Induction Of Prostaglandin Synthesis Research Articles

Interleukin-1 beta treatment alters prostaglandin-related mRNA expression and cytokine abundance in equine endometrial culture

Interleukin-1β (IL-1β) is a proinflammatory cytokine that modulates the immunoinflammatory response and induces prostaglandin synthesis. IL-1β has a variety of roles in the endometrium during inflammation, decidualization, pregnancy, and post-partum. It can cause changes in endometrial gene expression and may affect cytokine, chemokine, and prostaglandin-related pathways. The relationship between IL-1β, prostaglandins, and downstream inflammatory responses in the equine uterine environment is not fully known. Our objective was to determine the effect that IL-1β has on prostaglandin-related gene expression, as well as cytokine and chemokine abundance, in endometrial cell culture. Light breed mares (n=8) were examined daily by transrectal ultrasound until ovulation. An endometrial biopsy was collected at day 11 post ovulation, and used for primary endometrial cell culture. Cells were cultured in DMEM with 10% FBS. At 80% confluence, cells were either not supplemented or supplemented with: 100 nM Progesterone (Prog); 1 nM Estradiol-17β (Est); or 100 nM Prog and 1 nM Est (P+E). After 24 hours, cells were treated with recombinant equine IL-1β at either 10 ng/mL (Low) or 1000 ng/mL (High), or 0.2% DMSO as an untreated control. Twenty-four hours post-treatment, supernatant was collected, and a bead-based multiplex assay was used to quantify concentration of twelve cytokines and chemokines. Total RNA was extracted from the cells and mRNA expression was evaluatedfor 10 prostaglandin-related genes, using the ΔCT method with ACTB as the reference gene. Data analysis was performed using JMP Pro 16, using a restricted maximum likelihood model with treatment and supplementation as factors, and mare as a random factor. Treatment with IL-1β High resulted in increased levels of CCL2, CCL5, and CCL11 (p<0.001) in cell culture supernatant, as well as increased mRNA expression of PTGS2 (p<0.02), regardless of supplementation. Cells supplemented with Prog or P+E and treated with IL-1β High had increased expression of IL1R1, IL1RAP, PTGS1, and PTGES compared to non-supplemented cells (p<0.05). IL-1β High treatment increased LiF expression in cells supplemented with Prog or P+E compared to untreated cells (p<0.05). IL-1β likely acts to modulate inflammatory pathways in the endometrium, altering chemokine levels and activating expression of PTGS2, leading to changes in downstream prostaglandin synthesis and other related pathways. Progesterone appears to increase expression of several target genes when compared to non-supplemented cells. Progesterone has been shown to be involved in the suppression of several inflammatory pathways, and investigation into the ovarian steroid regulation of genes and proteins in the equine endometrium is warranted. Further studies on the effect of IL-1β on molecular pathways and prostaglandin regulation could lead to a greater understanding of the uterine environment in the pregnant and non-pregnant mare.

Prostaglandin synthesis enzymes' gene transcription in bitches with endometritis.

Endometritis is a major cause of infertility in many domestic species. However, until now the pathogenesis of the endometritis in the bitch is unclear. The aim of this study was to evaluate the gene transcription pattern of prostaglandin (PG) synthesis enzymes (cyclooxygenase [COX2], PTGES-1 and PGFS) in the endometrium of bitches with or without endometritis. Thirty mixed breed bitches in dioestrus, aged between 1 and 5years, and weighing between 10 and 30kg were used. After ovariohysterectomy (OVX), uterine biopsy samples were collected from the middle part of both horns. Then, endometrial epithelium was collected using the cytobrush method and mRNA analysis was performed by real-time RT-PCR. Data were analysed with Kruskal-Wallis anova using the sas® software. Uterine condition was identified by endometrial biopsies (normal endometria [n=11; NE], acute endometritis [n=10; AE] and chronic endometritis [n=9; CE]). The COX2, PTGES-1 and PGFS/AKR1C3 mRNA expression in bitches with and without endometritis was similar. Except for PGFS/AKR1C3, gene transcription of COX2 and PTGES-1 was significantly increased in AE compared with CE. In addition, COX2 gene transcription was significantly increased in AE compared with NE. In contrast, no differences were found for COX2, PTGES-1 and PGFS/AKR1C3 mRNA expression in the samples of NE compared with CE.

