WNK Inhibition Increases Surface Liquid pH and Host Defense in Cystic Fibrosis Airway Epithelia

In cystic fibrosis (CF), reduced HCO3- secretion acidifies the airway surface liquid (ASL), and the acidic pH disrupts host defenses. Thus, understanding the control of ASL pH (pHASL) in CF may help identify novel targets and facilitate therapeutic development. In diverse epithelia, the WNK (with-no-lysine [K]) kinases coordinate HCO3- and Cl- transport, but their functions in airway epithelia are poorly understood. Here, we tested the hypothesis that WNK kinases regulate CF pHASL. In primary cultures of differentiated human airway epithelia, inhibiting WNK kinases acutely increased both CF and non-CF pHASL. This response was HCO3- dependent and involved downstream SPAK/OSR1 (Ste20/SPS1-related proline-alanine-rich protein kinase/oxidative stress responsive 1 kinase). Importantly, WNK inhibition enhanced key host defenses otherwise impaired in CF. Human airway epithelia expressed two WNK isoforms in secretory cells and ionocytes, and knockdown of either WNK1 or WNK2 increased CF pHASL. WNK inhibition decreased Cl- secretion and the response to bumetanide, an NKCC1 (sodium-potassium-chloride cotransporter 1) inhibitor. Surprisingly, bumetanide alone or basolateral Cl- substitution also alkalinized CF pHASL. These data suggest that WNK kinases influence the balance between transepithelial Cl- versus HCO3- secretion. Moreover, reducing basolateral Cl- entry may increase HCO3- secretion and raise pHASL, thereby improving CF host defenses.

Clinical Efficacy of Controlled-Release Morphine Tablets Combined with Celecoxib in Pain Management and the Effects on WNK1 Expression

OBJECTIVES

This study was designed to evaluate the clinical efficacy of controlled-release morphine tablets combined with celecoxib in relieving osteocarcinoma-related pain and the effects of the combination on WNK1 expression.

METHODS

A total of 110 patients with osteocarcinoma-related pain were selected and divided into two groups based on the treatment administered, including the control group (treated with controlled-release morphine tablets alone) and the study group (treated with a combination of controlled-release morphine tablets and celecoxib). We compared the treatment efficacy, pain level (visual analog scale (VAS)), time of onset of breakthrough pain (BTP), dose of morphine, incidence of adverse events, quality of life (QOL) score, and With-no-lysine 1 (WNK1) expression in the peripheral blood (PB) as determined with qRT-PCR before and after treatment, of the two groups.

RESULTS

The total effective rate of the study group was higher than that of the control group, while the VAS score, time of onset of BTP, dose of morphine, incidence of adverse events, QOL score, and relative WNK1 expression in the PB were lower than those of the control group (p<0.05).

CONCLUSION

Combination treatment with controlled-release morphine tablets and celecoxib can be extensively used in the clinical setting because it effectively improves the symptoms, QOL score, and adverse effects in patients with osteocarcinoma-related pain.

Soluble bone-derived osteopontin promotes migration and stem-like behavior of breast cancer cells

Breast cancer is a leading cause of cancer death in women, with the majority of these deaths caused by metastasis to distant organs. The most common site of breast cancer metastasis is the bone, which has been shown to provide a rich microenvironment that supports the migration and growth of breast cancer cells. Additionally, growing evidence suggests that breast cancer cells that do successfully metastasize have a stem-like phenotype including high activity of aldehyde dehydrogenase (ALDH) and/or a CD44⁺CD24^- phenotype. In the current study, we tested the hypothesis that these ALDH^hiCD44⁺CD24^- breast cancer cells interact with factors in the bone secondary organ microenvironment to facilitate metastasis. Specifically, we focused on bone-derived osteopontin and its ability to promote the migration and stem-like phenotype of breast cancer cells. Our results indicate that bone-derived osteopontin promotes the migration, tumorsphere-forming ability and colony-forming ability of whole population and ALDH^hiCD44⁺CD24^- breast cancer cells in bone marrow-conditioned media (an ex vivo representation of the bone microenvironment) (p≤0.05). We also demonstrate that CD44 and RGD-dependent cell surface integrins facilitate this functional response to bone-derived osteopontin (p≤0.05), potentially through activation of WNK-1 and PRAS40-related pathways. Our findings suggest that soluble bone-derived osteopontin enhances the ability of breast cancer cells to migrate to the bone and maintain a stem-like phenotype within the bone microenvironment, and this may contribute to the establishment and growth of bone metastases.

Glucocorticoid-induced leucine zipper protein regulates sodium and potassium balance in the distal nephron

Glucocorticoid induced leucine zipper protein (GILZ) is an aldosterone-regulated protein that controls sodium transport in cultured kidney epithelial cells. Mice lacking GILZ have been reported previously to have electrolyte abnormalities. However, the mechanistic basis has not been explored. Here we provide evidence supporting a role for GILZ in modulating the balance of renal sodium and potassium excretion by regulating the sodium-chloride cotransporter (NCC) activity in the distal nephron. Gilz^-/- mice have a higher plasma potassium concentration and lower fractional excretion of potassium than wild type mice. Furthermore, knockout mice are more sensitive to NCC inhibition by thiazides than are the wild type mice, and their phosphorylated NCC expression is higher. Despite increased NCC activity, knockout mice do not have higher blood pressure than wild type mice. However, during sodium deprivation, knockout mice come into sodium balance more quickly, than do the wild type, without a significant increase in plasma renin activity. Upon prolonged sodium restriction, knockout mice develop frank hyperkalemia. Finally, in HEK293T cells, exogenous GILZ inhibits NCC activity at least in part by inhibiting SPAK phosphorylation. Thus, GILZ promotes potassium secretion by inhibiting NCC and enhancing distal sodium delivery to the epithelial sodium channel. Additionally, Gilz^-/- mice have features resembling familial hyperkalemic hypertension, a human disorder that manifests with hyperkalemia associated variably with hypertension.

With no lysine L-WNK1 isoforms are negative regulators of the K+-Cl- cotransporters

The K(+)-Cl(-) cotransporters (KCC1-KCC4) encompass a branch of the SLC12 family of electroneutral cation-coupled chloride cotransporters that translocate ions out of the cell to regulate various factors, including cell volume and intracellular chloride concentration, among others. L-WNK1 is an ubiquitously expressed kinase that is activated in response to osmotic stress and intracellular chloride depletion, and it is implicated in two distinct hereditary syndromes: the renal disease pseudohypoaldosteronism type II (PHAII) and the neurological disease hereditary sensory neuropathy 2 (HSN2). The effect of L-WNK1 on KCC activity is unknown. Using Xenopus laevis oocytes and HEK-293 cells, we show that the activation of KCCs by cell swelling was prevented by L-WNK1 coexpression. In contrast, the activity of the Na(+)-K(+)-2Cl(-) cotransporter NKCC1 was remarkably increased with L-WNK1 coexpression. The negative effect of L-WNK1 on the KCCs is kinase dependent. Elimination of the STE20 proline-alanine rich kinase (SPAK)/oxidative stress-responsive kinase (OSR1) binding site or the HQ motif required for the WNK-WNK interaction prevented the effect of L-WNK1 on KCCs, suggesting a required interaction between L-WNK1 molecules and SPAK. Together, our data support that NKCC1 and KCCs are coordinately regulated by L-WNK1 isoforms.

