Transcriptional regulation of the membrane-associated prostaglandin E2 synthase gene. Essential role of the transcription factor Egr-1

Low Salt Delivery Triggers Autocrine Release of Prostaglandin E2 From the Aldosterone-Sensitive Distal Nephron in Familial Hyperkalemic Hypertension Mice

Aberrant activation of with-no-lysine kinase (WNK)-STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) kinase signaling in the distal convoluted tubule (DCT) causes unbridled activation of the thiazide-sensitive sodium chloride cotransporter (NCC), leading to familial hyperkalemic hypertension (FHHt) in humans. Studies in FHHt mice engineered to constitutively activate SPAK specifically in the DCT (CA-SPAK mice) revealed maladaptive remodeling of the aldosterone sensitive distal nephron (ASDN), characterized by decrease in the potassium excretory channel, renal outer medullary potassium (ROMK), and epithelial sodium channel (ENaC), that contributes to the hyperkalemia. The mechanisms by which NCC activation in DCT promotes remodeling of connecting tubule (CNT) are unknown, but paracrine communication and reduced salt delivery to the ASDN have been suspected. Here, we explore the involvement of prostaglandin E2 (PGE2). We found that PGE2 and the terminal PGE2 synthase, mPGES1, are increased in kidney cortex of CA-SPAK mice, compared to control or SPAK KO mice. Hydrochlorothiazide (HCTZ) reduced PGE2 to control levels, indicating increased PGE2 synthesis is dependent on increased NCC activity. Immunolocalization studies revealed mPGES1 is selectively increased in the CNT of CA-SPAK mice, implicating low salt-delivery to ASDN as the trigger. Salt titration studies in an in vitro ASDN cell model, mouse CCD cell (mCCD-CL1), confirmed PGE2 synthesis is activated by low salt, and revealed that response is paralleled by induction of mPGES1 gene expression. Finally, inhibition of the PGE2 receptor, EP1, in CA-SPAK mice partially restored potassium homeostasis as it partially rescued ROMK protein abundance, but not ENaC. Together, these data indicate low sodium delivery to the ASDN activates PGE2 synthesis and this inhibits ROMK through autocrine activation of the EP1 receptor. These findings provide new insights into the mechanism by which activation of sodium transport in the DCT causes remodeling of the ASDN.

Expression of Enzymes Associated with Prostaglandin Synthesis in Equine Conceptuses

Simple Summary

The mobile preimplantative phase of equine gestation, taking place between day 9 and 16 after ovulation, is characterized by peristaltic contractions of the uterus caused by secretion of prostaglandins by the spheric equine conceptus. This mobility is necessary for maternal recognition of pregnancy in equids, taking place around day 14 after ovulation. The presented study investigated the spatial and temporal abundance of prostaglandin synthesis enzymes of the equine conceptus, elucidating a basal and an inducible system for prostaglandin E2. Prostaglandin F2α synthesis is restricted to the “periembryonic”pole area and relies on enzymatic conversion of prostaglandin E2. This scenario led to a model able to explain the embryonic forward motion driven by the peristaltic contractions of the uterus. In vitro incubation of primary trophoblast cell cultures with oxytocin showed no influence of this hormone on prostaglandin synthesis.

Abstract

In the horse, mobility of the conceptus is required for maternal recognition of pregnancy depending on secretion of prostaglandins by the conceptus. The aim of this study was to determine the expression and localization of key enzymes of the different pathways leading to synthesis of prostaglandin E2 and F2α in the equine conceptus during the mobility phase. Enzyme expression was analyzed via quantitative RT-PCR in total RNA samples of equine conceptuses collected on days 10 (n = 5), 12 (n = 12), 14 (n = 5) and 16 (n = 7) from healthy mares. Relative abundance of cyclooxygenase (COX)-2 mRNA was higher (p < 0.05) than of COX-1 irrespective of conceptus age and for phospholipase A2 on day 16 in comparison to all other days (p < 0.01). Abundance of mRNA of cytosolic and microsomal prostaglandin E synthase (PGES) and of carbonyl reductase (CBR) 1 was not influenced by conceptus age. Immunohistochemically, COX-1, COX-2, as well as cytosolic and microsomal PGES were present in both the ectodermal and endodermal layer of the yolk sac wall. CBR-1 was restricted to periembryonic disc area. The localisation of the key enzymes explains the mechanism of embryo mobility. In vitro incubation of primary trophoblast cell cultures with oxytocin had no effect on key enzyme synthesis.

Ellagitannins from Punica granatum leaves suppress microsomal prostaglandin E synthase-1 expression and induce lung cancer cells to undergo apoptosis

Prostaglandin E₂ (PGE₂), which is a potent pro-inflammatory lipid mediator, is biosynthesized from arachidonic acid by cyclooxygenase-2 (COX-2) and microsomal PGE synthase-1 (mPGES-1). Non-steroidal anti-inflammatory drugs (NSAIDs) are used clinically as COX inhibitors, but they have gastrointestinal and cardiovascular side-effects. Thus, the terminal enzyme mPGES-1 holds promise as the next therapeutic target. In this study, we found that the ellagitannins granatin A and granatin B isolated from pomegranate leaves, and geraniin, which is their structural analog, selectively suppressed mPGES-1 expression without affecting COX-2 in non-small cell lung carcinoma A549 cells. The ellagitannins also down-regulated tumor necrosis factor α, inducible nitric oxide synthase, and anti-apoptotic factor B-cell chronic lymphocytic leukemia/lymphoma 2, and induced A549 cells to undergo apoptosis. These findings indicate that the ellagitannins have anti-inflammatory and anti-carcinogenic effects, due to their specific suppression of mPGES-1.Abbreviations: Bcl-2: B-cell chronic lymphocytic leukemia/lymphoma 2; COX: cyclooxygenase; CRE: cAMP response element; DHHDP: dehydrohexahydroxydiphenoyl; Et₂O: diethyl ether; EtOAc: ethyl acetate; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; iNOS: inducible nitric oxide synthase; mPGES-1: microsomal prostaglandin E synthase-1; n-BuOH: water-saturated n-butanol; NSAIDs: non-steroidal anti-inflammatory drugs; NF-κB: nuclear factor-κB; PG: prostaglandin; TNF: tumor necrosis factor; TUNEL: terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.

Microsomal prostaglandin E synthase-1 is a critical factor in dopaminergic neurodegeneration in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by the loss of nigrostriatal dopaminergic neurons. Although increased production of prostaglandin E₂ (PGE₂) has been implicated in tissue damage in several pathological settings, the role of microsomal prostaglandin E synthase-1 (mPGES-1), an inducible terminal enzyme for PGE₂ synthesis, in dopaminergic neurodegeneration remains unclear. Here we show that mPGES-1 is up-regulated in the dopaminergic neurons of the substantia nigra of postmortem brain tissue from PD patients and in neurotoxin 6-hydroxydopamine (6-OHDA)-induced PD mice. The expression of mPGES-1 was also up-regulated in cultured dopaminergic neurons stimulated with 6-OHDA. The genetic deletion of mPGES-1 not only abolished 6-OHDA-induced PGE₂ production but also inhibited 6-OHDA-induced dopaminergic neurodegeneration both in vitro and in vivo. Nigrostriatal projections, striatal dopamine content, and neurological functions were significantly impaired by 6-OHDA administration in wild-type (WT) mice, but not in mPGES-1 knockout (KO) mice. Furthermore, in cultured primary mesencephalic neurons, addition of PGE₂ to compensate for the deficiency of 6-OHDA-induced PGE₂ production in mPGES-1 KO neurons recovered 6-OHDA toxicity to almost the same extent as that seen in WT neurons. These results suggest that induction of mPGES-1 enhances 6-OHDA-induced dopaminergic neuronal death through excessive PGE₂ production. Thus, mPGES-1 may be a valuable therapeutic target for treatment of PD.

