Cloning and localization of hFPS: a six-transmembrane mRNA splice variant of the human FP prostanoid receptor

A Review of Prostanoid Receptors: Expression, Characterization, Regulation, and Mechanism of Action

Prostaglandin signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain to cell survival. Disruption of normal prostanoid signaling is implicated in numerous disease states. Prostaglandin signaling is facilitated by G-protein-coupled, prostanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of prostanoid receptors with particular emphasis on human isoforms.

Efficacy and safety of bimatoprost in glaucoma and ocular hypertension in non-responder patients

AIM

To establish the efficacy and safety of bimatoprost 0.03% monotherapy in glaucoma and ocular hypertension (OHT) patients with inadequate intraocular pressure (IOP)on current therapy.

METHODS

Pre- and post-switch IOPs were analyzed for 59 consecutive patients who were switched from current therapy to bimatoprost monotherapy between 2011-2015. Demographic information, diagnosis, and any adverse events were recorded. Change in IOP post-pre switch was analyzed using a 2-sided Student's paired t-test at the 5% significance level.

RESULTS

There was a statistically significant mean reduction in IOP at the first follow up visit, which was maintained at subsequent follow up visits for patients regardless of diagnosis, or pre-switch treatment (P<0.001). Subgroup analysis also demonstrated a statistically significant mean reduction in IOP when looking at OHT patients only, as well as patients with any diagnosis switched from latanoprost monotherapy to bimatoprost monotherapy (P<0.001).

CONCLUSION

This is the largest independent data set which supports switching glaucoma patients with poor response to current treatment onto bimatoprost monotherapy before considering other adjuvant medical or more invasive therapy.

Recent progress in prostaglandin F2α ethanolamide (prostamide F2α) research and therapeutics

Prostamide (prostaglandin ethanolamide) research emerged from two distinct lines of research: 1) the unique pharmacology of the antiglaucoma drug bimatoprost and 2) the discovery that endocannabinoid anandamide was converted by COX-2 to a series of electrochemically neutral prostaglandin (PG) ethanolamides. Bimatoprost pharmacology was found to be virtually identical to that of prostamide F2α. The earliest studies relied on comparison of agonist potencies compared with PGF2α and synthetic prostaglandin F2α (FP) receptor agonists. The subsequent discovery of selective and potent prostamide receptor antagonists (AGN 211334-6, as shown in Fig. 3) was critical for distinguishing between prostamide and FP receptor-mediated effects. The prostamide F2α receptor was then modeled by cotransfecting the wild-type FP receptor with an mRNA splicing variant (altFP4).Bimatoprost is now used therapeutically for treating both glaucoma and eyelash hypotrichosis. Bimatoprost also stimulates hair growth in isolated human scalp hair follicles. A strong effect is also seen in mouse pelage hair, where bimatoprost essentially halves the onset of hair regrowth and the time to achieve full hair regrowth in shaved mice. Beyond glaucoma and hair growth, bimatoprost has potential for reducing fat deposition. Studies to date suggest that preadipocytes are the cellular target for bimatoprost. The discovery of the enzyme prostamide/PGF synthase was invaluable in elucidating the anatomic distribution of prostamide F2α. High expression in the central nervous system provided the impetus for later studies that described prostamide F2α as a nociceptive mediator in the spinal cord. At the translational level, bimatoprost has already provided therapeutics in two distinct areas and the use of both prostamide agonists and antagonists may provide other useful medicaments.

The roles played by highly truncated splice variants of G protein-coupled receptors

Alternative splicing of G protein-coupled receptor (GPCR) genes greatly increases the total number of receptor isoforms which may be expressed in a cell-dependent and time-dependent manner. This increased diversity of cell signaling options caused by the generation of splice variants is further enhanced by receptor dimerization. When alternative splicing generates highly truncated GPCRs with less than seven transmembrane (TM) domains, the predominant effect in vitro is that of a dominant-negative mutation associated with the retention of the wild-type receptor in the endoplasmic reticulum (ER). For constitutively active (agonist-independent) GPCRs, their attenuated expression on the cell surface, and consequent decreased basal activity due to the dominant-negative effect of truncated splice variants, has pathological consequences. Truncated splice variants may conversely offer protection from disease when expression of co-receptors for binding of infectious agents to cells is attenuated due to ER retention of the wild-type co-receptor. In this review, we will see that GPCRs retained in the ER can still be functionally active but also that highly truncated GPCRs may also be functionally active. Although rare, some truncated splice variants still bind ligand and activate cell signaling responses. More importantly, by forming heterodimers with full-length GPCRs, some truncated splice variants also provide opportunities to generate receptor complexes with unique pharmacological properties. So, instead of assuming that highly truncated GPCRs are associated with faulty transcription processes, it is time to reassess their potential benefit to the host organism.