Prostaglandin pathways in duodenal chemosensing.

Acid-sensing pathways, which trigger mucosal defense mechanisms in response to luminal acid, involve the rapid afferent-mediated "capsaicin pathway" and the sustained "prostaglandin (PG) pathway." Luminal acid quickly increases protective PG synthesis and release from epithelia, although the mechanism by which luminal acid induces PG synthesis is still mostly unknown. Acid exposure augments purinergic ATP-P2Y signaling by inhibition of intestinal alkaline phosphatase activity. Since P2Y activation increases intracellular Ca2+, we further hypothesized that ATP-P2Y signals increase the generation of H2O2 derived from dual oxidase, a member of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family activated by Ca2+. Our recent studies suggest that acid exposure increases H2O2 output, followed by phospholipase A2 and cyclooxygenase activation, increasing PG synthesis. Released prostaglandin E2 augments protective HCO3- and mucus secretion via EP4 receptor activation. Thus, the PG pathway as a component of duodenal acid sensing consists of acid-related intestinal alkaline phosphatase inhibition, ATP-P2Y signals, dual oxidase 2-derived H2O2 production, phospholipase A2 activation, prostaglandin E2 synthesis, and EP4 receptor activation. The PG pathway is also involved in luminal bacterial sensing in the duodenum via activation of pattern recognition receptors, including Toll-like receptors and nucleotide-binding oligomerization domain 2. The presence of acute mucosal responses to luminal bacteria suggests that the duodenum is important for host defenses and may reduce bacterial loading to the hindgut using H2O2, complementing gastric acidity and anti-bacterial bile acids.

Immune-induced fever is mediated by IL-6 receptors on brain endothelial cells coupled to STAT3-dependent induction of brain endothelial prostaglandin synthesis.

The cytokine IL-6, which is released upon peripheral immune challenge, is critical for the febrile response, but the mechanism by which IL-6 is pyrogenic has remained obscure. Here we generated mice with deletion of the membrane bound IL-6 receptor α (IL-6Rα) on neural cells, on peripheral nerves, on fine sensory afferent fibers, and on brain endothelial cells, respectively, and examined its role for the febrile response to peripherally injected lipopolysaccharide. We show that IL-6Rα on neural cells, peripheral nerves, and fine sensory afferents are dispensable for the lipopolysaccharide-induced fever, whereas IL-6Rα in the brain endothelium plays an important role. Hence deletion of IL-6Rα on brain endothelial cells strongly attenuated the febrile response, and also led to reduced induction of the prostaglandin synthesizing enzyme Cox-2 in the hypothalamus, the temperature-regulating center in the brain, as well as reduced expression of SOCS3, suggesting involvement of the STAT signaling pathway. Furthermore, deletion of STAT3 in the brain endothelium also resulted in attenuated fever. These data show that IL-6, when endogenously released during systemic inflammation, is pyrogenic by binding to IL-6Rα on brain endothelial cells to induce prostaglandin synthesis in these cells, probably in concerted action with other peripherally released cytokines.

Methylmercury induces prostaglandin synthesis in the cells forming the neurovascular unit

Methylmercury induces prostaglandin synthesis in the cells forming the neurovascular unit

Enhancement of Transformed Foci and Induction of Prostaglandins in Balb/c 3T3 Cells by Palytoxin: In Vitro Model Reproduces Carcinogenic Responses in Animal Models Regarding the Inhibitory Effect of Indomethacin and Reversal of Indomethacin's Effect by Exogenous Prostaglandins

