{"gene":"KCNJ1","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1994,"finding":"ROMK1 channel activity is regulated by phosphorylation/dephosphorylation: channel rundown involves a Mg2+-dependent dephosphorylation process, and PKA-dependent phosphorylation restores and increases channel open probability. Addition of exogenous PKA catalytic subunit increased open probability, and the specific PKA inhibitor PKI partially reversed this effect.","method":"Patch clamp (excised inside-out patches), pharmacological inhibitors (okadaic acid, calyculin A, orthovanadate), exogenous PKA catalytic subunit application","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal electrophysiological methods with pharmacological controls, replicated concept across multiple subsequent papers","pmids":["8058760"],"is_preprint":false},{"year":1999,"finding":"PKA activates ROMK1 channels by enhancing their interaction with membrane PIP2: PKA phosphorylation lowers the PIP2 concentration required for channel activation, and mutation of PKA phosphorylation sites decreases PIP2-channel interaction. PKA does not directly activate ROMK1 in membranes devoid of PIP2.","method":"Inside-out patch clamp, solution-binding assays with anti-PIP2 antibodies, ATP[gammaS] as PKA substrate, site-directed mutagenesis of PKA sites","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods (electrophysiology, binding assay, mutagenesis) in single rigorous study","pmids":["10318968"],"is_preprint":false},{"year":2007,"finding":"WNK1 and WNK4 stimulate clathrin-dependent endocytosis of ROMK1 by interacting with the endocytic scaffold protein intersectin (ITSN) via proline-rich motifs; kinase activity is not required. Disease-causing WNK4 mutations enhance interactions with both ITSN and ROMK1, increasing ROMK1 endocytosis.","method":"Co-immunoprecipitation, surface expression assays, endocytosis assays in heterologous cells, mutagenesis of proline-rich motifs","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional endocytosis assays with mechanistic mutagenesis, replicated for WNK1 and WNK4","pmids":["17380208"],"is_preprint":false},{"year":2002,"finding":"SGK1 and NHERF2 synergize to stimulate ROMK1 activity by increasing channel abundance in the plasma membrane; neither SGK1 nor NHERF2 alone is sufficient. NHERF2 and SGK1 together decrease channel decay after inhibition of vesicle insertion, indicating enhanced membrane trafficking.","method":"Two-electrode voltage clamp in Xenopus oocytes, brefeldin A inhibition of vesicle insertion, surface expression measurement","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 2 — clean co-expression functional assay with trafficking readout, independently confirmed in follow-up studies","pmids":["12444200"],"is_preprint":false},{"year":2003,"finding":"PKC inhibits ROMK1 channel activity by reducing membrane PIP2 content; ROMK1 mutants with reduced PIP2 affinity show increased sensitivity to PKC activation (phorbol ester). After PKC-induced inhibition in cell-attached patches, exogenous PIP2 restores channel activity in excised patches.","method":"Cell-attached and inside-out patch clamp in Xenopus oocytes, PIP2 content measurement, PMA/carbachol/calphostin-C pharmacology, mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods (electrophysiology, PIP2 measurement, pharmacology, mutagenesis) establishing a coherent mechanism","pmids":["12615924"],"is_preprint":false},{"year":2000,"finding":"Protein tyrosine kinase (PTK, c-Src) and protein tyrosine phosphatase (PTP-1D) regulate ROMK1 surface expression: inhibiting PTP increases internalization of ROMK1, while inhibiting PTK stimulates insertion of ROMK1 into the plasma membrane. Tyrosine residue Y337 of ROMK1 is essential for this regulation. PTK inhibition also requires intact microtubules for its exocytic effect.","method":"Two-electrode voltage clamp, patch clamp, co-expression of c-Src in Xenopus oocytes, pharmacological inhibitors (PAO, herbimycin A, colchicine, taxol, sucrose/concanavalin A), site-directed mutagenesis (Y337A)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with mutagenesis identifying specific regulatory residue, replicated in follow-up studies","pmids":["11114300"],"is_preprint":false},{"year":2001,"finding":"Inhibition of protein tyrosine phosphatase increases tyrosine phosphorylation of ROMK1 at Y337 and induces dynamin-dependent endocytosis of the channel, reducing surface expression by 65%. Dominant negative dynamin (K44A) completely blocks this endocytic effect.","method":"Confocal microscopy of GFP-ROMK1, biotin labeling, patch clamp, co-transfection with c-Src and dominant negative dynamin, mutagenesis (Y337A)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (imaging, biochemistry, electrophysiology, dominant negative) with mechanistic mutagenesis","pmids":["11719519"],"is_preprint":false},{"year":2002,"finding":"ROMK1 is a substrate of PKC; serine residues S4 and S201 are the two main PKC phosphorylation sites essential for surface expression of ROMK1. Mutating both sites (S4/201A) reduces surface expression to near-zero; phosphomimetic S4/201D mutation completely restores surface expression and K+ current.","method":"In vitro phosphorylation assay with 32P-ATP, site-directed mutagenesis, two-electrode voltage clamp, confocal microscopy of GFP-ROMK1, biotin surface labeling in HEK293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation combined with mutagenesis, imaging, and functional rescue","pmids":["12221079"],"is_preprint":false},{"year":2005,"finding":"ROMK1 is monoubiquitinated in native renal tissue; Lys22 is the ubiquitin-binding site. Mutation K22R abolishes ubiquitination and increases surface expression and channel activity without altering biophysical properties, demonstrating monoubiquitination reduces surface expression of ROMK1.","method":"Immunoprecipitation from renal cortex, site-directed mutagenesis of all intracellular lysines, two-electrode voltage clamp, confocal microscopy, biotin surface labeling in HEK293 cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — native tissue IP combined with systematic mutagenesis, imaging, and biochemical surface labeling","pmids":["15767585"],"is_preprint":false},{"year":2005,"finding":"WNK3 inhibits ROMK1 channel activity by reducing plasmalemmal surface expression; this inhibition is independent of WNK3 kinase activity and is mediated by the carboxyl terminus of WNK3. A kinase-inactivating mutation or PHA2-homologous missense mutation in WNK3 enhances inhibition of ROMK1.","method":"Two-electrode voltage clamp in Xenopus oocytes, surface expression measurements, kinase-dead and disease mutant constructs","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean functional assay with domain mutagenesis, single lab","pmids":["16357011"],"is_preprint":false},{"year":1998,"finding":"PKA-dependent regulation of ROMK1 channels requires an A kinase anchoring protein (AKAP79/75): ROMK1 alone does not respond to forskolin or cAMP, but co-expression with AKAP79 confers cAMP/PKA responsiveness. Both the membrane-targeting domain and PKAII-binding domain of AKAP are required.","method":"Two-electrode voltage clamp and patch clamp in Xenopus oocytes, RII overlay assay on kidney membranes, pharmacological inhibition with H89/PKI","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — multiple complementary functional and biochemical assays identifying AKAP as essential intermediary","pmids":["9707637"],"is_preprint":false},{"year":1998,"finding":"pH-dependent gating of ROMK1 (Kir1.1) involves conformational changes in both N terminus (Cys49) and C terminus (Cys308): both intracellular cysteines react with thiol reagents only in the closed (acidified) state, not in the open state, indicating protein domain movement during pH gating.","method":"Site-directed mutagenesis of all intracellular cysteines, state-dependent modification by water-soluble oxidants and sulfhydryl reagents, patch clamp","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis combined with state-dependent chemical modification in functional channels","pmids":["9852128"],"is_preprint":false},{"year":1996,"finding":"ROMK1 (Kir1.1) is regulated allosterically by both extracellular K+ concentration and intracellular pH. K+ regulation is determined by the core channel region (M1, M2, P), while pH coupling is determined by the N terminus, as shown by chimeric channel studies exchanging N-termini between ROMK1 and pH-insensitive IRK1.","method":"Site-directed mutagenesis, chimeric channel construction, two-electrode voltage clamp in Xenopus oocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — chimeric channel dissection with functional validation identifies distinct structural determinants","pmids":["8663367"],"is_preprint":false},{"year":1995,"finding":"The second transmembrane segment (M2) of ROMK1 is a straight alpha-helix with three distinct structural environments: lipid-facing (tolerant to both Trp and Ala), protein-interior-facing (tolerant to Ala only), and pore-facing (intolerant to either substitution), established by systematic perturbation scanning mutagenesis.","method":"Site-directed mutagenesis of 18 consecutive M2 residues with Trp and Ala substitutions, functional expression in Xenopus oocytes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with comprehensive functional readout defining transmembrane topology","pmids":["8618841"],"is_preprint":false},{"year":2000,"finding":"Multiple histidine residues in the C terminus of ROMK1 (His225, His274, His342, His354) contribute to CO2 and pH sensing; mutation of each reduces CO2 and pH sensitivity by 20-50%, and simultaneous mutation of all four eliminates CO2 sensitivity.","method":"Systematic site-directed mutagenesis of all histidine residues, patch clamp in Xenopus oocytes, CO2 and pH sensitivity measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — comprehensive systematic mutagenesis with quantitative functional readout","pmids":["10713095"],"is_preprint":false},{"year":2005,"finding":"The pH gate of Kir1.1 is located at the helix bundle crossing near the cytoplasmic end of the inner transmembrane helices: Leu160 residues from each subunit form a steric gate. Replacing L160 with glycine abolishes pH gating; polar substitutions (L160S, L160T) also eliminate gating, indicating size and hydrophobicity at this position are both required.","method":"Site-directed mutagenesis, patch clamp in Xenopus oocytes, homology modeling based on KirBac1.1 crystal structure","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis combined with structural modeling, multiple independent mutations tested","pmids":["15653740"],"is_preprint":false},{"year":2006,"finding":"Cysteine-scanning mutagenesis localizes the Kir1.1 pH gate to the transmembrane pore at position 175: a reintroduced cysteine at M2 position 175 is accessible to MTS reagents in the open state but protected from modification upon channel closure by low pH, indicating a conformational change that occludes the transmembrane pore.","method":"Cysteine-scanning mutagenesis, cytoplasmic-side MTS reagent modification (MTSEA, MTSET, MTSES, Ag+) in inside-out macropatches from Xenopus oocytes","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1 — state-dependent cysteine modification directly localizes gate position","pmids":["16891366"],"is_preprint":false},{"year":2002,"finding":"The ATP/PIP2 binding site in Kir1.1 is localized to a 39-amino acid region at the proximal C terminus; three conserved arginine residues (R188, R203, R217) are critical for nucleotide binding, and PIP2 competes with ATP at this site.","method":"MBP fusion protein binding assay with TNP-ATP fluorescent nucleotide, PIP2 