STK39 and WNK1 Are Potential Hypertension Susceptibility Genes in the BELHYPGEN Cohort

The serine/threonine kinase With-No-Lysine (K) Kinase 1 (WNK1) activates the thiazide-sensitive Na(+)/Cl(-) cotransporter through phosphorylation of STE20/SPS1-related proline/alanine-rich kinase, another serine/threonine kinase encoded by STK39. The aim of this study was to look for association between WNK1 and STK39 gene variants, and blood pressure (BP) and hypertension. Seven hundred seventy-nine Caucasian hypertensive patients (HYP) recruited in 6 academic centers from Belgium, and 906 normotensive (NT) controls were genotyped for 5 single nucleotide polymorphisms-rs3754777, rs6749447, rs35929607 (STK39), rs1468326, and rs765250 (WNK1)-using the Snapshot method. The rare TT genotype at the rs3754777 locus (STK39) was overrepresented in HYP versus NT (7.3% vs 3.0%, P = 0.0002). In the whole study population, the multivariable-adjusted odds ratio (OR) for having hypertension associated with the TT genotype was 5.9 (95% confidence interval: 2.2-15.6), and systolic BP was 10 mm Hg higher in TT compared with wild-type subjects (140.1 vs 130.4 mm Hg, P = 0.002). Similarly, the AA genotype at the rs1468326 locus (WNK1) was twice as frequent in HYP versus NT (5.5% vs 2.3%, P < 0.0001), and associated with an increased adjusted OR of hypertension (4.1; 1.5-11.7) and a higher systolic BP (139.8 vs 130.1 mm Hg, P = 0.003). In the whole cohort, a dose-dependent increase in systolic BP was observed according to the number of at-risk genotypes (0: 129.8 mm Hg; 1: 133.0 mm Hg; 2: 149.3 mm Hg, P = 0.02). Single nucleotide polymorphisms rs3754777 (STK39) and rs1468326 (WNK1) were associated with hypertension and BP in our multicenter Belgian case-control study, which supports the role of STK39 and WNK1 as potential hypertension susceptibility genes. Replication in different clinical settings and study of other candidate loci belonging to the same molecular pathway is warranted.

Inhibition of the kinase WNK1/HSN2 ameliorates neuropathic pain by restoring GABA inhibition

HSN2is a nervous system predominant exon of the gene encoding the kinase WNK1 and is mutated in an autosomal recessive, inherited form of congenital pain insensitivity. The HSN2-containing splice variant is referred to as WNK1/HSN2. We created a knockout mouse specifically lacking theHsn2exon ofWnk1 Although these mice had normal spinal neuron and peripheral sensory neuron morphology and distribution, the mice were less susceptible to hypersensitivity to cold and mechanical stimuli after peripheral nerve injury. In contrast, thermal and mechanical nociceptive responses were similar to control mice in an inflammation-induced pain model. In the nerve injury model of neuropathic pain, WNK1/HSN2 contributed to a maladaptive decrease in the activity of the K(+)-Cl(-)cotransporter KCC2 by increasing its inhibitory phosphorylation at Thr(906)and Thr(1007), resulting in an associated loss of GABA (γ-aminobutyric acid)-mediated inhibition of spinal pain-transmitting nerves. Electrophysiological analysis showed that WNK1/HSN2 shifted the concentration of Cl(-)such that GABA signaling resulted in a less hyperpolarized state (increased neuronal activity) rather than a more hyperpolarized state (decreased neuronal activity) in mouse spinal nerves. Pharmacologically antagonizing WNK activity reduced cold allodynia and mechanical hyperalgesia, decreased KCC2 Thr(906)and Thr(1007)phosphorylation, and restored GABA-mediated inhibition (hyperpolarization) of injured spinal cord lamina II neurons. These data provide mechanistic insight into, and a compelling therapeutic target for treating, neuropathic pain after nerve injury.

Alternatively spliced proline-rich cassettes link WNK1 to aldosterone action

The thiazide-sensitive NaCl cotransporter (NCC) is important for renal salt handling and blood-pressure homeostasis. The canonical NCC-activating pathway consists of With-No-Lysine (WNK) kinases and their downstream effector kinases SPAK and OSR1, which phosphorylate NCC directly. The upstream mechanisms that connect physiological stimuli to this system remain obscure. Here, we have shown that aldosterone activates SPAK/OSR1 via WNK1. We identified 2 alternatively spliced exons embedded within a proline-rich region of WNK1 that contain PY motifs, which bind the E3 ubiquitin ligase NEDD4-2. PY motif-containing WNK1 isoforms were expressed in human kidney, and these isoforms were efficiently degraded by the ubiquitin proteasome system, an effect reversed by the aldosterone-induced kinase SGK1. In gene-edited cells, WNK1 deficiency negated regulatory effects of NEDD4-2 and SGK1 on NCC, suggesting that WNK1 mediates aldosterone-dependent activity of the WNK/SPAK/OSR1 pathway. Aldosterone infusion increased proline-rich WNK1 isoform abundance in WT mice but did not alter WNK1 abundance in hypertensive Nedd4-2 KO mice, which exhibit high baseline WNK1 and SPAK/OSR1 activity toward NCC. Conversely, hypotensive Sgk1 KO mice exhibited low WNK1 expression and activity. Together, our findings indicate that the proline-rich exons are modular cassettes that convert WNK1 into a NEDD4-2 substrate, thereby linking aldosterone and other NEDD4-2-suppressing antinatriuretic hormones to NCC phosphorylation status.

WNK1-regulated inhibitory phosphorylation of the KCC2 cotransporter maintains the depolarizing action of GABA in immature neurons

Activation of Cl(-)-permeable γ-aminobutyric acid type A (GABAA) receptors elicits synaptic inhibition in mature neurons but excitation in immature neurons. This developmental "switch" in the GABA function depends on a postnatal decrease in intraneuronal Cl(-) concentration mediated by KCC2, a Cl(-)-extruding K(+)-Cl(-) cotransporter. We showed that the serine-threonine kinase WNK1 [with no lysine (K)] forms a physical complex with KCC2 in the developing mouse brain. Dominant-negative mutation, genetic depletion, or chemical inhibition of WNK1 in immature neurons triggered a hyperpolarizing shift in GABA activity by enhancing KCC2-mediated Cl(-) extrusion. This increase in KCC2 activity resulted from reduced inhibitory phosphorylation of KCC2 at two C-terminal threonines, Thr(906) and Thr(1007). Phosphorylation of both Thr(906) and Thr(1007) was increased in immature versus mature neurons. Together, these data provide insight into the mechanism regulating Cl(-) homeostasis in immature neurons, and suggest that WNK1-regulated changes in KCC2 phosphorylation contribute to the developmental excitatory-to-inhibitory GABA sequence.

