SGK1 activates Na+-K+-ATPase in amphibian renal epithelial cells

Inhibition the ubiquitination of ENaC and Na,K-ATPase with erythropoietin promotes alveolar fluid clearance in sepsis-induced acute respiratory distress syndrome

Sepsis-induced acute respiratory distress syndrome (ARDS) causes significant fatalities worldwide and lacks pharmacological intervention. Alveolar fluid clearance (AFC) plays a pivotal role in the remission of ARDS and is markedly impaired in the pathogenesis of ARDS. Here, we demonstrated that erythropoietin could effectively ameliorate lung injury manifestations and lethality, restore lung function and promote AFC in a rat model of lipopolysaccharide (LPS)-induced ARDS. Moreover, it was proven that EPO-induced restoration of AFC occurs through triggering the total protein expression of ENaC and Na,K-ATPase channels, enhancing their protein abundance in the membrane, and suppressing their ubiquitination for degeneration. Mechanistically, the data indicated the possible involvement of EPOR/JAK2/STAT3/SGK1/Nedd4-2 signaling in this process, and the pharmacological inhibition of the pathway markedly eliminated the stimulating effects of EPO on ENaC and Na,K-ATPase, and subsequently reversed the augmentation of AFC by EPO. Consistently, in vitro studies of alveolar epithelial cells paralleled with that EPO upregulated the expression of ENaC and Na,K-ATPase, and patch-clamp studies further demonstrated that EPO substantially strengthened sodium ion currents. Collectively, EPO could effectively promote AFC by improving ENaC and Na,K-ATPase protein expression and abundance in the membrane, dependent on inhibition of ENaC and Na,K-ATPase ubiquitination, and resulting in diminishing LPS-associated lung injuries.

Association between Decreased SGK1 and Increased Intestinal α-Synuclein in an MPTP Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a globally common progressive neurodegenerative disease resulting from the loss of dopaminergic neurons in the brain. Increased α-synuclein (α-syn) is associated with the degeneration of dopaminergic neurons and non-motor symptoms like gastrointestinal disorders. In this study, we investigated the association between serum/glucocorticoid-related kinase 1 (SGK1) and α-syn in the colon of a PD mouse model. SGK1 and α-syn expression patterns were opposite in the surrounding colon tissue, with decreased SGK1 expression and increased α-syn expression in the PD group. Immunofluorescence analyses revealed the colocation of SGK1 and α-syn; the PD group demonstrated weaker SGK1 expression and stronger α-syn expression than the control group. Immunoblotting analysis showed that Na+/K+ pump ATPase α1 expression levels were significantly increased in the PD group. In SW480 cells with SGK1 knockdown using SGK1 siRNA, decreasing SGK1 levels corresponded with significant increases in the expression levels of α-syn and ATPase α1. These results suggest that SGK1 significantly regulates Na+/K+ pump ATPase, influencing the relationship between electrolyte balance and fecal formation in the PD mouse model. Gastrointestinal disorders are some of the major prodromal symptoms of PD. Therefore, modulating SGK1 expression could be an important strategy for controlling PD.

Regulation of Porcine Oviduct Epithelium Functions via Progesterone and Estradiol Is Influenced by Cortisol

Preimplantation maternal stress, characterized by elevated glucocorticoids (GCs), has been linked to reproductive failures caused by impaired oviduct functionality, which is known to be predominantly regulated by the sex steroids, progesterone (P4) and (17)estradiol (E2). Although steroid receptors share analogous structures and binding preferences, the interaction between GCs and E2/P4 in the oviduct has attracted little attention. Using an air-liquid interface culture model, porcine oviduct epithelial cells were stimulated with single (cortisol, E2, P4) or hormone mixtures (cortisol/E2, cortisol/P4) for 12 hours and 72 hours. Cultures were subsequently assessed for epithelial morphometry, bioelectrical properties, and gene expression responses (steroid hormone signaling, oviductal function, immune response, and apoptosis). Results confirmed the suppressive role of P4 in regulating oviduct epithelium characteristics, which was partially opposed by E2. Besides increasing the ratio of ciliated cells, cortisol antagonized the effect of P4 on epithelial polarity and modified sex steroid-induced changes in transepithelial electrical properties. Both sex steroids affected the glucocorticoid receptor expression, while cortisol downregulated the expression of progesterone receptor. The overall gene expression pattern suggests that sex steroid dominates the cotreatment, but cortisol contributes by altering the gene responses to sex steroids. We conclude that besides its individual action, maternal cortisol interplays with sex steroids at phenotypic and molecular levels in the oviduct epithelium, thereby influencing the microenvironment of gametes and early embryos.

