Generation of WNK1 knockout cell lines by CRISPR/Cas-mediated genome editing

Inhibition of WNK Kinases in NK Cells Disrupts Cellular Osmoregulation and Control of Tumor Metastasis

INTRODUCTION

The serine/threonine with-no-lysine (WNK) kinase family function in blood pressure control, electrolyte homeostasis, and cellular osmoregulation. These kinases and their downstream effectors are considered promising therapeutic targets in hypertension and stroke. However, the role of WNK kinases in immune cells remains poorly understood.

METHODS

Using the small-molecule WNK kinase inhibitors WNK463 and WNK-IN-11, we investigated how WNK kinase inhibition affects natural killer (NK) cell physiology.

RESULTS

WNK kinase inhibition with WNK463 or WNK-IN-11 significantly decreased IL-2-activated NK cell volume, motility, and cytolytic activity. Treatment of NK cells with these inhibitors induced autophagy by activating AMPK and inhibiting mTOR signaling. Moreover, WNK kinase inhibition increased phosphorylation of Akt and c-Myc by misaligning activity of activating kinases and inhibitory phosphatases. Treatment of tumor-bearing mice with WNK463 impaired tumor metastasis control by adoptively transferred NK cells.

CONCLUSION

The catalytic activity of WNK kinases has a critical role of multiple aspects of NK cell physiology and their pharmacologic inhibition negatively impacts NK cell function.

Molecular Crowding: Physiologic Sensing and Control

The cytoplasm is densely packed with molecules that contribute to its nonideal behavior. Cytosolic crowding influences chemical reaction rates, intracellular water mobility, and macromolecular complex formation. Overcrowding is potentially catastrophic; to counteract this problem, cells have evolved acute and chronic homeostatic mechanisms that optimize cellular crowdedness. Here, we provide a physiology-focused overview of molecular crowding, highlighting contemporary advances in our understanding of its sensing and control. Long hypothesized as a form of crowding-induced microcompartmentation, phase separation allows cells to detect and respond to intracellular crowding through the action of biomolecular condensates, as indicated by recent studies. Growing evidence indicates that crowding is closely tied to cell size and fluid volume, homeostatic responses to physical compression and desiccation, tissue architecture, circadian rhythm, aging, transepithelial transport, and total body electrolyte and water balance. Thus, molecular crowding is a fundamental physiologic parameter that impacts diverse functions extending from molecule to organism.

A missense mutation of the WNK1 gene affects cold tolerance in Chinese domestic cattle

Inclement weather conditions, especially cold stress, have threatened the cattle industry. Cattle exposed to cold environments for a longer time suffer developmental delay, immunity decline, and eventually death. WNK1 is a member of With-no-lysine kinases (WNKs), widely expressed in animal organs and tissues. WNK1 and WNK4 are expressed in adipose tissue, and WNK4 promotes adipogenesis. WNK1 does not directly affect adipogenesis but has been shown to promote WNK4 expression in several tissues or organs. One missense mutation NC_037346.1:g.107692244, A > G, rs208265410 in the WNK1 gene was detected from the database of bovine genomic variation (BGVD). Here, we collected 328 individuals of 17 breeds representing four groups of Chinese cattle, northern group cattle, southern group cattle, central group cattle, and special group cattle (Tibetan cattle). We also collected the temperature and humidity data records from their relative locations. The frequencies of the G allele in Chinese breeds increased from northern China to southern China, and the frequencies of the A allele showed an opposite trend. Our results indicate that the WNK1 gene might be a candidate gene marker associated with cold tolerance.

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.

Intracellular Ion Control of WNK Signaling

The with no lysine (K) (WNK) kinases are an evolutionarily ancient group of kinases with atypical placement of the catalytic lysine and diverse physiological roles. Recent studies have shown that WNKs are directly regulated by chloride, potassium, and osmotic pressure. Here, we review the discovery of WNKs as chloride-sensitive kinases and discuss physiological contexts in which chloride regulation of WNKs has been demonstrated. These include the kidney, pancreatic duct, neurons, and inflammatory cells. We discuss the interdependent relationship of osmotic pressure and intracellular chloride in cell volume regulation. We review the recent demonstration of potassium regulation of WNKs and speculate on possible physiological roles. Finally, structural and mechanistic aspects of intracellular ion and osmotic pressure regulation of WNKs are discussed.