Regulation of mPGES-1 composition and cell growth via the MAPK signaling pathway in jurkat cells

Previous studies have suggested that microsomal prostaglandin E synthase-1 (mPGES-1) is highly expressed and closely associated with mitogen-activated protein kinase (MAPK) signaling pathways in various types of malignant cells. However, their expression patterns and function with respect to T-cell acute lymphoblastic leukemia (T-ALL) remain largely unknown. The present study investigated whether mPGES-1 served a crucial role in T-ALL and aimed to identify interactions between mPGES-1 and the MAPK signaling pathway in T-ALL. The results indicated that mPGES-1 overexpression in T-ALL jurkat cells was significantly decreased by RNA silencing. Decreasing mPGES-1 on a consistent basis may inhibit cell proliferation, induce apoptosis and arrest the cell cycle in T-ALL jurkat cells. Microarray and western blot analyses revealed that c-Jun N-terminal kinase served a role in the mPGES-1/prostaglandin E2/EP4/MAPK positive feedback loops. In addition, P38 and extracellular signal-regulated kinase 1/2 exhibited negative feedback effects on mPGES-1. In conclusion, the results suggested that cross-talk between mPGES-1 and the MAPK signaling pathway was very complex. Therefore, the combined regulation of mPGES-1 and the MAPK signaling pathway may be developed into a new candidate therapy for T-ALL in the future.

Impact of Cyclooxygenase-2 1195 G-Carrier Genotype Associated with Intestinal Metaplasia and Endoscopic Findings Based on Kyoto Classification

BACKGROUND/AIMS

We aimed to clarify whether cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) genotypes were associated with certain histological findings and endoscopical appearances based on Kyoto classification.

METHODS

We enrolled 285 Helicobacter pylori-infected gastritis patients. Genotypes of COX-2 1195, COX-2 1290, mPGES-1, interleukin-1β (IL-1β) 511 and tumour necrosis factor-α (TNF-α) 308 were analyzed. Genotyping was performed by polymerase chain reaction. Endoscopic appearances and histological assessment were determined by using Kyoto classification, operative link on gastritic intestinal metaplasia assessment and the updated Sydney system.

RESULTS

There was a significant (p = 0.027) relationship between the IL-1β 511 C-carrier and histological gastric inflammation in H. pylori-infected gastritis patients. There was a significant (p = 0.009) correlation between the COX-2 1195 G-carrier genotype and histological intestinal metaplasia in the gastric antrum of H. pylori-infected gastritis patients and gastric xanthoma (p = 0.027). The COX-2 1195 G-carrier genotype was also significantly (p = 0.038) associated with the score of endoscopic intestinal metaplasia based on Kyoto classification. The mPGES-1 genotype was significantly (p = 0.002) associated with endoscopic swelling of area.

CONCLUSION

Our results suggest that in Japan, there exists a significant correlation between the COX-2 1195 G-carrier genotype and intestinal metaplasia in histological and endoscopic findings based on Kyoto classification in H. pylori-infected gastric mucosa.

Fatty acid-binding protein 5 controls microsomal prostaglandin E synthase 1 (mPGES-1) induction during inflammation

Fatty acid-binding proteins (FABPs) are intracellular lipid carriers that regulate inflammation, and pharmacological inhibition of FABP5 reduces inflammation and pain. The mechanism(s) underlying the anti-inflammatory effects associated with FABP5 inhibition is poorly understood. Herein, we identify a novel mechanism through which FABP5 modulates inflammation. In mice, intraplantar injection of carrageenan induces acute inflammation that is accompanied by edema, enhanced pain sensitivity, and elevations in proinflammatory cytokines and prostaglandin E₂ (PGE₂). Inhibition of FABP5 reduced pain, edema, cytokine, and PGE₂ levels. PGE₂ is a major eicosanoid that enhances pain in the setting of inflammation, and we focused on the mechanism(s) through which FABP5 modulates PGE₂ production. Cyclooxygenase 2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES-1) are enzymes up-regulated at the site of inflammation and account for the bulk of PGE₂ biosynthesis. Pharmacological or genetic FABP5 inhibition suppressed the induction of mPGES-1 but not COX-2 in carrageenan-injected paws, which occurred predominantly in macrophages. The cytokine interleukin 1β (IL-1β) is a major inducer of mPGES-1 during inflammation. Using A549 cells that express FABP5, IL-1β stimulation up-regulated mPGES-1 expression, and mPGES-1 induction was attenuated in A549 cells bearing a knockdown of FABP5. IL-1β up-regulates mPGES-1 via NF-κB, which activates the mPGES-1 promoter. Knockdown of FABP5 reduced the activation and nuclear translocation of NF-κB and attenuated mPGES-1 promoter activity. Deletion of NF-κB-binding sites within the mPGES-1 promoter abrogated the ability of FABP5 to inhibit mPGES-1 promoter activation. Collectively, these results position FABP5 as a novel regulator of mPGES-1 induction and PGE₂ biosynthesis during inflammation.

The Role of mPGES-1 in Inflammatory Brain Diseases

Prostaglandin E₂ (PGE₂) has been thought to be an important mediator of inflammation in peripheral tissues, but recent studies clearly show the involvement of PGE₂ in inflammatory brain diseases. In some animal models of brain disease, the genetic disruption and chemical inhibition of cyclooxygenase (COX)-2 resulted in the reduction of PGE₂ and amelioration of symptoms, and it had been thought that PGE₂ produced by COX-2 may be involved in the progression of injuries. However, COX-2 produces not only PGE₂, but also some other prostanoids, and thus the protective effects of COX-2 inhibition, as well as severe side effects, may be caused by the inhibition of prostanoids other than PGE₂. Therefore, to elucidate the role of PGE₂, studies of microsomal prostaglandin E synthase-1 (mPGES-1), an inducible terminal enzyme for PGE₂ synthesis, have recently been an active area of research. Studies from mPGES-1 deficient mice provide compelling evidence for its role in a variety of inflammatory brain diseases, such as ischemic stroke, Alzheimer's disease and epilepsy, and clues for developing new therapeutic treatments for brain diseases by targeting mPGES-1. Considering that COX inhibitors may non-selectively suppress the production of many types of prostanoids that are essential for normal physiological functioning of the brain and peripheral tissues, as well as induce gastro-intestinal, renal and cardiovascular complications, mPGES-1 inhibitors are expected to be injury-selective and have fewer side-effects when treating human brain diseases. Thus, this paper focuses on recent studies that have demonstrated the involvement of mPGES-1 in pathological brain diseases.

Krüppel-Like Factor 12 Promotes Colorectal Cancer Growth through Early Growth Response Protein 1

Krüppel-like factor 12 (KLF12) is a transcription factor that plays a role in normal kidney development and repression of decidualization. KLF12 is frequently elevated in esophageal adenocarcinoma and has been reported to promote gastric cancer progression. Here, we examined the role of KLF12 in colorectal cancer (CRC). Indeed, KLF12 promotes tumor growth by directly activating early growth response protein 1 (EGR1). The levels of KLF12 and EGR1 correlate synergistically with a poor prognosis. These results indicate that KLF12 likely plays an important role in CRC and could serve as a potential prognostic marker and therapeutic target.

