Microsomal prostaglandin E2 synthase-1 in breast cancer: a potential target for therapy

The anti-tumour actions of cyclooxygenases (COX) are thought to be mediated by inhibition of prostaglandin E(2) (PGE(2)) synthesis. However, COX-2 inhibition also alters cellular production of other prostaglandins such as prostacyclin (PGI(2)). The latter action is believed to be important for the development of adverse cardio-vascular events. Microsomal PGES (mPGES-1) is an enzyme downstream to COX-2 and affects PGE(2) production only. It is possible that targeting mPGES-1 could decrease PGE(2) production without affecting PGI(2) production. In order to assess the potential of mPGES-1 as a target for therapy, we analysed its expression in breast cell lines and normal and malignant breast tissues. The expression of mPGES-1 and COX-2 was correlated in tumour cells and vascular endothelium, and with prognostic parameters in breast cancer. Although not detectable in normal epithelial cells, expression was noted in areas of fibrocystic change and in situ carcinoma. mPGES-1 expression was noted in 79% of breast cancer tissues. Its expression did not correlate with COX-2 overexpression or with prognostic markers of breast cancer. Endothelial cells did not show mPGES-1 expression. Upregulation of mPGES-1 is therefore frequent in pre-malignant and malignant breast disease. In this study, coordinate over-expression of COX-2 and mPGES-1 was not observed, particularly in the endothelial cells of blood vessels. Targeting mPGES-1 might prove to be an alternative therapeutic strategy to inhibit PGE2 production.     

Expression of cyclooxygenase-2 in osteosarcoma of bone.

Several studies indicate that cyclooxygenase-2 (COX-2) is overexpressed in human malignancies, where it produces high levels of prostaglandins and contributes to tumor growth. In this study we have analyzed the expression of COX-2 in a series of 48 skeletal osteosarcomas of different subtypes by immunohistochemistry. In addition, we examined the effects of the specific COX-2 inhibitor Celecoxib on the growth of the human osteosarcoma cell line SaOS-2. Immunoreactivity for COX-2 was observed in 39 out of 48 tumors (81.2%), 30 (76.9%) of which showed a moderate or diffuse immunostaining. Considering the group of 42 primary osteosarcomas, COX-2 immunoreactivity was significantly higher in high grade osteosarcomas, where moderate or diffuse expression was detected in 23 out of 32 cases (71.8%), than in low grade osteosarcomas, where moderate or diffuse expression was detected in 2 out of 10 cases (20%) (P = 0.008, Fisher exact test). In addition, low COX-2 expression was always associated with a good response to chemotherapy (5 out of 5 cases), whereas moderate or diffuse COX-2 expression was associated with a good response in 11 out of 20 cases (55%) (P = 0.12, Fisher exact test). In SaOS-2 osteosarcoma cells, which express COX-2, treatment with Celecoxib determined inhibition of cell proliferation and induction of apoptosis. These results indicate that COX-2 is expressed at high levels in high grade osteosarcomas and support the use of COX-2 inhibitors to improve both the tumor response to chemotherapy and the outcome of osteosarcoma patients.     

Induction of prostaglandin E2 production by leukemia inhibitory factor promotes migration of first trimester extravillous trophoblast cell line, HTR-8/SVneo

BACKGROUND: The invasion of first trimester extravillous trophoblast (EVT) to decidua is an important event in placentation. Leukemia inhibitory factor (LIF) is an essential factor for mouse implantation, and it is reported that LIF may be involved in human first trimester EVT invasion. Prostaglandin E2 (PGE2) is also known as a critical factor for first trimester EVT invasion. In this study, we investigated the role of LIF in PGE2 production and EVT invasion using a human first trimester EVT cell line, HTR-8/SVneo. METHODS AND RESULTS: Co-stimulation with LIF and IL-1beta induced higher amounts of PGE2 production and further migration of HTR-8/SVneo cells compared with that by stimulation with LIF or IL-1beta alone. Enhanced PGE2 production was most probably due to the enhanced expression of cyclooxygenase-2 (COX-2) and microsomal PGE synthase-1 (mPGES-1). PGE2 produced by HTR-8/SVneo cells promoted the migration of HTR-8/SVneo cells. A COX-2 inhibitor suppressed PGE2 production and the migration of HTR-8/SVneo cells. Agonists to PGE2 receptors, EP1, EP2 and EP4, promoted the migration of HTR-8/SVneo cells. Moreover, stimulation with LIF up-regulated EP1, EP2 and EP4 expression in HTR-8/SVneo cells. CONCLUSIONS: It is suggested that LIF participates in placentation through EVT invasion by up-regulating PGE2 production and PGE2 receptor expression in first trimester EVT.     

