{"gene":"WNK4","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2003,"finding":"Wild-type WNK4 inhibits NaCl cotransporter (NCC/NCCT)-mediated Na+ influx and reduces NCC membrane expression in Xenopus oocytes; this inhibition requires WNK4 kinase activity. PHAII-causing missense mutations in WNK4 (remote from kinase domain) abolish NCC inhibition. WNK4 and the C-terminus of NCC co-immunoprecipitate in HEK293T cells.","method":"Xenopus oocyte heterologous expression (22Na+ influx, surface biotinylation), kinase-dead mutagenesis, co-immunoprecipitation in HEK293T cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, functional oocyte assays with multiple mutants, surface expression quantification; foundational paper replicated extensively by independent labs","pmids":["12515852"],"is_preprint":false},{"year":2003,"finding":"WNK4 also inhibits the renal K+ channel ROMK via clathrin-dependent endocytosis, through a mechanism independent of WNK4 kinase activity and distinct from its inhibition of NCC. PHAII-causing WNK4 mutations increase ROMK inhibition while relieving NCC inhibition, establishing WNK4 as a molecular switch balancing NaCl reabsorption and K+ secretion.","method":"Xenopus oocyte expression, electrophysiology, clathrin-dependent endocytosis assays, mutagenesis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional oocyte assays with mechanistic dissection (kinase-dead mutants, endocytosis pathway), replicated by multiple independent labs","pmids":["14608358"],"is_preprint":false},{"year":2004,"finding":"PHAII-causing mutant WNK4 (D564A) increases transepithelial paracellular Cl- permeability in MDCK II cells. Wild-type and mutant WNK4 bind and phosphorylate claudins 1–4 (major tight-junction proteins); mutant WNK4 causes greater claudin phosphorylation than wild-type.","method":"Stable MDCK II cell lines with inducible WNK4 expression, transepithelial permeability measurements, in vitro kinase assay (claudin phosphorylation), co-immunoprecipitation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus functional cell permeability measurements, single lab but multiple orthogonal methods","pmids":["15070779"],"is_preprint":false},{"year":2004,"finding":"Wild-type WNK4 increases paracellular chloride permeability in mammalian kidney epithelia (MDCK cells with inducible expression) through a kinase-dependent mechanism. PHAII-mutant WNK4 produces markedly larger effects; kinase-dead WNK4 has no effect. WNK4 did not alter flux of uncharged solutes or expression/localization of selected tight-junction proteins.","method":"Electrophysiology on mammalian kidney epithelia with inducible WNK4, kinase-dead and PHAII-mutant constructs, pharmacological and electrochemical characterization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology with multiple WNK4 constructs, single lab, multiple orthogonal methods","pmids":["15465913"],"is_preprint":false},{"year":2004,"finding":"WNK4 is expressed in extrarenal polarized epithelia (sweat ducts, colonic crypts, pancreatic ducts, bile ducts, epididymis, blood-brain barrier endothelium). In these tissues WNK4 potently inhibits NKCC1 (>95% inhibition of 86Rb influx) and the Cl-/base exchanger SLC26A6 (CFEX) (>80% inhibition of 14C-formate uptake), but not pendrin.","method":"Xenopus oocyte expression, 86Rb influx assay, 14C-formate uptake assay, WNK4 tissue localization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional oocyte assays with multiple transport substrates and specificity controls, single lab","pmids":["14769928"],"is_preprint":false},{"year":2005,"finding":"WNK1 and WNK4 both interact with and phosphorylate SPAK and OSR1 in vitro. WNK1/WNK4 phosphorylate the T-loop residues of SPAK (Thr233) and OSR1 (Thr185) and a C-terminal serine (Ser373/Ser325). Phosphorylation of Thr185 in OSR1 activates it; Thr185Ala prevents activation, and Thr185Glu (phosphomimetic) increases basal activity >20-fold. Catalytically inactive WNK1/WNK4 fail to activate SPAK/OSR1.","method":"Immunoprecipitation from rat testis, in vitro kinase assay, phosphopeptide mapping, site-directed mutagenesis of SPAK/OSR1 T-loop residues","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, phosphopeptide mapping, replicated across labs","pmids":["16083423"],"is_preprint":false},{"year":2005,"finding":"WNK4 interacts with SPAK (via yeast two-hybrid and functional assays) and together activate NKCC1 and inhibit KCC2 in Xenopus oocytes. Catalytic activity of both WNK4 and SPAK is required. A SPAK-interaction-deficient WNK4 mutant (Phe997Ala) fails to activate NKCC1, establishing that WNK4 acts on NKCC1 indirectly through SPAK.","method":"Xenopus oocyte expression, yeast two-hybrid, kinase-dead mutagenesis, isotope flux assays","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus oocyte functional assays with multiple mutants, single lab","pmids":["15930150"],"is_preprint":false},{"year":2005,"finding":"WNK1 kinase domain physically associates with WNK4 kinase domain (co-immunoprecipitation). WNK1 suppresses WNK4-mediated NCC inhibition via this interaction but requires intact WNK1 kinase activity. The WNK4 C-terminal 222 amino acids are sufficient to inhibit NCC but are not blocked by WNK1; WNK1 inhibition requires an intact WNK4 kinase domain.","method":"Xenopus oocyte expression, co-immunoprecipitation, domain deletion/mutagenesis, 22Na+ flux assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal domain interaction mapping with Co-IP plus functional oocyte assays, single lab","pmids":["15841204"],"is_preprint":false},{"year":2006,"finding":"WNK4 wild-type significantly reduces NCC surface expression in Cos-7 mammalian cells; PHAII-mutant E562K does not. The effect is not due to clathrin-mediated endocytosis (dominant-negative dynamin K44A has no effect) but is reversed by the lysosomal inhibitor bafilomycin A1, indicating enhanced lysosomal degradation of NCC by WNK4.","method":"Surface biotinylation, co-immunoprecipitation, dominant-negative dynamin expression, pharmacological inhibitors (bafilomycin A1) in Cos-7 cells","journal":"Kidney international","confidence":"High","confidence_rationale":"Tier 2 / Moderate — surface biotinylation plus pharmacological inhibitor dissection in mammalian cells, Co-IP, single lab","pmids":["16688122"],"is_preprint":false},{"year":2006,"finding":"WNK4 controls blood pressure via regulation of mass and function of the distal convoluted tubule (DCT). TgWnk4(PHAII) mice show DCT hyperplasia, hypertension, hyperkalemia, and hypercalciuria; TgWnk4(WT) mice show opposite phenotypes. Genetic deficiency for NCC reverses all TgWnk4(PHAII) phenotypes, establishing that WNK4 PHAII effects are mediated through NCC.","method":"Transgenic mouse model (genomic WNK4 segments), NCC knockout epistasis, blood pressure/electrolyte measurements, kidney morphology","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in vivo (NCC KO rescues PHAII phenotype), replicated in multiple mouse models","pmids":["16964266"],"is_preprint":false},{"year":2006,"finding":"WNK4 enhances TRPV5-mediated Ca2+ uptake and increases TRPV5 surface expression in Xenopus oocytes; PHAII-causing WNK4 mutants retain ability to upregulate TRPV5.","method":"Xenopus oocyte expression, Ca2+ uptake assay, surface expression measurement","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — oocyte functional assays with multiple mutants but single lab; no Co-IP or structural validation","pmids":["17018846"],"is_preprint":false},{"year":2006,"finding":"WNK4 is a negative regulator of K+-Cl- cotransporters KCC1, KCC3, and KCC4; this inhibition requires WNK4 catalytic activity (abolished by D318A mutation). PHAII-causing WNK4 missense mutations do not affect inhibition of KCC4.","method":"Xenopus oocyte expression, isotope flux assays, kinase-dead mutagenesis","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — oocyte functional assays with mutagenesis, single lab","pmids":["17182532"],"is_preprint":false},{"year":2007,"finding":"WNK4 also inhibits ENaC (epithelial Na+ channel) activity via a kinase-independent mechanism requiring intact C-termini (PY motifs) in ENaC β- and γ-subunits. PHAII-causing WNK4 mutations eliminate ENaC inhibition. In vivo, PHAII-mutant WNK4 mice show markedly increased amiloride-sensitive Na+ flux in the colonic epithelium.","method":"Xenopus oocyte co-expression, C-terminal deletion/mutagenesis of ENaC subunits, amiloride-sensitive Na+ flux in transgenic mouse colonic epithelium","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — oocyte mechanistic dissection plus in vivo mouse validation, single lab","pmids":["17360470"],"is_preprint":false},{"year":2007,"finding":"SGK1 phosphorylates WNK4 (aldosterone-dependent kinase), and a WNK4 phosphomimetic mutant at the SGK1 site (S1169D) relieves WNK4 inhibition of both ENaC and ROMK, promoting increased K+ secretion. This identifies a functional state of WNK4 that is the opposite of the PHAII state.","method":"Xenopus oocyte expression, in vitro phosphorylation by SGK1, phosphomimetic mutagenesis (S1169D)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus functional oocyte experiments with phosphomimetic mutants, single lab","pmids":["17360471"],"is_preprint":false},{"year":2007,"finding":"In Wnk4(D561A/+) knockin mice (PHAII model), phosphorylated NCC is increased at the apical surface of distal convoluted tubule cells. OSR1 and SPAK phosphorylation are also increased. Apical ROMK localization and transepithelial Cl- permeability in cortical collecting ducts are unaffected. ENaC activation is a secondary compensatory effect (reversed by hydrochlorothiazide). PHAII pathogenesis is through OSR1/SPAK-NCC cascade activation.","method":"Knockin mouse model (D561A), immunohistochemistry, immunoblotting of phosphorylated NCC/OSR1/SPAK, patch clamp electrophysiology, hydrochlorothiazide treatment","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockin mouse model with multiple orthogonal in vivo measurements, extensively replicated","pmids":["17488636"],"is_preprint":false},{"year":2007,"finding":"WNK4 phosphorylates claudin-7 at Ser206 in the COOH-terminus (identified as a WNK4 phosphorylation site by mutagenesis). WNK4 and claudin-7 co-immunoprecipitate in kidney epithelial cells and co-localize in renal tubules. The PHAII-causing mutant WNK4 enhances claudin-7 phosphorylation and paracellular Cl- permeability more than wild-type.","method":"Co-immunoprecipitation in kidney epithelial cells, in vitro kinase assay, site-directed mutagenesis (Ser206), paracellular permeability measurement","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus in vitro kinase assay with mutagenesis, single lab","pmids":["17651736"],"is_preprint":false},{"year":2009,"finding":"WNK4 diverts NCC to lysosomes for degradation via an AP-3-dependent mechanism, reducing forward trafficking from the trans-Golgi network to the plasma membrane rather than increasing endocytosis. WNK4 increases NCC association with AP-3 adaptor complexes and increases lysosomal NCC accumulation (reversed by lysosomal protease inhibitor leupeptin, not proteasome inhibition).","method":"Surface lifetime analysis, direct forward trafficking measurements (trans-Golgi to plasma membrane), co-immunoprecipitation with endogenous AP-3, subcellular localization with leupeptin/proteasome inhibitors, WNK4 knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal trafficking assays with pharmacological dissection and endogenous AP-3 Co-IP, single lab","pmids":["19401467"],"is_preprint":false},{"year":2009,"finding":"Angiotensin II (AngII) increases NCC activity in Xenopus oocytes by abrogating WNK4 inhibition of NCC through a pathway requiring AngII receptor AT1R and WNK4. This effect is SPAK-dependent (dominant-negative SPAK or elimination of SPAK-binding motif in NCC prevents it). AngII does not alter WNK4 inhibition of ROMK. AngII increases phosphorylation of SPAK and NCC at activation sites in mpkDCT mammalian cells.","method":"Xenopus oocyte expression, dominant-negative SPAK, AT1R inhibitor losartan, immunoblotting of pSPAK and pNCC in mpkDCT cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — oocyte functional assays with pathway dissection plus mammalian cell phosphorylation studies, single lab; replicated in vivo by PMID 22550170","pmids":["19240212"],"is_preprint":false},{"year":2009,"finding":"WNK4 knockout mice (WNK4-/-) exhibit reduced NCC expression and phosphorylation, low blood pressure and increased Na/K excretion on low-salt diet. Phosphorylation of OSR1/SPAK and NCC is significantly reduced, establishing wild-type WNK4 as a positive regulator of the WNK-OSR1/SPAK-NCC cascade in vivo.","method":"WNK4 hypomorphic/knockout mouse model, immunoblotting of pOSR1/pSPAK/pNCC, blood pressure and urinary electrolyte measurements","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function mouse model with defined molecular and physiological phenotype, replicated by independent labs","pmids":["19633012"],"is_preprint":false},{"year":2009,"finding":"WNK4 enhances NCC degradation through a sortilin-mediated lysosomal pathway. Truncated sortilin (dominant-negative) prevents WNK4-induced NCC reduction. NCC co-immunoprecipitates with sortilin, and WNK4 increases co-localization of NCC with lysosomal marker cathepsin D.","method":"Co-transfection in Cos-7 cells, dominant-negative sortilin, co-immunoprecipitation, immunostaining with lysosomal marker","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus dominant-negative rescue plus immunostaining, single lab, no in vitro reconstitution","pmids":["19875813"],"is_preprint":false},{"year":2009,"finding":"SGK1 binds and phosphorylates WNK4 in vitro and in a human kidney cell line at two serine residues including one in an established SGK1 consensus sequence. Phosphomimetic mutations (aspartate) at these SGK1 target serines attenuate WNK4 inhibition of NCC in Xenopus oocytes. This defines the aldosterone/SGK1 → WNK4 → NCC pathway.","method":"In vitro kinase assay (SGK1 phosphorylation of WNK4), co-immunoprecipitation, phosphomimetic mutagenesis, Xenopus oocyte functional assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus Co-IP plus oocyte functional validation with phosphomimetics, single lab","pmids":["19690383"],"is_preprint":false},{"year":2010,"finding":"WNK4 stimulates caveola-mediated endocytosis of TRPV5, decreasing its cell-surface abundance. A region outside the kinase domain of WNK4 mediates TRPV5 endocytosis stimulation. This sets a lower basal TRPV5 level that allows PKC stimulation to produce a larger relative increase in TRPV5 current.","method":"Xenopus oocyte expression, electrophysiology (TRPV5 current), deletion analysis of WNK4 domains, caveola-mediated endocytosis assays, PKC activator (OAG) experiments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — oocyte functional assays with WNK4 deletion analysis, single lab","pmids":["20061383"],"is_preprint":false},{"year":2011,"finding":"Phenotypes of PHAII in Wnk4(D561A/+) knockin mice depend entirely on the WNK-OSR1/SPAK-NCC cascade: crossing with Spak(T243A) and Osr1(T185A) knock-in mice that cannot be activated by WNK kinases almost completely abolishes NCC phosphorylation and corrects hypertension, hyperkalemia, and metabolic acidosis in triple knock-in mice.","method":"Genetic epistasis in mice (triple knock-in), immunoblotting of pNCC, blood pressure and electrolyte measurements","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis with complete pathway rescue, single lab but rigorous genetic design","pmids":["21486947"],"is_preprint":false},{"year":2011,"finding":"β2-adrenergic receptor (β2AR) stimulation decreases WNK4 gene transcription via cAMP-dependent inhibition of HDAC8, increasing histone acetylation and glucocorticoid receptor binding to a negative glucocorticoid-responsive element in the WNK4 promoter, leading to NCC activation and salt-sensitive hypertension.","method":"In vitro β2AR stimulation, HDAC8 activity assay, chromatin immunoprecipitation (GR-promoter binding), rat models of salt-sensitive hypertension","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 / Moderate — ChIP, enzymatic assay of HDAC8, in vivo rat model, mechanistic pathway from receptor to WNK4 transcription, single lab","pmids":["21499270"],"is_preprint":false},{"year":2011,"finding":"WNK4 inhibits Maxi K (BK) channel activity in a kinase-dependent manner (kinase-dead D321A has no effect). WNK4 reduces total and cell-surface Maxi K expression through a lysosomal degradation pathway (reversed by bafilomycin A1 and leupeptin), not through clathrin-mediated endocytosis (dominant-negative dynamin K44A has no effect).","method":"Patch clamp electrophysiology in HEK αBK stable cells, surface biotinylation, pharmacological inhibitors, kinase-dead mutagenesis","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology combined with biochemical surface expression and pharmacological dissection, single lab","pmids":["21613417"],"is_preprint":false},{"year":2011,"finding":"WNK4 inhibits TRPC3-mediated Ca2+ influx in vascular smooth muscle cells (VSMCs), restricting vasoconstriction. WNK4 depletion increases TRPC3-mediated Ca2+ entry and vasoconstriction. PHAII-mutant (Q562E) and kinase-dead (D318A) WNK4 both fail to inhibit TRPC3, indicating kinase activity is required.","method":"WNK4 knockdown/knockout in VSMCs, Ca2+ influx measurements, vasoconstriction assays in small mesenteric arteries, kinase-dead and PHAII mutant expression","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined Ca2+ and vascular functional readouts, mutagenesis, single lab","pmids":["21670282"],"is_preprint":false},{"year":2011,"finding":"WNK4 inhibits ENaC activity in A6 distal nephron cells by reducing channel number at the apical membrane (not open probability) and by enhancing ENaC internalization independent of Nedd4-2-mediated ENaC ubiquitination. WNK4 also reduces the ENaC pool available for recycling. WNK4 associates with both wild-type and Liddle's mutant ENaC.","method":"Transepithelial current measurement and single-channel recording in A6 cells, Western blot of apical/total ENaC, internalization assays, Co-IP in HEK293 cells","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology plus biochemical trafficking assays, single lab","pmids":["23594824"],"is_preprint":false},{"year":2012,"finding":"AngII-mediated activation of NCC requires WNK4 in vivo: WNK4-/- mice cannot phosphorylate SPAK and NCC in response to low-salt diet or AngII infusion, placing WNK4 as an essential intermediary in the AngII→SPAK→NCC signaling pathway.","method":"WNK4 knockout mouse, AngII infusion and low-salt diet protocols, immunohistochemistry and immunoblotting of pSPAK and pNCC","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout epistasis with AngII challenge, replicated across labs","pmids":["22550170"],"is_preprint":false},{"year":2013,"finding":"KLHL3 (a BTB-Kelch adaptor) binds WNK4 and promotes its ubiquitination at ≥15 specific sites and subsequent degradation, thereby reducing WNK4 levels and ROMK surface reduction. PHAII-causing mutations in either KLHL3 or WNK4 impair this binding and ubiquitination. KLHL3 requires CUL3 (a RING E3 ligase scaffold) to form the functional complex.","method":"Mass spectrometry, co-immunoprecipitation (KLHL3-WNK4-CUL3), ubiquitination assay (polyubiquitination mapping of WNK4), in vivo WNK4 protein level measurement in mouse kidney","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — MS identification of ubiquitination sites, Co-IP, in vivo kidney protein levels, replicated by multiple independent labs","pmids":["23576762"],"is_preprint":false},{"year":2013,"finding":"The CUL3-KLHL3 E3 ligase complex ubiquitylates WNK4 (and WNK1) in vitro. KLHL3 binds WNK1/WNK4 but not SPAK/OSR1 or NCC/NKCC1. 13 out of 15 dominant KLHL3 disease mutations inhibit WNK binding. The KLHL3 interaction site in WNK1 maps to residues 479–667; equivalent WNK4 residues harbor PHAII mutations (E562K, Q565E) that abolish KLHL3 interaction.","method":"Co-immunoprecipitation, in vitro ubiquitylation assay with recombinant CUL3-KLHL3, siRNA knockdown (CUL3 in HeLa cells), domain mapping","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstituted ubiquitylation plus Co-IP plus siRNA plus interaction domain mapping, single lab but multiple orthogonal methods; replicated independently","pmids":["23387299"],"is_preprint":false},{"year":2013,"finding":"KLHL3 interacts with CUL3 and WNK4, induces WNK4 ubiquitination, and reduces WNK4 protein level. PHAII-causing mutations in KLHL3 or WNK4 reduce this interaction and ubiquitination, resulting in elevated WNK4 protein and increased SPAK/OSR1-NCC phosphorylation. Transgenic mice overexpressing WNK4 display PHAII phenotypes; WNK4 protein is increased in Wnk4(D561A/+) knockin mice.","method":"Co-immunoprecipitation (KLHL3-CUL3-WNK4), in vitro ubiquitination assay, transgenic mouse overexpression, Wnk4(D561A/+) knockin mouse immunoblot","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP, in vitro ubiquitination, transgenic and knockin mouse in vivo validation, replicated by multiple labs","pmids":["23453970"],"is_preprint":false},{"year":2013,"finding":"WNK4 inhibits BK channel (large-conductance Ca2+-activated K+ channel) activity. A region within WNK4 encompassing the autoinhibitory domain and a coiled-coil domain is required for BK inhibition. WNK4 increases ubiquitination and degradation of BK α-subunit, reducing plasma membrane expression.","method":"Electrophysiology in intercalated cell line and HEK293 cells, domain deletion of WNK4, ubiquitination assay, surface/whole-cell expression measurements","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology with domain mapping plus ubiquitination assay, single lab","pmids":["23885063"],"is_preprint":false},{"year":2014,"finding":"WNK4 effects on NCC are modulated by intracellular Cl- concentration ([Cl-]i). Under low [Cl-]i, WNK4 autophosphorylates at S335 (T-loop) and activates NCC. A chloride-binding pocket mutation (L322F) renders WNK4 constitutively autophosphorylated, converting it to a constitutive NCC activator. Eliminating kinase activity (D321A or D321K-K186D) or the autophosphorylation site (S335A) in WNK4-L322F abolishes NCC activation.","method":"Xenopus oocyte expression, measurement of [Cl-]i with Cl-sensitive fluorescent dye, WNK4 autophosphorylation assay, chloride-binding pocket mutagenesis, 22Na+ uptake","journal":"Journal of the American Society of Nephrology : JASN","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mechanistic in vitro autophosphorylation assay plus oocyte functional dissection with multiple mutants, single lab","pmids":["25542968"],"is_preprint":false},{"year":2014,"finding":"WNK4 is the major WNK kinase positively regulating NCC in the mouse kidney: WNK4-/- mice show near-complete loss of phosphorylated and total NCC despite compensatory upregulation of WNK1. Insulin- and low-potassium diet-induced NCC phosphorylation are both abolished in WNK4-/- mice.","method":"WNK4 knockout mouse, immunoblotting of pNCC/NCC, dietary and hormonal challenges (insulin, low-K diet)","journal":"Bioscience reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout with multiple physiological challenges, replicated by independent WNK4 knockout studies","pmids":["24655003"],"is_preprint":false},{"year":2014,"finding":"Angiotensin II signaling via protein kinase C (PKC) phosphorylates KLHL3 at serine 433 (a site frequently mutated in hypertension), preventing KLHL3 from binding and targeting WNK4 for degradation, thereby increasing WNK4 levels and NCC phosphorylation. AngII administration to mice induces renal KLHL3-S433 phosphorylation and increased WNK4 and NCC levels.","method":"In vitro PKC phosphorylation of KLHL3 at S433, co-immunoprecipitation, mouse AngII infusion with immunoblotting of pKLHL3-S433/WNK4/NCC, site-directed mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay, Co-IP, in vivo mouse validation, single lab","pmids":["25313067"],"is_preprint":false},{"year":2014,"finding":"WNK4 C-terminal truncation variants found in kidney lack a protein phosphatase 1 (PP1)-binding site; deletion of this site increases WNK4 kinase activity toward SPAK. Co-transfection with PP1 dephosphorylates WNK4; a PP1-binding site mutant is resistant to PP1. Full-length WNK4 is cleaved by a Zn2+-dependent metalloprotease in kidney lysates.","method":"LC-MS/MS identification of short WNK4 variants, co-transfection with PP1, kinase activity assay, WNK4 dephosphorylation assay, kidney lysate protease assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — LC-MS/MS plus kinase assay plus Co-IP with PP1, single lab","pmids":["29921588"],"is_preprint":false},{"year":2014,"finding":"WNK1 activates NCC via SPAK in a WNK4-independent manner. Conversely, WNK4 decreases WNK1- and WNK3-mediated NCC activation. WNK kinases form oligomers through their C-terminal coiled-coil domains, and this oligomerization is essential for their activity toward NCC.","method":"WNK1-FHHt/WNK4-/- double mutant mice, Xenopus oocyte expression, coiled-coil domain mutagenesis, co-immunoprecipitation","journal":"Hypertension (Dallas, Tex. : 1979)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in mice plus oocyte mechanistic dissection with domain mutagenesis, single lab","pmids":["25113964"],"is_preprint":false},{"year":2015,"finding":"c-Src phosphorylates WNK4 at Tyr1092, Tyr1094, and Tyr1143 (identified by Western blot and mass spectrometry). Both c-Src and protein tyrosine phosphatase PTP-1D co-immunoprecipitate with WNK4. Tyr1092Phe mutation markedly reduces WNK4-mediated ROMK inhibition; double mutant Y1092/1094F completely abolishes it. c-Src also prevents SGK1-induced phosphorylation of WNK4 at Ser1196, restoring WNK4 inhibition of ROMK.","method":"Mass spectrometry identification of phosphorylation sites, co-immunoprecipitation of c-Src/PTP-1D with WNK4, mutagenesis (Y1092F, Y1143F, double mutant), oocyte electrophysiology for ROMK activity","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — MS identification plus Co-IP plus mutagenesis plus functional oocyte assay, single lab with multiple orthogonal methods","pmids":["25805816"],"is_preprint":false},{"year":2016,"finding":"Chloride inhibits WNK4 kinase activity at lower concentrations than WNK1 or WNK3, within the physiological range of distal cell chloride. Mutation of the WNK4 chloride-binding motif (equivalent to that identified in WNK1) converts WNK4 effects on SPAK from inhibitory to stimulatory in mammalian cells. This explains how extracellular K+ affects NCC via intracellular Cl- acting on WNK4.","method":"In vitro kinase assay (WNK4 vs WNK1 vs WNK3 Cl- inhibition), chloride-binding motif mutagenesis in mammalian cells, in vivo dietary K+ manipulation with NCC phosphorylation readout","journal":"Kidney international","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus mutagenesis plus in vivo dietary manipulation, single lab","pmids":["26422504"],"is_preprint":false},{"year":2016,"finding":"Osmotic stress induces phosphorylation of WNK4 at Ser575 via the p38MAPK-MAPK-activated protein kinase (MK) pathway. WNK4 interacts with ASK3 (a MAP3K), and ASK3 kinase activity is required for WNK4 Ser575 phosphorylation. Hypotonic low-chloride stimulation also increases WNK4-Ser575 phosphorylation via p38MAPK-MK.","method":"LC-MS/MS identification of Ser575 phosphorylation, co-immunoprecipitation of WNK4 with ASK3, kinase-dead ASK3 rescue, p38MAPK pathway inhibitors","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS identification, Co-IP, kinase-dependent rescue, single lab","pmids":["26732173"],"is_preprint":false},{"year":2017,"finding":"PKC and PKA phosphorylate WNK4 at multiple sites (S47, S64, S1169, S1180, S1196) downstream of AngII signaling. Phosphorylation at S64 and S1196 promotes WNK4 T-loop phosphorylation at S332 (required for kinase activation) and increases SPAK phosphorylation. Volume depletion induces these phosphorylations in vivo predominantly in the distal convoluted tubule.","method":"Tandem mass spectrometry, phosphosite-specific antibodies, in vitro PKC/PKA kinase assays, in vivo volume depletion mouse model","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — MS site identification plus in vitro kinase assays plus in vivo mouse validation, single lab with multiple orthogonal methods","pmids":["28096417"],"is_preprint":false},{"year":2017,"finding":"WNK4 is expressed in adipose tissue and is induced early during adipocyte differentiation. WNK4 affects the DNA-binding ability of C/EBPβ and thereby regulates PPARγ expression. WNK4 siRNA-knockdown reduces PPARγ, C/EBPα expression and lipid accumulation. WNK4-/- mice show decreased PPARγ and C/EBPα in adipose tissue and partial resistance to high-fat diet-induced adiposity.","method":"WNK4 siRNA in 3T3-L1 and human mesenchymal stem cells, WNK4-/- mouse model, C/EBPβ DNA-binding assay, adipocyte differentiation assay","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in cells and mice with defined transcription factor binding assay, single lab","pmids":["28314693"],"is_preprint":false},{"year":2018,"finding":"Kidney-specific WNK1 isoform (KS-WNK1, which lacks the kinase domain) activates WNK4-T-loop phosphorylation at Ser335 and stimulates SPAK/NCC by physically interacting with WNK4 (co-immunoprecipitation) independent of changes in intracellular Cl-. Eliminating the WNK-WNK interaction domain in KS-WNK1 abolishes this activation.","method":"Xenopus oocyte expression, co-immunoprecipitation of KS-WNK1 and WNK4, WNK4-S335 phosphorylation assay, WNK interaction domain deletion, WNK inhibitor WNK463","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus phosphorylation assay plus functional oocyte dissection, single lab","pmids":["29846116"],"is_preprint":false},{"year":2019,"finding":"WNK4 is a physiological intracellular Cl- sensor: knockin mice carrying a Cl--insensitive WNK4 mutant fully recapitulate human PHAII. Dietary K+ restriction failed to increase NCC activity in knockin mice, and acute K+ administration failed to inactivate NCC in knockin mice (unlike wild-type). These results establish that Cl- regulation of WNK4 underlies the K+-mediated regulation of NCC.","method":"Cl--insensitive WNK4 knockin mouse model, NCC phosphorylation measurements under dietary K+ manipulation and acute K+ gavage","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockin mouse epistasis with multiple dietary and acute K+ challenges, rigorous mechanistic design","pmids":["30765526"],"is_preprint":false},{"year":2019,"finding":"In K+ deficiency, WNK4 and SPAK/OSR1 concentrate in cytoplasmic spherical domains termed 'WNK bodies' in the DCT. Phosphorylated SPAK/OSR1 is present within WNK bodies. In WNK4-deficient mice, larger WNK bodies form containing unphosphorylated WNK1, SPAK, and OSR1, indicating WNK4 is the primary active kinase in WNK bodies. WNK body formation requires Kir4.1 K+ channel-mediated DCT K+ sensing.","method":"Mouse dietary K+ manipulation, immunofluorescence microscopy of WNK bodies, WNK4-/- mouse, DCT-specific Kir4.1 conditional knockout mouse","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct subcellular localization with loss-of-function genetic models, single lab","pmids":["31736353"],"is_preprint":false},{"year":2019,"finding":"CaSR activation increases NCC activity via the WNK4-SPAK pathway: in Xenopus oocytes NCC stimulation by CaSR is WNK4-dependent; in HEK293 cells CaSR activation causes KLHL3 phosphorylation, increased WNK4 abundance and activity, and SPAK phosphorylation in a WNK4-dependent manner (blocked by WNK463). Acute CaSR agonist (R-568) in mice increases pNCC.","method":"Xenopus oocyte 22Na+ assay, HEK293 cell phosphorylation assays, WNK463 inhibitor, mouse in vivo CaSR activation","journal":"Journal of the American Society of Nephrology : JASN","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — oocyte functional assays plus cell signaling plus in vivo mouse, single lab","pmids":["29848507"],"is_preprint":false},{"year":2019,"finding":"WNK4-SPAK signaling promotes NKCC1 phosphorylation and NFκB activation in alveolar macrophages stimulated with LPS. WNK4 or SPAK knockout suppresses NKCC1 phosphorylation, NFκB activation, and acute lung injury; WNK4 D561A knockin (PHAII mutation) enhances inflammatory responses.","method":"WNK4-/-, SPAK-/-, WNK4(D561A/+) mice, primary alveolar macrophage culture, LPS stimulation, intrapulmonary LPS delivery, NFκB activation assay, NKCC1 phosphorylation immunoblot","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic mouse models with defined cellular pathway readout, single lab","pmids":["31786261"],"is_preprint":false},{"year":2011,"finding":"WNK4 inhibits BK (large-conductance Ca2+-activated K+) channels via activation of ERK and p38 MAPK (MAPK-dependent mechanism), partially through dynamin-dependent endocytosis. SGK1-mediated phosphorylation of WNK4 at S1169/S1196 abolishes WNK4's effects on BK channels and MAPK activation. The WNK4-ROMK inhibitory pathway, by contrast, is MAPK-independent.","method":"Perforated whole-cell patch clamp in HEK293T cells, MAPK inhibitors, dominant-negative dynamin (K44A), dynasore, SGK1 co-expression with phosphomimetic WNK4 mutants, native CCD electrophysiology","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology with pharmacological dissection plus mutagenesis, single lab","pmids":["23673010"],"is_preprint":false},{"year":2015,"finding":"KLHL3-mediated WNK4 degradation is also mediated by p62/SQSTM1-dependent selective autophagy in addition to proteasomal degradation. KLHL3 forms a complex with p62 (co-immunoprecipitation via kelch repeat domain). Under proteasome inhibition, p62 overexpression decreases WNK4 levels and p62 knockdown increases them. WNK4 co-localizes with KLHL3, p62, and LC3 (autophagosome marker) in cytoplasmic puncta.","method":"Co-immunoprecipitation, p62 overexpression/knockdown, autophagy inhibitor (3-methyladenine), proteasome inhibitor (epoxomicin), immunofluorescence (LC3 co-localization)","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus genetic and pharmacological dissection of degradation pathway, single lab","pmids":["26349538"],"is_preprint":false},{"year":2012,"finding":"The PHAII-causing WNK4 mutation R1185C is located in a calmodulin (CaM) binding site in the C-terminus and reduces WNK4 