Requirement of Na+/H+ Exchanger NHE1 for Vasopressin-Induced Osteogenic Signaling and Calcification in Human Aortic Smooth Muscle Cells

BACKGROUND/AIMS

Vasopressin is a powerful stimulator of vascular calcification, augmenting osteogenic signaling in vascular smooth muscle cells (VSMCs) including upregulation of transcription factors such as core-binding factor α-1 (CBFA1), msh homeobox 2 (MSX2), and SRY-Box 9 (SOX9), as well as of tissue-nonspecific alkaline phosphatase (ALPL). Vasopressin-induced osteogenic signaling and calcification require the serum- and glucocorticoid-inducible kinase 1 (SGK1). Known effects of SGK1 include upregulation of Na+/H+ exchanger 1 (NHE1). NHE1 further participates in the regulation of reactive oxygen species (ROS). NHE1 has been shown to participate in the orchestration of bone mineralization. The present study, thus, explored whether vasopressin modifies NHE1 expression and ROS generation, as well as whether pharmacological inhibition of NHE1 disrupts vasopressin-induced osteogenic signaling and calcification in VSMCs.

METHODS

Human aortic smooth muscle cells (HAoSMCs) were treated with vasopressin in the absence or presence of SGK1 silencing, SGK1 inhibitor GSK-650394, and NHE1 blocker cariporide. Transcript levels were determined by using quantitative real-time polymerase chain reaction, protein abundance by Western blotting, ROS generation with 2',7'-dichlorofluorescein diacetate fluorescence, and ALP activity and calcium content by using colorimetric assays.

RESULTS

Vasopressin significantly enhanced the NHE1 transcript and protein levels in HAoSMCs, effects significantly blunted by SGK1 inhibition with GSK-650394 or SGK1 silencing. Vasopressin increased ROS accumulation, an effect significantly blocked by the NHE1 inhibitor cariporide. Vasopressin further significantly increased osteogenic markers CBFA1, MSX2, SOX9, and ALPL transcript levels, as well as ALP activity and calcium content in HAoSMCs, all effects significantly blunted by SGK1 silencing or in the presence of GSK-650394 or cariporide.

CONCLUSION

Vasopressin stimulates NHE1 expression and ROS generation, an effect dependent on SGK1 and required for vasopressin-induced stimulation of osteogenic signaling and calcification of VSMCs.

Uncovering the interplay between pH receptors and immune cells: Potential drug targets (Review)

Extracellular acidosis is associated with various immunopathological states. The microenvironment of numerous solid tumours and inflammatory responses during acute or chronic infection are all related to a pH range of 5.5‑7.0. The relationship between inflammation and immune escape, cancer metabolism, and immunologic suppression drives researchers to focus on the effects of low pH on diverse components of disease immune monitoring. The potential effect of low extracellular pH on the immune function reveals the importance of pH in inflammatory and immunoreactive processes. In this review, the mechanism of how pH receptors, including monocarboxylate transporters (MCTs), Na⁺/H⁺ exchanger 1, carbonic anhydrases (CAs), vacuolar‑ATPase, and proton‑sensing G‑protein coupled receptors (GPCRs), modulate the immune system in disease, especially in cancer, were studied. Their role in immunocyte growth and signal transduction as part of the immune response, as well as cytokine production, have been documented in great detail. Currently, immunotherapy strategies have positive therapeutic effects for patients. However, the acidic microenvironment may block the effect of immunotherapy through compensatory feedback mechanisms, leading to drug resistance. Therefore, we highlight promising therapeutic developments regarding pH manipulation and provide a framework for future research.

