Common polymorphisms of cyclooxygenase-2 and prostaglandin E2 receptor and increased risk for acute coronary syndrome in coronary artery disease

The arachidonic acid metabolites participate in development of coronary artery disease (CAD) and the plaque's instability. We assessed two common genetic polymorphisms: of cyclooxygenase-2 (COX-2) (COX2.8473, rs5275) and prostaglandin EP2 receptor gene (uS5, rs708494) in patients with CAD. Out of 1,368 patients screened by coronary arteriography, two groups fulfilled the entry criteria and were studied: stable coronary disease (sCAD, n = 125) and acute coronary syndromes (ACS, n = 63). They did not differ in the main characteristics. All patients were on aspirin at least seven days prior to the study. In 70 control subjects, the same genotypes were ascertained, expression of cyclooxygenases in peripheral blood monocytes was assessed by flow cytometry, and in-vitro biosynthesis of PGE(2) was measured by mass spectrometry. COX-2 CC homozygotes (variant allele), were more common, while EP2 GG homozygotes (wild-type) were less common in ACS (p = 0.03 and p = 0.017) than in the sCAD group. A combined genotype characterized by the presence of the wild-type COX2.8743T allele and the wild type homozygous EP2uS5 genotype (TT or CT | GG) decreased risk ratio of ACS in CAD patients (relative risk 0.41; 95% confidence interval 0.21-0.81). COX-2 polymorphism in control subjects did not affect the enzyme expression or PGE(2) production by peripheral blood monocytes, but production of PGE(2) increased by 40.1% in the subjects homozygous for EP2 receptor allele uS5A following lipopolysaccharide stimulation. In conclusion, the combined COX-2 (COX2.8473) and the EP2 receptor (uS5) genotypes seem to influence CAD stability, but in peripheral blood monocytes only EP2 receptor modulates PGE(2) production.

Prostaglandin receptor EP2 protects dopaminergic neurons against 6-OHDA-mediated low oxidative stress

Dopaminergic neurons in the substantia nigra (SN) selectively die in Parkinson's disease (PD), but it is unclear how and why this occurs. Recent findings implicate prostaglandin E(2) (PGE(2)) and two of its four receptors, namely EP1 and EP2, as mediators of degenerative and protective events in situations of acute and chronic neuronal death. EP1 activation can exacerbate excitotoxic damage in stroke models and our recent study showed that EP1 activation may explain the selective sensitivity of dopaminergic neurons to oxidative stress. Conversely, EP2 activation may be neuroprotective, although toxic effects have also been demonstrated. Here we investigated if and how EP2 activation might alter the survival of dopaminergic neurons following selective low-level oxidative injury evoked by the neurotoxin 6-hydroxydopamine (6-OHDA) in primary neuronal cultures prepared from embryonic rat midbrain. We found that cultured dopaminergic neurons displayed EP2 receptors. Butaprost, a selective EP2 agonist, significantly reduced 6-OHDA neurotoxicity. EP2 receptors are coupled to stimulatory G-proteins (Gs), which activate adenylate cyclase, increasing cAMP synthesis, which then activates protein kinase A (PKA). Both dibutyryl cAMP and forskolin reduced dopaminergic cell loss after 6-OHDA exposure. Conversely, KT5720 and H-89, two structurally distinct high-affinity PKA inhibitors, abolished the protective effect of butaprost, implicating cAMP-dependent PKA activity in the neuroprotection by EP2 activation. Finally, we show that melanized dopaminergic neurons in the human SN express EP2. This pathway warrants consideration as a neuroprotective strategy for PD.

Molecular cloning and characterization of chicken prostaglandin E receptor subtypes 2 and 4 (EP2 and EP4)

Prostaglandin E(2) (PGE(2)) is an important chemical mediator responsible for regulation of many vital physiological processes. Four receptor subtypes have been identified to mediate its biological actions. Among these subtypes, prostaglandin E receptor subtypes 2 and 4 (EP(2) and EP(4)), both coupled to cAMP-protein kinase A (cAMP-PKA) signaling pathway, are proposed to play crucial roles under both physiological and pathological conditions. Though both receptors were extensively studied in mammals, little is known about their functionality and expression in non-mammalian species including chicken. In present study, the full-length cDNAs for chicken EP(2) and EP(4) receptors were first cloned from adult chicken ovary and testis, respectively. Chicken EP(2) is 356 amino acids in length and shows high amino acid identity to that of human (61%), mouse (63%), and rat (61%). On the other hand, the full-length cDNA of EP(4) gene encodes a precursor of 475 amino acids with a high degree of amino acid identity to that of mammals, including human (87%), mouse (86%), rat (84%), dog (85%), and cattle (83%), and a comparatively lower sequence identity to zebrafish (52%). RT-PCR assays revealed that EP(2) mRNA was expressed in all tissues examined including the oviduct, while EP(4) expression was detected only in a few tissues. Using the pGL3-CRE-luciferase reporter system, we also demonstrated that PGE(2) could induce luciferase activity in DF-1 cells expressing EP(2) and EP(4) in dose-dependent manners (EC(50): <1 nM), confirming that both receptors could be activated by PGE(2) and functionally coupled to the cAMP-PKA signaling pathway. Together, our study establishes a molecular basis to understand the physiological roles of PGE(2) in target tissues of chicken.