Exome sequencing identifies a novel gene, WNK1, for susceptibility to pelvic organ prolapse (POP)

Pelvic organ prolapse (POP) is a common gynecological disorder; however, the genetic components remain largely unidentified. Exome sequencing has been widely used to identify pathogenic gene mutations of several diseases because of its high chromosomal coverage and accuracy. In this study, we performed whole exome sequencing (WES), for the first time, on 8 peripheral blood DNA samples from representative POP cases. After filtering the sequencing data from the dbSNP database (build 138) and the 1000 Genomes Project, 2 missense variants in WNK1, c.2668G > A (p.G890R) and c.6761C> T (p.P2254L), were identified and further validated via Sanger sequencing. In validation stage, the c.2668G > A (p.G890R) variant and 8 additional variants were detected in 11 out of 161 POP patients. All these variants were absent in 231 healthy controls. Functional experiments showed that fibroblasts from the utero-sacral ligaments of POP with WNK1 mutations exhibited loose and irregular alignment compared with fibroblasts from healthy controls. In sum, our study identified a novel gene, WNK1, for POP susceptibility, expanded the causal mutation spectrums of POP, and provided evidence for the genetic diagnosis and medical management of POP in the future.

Hyperkalemic hypertension-associated cullin 3 promotes WNK signaling by degrading KLHL3

Familial hyperkalemic hypertension (FHHt) is a monogenic disease resulting from mutations in genes encoding WNK kinases, the ubiquitin scaffold protein cullin 3 (CUL3), or the substrate adaptor kelch-like 3 (KLHL3). Disease-associated CUL3 mutations abrogate WNK kinase degradation in cells, but it is not clear how mutant forms of CUL3 promote WNK stability. Here, we demonstrated that an FHHt-causing CUL3 mutant (CUL3 Δ403-459) not only retains the ability to bind and ubiquitylate WNK kinases and KLHL3 in cells, but is also more heavily neddylated and activated than WT CUL3. In cells, activated CUL3 Δ403-459 depleted KLHL3, preventing WNK degradation, despite increased CUL3-mediated WNK ubiquitylation; therefore, CUL3 loss in kidney should phenocopy FHHt in murine models. As predicted, nephron-specific deletion of Cul3 in mice did increase WNK kinase levels and the abundance of phosphorylated Na-Cl cotransporter (NCC). Over time, however, Cul3 deletion caused renal dysfunction, including hypochloremic alkalosis, diabetes insipidus, and salt-sensitive hypotension, with depletion of sodium potassium chloride cotransporter 2 and aquaporin 2. Moreover, these animals exhibited renal inflammation, fibrosis, and increased cyclin E. These results indicate that FHHt-associated CUL3 Δ403-459 targets KLHL3 for degradation, thereby preventing WNK degradation, whereas general loss of CUL3 activity - while also impairing WNK degradation - has widespread toxic effects in the kidney.

The WNK-SPAK/OSR1 pathway: master regulator of cation-chloride cotransporters

The WNK-SPAK/OSR1 kinase complex is composed of the kinases WNK (with no lysine) and SPAK (SPS1-related proline/alanine-rich kinase) or the SPAK homolog OSR1 (oxidative stress-responsive kinase 1). The WNK family senses changes in intracellular Cl(-) concentration, extracellular osmolarity, and cell volume and transduces this information to sodium (Na(+)), potassium (K(+)), and chloride (Cl(-)) cotransporters [collectively referred to as CCCs (cation-chloride cotransporters)] and ion channels to maintain cellular and organismal homeostasis and affect cellular morphology and behavior. Several genes encoding proteins in this pathway are mutated in human disease, and the cotransporters are targets of commonly used drugs. WNKs stimulate the kinases SPAK and OSR1, which directly phosphorylate and stimulate Cl(-)-importing, Na(+)-driven CCCs or inhibit the Cl(-)-extruding, K(+)-driven CCCs. These coordinated and reciprocal actions on the CCCs are triggered by an interaction between RFXV/I motifs within the WNKs and CCCs and a conserved carboxyl-terminal docking domain in SPAK and OSR1. This interaction site represents a potentially druggable node that could be more effective than targeting the cotransporters directly. In the kidney, WNK-SPAK/OSR1 inhibition decreases epithelial NaCl reabsorption and K(+) secretion to lower blood pressure while maintaining serum K(+). In neurons, WNK-SPAK/OSR1 inhibition could facilitate Cl(-) extrusion and promote γ-aminobutyric acidergic (GABAergic) inhibition. Such drugs could have efficacy as K(+)-sparing blood pressure-lowering agents in essential hypertension, nonaddictive analgesics in neuropathic pain, and promoters of GABAergic inhibition in diseases associated with neuronal hyperactivity, such as epilepsy, spasticity, neuropathic pain, schizophrenia, and autism.

[Association between single nucleotide polymorphisms in Wnk1 gene and ischemic stroke in Chinese Han population]

OBJECTIVE

To investigate the association between single nucleotide polymorphisms (SNPs) in Wnk1 gene and ischemic stroke in Chinese Han population.

METHODS

A hospital-based case-control study was carried out. The ischemic stroke group included 294 Chinese Han subjects, who were admitted with non-fatal ischemic stroke in departments of neurology of 5 hospitals in Xinjiang during January 2008 through December 2009. Control group included 314 age and sex-matched Han subjects without an inquired history of stroke, hospitalized in departments of surgery of these 5 hospitals. Ten tagging SNPs (tSNPs) of the Wnk1 gene were genotyped, and the association between these tSNPs and ischemic stroke were evaluated. The tSNPs (rs3858703, rs11611246, rs7305065, rs1990021, rs34408667, rs12309274, rs1012729, rs956868, rs12828016 and rs953361) were determined by the Multiplex SNaPshot platform. The data were analyzed by using t-test, Ξ2-test and logistic regression. Linkage disequilibrium and haplotype were analyzed by Haploview software.

RESULTS

The rates of alcohol drinking, hypertension ,diabetes and hyperlipidemia in ischemic stroke group were higher than those in control group (37.1% vs 21.0%, 62.9% vs 36.6%, 18.0% vs 6.1% and 36.4% vs 17.5%, respectively, all P<0.01). No significant difference in smoking rate was found between two groups. The genotyping loss rates of all sites were less than 1%. All the tSNPs were examined by Hardy-Weinberg equilibrium test except rs34408667. tSNP rs11611246 in the 4th intron of the Wnk1 gene was significantly associated with ischemic stroke. The distribution frequency of T allele in cases was significantly lower than that in male controls (30.3% vs 35.7%, P =0.046). When the samples were further stratified according to gender, rs11611246 was found to be associated with a reduced risk of ischemic stroke in male cases than in controls. GT and TT genotype frequencies were 43.3% and 7.2% in male cases, 43.1% and 15.2% in male controls, respectively (P=0.038). The T allele was associated with a reduced risk of ischemic stroke, with a per-allele OR of 0.702(95%CI:0.517-0.953, P=0.023) in male cases than in male controls. The significance remained after adjusting the covariates of age (P=0.022), or the covariates of age, BMI, cigarette smoking, alcohol drinking, hypertension, diabetes and hyperlipidemia (P=0.008). No association between other 9 tSNPs and ischemic stroke was noted in Chinese Han subjects.