competition assay, site-directed mutagenesis of arginine residues","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding assay with systematic mutagenesis identifying binding domain","pmids":["12381730"],"is_preprint":false},{"year":2006,"finding":"CFTR is required for ATP and glibenclamide sensitivity of the 30 pS Kir1.1 channel in TAL cells; both sensitivities are absent in CFTR knockout and deltaF508 mice. PKA activity abrogates the CFTR effect on ATP sensitivity, indicating CFTR provides a PKA-regulated switch determining the ratio of open to ATP-inhibited ROMK channels.","method":"Patch clamp in native TAL cells from CFTR knockout and deltaF508 mice, curcumin rescue experiment, PKA manipulation","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — clean genetic knockout with native cell electrophysiology plus pharmacological rescue","pmids":["16470247"],"is_preprint":false},{"year":2002,"finding":"ENaC up-regulates Kir1.1 (ROMK1) surface expression and currents, but only in the presence of CFTR; CFTR provides a mechanistic link for coordinated regulation of ENaC and ROMK1. SUR2B does not traffic to the plasma membrane when co-expressed with Kir1.1b.","method":"Two-electrode voltage clamp in Xenopus oocytes, surface expression analysis, co-expression of ENaC, CFTR, and Kir1.1 in various combinations","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — functional co-expression system with surface expression measurement, single lab","pmids":["11994290"],"is_preprint":false},{"year":2003,"finding":"SGK1 stimulates ROMK1 via phosphorylation at Ser44, which shifts the pH sensitivity of the channel to more acidic values; deletion of either the second PDZ domain of NHERF2 or the PDZ binding motif on ROMK1 abolishes the stimulatory effect of SGK1 on ROMK1 surface expression. SGK1 interacts with NHERF2 through the second PDZ domain of NHERF2.","method":"Pull-down assays, site-directed mutagenesis of Ser44, two-electrode voltage clamp in Xenopus oocytes, chemiluminescence surface expression assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — pull-down plus mutagenesis and functional readout, single lab","pmids":["14623317","12878206"],"is_preprint":false},{"year":2009,"finding":"POSH acts as an E3 ubiquitin ligase for ROMK1: POSH binds ROMK1 at its N terminus, stimulates ROMK1 ubiquitination (confirmed by in vitro ubiquitination assay), and promotes dynamin-dependent but clathrin-independent endocytosis of ROMK1. Deletion of the RING domain abolishes both ubiquitination and endocytic effects.","method":"Immunostaining, Co-IP, GST pulldown, electrophysiology, biotin surface labeling, in vitro ubiquitination assay, dominant-negative dynamin, RING domain deletion","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro ubiquitination assay plus multiple orthogonal cellular assays including dominant negative and domain deletion","pmids":["19710010"],"is_preprint":false},{"year":2004,"finding":"c-Src (Src family PTK) is co-expressed with ROMK in the TAL, CCD, and OMCD. Stimulation of PTK by phenylarsine oxide in CCD from high-K diet rats decreases ROMK apical/subapical membrane staining and increases intracellular staining, demonstrating PTK controls ROMK membrane localization in the CCD but not the TAL.","method":"Immunofluorescence staining, confocal microscopy, biotin labeling, dietary K manipulation in rats","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization experiment in native tubule segments with functional consequence, single lab","pmids":["15075184"],"is_preprint":false},{"year":2001,"finding":"SNARE proteins mediate PTK inhibition-induced exocytosis of ROMK1: tetanus toxin abolishes the herbimycin A-induced increase in surface ROMK1 channels, demonstrating SNARE-dependent exocytosis. Tyrosine dephosphorylation at Y337 is required for this exocytic insertion.","method":"Confocal microscopy, patch clamp, biotin surface labeling in HEK293 cells, tetanus toxin treatment, mutagenesis (Y337A)","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods with toxin inhibition of specific exocytic machinery, single lab","pmids":["12556363"],"is_preprint":false},{"year":2008,"finding":"WNK1 inhibits ROMK1 through its N-terminal proline-rich domain (aa 1-119); an N-linker domain (aa 120-220) antagonizes this inhibition; the kinase domain reverses the N-linker antagonism via charge-charge interactions between K233 and D368 (not kinase activity); the autoinhibitory domain and first coiled-coil domain further modulate the effect through intramolecular interactions.","method":"Domain deletion and mutagenesis of WNK1, two-electrode voltage clamp in Xenopus oocytes","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic domain mutagenesis with functional readout, single lab","pmids":["18550644"],"is_preprint":false},{"year":2010,"finding":"Angiotensin II inhibits ROMK1 channels by two mechanisms: (1) PKC-stimulated c-Src tyrosine phosphorylation of ROMK1 at Y337, and (2) synergizing WNK4-mediated inhibition via a PTK-dependent pathway. Losartan or PKC inhibition blocks the effect; the Y337A ROMK1 mutant is resistant to direct Ang II inhibition but not to WNK4-mediated inhibition restored by Ang II.","method":"Perforated whole-cell patch clamp in HEK293 cells, Western blot for tyrosine phosphorylation, pharmacological inhibitors (losartan, PKC inhibitor, PTK inhibitor), mutagenesis (Y337A), native CCD patch clamp in rats","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods, mutagenesis, and native tissue confirmation, single lab","pmids":["20927043"],"is_preprint":false},{"year":2015,"finding":"WNK4 is a substrate of c-Src at Y1092, Y1094, and Y1143; c-Src and PTP-1D co-immunoprecipitate with WNK4. Phosphorylation at Y1092/Y1094 is required for WNK4-mediated inhibition of ROMK; phosphorylation at Y1143 is required for PTP-1D association and for SGK1 to reverse WNK4 inhibition of ROMK.","method":"Western blot, mass spectrometry, co-immunoprecipitation, site-directed mutagenesis of WNK4 tyrosines, functional ROMK assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — mass spectrometry identification of phosphorylation sites combined with mutagenesis, Co-IP, and functional assay","pmids":["25805816"],"is_preprint":false},{"year":2014,"finding":"SPAK and OSR1 kinases reduce ROMK1 activity and membrane abundance in a catalytic activity-dependent manner: constitutively active SPAK (T233E) and OSR1 (T185E) reduce ROMK1 surface expression, while catalytically inactive mutants (D212A-SPAK, D164A-OSR1) have no effect.","method":"Dual electrode voltage clamp and chemiluminescence surface expression assay in Xenopus oocytes, constitutively active and kinase-dead mutants of SPAK and OSR1","journal":"Kidney & blood pressure research","confidence":"Medium","confidence_rationale":"Tier 2 — clean functional assay with catalytic mutants, single lab","pmids":["25322850"],"is_preprint":false},{"year":2001,"finding":"An 'IRA' amino acid triplet in the N-terminal extension of ROMK1 (positions 13-19) blocks interaction with SUR2B, preventing SUR2B from conferring glibenclamide sensitivity. Direct physical interaction between ROMK1 and SUR2B (demonstrated by in vitro co-translation and co-immunoprecipitation) is required for glibenclamide-sensitive K+ currents.","method":"N-terminal deletion and substitution mutagenesis of ROMK1, two-electrode voltage clamp in Xenopus oocytes, in vitro co-translation and co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro co-translation/IP combined with systematic mutagenesis and functional expression","pmids":["11567030"],"is_preprint":false},{"year":1998,"finding":"The NH2 terminus of ROMK1 (specifically serine-4) determines sensitivity to arachidonic acid (AA) inhibition. ROMK2 and ROMK3 splice variants lacking this N-terminal region show minimal AA inhibition; deletion of residues 2-37 or S4A mutation markedly reduces AA-induced inhibition. PKC phosphorylation at S4 also inhibits ROMK1.","method":"Patch clamp in Xenopus oocytes, NH2-terminal deletion and point mutagenesis, pharmacological inhibitors (calphostin C, chelerythrine, staurosporine)","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple splice variants compared with mutagenesis and pharmacology, single lab","pmids":["9458837"],"is_preprint":false},{"year":1999,"finding":"A Bartter syndrome-causing truncation mutation (Kir1.1a 331X) reaches the plasma membrane but locks the channel in a closed state. Co-expression with wild-type exerts a dominant negative effect; the extreme C terminus (residues 332-351) is an essential subunit interaction domain controlling oligomerization efficiency and open-state occupancy.","method":"Co-expression with wild-type in Xenopus oocytes, GFP fusion for plasma membrane localization, incremental C-terminal reconstruction, tetrameric concatemer approach, patch clamp","journal":"The Journal of general physiology","confidence":"High","confidence_rationale":"Tier 1 — systematic domain reconstruction with multiple functional assays and dominant negative analysis","pmids":["10532965"],"is_preprint":false},{"year":2009,"finding":"The immunoglobulin-like domain (IgLD) in the intracellular region of Kir1.1 is essential for thermodynamic stability, trafficking, and gating. Two Bartter syndrome mutations (A198T, Y314C) within the IgLD core impair channel biosynthesis and trafficking; channels that reach the surface are electrically silent due to helix-bundle gate closure and cannot rectify.","method":"Atomic model mapping of ABS mutations, thermodynamic stability calculations by computational mutagenesis, mammalian cell trafficking assay, patch clamp electrophysiology, compensatory mutation rescue","journal":"Channels (Austin, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 — structural modeling combined with functional trafficking and electrophysiology assays, single lab","pmids":["19221509"],"is_preprint":false},{"year":2009,"finding":"An intersubunit salt bridge (R128-E132) in the P-loop near the selectivity filter stabilizes the active state of Kir1.1. Disruption of this salt bridge causes inactivation even in 100 mM external K+; external Ba2+ or tertiapin-Q binding to the outer channel mouth prevents inactivation, indicating inactivation involves conformational changes near the selectivity filter analogous to C-type inactivation.","method":"Site-directed mutagenesis, two-electrode voltage clamp in Xenopus oocytes, external Ba2+ and tertiapin-Q pharmacology, variable external K+ manipulation","journal":"Biophysical journal","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis with pharmacological rescue, single lab","pmids":["19686653"],"is_preprint":false},{"year":2011,"finding":"High-K diet causes a large increase in apical ROMK expression in DCT2, CNT, and CD but not DCT1, accompanied by dramatically increased mature glycosylation, demonstrating dietary K+ regulates ROMK1 surface density through altered trafficking and glycosylation in a nephron-segment-specific manner.","method":"Immunofluorescence with new ROMK-specific antibodies verified on knockout mice, segmental markers, glycosylation state analysis by Western blot, dietary K manipulation","journal":"American journal of physiology. Renal physiology","confidence":"High","confidence_rationale":"Tier 2 — rigorous localization with knockout-validated antibodies, dietary manipulation, biochemical readout","pmids":["21454252"],"is_preprint":false},{"year":2016,"finding":"ROMK1 isoform-specific knockout mice (Romk1-/-) do not develop Bartter phenotype (no reduced NKCC2 activity or increased NCC), indicating no functional link between ROMK1 and NKCC2 in TAL. However, high K+ diet-stimulated K+ secretion in the collecting tubule is absent in Romk1-/-, demonstrating