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ABSTRACT: WNK1 is a widely expressed serine-threonine protein kinase that regulates multiple cellular and organ functions via diverse mechanisms. We previously reported that endothelial-specific deletion of Wnk1 in mice results in embryonic lethality with angiogenesis and cardiac defects occurring beginning at ~embryonic day E10.5. Here, we further investigated the signaling mechanism by which WNK1 regulates embryonic cardiovascular development. We found that mice with global deletion of Osr1, which encodes oxidative-stress responsive kinase-1, a protein kinase activated by WNK1, died in utero beginning at ~E11. The defects in Osr1-null yolk sacs and embryos were virtually identical to those observed in Wnk1-knockout: no mature large vessels in yolk sacs, defective angiogenesis in the brain and intersomitic vessels, and smaller chambers and reduced myocardial trabeculation in mutant hearts. Endothelial-specific deletion of Osr1 generated by crossing Osr1flox/flox mice with Tie2-Cre mice phenocopied defects caused by global Osr1 deletion. To investigate whether OSR1 acts downstream of WNK1 in embryonic angiogenesis, we generated a mouse line that carries a catalytically constitutive-active human OSR1 transgene in the ROSA26 locus under the control of a cassette of floxed transcription stop codons. We found that endothelial-specific expression of the constitutively active mutant OSR1, generated by Tie2-Cre-mediated excision of floxed stop codons in the mutated ROSA26 locus, rescues angiogenesis and cardiac defects in global Wnk1-null embryos. These results indicate that WNK1 activation of the OSR1 signaling cascade is an essential pathway that regulates angiogenesis and cardiac formation during mouse embryo development.
Journal of Biological Chemistry 02/2013; · 4.77 Impact Factor
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ABSTRACT: Klotho is a membrane protein predominantly produced in the kidney that exerts some antiageing effects. Ageing is associated with an increased risk of heart failure; whether Klotho is cardioprotective is unknown. Here we show that Klotho-deficient mice have no baseline cardiac abnormalities but develop exaggerated pathological cardiac hypertrophy and remodelling in response to stress. Cardioprotection by Klotho in normal mice is mediated by downregulation of TRPC6 channels in the heart. We demonstrate that deletion of Trpc6 prevents stress-induced exaggerated cardiac remodelling in Klotho-deficient mice. Furthermore, mice with heart-specific overexpression of TRPC6 develop spontaneous cardiac hypertrophy and remodelling. Klotho overexpression ameliorates cardiac pathologies in these mice and improves their long-term survival. Soluble Klotho present in the systemic circulation inhibits TRPC6 currents in cardiomyocytes by blocking phosphoinositide-3-kinase-dependent exocytosis of TRPC6 channels. These results provide a new perspective on the pathogenesis of cardiomyopathies and open new avenues for treatment of the disease.
Nature Communications 12/2012; 3:1238. · 7.40 Impact Factor
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ABSTRACT: Kidney-specific WNK1 (KS-WNK1) is a kinase-deficient variant of WNK1 that is expressed exclusively in the kidney. It is abundantly expressed in the distal convoluted tubule and to a lesser extent in the cortical thick ascending limb, connecting tubule and cortical collecting duct. KS-WNK1 inhibits NKCC2- and NCC-mediated Na(+) reabsorption in cTAL and DCT, respectively. Here, we investigated the role of KS-WNK1 in regulating Na(+) and K(+) transport in CCD using in vitro microperfusion of tubules isolated from KS-WNK1 knockout mice and control wild-type littermates. Because baseline K(+) secretion and Na(+) reabsorption were negligible in mouse CCD, we studied tubules isolated from mice fed a high-K(+) diet for 2 weeks. Compared to that in wild-type tubules, K(+) secretion was reduced in KS-WNK1 knockout CCD perfused at a low luminal fluid rate of ~1.5 nl/min. Na(+) reabsorption and the lumen-negative transepithelial potential difference (PD) were also lower in the KS-WNK1 knockout CCD compared to control CCD. Increasing the perfusion rate to ~5.5 nl/min stimulated K(+) secretion in the wild-type as well as knockout CCD. The magnitudes of flow-stimulated increase in K(+) secretion were similar in wild-type and knockout CCD. Maxi-K(+) channel inhibitor, iberiotoxin, had no effect on K(+) secretion when tubules were perfused at ~1.5 nl/min, but completely abrogated the flow-dependent increase in K(+) secretion at ~5.5 nl/min. These findings support the notion that KS-WNK1 stimulates ROMK-mediated K(+) secretion, but not flow-dependent K(+) secretion mediated by maxi-K(+) channels in CCD. In addition, KS-WNK1 plays a role in regulating Na(+) transport in the CCD.
