The WNKs: atypical protein kinases with pleiotropic actions

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Germline MYOF1::WNK4 and VPS25::MYOF1 Chimeras Generated by the Constitutional Translocation t(17;19)(q21;p13) in Two Siblings With Myelodysplastic Syndrome

BACKGROUND/AIM

Constitutional chromosomal aberrations are rare in hematologic malignancies and their pathogenetic role is mostly poorly understood. We present a comprehensive molecular characterization of a novel constitutional chromosomal translocation found in two siblings - sisters - diagnosed with myelodysplastic syndrome (MDS).

MATERIALS AND METHODS

Bone marrow and blood cells from the two patients were examined using G-banding, RNA sequencing, PCR, and Sanger sequencing.

RESULTS

We identified a balanced t(17;19)(q21;p13) translocation in both siblings' bone marrow, blood cells, and phytohemagglutinin-stimulated lymphocytes. The translocation generated a MYO1F::WNK4 chimera on the der(19)t(17;19), encoding a chimeric serine/threonine kinase, and a VPS25::MYO1F on the der(17), potentially resulting in an aberrant VPS25 protein.

CONCLUSION

The t(17;19)(q21;p13) translocation found in the two sisters probably predisposed them to myelodysplasia. How the MYO1F::WNK4 and/or VPS25::MYO1F chimeras, perhaps especially MYO1F::WNK4 that encodes a chimeric serine/threonine kinase, played a role in MDS pathogenesis, remains incompletely understood.

WNK kinase is a vasoactive chloride sensor in endothelial cells

Endothelial cells (ECs) line the wall of blood vessels and regulate arterial contractility to tune regional organ blood flow and systemic pressure. Chloride (Cl-) is the most abundant anion in ECs and the Cl- sensitive With-No-Lysine (WNK) kinase is expressed in this cell type. Whether intracellular Cl- signaling and WNK kinase regulate EC function to alter arterial contractility is unclear. Here, we tested the hypothesis that intracellular Cl- signaling in ECs regulates arterial contractility and examined the signaling mechanisms involved, including the participation of WNK kinase. Our data obtained using two-photon microscopy and cell-specific inducible knockout mice indicated that acetylcholine, a prototypical vasodilator, stimulated a rapid reduction in intracellular Cl- concentration ([Cl-]i) due to the activation of TMEM16A, a Cl- channel, in ECs of resistance-size arteries. TMEM16A channel-mediated Cl- signaling activated WNK kinase, which phosphorylated its substrate proteins SPAK and OSR1 in ECs. OSR1 potentiated transient receptor potential vanilloid 4 (TRPV4) currents in a kinase-dependent manner and required a conserved binding motif located in the channel C terminus. Intracellular Ca2+ signaling was measured in four dimensions in ECs using a high-speed lightsheet microscope. WNK kinase-dependent activation of TRPV4 channels increased local intracellular Ca2+ signaling in ECs and produced vasodilation. In summary, we show that TMEM16A channel activation reduces [Cl-]i, which activates WNK kinase in ECs. WNK kinase phosphorylates OSR1 which then stimulates TRPV4 channels to produce vasodilation. Thus, TMEM16A channels regulate intracellular Cl- signaling and WNK kinase activity in ECs to control arterial contractility.

Astrocytic chloride regulates brain function in health and disease

Chloride ions (Cl-) play a pivotal role in synaptic inhibition in the central nervous system, primarily mediated through ionotropic mechanisms. A recent breakthrough emphathizes the significant influence of astrocytic intracellular chloride concentration ([Cl-]i) regulation, a field still in its early stages of exploration. Typically, the [Cl-]i in most animal cells is maintained at lower levels than the extracellular chloride [Cl-]o, a critical balance to prevent cell swelling due to osmotic pressure. Various Cl- transporters are expressed differently across cell types, fine-tuning the [Cl-]i, while Cl- gradients are utilised by several families of Cl- channels. Although the passive distribution of ions within cells is governed by basic biophysical principles, astrocytes actively expend energy to sustain [Cl-]i at much higher levels than those achieved passively, and much higher than neuronal [Cl-]i. Beyond the role in volume regulation, astrocytic [Cl-]i is dynamically linked to brain states and influences neuronal signalling in actively behaving animals. As a vital component of brain function, astrocytic [Cl-]i also plays a role in the development of disorders where inhibitory transmission is disrupted. This review synthesises the latest insights into astrocytic [Cl-]i, elucidating its role in modulating brain function and its implications in various pathophysiological conditions.

Genome-wide identification and expression analysis of the WNK kinase gene family in soybean

WNK kinases are a unique class of serine/threonine protein kinases that lack a conserved catalytic lysine residue in the kinase domain, hence the name WNK (with no K, i.e., lysine). WNK kinases are involved in various physiological processes in plants, such as circadian rhythm, flowering time, and stress responses. In this study, we identified 26 WNK genes in soybean and analyzed their phylogenetic relationships, gene structures, chromosomal distribution, cis-regulatory elements, expression patterns, and conserved protein motifs. The soybean WNK genes were unevenly distributed on 15 chromosomes and underwent 21 segmental duplication events during evolution. We detected 14 types of cis-regulatory elements in the promoters of the WNK genes, indicating their potential involvement in different signaling pathways. The transcriptome database revealed tissue-specific and salt stress-responsive expression of WNK genes in soybean, the second of which was confirmed by salt treatments and qRT-PCR analysis. We found that most WNK genes were significantly up-regulated by salt stress within 3 h in both roots and leaves, except for WNK5, which showed a distinct expression pattern. Our findings provide valuable insights into the molecular characteristics and evolutionary history of the soybean WNK gene family and lay a foundation for further analysis of WNK gene functions in soybean.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01440-5.

Regional bias of tumor suppressor gene mutations of STARD8 and WNK2 in colon cancers

StAR-related lipid transfer domain protein 8 (STARD8), encoding a Rho-GTPase-activating protein, and WNK2, encoding a serine/threonine kinase are candidate tumor suppressor genes (TSGs) in human cancers. Inactivation of these genes that would promote cancer pathogenesis is largely unknown in colon cancer (CC). Our study addressed to address whether STARD8 and WNK2 genes are mutated in CC. STARD8 and WNK2 genes possess mononucleotide repeats in their exons, which could be the targets for frameshift mutations in cancers with high microsatellite instability (MSI-H). By single-strand conformation polymorphism (SSCP) analysis, we analyzed the repeated sequences in 140 CCs (95 CCs with MSI-H and 45 CCs with stable MSI (MSS)). By DNA sequencing, we found that five MSI-H CCs (5/95: 5.3%) harbored the frameshift mutations, whereas MSS CCs (0/45) did not. In addition, we detected regional heterogeneous frameshift mutations of these genes in four (25%) of 16 MSI-H CCs. In immunohistochemistry for WNK2, WNK2 expression in the MSI-H CCs was significantly lower than that in the MSS CCs. Our results for the mutation and expression indicate that STARD8 and WNK2 genes are altered at various levels (frameshift mutation, expression, and regional heterogeneity) in MSI-H CCs, which might play a role in the pathogenesis by inactivating their TSG functions.