binding to Ca2+/CaM. The R1185C mutation disrupts SGK1 phosphorylation at S1190 (eliminates it) and alters phosphorylation at adjacent SGK1 sites S1201 and S1217. The R1185C mutant enhances positive WNK4 effects on NKCC2. Ca2+/CaM inhibits phosphorylation at S1201.","method":"CaM binding assay, in vitro SGK1 phosphorylation of WNK4, Xenopus oocyte NKCC2 functional assay, site-directed mutagenesis","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding and kinase assays plus oocyte functional validation with mutagenesis, single lab","pmids":["23054253"],"is_preprint":false},{"year":2014,"finding":"Cab39 (calcium-binding protein 39) interacts with WNK4 and enables WNK4 to activate NKCC1 in a SPAK/OSR1-independent manner. WNK4 contains a PF2-like domain (resembling the SPAK/OSR1 CCT/PF2 domain) that directly interacts with the N-terminal domain of NKCC1, enabling WNK4 to anchor to and activate NKCC1 directly. Functional data and yeast two-hybrid confirm the WNK4-NKCC1 direct interaction via this domain.","method":"Yeast two-hybrid, modeling, Xenopus oocyte functional assays, domain deletion analysis, SPAK/OSR1-independent activation experiments","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus oocyte functional assays plus domain modeling, single lab","pmids":["24811174"],"is_preprint":false},{"year":2020,"finding":"NHA2 (sodium/proton exchanger) regulates WNK4 stability in the kidney: loss of NHA2 increases WNK4 ubiquitylation and proteasomal degradation via a KLHL3-dependent mechanism. NHA2 loss selectively attenuates KLHL3 phosphorylation, blunting PKA- and PKC-mediated decrease of WNK4 degradation.","method":"NHA2 knockout mouse, in vitro NHA2 knockdown, WNK4 ubiquitylation assay, KLHL3 phosphorylation assay, NHA2/NCC double knockout mice","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockout mouse plus in vitro ubiquitylation assay plus double-KO epistasis, single lab","pmids":["32956652"],"is_preprint":false},{"year":2021,"finding":"Rapid NCC dephosphorylation by high extracellular K+ requires inactivation of the WNK4-SPAK 'on switch': WNK4-SPAK signaling must be turned off for rapid NCC dephosphorylation by high K+ in vitro (HEK cells) and ex vivo (kidney slices). SPAK is rapidly dephosphorylated in DCT1 specifically upon acute K+ challenge in vivo. Extended WNK-SPAK activation attenuates sensitivity to subsequent rapid K+-induced dephosphorylation.","method":"HEK cell K+ challenge, ex vivo kidney slice acute K+ treatment, in vivo acute K+ loading with pSPAK/pNCC immunoblot, PP1/PP3 inhibitor studies","journal":"American journal of physiology. Renal physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro, ex vivo, and in vivo convergent experiments, single lab","pmids":["33719576"],"is_preprint":false}],"current_model":"WNK4 is a chloride-sensitive serine-threonine kinase that acts as a multifunctional molecular switch in the distal nephron: when intracellular Cl- is low (e.g., during K+ deficiency or volume depletion), WNK4 autophosphorylates its T-loop (Ser335) and phosphorylates/activates the downstream kinases SPAK and OSR1, which in turn phosphorylate and activate NCC, thereby promoting NaCl reabsorption; PHAII-causing gain-of-function WNK4 mutations cluster in the acidic motif and impair KLHL3-CUL3-mediated ubiquitination and degradation of WNK4, elevating WNK4 levels and constitutively activating the WNK4-SPAK-NCC cascade; WNK4 also regulates ROMK (inhibits via kinase-independent/clathrin-dependent endocytosis), ENaC, BK channels, KCCs, NKCC1, CFTR, TRPV5, TRPC3, and paracellular Cl- flux via claudin phosphorylation; its activity and abundance are regulated by AngII (via PKC phosphorylation of KLHL3-S433), aldosterone (via SGK1 phosphorylation of WNK4), Src-family kinases (via WNK4 Tyr1092/1094/1143 phosphorylation), PP1-mediated dephosphorylation, p62/SQSTM1-selective autophagy, and epigenetic control of WNK4 transcription through the β2AR-HDAC8-GR axis."},"narrative":{"mechanistic_narrative":"WNK4 is a chloride-sensitive serine-threonine kinase that functions as a master regulatory switch in the distal nephron, balancing renal NaCl reabsorption against K+ secretion and thereby controlling blood pressure and electrolyte homeostasis [PMID:12515852, PMID:14608358, PMID:16964266]. Its central effector arm is the WNK-SPAK/OSR1-NCC cascade: WNK4 binds and phosphorylates the T-loop residues of SPAK (Thr233) and OSR1 (Thr185) to activate them [PMID:16083423], and in vivo WNK4 is the dominant WNK kinase driving NCC phosphorylation and activation, since WNK4-/- mice lose nearly all phospho-NCC despite compensatory WNK1 upregulation [PMID:19633012, PMID:24655003]. WNK4 activity is gated by intracellular chloride: under low [Cl-]i it autophosphorylates its T-loop (Ser335) and switches from an NCC inhibitor to an NCC activator, and a chloride-insensitive knockin mouse recapitulates pseudohypoaldosteronism type II (PHAII) and abolishes K+-dependent NCC regulation, establishing WNK4 as the physiological Cl- sensor that translates extracellular K+ into NCC activity [PMID:25542968, PMID:30765526, PMID:26422504]. WNK4 abundance is set by CUL3-KLHL3-mediated ubiquitination and degradation; PHAII-causing mutations cluster in the acidic motif and impair KLHL3 binding, elevating WNK4 and constitutively activating the SPAK-NCC axis, with all PHAII phenotypes mediated through NCC and the SPAK/OSR1 cascade as shown by genetic epistasis [PMID:23576762, PMID:23387299, PMID:23453970, PMID:21486947, PMID:16964266]. This degradation node is tuned by hormonal signaling — angiotensin II acts via PKC phosphorylation of KLHL3-Ser433 to stabilize WNK4, while aldosterone-induced SGK1 and Src-family kinases phosphorylate WNK4 directly to modulate its output toward NCC and ROMK [PMID:25313067, PMID:19690383, PMID:25805816, PMID:28096417]. Beyond NCC, WNK4 acts as a broad transport coordinator, inhibiting ROMK via clathrin-dependent endocytosis [PMID:14608358], ENaC, KCCs, NKCC1, BK channels and SLC26A6, and phosphorylating tight-junction claudins to modulate paracellular Cl- permeability [PMID:15070779, PMID:14769928, PMID:15930150, PMID:17360470, PMID:17651736]. Activating WNK4 mutations cause PHAII (familial hyperkalemic hypertension) [PMID:16964266, PMID:17488636].","teleology":[{"year":2003,"claim":"Established WNK4 as a direct negative regulator of the thiazide-sensitive NCC and linked PHAII mutations to loss of this regulation, defining WNK4's core renal function.","evidence":"Xenopus oocyte heterologous expression with kinase-dead and PHAII mutants, surface biotinylation, and reciprocal Co-IP with NCC C-terminus","pmids":["12515852"],"confidence":"High","gaps":["Did not resolve whether NCC inhibition is direct or via downstream kinases","Mechanism of PHAII gain-of-function not yet defined at the molecular level"]},{"year":2003,"claim":"Showed WNK4 simultaneously inhibits ROMK by a kinase-independent endocytic mechanism opposite in direction to its NCC effect, framing WNK4 as a molecular switch balancing Na+ reabsorption and K+ secretion.","evidence":"Xenopus oocyte electrophysiology with clathrin-dependent endocytosis assays and PHAII/kinase-dead mutants","pmids":["14608358"],"confidence":"High","gaps":["Endocytic adaptor mediating ROMK internalization not identified","Physiological trigger that flips the switch in vivo not yet defined"]},{"year":2004,"claim":"Extended WNK4 substrate range to paracellular Cl- transport and extrarenal transporters, identifying claudins as phosphorylation substrates and NKCC1/SLC26A6 as targets.","evidence":"Inducible MDCK II epithelia with transepithelial permeability and in vitro claudin kinase assays; oocyte flux assays for NKCC1/SLC26A6","pmids":["15070779","15465913","14769928"],"confidence":"High","gaps":["In vivo relevance of claudin phosphorylation to PHAII not established","Specific claudin phosphosites not yet mapped"]},{"year":2005,"claim":"Identified SPAK and OSR1 as direct downstream kinase substrates of WNK4, defining the WNK-SPAK/OSR1 module that transmits WNK4 activity to cation-chloride cotransporters.","evidence":"In vitro kinase assays with phosphopeptide mapping of SPAK Thr233/OSR1 Thr185, T-loop mutagenesis, yeast two-hybrid, and oocyte flux assays","pmids":["16083423","15930150","15841204"],"confidence":"High","gaps":["How WNK1-WNK4 heterodimerization modulates the cascade quantitatively in vivo unclear","Whether SPAK/OSR1 mediate all WNK4 transport effects not yet tested genetically"]},{"year":2006,"claim":"Demonstrated in vivo that WNK4 controls blood pressure through DCT mass and NCC function, with NCC knockout fully reversing PHAII phenotypes, proving NCC is the principal mediator.","evidence":"Transgenic WNK4 mouse models with NCC-knockout epistasis and morphological/electrolyte phenotyping","pmids":["16964266"],"confidence":"High","gaps":["Did not resolve whether transgenic effect reflects altered WNK4 abundance versus intrinsic activity","Contribution of ROMK/ENaC to phenotype not dissected"]},{"year":2006,"claim":"Defined the cellular route of WNK4-driven NCC downregulation, showing it reduces NCC surface expression via lysosomal rather than proteasomal or clathrin-dependent pathways.","evidence":"Surface biotinylation in Cos-7 cells with dominant-negative dynamin and bafilomycin A1 inhibition","pmids":["16688122"],"confidence":"High","gaps":["Adaptor machinery routing NCC to lysosomes not yet identified","Whether wild-type-state lysosomal targeting differs mechanistically from PHAII-state not addressed"]},{"year":2007,"claim":"Broadened WNK4's regulatory targets to ENaC and connected WNK4 to aldosterone signaling via SGK1 phosphorylation, revealing a functional state opposite to PHAII.","evidence":"Oocyte co-expression with ENaC PY-motif mutants, in vivo colonic Na+ flux, and in vitro SGK1 phosphorylation with phosphomimetic mutagenesis","pmids":["17360470","17360471"],"confidence":"High","gaps":["Number and identity of physiologically relevant SGK1 sites not fully resolved at this stage","Quantitative contribution of ENaC regulation to whole-animal phenotype unclear"]},{"year":2007,"claim":"Pinned PHAII pathogenesis in a knockin model to apical NCC and SPAK/OSR1 hyperphosphorylation, with ENaC activation a secondary compensatory event.","evidence":"Wnk4(D561A/+) knockin mice with immunohistochemistry, phospho-immunoblotting, patch clamp, and thiazide treatment","pmids":["17488636"],"confidence":"High","gaps":["Did not explain how a remote PHAII mutation increases cascade activity at the molecular level","Claudin/paracellular contribution in vivo found minimal but not exhaustively excluded"]},{"year":2009,"claim":"Resolved the trafficking mechanism of WNK4-mediated NCC degradation as AP-3/sortilin-dependent diversion to lysosomes during forward trafficking rather than enhanced endocytosis.","evidence":"Forward-trafficking and surface-lifetime assays, endogenous AP-3 Co-IP, dominant-negative sortilin, and lysosomal protease inhibition","pmids":["19401467","19875813"],"confidence":"High","gaps":["How WNK4 kinase activity directs NCC into AP-3/sortilin pathway not mechanistically resolved","Sortilin findings rest on a single lab without reconstitution"]},{"year":2009,"claim":"Reversed the early oocyte view by establishing WNK4 as a positive in vivo regulator of NCC and connecting WNK4 to angiotensin II signaling through SPAK.","evidence":"WNK4 knockout/hypomorphic mice with phospho-NCC/SPAK/OSR1 immunoblotting; oocyte and mpkDCT AngII/AT1R/SPAK dissection","pmids":["19633012","19240212","19690383"],"confidence":"High","gaps":["Apparent inhibitor-versus-activator paradox not yet reconciled mechanistically","Direct sensor coupling AngII to WNK4 activity state not yet defined"]},{"year":2011,"claim":"Proved by triple-knockin genetics that PHAII phenotypes depend entirely on SPAK/OSR1 activation of NCC, and identified beta2AR-HDAC8-GR transcriptional control of WNK4 expression.","evidence":"Wnk4(D561A/+) crossed with Spak(T243A)/Osr1(T185A) knockin mice; HDAC8 activity assays, ChIP of GR at WNK4 promoter, and salt-sensitive rat models","pmids":["21486947","21499270"],"confidence":"High","gaps":["Whether transcriptional and post-translational WNK4 control converge physiologically not integrated","Tissue specificity of beta2AR-HDAC8 axis beyond kidney not established"]},{"year":2011,"claim":"Documented WNK4 regulation of additional channels (BK, TRPC3, TRPV5) extending its role to K+ secretion, vascular tone, and Ca2+ handling.","evidence":"Patch clamp and surface-expression assays in HEK/intercalated cells, VSMC knockdown with vasoconstriction readouts, and oocyte TRPV5 endocytosis assays","pmids":["21613417","21670282","20061383","23885063","23673010","17018846"],"confidence":"Medium","gaps":["These channel effects rely largely on single-lab oocyte/cell systems without in vivo confirmation","Mechanistic basis for kinase-dependent versus kinase-independent channel effects varies and is unresolved"]},{"year":2013,"claim":"Identified the CUL3-KLHL3 E3 ligase complex as the machinery that ubiquitinates and degrades WNK4, explaining how PHAII mutations in either WNK4 or KLHL3 elevate WNK4 abundance.","evidence":"Mass-spectrometry ubiquitination-site mapping, reconstituted in vitro ubiquitylation with recombinant CUL3-KLHL3, Co-IP, domain mapping, and in vivo kidney WNK4 levels","pmids":["23576762","23387299","23453970"],"confidence":"High","gaps":["How specific acidic-motif mutations impair KLHL3 binding structurally not resolved here","Relative contribution of WNK4 abundance versus intrinsic activity to PHAII not fully partitioned"]},{"year":2014,"claim":"Established WNK4 as a chloride-sensing kinase whose low-Cl-induced T-loop autophosphorylation (Ser335) converts it to an NCC activator, and showed AngII tunes WNK4 stability via PKC phosphorylation of KLHL3-Ser433.","evidence":"Oocyte [Cl-]i measurement with chloride-pocket mutants (L322F) and autophosphorylation assays; in vitro PKC phosphorylation of KLHL3-S433 with in vivo AngII infusion","pmids":["25542968","25313067","26422504","29921588","25113964"],"confidence":"High","gaps":["Structural basis of the WNK4 chloride-binding pocket not solved within the corpus","How PP1 dephosphorylation and WNK oligomerization integrate quantitatively with Cl- sensing unclear"]},{"year":2015,"claim":"Identified Src-family tyrosine phosphorylation and p62/SQSTM1-dependent selective autophagy as additional layers controlling WNK4 output toward ROMK and WNK4 turnover.","evidence":"Mass-spectrometry phosphosite mapping with Y1092/1094/1143 mutagenesis and oocyte ROMK assays; Co-IP and autophagy/proteasome inhibitor dissection of KLHL3-p62 complex","pmids":["25805816","26349538"],"confidence":"High","gaps":["In vivo physiological trigger for Src-mediated WNK4 tyrosine phosphorylation not defined","Relative flux through autophagic versus proteasomal WNK4 degradation in kidney not quantified"]},{"year":2019,"claim":"Confirmed in vivo that WNK4 chloride sensing is the molecular basis of K+-dependent NCC regulation and described condensation of WNK4-SPAK/OSR1 into Kir4.1-dependent 'WNK bodies' during K+ deficiency.","evidence":"Cl--insensitive WNK4 knockin mice with dietary/acute K+ challenges; immunofluorescence of WNK bodies in WNK4-/- and DCT Kir4.1 conditional knockout mice; CaSR-WNK4 signaling assays","pmids":["30765526","31736353","29848507"],"confidence":"High","gaps":["Functional role of WNK body condensation versus diffuse signaling not separated","Whether WNK bodies are required for, or merely accompany, NCC activation unresolved"]},{"year":2020,"claim":"Extended WNK4 regulation to NHA2-dependent stability control and dynamic K+-induced inactivation, and noted non-renal roles in adipogenesis and inflammation.","evidence":"NHA2-knockout mice with WNK4 ubiquitylation/KLHL3 phosphorylation assays; ex vivo/in vivo acute K+ dephosphorylation studies; WNK4-/- adipocyte and alveolar macrophage models","pmids":["32956652","33719576","28314693","31786261","29846116"],"confidence":"Medium","gaps":["Extrarenal WNK4 functions rest on single-lab loss-of-function studies without mechanistic depth","How NHA2 mechanistically couples to KLHL3 phosphorylation unclear"]},{"year":null,"claim":"How the multiple WNK4 inputs — chloride sensing, KLHL3-mediated degradation, hormonal phosphorylation, oligomerization, and WNK body condensation — are integrated quantitatively to set NCC activity under physiological conditions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structural/biophysical model of WNK4 activation states","Relative weighting of transcriptional, degradative, and phosphorylation control in vivo not established","Mechanistic link between channel-level effects and whole-organism phenotypes for non-NCC targets incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,5,6,15,32]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[5,32,40]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[32,38,43]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,12]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[44]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[17,20,27,34,37]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,4,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[28,29,30,48]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[8,16,19]}],"complexes":["WNK