CONCLUSION

The polymorphism of rs11611246 on the 4th intron of Wnk1 gene is associated with a reduced risk of ischemic stroke in Chinese Han population and the T allele might be a protective factor for ischemic stroke in male Chinese Hans.

Comparative analysis of the expression profile of Wnk1 and Wnk1/Hsn2 splice variants in developing and adult mouse tissues

The With No lysine (K) family of serine/threonine kinase (WNK) defines a small family of kinases with significant roles in ion homeostasis. WNK1 has been shown to have different isoforms due to what seems to be largely tissue specific splicing. Here, we used two distinct in situ hybridization riboprobes on developing and adult mouse tissues to make a comparative analysis of Wnk1 and its sensory associated splice isoform, Wnk1/Hsn2. The hybridization signals in developing mouse tissues, which were prepared at embryonic day e10.5 and e12.5, revealed a homogenous expression profile with both probes. At e15.5 and in the newborn mouse, the two probes revealed different expression profiles with prominent signals in nervous system tissues and also other tissues such as kidney, thymus and testis. In adult mouse tissues, the two expression profiles appeared even more restricted to the nervous tissues, kidney, thymus and testis, with no detectable signal in the other tissues. Throughout the nervous system, sensory tissues, as well as in Cornu Ammonis 1 (CA1), CA2 and CA3 areas of the hippocampus, were strongly labeled with both probes. Hybridization signals were also strongly detected in Schwann and supporting satellite cells. Our results show that the expression profiles of Wnk1 isoforms change during the development, and that the expression of the Wnk1 splice variant containing the Hsn2 exon is prominent during developing and in adult mouse tissues, suggesting its important role in the development and maintenance of the nervous system.

WNK signaling is involved in neural development via Lhx8/Awh expression

WNK kinase family is conserved among many species and regulates SPAK/OSR1 and ion co-transporters. Some mutations in human WNK1 or WNK4 are associated with Pseudohypoaldosteronism type II, a form of hypertension. WNK is also involved in developmental and cellular processes, but the molecular mechanisms underlying its regulation in these processes remain unknown. Here, we identify a new target gene in WNK signaling, Arrowhead and Lhx8, which is a mammalian homologue of Drosophila Arrowhead. In Drosophila, WNK was shown to genetically interact with Arrowhead. In Wnk1 knockout mice, levels of Lhx8 expression were reduced. Ectopic expression of WNK1, WNK4 or Osr1 in mammalian cells induced the expression of the Lhx8. Moreover, neural specification was inhibited by the knockdown of both Wnk1 and Wnk4 or Lhx8. Drosophila WNK mutant caused defects in axon guidance during embryogenesis. These results suggest that WNK signaling is involved in the morphological and neural development via Lhx8/Arrowhead.

WNK1/HSN2 mutation in human peripheral neuropathy deregulates KCC2 expression and posterior lateral line development in zebrafish (Danio rerio)

Hereditary sensory and autonomic neuropathy type 2 (HSNAII) is a rare pathology characterized by an early onset of severe sensory loss (all modalities) in the distal limbs. It is due to autosomal recessive mutations confined to exon "HSN2" of the WNK1 (with-no-lysine protein kinase 1) serine-threonine kinase. While this kinase is well studied in the kidneys, little is known about its role in the nervous system. We hypothesized that the truncating mutations present in the neural-specific HSN2 exon lead to a loss-of-function of the WNK1 kinase, impairing development of the peripheral sensory system. To investigate the mechanisms by which the loss of WNK1/HSN2 isoform function causes HSANII, we used the embryonic zebrafish model and observed strong expression of WNK1/HSN2 in neuromasts of the peripheral lateral line (PLL) system by immunohistochemistry. Knocking down wnk1/hsn2 in embryos using antisense morpholino oligonucleotides led to improper PLL development. We then investigated the reported interaction between the WNK1 kinase and neuronal potassium chloride cotransporter KCC2, as this transporter is a target of WNK1 phosphorylation. In situ hybridization revealed kcc2 expression in mature neuromasts of the PLL and semi-quantitative RT-PCR of wnk1/hsn2 knockdown embryos showed an increased expression of kcc2 mRNA. Furthermore, overexpression of human KCC2 mRNA in embryos replicated the wnk1/hsn2 knockdown phenotype. We validated these results by obtaining double knockdown embryos, both for wnk1/hsn2 and kcc2, which alleviated the PLL defects. Interestingly, overexpression of inactive mutant KCC2-C568A, which does not extrude ions, allowed a phenocopy of the PLL defects. These results suggest a pathway in which WNK1/HSN2 interacts with KCC2, producing a novel regulation of its transcription independent of KCC2's activation, where a loss-of-function mutation in WNK1 induces an overexpression of KCC2 and hinders proper peripheral sensory nerve development, a hallmark of HSANII.

A novel homozygous mutation in the WNK1/HSN2 gene causing hereditary sensory neuropathy type 2

Hereditary sensory and autonomic neuropathy type 2 is a rare disorder caused by recessive mutations in the WNK1/HSN2 gene located on chromosome 12p13.33. Phenotype of the patients is characterized by severe sensory loss affecting all sensory modalities. We report a novel homozygous Lys179fsX182 (HSN2); Lys965fsX968 (WNK1/HSN2) mutation causing an early childhood onset hereditary sensory and autonomic neuropathy type 2, with acromutilations in upper and lower limbs, and autonomic dysfunction. To the best of our knowledge this is the first genetically proven case of hereditary sensory and autonomic neuropathy type 2 originating from East Europe.

Effect of heterozygous deletion of WNK1 on the WNK-OSR1/ SPAK-NCC/NKCC1/NKCC2 signal cascade in the kidney and blood vessels

BACKGROUND

We found that a mechanism of hypertension in pseudohypoaldosteronism type II (PHAII) caused by a WNK4 missense mutation (D561A) was activation of the WNK-OSR1/SPAK-NCC signal cascade. However, the pathogenic effect of intronic deletions in WNK1 genes also observed in PHAII patients remains unclear. To understand the pathophysiological roles of WNK1 in vivo, WNK1(+/-)mice have been analyzed, because homozygous WNK1 knockout is embryonic lethal. Although WNK1(+/-) mice have been reported to have hypotension, detailed analyses of the WNK signal cascade in the kidney and other organs of WNK1(+/-) mice have not been performed.

METHOD

We assess the effect of heterozygous deletion of WNK1 on the WNK-OSR1/SPAK-NCC/NKCC1/NKCC2 signal cascade in the kidney and blood vessels.