Cell transforming activity of palytoxin, a non-TPA type tumor-promoter, was investigated with the two-stage transformation assay using Balb/c 3T3 cells. Palytoxin showed potent promoting activity; treatment at 1.9 pM or more increased the number of transformed foci after initiation by 3-methylcholanthrene (MCA). Determination of prostaglandin (PG) E2 and PGF(2alpha) concentrations in the culture medium revealed that palytoxin (1.9-3.7 pM for 24 h) stimulated the production of PG in Balb/c 3T3 cells (the concentration reached 3-4 microM), and treatment with PGE2 or PGF(2alpha) itself increased the number of transformed foci of Balb/c 3T3 cells after initiation by MCA. Neither palytoxin nor PGs showed initiating activity. Indomethacin suppressed the promoting activity of palytoxin, but not that of PGE2 and PGF(2alpha). Interestingly, concomitant treatment with PGE2 or PGF(2alpha) in addition to indomethacin markedly reversed the suppressive effect of indomethacin. These findings indicated that the in vitro transformation model could reproduce experiments that have been performed in animal models regarding the inhibitory effect of indomethacin on carcinogenic responses and reversal of indomethacin's effect by exogenous prostaglandin and, therefore, may provide insight into molecular modes of action of palytoxin. In the present study, palytoxin also induced prostaglandin synthesis, and therefore, the Balb/c 3T3 cell model should provide insight into the molecular mechanism by which palytoxin regulates prostaglandin biosynthesis.

Cardiac Anesthesia Management of a Patient With Bartter’s Syndrome

3 N 1962, FREDERIC BARTTER first described a syndrome that he found in 2 patients, characterized by hypokalemia, etabolic alkalosis, hyperaldosteronism, normal blood presure, decreased pressor responsiveness to angiotensin II infuion, and hyperplasia of the juxtaglomerular apparatus.1 The athogenesis and causes of this syndrome still remain unnown. The primary defect is centered on the lack of NaCl eabsorption in the ascending loop of Henle. The decreased evel of sodium chloride reabsorption in this portion of the loop hus cause a reduced medullar hypertonicity with a concentraion defect. Because chloride reabsorption does not take place, xtra sodium chloride accumulates in the distal tubule. In this ortion of the nephron, the excess sodium can be reabsorbed nd exchanged with potassium, resulting in increased K loss. he resulting hypokalemia induces prostaglandin synthesis and ctivation of the renin-angiotensin-aldosterone (RAA) system, hich in turn represents the starting point of a vicious circle.2 his disorder has been shown to be inherited as an autosomal ecessive trait in certain families. The annual incidence is about case per million people.3 This case report describes a patient with Bartter’s syndrome BS) who underwent elective coronary artery bypass graft urgery. These patients normally require a particular anesthetic anagement because of complicating factors including acidase disturbances, electrolyte imbalances, intravascular volume epletion, vascular insensitivity to pressor agents, and defects n platelet aggregation. To the best of the authors’ knowledge, his is one of the first cases to be reported in the cardiac nesthesia literature.

Nociceptin/orphanin FQ modulates human T cell function in vitro

Although nociceptin/orphanin FQ (N/OFQ) and its receptor (ORL-1) are widely distributed throughout the immune system, its role has yet to be elucidated. This study shows that N/OFQ (10 −14–10 −12 M) modulates T cell activation by up-regulating activation marker expression, e.g. CD28, leading to enhanced proliferation and modulation of TNFα secretion. However, on re-stimulated T cells N/OFQ causes inhibition of proliferation, which could be linked with N/OFQ up-regulating CTLA-4 expression. We have also shown that some of these effects are partly prostaglandin-dependent and that N/OFQ induces prostaglandin synthesis. This report suggests that N/OFQ could exert a key modulatory role in human T cell functions.

Ulcer Healing Effect Of Anti-Ulcer Agents: A Comparative Study

Gastric ulcer being the most prevalent gastrointestinal disorder is considered as a major therapeutic target. Large numbers of drugs ranging from proton pump inhibitors, H2 receptor antagonists to cytoprotective agents are being used for treatment of this disease. Purpose of the study: In the present study, we have made an attempt to compare the ulcer healing activity of four well known drugs, omeprazole, misoprostol, ranitidine and sucralfate which are known to act against ulcers through different routes. Celecoxib was used as negative control. Material and method: Ulcers were produced in Sprague-dawley rats by application of 40% acetic acid. Different drugs were given to ulcerated rats to check the effect of drugs on healing of ulcers. Further confirmation of extent of healing was done by histopathology of ulcerated stomach. Results: We found omeprazole being most effective drug followed by misoprostol, ranitidine, sucralfate while celecoxib delayed the normal ulcer healing. Omeprazole has reduced the ulcerated area to 2.0mm2 in comparison to controls of 19.5mm2, showing 89.74% healing in comparison to controls on 15th day. Conclusion: We conclude from the study that drugs which not only decrease the acid secretion but also increase cytoprotective activities are more effective in ulcer healing. The study provides further support to the fact that cyclooxygenase-2 iso-enzyme which induces prostaglandin synthesis plays a vital role in ulcer healing as depicted by delayed healing by celecoxib.