The Enigmatic Role of Serum & Glucocorticoid Inducible Kinase 1 in the Endometrium

The serum- and glucocorticoid-inducible kinase 1 (SGK1) is subject to genetic up-regulation by diverse stimulators including glucocorticoids, mineralocorticoids, dehydration, ischemia, radiation and hyperosmotic shock. To become active, the expressed kinase requires phosphorylation, which is accomplished by PI3K/PDK1 and mTOR dependent signaling. SGK1 enhances the expression/activity of various transport proteins including Na⁺/K⁺-ATPase as well as ion-, glucose-, and amino acid- carriers in the plasma membrane. SGK1 can further up-regulate diverse ion channels, such as Na⁺-, Ca²⁺-, K⁺- and Cl^– channels. SGK1 regulates expression/activity of a wide variety of transcription factors (such as FKHRL1/Foxo3a, β-catenin, NFκB and p53). SGK1 thus contributes to the regulation of transport, glycolysis, angiogenesis, cell survival, immune regulation, cell migration, tissue fibrosis and tissue calcification. In this review we summarized the current findings that SGK1 plays a crucial function in the regulation of endometrial function. Specifically, it plays a dual role in the regulation of endometrial receptivity necessary for implantation and, subsequently in pregnancy maintenance. Furthermore, fetal programming of blood pressure regulation requires maternal SGK1. Underlying mechanisms are, however, still ill-defined and there is a substantial need for additional information to fully understand the role of SGK1 in the orchestration of embryo implantation, embryo survival and fetal programming.

SGK1 Mediates Hypoxic Pulmonary Hypertension through Promoting Macrophage Infiltration and Activation

Inflammation plays a pivotal role in the development of pulmonary arterial hypertension (PAH). Meanwhile, serum glucocorticoid-regulated kinase-1 (SGK1) has been considered to be an important factor in the regulation of inflammation in some vascular disease. However, the role of SGK1 in hypoxia-induced inflammation and PAH is still unknown. WT and SGK1^−/− mice were exposed to chronic hypoxia to induce PAH. The quantitative PCR and immunohistochemistry were used to determine the expression of SGK1. The right ventricular hypertrophy index (RVHI), RV/BW ratio, right ventricle systolic pressure (RVSP), and percentage of muscularised vessels and medical wall thickness were measured to evaluate PAH development. The infiltration of macrophages and localization of SGK1 on cells were examined by histological analysis. The effects of SGK1 on macrophage function and cytokine expression were assessed by comparing WT and SGK1^−/− macrophages in vitro. SGK1 has high expression in hypoxia-induced PAH. Deficiency of SGK1 prevented the development of hypoxia-induced PAH and inhibited macrophage infiltration in the lung. In addition, SGK1 knockout inhibited the expression of proinflammatory cytokines in macrophages. SGK1-induced macrophage activation and proinflammatory response contributes to the development of PAH in hypoxia-treated mice. Thus, SGK1 might be considered a promising target for PAH treatment.

Serum- and glucocorticoid-inducible kinase 1 and the response to cell stress

Expression of the serum- and glucocorticoid-inducible kinase 1 (SGK1) is up-regulated by several types of cell stress, such as ischemia, radiation and hyperosmotic shock. The SGK1 protein is activated by a signaling cascade involving phosphatidylinositide-3-kinase (PI3K), 3-phosphoinositide-dependent kinase 1 (PDK1) and mammalian target of rapamycin (mTOR). SGK1 up-regulates Na⁺/K⁺-ATPase, a variety of carriers including Na⁺-,K⁺-,2Cl⁻- cotransporter (NKCC), NaCl cotransporter (NCC), Na⁺/H⁺ exchangers, diverse amino acid transporters and several glucose carriers such as Na⁺-coupled glucose transporter SGLT1. SGK1 further up-regulates a large number of ion channels including epithelial Na⁺ channel ENaC, voltagegated Na⁺ channel SCN5A, Ca²⁺ release-activated Ca²⁺ channel (ORAI1) with its stimulator STIM1, epithelial Ca²⁺ channels TRPV5 and TRPV6 and diverse K⁺ channels. Furthermore, SGK1 influences transcription factors such as nuclear factor kappa-B (NF-κB), p53 tumor suppressor protein, cAMP responsive element-binding protein (CREB), activator protein-1 (AP-1) and forkhead box O3 protein (FOXO3a). Thus, SGK1 supports cellular glucose uptake and glycolysis, angiogenesis, cell survival, cell migration, and wound healing. Presumably as last line of defense against tissue injury, SGK1 fosters tissue fibrosis and tissue calcification replacing energy consuming cells.

