Hypertonic induction of COX-2 expression in renal medullary epithelial cells requires transactivation of the EGFR

Thieno[2,3-d]pyrimidin-4(3H)-one Derivatives of Benzimidazole as Potential Anti- Breast Cancer (MDA-MB-231, MCF-7) Agents

AIMS

The purpose of this study was the synthesis of some new thienopyrimidine derivatives of 1,3-disubstituted benzimidazoles and the evaluation of their cytotoxicity against MDA-MB-231, MCF-7, and 3T3 cells lines.

BACKGROUND

An overexpression or mutational activation of TK receptors EGFR and HER2/neu is characteristic of tumors. It has been found that some thieno[2,3-d]pyrimidines exhibited better inhibitory activity against Epidermal Growth Factor Receptor (EGFR/ErbB-2) tyrosine kinase in comparison to aminoquinazolines. Breast cancer activity towards MDA-MB-231 and MCF-7 cell lines by inhibiting EGFR was revealed by a novel 2-arylbenzimidazole. This motivated the synthesis of new thienopyrimidines possessing benzimidazole fragments in order to evaluate their cytotoxicity to the above-mentioned cell lines.

OBJECTIVE

The objectives of the study were to design and synthesize a novel series of thieno[2,3-d]pyrimidines bearing biologically active moieties, such as 1,3-disubstituted-benzimidazole heterocycle, structurally similar to diaryl ureas in order to evaluate their cytotoxicity against MDA-MB-231, and MCF-7 breast cancer cell lines.

METHODS

N,N-disubstituted benzimidazole-2-one carbonitriles were synthesized by Aza-Michael addition and used as precursors to generate some of the new thieno[2,3-d]pyrimidines in acidic medium The interaction of chloroethyl-2-thienopyrimidines, 2-amino-benzimidazole and benzimidazol-2-one nitriles under solid-liquid transfer catalysis conditions led to new thienopyrimidines. MTT assay for cell survival was performed in order to evaluate the cytotoxicity of the tested compounds. A fluorescence study was conducted to elucidate some aspects of the mechanism of action.

RESULTS

The effects of nine synthesized compounds were investigated towards MDA-MB-231, MCF-7 and 3T3 cell lines. Thieno[2,3-d]pyirimidine-4-one 16 (IC₅₀ - 0.058μM) and 21 (IC₅₀ - 0.029μM) possess high cytotoxicity against MDA-MB-231 cells after 24h. The most cytotoxic compounds against breast cancer MCF-7 cells was compound 21 (IC₅₀ - 0.074μM), revealing lower cytotoxicity against mouse fibroblast 3T3 cells with IC₅₀ - 0.20μM. SAR analysis was performed. Fluorescence study of the treatment of MDA-MB cells with compound 21 was carried out in order to clarify some aspects of the mechanism of action.

CONCLUSION

The relationship between cytotoxicity of compounds 14 and 20 against MCF-7 and 3T3 cells can suggest a similar mechanism of action. The antitumor potential of the tested compounds proves the necessity for further investigation to estimate the exact inhibition pathway in the cellular processes. The fluorescence study of the treatment of MDA-MB cells with compound 21 showed a rapid process of apoptosis.

The interaction partners of (pro)renin receptor in the distal nephron

The (pro)renin receptor (PRR), a key regulator of intrarenal renin-angiotensin system (RAS), is predominantly presented in podocytes, proximal tubules, distal convoluted tubules, and the apical membrane of collecting duct A-type intercalated cells, and plays a crucial role in hypertension, cardiovascular disease, kidney disease, and fluid homeostasis. In addition to its well-known renin-regulatory function, increasing evidence suggests PRR can also act in a variety of intracellular signaling cascades independently of RAS in the renal medulla, including Wnt/β-catenin signaling, cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂ ) signaling, and the apelinergic system, and work as a component of the vacuolar H⁺ -ATPase. PRR and these pathways regulate the expression/activity of each other that controlling blood pressure and renal functions. In this review, we highlight recent findings regarding the antagonistic interaction between PRR and ELABELA/apelin, the mutually stimulatory relationship between PRR and COX-2/PGE₂ or Wnt/β-catenin signaling in the renal medulla, and their involvement in the regulation of intrarenal RAS thereby control blood pressure, renal injury, and urine concentrating ability in health and patho-physiological conditions. We also highlight the latest progress in the involvement of PRR for the vacuolar H⁺ -ATPase activity.

Sequential and synchronized hypertonicity-induced activation of Rel-family transcription factors is required for osmoprotection in renal cells

NF-κB and TonEBP belong to the Rel-superfamily of transcription factors. Several specific stimuli, including hypertonicity which is a key factor for renal physiology, are able to activate them. It has been reported that, after hypertonic challenge, NF-κB activity can be modulated by TonEBP, considered as the master regulator of transcriptional activity in the presence of changes in environmental tonicity. In the present work we evaluated whether hypertonicity-induced gene transcription mediated by p65/RelA and TonEBP occurs by an independent action of each transcription factor or by acting together. To do this, we evaluated the expression of their specific target genes and cyclooxygenase-2 (COX-2), a common target of both transcription factors, in the renal epithelial cell line Madin-Darby canine kidney (MDCK) subjected to hypertonic environment. The results herein indicate that hypertonicity activates the Rel-family transcription factors p65/RelA and TonEBP in MDCK cells, and that both are required for hypertonic induction of COX-2 and of their specific target genes. In addition, present data show that p65/RelA modulates TonEBP expression and both colocalize in nuclei of hypertonic cultures of MDCK cells. Thus, a sequential and synchronized action p65/RelA → TonEBP would be necessary for the expression of hypertonicity-induced protective genes.

