Prostaglandin E2 receptor EP1 transactivates EGFR/MET receptor tyrosine kinases and enhances invasiveness in human hepatocellular carcinoma cells

Recent evidence indicates that cyclooxygenase-2 (COX-2) and epidermal growth factor receptor (EGFR) are involved in hepatocarcinogenesis. This study was designed to evaluate the possible interaction between the COX-2 and EGFR signaling pathways in human hepatocellular carcinoma (HCC) cells. Immunohistochemical analysis using serial sections of human HCC tissues revealed positive correlation between COX-2 and EGFR in HCC cells (P < 0.01). Overexpression of COX-2 in cultured HCC cells (Hep3B) or treatment with PGE(2) or the selective EP(1) receptor agonist, ONO-DI-004, increased EGFR phosphorylation and tumor cell invasion. The PGE(2)-induced EGFR phosphorylation and cell invasiveness were blocked by the EP(1) receptor siRNA or antagonist ONO-8711 and by two EGFR tyrosine kinase inhibitors, AG1478 and PD153035. The EP(1)-induced EGFR transactivation and cell invasion involves c-Src, in light of the presence of native binding complex of EP(1)/Src/EGFR and the inhibition of PGE(2)-induced EGFR phosphorylation and cell invasion by the Src siRNA and the Src inhibitor, PP2. Further, overexpression of COX-2 or treatment with PGE(2) also induced phosphorylation of c-Met, another receptor tyrosine kinase critical for HCC cell invasion. Moreover, activation of EGFR by EGF increased COX-2 promoter activity and protein expression in Hep3B and Huh-7 cells, whereas blocking PGE(2) synthesis or EP(1) attenuated EGFR phosphorylation induced by EGF, suggesting that the COX-2/PGE(2)/EP(1) pathway also modulate the activation of EGFR by its cognate ligand. These findings disclose a cross-talk between the COX-2/PGE(2)/EP(1) and EGFR/c-Met signaling pathways that coordinately regulate human HCC cell invasion.     

A novel positive feedback loop between peroxisome proliferator-activated receptor-delta and prostaglandin E2 signaling pathways for human cholangiocarcinoma cell growth

Peroxisome proliferator-activated receptor-delta (PPARdelta) is a nuclear receptor implicated in lipid oxidation and the pathogenesis of obesity and diabetes. This study was designed to examine the potential effect of PPARdelta on human cholangiocarcinoma cell growth and its mechanism of actions. Overexpression of PPARdelta or activation of PPARdelta by its pharmacological ligand, GW501516, at low doses (0.5-50 nM) promoted the growth of three human cholangiocarcinoma cell lines (CCLP1, HuCCT1, and SG231). This effect was mediated by induction of cyclooxygenase-2 (COX-2) gene expression and production of prostaglandin E2 (PGE2) that in turn transactivated epidermal growth factor receptor (EGFR) and Akt. In support of this, inhibition of COX-2, EGFR, and Akt prevented the PPARdelta-induced cell growth. Furthermore, PPARdelta activation or PGE2 treatment induced the phosphorylation of cytosolic phospholipase A2alpha (cPLA2alpha), a key enzyme that releases arachidonic acid (AA) substrate for PG production via COX. Overexpression or activation of cPLA2alpha enhanced PPARdelta binding to PPARdelta response element (DRE) and increased PPARdelta reporter activity, indicating a novel role of cPLA2alpha for PPARdelta activation. Consistent with this, AA enhanced the binding of PPARdelta to DRE, in vitro, suggesting a direct role of AA for PPARdelta activation. In contrast, although PGE2 treatment increased the DRE reporter activity in intact cells, it failed to induce PPARdelta binding to DRE in cell-free system, suggesting that cPLA2alpha-mediated AA release is required for PGE2-induced PPARdelta activation. Taken together, these observations reveal that PPARdelta induces COX-2 expression in human cholangiocarcinoma cells and that the COX-2-derived PGE2 further activates PPARdelta through phosphorylation of cPLA2alpha. This positive feedback loop plays an important role for cholangiocarcinoma cell growth and may be targeted for chemoprevention and treatment.     