Dendritic cell infiltration pattern along the colorectal adenoma-carcinoma sequence

We have previously reported that the dendritic cell (DC) functional index cytokine interleukin-12 was significantly decreased in colorectal carcinoma (CRC) tissues. In this study, the DC infiltration pattern and the density of mature DCs (mDCs; labeled by anti-CD83 and anti-CD208) and immature DCs (iDCs; labeled by anti-CD1alpha) were characterized using immunohistochemistry (IHC) in tissue samples from 23 patients with CRC, 33 patients with colorectal adenoma (CRA), and 19 healthy controls. In addition, the DC function inhibitor cyclooxygenase-2 (COX-2) and the downstream signal molecule prostaglandin E2 (PGE2) and related receptors EP2/EP4 were measured by quantitative real-time PCR and double immunofluorescence staining. The IHC analyses revealed changed densities of mDCs and iDCs in the tumor microenvironment; in CRA and CRC, the density of mDCs was decreased, but the density of iDCs was gradually increased. Furthermore, the distribution patterns of DCs were also altered. In CRA, mDCs were abundantly distributed in the subepithelial stroma of the adenomatous mass. In CRC, the distribution of mDCs in the tumor stroma was not homogeneous, and mDCs residing in the stroma at invading edges were more frequently found compared with in the intratumoral stroma (P<0.05). Increased iDCs were found in the intratumoral mass in CRC, and some infiltrated into the malignant epithelium. By quantitative real-time PCR, a gradually increased level of COX-2 mRNA was demonstrated in the local tissues along the adenoma-carcinoma sequence, and double immunofluorescence staining showed a colocalization of PGE2 receptors EP2/EP4 with mDCs in the stroma of CRC. In conclusion, our current findings revealed an altered DC infiltration pattern along the adenoma-carcinoma sequence; gradually increased COX-2 expression might contribute to the DC functional defect.

Prostaglandin E2 reduces extracellular ATP-induced migration in cultured rat microglia

Treatment with 100 microM adenosine triphosphate (ATP) for 120 min augmented migration of cultured rat microglia by about 4-fold. This augmentation was effectively reduced by 0.1-10 microM prostaglandin E(2) (PGE(2)). PGE(2)-mediated reduction was reversed by the EP2 antagonist AH6809 at 10 microM. The EP2 agonist butaprost also reduced ATP-induced migration at 10 microM, whereas the EP1 agonist 17-phenyl trinor PGE(2), the EP3 agonist sulprostone, and the EP4 agonist PGE(1) alcohol all had no effect at 10 microM. In addition, ATP-induced migration was reduced by the adenylate cyclase activator forskolin at 100 microM, whereas the adenylate cyclase inhibitor SQ22536 reversed the effect of PGE(2) on ATP-induced migration at 100 microM. Over the same experimental duration, PGE(2), butaprost, and forskolin had little effect on cell viability. These findings indicate that ATP-induced microglial migration is reduced by PGE(2) through EP2 and adenylate cyclase.

Cyclooxygenase-2 derived PGE2 and PGI2 play an important role via EP2 and PPARdelta receptors in early steps of oil induced decidualization in mice

Differentiation of endometrial stromal cells into decidual cells (decidualization) is prerequisite for blastocyst implantation. Different prostanoids are shown to be involved in the cascade of events found in implantation and decidualization. Previous reports described that cyclooxygenase-2 (COX2) derived prostacyclin (PGI2) plays an important role via peroxisome proliferator activated receptor (PPARdelta) nuclear receptor in implantation and decidualization. Herein, we investigated the role of COX2 derived PGE2 and PGI2 and examined the protein expression and regulation of COX1, COX2, membrane-bound prostaglandin E synthase (mPGES-1), prostaglandin I synthase (PGIS), PGE2 receptor (EP2) and PPARdelta in hormone primed oil infused uterine horn as well as in non-infused uterine horn (control horn). Our results show that selective COX2 inhibitor (Nimesulide) inhibits decidualization while COX1 inhibitor (SC560) does not affect decidualization. COX2, mPGES-1, PGIS, EP2 and PPARdelta immunostaining are strongly observed at 24 h and 48 h in oil-induced horn and than significantly reduced at 72 h and 120 h and absent in non-infused horn. However COX1 immunostaining is observed in infused as well as in non-infused horn. Our immunohistochemical studies corroborated well with follow up western blotting of the same proteins. PGE2 and PGI2 products were also elevated at 24h and 48 h after oil induction in infused horn in comparison to control horn. Our data suggest that COX2 derived both PGE2 and PGI2 mediate its function via EP2 and PPARdelta receptors in early steps of decidualization in mice.