To die or not to die SGK1-sensitive ORAI/STIM in cell survival

The pore forming Ca²⁺ release activated Ca²⁺ channel (CRAC) isoforms ORAI1-3 and their regulators STIM1,2 accomplish store operated Ca²⁺ entry (SOCE). Activation of SOCE may lead to cytosolic Ca²⁺ oscillations, which in turn support cell proliferation and cell survival. ORAI/STIM and thus SOCE are upregulated by the serum and glucocorticoid inducible kinase SGK1, a kinase under powerful genomic regulation and activated by phosphorylation via the phosphoinositol-3-phosphate pathway. SGK1 enhances ORAI1 abundance partially by phosphorylation of Nedd4-2, an ubiquitin ligase priming the channel protein for degradation. The SGK1-phosphorylated Nedd4-2 binds to the protein 14-3-3 and is thus unable to ubiquinate ORAI1. SGK1 further increases the ORAI1 and STIM1 protein abundance by activating nuclear factor kappa B (NF-κB), a transcription factor upregulating the expression of STIM1 and ORAI1. SGK1-sensitive upregulation of ORAI/STIM and thus SOCE is triggered by a wide variety of hormones and growth factors, as well as several cell stressors including ischemia, radiation, and cell shrinkage. SGK1 dependent upregulation of ORAI/STIM confers survival of tumor cells and thus impacts on growth and therapy resistance of cancer. On the other hand, SGK1-dependent upregulation of ORAI1 and STIM1 may support survival of neurons and impairment of SGK1-dependent ORAI/STIM activity may foster neurodegeneration. Clearly, further experimental effort is needed to define the mechanisms linking SGK1-dependent upregulation of ORAI1 and STIM1 to cell survival and to define the impact of SGK1-dependent upregulation of ORAI1 and STIM1 on malignancy and neurodegenerative disease.

Two Liters a Day Keep the Doctor Away? Considerations on the Pathophysiology of Suboptimal Fluid Intake in the Common Population

Suboptimal fluid intake may require enhanced release of antidiuretic hormone (ADH) or vasopressin for the maintenance of adequate hydration. Enhanced copeptin levels (reflecting enhanced vasopressin levels) in 25% of the common population are associated with enhanced risk of metabolic syndrome with abdominal obesity, type 2 diabetes, hypertension, coronary artery disease, heart failure, vascular dementia, cognitive impairment, microalbuminuria, chronic kidney disease, inflammatory bowel disease, cancer, and premature mortality. Vasopressin stimulates the release of glucocorticoids which in turn up-regulate the serum- and glucocorticoid-inducible kinase 1 (SGK1). Moreover, dehydration upregulates the transcription factor NFAT5, which in turn stimulates SGK1 expression. SGK1 is activated by insulin, growth factors and oxidative stress via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase PDK1 and mTOR. SGK1 is a powerful stimulator of Na+/K+-ATPase, carriers (e.g. the Na+,K+,2Cl- cotransporter NKCC, the NaCl cotransporter NCC, the Na+/H+ exchanger NHE3, and the Na+ coupled glucose transporter SGLT1), and ion channels (e.g. the epithelial Na+ channel ENaC, the Ca2+ release activated Ca2+ channel Orai1 with its stimulator STIM1, and diverse K+ channels). SGK1 further participates in the regulation of the transcription factors nuclear factor kappa-B NFκB, p53, cAMP responsive element binding protein (CREB), activator protein-1, and forkhead transcription factor FKHR-L1 (FOXO3a). Enhanced SGK1 activity fosters the development of hypertension, obesity, diabetes, thrombosis, stroke, inflammation including inflammatory bowel disease and autoimmune disease, cardiac fibrosis, proteinuria, renal failure as well as tumor growth. The present brief review makes the case that suboptimal fluid intake in the common population may enhance vasopressin and glucocorticoid levels thus up-regulating SGK1 expression and favouring the development of SGK1 related pathologies.

