EP3 receptor isoforms are differentially expressed in subpopulations of primate granulosa cells and couple to unique G-proteins

Prostaglandin and prostaglandin receptors: present and future promising therapeutic targets for pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH), Group 1 pulmonary hypertension (PH), is a type of pulmonary vascular disease characterized by abnormal contraction and remodeling of the pulmonary arterioles, manifested by pulmonary vascular resistance (PVR) and increased pulmonary arterial pressure, eventually leading to right heart failure or even death. The mechanisms involved in this process include inflammation, vascular matrix remodeling, endothelial cell apoptosis and proliferation, vasoconstriction, vascular smooth muscle cell proliferation and hypertrophy. In this study, we review the mechanisms of action of prostaglandins and their receptors in PAH.

MAIN BODY

PAH-targeted therapies, such as endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, activators of soluble guanylate cyclase, prostacyclin, and prostacyclin analogs, improve PVR, mean pulmonary arterial pressure, and the six-minute walk distance, cardiac output and exercise capacity and are licensed for patients with PAH; however, they have not been shown to reduce mortality. Current treatments for PAH primarily focus on inhibiting excessive pulmonary vasoconstriction, however, vascular remodeling is recalcitrant to currently available therapies. Lung transplantation remains the definitive treatment for patients with PAH. Therefore, it is imperative to identify novel targets for improving pulmonary vascular remodeling in PAH. Studies have confirmed that prostaglandins and their receptors play important roles in the occurrence and development of PAH through vasoconstriction, vascular smooth muscle cell proliferation and migration, inflammation, and extracellular matrix remodeling.

CONCLUSION

Prostacyclin and related drugs have been used in the clinical treatment of PAH. Other prostaglandins also have the potential to treat PAH. This review provides ideas for the treatment of PAH and the discovery of new drug targets.

Characterization of the first insect prostaglandin (PGE2) receptor: MansePGE2R is expressed in oenocytoids and lipoteichoic acid (LTA) increases transcript expression

In arthropods, eicosanoids derived from the oxygenated metabolism of arachidonic acid are significant in mediating immune responses. However, the lack of information about insect eicosanoid receptors is an obstacle to completely decipher immune mechanisms underlying both eicosanoid downstream signal cascades and their relationship to immune pathogen-associated molecular patterns (PAMPs). Here, we cloned and sequenced a G protein-coupled receptor (MW 46.16 kDa) from the model lepidopteran, Manduca sexta (Sphingidae). The receptor shares similarity of amino acid motifs to human prostaglandin E₂ (PGE₂) receptors, and phylogenetic analysis supports its classification as a prostaglandin receptor. In agreement, the recombinant receptor was activated by PGE₂ resulting in intracellular cAMP increase, and therefore designated MansePGE₂R. Expression of MansePGE₂R in Sf9 cells in which the endogenous orthologous receptor had been silenced showed similar cAMP increase upon PGE₂ challenge. Receptor transcript expression was identified in various tissues in larvae and female adults, including Malpighian tubules, fat body, gut and hemocytes, and in female ovaries. In addition to the cDNA cloned that encodes the functional receptor, an mRNA was found featuring the poly-A tail but lacking the predicted transmembrane (TM) regions 2 and 3, suggesting the possibility that internally deleted receptor proteins exist in insects. Immunocytochemistry and in situ hybridization revealed that among hemocytes, the receptor was exclusively localized in the oenocytoids. Larval immune challenges injecting bacterial components showed that lipoteichoic acid (LTA) increased MansePGE₂R expression in hemocytes. In contrast, injection of LPS or peptidoglycan did not increase MansePGE₂R transcript levels in hemocytes, suggesting the LTA-associated increase in receptor transcript is regulated through a distinct pathway. This study provides the first characterization of an eicosanoid receptor in insects, and paves the way for establishing the hierarchy in signaling steps required for establishing insect immune responses to infections.

EP3 receptor antagonist L798,106 reduces proliferation and migration of SK-BR-3 breast cancer cells