ROMK1 is specifically required for dietary K+-induced K+ secretion.","method":"ES cell Cre-LoxP selective deletion of Romk1-specific exon 1, patch clamp of collecting tubule SK channels, immunofluorescence, dietary K manipulation, comparison with global Romk-/- knockout","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean isoform-specific knockout with multiple functional and biochemical readouts","pmids":["26728465"],"is_preprint":false},{"year":2014,"finding":"Kir1.1 (ROMK) channels are required for gastric acid secretion and co-localize with the beta-subunit of H+/K+-ATPase in gastric parietal cells. In Kir1.1-deficient mice, secretagogue-stimulated acid secretion is absent; luminal K+ restores acid secretion, demonstrating Kir1.1 provides a K+ recycling pathway essential for H+/K+-ATPase function in parietal cells.","method":"Kir1.1 knockout mice, immunofluorescence co-localization, whole-stomach acid secretion, perfused gastric gland secretion assay, luminal tertiapin-Q and XE991 inhibition","journal":"Pflugers Archiv : European journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with direct functional assay in native tissue and pharmacological confirmation","pmids":["25127675"],"is_preprint":false},{"year":2017,"finding":"Small-molecule inhibitor VU590 blocks Kir1.1 within the pore in a voltage- and K+-dependent manner; asparagine N171 is the only pore-lining residue required for high-affinity block, and negatively charged substitutions (N171D/E) weaken block, while equivalent negative charge in Kir7.1 enhances block, revealing differential roles of pore polarity in determining inhibitor pharmacology.","method":"Molecular modeling, site-directed mutagenesis, patch clamp electrophysiology","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 — mutagenesis with structural modeling and functional validation, single lab","pmids":["28619748"],"is_preprint":false},{"year":2009,"finding":"FRET measurements show that during pHi gating of Kir1.1, the cytoplasmic pore conformation changes: N- and C-termini move apart from each other when the channel is open (high pH), and move closer when closed (low pH).","method":"FRET with ECFP-Kir1.1-EYFP fusion constructs, pH manipulation in Xenopus oocytes","journal":"Journal of biomedical science","confidence":"Medium","confidence_rationale":"Tier 1 — direct FRET measurement of conformational change during gating, single lab","pmids":["19272129"],"is_preprint":false},{"year":2017,"finding":"NHERF1 knockdown in M-1 CCD cells reduces surface expression of ROMK1 (detected by biotin labeling) and decreases Ba2+-sensitive whole-cell K+ current and the number of active channels in patches, demonstrating NHERF1 is required for ROMK1 surface expression and function in native collecting duct cells.","method":"NHERF1 siRNA knockdown in M-1 cells, cell surface biotinylation assay, patch clamp electrophysiology, transfection with EGFP-ROMK1","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — knockdown in relevant native cell type with both biochemical and electrophysiological readouts","pmids":["28533091"],"is_preprint":false},{"year":1994,"finding":"Human ROMK1 gene produces multiple transcript isoforms (ROMK1A, 1B, 1C) through alternative splicing and use of multiple promoters from a single locus at chromosome 11q24. ROMK1A encodes a functional Ba2+-sensitive inwardly rectifying K+ channel when expressed in Xenopus oocytes.","method":"cDNA cloning, RT-PCR, alternative splicing analysis, fluorescence in situ hybridization, Xenopus oocyte expression and two-electrode voltage clamp","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 2 — molecular cloning with functional expression, mapped to chromosome","pmids":["8190102"],"is_preprint":false}],"current_model":"ROMK1 (Kir1.1/KCNJ1) is an inwardly rectifying K+ channel in the kidney apical membrane that mediates K+ secretion and recycling; its channel activity and surface expression are tightly regulated by phosphorylation (PKA via AKAP scaffolding increases PIP2 affinity; PKC phosphorylation at S4/S201 is required for surface expression; SGK1 phosphorylation at S44 via NHERF2 shifts pH sensitivity; tyrosine phosphorylation at Y337 by c-Src drives dynamin-dependent endocytosis), by ubiquitination (monoubiquitination at K22 reduces surface expression via POSH E3 ligase), by WNK kinases (WNK1/WNK3/WNK4 reduce surface expression through intersectin-dependent endocytosis and SPAK/OSR1 activation), by direct interaction with PIP2 (essential for channel opening), and by intracellular pH gating through a steric gate formed by leucine residues at the inner helix bundle crossing."},"narrative":{"teleology":[{"year":1994,"claim":"Cloning of KCNJ1 revealed it encodes a Ba²⁺-sensitive inwardly rectifying K⁺ channel with multiple alternatively spliced isoforms from a single locus, establishing the molecular identity of the renal secretory K⁺ channel.","evidence":"cDNA cloning, chromosomal mapping by FISH, functional expression in Xenopus oocytes","pmids":["8190102"],"confidence":"High","gaps":["Nephron segment-specific functions of individual splice variants were unknown","Regulatory mechanisms governing channel activity had not been explored"]},{"year":1994,"claim":"Demonstrating that PKA phosphorylation restores channel activity after rundown established that ROMK is tonically regulated by a phosphorylation–dephosphorylation cycle, raising the question of how PKA is coupled to the channel.","evidence":"Excised inside-out patch clamp with exogenous PKA catalytic subunit and phosphatase inhibitors","pmids":["8058760"],"confidence":"High","gaps":["Identity of the PKA anchoring mechanism was unknown","Whether PKA acts directly on the channel or through an intermediary was unresolved"]},{"year":1996,"claim":"Chimeric channel studies between ROMK1 and pH-insensitive IRK1 showed that extracellular K⁺ sensing maps to the core pore region while pH gating maps to the N-terminus, establishing that these two regulatory modalities are structurally separable.","evidence":"N-terminal chimera construction with two-electrode voltage clamp in oocytes","pmids":["8663367"],"confidence":"High","gaps":["The molecular identity of pH-sensing residues was not determined","Location of the physical gate was unknown"]},{"year":1998,"claim":"Discovery that AKAP79 is required for cAMP/PKA responsiveness of ROMK1 resolved how PKA is functionally coupled to the channel — through a scaffolding protein that localizes PKA to the channel.","evidence":"Co-expression of AKAP79 with ROMK1 in oocytes; RII overlay on kidney membranes","pmids":["9707637"],"confidence":"High","gaps":["Whether AKAP directly binds ROMK1 or acts through an intermediary was unresolved","The PKA phosphorylation sites on ROMK had not been linked to a downstream effector mechanism"]},{"year":1998,"claim":"State-dependent thiol modification of cysteines at positions 49 (N-terminus) and 308 (C-terminus) showed that pH gating involves coordinated conformational changes in both cytoplasmic domains, advancing understanding beyond the N-terminal chimera mapping.","evidence":"Systematic cysteine mutagenesis with state-dependent sulfhydryl reagent modification and patch clamp","pmids":["9852128"],"confidence":"High","gaps":["The transmembrane location of the physical gate remained unknown","Identity of pH-sensing residues was still unresolved"]},{"year":1999,"claim":"Linking PKA phosphorylation to enhanced PIP₂ interaction established the mechanistic basis for PKA activation: PKA does not directly open the channel but lowers the PIP₂ threshold for channel activation, unifying phosphorylation and lipid regulation.","evidence":"Inside-out patch clamp with anti-PIP₂ antibodies, ATP[γS] as PKA substrate, PKA site mutagenesis","pmids":["10318968"],"confidence":"High","gaps":["The PIP₂ binding site on the channel had not been mapped","How PKC and other kinases intersect with PIP₂ regulation was unknown"]},{"year":2000,"claim":"Identification of Y337 as the c-Src phosphorylation site controlling ROMK1 endocytosis versus exocytosis established tyrosine phosphorylation as a bidirectional trafficking switch, with multiple C-terminal histidines (H225, H274, H342, H354) concurrently identified as pH/CO₂ sensors.","evidence":"c-Src co-expression, PTK/PTP pharmacology, Y337A mutagenesis, microtubule disruption (oocytes and HEK293); systematic histidine mutagenesis with CO₂ sensitivity measurements","pmids":["11114300","10713095"],"confidence":"High","gaps":["The endocytic machinery involved (dynamin, clathrin) had not been characterized","How dietary K⁺ signals converge on the Y337 pathway in vivo was unknown"]},{"year":2001,"claim":"Showing that Y337 tyrosine phosphorylation triggers dynamin-dependent endocytosis while dephosphorylation drives SNARE-dependent exocytosis completed the trafficking model, with the SUR2B interaction domain mapped to the ROMK1 N-terminal 'IRA' motif.","evidence":"Dominant-negative dynamin K44A, tetanus toxin inhibition of exocytosis, GFP-ROMK1 imaging, biotin labeling; N-terminal deletion/substitution mutagenesis and co-IP for SUR2B interaction","pmids":["11719519","12556363","11567030"],"confidence":"High","gaps":["The E3 ubiquitin ligase involved in ROMK internalization was unknown","Whether clathrin-dependent or -independent pathways mediate endocytosis was not resolved"]},{"year":2002,"claim":"Three advances converged: PKC phosphorylation sites S4/S201 were shown essential for surface expression; SGK1/NHERF2 were identified as cooperative stimulators of channel trafficking; and the PIP₂/ATP binding site was mapped to a 39-amino-acid C-terminal region with critical arginines R188/R203/R217.","evidence":"In vitro ³²P phosphorylation, S4/S201 mutagenesis, confocal and biotin labeling (PKC); oocyte co-expression with brefeldin A (SGK1/NHERF2); MBP fusion binding assay with TNP-ATP and PIP₂ competition (binding site)","pmids":["12221079","12444200","12381730"],"confidence":"High","gaps":["How SGK1 phosphorylation of ROMK alters pH sensitivity was not yet shown","Physiological stimuli upstream of PKC and SGK1 at the channel were not defined"]},{"year":2003,"claim":"SGK1 was shown to phosphorylate ROMK1 at Ser44, shifting pH sensitivity to more acidic values, through a mechanism requiring the NHERF2 PDZ scaffold — linking kinase, scaffold, and gating modulation into a single regulatory axis.","evidence":"Pull-down assays, S44 mutagenesis, oocyte voltage clamp, chemiluminescence surface expression","pmids":["14623317","12878206"],"confidence":"Medium","gaps":["Whether SGK1-NHERF2-ROMK complex forms in native kidney was not demonstrated","The interplay between SGK1 and WNK pathways on ROMK was unknown"]},{"year":2005,"claim":"The pH gate was physically localized to Leu160 at the inner helix bundle crossing (steric gate requiring both size and hydrophobicity), and monoubiquitination at K22 was identified as a signal reducing surface expression in native kidney, establishing two fundamentally distinct regulatory mechanisms.","evidence":"L160 mutagenesis with homology modeling and patch clamp (gate); immunoprecipitation from renal cortex with systematic lysine mutagenesis and biotin labeling (ubiquitination)","pmids":["15653740","15767585"],"confidence":"High","gaps":["The E3 ligase responsible for K22 ubiquitination was unidentified","How pH-sensor histidines communicate to the L160 gate was structurally unresolved"]},{"year":2006,"claim":"Cysteine accessibility experiments pinpointed position 175 in M2 as the site of pH-dependent pore occlusion, and CFTR was shown to be required for ATP sensitivity of native ROMK channels in TAL, revealing an unexpected functional coupling between two channels.","evidence":"State-dependent