bodies","WNK kinase oligomer"],"partners":["SPAK","OSR1","KLHL3","CUL3","SGK1","WNK1","NCC","CAM"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96J92","full_name":"Serine/threonine-protein kinase WNK4","aliases":["Protein kinase lysine-deficient 4","Protein kinase with no lysine 4"],"length_aa":1243,"mass_kda":134.7,"function":"Serine/threonine-protein kinase component of the WNK4-SPAK/OSR1 kinase cascade, which acts as a key regulator of ion transport in the distal nephron and blood pressure (By similarity). The WNK4-SPAK/OSR1 kinase cascade is composed of WNK4, which mediates phosphorylation and activation of downstream kinases OXSR1/OSR1 and STK39/SPAK (PubMed:16832045). Following activation, OXSR1/OSR1 and STK39/SPAK catalyze phosphorylation of ion cotransporters, such as SLC12A1/NKCC2, SLC12A2/NKCC1, SLC12A3/NCC, SLC12A5/KCC2 or SLC12A6/KCC3, regulating their activity (PubMed:16832045, PubMed:22989884). Acts as a molecular switch that regulates the balance between renal salt reabsorption and K(+) secretion by modulating the activities of renal transporters and channels, including the Na-Cl cotransporter SLC12A3/NCC and the K(+) channel, KCNJ1/ROMK (By similarity). Regulates NaCl reabsorption in the distal nephron by activating the thiazide-sensitive Na-Cl cotransporter SLC12A3/NCC in distal convoluted tubule cells of kidney: activates SLC12A3/NCC in a OXSR1/OSR1- and STK39/SPAK-dependent process (By similarity). Also acts as a scaffold protein independently of its protein kinase activity: negatively regulates cell membrane localization of various transporters and channels (CFTR, KCNJ1/ROMK, SLC4A4, SLC26A9 and TRPV4) by clathrin-dependent endocytosis (By similarity). Also inhibits the activity of the epithelial Na(+) channel (ENaC) SCNN1A, SCNN1B, SCNN1D in a inase-independent mechanism (By similarity). May also phosphorylate NEDD4L (PubMed:20525693)","subcellular_location":"Cell junction, tight junction","url":"https://www.uniprot.org/uniprotkb/Q96J92/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/WNK4","classification":"Not Classified","n_dependent_lines":27,"n_total_lines":1208,"dependency_fraction":0.022350993377483443},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/WNK4","total_profiled":1310},"omim":[{"mim_id":"614496","title":"PSEUDOHYPOALDOSTERONISM, TYPE IIE; PHA2E","url":"https://www.omim.org/entry/614496"},{"mim_id":"614495","title":"PSEUDOHYPOALDOSTERONISM, TYPE IID; PHA2D","url":"https://www.omim.org/entry/614495"},{"mim_id":"614492","title":"PSEUDOHYPOALDOSTERONISM, TYPE IIC; PHA2C","url":"https://www.omim.org/entry/614492"},{"mim_id":"614491","title":"PSEUDOHYPOALDOSTERONISM, TYPE IIB; PHA2B","url":"https://www.omim.org/entry/614491"},{"mim_id":"605775","title":"KELCH-LIKE 3; KLHL3","url":"https://www.omim.org/entry/605775"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"kidney","ntpm":41.5},{"tissue":"prostate","ntpm":13.8}],"url":"https://www.proteinatlas.org/search/WNK4"},"hgnc":{"alias_symbol":[],"prev_symbol":["PRKWNK4"]},"alphafold":{"accession":"Q96J92","domains":[{"cath_id":"3.30.200.20","chopping":"160-257","consensus_level":"medium","plddt":86.3327,"start":160,"end":257},{"cath_id":"1.10.510.10","chopping":"259-435","consensus_level":"medium","plddt":88.1233,"start":259,"end":435},{"cath_id":"3.10.20.90","chopping":"442-530","consensus_level":"high","plddt":81.6443,"start":442,"end":530},{"cath_id":"3.10.20.90","chopping":"676-750","consensus_level":"high","plddt":87.6691,"start":676,"end":750}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J92","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J92-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96J92-F1-predicted_aligned_error_v6.png","plddt_mean":57.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=WNK4","jax_strain_url":"https://www.jax.org/strain/search?query=WNK4"},"sequence":{"accession":"Q96J92","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96J92.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96J92/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96J92"}},"corpus_meta":[{"pmid":"16083423","id":"PMC_16083423","title":"The WNK1 and WNK4 protein kinases that are mutated in Gordon's hypertension syndrome phosphorylate and activate SPAK and OSR1 protein kinases.","date":"2005","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/16083423","citation_count":435,"is_preprint":false},{"pmid":"12515852","id":"PMC_12515852","title":"Molecular pathogenesis of inherited hypertension with hyperkalemia: the Na-Cl cotransporter is inhibited by wild-type but not mutant WNK4.","date":"2003","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/12515852","citation_count":321,"is_preprint":false},{"pmid":"14608358","id":"PMC_14608358","title":"WNK4 regulates the balance between renal NaCl reabsorption and K+ secretion.","date":"2003","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/14608358","citation_count":301,"is_preprint":false},{"pmid":"16964266","id":"PMC_16964266","title":"Wnk4 controls blood pressure and potassium homeostasis via regulation of mass and activity of the distal convoluted tubule.","date":"2006","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16964266","citation_count":300,"is_preprint":false},{"pmid":"17488636","id":"PMC_17488636","title":"Molecular pathogenesis of pseudohypoaldosteronism type II: generation and analysis of a Wnk4(D561A/+) knockin mouse model.","date":"2007","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/17488636","citation_count":266,"is_preprint":false},{"pmid":"22550170","id":"PMC_22550170","title":"Activation of the renal Na+:Cl- cotransporter by angiotensin II is a WNK4-dependent process.","date":"2012","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/22550170","citation_count":232,"is_preprint":false},{"pmid":"15930150","id":"PMC_15930150","title":"Volume sensitivity of cation-Cl- cotransporters is modulated by the interaction of two kinases: Ste20-related proline-alanine-rich kinase and WNK4.","date":"2005","source":"American journal of physiology. Cell physiology","url":"https://pubmed.ncbi.nlm.nih.gov/15930150","citation_count":220,"is_preprint":false},{"pmid":"26422504","id":"PMC_26422504","title":"Unique chloride-sensing properties of WNK4 permit the distal nephron to modulate potassium homeostasis.","date":"2016","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/26422504","citation_count":214,"is_preprint":false},{"pmid":"15070779","id":"PMC_15070779","title":"Disease-causing mutant WNK4 increases paracellular chloride permeability and phosphorylates claudins.","date":"2004","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/15070779","citation_count":213,"is_preprint":false},{"pmid":"23576762","id":"PMC_23576762","title":"Kelch-like 3 and Cullin 3 regulate electrolyte homeostasis via ubiquitination and degradation of WNK4.","date":"2013","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/23576762","citation_count":205,"is_preprint":false},{"pmid":"19240212","id":"PMC_19240212","title":"Angiotensin II signaling increases activity of the renal Na-Cl cotransporter through a WNK4-SPAK-dependent pathway.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19240212","citation_count":201,"is_preprint":false},{"pmid":"21499270","id":"PMC_21499270","title":"Epigenetic modulation of the renal β-adrenergic-WNK4 pathway in salt-sensitive hypertension.","date":"2011","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/21499270","citation_count":188,"is_preprint":false},{"pmid":"23453970","id":"PMC_23453970","title":"Impaired KLHL3-mediated ubiquitination of WNK4 causes human hypertension.","date":"2013","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/23453970","citation_count":181,"is_preprint":false},{"pmid":"23387299","id":"PMC_23387299","title":"The CUL3-KLHL3 E3 ligase complex mutated in Gordon's hypertension syndrome interacts with and ubiquitylates WNK isoforms: disease-causing mutations in KLHL3 and WNK4 disrupt interaction.","date":"2013","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/23387299","citation_count":180,"is_preprint":false},{"pmid":"15841204","id":"PMC_15841204","title":"Mechanisms of WNK1 and WNK4 interaction in the regulation of thiazide-sensitive NaCl cotransport.","date":"2005","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/15841204","citation_count":143,"is_preprint":false},{"pmid":"15465913","id":"PMC_15465913","title":"Paracellular Cl- permeability is regulated by WNK4 kinase: insight into normal physiology and hypertension.","date":"2004","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/15465913","citation_count":136,"is_preprint":false},{"pmid":"25542968","id":"PMC_25542968","title":"The Effect of WNK4 on the Na+-Cl- Cotransporter Is Modulated by Intracellular Chloride.","date":"2014","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/25542968","citation_count":134,"is_preprint":false},{"pmid":"17360471","id":"PMC_17360471","title":"An SGK1 site in WNK4 regulates Na+ channel and K+ channel activity and has implications for aldosterone signaling and K+ homeostasis.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17360471","citation_count":131,"is_preprint":false},{"pmid":"14769928","id":"PMC_14769928","title":"WNK4 regulates apical and basolateral Cl- flux in extrarenal epithelia.","date":"2004","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/14769928","citation_count":130,"is_preprint":false},{"pmid":"19690383","id":"PMC_19690383","title":"Aldosterone mediates activation of the thiazide-sensitive Na-Cl cotransporter through an SGK1 and WNK4 signaling pathway.","date":"2009","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/19690383","citation_count":119,"is_preprint":false},{"pmid":"16688122","id":"PMC_16688122","title":"WNK4 kinase regulates surface expression of the human sodium chloride cotransporter in mammalian cells.","date":"2006","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/16688122","citation_count":111,"is_preprint":false},{"pmid":"17360470","id":"PMC_17360470","title":"WNK4 regulates activity of the epithelial Na+ channel in vitro and in vivo.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17360470","citation_count":107,"is_preprint":false},{"pmid":"24655003","id":"PMC_24655003","title":"WNK4 is the major WNK positively regulating NCC in the mouse kidney.","date":"2014","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/24655003","citation_count":101,"is_preprint":false},{"pmid":"19633012","id":"PMC_19633012","title":"Targeted disruption of the Wnk4 gene decreases phosphorylation of Na-Cl cotransporter, increases Na excretion and lowers blood pressure.","date":"2009","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/19633012","citation_count":93,"is_preprint":false},{"pmid":"19401467","id":"PMC_19401467","title":"WNK4 diverts the thiazide-sensitive NaCl cotransporter to the lysosome and stimulates AP-3 interaction.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19401467","citation_count":89,"is_preprint":false},{"pmid":"25313067","id":"PMC_25313067","title":"Angiotensin II signaling via protein kinase C phosphorylates Kelch-like 3, preventing WNK4 degradation.","date":"2014","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/25313067","citation_count":85,"is_preprint":false},{"pmid":"25113964","id":"PMC_25113964","title":"WNK-SPAK-NCC cascade revisited: WNK1 stimulates the activity of the Na-Cl cotransporter via SPAK, an effect antagonized by WNK4.","date":"2014","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/25113964","citation_count":82,"is_preprint":false},{"pmid":"30765526","id":"PMC_30765526","title":"WNK4 kinase is a physiological intracellular chloride sensor.","date":"2019","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/30765526","citation_count":81,"is_preprint":false},{"pmid":"22549242","id":"PMC_22549242","title":"Aldosterone does not require angiotensin II to activate NCC through a WNK4-SPAK-dependent pathway.","date":"2012","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/22549242","citation_count":76,"is_preprint":false},{"pmid":"17018846","id":"PMC_17018846","title":"WNK4 enhances TRPV5-mediated calcium transport: potential role in hypercalciuria of familial hyperkalemic hypertension caused by gene mutation of WNK4.","date":"2006","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17018846","citation_count":74,"is_preprint":false},{"pmid":"24821705","id":"PMC_24821705","title":"Impaired degradation of WNK1 and WNK4 kinases causes PHAII in mutant KLHL3 knock-in mice.","date":"2014","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24821705","citation_count":72,"is_preprint":false},{"pmid":"15292344","id":"PMC_15292344","title":"Hypercalciuria in familial hyperkalemia and hypertension accompanies hyperkalemia and precedes hypertension: description of a large family with the Q565E WNK4 mutation.","date":"2004","source":"The Journal of clinical endocrinology and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/15292344","citation_count":72,"is_preprint":false},{"pmid":"16775035","id":"PMC_16775035","title":"WNK1 affects surface expression of the ROMK potassium channel independent of WNK4.","date":"2006","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/16775035","citation_count":71,"is_preprint":false},{"pmid":"17182532","id":"PMC_17182532","title":"WNK4 kinase is a negative regulator of K+-Cl- cotransporters.","date":"2006","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17182532","citation_count":66,"is_preprint":false},{"pmid":"19875813","id":"PMC_19875813","title":"WNK4 enhances the degradation of NCC through a sortilin-mediated lysosomal pathway.","date":"2009","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/19875813","citation_count":66,"is_preprint":false},{"pmid":"16788137","id":"PMC_16788137","title":"Regulation of the expression of the Na/Cl cotransporter by WNK4 and WNK1: evidence that accelerated dynamin-dependent endocytosis is not involved.","date":"2006","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/16788137","citation_count":65,"is_preprint":false},{"pmid":"15998707","id":"PMC_15998707","title":"A new kindred with pseudohypoaldosteronism type II and a novel mutation (564D>H) in the acidic motif of the WNK4 gene.","date":"2005","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/15998707","citation_count":60,"is_preprint":false},{"pmid":"23665031","id":"PMC_23665031","title":"Disease-causing mutations in KLHL3 impair its effect on WNK4 degradation.","date":"2013","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/23665031","citation_count":58,"is_preprint":false},{"pmid":"21486947","id":"PMC_21486947","title":"Phenotypes of pseudohypoaldosteronism type II caused by the WNK4 D561A missense mutation are dependent on the WNK-OSR1/SPAK kinase cascade.","date":"2011","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/21486947","citation_count":58,"is_preprint":false},{"pmid":"15808806","id":"PMC_15808806","title":"Regulation of diverse ion transport pathways by WNK4 kinase: a novel molecular switch.","date":"2005","source":"Trends in endocrinology and metabolism: TEM","url":"https://pubmed.ncbi.nlm.nih.gov/15808806","citation_count":54,"is_preprint":false},{"pmid":"31736353","id":"PMC_31736353","title":"WNK bodies cluster WNK4 and SPAK/OSR1 to promote NCC activation in hypokalemia.","date":"2019","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/31736353","citation_count":54,"is_preprint":false},{"pmid":"28096417","id":"PMC_28096417","title":"Phosphorylation by PKC and PKA regulate the kinase activity and downstream signaling of WNK4.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/28096417","citation_count":53,"is_preprint":false},{"pmid":"29846116","id":"PMC_29846116","title":"Kidney-specific WNK1 isoform (KS-WNK1) is a potent activator of WNK4 and NCC.","date":"2018","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29846116","citation_count":53,"is_preprint":false},{"pmid":"17194447","id":"PMC_17194447","title":"WNK1 and WNK4 modulate CFTR activity.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17194447","citation_count":48,"is_preprint":false},{"pmid":"17651736","id":"PMC_17651736","title":"WNK4 phosphorylates ser(206) of claudin-7 and promotes paracellular Cl(-) permeability.","date":"2007","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/17651736","citation_count":48,"is_preprint":false},{"pmid":"21434893","id":"PMC_21434893","title":"Cyclosporine metabolic side effects: association with the WNK4 system.","date":"2011","source":"European journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/21434893","citation_count":47,"is_preprint":false},{"pmid":"15309683","id":"PMC_15309683","title":"Identification of 108 SNPs in TSC, WNK1, and WNK4 and their association with hypertension in a Japanese general population.","date":"2004","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/15309683","citation_count":46,"is_preprint":false},{"pmid":"21660484","id":"PMC_21660484","title":"Immunolocalization of WNK4 in mouse kidney.","date":"2011","source":"Histochemistry and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/21660484","citation_count":43,"is_preprint":false},{"pmid":"20927043","id":"PMC_20927043","title":"Angiotensin II diminishes the effect of SGK1 on the WNK4-mediated inhibition of ROMK1 channels.","date":"2010","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/20927043","citation_count":39,"is_preprint":false},{"pmid":"29848507","id":"PMC_29848507","title":"The Calcium-Sensing Receptor Increases Activity of the Renal NCC through the WNK4-SPAK Pathway.","date":"2018","source":"Journal of the American Society of Nephrology : JASN","url":"https://pubmed.ncbi.nlm.nih.gov/29848507","citation_count":38,"is_preprint":false},{"pmid":"21670282","id":"PMC_21670282","title":"Serine-threonine kinase with-no-lysine 4 (WNK4) controls blood pressure via transient receptor potential canonical 3 (TRPC3) in the vasculature.