Glucocorticoids Promote Na+ Excretion in the Renal Epithelia of Heart Failure Rats by Suppressing Transporter Proteins Involved in Acute Sodium Loading

ABSTRACT

Glucocorticoid receptors are essential for normal development and stress responses. Their role in H 2 O and Na + metabolism, especially in chronic heart failure (CHF), is not well defined. In a previous study, we found that glucocorticoids potentiate urination in CHF and promote H 2 O excretion by inhibiting the vasopressin receptor 2 pathway. The present study examines the effect of glucocorticoids on renal Na + excretion and the underlying mechanisms in CHF rats with acute sodium loading. CHF was induced by left coronary artery ligation for 8 weeks. Rats were randomly assigned to 5 groups: control, CHF, dexamethasone (DEX)-administered CHF, DEX-administered CHF treated with RU486 (mifepristone, a glucocorticoid receptor antagonist), and RU486-treated CHF. An acute sodium loading test was performed 6 hours after DEX administration. Blood and urine samples were collected, and hemodynamics were measured. The expression and localization of Na + transporter proteins were determined by immunoblotting and immunohistochemistry. DEX increased the urine volume and urinary sodium and improved cardiac function and the estimated glomerular filtration rate in CHF rats. The upregulation of the epithelial sodium channel β and γ subunits, Na-K-2Cl cotransporter, serum glucocorticoid-regulated kinase 1 (SGK1), and Na + /K + -ATPase in the renal epithelium of CHF rats was downregulated by DEX. These beneficial effects were abolished by RU486. The expression of natriuretic peptide receptor A was opposite that of the above proteins. Glucocorticoids might induce profound natriuresis in CHF rats during acute sodium loading, which is associated with downregulating some Na + transporter proteins in the renal epithelium and improving intrarenal hemodynamics.

CDK5/NFAT5-Regulated Transporters Involved in Osmoregulation in Fejervarya cancrivora

Crab-eating frogs (Fejervarya cancrivora) can live in brackish water with a salinity of up to 18‱, although most amphibians are not able to tolerate such high saline environments. To investigate its potential osmoregulation, we conducted experiments in F. cancrivora and F. multistriata. The results showed that F. cancrivora made use of ions (such as Na+ and Cl−) to increase intracellular concentrations via the Na+/K+-ATPase (NKA) enzyme. The mRNA expression of aldose reductase (AR) was significantly higher in F. cancrivora (p < 0.05), indicating that more organic osmolytes were produced and transported to maintain cellular homeosis. The mRNA expressions of Aquaporin 1 (AQP1) and AQP3 in kidney were significantly higher in F. cancrivora, while AQP expression in skin was higher in F. multistriata (p < 0.05). The mRNA level in activating the transcription of the nuclear factor of activated T cells-5 (NFAT5) which is one of the target genes of regulating the cellular response to hypertonicity, was higher in F. cancrivora. The protein expression of CDK5, the upstream protein of the NFAT5 pathway, was 2 times higher in F. cancrivora. Therefore, we can conclude that CDK5/NFAT5-regulated transporters might be involved in osmoregulation in F. cancrivora.

SGK1, autophagy and cancer: an overview

BACKGROUND

The serum and glucocorticoid-induced kinase-1 (SGK1) belonging to the AGC protein kinase family phosphorylates serine and threonine residues of target proteins. It regulates numerous ion channels and transporters and promotes survival under cellular stress. Unique to SGK1 is a tight control at transcriptional and post-transcriptional levels. SGK1 regulates multiple signal transduction pathways related to tumor development. Several studies have reported that SGK1 is upregulated in different types of human malignancies and induces resistance against inhibitors, drugs, and targeted therapies.