RESULTS

Contrary to the previous report, the blood pressure of WNK1(+/-) mice was not decreased, even under a low-salt diet. Under a WNK4(D561A/+) background, the heterozygous deletion of the WNK1 gene did not reduce the high blood pressure either. We then evaluated the phosphorylation status of OSR1, SPAK, NCC, NKCC1, and NKCC2 in the kidney, but no significant decrease in the phosphorylation was observed in WNK1(+/-) mice or WNK1(+/-)WNK4(D561A/+) mice. In contrast, a significant decrease in NKCC1 phosphorylation in the aorta and a decreased pressure-induced myogenic response in the mesenteric arteries were observed in WNK1(+/-) mice.

CONCLUSION

The contribution of WNK1 to total WNK kinase activity in the kidney may be small, but that WNK1 may play a substantial role in the regulation of blood pressure in the arteries.

Taurine inhibits K+-Cl- cotransporter KCC2 to regulate embryonic Cl- homeostasis via with-no-lysine (WNK) protein kinase signaling pathway

GABA inhibits mature neurons and conversely excites immature neurons due to lower K(+)-Cl(-) cotransporter 2 (KCC2) expression. We observed that ectopically expressed KCC2 in embryonic cerebral cortices was not active; however, KCC2 functioned in newborns. In vitro studies revealed that taurine increased KCC2 inactivation in a phosphorylation-dependent manner. When Thr-906 and Thr-1007 residues in KCC2 were substituted with Ala (KCC2T906A/T1007A), KCC2 activity was facilitated, and the inhibitory effect of taurine was not observed. Exogenous taurine activated the with-no-lysine protein kinase 1 (WNK1) and downstream STE20/SPS1-related proline/alanine-rich kinase (SPAK)/oxidative stress response 1 (OSR1), and overexpression of active WNK1 resulted in KCC2 inhibition in the absence of taurine. Phosphorylation of SPAK was consistently higher in embryonic brains compared with that of neonatal brains and down-regulated by a taurine transporter inhibitor in vivo. Furthermore, cerebral radial migration was perturbed by a taurine-insensitive form of KCC2, KCC2T906A/T1007A, which may be regulated by WNK-SPAK/OSR1 signaling. Thus, taurine and WNK-SPAK/OSR1 signaling may contribute to embryonic neuronal Cl(-) homeostasis, which is required for normal brain development.

A new methodology for quantification of alternatively spliced exons reveals a highly tissue-specific expression pattern of WNK1 isoforms

Mutations in the WNK1 gene, encoding a serine-threonine kinase of the WNK (With No lysine (K)) family, have been implicated in two rare human diseases, Familial Hyperkalemic Hypertension (FHHt) and Hereditary Sensory and Autonomic Neuropathy type 2 (HSAN2). Alternative promoters give rise to a ubiquitous isoform, L-WNK1, and a kidney-specific isoform, KS-WNK1. Several other isoforms are generated through alternative splicing of exons 9, 11 and 12 but their precise tissue distribution is not known. Two additional exons, 8b and HSN2, involved in HSAN2, are thought to be specifically expressed in the nervous system. The purpose of this study was to establish an exhaustive description of all WNK1 isoforms and to quantify their relative level of expression in a panel of human and mouse tissues and in mouse nephron segments. For the latter purpose, we developed a new methodology allowing the determination of the proportions of the different isoforms generated by alternative splicing. Our results evidenced a striking tissue-specific distribution of the different isoforms and the unexpected presence of exon HSN2 in many tissues other than the nervous system. We also found exon 26 to be alternatively spliced in human and identified two new exons, 26a and 26b, within intron 26, specifically expressed in nervous tissues both in humans and mice. WNK1 should therefore no longer be designated as a 28- but as a 32-exon gene, with 8 of them - 8b, HSN2, 9, 11, 12, 26, 26a and 26b - alternatively spliced in a tissue-specific manner. These tissue-specific isoforms must be considered when studying the different roles of this ubiquitous kinase.

Advances in WNK signaling of salt and potassium metabolism: clinical implications

Recent evidence due to the discovery of a family of kinases implicated in arterial hypertension now points to the underlying molecular mechanisms that dictate Na(+), K(+) and water handling in the nephron. These new key players need to be understood in order to fully comprehend the pathophysiology, manifestations, and treatment of common clinical entities such as hypovolemic shock, congestive heart failure, primary hyperaldosteronism, nephrotic syndrome and hypertension. It is through the analysis of the volume status and electrolyte abnormalities that commonly present with these diseases that we can begin to create a link between the abstract concept of a kinase regulation and how a patient will respond to a particular treatment. This review is an attempt to bridge that gap.

Independent regulation of Na+ and K+ balance by the kidney

The understanding of the independent regulation of sodium and potassium by the kidney has remained elusive. Recent evidence now points to dissimilar regulatory mechanisms in ion handling, dependent on the presence of either aldosterone alone or angiotensin II with aldosterone among other factors. This review summarizes past and present information in an attempt to reconcile the current concepts of differential regulation of sodium and potassium balance through the with-no-lysine (K) kinase (WNK) system and the previous knowledge regarding ion transport mechanisms in the distal nephron.

Novel polymorphic AluYb8 insertion in the WNK1 gene is associated with blood pressure variation in Europeans

Mutations in WNK1 and WNK4 cause familial hypertension, the Gordon syndrome. WNK1 and WNK4 conserved noncoding regions were targeted to polymorphism screening using DHPLC and DGGE. The scan identified an undescribed polymorphic AluYb8 insertion in WNK1 intron 10. Screening in primates revealed that this Alu-insertion has probably occurred in human lineage. Genotyping in 18 populations from Europe, Asia, and Africa (n = 854) indicated an expansion of the WNK1 AluYb8 bearing chromosomes out of Africa. The allele frequency in Sub-Saharan Africa was ∼3.3 times lower than in other populations (4.8 vs. 15.8%; P = 9.7 × 10⁻⁹). Meta-analysis across three European sample sets (n = 3,494; HYPEST, Estonians; BRIGHT, the British; CADCZ, Czech) detected significant association of the WNK1 AluYb8 insertion with blood pressure (BP; systolic BP, P = 4.03 × 10⁻³, effect 1.12; diastolic BP, P = 1.21 × 10⁻², effect 0.67). Gender-stratified analysis revealed that this effect might be female-specific (n = 2,088; SBP, P = 1.99 × 10⁻³, effect 1.59; DBP P = 3.64 × 10⁻⁴, effect 1.23; resistant to Bonferroni correction), whereas no statistical support was identified for the association with male BP (n = 1,406). In leucocytes, the expressional proportions of the full-length WNK1 transcript and the splice-form skipping exon 11 were significantly shifted in AluYb8 carriers compared to noncarriers. The WNK1 AluYb8 insertion might affect human BP via altering the profile of alternatively spliced transcripts. Hum Mutat 32:1–9, 2011. © 2011 Wiley-Liss, Inc.