Purpose: COX-2 overexpression and elevated levels of prostaglandin E2 (PGE2) play an important role in breast cancer carcinogenesis. Recently, expression of the PGE2 receptor EP3 has been shown to be a positive prognostic factor in breast cancer. This study analyzes the functional aspects of targeting EP3 in breast cancer cell lines. Material and methods: EP3 and EP1 expressions were determined in five breast cancer cell lines on the mRNA- and the protein-level. The selected cell lines were subsequently stimulated for 24-72 hrs with 10-1,000 nM of PGE2, the EP1/EP3 agonist sulprostone and the EP3 antagonist L798,106. Cell proliferation was determined via BrdU-assay, migration via scratch assay, EP3, Gi-protein and p-ERK1/2 expressions via Western blot and cAMP concentrations via ELISA. The Mann-Whitney-U-test was used to test for statistical significance. Results: The cell lines T-47D (EP3 expression 77.7%) and SK-BR-3 (EP3 expression 48.7%) were chosen. EP3 antagonism reduced its expression on SK-BR-3 significantly, while no effect was observed on T-47D. The proliferation and migration of SK-BR-3 cells were significantly reduced due to treatment with the EP1/3 agonist, the EP3 antagonist or a combination of both. Neither agonism nor antagonism influenced cell proliferation or migration in T-47D. In SK-BR-3, EP3 antagonism showed a significant decrease in Gi-protein levels, an increase in cAMP levels, and no significant change in p-ERK1/2 expression. Conclusion: Antagonism of the EP3 receptor results in a reduced proliferation and migration of SK-BR-3 breast cancer cells, potentially mediated via a Gi-protein-cAMP pathway. The results suggest that EP3 plays a role in tumorigenesis. This is in accordance with the cell culture data of other gynecological tumors, but it is conflicting in so far, as positive EP3 expression is clinically a positive prognostic marker in breast cancer. Therefore, other factors may be important in explaining this contradiction.

Prostaglandin E2 as a Regulator of Immunity to Pathogens

The body is exposed to foreign pathogens every day, but remarkably, most pathogens are effectively cleared by the innate immune system without the need to invoke the adaptive immune response. Key cellular components of the innate immune system include macrophages and neutrophils and the recruitment and function of these cells are tightly regulated by chemokines and cytokines in the tissue space. Innate immune responses are also known to regulate development of adaptive immune responses often via the secretion of various cytokines. In addition to these protein regulators, numerous lipid mediators can also influence innate and adaptive immune functions. In this review, we cover one particular lipid regulator, prostaglandin E2 (PGE2) and describe its synthesis and signaling and what is known about the ability of this lipid to regulate immunity and host defense against viral, fungal and bacterial pathogens.

Potential role of polyunsaturated fatty acids, with particular regard to the signaling pathways of arachidonic acid and its derivatives in the process of maturation of the oocytes: Contemporary review

Oocyte meiotic maturation is one of the significant physiological requirements for ovulation and fertility. It is believed that Cyclic Adenosine Monophosphate, protein kinase A and protein kinase C pathways along with eicosanoids, particularly prostaglandin E_2, and steroids are the key factors regulating mammalian oocyte maturation. The aim of the current study was to highlight the molecular events triggered by arachidonic acid during oocyte meiotic arrest and resumption at the time of gonadotrophin surge. It should be noted that arachidonic acid release is tightly regulated by Follicle-stimulating and Luteinizing hormones during oocyte development.

EP3 activation facilitates bladder excitability via HCN channels on ICCs

EP3 is a receptor for prostaglandin E2 (PGE2), and although its effect on bladder excitability has attracted considerable attention, the underlying mechanism remains unclear. To investigate whether the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in the interstitial cells of Cajal (ICCs) of the bladder are involved in the effect of EP3 activation on bladder excitability, wild-type mice, HCN1 knockout (HCN1^-/-) mice and rats were used in our study. Double immunofluorescence staining and immunoprecipitation assays demonstrated the interaction between EP3 and the HCN channels. Sulprostone is a selective agonist of EP3. The current density of HCN channels was enhanced by sulprostone or PGE2 using whole-cell patch clamping. Western blot analyses showed that the expression levels of HCN1 and HCN4 were higher in bladders that had undergone intravesical instillation with sulprostone than in bladders treated with normal saline (NS). Both PGE2 and sulprostone increased the calcium concentration of the ICCs, and their effects were inhibited by ZD7288 (antagonist of HCN channels) treatment. In bladder detrusor strip testing, both PGE2 and sulprostone enhanced the amplitude of the bladder detrusor in HCN1^-/- mice; however, these effects were less than those in the wild-type mice. Furthermore, the effects of PGE2 and sulprostone were inhibited by ZD7288. Taken together, our results indicate that EP3 is expressed in bladder ICCs and facilitates bladder excitability via HCN channels. This study provides more comprehensive insights into the mechanism between inflammation and bladder excitability and highlights methods that can resolve bladder hyperactivity.

Mapping PTGERs to the Ovulatory Follicle: Regional Responses to the Ovulatory PGE2 Signal

Prostaglandin E2 (PGE2) is a key intrafollicular mediator of ovulation in many, if not all, mammalian species. PGE2 acts at follicular cells via four distinct PGE2 receptors (PTGERs). Within the ovulatory follicle, each cell type (e.g., oocyte, cumulus granulosa cell, mural granulosa cell, theca cell, endothelial cell) expresses a different subset of the four PTGERs. Expression of a subset of PTGERs has consequences for the generation of intracellular signals and ultimately the unique functions of follicular cells that respond to PGE2. Just as the ovulatory LH surge regulates PGE2 synthesis, the LH surge also regulates expression of the four PTGERs. The pattern of expression of the four PTGERs among follicular cells before and after the LH surge forms a spatial and temporal map of PGE2 responses. Differential PTGER expression, coupled with activation of cell-specific intracellular signals, may explain how a single paracrine mediator can have pleotropic actions within the ovulatory follicle. Understanding the role of each PTGER in ovulation may point to previously unappreciated opportunities to both promote and prevent fertility.