T cell migration requires ion and water influx to regulate actin polymerization

Migration of T cells is essential for their ability to mount immune responses. Chemokine-induced T cell migration requires WNK1, a kinase that regulates ion influx into the cell. However, it is not known why ion entry is necessary for T cell movement. Here we show that signaling from the chemokine receptor CCR7 leads to activation of WNK1 and its downstream pathway at the leading edge of migrating CD4+ T cells, resulting in ion influx and water entry by osmosis. We propose that WNK1-induced water entry is required to swell the membrane at the leading edge, generating space into which actin filaments can polymerize, thereby facilitating forward movement of the cell. Given the broad expression of WNK1 pathway proteins, our study suggests that ion and water influx are likely to be essential for migration in many cell types, including leukocytes and metastatic tumor cells.

Expression pattern analysis and characterization of the hereditary sensory and autonomic neuropathy 2 A (HSAN2A) gene with no lysine kinase (WNK1) in human dorsal root ganglion

Inherited painless neuropathies arise due to genetic insults that either block the normal signaling of or destroy the sensory afferent neurons in the dorsal root ganglion (DRG) responsible for transducing noxious stimuli. Complete loss of these neurons leads to profound insensitivity to all sensory modalities including pain. Hereditary sensory and autonomic neuropathy type 2 (HSNAII) is a rare genetic neuropathy characterized by a progressive distal early onset sensory loss. This syndrome is caused by autosomal recessive mutations in the with-no-lysine protein kinase 1 (WNK1) serine-threonine kinase gene. Of interest, disease-associated mutations are found in the large exon, termed "HSN2," which encodes a 498 amino acid domain C-terminal to the kinase domain. These mutations lead to truncation of the HSN2-containing proteins through the addition of an early stop codon (nonsense mutation) leading to loss of the C-terminal domains of this large protein. The present study evaluates the transcripts, gene structure, and protein structure of HSN2-containing WNK1 splice variants in DRG and spinal cord in order to establish the basal expression patterns of WNK1 and HSN2-containing WNK1 splice variants using multiplex fluorescent situ hybridization. We hypothesized that these transcripts would be enriched in pain-sensing DRG neurons, and, potentially, that enrichment in nociceptive neurons was responsible for the painless phenotypes observed. However, our in-depth analyses revealed that the HSN2-WNK1 splice variants were ubiquitously expressed but were not enriched in tachykinin 1-expressing C-fiber neurons, a class of neurons with a highly nociceptive character. We subsequently identified other subpopulations of DRG neurons with higher levels of HSN2-WNK1 expression, including mechanosensory large fibers. These data are inconsistent with the hypothesis that this transcript is enriched in nociceptive fibers, and instead suggest it may be related to general axon maintenance, or that nociceptive fibers are more sensitive to the genetic insult. These findings clarify the molecular and cellular expression pattern of this painless neuropathy gene in human tissue.

Unanticipated domain requirements for Drosophila Wnk kinase in vivo

WNK (With no Lysine [K]) kinases have critical roles in the maintenance of ion homeostasis and the regulation of cell volume. Their overactivation leads to pseudohypoaldosteronism type II (Gordon syndrome) characterized by hyperkalemia and high blood pressure. More recently, WNK family members have been shown to be required for the development of the nervous system in mice, zebrafish, and flies, and the cardiovascular system of mice and fish. Furthermore, human WNK2 and Drosophila Wnk modulate canonical Wnt signaling. In addition to a well-conserved kinase domain, animal WNKs have a large, poorly conserved C-terminal domain whose function has been largely mysterious. In most but not all cases, WNKs bind and activate downstream kinases OSR1/SPAK, which in turn regulate the activity of various ion transporters and channels. Here, we show that Drosophila Wnk regulates Wnt signaling and cell size during the development of the wing in a manner dependent on Fray, the fly homolog of OSR1/SPAK. We show that the only canonical RF(X)V/I motif of Wnk, thought to be essential for WNK interactions with OSR1/SPAK, is required to interact with Fray in vitro. However, this motif is unexpectedly dispensable for Fray-dependent Wnk functions in vivo during fly development and fluid secretion in the Malpighian (renal) tubules. In contrast, a structure function analysis of Wnk revealed that the less-conserved C-terminus of Wnk, that recently has been shown to promote phase transitions in cell culture, is required for viability in vivo. Our data thus provide novel insights into unexpected in vivo roles of specific WNK domains.

WNK1 mediates amphiregulin-induced MMP9 expression and cell invasion in human extravillous trophoblast cells

The invasion of human extravillous trophoblast (EVT) cells is a critical event required for a successful pregnancy. Amphiregulin, a ligand of the epidermal growth factor receptor (EGFR), has been shown to stimulate cell invasion in an immortalized human EVT cell line, HTR-8/SVneo. The with-no-lysine kinase 1 (WNK1) is involved in regulating cell invasion. It is known that WNK1 is expressed in the human placenta, but its role in human EVT cells remains unknown. In the present study, we show that AREG treatment phosphorylated WNK1 at Thr60 in both HTR-8/SVneo and primary human EVT cells. The stimulatory effect of AREG on WNK1 phosphorylation was mediated by the activation of PI3K/AKT, but not the ERK1/2 signaling pathway. AREG upregulated matrix metalloproteinase 9 (MMP9) but not MMP2. In addition, cell invasiveness was increased in response to the treatment of AREG. Using the siRNA-mediated knockdown approach, our results showed that the knockdown of WNK1 attenuated the AREG-induced upregulation of MMP9 expression and cell invasion. Moreover, the expression of WNK1 was downregulated in the placentas with preeclampsia, a disease resulting from insufficiency of EVT cell invasion during pregnancy. This study discovers the physiological function of WNK1 in human EVT cells and provides important insights into the regulation of MMP9 and cell invasion in human EVT cells.

WNK1 promotes water homeostasis by acting as a central osmolality sensor for arginine vasopressin release

Maintaining internal osmolality constancy is essential for life. Release of arginine vasopressin (AVP) in response to hyperosmolality is critical. Current hypotheses for osmolality sensors in circumventricular organs (CVOs) of the brain focus on mechanosensitive membrane proteins. The present study demonstrated that intracellular protein kinase WNK1 was involved. Focusing on vascular-organ-of-lamina-terminalis (OVLT) nuclei, we showed that WNK1 kinase was activated by water restriction. Neuron-specific conditional KO (cKO) of Wnk1 caused polyuria with decreased urine osmolality that persisted in water restriction and blunted water restriction-induced AVP release. Wnk1 cKO also blunted mannitol-induced AVP release but had no effect on osmotic thirst response. The role of WNK1 in the osmosensory neurons in CVOs was supported by neuronal pathway tracing. Hyperosmolality-induced increases in action potential firing in OVLT neurons was blunted by Wnk1 deletion or pharmacological WNK inhibitors. Knockdown of Kv3.1 channel in OVLT by shRNA reproduced the phenotypes. Thus, WNK1 in osmosensory neurons in CVOs detects extracellular hypertonicity and mediates the increase in AVP release by activating Kv3.1 and increasing action potential firing from osmosensory neurons.