Non-peptidergic small diameter primary afferents expressing VGluT2 project to lamina I of mouse spinal dorsal horn

The aim of this study was to investigate the expression of prostaglandin EP1 receptor within the ventrolateral periaqueductal grey (VL PAG). The role of VL PAG EP1 receptor in controlling thermonociception and rostral ventromedial medulla (RVM) activity in healthy and neuropathic rats was also examined. EP1 receptor was indeed found to be expressed within the VL PAG and co-localized with vesicular GABA transporter. Intra-VL PAG microinjection of ONO-DI-004, a selective EP1 receptor agonist, dose-dependently reduced tail flick latency as well as respectively increasing and decreasing the spontaneous activity of ON and OFF cells. Furthermore, it increased the ON cell burst and OFF cell pause. Intra-VL PAG prostaglandin E2 (PGE2) behaved similarly to ONO-DI-004. The effects of ONO-DI-004 and PGE2 were antagonized by intra-VL PAG L335677, a selective EP1 receptor antagonist. L335677 dose-dependently increased the tail flick latency and ongoing activity of the OFF cells, while reducing the ongoing ON cell activity. It also decreased the ON cell burst and OFF cell pause. In neuropathic rats using spare nerve injury (SNI) of the sciatic nerve model, EP1 receptor expression decreased in the VL PAG. However, ONO-DI-004 and L335677 were able to alter pain responses and ON and OFF cell activity, as they did in healthy animals. Collectively, these data show that within the VL PAG, EP1 receptor has a facilitatory effect on the nociceptive response and consistently affects RVM neuron activity. Thus, the blockade of EP1 receptor in the VL PAG leads to antinociception in neuropathic pain conditions, despite its down-regulation. The expression of EP1 receptor on GABAergic neurons is consistent with an EP1 receptor blockade-induced disinhibition of the antinociceptive descending pathway at VL PAG level.     

Cyclooxygenases and prostaglandin E2 receptors in growth plate chondrocytes in vitro and in situ--prostaglandin E2 dependent proliferation of growth plate chondrocytes

Prostaglandin E2 (PGE2) plays an important role in bone development and metabolism. To interfere therapeutically in the PGE2 pathway, however, knowledge about the involved enzymes (cyclooxygenases) and receptors (PGE2 receptors) is essential. We therefore examined the production of PGE2 in cultured growth plate chondrocytes in vitro and the effects of exogenously added PGE2 on cell proliferation. Furthermore, we analysed the expression and spatial distribution of cyclooxygenase (COX)-1 and COX-2 and PGE2 receptor types EP1, EP2, EP3 and EP4 in the growth plate in situ and in vitro. PGE2 synthesis was determined by mass spectrometry, cell proliferation by DNA [3H]-thymidine incorporation, mRNA expression of cyclooxygenases and EP receptors by RT-PCR on cultured cells and in homogenized growth plates. To determine cellular expression, frozen sections of rat tibial growth plate and primary chondrocyte cultures were stained using immunohistochemistry with polyclonal antibodies directed towards COX-1, COX-2, EP1, EP2, EP3, and EP4. Cultured growth plate chondrocytes transiently secreted PGE2 into the culture medium. Although both enzymes were expressed in chondrocytes in vitro and in vivo, it appears that mainly COX-2 contributed to PGE2-dependent proliferation. Exogenously added PGE2 stimulated DNA synthesis in a dose-dependent fashion and gave a bell-shaped curve with a maximum at 10-8 M. The EP1/EP3 specific agonist sulprostone and the EP1-selective agonist ONO-D1-004 increased DNA synthesis. The effect of PGE2 was suppressed by ONO-8711. The expression of EP1, EP2, EP3, and EP4 receptors in situ and in vitro was observed; EP2 was homogenously expressed in all zones of the growth plate in situ, whereas EP1 expression was inhomogenous, with spared cells in the reserve zone. In cultured cells these four receptors were expressed in a subset of cells only. The most intense staining for the EP1 receptor was found in polygonal cells surrounded by matrix. Expression of receptor protein for EP3 and EP4 was observed also in rat growth plates. In cultured chrondrocytes, however, only weak expression of EP3 and EP4 receptor was detected. We suggest that in growth plate chondrocytes, COX-2 is responsible for PGE2 release, which stimulates cell proliferation via the EP1 receptor.     

