Immunolocalization of adipocytes and prostaglandin E2 and its four receptor proteins EP1, EP2, EP3, and EP4 in the caprine cervix during spontaneous term labor

The mechanisms of cervical ripening and dilation in mammals remain obscure. Information is lacking about the localization of prostaglandin E(2) (PGE(2))-producing cells and PGE(2) receptors (EP) in intrapartum cervix and whether cervical dilation at parturition is an active process. To reveal these mechanisms, immunolocalization of EP1-EP4 (official gene symbols PTGER1-PTGER4) and PGE(2)-producing cells in caprine cervix during nonpregnancy, pregnancy, and parturition was assayed by immunohistochemistry (IHC); the mRNA expression levels of PTGS2, PTGER2 (EP2), and PTGER4 (EP4) were determined using quantitative PCR; and the existence of adipocytes in the cervix at various stages was demonstrated with Oil Red O staining and IHC of perilipin A. The results suggested that in intrapartum caprine cervix staining of the PGE(2) was observed in the overall tissues, for example, blood vessels, canal or glandular epithelia, serosa, circular and longitudinal muscles, and stroma in addition to adipocytes; EP2 was detectable in all the tissues other than glandular epithelia; EP4 was strongly expressed in all the tissues other than serosa; EP1 was detected mainly in arterioles and canal or glandular epithelia; and EP3 was poorly expressed only in stroma, canal epithelia, and circular muscles. Little or no expression of EP2, EP3, and EP4 as well as PGE(2) in all cervical tissues was observed during nonpregnancy and pregnancy except for the strong expression of EP1 in canal or glandular epithelia during pregnancy. The mRNA expression levels of PTGS2, PTGER2, and PTGER4 were significantly higher in intrapartum than nonpregnant and midpregnant cervices (P < 0.01). Adipocytes appear only in the intrapartum cervix. These results support the concept that PGE(2) modulates specific functions in various anatomical structures of the caprine cervix at labor and the appearance of adipocytes at labor is likely related to caprine cervical dilation.     

Prostaglandin E2 stimulates cystogenesis through EP4 receptor in IMCD-3 cells

Previously, we demonstrated that prostaglandin E(2) (PGE(2)) induced cAMP and cyst formation through PGE(2) receptor-2 (EP2) activity in human autosomal-dominant polycystic kidney disease (ADPKD) epithelial cells. In this study, we determined the role of EP2 and EP4 receptors in mediating PGE(2) stimulation of cAMP signaling and cystogenesis in mouse renal epithelial cells using the inner medullary collecting duct-3 (IMCD-3) cell line. In contrast to human ADPKD cells, using novel EP2 and EP4 antagonists, we found that IMCD-3 cells expressed functional EP4 but not EP2, which stimulated cAMP formation and led to cyst formation in 3D culture system. The involvement of EP4 receptors in IMCD-3 cells was further supported by the specific effect of EP4 siRNA that inhibited PGE(2)-induced cystogenesis. We also observed different cellular localization of EP2 or EP4 receptors in IMCD-3 transfected cells. Collectively, our results suggest an important role of different expression of EP2 or EP4 receptors in the regulation of cystogenesis.     

Prostaglandin E2 is generally required for human dendritic cell migration and exerts its effect via EP2 and EP4 receptors

The control of dendritic cell (DC) migration is pivotal for the initiation of cellular immune responses. In this study, we demonstrate that the migration of human monocyte-derived (Mo)DCs as well as of ex vivo peripheral blood DCs toward CCL21, CXCL12, and C5a is stringently dependent on the presence of the proinflammatory mediator PGE2, although DCs expressed CXCR4 and C5aR on their surface and DC maturation was accompanied by CCR7 up-regulation independently of PGE2. The necessity of exogenous PGE2 for DC migration is not due to the suppression of PGE2 synthesis by IL-4, which is used for MoDC differentiation, because maturation-induced endogenous production of PGE2 cannot promote DC migration. Surprisingly, PGE2 was absolutely required at early time points of maturation to enable MoDC chemotaxis, whereas PGE2 addition during terminal maturation events was ineffective. In contrast to mouse DCs, which exclusively rely on EP4 receptor triggering for migration, human MoDCs require a signal mediated by EP2 or EP4 either alone or in combination. Our results provide clear evidence that PGE2 is a general and mandatory factor for the development of a migratory phenotype of human MoDCs as well as for peripheral blood myeloid DCs.     

