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Cervical cancer is one of the leading gynecological malignancies in women. We have recently shown that seminal plasma (SP) can regulate the inflammatory cyclooxygenase-prostaglandin pathway and enhance the growth of cervical epithelial tumours in vivo by promoting cellular proliferation and alteration of vascular function. This study investigated the molecular mechanism whereby SP regulates vascular function using an in vitro model system of HeLa cervical adenocarcinoma cells and human umbilical vein endothelial cells (HUVECs). We found that SP rapidly enhanced the expression of the angiogenic chemokines, interleukin (IL)-8 and growth regulated oncogene alpha (GRO) in HeLa cells in a time-dependent manner. We investigated the molecular mechanism of SP-mediated regulation of IL-8 and GRO using a panel of chemical inhibitors of cell signalling. We found that treatment of HeLa cells with SP elevated expression of IL-8 and GRO by transactivation of the epidermal growth factor receptor, activation of extracellular signal-regulated kinase and induction of cyclooxygenase enzymes and nuclear factor kappa B. We investigated the impact of IL-8 and GRO, released from HeLa cells after treatment with SP, on vascular function using a co-culture model system of conditioned medium (CM) from HeLa cells, treated with or without SP, and HUVECs. We found that CM from HeLa cells induced the arrangement of endothelial cells into a network of tube-like structures via the CXCR2 receptor on HUVECs. Taken together our data outline a molecular mechanism whereby SP can alter vascular function in cervical cancers via the pro-angiogenic chemokines, IL-8 and GRO.

Lipoxin A4is a lipid mediator that elicits anti-inflammatory and pro-resolution actions via its receptor, formyl peptide receptor 2 (FPR2/ALX). In this study, we aimed to investigate the expression and potential role of lipoxin A4and FPR2/ALX in the regulation of inflammation associated with cyclical remodeling of the human endometrium across the menstrual cycle and during early pregnancy. Using quantitative RT-PCR analysis, we found that FPR2/ALX expression is upregulated during the menstrual phase of the cycle and in decidua tissue from the first trimester of pregnancy. We localized the site of expression of FPR2/ALX in menstrual phase endometrium and first-trimester decidua tissue to glandular epithelial cells and cells within the stromal compartment, including cells lining the blood vessels and immune cells. Measurement of serum lipoxin A4by ELISA revealed no difference in its levels across the menstrual cycle but an elevation in early pregnancy (P4was regulated by human chorionic gonadotrophin (hCG) during early pregnancy, because treatment of human decidua tissue with hCG increased lipoxin A4release (P4can suppress phorbol myristate acetate-induced expression of the inflammatory cytokines interleukin 6 and 8 in human endometrium and decidua tissue. These results demonstrate for the first time that lipoxin A4and its receptor FPR2/ALX can regulate inflammatory events in the human endometrium and decidua of early pregnancy.

Prokineticin 1 (PROK1) signalling via prokineticin receptor 1 (PROKR1) regulates the expression of several genes with important roles in endometrial receptivity and implantation. This study investigated PROK1 regulation of Dickkopf 1 (DKK1) expression, a negative regulator of canonical Wnt signalling, and its function in the non-pregnant endometrium and first trimester decidua. DKK1 mRNA expression is elevated during the mid-secretory phase of the menstrual cycle and expression increases further in first trimester decidua. DKK1 protein expression is localized to glandular epithelial and stromal cells during the proliferative, early- and mid-secretory phases, whereas expression is confined to the stroma in the late-secretory phase and first trimester decidua. PROK1 induces the expression of DKK1 in endometrial epithelial cells stably expressing PROKR1 and in first trimester decidua explants, via a Gq-calcium-calcineurin-nuclear factor of activated T-cells-mediated pathway. Endometrial epithelial cell proliferation is negatively regulated by PROK1-PROKR1 signalling. We demonstrate that this effect on cell proliferation occurs via DKK1 expression, as siRNA targeted against DKK1 reduces the PROK1-induced decrease in proliferation. Furthermore, decidualization of primary human endometrial stromal cells with progesterone and cyclic adenosine monophosphate is inhibited by miRNA knock down of PROK1 or DKK1. These data demonstrate important roles for PROK1 and DKK1 during endometrial receptivity and early pregnancy, which include regulation of endometrial cell proliferation and decidualization.

