Prostaglandin E2 facilitates subcellular translocation of the EP4 receptor in neuroectodermal NE-4C stem cells

Prostaglandin E2 (PGE₂) is a lipid mediator released from the phospholipid membranes that mediates important physiological functions in the nervous system via activation of four EP receptors (EP1-4). There is growing evidence for the important role of the PGE₂/EP4 signaling in the nervous system. Previous studies in our lab show that the expression of the EP4 receptor is significantly higher during the neurogenesis period in the mouse. We also showed that in mouse neuroblastoma cells, the PGE₂/EP4 receptor signaling pathway plays a role in regulation of intracellular calcium via a phosphoinositide 3-kinase (PI3K)-dependent mechanism. Recent research indicates that the functional importance of the EP4 receptor depends on its subcellular localization. PGE₂-induced EP4 externalization to the plasma membrane of primary sensory neurons has been shown to play a role in the pain pathway. In the present study, we detected a novel PGE₂–dependent subcellular trafficking of the EP4 receptor in neuroectodermal (NE-4C) stem cells and differentiated NE-4C neuronal cells. We show that PGE₂ induces EP4 externalization from the Golgi apparatus to the plasma membrane in NE-4C stem cells. We also show that the EP4 receptors translocate to growth cones of differentiating NE-4C neuronal cells and that a higher level of PGE₂ enhances its growth cone localization. These results demonstrate that the EP4 receptor relocation to the plasma membrane and growth cones in NE-4C cells is PGE₂ dependent. Thus, the functional role of the PGE₂/EP4 pathway in the developing nervous system may depend on the subcellular localization of the EP4 receptor.     

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 receptors: advances in the study of EP3 receptor signaling

Prostaglandin (PG) E(2) produces a broad range of physiological and pharmacological actions in diverse tissues through specific receptors on plasma membranes for maintenance of local homeostasis in the body. PGE receptors are divided into four subtypes, EP1, EP2, EP3, and EP4, which have been identified and cloned. These EP receptors are members of the G-protein coupled receptor family. Among these subtypes, the EP3 receptor is unique in its ability to couple to multiple G proteins. EP3 receptor signals are primarily involved in inhibition of adenylyl cyclase via G(i) activation, and in Ca(2+)-mobilization through G(beta)(gamma) from G(i). Along with G(i) activation, the EP3 receptor can stimulate cAMP production via G(s) activation. Recent evidence indicates that the EP3 receptor can augment G(s)-coupled receptor-stimulated adenylyl cyclase activity, and can also be coupled to the G(13) protein, resulting in activation of the small G protein Rho followed by morphological changes in neuronal cells. This article focuses on recent studies on the novel pathways of EP3 receptor signaling.     

Mouse EP3 alpha, beta, and gamma receptor variants reduce tumor cell proliferation and tumorigenesis in vivo

Prostaglandin E(2), which exerts its functions by binding to four G protein-coupled receptors (EP1-4), is implicated in tumorigenesis. Among the four E-prostanoid (EP) receptors, EP3 is unique in that it exists as alternatively spliced variants, characterized by differences in the cytoplasmic C-terminal tail. Although three EP3 variants, alpha, beta, and gamma, have been described in mice, their functional significance in regulating tumorigenesis is unknown. In this study we provide evidence that expressing murine EP3 alpha, beta, and gamma receptor variants in tumor cells reduces to the same degree their tumorigenic potential in vivo. In addition, activation of each of the three mEP3 variants induces enhanced cell-cell contact and reduces cell proliferation in vitro in a Rho-dependent manner. Finally, we demonstrate that EP3-mediated RhoA activation requires the engagement of the heterotrimeric G protein G(12). Thus, our study provides strong evidence that selective activation of each of the three variants of the EP3 receptor suppresses tumor cell function by activating a G(12)-RhoA pathway.     

Different membrane targeting of prostaglandin EP3 receptor isoforms dependent on their carboxy-terminal tail structures

Mouse prostaglandin EP3 receptor consists of three isoforms, EP3alpha, beta and gamma, with different carboxy-terminal tails. To assess the role of their carboxy-terminal tails in membrane targeting, we examined subcellular localization of myc-tagged EP3 isoforms expressed in MDCK cells. Two isoforms, EP3alpha and EP3beta, were localized in the intracellular compartment but not in the plasma membrane, while the EP3gamma isoform was found in the lateral plasma membrane and in part in the intracellular compartment. Mutant EP3 receptor lacking the carboxy-terminal tail was localized in the intracellular compartment but not in the plasma membrane. Thus, EP3 isoforms differ in subcellular targeting, and the carboxy-terminal tails play an important role in determination of the membrane targeting of EP3 receptor.     