RESULTS AND CONCLUSION

This review highlights the cellular functions of SGK1, its crucial role in cancer development, and clinical insights for SGK1 targeted therapies. Furthermore, the role of SGK1-mediated autophagy as a potential therapeutic target for cancer has been discussed.

Glucocorticoids Reverse Diluted Hyponatremia Through Inhibiting Arginine Vasopressin Pathway in Heart Failure Rats

Background

Arginine vasopressin dependent antidiuresis plays a key role in water‐sodium retention in heart failure. In recent years, the role of glucocorticoids in the control of body fluid homeostasis has been extensively investigated. Glucocorticoid deficiency can activate V2R (vasopressin receptor 2), increase aquaporins expression, and result in hyponatremia, all of which can be reversed by glucocorticoid supplement.

Methods and Results

Heart failure was induced by coronary artery ligation for 8 weeks. A total of 32 rats were randomly assigned to 4 groups (n=8/group): sham surgery group, congestive heart failure group, dexamethasone group, and dexamethasone in combination with glucocorticoid receptor antagonist RU486 group. An acute water loading test was administered 6 hours after drug administration. Left ventricular function was measured by a pressure‐volume catheter. Protein expressions were determined by immunohistochemistry and immunoblotting. The pressure‐volume loop analysis showed that dexamethasone improves cardiac function in rats with heart failure. Western blotting confirmed that dexamethasone remarkably reduces the expressions of V2R, aquaporin 2, and aquaporin 3 in the renal‐collecting ducts. As a result of V2R downregulation, the expressions of glucocorticoid regulated kinase 1, apical epithelial sodium channels, and the furosemide‐sensitive Na‐K‐2Cl cotransporter were also downregulated. These favorable effects induced by dexamethasone were mostly abolished by the glucocorticoid receptor inhibitor RU486, indicating that the aforementioned effects are glucocorticoid receptor mediated.

Conclusions

Glucocorticoids can reverse diluted hyponatremia via inhibiting the vasopressin receptor pathway in rats with heart failure.

Electrolyte transport in the renal collecting duct and its regulation by the renin-angiotensin-aldosterone system

Distal nephron of the kidney plays key roles in fluid volume and electrolyte homeostasis by tightly regulating reabsorption and excretion of Na⁺, K⁺, and Cl^- Studies to date demonstrate the detailed electrolyte transport mechanisms in principal cells of the cortical collecting duct, and their regulation by renin-angiotensin-aldosterone system (RAAS). In recent years, however, accumulating data indicate that intercalated cells, another cell type that is present in the cortical collecting duct, also play active roles in the regulation of blood pressure. Notably, pendrin in β-intercalated cells not only controls acid/base homeostasis, but is also one of the key components controlling salt and K⁺ transport in distal nephron. We have recently shown that pendrin is regulated by the co-ordinated action of angiotensin II (AngII) and aldosterone, and at the downstream of AngII, mammalian target of rapamycin (mTOR) signaling regulates pendrin through inhibiting the kinase unc51-like-kinase 1 and promoting dephosphorylation of mineralocorticoid receptor (MR). In this review, we summarize recent advances in the current knowledge on the salt transport mechanisms in the cortical collecting duct, and their regulation by the RAAS.