DJ-1/Park7 Sensitive Na+ /H+ Exchanger 1 (NHE1) in CD4+ T Cells

DJ-1/Park7 is a redox-sensitive chaperone protein counteracting oxidation and presumably contributing to the control of oxidative stress responses and thus inflammation. DJ-1 gene deletion exacerbates the progression of Parkinson's disease presumably by augmenting oxidative stress. Formation of reactive oxygen species (ROS) is paralleled by activation of the Na⁺ /H⁺ exchanger 1 (NHE1). ROS formation in CD4⁺ T cells plays a decisive role in regulating inflammatory responses. In the present study, we explored whether DJ-1 is expressed in CD4⁺ T cells, and affects ROS production as well as NHE1 in those cells. To this end, DJ-1 and NHE1 transcript, and protein levels were quantified by qRT-PCR and Western blotting, respectively, intracellular pH (pH_i ) utilizing bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence, NHE activity from realkalinization after an ammonium pulse, and ROS production utilizing 2',7' -dichlorofluorescin diacetate (DCFDA) fluorescence. As a result DJ-1 was expressed in CD4⁺ T cells. ROS formation, NHE1 transcript levels, NHE1 protein, and NHE activity were higher in CD4⁺ T cells from DJ-1 deficient mice than in CD4⁺ T cells from wild type mice. Antioxidant N-acetyl-cysteine (NAC) and protein tyrosine kinase (PTK) inhibitor staurosporine decreased the NHE activity in DJ-1 deficient CD4⁺ T cells, and blunted the difference between DJ-1^-/- and DJ-1^+/+ CD4⁺ T cells, an observation pointing to a role of ROS in the up-regulation of NHE1 in DJ-1^-/- CD4⁺ T cells. In conclusion, DJ-1 is a powerful regulator of ROS production as well as NHE1 expression and activity in CD4⁺ T cells. J. Cell. Physiol. 232: 3050-3059, 2017. © 2016 Wiley Periodicals, Inc.

In human T cells mifepristone antagonizes glucocorticoid non-genomic rapid responses in terms of Na(+)/H(+)-exchange 1 activity, but not ezrin/radixin/moesin phosphorylation

Glucocorticoids (GCs) and progesterone have been employed as immunosuppressive agents during pregnancy for many years. Intracellular acidification by GCs is due to a rapid non-genomic inhibition of membrane Na(+)/H(+)-exchange 1 (NHE1) activity and is followed by immunosuppression of PHA-stimulated proliferation. NHE1 is tethered to the cortical actin cytoskeleton through ezrin/radixin/moesin (ERM) proteins within lipid rafts; these regulate cell shape, migration and resistance to apoptosis. We explored whether mifepristone (RU486), an antagonist of GCs in T cells, is able to completely block rapid non-genomic responses, namely NHE1 activity and the phosphorylation C-terminal residues of ERM proteins at threonine (cp-ERM). GCs stimulate a rapid non-genomic cp-ERM response in cells within 5min. RU486 antagonized the GC-induced rapid decrease in NHE1 activity, and arrested PHA-stimulated T cells at G0/G1 phase but had no effect on the rapid increase in cp-ERM, which persisted for 24h. However, the cp-ERM response was blocked by staurosporine in both resting and GC stimulated cells. The results of RU486 antagonized the GC induced rapid decrease in NHE1 ion transport activity, but not the increase cp-ERM. This suggests that RU486 in T cells exerts its antagonistic effects at NHE1 containing plasma membrane sites and not where cp-ERM links lipid rafts to cortical cytoskeletons.