AJP Renal Physiology 11/2012; · 4.42 Impact Factor
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ABSTRACT: Epithelial ion transport is essential to renal homeostatic function, and it is dysregulated in several diseases, such as hypertension. An understanding of the insect renal (Malpighian) tubule yields insights into conserved epithelial ion transport processes in higher organisms and also has implications for the control of insect infectious disease vectors. Here, we examine the role of the Na(+)-K(+)-2Cl(-) (NKCC) cotransporter Ncc69 in Drosophila tubule function. Ncc69 mutant tubules have decreased rates of fluid secretion and K(+) flux, and these phenotypes were rescued by expression of wild-type Ncc69 in the principal cells of the tubule. Na(+) flux was unaltered in Ncc69 mutants, suggesting Na(+) recycling across the basolateral membrane. In unstimulated tubules, the principal role of the Na(+)-K(+)-ATPase is to generate a favorable electrochemical gradient for Ncc69 activity: while the Na(+)-K(+)-ATPase inhibitor ouabain decreased K(+) flux in wild-type tubules, it had no effect in Ncc69 mutant tubules. However, in the presence of cAMP, which stimulates diuresis, additional Na(+)-K(+)-ATPase-dependent K(+) transport pathways are recruited. In studying the effects of capa-1 on wild-type and Ncc69 mutant tubules, we found a novel antidiuretic role for this hormone that is dependent on intact Ncc69, as it was abolished in Ncc69 mutant tubules. Thus, Ncc69 plays an important role in transepithelial ion and fluid transport in the fly renal tubule and is a target for regulation in antidiuretic states.
AJP Cell Physiology 08/2012; 303(8):C883-94. · 3.54 Impact Factor
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ABSTRACT: Kidney-specific WNK1 (KS-WNK1) is a variant of full-length WNK1. Previous studies have reported that KS-WNK1 is predominantly expressed in the distal convoluted tubule (DCT) where it regulates sodium-chloride cotransporter. The role of KS-WNK1 in other nephron segments is less clear. Here, we measured the expression of KS-WNK1 transcript in microdissected renal tubules and found that KS-WNK1 was most abundant in the DCT, followed by cortical thick ascending limb (cTAL), connecting tubule, and cortical collecting duct. A high K(+) diet enhanced the expression of KS-WNK1 in the DCT and cTAL, selectively. It has been reported that a high-K diet suppresses Na(+) reabsorption in TAL. To understand the role of KS-WNK1 in Na(+) transport in cTAL and the regulation by dietary K(+), we examined Na(+) reabsorption using in vitro microperfusion in cTAL isolated from KS-WNK1-knockout mice and wild-type littermates fed either a control-K(+) or high-K(+) diet. Furosemide-sensitive Na(+) reabsorption in cTAL was higher in KS-WNK1-knockout (KO) mice than in wild-type. A high-K(+) diet inhibited Na(+) reabsorption in cTAL from wild-type mice, but the inhibition was eliminated in KS-WNK1-KO mice. We further examined the role of KS-WNK1 using transgenic mice that overexpress KS-WNK1. Na(+) reabsorption in cTAL was lower in transgenic than in wild-type mice. In whole animal clearance studies, a high-K(+) diet increased daily urine volume and urinary Na(+) and K(+) excretion in wild-type mice, which was blunted in KS-WNK1-KO mice. Thus KS-WNK1 inhibits Na(+) reabsorption in cTAL and mediates the inhibition of Na(+) reabsorption in the segment by a high-K diet.