WNK1 is a chloride-stimulated scaffold that regulates mTORC2 activity and ion transport

Mammalian (or mechanistic) target of rapamycin complex 2 (mTORC2) is a kinase complex that targets predominantly Akt family proteins, SGK1 and protein kinase C (PKC), and has well-characterized roles in mediating hormone and growth factor effects on a wide array of cellular processes. Recent evidence suggests that mTORC2 is also directly stimulated in renal tubule cells by increased extracellular K+ concentration, leading to activation of the Na+ channel, ENaC, and increasing the electrical driving force for K+ secretion. We identify here a signaling mechanism for this local effect of K+. We show that an increase in extracellular [K+] leads to a rise in intracellular chloride (Cl-), which stimulates a previously unknown scaffolding activity of the protein 'with no lysine-1' (WNK1) kinase. WNK1 interacts selectively with SGK1 and recruits it to mTORC2, resulting in enhanced SGK1 phosphorylation and SGK1-dependent activation of ENaC. This scaffolding effect of WNK1 is independent of its own kinase activity and does not cause a generalized stimulation of mTORC2 kinase activity. These findings establish a novel WNK1-dependent regulatory mechanism that harnesses mTORC2 kinase activity selectively toward SGK1 to control epithelial ion transport and electrolyte homeostasis.

WNK kinases sense molecular crowding and rescue cell volume via phase separation

When challenged by hypertonicity, dehydrated cells must recover their volume to survive. This process requires the phosphorylation-dependent regulation of SLC12 cation chloride transporters by WNK kinases, but how these kinases are activated by cell shrinkage remains unknown. Within seconds of cell exposure to hypertonicity, WNK1 concentrates into membraneless condensates, initiating a phosphorylation-dependent signal that drives net ion influx via the SLC12 cotransporters to restore cell volume. WNK1 condensate formation is driven by its intrinsically disordered C terminus, whose evolutionarily conserved signatures are necessary for efficient phase separation and volume recovery. This disorder-encoded phase behavior occurs within physiological constraints and is activated in vivo by molecular crowding rather than changes in cell size. This allows kinase activity despite an inhibitory ionic milieu and permits cell volume recovery through condensate-mediated signal amplification. Thus, WNK kinases are physiological crowding sensors that phase separate to coordinate a cell volume rescue response.

Regulation of the p38-MAPK pathway by hyperosmolarity and by WNK kinases

p38-MAPK is a stress-response kinase activated by hyperosmolarity. Here we interrogated the pathways involved. We show that p38-MAPK signaling is activated by hyperosmotic stimulation in various solutions, cell types and colonic organoids. Hyperosmolarity sensing is detected at the level of the upstream activators of p38-MAPK: TRAF2/ASK1 (but not Rac1) and MKK3/6/4. While WNK kinases are known osmo-sensors, we found, unexpectedly, that short (2 h) inhibition of WNKs (with WNK463) led to elevated p38-MAPK activity under hyperosmolarity, which was mediated by WNK463-dependent stimulation of TAK1 or TRAF2/ASK1, the upstream activators of MKK3/6/4. However, this effect was temporary and was reversed by long-term (2 days) incubation with WNK463. Accordingly, 2 days (but not 2 h) inhibition of p38-MAPK or its upstream activators ASK1 or TAK1, or WNKs, diminished regulatory volume increase (RVI) following cell shrinkage under hyperosmolarity. We also show that RVI mediated by the ion transporter NKCC1 is dependent on p38-MAPK. Since WNKs are known activators of NKCC1, we propose a WNK- > NKCC1- > p38-MAPK pathway that controls RVI. This pathway is augmented by NHE1. Additionally, hyperosmolarity inhibited mTORC1 activation and cell proliferation. Thus, activation of p38-MAPK and WNKs is important for RVI and for cell proliferation.