Expression of prostanoid receptors in human lower segment pregnant myometrium

Prostanoids, especially prostaglandin (PG) E(2), are important mediators of uterine relaxation and contractions during gestation and parturition. Inhibitors of PG formation as well as PG analogues are used to modulate uterine tonus. So far, only limited data are available regarding the expression of prostanoid receptors in human pregnant myometrium. In the present study, the expression of the receptors for PGE(2) (EP1, EP2, EP3, EP4), PGF(2alpha) (FP), prostacyclin (IP), and thromboxane A(2) (TP) in human pregnant myometrium was studied by RT-PCR, in situ hybridization and immunohistochemistry. Myometrial tissue was obtained from five women at term and not in labour and from two women who delivered preterm. Tissue specimens were excised from the upper edge of the transverse lower uterine segment incision. In all tissues analysed, EP1, EP2, EP3, EP4, FP, TP and IP receptor mRNA and protein was detected. mRNA expression for PGD(2) (DP) receptor was not detected in the majority of tissue specimens. EP1, EP2, EP4, IP, TP and FP receptor protein was detected on myometrial smooth muscle cells, whereas EP3 receptor protein was only expressed by stromal and endothelial cells. In situ hybridization experiments yielded similar results. The expression of the EP2 receptor mRNA was inversely related to gestational age. We suggest that the contractile effect of PGE(2) at term is probably mediated directly by the EP1 receptor expressed in myometrial smooth muscle cells and indirectly by the EP3 receptor expressed in stromal cells and a decrease in EP2 receptor expression.     

Central PGE2 exhibits anxiolytic-like activity via EP1 and EP4 receptors in a manner dependent on serotonin 5-HT1A, dopamine D1 and GABAA receptors

We found that centrally administered prostaglandin (PG) E(2) exhibited anxiolytic-like activity in the elevated plus-maze and open field test in mice. Agonists selective for EP(1) and EP(4) receptors, among four receptor subtypes for PGE(2), mimicked the anxiolytic-like activity of PGE(2). The anxiolytic-like activity of PGE(2) was blocked by an EP(1) or EP(4) antagonist, as well as in EP(4) but not EP(1) knockout mice. Central activation of either EP(1) or EP(4) receptors resulted in anxiolytic-like activity. The PGE(2)-induced anxiolytic-like activity was inhibited by antagonists for serotonin 5-HT(1A), dopamine D(1) and GABA(A) receptors. Taken together, PGE(2) exhibits anxiolytic-like activity via EP(1) and EP(4) receptors, with downstream involvement of 5-HT(1A), D(1) and GABA(A) receptor systems.     

Prostaglandin e and f receptor expression and myometrial sensitivity at labor onset in the sheep

Prostaglandins (PGs) play a pivotal role in the initiation and progression of term and preterm labor. Uterine activity is stimulated primarily by PGE(2) and PGF(2alpha) acting on prostaglandin E (EP) and prostaglandin F (FP) receptors, respectively. Activation of FP receptors strongly stimulates the myometrium, whereas stimulation of EP receptors may lead to contraction or relaxation, depending on the EP subtype (EP1-4) expression. Thus, the relative expression of FP and EP1-4 may determine the responsiveness to PGE(2) and PGF(2alpha). The aims of this study were to characterize the expression of EP1-4 and FP in intrauterine tissues and placentome, together with myometrial responsiveness to PG, following the onset of dexamethasone-induced preterm and spontaneous term labor. Receptor mRNA expression was measured using quantitative real-time polymerase chain reaction using species-specific primers. There was no increase in myometrial contractile receptor expression at labor onset, nor was there a change in sensitivity to PGE(2) and PGF(2alpha). This suggests expression of these receptors reaches maximal levels by late gestation in sheep. Placental tissue showed a marked increase in EP2 and EP3 receptor expression, the functions of which are unknown at this time. Consistent with previous reports, these results suggest that PG synthesis is the main factor in the regulation of uterine contractility at labor. This is the first study to simultaneously report PG E and F receptor expression in the key gestational tissues of the sheep using species-specific primers at induced-preterm and spontaneous labor onset.     