Prostaglandins induce early growth response 1 transcription factor mediated microsomal prostaglandin E2 synthase up-regulation for colorectal cancer progression

Cyclooxygenase2 (COX2) has been associated with cell growth, invasiveness, tumor progression and metastasis of colorectal carcinomas. However, the downstream prostaglandin (PG)-PG receptor pathway involved in these effects is poorly characterized.We studied the PG-pathway in gene expression databases and we found that PTGS2 (prostaglandin G/H synthase and cyclooxygenase) and PTGES (prostaglandin E synthase) are co-expressed in human colorectal tumors. Moreover, we detected that COX2 and microsomal Prostaglandin E2 synthase 1 (mPGES1) proteins are both up-regulated in colorectal human tumor biopsies.Using colon carcinoma cell cultures we found that COX2 overexpression significantly increased mPGES1 mRNA and protein. This up-regulation was due to an increase in early growth response 1 (EGR1) levels and its transcriptional activity. EGR1 was induced by COX2-generated PGF2α. A PGF2α receptor antagonist, or EGR1 silencing, inhibited the mPGES1 induction by COX2 overexpression. Moreover, using immunodeficient mice, we also demonstrated that both COX2- and mPGES1-overexpressing carcinoma cells were more efficient forming tumors.Our results describe for the first time the molecular pathway correlating PTGS2 and PTGES in colon cancer progression. We demonstrated that in this pathway mPGES1 is induced by COX2 overexpression, via autocrine PGs release, likely PGF2α, through an EGR1-dependent mechanism. This signaling provides a molecular explanation to PTGS2 and PTGES association and contribute to colon cancer advance, pointing out novel potential therapeutic targets in this oncological context.

Expression, regulation and function of Egr1 during implantation and decidualization in mice

Abstract Early growth response gene 1 (Egr1), a zinc finger transcriptional factor, plays an important role in regulating cell proliferation, differentiation and angiogenesis. Current data have shown that Egr1 is involved in follicular development, ovulation, luteinization and placental angiogenesis. However, the expression, regulation and function of Egr1 in mouse uterus during embryo implantation and decidualization are poorly understood. Here we showed that Egr1 was strongly expressed in the subluminal stroma surrounding the implanting blastocyst on day 5 of pregnancy. Injection of Egr1 siRNA into the mouse uterine horn could obviously reduce the number of implanted embryos and affect the uterine vascular permeability. Further study found that Egr1 played a role through influencing the expression of cyclooxygenase-2 (Cox-2), microsomal prostaglandin E synthase 1 (mPGES-1), vascular endothelial growth factor (Vegf), transformation related protein 53 (Trp53) and matrix metallopeptidase 9 (Mmp9) genes in the process of mouse embryo implantation. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) might direct the expression of Egr1 in the uterine stromal cells. Under in vivo and in vitro artificial decidualization, Egr1 expression was significantly decreased. Overexpression of Egr1 downregulated the expression of decidual marker decidual/trophoblast PRL-related protein (Dtprp) in the uterine stromal cells, while inhibition of Egr1 upregulated the expression of Dtprp under in vitro decidualization. Estrogen and progesterone could regulate the expression of Egr1 in the ovariectomized mouse uterus and uterine stromal cells. These results suggest that Egr1 may be essential for embryo implantation and decidualization.

Inhibition of lipopolysaccharide-induced gene expression by liver X receptor ligands in macrophages involves interference with early growth response factor 1

Liver X receptors (LXRs) are nuclear receptors that act as ligand-dependent transcription factors forming permissive heterodimers with retinoid X receptors (RXRs). In this study we aimed to assess the effect of LXR/RXR activation on the transcriptional induction of pro-inflammatory genes including cyclooxygenase-2 (COX-2) and microsomal prostaglandin E2 synthase-1 (mPGES-1) in activated macrophages. Our study shows that LXR ligands such as oxysterols, GW3965 or TO901317, as well as RXR ligands like 9cis retinoic acid or SR11237, decreased LPS-induced expression of COX-2 and mPGES-1. Consequently, LPS-dependent PGE2 production was substantially reduced in macrophages treated with LXR/RXR ligands. The inhibitory effects of LXR/RXR activation on LPS-induced expression of COX-2 and mPGES-1 in macrophages, occurred by a mechanism involving interference with transcriptional activation of these genes. LXR/RXR activation interfered with the activity of transcription factors essential in the up-regulation of the expression of pro-inflammatory genes in these cells, such as NFκB, but also Egr-1, which had not been previously associated with LXR-mediated gene repression. As this transcription factor is involved in the regulation of a variety of genes involved in inflammatory processes, LXR and RXR-mediated interference with Egr-1 signaling could represent an important event mediating the anti-inflammatory effects of these receptors in macrophages.

Anti-inflammatory effects of 7-hydroxyl-1-methylindole-3-acetonitrile, a synthetic arvelexin derivative, on the macrophages through destabilizing mPGES-1 mRNA and suppressing NF-κB activation

We previously demonstrated that 7-hydroxyl-1-methylindole-3-acetonitrile (7-HMIA), a synthesized analog of arvelexin, showed the strong inhibitory effects on LPS-induced NO and PGE2 production in macrophages. In this study, we focused on elucidating the anti-inflammatory properties of 7-HMIA and the mechanisms involved using in vitro and in vivo experimental models. In LPS-induced RAW 264.7 macrophages, 7-HMIA significantly inhibited the release of proinflammatory mediators such as prostaglandin E2 (PGE2), nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6). We also found that 7-HMIA suppressed PGE2 production not by inhibiting cyclooxygenase-2 (COX-2) expression or activity, but rather by suppressing the mRNA stability of microsomal prostaglandin E synthase (mPGES-1). Furthermore, 7-HMIA mediated attenuation of inducible NO synthase (iNOS), TNF-α, and IL-6 was closely associated with suppression of transcriptional activities of nuclear factor-kappa B (NF-κB), by decreasing p65 nuclear translocation and Akt phosphorylation. Animal studies revealed that 7-HMIA potently suppressed the carrageenan-induced paw edema and myeloperoxidase (MPO) activity in paw tissues. Taken together, our data indicated that the molecular basis for the anti-inflammatory properties of 7-HMIA involved the inhibition of mRNA stability of mPGES-1 and PI3K/Akt-mediated NF-κB pathways.

A mouse strain less responsive to dioxin-induced prostaglandin E2 synthesis is resistant to the onset of neonatal hydronephrosis

Dioxin is a ubiquitous environmental pollutant that induces toxicity when bound to the aryl hydrocarbon receptor (AhR). Significant differences in susceptibility of mouse strains to dioxin toxicity are largely accounted for by the dissociation constant of binding to dioxins of AhR subtypes encoded by different alleles. We showed that cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1), components of a prostanoid synthesis pathway, play essential roles in the onset of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced hydronephrosis of neonatal mice. Although C57BL/6J and BALB/cA mice harbor AhR receptors highly responsive to TCDD, they were found by chance to differ significantly in the incidence of TCDD-induced hydronephrosis. Therefore, the goal of the present study was to determine the molecular basis of this difference in susceptibility to TCDD toxicity. For this purpose, we administered C57BL/6J and BALB/cA dams' TCDD at an oral dose of 15 or 80 μg/kg on postnatal day (PND) 1 to expose pups to TCDD via lactation, and the pups' kidneys were collected on PND 7. The incidence of hydronephrosis in C57BL/6J pups (64%) was greater than in BALB/cA pups (0%, p < 0.05), despite similarly increased levels of COX-2 mRNA. The incidence of hydronephrosis in these mouse strains paralleled the levels of renal mPGES-1 mRNA and early growth response 1 (Egr-1) that modulates mPGES-1 gene expression, as well as PGE2 concentrations in urine. Although these mouse strains possess AhR alleles tightly bound to TCDD, their difference in incidence and severity of hydronephrosis can be explained, in part, by differences in the expression of mPGES-1 and Egr-1.