Elevated intracellular Na+ and osmolarity stimulate catalytic activity of the ubiquitin ligase Nedd4-2

Regulation of catalytic activity of E3 ubiquitin ligases is critical for their cellular functions. We identified an unexpected mode of regulation of E3 catalytic activity by ions and osmolarity; enzymatic activity of the HECT family E3 Nedd4-2/Nedd4L is enhanced by increased intracellular Na⁺ ([Na⁺]_i) and by hyperosmolarity. This stimulated activity is mediated by activation of p38-MAPK and is inhibited by WNKs. Moreover, protease (Furin)-mediated activation of the epithelial Na⁺ channel ENaC (a bona fide Nedd4-2 substrate), which leads to increased [Na⁺]_i and osmolarity, results in enhanced Nedd4-2 catalytic activity. This enhancement is inhibited by a Furin inhibitor, by a protease-resistant ENaC mutant, or by treatment with the ENaC inhibitor amiloride. Moreover, WNK inhibition, which stimulates catalytic activity of Nedd4-2, leads to reduced levels of cell-surface ENaC and reduced channel activity. ENaC activity does not affect Nedd4-2:ENaC binding. Therefore, these results demonstrate activation of a ubiquitin ligase by Na⁺ and osmotic changes. Importantly, they reveal a negative feedback loop in which active ENaC leads to stimulation of catalytic activity of its own suppressor, Nedd4-2, to protect cells from excessive Na⁺ loading and hyperosmotic stress and to protect the animal from hypertension.

A Human In Vitro Model to Study Adenoviral Receptors and Virus Cell Interactions

To develop adenoviral cell- or tissue-specific gene delivery, understanding of the infection mechanisms of adenoviruses is crucial. Several adenoviral attachment proteins such as CD46, CAR and sialic acid have been identified and studied. However, most receptor studies were performed on non-human cells. Combining our reporter gene-tagged adenovirus library with an in vitro human gene knockout model, we performed a systematic analysis of receptor usage comparing different adenoviruses side-by-side. The CRISPR/Cas9 system was used to knockout CD46 and CAR in the human lung epithelial carcinoma cell line A549. Knockout cells were infected with 22 luciferase-expressing adenoviruses derived from adenovirus species B, C, D and E. HAdV-B16, -B21 and -B50 from species B1 as well as HAdV-B34 and -B35 were found to be CD46-dependent. HAdV-C5 and HAdV-E4 from species E were found to be CAR-dependent. Regarding cell entry of HAdV-B3 and -B14 and all species D viruses, both CAR and CD46 play a role, and here, other receptors or attachment structures may also be important since transductions were reduced but not completely inhibited. The established human knockout cell model enables the identification of the most applicable adenovirus types for gene therapy and to further understand adenovirus infection biology.

Osmosensing by WNK Kinases

With No Lysine (K) WNK kinases regulate electro-neutral cotransporters that are controlled by osmotic stress and chloride. We showed previously that autophosphorylation of WNK1 is inhibited by chloride, raising the possibility that WNKs are activated by osmotic stress. Here we demonstrate that unphosphorylated WNK isoforms 3 and 1 autophosphorylate in response to osmotic pressure in vitro, applied with the crowding agent polyethylene glycol (PEG)400 or osmolyte ethylene glycol (EG), and that this activation is opposed by chloride. Small angle x-ray scattering of WNK3 in the presence and absence of PEG400, static light scattering in EG, and crystallography of WNK1 were used to understand the mechanism. Osmosensing in WNK3 and WNK1 appears to occur through a conformational equilibrium between an inactive, unphosphorylated, chloride-binding dimer and an autophosphorylation-competent monomer. An improved structure of the inactive kinase domain of WNK1, and a comparison with the structure of a monophosphorylated form of WNK1, suggests that large cavities, greater hydration, and specific bound water may participate in the osmosensing mechanism. Our prior work showed that osmolytes have effects on the structure of phosphorylated WNK1, suggestive of multiple stages of osmotic regulation in WNKs.

WNK1 is an assembly factor for the human ER membrane protein complex

The assembly of nascent proteins into multi-subunit complexes is a tightly regulated process that must occur at high fidelity to maintain cellular homeostasis. The ER membrane protein complex (EMC) is an essential insertase that requires seven membrane-spanning and two soluble cytosolic subunits to function. Here, we show that the kinase with no lysine 1 (WNK1), known for its role in hypertension and neuropathy, functions as an assembly factor for the human EMC. WNK1 uses a conserved amphipathic helix to stabilize the soluble subunit, EMC2, by binding to the EMC2-8 interface. Shielding this hydrophobic surface prevents promiscuous interactions of unassembled EMC2 and directly competes for binding of E3 ubiquitin ligases, permitting assembly. Depletion of WNK1 thus destabilizes both the EMC and its membrane protein clients. This work describes an unexpected role for WNK1 in protein biogenesis and defines the general requirements of an assembly factor that will apply across the proteome.