Diabetic microangiopathy: Pathogenetic insights and novel therapeutic approaches

Diabetic microangiopathy, including retinopathy, is characterized by abnormal growth and leakage of small blood vessels, resulting in local edema and functional impairment of the depending tissues. Mechanisms leading to the impairment of microcirculation in diabetes are multiple and still largely unclear. However, a dysregulated vascular regeneration appears to play a key role. In addition, oxidative and hyperosmolar stress, as well as the activation of inflammatory pathways triggered by advanced glycation end-products and toll-like receptors, have been recognized as key underlying events_. Here, we review recent knowledge on cellular and molecular pathways of microvascular disease in diabetes. We also highlight how new insights into pathogenic mechanisms of vascular damage in diabetes may indicate new targets for prevention and treatment.

High glucose-induced hyperosmolarity contributes to COX-2 expression and angiogenesis: implications for diabetic retinopathy

Background

We tested the hypothesis that glucose-induced hyperosmolarity, occurring in diabetic hyperglycemia, promotes retinal angiogenesis, and that interference with osmolarity signaling ameliorates excessive angiogenesis and retinopathy in vitro and in vivo.

Methods and Results

We incubated human aortic (HAECs) and dermal microvascular endothelial cells (HMVECs) with glucose or mannitol for 24 h and tested them for protein levels and in vitro angiogenesis. We used the Ins2 Akita mice as a model of type 1 diabetes to test the in vivo relevance of in vitro observations. Compared to incubations with normal (5 mmol/L) glucose concentrations, cells exposed to both high glucose and high mannitol (at 30.5 or 50.5 mmol/L) increased expression of the water channel aquaporin-1 (AQP1) and cyclooxygenase (COX)-2. This was preceded by increased activity of the osmolarity-sensitive transcription factor Tonicity enhancer binding protein (TonEBP), and enhanced endothelial migration and tubulization in Matrigel, reverted by treatment with AQP1 and TonEBP siRNA. Retinas of Ins2 Akita mice showed increased levels of AQP1 and COX-2, as well as angiogenesis, all reverted by AQP1 siRNA intravitreal injections.

Conclusions

Glucose-related hyperosmolarity seems to be able to promote angiogenesis and retinopathy through activation of TonEBP and possibly increasing expression of AQP1 and COX-2. Osmolarity signaling may be a target for therapy.

Epidermal Growth Factor Receptor Transactivation: Mechanisms, Pathophysiology, and Potential Therapies in the Cardiovascular System

Epidermal growth factor receptor (EGFR) activation impacts the physiology and pathophysiology of the cardiovascular system, and inhibition of EGFR activity is emerging as a potential therapeutic strategy to treat diseases including hypertension, cardiac hypertrophy, renal fibrosis, and abdominal aortic aneurysm. The capacity of G protein-coupled receptor (GPCR) agonists, such as angiotensin II (AngII), to promote EGFR signaling is called transactivation and is well described, yet delineating the molecular processes and functional relevance of this crosstalk has been challenging. Moreover, these critical findings are dispersed among many different fields. The aim of our review is to highlight recent advancements in defining the signaling cascades and downstream consequences of EGFR transactivation in the cardiovascular renal system. We also focus on studies that link EGFR transactivation to animal models of the disease, and we discuss potential therapeutic applications.

Coordinate regulation between the nuclear receptor peroxisome proliferator-activated receptor-γ and cyclooxygenase-2 in renal epithelial cells

The peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors involved in lipid metabolism and glucose utilization, in cell growth, differentiation and apoptosis, and in the regulation of pro-inflammatory genes expression such as cyclooxygenase-2 (COX-2). PPARγ is the main isoform in the renal inner medulla where it is believed to possess nephroprotective actions. In this kidney zone, COX-2 acts as an osmoprotective gene and its expression is modulated by changes in interstitial osmolarity. In the present work we evaluated whether hyperosmolar-induced COX-2 expression is modulated by PPARγ in renal epithelial cells MDCK subjected to high NaCl medium. The results presented herein show that ligand-activated PPARγ repressed COX-2 expression. But more important, the present findings show that hyperosmolar medium decreased PPARγ protein and increases the PPARγ phosphorylated form, which is inactive. ERK1/2 and p38 activation precedes PPARγ disappearance and induced-COX-2 expression. Therefore, the decrease in PPARγ expression is required for hyperosmotic induction of COX-2. We also found that PGE2, the main product of COX-2 in MDCK cells, induced these changes in PPARγ protein. Our results may alert on the long term use of thiazolidinediones (TZD) since they could affect renal medullary function that depends on COX-2 for cellular protection against osmotic stress.