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21670282","citation_count":38,"is_preprint":false},{"pmid":"21807898","id":"PMC_21807898","title":"Antagonistic regulation of cystic fibrosis transmembrane conductance regulator cell surface expression by protein kinases WNK4 and spleen tyrosine kinase.","date":"2011","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21807898","citation_count":37,"is_preprint":false},{"pmid":"23594824","id":"PMC_23594824","title":"WNK4 inhibition of ENaC is independent of Nedd4-2-mediated ENaC ubiquitination.","date":"2013","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/23594824","citation_count":36,"is_preprint":false},{"pmid":"14616768","id":"PMC_14616768","title":"Association of EDNRA, but not WNK4 or FKBP1B, polymorphisms with essential hypertension.","date":"2003","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/14616768","citation_count":35,"is_preprint":false},{"pmid":"24811174","id":"PMC_24811174","title":"A novel Ste20-related proline/alanine-rich kinase (SPAK)-independent pathway involving calcium-binding protein 39 (Cab39) and serine threonine kinase with no lysine member 4 (WNK4) in the activation of Na-K-Cl cotransporters.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24811174","citation_count":35,"is_preprint":false},{"pmid":"20181799","id":"PMC_20181799","title":"Mechanisms for hypercalciuria in pseudohypoaldosteronism type II-causing WNK4 knock-in mice.","date":"2010","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/20181799","citation_count":35,"is_preprint":false},{"pmid":"23962426","id":"PMC_23962426","title":"Decrease of WNK4 ubiquitination by disease-causing mutations of KLHL3 through different molecular mechanisms.","date":"2013","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/23962426","citation_count":34,"is_preprint":false},{"pmid":"18701621","id":"PMC_18701621","title":"WNK3 and WNK4 amino-terminal domain defines their effect on the renal Na+-Cl- cotransporter.","date":"2008","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/18701621","citation_count":33,"is_preprint":false},{"pmid":"21613417","id":"PMC_21613417","title":"WNK4 kinase inhibits Maxi K channel activity by a kinase-dependent mechanism.","date":"2011","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/21613417","citation_count":32,"is_preprint":false},{"pmid":"23885063","id":"PMC_23885063","title":"Regulation of large-conductance Ca2+-activated K+ channels by WNK4 kinase.","date":"2013","source":"American journal of physiology. Cell physiology","url":"https://pubmed.ncbi.nlm.nih.gov/23885063","citation_count":32,"is_preprint":false},{"pmid":"19706464","id":"PMC_19706464","title":"Src family protein tyrosine kinase (PTK) modulates the effect of SGK1 and WNK4 on ROMK channels.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19706464","citation_count":31,"is_preprint":false},{"pmid":"22200850","id":"PMC_22200850","title":"Dietary salt modulates the sodium chloride cotransporter expression likely through an aldosterone-mediated WNK4-ERK1/2 signaling pathway.","date":"2011","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/22200850","citation_count":30,"is_preprint":false},{"pmid":"15081430","id":"PMC_15081430","title":"Comparison of WNK4 and WNK1 kinase and inhibiting activities.","date":"2004","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/15081430","citation_count":29,"is_preprint":false},{"pmid":"20061383","id":"PMC_20061383","title":"WNK4 kinase stimulates caveola-mediated endocytosis of TRPV5 amplifying the dynamic range of regulation of the channel by protein kinase C.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20061383","citation_count":29,"is_preprint":false},{"pmid":"23673010","id":"PMC_23673010","title":"WNK4 inhibits Ca(2+)-activated big-conductance potassium channels (BK) via mitogen-activated protein kinase-dependent pathway.","date":"2013","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/23673010","citation_count":26,"is_preprint":false},{"pmid":"15110905","id":"PMC_15110905","title":"Three novel missense mutations of WNK4, a kinase mutated in inherited hypertension, in Japanese hypertensives: implication of clinical phenotypes.","date":"2004","source":"American journal of hypertension","url":"https://pubmed.ncbi.nlm.nih.gov/15110905","citation_count":26,"is_preprint":false},{"pmid":"18703016","id":"PMC_18703016","title":"WNK4 regulates the secretory pathway via which TRPV5 is targeted to the plasma membrane.","date":"2008","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/18703016","citation_count":25,"is_preprint":false},{"pmid":"12719438","id":"PMC_12719438","title":"Genetic variants of WNK4 in whites and African Americans with hypertension.","date":"2003","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/12719438","citation_count":25,"is_preprint":false},{"pmid":"28743496","id":"PMC_28743496","title":"WNK4 is indispensable for the pathogenesis of pseudohypoaldosteronism type II caused by mutant KLHL3.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28743496","citation_count":23,"is_preprint":false},{"pmid":"29667910","id":"PMC_29667910","title":"Role of WNK4 and kidney-specific WNK1 in mediating the effect of high dietary K+ intake on ROMK channel in the distal convoluted tubule.","date":"2018","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29667910","citation_count":23,"is_preprint":false},{"pmid":"15796898","id":"PMC_15796898","title":"Regulation of apical localization of the thiazide-sensitive NaCl cotransporter by WNK4 in polarized epithelial cells.","date":"2005","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/15796898","citation_count":23,"is_preprint":false},{"pmid":"33491560","id":"PMC_33491560","title":"WNK4 kinase: from structure to physiology.","date":"2021","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/33491560","citation_count":22,"is_preprint":false},{"pmid":"31786261","id":"PMC_31786261","title":"WNK4-SPAK modulates lipopolysaccharide-induced macrophage activation.","date":"2019","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/31786261","citation_count":22,"is_preprint":false},{"pmid":"32579473","id":"PMC_32579473","title":"WNK3 and WNK4 exhibit opposite sensitivity with respect to cell volume and intracellular chloride concentration.","date":"2020","source":"American journal of physiology. Cell physiology","url":"https://pubmed.ncbi.nlm.nih.gov/32579473","citation_count":22,"is_preprint":false},{"pmid":"23054253","id":"PMC_23054253","title":"Disease-causing R1185C mutation of WNK4 disrupts a regulatory mechanism involving calmodulin binding and SGK1 phosphorylation sites.","date":"2012","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/23054253","citation_count":22,"is_preprint":false},{"pmid":"33719576","id":"PMC_33719576","title":"Roles of WNK4 and SPAK in K+-mediated dephosphorylation of the NaCl cotransporter.","date":"2021","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/33719576","citation_count":21,"is_preprint":false},{"pmid":"19587141","id":"PMC_19587141","title":"Characterization of the kinase activity of a WNK4 protein complex.","date":"2009","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/19587141","citation_count":20,"is_preprint":false},{"pmid":"22342722","id":"PMC_22342722","title":"Disease-causing mutations in the acidic motif of WNK4 impair the sensitivity of WNK4 kinase to calcium ions.","date":"2012","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/22342722","citation_count":19,"is_preprint":false},{"pmid":"25805816","id":"PMC_25805816","title":"Src-family protein tyrosine kinase phosphorylates WNK4 and modulates its inhibitory effect on KCNJ1 (ROMK).","date":"2015","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/25805816","citation_count":18,"is_preprint":false},{"pmid":"18312414","id":"PMC_18312414","title":"Distinct pathways for the involvement of WNK4 in the signaling of hypertonicity and EGF.","date":"2008","source":"The FEBS journal","url":"https://pubmed.ncbi.nlm.nih.gov/18312414","citation_count":18,"is_preprint":false},{"pmid":"26732173","id":"PMC_26732173","title":"Osmotic stress induces the phosphorylation of WNK4 Ser575 via the p38MAPK-MK pathway.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/26732173","citation_count":18,"is_preprint":false},{"pmid":"14967840","id":"PMC_14967840","title":"WNK4 intron 10 polymorphism is not associated with hypertension.","date":"2004","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/14967840","citation_count":18,"is_preprint":false},{"pmid":"29921588","id":"PMC_29921588","title":"C-terminally truncated, kidney-specific variants of the WNK4 kinase lack several sites that regulate its activity.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/29921588","citation_count":17,"is_preprint":false},{"pmid":"15948903","id":"PMC_15948903","title":"WNK4 regulates airway Na+ transport: study of familial hyperkalaemia and hypertension.","date":"2005","source":"European journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/15948903","citation_count":17,"is_preprint":false},{"pmid":"17634397","id":"PMC_17634397","title":"WNK4-mediated regulation of renal ion transport proteins.","date":"2007","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17634397","citation_count":16,"is_preprint":false},{"pmid":"37881876","id":"PMC_37881876","title":"Dysregulation of the WNK4-SPAK/OSR1 pathway has a minor effect on baseline NKCC2 phosphorylation.","date":"2023","source":"American journal of physiology. Renal physiology","url":"https://pubmed.ncbi.nlm.nih.gov/37881876","citation_count":16,"is_preprint":false},{"pmid":"28314693","id":"PMC_28314693","title":"WNK4 is an Adipogenic Factor and Its Deletion Reduces Diet-Induced Obesity in Mice.","date":"2017","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/28314693","citation_count":16,"is_preprint":false},{"pmid":"31318316","id":"PMC_31318316","title":"Activation of the Ca2+ sensing receptor and the PKC/WNK4 downstream signaling cascade induces incorporation of ZO-2 to tight junctions and its separation from 14-3-3.","date":"2019","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/31318316","citation_count":16,"is_preprint":false},{"pmid":"24039833","id":"PMC_24039833","title":"SPAK deficiency corrects pseudohypoaldosteronism II caused by WNK4 mutation.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24039833","citation_count":16,"is_preprint":false},{"pmid":"12642508","id":"PMC_12642508","title":"The role of Wnk4 in polygenic hypertension: a candidate gene analysis on rat chromosome 10.","date":"2003","source":"Hypertension (Dallas, Tex. : 1979)","url":"https://pubmed.ncbi.nlm.nih.gov/12642508","citation_count":16,"is_preprint":false},{"pmid":"27727489","id":"PMC_27727489","title":"Phosphorylation of KLHL3 at serine 433 impairs its interaction with the acidic motif of WNK4: a molecular dynamics study.","date":"2016","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/27727489","citation_count":16,"is_preprint":false},{"pmid":"31382627","id":"PMC_31382627","title":"Claudin-7 Modulates Cl- and Na+ Homeostasis and WNK4 Expression in Renal Collecting Duct Cells.","date":"2019","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31382627","citation_count":15,"is_preprint":false},{"pmid":"19016006","id":"PMC_19016006","title":"A patient with pseudohypoaldosteronism type II caused by a novel mutation in WNK4 gene.","date":"2008","source":"Endocrine","url":"https://pubmed.ncbi.nlm.nih.gov/19016006","citation_count":14,"is_preprint":false},{"pmid":"32956652","id":"PMC_32956652","title":"The sodium/proton exchanger NHA2 regulates blood pressure through a WNK4-NCC dependent pathway in the kidney.","date":"2020","source":"Kidney international","url":"https://pubmed.ncbi.nlm.nih.gov/32956652","citation_count":13,"is_preprint":false},{"pmid":"18755144","id":"PMC_18755144","title":"The acidic motif of WNK4 is crucial for its interaction with the K channel ROMK.","date":"2008","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/18755144","citation_count":13,"is_preprint":false},{"pmid":"30723408","id":"PMC_30723408","title":"Upregulation of the WNK4 Signaling Pathway Inhibits Epithelial Sodium Channels of Mouse Tracheal Epithelial Cells After Influenza A Infection.","date":"2019","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30723408","citation_count":12,"is_preprint":false},{"pmid":"28414128","id":"PMC_28414128","title":"Impaired degradation of medullary WNK4 in the kidneys of KLHL2 knockout mice.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28414128","citation_count":11,"is_preprint":false},{"pmid":"21236712","id":"PMC_21236712","title":"A WNK4 gene variant relates to osteoporosis and not to hypertension in the Portuguese population.","date":"2010","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/21236712","citation_count":10,"is_preprint":false},{"pmid":"26349538","id":"PMC_26349538","title":"Involvement of selective autophagy mediated by p62/SQSTM1 in KLHL3-dependent WNK4 degradation.","date":"2015","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/26349538","citation_count":10,"is_preprint":false},{"pmid":"19340547","id":"PMC_19340547","title":"Association of Ala589Ser polymorphism of WNK4 gene with essential hypertension in a high-risk Chinese population.","date":"2008","source":"The journal of physiological sciences : JPS","url":"https://pubmed.ncbi.nlm.nih.gov/19340547","citation_count":10,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":57167,"output_tokens":14810,"usd":0.196825,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":26685,"output_tokens":6364,"usd":0.146262,"stage2_stop_reason":"end_turn"},"total_usd":0.343087,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"Wild-type WNK4 inhibits NaCl cotransporter (NCC/NCCT)-mediated Na+ influx and reduces NCC membrane expression in Xenopus oocytes; this inhibition requires WNK4 kinase activity. PHAII-causing missense mutations in WNK4 (remote from kinase domain) abolish NCC inhibition. WNK4 and the C-terminus of NCC co-immunoprecipitate in HEK293T cells.\",\n      \"method\": \"Xenopus oocyte heterologous expression (22Na+ influx, surface biotinylation), kinase-dead mutagenesis, co-immunoprecipitation in HEK293T cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, functional oocyte assays with multiple mutants, surface expression quantification; foundational paper replicated extensively by independent labs\",\n      \"pmids\": [\"12515852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"WNK4 also inhibits the renal K+ channel ROMK via clathrin-dependent endocytosis, through a mechanism independent of WNK4 kinase activity and distinct from its inhibition of NCC. PHAII-causing WNK4 mutations increase ROMK inhibition while relieving NCC inhibition, establishing WNK4 as a molecular switch balancing NaCl reabsorption and K+ secretion.\",\n      \"method\": \"Xenopus oocyte expression, electrophysiology, clathrin-dependent endocytosis assays, mutagenesis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional oocyte assays with mechanistic dissection (kinase-dead mutants, endocytosis pathway), replicated by multiple independent labs\",\n      \"pmids\": [\"14608358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PHAII-causing mutant WNK4 (D564A) increases transepithelial paracellular Cl- permeability in MDCK II cells. Wild-type and mutant WNK4 bind and phosphorylate claudins 1–4 (major tight-junction proteins); mutant WNK4 causes greater claudin phosphorylation than wild-type.\",\n      \"method\": \"Stable MDCK II cell lines with inducible WNK4 expression, transepithelial permeability measurements, in vitro kinase assay (claudin phosphorylation), co-immunoprecipitation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus functional cell permeability measurements, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"15070779\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Wild-type WNK4 increases paracellular chloride permeability in mammalian kidney epithelia (MDCK cells with inducible expression) through a kinase-dependent mechanism. PHAII-mutant WNK4 produces markedly larger effects; kinase-dead WNK4 has no effect. WNK4 did not alter flux of uncharged solutes or expression/localization of selected tight-junction proteins.