PGE2 exerts its effect on the LPS-induced release of TNF-alpha, ET-1, IL-1alpha, IL-6 and IL-10 via the EP2 and EP4 receptor in rat liver macrophages

Lipopolysaccharide (LPS) induces a release of tumor necrosis factor (TNF)-alpha, endothelin (ET)-1, interleukin (IL)-1alpha, IL-6 and IL-10 in rat liver macrophages (Kupffer cells). Prostaglandin (PG)E2 inhibits the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and enhances the release of the anti-fibrogenic mediators IL-6 and IL-10. This effect of PGE2 is mimicked by specific agonists for the PGE2 receptors EP2 and EP4; whereas, agonists for the PGE2 receptors EP1 and EP3 are inactive. Rat liver macrophages express mRNA encoding the PGE2 receptors EP2 and EP4 but not the PGE2 receptors EP1 and EP3. These data suggest that PGE2 exerts its anti-fibrogenic effect through the EP2 and EP4 receptor by inhibiting the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and by enhancing the release of the anti-fibrogenic mediators IL-6 and IL-10 in liver macrophages.     

Functional domains essential for Gs activity in prostaglandin EP2 and EP3 receptors

The interaction of cell surface hormone receptors with heterotrimeric G proteins is crucial for hormonal actions. The domains of the receptor, which interact with and activate G protein, have been extensively studied. However, precise molecular mechanisms underlying regulation of the receptor-induced G protein activation are still poorly understood. Prostaglandin E(2) (PGE(2)) receptors comprise of four subtypes, EP1, EP2, EP3 and EP4. Among them, EP2 and EP4 couple to Gs and EP3 to Gi. To assess the functional domains essential for Gs activation in prostanoid receptors, EP2, EP3beta and each intracellular loop- (IC-) interchanged EP2/EP3 chimeras were tested for agonist binding and functional responses. In EP2 receptor, substitution of IC1 or IC3 resulted in loss of binding activity, while substitution of IC2, N- (IC2N) or C-terminal half region of IC2 (IC2C) had no effects on the binding activity. Wild-type EP2 and IC2C-substituted EP2 showed agonist-induced Gs activity, but IC2- and IC2N-substituted EP2 failed to elicit Gs activity upon agonist stimulation. On the other hand, in EP3 receptor substitution of IC1 resulted in loss of PGE(2) binding, while substitution of IC2, IC3, IC2N or IC2C had no effects on binding activity. Wild-type EP3beta, IC3- or IC2C-substituted EP3 failed to show Gs activity upon agonist stimulation, but IC2- or IC2N-substituted EP3 chimera showed agonist-dependent Gs activity. These results indicated that the second intracellular loop of the EP2 plays an essential role in activation of Gs.     

Prostaglandin E2 induced functional expression of early growth response factor-1 by EP4, but not EP2, prostanoid receptors via the phosphatidylinositol 3-kinase and extracellular signal-regulated kinases