Kruppel-like factor 5 transcription factor promotes microsomal prostaglandin E2 synthase 1 gene transcription in breast cancer

The KLF5 (Krüppel-like factor 5) transcription factor is specifically expressed in a subset of estrogen receptor α-negative breast cancers. Although KLF5 promotes breast cancer cell cycle progression, survival, and tumorigenesis, the mechanism by which KLF5 promotes breast cancer is still not entirely understood. Here, we demonstrate that mPGES1, encoding microsomal prostaglandin E2 synthase 1 (mPGES1), is a KLF5 direct downstream target gene. KLF5 overexpression or knockdown positively altered the levels of mPGES1 mRNA and protein in multiple breast cell lines. 12-O-Tetradecanoylphorbol-13-acetate induced the expression of both KLF5 and mPGES1 in dosage- and time-dependent manners. The induction of KLF5 was essential for 12-O-tetradecanoylphorbol-13-acetate to induce mPGES1 expression. Additionally, KLF5 bound to the mPGES1 gene proximal promoter and activated its transcription. Both KLF5 and mPGES1 promoted prostaglandin E2 production; regulated p21, p27, and Survivin downstream gene expression; and likewise stimulated cell proliferation. Overexpression of mPGES1 partially rescued the KLF5 knockdown-induced downstream gene expression changes and growth arrest in MCF10A cells. Finally, we demonstrate that the expression of mPGES1 was positively correlated with the estrogen receptor α/progesterone receptor/HER2 triple-negative status. These findings suggest that mPGES1 is a target gene of KLF5, making it a new biomarker and a potential therapeutic target for triple-negative breast cancers.

CCAAT/enhancer binding protein β regulates prostaglandin E synthase expression and prostaglandin E2 production in activated microglial cells

The eicosanoid prostaglandin E2 (PGE2 ) plays important roles in neuroinflammation and it is produced by the sequential action of the enzymes cyclooxygenase-2 (COX-2) and prostaglandin E synthase (PTGES). The expression of both enzymes and the production of PGE2 are increased in neuroinflammation. The objective of this study was to elucidate whether the transcription factor CCAAT/enhancer binding protein β (C/EBPβ) regulates the expression of prostaglandin synthesis enzymes in neuroinflammation. To this aim, the expression of these enzymes in wild-type and C/EBPβ-null mice was analyzed in vitro and in vivo. In mixed glial cultures, lipopolysaccharide (LPS) ± interferon γ (IFN-γ) induced C/EBPβ binding to COX-2 and PTGES promoters. LPS ± IFN-γ-induced increases in PTGES expression and in PGE2 production in mixed glial and microglial cultures were abrogated in the absence of C/EBPβ. Also, increased brain PTGES expression induced by systemic LPS administration was markedly reduced in C/EBPβ-null mice. In contrast to PTGES, the induction of COX-2 expression in vitro or in vivo was not markedly affected by the absence of C/EBPβ. These results demonstrate that C/EBPβ regulates PTGES expression and PGE2 production by activated microglial cells in vitro and point to C/EBPβ as a regulator of PTGES expression in vivo in the inflamed central nervous system. Altogether, these findings strengthen the proposed role of C/EBPβ as a key player in the orchestration of neuroinflammatory gene response.

The multiple faces of prostaglandin E2 G-protein coupled receptor signaling during the dendritic cell life cycle

Many processes regulating immune responses are initiated by G-protein coupled receptors (GPCRs) and report biochemical changes in the microenvironment. Dendritic cells (DCs) are the most potent antigen-presenting cells and crucial for the regulation of innate and adaptive immune responses. The lipid mediator Prostaglandin E2 (PGE2) via four GPCR subtypes (EP1-4) critically regulates DC generation, maturation and migration. The role of PGE₂ signaling in DC biology was unraveled by the characterization of EP receptor subtype expression in DC progenitor cells and DCs, the identification of the signaling pathways initiated by these GPCR subtypes and the classification of DC responses to PGE₂ at different stages of differentiation. Here, we review the advances in PGE₂ signaling in DCs and describe the efforts still to be made to understand the spatio-temporal fine-tuning of PGE₂ responses by DCs.

Sulforaphane inhibits prostaglandin E2 synthesis by suppressing microsomal prostaglandin E synthase 1

Sulforaphane (SFN) is a dietary cancer preventive with incompletely characterized mechanism(s) of cancer prevention. Since prostaglandin E2 (PGE2) promotes cancer progression, we hypothesized that SFN may block PGE2 synthesis in cancer cells. We found that SFN indeed blocked PGE2 production in human A549 cancer cells not by inhibiting COX-2, but rather by suppressing the expression of microsomal prostaglandin E synthase (mPGES-1), the enzyme that directly synthesizes PGE2. We identified the Hypoxia Inducible Factor 1 alpha (HIF-1α) as the target of SFN-mediated mPGES-1 suppression. SFN suppressed HIF-1α protein expression and the presence of HIF-1α at the mPGES-1 promoter, resulting in reduced transcription of mPGES-1. Finally, SFN also reduced expression of mPGES-1 and PGE2 production in A549 xenograft tumors in mice. Together, these results point to the HIF-1α, mPGES-1 and PGE2 axis as a potential mediator of the anti-cancer effects of SFN, and illustrate the potential of SFN for therapeutic control of cancer and inflammation. Harmful side effects in patients taking agents that target the more upstream COX-2 enzyme render the downstream target mPGES-1 a significant target for anti-inflammatory therapy. Thus, SFN could prove to be an important therapeutic approach to both cancer and inflammation.

Effect of sphingosine kinase 1 inhibition on blood pressure

Accumulating evidence suggests that sphingosine kinase 1 (SphK1) plays a key role in carcinogenesis by regulating cyclooxygenase-2 (COX-2) expression. Recent clinical studies have revealed that COX-2 inhibitors cause adverse cardiovascular side effects, likely due to inhibition of prostacyclin (PGI(2)). In this work, we investigated the roles of SphK1 inhibition on blood pressure (BP). The results show that lack of SphK1 expression did not exacerbate angiotensin II (Ang II)-induced acute hypertension, whereas celecoxib, a COX-2 inhibitor, augmented and sustained higher BP in mice. Interestingly, SphK1-knockout mice inhibited prostaglandin E(2) (PGE(2)) but not PGI(2) production in response to Ang II, whereas celecoxib blocked both PGE(2) and PGI(2) production. Mechanistically, SphK1 down-regulation by siRNA in human umbilical vein endothelial cells decreased cytokine-induced PGE(2) production primarily through inhibition of microsomal PGE synthase-1 (mPGES-1), not COX-2. SphK1 down-regulation also decreased MKK6 expression, which phosphorylates and activates P38 MAPK, which, in turn, regulates early growth response-1 (Egr-1), a transcription factor of mPGES-1. Together, these data indicate that SphK1 regulates PGE(2) production by mPGES-1 expression via the p38 MAPK pathway, independent of COX-2 signaling, in endothelial cells, suggesting that SphK1 inhibition may be a promising strategy for cancer chemoprevention with lack of the adverse cardiovascular side effects associated with coxibs.