Treadmill exercise ameliorates ischemia-induced brain edema while suppressing Na⁺/H⁺ exchanger 1 expression

Exercise may be one of the most effective and sound therapies for stroke; however, the mechanisms underlying the curative effects remain unclear. In this study, the effects of forced treadmill exercise with electric shock on ischemic brain edema were investigated. Wistar rats were subjected to transient (90 min) middle cerebral artery occlusion (tMCAO). Eighty nine rats with substantially large ischemic lesions were evaluated using magnetic resonance imaging (MRI) and were randomly assigned to exercise and non-exercise groups. The rats were forced to run at 4-6m/s for 10 min/day on days 2, 3 and 4. Brain edema was measured on day 5 by MRI, histochemical staining of brain sections and tissue water content determination (n=7, each experiment). Motor function in some rats was examined on day 30 (n=6). Exercise reduced brain edema (P<0.05-0.001, varied by the methods) and ameliorated motor function (P<0.05). The anti-glucocorticoid mifepristone or the anti-mineralocorticoid spironolactone abolished these effects, but orally administered corticosterone mimicked the ameliorating effects of exercise. Exercise prevented the ischemia-induced expression of mRNA encoding aquaporin 4 (AQP4) and Na(+)/H(+) exchangers (NHEs) (n=5 or 7, P<0.01). Microglia and NG2 glia expressed NHE1 in the peri-ischemic region of rat brains and also in mixed glial cultures. Corticosterone at ~10nM reduced NHE1 and AQP4 expression in mixed glial and pure microglial cultures. Dexamethasone and aldosterone at 10nM did not significantly alter NHE1 and AQP4 expression. Exposure to a NHE inhibitor caused shrinkage of microglial cells. These results suggest that the stressful short-period and slow-paced treadmill exercise suppressed NHE1 and AQP4 expression resulting in the amelioration of brain edema at least partly via the moderate increase in plasma corticosterone levels.

Lazaroid U-74389G inhibits the osteoblastic differentiation of IL-1β-indcued aortic valve interstitial cells through glucocorticoid receptor and inhibition of NF-κB pathway

BACKGROUND

Aortic valve calcification is characterized as the active process of aortic valve interstitial cells (AVICs), and considered as an inflammatory disease. As an antioxidant, the anti-inflammatory activity of Lazaroid has been exhibited in various models. We hypothesized that Lazaroid U-74389G would inhibit the osteoblastic differentiation of AVICs induced by IL-1β.

METHODS

Normal tricuspid aortic valve leaflets were collected from patients with acute aortic dissection (Type A) undergoing the Bentall procedure. AVICs were isolated and stimulated with IL-1β in presence or absence of U-74389G in culture. Cell lysates were analyzed for osteogenic markers and nuclear factor-κB using real-time PCR and Immunoblotting. Culture media was analyzed for IL-6 and IL-8 with enzyme-linked immunosorbent assay. Alizarin Red Staining was adopted to demonstrate the calcium deposition.

RESULTS

The expression of alkaline phosphatase and bone morphogenetic protein, accompanied by the production of IL-6 and IL-8, was up-regulated in response to IL-1β and was inhibited by the addition of U-74389G. The NF-κB pathway was activated by IL-1β and involved in the suppression of U-74389G on osteoblastic differentiation in AVICs. The negative effects of U-74389G on ostengenic gene expression and mineralization of AVICs were blocked by glucocorticoid receptor antagonist mifepristone and the NF-κB inhibitor Bay 11-7082.

CONCLUSIONS

U-74389G inhibits the pro-osteogenic response to IL-1β stimulation in AVICs. The osteoblastic differentiation and mineralization of AVICs were inhabited by U-74389G though the modulation of NF-κB activation, and this pathway could be potential therapeutic targets for medical treatment of calcified aortic valve disease.

Endothelial Na+/H+ exchanger NHE1 participates in redox-sensitive leukocyte recruitment triggered by methylglyoxal

Background

Excessive levels of methylglyoxal (MG) encountered in diabetes foster enhanced leukocyte-endothelial cell interactions, mechanisms of which are incompletely understood. MG genomically upregulates endothelial serum- and glucocorticoid-inducible kinase 1 (SGK1) which orchestrates leukocyte recruitment by regulating the activation and expression of transcription factors and adhesion molecules. SGK1 regulates a myriad of ion channels and carriers including the Na⁺/H⁺ exchanger NHE1. Here, we explored the effect of MG on SGK1-dependent NHE1 activation and the putative role of NHE1 activation in MG-induced leukocyte recruitment and microvascular hyperpermeability.