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways. Here, we discuss new developments in our understanding of the actions of PGE2 that have been uncovered utilizing receptor specific agonists and antagonists, EP receptor and PG synthase knockout mice, polyuric animal models, and the new understanding of the molecular regulation of collecting duct water permeability. The role of PGE2 in urinary concentration comprises a variety of mechanisms, which are not fully understood and likely depend on which receptor is activated under a particular physiologic condition. EP3 and microsomal PG synthase type 1 play a role in decreasing collecting duct water permeability and increasing water excretion, whereas EP2 and EP4 can bypass vasopressin signaling and increase water reabsorption through two different intracellular signaling pathways. PGE2 has an intricate role in urinary concentration, and we now suggest how targeting specific prostanoid receptor signaling pathways could be exploited for the treatment of disorders in water balance.

Toll-like receptor 4 activates NF-κB and MAP kinase pathways to regulate expression of proinflammatory COX-2 in renal medullary collecting duct cells

Binding of bacterial LPS to the Toll-like receptor 4 (TLR4) complex of inner medullary collecting duct (IMCD) cells plays a central role in recognition of ascending bacterial infections and activation of proinflammatory responses. Since proinflammatory cyclooxygenase (COX)-2 is induced in IMCD cells upon LPS exposure, the present study addressed the question of whether TLR4 mediates COX-2 induction in IMCD cells and characterized the underlying signaling mechanisms. Enhanced COX-2 expression and activity in the presence of LPS was diminished by TLR4 inhibition. LPS induced a TLR4-dependent stimulation of NF-κB and the MAPKs p38, ERK1/2, and JNK. Activation of NF-κB was under negative control of JNK, as inhibition of JNK increased NF-κB activity and COX-2 expression. Phosphorylation of p38 and ERK1/2 required TLR4-dependent release of TGF-α with subsequent activation of the epidermal growth factor receptor (EGFR), whereas JNK activation was EGFR independent. Inhibition of p38 or ERK1/2 had no significant effect on LPS-induced NF-κB activation, nor on activator protein 1-, cAMP response element-, or serum response element-driven reporter constructs. However, the transcriptional regulator SP-1 appears to contribute to COX-2 expression after LPS exposure. In conclusion, these results propose that LPS mediates enhanced COX-2 expression in IMCD cells by 1) TLR4-mediated activation of the NF-κB signaling pathway, 2) TLR4-dependent release of TGF-α with subsequent activation of the EGFR and downstream MAPKs p38 and ERK1/2, and 3) TLR4-mediated, EGFR-independent activation of JNK that negatively regulates NF-κB activation.

Osmoadaptation of Mammalian cells - an orchestrated network of protective genes

In mammals, the cells of the renal medulla are physiologically exposed to interstitial osmolalities several-fold higher that found in any other tissue. Nevertheless, these cells not only have the ability to survive in this harsh environment, but also to function normally, which is critical for maintenance of systemic electrolyte and fluid homeostasis. Over the last two decades, a substantial body of evidence has accumulated, indicating that sequential and well orchestrated genomic responses are required to provide tolerance to osmotic stress. This includes the enhanced expression and action of immediate-early genes, growth arrest and DNA damage inducible genes (GADDs), genes involved in cell cycle control and apoptosis, heat shock proteins, and ultimately that of genes involved in the intracellular accumulation of nonperturbing organic osmolytes. The present review summarizes the sequence of genomic responses conferring resistance against osmotic stress. In addition, the regulatory mechanisms mediating the coordinated genomic response to osmotic stress will be highlighted.

TRPV1 activation is required for hypertonicity-stimulated inflammatory cytokine release in human corneal epithelial cells

PURPOSE

To determine whether hypertonic stress promotes increases in inflammatory cytokine release through transient receptor potential vanilloid channel type 1 (TRPV1) signaling pathway activation in human corneal epithelial cells (HCECs).

METHODS

Hyperosmotic medium was prepared by supplementing isotonic Ringers solution with sucrose. Ca2+ signaling was measured in fura2-AM-loaded HCECs using a single-cell fluorescence imaging system. Western blot analysis evaluated the phosphorylation status of EGFR, ERK, p38 MAPK, and nuclear factor (NF)-κB. ELISA assessed the effect of TRPV1 activation on the release of IL-6 and IL-8.

RESULTS

A 450 mOsm hypertonic stress elicited 2-fold Ca2+ transients that were suppressed by the TRPV1-selective antagonists capsazepine and JYL 1421. Such transients were enhanced by PGE2. Hypertonicity-induced EGF receptor (EGFR) transactivation was suppressed by preincubating HCECs with capsazepine, matrix metalloproteinase 1 (MMP1) inhibitor TIMP-1, broad-spectrum MMP inhibitor GM 6001, heparin-bound (HB)-EGF inhibitor CRM 197, or EGFR inhibitor AG 1478. ERK and p38 MAPK and NF-κB activation after EGFR transactivation occurred in tonicity and in a time-dependent manner. Hypertonicity-induced increases in IL-6 and IL-8 releases were suppressed by exposure to capsazepine, AG 1478, ERK inhibitor PD 98059, p38 inhibitor SB 203580, or NF-κB inhibitor PDTC.