Prostanoids as regulators of innate and adaptive immunity

Potent, oxygenated lipid molecules called prostanoids regulate a wide variety of physiological responses and pathological processes. Prostanoids are produced by various cell types and act on target cells through specific G protein-coupled receptors. Although prostanoids have historically been considered acute inflammation mediators, studies using specific receptor knockout mice indicate that prostanoids, in fact, regulate various aspects of both innate and adaptive immunity. Each prostanoid, depending on which receptor it acts on, exerts specific effects on immune cells such as macrophages, dendritic cells, and T and B lymphocytes, often in concert with microbial ligands and cytokines, to affect the strength, quality, and duration of immune responses. Prostanoids are also relevant to immunopathology, from inflammation to autoimmunity and cancer. Here, we review the role of prostanoids in regulating immunity, their involvement in immunopathology, and areas of insight that may lead to new therapeutic opportunities.

Efficacy and safety of switching from topical latanoprost to bimatoprost in patients with normal-tension glaucoma

PURPOSE

The aim of this study was to evaluate the efficacy and safety of bimatoprost in Japanese patients with normal-tension glaucoma (NTG) who showed insufficient response to latanoprost.

METHODS

A prospective, nonrandomized study was conducted in patients with NTG, with ≤20% intraocular pressure (IOP) decrease from pretreatment baseline with latanoprost monotherapy who had been switched to bimatoprost. The IOP was measured at 4, 8, and 12 weeks after the switch to bimatoprost. In 12 weeks after the switch to bimatoprost, efficacy and safety were evaluated.

RESULTS

Postswitch to bimatoprost, IOP was significantly reduced at every visit. Bimatoprost produced significantly greater mean% IOP reduction rate from pretreatment than that of latanoprost at week 12 (P<0.01). There was a significant correlation between% IOP reduction of bimatoprost and that of latanoprost (Pearson r(2)=0.374; P=0.007). No significant difference was observed in the mean scores of conjunctival hyperemia and corneal epithelial disorder between bimatoprost-treated eyes and latanoprost-treated eyes.

CONCLUSIONS

Significant additional IOP lowering was achieved by switching to bimatoprost in Japanese patients with NTG with insufficient response to latanoprost. Bimatoprost treatment was safe and well tolerated.

Labour is associated with decreased expression of the PGF2alpha receptor (PTGFR) and a novel PTGFR splice variant in human myometrium but not decidua

The prostaglandin F(2α) receptor (PTGFR) is believed to play a role in the process of parturition. The main support for this comes from animal studies; however, in humans, the evidence is less clear. The gene coding for PTGFR may be subject to alternative splicing to generate alternate variants with different signalling pathways. We have determined regional (upper versus lower segment) and labour-associated expression of PTGFR mRNA and a recently identified splice variant of PTGFR in human myometrium and decidua. We also examined the effect of the inflammatory cytokine interleukin-1β (IL-1β) on PTGFR mRNA expression in a model of cultured human myometrial smooth muscle cells. We identified a PTGFR transcript variant 2 (PTGFR-v2) generated by alternate splicing in human myometrium and decidua. The PTGFR-v2 contains an additional 71 base pair exon, which results in a truncated protein at 297 amino acids compared with the PTGFR transcript variant 1 (PTGFR-v1) at 359 amino acids. In contrast to our hypothesis, we demonstrate that PTGFR-v1 and PTGFR-v2 mRNA expression is not significantly higher in upper segment compared with lower segment paired samples. We also show a labour-associated decrease in PTGFR-v1 and PTGFR-v2 mRNA expression in lower segment myometrial samples. IL-1β-stimulated mRNA expression of both PTGFR variants in a distinct time-dependent manner in myometrial cell cultures. We suggest that the role of the PTGFR in the human uterus requires further validation prior to pursuing it as a target for the treatment of preterm labour. In addition, the presence of distinct variants suggests further levels of gene regulation within the pregnant uterus.