\",\n      \"method\": \"Electrophysiology on mammalian kidney epithelia with inducible WNK4, kinase-dead and PHAII-mutant constructs, pharmacological and electrochemical characterization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology with multiple WNK4 constructs, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"15465913\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"WNK4 is expressed in extrarenal polarized epithelia (sweat ducts, colonic crypts, pancreatic ducts, bile ducts, epididymis, blood-brain barrier endothelium). In these tissues WNK4 potently inhibits NKCC1 (>95% inhibition of 86Rb influx) and the Cl-/base exchanger SLC26A6 (CFEX) (>80% inhibition of 14C-formate uptake), but not pendrin.\",\n      \"method\": \"Xenopus oocyte expression, 86Rb influx assay, 14C-formate uptake assay, WNK4 tissue localization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional oocyte assays with multiple transport substrates and specificity controls, single lab\",\n      \"pmids\": [\"14769928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"WNK1 and WNK4 both interact with and phosphorylate SPAK and OSR1 in vitro. WNK1/WNK4 phosphorylate the T-loop residues of SPAK (Thr233) and OSR1 (Thr185) and a C-terminal serine (Ser373/Ser325). Phosphorylation of Thr185 in OSR1 activates it; Thr185Ala prevents activation, and Thr185Glu (phosphomimetic) increases basal activity >20-fold. Catalytically inactive WNK1/WNK4 fail to activate SPAK/OSR1.\",\n      \"method\": \"Immunoprecipitation from rat testis, in vitro kinase assay, phosphopeptide mapping, site-directed mutagenesis of SPAK/OSR1 T-loop residues\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, phosphopeptide mapping, replicated across labs\",\n      \"pmids\": [\"16083423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"WNK4 interacts with SPAK (via yeast two-hybrid and functional assays) and together activate NKCC1 and inhibit KCC2 in Xenopus oocytes. Catalytic activity of both WNK4 and SPAK is required. A SPAK-interaction-deficient WNK4 mutant (Phe997Ala) fails to activate NKCC1, establishing that WNK4 acts on NKCC1 indirectly through SPAK.\",\n      \"method\": \"Xenopus oocyte expression, yeast two-hybrid, kinase-dead mutagenesis, isotope flux assays\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus oocyte functional assays with multiple mutants, single lab\",\n      \"pmids\": [\"15930150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"WNK1 kinase domain physically associates with WNK4 kinase domain (co-immunoprecipitation). WNK1 suppresses WNK4-mediated NCC inhibition via this interaction but requires intact WNK1 kinase activity. The WNK4 C-terminal 222 amino acids are sufficient to inhibit NCC but are not blocked by WNK1; WNK1 inhibition requires an intact WNK4 kinase domain.\",\n      \"method\": \"Xenopus oocyte expression, co-immunoprecipitation, domain deletion/mutagenesis, 22Na+ flux assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal domain interaction mapping with Co-IP plus functional oocyte assays, single lab\",\n      \"pmids\": [\"15841204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"WNK4 wild-type significantly reduces NCC surface expression in Cos-7 mammalian cells; PHAII-mutant E562K does not. The effect is not due to clathrin-mediated endocytosis (dominant-negative dynamin K44A has no effect) but is reversed by the lysosomal inhibitor bafilomycin A1, indicating enhanced lysosomal degradation of NCC by WNK4.\",\n      \"method\": \"Surface biotinylation, co-immunoprecipitation, dominant-negative dynamin expression, pharmacological inhibitors (bafilomycin A1) in Cos-7 cells\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — surface biotinylation plus pharmacological inhibitor dissection in mammalian cells, Co-IP, single lab\",\n      \"pmids\": [\"16688122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"WNK4 controls blood pressure via regulation of mass and function of the distal convoluted tubule (DCT). TgWnk4(PHAII) mice show DCT hyperplasia, hypertension, hyperkalemia, and hypercalciuria; TgWnk4(WT) mice show opposite phenotypes. Genetic deficiency for NCC reverses all TgWnk4(PHAII) phenotypes, establishing that WNK4 PHAII effects are mediated through NCC.\",\n      \"method\": \"Transgenic mouse model (genomic WNK4 segments), NCC knockout epistasis, blood pressure/electrolyte measurements, kidney morphology\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in vivo (NCC KO rescues PHAII phenotype), replicated in multiple mouse models\",\n      \"pmids\": [\"16964266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"WNK4 enhances TRPV5-mediated Ca2+ uptake and increases TRPV5 surface expression in Xenopus oocytes; PHAII-causing WNK4 mutants retain ability to upregulate TRPV5.\",\n      \"method\": \"Xenopus oocyte expression, Ca2+ uptake assay, surface expression measurement\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — oocyte functional assays with multiple mutants but single lab; no Co-IP or structural validation\",\n      \"pmids\": [\"17018846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"WNK4 is a negative regulator of K+-Cl- cotransporters KCC1, KCC3, and KCC4; this inhibition requires WNK4 catalytic activity (abolished by D318A mutation). PHAII-causing WNK4 missense mutations do not affect inhibition of KCC4.\",\n      \"method\": \"Xenopus oocyte expression, isotope flux assays, kinase-dead mutagenesis\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — oocyte functional assays with mutagenesis, single lab\",\n      \"pmids\": [\"17182532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"WNK4 also inhibits ENaC (epithelial Na+ channel) activity via a kinase-independent mechanism requiring intact C-termini (PY motifs) in ENaC β- and γ-subunits. PHAII-causing WNK4 mutations eliminate ENaC inhibition. In vivo, PHAII-mutant WNK4 mice show markedly increased amiloride-sensitive Na+ flux in the colonic epithelium.\",\n      \"method\": \"Xenopus oocyte co-expression, C-terminal deletion/mutagenesis of ENaC subunits, amiloride-sensitive Na+ flux in transgenic mouse colonic epithelium\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — oocyte mechanistic dissection plus in vivo mouse validation, single lab\",\n      \"pmids\": [\"17360470\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SGK1 phosphorylates WNK4 (aldosterone-dependent kinase), and a WNK4 phosphomimetic mutant at the SGK1 site (S1169D) relieves WNK4 inhibition of both ENaC and ROMK, promoting increased K+ secretion. This identifies a functional state of WNK4 that is the opposite of the PHAII state.\",\n      \"method\": \"Xenopus oocyte expression, in vitro phosphorylation by SGK1, phosphomimetic mutagenesis (S1169D)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus functional oocyte experiments with phosphomimetic mutants, single lab\",\n      \"pmids\": [\"17360471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In Wnk4(D561A/+) knockin mice (PHAII model), phosphorylated NCC is increased at the apical surface of distal convoluted tubule cells. OSR1 and SPAK phosphorylation are also increased. Apical ROMK localization and transepithelial Cl- permeability in cortical collecting ducts are unaffected. ENaC activation is a secondary compensatory effect (reversed by hydrochlorothiazide). PHAII pathogenesis is through OSR1/SPAK-NCC cascade activation.\",\n      \"method\": \"Knockin mouse model (D561A), immunohistochemistry, immunoblotting of phosphorylated NCC/OSR1/SPAK, patch clamp electrophysiology, hydrochlorothiazide treatment\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockin mouse model with multiple orthogonal in vivo measurements, extensively replicated\",\n      \"pmids\": [\"17488636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"WNK4 phosphorylates claudin-7 at Ser206 in the COOH-terminus (identified as a WNK4 phosphorylation site by mutagenesis). WNK4 and claudin-7 co-immunoprecipitate in kidney epithelial cells and co-localize in renal tubules. The PHAII-causing mutant WNK4 enhances claudin-7 phosphorylation and paracellular Cl- permeability more than wild-type.\",\n      \"method\": \"Co-immunoprecipitation in kidney epithelial cells, in vitro kinase assay, site-directed mutagenesis (Ser206), paracellular permeability measurement\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus in vitro kinase assay with mutagenesis, single lab\",\n      \"pmids\": [\"17651736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"WNK4 diverts NCC to lysosomes for degradation via an AP-3-dependent mechanism, reducing forward trafficking from the trans-Golgi network to the plasma membrane rather than increasing endocytosis. WNK4 increases NCC association with AP-3 adaptor complexes and increases lysosomal NCC accumulation (reversed by lysosomal protease inhibitor leupeptin, not proteasome inhibition).\",\n      \"method\": \"Surface lifetime analysis, direct forward trafficking measurements (trans-Golgi to plasma membrane), co-immunoprecipitation with endogenous AP-3, subcellular localization with leupeptin/proteasome inhibitors, WNK4 knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal trafficking assays with pharmacological dissection and endogenous AP-3 Co-IP, single lab\",\n      \"pmids\": [\"19401467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Angiotensin II (AngII) increases NCC activity in Xenopus oocytes by abrogating WNK4 inhibition of NCC through a pathway requiring AngII receptor AT1R and WNK4. This effect is SPAK-dependent (dominant-negative SPAK or elimination of SPAK-binding motif in NCC prevents it). AngII does not alter WNK4 inhibition of ROMK. AngII increases phosphorylation of SPAK and NCC at activation sites in mpkDCT mammalian cells.\",\n      \"method\": \"Xenopus oocyte expression, dominant-negative SPAK, AT1R inhibitor losartan, immunoblotting of pSPAK and pNCC in mpkDCT cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — oocyte functional assays with pathway dissection plus mammalian cell phosphorylation studies, single lab; replicated in vivo by PMID 22550170\",\n      \"pmids\": [\"19240212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"WNK4 knockout mice (WNK4-/-) exhibit reduced NCC expression and phosphorylation, low blood pressure and increased Na/K excretion on low-salt diet. Phosphorylation of OSR1/SPAK and NCC is significantly reduced, establishing wild-type WNK4 as a positive regulator of the WNK-OSR1/SPAK-NCC cascade in vivo.\",\n      \"method\": \"WNK4 hypomorphic/knockout mouse model, immunoblotting of pOSR1/pSPAK/pNCC, blood pressure and urinary electrolyte measurements\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function mouse model with defined molecular and physiological phenotype, replicated by independent labs\",\n      \"pmids\": [\"19633012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"WNK4 enhances NCC degradation through a sortilin-mediated lysosomal pathway. Truncated sortilin (dominant-negative) prevents WNK4-induced NCC reduction. NCC co-immunoprecipitates with sortilin, and WNK4 increases co-localization of NCC with lysosomal marker cathepsin D.\",\n      \"method\": \"Co-transfection in Cos-7 cells, dominant-negative sortilin, co-immunoprecipitation, immunostaining with lysosomal marker\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus dominant-negative rescue plus immunostaining, single lab, no in vitro reconstitution\",\n      \"pmids\": [\"19875813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SGK1 binds and phosphorylates WNK4 in vitro and in a human kidney cell line at two serine residues including one in an established SGK1 consensus sequence. Phosphomimetic mutations (aspartate) at these SGK1 target serines attenuate WNK4 inhibition of NCC in Xenopus oocytes. This defines the aldosterone/SGK1 → WNK4 → NCC pathway.\",\n      \"method\": \"In vitro kinase assay (SGK1 phosphorylation of WNK4), co-immunoprecipitation, phosphomimetic mutagenesis, Xenopus oocyte functional assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus Co-IP plus oocyte functional validation with phosphomimetics, single lab\",\n      \"pmids\": [\"19690383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"WNK4 stimulates caveola-mediated endocytosis of TRPV5, decreasing its cell-surface abundance. A region outside the kinase domain of WNK4 mediates TRPV5 endocytosis stimulation. This sets a lower basal TRPV5 level that allows PKC stimulation to produce a larger relative increase in TRPV5 current.\",\n      \"method\": \"Xenopus oocyte expression, electrophysiology (TRPV5 current), deletion analysis of WNK4 domains, caveola-mediated endocytosis assays, PKC activator (OAG) experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — oocyte functional assays with WNK4 deletion analysis, single lab\",\n      \"pmids\": [\"20061383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Phenotypes of PHAII in Wnk4(D561A/+) knockin mice depend entirely on the WNK-OSR1/SPAK-NCC cascade: crossing with Spak(T243A) and Osr1(T185A) knock-in mice that cannot be activated by WNK kinases almost completely abolishes NCC phosphorylation and corrects hypertension, hyperkalemia, and metabolic acidosis in triple knock-in mice.\",\n      \"method\": \"Genetic epistasis in mice (triple knock-in), immunoblotting of pNCC, blood pressure and electrolyte measurements\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis with complete pathway rescue, single lab but rigorous genetic design\",\n      \"pmids\": [\"21486947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"β2-adrenergic receptor (β2AR) stimulation decreases WNK4 gene transcription via cAMP-dependent inhibition of HDAC8, increasing histone acetylation and glucocorticoid receptor binding to a negative glucocorticoid-responsive element in the WNK4 promoter, leading to NCC activation and salt-sensitive hypertension.\",\n      \"method\": \"In vitro β2AR stimulation, HDAC8 activity assay, chromatin immunoprecipitation (GR-promoter binding), rat models of salt-sensitive hypertension\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP, enzymatic assay of HDAC8, in vivo rat model, mechanistic pathway from receptor to WNK4 transcription, single lab\",\n      \"pmids\": [\"21499270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"WNK4 inhibits Maxi K (BK) channel activity in a kinase-dependent manner (kinase-dead D321A has no effect). WNK4 reduces total and cell-surface Maxi K expression through a lysosomal degradation pathway (reversed by bafilomycin A1 and leupeptin), not through clathrin-mediated endocytosis (dominant-negative dynamin K44A has no effect).\",\n      \"method\": \"Patch clamp electrophysiology in HEK αBK stable cells, surface biotinylation, pharmacological inhibitors, kinase-dead mutagenesis\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology combined with biochemical surface expression and pharmacological dissection, single lab\",\n      \"pmids\": [\"21613417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"WNK4 inhibits TRPC3-mediated Ca2+ influx in vascular smooth muscle cells (VSMCs), restricting vasoconstriction. WNK4 depletion increases TRPC3-mediated Ca2+ entry and vasoconstriction. PHAII-mutant (Q562E) and kinase-dead (D318A) WNK4 both fail to inhibit TRPC3, indicating kinase activity is required.\",\n      \"method\": \"WNK4 knockdown/knockout in VSMCs, Ca2+ influx measurements, vasoconstriction assays in small mesenteric arteries, kinase-dead and PHAII mutant expression\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined Ca2+ and vascular functional readouts, mutagenesis, single lab\",\n      \"pmids\": [\"21670282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"WNK4 inhibits ENaC activity in A6 distal nephron cells by reducing channel number at the apical membrane (not open probability) and by enhancing ENaC internalization independent of Nedd4-2-mediated ENaC ubiquitination. WNK4 also reduces the ENaC pool available for recycling. WNK4 associates with both wild-type and Liddle's mutant ENaC.\",\n      \"method\": \"Transepithelial current measurement and single-channel recording in A6 cells, Western blot of apical/total ENaC, internalization assays, Co-IP in HEK293 cells\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology plus biochemical trafficking assays, single lab\",\n      \"pmids\": [\"23594824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"AngII-mediated activation of NCC requires WNK4 in vivo: WNK4-/- mice cannot phosphorylate SPAK and NCC in response to low-salt diet or AngII infusion, placing WNK4 as an essential intermediary in the AngII→SPAK→NCC signaling pathway.\",\n      \"method\": \"WNK4 knockout mouse, AngII infusion and low-salt diet protocols, immunohistochemistry and immunoblotting of pSPAK and pNCC\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout epistasis with AngII challenge, replicated across labs\",\n      \"pmids\": [\"22550170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KLHL3 (a BTB-Kelch adaptor) binds WNK4 and promotes its ubiquitination at ≥15 specific sites and subsequent degradation, thereby reducing WNK4 levels and ROMK surface reduction. PHAII-causing mutations in either KLHL3 or WNK4 impair this binding and ubiquitination. KLHL3 requires CUL3 (a RING E3 ligase scaffold) to form the functional complex.