Interleukin-11 (IL-11) up-regulates the proliferative and invasive capacity of many cancers. Coexpression of glycoprotein 130 (GP130) and IL-11 receptor alpha (IL-11R alpha) is necessary for high-affinity binding of IL-11 to IL-11R alpha. This study investigated the expression of IL-11 and role of prostaglandin F-2 alpha-F-prostanoid receptor (FP receptor) signaling in the modulation of IL-11 expression in endometrial adenocarcinoma cells. Localization of IL-11, IL-11R alpha, and GP130 expression was performed by immunohistochemistry. IL-11 and regulator of calcineurin I isoform 4 (RCAN1-4) mRNA and protein expression were determined by real-time RT-PCR and/or enzyme-linked immunosorbent assay/Western blot analysis using Ishikawa endometrial adenocarcinoma cells stably expressing the FP receptor (FPS cells) and endometrial adenocarcinoma explants. IL-11 mRNA expression was significantly elevated in endometrial adenocarcinoma samples compared with normal endometrium and increased with tumor grade. IL-11 protein expression localized with FP receptor, IL-11R alpha, and GP130 in the neoplastic glandular epithelium of endometrial adenocarcinomas. Prostaglandin F-2 alpha-FP receptor signaling significantly elevated the expression of IL-11 mRNA and protein in a Gq-protein kinase C-calcium-calcineurin-nuclear factor of activated T cells-dependent manner in FPS cells. The calcineurin signaling pathway is known to be controlled by the RCAN (RCAN1-4). indeed, RCAN1-4 expression was significantly elevated in well-differentiated endometrial adenocarcinoma compared with normal endometrium and was found to decrease with tumor grade and negatively regulate IL-11 expression in vitro. This study has highlighted a new mechanism regulating IL-11 expression in endometrial adenocarcinoma cells by the FP receptor via the calcium-calcineurin-nuclear factor of activated T cells pathway. (Am J Pathol 2010, 176:435-445; DOI: 10.2353/ajpath.2010.090403)

In endometrial adenocarcinomas COX-2 and F-series prostanoid (FP) receptor expression and prostanoid biosynthesis (PGE(2) and PGF(2alpha)) are elevated. In the present study, we investigated the effect of PGE(2) and PGF(2alpha) on the expression of COX-2 via the FP receptor in endometrial adenocarcinoma cells stably expressing the FP receptor (FPS cells). Using chemical inhibitors of intracellular signaling pathways, reporter gene assays and quantitative RT-PCR analysis, we show that PGE(2) and PGF(2alpha) can mobilize inositol 1,4,5-trisphosphate, induce ERK1/2 phosphorylation via the phospholipase Cbeta-protein kinase A-epidermal growth factor receptor pathway and induce cyclooxygenase-2 (COX-2) expression via the FP receptor. In addition we show that the PGE(2) or PGF(2alpha)-regulation of COX-2 via the FP receptor is mediated via the cAMP response element (CRE) binding site on the COX-2 promoter. These data indicate that PGE(2) and PGF(2alpha) biosynthesized locally within endometrial adenocarcinomas can regulate tumor cell function in an autocrine/paracrine manner via the FP receptor.

E-series prostanoid (EP)4 receptor is up-regulated in numerous cancers, including cervical carcinomas, and has been implicated in mediating the effects of prostaglandin (PG)E2 in tumorigenesis. In addition to regulation by endogenously biosynthesized PGE2, neoplastic cervical epithelial cells in sexually active women may also be regulated by PGs present in seminal plasma. In this study, we investigated the signal transduction pathways mediating the role of seminal plasma and PGE2 in the regulation of tumorigenic and angiogenic genes via the EP4 receptor in cervical adenocarcinoma (HeLa) cells. HeLa cells were stably transfected with EP4 receptor in the sense orientation. Seminal plasma and PGE2 signaling via the EP4 receptor induced the activation of cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) promoters, expression of COX-2 and VEGF mRNA and protein, and secretion of VEGF protein into the culture medium. Treatment of HeLa cells with seminal plasma or PGE2 also rapidly induced the phosphorylation of ERK1/2 via the EP4 receptor. Preincubation of cells with a specific EP4 receptor antagonist (ONO-AE2-227) or chemical inhibitors of epidermal growth factor receptor (EGFR) tyrosine kinase or MAPK kinase or cotransfection of cells with dominant-negative mutant cDNA targeted against the EGFR, serine/threonine kinase Raf, or MAPK kinase abolished the EP4-induced activation of COX-2, VEGF, and ERK1/2. Therefore, we have demonstrated that seminal plasma and PGE2 can promote the expression of tumorigenic and angiogenic factors, in cervical adenocarcinoma cells via the EP4 receptor, EGFR, and ERK1/2 signaling pathways.