A novel alternatively spliced isoform of the mu-opioid receptor: functional antagonism

Background

Opioids are the most widely used analgesics for the treatment of clinical pain. They produce their therapeutic effects by binding to μ-opioid receptors (MORs), which are 7 transmembrane domain (7TM) G-protein-coupled receptors (GPCRs), and inhibiting cellular activity. However, the analgesic efficacy of opioids is compromised by side-effects such as analgesic tolerance, dependence and opioid-induced hyperalgesia (OIH). In contrast to opioid analgesia these side effects are associated with cellular excitation. Several hypotheses have been advanced to explain these phenomena, yet the molecular mechanisms underlying tolerance and OIH remain poorly understood.

Results

We recently discovered a new human alternatively spliced isoform of MOR (MOR1K) that is missing the N-terminal extracellular and first transmembrane domains, resulting in a 6TM GPCR variant. To characterize the pattern of cellular transduction pathways activated by this human MOR1K isoform, we conducted a series of pharmacological and molecular experiments. Results show that stimulation of MOR1K with morphine leads to excitatory cellular effects. In contrast to stimulation of MOR1, stimulation of MOR1K leads to increased Ca²⁺ levels as well as increased nitric oxide (NO) release. Immunoprecipitation experiments further reveal that unlike MOR1, which couples to the inhibitory Gα_i/o complex, MOR1K couples to the stimulatory Gα_s complex.

Conclusion

The major MOR1 and the alternative MOR1K isoforms mediate opposite cellular effects in response to morphine, with MOR1K driving excitatory processes. These findings warrant further investigations that examine animal and human MORK1 expression and function following chronic exposure to opioids, which may identify MOR1K as a novel target for the development of new clinically effective classes of opioids that have high analgesic efficacy with diminished ability to produce tolerance, OIH, and other unwanted side-effects.

Prostanoid DP receptor (PTGDR) variants in mothers with post-coital associated preterm births: preliminary observations

OBJECTIVE

To describe prostanoid DP receptor (PTGDR) variants in women with preterm births who admitted to coital activity (CA) within 24 h of labor.

STUDY DESIGN

To achieve >80% statistical power, a pilot case-control study compared 24 premature births from mothers with CA (Group 1), 30 mothers of premature infants who did not have CA (Group 2 non-coital activity) and 95 non-coital activity mothers with term births (Group 3 controls). Four functional PTDGR single nucleotide polymorphisms (SNPs) were evaluated: T-549C, C-441/T, T-197C and G+1044A. PHASE 2.0.2 and SAS 9.2 were used for analysis.

RESULT

All SNPs were in Hardy-Weinberg equilibrium in controls. The C-441/T genotype frequency was significantly increased among Group 1 women relative to Group 2 and 3 women (odds ratio (OR): 30.1, 95% confidence interval (CI) 6.9-191 and 25.7 95%CI 25.7-not computible, respectively). Of the possible haplotypes among the groups, the TCTG haplotype (T-549C, C-441/T, T-197C and G+1044A) was significantly more frequent in Group 1 women compared with the control groups (OR 53.4, 95%CI 10.3-554.8).

CONCLUSIONS

A differential genomic pattern of PTGDR polymorphisms was identified in a sub-set of mothers which was associated with an increased risk of post-coital preterm birth.

Alternative splicing of G protein-coupled receptors: physiology and pathophysiology

The G protein-coupled receptors (GPCRs) are a superfamily of transmembrane receptors that have a broad distribution and can collectively recognise a diverse array of ligands. Activation or inhibition of GPCR signalling can affect many (patho)physiological processes, and consequently they are a major target for existing and emerging drug therapies. A common observation has been that the pharmacological, signalling and regulatory properties of GPCRs can differ in a cell- and tissue-specific manner. Such "phenotypic" diversity might be attributable to post-translational modifications and/or association of GPCRs with accessory proteins, however, post-transcriptional mechanisms are also likely to contribute. Although approximately 50% of GPCR genes are intronless, those that possess introns can undergo alternative splicing, generating GPCR subtype isoforms that may differ in their pharmacological, signalling and regulatory properties. In this review we shall highlight recent research into GPCR splice variation and discuss the potential consequences this might have for GPCR function in health and disease.