ErbB receptors in fetal endothelium—A potential linkage point for inflammation-associated neonatal disorders

Objective: ErbB receptors and their ligands play crucial roles in development. During late gestation, they might also be involved in the pathogenesis of prematurity-associated disorders. ErbB receptor dimerization leads to a diversity of biologic signals. We studied the expression and localization patterns of erbB receptors in the developing human umbilical endothelial cell system. It is still unclear, whether expression patterns might be developmentally regulated and depend on the cell type studied. Methods: Primary human umbilical venous endothelial cells (HUVEC) and arterial endothelial cells (HUAEC) were isolated between 24 and 42 weeks of gestation and used for immunoprecipitation, Western blotting, and confocal microscopy. Results: All four erbB receptors were present in HUVEC and HUAEC. Expression patterns were similar for cell types at gestational ages examined. ErbB4 always co-precipitated with erbB1 in both cell types independent of the gestational age. Confocal microscopy revealed that all erbB receptors were localized in the nucleus, erbB1 and erbB3 in the nucleoli, while erbB2 and erbB4 spared the nucleolar region. All receptors showed a tendency to co-localize. Growth factor stimulation altered localization patterns. Cellular subfractionation experiments for erbB4 largely confirmed microscopy results. Pretreatment with lipopolysaccharide enhanced this nuclear localization of erbB4, particularly of its intracellular domain. Conclusions: All erbB receptors are present in both HUVEC and HUAEC at all gestational ages tested. ErbB receptor expression patterns were independent of the developmental stage of the endothelial cell, at least in the third trimester. We speculate that endothelial erbB receptors might play a role in normal development in mid and late gestation. We also speculate that these findings, together with the known involvement of erbB receptors in development, inflammation, and angiogenesis, will open new avenues for erbB receptor-related research in the pathogenesis of fetal and neonatal inflammation-associated disorders.     

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.     

ErbB receptors in fetal endothelium--a potential linkage point for inflammation-associated neonatal disorders

Objective: ErbB receptors and their ligands play crucial roles in development. During late gestation, they might also be involved in the pathogenesis of prematurity-associated disorders. ErbB receptor dimerization leads to a diversity of biologic signals. We studied the expression and localization patterns of erbB receptors in the developing human umbilical endothelial cell system. It is still unclear, whether expression patterns might be developmentally regulated and depend on the cell type studied. Methods: Primary human umbilical venous endothelial cells (HUVEC) and arterial endothelial cells (HUAEC) were isolated between 24 and 42 weeks of gestation and used for immunoprecipitation, Western blotting, and confocal microscopy. Results: All four erbB receptors were present in HUVEC and HUAEC. Expression patterns were similar for cell types at gestational ages examined. ErbB4 always co-precipitated with erbB1 in both cell types independent of the gestational age. Confocal microscopy revealed that all erbB receptors were localized in the nucleus, erbB1 and erbB3 in the nucleoli, while erbB2 and erbB4 spared the nucleolar region. All receptors showed a tendency to co-localize. Growth factor stimulation altered localization patterns. Cellular subfractionation experiments for erbB4 largely confirmed microscopy results. Pretreatment with lipopolysaccharide enhanced this nuclear localization of erbB4, particularly of its intracellular domain. Conclusions: All erbB receptors are present in both HUVEC and HUAEC at all gestational ages tested. ErbB receptor expression patterns were independent of the developmental stage of the endothelial cell, at least in the third trimester. We speculate that endothelial erbB receptors might play a role in normal development in mid and late gestation. We also speculate that these findings, together with the known involvement of erbB receptors in development, inflammation, and angiogenesis, will open new avenues for erbB receptor-related research in the pathogenesis of fetal and neonatal inflammation-associated disorders.     

Nuclear prostaglandin signaling system: biogenesis and actions via heptahelical receptors

Prostaglandins are ubiquitous lipid mediators that play pivotal roles in cardiovascular homeostasis, reproduction, and inflammation, as well as in many important cellular processes including gene expression and cell proliferation. The mechanism of action of these lipid messengers is thought to be primarily dependent on their interaction with specific cell surface receptors that belong to the heptahelical transmembrane spanning G protein-coupled receptor superfamily. Accumulating evidence suggests that these receptors may co-localize at the cell nucleus where they can modulate gene expression through a series of biochemical events. In this context, we have recently demonstrated that prostaglandin E2-EP3 receptors display an atypical nuclear compartmentalization in cerebral microvascular endothelial cells. Stimulation of these nuclear EP3 receptors leads to an increase of eNOS RNA in a cell-free isolated nuclear system. This review will emphasize these findings and describe how nuclear prostaglandin receptors, notably EP3 receptors, may affect gene expression, specifically of eNOS, by identifying putative transducing elements located within this organelle. The potential sources of lipid ligand activators for these intracellular sites will also be addressed. The expressional control of G-protein-coupled receptors located at the perinuclear envelope constitutes a novel and distinctive mode of gene regulation.     