The menstrual cycle is a complex interaction of sex steroids, prostanoids, and cytokines that lead to coordinated tissue degradation, regeneration and repair. The transcription factor hypoxia-inducible factor (HIF-1) plays critical roles in cellular responses to hypoxia, the generation of an inflammatory response and vasculogenesis through transcriptional activation of angiogenic genes. We hypothesize that HIF-1 is expressed in human endometrium and that locally synthesized prostaglandins (PGE2 and PGF(2alpha)) regulate HIF-1 activity. Here we demonstrate that PGE2 up-regulates HIF-1alpha mRNA and protein via the E-series prostanoid receptor 2 (EP2), and this up-regulation is dependent on epidermal growth factor receptor kinase activity. We show the tight temporal-spatial confinement of HIF-1alpha protein expression in endometrium across the cycle. HIF-1alpha is expressed exclusively during the secretory and menstrual phases. Protein expression is maximal at progesterone withdrawal during the late secretory and menstrual phase. HIF-1alpha protein colocalizes with prostaglandin EP2 receptor in glandular cells. In contrast, HIF-1beta/aryl receptor nuclear translocator 1 expression occurs throughout the cycle but is maximal in glandular cells during the proliferative phase. This provides evidence for a role for HIF-1 in the menstrual cycle and demonstrates that HIF-1 activation in human endometrium may occur via a PGE2-regulated pathway and provides a coordinated pathway from progesterone withdrawal through to angiogenic gene expression via HIF-1.

Prostaglandin (PG) E2 promotes tumor growth via interaction with its G protein-coupled receptors and activation of intracellular signaling. Tuberous sclerosis 2 (tuberin) is a tumor suppressor, which negatively regulates cell growth. Its phosphorylation results in its inactivation and targeted down- regulation, thus lifting the growth inhibition effects. This study investigated the expression and localization of tuberin in neoplastic and normal endometrium and the effect of PGE2 on phosphorylation of tuberin via the Akt pathway. Quantitative RT-PCR and Western blot analysis demonstrated reduced expression of tuberin in neoplastic tissue, compared with normal endometrial tissue. Tuberin expression was localized by immunohistochemistry to the glandular epithelial compartment in neoplastic and normal endometrium. We investigated the effect of PGE2 on phosphorylation of tuberin via the Akt pathway. Treatment of neoplastic and normal endometrium with 100 nm PGE2 enhanced phosphorylated tuberin immunoreactivity in the glandular epithelium. PGE2 also phosphorylated Akt and tuberin in Ishikawa endometrial adenocarcinoma cells, leading to a reduction in expression of total tuberin protein. Cotreatment of cells with wortmannin or LY294002 inhibited the PGE2-induced phosphorylation of Akt and tuberin. These data suggest that PGE2 signaling may promote endometrial tumorigenesis by inactivation of tuberin after its phosphorylation via the Akt signaling pathway.