Regulation of vascular endothelial cell growth factor expression in mouse mammary tumor cells by the EP2 subtype of the prostaglandin E2 receptor

Prostaglandin E(2) (PGE(2)), a major metabolite of the cyclooxygenase pathway in the mammary gland, induces angiogenesis during mammary tumor progression. To better define the molecular mechanisms involved, we examined the role of the G protein-coupled receptors (GPCR) for PGE(2) in mammary tumor cell lines isolated from MMTV-cyclooxygenase-2 (COX-2) transgenic mice. Expression of the EP2 subtype of the PGE(2) receptor was correlated with the tumorigenic phenotype and the ability to induce vascular endothelial growth factor (VEGF). Overexpression of EP2 by adenoviral transduction into EP2-null cells resulted in the induction of VEGF expression in response to PGE(2) and CAY10399, an EP2 receptor agonist. The induction of VEGF by the EP2 receptor did not require the hypoxia inducible factor (HIF)-1alpha pathway, MAP kinase pathway, or phosphoinositide-3-kinase/Akt pathway, but required the cAMP/protein kinase A pathway. These results suggest that EP2 receptor is a critical element for PGE(2) mediated VEGF induction in mouse mammary tumor cells.     

Vasoconstriction induced by activation of EP1 and EP3 receptors in human lung: effects of ONO-AE-248, ONO-DI-004, ONO-8711 or ONO-8713

This study investigated the effects and selectivity of ONO-AE-248, ONO-DI-004, ONO-8711 and ONO-8713 on EP1 and EP3 receptors in human pulmonary vessels. The prostanoid receptors involved in the vasoconstriction of human pulmonary arteries (HPA) are TP and EP3 whereas in pulmonary veins (HPV), this response is associated with TP and EP1. The experiments were performed in presence of BAY u3405 (TP antagonist). ONO-DI-004 (EP1 agonist) and ONO-AE-248 (EP3 agonist), exhibited little or no activity in HPV whereas contractions were induced in HPA with ONO-AE-248. In HPV, the contractions produced with sulprostone (EP1,3 agonist) were blocked in a non competitive manner by both EP1 antagonists (ONO-8711, 30 microM; ONO-8713, 10 microM). The involvement of EP1 mediated contraction in HPV was also observed during the vasorelaxations induced with PGE1 and 5-cis-carba-PGI2. In pre-contracted HPV treated with AH6809 (30 microM; EP1 antagonist) the PGE1 vasorelaxations were potentiated, while unchanged in HPA. These results demonstrate the selectivity of ONO-AE-248 for the EP3 receptor in HPA, ONO-DI-004 was ineffective on the EP1 receptor present in HPV while ONO-8713 was the more potent EP1 antagonist used in this tissue.     

Autocrine/paracrine prostaglandin E2 production by non-small cell lung cancer cells regulates matrix metalloproteinase-2 and CD44 in cyclooxygenase-2-dependent invasion

Tumor cyclooxygenase-2 (COX-2) expression is known to be associated with enhanced tumor invasiveness. In the present study, we evaluated the importance of the COX-2 product prostaglandin E2 (PGE2) and its signaling through the EP4 receptor in mediating non-small cell lung cancer (NSCLC) invasiveness. Genetic inhibition of tumor COX-2 led to diminished matrix metalloproteinase (MMP)-2, CD44, and EP4 receptor expression and invasion. Treatment of NSCLC cells with exogenous 16,16-dimethylprostaglandin E2 significantly increased EP4 receptor, CD44, and MMP-2 expression and matrigel invasion. In contrast, anti-PGE2 decreased EP4 receptor, CD44, and MMP-2 expression in NSCLC cells. EP4 receptor signaling was found to be central to this process, because antisense oligonucleotide-mediated inhibition of tumor cell EP4 receptors significantly decreased CD44 expression. In addition, agents that increased intracellular cAMP, as is typical of EP4 receptor signaling, markedly increased CD44 expression. Moreover, MMP-2-AS treatment decreased PGE2-mediated CD44 expression, and CD44-AS treatment decreased MMP-2 expression. Thus, PGE2-mediated effects through EP4 required the parallel induction of both CD44 and MMP-2 expression because genetic inhibition of either MMP-2 or CD44 expression effectively blocked PGE2-mediated invasion in NSCLC. These findings indicate that PGE2 regulates COX-2-dependent, CD44- and MMP-2-mediated invasion in NSCLC in an autocrine/paracrine manner via EP receptor signaling. Thus, blocking PGE2 production or activity by genetic or pharmacological interventions may prove to be beneficial in chemoprevention or treatment of NSCLC.     