Loss of prostaglandin F2alpha, but not thromboxane, responsiveness in pregnant human myometrium during labour

Prostaglandins (PG) E2, PGF2alpha and thromboxane (TX) mediate uterine contractility by targeting prostonoid EP, FP and TP receptors respectively. The aim of this study was to elucidate the function of these receptors in isolated human myometrium taken at term gestation prior to and following labour onset. Lower segment myometrial strips were immersed in organ baths in oxygenated Krebs' solution at 37 degrees C and connected to isometric force transducers. After equilibration, spontaneous activity and concentration responses to PGE2, PGF2alpha and U46619 (a stable TX mimetic) were measured as area under the curve and expressed as a percentage of the final contraction induced by hypotonic shock. Results were expressed as arithmetic means+/-s.e.m. and analysed using two-way ANOVA with Bonferroni's post hoc test. Myometrium excised at late gestation displayed the greatest spontaneous activity compared with the tissues taken during labour (P<0.001). Excitation evoked by PGF2alpha (P<0.01) and PGE2 at 10(-5) mol/l were attenuated after labour onset. U46619 consistently stimulated concentration-dependent contractions (P<0.001) and selective antagonists confirmed TP-mediated effects. The maintained responses to TX indicate crucial roles for TP receptors in the muscular tonus of the parturient uterus. This receptor and its secondary messenger system represent effective myometrial targets for tocolytic agents in both pregnancy and labour-associated disorders.

Function of COX-2 and prostaglandins in neurological disease

Induction of COX-2 expression and enzymatic activity promotes neuronal injury in a number of models of neurological disease. Inhibition of COX-2 activity, either genetically or pharmacologically, has been shown to be neuroprotective in rodent models of stroke, Parkinson's disease, and amyotrophic lateral sclerosis. Inhibition of COX activity with nonsteroidal anti-inflammatory drugs (NSAIDs) reduces inflammation and amyloid accumulation in murine transgenic models of Familial Alzheimer's disease, and the use of NSAIDs decreases the risk of developing Alzheimer's disease in healthy aging populations. COX-mediated neuronal injury is presumed be due to downstream effects of one or more prostaglandin products including PGE2, PGD2, PGF2alpha, PGI2 (prostacylin) and TXA2 (thromboxane) that effect cellular changes through activation of specific prostaglandin receptor subtypes and second messenger systems. In this proceeding, we review recent data demonstrating effects of prostaglandin signaling on neuronal viability that are paradoxically protective, when taken in the context that COX-2 induces neuronal injury in the setting of excitotoxicity. Conversely, in the context of an inflammatory stimulus, the EP2 receptor enhances neuronal injury. These findings argue for an additional level of complexity in the prostaglandin response in neurological disease.

EP2 and EP4 receptors regulate aromatase expression in human adipocytes and breast cancer cells. Evidence of a BRCA1 and p300 exchange

Cytochrome P450 aromatase (aromatase), a product of the CYP19 gene, catalyzes the synthesis of estrogens from androgens. Because aromatase-dependent estrogen biosynthesis has been linked to hormone-dependent breast carcinogenesis, it is important to elucidate the mechanisms that regulate CYP19 gene expression. The main objective of this study was to identify the receptors (EP) for prostaglandin E(2) (PGE(2)) that mediate the induction of CYP19 transcription in human adipocytes and breast cancer cells. Treatment with PGE(2) induced aromatase, an effect that was mimicked by either EP(2) or EP(4) agonists. Antagonists of EP(2) or EP(4) or small interference RNA-mediated down-regulation of these receptors suppressed PGE(2)-mediated induction of aromatase. PGE(2) via EP(2) and EP(4) stimulated the cAMP-->protein kinase A pathway resulting in enhanced interaction between P-CREB, p300, and the aromatase promoter I.3/II. Overexpressing a mutant form of p300 that lacks histone acetyltransferase activity suppressed PGE(2)-mediated induction of aromatase promoter activity. PGE(2) via EP(2) and EP(4) also caused a reduction in both the amounts of BRCA1 and the interaction between BRCA1 and the aromatase promoter I.3/II. Activation of the aromatase promoter by PGE(2) was suppressed by overexpressing wild-type BRCA1. Silencing of EP(2) or EP(4) also blocked PGE(2)-mediated induction of the progesterone receptor, a prototypic estrogen-response gene. In a mouse model, overexpressing COX-2 in the mammary gland, a known inducer of PGE(2) synthesis, led to increased aromatase mRNA and activity and reduced amounts of BRCA1; these effects were reversed by knocking out EP(2). Taken together, these results suggest that PGE(2) via EP(2) and EP(4) activates the cAMP-->PKA-->CREB pathway leading to enhanced CYP19 transcription and increased aromatase activity. Reciprocal changes in the interaction between BRCA1, p300, and the aromatase promoter I.3/II contributed to the inductive effects of PGE(2).