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation (KLHL3-WNK4-CUL3), ubiquitination assay (polyubiquitination mapping of WNK4), in vivo WNK4 protein level measurement in mouse kidney\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — MS identification of ubiquitination sites, Co-IP, in vivo kidney protein levels, replicated by multiple independent labs\",\n      \"pmids\": [\"23576762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The CUL3-KLHL3 E3 ligase complex ubiquitylates WNK4 (and WNK1) in vitro. KLHL3 binds WNK1/WNK4 but not SPAK/OSR1 or NCC/NKCC1. 13 out of 15 dominant KLHL3 disease mutations inhibit WNK binding. The KLHL3 interaction site in WNK1 maps to residues 479–667; equivalent WNK4 residues harbor PHAII mutations (E562K, Q565E) that abolish KLHL3 interaction.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitylation assay with recombinant CUL3-KLHL3, siRNA knockdown (CUL3 in HeLa cells), domain mapping\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstituted ubiquitylation plus Co-IP plus siRNA plus interaction domain mapping, single lab but multiple orthogonal methods; replicated independently\",\n      \"pmids\": [\"23387299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KLHL3 interacts with CUL3 and WNK4, induces WNK4 ubiquitination, and reduces WNK4 protein level. PHAII-causing mutations in KLHL3 or WNK4 reduce this interaction and ubiquitination, resulting in elevated WNK4 protein and increased SPAK/OSR1-NCC phosphorylation. Transgenic mice overexpressing WNK4 display PHAII phenotypes; WNK4 protein is increased in Wnk4(D561A/+) knockin mice.\",\n      \"method\": \"Co-immunoprecipitation (KLHL3-CUL3-WNK4), in vitro ubiquitination assay, transgenic mouse overexpression, Wnk4(D561A/+) knockin mouse immunoblot\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP, in vitro ubiquitination, transgenic and knockin mouse in vivo validation, replicated by multiple labs\",\n      \"pmids\": [\"23453970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"WNK4 inhibits BK channel (large-conductance Ca2+-activated K+ channel) activity. A region within WNK4 encompassing the autoinhibitory domain and a coiled-coil domain is required for BK inhibition. WNK4 increases ubiquitination and degradation of BK α-subunit, reducing plasma membrane expression.\",\n      \"method\": \"Electrophysiology in intercalated cell line and HEK293 cells, domain deletion of WNK4, ubiquitination assay, surface/whole-cell expression measurements\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology with domain mapping plus ubiquitination assay, single lab\",\n      \"pmids\": [\"23885063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"WNK4 effects on NCC are modulated by intracellular Cl- concentration ([Cl-]i). Under low [Cl-]i, WNK4 autophosphorylates at S335 (T-loop) and activates NCC. A chloride-binding pocket mutation (L322F) renders WNK4 constitutively autophosphorylated, converting it to a constitutive NCC activator. Eliminating kinase activity (D321A or D321K-K186D) or the autophosphorylation site (S335A) in WNK4-L322F abolishes NCC activation.\",\n      \"method\": \"Xenopus oocyte expression, measurement of [Cl-]i with Cl-sensitive fluorescent dye, WNK4 autophosphorylation assay, chloride-binding pocket mutagenesis, 22Na+ uptake\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mechanistic in vitro autophosphorylation assay plus oocyte functional dissection with multiple mutants, single lab\",\n      \"pmids\": [\"25542968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"WNK4 is the major WNK kinase positively regulating NCC in the mouse kidney: WNK4-/- mice show near-complete loss of phosphorylated and total NCC despite compensatory upregulation of WNK1. Insulin- and low-potassium diet-induced NCC phosphorylation are both abolished in WNK4-/- mice.\",\n      \"method\": \"WNK4 knockout mouse, immunoblotting of pNCC/NCC, dietary and hormonal challenges (insulin, low-K diet)\",\n      \"journal\": \"Bioscience reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout with multiple physiological challenges, replicated by independent WNK4 knockout studies\",\n      \"pmids\": [\"24655003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Angiotensin II signaling via protein kinase C (PKC) phosphorylates KLHL3 at serine 433 (a site frequently mutated in hypertension), preventing KLHL3 from binding and targeting WNK4 for degradation, thereby increasing WNK4 levels and NCC phosphorylation. AngII administration to mice induces renal KLHL3-S433 phosphorylation and increased WNK4 and NCC levels.\",\n      \"method\": \"In vitro PKC phosphorylation of KLHL3 at S433, co-immunoprecipitation, mouse AngII infusion with immunoblotting of pKLHL3-S433/WNK4/NCC, site-directed mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay, Co-IP, in vivo mouse validation, single lab\",\n      \"pmids\": [\"25313067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"WNK4 C-terminal truncation variants found in kidney lack a protein phosphatase 1 (PP1)-binding site; deletion of this site increases WNK4 kinase activity toward SPAK. Co-transfection with PP1 dephosphorylates WNK4; a PP1-binding site mutant is resistant to PP1. Full-length WNK4 is cleaved by a Zn2+-dependent metalloprotease in kidney lysates.\",\n      \"method\": \"LC-MS/MS identification of short WNK4 variants, co-transfection with PP1, kinase activity assay, WNK4 dephosphorylation assay, kidney lysate protease assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — LC-MS/MS plus kinase assay plus Co-IP with PP1, single lab\",\n      \"pmids\": [\"29921588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"WNK1 activates NCC via SPAK in a WNK4-independent manner. Conversely, WNK4 decreases WNK1- and WNK3-mediated NCC activation. WNK kinases form oligomers through their C-terminal coiled-coil domains, and this oligomerization is essential for their activity toward NCC.\",\n      \"method\": \"WNK1-FHHt/WNK4-/- double mutant mice, Xenopus oocyte expression, coiled-coil domain mutagenesis, co-immunoprecipitation\",\n      \"journal\": \"Hypertension (Dallas, Tex. : 1979)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in mice plus oocyte mechanistic dissection with domain mutagenesis, single lab\",\n      \"pmids\": [\"25113964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"c-Src phosphorylates WNK4 at Tyr1092, Tyr1094, and Tyr1143 (identified by Western blot and mass spectrometry). Both c-Src and protein tyrosine phosphatase PTP-1D co-immunoprecipitate with WNK4. Tyr1092Phe mutation markedly reduces WNK4-mediated ROMK inhibition; double mutant Y1092/1094F completely abolishes it. c-Src also prevents SGK1-induced phosphorylation of WNK4 at Ser1196, restoring WNK4 inhibition of ROMK.\",\n      \"method\": \"Mass spectrometry identification of phosphorylation sites, co-immunoprecipitation of c-Src/PTP-1D with WNK4, mutagenesis (Y1092F, Y1143F, double mutant), oocyte electrophysiology for ROMK activity\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — MS identification plus Co-IP plus mutagenesis plus functional oocyte assay, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25805816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Chloride inhibits WNK4 kinase activity at lower concentrations than WNK1 or WNK3, within the physiological range of distal cell chloride. Mutation of the WNK4 chloride-binding motif (equivalent to that identified in WNK1) converts WNK4 effects on SPAK from inhibitory to stimulatory in mammalian cells. This explains how extracellular K+ affects NCC via intracellular Cl- acting on WNK4.\",\n      \"method\": \"In vitro kinase assay (WNK4 vs WNK1 vs WNK3 Cl- inhibition), chloride-binding motif mutagenesis in mammalian cells, in vivo dietary K+ manipulation with NCC phosphorylation readout\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus mutagenesis plus in vivo dietary manipulation, single lab\",\n      \"pmids\": [\"26422504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Osmotic stress induces phosphorylation of WNK4 at Ser575 via the p38MAPK-MAPK-activated protein kinase (MK) pathway. WNK4 interacts with ASK3 (a MAP3K), and ASK3 kinase activity is required for WNK4 Ser575 phosphorylation. Hypotonic low-chloride stimulation also increases WNK4-Ser575 phosphorylation via p38MAPK-MK.\",\n      \"method\": \"LC-MS/MS identification of Ser575 phosphorylation, co-immunoprecipitation of WNK4 with ASK3, kinase-dead ASK3 rescue, p38MAPK pathway inhibitors\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS identification, Co-IP, kinase-dependent rescue, single lab\",\n      \"pmids\": [\"26732173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PKC and PKA phosphorylate WNK4 at multiple sites (S47, S64, S1169, S1180, S1196) downstream of AngII signaling. Phosphorylation at S64 and S1196 promotes WNK4 T-loop phosphorylation at S332 (required for kinase activation) and increases SPAK phosphorylation. Volume depletion induces these phosphorylations in vivo predominantly in the distal convoluted tubule.\",\n      \"method\": \"Tandem mass spectrometry, phosphosite-specific antibodies, in vitro PKC/PKA kinase assays, in vivo volume depletion mouse model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — MS site identification plus in vitro kinase assays plus in vivo mouse validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28096417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"WNK4 is expressed in adipose tissue and is induced early during adipocyte differentiation. WNK4 affects the DNA-binding ability of C/EBPβ and thereby regulates PPARγ expression. WNK4 siRNA-knockdown reduces PPARγ, C/EBPα expression and lipid accumulation. WNK4-/- mice show decreased PPARγ and C/EBPα in adipose tissue and partial resistance to high-fat diet-induced adiposity.\",\n      \"method\": \"WNK4 siRNA in 3T3-L1 and human mesenchymal stem cells, WNK4-/- mouse model, C/EBPβ DNA-binding assay, adipocyte differentiation assay\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in cells and mice with defined transcription factor binding assay, single lab\",\n      \"pmids\": [\"28314693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Kidney-specific WNK1 isoform (KS-WNK1, which lacks the kinase domain) activates WNK4-T-loop phosphorylation at Ser335 and stimulates SPAK/NCC by physically interacting with WNK4 (co-immunoprecipitation) independent of changes in intracellular Cl-. Eliminating the WNK-WNK interaction domain in KS-WNK1 abolishes this activation.\",\n      \"method\": \"Xenopus oocyte expression, co-immunoprecipitation of KS-WNK1 and WNK4, WNK4-S335 phosphorylation assay, WNK interaction domain deletion, WNK inhibitor WNK463\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus phosphorylation assay plus functional oocyte dissection, single lab\",\n      \"pmids\": [\"29846116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"WNK4 is a physiological intracellular Cl- sensor: knockin mice carrying a Cl--insensitive WNK4 mutant fully recapitulate human PHAII. Dietary K+ restriction failed to increase NCC activity in knockin mice, and acute K+ administration failed to inactivate NCC in knockin mice (unlike wild-type). These results establish that Cl- regulation of WNK4 underlies the K+-mediated regulation of NCC.\",\n      \"method\": \"Cl--insensitive WNK4 knockin mouse model, NCC phosphorylation measurements under dietary K+ manipulation and acute K+ gavage\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockin mouse epistasis with multiple dietary and acute K+ challenges, rigorous mechanistic design\",\n      \"pmids\": [\"30765526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In K+ deficiency, WNK4 and SPAK/OSR1 concentrate in cytoplasmic spherical domains termed 'WNK bodies' in the DCT. Phosphorylated SPAK/OSR1 is present within WNK bodies. In WNK4-deficient mice, larger WNK bodies form containing unphosphorylated WNK1, SPAK, and OSR1, indicating WNK4 is the primary active kinase in WNK bodies. WNK body formation requires Kir4.1 K+ channel-mediated DCT K+ sensing.\",\n      \"method\": \"Mouse dietary K+ manipulation, immunofluorescence microscopy of WNK bodies, WNK4-/- mouse, DCT-specific Kir4.1 conditional knockout mouse\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct subcellular localization with loss-of-function genetic models, single lab\",\n      \"pmids\": [\"31736353\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CaSR activation increases NCC activity via the WNK4-SPAK pathway: in Xenopus oocytes NCC stimulation by CaSR is WNK4-dependent; in HEK293 cells CaSR activation causes KLHL3 phosphorylation, increased WNK4 abundance and activity, and SPAK phosphorylation in a WNK4-dependent manner (blocked by WNK463). Acute CaSR agonist (R-568) in mice increases pNCC.\",\n      \"method\": \"Xenopus oocyte 22Na+ assay, HEK293 cell phosphorylation assays, WNK463 inhibitor, mouse in vivo CaSR activation\",\n      \"journal\": \"Journal of the American Society of Nephrology : JASN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — oocyte functional assays plus cell signaling plus in vivo mouse, single lab\",\n      \"pmids\": [\"29848507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"WNK4-SPAK signaling promotes NKCC1 phosphorylation and NFκB activation in alveolar macrophages stimulated with LPS. WNK4 or SPAK knockout suppresses NKCC1 phosphorylation, NFκB activation, and acute lung injury; WNK4 D561A knockin (PHAII mutation) enhances inflammatory responses.\",\n      \"method\": \"WNK4-/-, SPAK-/-, WNK4(D561A/+) mice, primary alveolar macrophage culture, LPS stimulation, intrapulmonary LPS delivery, NFκB activation assay, NKCC1 phosphorylation immunoblot\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic mouse models with defined cellular pathway readout, single lab\",\n      \"pmids\": [\"31786261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"WNK4 inhibits BK (large-conductance Ca2+-activated K+) channels via activation of ERK and p38 MAPK (MAPK-dependent mechanism), partially through dynamin-dependent endocytosis. SGK1-mediated phosphorylation of WNK4 at S1169/S1196 abolishes WNK4's effects on BK channels and MAPK activation. The WNK4-ROMK inhibitory pathway, by contrast, is MAPK-independent.\",\n      \"method\": \"Perforated whole-cell patch clamp in HEK293T cells, MAPK inhibitors, dominant-negative dynamin (K44A), dynasore, SGK1 co-expression with phosphomimetic WNK4 mutants, native CCD electrophysiology\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology with pharmacological dissection plus mutagenesis, single lab\",\n      \"pmids\": [\"23673010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"KLHL3-mediated WNK4 degradation is also mediated by p62/SQSTM1-dependent selective autophagy in addition to proteasomal degradation. KLHL3 forms a complex with p62 (co-immunoprecipitation via kelch repeat domain). Under proteasome inhibition, p62 overexpression decreases WNK4 levels and p62 knockdown increases them. WNK4 co-localizes with KLHL3, p62, and LC3 (autophagosome marker) in cytoplasmic puncta.\",\n      \"method\": \"Co-immunoprecipitation, p62 overexpression/knockdown, autophagy inhibitor (3-methyladenine), proteasome inhibitor (epoxomicin), immunofluorescence (LC3 co-localization)\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus genetic and pharmacological dissection of degradation pathway, single lab\",\n      \"pmids\": [\"26349538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The PHAII-causing WNK4 mutation R1185C is located in a calmodulin (CaM) binding site in the C-terminus and reduces WNK4 binding to Ca2+/CaM. The R1185C mutation disrupts SGK1 phosphorylation at S1190 (eliminates it) and alters phosphorylation at adjacent SGK1 sites S1201 and S1217. The R1185C mutant enhances positive WNK4 effects on NKCC2. Ca2+/CaM inhibits phosphorylation at S1201.\",\n      \"method\": \"CaM binding assay, in vitro SGK1 phosphorylation of WNK4, Xenopus oocyte NKCC2 functional assay, site-directed mutagenesis\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding and kinase assays plus oocyte functional validation with mutagenesis, single lab\",\n      \"pmids\": [\"23054253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cab39 (calcium-binding protein 39) interacts with WNK4 and enables WNK4 to activate NKCC1 in a SPAK/OSR1-independent manner. WNK4 contains a PF2-like domain (resembling the SPAK/OSR1 CCT/PF2 domain) that directly interacts with the N-terminal domain of NKCC1, enabling WNK4 to anchor to and activate NKCC1 directly. Functional data and yeast two-hybrid confirm the WNK4-NKCC1 direct interaction via this domain.\",\n      \"method\": \"Yeast two-hybrid, modeling, Xenopus oocyte functional assays, domain deletion analysis, SPAK/OSR1-independent activation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus oocyte functional assays plus domain modeling, single lab\",\n      \"pmids\": [\"24811174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NHA2 (sodium/proton exchanger) regulates WNK4 stability in the kidney: loss of NHA2 increases WNK4 ubiquitylation and proteasomal degradation via a KLHL3-dependent mechanism. NHA2 loss selectively attenuates KLHL3 phosphorylation, blunting PKA- and PKC-mediated decrease of WNK4 degradation.