Prostaglandin (PG) E(2) E-series prostanoid-2 (EP2) receptor is elevated in numerous carcinomas including the endometrium and has been implicated in mediating the effects of PGE(2) on vascular function. In this study, we investigated the intracellular signaling pathways that are activated by the EP2 receptor and their role in regulation of the expression of vascular endothelial growth factor in endometrial adenocarcinoma (Ishikawa) cells. Ishikawa cells were stably transfected with EP2 receptor cDNA in the sense or antisense directions. Treatment of Ishikawa cells with PGE(2) rapidly induced transactivation of the epidermal growth factor receptor (EGFR) and activation of ERK1/2 via the EP2 receptor. Preincubation of cells with chemical inhibitors of protein kinase A, c-Src, and EGFR kinase abolished the EP2-induced activation of EGFR and ERK1/2. PGE(2) signaling via the EP2 receptor also promoted the mRNA expression and secretion of vascular endothelial growth factor protein in Ishikawa cells. This effect was inhibited by preincubation with chemical inhibitors of EGFR kinase, ERK1/2 signaling, and small inhibitory RNA molecules targeted against the EGFR. Therefore, we have demonstrated that elevated EP2 receptor expression may facilitate the PGE(2)-induced release of proangiogenic factors in reproductive tumor cells via intracellular cAMP-mediated transactivation of the EGFR and ERK1/2 pathways.

Prostaglandin F(2 alpha)(PGF(2 alpha)) is a bioactive lipid biosynthesized by cyclooxygenase (COX) enzymes and mediates its biological activity via the heptahelical G(q)-coupled PGF(2 alpha)receptor (FP receptor). This study investigated the expression and molecular signaling of the FP receptor in human endometrial adenocarcinomas. Real-time RT-PCR and Western blot analysis confirmed FP receptor expression in endometrial adenocarcinoma of all grades and differentiation. The expression of FP receptor was up-regulated in all endometrial adenocarcinomas compared with normal endometrium. The site of FP receptor expression was localized by in situ hybridization and immunohistochemistry to the neoplastic epithelial cells in all adenocarcinomas. Treatment of endometrial adenocarcinoma explants with PGF(2 alpha) resulted in mobilization of inositol phosphate signaling, indicating functional FP receptor expression. We investigated whether PGF(2 alpha) could trans-activate the epidermal growth factor receptor (EGFR) and trigger the MAPK signaling pathway. Treatment of adenocarcinoma explants and endometrial adenocarcinoma cells (Ishikawa) with PGF(2 alpha)-phosphorylated EGFR, triggered MAPK signaling and enhanced the proliferation of Ishikawa cells. Inactivation of phospholipase C, EGFR kinase, and MAPK kinase with specific inhibitors abolished PGF(2 alpha)-induced trans-activation of EGFR, MAPK signaling, and Ishikawa cell proliferation. These data suggest that PGF(2 alpha)-FP receptor promote endometrial tumorigenesis via a phospholipase C-mediated phosphorylation of the EGFR and MAPK signaling pathways.

Prostaglandins, thromboxanes (TX) and leukotrienes, collectively referred to as eicosanoids, are cyclooxygenase (COX) metabolites of arachidonic acid (AA). Prostaglandins, have been recognised for many years as key molecules in regulating reproductive tract physiology and pathology. Numerous recent studies in in vitro model systems and knockout mouse models have demonstrated specific functional roles for the respective cyclooxygenase enzymes, prostaglandins and prostanoid receptors. Here we review the findings obtained in several of these studies with emphasis on the roles played by cyclooxygenase enzymes and prostaglandins, specifically prostaglandin E2 (PGE2) and F2alpha in reproductive tract physiology and pathology.