P2Y1, P2Y6, and P2Y12 receptors in rat splenic sinus endothelial cells: an immunohistochemical and ultrastructural study

Localization of three P2X and six P2Y receptors in sinus endothelial cells of the rat spleen was examined by immunofluorescent microscopy, and ultrastructural localization of the detected receptors was examined by immunogold electron microscopy. In immunofluorescent microscopy, labeling for anti-P2Y1, P2Y6, and P2Y12 receptors was detected in endothelial cells, but P2X1, P2X2, P2X4, P2Y2, P2Y4, and P2Y13 receptors was not detected. P2Y1 and P2Y12 receptors were prominently localized in the basal parts of endothelial cells. P2Y6 receptor was not only predominantly localized in the basal parts of endothelial cells, but also in the superficial layer. Triple immunofluorescent staining for a combination of two P2Y receptors and actin filaments showed that P2Y1, P2Y6, and P2Y12 receptors were individually localized in endothelial cells. Phospholipase C-β3, phospholipase C- γ2, and inositol-1,4,5-trisphosphate receptors, related to the release of the intracellular Ca²⁺ from the endoplasmic reticulum, were also predominantly localized in the basal parts of endothelial cells. In immunogold electron microscopy, labeling for P2Y1, P2Y6, and P2Y12 receptors were predominantly localized in the basal part of endothelial cells and, in addition, in the junctional membrane, basal plasma membrane, and caveolae in the basal part of endothelial cells. Labeling for phospholipase C-β3 and phospholipase C-γ2 was dominantly localized in the basal parts and in close proximity to the plasma membranes of endothelial cells. The possible functional roles of these P2Y receptors in splenic sinus endothelial cells are discussed.     

A cluster of aromatic amino acids in the i2 loop plays a key role for Gs coupling in prostaglandin EP2 and EP3 receptors

To assess the structural requirements for G(s) coupling by prostaglandin E receptors (EPs), the G(s)-coupled EP2 and G(i)-coupled EP3beta receptors were used to generate hybrid receptors. Interchanging of the whole i2 loop and its N-terminal half (i2N) had no effect on the binding of both receptors expressed in HEK293 cells. Agonist-induced cAMP formation was observed in wild type EP2 but not in the i2 loop- or i2N-substituted EP2. Wild type EP3beta left cAMP levels unaffected, whereas i2 loop- and i2N-substituted EP3 gained agonist-induced adenylyl cyclase stimulation. In EP2, the ability to stimulate cAMP formation was lost by mutation of Tyr(143) into Ala but retained by mutations into Phe, Trp, and Leu. Consistent with this observation, substitution of the equivalent His(140) enabled EP3beta to stimulate cAMP formation with the rank order of Phe > Tyr > Trp > Leu. The point mutation of His(140) into Phe was effective in another EP3 variant in which its C-terminal tail is different or lacking. Simultaneous mutation of the adjacent Trp(141) to Ala but not at the following Tyr(142) weakened the acquired ability to stimulate cAMP levels in the EP3 mutant. Mutation of EP2 at adjacent Phe(144) to Ala but not at Tyr(145) reduced the efficiency of agonist-induced cAMP formation. In Chinese hamster ovary cells stably expressing G(s)-acquired EP3 mutant, an agonist-dependent cAMP formation was observed, and pertussis toxin markedly augmented cAMP formation. These results suggest that a cluster of hydrophobic aromatic amino acids in the i2 loop plays a key role for G(s) coupling.     

The prostaglandin EP4 receptor is a master regulator of the expression of PGE2 receptors following inflammatory activation in human monocytic cells

Prostaglandin E₂ (PGE₂) is responsible for inflammatory symptoms. However, PGE₂ also suppresses pro-inflammatory cytokine production. There are at least 4 subtypes of PGE₂ receptors, EP1–EP4, but it is unclear which of these specifically control cytokine production. The aim of this study was to determine which of the different receptors, EP1R–EP4R modulate production of tumor necrosis factor-α (TNF-α) in human monocytic cells.Human blood, or the human monocytic cell line THP-1 were stimulated with LPS. The actions of PGE₂, alongside selective agonists of EP1–EP4 receptors, were assessed on LPS-induced TNF-α, IL-1β and IL-10 release. The expression profiles of EP2R and EP4R in monocytes and THP-1 cells were characterised by RT-qPCR. In addition, the production of cytokines was evaluated following knockdown of the receptors using siRNA and over-expression of the receptors by transfection with constructs.PGE₂ and also EP2 and EP4 agonists (but not EP1 or EP3 agonists) suppressed TNF-α production in blood and THP-1 cells. LPS also up regulated expression of EP2R and EP4R but not EP1 or EP3. siRNA for either EP2R or EP4R reversed the suppressive actions of PGE₂ on cytokine production and overexpression of EP2R and EP4R enhanced the suppressive actions of PGE₂.This indicates that PGE₂ suppression of TNF-α by human monocytic cells occurs via EP2R and EP4R expression. However EP4Rs also control their own expression and that of EP2 whereas the EP2R does not affect EP4R expression. This implies that EP4 receptors have an important master role in controlling inflammatory responses.     