CONCLUSIONS

Hypertonic stress-elicited TRPV1 channel stimulation mediates increases in a proinflammatory cytokine IL-6 and a chemoattractant IL-8 by eliciting EGFR transactivation, MAPK, and NF-κB activation. Selective drug modulation of either TRPV1 activity or its signaling mediators may yield a novel approach to suppressing inflammatory responses occurring in dry eye syndrome.

Epidermal growth factor increases claudin-4 expression mediated by Sp1 elevation in MDCK cells

Epidermal growth factor (EGF) increases claudin-4 expression in Madin-Darby canine kidney (MDCK) cells. Here we examined what regulatory mechanisms are involved in the EGF-induced claudin-4 elevation. EGF transiently increased claudin-4 mRNA at 3h and persistently increased its protein for 24h without affecting claudin-1 expression. EGF increased p-ERK1/2 levels, which were inhibited by U0126, a MEK inhibitor. The exogenous expression of constitutively activated MEK increased claudin-4 expression. These results indicate that the activation of ERK1/2 is involved in the EGF-induced claudin-4 elevation. EGF increased Sp1 expression within 1h, which was inhibited by U0126. In immunocytochemistry, Sp1 was distributed in nucleus in control and the EGF-treated cells. The EGF-induced claudin-4 elevation was inhibited by mithramycin, a Sp1 inhibitor, and Sp1 small interfering RNA. We suggest that EGF activates a MEK/ERK pathway and increases Sp1 expression, resulting in an elevation of claudin-4 expression.

EGF receptor signaling is involved in expression of osmoprotective TonEBP target gene aldose reductase under hypertonic conditions

Renal medullary cells adapt to their hyperosmotic environment by enhanced expression of various osmoprotective genes. Although it is clearly established that TonEBP contributes to the expression of these genes, neither the precise signaling mechanism by which hypertonicity activates TonEBP is completely understood, nor is it known whether a membrane-bound osmosenser, corresponding to yeast and bacteria, is present in mammalian cells. We found evidence that metalloproteinase (MMP)-dependent activation of the epidermal growth factor receptor (EGFR) signals to TonEBP and stimulates the expression of the TonEBP target gene aldose reductase (AR) under hypertonic conditions. Phosphorylation of EGFR and the downstream MAP kinases ERK1/2 and p38 was significantly enhanced by high NaCl in Madin-Darby canine kidney (MDCK) cells. Conversely, the broad-spectrum MMP inhibitor GM6001 or the EGFR inhibitor AG1478 diminished phosphorylation of EGFR, p38, and ERK1/2, the induction of AR mRNA and protein, and AR promoter reporter activity in response to hypertonicity. Accordingly, neutralizing antibodies against the putative EGFR ligand transforming growth factor-alpha (TGF-alpha) abolished AR induction during osmotic stress. Furthermore, tonicity-induced phosphorylation of p38 and ERK1/2 and expression of AR were reduced significantly in MDCK cells transfected with a dominant-negative Ras construct. These effects were not caused by reduced nuclear abundance of TonEBP during osmotic stress; however, inhibition of EGFR or p38 diminished TonEBP transactivation activity under hypertonic conditions. The contribution of MMP/EGFR signaling in vivo was confirmed in C57BL/6 mice, in which treatment with GM6001 was associated with reduced AR induction following dehydration. Taken together, these results indicate that osmotic stress induces MMP-dependent activation of EGFR, likely via shedding of TGF-alpha, and downstream activation of Ras and the MAP kinases p38 and ERK1/2, which stimulate TonEBP transactivation activity. This EGFR-Ras-MAPK pathway contributes to TonEBP transcriptional activation and targets gene expression during osmotic stress, thus establishing a membrane-associated signal input that contributes to the regulation of TonEBP activity.

PGE2 potentiates tonicity-induced COX-2 expression in renal medullary cells in a positive feedback loop involving EP2-cAMP-PKA signaling