The prevalence of cervical cancer in South African women is reported as being the highest in the world, occurring, on the average, in 60 of every 100,000 women. Cervical cancer is thus considered an important clinical problem in sub-Saharan AFRICA: Recent studies have suggested that epithelial tumors may be regulated by cyclooxygenase (COX) enzyme products. The purpose of this study was to determine whether cyclooxygenase-2 (COX-2) expression and PGE(2) synthesis are up-regulated in cervical cancers. Real-time quantitative RT-PCR and Western blot analysis confirmed COX-2 ribonucleic acid and protein expression in all cases of squamous cell carcinoma (n = 8) and adenocarcinoma (n = 2) investigated. In contrast, minimal expression of COX-2 was detected in histologically normal cervix (n = 5). Immunohistochemical analyses localized COX-2 expression and PGE(2) synthesis to neoplastic epithelial cells of all squamous cell (n = 10) and adenocarcinomas (n = 10) studied. Immunoreactive COX-2 and PGE(2) were also colocalized to endothelial cells lining the microvasculature. Minimal COX-2 and PGE(2) immunoreactivity were detected in normal cervix (n = 5). To establish whether PGE(2) has an autocrine/paracrine effect in cervical carcinomas, we investigated the expression of two subtypes of PGE(2) receptors, namely EP2 and EP4, by real-time quantitative RT-PCR. Expression of EP2 and EP4 receptors was significantly higher in carcinoma tissue (n = 8) than in histologically normal cervix (n = 5; P0.01). Finally, the functionality of the EP2/EP4 receptors was assessed by investigating cAMP generation after in vitro culture of cervical cancer biopsies and normal cervix in the presence or absence of 300 nmol/L PGE(2). cAMP production was detected in all carcinoma tissue after treatment with exogenous PGE(2) and was significantly higher in carcinoma tissue (n = 7) than in normal cervix (n = 5; P0.05). The fold induction of cAMP in response to PGE(2) was 51.1 +/- 12.3 in cervical carcinoma tissue compared with 5.8 +/- 2.74 in normal cervix. These results confirm that COX-2, EP2, and EP4 expression and PGE(2) synthesis are up-regulated in cervical cancer tissue and suggest that PGE(2) may regulate neoplastic cell function in cervical carcinoma in an autocrine/paracrine manner via the EP2/EP4 receptors.

Inflammatory processes are central to reproductive events including ovulation, menstruation, implantation and labour, while inflammatory dysregulation is a feature of numerous reproductive pathologies. In recent years, there has been much research into the endogenous mechanisms by which inflammatory reactions are terminated and tissue homoeostasis is restored, a process termed resolution. The identification and characterisation of naturally occurring pro-resolution mediators including lipoxins and annexin A1 has prompted a shift in the field of anti-inflammation whereby resolution is now observed as an active process, triggered as part of a normal inflammatory response. This review will address the process of resolution, discuss available evidence for expression of pro-resolution factors in the reproductive tract and explore possible roles for resolution in physiological reproductive processes and associated pathologies.

Murine knock-out models and blastocyst co-culture studies have identified prostaglandin-endoperoxide synthase (PTGS) 2, pros- taglandin (PG) E receptor 2 (PTGER2) and the chemokine receptor CXCR4 as important regulators of early pregnancy events. In vitro studies and studies in non-human primates have shown that these proteins are regulated in the endometrium by the early embryonic signal, chorionic gon- adotrophin (CG). Here we show that expressions of PTGER2 and CXCR4 are elevated during the mid-secretory phase of the menstrual cycle and decidua of early pregnancy in humans. Using first trimester decidua explants, we show that CG induces expression of PTGS2 and biosynthesis of PGE2, and expression of PTGER2. Subsequently, PGE2via PTGER2 induces expression of CXCR4. Using an in vitro model system of Ishikawa endometrial epithelial cells stably expressing PTGER2 and human first trimester decidua explants, we demonstrate that CXCR4 expression is regulated by PTGER2 via the epidermal growth factor receptor (EGFR)-phosphatidylinositol-3-kinase (PI3K)-extracellular signal-regulated kinase (ERK1/2) pathway.Taken together, our data suggest that early embryonic signals may regulate fetal-maternal crosstalk in the human endometrium by inducing CXCR4 expression via the PGE2-PTGER2-mediated induction of the EGFR, PI3K and ERK1/2 pathways.

The prostaglandin F2α (PGF2α) receptor (FP) is elevated in endometrial adenocarcinoma. This study found that PGF2α signaling via FP regulates expression of chemokine (C-X-C motif) ligand 1 (CXCL1) in endometrial adenocarcinoma cells. Expression of CXCL1 and its receptor, CXCR2, are elevated in cancer tissue compared with normal endometrium and localized to glandular epithelium, endothelium, and stroma. Treatment of Ishikawa cells stably transfected with the FP receptor (FPS cells) with 100 nmol/L PGF2α increased CXCL1 promoter activity, mRNA, and protein expression, and these effects were abolished by cotreatment of cells with FP antagonist or chemical inhibitors of Gq, epidermal growth factor receptor, and extracellular signal-regulated kinase. Similarly, CXCL1 was elevated in response to 100 nmol/L PGF2α in endometrial adenocarcinoma explant tissue. CXCL1 is a potent neutrophil chemoattractant. The expression of CXCR2 colocalized to neutrophils in endometrial adenocarcinoma and increased neutrophils were present in endometrial adenocarcinoma compared with normal endometrium. Conditioned media from PGF2α-treated FPS cells stimulated neutrophil chemotaxis, which could be abolished by CXCL1 protein immunoneutralization of the conditioned media or antagonism of CXCR2. Finally, xenograft tumors in nude mice arising from inoculation with FPS cells showed increased neutrophil infiltration compared with tumors arising from wild-type cells or following treatment of mice bearing FPS tumors with CXCL1-neutralizing antibody. In conclusion, our results show a novel PGF2α-FP pathway that may regulate the inflammatory microenvironment in endometrial adenocarcinoma via neutrophil chemotaxis. [Cancer Res 2009;69(14):5726–33]