Expression of cyclooxygenase-1/-2, microsomal prostaglandin-E synthase-1 and E-prostanoid receptor 2 and regulation of inflammatory mediators by PGE2 in the amoeboid microglia in hypoxic postnatal rats and murine BV-2 cells

This study aimed to investigate the effect of hypoxia on the expression of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), microsomal prostaglandin-E synthase (mPGES-1), E-prostanoid receptor 2 (EP2) in microglia; and the roles of EP2-cyclic adenosine monophosphate (cAMP) signaling pathway in the prostaglandin E₂ (PGE₂) regulation of inflammatory mediators released by hypoxic BV-2 cells. Immunoexpression of COX-1, COX-2, mPGES-1 and EP2 was localized in the amoeboid microglial cells (AMC), a nascent brain macrophage in the developing brain, as confirmed by double labeling with OX-42 and lectin, specific markers of microglia. AMC emitted a more intense immunofluorescence in hypoxic rats when compared with the matching controls. In postnatal rats subjected to hypoxia, mRNA and protein expression levels of COX-1, COX-2 and mPGES-1 along with tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), inducible nitric-oxide synthase (iNOS) and PGE₂ product in the callosal tissue were significantly increased. The results were shared in the BV-2 cells except for COX-1 mRNA and protein whose levels remained unaltered. Interestingly, treatment with EP2 antagonist AH-6809 resulted in suppression of hypoxia induced EP2, IL-1β and iNOS mRNA and protein expression, TNF-α protein expression and intracellular cAMP level in BV-2 cells. It is suggested that PGE₂ may regulate above inflammatory mediators in the activated microglia via EP2-cAMP signaling pathway in hypoxic conditions.     

Expression of prostaglandin E synthases in periodontitis immunolocalization and cellular regulation

The inflammatory mediator prostaglandin E(2) (PGE(2)) is implicated in the pathogenesis of chronic inflammatory diseases including periodontitis; it is synthesized by cyclooxygenases (COX) and the prostaglandin E synthases mPGES-1, mPGES-2, and cPGES. The distribution of PGES in gingival tissue of patients with periodontitis and the contribution of these enzymes to inflammation-induced PGE(2) synthesis in different cell types was investigated. In gingival biopsies, positive staining for PGES was observed in fibroblasts and endothelial, smooth muscle, epithelial, and immune cells. To further explore the contribution of PGES to inflammation-induced PGE(2) production, in vitro cell culture experiments were performed using fibroblasts and endothelial, smooth muscle, and mast cells. All cell types expressed PGES and COX-2, resulting in basal levels of PGE(2) synthesis. In response to tumor necrosis factor (TNF-α), IL-1β, and cocultured lymphocytes, however, mPGES-1 and COX-2 protein expression increased in fibroblasts and smooth muscle cells, accompanied by increased PGE(2), whereas mPGES-2 and cPGES were unaffected. In endothelial cells, TNF-α increased PGE(2) production only via COX-2 expression, whereas in mast cells the cytokines did not affect PGE(2) enzyme expression or PGE(2) production. Furthermore, PGE(2) production was diminished in gingival fibroblasts derived from mPGES-1 knockout mice, compared with wild-type fibroblasts. These results suggest that fibroblasts and smooth muscle cells are important sources of mPGES-1, which may contribute to increased PGE(2) production in the inflammatory condition periodontitis.     

Seminal plasma activates cyclooxygenase-2 and prostaglandin E2 receptor expression and signalling in cervical adenocarcinoma cells