Prostaglandin E2 regulates cell migration via the intracellular activation of the epidermal growth factor receptor

Over the past decade cyclooxygenase-2-derived prostaglandins have been implicated in the development and progression of many types of cancer. Recently our laboratory has shown that treatment with prostaglandin E2 (PGE2) induces increased proliferation, migration, and invasiveness of colorectal carcinoma cells (Sheng, H., Shao, J., Washington, M. K., and DuBois, R. N. (2001) J. Biol. Chem. 276, 18075-18081). The stimulatory effects of PGE2 were dependent upon the activation of the phosphatidylinositol 3-kinase/Akt pathway. However, the exact signaling cascade responsible for phosphatidylinositol 3-kinase/Akt activation by PGE2 remains poorly defined. In the present study, we demonstrate that the PGE2-induced migration and invasion occurs via rapid transactivation and phosphorylation of the epidermal growth factor receptor (EGFR). Within minutes following treatment, PGE2 induces the activation of Akt. This effect was completely abolished by EGFR-specific tyrosine kinase inhibitors providing evidence for the role of the EGFR in this response. The rapid transactivation of the EGFR occurs via an intracellular Src-mediated event but not through the release of an extracellular epidermal growth factor-like ligand. EGFR transactivation was also observed in vivo by the direct comparison of normal and malignant human colorectal samples. These results suggest that in developing colonic carcinomas, the early effects of cyclooxygenase-2-derived PGE2 are in part mediated by the EGFR, and this transactivation is responsible for subsequent down-stream effects including the stimulation of cell migration and invasion.     

PGE2-induced hypertrophy of cardiac myocytes involves EP4 receptor-dependent activation of p42/44 MAPK and EGFR transactivation

Upon induction of cyclooxygenase-2 (COX-2), neonatal ventricular myocytes (VMs) mainly synthesize prostaglandin E2 (PGE2). The biological effects of PGE2 are mediated through four different G protein-coupled receptor (GPCR) subtypes (EP(1-4)). We have previously shown that PGE2 stimulates cAMP production and induces hypertrophy of VMs. Because the EP4 receptor is coupled to adenylate cyclase and increases in cAMP, we hypothesized that PGE2 induces hypertrophic growth of cardiac myocytes through a signaling cascade that involves EP4-cAMP and activation of protein kinase A (PKA). To test this, we used primary cultures of VMs and measured [3H]leucine incorporation into total protein. An EP4 antagonist was able to partially block PGE2 induction of protein synthesis and prevent PGE2-dependent increases in cell surface area and activity of the atrial natriuretic factor promoter, which are two other indicators of hypertrophic growth. Surprisingly, a PKA inhibitor had no effect. In other cell types, G protein-coupled receptor activation has been shown to transactivate the epidermal growth factor receptor (EGFR) and result in p42/44 mitogen-activated protein kinase (MAPK) activation and cell growth. Immunoprecipitation of myocyte lysates demonstrated that the EGFR was rapidly phosphorylated by PGE2 in VMs, and the EP4 antagonist blocked this. In addition, the selective EGFR inhibitor AG-1478 completely blocked PGE2-induced protein synthesis. We also found that PGE2 rapidly phosphorylated p42/44 MAPK, which was inhibited by the EP4 antagonist and by AG-1478. Finally, the p42/44 MAPK inhibitor PD-98053 (25 micromol/l) blocked PGE2-induced protein synthesis. Altogether, we believe these are the first data to suggest that PGE2 induces protein synthesis in cardiac myocytes in part via activation of the EP4 receptor and subsequent activation of p42/44 MAPK. Activation of p42/44 MAPK is independent of the common cAMP-PKA pathway and involves EP4-dependent transactivation of EGFR.     