Prostaglandin (PG) F(2alpha) is a potent bioactive lipid in the female reproductive tract, and exerts its function after coupling with its heptahelical G-protein-coupled receptor [F-series-prostanoid (FP) receptor] to initiate cell signaling and target gene transcription. In the present study, we found elevated expression of fibroblast growth factor (FGF) 2, FGF receptor 1 (FGFR1), and FP receptor, colocalized within the neoplastic epithelial cells of endometrial adenocarcinomas. We investigated a role for PGF(2alpha)-FP receptor interaction in modulating FGF2 expression and signaling using an endometrial adenocarcinoma cell line stably expressing the FP receptor to the levels detected in endometrial adenocarcinomas (FPS cells) and endometrial adenocarcinoma tissue explants. PGF(2alpha)-FP receptor activation rapidly induced FGF2 mRNA expression, and elevated FGF2 protein expression and secretion into the culture medium in FPS cells and endometrial adenocarcinoma explants. The effect of PGF(2alpha) on the expression and secretion of FGF2 could be abolished by treatment of FPS cells and endometrial tissues with an FP receptor antagonist (AL8810) and inhibitor of ERK (PD98059). Furthermore, we have shown that FGF2 can promote the expression of FGF2 and cyclooxygenase-2, and enhance proliferation of endometrial adenocarcinoma cells via the FGFR1 and ERK pathways, thereby establishing a positive feedback loop to regulate neoplastic epithelial cell function in endometrial adenocarcinomas.

Prostaglandins are bioactive lipids produced from arachidonic acid by cyclooxygenase enzymes and specific terminal prostanoid synthase enzymes. Following biosynthesis, prostaglandins exert an autocrine/paracrine function by coupling to specific prostanoid G protein-coupled receptors to activate intracellular signaling and gene transcription. For many years prostaglandins have been recognised as key molecules in reproductive biology by regulating ovulation, endometrial physiology and proliferation of endometrial glands and menstruation. More recently a role for COX enzymes and prostaglandins has been ascertained in reproductive tract pathology, including dysmenorrhea, endometriosis, menorrhagia and cancer. Emerging evidence supports a role for COX enzymes, prostaglandins and prostaglandin receptor signaling pathways in a multitude of phenotypic changes in reproductive tissues including the promotion of angiogenesis and vascular function. Here we provide an overview of some of the findings from these studies with specific emphasis on the role of cyclooxygenase enzymes, prostaglandins and their receptors in benign and neoplastic pathologies of the human endometrium.

Prostacyclin (PGI) is a member of the prostanoid family of lipid mediators that mediates its effects through a seven-transmembrane G protein-coupled receptor (IP receptor). Recent studies have ascertained a role for prostanoid-receptor signaling in angiogenesis. In this study we examined the temporal-spatial expression of the IP receptor within normal human endometrium and additionally explored the signaling pathways mediating the role of IP receptor in activation of target angiogenic genes. Quantitative RT-PCR analysis demonstrated the highest endometrial expression of the IP receptor during the menstrual phase compared with all other stages of the menstrual cycle. Immunohistochemical analysis localized the site of IP receptor expression to the glandular epithelial compartment with stromal and perivascular cell immunoreactivity. Expression of the immunoreactive IP receptor protein was greatest during the proliferative and early secretory phases of the menstrual cycle. To explore the role of the IP receptor in glandular epithelial cells, we used the Ishikawa endometrial epithelial cell line. Stimulation of Ishikawa cells and human endometrial biopsy explants with 100 nm iloprost (a PGI analog) rapidly activated ERK1/2 signaling and induced the expression of proangiogenic genes, basic fibroblast growth factor, angiopoietin-1, and angiopoietin-2, in an epidermal growth factor receptor (EGFR)-dependent manner. Furthermore, EGFR colocalized with IP receptor in the glandular epithelial compartment. These data suggest that PGI-IP interaction within glandular epithelial cells can promote the expression of proangiogenic genes in human endometrium via cross talk with the EGFR.