C. elegans STK39/SPAK ortholog-mediated inhibition of ClC anion channel activity is regulated by WNK-independent ERK kinase signaling

Mammalian Ste20-like proline/alanine-rich kinase (SPAK) and oxidative stress-responsive 1 (OSR1) kinases phosphorylate and regulate cation-coupled Cl(-) cotransporter activity in response to cell volume changes. SPAK and OSR1 are activated via phosphorylation by upstream with-no-lysine (WNK) kinases. In Caenorhabditis elegans, the SPAK/OSR1 ortholog germinal center kinase (GCK)-3 binds to and regulates the activity of the cell volume- and meiotic cell cycle-dependent ClC anion channel CLH-3b. We tested the hypothesis that WNK kinases function in the GCK-3/CLH-3b signaling cascade. CLH-3b heterologously expressed in human embryonic kidney (HEK) cells was unaffected by coexpression with the single C. elegans WNK kinase, WNK-1, or kinase-dead WNK-1 dominant-negative mutants. RNA interference (RNAi) knockdown of the single Drosophila WNK kinase had no effect on the activity of CLH-3b expressed in Drosophila S2 cells. Similarly, RNAi silencing of C. elegans WNK-1 had no effect on basal or cell volume-sensitive activity of CLH-3b expressed endogenously in worm oocytes. Previous yeast 2-hybrid studies suggested that ERK kinases may function upstream of GCK-3. Pharmacological inhibition of ERK signaling disrupted CLH-3b activity in HEK cells in a GCK-3-dependent manner. RNAi silencing of the C. elegans ERK kinase MPK-1 or the ERK phosphorylating/activating kinase MEK-2 constitutively activated native CLH-3b. MEK-2 and MPK-1 play important roles in regulating the meiotic cell cycle in C. elegans oocytes. Cell cycle-dependent changes in MPK-1 correlate with the pattern of CLH-3b activation observed during oocyte meiotic maturation. We postulate that MEK-2/MPK-1 functions upstream from GCK-3 to regulate its activity during cell volume and meiotic cell cycle changes.

Altered expression of regulators of the cortical chloride transporters NKCC1 and KCC2 in schizophrenia

CONTEXT

Disturbances in markers of cortical γ-aminobutyric acid neurotransmission are a common finding in schizophrenia. The nature of γ-aminobutyric acid neurotransmission (hyperpolarizing or depolarizing) depends on the local intracellular chloride concentration. In the central nervous system, the intracellular chloride level is determined by the activity of 2 cation-chloride transporters, NKCC1 and KCC2. The activities of these transporters are in turn regulated by a network of serine-threonine kinases that includes OXSR1, STK39, and the WNK kinases WNK1, WNK3, and WNK4.

OBJECTIVE

To compare the levels of NKCC1, KCC2, OXSR1, STK39, WNK1, WNK3, and WNK4 transcripts in prefrontal cortex area 9 between subjects with schizophrenia and healthy comparison subjects.

DESIGN

Real-time quantitative polymerase chain reaction technique was used to measure transcript levels in the prefrontal cortex.

SETTING

Human brain specimens were obtained from autopsies conducted at the Allegheny County Medical Examiner's Office, Pittsburgh, Pennsylvania.

PARTICIPANTS

Postmortem brain specimens from 42 subjects with schizophrenia and 42 matched healthy comparison subjects. Brain specimens from 18 macaque monkeys exposed to haloperidol, olanzapine, or sham long-term.

MAIN OUTCOME MEASURES

Relative expression levels for NKCC1, KCC2, OXSR1, STK39, WNK1, WNK3, and WNK4 transcripts compared with the mean expression level of 3 housekeeping transcripts.

RESULTS

OXSR1 and WNK3 transcripts were substantially overexpressed in subjects with schizophrenia relative to comparison subjects. In contrast, NKCC1, KCC2, STK39, WNK1, and WNK4 transcript levels did not differ between subject groups. OXSR1 and WNK3 transcript expression levels were not changed in antipsychotic-exposed monkeys and were not affected by potential confounding factors in the subjects with schizophrenia.

CONCLUSION

In schizophrenia, increased expression levels, and possibly increased kinase activities, of OXSR1 and WNK3 may shift the balance of chloride transport by NKCC1 and KCC2 and alter the nature of γ-aminobutyric acid neurotransmission in the prefrontal cortex.

Downregulation of NCC and NKCC2 cotransporters by kidney-specific WNK1 revealed by gene disruption and transgenic mouse models

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.

Potassium transport--an update

Potassium homeostasis depends on the coordinated interaction between tightly regulated potassium transfer in and out of the extracellular fluid compartment, and renal excretion or retention of potassium. Potassium transport along the nephron involves extensive proximal tubule reabsorption of potassium. Potassium is also reabsorbed along the thick ascending limb of Henle's loop. Regulated potassium secretion, or potassium reabsorption in exchange for hydrogen ions along the connecting tubule and collecting tubule, is responsible for potassium excretion. Renal potassium transport is modulated by potassium intake, several hormones, acid-base factors and distal nephron sodium delivery. WNK family kinases have also emerged as factors regulating sodium and potassium transport in the distal nephron.

The fatty acid synthase fasn-1 acts upstream of WNK and Ste20/GCK-VI kinases to modulate antimicrobial peptide expression in C. elegans epidermis

An important part of the innate immune response of the nematode C. elegans to fungal infection is the rapid induction of antimicrobial peptide gene expression. One of these genes, nlp‑29, is expressed at a low level in adults under normal conditions. Its expression is up-regulated in the epidermis by infection with Drechmeria coniospora, but also by physical injury and by osmotic stress. For infection and wounding, the induction is dependent on a p38 MAP kinase cascade, but for osmotic stress, this pathway is not required. To characterize further the pathways that control the expression of nlp‑29, we carried out a genetic screen for negative regulatory genes. We isolated a number of Peni (peptide expression no infection) mutants and cloned one. It corresponds to fasn‑1, the nematode ortholog of vertebrate fatty acid synthase. We show here that a pathway involving fatty acid synthesis and the evolutionary conserved wnk‑1 and gck‑3/Ste20/GCK‑VI kinases modulates nlp‑29 expression in the C. elegans epidermis, independently of p38 MAPK signaling. The control of the antimicrobial peptide gene nlp‑29 thus links different physiological processes, including fatty acid metabolism, osmoregulation, maintenance of epidermal integrity and the innate immune response to infection.

Regulation of a third conserved phosphorylation site in SGK1

SGK1 (serum- and glucocorticoid-induced kinase 1) is a member of the AGC branch of the protein kinase family. Among well described functions of SGK1 is the regulation of epithelial transport through phosphorylation of the ubiquitin protein ligase Nedd4-2 (neuronal precursor cell expressed developmentally down-regulated 4-2). The activation of SGK1 has been widely accepted to be dependent on the phosphorylation of Thr256 in the activation loop and Ser422 in the hydrophobic motif near the C terminus. Here, we report the identification of two additional phosphorylation sites, Ser397 and Ser401. Both are required for maximum SGK1 activity induced by extracellular agents or by coexpression with other protein kinases, with the largest loss of activity from mutation of Ser397. Coexpression with active Akt1 increased the phosphorylation of Ser397 and thereby SGK1 kinase activity. SGK1 activation was further augmented by coexpression with the protein kinase WNK1 (with no lysine kinase 1). These findings reveal further complexity underlying the regulation of SGK1 activity.