Involvement of PGE2 and the cAMP signalling pathway in the up-regulation of COX-2 and mPGES-1 expression in LPS-activated macrophages

PG (prostaglandin) E2 plays an important role in the modulation of the immune response and the inflammatory process. In the present study, we describe a PGE2 positive feedback for COX (cyclo-oxygenase)-2 and mPGES-1 [microsomal PGES (PGE synthase)-1] expression in the macrophage cell line RAW 264.7. Our results show that PGE2 induces COX-2 and mPGES-1 expression, an effect mimicked by dbcAMP (dibutyryl-cAMP) or forskolin. Furthermore, the cAMP signalling pathway co-operates with LPS (lipopolysaccharide) in the induction of COX-2 and mPGES-1 transcriptional activation. Analysis of the involvement of PGE receptors [EPs (E-prostanoids)] showed that incubation with EP2 agonists up-regulated both COX2 and mPGES-1 mRNA levels. Moreover, EP2 receptor overexpression enhanced the transcriptional activation of COX2 and mPGES-1 promoters. This induction was repressed by the PKA (protein kinase A) inhibitor H89. Activation of the PGE2/EP2/PKA signalling pathway induced the phosphorylation of CREB [CRE (cAMP-response element)-binding protein] in macrophages and stimulated the specific binding of this transcription factor to COX2 and mPGES-1 promoters. Deletion or mutation of potential CRE sites in both promoters diminished their transcriptional activity. In summary, the results of the present study demonstrate that activation of PKA/CREB signalling through the EP2 receptor by PGE2 plays a key role in the expression of COX-2 and mPGES-1 in activated macrophages.

Capsaicin, a TRPV1 Ligand, Suppresses Bone Resorption by Inhibiting the Prostaglandin E Production of Osteoblasts, and Attenuates the Inflammatory Bone Loss Induced by Lipopolysaccharide

Capsaicin, a transient receptor potential vanilloid type 1 (TRPV1) ligand, regulates nerve-related pain-sensitive signals, inflammation, and cancer growth. Capsaicin suppresses interleukin-1-induced osteoclast differentiation, but its roles in bone tissues and bone diseases are not known. This study examined the effects of capsaicin on inflammatory bone resorption and prostaglandin E (PGE) production induced by lipopolysaccharide (LPS) in vitro and on bone mass in LPS-treated mice in vivo. Capsaicin suppressed osteoclast formation, bone resorption, and PGE production induced by LPS in vitro. Capsaicin suppressed the expression of cyclooxygenase-2 (COX-2) and membrane-bound PGE synthase-1 (mPGES-1) mRNAs and PGE production induced by LPS in osteoblasts. Capsaicin may suppress PGE production by inhibiting the expression of COX-2 and mPGES-1 in osteoblasts and LPS-induced bone resorption by TRPV1 signals because osteoblasts express TRPV1. LPS treatment markedly induced bone loss in the femur in mice, and capsaicin significantly restored the inflammatory bone loss induced by LPS in mice. TRPV1 ligands like capsaicin may therefore be potentially useful as clinical drugs targeting bone diseases associated with inflammatory bone resorption.

Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE2 (prostaglandin E2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE2 terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-1 (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1β (interleukin 1β) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near −8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBPβ (CCAAT/enhancer-binding protein β) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBPβ binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBPβ in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBPβ highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.

Identification and development of mPGES-1 inhibitors: where we are at?

Microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal synthase responsible for the synthesis of the pro-tumorigenic prostaglandin E(2) (PGE(2)). mPGES-1 is overexpressed in a wide variety of cancers. Since its discovery in 1997 by Bengt Samuelsson and collaborators, the enzyme has been the object of over 200 peer-reviewed articles. Although today mPGES-1 is considered a validated and promising therapeutic target for anticancer drug discovery, challenges in inhibitor design and selectivity are such that up to this date there are only a few published records of small-molecule inhibitors targeting the enzyme and exhibiting some in vivo anticancer activity. This review summarizes the structures, and the in vitro and in vivo activities of these novel mPGES-1 inhibitors. Challenges that have been encountered are also discussed.

Expression of microsomal prostaglandin E synthase-1 in the spinal cord in a transgenic mouse model of amyotrophic lateral sclerosis

Prostaglandin E(2) (PGE(2)) is a key molecule involved in the neuroinflammatory processes that characterize amyotrophic lateral sclerosis (ALS). Although PGE(2) synthesis is regulated by PGE(2) synthases (PGESs), the pathological role of PGESs in ALS still remains unknown. Experiments were performed to elucidate the expression of PGESs and the localization of microsomal PGES-1 (mPGES-1) in neurons and glial cells in the spinal cord of ALS model (G93A) mice. Neurological symptom was observed in G93A mice from 14 weeks by the tail suspension test, and rotarod performances were decreased at 16 weeks and older. Western blotting revealed that the level of mPGES-1 was increased in G93A mice at 15 weeks and older. In contrast, the levels of cytosolic PGES and mPGES-2 did not change at any age. Immunohistochemical analysis demonstrated that age-dependent expression of mPGES-1 was found in motor neurons in G93A mice at 11 and 15 weeks. Immunoreactivity of mPGES-1 was also co-localized in Iba1-positive microglia in G93A mice at 15 weeks. These results suggest that mPGES-1 in motor neurons may play a role in the pathogenesis of ALS and that mPGES-1 may work sequentially in motor neurons and activated microglia to produce ALS symptoms in G93A mice.

Matrix metalloproteinase-dependent microsomal prostaglandin E synthase-1 expression in macrophages: role of TNF-α and the EP4 prostanoid receptor

Matrix metalloproteinase (MMP)-9 contributes to the pathogenesis of chronic inflammatory diseases and cancer. Thus, identifying targetable components of signaling pathways that regulate MMP-9 expression may have broad therapeutic implications. Our previous studies revealed a nexus between metalloproteinases and prostanoids whereby MMP-1 and MMP-3, commonly found in inflammatory and neoplastic foci, stimulate macrophage MMP-9 expression via the release of TNF-α and subsequent induction of cyclooxygenase-2 and PGE(2) engagement of EP4 receptor. In the current study, we determined whether MMP-induced cyclooxygenase-2 expression was coupled to the expression of prostaglandin E synthase family members. We found that MMP-1- and MMP-3-dependent release of TNF-α induced rapid and transient expression of early growth response protein 1 in macrophages followed by sustained elevation in microsomal prostaglandin synthase 1 (mPGES-1) expression. Metalloproteinase-induced PGE(2) levels and MMP-9 expression were markedly attenuated in macrophages in which mPGES-1 was silenced, thereby identifying mPGES-1 as a therapeutic target in the regulation of MMP-9 expression. Finally, the induction of mPGES-1 was regulated, in part, through a positive feedback loop dependent on PGE(2) binding to EP4. Thus, in addition to inhibiting macrophage MMP-9 expression, EP4 antagonists emerge as potential therapy to reduce mPGES-1 expression and PGE(2) levels in inflammatory and neoplastic settings.