Genomic and rapid effects of aldosterone: what we know and do not know thus far

Aldosterone is the most known mineralocorticoid hormone synthesized by the adrenal cortex. The genomic pathway displayed by aldosterone is attributed to the mineralocorticoid receptor (MR) signaling. Even though the rapid effects displayed by aldosterone are long known, our knowledge regarding the receptor responsible for such event is still poor. It is intense that the debate whether the MR or another receptor-the "unknown receptor"-is the receptor responsible for the rapid effects of aldosterone. Recently, G protein-coupled estrogen receptor-1 (GPER-1) was elegantly shown to mediate some aldosterone-induced rapid effects in several tissues, a fact that strongly places GPER-1 as the unknown receptor. It has also been suggested that angiotensin receptor type 1 (AT1) also participates in the aldosterone-induced rapid effects. Despite this open question, the relevance of the beneficial effects of aldosterone is clear in the kidneys, colon, and CNS as aldosterone controls the important water reabsorption process; on the other hand, detrimental effects displayed by aldosterone have been reported in the cardiovascular system and in the kidneys. In this line, the MR antagonists are well-known drugs that display beneficial effects in patients with heart failure and hypertension; it has been proposed that MR antagonists could also play an important role in vascular disease, obesity, obesity-related hypertension, and metabolic syndrome. Taken altogether, our goal here was to (1) bring a historical perspective of both genomic and rapid effects of aldosterone in several tissues, and the receptors and signaling pathways involved in such processes; and (2) critically address the controversial points within the literature as regarding which receptor participates in the rapid pathway display by aldosterone.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Mineralocorticoid receptor and NaCl transport mechanisms in the renal distal nephron

A key role of aldosterone and mineralocorticoid receptor is to regulate fluid volume and K⁺ homeostasis in the body by acting on the renal distal nephron. Global responses of the kidney to elevated aldosterone levels are determined by the coordinate action of different constituent tubule cells, including principal cells, intercalated cells and distal convoluted tubule cells. Recent studies on genetic mutations causing aldosterone overproduction have identified the molecules involved in aldosterone biosynthesis in the adrenal gland, and there is also increasing evidence for mechanisms and signaling pathways regulating the balance between renal NaCl reabsorption and K⁺ secretion, the two major effects of aldosterone. In particular, recent studies have demonstrated that mineralocorticoid receptor in intercalated cells is selectively regulated by phosphorylation, which prevents ligand binding and activation. Moreover, the ubiquitin ligase complex composed of Kelch-like 3 and Cullin 3 acts downstream of angiotensin II and plasma K⁺ alterations, regulating Na-Cl cotransporter independently of aldosterone in distal convoluted tubule cells. These and other effects are integrated to produce appropriate kidney responses in a high-aldosterone state, and are implicated in fluid and electrolyte disorders in humans. This review summarizes the current knowledge on mechanisms modulating mineralocorticoid receptor and its downstream effectors in the distal nephron.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Nongenomic effects via the mineralocorticoid receptor

The mineralocorticoid receptor (MR) belongs to the steroid hormone receptor family and classically functions as a ligand-dependent transcription factor. It is involved in water-electrolyte homeostasis and blood pressure regulation but independent from these effects also furthers inflammation, fibrosis, hypertrophy and remodeling in cardiovascular tissues. Next to genomic effects, aldosterone elicits very rapid actions within minutes that do not require transcription or translation and that occur not only in classical MR epithelial target organs like kidney and colon but also in nonepithelial tissues like heart, vasculature and adipose tissue. Most of these effects can be mediated by classical MR and its crosstalk with different signaling cascades. Near the plasma membrane, the MR seems to be associated with caveolin and striatin as well as with receptor tyrosine kinases like EGFR, PDGFR and IGF1R and G protein-coupled receptors like AT1 and GPER1, which then mediate nongenomic aldosterone effects. GPER1 has also been named a putative novel MR. There is a close interaction and functional synergism between the genomic and the nongenomic signaling so that nongenomic signaling can lead to long-term effects and support genomic actions. Therefore, understanding nongenomic aldosterone/MR effects is of potential relevance for modulating genomic aldosterone effects and may provide additional targets for intervention.

Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways

The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.

Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis

The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na⁺ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na⁺ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na⁺ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.