Effects of gestational age on prostaglandin EP receptor expression and functional involvement during in vitro contraction of the guinea pig uterus

Prostaglandin E(2) (PGE(2)) exerts diverse biological effects through four G-protein-coupled cell surface receptor subtypes, EP1-4. This study's objective was to characterize EP1-4 receptor mRNA expression within pregnant guinea pig myometrium during early implantation stage (gestation day [GD] 6) and late stage gestation (GD 50) and evaluate in vitro contractile activity of receptor subtype selective agonists. Using RT-PCR, qualitative gene expression patterns of EP2, EP3, and EP4 mRNA were detected in the myometrium and remained unchanged between the gestational ages. EP1 mRNA remained undetected in pregnant tissue. In vitro contractile activity was evaluated in GD 6 and GD 50 myometrium using vehicle and EP agonists PGE(2), 17-phenyl trinor PGE(2), sulprostone, misoprostol, and CP-533,536. All spasmogens in pregnant myometrium were EP1/EP3 selective agonists, though likely acting via EP3 receptors in this test model. CP-533,536--a highly selective EP2 receptor agonist--and the vehicle failed to induce myometrial contraction at both gestational ages.

Prostaglandin E2 induces vascular endothelial growth factor secretion in prostate cancer cells through EP2 receptor-mediated cAMP pathway

Prostaglandin E2 (PGE2) has been shown to induce expression of vascular endothelial growth factor (VEGF) and other signaling molecules in several cancers. PGE2 elicits its functions though four G-protein coupled membrane receptors (EP1-4). In this study, we investigated the role of EP receptors in PGE2-induced molecular events in prostate cancer cells. qRT-PCR analysis revealed that PC-3 cells express a substantially higher level of EP2 and moderately higher EP4 than DU145 and LNCaP cells. LNCaP cells had virtually no detectable EP2 mRNA. EP1 and EP3 mRNAs were not detected in these cells. Treatment of prostate cancer cells with PGE2 (1 nM-10 microM) increased both VEGF secretion and cyclic adenosine monophosphate (cAMP) production. Levels of induction in PC-3 cells were greater than in DU145 and LNCaP cells. The selective EP2 agonist CAY10399 also significantly increased VEGF secretion and cAMP production in PC-3 cells, but not in DU145 and LNCaP cells. Moreover, PGE2 and CAY10399 increased mitogen activated protein kinase/extracellular signal regulated kinase (MAPK/Erk) and Akt phosphorylation in PC-3 and DU145 cells, but not in LNCaP cells. However, neither the MAPK/Erk inhibitor U0126 nor the PI3K/Akt inhibitor LY294002 abolished PGE2-induced VEGF secretion in PC-3 cells. We further demonstrated that the adenylate cyclase activator forskolin and the cAMP anologue 8-bromo-cAMP mimicked the effects of PGE2 on VEGF secretion in PC-3 cells. Meanwhile, the adenylate cyclase inhibitor 2'5'-dideoxyadenosine, at concentrations that inhibited PGE2-induced cAMP, significantly blocked PGE2-induced VEGF secretion in PC-3 cells. We conclude that PGE2-induced VEGF secretion in prostate cancer cells is mediated through EP2-, and possibly EP4-, dependent cAMP signaling pathways.

Association between genetic variations in prostaglandin E2 receptor subtype EP3 gene (Ptger3) and asthma in the Korean population

BACKGROUND

Recent investigations suggest that prostaglandin E2 (PGE2) is important in the pathogenesis of not only aspirin-intolerant asthma but also asthma unrelated to aspirin intolerance.

OBJECTIVES

This study was conducted to evaluate the effects of variations in the gene coding PGE2 receptor subtype EP1-4 (Ptger1-4) on the risk of asthma in the Korean population.

METHODS

Nineteen single nucleotide polymorphisms (SNPs) were selected after re-sequencing Ptger1-4 and were genotyped in 480 asthmatics and 140 healthy controls, who were randomly recruited.

RESULTS

By logistic regression analyses controlling for age and sex, 1388T>C in Ptger3 was found to be significantly associated with asthma [P=0.002, odds ratio (95% confidence interval)=0.63 (0.46-0.85) in the allele model], and this remained significant after applying the Bonferroni correction. In terms of haplotype, the frequency of the C-C-A-A haplotype in Ptger3 was significantly lower in asthmatics than in healthy controls (P=0.004). Moreover, the prevalence of this haplotype was significantly lower in moderate-to-severe asthmatics than in mild asthmatics (P=0.045; mild vs. moderate and P=0.034; mild vs. severe). However, no association was found between any genetic variation in Ptger1, Ptger2, or Ptger4 and asthma.

CONCLUSION

The present study demonstrated that genetic variations in Ptger3 are significantly associated with the risk and severity of asthma in the Korean population.