EGFR signaling upregulates expression of microsomal prostaglandin E synthase-1 in cancer cells leading to enhanced tumorigenicity

In this report we describe the contribution of prostaglandin E(2) (PGE(2)) derived from the inducible microsomal PGE-synthase type-1 (mPGES-1) to the epidermal growth factor receptor (EGFR) oncogenic drive in tumor epithelial cells and in tumor-bearing mice. EGFR stimulation upregulated expression of mPGES-1 in HT-29, A431 and A549 cancer cells. Egr-1, a transcription factor induced by EGF, mediated this response. The Egr-1 rise provoked the overexpression of mPGES-1 messenger and protein, and enhanced PGE(2) formation. These changes were suppressed either by silencing Egr-1, or by upstream blockade of EGFR or ERK1/2 signals. Further, in a clonogenic assay on tumor cells, EGF induced a florid tumorigenic phenotype, which regressed when mPGES-1 was silenced or knocked down. EGF-induced mPGES-1 overexpression in epithelial cell reduced E-cadherin expression, whereas enhancing that of vimentin, suggesting an incipient mesenchymal phenotype. Additionally, inhibiting the EGFR in mice bearing the A431 tumor, the mPGES-1 expression and the tumor growth, exhibited a parallel decline. In conclusion, these findings provide novel evidence that a tight cooperation between the EGF/EGFR and mPGES-1 leads to a significant tumorigenic gain in epithelial cells, and provide clues for controlling the vicious association.

Dimethylcelecoxib induces an inhibitory complex consisting of HDAC1/NF-κB(p65)RelA leading to transcriptional downregulation of mPGES-1 and EGR1

Dimethylcelecoxib, a non-COX-2 inhibiting derivative of celecoxib, inhibits PGE(2) synthesis by transcriptional inhibition of mPGES-1. Previously we demonstrated that DMC downregulates EGR1 expression and increases nuclear NF-κB in human cervical cancer cells (HeLa). Both transcription factors are important regulators of mPGES-1 expression. Here we show that treatment of HeLa cells with DMC inhibits EGR1 promoter activity by influencing the transactivation activity of NF-κB. Mutation of the NF-κB motif as well as downregulation of NF-κB(p65)RelA using siRNA repealed the inhibitory effect of DMC on the EGR1 promoter. The transactivation activity of NF-κB is regulated by various co-activators or co-repressors. One of these co-repressors is HDAC1. DMC did not influence HDAC1 expression, but the HDAC activity was enhanced under DMC influence. After DMC treatment NF-κB co-immunoprecipitated with HDAC1. Electromobility shift assays depicted an increased interaction between NF-κB-HDAC1 and DNA containing NF-κB binding motives. Performing CHIP-assays we finally demonstrated the interaction of NF-κB and HDAC1 at the EGR1 promoter that was in part reversed by the HDAC1 inhibitor trichostatin A. Using siRNA against HDAC1 we could repeal the inhibitory effect of DMC on the EGR1 promoter. In conclusion we demonstrated that treatment of HeLa cells with DMC leads to an enhanced formation of a complex consisting of NF-κB and HDAC1 that binds to the EGR1 promoter resulting in downregulation of EGR1 expression which plays a major role for transcriptional inhibition of mGPES-1 expression. How these effects of DMC may contribute to a potential therapeutical benefit of various diseases is discussed.

Microsomal prostaglandin e synthase-1 in rheumatic diseases

Microsomal prostaglandin E synthase-1 (mPGES-1) is a well-recognized target for the development of novel anti-inflammatory drugs that can reduce symptoms of inflammation in rheumatic diseases and other inflammatory conditions. In this review, we focus on mPGES-1 in rheumatic diseases with the aim to cover the most recent advances in the understanding of mPGES-1 in rheumatoid arthritis, osteoarthritis, and inflammatory myopathies. Novel findings regarding regulation of mPGES-1 cell expression as well as enzyme inhibitors are also summarized.

Valproic Acid Suppresses Interleukin-1ß-induced Microsomal Prostaglandin E2 Synthase-1 Expression in Chondrocytes Through Upregulation of NAB1

Objective.

Microsomal prostaglandin E2 synthase-1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE2. Early growth response factor-1 (Egr-1) is a key transcription factor in the regulation of mPGES-1, and its activity is negatively regulated by the corepressor NGF1-A-binding protein-1 (NAB1). We examined the effects of valproic acid (VA), a histone deacetylase inhibitor, on interleukin 1ß (IL-1ß)-induced mPGES-1 expression in human chondrocytes, and evaluated the roles of Egr-1 and NAB1 in these effects.

Methods.

Chondrocytes were stimulated with IL-1 in the absence or presence of VA, and the level of mPGES-1 protein and mRNA expression were evaluated using Western blotting and real-time reverse-transcription polymerase chain reaction (PCR), respectively. mPGES-1 promoter activity was analyzed in transient transfection experiments. Egr-1 and NAB1 recruitment to the mPGES-1 promoter was evaluated using chromatin immunoprecipitation assays. Small interfering RNA (siRNA) approaches were used to silence NAB1 expression.

Results.

VA dose-dependently suppressed IL-1-induced mPGES-1 protein and mRNA expression as well as its promoter activation. Treatment with VA did not alter IL-1-induced Egr-1 expression, or its recruitment to the mPGES-1 promoter, but prevented its transcriptional activity. The suppressive effect of VA requires de novo protein synthesis. VA induced the expression of NAB1, and its recruitment to the mPGES-1 promoter, suggesting that NAB1 may mediate the suppressive effect of VA. Indeed, NAB1 silencing with siRNA blocked VA-mediated suppression of IL-1-induced mPGES-1 expression.

Conclusion.

VA inhibited IL-1-induced mPGES-1 expression in chondrocytes. The suppressive effect of VA was not due to reduced expression or recruitment of Egr-1 to the mPGES-1 promoter and involved upregulation of NAB1.

Potential roles of microsomal prostaglandin E synthase-1 in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease which primarily affects the synovial joints leading to inflammation, pain and joint deformities. Nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, both of which inhibit cyclooxygenase (COX), have been extensively used for treating RA patients. Prostaglandin E synthase (PGES) is a specific biosynthetic enzyme that acts downstream of COX and converts prostaglandin (PG) H(2) to PGE(2). Among PGES isozymes, microsomal PGES-1 (mPGES-1) has been shown to be induced in a variety of cells and tissues under inflammatory conditions. The induction of mPGES-1 in the synovial tissue of RA patients is closely associated with the activation of the tissue by proinflammatory cytokines. Although selective mPGES-1 inhibitors have not yet been widely available, mice lacking mPGES-1 (mPGES-1(-/-) mice) have been generated to evaluate the physiological and pathological roles of mPGES-1 in vivo. Recent studies utilizing mPGES-1(-/-) mice have demonstrated the significance of mPGES-1 in the process of chronic inflammation and evocation of humoral immune response in autoimmune arthritis models. These recent findings highlight mPGES-1 as a novel therapeutic target for the treatment of autoimmune inflammatory diseases, including RA. Currently, both natural and synthetic chemicals are being tested for inhibition of mPGES-1 activity to produce PGE(2). The present review focuses on the recent advances in understanding the role of mPGES-1 in the pathophysiology of RA.