Hepatic serum- and glucocorticoid-regulated protein kinase 1 (SGK1) regulates insulin sensitivity in mice via extracellular-signal-regulated kinase 1/2 (ERK1/2)

Insulin resistance is a major hallmark of metabolic syndromes, including Type 2 diabetes. Although numerous functions of SGK1 (serum- and glucocorticoid-regulated kinase 1) have been identified, a direct effect of SGK1 on insulin sensitivity has not been previously reported. In the present study, we generated liver-specific SGK1-knockout mice and found that these mice developed glucose intolerance and insulin resistance. We also found that insulin signalling is enhanced or impaired in Hep1-6 cells infected with adenoviruses expressing SGK1 (Ad-SGK1) or shRNA directed against the coding region of SGK1 (Ad-shSGK1) respectively. In addition, we determined that SGK1 inhibits ERK1/2 (extracellular-signal-regulated kinase 1/2) activity in liver and Ad-shERK1/2-mediated inhibition of ERK1/2 reverses the attenuated insulin sensitivity in Ad-shSGK1 mice. Finally, we found that SGK1 functions are compromised under insulin-resistant conditions and overexpression of SGK1 by Ad-SGK1 significantly ameliorates insulin resistance in both glucosamine-treated HepG2 cells and livers of db/db mice, a genetic model of insulin resistance.

Epithelial sodium channel regulation by cell surface-associated serum- and glucocorticoid-regulated kinase 1

Serum- and glucocorticoid-regulated kinase 1 (sgk1) participates in diverse biological processes, including cell growth, apoptosis, and sodium homeostasis. In the cortical collecting duct of the kidney, sgk1 regulates sodium transport by stimulating the epithelial sodium channel (ENaC). Control of subcellular localization of sgk1 may be an important mechanism for modulating specificity of sgk1 function; however, which subcellular locations are required for sgk1-regulated ENaC activity in collecting duct cells has yet to be established. Using cell surface biotinylation studies, we detected endogenous sgk1 at the apical cell membrane of aldosterone-stimulated mpkCCD(c14) collecting duct cells. The association of sgk1 with the cell membrane was enhanced when ENaC was co-transfected with sgk1 in kidney cells, suggesting that ENaC brings sgk1 to the cell surface. Furthermore, association of endogenous sgk1 with the apical cell membrane of mpkCCD(c14) cells could be modulated by treatments that increase or decrease ENaC expression at the apical membrane; forskolin increased the association of sgk1 with the apical surface, whereas methyl-β-cyclodextrin decreased the association of sgk1 with the apical surface. Single channel recordings of excised inside-out patches from the apical membrane of aldosterone-stimulated A6 collecting duct cells revealed that the open probability of ENaC was sensitive to the sgk1 inhibitor GSK650394, indicating that endogenous sgk1 is functionally active at the apical cell membrane. We propose that the association of sgk1 with the apical cell membrane, where it interacts with ENaC, is a novel means by which sgk1 specifically enhances ENaC activity in aldosterone-stimulated collecting duct cells.

Role of epithelial sodium channels and their regulators in hypertension

The kidney has a central role in the regulation of blood pressure, in large part through its role in the regulated reabsorption of filtered Na(+). Epithelial Na(+) channels (ENaCs) are expressed in the most distal segments of the nephron and are a target of volume regulatory hormones. A variety of factors regulate ENaC activity, including several aldosterone-induced proteins that are present within an ENaC regulatory complex. Proteases also regulate ENaC by cleaving the channel and releasing intrinsic inhibitory tracts. Polymorphisms or mutations within channel subunits or regulatory pathways that enhance channel activity may contribute to an increase in blood pressure in individuals with essential hypertension.

IL-1beta-induced cortisol stimulates lung fluid absorption in fetal guinea pigs via SGK-mediated Nedd4-2 inhibition

We tested the hypothesis that interleukin (IL)-1beta-induced cortisol synthesis stimulates distal lung fluid absorption in fetal guinea pigs via induction of serum- and glucocorticoid-regulated kinase (SGK) and inhibition of neural precursor cell expressed, developmentally downregulated protein 4-2 (Nedd4-2). IL-1beta was subcutaneously administered daily to timed-pregnant guinea pigs over 3 days. Fetuses were obtained by abdominal hysterotomy at gestation day (GD)61 and GD68 and instilled with an isosmolar 5% albumin solution into the lungs. Distal lung fluid movement was measured over 1 h from the change in distal air space protein concentration. Fetal lungs were secreting lung fluid at GD61 while absorbing lung fluid at GD68. Distal lung fluid absorption was induced at GD61 by IL-1beta but unaffected at GD68. Plasma cortisol concentrations were increased by IL-1beta at GD61 and endogenously at GD68. Distal lung fluid absorption was measured and correlated to SGK and Nedd4-2 expression and to alpha-epithelial Na channel (ENaC) expression. SGK was increased by IL-1beta and late during gestation (GD68), while Nedd4-2 was decreased by IL-1beta and late during gestation. alpha-ENaC was induced by IL-1beta at GD61 and increased late during gestation. Thus our study suggests that cortisol-stimulated fetal lung fluid absorption is mediated by increased ENaC expression and may be governed by the SGK/Nedd4-2 pathway. These observations may explain why babies delivered preterm after intrauterine inflammation have a reduced risk of developing severe respiratory distress.