PTGER1 and PTGER2 receptors mediate regulation of progesterone synthesis and type 1 11beta-hydroxysteroid dehydrogenase activity by prostaglandin E2 in human granulosa lutein cells

In luteinizing granulosa cells, prostaglandin E(2) (PGE(2)) can exert luteotrophic actions, apparently via the cAMP signalling pathway. In addition to stimulating progesterone synthesis, PGE(2) can also stimulate oxidation of the physiological glucocorticoid, cortisol, to its inactive metabolite, cortisone, by the type 1 11beta-hydroxysteroid dehydrogenase (11betaHSD1) enzyme in human granulosa-lutein cells. Having previously shown these human ovarian cells to express functional G-protein coupled, E-series prostaglandin (PTGER)1, PTGER2 and PTGER4 receptors, the aim of this study was to delineate the roles of PTGER1 and PTGER2 receptors in mediating the effects of PGE(2) on steroidogenesis and cortisol metabolism in human granulosa-lutein cells. PGE(2)-stimulated concentration-dependent increases in both progesterone production and cAMP accumulation (by 1.9 +/- 0.1- and 18.7 +/- 6.8-fold respectively at 3000 nM PGE(2)). While a selective PTGER1 antagonist, SC19220, could partially inhibit the steroidogenic response to PGE(2) (by 55.9 +/- 4.1% at 1000 nM PGE(2)), co-treatment with AH6809, a mixed PTGER1/PTGER2 receptor antagonist, completely abolished the stimulation of progesterone synthesis at all tested concentrations of PGE(2) and suppressed the stimulation of cAMP accumulation. Both PGE(2) and butaprost (a preferential PTGER2 receptor agonist) stimulated concentration-dependent increases in cortisol oxidation by 11betaHSD1 (by 42.5 +/- 3.1 and 40.0 +/- 3.0% respectively, at PGE(2) and butaprost concentrations of 1000 nM). Co-treatment with SC19220 enhanced the ability of both PGE(2) and butaprost to stimulate 11betaHSD1 activity (by 30.2 +/- 0.2 and 30.5 +/- 0.6% respectively), whereas co-treatment with AH6809 completely abolished the 11betaHSD1 responses to PGE(2) and butaprost. These findings implicate the PTGER2 receptor-cAMP signalling pathway in the stimulation of progesterone production and 11betaHSD1 activity by PGE(2) in human granulosa-lutein cells.

Stimulation of prostanoid IP and EP2 receptors dilates retinal arterioles and increases retinal and choroidal blood flow in rats

We examined the effects of vasodilatory prostaglandins (prostacyclin and prostaglandin E(2)) and selective agonists for prostanoid EP(2) and EP(4) receptor on the diameters of retinal blood vessels and fundus (retinal/choroidal) blood flow in rats. Male Wistar rats (8- to 10-week-old) were treated with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye and infused with a mixture solution of norepinephrine and epinephrine (1:9) to maintain adequate systemic circulation under artificial ventilation. Fundus images were captured with a digital camera that was equipped with the special objective lens for small animals, and the diameters of retinal arterioles and venules were measured on a personal computer. Fundus blood flow was estimated using a laser Doppler flowmetry. Intravenous infusions of prostacyclin and prostaglandin E(2) dilated retinal blood vessels, increased fundus blood flow and decreased systemic blood pressure in a dose-dependent manner. The effects of vasodilatory prostaglandins on retinal arterioles were greater than those on retinal venules. Similarly, a prostanoid EP(2) receptor agonist (ONO-AE1-259-01) dilated retinal blood vessels, and increased fundus blood flow and decreased systemic blood pressure. However, a prostanoid EP(4) receptor agonist (ONO-AE1-329) failed to increase fundus blood flow, despite its comparable depressor response with those to vasodilatory prostaglandins and the prostanoid EP(2) receptor agonist. The responses to forskolin, an activator of adenylyl cyclase, were very similar to those to prostacyclin and the prostanoid EP(2) receptor agonist. These results suggest that prostacyclin and prostaglandin E(2) act as vasodilators in retinal and choroidal circulation, and prostanoid IP and EP(2) receptors play an important role in the regulation of ocular hemodynamics in rats.