MTS modification at engineered cysteine 175 in macropatches (gate); patch clamp in native TAL cells from CFTR knockout and ΔF508 mice (CFTR coupling)","pmids":["16891366","16470247"],"confidence":"High","gaps":["The molecular mechanism of CFTR-ROMK coupling was not elucidated","How the L160 steric gate and position 175 conformational change relate structurally was unclear"]},{"year":2007,"claim":"WNK1 and WNK4 were shown to stimulate ROMK1 endocytosis through a kinase-activity-independent mechanism involving proline-rich motif interactions with the endocytic scaffold intersectin, with disease-causing WNK4 mutations enhancing this interaction — directly linking pseudohypoaldosteronism type II genetics to ROMK trafficking.","evidence":"Co-IP, surface expression and endocytosis assays in heterologous cells, proline-rich motif mutagenesis","pmids":["17380208"],"confidence":"High","gaps":["Whether WNK-intersectin-mediated endocytosis is clathrin-dependent in native tubules was unconfirmed","Downstream kinases (SPAK/OSR1) in this pathway had not been tested on ROMK"]},{"year":2009,"claim":"Multiple structural and regulatory insights converged: POSH was identified as the E3 ligase for ROMK1 ubiquitination driving dynamin-dependent endocytosis; FRET measurements showed N/C-terminal separation during pH-dependent opening; Bartter mutations in the IgLD impaired folding/trafficking; and an intersubunit salt bridge (R128-E132) was shown to prevent C-type-like inactivation.","evidence":"In vitro ubiquitination assay and RING domain deletion (POSH); FRET with ECFP/EYFP fusions (conformation); computational thermodynamic stability with trafficking assay (IgLD); mutagenesis with Ba²⁺/tertiapin-Q rescue (salt bridge)","pmids":["19710010","19272129","19221509","19686653"],"confidence":"High","gaps":["Whether POSH-mediated ubiquitination is regulated by dietary K⁺ in vivo was unknown","Complete structural model of the cytoplasmic domain during gating transitions was lacking"]},{"year":2010,"claim":"Angiotensin II was shown to inhibit ROMK through a dual mechanism — PKC-activated c-Src phosphorylation at Y337 and enhancement of WNK4-mediated inhibition — integrating hormonal signaling with the previously characterized kinase and trafficking pathways.","evidence":"Perforated patch clamp in HEK293 cells, Western blot for pY337, losartan/PKC/PTK inhibitors, Y337A mutagenesis, native CCD patch clamp","pmids":["20927043"],"confidence":"Medium","gaps":["Whether aldosterone opposes Ang II effects on ROMK through SGK1 in the same cells was not tested","In vivo confirmation with Ang II receptor knockout was lacking"]},{"year":2011,"claim":"Knockout-validated immunolocalization showed that high-K⁺ diet dramatically increases apical ROMK expression selectively in DCT2/CNT/CD (not DCT1), with increased mature glycosylation — establishing the in vivo nephron-segment specificity of K⁺-adaptive ROMK trafficking.","evidence":"ROMK-specific antibodies validated on Romk⁻/⁻ mice, segmental markers, glycosylation analysis, dietary K⁺ manipulation","pmids":["21454252"],"confidence":"High","gaps":["The signaling pathway linking plasma K⁺ to increased ROMK glycosylation/trafficking was unidentified","Whether WNK-SPAK axis mediates the segment-specific response was not tested"]},{"year":2014,"claim":"SPAK/OSR1 were shown to reduce ROMK1 surface expression in a kinase-activity-dependent manner, and Kir1.1 knockout revealed an essential role in gastric acid secretion by providing K⁺ recycling for H⁺/K⁺-ATPase — extending ROMK function beyond the kidney.","evidence":"Constitutively active and kinase-dead SPAK/OSR1 mutants with oocyte voltage clamp (SPAK/OSR1); Kir1.1⁻/⁻ mice with whole-stomach and perfused gland acid secretion, tertiapin-Q inhibition (gastric)","pmids":["25322850","25127675"],"confidence":"High","gaps":["Whether WNK kinases activate SPAK/OSR1 to reduce ROMK in the same signaling cascade was not directly demonstrated","Compensatory K⁺ channels in ROMK⁻/⁻ stomach were not characterized"]},{"year":2015,"claim":"c-Src was shown to phosphorylate WNK4 at Y1092/Y1094 (required for WNK4-mediated ROMK inhibition) and Y1143 (required for PTP-1D binding and SGK1 reversal), establishing WNK4 itself as a regulated signaling node integrating c-Src and SGK1 inputs onto ROMK.","evidence":"Mass spectrometry phosphosite identification, Co-IP with PTP-1D, WNK4 tyrosine mutagenesis, functional ROMK assay","pmids":["25805816"],"confidence":"High","gaps":["In vivo confirmation that these WNK4 tyrosine phosphorylation events regulate ROMK in native kidney was not provided","Whether other WNK isoforms are similarly tyrosine-phosphorylated was not explored"]},{"year":2016,"claim":"Isoform-specific ROMK1 knockout demonstrated that ROMK1 is dispensable for NKCC2 activity in TAL but required for dietary K⁺-induced K⁺ secretion in the collecting duct, resolving the specific physiological role of the ROMK1 splice variant.","evidence":"Cre-LoxP deletion of Romk1-specific exon 1, patch clamp of CCD SK channels, dietary K⁺ challenge","pmids":["26728465"],"confidence":"High","gaps":["Which ROMK isoform mediates K⁺ recycling in the TAL remains to be determined with isoform-specific knockouts","Compensatory upregulation of BK or other K⁺ channels in Romk1⁻/⁻ CCD was not fully characterized"]},{"year":2017,"claim":"NHERF1 was shown to be required for ROMK1 surface expression in collecting duct cells, and Asn171 was identified as the critical pore-lining residue for VU590 inhibitor block, advancing both the physiological scaffold requirements and pharmacological targeting of the channel.","evidence":"NHERF1 siRNA knockdown in M-1 cells with biotinylation and patch clamp; N171 mutagenesis with molecular modeling and electrophysiology","pmids":["28533091","28619748"],"confidence":"Medium","gaps":["Whether NHERF1 and NHERF2 serve redundant or distinct roles at the apical membrane is unresolved","No high-resolution structure of ROMK with VU590 bound exists"]},{"year":null,"claim":"A high-resolution cryo-EM or crystal structure of full-length Kir1.1 in open and closed (pH-gated) states is lacking, preventing atomic-level understanding of how pH-sensor histidines, PIP₂ binding, and the L160 steric gate are allosterically coupled.","evidence":"","pmids":[],"confidence":"High","gaps":["No experimental structure of Kir1.1 has been reported","The conformational pathway linking cytoplasmic pH sensors to the transmembrane gate is modeled but not structurally resolved","How dietary K⁺ sensing is transduced to the WNK-SPAK-ROMK axis at the molecular level remains undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,4,30,39]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,6,7,8,33,34,38]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,39]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,25,26]}],"complexes":[],"partners":["CFTR","NHERF2","NHERF1","POSH","WNK1","WNK4","ITSN1","AKAP79"],"other_free_text":[]},"mechanistic_narrative":"KCNJ1 (Kir1.1/ROMK) is an inwardly rectifying potassium channel that mediates K⁺ secretion in the distal nephron and K⁺ recycling for H⁺/K⁺-ATPase function in gastric parietal cells [PMID:26728465, PMID:25127675]. Channel open probability is controlled by intracellular pH through a steric gate formed by Leu160 at the inner helix bundle crossing, with multiple C-terminal histidines serving as pH sensors, while PIP₂ binding at a proximal C-terminal arginine-rich domain is obligatory for channel opening and is enhanced by PKA phosphorylation via AKAP scaffolding [PMID:15653740, PMID:10713095, PMID:12381730, PMID:10318968, PMID:9707637]. Surface expression is dynamically regulated: PKC phosphorylation at S4/S201 is required for plasma membrane delivery, c-Src phosphorylation at Y337 drives dynamin-dependent endocytosis, monoubiquitination at K22 by the E3 ligase POSH promotes internalization, and WNK kinases (WNK1/3/4) reduce surface abundance through intersectin-dependent clathrin-mediated endocytosis independently of their kinase activity [PMID:12221079, PMID:11719519, PMID:19710010, PMID:17380208]. Loss-of-function mutations in the gene cause antenatal Bartter syndrome, with disease-relevant mutations in the intracellular immunoglobulin-like domain impairing channel folding, trafficking, and gating [PMID:10532965, PMID:19221509]."},"prefetch_data":{"uniprot":{"accession":"P48048","full_name":"ATP-sensitive inward rectifier potassium channel 1","aliases":["ATP-regulated potassium channel ROM-K","Inward rectifier K(+) channel Kir1.1","Potassium channel, inwardly rectifying subfamily J member 1"],"length_aa":391,"mass_kda":44.8,"function":"Inward rectifier potassium channels are characterized by a greater tendency to allow potassium to flow into the cell rather than out of it. Their voltage dependence is regulated by the concentration of extracellular potassium; as external potassium is raised, the voltage range of the channel opening shifts to more positive voltages. The inward rectification is mainly due to the blockage of outward current by internal magnesium. This channel is activated by internal ATP and can be blocked by external barium. In the kidney, probably plays a major role in potassium homeostasis","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P48048/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNJ1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNJ1","total_profiled":1310},"omim":[{"mim_id":"613980","title":"ATRIAL FIBRILLATION, FAMILIAL, 9; ATFB9","url":"https://www.omim.org/entry/613980"},{"mim_id":"609670","title":"MIGRAINE WITH AURA, SUSCEPTIBILITY TO, 9","url":"https://www.omim.org/entry/609670"},{"mim_id":"607364","title":"BARTTER SYNDROME, TYPE 3; BARTS3","url":"https://www.omim.org/entry/607364"},{"mim_id":"605722","title":"POTASSIUM CHANNEL, INWARDLY RECTIFYING, SUBFAMILY J, MEMBER 16; KCNJ16","url":"https://www.omim.org/entry/605722"},{"mim_id":"605232","title":"PROTEIN KINASE, LYSINE-DEFICIENT 1; WNK1","url":"https://www.omim.org/entry/605232"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"kidney","ntpm":184.8}],"url":"https://www.proteinatlas.org/search/KCNJ1"},"hgnc":{"alias_symbol":["Kir1.1","ROMK1"],"prev_symbol":[]},"alphafold":{"accession":"P48048","domains":[{"cath_id":"1.10.287.70","chopping":"59-184","consensus_level":"high","plddt":91.9423,"start":59,"end":184},{"cath_id":"2.60.40.1400","chopping":"189-369","consensus_level":"high","plddt":89.9823,"start":189,"end":369}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P48048","model_url":"https://alphafold.ebi.ac.uk/files/AF-P48048-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P48048-F1-predicted_aligned_error_v6.png","plddt_mean":84.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNJ1","jax_strain_url":"https://www.jax.org/strain/search?query=KCNJ1"},"sequence":{"accession":"P48048","fasta_url":"https://rest.uniprot.org/uniprotkb/P48048.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P48048/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P48048"}},"corpus_meta":[{"pmid":"8058760","id":"PMC_8058760","title":"Regulation of ROMK1 K+ channel activity involves phosphorylation processes.","date":"1994","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/8058760","citation_count":132,"is_preprint":false},{"pmid":"10318968","id":"PMC_10318968","title":"Regulation of ROMK1 channel by protein kinase A via a phosphatidylinositol 4,5-bisphosphate-dependent mechanism.","date":"1999","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/10318968","citation_count":126,"is_preprint":false},{"pmid":"17380208","id":"PMC_17380208","title":"Intersectin links WNK kinases to endocytosis of ROMK1.","date":"2007","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/17380208","citation_count":119,"is_preprint":false},{"pmid":"12444200","id":"PMC_12444200","title":"The serum and glucocorticoid-inducible kinase SGK1 and the Na+/H+ exchange regulating factor NHERF2 synergize to stimulate the renal outer medullary K+ channel ROMK1.","date":"2002","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/12444200","citation_count":105,"is_preprint":false},{"pmid":"21454252","id":"PMC_21454252","title":"Differential regulation of ROMK (Kir1.1) in distal nephron segments by dietary potassium.","date":"2011","source":"American journal of physiology. 