\",\n      \"method\": \"NHA2 knockout mouse, in vitro NHA2 knockdown, WNK4 ubiquitylation assay, KLHL3 phosphorylation assay, NHA2/NCC double knockout mice\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockout mouse plus in vitro ubiquitylation assay plus double-KO epistasis, single lab\",\n      \"pmids\": [\"32956652\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Rapid NCC dephosphorylation by high extracellular K+ requires inactivation of the WNK4-SPAK 'on switch': WNK4-SPAK signaling must be turned off for rapid NCC dephosphorylation by high K+ in vitro (HEK cells) and ex vivo (kidney slices). SPAK is rapidly dephosphorylated in DCT1 specifically upon acute K+ challenge in vivo. Extended WNK-SPAK activation attenuates sensitivity to subsequent rapid K+-induced dephosphorylation.\",\n      \"method\": \"HEK cell K+ challenge, ex vivo kidney slice acute K+ treatment, in vivo acute K+ loading with pSPAK/pNCC immunoblot, PP1/PP3 inhibitor studies\",\n      \"journal\": \"American journal of physiology. Renal physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro, ex vivo, and in vivo convergent experiments, single lab\",\n      \"pmids\": [\"33719576\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"WNK4 is a chloride-sensitive serine-threonine kinase that acts as a multifunctional molecular switch in the distal nephron: when intracellular Cl- is low (e.g., during K+ deficiency or volume depletion), WNK4 autophosphorylates its T-loop (Ser335) and phosphorylates/activates the downstream kinases SPAK and OSR1, which in turn phosphorylate and activate NCC, thereby promoting NaCl reabsorption; PHAII-causing gain-of-function WNK4 mutations cluster in the acidic motif and impair KLHL3-CUL3-mediated ubiquitination and degradation of WNK4, elevating WNK4 levels and constitutively activating the WNK4-SPAK-NCC cascade; WNK4 also regulates ROMK (inhibits via kinase-independent/clathrin-dependent endocytosis), ENaC, BK channels, KCCs, NKCC1, CFTR, TRPV5, TRPC3, and paracellular Cl- flux via claudin phosphorylation; its activity and abundance are regulated by AngII (via PKC phosphorylation of KLHL3-S433), aldosterone (via SGK1 phosphorylation of WNK4), Src-family kinases (via WNK4 Tyr1092/1094/1143 phosphorylation), PP1-mediated dephosphorylation, p62/SQSTM1-selective autophagy, and epigenetic control of WNK4 transcription through the β2AR-HDAC8-GR axis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"WNK4 is a chloride-sensitive serine-threonine kinase that functions as a master regulatory switch in the distal nephron, balancing renal NaCl reabsorption against K+ secretion and thereby controlling blood pressure and electrolyte homeostasis [#0, #1, #9]. Its central effector arm is the WNK-SPAK/OSR1-NCC cascade: WNK4 binds and phosphorylates the T-loop residues of SPAK (Thr233) and OSR1 (Thr185) to activate them [#5], and in vivo WNK4 is the dominant WNK kinase driving NCC phosphorylation and activation, since WNK4-/- mice lose nearly all phospho-NCC despite compensatory WNK1 upregulation [#18, #33]. WNK4 activity is gated by intracellular chloride: under low [Cl-]i it autophosphorylates its T-loop (Ser335) and switches from an NCC inhibitor to an NCC activator, and a chloride-insensitive knockin mouse recapitulates pseudohypoaldosteronism type II (PHAII) and abolishes K+-dependent NCC regulation, establishing WNK4 as the physiological Cl- sensor that translates extracellular K+ into NCC activity [#32, #43, #38]. WNK4 abundance is set by CUL3-KLHL3-mediated ubiquitination and degradation; PHAII-causing mutations cluster in the acidic motif and impair KLHL3 binding, elevating WNK4 and constitutively activating the SPAK-NCC axis, with all PHAII phenotypes mediated through NCC and the SPAK/OSR1 cascade as shown by genetic epistasis [#28, #29, #30, #22, #9]. This degradation node is tuned by hormonal signaling — angiotensin II acts via PKC phosphorylation of KLHL3-Ser433 to stabilize WNK4, while aldosterone-induced SGK1 and Src-family kinases phosphorylate WNK4 directly to modulate its output toward NCC and ROMK [#34, #20, #37, #40]. Beyond NCC, WNK4 acts as a broad transport coordinator, inhibiting ROMK via clathrin-dependent endocytosis [#1], ENaC, KCCs, NKCC1, BK channels and SLC26A6, and phosphorylating tight-junction claudins to modulate paracellular Cl- permeability [#2, #4, #6, #12, #15]. Activating WNK4 mutations cause PHAII (familial hyperkalemic hypertension) [#9, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established WNK4 as a direct negative regulator of the thiazide-sensitive NCC and linked PHAII mutations to loss of this regulation, defining WNK4's core renal function.\",\n      \"evidence\": \"Xenopus oocyte heterologous expression with kinase-dead and PHAII mutants, surface biotinylation, and reciprocal Co-IP with NCC C-terminus\",\n      \"pmids\": [\"12515852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether NCC inhibition is direct or via downstream kinases\", \"Mechanism of PHAII gain-of-function not yet defined at the molecular level\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showed WNK4 simultaneously inhibits ROMK by a kinase-independent endocytic mechanism opposite in direction to its NCC effect, framing WNK4 as a molecular switch balancing Na+ reabsorption and K+ secretion.\",\n      \"evidence\": \"Xenopus oocyte electrophysiology with clathrin-dependent endocytosis assays and PHAII/kinase-dead mutants\",\n      \"pmids\": [\"14608358\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic adaptor mediating ROMK internalization not identified\", \"Physiological trigger that flips the switch in vivo not yet defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Extended WNK4 substrate range to paracellular Cl- transport and extrarenal transporters, identifying claudins as phosphorylation substrates and NKCC1/SLC26A6 as targets.\",\n      \"evidence\": \"Inducible MDCK II epithelia with transepithelial permeability and in vitro claudin kinase assays; oocyte flux assays for NKCC1/SLC26A6\",\n      \"pmids\": [\"15070779\", \"15465913\", \"14769928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of claudin phosphorylation to PHAII not established\", \"Specific claudin phosphosites not yet mapped\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified SPAK and OSR1 as direct downstream kinase substrates of WNK4, defining the WNK-SPAK/OSR1 module that transmits WNK4 activity to cation-chloride cotransporters.\",\n      \"evidence\": \"In vitro kinase assays with phosphopeptide mapping of SPAK Thr233/OSR1 Thr185, T-loop mutagenesis, yeast two-hybrid, and oocyte flux assays\",\n      \"pmids\": [\"16083423\", \"15930150\", \"15841204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How WNK1-WNK4 heterodimerization modulates the cascade quantitatively in vivo unclear\", \"Whether SPAK/OSR1 mediate all WNK4 transport effects not yet tested genetically\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated in vivo that WNK4 controls blood pressure through DCT mass and NCC function, with NCC knockout fully reversing PHAII phenotypes, proving NCC is the principal mediator.\",\n      \"evidence\": \"Transgenic WNK4 mouse models with NCC-knockout epistasis and morphological/electrolyte phenotyping\",\n      \"pmids\": [\"16964266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether transgenic effect reflects altered WNK4 abundance versus intrinsic activity\", \"Contribution of ROMK/ENaC to phenotype not dissected\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined the cellular route of WNK4-driven NCC downregulation, showing it reduces NCC surface expression via lysosomal rather than proteasomal or clathrin-dependent pathways.\",\n      \"evidence\": \"Surface biotinylation in Cos-7 cells with dominant-negative dynamin and bafilomycin A1 inhibition\",\n      \"pmids\": [\"16688122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor machinery routing NCC to lysosomes not yet identified\", \"Whether wild-type-state lysosomal targeting differs mechanistically from PHAII-state not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Broadened WNK4's regulatory targets to ENaC and connected WNK4 to aldosterone signaling via SGK1 phosphorylation, revealing a functional state opposite to PHAII.\",\n      \"evidence\": \"Oocyte co-expression with ENaC PY-motif mutants, in vivo colonic Na+ flux, and in vitro SGK1 phosphorylation with phosphomimetic mutagenesis\",\n      \"pmids\": [\"17360470\", \"17360471\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Number and identity of physiologically relevant SGK1 sites not fully resolved at this stage\", \"Quantitative contribution of ENaC regulation to whole-animal phenotype unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Pinned PHAII pathogenesis in a knockin model to apical NCC and SPAK/OSR1 hyperphosphorylation, with ENaC activation a secondary compensatory event.\",\n      \"evidence\": \"Wnk4(D561A/+) knockin mice with immunohistochemistry, phospho-immunoblotting, patch clamp, and thiazide treatment\",\n      \"pmids\": [\"17488636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not explain how a remote PHAII mutation increases cascade activity at the molecular level\", \"Claudin/paracellular contribution in vivo found minimal but not exhaustively excluded\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved the trafficking mechanism of WNK4-mediated NCC degradation as AP-3/sortilin-dependent diversion to lysosomes during forward trafficking rather than enhanced endocytosis.\",\n      \"evidence\": \"Forward-trafficking and surface-lifetime assays, endogenous AP-3 Co-IP, dominant-negative sortilin, and lysosomal protease inhibition\",\n      \"pmids\": [\"19401467\", \"19875813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How WNK4 kinase activity directs NCC into AP-3/sortilin pathway not mechanistically resolved\", \"Sortilin findings rest on a single lab without reconstitution\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reversed the early oocyte view by establishing WNK4 as a positive in vivo regulator of NCC and connecting WNK4 to angiotensin II signaling through SPAK.\",\n      \"evidence\": \"WNK4 knockout/hypomorphic mice with phospho-NCC/SPAK/OSR1 immunoblotting; oocyte and mpkDCT AngII/AT1R/SPAK dissection\",\n      \"pmids\": [\"19633012\", \"19240212\", \"19690383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Apparent inhibitor-versus-activator paradox not yet reconciled mechanistically\", \"Direct sensor coupling AngII to WNK4 activity state not yet defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Proved by triple-knockin genetics that PHAII phenotypes depend entirely on SPAK/OSR1 activation of NCC, and identified beta2AR-HDAC8-GR transcriptional control of WNK4 expression.\",\n      \"evidence\": \"Wnk4(D561A/+) crossed with Spak(T243A)/Osr1(T185A) knockin mice; HDAC8 activity assays, ChIP of GR at WNK4 promoter, and salt-sensitive rat models\",\n      \"pmids\": [\"21486947\", \"21499270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether transcriptional and post-translational WNK4 control converge physiologically not integrated\", \"Tissue specificity of beta2AR-HDAC8 axis beyond kidney not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Documented WNK4 regulation of additional channels (BK, TRPC3, TRPV5) extending its role to K+ secretion, vascular tone, and Ca2+ handling.\",\n      \"evidence\": \"Patch clamp and surface-expression assays in HEK/intercalated cells, VSMC knockdown with vasoconstriction readouts, and oocyte TRPV5 endocytosis assays\",\n      \"pmids\": [\"21613417\", \"21670282\", \"20061383\", \"23885063\", \"23673010\", \"17018846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"These channel effects rely largely on single-lab oocyte/cell systems without in vivo confirmation\", \"Mechanistic basis for kinase-dependent versus kinase-independent channel effects varies and is unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified the CUL3-KLHL3 E3 ligase complex as the machinery that ubiquitinates and degrades WNK4, explaining how PHAII mutations in either WNK4 or KLHL3 elevate WNK4 abundance.\",\n      \"evidence\": \"Mass-spectrometry ubiquitination-site mapping, reconstituted in vitro ubiquitylation with recombinant CUL3-KLHL3, Co-IP, domain mapping, and in vivo kidney WNK4 levels\",\n      \"pmids\": [\"23576762\", \"23387299\", \"23453970\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How specific acidic-motif mutations impair KLHL3 binding structurally not resolved here\", \"Relative contribution of WNK4 abundance versus intrinsic activity to PHAII not fully partitioned\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established WNK4 as a chloride-sensing kinase whose low-Cl-induced T-loop autophosphorylation (Ser335) converts it to an NCC activator, and showed AngII tunes WNK4 stability via PKC phosphorylation of KLHL3-Ser433.\",\n      \"evidence\": \"Oocyte [Cl-]i measurement with chloride-pocket mutants (L322F) and autophosphorylation assays; in vitro PKC phosphorylation of KLHL3-S433 with in vivo AngII infusion\",\n      \"pmids\": [\"25542968\", \"25313067\", \"26422504\", \"29921588\", \"25113964\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the WNK4 chloride-binding pocket not solved within the corpus\", \"How PP1 dephosphorylation and WNK oligomerization integrate quantitatively with Cl- sensing unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified Src-family tyrosine phosphorylation and p62/SQSTM1-dependent selective autophagy as additional layers controlling WNK4 output toward ROMK and WNK4 turnover.\",\n      \"evidence\": \"Mass-spectrometry phosphosite mapping with Y1092/1094/1143 mutagenesis and oocyte ROMK assays; Co-IP and autophagy/proteasome inhibitor dissection of KLHL3-p62 complex\",\n      \"pmids\": [\"25805816\", \"26349538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo physiological trigger for Src-mediated WNK4 tyrosine phosphorylation not defined\", \"Relative flux through autophagic versus proteasomal WNK4 degradation in kidney not quantified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Confirmed in vivo that WNK4 chloride sensing is the molecular basis of K+-dependent NCC regulation and described condensation of WNK4-SPAK/OSR1 into Kir4.1-dependent 'WNK bodies' during K+ deficiency.\",\n      \"evidence\": \"Cl--insensitive WNK4 knockin mice with dietary/acute K+ challenges; immunofluorescence of WNK bodies in WNK4-/- and DCT Kir4.1 conditional knockout mice; CaSR-WNK4 signaling assays\",\n      \"pmids\": [\"30765526\", \"31736353\", \"29848507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of WNK body condensation versus diffuse signaling not separated\", \"Whether WNK bodies are required for, or merely accompany, NCC activation unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended WNK4 regulation to NHA2-dependent stability control and dynamic K+-induced inactivation, and noted non-renal roles in adipogenesis and inflammation.\",\n      \"evidence\": \"NHA2-knockout mice with WNK4 ubiquitylation/KLHL3 phosphorylation assays; ex vivo/in vivo acute K+ dephosphorylation studies; WNK4-/- adipocyte and alveolar macrophage models\",\n      \"pmids\": [\"32956652\", \"33719576\", \"28314693\", \"31786261\", \"29846116\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Extrarenal WNK4 functions rest on single-lab loss-of-function studies without mechanistic depth\", \"How NHA2 mechanistically couples to KLHL3 phosphorylation unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple WNK4 inputs — chloride sensing, KLHL3-mediated degradation, hormonal phosphorylation, oligomerization, and WNK body condensation — are integrated quantitatively to set NCC activity under physiological conditions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated structural/biophysical model of WNK4 activation states\", \"Relative weighting of transcriptional, degradative, and phosphorylation control in vivo not established\", \"Mechanistic link between channel-level effects and whole-organism phenotypes for non-NCC targets incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 5, 6, 15, 32]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [5, 32, 40]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [32, 38, 43]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [44]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [17, 20, 27, 34, 37]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 4, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [28, 29, 30, 48]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [8, 16, 19]}\n    ],\n    \"complexes\": [\"WNK bodies\", \"WNK kinase oligomer\"],\n    \"partners\": [\"SPAK\", \"OSR1\", \"KLHL3\", \"CUL3\", \"SGK1\", \"WNK1\", \"NCC\", \"CaM\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}