Prostaglandin E(2) (PGE(2)) mediates its physiological effects by interactions with a subfamily of G-protein-coupled receptors known as EP receptors. These receptors consist of four primary subtypes named EP(1), EP(2), EP(3), and EP(4). The EP(2) and EP(4) subtypes are known to couple to Galpha(s) and stimulate intracellular cyclic 3,5- adenosine monophosphate formation, whereas the EP(1) and EP(3) receptors are known to couple to Galpha(q) and Galpha(i), respectively. Recently we found that EP(2) and EP(4) receptors can activate T-cell factor signaling; however, EP(2) receptors did this primarily through a cAMP-dependent protein kinase-dependent pathway, whereas EP(4) receptors primarily utilized a phosphatidylinositol 3-kinase (PI3K)-dependent pathway (Fujino, H., West, K. A., and Regan, J. W. (2002) J. Biol. Chem. 277, 2614-2619). We now report that PGE(2) stimulation of EP(4) receptors, but not EP(2) receptors, leads to phosphorylation of the extracellular signal-regulated kinases (ERKs) through a PI3K-dependent mechanism. Furthermore, this activation of PI3K/ERK signaling by the EP(4) receptors induces the functional expression of early growth response factor-1 (EGR-1). Under the same conditions induction of EGR-1 protein expression was not observed following PGE(2) stimulation of EP(2) receptors. These findings point to important differences in the signaling potential of the EP(2) and EP(4) receptors, which could be significant with respect to the potential involvement of EP(4) receptors in inflammation and cancer.     

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.     

Prostaglandin E2 protects gastric mucosal cells from apoptosis via EP2 and EP4 receptor activation

Prostaglandin E(2) (PGE(2)) has a strong protective effect on the gastric mucosa in vivo; however, the molecular mechanism of a direct cytoprotective effect of PGE(2) on gastric mucosal cells has yet to be elucidated. Although we reported previously that PGE(2) inhibited gastric irritant-induced apoptotic DNA fragmentation in primary cultures of guinea pig gastric mucosal cells, we show here that PGE(2) inhibits the ethanol-dependent release of cytochrome c from mitochondria. Of the four main subtypes of PGE(2) receptors, we also demonstrated, using subtype-specific agonists, that EP(2) and EP(4) receptors are involved in the PGE(2)-mediated protection of gastric mucosal cells from ethanol-induced apoptosis. Activation of EP(2) and EP(4) receptors is coupled with an increase in cAMP, for which a cAMP analogue was found here to inhibit the ethanol-induced apoptosis. The increase in cAMP is known to activate both protein kinase A (PKA) and phosphatidylinositol 3-kinase pathways. An inhibitor of PKA but not of phosphatidylinositol 3-kinase blocked the PGE(2)-mediated protection of cells from ethanol-induced apoptosis, suggesting that a PKA pathway is mainly responsible for the PGE(2)-mediated inhibition of apoptosis. Based on these results, we considered that PGE(2) inhibited gastric irritant-induced apoptosis in gastric mucosal cells via induction of an increase in cAMP and activation of PKA, and that this effect was involved in the PGE(2)-mediated protection of the gastric mucosa from gastric irritants in vivo.     

Prostaglandin E(2) receptors, EP2 and EP4, differentially modulate TNF-alpha and IL-6 production induced by lipopolysaccharide in mouse peritoneal neutrophils

The expression and function of prostaglandin (PG) E(2) receptors were examined in mouse neutrophils exudated into the peritoneal cavity by casein treatment. Expressions of the EP2 and EP4 receptors were detected in neutrophils by Northern blot, but those of EP1 and EP3 receptors were not detected by RT-PCR. EP2-selective agonist, ONO-AE1-259, and EP4-selective agonist, ONO-AE1-329, stimulated cAMP formation in the cells. PGE(2) affected the TNF-alpha and IL-6 production in lipopolysaccharide (LPS)-treated neutrophils; it suppressed the TNF-alpha production and enhanced the IL-6 production. The PGE(2) effects were mimicked by dibutyryl cAMP. This is the first study of the enhancement of IL-6 production by cAMP-elevating reagents in neutrophils. Using neutrophils from EP2- and EP4-deficient mice in combination with EP2- and EP4-selective agonists, it was found that the augmentation of IL-6 was mediated mainly by the EP2 receptor and the suppression of TNF-alpha by the EP4 receptor and partially by the EP2 receptor. These findings indicate that casein-induced peritoneal neutrophils express Gs-coupled PGE(2) receptors, EP2 and EP4, which might differentially regulate the LPS-induced production of TNF-alpha and IL-6.     

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.