Cyooxygenase-2 (COX-2)-derived PGE2 is critical for the integrity and function of renal medullary cells during antidiuresis. The present study extended our previous finding that tonicity-induced COX-2 expression is further stimulated by the major COX-2 product PGE2 and investigated the underlying signaling pathways and the functional relevance of this phenomenon. Hyperosmolality stimulated COX-2 expression and activity in Madin-Darby canine kidney (MDCK) cells, a response that was further increased by PGE2-cAMP signaling, suggesting the existence of a positive feedback loop. This effect was diminished by AH-6809, an EP2 antagonist, and by the PKA inhibitor H-89, but not by AH-23848, an EP4 antagonist. The effect of PGE2 was mimicked by forskolin and dibutyryl-cAMP, suggesting that the stimulatory effect of PGE2 on COX-2 is mediated by a cAMP-PKA-dependent mechanism. Accordingly, cAMP-responsive element (CRE)-driven reporter activity paralleled the effects of PGE2, AH-6809, AH-23848, H-89, forskolin, and dibutyryl-cAMP on COX-2 expression. In addition, the stimulatory effect of PGE2 on tonicity-induced COX-2 expression was blunted in cells transfected with dominant-negative CRE binding (CREB) protein, as was the case in a COX-2 promoter reporter construct in which a putative CRE was deleted. Furthermore, PGE2 resulted in PKA-dependent phosphorylation of the pro-apoptotic protein Bad at Ser155, a mechanism that is known to inactivate Bad, which coincided with reduced caspase-3 activity during osmotic stress. Conversely, pharmacological interruption of the PGE2-EP2-cAMP-PKA pathway abolished Ser155 phosphorylation of Bad and blunted the protective effect of PGE2 on cell survival during osmotic stress. These observations indicate the existence of a positive feedback loop of PGE2 on COX-2 expression during osmotic stress, an effect that apparently is mediated by EP2-cAMP-PKA signaling, and that contributes to cell survival under hypertonic conditions.

Ectodomain shedding of pro-TGF-alpha is required for COX-2 induction and cell survival in renal medullary cells exposed to osmotic stress

In the renal medulla, cyclooxygenase (COX)-2 is induced by osmotic stress as present in this kidney region during antidiuresis. Increasing evidence suggests that EGF receptor (EGFR) signaling is involved in this process. The aim of the present study was to examine the mechanisms responsible for COX-2 expression and PGE(2) production during hypertonic conditions and to identify potential autocrine/paracrine EGFR ligands. Immunohistochemisty and Western blot analysis revealed abundant expression of the pro-EGFR ligand pro-transforming growth factor (TGF)-alpha in renal medullary cells in vivo and in cultured Madin-Darby canine kidney cells. In Madin-Darby canine kidney cells, hypertonicity rapidly increased TNF-alpha converting enzyme (TACE)-dependent ectodomain shedding of pro-TGF-alpha; phosphorylation of EGFR, p38, and ERK1/2; expression of COX-2; and production of PGE(2). Conversely, TACE inhibition prevented TGF-alpha release; EGFR, p38, and ERK1/2 activation; and COX-2 expression. Furthermore, cell survival was reduced substantially, a response that could be reversed by the addition of PGE(2). Simultaneous addition of recombinant TGF-alpha during TACE inhibition restored EGFR and MAPK phosphorylation, COX-2 expression, PGE(2) production, and cell survival during osmotic stress. These results indicate that hypertonicity induces TACE-mediated ectodomain shedding of pro-TGF-alpha, which subsequently activates COX-2 expression in an autocrine/paracrine fashion, via EGFR and MAPKs. We conclude that tonicity-induced TGF-alpha release is required for COX-2 expression, PGE(2) synthesis, and survival of renal medullary cells during osmotic stress.

Cellular Response to Hyperosmotic Stresses

Cells in the renal inner medulla are normally exposed to extraordinarily high levels of NaCl and urea. The osmotic stress causes numerous perturbations because of the hypertonic effect of high NaCl and the direct denaturation of cellular macromolecules by high urea. High NaCl and urea elevate reactive oxygen species, cause cytoskeletal rearrangement, inhibit DNA replication and transcription, inhibit translation, depolarize mitochondria, and damage DNA and proteins. Nevertheless, cells can accommodate by changes that include accumulation of organic osmolytes and increased expression of heat shock proteins. Failure to accommodate results in cell death by apoptosis. Although the adapted cells survive and function, many of the original perturbations persist, and even contribute to signaling the adaptive responses. This review addresses both the perturbing effects of high NaCl and urea and the adaptive responses. We speculate on the sensors of osmolality and document the multiple pathways that signal activation of the transcription factor TonEBP/OREBP, which directs many aspects of adaptation. The facts that numerous cellular functions are altered by hyperosmolality and remain so, even after adaptation, indicate that both the effects of hyperosmolality and adaptation to it involve profound alterations of the state of the cells.

Hypertonic sodium choloride and mannitol induces COX-2 via different signaling pathways in mouse cortical collecting duct M-1 cells

The kidney cortical collecting duct is an important site for the maintenance of sodium balance. Previous studies have shown that, in renal medullary cells, hypertonic stress induces expression of cyclooxygenase-2 (COX-2) via NF-kappaB activation, but little is known about COX-2 expression in response to hypertonicity in the cortical collecting duct. Therefore, we examined the mechanism of hypertonic induction of COX-2 in M-1 cells derived from mouse cortical collecting duct. Induction of COX-2 protein was detected within 6 h of treatment with hypertonic sodium chloride. The treatment also increased COX-2 mRNA accumulation in a cycloheximide-independent manner, suggesting that ongoing protein synthesis is not required for COX-2 induction. Using reporter plasmids containing 0.2-, 0.3-, and 1.5-kb fragments of the COX-2 promoter, we found that hypertonic induction of COX-2 was due to an increase in promoter activity. The COX-2-inductive effect of hypertonicity was inhibited by SB203580, indicating that the effect is mediated by p38 MAPK. Since p38 MAPK can activate NF-kappaB, we made point mutations in the NF-kappaB binding site within the COX-2 promoter. The mutations did not block the induction of COX-2 promoter activity by hypertonic sodium chloride, and hypertonic sodium chloride failed to activate NF-kappaB binding site-driven reporter gene constructs. In contrast, hypertonic mannitol activated NF-kappaB, indicating that hypertonic mannitol and hypertonic sodium chloride activate COX-2 by different mechanisms. Thus, induction of COX-2 expression in M-1 cells by hypertonic sodium chloride does not involve activation of NF-kappaB. Furthermore, the signal transduction pathways that respond to hypertonic stress vary for different osmolytes in cortical collecting duct cells.