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Nefrologia","url":"https://pubmed.ncbi.nlm.nih.gov/11795013","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51623,"output_tokens":9740,"usd":0.150484},"stage2":{"model":"claude-opus-4-6","input_tokens":13591,"output_tokens":5209,"usd":0.29727},"total_usd":0.447754,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1994,\n      \"finding\": \"ROMK1 channel activity is regulated by phosphorylation/dephosphorylation: channel rundown involves a Mg2+-dependent dephosphorylation process, and PKA-dependent phosphorylation restores and increases channel open probability. Addition of exogenous PKA catalytic subunit increased open probability, and the specific PKA inhibitor PKI partially reversed this effect.\",\n      \"method\": \"Patch clamp (excised inside-out patches), pharmacological inhibitors (okadaic acid, calyculin A, orthovanadate), exogenous PKA catalytic subunit application\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal electrophysiological methods with pharmacological controls, replicated concept across multiple subsequent papers\",\n      \"pmids\": [\"8058760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PKA activates ROMK1 channels by enhancing their interaction with membrane PIP2: PKA phosphorylation lowers the PIP2 concentration required for channel activation, and mutation of PKA phosphorylation sites decreases PIP2-channel interaction. PKA does not directly activate ROMK1 in membranes devoid of PIP2.\",\n      \"method\": \"Inside-out patch clamp, solution-binding assays with anti-PIP2 antibodies, ATP[gammaS] as PKA substrate, site-directed mutagenesis of PKA sites\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (electrophysiology, binding assay, mutagenesis) in single rigorous study\",\n      \"pmids\": [\"10318968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"WNK1 and WNK4 stimulate clathrin-dependent endocytosis of ROMK1 by interacting with the endocytic scaffold protein intersectin (ITSN) via proline-rich motifs; kinase activity is not required. Disease-causing WNK4 mutations enhance interactions with both ITSN and ROMK1, increasing ROMK1 endocytosis.\",\n      \"method\": \"Co-immunoprecipitation, surface expression assays, endocytosis assays in heterologous cells, mutagenesis of proline-rich motifs\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional endocytosis assays with mechanistic mutagenesis, replicated for WNK1 and WNK4\",\n      \"pmids\": [\"17380208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SGK1 and NHERF2 synergize to stimulate ROMK1 activity by increasing channel abundance in the plasma membrane; neither SGK1 nor NHERF2 alone is sufficient. NHERF2 and SGK1 together decrease channel decay after inhibition of vesicle insertion, indicating enhanced membrane trafficking.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, brefeldin A inhibition of vesicle insertion, surface expression measurement\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean co-expression functional assay with trafficking readout, independently confirmed in follow-up studies\",\n      \"pmids\": [\"12444200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PKC inhibits ROMK1 channel activity by reducing membrane PIP2 content; ROMK1 mutants with reduced PIP2 affinity show increased sensitivity to PKC activation (phorbol ester). After PKC-induced inhibition in cell-attached patches, exogenous PIP2 restores channel activity in excised patches.\",\n      \"method\": \"Cell-attached and inside-out patch clamp in Xenopus oocytes, PIP2 content measurement, PMA/carbachol/calphostin-C pharmacology, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (electrophysiology, PIP2 measurement, pharmacology, mutagenesis) establishing a coherent mechanism\",\n      \"pmids\": [\"12615924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Protein tyrosine kinase (PTK, c-Src) and protein tyrosine phosphatase (PTP-1D) regulate ROMK1 surface expression: inhibiting PTP increases internalization of ROMK1, while inhibiting PTK stimulates insertion of ROMK1 into the plasma membrane. Tyrosine residue Y337 of ROMK1 is essential for this regulation. PTK inhibition also requires intact microtubules for its exocytic effect.\",\n      \"method\": \"Two-electrode voltage clamp, patch clamp, co-expression of c-Src in Xenopus oocytes, pharmacological inhibitors (PAO, herbimycin A, colchicine, taxol, sucrose/concanavalin A), site-directed mutagenesis (Y337A)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with mutagenesis identifying specific regulatory residue, replicated in follow-up studies\",\n      \"pmids\": [\"11114300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Inhibition of protein tyrosine phosphatase increases tyrosine phosphorylation of ROMK1 at Y337 and induces dynamin-dependent endocytosis of the channel, reducing surface expression by 65%. Dominant negative dynamin (K44A) completely blocks this endocytic effect.\",\n      \"method\": \"Confocal microscopy of GFP-ROMK1, biotin labeling, patch clamp, co-transfection with c-Src and dominant negative dynamin, mutagenesis (Y337A)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (imaging, biochemistry, electrophysiology, dominant negative) with mechanistic mutagenesis\",\n      \"pmids\": [\"11719519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ROMK1 is a substrate of PKC; serine residues S4 and S201 are the two main PKC phosphorylation sites essential for surface expression of ROMK1. Mutating both sites (S4/201A) reduces surface expression to near-zero; phosphomimetic S4/201D mutation completely restores surface expression and K+ current.\",\n      \"method\": \"In vitro phosphorylation assay with 32P-ATP, site-directed mutagenesis, two-electrode voltage clamp, confocal microscopy of GFP-ROMK1, biotin surface labeling in HEK293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation combined with mutagenesis, imaging, and functional rescue\",\n      \"pmids\": [\"12221079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ROMK1 is monoubiquitinated in native renal tissue; Lys22 is the ubiquitin-binding site. Mutation K22R abolishes ubiquitination and increases surface expression and channel activity without altering biophysical properties, demonstrating monoubiquitination reduces surface expression of ROMK1.\",\n      \"method\": \"Immunoprecipitation from renal cortex, site-directed mutagenesis of all intracellular lysines, two-electrode voltage clamp, confocal microscopy, biotin surface labeling in HEK293 cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — native tissue IP combined with systematic mutagenesis, imaging, and biochemical surface labeling\",\n      \"pmids\": [\"15767585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"WNK3 inhibits ROMK1 channel activity by reducing plasmalemmal surface expression; this inhibition is independent of WNK3 kinase activity and is mediated by the carboxyl terminus of WNK3. A kinase-inactivating mutation or PHA2-homologous missense mutation in WNK3 enhances inhibition of ROMK1.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, surface expression measurements, kinase-dead and disease mutant constructs\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean functional assay with domain mutagenesis, single lab\",\n      \"pmids\": [\"16357011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PKA-dependent regulation of ROMK1 channels requires an A kinase anchoring protein (AKAP79/75): ROMK1 alone does not respond to forskolin or cAMP, but co-expression with AKAP79 confers cAMP/PKA responsiveness. Both the membrane-targeting domain and PKAII-binding domain of AKAP are required.\",\n      \"method\": \"Two-electrode voltage clamp and patch clamp in Xenopus oocytes, RII overlay assay on kidney membranes, pharmacological inhibition with H89/PKI\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary functional and biochemical assays identifying AKAP as essential intermediary\",\n      \"pmids\": [\"9707637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"pH-dependent gating of ROMK1 (Kir1.1) involves conformational changes in both N terminus (Cys49) and C terminus (Cys308): both intracellular cysteines react with thiol reagents only in the closed (acidified) state, not in the open state, indicating protein domain movement during pH gating.\",\n      \"method\": \"Site-directed mutagenesis of all intracellular cysteines, state-dependent modification by water-soluble oxidants and sulfhydryl reagents, patch clamp\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis combined with state-dependent chemical modification in functional channels\",\n      \"pmids\": [\"9852128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"ROMK1 (Kir1.1) is regulated allosterically by both extracellular K+ concentration and intracellular pH. K+ regulation is determined by the core channel region (M1, M2, P), while pH coupling is determined by the N terminus, as shown by chimeric channel studies exchanging N-termini between ROMK1 and pH-insensitive IRK1.\",\n      \"method\": \"Site-directed mutagenesis, chimeric channel construction, two-electrode voltage clamp in Xenopus oocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chimeric channel dissection with functional validation identifies distinct structural determinants\",\n      \"pmids\": [\"8663367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The second transmembrane segment (M2) of ROMK1 is a straight alpha-helix with three distinct structural environments: lipid-facing (tolerant to both Trp and Ala), protein-interior-facing (tolerant to Ala only), and pore-facing (intolerant to either substitution), established by systematic perturbation scanning mutagenesis.\",\n      \"method\": \"Site-directed mutagenesis of 18 consecutive M2 residues with Trp and Ala substitutions, functional expression in Xenopus oocytes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with comprehensive functional readout defining transmembrane topology\",\n      \"pmids\": [\"8618841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Multiple histidine residues in the C terminus of ROMK1 (His225, His274, His342, His354) contribute to CO2 and pH sensing; mutation of each reduces CO2 and pH sensitivity by 20-50%, and simultaneous mutation of all four eliminates CO2 sensitivity.\",\n      \"method\": \"Systematic site-directed mutagenesis of all histidine residues, patch clamp in Xenopus oocytes, CO2 and pH sensitivity measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — comprehensive systematic mutagenesis with quantitative functional readout\",\n      \"pmids\": [\"10713095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The pH gate of Kir1.1 is located at the helix bundle crossing near the cytoplasmic end of the inner transmembrane helices: Leu160 residues from each subunit form a steric gate. Replacing L160 with glycine abolishes pH gating; polar substitutions (L160S, L160T) also eliminate gating, indicating size and hydrophobicity at this position are both required.