The inducible prostaglandin E synthase mPGES-1 regulates growth of endometrial tissues and angiogenesis in a mouse implantation model

Endometriosis is one of the most common gynecological diseases in women of reproductive age. Although cyclooxygenase (COX)-2 inhibitors are effective in the treatment of endometriosis, the adverse cardiovascular effects associated with these inhibitors have limited their use. Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible enzyme downstream of COX-2 in prostaglandin E(2) biosynthesis. Previously, we developed mPGES-1 knockout mice (mPGES-1(-/-)) and have identified for the first time the roles of ectopic lesion- and host-associated mPGES-1 in angiogenesis and the growth of endometrial tissues. When mPGES-1(-/-) endometrial fragments were implanted into wild type (WT) mice (mPGES-1(-/-)→WT), or WT fragments implanted into mPGES-1(-/-) mice (WT→mPGES-1(-/-)), the growth of the implants was suppressed at days 14 and 28 after implantation, compared toWT→WT transplantation. An even greater degree of suppression was observed in mPGES-1(-/-) endometrial fragments implanted into mPGES-1(-/-) mice (mPGES-1(-/-)→mPGES-1(-/-)). After WT-WT implantation, mPGES-1 expression was localized at the border of the implanted endometrial tissues. Microvessel density, determined by CD31 immunostaining, was markedly suppressed in the mPGES-1(-/-) endometrial fragments implanted into mPGES-1(-/-) mice, with some suppression also observed in the mPGES-1(-/-)→WT and WT→mPGES-1(-/-) groups. The expression of vascular endothelial growth factor (VEGF-A) was significantly reduced in mPGES-1(-/-) endometrial tissues implanted into mPGES-1(-/-) mice at days 14 and 28, in comparison to the WT→WT group. These results suggested that mPGES-1 enhanced angiogenesis and growth of the endometrial implant, and indicate that mPGES-1 may be a good therapeutic target for endometriosis.

Role of microsomal prostaglandin E synthase-1 in the facilitation of angiogenesis and the healing of gastric ulcers

The importance of prostaglandin E(2) in various pathophysiological events emphasizes the necessity of understanding the role of PGE synthases (PGESs) in vivo. However, there has been no report on the functional relevance of microsomal PGES-1 (mPGES-1) to the physiological healing processes of gastric ulcers, or to angiogenesis, which is indispensable to the healing processes. In this report, we tested whether mPGES-1 plays a role in the healing of gastric ulcers and in the enhancement of angiogenesis using mPGES-1 knockout mice (mPGES-1 KO mice) and their wild-type (WT) counterparts. Gastric ulcers were induced by the serosal application of 100% acetic acid, and the areas of the ulcers were measured thereafter. mPGES-1 together with cyclooxygenase-2 were induced in the granulation tissues compared with normal stomach tissues. The healing of acetic acid-induced ulcers was significantly delayed in mPGES-1 KO mice compared with WT. This was accompanied with reduced angiogenesis in ulcer granulation tissues, as estimated by CD31 mRNA levels determined by real-time PCR and the microvessel density in granulation tissues. The mRNA levels of proangiogenic growth factors, such as transforming growth factor-β, basic fibroblast growth factor, and connective tissue growth factor in ulcer granulation tissues determined were reduced in mPGES-1 KO mice compared with WT. The present results suggest that mPGES-1 enhances the ulcer-healing processes and the angiogenesis indispensable to ulcer healing, and that a selective mPGES-1 inhibitor should be used with care in patients with gastric ulcers.

Cyclooxygenase-2 signaling in vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

Inflammation and its role in a coordinated fibroplastic response, which disrupts the structure of the vocal folds following injury, is critical. Cyclooxygenase-2 (COX-2) is an important enzyme involved in both inflammation and fibrosis; in addition, it is a prime target for therapeutic intervention. We sought to study this pathway in vocal fold fibroblasts to provide a foundation for future interventional studies.

STUDY DESIGN

In vitro.

METHODS

Human vocal fold fibroblasts were incubated with IL-1 beta to determine the effects on COX-2 signaling, along with upstream regulatory mechanisms and downstream mediators of wound healing. In vitro methods to assess mRNA expression, as well as intracellular and secreted protein (sodium dodecyl sulfate polyacrylamide gel electrophoresis and enzyme-linked immunosorbent assay) were employed.

RESULTS

IL-1 beta regulation of COX-2 mRNA and protein levels was dose and time dependent and IL-1 beta altered PGE(2) metabolism, via regulation of both synthetic and degradative enzymes. IL-1 beta increased nuclear factor (NF)-kappaB activation and nuclear translocation. Inhibition of the p50 and p65 subunits of NF-kappaB decreased IL-1 beta-induced COX-2 transcription. IL-1 beta also altered mRNA expression of four cell-surface prostaglandin receptors.

CONCLUSIONS

Inflammation and fibrosis are important in the vocal fold pathophysiologic response to injury. Our data suggest that COX-2 and PGE(2) are inducible in human vocal fold fibroblasts, and this response appears to be NF-kappaB-dependent. We purport this fundamental investigation will lead to increased insight regarding injury and repair in the vocal folds, with the ultimate goal of developing novel clinical care paradigms.

Regulation of microsomal prostaglandin E2 synthase-1 and 5-lipoxygenase-activating protein/5-lipoxygenase by 4-hydroxynonenal in human osteoarthritic chondrocytes

INTRODUCTION

This study aimed to investigate whether hydroxynonenal (HNE) depletion is responsible for the switch from cyclooxygenase-2 (COX-2) and microsomal prostaglandin E2 synthase-1 (mPGES-1) to 5-lipoxygenase-activating protein (FLAP) and 5-lipoxygenase (5-LOX).

METHODS

For COX-2 and mPGES-1 studies, human osteoarthritic chondrocytes were stimulated at different incubation times (up to 24 hours) with a single or repetitive addition of 10 muM HNE to the cultures at 2-hour intervals, up to 14 hours. For 5-LOX and FLAP studies, cells were treated with a single addition of 10 muM HNE for 24 hours, 48 hours, and 72 hours in the presence or absence of naproxen (a nonspecific COX-2 inhibitor) or antibody anti-transforming growth factor-beta 1 (TGF-beta1). The protein levels of COX-2, mPGES-1 and early growth response factor-1 (Egr-1) transcription factor were evaluated by western blot, and those of prostaglandin E2 (PGE2), leukotriene B4 (LTB4) and TGF-beta1 were determined with commercial kits. The levels of mPGES-1, FLAP and 5-LOX mRNA were measured by real-time RT-PCR. Transient transfection was performed to determine promoter activities of mPGES-1 and 5-LOX.

RESULTS

Single addition of 10 muM HNE to cultured chondrocytes induced PGE2 release as well as COX-2 and mPGES-1 expression at the protein and mRNA levels, with a plateau reached respectively at 8 and 16 hours of incubation, followed by a subsequent decline. However, repeated treatments with HNE prevented the decline of COX-2 and mPGES-1 expression that occurred with a single aldehyde addition. HNE induced mPGES-1 promoter activity, possibly through transcription factor Egr-1 activation. After 48 hours, when COX-2 expression decreased, the LTB4 level rose through 5-LOX and FLAP upregulation. The addition of naproxen to cultured chondrocytes revealed that FLAP and 5-LOX regulation by HNE required PGE2 production. Furthermore, our data showed that HNE significantly induced TGF-beta1 production. The addition of anti-TGF-beta1 antibody reduced HNE-induced 5-LOX and FLAP expression by 40%, indicating the partial involvement of a TGF-beta1-dependent mechanism.

CONCLUSIONS

Our data demonstrate that the shunt to the FLAP and 5-LOX pathway in HNE-induced human osteoarthritic chondrocytes is attributed to COX-2 and mPGES-1 inhibition, probably due to HNE depletion. PGE2 and TGF-beta1 are suggested to be involved in this regulation.