AJP Renal Physiology 07/2012; 303(5):F667-73. · 4.42 Impact Factor
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ABSTRACT: The pathogenesis of thyrotoxic periodic paralysis has long been thought related to increased Na(+)-K(+) ATPase activity stimulated by thyroid hormone and/or hyperadrenergic activity and hyperinsulinemia. This mechanism alone, however, cannot adequately explain how hypokalemia occurs during acute attacks or the associated paradoxical depolarization of the resting membrane potential. Recent findings that loss of function mutations of the skeletal muscle-specific inward rectifying K(+) (Kir) channel, Kir2.6, associate with thyrotoxic periodic paralysis provide new insights into how reduced outward K(+) efflux in skeletal muscle, from either channel mutations or inhibition by hormones (adrenalin or insulin), can lead to a vicious cycle of hypokalemia and paradoxical depolarization, which in turn, inactivates Na(+) channels and causes muscle unexcitability and paralysis.
Journal of the American Society of Nephrology 03/2012; 23(6):985-8. · 9.66 Impact Factor
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ABSTRACT: Previous studies reporting an association between high BP and high sodium and low potassium intake or urinary sodium/potassium ratio (U[Na(+)]/[K(+)]) primarily included white men and did not control for cardiovascular risk factors.
This cross-sectional study investigated the association of U[Na(+)]/[K(+)] with BP in 3303 participants using robust linear regression.
Mean age was 43±10 years, 56% of participants were women, and 52% were African American. BP was higher in African Americans than in non-African Americans, 131/81±20/11 versus 120/76±16/9 mmHg (P<0.001). Mean U[Na(+)]/[K(+)] was 4.4±3.0 in African Americans and 4.1±2.5 in non-African Americans (P=0.002), with medians (interquartile ranges) of 3.7 (3.2) and 3.6 (2.8). Systolic BP increased by 1.6 mmHg (95% confidence interval, 1.0, 2.2) and diastolic BP by 1.0 mmHg (95% confidence interval, 0.6, 1.4) for each 3-unit increase in U[Na(+)]/[K(+)] (P<0.001 for both). This association remained significant after adjusting for diabetes mellitus, smoking, body mass index, total cholesterol, GFR, and urine albumin/creatinine ratio. There was no interaction between African-American race and U[Na(+)]/[K(+)], but for any given value of U[Na(+)]/[K(+)], both systolic BP and diastolic BP were higher in African Americans than in non-African Americans. The diastolic BP increase was higher in men than in women per 3-unit increase in U[Na(+)]/[K(+)] (1.6 versus 0.9 mmHg, interaction P=0.03).
Dietary Na(+) excess and K(+) deficiency may play an important role in the pathogenesis of hypertension independent of cardiovascular risk factors. This association may be more pronounced in men than in women.
Clinical Journal of the American Society of Nephrology 11/2011; 7(2):315-22. · 5.23 Impact Factor
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ABSTRACT: PLC-β signaling is generally thought to be mediated by allosteric activation by G proteins and Ca(2+). Although availability of the phosphatidylinositol-4,5-biphosphate (PIP(2)) substrate is limiting in some cases, its production has not been shown to be independently regulated as a signaling mechanism. WNK1 protein kinase is known to regulate ion homeostasis and cause hypertension when expression is increased by gene mutations. However, its signaling functions remain largely elusive.
Using diacylglycerol-stimulated TRPC6 and inositol trisphosphate-mediated Ca(2+) transients as cellular biosensors, we show that WNK1 stimulates PLC-β signaling in cells by promoting the synthesis of PIP(2) via stimulation of phosphatidylinositol 4-kinase IIIα. WNK1 kinase activity is not required. Stimulation of PLC-β by WNK1 and by Gα(q) are synergistic; WNK1 activity is essential for regulation of PLC-β signaling by G(q)-coupled receptors, and basal input from G(q) is necessary for WNK1 signaling via PLC-β. WNK1 further amplifies PLC-β signaling when it is phosphorylated by Akt kinase in response to insulin-like growth factor.