\",\n      \"method\": \"Site-directed mutagenesis, patch clamp in Xenopus oocytes, homology modeling based on KirBac1.1 crystal structure\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with structural modeling, multiple independent mutations tested\",\n      \"pmids\": [\"15653740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cysteine-scanning mutagenesis localizes the Kir1.1 pH gate to the transmembrane pore at position 175: a reintroduced cysteine at M2 position 175 is accessible to MTS reagents in the open state but protected from modification upon channel closure by low pH, indicating a conformational change that occludes the transmembrane pore.\",\n      \"method\": \"Cysteine-scanning mutagenesis, cytoplasmic-side MTS reagent modification (MTSEA, MTSET, MTSES, Ag+) in inside-out macropatches from Xenopus oocytes\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — state-dependent cysteine modification directly localizes gate position\",\n      \"pmids\": [\"16891366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The ATP/PIP2 binding site in Kir1.1 is localized to a 39-amino acid region at the proximal C terminus; three conserved arginine residues (R188, R203, R217) are critical for nucleotide binding, and PIP2 competes with ATP at this site.\",\n      \"method\": \"MBP fusion protein binding assay with TNP-ATP fluorescent nucleotide, PIP2 competition assay, site-directed mutagenesis of arginine residues\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding assay with systematic mutagenesis identifying binding domain\",\n      \"pmids\": [\"12381730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CFTR is required for ATP and glibenclamide sensitivity of the 30 pS Kir1.1 channel in TAL cells; both sensitivities are absent in CFTR knockout and deltaF508 mice. PKA activity abrogates the CFTR effect on ATP sensitivity, indicating CFTR provides a PKA-regulated switch determining the ratio of open to ATP-inhibited ROMK channels.\",\n      \"method\": \"Patch clamp in native TAL cells from CFTR knockout and deltaF508 mice, curcumin rescue experiment, PKA manipulation\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic knockout with native cell electrophysiology plus pharmacological rescue\",\n      \"pmids\": [\"16470247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ENaC up-regulates Kir1.1 (ROMK1) surface expression and currents, but only in the presence of CFTR; CFTR provides a mechanistic link for coordinated regulation of ENaC and ROMK1. SUR2B does not traffic to the plasma membrane when co-expressed with Kir1.1b.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, surface expression analysis, co-expression of ENaC, CFTR, and Kir1.1 in various combinations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional co-expression system with surface expression measurement, single lab\",\n      \"pmids\": [\"11994290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SGK1 stimulates ROMK1 via phosphorylation at Ser44, which shifts the pH sensitivity of the channel to more acidic values; deletion of either the second PDZ domain of NHERF2 or the PDZ binding motif on ROMK1 abolishes the stimulatory effect of SGK1 on ROMK1 surface expression. SGK1 interacts with NHERF2 through the second PDZ domain of NHERF2.\",\n      \"method\": \"Pull-down assays, site-directed mutagenesis of Ser44, two-electrode voltage clamp in Xenopus oocytes, chemiluminescence surface expression assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pull-down plus mutagenesis and functional readout, single lab\",\n      \"pmids\": [\"14623317\", \"12878206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"POSH acts as an E3 ubiquitin ligase for ROMK1: POSH binds ROMK1 at its N terminus, stimulates ROMK1 ubiquitination (confirmed by in vitro ubiquitination assay), and promotes dynamin-dependent but clathrin-independent endocytosis of ROMK1. Deletion of the RING domain abolishes both ubiquitination and endocytic effects.\",\n      \"method\": \"Immunostaining, Co-IP, GST pulldown, electrophysiology, biotin surface labeling, in vitro ubiquitination assay, dominant-negative dynamin, RING domain deletion\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ubiquitination assay plus multiple orthogonal cellular assays including dominant negative and domain deletion\",\n      \"pmids\": [\"19710010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"c-Src (Src family PTK) is co-expressed with ROMK in the TAL, CCD, and OMCD. Stimulation of PTK by phenylarsine oxide in CCD from high-K diet rats decreases ROMK apical/subapical membrane staining and increases intracellular staining, demonstrating PTK controls ROMK membrane localization in the CCD but not the TAL.\",\n      \"method\": \"Immunofluorescence staining, confocal microscopy, biotin labeling, dietary K manipulation in rats\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment in native tubule segments with functional consequence, single lab\",\n      \"pmids\": [\"15075184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SNARE proteins mediate PTK inhibition-induced exocytosis of ROMK1: tetanus toxin abolishes the herbimycin A-induced increase in surface ROMK1 channels, demonstrating SNARE-dependent exocytosis. Tyrosine dephosphorylation at Y337 is required for this exocytic insertion.\",\n      \"method\": \"Confocal microscopy, patch clamp, biotin surface labeling in HEK293 cells, tetanus toxin treatment, mutagenesis (Y337A)\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with toxin inhibition of specific exocytic machinery, single lab\",\n      \"pmids\": [\"12556363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"WNK1 inhibits ROMK1 through its N-terminal proline-rich domain (aa 1-119); an N-linker domain (aa 120-220) antagonizes this inhibition; the kinase domain reverses the N-linker antagonism via charge-charge interactions between K233 and D368 (not kinase activity); the autoinhibitory domain and first coiled-coil domain further modulate the effect through intramolecular interactions.\",\n      \"method\": \"Domain deletion and mutagenesis of WNK1, two-electrode voltage clamp in Xenopus oocytes\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic domain mutagenesis with functional readout, single lab\",\n      \"pmids\": [\"18550644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Angiotensin II inhibits ROMK1 channels by two mechanisms: (1) PKC-stimulated c-Src tyrosine phosphorylation of ROMK1 at Y337, and (2) synergizing WNK4-mediated inhibition via a PTK-dependent pathway. Losartan or PKC inhibition blocks the effect; the Y337A ROMK1 mutant is resistant to direct Ang II inhibition but not to WNK4-mediated inhibition restored by Ang II.\",\n      \"method\": \"Perforated whole-cell patch clamp in HEK293 cells, Western blot for tyrosine phosphorylation, pharmacological inhibitors (losartan, PKC inhibitor, PTK inhibitor), mutagenesis (Y337A), native CCD patch clamp in rats\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, mutagenesis, and native tissue confirmation, single lab\",\n      \"pmids\": [\"20927043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"WNK4 is a substrate of c-Src at Y1092, Y1094, and Y1143; c-Src and PTP-1D co-immunoprecipitate with WNK4. Phosphorylation at Y1092/Y1094 is required for WNK4-mediated inhibition of ROMK; phosphorylation at Y1143 is required for PTP-1D association and for SGK1 to reverse WNK4 inhibition of ROMK.\",\n      \"method\": \"Western blot, mass spectrometry, co-immunoprecipitation, site-directed mutagenesis of WNK4 tyrosines, functional ROMK assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mass spectrometry identification of phosphorylation sites combined with mutagenesis, Co-IP, and functional assay\",\n      \"pmids\": [\"25805816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SPAK and OSR1 kinases reduce ROMK1 activity and membrane abundance in a catalytic activity-dependent manner: constitutively active SPAK (T233E) and OSR1 (T185E) reduce ROMK1 surface expression, while catalytically inactive mutants (D212A-SPAK, D164A-OSR1) have no effect.\",\n      \"method\": \"Dual electrode voltage clamp and chemiluminescence surface expression assay in Xenopus oocytes, constitutively active and kinase-dead mutants of SPAK and OSR1\",\n      \"journal\": \"Kidney & blood pressure research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean functional assay with catalytic mutants, single lab\",\n      \"pmids\": [\"25322850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"An 'IRA' amino acid triplet in the N-terminal extension of ROMK1 (positions 13-19) blocks interaction with SUR2B, preventing SUR2B from conferring glibenclamide sensitivity. Direct physical interaction between ROMK1 and SUR2B (demonstrated by in vitro co-translation and co-immunoprecipitation) is required for glibenclamide-sensitive K+ currents.\",\n      \"method\": \"N-terminal deletion and substitution mutagenesis of ROMK1, two-electrode voltage clamp in Xenopus oocytes, in vitro co-translation and co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro co-translation/IP combined with systematic mutagenesis and functional expression\",\n      \"pmids\": [\"11567030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The NH2 terminus of ROMK1 (specifically serine-4) determines sensitivity to arachidonic acid (AA) inhibition. ROMK2 and ROMK3 splice variants lacking this N-terminal region show minimal AA inhibition; deletion of residues 2-37 or S4A mutation markedly reduces AA-induced inhibition. PKC phosphorylation at S4 also inhibits ROMK1.\",\n      \"method\": \"Patch clamp in Xenopus oocytes, NH2-terminal deletion and point mutagenesis, pharmacological inhibitors (calphostin C, chelerythrine, staurosporine)\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple splice variants compared with mutagenesis and pharmacology, single lab\",\n      \"pmids\": [\"9458837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"A Bartter syndrome-causing truncation mutation (Kir1.1a 331X) reaches the plasma membrane but locks the channel in a closed state. Co-expression with wild-type exerts a dominant negative effect; the extreme C terminus (residues 332-351) is an essential subunit interaction domain controlling oligomerization efficiency and open-state occupancy.\",\n      \"method\": \"Co-expression with wild-type in Xenopus oocytes, GFP fusion for plasma membrane localization, incremental C-terminal reconstruction, tetrameric concatemer approach, patch clamp\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic domain reconstruction with multiple functional assays and dominant negative analysis\",\n      \"pmids\": [\"10532965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The immunoglobulin-like domain (IgLD) in the intracellular region of Kir1.1 is essential for thermodynamic stability, trafficking, and gating. Two Bartter syndrome mutations (A198T, Y314C) within the IgLD core impair channel biosynthesis and trafficking; channels that reach the surface are electrically silent due to helix-bundle gate closure and cannot rectify.\",\n      \"method\": \"Atomic model mapping of ABS mutations, thermodynamic stability calculations by computational mutagenesis, mammalian cell trafficking assay, patch clamp electrophysiology, compensatory mutation rescue\",\n      \"journal\": \"Channels (Austin, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — structural modeling combined with functional trafficking and electrophysiology assays, single lab\",\n      \"pmids\": [\"19221509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"An intersubunit salt bridge (R128-E132) in the P-loop near the selectivity filter stabilizes the active state of Kir1.1. Disruption of this salt bridge causes inactivation even in 100 mM external K+; external Ba2+ or tertiapin-Q binding to the outer channel mouth prevents inactivation, indicating inactivation involves conformational changes near the selectivity filter analogous to C-type inactivation.