Microsomal prostaglandin E synthase-1 and cyclooxygenase-2 are both required for ischaemic excitotoxicity

BACKGROUND AND PURPOSE

Although both microsomal prostaglandin E synthase (mPGES)-1 and cyclooxygenase (COX)-2 are critical factors in stroke injury, but the interactions between these enzymes in the ischaemic brain is still obscure. This study examines the hypothesis that mPGES-1 activity is required for COX-2 to cause neuronal damage in ischaemic injury.

EXPERIMENTAL APPROACH

We used a glutamate-induced excitotoxicity model in cultures of rat or mouse hippocampal slices and a mouse middle cerebral artery occlusion-reperfusion model in vivo. The effect of a COX-2 inhibitor on neuronal damage in mPGES-1 knockout (KO) mice was compared with that in wild-type (WT) mice.

KEY RESULTS

In rat hippocampal slices, glutamate-induced excitotoxicity, as well as prostaglandin (PG) E(2) production and PGES activation, was significantly attenuated by either MK-886 or NS-398, inhibitors of mPGES-1 and COX-2 respectively; however, co-application of these inhibitors had neither an additive nor a synergistic effect. The protective effect of NS-398 on the excitotoxicity observed in WT slices was completely abolished in mPGES-1 KO slices, which showed less excitotoxicity than WT slices. In the transient focal ischaemia model, mPGES-1 and COX-2 were co-localized in the infarct region of the cortex. Injection of NS-398 reduced not only ischaemic PGE(2) production, but also ischaemic injuries in WT mice, but not in mPGES-1 KO mice, which showed less dysfunction than WT mice.

CONCLUSION AND IMPLICATIONS

Microsomal prostaglandin E synthase-1 and COX-2 are co-induced by excess glutamate in ischaemic brain. These enzymes are co-localized and act together to exacerbate stroke injury, by excessive PGE(2) production.

Early growth response-1 worsens ventilator-induced lung injury by up-regulating prostanoid synthesis

RATIONALE

Ventilator-induced lung injury (VILI) is common and serious and may be mediated in part by prostanoids. We have demonstrated increased expression of the early growth response-1 (Egr1) gene by injurious ventilation, but whether-or how-such up-regulation contributes to injury is unknown.

OBJECTIVES

We sought to define the role of Egr1 in the pathogenesis of VILI.

METHODS

An in vivo murine model of VILI was used, and Egr1(+/+) (wild-type) and Egr1(-/-) mice were studied; the effects of prostaglandin E receptor subtype 1 (EP1) inhibition were assessed.

MEASUREMENTS AND MAIN RESULTS

Injurious ventilation caused lung injury in wild-type mice, but less so in Egr1(-/-) mice. The injury was associated with expression of EGR1 protein, which was localized to type II cells and macrophages and was concentrated in nuclear extracts. There was a concomitant increase in expression of phosphorylated p44/p42 mitogen-activated protein kinases. The prostaglandin E synthase (mPGES-1) gene has multiple EGR1 binding sites on its promoter, and induction of mPGES-1 mRNA (as well as the prostanoid product, PGE2) by injurious ventilation was highly dependent on the presence of the Egr1 gene. PGE2 mediates many lung effects via EP1 receptors, and EP1 blockade (with ONO-8713) lessened lung injury.

CONCLUSIONS

This is the first demonstration of a mechanism whereby expression of a novel gene (Egr1) can contribute to VILI via a prostanoid-mediated pathway.

Ellagic acid inhibits lipopolysaccharide-induced expression of enzymes involved in the synthesis of prostaglandin E2 in human monocytes

Ellagic acid, a natural polyphenol found in certain fruits, nuts and vegetables, has in recent years been the subject of intense research within the fields of cancer and inflammation. Pain, fever and swelling, all typical symptoms of inflammation, are ascribed to elevated levels of PGE2. In the present study, we have investigated the effects of ellagic acid on PGE2 release and on prostaglandin-synthesising enzymes in human monocytes. Ellagic acid was found to inhibit Ca ionophore A23187-, phorbol myristate acetate- and opsonised zymosan-induced release of PGE2 from monocytes pre-treated with the inflammatory agent lipopolysaccharide. Ellagic acid suppressed the lipopolysaccharide-induced increase in protein expression of cyclo-oxygenase-2 (COX-2), microsomal PGE synthase-1 (mPGEs-1) and cytosolic phospholipase A2α (cPLA2α), while it had no effect on the constitutively expressed COX-1 protein. Ellagic acid had no apparent inhibitory effect on these enzymes when the activities were determined in cell-free assays. We conclude that the inhibitory effect of ellagic acid on PGE2 release from monocytes is due to a suppressed expression of COX-2, mPGEs-1 and cPLA2α, rather than a direct effect on the activities of these enzymes.

Prostaglandin E(2) synthase inhibition as a therapeutic target

BACKGROUND

Most NSAIDs function by inhibiting biosynthesis of PGE(2) by inhibition of COX-1 and/or COX-2. Since COX-1 has a protective function in the gastro-intestinal tract (GIT), non-selective inhibition of both cycloxy genases leads to moderate to severe gastro-intestinal intolerance. Attempts to identify selective inhibitors of COX-2, led to the identification of celecoxib and rofecoxib. However, long-term use of these drugs has serious adverse effects of sudden myocardial infarction and thrombosis. Drug-mediated imbalance in the levels of prostaglandin I(2) (PGI(2)) and thromboxane A(2) (TXA(2)) with a bias towards TXA(2) may be the primary reason for these events. This resulted in the drugs being withdrawn from the market, leaving a need for an effective and safe anti-inflammatory drug.

METHODS

Recently, the focus of research has shifted to enzymes downstream of COX in the prosta glandin biosynthetic pathway such as prostaglandin E(2) synthases. Microsomal prostaglandin E(2) synthase-1 (mPGES-1) specifically isomerizes PGH(2) to PGE(2), under inflammatory conditions. In this review, we examine the biology of mPGES-1 and its role in disease. Progress in designing molecules that can selectively inhibit mPGES-1 is reviewed.

CONCLUSION

mPGES-1 has the potential to be a target for anti-inflammatory therapy, devoid of adverse GIT and cardiac effects and warrants further investigation.

NF-kappaB induces PGE2-synthesizing enzymes in neurons

The transcription factor NF-kappaB is activated in neurons and promotes neuronal death in cerebral ischemia. Its target genes include cytosolic phospholipase A-2 (cPLA-2), cyclooxygenase-2 (COX-2), and microsomal prostaglandin E(2) synthase-1 (mPGES-1), three genes that are involved in the synthesis of prostaglandin E(2) (PGE(2)). In our study, oxygen glucose deprivation (OGD), an in vitro model of cerebral ischemia, activated NF-kappaB activity in primary cortical neurons. Furthermore, OGD and the NF-kappaB activator tumor necrosis factor stimulated the expression of cPLA-2, cyclooxygenase-2 (COX-2), and mPGES-1 and increased the release of PGE(2) from neurons. Expression of a constitutively active IkappaB kinase (IKK) or the NF-kappaB subunit p65 in neurons stimulated the transcription of cPLA-2, COX-2, and mPGES-1. Finally, inhibition of IKK in neurons blocked the induction of the three genes involved in PGE(2) synthesis in vivo. In summary, NF-kappaB controls the neuronal expression of three genes involved in PGE(2) synthesis in cerebral ischemia.