Inhaled furosemide: a whole new mechanism of action

The use of aerosolized furosemide has been increasing throughout Mexico, primarily because of its mechanism and site of action as well as its local and systemic effect. We hypothesize that its effect on the respiratory system is totally independent from its diuretic activity and that it is primarily caused by its interaction with the chlorine channels. Furthermore, there is also evidence that furosemide induces prostaglandin synthesis, blocks the sodium–calcium pump, producing relaxation of the smooth muscle that narrows the airway and causes reduced nerve responsiveness to the Neurokinin A produced in acute asthma attacks.

Helicobacter pylori and NSAIDs--what interaction.

Much controversy surrounds the interaction of Helicobacter pylori infection and the use of Aspirin (ASA) or non-aspirin nonsteroidal anti-inflammatory drugs (NANSAIDs). The issue is comprised of many components, best dealt with singly. In summary, the severity of drug-associated gastritis, but not its incidence or prevalence, is influenced by infection prior to ASA or NANSAID therapy. Furthermore, the severity of dyspeptic symptoms appears worse in infected drug users. Both Chemical and Helicobacter gastritis, by increasing neutrophils in the tissue, lead to ulcers, although the induction of prostaglandin synthesis by inflammation in some circumstances may also be mildly protective. More ulcers are found in Hp+ve than Hp-ve users of NSAIDS, but ulcers in the stomach may heal more easily with acid suppressive therapy in infected patients. Eradication of infection is beneficial in aspirin users and in those beginning NANSAID therapy. Adaptation to aspirin is confined to Hp-ve cases. However, in long-term users of NANSAIDs, H. pylori eradication does not appear to speed ulcer healing, reduce recurrence, or prevent complications. These are best achieved by long-term maintenance therapy with a proton-pump inhibitor drug.

Transcriptional Activation of the Cyclooxygenase-2 Gene in Endotoxin-treated RAW 264.7 Macrophages

Cyclooxygenase-2 (COX-2), the enzyme primarily responsible for induced prostaglandin synthesis, is an immediate early gene induced by endotoxin in macrophages. We investigated the cis-acting elements of the COX-2 5'-flanking sequence, the transcription factors and signaling pathways responsible for transcriptional activation of the COX-2 gene in endotoxin-treated murine RAW 264.7 macrophages. Luciferase reporter constructs with alterations in presumptive cis-acting transcriptional regulatory elements demonstrate that the cyclic AMP-response element and two nuclear factor interleukin-6 (CCAAT/enhancer-binding protein (C/EBP)) sites of the COX-2 promoter are required for optimal endotoxin-dependent induction. In contrast, the E-box and NF-kappaB sites are not required for endotoxin-dependent induction. Inhibition of endotoxin-induced NF-kappaB activation by expression of an inhibitor-kappaB alpha mutant does not block endotoxin-dependent COX-2 reporter activity. Overexpression of c-Jun, C/EBPbeta, and C/EBPdelta enhances induction of the COX-2 reporter, while overexpression of cyclic AMP-response element-binding protein or "dominant negative" C/EBPbeta represses COX-2 induction. In addition, endotoxin rapidly and transiently elicits c-Jun phosphorylation in RAW 264.7 macrophages. Cotransfection of the COX-2 reporter with dominant negative expression vectors shows that endotoxin-induced COX-2 gene expression requires signaling through a Ras-independent pathway involving the adapter protein ECSIT and the signaling kinases MEKK1 and JNK. In contrast, endotoxin-induced COX-2 reporter activity is not blocked by overexpression of dominant-negative forms of Raf-1, ERK1, or ERK2.