WNK1 is a novel regulator of PLC-β that acts by controlling substrate availability. WNK1 thereby coordinates signaling between G protein and Akt kinase pathways. Because PIP(2) is itself a signaling molecule, regulation of PIP(2) synthesis by WNK1 also allows the cell to initiate PLC signaling while independently controlling the effects of PIP(2) on other targets. These findings describe a new signaling pathway for Akt-activating growth factors, a mechanism for G protein-growth factor crosstalk, and a means to independently control PLC signaling and PIP(2) availability.
Current biology: CB 11/2011; 21(23):1979-87. · 10.99 Impact Factor
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ABSTRACT: Thiazide diuretics are used to prevent the recurrence of calcium-containing kidney stones. The ability of these drugs to reduce urinary calcium excretion has a key role in this process. Although studies have shown a reduction in the recurrence rate of calcium-containing stones in patients treated with thiazides, whether hypocalciuria results from increased calcium reabsorption in the proximal or distal nephron is still unclear. When extracellular fluid volume is considerably reduced, the proximal tubule is likely to have a major role in thiazide-induced hypocalciuria. This process frequently occurs when high doses of thiazides and sodium restriction are prescribed for the treatment of kidney stone disease. The distal tubule is predominantly involved in NaCl cotransporter inhibition-induced hypocalciuria when the extracellular fluid volume is not reduced, a clinical scenario observed in patients with Gitelman syndrome. In this Perspectives article, we discuss the evidence supporting the hypocalciuric effects of NaCl cotransporter inhibition in the proximal and distal nephron.
Nature Reviews Nephrology 09/2011; 7(11):669-74. · 7.09 Impact Factor
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ABSTRACT: Hypokalemic periodic paralysis (hypoKPP) is characterized by episodic flaccid paralysis of muscle and acute hypokalemia during attacks. Familial forms of hypoKPP are predominantly caused by mutations of either voltage-gated Ca(2+) or Na(+) channels. The pathogenic gene mutation in non-familial hypoKPP, consisting mainly of thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis (SPP), is largely unknown. Recently, mutations in KCNJ18, which encodes a skeletal muscle-specific inwardly rectifying K(+) channel Kir2.6, were reported in some TPP patients. Whether mutations of Kir2.6 occur in other patients with non-familial hypoKPP and how mutations of the channel predispose patients to paralysis are unknown. Here, we report one conserved heterozygous mutation in KCNJ18 in two TPP patients and two separate heterozygous mutations in two SPP patients. These mutations result in V168M, R43C, and A200P amino acid substitution of Kir2.6, respectively. Compared with the wild type channel, whole-cell currents of R43C and V168M mutants were reduced by ∼78 and 43%, respectively. No current was detected for the A200P mutant. Single channel conductance and open probability were reduced for R43C and V168M, respectively. Biotinylation assays showed reduced cell surface abundance for R43C and A200P. All three mutants exerted dominant negative inhibition on wild type Kir2.6 as well as wild type Kir2.1, another Kir channel expressed in the skeletal muscle. Thus, mutations of Kir2.6 are associated with SPP as well as TPP. We suggest that decreased outward K(+) current from hypofunction of Kir2.6 predisposes the sarcolemma to hypokalemia-induced paradoxical depolarization during attacks, which in turn leads to Na(+) channel inactivation and inexcitability of muscles.
Journal of Biological Chemistry 06/2011; 286(31):27425-35. · 4.77 Impact Factor
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ABSTRACT: Hypokalemic periodic paralysis (hypoKPP) is characterized by episodic flaccid paralysis of muscle and acute hypokalemia during
attacks. Familial forms of hypoKPP are predominantly caused by mutations of either voltage-gated Ca2+ or Na+ channels. The
pathogenic gene mutation in non-familial hypoKPP, consisting mainly of thyrotoxic periodic paralysis (TPP) and sporadic periodic
paralysis (SPP), is largely unknown. Recently, mutations in KCNJ18, which encodes a skeletal muscle specific-inwardly rectifying
K+ channel Kir2.6, were reported in some TPP patients. Whether mutations of Kir2.6 occur in other patients with non-familial
hypoKPP and how mutations of the channel predispose patients to paralysis are unknown. Here, we report one conserved heterozygous
mutation in KCNJ18 in two TPP patients and two separate heterozygous mutations in two SPP patients. These mutations result
in V168M, R43C, and A200P amino acid substitution of Kir2.6, respectively. Compared to the wild type channel, whole-cell currents
of R43C and V168M mutants were reduced by ~78% and 43%, respectively. No current was detected for the A200P mutant. Single
channel conductance and open probability were reduced for R43C and V168M, respectively. Biotinylation assays showed reduced
cell surface abundance for R43C and A200P. All three mutants exerted dominant-negative inhibition on wild type Kir2.6 as well
as wild type Kir2.1, another Kir channel expressed in the skeletal muscle. Thus, mutations of Kir2.6 are associated with SPP
as well as TPP. We suggest that decreased outward K+ current from hypofunction of Kir2.6 predisposes the sarcolemma to hypokalemia-induced
paradoxical depolarization during attacks, which in turn leads to Na+ channel inactivation and inexcitability of muscles.