Aldosterone regulation of intestinal Na absorption involves SGK-mediated changes in NHE3 and Na+ pump activity

Aldosterone-induced intestinal Na(+) absorption is mediated by increased activities of apical membrane Na(+)/H(+) exchange (aNHE3) and basolateral membrane Na(+)-K(+)-ATPase (BLM-Na(+)-K(+)-ATPase) activities. Because the processes coordinating these events were not well understood, we investigated human intestinal Caco-2BBE cells where aldosterone increases within 2-4 h of aNHE3 and alpha-subunit of BLM-Na(+)-K(+)-ATPase, but not total abundance of these proteins. Although aldosterone activated Akt2 and serum glucorticoid kinase-1 (SGK-1), the latter through stimulation of phosphatidylinositol 3-kinase (PI3K), only the SGK-1 pathway mediated its effects on Na(+)-K(+)-ATPase. Ouabain inhibition of the early increase in aldosterone-induced Na(+)-K(+)-ATPase activation blocked most of the apical NHE3 insertion, possibly by inhibiting Na(+)-K(+)-ATPase-induced changes in intracellular sodium concentration ([Na](i)). Over the next 6-48 h, further increases in aNHE3 and BLM-Na(+)-K(+)-ATPase activity and total protein expression were observed to be largely mediated by aldosterone-activated SGK-1 pathway. Aldosterone-induced increases in NHE3 mRNA, for instance, could be inhibited by RNA silencing of SGK-1, but not Akt2. Additionally, aldosterone-induced increases in NHE3 promoter activity were blocked by silencing SGK-1 as well as pharmacological inhibition of PI3K. In conclusion, aldosterone-stimulated intestinal Na(+) absorption involves two phases. The first phase involves stimulation of PI3K, which increases SGK-dependent insertion and function of BLM-Na(+)-K(+)-ATPase and subsequent increased membrane insertion of aNHE3. The latter may be caused by Na(+)-K(+)-ATPase-induced changes in [Na] or transcellular Na flux. The second phase involves SGK-dependent increases in total NHE3 and Na(+)-K(+)-ATPase protein expression and activities. The coordination of apical and BLM transporters after aldosterone stimulation is therefore a complex process that requires multiple time- and interdependent cellular processes.

Membrane ERalpha-dependent activation of PKCalpha in endometrial cancer cells by estradiol

The purpose of this study was to investigate the role of the oestrogen receptor subtypes ERalpha and ERbeta in mediating the non-genomic effects of 17-beta-estradiol (E(2)) in two human endometrial cancer cell lines (RL95-2 and HEC-1A) expressing different levels of these receptor subtypes. Western blotting analysis using phosphorylation site-specific antibodies showed that physiological concentrations of E(2) rapidly (<20 min) activated PKCalpha, but not PKCdelta in the RL95-2 cell line. E(2) had no effect on PKCalpha or PKCdelta activity in the HEC-1A cell line and suppressed basal levels of PKA activity in both cell lines. PKCalpha activation coincided with its membrane translocation. ERalpha was detected in the RL95-2 cell line by Western blotting and RT-PCR but not in the HEC-1A cells, which did express ERbeta. A selective ERalpha agonist PPT had the same effect as E(2) on PKCalpha activation in the RL95-2 cells, but the selective ERbeta agonist DPN had no such effect. A 46kDa variant of ERalpha increased in abundance in the cell membrane within 20 min of E(2) treatment suggesting that ERalpha mediated the E(2) non-genomic effects on PKCalpha through the formation of a membrane associated signalling complex.