Critical Evaluation of ECV304 as a Human Endothelial Cell Model Defined by Genetic Analysis and Functional Responses: A Comparison with the Human Bladder Cancer Derived Epithelial Cell Line T24/83

Early reports indicated that ECV304 was a spontaneously-transformed line derived from a Japanese human umbilical vein endothelial cells (HUVEC) culture. Many morphological, immunochemical, and genetic studies provided further evidence that ECV304 was a valuable biomedical research tool and could be used to study processes that include angiogenesis in vitro and signal transduction by a variety of G protein-coupled receptors. However, several distinct differences between ECV304 and HUVEC are now apparent and recent reports have indicated genetic similarity between ECV304 and T24/83, a human bladder cancer cell line. To further assess the utility of ECV304 as a human endothelial cell model, we compared the functional responses of ECV304 and T24/83 to a range of G protein-coupled receptor agonists. We also used DNA fingerprinting to karyotype both ECV304 and T24/83. Both ATP and uridine triphosphate (UTP) stimulated inositol phosphate metabolism in ECV304 without alteration of cAMP levels. Comparative data using selective P2Y receptor agonists indicated that this response, leading to calcium mobilization from intracellular stores, was predominantly mediated by the activation of P2Y2 receptors. Similar responses were recorded from both ECV304 and T24/83 cells. ECV304 expressed a relatively high basal activity of NOS that was reduced by L-NAME and stimulated by P2Y2 receptor agonists. In contrast, P2Y2 receptor activation did not induce prostaglandin synthesis in ECV304. Both ECV304 and T24/83 express receptors for adenosine, adrenaline, and calcitonin, which stimulate adenylate cyclase. Proliferation of ECV304 and T24/83 cells, measured by the incorporation of [3H]thymidine into DNA, was largely serum-independent. This was in contrast to parallel experiments with porcine and bovine aortic endothelial cells that indicated a marked serum-dependent increase in DNA synthesis. Genetic analysis confirmed that ECV304 and T24/83 are identical. ECV304 displays some endothelial characteristics and is useful for the study of receptor pharmacology. However, ECV304 is not of HUVEC origin and is therefore an inappropriate cell line to study endothelial cell biology.

Epidermal growth factor increases basal mucosal blood flow in the rat colon, a prostaglandin dependent effect.

Non-mitogenic biological activity such as modulation of mucosal blood flow is suspected to convey the protective effects of epidermal growth factor (EGF) in vivo. The aims of our present study were to determine the effects of EGF on colonic mucosal blood flow and injury induced hyperaemia in rats. Rats were pretreated with i.p. injections of vehicle, EGF, or indomethacin and EGF prior to mucosal injury. Basal mucosal blood flow and injury induced hyperaemia at the border of the damaged mucosa was determined by using reflectance spectrophotometry. EGF significantly increased basal mucosal blood flow but did not further enhance injury induced hyperaemia. The EGF induced increase in basal mucosal blood flow was completely abolished by indomethacin pretreatment. EGF induces an increase of basal mucosal blood flow through induction of prostaglandin synthesis. We hypothesize that the increase in mucosal blood flow contributes to the ability of EGF to protect the colonic mucosa against injury.

Transcriptional Regulation of the Cyclooxygenase-2 Gene by Diverse Ligands in Murine Osteoblasts

Osteoblasts produce prostaglandins in response to a wide variety of stimuli. Induced prostaglandin synthesis is generally the consequence of elevated cyclooxygenase-2 (COX-2) expression. Agents as diverse as serum, bFGF, PDGF, PGE2, or [TNFα + IL1β] rapidly induce expression of COX-2 protein in murine MC3T3-E1 osteogenic cells. Transient transfection studies using reporter constructs containing either wild-type COX-2 regulatory sequences or mutated cis-acting sequences linked to a luciferase reporter gene identify a CRE site and two NF-IL6 (C/EBP) sites which play important roles in the regulation of COX-2 expression in response to all these agents in osteoblasts. Induction of wild-type COX-2 reporter gene expression in MC3T3-E1 cells by all these agents involves signaling through the MEKK/JNK pathway and activation of both c-Jun and the C/EBP family of transcription factors.

Functional coupling and differential regulation of the phospholipase A2-cyclooxygenase pathways in inflammation.