B cell-intrinsic requirement for WNK1 kinase in antibody responses in mice

Migration and adhesion play critical roles in B cells, regulating recirculation between lymphoid organs, migration within lymphoid tissue, and interaction with CD4+ T cells. However, there is limited knowledge of how B cells integrate chemokine receptor and integrin signaling with B cell activation to generate efficient humoral responses. Here, we show that the WNK1 kinase, a regulator of migration and adhesion, is essential in B cells for T-dependent and -independent antibody responses. We demonstrate that WNK1 transduces signals from the BCR, CXCR5, and CD40, and using intravital imaging, we show that WNK1 regulates migration of naive and activated B cells, and their interactions with T cells. Unexpectedly, we show that WNK1 is required for BCR- and CD40-induced proliferation, acting through the OXSR1 and STK39 kinases, and for efficient B cell-T cell collaboration in vivo. Thus, WNK1 is critical for humoral immune responses, by regulating B cell migration, adhesion, and T cell-dependent activation.

Lateral Diffusion of NKCC1 Contributes to Chloride Homeostasis in Neurons and Is Rapidly Regulated by the WNK Signaling Pathway

An upregulation of the Na⁺-K⁺-2Cl^- cotransporter NKCC1, the main chloride importer in mature neurons, can lead to depolarizing/excitatory responses mediated by GABA type A receptors (GABA_ARs) and, thus, to hyperactivity. Understanding the regulatory mechanisms of NKCC1 would help prevent intra-neuronal chloride accumulation that occurs in pathologies with defective inhibition. The cell mechanisms regulating NKCC1 are poorly understood. Here, we report in mature hippocampal neurons that GABAergic activity controls the membrane diffusion and clustering of NKCC1 via the chloride-sensitive WNK lysine deficient protein kinase 1 (WNK1) and the downstream Ste20 Pro-line Asparagine Rich Kinase (SPAK) kinase that directly phosphorylates NKCC1 on key threonine residues. At rest, this signaling pathway has little effect on intracellular Cl^- concentration, but it participates in the elevation of intraneuronal Cl^- concentration in hyperactivity conditions associated with an up-regulation of NKCC1. The fact that the main chloride exporter, the K⁺-Cl^- cotransporter KCC2, is also regulated in mature neurons by the WNK1 pathway indicates that this pathway will be a target of choice in the pathology.

Diuretic resistance in patients with kidney disease: Challenges and opportunities

Edema caused by kidney disease is called renal edema. Edema is a common symptom of many human kidney diseases. Patients with renal edema often need to take diuretics.However, After taking diuretics, patients with kidney diseases are prone to kidney congestion, decreased renal perfusion, decreased diuretics secreted by renal tubules, neuroendocrine system abnormalities, abnormal ion transporter transport, drug interaction, electrolyte disorder, and hypoproteinemia, which lead to ineffective or weakened diuretic use and increase readmission rate and mortality. The main causes and coping strategies of diuretic resistance in patients with kidney diseases were described in detail in this report. The common causes of DR included poor diet (electrolyte disturbance and hypoproteinemia due to patients' failure to limit diet according to correct sodium, chlorine, potassium, and protein level) and poor drug compliance (the patient did not take adequate doses of diuretics. true resistance occurs only if the patient takes adequate doses of diuretics, but they are not effective), changes in pharmacokinetics and pharmacodynamics, electrolyte disorders, changes in renal adaptation, functional nephron reduction, and decreased renal blood flow. Common treatment measures include increasing in the diuretic dose and/or frequency, sequential nephron blockade,using new diuretics, ultrafiltration treatment, etc. In clinical work, measures should be taken to prevent or delay the occurrence and development of DR in patients with kidney diseases according to the actual situation of patients and the mechanism of various causes. Currently, there are many studies on DR in patients with heart diseases. Although the phenomenon of DR in patients with kidney diseases is common, there is a relatively little overview of the mechanism and treatment strategy of DR in patients with kidney diseases. Therefore, this paper hopes to show the information on DR in patients with kidney diseases to clinicians and researchers and broaden the research direction and ideas to a certain extent.

Molecular Mechanisms of Na-Cl Cotransporter in Relation to Hypertension in Chronic Kidney Disease

Chronic kidney disease (CKD) is a common clinical disease with an increasing incidence, affecting 10 to 15% of the world's population. Hypertension is the most common and modifiable risk factor for preventing adverse cardiovascular outcomes in patients with CKD. A survey from developed countries shows that 47% of hypertensive patients over the age of 20 have uncontrolled blood pressure (BP), and the control rate is even lower in developing countries. CKD is both a common cause of uncontrolled hypertension and a risk factor for altered sequelae. In particular, studies have demonstrated that abnormal blood-pressure patterns in CKD patients, such as non-dipping-blood-pressure patterns, are associated with a significantly increased risk of cardiovascular (CV) disease. The distal convoluted tubule (DCT) is a region of the kidney, and although only 5-10% of the sodium (Na⁺) filtered by the glomerulus is reabsorbed by DCT, most studies agree that Na-Cl cotransporter (NCC) in human, rabbit, mouse, and rat kidneys is the most important route of sodium reabsorption across the DCT for maintaining the homeostasis of sodium. The regulation of NCC involves a large and complex network structure, including certain physiological factors, kinases, scaffold proteins, transporter phosphorylation, and other aspects. This regulation network includes various levels. Naturally, cross-talk between the components of this system must occur in order to relay the important signals to the transporter to play its role. Knowledge of the mechanisms regulating NCC activation is critical for understanding and treating hypertension and CKD. Previous studies from our laboratory have investigated the mechanisms through which NCC is activated in several different models. In the following sections, we review the literature on the mechanisms of NCC in relation to hypertension in CKD.

TRPC Channels in the Physiology and Pathophysiology of the Renal Tubular System: What Do We Know?

The study of transient receptor potential (TRP) channels has dramatically increased during the past few years. TRP channels function as sensors and effectors in the cellular adaptation to environmental changes. Here, we review literature investigating the physiological and pathophysiological roles of TRPC channels in the renal tubular system with a focus on TRPC3 and TRPC6. TRPC3 plays a key role in Ca²⁺ homeostasis and is involved in transcellular Ca²⁺ reabsorption in the proximal tubule and the collecting duct. TRPC3 also conveys the osmosensitivity of principal cells of the collecting duct and is implicated in vasopressin-induced membrane translocation of AQP-2. Autosomal dominant polycystic kidney disease (ADPKD) can often be attributed to mutations of the PKD2 gene. TRPC3 is supposed to have a detrimental role in ADPKD-like conditions. The tubule-specific physiological functions of TRPC6 have not yet been entirely elucidated. Its pathophysiological role in ischemia-reperfusion injuries is a subject of debate. However, TRPC6 seems to be involved in tumorigenesis of renal cell carcinoma. In summary, TRPC channels are relevant in multiples conditions of the renal tubular system. There is a need to further elucidate their pathophysiology to better understand certain renal disorders and ultimately create new therapeutic targets to improve patient care.