V2 vasopressin receptor deficiency causes changes in expression and function of renal and hypothalamic components involved in electrolyte and water homeostasis

Polyuria, hypernatremia, and hypovolemia are the major clinical signs of inherited nephrogenic diabetes insipidus (NDI). Hypernatremia is commonly considered a secondary sign caused by the net loss of water due to insufficient insertion of aquaporin-2 water channels into the apical membrane of the collecting duct cells. In the present study, we employed transcriptome-wide expression analysis to study gene expression in V2 vasopressin receptor (Avpr2)-deficient mice, an animal model for X-linked NDI. Gene expression changes in NDI mice indicate increased proximal tubular sodium reabsorption. Expression of several key genes including Na+-K+-ATPase and carbonic anhydrases was increased at the mRNA levels and accompanied by enhanced enzyme activities. In addition, altered expression was also observed for components of the eicosanoid and thyroid hormone pathways, including cyclooxygenases and deiodinases, in both kidney and hypothalamus. These effects are likely to contribute to the clinical NDI phenotype. Finally, our data highlight the involvement of the renin-angiotensin-aldosterone system in NDI pathophysiology and provide clues to explain the effectiveness of diuretics and indomethacin in the treatment of NDI.

Rapid responses to aldosterone in the kidney and colon

Aldosterone is a crucial modulator of ion transport across high resistance epithelia and regulates whole body electrolyte balance through its effects on the kidney and colon. The net consequence of aldosterone release is to promote salt conservation. The genomic mechanism of aldosterone action is relatively well characterized and the role of the classical mineralocorticoid receptor as a ligand-dependent transcription factor is well established. The rapid effects of aldosterone on target tissues are less well understood and there is still controversy over the identity of the aldosterone non-genomic receptor. Greater understanding of the physiological consequences of aldosterone's rapid responses in the kidney and colon has been achieved through the identification of definite and putative membrane targets and their signaling regulators.

Rapid Responses to Steroid Hormones in the Kidney

Rapid signalling responses stimulated by steroid hormones have been detected in various tissues including the nephron. The significance of these responses in modulating the physiological effects elicited by mineralocorticoids, glucocorticoids and the reproductive hormones in the kidney is now becoming more evident. This review outlines how rapid signalling responses stimulated by these hormones are coupled to the regulation of membrane transport targets that impact upon the reabsorptive and excretory functions of the kidney.

Prolactin increases Na+ transport across adult bullfrog skin via stimulation of both ENaC and Na+/K+-pump

PRL is involved in osmoregulation in lower vertebrates. Its serum concentration starts to increase during the metamorphosis of bullfrog tadpoles. Adult bullfrog skin transports Na(+) from the apical to the basolateral side across the skin. PRL is involved in the regulation of this transport. We investigated the effect of ovine PRL on the epithelial Na(+) channel (ENaC), Na(+)/K(+)-pump, and basolateral K(+) channels, which regulate Na(+) transport across adult bullfrog skin, by measuring the short-circuit current (SCC). At 0.1 microg/ml, PRL had no effect on the SCC. PRL (1 microg/ml) was sufficient to stimulate the SCC since 1 and 10 microg/ml of PRL each increased SCC 1.8-fold. Current-fluctuation analysis revealed that PRL (10 microg/ml) increased the density of active ENaC almost 1.8-fold. The effect of PRL on the Na(+)/K(+)-pump was investigated using apically nystatin-permeabilized skin with Ca-free Na-Ringers' solution on each side. PRL (10 microg/ml) increased SCC in this condition around 1.1-fold, suggesting that PRL stimulates the Na(+)/K(+)-pump [although PRL (1 microg/ml) had no effect on this SCC]. The effect of PRL on basolateral K(+) channels was investigated using apically nystatin-permeabilized skin with high-K Ringer's solution on the apical side. PRL (10 microg/ml) had no effect on the SCC, suggesting that PRL does not affect basolateral K(+) channels. Thus, although PRL stimulates the Na(+)/K(+)-pump, this effect probably contributes less than that on ENaC to the regulation of Na(+) transport across adult bullfrog skin.