Prostaglandins generated by the phospholipase A2 (PLA2)/cyclooxygenase (COX) pathway are well known to mediate diverse intracellular and extracellular effects that regulate mammalian development, vascular function, renal physiology, parturition, and immune responses to infection or wounding. In immune-mediated diseases and in certain cancers, this pathway is aberrantly up-regulated and excessive prostaglandin production contributes to the pathology. It is now known that there are two isoforms of COX and multiple secreted and intracellular PLA2 enzymes. The use of isoform-specific inhibitors, coupled with antisense and in vivo gene deletion experiments, has identified independent pathways of arachidonic acid metabolism, which are differentially regulated at the levels of gene expression, protein phosphorylation, and cellular localization. There is cross-talk between the pathways at the level of PLA2 and substrate supply to the two isoforms of COX is apparently compartmentalized. Knockout studies have shown that the two COX isoforms play independent roles in immediate and delayed agonist-induced prostaglandin synthesis. Cytosolic PLA2-alpha is essential for both responses. Inducible secreted forms of PLA2 are, as yet, not essential for either response with the exception of the in vitro murine mast cell immediate response and instances of murine macrophage prostaglandin synthesis. These enzymes amplify the delayed response and are likely to modulate the severity of immune-mediated diseases.

Acute Hemodynamic Interaction of Aspirin and Ticlopidine With Enalapril

Coprescription of aspirin and ACE inhibitors is frequent in heart failure caused by coronary artery disease. Negative interaction between aspirin and enalapril has been reported, presumably through inhibition by aspirin of ACE inhibitor-induced prostaglandin synthesis. Ticlopidine is a potent antiplatelet agent without interaction with prostaglandin synthesis. The objective of this study was to compare the influence of a coadministration of ticlopidine or aspirin on the hemodynamic effects of an ACE inhibitor (enalapril) in patients with chronic heart failure. Twenty patients with severe heart failure were enrolled in a double-blind comparative trial and allocated to ticlopidine (500 mg daily, 12 patients) or aspirin (325 mg daily, 8 patients). Hemodynamic evaluation was performed after 7 days of treatment, every hour for 4 hours after an oral administration of 10 mg of enalapril. Significant reductions in systemic vascular resistance were observed in the ticlopidine group, in contrast to no significant decrease in the aspirin group. A significant (P=0.03) time-by-treatment interaction indicated significant aspirin-enalapril drug interaction. Total pulmonary resistance decreased significantly in both groups, with no difference between patients assigned to aspirin or ticlopidine. Enalapril reduced systemic vascular resistance more effectively when given in combination with ticlopidine than with aspirin. In contrast, the reduction in total pulmonary resistance is similar when enalapril is administered in combination with aspirin or ticlopidine. Negative aspirin-enalapril interaction on prostaglandin synthesis presumably alters vasodilatation in systemic vessels, whereas prostaglandin-independent actions of ACE inhibition such as pulmonary arterial vasodilatation are maintained.

Prostaglandin Endoperoxide Synthase-2 Contributes to the Endothelin/Sarafotoxin-Induced Prostaglandin E2 Synthesis in Mouse Osteoblastic Cells (MC3T3-E1): Evidence for a Protein Tyrosine Kinase-Signaling Pathway and Involvement of Protein Kinase C

Endothelin (ET) peptides are potent growth factors binding to G protein-coupled receptors. Sarafotoxins (S6) isolated from Atractaspis engaddensis are highly homologous to endothelins. In this study, we have investigated the effects of endothelin/sarafotoxin peptides on the prostaglandin synthesizing system in an osteoblast-like cell line, MC3T3-E1. ET-1, ET-2, β-ET, and S6b rapidly stimulated prostaglandin E2 production within 5 min, whereas ET-3, S6a, and S6c did not. ET-1, ET-2, β-ET, S6b, and S6a induced prostaglandin synthesis after 3 h of incubation. Antagonizing these effects with BQ-123, PD 142893, BQ-788, and S6c suggests signaling through an ETA receptor subtype in osteoblasts. Long-term prostaglandin synthesis was blocked by NS-398, and reduced to short-term levels by cycloheximide and actinomycin D, indicating induction of PGHS-2. There was only minor enhancement of cAMP accumulation by the agonists, which had no effect on prostaglandin synthesis. Induction of PGHS-2 was furthermore demonstrated by Northern blot analysis of PGHS-2 messenger RNA. Depletion of protein kinase C with TPA largely blunted the response. Genistein, an inhibitor of protein tyrosine kinases, also blocked long-term prostaglandin E2 formation. We conclude that in osteoblast-like MC3T3-E1 cells, ET-1, ET-2, β-ET, S6b, and S6a peptides induce PGHS-2 through a protein tyrosine kinase-dependent and protein kinase C-dependent pathway, signaling through ETA receptor occupancy.