Endothelin-1-induced prostaglandin E2-EP2, EP4 signaling regulates vascular endothelial growth factor production and ovarian carcinoma cell invasion

Cyclooxygenase (COX)-1- and COX-2-derived prostaglandins are implicated in the development and progression of several malignancies. We have recently demonstrated that treatment of ovarian carcinoma cells with endothelin-1 (ET-1) induces expression of both COX-1 and COX-2, which contributes to vascular endothelial growth factor (VEGF) production. In this study, we show that in HEY and OVCA 433 ovarian carcinoma cells, ET-1, through the binding with ETA receptor (ETAR), induces prostaglandin E2 (PGE2) production, as the more represented PG types, and increases the expression of PGE2 receptor type 2 (EP2) and type 4 (EP4). The use of pharmacological EP agonists and antagonists indicates that ET-1 and PGE2 stimulate VEGF production principally through EP2 and EP4 receptors. At the mechanistic level, we prove that the induction of PGE2 and VEGF by ET-1 involves Src-mediated epidermal growth factor receptor transactivation. Finally, we demonstrate that ETAR-mediated activation of PGE2-dependent signaling participates in the regulation of the invasive behavior of ovarian carcinoma cells by activating tumor-associated matrix metalloproteinase. These results implicate EP2 and EP4 receptors in the induction of VEGF expression and cell invasiveness by ET-1 and provide a mechanism by which ETAR/ET-1 can promote and interact with PGE2-dependent machinery to amplify its proangiogenic and invasive phenotype in ovarian carcinoma cells. Pharmacological blockade of ETAR can therefore represent an additional strategy to control PGE2 signaling, which has been associated with ovarian carcinoma progression.     

Prostaglandin E2 transactivates EGF receptor: a novel mechanism for promoting colon cancer growth and gastrointestinal hypertrophy

Prostaglandins (PGs), bioactive lipid molecules produced by cyclooxygenase enzymes (COX-1 and COX-2), have diverse biological activities, including growth-promoting actions on gastrointestinal mucosa. They are also implicated in the growth of colonic polyps and cancers. However, the precise mechanisms of these trophic actions of PGs remain unclear. As activation of the epidermal growth factor receptor (EGFR) triggers mitogenic signaling in gastrointestinal mucosa, and its expression is also upregulated in colonic cancers and most neoplasms, we investigated whether PGs transactivate EGFR. Here we provide evidence that prostaglandin E2 (PGE2) rapidly phosphorylates EGFR and triggers the extracellular signal-regulated kinase 2 (ERK2)--mitogenic signaling pathway in normal gastric epithelial (RGM1) and colon cancer (Caco-2, LoVo and HT-29) cell lines. Inactivation of EGFR kinase with selective inhibitors significantly reduces PGE2-induced ERK2 activation, c-fos mRNA expression and cell proliferation. Inhibition of matrix metalloproteinases (MMPs), transforming growth factor-alpha (TGF-alpha) or c-Src blocked PGE2-mediated EGFR transactivation and downstream signaling indicating that PGE2-induced EGFR transactivation involves signaling transduced via TGF-alpha, an EGFR ligand, likely released by c-Src-activated MMP(s). Our findings that PGE2 transactivates EGFR reveal a previously unknown mechanism by which PGE2 mediates trophic actions resulting in gastric and intestinal hypertrophy as well as growth of colonic polyps and cancers.     

Prostaglandin E(2) metabolism is activated in Schwann cell lines derived from human NF1 malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are characteristic of Neurofibromatosis type 1 (NF1), a human genetic disorder affecting approximately 1 in 3000 individuals. The absence of neurofibromin in Schwann cells results in hyperactivation of Ras, which contributes to Schwann cell hyperplasia. However, additional intracellular abnormalities in Schwann cells might contribute to the malignancy. We now report that cell lines derived from MPNSTs secrete elevated levels of prostaglandin E(2) (PGE(2)), express higher levels of phosphorylated mitogen-activated protein kinase (MAPK), phosphorylated cytosolic phospholipaseA(2) (cPLA(2)) and cyclooxygenase 2 (COX-2) when compared to normal adult human Schwann cells (nhSCs). PCR analysis reveals that NF1 MPNST cell lines express mRNA for both EP2 and EP4 prostaglandin E2 receptors, whereas nhSCs express only the EP4 receptor. COX-2 inhibitors and PGE(2) receptor antagonists decrease the proliferation of MPNST cell lines. These results indicate that prostaglandin metabolism is activated in MPNSTs and might contribute to tumor growth in NF1.     