Enhanced cyclooxygenase (COX) expression and prostaglandin E2 (PGE2) synthesis are regarded as promoters of neoplastic cell proliferation and angiogenesis. Expression of COX-2 and synthesis of PGE2 are up-regulated in cervical carcinomas. In sexually active women, growth and invasiveness of neoplastic cervical epithelial cells may be also under the direct influence of PGE2 present in seminal plasma. The aims of this study were to investigate the effect of seminal plasma and PGE2 on the expression of COX-2 and expression and signalling of the PGE2 receptor subtypes (EP1-EP4) in HeLa (cervical adenocarcinoma) cells. Treatment of HeLa cells with seminal plasma or PGE2 resulted in up-regulation of COX-2 expression (P < 0.05). In addition, seminal plasma induced the mRNA expression of EP1, EP2 and EP4 receptors, whilst PGE2 treatment of HeLa cells induced the expression of the EP4 receptor (P < 0.05). This was coincident with a rapid accumulation of adenosine 3',5'-cyclic monophosphate (cAMP) in HeLa cells stimulated with seminal plasma or PGE2, which was greater in seminal plasma stimulated cells compared with PGE2 stimulated cells (P < 0.05). Subsequently, we investigated whether the effect of seminal plasma on cAMP signalling in HeLa cells was mediated via the cAMP-linked EP2/EP4 receptors. Stimulation of HeLa cells with seminal plasma or PGE2 resulted in an augmented cAMP accumulation in cells transfected with the EP2 or EP4 receptor cDNA compared with control transfected cells (P < 0.05). These data suggest that, in sexually active women, seminal plasma may play a role in modulating neoplastic cell function and cervical tumorigenesis.     

GPx2 counteracts PGE2 production by dampening COX-2 and mPGES-1 expression in human colon cancer cells

GPx2, the gastrointestinal glutathione peroxidase, is a selenoprotein predominantly expressed in the intestine. An anti-inflammatory and anticarcinogenic potential has been inferred from the development of colitis and intestinal cancer in GPx1 and GPx2 double knockout mice. Further, induction by Nrf2 activators classifies GPx2 as a protective enzyme. In contrast, enhanced COX-2 expression is consistently associated with inflammation. The antagonistic roles and an intriguing co-localization of GPx2 and COX-2 prompted us to investigate their possible mutual regulation. Both enzymes were upregulated in tissues of patients with colorectal cancer and colitis, and co-localized in the endoplasmic reticulum. A stable knockdown of GPx2 in HT-29 cells by siRNA resulted in a high basal and IL-1-induced expression of COX-2 and mPGES-1, enzymes required for the production of the pro-inflammatory PGE(2). Accordingly, si-GPx2 cells released high concentrations of PGE(2). Observed effects were specific for GPx2, since COX-2 and mPGES-1 expression was not affected by selenium-deprivation which resulted in the disappearance of GPx1. It is concluded that GPx2 by compartmentalized removal of hydroperoxides silences COX-2 activity and suppresses PGE(2)-dependent COX-2 expression. Thus, GPx2 may prevent undue responses to inflammatory stimuli and, in consequence, inflammation-driven initiation of carcinogenesis.     

机动车尾气诱发大鼠慢性阻塞性肺疾病并上调气道上皮细胞COX-2/PGE2/EP受体信号通路

目的：探究机动车尾气(MVE)长期暴露引起大鼠慢性阻塞性肺疾病(COPD)发生时,气道上皮细胞中环加氧酶2(COX-2)/前列腺素E₂(PGE₂)/E-前列腺素类激素(EP)受体信号通路成员的表达变化。方法：(1)动物实验：健康雄性SD纯系大鼠(SPF级)16只,随机分为2组：MVE暴露组(n=8)和空白对照(CTL)组(n=8)。采用MVE暴露6个月的方法建立COPD大鼠模型。造模结束后,使用Buxco小动物有创肺功能仪检测大鼠肺功能;肺组织切片行HE染色并评估肺组织病理变化;ELISA法检测大鼠支气管肺泡灌洗液(BALF)中炎症因子白细胞介素6(IL-6)、肿瘤坏死因子α(TNF-α)和PGE₂的水平,评估大鼠肺部炎症情况;采用免疫荧光及Western blot法检测肺组织COX-2及EP受体蛋白水平;提取肺组织核蛋白,Western blot检测MVE对肺组织NF-κB核转位的影响。(2)细胞实验：采用MVE细颗粒物(PM2.5)标准品刺激人正常支气管上皮细胞BEAS-2B。ELISA法检测细胞培养液中PGE     

Expression of cyclooxygenase-1 and -2 in canine nasal carcinomas

Cyclooxygenase-1 (COX-1) and cyclooxygenase -2 (COX-2) are known to play a role in the carcinogenesis of many human and animal primary epithelial tumours. However, expression of COX-1 and -2 has not been investigated in canine nasal epithelial carcinoma, a rare form of neoplasia. COX-1 immunolabelling was demonstrated in normal canine nasal mucosa and in a minority of neoplastic specimens. Cytoplasmic COX-2, however, was strongly expressed in the majority of canine nasal carcinomas. In addition, COX-2 expression was demonstrated in dysplastic epithelium and in a proportion of stromal cells. Co-expression of both enzyme isoforms was revealed by confocal laser scanning microscopy. The results indicate that COX-2 is overexpressed in a proportion of naturally occurring canine nasal carcinomas, suggesting its possible role in canine nasal tumorigenesis.     