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.     

Receptor isoform-specific interaction of prostaglandin EP3 receptor with muskelin

By using the yeast two-hybrid system, muskelin was found to bind with the carboxy-terminal tail of the prostaglandin EP3 receptor alpha isoform but not with either the beta or gamma isoform. A direct interaction between the carboxy-terminal tail of the alpha isoform and muskelin was confirmed in vitro using recombinant fusion proteins. Analysis by confocal microscopy indicated that the isoform and muskelin were distributed at the plasma membrane in transfected cells. When the isoform was stimulated by agonist, the receptor was internalized in the cells expressing the receptor alone, but this internalization was partially inhibited by the cotransfection with muskelin. Furthermore, muskelin enhanced the Gi activity of the isoform. Thus, muskelin appears to be an isoform-specific anchoring protein for the EP3 receptor.     

Bone marrow-derived EP3-expressing stromal cells enhance tumor-associated angiogenesis and tumor growth

Recent results suggest that bone marrow (BM)-derived hematopoietic cells are major components of tumor stroma and play crucial roles in tumor growth and angiogenesis. An E-type prostaglandin is known to regulate angiogenesis. We examined the role of BM-derived cells expressing an E-type prostaglandin receptor subtype (EP3) in tumor-induced angiogenesis and tumor growth. The replacement of wild-type (WT) BM with BM cells (BMCs) from green fluorescent protein (GFP) transgenic mice revealed that the stroma developed via the recruitment of BMCs. Selective knockdown of EP3 by recruitment of genetically modified BMCs lacking EP3 receptors was performed by transplantation of BMCs from EP3 knockout (EP3^−/−) mice. Tumor growth and tumor-associated angiogenesis were suppressed in WT mice transplanted with BMCs from EP3^−/− mice, but not in mice transplanted with BMCs from either EP1^−/−, EP2^−/−, or EP4^−/− mice. Immunohistochemical analysis revealed that vascular endothelial growth factor (VEGF) expression was suppressed in the stroma of mice transplanted with BMCs from EP3^−/− mice. EP3 signaling played a significant role in the recruitment of VEGFR-1- and VEGFR-2-positive cells from the BM to the stroma. These results indicate that the EP3 signaling expressed in bone marrow-derived cells has a crucial role in tumor-associated angiogenesis and tumor growth with upregulation of the expression of the host stromal VEGF together with the recruitment of VEGFR-1/VEGFR-2-positive. The present study suggests that the blockade of EP3 signaling and the recruitment of EP3-expressing stromal cells may become a novel strategy to treat solid tumors.     

The ErbB4 receptor in fetal rat lung fibroblasts and epithelial type II cells

ErbB receptors are important regulators of fetal organ development, including the fetal lung. They exhibit diversity in signaling potential, acting through homo- and heterodimers to cause different biological responses. We hypothesized that ErbB receptors show cell-specific and stimuli-specific activation, heterodimerization, and cellular localization patterns in fetal lung. We investigated this using immunoblotting, co-immunoprecipitation, and confocal microscopy in primary isolated E19 fetal rat lung fibroblasts and epithelial type II cells, stimulated with epidermal growth factor, transforming growth factor alpha, neuregulin 1beta, or treated with conditioned medium (CM) from the respective other cell type. Fetal type II cells expressed significantly more ErbB1, ErbB2, and ErbB3 protein than fibroblasts. ErbB4 was consistently identified by co-immunoprecipitation of all other ErbB receptors in both cell types independent of the treatments. Downregulation of ErbB4 in fibroblasts initiated cell-cell communication that stimulated surfactant phospholipid synthesis in type II cells. Confocal microscopy in type II cells revealed nuclear localization of all receptors, most prominently for ErbB4. Neuregulin treatment resulted in relocation to the extra-nuclear cytoplasmic region, which was distinct from fibroblast CM treatment which led to nuclear localization of ErbB4 and ErbB2, inducing co-localization of both receptors. We speculate that ErbB4 plays a prominent role in fetal lung mesenchyme-epithelial communication.     

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.     

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.