WNK kinases, renal ion transport and hypertension

Two members of a recently discovered family of protein kinases are the cause of an inherited disease known as pseudohypoaldosteronism type II (PHAII). These patients exhibit arterial hypertension together with hyperkalemia and metabolic acidosis. This is a mirror image of Gitelman disease that is due to inactivating mutations of the SLC12A3 gene that encodes the thiazide-sensitive Na(+):Cl(-) cotransporter. The uncovered genes causing PHAII encode for serine/threonine kinases known as WNK1 and WNK4. Physiological and biochemical studies have revealed that WNK1 and WNK4 modulate the activity of several transport pathways of the aldosterone-sensitive distal nephron, thus increasing our understanding of how diverse renal ion transport proteins are coordinated to regulate normal blood pressure levels. Observations discussed in the present work place WNK1 and WNK4 as genes involved in the genesis of essential hypertension and as potential targets for the development of antihypertensive drugs.

Evolutionarily conserved WNK and Ste20 kinases are essential for acute volume recovery and survival after hypertonic shrinkage in Caenorhabditis elegans

Members of the germinal center kinase (GCK)-VI subfamily of Ste20 kinases regulate a Caenorhabditis elegans ClC anion channel and vertebrate SLC12 cation-Cl(-) cotransporters. With no lysine (K) (WNK) protein kinases interact with and activate the mammalian GCK-VI kinases proline-alanine-rich Ste20-related kinase (PASK) and oxidative stress-responsive 1 (OSR1). We demonstrate here for the first time that GCK-VI kinases play an essential role in whole animal osmoregulation. RNA interference (RNAi) knockdown of the single C. elegans GCK-VI kinase, GCK-3, dramatically inhibits systemic volume recovery and survival after hypertonic shrinkage. Tissue-specific RNAi suggests that GCK-3 functions primarily in the hypodermis and intestine to mediate volume recovery. The single C. elegans WNK kinase, WNK-1, binds to GCK-3, and wnk-1 knockdown gives rise to a phenotype qualitatively similar to that of gck-3(RNAi) worms. Knockdown of the two kinases together has no additive effect, suggesting that WNK-1 and GCK-3 function in a common pathway. We postulate that WNK-1 functions upstream of GCK-3 in a manner similar to that postulated for its mammalian homologs. Phylogenetic analysis of kinase functional domains suggests that the interaction between GCK-VI and WNK kinases first occurred in an early metazoan and therefore likely coincided with the need of multicellular animals to tightly regulate transepithelial transport processes that mediate systemic osmotic homeostasis.

Biological Cross-talk between WNK1 and the Transforming Growth Factor β-Smad Signaling Pathway

WNKs (with no lysine (K)), unique serine/threonine protein kinases, have been best studied in the context of cell volume regulation and ion homeostasis. Here we describe a biological link between WNKs and transforming growth factor (TGF) beta-Smad signaling. Both WNK1 and WNK4 directly bind to and phosphorylate Smad2. Knockdown of WNK1 in HeLa cells using small interfering RNA reduces Smad2 protein expression; this decrease is at least partially due to down-regulation of Smad2 transcription. In contrast, phosphorylated Smad2 significantly accumulated in the nucleus as a consequence of depletion of WNK1, resulting in Smad-mediated transcriptional responses. In addition, TGFbeta-induced target gene transcripts were increased in WNK1 small interfering RNA cells. These findings suggest WNK1 as a dual modulator of TGFbeta-Smad signaling pathways.

Intersectin links WNK kinases to endocytosis of ROMK1

With-no-lysine (WNK) kinases are a novel family of protein kinases characterized by an atypical placement of the catalytic lysine. Mutations of 2 family members, WNK1 and WNK4, cause pseudohypoaldosteronism type 2 (PHA2), an autosomal-dominant disease characterized by hypertension and hyperkalemia. WNK1 and WNK4 stimulate clathrin-dependent endocytosis of renal outer medullar potassium 1 (ROMK1), and PHA2-causing mutations of WNK4 increase the endocytosis. How WNKs stimulate endocytosis of ROMK1 and how mutations of WNK4 increase the endocytosis are unknown. Intersectin (ITSN) is a multimodular endocytic scaffold protein. Here we show that WNK1 and WNK4 interacted with ITSN and that the interactions were crucial for stimulation of endocytosis of ROMK1 by WNKs. The stimulation of endocytosis of ROMK1 by WNK1 and WNK4 required specific proline-rich motifs of WNKs, but did not require their kinase activity. WNK4 interacted with ROMK1 as well as with ITSN. Disease-causing WNK4 mutations enhanced interactions of WNK4 with ITSN and ROMK1, leading to increased endocytosis of ROMK1. These results provide a molecular mechanism for stimulation of endocytosis of ROMK1 by WNK kinases.

Molecular genetics of hereditary sensory neuropathies

Hereditary sensory neuropathies (HSN), also known as hereditary sensory and autonomic neuropathies (HSAN), are a clinically and genetically heterogeneous group of disorders. They are caused by neuronal atrophy and degeneration, predominantly affecting peripheral sensory and autonomic neurons. Both congenital and juvenile to adulthood onset is possible. Currently, the classification of the HSN depends on the mode of inheritance, age at onset, and clinical presentation. Hallmark features are progressive sensory loss, chronic skin ulcers, and other skin abnormalities. Spontaneous fractures and neuropathic arthropathy are frequent complications and often necessitate amputations. Autonomic features vary between different subgroups. Distal muscle weakness and wasting may be present and is sometimes so prominent that it becomes difficult to distinguish HSN from Charcot-Marie-Tooth syndrome. Recent major advances in molecular genetics have led to the identification of seven gene loci and six-disease causing genes for autosomal-dominant and autosomal-recessive HSN. These genes have been shown to play roles in lipid metabolism and the regulation of intracellular vesicular transport, but also a presumptive transcriptional regulator, a nerve growth factor receptor, and a nerve growth factor have been described among the causative genes in HSN. Nevertheless, it remains unclear how mutations in the known genes lead to the phenotype of HSN. In this review, we summarize the recent progress of the molecular genetics of the HSN and the implicated genes.

The Inherited Neuropathies

Neuropathy is one of the most common referrals to neurologic clinics. Patients often undergo extensive testing for acquired etiologies; inherited causes are common. Increasingly, genetic causes are becoming known and commercial testing available. The rate of recent discovery has been rapid and relates to the extent of single gene disorders of nerve, the ease of peripheral nervous system functional examination, and readily accessible pathologic tissue. Foremost in the rate of recent discoveries is the work and tools of the human genome project. the rapidity of the ongoing discovery requires clinicians to be familiar with molecular biologic discoveries and consider wisely which testing should be performed.