The Drosophila Malpighian tubule as a model for mammalian tubule function

PURPOSE OF REVIEW

Studies of the genetic model organism, Drosophila melanogaster, have unraveled molecular pathways relevant to human physiology and disease. The Malpighian tubule, the Drosophila renal epithelium, is described here, including tools available to study transport; conserved transporters, channels, and the signaling pathways regulating them; and fly models of kidney stone disease.

RECENT FINDINGS

Tools to measure Malpighian tubule transport continue to advance, including use of a transgenic sensor to quantify intracellular pH and proton fluxes. A recent study generated an RNA-sequencing-based atlas of tissue-specific gene expression, with resulting insights into Malpighian tubule gene expression of transporters and channels. Advances have been made in understanding the molecular physiology of the With No Lysine kinase-Ste20-related proline/alanine rich kinase/oxidative stress response kinase cascade that regulates epithelial ion transport in flies and mammals. New studies in Drosophila kidney stone models have characterized zinc transporters and used Malpighian tubules to study the efficacy of a plant metabolite in decreasing stone burden.

SUMMARY

Study of the Drosophila Malpighian tubule affords opportunities to better characterize the molecular physiology of epithelial transport mechanisms relevant to mammalian renal physiology.

Potassium acts through mTOR to regulate its own secretion

Potassium (K+) secretion by kidney tubule cells is central to electrolyte homeostasis in mammals. In the K+ secretory "principal" cells of the distal nephron, electrogenic Na+ transport by the epithelial sodium channel (ENaC) generates the electrical driving force for K+ transport across the apical membrane. Regulation of this process is attributable in part to aldosterone, which stimulates the gene transcription of the ENaC-regulatory kinase, SGK1. However, a wide range of evidence supports the conclusion that an unidentified aldosterone-independent pathway exists. We show here that in principal cells, K+ itself acts through the type 2 mTOR complex (mTORC2) to activate SGK1, which stimulates ENaC to enhance K+ excretion. The effect depends on changes in K+ concentration on the blood side of the cells, and requires basolateral membrane K+-channel activity. However, it does not depend on changes in aldosterone, or on enhanced distal delivery of Na+ from upstream nephron segments. These data strongly support the idea that K+ is sensed directly by principal cells to stimulate its own secretion by activating the mTORC2-SGK1 signaling module, and stimulate ENaC. We propose that this local effect acts in concert with aldosterone and increased Na+ delivery from upstream nephron segments to sustain K+ homeostasis.

Loss-of-function approaches in comparative physiology: is there a future for knockdown experiments in the era of genome editing?

Loss-of-function technologies, such as morpholino- and RNAi-mediated gene knockdown, and TALEN- and CRISPR/Cas9-mediated gene knockout, are widely used to investigate gene function and its physiological significance. Here, we provide a general overview of the various knockdown and knockout technologies commonly used in comparative physiology and discuss the merits and drawbacks of these technologies with a particular focus on research conducted in zebrafish. Despite their widespread use, there is an ongoing debate surrounding the use of knockdown versus knockout approaches and their potential off-target effects. This debate is primarily fueled by the observations that, in some studies, knockout mutants exhibit phenotypes different from those observed in response to knockdown using morpholinos or RNAi. We discuss the current debate and focus on the discrepancies between knockdown and knockout phenotypes, providing literature and primary data to show that the different phenotypes are not necessarily a direct result of the off-target effects of the knockdown agents used. Nevertheless, given the recent evidence of some knockdown phenotypes being recapitulated in knockout mutants lacking the morpholino or RNAi target, we stress that results of knockdown experiments need to be interpreted with caution. We ultimately argue that knockdown experiments should not be discontinued if proper control experiments are performed, and that with careful interpretation, knockdown approaches remain useful to complement the limitations of knockout studies (e.g. lethality of knockout and compensatory responses).