\",\n      \"method\": \"Site-directed mutagenesis, two-electrode voltage clamp in Xenopus oocytes, external Ba2+ and tertiapin-Q pharmacology, variable external K+ manipulation\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis with pharmacological rescue, single lab\",\n      \"pmids\": [\"19686653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"High-K diet causes a large increase in apical ROMK expression in DCT2, CNT, and CD but not DCT1, accompanied by dramatically increased mature glycosylation, demonstrating dietary K+ regulates ROMK1 surface density through altered trafficking and glycosylation in a nephron-segment-specific manner.\",\n      \"method\": \"Immunofluorescence with new ROMK-specific antibodies verified on knockout mice, segmental markers, glycosylation state analysis by Western blot, dietary K manipulation\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — rigorous localization with knockout-validated antibodies, dietary manipulation, biochemical readout\",\n      \"pmids\": [\"21454252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ROMK1 isoform-specific knockout mice (Romk1-/-) do not develop Bartter phenotype (no reduced NKCC2 activity or increased NCC), indicating no functional link between ROMK1 and NKCC2 in TAL. However, high K+ diet-stimulated K+ secretion in the collecting tubule is absent in Romk1-/-, demonstrating ROMK1 is specifically required for dietary K+-induced K+ secretion.\",\n      \"method\": \"ES cell Cre-LoxP selective deletion of Romk1-specific exon 1, patch clamp of collecting tubule SK channels, immunofluorescence, dietary K manipulation, comparison with global Romk-/- knockout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean isoform-specific knockout with multiple functional and biochemical readouts\",\n      \"pmids\": [\"26728465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Kir1.1 (ROMK) channels are required for gastric acid secretion and co-localize with the beta-subunit of H+/K+-ATPase in gastric parietal cells. In Kir1.1-deficient mice, secretagogue-stimulated acid secretion is absent; luminal K+ restores acid secretion, demonstrating Kir1.1 provides a K+ recycling pathway essential for H+/K+-ATPase function in parietal cells.\",\n      \"method\": \"Kir1.1 knockout mice, immunofluorescence co-localization, whole-stomach acid secretion, perfused gastric gland secretion assay, luminal tertiapin-Q and XE991 inhibition\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with direct functional assay in native tissue and pharmacological confirmation\",\n      \"pmids\": [\"25127675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Small-molecule inhibitor VU590 blocks Kir1.1 within the pore in a voltage- and K+-dependent manner; asparagine N171 is the only pore-lining residue required for high-affinity block, and negatively charged substitutions (N171D/E) weaken block, while equivalent negative charge in Kir7.1 enhances block, revealing differential roles of pore polarity in determining inhibitor pharmacology.\",\n      \"method\": \"Molecular modeling, site-directed mutagenesis, patch clamp electrophysiology\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with structural modeling and functional validation, single lab\",\n      \"pmids\": [\"28619748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"FRET measurements show that during pHi gating of Kir1.1, the cytoplasmic pore conformation changes: N- and C-termini move apart from each other when the channel is open (high pH), and move closer when closed (low pH).\",\n      \"method\": \"FRET with ECFP-Kir1.1-EYFP fusion constructs, pH manipulation in Xenopus oocytes\",\n      \"journal\": \"Journal of biomedical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct FRET measurement of conformational change during gating, single lab\",\n      \"pmids\": [\"19272129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NHERF1 knockdown in M-1 CCD cells reduces surface expression of ROMK1 (detected by biotin labeling) and decreases Ba2+-sensitive whole-cell K+ current and the number of active channels in patches, demonstrating NHERF1 is required for ROMK1 surface expression and function in native collecting duct cells.\",\n      \"method\": \"NHERF1 siRNA knockdown in M-1 cells, cell surface biotinylation assay, patch clamp electrophysiology, transfection with EGFP-ROMK1\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — knockdown in relevant native cell type with both biochemical and electrophysiological readouts\",\n      \"pmids\": [\"28533091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Human ROMK1 gene produces multiple transcript isoforms (ROMK1A, 1B, 1C) through alternative splicing and use of multiple promoters from a single locus at chromosome 11q24. ROMK1A encodes a functional Ba2+-sensitive inwardly rectifying K+ channel when expressed in Xenopus oocytes.\",\n      \"method\": \"cDNA cloning, RT-PCR, alternative splicing analysis, fluorescence in situ hybridization, Xenopus oocyte expression and two-electrode voltage clamp\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — molecular cloning with functional expression, mapped to chromosome\",\n      \"pmids\": [\"8190102\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ROMK1 (Kir1.1/KCNJ1) is an inwardly rectifying K+ channel in the kidney apical membrane that mediates K+ secretion and recycling; its channel activity and surface expression are tightly regulated by phosphorylation (PKA via AKAP scaffolding increases PIP2 affinity; PKC phosphorylation at S4/S201 is required for surface expression; SGK1 phosphorylation at S44 via NHERF2 shifts pH sensitivity; tyrosine phosphorylation at Y337 by c-Src drives dynamin-dependent endocytosis), by ubiquitination (monoubiquitination at K22 reduces surface expression via POSH E3 ligase), by WNK kinases (WNK1/WNK3/WNK4 reduce surface expression through intersectin-dependent endocytosis and SPAK/OSR1 activation), by direct interaction with PIP2 (essential for channel opening), and by intracellular pH gating through a steric gate formed by leucine residues at the inner helix bundle crossing.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KCNJ1 (Kir1.1/ROMK) is an inwardly rectifying potassium channel that mediates K⁺ secretion in the distal nephron and K⁺ recycling for H⁺/K⁺-ATPase function in gastric parietal cells [PMID:26728465, PMID:25127675]. Channel open probability is controlled by intracellular pH through a steric gate formed by Leu160 at the inner helix bundle crossing, with multiple C-terminal histidines serving as pH sensors, while PIP₂ binding at a proximal C-terminal arginine-rich domain is obligatory for channel opening and is enhanced by PKA phosphorylation via AKAP scaffolding [PMID:15653740, PMID:10713095, PMID:12381730, PMID:10318968, PMID:9707637]. Surface expression is dynamically regulated: PKC phosphorylation at S4/S201 is required for plasma membrane delivery, c-Src phosphorylation at Y337 drives dynamin-dependent endocytosis, monoubiquitination at K22 by the E3 ligase POSH promotes internalization, and WNK kinases (WNK1/3/4) reduce surface abundance through intersectin-dependent clathrin-mediated endocytosis independently of their kinase activity [PMID:12221079, PMID:11719519, PMID:19710010, PMID:17380208]. Loss-of-function mutations in the gene cause antenatal Bartter syndrome, with disease-relevant mutations in the intracellular immunoglobulin-like domain impairing channel folding, trafficking, and gating [PMID:10532965, PMID:19221509].\",\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Cloning of KCNJ1 revealed it encodes a Ba²⁺-sensitive inwardly rectifying K⁺ channel with multiple alternatively spliced isoforms from a single locus, establishing the molecular identity of the renal secretory K⁺ channel.\",\n      \"evidence\": \"cDNA cloning, chromosomal mapping by FISH, functional expression in Xenopus oocytes\",\n      \"pmids\": [\"8190102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nephron segment-specific functions of individual splice variants were unknown\", \"Regulatory mechanisms governing channel activity had not been explored\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrating that PKA phosphorylation restores channel activity after rundown established that ROMK is tonically regulated by a phosphorylation–dephosphorylation cycle, raising the question of how PKA is coupled to the channel.\",\n      \"evidence\": \"Excised inside-out patch clamp with exogenous PKA catalytic subunit and phosphatase inhibitors\",\n      \"pmids\": [\"8058760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the PKA anchoring mechanism was unknown\", \"Whether PKA acts directly on the channel or through an intermediary was unresolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Chimeric channel studies between ROMK1 and pH-insensitive IRK1 showed that extracellular K⁺ sensing maps to the core pore region while pH gating maps to the N-terminus, establishing that these two regulatory modalities are structurally separable.\",\n      \"evidence\": \"N-terminal chimera construction with two-electrode voltage clamp in oocytes\",\n      \"pmids\": [\"8663367\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular identity of pH-sensing residues was not determined\", \"Location of the physical gate was unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Discovery that AKAP79 is required for cAMP/PKA responsiveness of ROMK1 resolved how PKA is functionally coupled to the channel — through a scaffolding protein that localizes PKA to the channel.\",\n      \"evidence\": \"Co-expression of AKAP79 with ROMK1 in oocytes; RII overlay on kidney membranes\",\n      \"pmids\": [\"9707637\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether AKAP directly binds ROMK1 or acts through an intermediary was unresolved\", \"The PKA phosphorylation sites on ROMK had not been linked to a downstream effector mechanism\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"State-dependent thiol modification of cysteines at positions 49 (N-terminus) and 308 (C-terminus) showed that pH gating involves coordinated conformational changes in both cytoplasmic domains, advancing understanding beyond the N-terminal chimera mapping.\",\n      \"evidence\": \"Systematic cysteine mutagenesis with state-dependent sulfhydryl reagent modification and patch clamp\",\n      \"pmids\": [\"9852128\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The transmembrane location of the physical gate remained unknown\", \"Identity of pH-sensing residues was still unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Linking PKA phosphorylation to enhanced PIP₂ interaction established the mechanistic basis for PKA activation: PKA does not directly open the channel but lowers the PIP₂ threshold for channel activation, unifying phosphorylation and lipid regulation.\",\n      \"evidence\": \"Inside-out patch clamp with anti-PIP₂ antibodies, ATP[γS] as PKA substrate, PKA site mutagenesis\",\n      \"pmids\": [\"10318968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The PIP₂ binding site on the channel had not been mapped\", \"How PKC and other kinases intersect with PIP₂ regulation was unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identification of Y337 as the c-Src phosphorylation site controlling ROMK1 endocytosis versus exocytosis established tyrosine phosphorylation as a bidirectional trafficking switch, with multiple C-terminal histidines (H225, H274, H342, H354) concurrently identified as pH/CO₂ sensors.