EP2 receptor mediates PGE2-induced cystogenesis of human renal epithelial cells

Autosomal-dominant polycystic kidney disease (ADPKD) is characterized by formation of cysts from tubular epithelial cells. Previous studies indicate that secretion of prostaglandin E2 (PGE2) into cyst fluid and production of cAMP underlie cyst expansion. However, the mechanism by which PGE2 directly stimulates cAMP formation and modulates cystogenesis is still unclear, because the particular E-prostanoid (EP) receptor mediating the PGE2 effect has not been characterized. Our goal is to define the PGE2 receptor subtype involved in ADPKD. We used a three-dimensional cell-culture system of human epithelial cells from normal and ADPKD kidneys in primary cultures to demonstrate that PGE2 induces cyst formation. Biochemical evidence gathered by using real-time RT-PCR mRNA analysis and immunodetection indicate the presence of EP2 receptor in cystic epithelial cells in ADPKD kidney. Pharmacological evidence obtained by using PGE2-selective analogs further demonstrates that EP2 mediates cAMP formation and cystogenesis. Functional evidence for a role of EP2 receptor in mediating cAMP signaling was also provided by inhibiting EP2 receptor expression with transfection of small interfering RNA in cystic epithelial cells. Our results indicate that PGE2 produced in cyst fluid binds to adjacent EP2 receptors located on the apical side of cysts and stimulates EP2 receptor expression. PGE2 binding to EP2 receptor leads to cAMP signaling and cystogenesis by a mechanism that involves protection of cystic epithelial cells from apoptosis. The role of EP2 receptor in mediating the PGE2 effect on stimulating cyst formation may have direct pharmacological implications for the treatment of polycystic kidney disease.

Sequential Down-regulation of E-Cadherin with Squamous Cell Carcinoma Progression: Loss of E-Cadherin via a Prostaglandin E2-EP2–Dependent Posttranslational Mechanism

The incidence of skin cancer is on the rise, with over 1 million new cases yearly. Although it is known that squamous cell cancers (SCC) are caused by UV light, the mechanism(s) involved remains poorly understood. In vitro studies with epithelial cells or reports examining malignant skin lesions suggest that loss of E-cadherin-mediated cell-cell contacts may contribute to SCCs. Other studies show a pivotal role for cyclooxygenase-dependent prostaglandin E2 (PGE2) synthesis in this process. Using chronically UV-irradiated SKH-1 mice, we show a sequential loss of E-cadherin-mediated cell-cell contacts as lesions progress from dysplasia to SCCs. This E-cadherin down-regulation was also evident after acute UV exposure in vivo. In both chronic and acute UV injury, E-cadherin levels declined at a time when epidermal PGE2 synthesis was enhanced. Inhibition of PGE2 synthesis by indomethacin in vitro, targeted deletion of EP2 in primary mouse keratinocyte (PMK) cultures or deletion of the EP2 receptor in vivo abrogated this UV-induced E-cadherin down-regulation. In contrast, addition of PGE2 or the EP2 receptor agonist butaprost to PMK produced a dose- and time-dependent decrease in E-cadherin. We also show that UV irradiation, via the PGE2-EP2 signaling pathway, may initiate tumorigenesis in keratinocytes by down-regulating E-cadherin-mediated cell-cell contacts through its mobilization away from the cell membrane, internalization into the cytoplasm, and shuttling through the lysosome and proteasome degradation pathways. Further understanding of how UV-PGE2-EP2 down-regulates E-cadherin may lead to novel chemopreventative strategies for the treatment of skin and other epithelial cancers.

EP1-4 subtype, COX and PPAR gamma receptor expression in colorectal cancer in prediction of disease-specific mortality

The importance of prostaglandins in tumor growth and progression is well recognized, including antineoplastic activities by cyclooxygenase (COX) inhibitors. Variation in treatment response to COX inhibition has questioned differences in expression of cell surface and nuclear membrane receptors among tumors with different disease progression. The purpose of this study was to evaluate whether EP(1-4) subtype, PPAR gamma receptor and COX-1/COX-2 expression in colorectal cancer are related to tumor-specific mortality. Reverse transcription-polymerase chain reaction and immunohistochemistry were used to demonstrate expression and protein appearance in tumor tissue compared with normal colon tissue. EP(1) and EP(2) subtype receptor protein was highly present in tumor cells, EP(3) occurred occasionally and EP(4) was not visible. PPAR gamma, EP(2) and EP(4) mRNA were significantly higher in normal colon tissue compared with tumor tissue, without any distinct relationship to Dukes A-D tumor stage. Multivariate analyses indicated that increased tumor tissue EP(2) and COX-2 expression predicted poor survival (p<0.001). COX-1 expression was significantly higher than COX-2 expression in normal colon tissue. Average COX-2 mRNA was not increased in tumor tissue compared with normal colon. However, most tumor cells stained positive for COX-2 protein, which was low or undetectable in normal mucosa cells. COX-1 protein was preferentially visible in stroma. EP(1-4) subtype receptor mRNAs were generally positively correlated to both COX-1 and COX-2 in tumor tissue, but not in normal colon. Our results imply that both prostaglandin production (COX-2) and signaling via EP(1-4) subtype receptors, particularly EP(2), predict disease-specific mortality in colorectal cancer.