Role of WNK Kinases in the Modulation of Cell Volume

Ion Transport across the cell membrane is required to maintain cell volume homeostasis. In response to changes in extracellular osmolarity, most cells activate specific metabolic or membrane-transport pathways to respond to cell swelling or shrinkage and return their volume to its normal resting state. This process involves the rapid adjustment of the activities of channels and transporters that mediate flux of K⁺, Na⁺, Cl^-, and small organic osmolytes. Cation chloride cotransporters (CCCs) NKCCs and KCCs are a family of membrane proteins modulated by changes in cell volume and/or in the intracellular chloride concentration ([Cl^-]_i). Cell swelling triggers regulatory volume decrease (RVD), promoting solute and water efflux to restore normal cell volume. Swelling-activated KCCs mediate RVD in most cell types. In contrast, cell shrinkage triggers regulatory volume increase (RVI), which involves the activation of the NKCC1 cotransporter of the CCC family. Regulation of the CCCs during RVI and RVD by protein phosphorylation is a well-characterized mechanism, where WNK kinases and their downstream kinase substrates, SPAK and OSR1 constitute the essential phospho-regulators. WNKs-SPAK/OSR1-CCCs complex is required to regulate cell shrinkage-induced RVI or cell swelling-induced RVD via activating or inhibitory phosphorylation of NKCCs or KCCs, respectively. WNK1 and WNK4 kinases have been established as [Cl^-]_i sensors/regulators, while a role for WNK3 kinase as a cell volume-sensing kinase has emerged and is proposed in this chapter.

Comparative analysis of lipid-mediated CRISPR-Cas9 genome editing techniques

CRISPR-Cas technology has revolutionized genome engineering. While Cas9 was not the first programmable endonuclease identified, its simplicity of use has driven widespread adoption in a short period of time. While CRISPR-Cas genome editing holds enormous potential for clinical applications, its use in laboratory settings for genotype-phenotype studies and genome-wide screens has led to breakthroughs in the understanding of many molecular pathways. Numerous protocols have been described for introducing CRISPR-Cas components into cells, and here we sought to simplify and optimize a protocol for genome editing using readily available and inexpensive tools. We compared plasmid, ribonucleoprotein (RNP), and RNA transfection to determine which was method was most optimal for editing cells in a laboratory setting. We limited our comparison to lipofection-mediated introduction because the reagents are widely available. To facilitate optimization, we developed a novel reporter assay to measure gene disruption and the introduction of a variety of exogenous DNA tags. Each method efficiently disrupted endogenous genes and was able to stimulate the introduction of foreign DNA at specific sites, albeit to varying efficiencies. RNP transfection produced the highest level of gene disruption and was the most rapid and efficient method overall. Finally, we show that very short homology arms of 30 base pairs can mediate site-specific editing. The methods described here should broaden the accessibility of RNP-mediated lipofection for laboratory genome-editing experiments.

Overexpression of WNK1 in POMC-expressing neurons reduces weigh gain via WNK4-mediated degradation of Kir6.2

"With no lysine" (WNK) kinases have been shown to regulate various ion transporters in various tissues, but studies on the function of WNK kinases in the brain have been limited. In this study, we discovered that WNK1 and WNK4 in POMC-expressing neuronal cells in WNK1 overexpressed transgenic mice (WNK1 TG) decrease appetite via degradation of Kir6.2. Weight gain after 20 weeks of age was delayed in WNK1 TG mice as a result of reduced food intake. Expression of WNK1 and proopiomelanocortin (POMC) was higher in POMC-expressing neurons in the hypothalamus of WNK1 TG mice than in WT mice. Immunostaining of serial sections of the hypothalamus revealed that POMC-expressing neurons were smaller in WNK1 TG mice than in WT mice. In addition, expression of Kir6.2 was significantly reduced in WNK1 TG mice. Overexpression and knockdown of WNK4 demonstrated that WNK4 regulates protein expression of Kir6.2 via protein-protein interaction. Accordingly, reduced age-dependent weight gain of WNK1 TG mice seems to be related with the decreased Kir6.2 expression via WNK1- and WNK4-regulated protein stability of Kir6.2.