WNK3 kinase maintains neuronal excitability by reducing inwardly rectifying K+ conductance in layer V pyramidal neurons of mouse medial prefrontal cortex

The with-no-lysine (WNK) family of serine-threonine kinases and its downstream kinases of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and oxidative stress-responsive kinase-1 (OSR1) may regulate intracellular Cl− homeostasis through phosphorylation of cation-Cl− co-transporters. WNK3 is expressed in fetal and postnatal brains, and its expression level increases during development. Its roles in neurons, however, remain uncertain. Using WNK3 knockout (KO) mice, we investigated the role of WNK3 in the regulation of the intracellular Cl− concentration ([Cl−]i) and the excitability of layer V pyramidal neurons in the medial prefrontal cortex (mPFC). Gramicidin-perforated patch-clamp recordings in neurons from acute slice preparation at the postnatal day 21 indicated a significantly depolarized reversal potential for GABAA receptor-mediated currents by 6 mV, corresponding to the higher [Cl−]i level by ~4 mM in KO mice than in wild-type littermates. However, phosphorylation levels of SPAK and OSR1 and those of neuronal Na+-K+-2Cl− co-transporter NKCC1 and K+-Cl− co-transporter KCC2 did not significantly differ between KO and wild-type mice. Meanwhile, the resting membrane potential of neurons was more hyperpolarized by 7 mV, and the minimum stimulus current necessary for firing induction was increased in KO mice. These were due to an increased inwardly rectifying K+ (IRK) conductance, mediated by classical inwardly rectifying (Kir) channels, in KO neurons. The introduction of an active form of WNK3 into the recording neurons reversed these changes. The potential role of KCC2 function in the observed changes of KO neurons was investigated by applying a selective KCC2 activator, CLP290. This reversed the enhanced IRK conductance in KO neurons, indicating that both WNK3 and KCC2 are intimately linked in the regulation of resting K+ conductance. Evaluation of synaptic properties revealed that the frequency of miniature excitatory postsynaptic currents (mEPSCs) was reduced, whereas that of inhibitory currents (mIPSCs) was slightly increased in KO neurons. Together, the impact of these developmental changes on the membrane and synaptic properties was manifested as behavioral deficits in pre-pulse inhibition, a measure of sensorimotor gating involving multiple brain regions including the mPFC, in KO mice. Thus, the basal function of WNK3 would be the maintenance and/or development of both intrinsic and synaptic excitabilities.

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.

An update regarding the role of WNK kinases in cancer

Mammalian WNK kinases (WNKs) are serine/threonine kinases that contain four members, WNK1-4. They function to maintain ion homeostasis and regulate blood pressure in mammals. Recent studies have revealed that the dysregulation of WNKs contributes to tumor growth, metastasis, and angiogenesis through complex mechanisms, especially through phosphorylating kinase substrates SPS1-related proline/alanine-rich kinase (SPAK) and oxidative stress-responsive kinase 1 (OSR1). Here, we review and discuss the relationships between WNKs and several key factors/biological processes in cancer, including ion channels, cation chloride cotransporters, sodium bicarbonate cotransporters, signaling pathways, angiogenesis, autophagy, and non-coding RNAs. In addition, the potential drugs for targeting WNK-SPAK/OSR1 signaling have also been discussed. This review summarizes and discusses knowledge of the roles of WNKs in cancer, which provides a comprehensive reference for future studies.

The Post-Translational Modification Networking in WNK-Centric Hypertension Regulation and Electrolyte Homeostasis

The with-no-lysine (WNK) kinase family, comprising four serine-threonine protein kinases (WNK1-4), were first linked to hypertension due to their mutations in association with pseudohypoaldosteronism type II (PHAII). WNK kinases regulate crucial blood pressure regulators, SPAK/OSR1, to mediate the post-translational modifications (PTMs) of their downstream ion channel substrates, such as sodium chloride co-transporter (NCC), epithelial sodium chloride (ENaC), renal outer medullary potassium channel (ROMK), and Na/K/2Cl co-transporters (NKCCs). In this review, we summarize the molecular pathways dysregulating the WNKs and their downstream target renal ion transporters. We summarize each of the genetic variants of WNK kinases and the small molecule inhibitors that have been discovered to regulate blood pressure via WNK-triggered PTM cascades.

Synaptotagmin 1-mediated cell membrane penetration and dopamine release enhancement by latroeggtoxin-VI

Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin mined from the egg transcriptome of spider L. tredecimguttatus, was previously found to promote the release of dopamine from PC12 cells. However, the relevant molecular mechanism has not been fully clear. Here LETX-VI was demonstrated to rapidly penetrate the plasma membrane of PC12 cells via the vesicle exocytosis/endocytosis cycle, during which vesicular transmembrane protein synaptotagmin 1 (Syt1) functions as a receptor, with its vesicle luminal domain interacting with the C-terminal region of LETX-VI. The C-terminal sequence of LETX-VI is the functional region for both entering cells and promoting dopamine release. After gaining entry into the PC12 cells, LETX-VI down-regulated the phosphorylation levels of Syt1 at T201 and T195, thereby facilitating vesicle fusion with plasma membrane and thus promoting dopamine release. The relevant mechanism analysis indicated that LETX-VI has a protein phosphatase 2A (PP2A) activator activity. The present work has not only probed into the Syt1-mediated action mechanism of LETX-VI, but also revealed the structure-function relationship of the toxin, thus suggesting its potential applications in the drug transmembrane delivery and treatment of the diseases related to dopamine release and PP2A activity deficiency.

WNK1 collaborates with TGF-β in endothelial cell junction turnover and angiogenesis

Angiogenesis is essential for growth of new blood vessels, remodeling existing vessels, and repair of damaged vessels, and these require reorganization of endothelial cell-cell junctions through a partial endothelial-mesenchymal transition. Homozygous disruption of the gene encoding the protein kinase WNK1 results in lethality in mice near embryonic day (E) 12 due to impaired angiogenesis. This angiogenesis defect can be rescued by endothelial-specific expression of an activated form of the WNK1 substrate kinase OSR1. We show that inhibition of WNK1 kinase activity not only prevents sprouting of endothelial cells from aortic slices but also vessel extension in inhibitor-treated embryos ex vivo. Mutations affecting TGF-β signaling also result in abnormal vascular development beginning by E10 and, ultimately, embryonic lethality. Previously, we demonstrated cross-talk of WNK1 with TGF-β-regulated SMAD signaling, and OSR1 was identified as a component of the TGF-β interactome. However, molecular events jointly regulated by TGF-β and WNK1/OSR1 have not been delineated. Here, we show that inhibition of WNK1 promotes TGF-β-dependent degradation of the tyrosine kinase receptor AXL, which is involved in TGF-β-mediated cell migration and angiogenesis. We also show that interaction between OSR1 and occludin, a protein associated with endothelial tight junctions, is an essential step to enable tight junction turnover. Furthermore, we show that these phenomena are WNK1 dependent, and sensitive to TGF-β. These findings demonstrate intimate connections between WNK1/OSR1 and multiple TGF-β-sensitive molecules controlling angiogenesis and suggest that WNK1 may modulate many TGF-β-regulated functions.

WNK1 in Malignant Behaviors: A Potential Target for Cancer?

Metastasis is the major cause of mortality in cancer patients. Analyses of mouse models and patient data have implicated the protein kinase WNK1 as one of a handful of genes uniquely linked to a subset of invasive cancers. WNK1 signaling pathways are widely implicated in the regulation of ion co-transporters and in controlling cell responses to osmotic stress. In this review we will discuss its actions in tumor malignancy in human cancers and present evidence for its function in invasion, migration, angiogenesis and mesenchymal transition.