Methods

Using RT-PCR and immunoblotting, we analyzed NHE1 mRNA and protein levels in murine microvascular SVEC4-10EE2 endothelial cells (EE2 ECs). NHE1 phosphorylation was detected using a specific antibody against the 14-3-3 binding motif at phospho-Ser⁷⁰³. SGK in EE2 ECs was silenced using targeted siRNA. ROS production was determined using DCF-dependent fluorescence. Leukocyte recruitment and microvascular permeability in murine cremasteric microvasculature were measured using intravital microscopy. The expression of endothelial adhesion molecules was determined by immunoblotting and confocal imaging analysis.

Results

MG treatment significantly upregulated NHE1 mRNA and dose-dependently increased total- and phospho-NHE1. Treatment with SGK1 inhibitor GSK650394, antioxidant Tempol and silencing SGK all blunted MG-triggered phospho-NHE1 upregulation in EE2 ECs. NHE1 inhibitor cariporide attenuated MG-triggered ROS production, leukocyte adhesion and emigration and microvascular hyperpermeability, without affecting leukocyte rolling. Cariporide treatment did not alter MG-triggered upregulation of P- and E-selectins, but reduced endothelial ICAM-1 expression.

Conclusion

MG elicits SGK1-dependent activation of endothelial Na⁺/H⁺ exchanger NHE1 which participates in MG-induced ROS production, upregulation of endothelial ICAM-1, leukocyte recruitment and microvascular hyperpermeability. Pharmacological inhibition of NHE1 attenuates the proinflammatory effects of excessive MG and may, thus, be beneficial in diabetes-associated inflammation.

Membrane androgen receptor sensitive Na+/H+ exchanger activity in prostate cancer cells

Membrane androgen receptors (mAR) are expressed in several tumors. mAR activation by testosterone albumin conjugates (TAC) suppresses tumor growth and migration. mAR signaling involves phosphoinositide-3-kinase (PI3K) and Rho-associated protein kinase (ROCK). PI3K stimulates serum- and glucocorticoid-inducible kinase SGK1, which in turn activates Na(+)/H(+)-exchangers (NHE). In prostate cancer cells cytosolic pH (pHi) was determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-fluorescence and NHE-activity utilizing Na(+)-dependent cytosolic realkalinization following an ammonium pulse. TAC (100 nM) significantly increased pHi and NHE-activity, effects abrogated by NHE1-inhibitor cariporide (10 μM), SGK1-inhibitors EMD638683 (50 μM) and GSK650349 (10 μM) and ROCK-inhibitors Y-27632 (10 μM) and fasudil (100 μM). TAC treatment rapidly and significantly increased cell volume and actin polymerization, effects abolished in the presence of cariporide. Thus, mAR-activation activates cariporide-sensitive Na(+)/H(+)-exchangers, an effect requiring SGK1 and ROCK activity.

Regulation of transport across cell membranes by the serum- and glucocorticoid-inducible kinase SGK1

The serum- and glucocorticoid-inducible kinase 1 (SGK1) is genomically upregulated by cell stress including energy depletion and hyperosmotic shock as well as a variety of hormones including glucocorticoids, mineralocorticoids and TGFβ. SGK1 is activated by insulin, growth factors and oxidative stress via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase PDK1 and mTOR. SGK1 is a powerful stimulator of Na(+)/K(+)-ATPase, carriers (e.g., NCC, NKCC, NHE1, NHE3, SGLT1, several amino acid transporters) and ion channels (e.g., ENaC, SCN5A, TRPV4-6, ORAI1/STIM1, ROMK, KCNE1/KCNQ1, GluR6, CFTR). Mechanisms employed by SGK1 in transport regulation include direct phosphorylation of target transport proteins, phosphorylation and thus activation of other transport regulating kinases, stabilization of membrane proteins by phosphorylation and thus inactivation of the ubiquitin ligase NEDD4-2, as well as stimulation of transport protein expression by upregulation transcription factors (e.g., nuclear factor kappa-B [NFκB]) and by fostering of protein translation. SGK1 sensitivity of pump, carrier and channel activities participate in the regulation of epithelial transport, cardiac and neuronal excitability, degranulation, platelet function, migration, cell proliferation and apoptosis. SGK1-sensitive functions do not require the presence of SGK1 but are markedly upregulated by SGK1. Accordingly, the phenotype of SGK1 knockout mice is mild. The mice are, however, less sensitive to excessive activation of transport by glucocorticoids, mineralocorticoids, insulin and inflammation. Moreover, excessive SGK1 activity contributes to the pathophysiology of hypertension, obesity, diabetes, thrombosis, stroke, inflammation, autoimmune disease, fibrosis and tumor growth.