Potassium-regulated distal tubule WNK bodies are kidney-specific WNK1 dependent

WNK bodies are large punctate membraneless cytosolic signaling foci that sequester WNK serine–threonine kinases and form in renal distal tubular epithelial cells during shifts in total body potassium balance. The assembly of these structures requires KS-WNK1, a truncated isoform of the WNK1 gene that is exclusively expressed in the distal tubule.

With-no-lysine (WNK) kinases coordinate volume and potassium homeostasis by regulating renal tubular electrolyte transport. In the distal convoluted tubule (DCT), potassium imbalance causes WNK signaling complexes to concentrate into large discrete foci, which we call “WNK bodies.” Although these structures have been reported previously, the mechanisms that drive their assembly remain obscure. Here, we show that kidney-specific WNK1 (KS-WNK1), a truncated kinase-defective WNK1 isoform that is highly expressed in the DCT, is critical for WNK body formation. While morphologically distinct WNK bodies were evident in the distal tubules of mice subjected to dietary potassium loading and restriction, KS-WNK1 knockout mice were deficient in these structures under identical conditions. Combining in vivo observations in kidney with reconstitution studies in cell culture, we found that WNK bodies are dynamic membraneless foci that are distinct from conventional organelles, colocalize with the ribosomal protein L22, and cluster the WNK signaling pathway. The formation of WNK bodies requires an evolutionarily conserved cysteine-rich hydrophobic motif harbored within a unique N-terminal exon of KS-WNK1. We propose that WNK bodies are not pathological aggregates, but rather are KS-WNK1–dependent microdomains of the DCT cytosol that modulate WNK signaling during physiological shifts in potassium balance.

Applications of CRISPR/Cas9 in retinal degenerative diseases

Gene therapy is a potentially effective treatment for retinal degenerative diseases. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system has been developed as a new genome-editing tool in ophthalmic studies. Recent advances in researches showed that CRISPR/Cas9 has been applied in generating animal models as well as gene therapy in vivo of retinitis pigmentosa (RP) and leber congenital amaurosis (LCA). It has also been shown as a potential attempt for clinic by combining with other technologies such as adeno-associated virus (AAV) and induced pluripotent stem cells (iPSCs). In this review, we highlight the main points of further prospect of using CRISPR/Cas9 in targeting retinal degeneration. We also emphasize the potential applications of this technique in treating retinal degenerative diseases.

Functional kinomics establishes a critical node of volume-sensitive cation-Cl- cotransporter regulation in the mammalian brain

Cell volume homeostasis requires the dynamically regulated transport of ions across the plasmalemma. While the ensemble of ion transport proteins involved in cell volume regulation is well established, the molecular coordinators of their activities remain poorly characterized. We utilized a functional kinomics approach including a kinome-wide siRNA-phosphoproteomic screen, a high-content kinase inhibitor screen, and a kinase trapping-Orbitrap mass spectroscopy screen to systematically identify essential kinase regulators of KCC3 Thr991/Thr1048 phosphorylation - a key signaling event in cell swelling-induced regulatory volume decrease (RVD). In the mammalian brain, we found the Cl--sensitive WNK3-SPAK kinase complex, required for cell shrinkage-induced regulatory volume decrease (RVI) via the stimulatory phosphorylation of NKCC1 (Thr203/Thr207/Thr212), is also essential for the inhibitory phosphorylation of KCC3 (Thr991/Thr1048). This is mediated in vivo by an interaction between the CCT domain in SPAK and RFXV/I domains in WNK3 and NKCC1/KCC3. Accordingly, genetic or pharmacologic WNK3-SPAK inhibition prevents cell swelling in response to osmotic stress and ameliorates post-ischemic brain swelling through a simultaneous inhibition of NKCC1-mediated Cl- uptake and stimulation of KCC3-mediated Cl- extrusion. We conclude that WNK3-SPAK is an integral component of the long-sought "Cl-/volume-sensitive kinase" of the cation-Cl- cotransporters, and functions as a molecular rheostat of cell volume in the mammalian brain.

WNK Kinases in Development and Disease

WNK (With-No-Lysine (K)) kinases are serine-threonine kinases characterized by an atypical placement of a catalytic lysine within the kinase domain. Mutations in human WNK1 or WNK4 cause an autosomal dominant syndrome of hypertension and hyperkalemia, reflecting the fact that WNK kinases are critical regulators of renal ion transport processes. Here, the role of WNKs in the regulation of ion transport processes in vertebrate and invertebrate renal function, cellular and organismal osmoregulation, and cell migration and cerebral edema will be reviewed, along with emerging literature demonstrating roles for WNKs in cardiovascular and neural development, Wnt signaling, and cancer. Conserved roles for these kinases across phyla are emphasized.

