hsp90 system) and lipid raft/T-tubular partitioning as determinants of hERG surface delivery and biophysics.\",\n      \"evidence\": \"Proteomics, reciprocal Co-IP, siRNA, rescue, and membrane fractionation with cholesterol manipulation in HEK293/HL-1 and cardiomyocytes\",\n      \"pmids\": [\"17569659\", \"18708743\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Hierarchy among co-chaperones not fully ordered\", \"Causal link between raft residence and native IKr gating not proven in vivo\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved opposing roles of Hsp70 and Hsc70 in hERG ubiquitination and stability and showed mutant channels bind Hsc70 more avidly, linking chaperone choice to degradation and demonstrating heat-shock rescue of IKr in cardiomyocytes.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, siRNA, electrophysiology in HEK293 and HL-1 cells\",\n      \"pmids\": [\"21183741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase coupling chaperone state to ubiquitination not identified here\", \"Therapeutic feasibility of heat-shock induction untested in vivo\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected trafficking-deficient mutants to ER chaperone surveillance and the unfolded protein response, and showed PAS-domain mutations form a biophysically distinct class often refractory to pore-blocker rescue.\",\n      \"evidence\": \"Co-IP with calnexin/calreticulin, ATF6/UPR readouts, in vitro PAS-domain unfolding, and trafficking/rescue assays\",\n      \"pmids\": [\"22242185\", \"22396785\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"UPR contribution to arrhythmogenesis in vivo unestablished\", \"Why PAS mutants resist pore-blocker rescue mechanistically unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped the intramolecular N-Cap/PAS–cNBH/C-linker interactions governing slow deactivation and demonstrated that the 1b isoform and 1a PAS domain set native IKr magnitude and repolarization stability in human cardiomyocytes.\",\n      \"evidence\": \"Mutant cycle electrophysiology and shRNA/PAS-fragment manipulation in hiPSC-derived cardiomyocytes\",\n      \"pmids\": [\"25074935\", \"25453103\", \"26775140\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of N-Cap/cNBH contacts at atomic resolution not provided\", \"Quantitative 1a:1b ratio in human heart unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined transcriptional and gating-architecture contributions, showing Tbx20 directly drives KCNH2 expression and that the S4-S5 linker integrates cytoplasmic signals rather than acting as a rigid lever.\",\n      \"evidence\": \"Tbx20 overexpression/variant analysis in hiPSC-CMs and split-channel/MTS gating experiments\",\n      \"pmids\": [\"28049825\", \"29270671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Broader transcriptional network controlling KCNH2 not mapped\", \"Physiological signals relayed through the S4-S5 linker not enumerated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended KCNH2 function beyond ion conduction by placing it upstream of FAK/AKT-FOXO3A cardiomyocyte survival signaling in a sepsis model.\",\n      \"evidence\": \"Kcnh2+/- rat model with echocardiography, Western blot, AKT activation, and FOXO3A siRNA rescue\",\n      \"pmids\": [\"33263944\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Epistasis established by pharmacology without direct molecular interaction data\", \"Whether channel conduction or a non-conducting role drives the effect unresolved\", \"Not confirmed independently\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the chaperone/quality-control network, lipid environment, transcriptional control, and signaling inputs are integrated to set native IKr and how this can be therapeutically rescued in patient myocardium remains incompletely defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified in vivo model linking trafficking machinery to arrhythmia outcome\", \"Atomic structures of full-length channel with regulatory domains absent from corpus\", \"Allele-specific rescuability not predictable from sequence\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 8, 9]},\n      {\"term_id\": \"GO:0005216\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": []}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 7, 14]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 18, 20]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [3, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [8, 9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 5, 20]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 18, 30]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 15]}\n    ],\n    \"complexes\": [\"IKr channel (hERG 1a/1b heteromer)\", \"KCNQ1/KCNE1 channel complex\"],\n    \"partners\": [\"KCNQ1\", \"KCNE1\", \"FKBP38\", \"HSPA8\", \"HSPA1A\", \"YWHAE\", \"RAB11B\", \"CANX\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}