Targeting membrane androgen receptors in tumors

INTRODUCTION

In the last decade androgen actions that are originated from non-genomic, rapid signaling have been described in a large number of cell models and tissues. These effects are initiated through the stimulation of membrane androgen-binding sites or receptors (mAR). Although the molecular identity of mARs remains elusive, their activation is known to trigger multiple non-genomic signaling cascades and to regulate numerous cell responses. In recent years specific interest is being paid to the role of mARs in tumors. Specifically, it was demonstrated that mAR activation by non-permeable testosterone conjugates induced potent anti-tumorigenic responses in prostate, breast, colon and glial tumors. In addition, in vivo animal studies further emphasized the potential clinical importance of these receptors.

AREAS COVERED

This review will summarize the current knowledge on the mAR-induced non-genomic, rapid androgen actions. It will focus on the molecular signaling pathways governed by mAR activation, discuss latest attempts to elucidate the molecular identity of mAR, address the plethora of cell responses initiated by mAR and evaluate the potential role of mAR and mAR-specific signaling as possible therapeutic targets in tumors.

EXPERT OPINION

mAR and mAR-induced specific signaling may represent novel therapeutic targets in tumors through the development of specific testosterone analogs.

Therapeutic potential of serum and glucocorticoid inducible kinase inhibition

INTRODUCTION

Expression of serum-and-glucocorticoid-inducible kinase-1 (SGK1) is low in most cells, but dramatically increases under certain pathophysiological conditions, such as glucocorticoid or mineralocorticoid excess, inflammation with TGFβ release, hyperglycemia, cell shrinkage and ischemia. SGK1 is activated by insulin and growth factors via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase and mammalian target of rapamycin. SGK1 sensitive functions include activation of ion channels (including epithelial Na(+) channel ENaC, voltage gated Na(+) channel SCN5A transient receptor potential channels TRPV4 - 6, Ca(2+) release activated Ca(2+) channel Orai1/STIM1, renal outer medullary K(+) channel ROMK, voltage gated K(+) channels KCNE1/KCNQ1, kainate receptor GluR6, cystic fibrosis transmembrane regulator CFTR), carriers (including Na(+),Cl(-) symport NCC, Na(+),K(+),2Cl(-) symport NKCC, Na(+)/H(+) exchangers NHE1 and NHE3, Na(+), glucose symport SGLT1, several amino acid transporters), and Na(+)/K(+)-ATPase. SGK1 regulates several enzymes (e.g., glycogen synthase kinase-3, ubiquitin-ligase Nedd4-2) and transcription factors (e.g., forkhead transcription factor 3a, β-catenin, nuclear factor kappa B).

AREAS COVERED

The phenotype of SGK1 knockout mice is mild and SGK1 is apparently dispensible for basic functions. Excessive SGK1 expression and activity, however, contributes to the pathophysiology of several disorders, including hypertension, obesity, diabetes, thrombosis, stroke, fibrosing disease, infertility and tumor growth. A SGK1 gene variant (prevalence ∼ 3 - 5% in Caucasians and ∼ 10% in Africans) is associated with hypertension, stroke, obesity and type 2 diabetes. SGK1 inhibitors have been developed and shown to reduce blood pressure of hyperinsulinemic mice and to counteract tumor cell survival.

EXPERT OPINION

Targeting SGK1 may be a therapeutic option in several clinical conditions, including metabolic syndrome and tumor growth.