NFAT3 is Required for EGF-Induced COX-2 Transcription, but Neither iNOS Transcription Nor Cell Transformation in Cl 41 Cells

Epidermal growth factor (EGF) has been reported to act as a tumor promoter in several tissues, such as skin, in association with the induction of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). However, molecular mechanisms involved in these regulations are not well defined. This study addressed a potential role of nuclear factor of activated T cells 3 (NFAT3) in EGF-induced COX-2 and iNOS transcription and cell transformation in mouse epidermal Cl 41 cells. We found that EGF markedly induced anchorage-independent growth (cell transformation) of Cl 41 cells, as well as COX-2 (> 6-fold) and iNOS (> 5-fold) promoter-dependent transcription. The EGF-induced COX-2 transcription was blocked by knockdown of NFAT3 with NFAT3 siRNA, whereas the transcription of iNOS and cell transformation induced by EGF were not affected. Although our recent studies supported that NFAT3 plays an essential role in chemical carcinogen benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE)-induced cell transformation, the data presented here demonstrated that NFAT3 is required for EGF-induced COX-2 transcription, but neither iNOS transcription nor cell transformation, indicating that the role of NFAT3 in regulating cell transformation is carcinogen-specific.

Hypertonic sodium chloride induction of cyclooxygenase-2 occurs independently of NF-kappaB and is inhibited by the glucocorticoid receptor in A549 cells

Cellular response to a hypertonic environment is important for fluid clearance in the lung. Hypertonicity modulates prostaglandin synthesis by influencing cyclooxygenase-2 (COX-2) expression in tissues such as liver and kidney via a mitogen-activated protein kinase (MAPK)-dependent pathway. However, little is known about COX-2 expression in response to hypertonicity in the lung. COX-2 mRNA accumulation induced by hypertonic NaCl was detected after 1 h of treatment, and COX-2 mRNA continued to accumulate until 18 h, the longest time point examined, in human alveolar epithelial A549 cells. This induction was a transcriptional event that occurred in the absence of the protein synthesis inhibitor cycloheximide and was the result of enhanced promoter activity, as examined with the use of full-length COX-2 promoter-driven reporter plasmids. The induction of COX-2 expression by hypertonic NaCl did not require the activation of NF-kappaB. The p38 MAPK inhibitor, SB203580, or MEK1/2 inhibitor, U0126, inhibited hypertonic induction of COX-2 expression. We examined whether the hypertonic induction of COX-2 was under the influence of glucocorticoid; we found that COX-2 promoter activity and mRNA and protein levels were depressed by dexamethasone and antagonized by the glucocorticoid receptor (GR) antagonist RU486. Our data demonstrate that the induction of COX-2 expression by hypertonic NaCl occurs independently of NF-kappaB and is inhibited by the GR in A549 cells.

Coordinate control of prostaglandin E2 synthesis and uptake by hyperosmolarity in renal medullary interstitial cells

During water deprivation, prostaglandin E(2) (PGE(2)), formed by renal medullary interstitial cells (RMICs), feedback inhibits the actions of antidiuretic hormone. Interstitial PGE(2) concentrations represent the net of both PGE(2) synthesis by cyclooxygenase (COX) and PGE(2) uptake by carriers such as PGT. We used cultured RMICs to examine the effects of hyperosmolarity on both PG synthesis and PG uptake in the same RMIC. RMICs expressed endogenous PGT as assessed by mRNA and immunoblotting. RMICs rapidly took up [(3)H]PGE(2) to a level 5- to 10-fold above background and with a characteristic time-dependent "overshoot." Inhibitory constants (K(i)) for various PGs and PGT inhibitors were similar between RMICs and the cloned rat PGT. Increasing extracellular hyperosmolarity to the range of 335-485 mosM increased the net release of PGE(2) by RMICs, an effect that was concentration dependent, maximal by 24 h, reversible, and associated with increased expression of COX-2. Over the same time period, there was decreased cell-surface activity of PGT due to internalization of the transporter. With continued exposure to hyperosmolarity over 7-10 days, PGE(2) release remained elevated, COX-2 returned to baseline, and PGT-mediated uptake became markedly reduced. Our findings suggest that hyperosmolarity induces coordinated changes in COX-2-mediated PGE(2) synthesis and PGT-mediated PGE(2) uptake in RMICs.