Induction of Microsomal Prostaglandin E Synthase-1 in Human Gingival Fibroblasts

It is well established that prostaglandin E2 (PGE2) plays an important role in inflammatory diseases including periodontitis. Previously we have reported that the inflammatory mediators interleukin-1beta, (IL-1beta) and tumor necrosis factor alpha (TNFalpha) stimulate PGE2 synthesis by inducing mRNA expression of cyclooxygenase-2 (COX-2) in human gingival fibroblasts. In present study the involvement of microsomal prostaglandin E synthase-1 (mPGES-1) in relation to PGE2 production was investigated. The results showed that IL-1beta as well as TNFalpha induced mPGES-1 mRNA and protein expression accompanied by enhanced PGE2 production in gingival fibroblasts. The anti-inflammatory steroid dexamethasone (DEX) inhibited mPGES-1 mRNA and protein expression as well as PGE2 production induced by IL-1beta or TNFalpha. The COX-2 specific inhibitor, celecoxib, in contrast to the nonspecific COX inhibitor, indomethacin, markedly reduced mPGES-1 expression induced by IL-1beta. The results demonstrate that mPGES-1 regulates PGE2 production in gingival fibroblasts stimulated by inflammatory mediators IL-1beta and TNFa. This novel pathway may be a potential target for treatment strategies of periodontal disease.     

Expression and regulation of prostaglandin E synthase isoforms in human myometrium with labour

Since the controversies regarding the use of non-steroidal anti-inflammatory drugs (NSAIDs) and selective cyclo-oxygenase (COX)-2 antagonists for the treatment of preterm labour (PTL), more emphasis has been placed on investigating the terminal synthases involved in the production of prostaglandins (PGs) to allow more targeted therapy in PTL. Prostaglandin E(2) (PGE(2)) is synthesized by one of three enzymes, cytosolic prostaglandin E synthase (cPGES), microsomal PGES-1 (mPGES-1) and microsomal PGES-2 (mPGES-2). We have determined (i) the immuno-localization of all three PGES enzymes in lower segment pregnant human myometrium, (ii) the expression of PGES and COX-2 mRNA expression at term and preterm gestation with and without labour and (iii) the effect of interleukin (IL)-1beta on COX-2 and PGES mRNA and protein expression in human myometrial smooth muscle (HMSM) cell cultures. We show mPGES-1 protein located predominantly in myometrial and vascular smooth muscle cells (SMCs), whilst mPGES-2 protein is largely in stromal cells surrounding the SMC and cPGES is diffusely located throughout the myometrium. Expression of mPGES-2 mRNA increased with term labour and PTL and expression of COX-2 and mPGES-1 mRNA with term labour, whereas cPGES expression did not change. IL-1beta stimulated release of PGE(2) by HMSM cells and increased COX-2 and mPGES-1 mRNA and protein expression. Thus, COX-2 expression and mPGES-1 expression are co-ordinately up-regulated in lower segment myometrium with term labour and with IL-1beta treatment in HMSM cells.     

Misoprostol, an anti-ulcer agent and PGE2 receptor agonist, protects against cerebral ischemia

Induction of COX-2 activity in cerebral ischemia results in increased neuronal injury and infarct size. Recent studies investigating neurotoxic mechanisms of COX-2 demonstrate both toxic and paradoxically protective effects of downstream prostaglandin receptor signaling pathways. We tested whether misoprostol, a PGE(2) receptor agonist that is utilized clinically as an anti-ulcer agent and signals through the protective PGE(2) EP2, EP3, and EP4 receptors, would reduce brain injury in the murine middle cerebral artery occlusion-reperfusion (MCAO-RP) model. Administration of misoprostol, at the time of MCAO or 2h after MCAO, resulted in significant rescue of infarct volume at 24 and 72h. Immunocytochemistry demonstrated dynamic regulation of the EP2 and EP4 receptors during reperfusion in neurons and endothelial cells of cerebral cortex and striatum, with limited expression of EP3 receptor. EP3-/- mice had no significant changes in infarct volume compared to control littermates. Moreover, administration of misoprostol to EP3+/+ and EP3-/- mice showed similar levels of infarct rescue, indicating that misoprostol protection was not mediated through the EP3 receptor. Taken together, these findings suggest a novel function for misoprostol as a protective agent in cerebral ischemia acting via the PGE(2) EP2 and/or EP4 receptors.     