Role of the prostanoid FP receptor in action potential generation and phenotypic transformation of NRK fibroblasts

By using an shRNA approach to knockdown the expression of the prostaglandin (PG)-F(2alpha) receptor (FP-R), the role of PGF(2alpha) in the process of phenotypic transformation of normal rat kidney (NRK) fibroblasts has been studied. Our data show that PGF(2alpha) up-regulates Cox-2 expression both at the mRNA and protein level, indicating that activation of FP-R in NRK fibroblasts induces a positive feedback loop in the production PGF(2alpha). Knockdown of FP-R expression fully impaired the ability of PGF(2alpha) to induce a calcium response and subsequent depolarization in NRK cells. However, these cells could still undergo phenotypic transformation when treated with a combination of EGF and retinoic acid, but in contrast to the wild-type cells, this process was not accompanied by a membrane depolarization to -20 mV. Knockdown of FP-R expression also impaired the spontaneous firing of calcium action potentials by density-arrested NRK cells. These data show that a membrane depolarization is not a prerequisite for the acquisition of a transformed phenotype. Furthermore, our data provide the first direct evidence that activity of PGF(2alpha) by putative pacemaker cells underlies the generation of calcium action potentials in NRK monolayers.

Identification and pharmacological characterization of the prostaglandin FP receptor and FP receptor variant complexes

Background and purpose: A prostamide analogue, bimatoprost, has been shown to be effective in reducing intraocular pressure, but its precise mechanism of action remains unclear. Hence, to elucidate the molecular mechanisms of this effect of bimatoprost, we focused on pharmacologically characterizing prostaglandin FP receptor (FP) and FP receptor variant (altFP) complexes.

Experimental approach: FP receptor mRNA variants were identified by reverse transcription-polymerase chain reaction. The FP-altFP4 heterodimers were established in HEK293/EBNA cells co-expressing FP and altFP4 receptor variants. A fluorometric imaging plate reader was used to study Ca²⁺ mobilization. Upregulation of cysteine-rich angiogenic protein 61 (Cyr61) mRNA was measured by Northern blot analysis, and phosphorylation of myosin light chain (MLC) by western analysis.

Key results: Six splicing variants of FP receptor mRNA were identified in human ocular tissues. Immunoprecipitation confirmed that the FP receptor is dimerized with altFP4 receptors in HEK293/EBNA cells co-expressing FP and altFP4 receptors. In the studies of the kinetic profile for Ca²⁺ mobilization, prostaglandin F_2α (PGF_2α) elicited a rapid increase in intracellular Ca²⁺ followed by a steady state phase. In contrast, bimatoprost elicited an immediate increase in intracellular Ca²⁺ followed by a second phase. The prostamide antagonist, AGN211335, selectively and dose-dependently inhibited the bimatoprost-initiated second phase of Ca²⁺ mobilization, Cyr61 mRNA upregulation and MLC phosphorylation, but did not block the action of PGF_2α.

Conclusion and implications: Bimatoprost lacks effects on the FP receptor but may interact with the FP-altFP receptor heterodimer to induce alterations in second messenger signalling. Hence, FP-altFP complexes may represent the underlying basis of bimatoprost pharmacology.

Prostamides (prostaglandin-ethanolamides) and their pharmacology

The prostamides are part of a large and continually expanding series of pharmacologically unique neutral lipids. They are COX-2 derived oxidation products of the endocannabinoid/endovanniloid anandamide. Prostamide pharmacology is unique and, as in the case of the endocannabinoids anandamide and 2-arachidonylglycerol, bears little resemblance to that of the corresponding free acids. By virtue of its close relationship to the anti-glaucoma drug bimatoprost, prostamide F(2alpha) has received the greatest research attention. Prostamide F(2alpha) and bimatoprost effects appear independent of prostanoid FP receptor activation, according to a litany of agonist studies. Studies involving freshly isolated and separate feline iridial smooth muscle cells revealed that bimatoprost and FP receptor agonists stimulated different cells, without exception. This suggests the existence of receptors that preferentially recognize prostamide F(2alpha). The recent discovery of prostamide antagonists has provided further support for prostamide receptors as discrete entities. The prototypical prostamide antagonists, AGN 204396 and 7, blocked the effects of prostamide F(2alpha) and bimatoprost but not those of PGF(2alpha) and FP receptor agonists in the feline iris. Second generation more potent prostamide antagonists, such as AGN 211334, should allow the role of prostamides in health and disease to be elucidated. From the therapeutics standpoint, the prostamide F(2alpha) analogue bimatoprost is the most efficacious ocular hypotensive agent currently available for the treatment of glaucoma.