Upregulation of intestinal NHE3 following saline ingestion

BACKGROUND

Little is known about the effect of salt content of ingested fluid on intestinal transport processes. Osmosensitive genes include the serum- and glucocorticoid-inducible kinase SGK1, which is up-regulated by hyperosmolarity and cell shrinkage. SGK1 is in turn a powerful stimulator of the intestinal Na(+)/H(+) exchanger NHE3. The present study was thus performed to elucidate, whether the NaCl content of beverages influences NHE3 activity.

METHODS

Mice were offered access to either plain water or isotonic saline ad libitum. NHE3 transcript levels and protein abundance in intestinal tissue were determined by confocal immunofluorescent microscopy, RT-PCR and western blotting, cytosolic pH (pHi) in intestinal cells from 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence and Na(+)/H(+) exchanger activity from the Na(+) dependent realkalinization following an ammonium pulse.

RESULTS

Saline drinking significantly enhanced fluid intake and increased NHE3 transcript levels, NHE3 protein and Na(+)/H(+) exchanger activity.

CONCLUSIONS

Salt content of ingested fluid has a profound effect on intestinal Na(+)/H(+) exchanger expression and activity.

Photodynamic therapy-generated cancer vaccine elicits acute phase and hormonal response in treated mice

Photodynamic therapy (PDT)-generated cancer vaccines have shown promising results in preclinical studies and are being introduced in the clinics. Using an SCCVII mouse squamous cell carcinoma-based whole-cell autologous PDT vaccine model developed in our previous work, we have examined systemic effects in vaccinated mice that could be related to the induction of acute phase response. The upregulation of gene encoding serum amyloid P component (prototypic mouse acute phase reactant) was detected in the liver and to a lesser degree in the tumor of vaccinated mice at 24 h post-PDT vaccine treatment. A strong upregulation of gene for heat shock protein 70 was found in both the liver and tumor of mice at 4 h after their PDT vaccine treatment. Changes in the expression of genes for glucocorticoid-induced leucine zipper and serum- and glucocorticoid-regulated kinase 1 that are highly responsive to glucocorticoid modulation were uncovered in both the tumor and liver of vaccinated mice. A rise in the levels of serum corticosterone was detected in mice at 24 h after PDT vaccine treatment. The results indicate that a sudden appearance of a large number of PDT vaccine cells elicits host responses for securing their optimized clearance, which in addition to producing seminal acute phase reactants includes the engagement of glucocorticoid hormones. It is becoming increasingly clear that a consummate execution of this process of PDT vaccine cell removal is critical for tumor antigen recognition and the attainment of potent antitumor immune response.

Regulation of Orai1/STIM1 by the kinases SGK1 and AMPK

STIM and Orai isoforms orchestrate store operated Ca2+ entry (SOCE) and thus cytosolic Ca2+ fluctuations following stimulation by hormones, growth factors and further mediators. Orai1 is a target of Nedd4-2, an ubiquitin ligase preparing several plasma membrane proteins for degradation. Phosphorylation of Nedd4-2 by the serum and glucocorticoid inducible kinase SGK1 leads to the binding of Nedd4-2 to the protein 14-3-3 thus preventing its interaction with Orai1. Nedd4-2 is activated by the energy sensing AMP activated kinase AMPK. Thus, SGK1 disrupts and AMPK fosters degradation of Orai1. New synthesis of both, Orai1 and STIM1, is stimulated by the transcription factor NF-κB (nuclear factor kappa B), which binds to the respective promoter regions of the genes encoding STIM1 and Orai1. SGK1 upregulates and AMPK presumably downregulates NF-κB and thus de novo synthesis of Orai1 and STIM1 proteins. The regulation by SGK1 links SOCE to the signaling of a wide variety of hormones and growth factors, the AMPK dependent regulation of Orai1 and STIM1 may serve to limit inadequate activation of SOCE following energy depletion, which is otherwise expected to activate SOCE by depletion of intracellular Ca2+ stores due to impairment of the ATP consuming sarco/endoplasmatic reticulum Ca2+ ATPase SERCA.