Small-molecule WNK inhibition regulates cardiovascular and renal function

The With-No-Lysine (K) (WNK) kinases play a critical role in blood pressure regulation and body fluid and electrolyte homeostasis. Herein, we introduce the first orally bioavailable pan-WNK-kinase inhibitor, WNK463, that exploits unique structural features of the WNK kinases for both affinity and kinase selectivity. In rodent models of hypertension, WNK463 affects blood pressure and body fluid and electro-lyte homeostasis, consistent with WNK-kinase-associated physiology and pathophysiology.

Investigation of the functional role of human Interleukin-8 gene haplotypes by CRISPR/Cas9 mediated genome editing

Interleukin-8 (IL-8) gene polymorphisms have been considered as susceptibility factors in periodontal disease. However, the functional roles of IL-8 gene haplotypes have not been investigated. Here, we demonstrate for the first time the use of the CRISPR/Cas9 system to engineer the IL-8 gene, and tested the functionality of different haplotypes. Two sgRNAs vectors targeting the IL-8 gene and the naked homologous repair DNA carrying different haplotypes were used to successfully generate HEK293T cells carrying the AT genotype at the first SNP - rs4073 (alias -251), TT genotype at the second SNP - rs2227307 (alias +396), TC or CC genotypes at the third SNP - rs2227306 (alias +781) at the IL-8 locus. When stimulated with Poly I:C, ATC/TTC haplotype, cells significantly up-regulated the IL-8 at both transcriptional and translational levels. To test whether ATC/TTC haplotype is functional, we used a trans-well assay to measure the transmigration of primary neutrophils incubated with supernatants from the Poly I:C stimulation experiment. ATC/TTC haplotype cells significantly increased transmigration of neutrophils confirming the functional role for this IL-8 haplotype. Taken together, our data provides evidence that carriage of the ATC/TTC haplotype in itself may increase the influx of neutrophils in inflammatory lesions and influence disease susceptibility.

Hypertension: the missing WNKs

The With no Lysine [K] (WNK) family of enzymes are central in the regulation of blood pressure. WNKs have been implicated in hereditary hypertension disorders, mainly through control of the activity and levels of ion cotransporters and channels. Actions of WNKs in the kidney have been heavily investigated, and recent studies have provided insight into not only the regulation of these enzymes but also how mutations in WNKs and their interacting partners contribute to hypertensive disorders. Defining the roles of WNKs in the cardiovascular system will provide clues about additional mechanisms by which WNKs can regulate blood pressure. This review summarizes recent developments in the regulation of the WNK signaling cascade and its role in regulation of blood pressure.

Mitogen-activated protein kinases as key players in osmotic stress signaling

BACKGROUND

Osmotic stress arises from the difference between intracellular and extracellular osmolality. It induces cell swelling or shrinkage as a consequence of water influx or efflux, which threatens cellular activities. Mitogen-activated protein kinases (MAPKs) play central roles in signaling pathways in osmotic stress responses, including the regulation of intracellular levels of inorganic ions and organic osmolytes.

SCOPE OF REVIEW

The present review summarizes the cellular osmotic stress response and the function and regulation of the vertebrate MAPK signaling pathways involved. We also describe recent findings regarding apoptosis signal-regulating kinase 3 (ASK3), a MAP3K member, to demonstrate its regulatory effects on signaling molecules beyond MAPKs.

MAJOR CONCLUSIONS

MAPKs are rapidly activated by osmotic stress and have diverse roles, such as cell volume regulation, gene expression, and cell survival/death. There is significant cell type specificity in the function and regulation of MAPKs. Based on its activity change during osmotic stress and its regulation of the WNK1-SPAK/OSR1 pathway, ASK3 is expected to play important roles in osmosensing mechanisms and cellular functions related to osmoregulation.