The Less Well-Known Little Brothers: The SLC9B/NHA Sodium Proton Exchanger Subfamily—Structure, Function, Regulation and Potential Drug-Target Approaches

The SLC9 gene family encodes Na+/H+ exchangers (NHEs), a group of membrane transport proteins critically involved in the regulation of cytoplasmic and organellar pH, cell volume, as well as systemic acid-base and volume homeostasis. NHEs of the SLC9A subfamily (NHE 1–9) are well-known for their roles in human physiology and disease. Much less is known about the two members of the SLC9B subfamily, NHA1 and NHA2, which share higher similarity to prokaryotic NHEs than the SLC9A paralogs. NHA2 (also known as SLC9B2) is ubiquitously expressed and has recently been shown to participate in renal blood pressure and electrolyte regulation, insulin secretion and systemic glucose homeostasis. In addition, NHA2 has been proposed to contribute to the pathogenesis of polycystic kidney disease, the most common inherited kidney disease in humans. NHA1 (also known as SLC9B1) is mainly expressed in testis and is important for sperm motility and thus male fertility, but has not been associated with human disease thus far. In this review, we present a summary of the structure, function and regulation of expression of the SLC9B subfamily members, focusing primarily on the better-studied SLC9B paralog, NHA2. Furthermore, we will review the potential of the SLC9B subfamily as drug targets.

UBR5 is a novel regulator of WNK1 stability

The with no lysine (K) 1 (WNK1) protein kinase maintains cellular ion homeostasis in many tissues through actions on ion cotransporters and channels. Increased accumulation of WNK1 protein leads to pseudohypoaldosteronism type II (PHAII), a form of familial hypertension. WNK1 can be degraded via its adaptor-dependent recruitment to the Cullin3-RBX1 E3 ligase complex by the ubiquitin-proteasome system. Disruption of this process also leads to disease. To determine if this is the primary mechanism of WNK1 turnover, we examined WNK1 protein stability and degradation by measuring its rate of decay after blockade of translation. Here, we show that WNK1 protein degradation exhibits atypical kinetics in Hela cells. Consistent with this apparent complexity, we found that multiple degradative pathways can modulate cellular WNK1 protein amount. WNK1 protein is degraded not only by the proteasome, but also by the lysosome. Non-lysosomal cysteine proteases calpain and caspases also influence WNK1 degradation, as inhibitors of these proteases modestly increased WNK1 protein expression. Importantly, we discovered that the E3 ubiquitin ligase UBR5 interacts with WNK1 and its deficiency results in increased WNK1 protein. Our results further demonstrate that increased WNK1 in UBR5-depleted cells is attributable to reduced lysosomal degradation of WNK1 protein. Taken together, our findings provide insights into the multiplicity of degradative pathways involved in WNK1 turnover and uncover UBR5 as a previously unknown regulator of WNK1 protein stability that leads to lysosomal degradation of WNK1 protein.

Discovery of potential competitive inhibitors against With-No-Lysine kinase 1 for treating hypertension by virtual screening, inverse pharmacophore-based lead optimization, and molecular dynamics simulations

The With-No-Lysine (WNK) has received attention because of its involvement in hypertension. Genetic mutation in the genes of WNK, leading to its overexpression, has been reported in Familial Hyperkalaemic Hypertension, and thus WNK is considered a potential drug target. Herein, we have performed a high-throughput virtual screening of ~11,000 compounds, mainly the natural phytochemical compounds and kinase inhibitory libraries, to find potential competitive inhibitors against WNK1. Initially, candidates with a docking score of ~ -10.0 kcal/mol or less were selected to further screen their good pharmacological properties by applying absorption, distribution, metabolism, excretion, and toxicity (ADMET). Finally, six docked compounds bearing appreciable binding affinities and WNK1 selectivity were complimented with 500 ns long all-atom molecular dynamic simulations. Subsequently, the MMPBSA scheme (Molecular Mechanics Poisson Boltzmann Surface Area) suggested three phytochemical compounds, C00000947, C00020451, and C00005031, with favourable binding affinity against WNK1. Among them, C00000947 acts as the most potent competitive inhibitor of WNK1. Further, inverse pharmacophore-based lead optimization of the C00000947 leads to one potential compound, meciadanol, which shows better binding affinity and specificity than C00000947 towards WNK1, which may be further exploited to develop effective therapeutics against WNK1-associated hypertension after in vitro and in vivo validation.

Genome-wide identification and evolution of WNK kinases in Bambusoideae and transcriptional profiling during abiotic stress in Phyllostachys edulis

With-no-lysine (WNK) kinases play vital roles in abiotic stress response, circadian rhythms, and regulation of flowering time in rice, Arabidopsis, and Glycine max. However, there are no previous reports of WNKs in the Bambusoideae, although genome sequences are available for diploid, tetraploid, and hexaploid bamboo species. In the present study, we identified 41 WNK genes in five bamboo species and analysed gene evolution, phylogenetic relationship, physical and chemical properties, cis-elements, and conserved motifs. We predicted the structure of PeWNK proteins of moso bamboo and determined the exposed, buried, structural and functional amino acids. Real-time qPCR analysis revealed that PeWNK5, PeWNK7, PeWNK8, and PeWNK11 genes are involved in circadian rhythms. Analysis of gene expression of different organs at different developmental stages revealed that PeWNK genes are tissue-specific. Analysis of various abiotic stress transcriptome data (drought, salt, SA, and ABA) revealed significant gene expression levels in all PeWNKs except PeWNK11. In particular, PeWNK8 and PeWNK9 were significantly down- and up-regulated, respectively, after abiotic stress treatment. A co-expression network of PeWNK genes also showed that PeWNK2, PeWNK4, PeWNK7, and PeWNK8 were co-expressed with transcriptional regulators related to abiotic stress. In conclusion, our study identified the PeWNKs of moso bamboo involved in circadian rhythms and abiotic stress response. In addition, this study serves as a guide for future functional genomic studies of the WNK genes of the Bambusoideae.

Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology

Regulated Na⁺ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na⁺ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na⁺ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K⁺, Ca⁺⁺, Mg⁺⁺, Cl^-, and HCO₃^-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na⁺ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na⁺ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na⁺ and K⁺ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K⁺ concentrations are involved in the reciprocal regulation of Na⁺-Cl^- cotransporter (NCC) and ENaC activity to adjust renal K⁺ secretion to dietary intake.

With no lysine kinases: the key regulatory networks and phytohormone cross talk in plant growth, development and stress response

With No Lysine kinases (WNKs) are a distinct family of Serine/Threonine protein kinase with unique arrangement of catalytic residues in kinase domain. In WNK, an essential catalytic lysine requisite for attaching ATP and phosphorylation reaction is located in subdomain I, instead of subdomain II, which is essentially a typical feature of other Ser/Thr kinases. WNKs are identified in diverse organisms including multicellular and unicellular organisms. Mammalian WNKs are well characterized at structural and functional level, while plant WNKs are not explored much except few recent studies. Plant WNKs role in various physiological processes viz. ion maintenance, osmotic stress, pH homeostasis, circadian rhythms, regulation of flowering time, proliferation and organ development, and abiotic stresses are known, but the mechanisms involved are unclear. Plant WNKs are known to be involved in enhanced drought and salt stress response via ABA-signaling pathway, but the complete signaling cascade is yet to be elucidated. The current review will discuss the interplay between WNKs and growth regulators and their cross talks in plant growth and development. We have also highlighted the link between the stress phytohormones and WNK members in regulating abiotic stress responses in plants. The present review will provide an overall known mechanism on the involvement of WNKs in plant growth and development and abiotic stress response and highlight its role/applications in the development of stress-tolerant plants.