Specific components of prostanoid-signaling pathways are present in non-small cell lung cancer cells

In the present study, we measured prostanoid synthesis and the expression of genes associated with prostanoid signaling in human non-small cell lung carcinoma (NSCLC) cell lines and in primary human tumors. Consistent with the proposed growth promoting role of PGE2, we found that NSCLC cell lines frequently co-expressed the genes encoding cyclooxygenase-2 and the prostaglandin E2 (PGE2) receptors EP1, 2 and 4 concomitant with the synthesis of PGE2. In contrast, NSCLC cells did not synthesize appreciable amounts of prostaglandin I2 (PGI2, prostacyclin), lacked PGI2 synthase (PGIS) and did not express the gene coding for the PGI2 receptor IP at detectable levels. In agreement with this finding, PGIS mRNA levels were dramatically diminished in primary human tumor samples as compared to matched normal lung tissue. Finally, thromboxane A2 (TxA2) was synthesized in NSCLC cell lines, but transcription of the gene coding for the TxA2 receptor TP was not observed in these cells. In marked contrast, lung fibroblasts synthesized all three prostanoids and their receptors at high levels. While the observed expression patterns were consistent with the existence of autocrine/paracrine PGE2 signaling loops in NSCLC cells, PGI2- and TxA2-mediated signals may play a role in tumor stroma cells.

Association between prostaglandin E2 receptor gene and essential hypertension

BACKGROUND

Essential hypertension (EH) is a complex multifactorial polygenic disorder that is thought to result from an interaction between an individual's genetic makeup and various environmental factors. In the kidney, prostaglandins (PGs) are important mediators of vascular tone and salt and water homeostasis, and are involved in the mediation and/or modulation of hormonal action. In previous studies, mice deficient in the prostaglandin E2 (PGE(2)) EP2 receptor had resting systolic blood pressure (BP) that was significantly lower than that of wild-type controls. The BP of those mice increased when they were put on a high-salt diet, suggesting that the EP2 receptor is involved in sodium handling by the kidney. In the present study, we investigated the association between EH and nucleotide polymorphisms in the gene encoding the prostaglandin E2 receptor subtype EP2 (PTGER2).

METHODS

We selected three single-nucleotide polymorphisms (SNP) in the human PTGER2 gene (rs1254601, rs2075797, and rs17197), and we performed a genetic association study of 266 EH patients and 253 age-matched normotensive (NT) controls.

RESULTS

There was no significant difference in overall distribution of genotypes or alleles of any of the SNP between the EH and NT groups. However, among men, the A/A type of the SNP rs17197 (rs17197, A/G in 3'UTR) was significantly more frequent in EH subjects than in NT subjects (P=0.041).

CONCLUSION

The present findings suggest that rs17197 is useful as a genetic marker of EH in men.

Prostaglandin E(2) receptors in bone formation

Prostaglandins, PGE(2) in particular, have diverse actions on various organs, including inflammation, bone healing, bone formation, embryo implantation, induction of labour and vasodilatation, among others. However, systemic side effects have limited their clinical utility. The pharmacological activities of PGE(2) are mediated through four G protein-coupled receptor subtypes, EP1-EP4. Recent studies have shown that EP2 and EP4 receptors play important roles in regulating bone formation and resorption. EP2 and EP4 receptor-selective agonists have been shown to stimulate local or systemic bone formation, augment bone mass and accelerate the healing of fractures or bone defects in animal models upon local or systemic administration, thus, potentially offering new therapeutic options for enhancing bone formation and bone repair in humans. This review will focus on the studies related to bone formation and bone healing in the EP receptor knockout (KO) mice and the EP2 or EP4 receptor-selective agonist treated animal models.

The PGE2-induced inhibition of the PLD activation pathway stimulated by fMLP in human neutrophils is mediated by PKA at the PI3-Kgamma level

Prostaglandin E2 (PGE2), an eicosanoid that modulates inflammation, inhibits several chemoattractant-elicited functions in neutrophils such as chemotaxis, production of superoxide anions, adhesion, secretion of cytotoxic enzymes and synthesis of leukotriene B4. We previously reported that PGE2 inhibits the fMLP signaling pathway that leads to PLD activation through suppression of PI3-Kgamma activity and the decreased recruitment to membranes of PLD activation factors, PKC, Rho and Arf-GTPases. This effect is mediated via the EP2 receptors known to raise cAMP in cells. The inhibition of most fMLP-induced functional responses by PGE2 via EP2 receptors is mediated by PKA, except the chemotactic response. We have investigated the role of PKA in the EP2-mediated inhibition of the PLD activation pathway. H-89, a selective PKA pharmacological inhibitor suppressed the inhibitory effects of PGE2 at all stages of the PLD pathway activated by fMLP, i.e. PLD activity, translocation to membranes of PKCalpha, Rho and Arf-GTPases, calcium influx, tyrosine phosphorylation of proteins and finally translocation of p110gamma catalytic subunit of PI3-K to membranes. However, neither PLD nor PI3-Kgamma was substrate of PKA. These data provide evidence that PGE2-stimulated PKA activity regulates the PLD pathway stimulated by fMLP at the level of PI3-Kgamma and that the inhibition of PI3-Kgamma activation by PKA is a complex mechanism that remains to be completely elucidated.