Prostaglandin endoperoxide synthase-2 contributes to the endothelin/sarafotoxin-induced prostaglandin E2 synthesis in mouse osteoblastic cells (MC3T3-E1): evidence for a protein tyrosine kinase-signaling pathway and involvement of protein kinase C.

Endothelin (ET) peptides are potent growth factors binding to G protein-coupled receptors. Sarafotoxins (S6) isolated from Atractaspis engaddensis are highly homologous to endothelins. In this study, we have investigated the effects of endothelin/sarafotoxin peptides on the prostaglandin synthesizing system in an osteoblast-like cell line, MC3T3-E1. ET-1, ET-2, beta-ET, and S6b rapidly stimulated prostaglandin E2 production within 5 min, whereas ET-3, S6a, and S6c did not. ET-1, ET-2, beta-ET, S6b, and S6a induced prostaglandin synthesis after 3 h of incubation. Antagonizing these effects with BQ-123, PD 142893, BQ-788, and S6c suggests signaling through an ET(A) receptor subtype in osteoblasts. Long-term prostaglandin synthesis was blocked by NS-398, and reduced to short-term levels by cycloheximide and actinomycin D, indicating induction of PGHS-2. There was only minor enhancement of cAMP accumulation by the agonists, which had no effect on prostaglandin synthesis. Induction of PGHS-2 was furthermore demonstrated by Northern blot analysis of PGHS-2 messenger RNA. Depletion of protein kinase C with TPA largely blunted the response. Genistein, an inhibitor of protein tyrosine kinases, also blocked long-term prostaglandin E2 formation. We conclude that in osteoblast-like MC3T3-E1 cells, ET-1, ET-2, beta-ET, S6b, and S6a peptides induce PGHS-2 through a protein tyrosine kinase-dependent and protein kinase C-dependent pathway, signaling through ET(A) receptor occupancy.

An accessory role for ceramide in interleukin-1beta induced prostaglandin synthesis.

Interleukin-1beta (IL-1) is a potent inducer of prostaglandin E2 (PGE2) synthesis. We previously showed that ceramide accumulates in fibroblasts treated with IL-1 and that it enhances IL-1-induced PGE2 production. The present study was undertaken to determine the mechanism(s) by which ceramide and IL-1 interact to enhance PGE2 production by examining their respective effects on the rate-limiting enzymes in PGE2 synthesis, cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and cytosolic phospholipase A2 (cPLA2). IL-1-induced PGE2 synthesis required approximately 8 h even though COX-1 was constitutively expressed (both mRNA and protein) and enzymatically active in untreated cells. Conversely, COX-2 mRNA was barely detectable in untreated cells but within 2 h, ceramide or IL-1 alone induced a 5 and 20 fold increase in COX-2 mRNA, respectively. However, IL-1 induced COX-2 protein synthesis was only detectable 6-7 h after maximal COX-2 mRNA induction; COX-2 protein accumulation was not induced by ceramide alone. Ceramide however, reduced the length of time required for IL-1 to induce COX-2 protein accumulation and increased COX-2 protein accumulation. IL-1 induced a 15 fold increase in COX-1 mRNA including an alternatively spliced form of COX-1. IL-1, but not ceramide induced cPLA2 mRNA and protein expression which corresponded with the initiation of PGE2 synthesis. These observations indicate that, (1) while either ceramide or IL-1 rapidly induced COX-2 mRNA, COX-2 protein only accumulated in IL-1 treated cells after a delay of 6-7 h, (2) IL-1-induced PGE2 synthesis required both COX-2 and cPLA2 protein synthesis and, (3) ceramide enhanced (temporally and quantitatively) IL-1-induced COX-2 protein