\",\n      \"evidence\": \"c-Src co-expression, PTK/PTP pharmacology, Y337A mutagenesis, microtubule disruption (oocytes and HEK293); systematic histidine mutagenesis with CO₂ sensitivity measurements\",\n      \"pmids\": [\"11114300\", \"10713095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The endocytic machinery involved (dynamin, clathrin) had not been characterized\", \"How dietary K⁺ signals converge on the Y337 pathway in vivo was unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showing that Y337 tyrosine phosphorylation triggers dynamin-dependent endocytosis while dephosphorylation drives SNARE-dependent exocytosis completed the trafficking model, with the SUR2B interaction domain mapped to the ROMK1 N-terminal 'IRA' motif.\",\n      \"evidence\": \"Dominant-negative dynamin K44A, tetanus toxin inhibition of exocytosis, GFP-ROMK1 imaging, biotin labeling; N-terminal deletion/substitution mutagenesis and co-IP for SUR2B interaction\",\n      \"pmids\": [\"11719519\", \"12556363\", \"11567030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The E3 ubiquitin ligase involved in ROMK internalization was unknown\", \"Whether clathrin-dependent or -independent pathways mediate endocytosis was not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Three advances converged: PKC phosphorylation sites S4/S201 were shown essential for surface expression; SGK1/NHERF2 were identified as cooperative stimulators of channel trafficking; and the PIP₂/ATP binding site was mapped to a 39-amino-acid C-terminal region with critical arginines R188/R203/R217.\",\n      \"evidence\": \"In vitro ³²P phosphorylation, S4/S201 mutagenesis, confocal and biotin labeling (PKC); oocyte co-expression with brefeldin A (SGK1/NHERF2); MBP fusion binding assay with TNP-ATP and PIP₂ competition (binding site)\",\n      \"pmids\": [\"12221079\", \"12444200\", \"12381730\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SGK1 phosphorylation of ROMK alters pH sensitivity was not yet shown\", \"Physiological stimuli upstream of PKC and SGK1 at the channel were not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"SGK1 was shown to phosphorylate ROMK1 at Ser44, shifting pH sensitivity to more acidic values, through a mechanism requiring the NHERF2 PDZ scaffold — linking kinase, scaffold, and gating modulation into a single regulatory axis.\",\n      \"evidence\": \"Pull-down assays, S44 mutagenesis, oocyte voltage clamp, chemiluminescence surface expression\",\n      \"pmids\": [\"14623317\", \"12878206\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SGK1-NHERF2-ROMK complex forms in native kidney was not demonstrated\", \"The interplay between SGK1 and WNK pathways on ROMK was unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The pH gate was physically localized to Leu160 at the inner helix bundle crossing (steric gate requiring both size and hydrophobicity), and monoubiquitination at K22 was identified as a signal reducing surface expression in native kidney, establishing two fundamentally distinct regulatory mechanisms.\",\n      \"evidence\": \"L160 mutagenesis with homology modeling and patch clamp (gate); immunoprecipitation from renal cortex with systematic lysine mutagenesis and biotin labeling (ubiquitination)\",\n      \"pmids\": [\"15653740\", \"15767585\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The E3 ligase responsible for K22 ubiquitination was unidentified\", \"How pH-sensor histidines communicate to the L160 gate was structurally unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Cysteine accessibility experiments pinpointed position 175 in M2 as the site of pH-dependent pore occlusion, and CFTR was shown to be required for ATP sensitivity of native ROMK channels in TAL, revealing an unexpected functional coupling between two channels.\",\n      \"evidence\": \"State-dependent MTS modification at engineered cysteine 175 in macropatches (gate); patch clamp in native TAL cells from CFTR knockout and ΔF508 mice (CFTR coupling)\",\n      \"pmids\": [\"16891366\", \"16470247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The molecular mechanism of CFTR-ROMK coupling was not elucidated\", \"How the L160 steric gate and position 175 conformational change relate structurally was unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"WNK1 and WNK4 were shown to stimulate ROMK1 endocytosis through a kinase-activity-independent mechanism involving proline-rich motif interactions with the endocytic scaffold intersectin, with disease-causing WNK4 mutations enhancing this interaction — directly linking pseudohypoaldosteronism type II genetics to ROMK trafficking.\",\n      \"evidence\": \"Co-IP, surface expression and endocytosis assays in heterologous cells, proline-rich motif mutagenesis\",\n      \"pmids\": [\"17380208\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether WNK-intersectin-mediated endocytosis is clathrin-dependent in native tubules was unconfirmed\", \"Downstream kinases (SPAK/OSR1) in this pathway had not been tested on ROMK\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Multiple structural and regulatory insights converged: POSH was identified as the E3 ligase for ROMK1 ubiquitination driving dynamin-dependent endocytosis; FRET measurements showed N/C-terminal separation during pH-dependent opening; Bartter mutations in the IgLD impaired folding/trafficking; and an intersubunit salt bridge (R128-E132) was shown to prevent C-type-like inactivation.\",\n      \"evidence\": \"In vitro ubiquitination assay and RING domain deletion (POSH); FRET with ECFP/EYFP fusions (conformation); computational thermodynamic stability with trafficking assay (IgLD); mutagenesis with Ba²⁺/tertiapin-Q rescue (salt bridge)\",\n      \"pmids\": [\"19710010\", \"19272129\", \"19221509\", \"19686653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether POSH-mediated ubiquitination is regulated by dietary K⁺ in vivo was unknown\", \"Complete structural model of the cytoplasmic domain during gating transitions was lacking\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Angiotensin II was shown to inhibit ROMK through a dual mechanism — PKC-activated c-Src phosphorylation at Y337 and enhancement of WNK4-mediated inhibition — integrating hormonal signaling with the previously characterized kinase and trafficking pathways.\",\n      \"evidence\": \"Perforated patch clamp in HEK293 cells, Western blot for pY337, losartan/PKC/PTK inhibitors, Y337A mutagenesis, native CCD patch clamp\",\n      \"pmids\": [\"20927043\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether aldosterone opposes Ang II effects on ROMK through SGK1 in the same cells was not tested\", \"In vivo confirmation with Ang II receptor knockout was lacking\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Knockout-validated immunolocalization showed that high-K⁺ diet dramatically increases apical ROMK expression selectively in DCT2/CNT/CD (not DCT1), with increased mature glycosylation — establishing the in vivo nephron-segment specificity of K⁺-adaptive ROMK trafficking.\",\n      \"evidence\": \"ROMK-specific antibodies validated on Romk⁻/⁻ mice, segmental markers, glycosylation analysis, dietary K⁺ manipulation\",\n      \"pmids\": [\"21454252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The signaling pathway linking plasma K⁺ to increased ROMK glycosylation/trafficking was unidentified\", \"Whether WNK-SPAK axis mediates the segment-specific response was not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"SPAK/OSR1 were shown to reduce ROMK1 surface expression in a kinase-activity-dependent manner, and Kir1.1 knockout revealed an essential role in gastric acid secretion by providing K⁺ recycling for H⁺/K⁺-ATPase — extending ROMK function beyond the kidney.\",\n      \"evidence\": \"Constitutively active and kinase-dead SPAK/OSR1 mutants with oocyte voltage clamp (SPAK/OSR1); Kir1.1⁻/⁻ mice with whole-stomach and perfused gland acid secretion, tertiapin-Q inhibition (gastric)\",\n      \"pmids\": [\"25322850\", \"25127675\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether WNK kinases activate SPAK/OSR1 to reduce ROMK in the same signaling cascade was not directly demonstrated\", \"Compensatory K⁺ channels in ROMK⁻/⁻ stomach were not characterized\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"c-Src was shown to phosphorylate WNK4 at Y1092/Y1094 (required for WNK4-mediated ROMK inhibition) and Y1143 (required for PTP-1D binding and SGK1 reversal), establishing WNK4 itself as a regulated signaling node integrating c-Src and SGK1 inputs onto ROMK.\",\n      \"evidence\": \"Mass spectrometry phosphosite identification, Co-IP with PTP-1D, WNK4 tyrosine mutagenesis, functional ROMK assay\",\n      \"pmids\": [\"25805816\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo confirmation that these WNK4 tyrosine phosphorylation events regulate ROMK in native kidney was not provided\", \"Whether other WNK isoforms are similarly tyrosine-phosphorylated was not explored\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Isoform-specific ROMK1 knockout demonstrated that ROMK1 is dispensable for NKCC2 activity in TAL but required for dietary K⁺-induced K⁺ secretion in the collecting duct, resolving the specific physiological role of the ROMK1 splice variant.\",\n      \"evidence\": \"Cre-LoxP deletion of Romk1-specific exon 1, patch clamp of CCD SK channels, dietary K⁺ challenge\",\n      \"pmids\": [\"26728465\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which ROMK isoform mediates K⁺ recycling in the TAL remains to be determined with isoform-specific knockouts\", \"Compensatory upregulation of BK or other K⁺ channels in Romk1⁻/⁻ CCD was not fully characterized\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"NHERF1 was shown to be required for ROMK1 surface expression in collecting duct cells, and Asn171 was identified as the critical pore-lining residue for VU590 inhibitor block, advancing both the physiological scaffold requirements and pharmacological targeting of the channel.\",\n      \"evidence\": \"NHERF1 siRNA knockdown in M-1 cells with biotinylation and patch clamp; N171 mutagenesis with molecular modeling and electrophysiology\",\n      \"pmids\": [\"28533091\", \"28619748\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NHERF1 and NHERF2 serve redundant or distinct roles at the apical membrane is unresolved\", \"No high-resolution structure of ROMK with VU590 bound exists\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution cryo-EM or crystal structure of full-length Kir1.1 in open and closed (pH-gated) states is lacking, preventing atomic-level understanding of how pH-sensor histidines, PIP₂ binding, and the L160 steric gate are allosterically coupled.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental structure of Kir1.1 has been reported\", \"The conformational pathway linking cytoplasmic pH sensors to the transmembrane gate is modeled but not structurally resolved\", \"How dietary K⁺ sensing is transduced to the WNK-SPAK-ROMK axis at the molecular level remains undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 4, 30, 39]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 6, 7, 8, 33, 34, 38]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 39]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 25, 26]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CFTR\",\n      \"NHERF2\",\n      \"NHERF1\",\n      \"POSH\",\n      \"WNK1\",\n      \"WNK4\",\n      \"ITSN1\",\n      \"AKAP79\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}