p38 and EGF receptor kinase-mediated activation of the phosphatidylinositol 3-kinase/Akt pathway is required for Zn2+-induced cyclooxygenase-2 expression

Cyclooxygenase 2 (COX-2) expression is induced by physiological and inflammatory stimuli. Regulation of COX-2 expression is stimulus and cell type specific. Exposure to Zn2+ has been associated with activation of multiple intracellular signaling pathways as well as the induction of COX-2 expression. This study aims to elucidate the role of intracellular signaling pathways in Zn2+-induced COX-2 expression in human bronchial epithelial cells. Inhibitors of the phosphatidylinositol 3-kinase (PI3K) potently block Zn2+-induced COX-2 mRNA and protein expression. Overexpression of adenoviral constructs encoding dominant-negative Akt kinase downstream of PI3K or wild-type phosphatase and tensin homolog deleted on chromosome 10, an important PI3K phosphatase, suppresses COX-2 mRNA expression induced by Zn2+. Zn2+ exposure induces phosphorylation of the tyrosine kinases, including Src and EGF receptor (EGFR), and the p38 mitogen-activated protein kinase. Blockage of these kinases results in inhibition of Zn2+-induced Akt phosphorylation as well as COX-2 protein expression. Overexpression of dominant negative p38 constructs suppresses Zn2+-induced increase in COX-2 promoter activity. In contrast, the c-Jun NH2-terminal kinase and the extracellular signal-regulated kinases have minimal effect on Akt phosphorylation and COX-2 expression. Inhibition of p38, Src, and EGFR kinases with pharmacological inhibitors markedly reduces Akt phosphorylation induced by Zn2+. However, the PI3K inhibitors do not show inhibitory effects on p38, Src, and EGFR. These data suggest that p38 and EGFR kinase-mediated Akt activation is required for Zn2+-induced COX-2 expression and that the PI3K/Akt signaling pathway plays a central role in this event.

Altered expression of selected genes in kidney of rats with lithium-induced NDI

Lithium treatment is associated with development of nephrogenic diabetes insipidus, caused in part by downregulation of collecting duct aquaporin-2 (AQP2) and AQP3 expression. In the present study, we carried out cDNA microarray screening of gene expression in the inner medulla (IM) of lithium-treated and control rats, and selected genes were then investigated at the protein level by immunoblotting and/or immunohistochemistry. The following genes exhibited significantly altered transcription and mRNA expression levels, and these were compatible with the changes in protein expression. 11β-Hydroxysteroid dehydrogenase type 2 protein expression in the IM was markedly increased (198 ± 25% of controls, n = 6), and immunocytochemistry demonstrated an increased labeling of IM collecting duct (IMCD) principal cells. This indicated altered renal mineralocorticoid/glucocorticoid responses in lithium-treated rats. The inhibitor of cyclin-dependent kinases p27 (KIP) protein expression was significantly decreased or undetectable in the IMCD cells, pointing to increased cellular proliferation and remodeling. Heat shock protein 27 protein expression was decreased in the IM (64 ± 6% of controls, n = 6), likely to be associated with the decreased medullary osmolality in lithium-treated rats. Consistent with this, lens aldose reductase protein expression was markedly decreased in the IM (16 ± 2% of controls, n = 6), and immunocytochemistry revealed decreased expression in the thin limb cells in the middle and terminal parts of the IM. Ezrin protein expression was upregulated in the IM (158 ± 16% of controls, n = 6), where it was predominantly expressed in the apical and cytoplasmic domain of the IMCD cells. Increased ezrin expression indicated remodeling of the actin cytoskeleton and/or altered regulation of IMCD transporters. In conclusion, the present study demonstrates changes in gene expression not only in the collecting duct but also in the thin limb of the loop of Henle in the IM, and several of these genes are linked to altered sodium and water reabsorption, cell cycling, and changes in interstitial osmolality.

The γ-subunit of Na-K-ATPase is incorporated into plasma membranes of mouse IMCD3 cells in response to hypertonicity

Hypertonicity mediated by chloride upregulates the expression of the γ-subunit of Na-K-ATPase in cultured cells derived from the murine inner medullary collecting duct (IMCD3; Capasso JM, Rivard CJ, Enomoto LM, and Berl T. Proc Natl Acad Sci USA 100: 6428–6433, 2003). The purpose of this study was to examine the cellular locations and the time course of γ-subunit expression after long-term adaptation and acute hypertonic challenges induced with different salts. Cells were analyzed by confocal immunofluorescence and immunoelectron microscopy with antibodies against the COOH terminus of the Na-K-ATPase γ-subunit or the γbsplice variant. Cells grown in 300 mosmol/kgH2O showed no immunoreactivity for the γ-subunit, whereas cells adapted to 600 or 900 mosmol/kgH2O demonstrated distinct reactivity located at the plasma membrane of all cells. IMCD3 cell cultures acutely challenged to 550 mosmol/kgH2O with sodium chloride or choline chloride showed incorporation of γ into plasma membrane 12 h after osmotic challenge and distinct membrane staining in ∼40% of the cells 48 h after osmotic shock. In contrast, challenging the IMCD3 cells to 550 mosmol/kgH2O by addition of sodium acetate did not result in expression of the γ-subunit in the membranes of surviving cells after 48 h. The present results demonstrate that the Na-K-ATPase γ-subunit becomes incorporated into the basolateral membrane of IMCD3 cells after both acute hyperosmotic challenge and hyperosmotic adaptation. We conclude that the γ-subunit has an important role in the function of Na-K-ATPase to sustain the cellular cation balance over the plasma membrane in a hypertonic environment.