GENERAL SIGNIFICANCE

MAPKs are essential for various cellular responses to osmotic stress; thus, the identification of the upstream regulators of MAPK pathways will provide valuable clues regarding the cellular osmosensing mechanism, which remains elusive in mammals. The elucidation of in vivo MAPK functions is also important because osmotic stress in physiological and pathophysiological conditions often results from changes in the intracellular osmolality. These studies potentially contribute to the establishment of therapeutic strategies against diseases that accompany osmotic perturbation.

Cell-specific regulation of L-WNK1 by dietary K

Flow-induced K(+) secretion in the aldosterone-sensitive distal nephron is mediated by high-conductance Ca(2+)-activated K(+) (BK) channels. Familial hyperkalemic hypertension (pseudohypoaldosteronism type II) is an inherited form of hypertension with decreased K(+) secretion and increased Na(+) reabsorption. This disorder is linked to mutations in genes encoding with-no-lysine kinase 1 (WNK1), WNK4, and Kelch-like 3/Cullin 3, two components of an E3 ubiquitin ligase complex that degrades WNKs. We examined whether the full-length (or "long") form of WNK1 (L-WNK1) affected the expression of BK α-subunits in HEK cells. Overexpression of L-WNK1 promoted a significant increase in BK α-subunit whole cell abundance and functional channel expression. BK α-subunit abundance also increased with coexpression of a kinase dead L-WNK1 mutant (K233M) and with kidney-specific WNK1 (KS-WNK1), suggesting that the catalytic activity of L-WNK1 was not required to increase BK expression. We examined whether dietary K(+) intake affected L-WNK1 expression in the aldosterone-sensitive distal nephron. We found a paucity of L-WNK1 labeling in cortical collecting ducts (CCDs) from rabbits on a low-K(+) diet but observed robust staining for L-WNK1 primarily in intercalated cells when rabbits were fed a high-K(+) diet. Our results and previous findings suggest that L-WNK1 exerts different effects on renal K(+) secretory channels, inhibiting renal outer medullary K(+) channels and activating BK channels. A high-K(+) diet induced an increase in L-WNK1 expression selectively in intercalated cells and may contribute to enhanced BK channel expression and K(+) secretion in CCDs.

Long noncoding RNAs as potential biomarkers in gastric cancer: Opportunities and challenges

Gastric cancer (GC) is a major threat to human health, and its prognosis is poor due to the lack of appropriate biomarkers. LncRNAs are a group of non-protein-coding RNAs that regulate gene expression at the transcriptional or posttranscriptional level. LncRNAs play essential roles in GC initiation and development in the same way as oncogenes or tumour suppressor genes. Recent investigations have revealed that lncRNAs are often aberrantly expressed in GC; are involved in cell proliferation, apoptosis, migration and invasion; and correlate with the malignant phenotype of GC. LncRNAs, especially the lncRNAs present in the blood and gastric juice, show potential value as biomarkers for the diagnosis of GC or for determining disease prognosis. However, there are still many challenges to be faced before lncRNAs can be used in clinical applications. In this review, we summarise lncRNAs as the potential biomarkers for GC and the current challenges associated with the clinical application.

A protocol for the identification and validation of novel genetic causes of kidney disease

BACKGROUND

Genetic renal diseases (GRD) are a heterogeneous and incompletely understood group of disorders accounting for approximately 10 % of those diagnosed with kidney disease. The advent of Next Generation sequencing and new approaches to disease modelling may allow the identification and validation of novel genetic variants in patients with previously incompletely explained or understood GRD.

METHODS/DESIGN

This study will recruit participants in families/trios from a multidisciplinary sub-specialty Renal Genetics Clinic where known genetic causes of GRD have been excluded or where genetic testing is not available. After informed patient consent, whole exome and/or genome sequencing will be performed with bioinformatics analysis undertaken using a customised variant assessment tool. A rigorous process for participant data management will be undertaken. Novel genetic findings will be validated using patient-derived induced pluripotent stem cells via differentiation to renal and relevant extra-renal tissue phenotypes in vitro. A process for managing the risk of incidental findings and the return of study results to participants has been developed.

DISCUSSION

This investigator-initiated approach brings together experts in nephrology, clinical and molecular genetics, pathology and developmental biology to discover and validate novel genetic causes for patients in Australia affected by GRD without a known genetic aetiology or pathobiology.

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.