Upstream Open Reading Frame Mediated Translation of WNK8 Is Required for ABA Response in Arabidopsis

With no lysine (K) (WNK) kinases comprise a family of serine/threonine kinases belonging to an evolutionary branch of the eukaryotic kinome. These special kinases contain a unique active site and are found in a wide range of eukaryotes. The model plant Arabidopsis has been reported to have 11 WNK members, of which WNK8 functions as a negative regulator of abscisic acid (ABA) signaling. Here, we found that the expression of WNK8 is post-transcriptionally regulated through an upstream open reading frame (uORF) found in its 5′ untranslated region (5′-UTR). This uORF has been predicted to encode a conserved peptide named CPuORF58 in both monocotyledons and dicotyledons. The analysis of the published ribosome footprinting studies and the study of the frameshift CPuORF58 peptide with altered repression capability suggested that this uORF causes ribosome stalling. Plants transformed with the native WNK8 promoter driving WNK8 expression were comparable with wild-type plants, whereas the plants transformed with a similar construct with mutated CPuORF58 start codon were less sensitive to ABA. In addition, WNK8 and its downstream target RACK1 were found to synergistically coordinate ABA signaling rather than antagonistically modulating glucose response and flowering in plants. Collectively, these results suggest that the WNK8 expression must be tightly regulated to fulfill the demands of ABA response in plants.

Inhibiting with-no-lysine kinases enhances K+/Cl- cotransporter 2 activity and limits status epilepticus

First-in-line benzodiazepine treatment fails to terminate seizures in about 30% of epilepsy patients, highlighting a need for novel antiseizure strategies. Impaired GABAergic inhibition is key to the development of such benzodiazepine-resistant seizures, as well as the pathophysiology of status epilepticus (SE). It is emerging that reduced or impaired neuronal K+/Cl- cotransporter 2 (KCC2) activity contributes to deficits in γ-aminobutyric acid (GABA)-mediated inhibition and increased seizure vulnerability. The with-no-lysine kinase (WNK)-STE20/SPS1-related proline/alanine-rich (SPAK) kinase signaling pathway inhibits neuronal KCC2 via KCC2-T1007 phosphorylation. A selective WNK kinase inhibitor, WNK463, was recently synthesized by Novartis. Exploiting WNK463, we test the hypothesis that pharmacological WNK inhibition will enhance KCC2 activity, increase the efficacy of GABAergic inhibition, and thereby limit seizure activity in animal models. Immunoprecipitation and Western blot analysis were used to examine WNK463's effects on KCC2-T1007 phosphorylation, in vitro and in vivo. A thallium (Tl+) uptake assay was used in human embryonic kidney (HEK-293) cells expressing KCC2 to test WNK463's effects on KCC2-mediated Tl+ transport. Gramicidin-perforated- and whole-cell patch-clamp recordings in cortical rat neurons were used to examine WNK463's effects on KCC2-mediated Cl- transport. In mouse brain slices (entorhinal cortex), field recordings were utilized to examine WNK463's effects on 4-aminopyridine-induced seizure activity. Last, WNK463 was directly deliver to the mouse hippocampus in vivo and tested in a kainic acid model of diazepam-resistant SE. WNK463 significantly reduces KCC2-T1007 phosphorylation in vitro and in vivo (mice). In human embryonic kidney 293 (HEK-293) cells expressing KCC2, WNK463 greatly enhanced the rates Tl+ transport. However, the drug did not enhance Tl+ transport in cells expressing a KCC2-phospho null T1007 mutant. In cultured rat neurons, WNK463 rapidly reduced intracellular Cl- and consequently hyperpolarized the Cl- reversal potential (EGABA). In mature neurons that were artificially loaded with 30 mM Cl-, WNK463 significantly enhanced KCC2-mediated Cl- export and hyperpolarized EGABA. In a 4-aminopyridine model of acute seizures, WNK463 reduced the frequency and number of seizure-like events (SLEs). Finally, in an in vivo kainic acid (KA) model of diazepam-resistant SE, WNK463 slowed the onset and reduced the severity of KA-induced status epilepticus. Last, WNK463 prevented the development of pharmaco-resistance to diazepam in drug-treated mice. Our findings demonstrate that acute WNK463 treatment potentiates KCC2 activity in neurons and limits seizure burden in two well-established models of seizures and epilepsy. Our work suggests that agents which act to increase KCC2 activity may be useful adjunct therapeutics to alleviate diazepam-resistant SE.

Axon morphogenesis and maintenance require an evolutionary conserved safeguard function of Wnk kinases antagonizing Sarm and Axed

The molecular and cellular mechanisms underlying complex axon morphogenesis are still poorly understood. We report a novel, evolutionary conserved function for the Drosophila Wnk kinase (dWnk) and its mammalian orthologs, WNK1 and 2, in axon branching. We uncover that dWnk, together with the neuroprotective factor Nmnat, antagonizes the axon-destabilizing factors D-Sarm and Axundead (Axed) during axon branch growth, revealing a developmental function for these proteins. Overexpression of D-Sarm or Axed results in axon branching defects, which can be blocked by overexpression of dWnk or Nmnat. Surprisingly, Wnk kinases are also required for axon maintenance of adult Drosophila and mouse cortical pyramidal neurons. Requirement of Wnk for axon maintenance is independent of its developmental function. Inactivation of dWnk or mouse Wnk1/2 in mature neurons leads to axon degeneration in the adult brain. Therefore, Wnk kinases are novel signaling components that provide a safeguard function in both developing and adult axons.

Characterization of chemical components with diuretic potential from Pyrrosia petiolosa

Three compounds with diuretic potential were identified from the 95% ethanol extract of Pyrrosia petiolosa (Christ) Ching. Among them, one was a new benzanilide named petiolide A (1), and the other two were phenolic derivatives barbatic acid (2) and kaempferol (3). Their structures were elucidated based on extensive spectral analyses and comparison with the literature data. The docking experiments of all compounds into the active site of the With-No-Lysine kinase 1 (WNK1) domain demonstrated that kaempferol (3) was the most effective component with diuretic potential for its comparative diuretic effect to that of an orally bioavailable WNK inhibitor WNK463 (docking score -10.99 vs -11.09).[Formula: see text].