Journal of Biological Chemistry 06/2011; · 4.77 Impact Factor
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ABSTRACT: Klotho which was originally identified as an anti-aging protein is emerging as a substance with multiple effects on many systems including mineral homeostasis. In addition to its membrane-bound function as a co-receptor for fibroblast growth factor-23, soluble Klotho exerts effects as a circulating substance in plasma and urine. Novel features of this system include its autocrine-paracrine-endocrine glycan-modifying enzymatic function in the urinary lumen on calcium and phosphate transporters. Klotho induces phosphaturia by inhibiting the proximal tubule Na-coupled phosphate transporter. The action of Klotho is enzymatic in nature which includes alteration of transport activity and the more traditional means of regulation by trafficking. Klotho reduces calciuria by its distal as a sialidase directly on the apical calcium channel. Desialidation of the channel exposes glycan residues that promote binding to galectin-1, resulting in stabilization of residence on the plasma membrane. Through its systematic as well as renal actions, Klotho is emerging as a principal calciophosphoregulatory hormone.
Pflügers Archiv - European Journal of Physiology 03/2011; 462(2):185-93. · 4.46 Impact Factor
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ABSTRACT: WNK1 (with-no-lysine[K]-1) is a protein kinase of which mutations cause a familial hypertension and hyperkalemia syndrome known as pseudohypoaldosteronism type 2 (PHA2). Kidney-specific (KS) WNK1 is an alternatively spliced form of WNK1 kinase missing most of the kinase domain. KS-WNK1 downregulates the Na(+)-Cl(-) cotransporter NCC by antagonizing the effect of full-length WNK1 when expressed in Xenopus oocytes. The physiological role of KS-WNK1 in the regulation of NCC and potentially other Na(+) transporters in vivo is unknown. Here, we report that mice overexpressing KS-WNK1 in the kidney exhibited renal Na(+) wasting, elevated plasma levels of angiotensin II and aldosterone yet lower blood pressure relative to wild-type littermates. Immunofluorescent staining revealed reduced surface expression of total and phosphorylated NCC and the Na(+)-K(+)-2Cl(-) cotransporter NKCC2 in the distal convoluted tubule and the thick ascending limb of Henle's loop, respectively. Conversely, mice with targeted deletion of exon 4A (the first exon for KS-WNK1) exhibited Na(+) retention, elevated blood pressure on a high-Na(+) diet and increased surface expression of total and phosphorylated NCC and NKCC2 in respective nephron segments. Thus, KS-WNK1 is a negative regulator of NCC and NKCC2 in vivo and plays an important role in the control of Na(+) homeostasis and blood pressure. These results have important implications to the pathogenesis of PHA2 with WNK1 mutations.