Prostaglandins Enhance Epidermal Growth Factor-Induced DNA Synthesis in Hepatocytes by Stimulation of E Prostanoid 3 and F Prostanoid Receptors

Prostaglandins stimulate hepatocyte proliferation in vivo and in vitro. We have examined the role of E prostanoid (EP) and F prostanoid receptors (FP) in enhancing the growth-stimulatory effect of epidermal growth factor (EGF) in cultured hepatocytes. The EP2 receptor agonist butaprost had no significant effect on EGF-induced DNA synthesis. EP1 receptor-selective antagonists did not affect the enhancement by prostaglandin E(2) of EGF-stimulated DNA synthesis. Sulprostone, misoprostol, and fluprostenol strongly enhanced DNA synthesis and inhibited glucagon-stimulated cAMP accumulation, indicating that they all activated EP3 receptors. Sulprostone and fluprostenol, and to a lesser extent misoprostol, stimulated accumulation of inositol phosphates. The effects of fluprostenol and sulprostone on phospholipase C (PLC) were inhibited by the FP receptor antagonist AL-8810 [9 alpha, 15R-dihydroxy-11 beta-fluoro-15-(2,3-dihydro-1H-inden-2-yl)-16,17,18,19,20-pentanor-prosta-5Z, 13E-dien-1-oic acid], indicating that this effect was mediated by FP receptors. Inhibition of protein kinase C with GF109203X [2-[1-(3-dimetylaminopropyl)-1H-indol-3-yl]-maleimide] resulted in a partial reduction of the growth stimulation induced by fluprostenol, indicating a minor role of FP receptors. Combining fluprostenol with misoprostol, but not with sulprostone, resulted in partially additive effects on DNA synthesis, suggesting that both EP3 and FP receptors are involved. Combining sulprostone with misoprostol did not result in additive effects on DNA synthesis, suggesting that EP4 receptors were not involved. We conclude that, although a minor effect is exerted by FP receptors, the growth-stimulatory effects of prostaglandins in rat hepatocytes are mediated mainly by EP3 receptors. We have found no evidence of EP1 receptor involvement.

Indomethacin decreases EP2 prostanoid receptor expression in colon cancer cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) can decrease the risk of colorectal cancer; however, it has not been established if this effect is solely through their ability to inhibit cyclooxygenase (COX). In this study the effects of indomethacin, a potent NSAID and nonselective COX inhibitor, was examined in LS174T human colon cancer cells. These cells were found to express EP2 prostanoid receptors, but not the EP1, EP3 or EP4 subtypes. Pretreatment of LS174T cells with indomethacin produced a complete inhibition of prostaglandin E(2) (PGE(2)) stimulated cyclic AMP (cAMP) formation in a dose dependent manner with an IC(50) of 21 microM. Interestingly, the inhibition of PGE(2)-stimulated cAMP formation by indomethacin was accompanied by a decrease in EP2 mRNA expression and by a decrease in the whole cell specific binding of [(3)H]PGE(2). Thus, treatment of LS174T cells with indomethacin causes a down regulation of EP2 prostanoid receptors expression that may be independent of COX inhibition.

Epigenetic silencing of prostaglandin E receptor 2 (PTGER2) is associated with progression of neuroblastomas

We previously identified a cluster of prostanoid receptor genes, prostaglandin D2 receptor (PTGDR) and prostaglandin E receptor 2 (PTGER2), as possible targets for DNA methylation in advanced types of neuroblastoma (NB) using bacterial artificial chromosome array-based methylated CpG island amplification method. Among them, in this study, we found that PTGER2 was frequently silenced in NB cell lines, especially in those with MYCN amplification, through epigenetic mechanisms. In NB cell lines, DNA methylation pattern within a part of CpG island was inversely correlated with PTGER2 expression, and histone H3 and H4 deacetylation and histone H3 lysine 9 methylation within the putative promoter region were more directly correlated with silencing of this gene. Methylation of PTGER2 was observed more frequently in advanced-type of primary NBs compared with early-stage tumors. Growth of NB cells lacking endogenous PTGER2 expression was inhibited by restoration of the gene product by transient and stable transfection. A PTGER2-selective agonist, butaprost, increased intracellular cyclic adenosine monophosphate (cAMP) level, inhibited cell growth and induced apoptosis of NB cells stably expressing exogenous PTGER2. 8-Bromo-cAMP also inhibited growth of NB cells lacking PTGER2 expression, but not cells expressing this gene. Taken together, it is suggested that NB cells may lose responsiveness to PTGER2-mediated growth inhibition/apoptosis through epigenetic silencing of PTGER2 and/or disruption of downstream cAMP-dependent pathway during the neuroblastomagenesis.

Discovery of novel prostaglandin analogs of PGE2 as potent and selective EP2 and EP4 receptor agonists

Analogs of PGE(2) with introduction of diene groups at the omega-side chain have been synthesized and evaluated for their binding affinity for EP(2) and EP(4) receptors. An optimized analog (compound 9b) showed high potency and selectivity for the EP(4) receptor over other known receptors.