Association between genetic polymorphisms of the prostaglandin F2alpha receptor gene and response to latanoprost

PURPOSE

To evaluate the relationship between polymorphisms of the prostaglandin F(2alpha) receptor (FP receptor) gene and the effectiveness of topical latanoprost treatment in normal volunteers.

DESIGN

Prospective nonrandomized trial.

PARTICIPANTS

One hundred normal volunteers were recruited into the study.

METHODS

Baseline intraocular pressures (IOPs) of both eyes of 100 normal subjects were measured at 3 time points. Latanoprost (0.005%) was applied to one eye once daily for 7 days. Diurnal IOP was measured again on day 7. Response to latanoprost was evaluated by percent IOP reduction in the treated eye minus IOP fluctuations of the nontreated eye. We classified subjects by the mean diurnal percent IOP reduction (%DeltaIOP) into 3 groups: low responders (%DeltaIOP<10), medium responders (10< or =%DeltaIOP<25), and high responders (%DeltaIOP> or =25). Single-nucleotide polymorphisms (SNPs) in the FP receptor gene were searched, and the genotype was determined mainly by direct DNA sequencing. A promoter assay with a reporter luciferase gene was also performed.

MAIN OUTCOME MEASURES

Mean diurnal percent IOP reduction and genotyping of SNPs in the FP receptor gene.

RESULTS

Ten SNPs were identified in this study. One, rs3753380, was located in the promoter region of the FP receptor gene and was significantly correlated with %DeltaIOP (CC, 20.3%+/-1.5% [mean +/- standard error]; CT + TT, 15.6%+/-1.2%; P = 0.0316). Mean diurnal percent IOP reduction was not associated with the other SNPs. When the category classified by %DeltaIOP was analyzed, not only rs3753380 but also rs3766355, an SNP in intron 1, were associated with the degree of response to latanoprost. The promoter assay revealed that the C allele of rs3766355 and T allele of rs3753380 were found in constructs with lower transcriptional activity of the FP receptor gene.

CONCLUSIONS

rs3753380 and rs3766355, SNPs in the promoter and intron 1 regions of the FP receptor gene, correlate with a response to short-term latanoprost treatment in normal volunteers. The genotype of these SNPs may be an important determinant of variability in response to latanoprost.

Prostanoids as pharmacological targets in COPD and asthma

COPD (Chronic Obstructive Pulmonary Disease) and bronchial asthma are two severe lung diseases which represent a major problem of world public health. Leukotrienes and prostanoids play an important role in the pathogenesis of pulmonary diseases. Prostanoids: prostaglandins (PGs) and thromboxane A2 (TXA2), the cyclooxygenase metabolites of arachidonic acid are implicated in the inflammatory cascade that occurs in asthmatic airways. Recently, the roles played by isoprostanes or prostaglandin-like compounds nonenzymatically generated via peroxidation of membrane phospholipids by reactive oxygen species, in particular F2-isoprostanes, in pulmonary pathophysiology have been highlighted. This article aims to provide an overview of the role of prostanoids and isoprostanes in the pathogenesis of COPD and asthma and to discuss the pharmacological strategies developed in prevention and/or treatment of these pathologies.

Eicosanoids and the vascular endothelium

Cyclooxygenase (COX) enzymes catalyse the biotransformation of arachidonic acid to prostaglandins which subserve important functions in cardiovascular homeostasis. Prostacyclin (PGI2) and prostaglandin (PG)E2, dominant products of COX activityin macro- and microvascular endothelial cells, respectively, in vitro, modulate the interaction of blood cells with the vasculature and contribute to the regulation of blood pressure. COXs are the target for inhibition by nonsteroidal anti-inflammatory drugs (NSAIDs--which include those selective for COX-2) and for aspirin. Modulation of the interaction between COX products of the vasculature and platelets underlies both the cardioprotection afforded by aspirin and the cardiovascular hazard which characterises specific inhibitors of COX-2.