Involvement of tyrosine kinases on cyclooxygenase expression and prostaglandin E2 production in human gingival fibroblasts stimulated with interleukin-1beta and epidermal growth factor

The purpose of the present study was to investigate the involvement of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and tyrosine kinase on prostaglandin E2 (PGE2) production in human gingival fibroblasts stimulated by interleukin-1beta (IL-1beta) and/or epidermal growth factor (EGF). The cytokine IL-1beta and to a lesser extent EGF, enhanced COX-2 mRNA levels in gingival fibroblasts. Simultaneous treatment with EGF and IL-1beta resulted in enhanced COX-2 mRNA levels accompanied by a synergistic stimulation of PGE2 biosynthesis compared to the cells treated with IL-1beta or EGF alone. Neither IL-1beta EGF nor the combination of IL-1beta and EGF enhanced COX-1 mRNA levels in gingival fibroblasts. The tyrosine kinase inhibitors, Herbimycin A and PD 153035 hydrochloride, reduced COX-2 mRNA levels as well as PGE2 production induced by IL-1beta or the combination of IL-1beta and EGF whereas COX-1 mRNA levels were not affected. Furthermore, the COX-2 specific inhibitor, NS-398, abolished the PGE2 production induced by IL-1beta, EGF, or the combination. These results indicate that the synergy between IL-1beta and EGF on PGE2 production is due to an enhanced gene expression of COX-2 and that tyrosine kinase(s) are involved in the signal transduction of COX-2 in gingival fibroblasts.     

Regulation of bone morphogenetic protein-2 expression by endogenous prostaglandin E2 in human mesenchymal stem cells

Cyclooxygenase (COX)-2 is generally known as an inducible enzyme, and it produces arachidonic acid to prostaglandin E2 (PGE2), which modulates bone metabolism. Here, we investigated the expression and role of COX isomers in human mesenchymal stem cells. Human mesenchymal stem cells constitutively expressed COX-2 as well as COX-1, and secretion of PGE2 was completely inhibited by NS-398, a specific inhibitor of COX-2. Levels of secreted PGE2 were strikingly higher in human mesenchymal stem cells than in osteoblastic cells differentiated from the mesenchymal cells. This higher production of PGE2 in mesenchymal stem cells was due to higher expression of membrane-associated PGE synthase (mPGES) regulated by early growth response factor-1 (Egr-1). Treatment of human mesenchymal stem cells with NS-398 suppressed expression of bone morphogenetic protein-2 (BMP-2). The suppression of BMP-2 by NS-398 was abrogated by an EP4 receptor agonist as well as by PGE2. Moreover, BMP-2 expression was suppressed by an EP4 receptor antagonist. These data indicate that PGE2 produced by COX-2 increases BMP-2 expression via binding the EP4 receptor.     

Suppression of prostaglandin E2 receptor subtype EP2 by PPARgamma ligands inhibits human lung carcinoma cell growth

Prostaglandin E(2) (PGE(2)), a major cyclooxygenase (COX-2) metabolite, plays important roles in tumor biology and its functions are mediated through one or more of its receptors EP1, EP2, EP3, and EP4. We have shown that the matrix glycoprotein fibronectin stimulates lung carcinoma cell proliferation via induction of COX-2 expression with subsequent PGE(2) protein biosynthesis. Ligands of peroxisome proliferator-activated receptor gamma (PPARgamma) inhibited this effect and induced cellular apoptosis. Here, we explore the role of the PGE(2) receptor EP2 in this process and whether the inhibition observed with PPARgamma ligands is related to effects on this receptor. We found that human non-small cell lung carcinoma cell lines (H1838 and H2106) express EP2 receptors, and that the inhibition of cell growth by PPARgamma ligands (GW1929, PGJ2, ciglitazone, troglitazone, and rosiglitazone [also known as BRL49653]) was associated with a significant decrease in EP2 mRNA and protein levels. The inhibitory effects of BRL49653 and ciglitazone, but not PGJ2, were reversed by a specific PPARgamma antagonist GW9662, suggesting the involvement of PPARgamma-dependent and -independent mechanisms. PPARgamma ligand treatment was associated with phosphorylation of extracellular regulated kinase (Erk), and inhibition of EP2 receptor expression by PPARgamma ligands was prevented by PD98095, an inhibitor of the MEK-1/Erk pathway. Butaprost, an EP2 agonist, like exogenous PGE(2) (dmPGE(2)), increased lung carcinoma cell growth, however, GW1929 and troglitazone blocked their effects. Our studies reveal a novel role for EP2 in mediating the proliferative effects of PGE(2) on lung carcinoma cells. PPARgamma ligands inhibit human lung carcinoma cell growth by decreasing the expression of EP2 receptors through Erk signaling and PPARgamma-dependent and -independent pathways.