Alternative RNA splicing: contribution to pain and potential therapeutic strategy

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Alternative pre-mRNA splicing generates multiple proteins from a single gene.

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Control of alternative splicing is a likely therapy in cancer and other disorders.

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Key molecules in pain pathways – GPCRs and channels – are alternatively spliced.

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It is proposed that alternative splicing may be a therapeutic target in pain.

Since the sequencing of metazoan genomes began, it has become clear that the number of expressed proteins far exceeds the number of genes. It is now estimated that more than 98% of human genes give rise to multiple proteins through alternative pre-mRNA splicing. In this review, we highlight the known alternative splice variants of many channels, receptors, and growth factors that are important in nociception and pain. Recently, pharmacological control of alternative splicing has been proposed as potential therapy in cancer, wet age-related macular degeneration, retroviral infections, and pain. Thus, we also consider the effects that known splice variants of molecules key to nociception/pain have on nociceptive processing and/or analgesic action, and the potential for control of alternative pre-mRNA splicing as a novel analgesic strategy.

Prostaglandin E2 promotes human cholangiocarcinoma cell proliferation, migration and invasion through the upregulation of β-catenin expression via EP3-4 receptor

Prostaglandin E2 (PGE2) is involved in cholangiocarcinoma cell proliferation, migration and invasion through E prostanoid receptors, including EP1, EP2 and EP4. However, the functions and the mechanisms of those splice variants of EP3 receptors in promoting liver cancer cell growth and invasion remain to be elucidated. In our previous studies, four isoforms of EP3 receptors, EP3-4, EP3-5, EP3-6 and EP3-7 receptors, were detected in CCLP1 and HuCCT1 cells. However, the functions of these receptors in these cells have yet to be determined. It was reported that β-catenin is closely correlated with malignancy, including cholangiocarcinoma. The present study was designed to examine the effects of 4-7 isoforms of EP3 in promoting cholangiocarcinoma progression and the mechanisms by which PGE2 increases β-catenin protein via EP3 receptors. The results showed that PGE2 promotes cholangiocarcinoma progression via the upregulation of β-catenin protein, and the EP3-4 receptor pathway is mainly responsible for this regulation. These findings reveal that PGE2 upregulated the cholangiocarcinoma cell β-catenin protein through the EP3-4R/Src/EGFR/PI3K/AKT/GSK-3β pathway. The present study identified the functions of EP3 and the mechanisms by which PGE2 regulates β-catenin expression and promoted cholangiocarcinoma cell growth and invasion.

Angiogenesis in the primate ovulatory follicle is stimulated by luteinizing hormone via prostaglandin E2

Rapid angiogenesis occurs as the ovulatory follicle is transformed into the corpus luteum. To determine if luteinizing hormone (LH)-stimulated prostaglandin E2 (PGE2) regulates angiogenesis in the ovulatory follicle, cynomolgus macaques received gonadotropins to stimulate multiple follicular development and chorionic gonadotropin (hCG) substituted for the LH surge to initiate ovulatory events. Before hCG, vascular endothelial cells were present in the perifollicular stroma but not amongst granulosa cells. Endothelial cells entered the granulosa cell layer 24-36 h after hCG, concomitant with the rise in follicular PGE2 and prior to ovulation, which occurs about 40 h after hCG. Intrafollicular administration of the PG synthesis inhibitor indomethacin was coupled with PGE2 replacement to demonstrate that indomethacin blocked and PGE2 restored follicular angiogenesis in a single, naturally developed monkey follicle in vivo. Intrafollicular administration of indomethacin plus an agonist selective for a single PGE2 receptor showed that PTGER1 and PTGER2 agonists most effectively stimulated angiogenesis within the granulosa cell layer. Endothelial cell tracing and three-dimensional reconstruction indicated that these capillary networks form via branching angiogenesis. To further explore how PGE2 mediates follicular angiogenesis, monkey ovarian microvascular endothelial cells (mOMECs) were isolated from ovulatory follicles. The mOMECs expressed all four PGE2 receptors in vitro. PGE2 and all PTGER agonists increased mOMEC migration. PTGER1 and PTGER2 agonists promoted sprout formation while the PTGER3 agonist inhibited sprouting in vitro. While PTGER1 and PTGER2 likely promote the formation of new capillaries, each PGE2 receptor may mediate aspects of PGE2's actions and, therefore, LH's ability to regulate angiogenesis in the primate ovulatory follicle.