Dexamethasone increases Na+/K+ ATPase activity in insulin secreting cells through SGK1

Glucocorticoids blunt insulin release, an effect partially due to activation of Kv channels. Similar to those channels Na+/K+ ATPase activity repolarizes the plasma membrane. The present study explored whether glucocorticoids increase the Na+/K+ ATPase activity in pancreatic beta-cells. The glucocorticoid dexamethasone (100 nmol/l for 1 day) significantly increased Na+/K+ ATPase alpha1/beta1-subunit transcript levels and ouabain-sensitive outward current reflecting Na+/K+ ATPase activity in INS-1 cells, effects blunted by glucocorticoid-receptor-blocker RU487 (1 micromol/l). Dexamethasone (100 nmol/l) increased K+ current in beta-cells from wild type mice but not from knockout mice lacking functional serum and glucocorticoid inducible kinase SGK1. Thus, glucocorticoids indeed up-regulate Na+/K+ ATPase activity, an effect requiring SGK1.

Glucocorticoid regulation of genes in the amiloride-sensitive sodium transport pathway by semicircular canal duct epithelium of neonatal rat

The lumen of the inner ear has an unusually low concentration of endolymphatic Na+, which is important for transduction processes. We have recently shown that glucocorticoid receptors (GR) stimulate absorption of Na+by semicircular canal duct (SCCD) epithelia. In the present study, we sought to determine the presence of genes involved in the control of the amiloride-sensitive Na+transport pathway in rat SCCD epithelia and whether their level of expression was regulated by glucocorticoids using quantitative real-time RT-PCR. Transcripts were present for α-, β-, and γ-subunits of the epithelial sodium channel (ENaC); the α1-, α3-, β1-, and β3-isoforms of Na+-K+-ATPase; inwardly rectifying potassium channels [IC50of short circuit current ( Isc) for Ba2+: 210 μM] Kir2.1, Kir2.2, Kir2.3, Kir2.4, Kir3.1, Kir3.3, Kir4.1, Kir4.2, Kir5.1, and Kir7.1; sulfonyl urea receptor 1 (SUR1); GR; mineralocorticoid receptor (MR); 11β-hydroxysteroid dehydrogenase (11β-HSD) types 1 and 2; serum- and glucocorticoid-regulated kinase 1 (Sgk1); and neural precursor cell-expressed developmentally downregulated 4-2 (Nedd4-2). On the other hand, transcripts for the α4-subunit of Na+-K+-ATPase, Kir1.1, Kir3.2, Kir3.4, Kir6.1, Kir6.2, and SUR2 were found to be absent, and Iscwas not inhibited by glibenclamide. Dexamethasone (100 nM for 24 h) not only upregulated the transcript expression of α-ENaC (∼4-fold), β2-subunit (∼2-fold) and β3-subunit (∼8-fold) of Na+-K+-ATPase, Kir2.1 (∼5-fold), Kir2.2 (∼9-fold), Kir2.4 (∼3-fold), Kir3.1 (∼ 3- fold), Kir3.3 (∼2-fold), Kir4.2 (∼3-fold ), Kir7.1 (∼2-fold), Sgk1 (∼4-fold), and Nedd4-2 (∼2-fold) but also downregulated GR (∼3-fold) and 11β-HSD1 (∼2-fold). Expression of GR and 11β-HSD1 was higher than MR and 11β-HSD2 in the absence of dexamethasone. Dexamethasone altered transcript expression levels (α-ENaC and Sgk1) by activation of GR but not MR. Proteins were present for the α-, β-, and γ-subunits of ENaC and Sgk1, and expression of α- and γ-ENaC was upregulated by dexamethasone. These findings are consistent with the genomic stimulation by glucocorticoids of Na+absorption by SCCD and provide an understanding of the therapeutic action of glucocorticoids in the treatment of Meniere's disease.