Human Molecular Genetics 03/2011; 20(5):855-66. · 7.64 Impact Factor
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ABSTRACT: WNK kinases stimulate endocytosis of ROMK channels to regulate renal K+ handling. Phosphatidylinositol 3-kinase (PI3K)-activating hormones, such as insulin and IGF 1, phosphorylate WNK1, but how this affects the regulation of ROMK abundance is unknown. Here, serum starvation of ROMK-transfected HEK cells led to an increase of ROMK current density; subsequent addition of insulin or IGF1 inhibited ROMK currents in a PI3K-dependent manner. Serum and insulin also increased phosphorylation of the downstream kinases Akt1 and SGK1 as well as WNK1. A biotinylation assay suggested that insulin and IGF1 inhibit ROMK by enhancing its endocytosis, a process that WNK1 may mediate. Knockdown of WNK1 with siRNA or expression of a phospho-deficient WNK1 mutant (T58A) both prevented insulin-induced inhibition of ROMK currents, suggesting that phosphorylation at Threonine-58 of WNK1 is important to mediate the inhibition of ROMK by PI3K-activating hormones or growth factors. In vitro and in vivo kinase assays supported the notion that Akt1 and SGK1 can phosphorylate WNK1 at this site, and we established that Akt1 and SGK1 synergistically inhibit ROMK through WNK1. We used dominant-negative intersectin and dynamin constructs to show that SGK1-mediated phosphorylation of WNK1 inhibits ROMK by promoting its endocytosis. Taken together, these results suggest that PI3K-activating hormones inhibit ROMK by enhancing its endocytosis via a mechanism that involves phosphorylation of WNK1 by Akt1 and SGK1.
Journal of the American Society of Nephrology 02/2011; 22(3):460-71. · 9.66 Impact Factor
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ABSTRACT: It is well known that sodium reabsorption and aldosterone play important roles in potassium secretion by the aldosterone-sensitive distal nephron. Sodium- and aldosterone-independent mechanisms also exist. This review focuses on some recent studies that provide novel insights into the sodium- and aldosterone-independent potassium secretion by the aldosterone-sensitive distal nephron. In addition, we discuss a study reporting on the regulation of the mammalian potassium kidney channel ROMK by intracellular and extracellular magnesium, which may be important in the pathogenesis of persistent hypokalemia in patients with concomitant potassium and magnesium deficiency. We also discuss outstanding questions and propose working models for future investigation.
AJP Renal Physiology 01/2011; 300(4):F821-7. · 4.42 Impact Factor
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ABSTRACT: The Ca(2+)-sensing receptor (CaR) regulates salt and water transport in the kidney as demonstrated by the association of gain of function CaR mutations with a Bartter syndrome-like, salt-wasting phenotype, but the precise mechanism for this effect is not fully established. We found previously that the CaR interacts with and inactivates an inwardly rectifying K(+) channel, Kir4.1, which is expressed in the distal nephron that contributes to the basolateral K(+) conductance, and in which loss of function mutations are associated with a complex phenotype that includes renal salt wasting. We now find that CaR inactivates Kir4.1 by reducing its cell surface expression. Mutant CaRs reduced Kir4.1 cell surface expression and current density in HEK-293 cells in proportion to their signaling activity. Mutant, activated Gα(q) reduced cell surface expression and current density of Kir4.1, and these effects were blocked by RGS4, a protein that blocks signaling via Gα(i) and Gα(q). Other α subunits had insignificant effects. Knockdown of caveolin-1 blocked the effect of Gα(q) on Kir4.1, whereas knockdown of the clathrin heavy chain had no effect. CaR had no comparable effect on the renal outer medullary K(+) channel, an apical membrane distal nephron K(+) channel that is internalized by clathrin-coated vesicles. Co-immunoprecipitation studies showed that the CaR and Kir4.1 physically associate with caveolin-1 in HEK cells and in kidney extracts. Thus, the CaR decreases cell surface expression of Kir4.1 channels via a mechanism that involves Gα(q) and caveolin. These results provide a novel molecular basis for the inhibition of renal NaCl transport by the CaR.