CELL SURVIVAL IN THE HOSTILE ENVIRONMENT OF THE RENAL MEDULLA

The countercurrent system in the medulla of the mammalian kidney provides the basis for the production of urine of widely varying osmolalities, but necessarily entails extreme conditions for medullary cells, i.e., high concentrations of solutes (mainly NaCl and urea) in antidiuresis, massive changes in extracellular solute concentrations during the transitions from antidiuresis to diuresis and vice versa, and low oxygen tension. The strategies used by medullary cells to survive in this hostile milieu include accumulation of organic osmolytes and heat shock proteins, the extensive use of the glycolysis for energy production, and a well-orchestrated network of signaling pathways coordinating medullary circulation and tubular work.

EphA2: expression in the renal medulla and regulation by hypertonicity and urea stress in vitro and in vivo

EphA2, a member of the large family of Eph receptor tyrosine kinases, is highly expressed in epithelial tissue and has been implicated in cell-cell and cell-matrix interactions, as well as cell growth and survival. Expression of EphA2 mRNA and protein was markedly upregulated by both hypertonic stress and by elevated urea concentrations in cells derived from the murine inner medullary collecting duct. This upregulation likely required transactivation of the epidermal growth factor (EGF) receptor tyrosine kinase and metalloproteinase-dependent ectodomain cleavage of an EGF receptor ligand, based on pharmacological inhibitor studies. A human EphA2 promoter fragment spanning nucleotides -4030 to +21 relative to the putative EphA2 transcriptional start site was responsive to tonicity but insensitive to urea. A promoter fragment spanning -1890 to +128 recapitulated both tonicity- and urea-dependent upregulation of expression, consistent with transcriptional activation. Neither the bona fide p53 response element at approximately -1.5 kb nor a pair of putative TonE elements at approximately -3 kb conferred the tonicity responsiveness. EphA2 mRNA and protein were expressed at low levels in rat renal cortex but at high levels in the collecting ducts of the renal medulla and papilla. Water deprivation in rats increased EphA2 expression in renal papilla, whereas dietary supplementation with 20% urea increased EphA2 expression in outer medulla. These data indicate that transcription and expression of the EphA2 receptor tyrosine kinase are regulated by tonicity and urea in vitro and suggest that this phenomenon is also operative in vivo. Renal medullary EphA2 expression may represent an adaptive response to medullary hypertonicity or urea exposure.

Role of proneuregulin 1 cleavage and human epidermal growth factor receptor activation in hypertonic aquaporin induction

Mammalian cells are confronted with changes in extracellular osmolality at various sites, including the aqueous layer above the lung epithelium. Hypertonic shock induces the activation of mitogen-activated protein kinases and the expression of a defined set of genes, including aquaporins. We investigated upstream components of the response to hypertonicity in lung epithelial cells and found that before extracellular signal-regulated kinase activation and aquaporin synthesis, the membrane-bound prohormone neuregulin 1-beta is cleaved and binds to human epidermal growth factor receptor 3 (HER3). The signaling is prevented by matrix metalloproteinase inhibition, inhibition of neuregulin 1-beta binding to HER3, and inhibition of HER tyrosine kinase activity. Inhibition of HER activation interferes with the hypertonic induction of two different aquaporins in three distinct cell lines of mouse and human origin. We propose that ligand-dependent HER activation constitutes a generalized signaling principle in the mammalian hypertonic stress response relevant to aquaporin expression.

Cyclooxygenase 2 (COX2) expression is associated with poor outcome in ER-negative, but not ER-positive, breast cancer

AIMS

Inflammation and hormonal signalling induce cyclooxygenase 2 (COX2) expression in solid tumours. COX2 expression is linked to neovascularization and tumour growth. HER2 modulates colorectal cancer COX2 expression. We investigated interactions between COX2 and HER1-4 in breast cancer.

METHODS AND RESULTS

COX2 expression was localized to epithelial cells with 21.2% of cases expressing higher levels than normal epithelium. Elevated COX2 expression was not associated with size, grade, high Nottingham prognostic index (NPI) or oestrogen receptor (ER) negativity. No association was observed between COX2 and HER1-4 expression. High COX2 expression was associated with reduced disease-free survival (P = 0.03) and disease-related survival in ER-negative (P = 0.046) but not ER-positive disease (P = 0.835).

CONCLUSION

HER1, 2, 3 and 4 are not associated with high breast tumour COX2 expression. COX2 is frequently expressed in breast carcinoma cells and adjacent epithelium. COX2 may be an important factor in promoting tumour progression in ER-negative tumours and a potential drug target in breast tumours.