Prostaglandins are bioactive lipids that exert an autocrine or paracrine function by binding to specific G-protein-coupled receptors (GPCRs) to activate intracellular signalling and gene transcription. Prostaglandins are key regulators of reproductive processes, including ovulation, implantation and menstruation. Prostaglandins have been ascertained to have a role in various pathological changes of the reproductive tract including menorrhagia, dysmenorrhea, endometriosis and cancer. Although the mechanism by which prostaglandins modulate these changes remains unclear, much evidence suggests that prostaglandins and their receptors and downstream signalling pathways are involved in angiogenesis and in alterations in cell adhesion, morphology, motility, invasion and metastases. The potential role of prostaglandin receptors in pathological changes of the endometrium has significance for the future development of therapeutic interventions.

Prostaglandins are bioactive lipids produced from arachidonic acid by cyclooxygenase (COX) enzymes and specific terminal prostanoid synthase enzymes. After biosynthesis, prostaglandins exert an autocrine-paracrine function by coupling to specific prostanoid G protein-coupled receptors to activate intracellular signalling and gene transcription. For many years, prostaglandins have been recognized as key molecules in reproductive biology by regulating ovulation, endometrial physiology and proliferation of endometrial glands and menstruation. More recently, a role for COX enzymes and prostaglandins has been ascertained in reproductive tract pathology, including carcinomas, menorrhagia, dysmenorrhoea and endometriosis. Although the mechanism by which prostaglandins modulate these pathologies is still unclear, a large body of evidence supports a role for COX enzymes, prostaglandins and prostaglandin receptor signalling pathways in angiogenesis, apoptosis and proliferation, tissue invasion and metastases and immunosuppression. Here, an overview is provided of some of the findings from these studies with specific emphasis on the role of COX enzymes, prostaglandin E(2) and F(2alpha) in disorders of endometrial proliferation and menstruation in non-pregnant women.

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.

The prostaglandin endoperoxide synthase (PTGS) pathway is a potent driver of tumour development in humans by enhancing the biosynthesis and signalling of prostaglandin (PG) E(2). PTGS2 expression and PGE(2) biosynthesis is elevated in endometrial adenocarcinoma, however the mechanism whereby PTGS and PGE2 regulate endometrial tumour growth is unknown. Here we investigated (a) the expression profile of the PGE synthase enzymes (PTGES, PTGES-2, PTGES-3) and PGE receptors (PTGER1-4) in endometrial adenocarcinomas compared with normal endometrium and (b) the role of PTGER4 in endometrial tumorigenesis in vivo. We found elevated expression of PTGES2 and PTGER4 and suppression of PTGER1 and PTGER3 in endometrial adenocarcinomas compared with normal endometrium. Using WT Ishikawa endometrial adenocarcinoma cells and Ishikawa cells stably transfected with the full length PTGER4 cDNA (PTGER4 cells) xenografted in the dorsal flanks of nude mice, we show that PTGER4 rapidly and significantly enhances tumour growth rate. Coincident with enhanced PTGER4-mediated tumour growth we found elevated expression of PTGS2 in PTGER4 xenografts compared with WT xenografts. Furthermore we found that the augmented growth rate of the PTGER4 xenografts was not due to enhanced angiogenesis, but regulated by an increased proliferation index and hypoxia. In vitro, we found that PGE2 and hypoxia independently induce expression of PTGER4 indicating two independent pathways regulating prostanoid receptor expression. Finally we have shown that PGE2 and hypoxia synergise to promote cellular proliferation of endometrial adenocarcinoma cells.