Journal of Biological Chemistry 11/2010; 286(3):1828-35. · 4.77 Impact Factor
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Journal of the American Society of Nephrology 10/2010; 21(11):1812-4. · 9.66 Impact Factor
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Charles J Heise,
Bing-e Xu,
Staci L Deaton,
Seung-Kuy Cha,
Chih-Jen Cheng,
Svetlana Earnest,
Samarpita Sengupta,
Yu-Chi Juang,
Steve Stippec,
Yingda Xu,
Yingming Zhao, Chou-Long Huang,
Melanie H Cobb
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ABSTRACT: The four WNK (with no lysine (K)) protein kinases affect ion balance and contain an unusual protein kinase domain due to the unique placement of the active site lysine. Mutations in two WNKs cause a heritable form of ion imbalance culminating in hypertension. WNK1 activates the serum- and glucocorticoid-induced protein kinase SGK1; the mechanism is noncatalytic. SGK1 increases membrane expression of the epithelial sodium channel (ENaC) and sodium reabsorption via phosphorylation and sequestering of the E3 ubiquitin ligase neural precursor cell expressed, developmentally down-regulated 4-2 (Nedd4-2), which otherwise promotes ENaC endocytosis. Questions remain about the intrinsic abilities of WNK family members to regulate this pathway. We find that expression of the N termini of all four WNKs results in modest to strong activation of SGK1. In reconstitution experiments in the same cell line all four WNKs also increase sodium current blocked by the ENaC inhibitor amiloride. The N termini of the WNKs also have the capacity to interact with SGK1. More detailed analysis of activation by WNK4 suggests mechanisms in common with WNK1. Further evidence for the importance of WNK1 in this process comes from the ability of Nedd4-2 to bind to WNK1 and the finding that endogenous SGK1 has reduced activity if WNK1 is knocked down by small interfering RNA.
Journal of Biological Chemistry 08/2010; 285(33):25161-7. · 4.77 Impact Factor
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Charles J. Heise,
Bing-e Xu,
Staci L. Deaton,
Seung-Kuy Cha,
Chih-Jen Cheng,
Svetlana Earnest,
Samarpita Sengupta,
Yu-Chi Juang,
Steve Stippec,
Yingda Xu,
Yingming Zhao, Chou-Long Huang,
Melanie H. Cobb
[show abstract]
[hide abstract]
ABSTRACT: The four WNK (with no lysine (K)) protein kinases affect ion balance and contain an unusual protein kinase domain due to the unique placement of the active
site lysine. Mutations in two WNKs cause a heritable form of ion imbalance culminating in hypertension. WNK1 activates the
serum- and glucocorticoid-induced protein kinase SGK1; the mechanism is noncatalytic. SGK1 increases membrane expression of
the epithelial sodium channel (ENaC) and sodium reabsorption via phosphorylation and sequestering of the E3 ubiquitin ligase
neural precursor cell expressed, developmentally down-regulated 4-2 (Nedd4-2), which otherwise promotes ENaC endocytosis.
Questions remain about the intrinsic abilities of WNK family members to regulate this pathway. We find that expression of
the N termini of all four WNKs results in modest to strong activation of SGK1. In reconstitution experiments in the same cell
line all four WNKs also increase sodium current blocked by the ENaC inhibitor amiloride. The N termini of the WNKs also have
the capacity to interact with SGK1. More detailed analysis of activation by WNK4 suggests mechanisms in common with WNK1.
Further evidence for the importance of WNK1 in this process comes from the ability of Nedd4-2 to bind to WNK1 and the finding
that endogenous SGK1 has reduced activity if WNK1 is knocked down by small interfering RNA.
Journal of Biological Chemistry 08/2010; 285(33):25161-25167. · 4.77 Impact Factor
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Chou-Long Huang
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ABSTRACT: Klotho is an anti-aging protein predominantly expressed in the kidney, parathyroid glands, and choroid plexus of the brain. It is a single-pass transmembrane protein with a large extracellular domain. The extracellular domain of Klotho is cleaved and released into extracellular fluid, including blood, urine, and cerebrospinal fluid. The membrane-bound full-length Klotho and secreted extracellular domain of Klotho have distinct functions. Membrane Klotho interacts with fibroblast growth factor (FGF) receptors to form high-affinity receptors for FGF23. Secreted Klotho functions as a humoral factor that regulates several ion channels and transporters, and other processes, including insulin and insulin-like growth factor signaling. This mini-review focuses on the mechanisms of regulation of cell-surface abundance of ion channels by secreted Klotho and the importance of these effects of Klotho in physiology and pathological conditions.
Kidney International 03/2010; 77(10):855-60. · 6.61 Impact Factor