Prostaglandin E(2) induces caspase-dependent apoptosis in rat cortical cells.

Up-regulation of neuronal cyclooxygenase-2 (COX-2) and the elevation in prostaglandin E(2) (PGE(2)) have been reported to occur after cerebral ischemic insult. To evaluate whether the COX-2 reaction product PGE(2) is directly related to induction of apoptosis in neuronal cells, the effect of PGE(2) on cell viability was examined in rat cortical cells. PGE(2) induced apoptosis in a dose-dependent manner (5-25 microM) 48 h after addition to the cells, which was characterized by cell shrinkage, nuclear condensation or fragmentation, and internucleosomal DNA fragmentation. Neither 17-phenyl trinor-prostaglandin E(2) (an EP1 agonist) or sulprostone (an EP3 agonist) induced cell death, whereas butaprost (an EP2 agonist) induced apoptotic cell death. In addition, PGE(2) activated caspase-3 in a time-dependent manner until 24 h after treatment. The apoptosis induced by PGE(2) was prevented by a caspase-3 inhibitor in a dose-dependent manner. In contrast, dibutyryl cyclic adenosine monophosphate also induced apoptotic cell death in a dose-dependent manner (20-100 microM). These results suggest that PGE(2), acting via an EP2-like receptor, induces apoptosis in neurons.     

Cyclooxygenase-2 expression and effect of celecoxib in flurothyl-induced neonatal seizure

Endogenous PGE(2) dynamically regulates membrane excitability, synaptic transmission and plasticity. Neonatal seizures are associated with a number of activity-dependent changes in brain development including altered synaptogenesis and synaptic plasticity as well as reduction in neurogenesis. Thus, it is reasonable to hypothesize that alteration of cyclooxygenase-2 (COX-2) expression induced by neonatal seizure may influence brain development. We evaluated the expression of COX-2 and microsomal prostaglandin E synthase (mPGES) by Western blot analysis and immnohistochemistry in flurothyl-induced neonatal seizure and also studied the effect of celecoxib on seizure induction. Seven to 10 days old Sprague-Dawley rats were used for control (n = 18) and experimental group (n = 30). Recurrent seizure group showed more increased level of COX-2 expression than control group. However, the level of mPGES-2 expression was similar in both groups, and mPGES-1 was not detected. Hippocampus of control rats showed endogenous COX-2 expression, which was localized mainly in CA3 region. This localization pattern was similar in recurrent seizure rats, but intensity of COX-2 expression was more increased than in control rats. Celecoxib treatment significantly delayed the seizure attack and also reduced COX-2 expression. In conclusion, this study suggests that COX-2 expression is related to epileptogenesis in flurothyl-induced neonatal seizure model and shows the possibility that its inhibition lessens functional impairments that occurred in neonatal seizure.     

IL-3 is an important differentiation factor for the development of prostaglandin E2-producing macrophages between C57BL/6 and BALB/c mice

We have previously reported that peritoneal and splenic macrophages from Th2-dominant BALB/c mice produced higher amounts of prostaglandin (PG) E2 than cells from C57BL/6 mice. In this study, we investigated how macrophages from BALB/c mice acquire the ability of enhanced PGE2 production, using bone marrow-derived macrophages differentiated by M-CSF, GM-CSF or IL-3. There is no strain difference in PGE2 production by GM-CSF- and M-CSF-differentiated macrophages; however, IL-3-differentiated macrophages from BALB/c mice produced higher amounts of PGE2 and lower amounts of type I cytokines than cells from C57BL/6 mice. IL-3-differentiated macrophages from BALB/c mice expressed larger amounts of mRNA of membrane-bound (microsomal) PGE synthase-1 (mPGES-1). The amounts of PGE2 produced by macrophages were significantly reduced in mPGES-1-deficient mice, and these mice displayed enhanced Th1 responses after Propionibacterium acnes treatment compared with wild-type mice. Microarray analysis revealed 63 genes that are differentially expressed more than fivefold in macrophages between C57BL/6 and BALB/c mice. These results indicate that mPGES-1-mediated PGE2 produced by macrophages regulates immune responses, and IL-3 is an important factor for the differentiation of macrophages that produce higher amounts of PGE2 through mPGES-1 activity in BALB/c mice.