A positive feedback loop that regulates cyclooxygenase-2 expression and prostaglandin F2alpha synthesis via the F-series-prostanoid receptor and extracellular signal-regulated kinase 1/2 signaling pathway

Cyclooxygenase (COX) enzymes catalyze the biosynthesis of eicosanoids, including prostaglandin (PG) F2alpha. PGF2alpha exerts its autocrine/paracrine function by coupling to its 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 COX-2 and FP receptor colocalized together within the neoplastic epithelial cells of endometrial adenocarcinomas. We investigated a role for PGF2alpha-FP receptor interaction in modulating COX-2 expression and PGF2alpha biosynthesis using an endometrial adenocarcinoma cell line stably transfected with the FP receptor cDNA (FPS cells). PGF2alpha-FP receptor activation rapidly induced COX-2 promoter, mRNA, and protein expression in FPS cells. These effects of PGF2alpha on the expression of COX-2 could be abolished by treatment of FPS cells with an FP receptor antagonist (AL8810) and chemical inhibitor of ERK1/2 kinase (PD98059), or by inactivation of ERK1/2 signaling with dominant-negative mutant isoforms of Ras or ERK1/2 kinase. We further confirmed that elevated COX-2 protein in FPS cells could biosynthesize PGF2alpha de novo to promote a positive feedback loop to facilitate endometrial tumorigenesis. Finally, we have shown that PGF2alpha could potentiate tumorigenesis in endometrial adenocarcinoma explants by inducing the expression of COX-2 mRNA.

Uteroglobin inhibits prostaglandin F2alpha receptor-mediated expression of genes critical for the production of pro-inflammatory lipid mediators

Prematurity is one of the leading causes of infant mortality. It may result from intrauterine infection, which mediates premature labor by stimulating the production of inflammatory lipid mediators such as prostaglandin F2alpha (PGF2alpha). The biological effects of PGF2alpha are mediated via the G protein-coupled receptor FP; however, the molecular mechanism(s) of FP signaling that mediates inflammatory lipid mediator production remains unclear. We reported previously that in the human uterus, a composite organ in which fibroblast, epithelial, and smooth muscle cells are the major constituents, an inverse relationship exists between the levels of PGF2alpha and a steroid-inducible anti-inflammatory protein, uteroglobin. Here we report that, in NIH 3T3 fibroblasts and human uterine smooth muscle cells, FP signaling is mediated via multi-kinase pathways in a cell type-specific manner to activate NF-kappaB, thus stimulating the expression of cyclooxygenase-2. Cyclooxygenase-2 is a critical enzyme for the production of prostaglandins from arachidonic acid, which is released from membrane phospholipids by phospholipase A2, the expression of which is also stimulated by PGF2alpha. Most importantly, uteroglobin inhibits FP-mediated NF-kappaB activation and cyclooxygenase-2 gene expression by binding and most likely by sequestering PGF2alpha into its central hydrophobic cavity, thereby preventing FP-PGF2alpha interaction and suppressing the production of inflammatory lipid mediators. We propose that uteroglobin plays important roles in maintaining homeostasis in organs that are vulnerable to inadvertent stimulation of FP-mediated inflammatory response.

Pharmacology and signaling of prostaglandin receptors: multiple roles in inflammation and immune modulation

Prostaglandins are lipid-derived autacoids that modulate many physiological systems including the CNS, cardiovascular, gastrointestinal, genitourinary, endocrine, respiratory, and immune systems. In addition, prostaglandins have been implicated in a broad array of diseases including cancer, inflammation, cardiovascular disease, and hypertension. Prostaglandins exert their effects by activating rhodopsin-like seven transmembrane spanning G protein-coupled receptors (GPCRs). The prostanoid receptor subfamily is comprised of eight members (DP, EP1-4, FP, IP, and TP), and recently, a ninth prostaglandin receptor was identified-the chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2). The precise roles prostaglandin receptors play in physiologic and pathologic settings are determined by multiple factors including cellular context, receptor expression profile, ligand affinity, and differential coupling to signal transduction pathways. This complexity is highlighted by the diverse and often opposing effects of prostaglandins within the immune system. In certain settings, prostaglandins function as pro-inflammatory mediators, but in others, they appear to have anti-inflammatory properties. In this review, we will discuss the pharmacology and signaling of the nine known prostaglandin GPCRs and highlight the specific roles that these receptors play in inflammation and immune modulation.