Chloride sensing by WNK1 regulates NLRP3 inflammasome activation and pyroptosis

The NLRP3 inflammasome mediates the production of proinflammatory cytokines and initiates inflammatory cell death. Although NLRP3 is essential for innate immunity, aberrant NLRP3 inflammasome activation contributes to a wide variety of inflammatory diseases. Understanding the pathways that control NLRP3 activation will help develop strategies to treat these diseases. Here we identify WNK1 as a negative regulator of the NLRP3 inflammasome. Macrophages deficient in WNK1 protein or kinase activity have increased NLRP3 activation and pyroptosis compared with control macrophages. Mice with conditional knockout of WNK1 in macrophages have increased IL-1β production in response to NLRP3 stimulation compared with control mice. Mechanistically, WNK1 tempers NLRP3 activation by balancing intracellular Cl- and K+ concentrations during NLRP3 activation. Collectively, this work shows that the WNK1 pathway has a critical function in suppressing NLRP3 activation and suggests that pharmacological inhibition of this pathway to treat hypertension might have negative clinical implications.

An RNAi screen of the kinome in epithelial follicle cells of the Drosophila melanogaster ovary reveals genes required for proper germline death and clearance

Programmed cell death and cell corpse clearance are an essential part of organismal health and development. Cell corpses are often cleared away by professional phagocytes such as macrophages. However, in certain tissues, neighboring cells known as nonprofessional phagocytes can also carry out clearance functions. Here, we use the Drosophila melanogaster ovary to identify novel genes required for clearance by nonprofessional phagocytes. In the Drosophila ovary, germline cells can die at multiple time points. As death proceeds, the epithelial follicle cells act as phagocytes to facilitate the clearance of these cells. We performed an unbiased kinase screen to identify novel proteins and pathways involved in cell clearance during two death events. Of 224 genes examined, 18 demonstrated severe phenotypes during developmental death and clearance while 12 demonstrated severe phenotypes during starvation-induced cell death and clearance, representing a number of pathways not previously implicated in phagocytosis. Interestingly, it was found that several genes not only affected the clearance process in the phagocytes, but also non-autonomously affected the process by which germline cells died. This kinase screen has revealed new avenues for further exploration and investigation.

Prognostic and Clinical Implications of WNK Lysine Deficient Protein Kinase 1 Expression in Patients With Hepatocellular Carcinoma

BACKGROUND/AIM

Hepatocellular carcinoma (HCC) is a particularly malignant form of cancer prevalent throughout the world; however, there is a pressing need for HCC biomarkers to facilitate prognosis and risk assessment.

PATIENTS AND METHODS

This paper reports on the potential prognostic value of WNK lysine deficient protein kinase 1 (WNK1) in cases of HCC. We analyzed the expression of WNK1 at the mRNA level using omics data from the UALCAN database. We then verified our findings through the immunohistochemical (IHC) staining of various human cancer tissue as well as 59 HCC samples paired with corresponding normal tissues. The prognostic value of mRNA or protein expression by WNK1 was evaluated using the Kaplan-Meier method.

RESULTS

Initial screening results revealed significantly higher WNK1 expression levels in HCC tissue compared to normal tissue. Verification using the paired HCC samples confirmed that the expression of WNK1 was indeed significantly higher in HCC tissue samples than in adjacent normal tissues. High WNK1 expression levels were significantly correlated with clinicopathological variables, including gender and histologic grade. Kaplan-Meier survival analysis revealed that high WNK1 expression levels were associated with poor HCC prognosis. Finally, univariate and multivariate analysis identified WNK1 as a prognostic factor for TNM stage in cases of HCC.

CONCLUSION

In summary, WNK1 is overexpressed at the mRNA and protein levels, and correlated with poor prognosis. Thus, WNK1 expression could potentially be used as a biomarker in HCC prognosis.

Function and Regulation of the Epithelial Na+ Channel ENaC

The Epithelial Na⁺ Channel, ENaC, comprised of 3 subunits (αβγ, or sometimes δβγENaC), plays a critical role in regulating salt and fluid homeostasis in the body. It regulates fluid reabsorption into the blood stream from the kidney to control blood volume and pressure, fluid absorption in the lung to control alveolar fluid clearance at birth and maintenance of normal airway surface liquid throughout life, and fluid absorption in the distal colon and other epithelial tissues. Moreover, recent studies have also revealed a role for sodium movement via ENaC in nonepithelial cells/tissues, such as endothelial cells in blood vessels and neurons. Over the past 25 years, major advances have been made in our understanding of ENaC structure, function, regulation, and role in human disease. These include the recently solved three-dimensional structure of ENaC, ENaC function in various tissues, and mutations in ENaC that cause a hereditary form of hypertension (Liddle syndrome), salt-wasting hypotension (PHA1), or polymorphism in ENaC that contributes to other diseases (such as cystic fibrosis). Moreover, great strides have been made in deciphering the regulation of ENaC by hormones (e.g., the mineralocorticoid aldosterone, glucocorticoids, vasopressin), ions (e.g., Na⁺ ), proteins (e.g., the ubiquitin-protein ligase NEDD4-2, the kinases SGK1, AKT, AMPK, WNKs & mTORC2, and proteases), and posttranslational modifications [e.g., (de)ubiquitylation, glycosylation, phosphorylation, acetylation, palmitoylation]. Characterization of ENaC structure, function, regulation, and role in human disease, including using animal models, are described in this article, with a special emphasis on recent advances in the field. © 2021 American Physiological Society. Compr Physiol 11:1-29, 2021.

Human adenylate kinase 6 regulates WNK1 (with no lysine kinase-1) phosphorylation states and affects ion homeostasis in NT2 cells

Adenylate kinase 6 (AK6), a nucleus localized phosphotransferase in mammalians, shows ubiquitously expression and broad substrate activity in different tissues and cell types. Although the function of AK6 has been extensively studied in different cancer cell lines, its role in mammalian germline is still unknown. Here we showed that knockdown of AK6 inhibits cell proliferation and promotes cell apoptosis in human testicular carcinoma (NT2 cells). Co-immunoprecipitation experiment and in vitro pull down assay identified WNK1 (with no lysine kinase-1) as one of the AK6 interacting proteins in NT2 cells. Moreover, we found that AK6 regulates the phosphorylation states of WNK1 (Thr60) and affects phosphorylation level of Akt (Ser473) upon hypotonic condition, probably affecting chloride channel and regulating ion transport and homeostasis in NT2 cells and consequently contributing to the decreased cell proliferation rate. In conclusion, AK6 regulates WNK1 phosphorylation states and affects ion homeostasis in NT2 cells. These findings provide new insights into the function of AK6 and WNK1 in human testicular carcinoma. This work also provides foundation for further mechanism study of AK6 in spermatogenesis.