Regulation of activity and localization of the WNK1 protein kinase by hyperosmotic stress

Mutations within the WNK1 (with-no-K[Lys] kinase-1) gene cause Gordon's hypertension syndrome. Little is known about how WNK1 is regulated. We demonstrate that WNK1 is rapidly activated and phosphorylated at multiple residues after exposure of cells to hyperosmotic conditions and that activation is mediated by the phosphorylation of its T-loop Ser382 residue, possibly triggered by a transautophosphorylation reaction. Activation of WNK1 coincides with the phosphorylation and activation of two WNK1 substrates, namely, the protein kinases STE20/SPS1-related proline alanine–rich kinase (SPAK) and oxidative stress response kinase-1 (OSR1). Small interfering RNA depletion of WNK1 impairs SPAK/OSR1 activity and phosphorylation of residues targeted by WNK1. Hyperosmotic stress induces rapid redistribution of WNK1 from the cytosol to vesicular structures that may comprise trans-Golgi network (TGN)/recycling endosomes, as they display rapid movement, colocalize with clathrin, adaptor protein complex 1 (AP-1), and TGN46, but not the AP-2 plasma membrane–coated pit marker nor the endosomal markers EEA1, Hrs, and LAMP1. Mutational analysis suggests that the WNK1 C-terminal noncatalytic domain mediates vesicle localization. Our observations shed light on the mechanism by which WNK1 is regulated by hyperosmotic stress.

WNK1 and WNK4 modulate CFTR activity

The cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated chloride channel. WNK kinases are widely expressed modulators of ion transport. WNK1 and WNK4, two WNK kinases that are mutated in familial hyperkalemic hypertension (FHHt), are co-expressed with CFTR in several organs, raising the possibility that WNK kinases might alter CFTR activity in vivo or that CFTR could be involved in the pathogenesis of FHHt. Here, we report that WNK1 co-localizes with CFTR protein in pulmonary epithelial cells. Co-expression of WNK1 or WNK4 with CFTR in Xenopus laevis oocytes suppresses chloride channel activity. The effect of WNK4 is dose dependent and occurs, at least in part, by reducing CFTR protein abundance at the plasma membrane. This effect is independent of WNK4 kinase activity. In contrast, the effect of WNK1 on CFTR activity requires intact WNK1 kinase activity. Moreover WNK1 and WNK4 exhibit additive CFTR inhibition. Previous reports suggest that patients with FHHt exhibit mild changes in nasal potential difference that resemble the more severe changes that occur in cystic fibrosis. We report that the FHHt-causing mutant WNK4 Q562E is a more potent inhibitor of CFTR activity than is the wild-type WNK4. Taken together, these results suggest that WNK1 and WNK4 may modulate CFTR activity; they further suggest that WNK kinases may be potential therapeutic targets for cystic fibrosis.

Down-regulation of WNK1 protein kinase in neural progenitor cells suppresses cell proliferation and migration

WNK1, a Ser/Thr protein kinase, is widely expressed in many tissues. Its biological functions are largely unknown. Disruption of the WNK1 gene in mice leads to embryonic lethality at day 13, implicating a critical role of WNK1 in embryonic development. To investigate this potential function, we used antisense strategy to knock down the expression of WNK1 in a mouse neural progenitor cell line, C17.2. Down-regulation of WNK1 in C17.2 cells greatly reduced cell growth. Addition of epidermal growth factor (EGF), a mitogen for C17.2 cells, had no effect on growth. The WNK1-knockdown cells showed a flat and rounded morphology, characteristic of the immature and non-differentiated phenotype of the progenitor cells; this was further demonstrated by immunostaining for the progenitor and neuronal markers. Migration of the WNK1-knockdown C17.2 cells was reduced as tested in culture dishes or Matrigel-covered chambers. Moreover, activation of extracellular signal-regulated kinase (ERK1)/2 and ERK5 by EGF in the WNK1-knockdown cells was suppressed. These results demonstrate a novel function of WNK1 in proliferation, migration, and differentiation of neural progenitor cells, likely by mechanisms involving activation of the mitogen-activated protein (MAP) kinase ERK1/2 and/or ERK5 pathways.

WNK protein kinases modulate cellular Cl- flux by altering the phosphorylation state of the Na-K-Cl and K-Cl cotransporters

Precise control of cellular Cl(-) transport is necessary for many fundamental physiological processes. For example, the intracellular concentration of Cl(-), fine-tuned through the coordinated action of cellular Cl(-) influx and efflux mechanisms, determines whether a neuron's response to GABA is excitatory or inhibitory. In epithelia, synchrony between apical and basolateral Cl(-) flux, and transcellular and paracellular Cl(-) transport, is necessary for efficient transepithelial Cl(-) reabsorption or secretion. In cells throughout the body, coordination of Cl(-) entry and exit mechanisms help defend against changes in cell volume. The Na-K-Cl and K-Cl cotransporters of the SLC12 gene family are important molecular determinants of Cl(-) entry and exit, respectively, in these systems. The WNK serine-threonine kinase family, members of which are mutated in an inherited form of human hypertension, are components of a signaling pathway that coordinates Cl(-) influx and efflux through SLC12 cotransporters to dynamically regulate intracellular Cl(-) activity.

Role of with-no-lysine [K] kinases in the pathogenesis of Gordon's syndrome

Gordon's syndrome, also known as pseudohypoaldosteronism type II (PHA II) or familial hypertension with hyperkalemia, is an autosomal-dominant disease characterized by hypertension, hyperkalemia, hyperchloremic metabolic acidosis, and normal glomerular filtration rate. Recent positional cloning has linked mutations of WNK1 and WNK4 to Gordon's syndrome. With-no-lysine [K] (WNK) kinases are a new family of large serine-threonine protein kinases with an atypical placement of the catalytic lysine. Here, we review the pathogenesis of PHA II based on current understanding of the actions of WNK1 and WNK4 on Na+ and K+ handling in the renal distal tubule.

Novel mutation in the HSN2 gene in a Korean patient with hereditary sensory and autonomic neuropathy type 2

Hereditary sensory and autonomic neuropathies (HSAN) are a group of clinically and genetically heterogeneous disorders that are associated with sensory dysfunction. Among these, HSAN type 2 (HSAN2; MIM 201300) is a rare recessive disease that is characterized by an early age of onset with distal and proximal sensory loss, dysfunction of the autonomic nervous system, loss of the tendon reflex, the presence of various mutilations, and the slow progression of the disease over time. The authors report a Korean patient with the clinical features of HSAN2, who was compound heterozygous for two loss-of-function mutations in the HSN2 gene: c.217C > T (Gln73X) and c.1134_1135insT (Asp379fsX1). The Gln73X mutation was a novel mutation while the Asp379fsX1 mutation has recently been reported in a Japanese patient with HSAN2. These results expanded the spectrum of mutations of the HSN2 gene by identifying a novel truncating mutation in a Korean patient and further support the hypothesis that HSN2 is a causative gene for HSAN2.