Mutation affecting the conserved acidic WNK1 motif causes inherited hyperkalemic hyperchloremic acidosis

Gain-of-function mutations in with no lysine (K) 1 (WNK1) and WNK4 genes are responsible for familial hyperkalemic hypertension (FHHt), a rare, inherited disorder characterized by arterial hypertension and hyperkalemia with metabolic acidosis. More recently, FHHt-causing mutations in the Kelch-like 3-Cullin 3 (KLHL3-CUL3) E3 ubiquitin ligase complex have shed light on the importance of WNK's cellular degradation on renal ion transport. Using full exome sequencing for a 4-generation family and then targeted sequencing in other suspected cases, we have identified new missense variants in the WNK1 gene clustering in the short conserved acidic motif known to interact with the KLHL3-CUL3 ubiquitin complex. Affected subjects had an early onset of a hyperkalemic hyperchloremic phenotype, but normal blood pressure values"Functional experiments in Xenopus laevis oocytes and HEK293T cells demonstrated that these mutations strongly decrease the ubiquitination of the kidney-specific isoform KS-WNK1 by the KLHL3-CUL3 complex rather than the long ubiquitous catalytically active L-WNK1 isoform. A corresponding CRISPR/Cas9 engineered mouse model recapitulated both the clinical and biological phenotypes. Renal investigations showed increased activation of the Ste20 proline alanine-rich kinase-Na+-Cl- cotransporter (SPAK-NCC) phosphorylation cascade, associated with impaired ROMK apical expression in the distal part of the renal tubule. Together, these new WNK1 genetic variants highlight the importance of the KS-WNK1 isoform abundance on potassium homeostasis.

Targeting the WNK-SPAK/OSR1 Pathway and Cation-Chloride Cotransporters for the Therapy of Stroke

Stroke is one of the major culprits responsible for morbidity and mortality worldwide, and the currently available pharmacological strategies to combat this global disease are scanty. Cation-chloride cotransporters (CCCs) are expressed in several tissues (including neurons) and extensively contribute to the maintenance of numerous physiological functions including chloride homeostasis. Previous studies have implicated two CCCs, the Na+-K+-Cl- and K+-Cl- cotransporters (NKCCs and KCCs) in stroke episodes along with their upstream regulators, the with-no-lysine kinase (WNKs) family and STE20/SPS1-related proline/alanine rich kinase (SPAK) or oxidative stress response kinase (OSR1) via a signaling pathway. As the WNK-SPAK/OSR1 pathway reciprocally regulates NKCC and KCC, a growing body of evidence implicates over-activation and altered expression of NKCC1 in stroke pathology whilst stimulation of KCC3 during and even after a stroke event is neuroprotective. Both inhibition of NKCC1 and activation of KCC3 exert neuroprotection through reduction in intracellular chloride levels and thus could be a novel therapeutic strategy. Hence, this review summarizes the current understanding of functional regulations of the CCCs implicated in stroke with particular focus on NKCC1, KCC3, and WNK-SPAK/OSR1 signaling and discusses the current and potential pharmacological treatments for stroke.

WNK4 kinase: from structure to physiology

With no lysine kinase-4 (WNK4) belongs to a serine-threonine kinase family characterized by the atypical positioning of its catalytic lysine. Despite the fact that WNK4 has been found in many tissues, the majority of its study has revolved around its function in the kidney, specifically as a positive regulator of the thiazide-sensitive NaCl cotransporter (NCC) in the distal convoluted tubule of the nephron. This is explained by the description of gain-of-function mutations in the gene encoding WNK4 that causes familial hyperkalemic hypertension. This disease is mainly driven by increased downstream activation of the Ste20/SPS1-related proline-alanine-rich kinase/oxidative stress responsive kinase-1-NCC pathway, which increases salt reabsorption in the distal convoluted tubule and indirectly impairs renal K⁺ secretion. Here, we review the large volume of information that has accumulated about different aspects of WNK4 function. We first review the knowledge on WNK4 structure and enumerate the functional domains and motifs that have been characterized. Then, we discuss WNK4 physiological functions based on the information obtained from in vitro studies and from a diverse set of genetically modified mouse models with altered WNK4 function. We then review in vitro and in vivo evidence on the different levels of regulation of WNK4. Finally, we go through the evidence that has suggested how different physiological conditions act through WNK4 to modulate NCC activity.

Characterizing an allosteric inhibitor-induced inactive state in with-no-lysine kinase 1 using Gaussian accelerated molecular dynamics simulations

The binding of an allosteric inhibitor in WNK1 leads to the inactive state.

Physiological Processes Modulated by the Chloride-Sensitive WNK-SPAK/OSR1 Kinase Signaling Pathway and the Cation-Coupled Chloride Cotransporters

The role of Cl^– as an intracellular signaling ion has been increasingly recognized in recent years. One of the currently best described roles of Cl^– in signaling is the modulation of the With-No-Lysine (K) (WNK) – STE20-Proline Alanine rich Kinase (SPAK)/Oxidative Stress Responsive Kinase 1 (OSR1) – Cation-Coupled Cl^–Cotransporters (CCCs) cascade. Binding of a Cl^– anion to the active site of WNK kinases directly modulates their activity, promoting their inhibition. WNK activation due to Cl^– release from the binding site leads to phosphorylation and activation of SPAK/OSR1, which in turn phosphorylate the CCCs. Phosphorylation by WNKs-SPAK/OSR1 of the Na⁺-driven CCCs (mediating ions influx) promote their activation, whereas that of the K⁺-driven CCCs (mediating ions efflux) promote their inhibition. This results in net Cl^– influx and feedback inhibition of WNK kinases. A wide variety of alterations to this pathway have been recognized as the cause of several human diseases, with manifestations in different systems. The understanding of WNK kinases as Cl^– sensitive proteins has allowed us to better understand the mechanistic details of regulatory processes involved in diverse physiological phenomena that are reviewed here. These include cell volume regulation, potassium sensing and intracellular signaling in the renal distal convoluted tubule, and regulation of the neuronal response to the neurotransmitter GABA.

Critical role of WNK1 in MYC-dependent early mouse thymocyte development

WNK1, a kinase that controls kidney salt homeostasis, also regulates adhesion and migration in CD4⁺ T cells. Wnk1 is highly expressed in thymocytes, and since migration is important for thymocyte maturation, we investigated a role for WNK1 in mouse thymocyte development. We find that WNK1 is required for the transition of double negative (DN) thymocytes through the β-selection checkpoint and subsequent proliferation and differentiation into double positive (DP) thymocytes. Furthermore, we show that WNK1 negatively regulates LFA1-mediated adhesion and positively regulates CXCL12-induced migration in DN thymocytes. Despite this, migration defects of WNK1-deficient thymocytes do not account for the developmental arrest. Instead, we show that in DN thymocytes WNK1 transduces pre-TCR signals via OXSR1 and STK39 kinases, and the SLC12A2 ion co-transporter that are required for post-transcriptional upregulation of MYC and subsequent proliferation and differentiation into DP thymocytes. Thus, a pathway regulating ion homeostasis is a critical regulator of thymocyte development.

Kinase Interaction Network Expands Functional and Disease Roles of Human Kinases

Protein kinases are essential for signal transduction and control of most cellular processes, including metabolism, membrane transport, motility, and cell cycle. Despite the critical role of kinases in cells and their strong association with diseases, good coverage of their interactions is available for only a fraction of the 535 human kinases. Here, we present a comprehensive mass-spectrometry-based analysis of a human kinase interaction network covering more than 300 kinases. The interaction dataset is a high-quality resource with more than 5,000 previously unreported interactions. We extensively characterized the obtained network and were able to identify previously described, as well as predict new, kinase functional associations, including those of the less well-studied kinases PIM3 and protein O-mannose kinase (POMK). Importantly, the presented interaction map is a valuable resource for assisting biomedical studies. We uncover dozens of kinase-disease associations spanning from genetic disorders to complex diseases, including cancer.