Deficiency of long-chain acyl-CoA synthetase 4 leads to lipopolysaccharide-induced mortality in a mouse model of septic shock.

Long-chain acyl-CoA synthetase 4 (ACSL4) converts free highly unsaturated fatty acids (HUFAs) into their acyl-CoA esters and is important for HUFA utilization. HUFA-containing phospholipids produced via ACSL4-dependent reactions are involved in pathophysiological events such as inflammatory responses and ferroptosis as a source for lipid mediators and/or a target of oxidative stress, respectively. However, the in vivo role of ACSL4 in inflammatory responses is not fully understood. This study sought to define the effects of ACSL4 deficiency on lipopolysaccharide (LPS)-induced systemic inflammatory responses using global Acsl4 knockout (Acsl4 KO) mice. Intraperitoneal injection of LPS-induced more severe symptoms, including diarrhea, hypothermia, and higher mortality, in Acsl4 KO mice within 24 h compared with symptoms in wild-type (WT) mice. Intestinal permeability induced 3 h after LPS challenge was also enhanced in Acsl4 KO mice compared with that in WT mice. In addition, plasma levels of some eicosanoids in Acsl4 KO mice 6 h post-LPS injection were 2- to 9-fold higher than those in WT mice. The increased mortality observed in LPS-treated Acsl4 KO mice was significantly improved by treatment with the general cyclooxygenase inhibitor indomethacin with a partial reduction in the severity of illness index for hypothermia, diarrhea score, and intestinal permeability. These results suggest that ACSL4 deficiency enhances susceptibility to endotoxin at least partly through the overproduction of cyclooxygenase-derived eicosanoids.

Gene deletion of long-chain acyl-CoA synthetase 4 attenuates xenobiotic chemical-induced lung injury via the suppression of lipid peroxidation.

Long-chain acyl-CoA synthetase (ACSL) 4 converts polyunsaturated fatty acids (PUFAs) into their acyl-CoAs and plays an important role in maintaining PUFA-containing membrane phospholipids. Here we demonstrated decreases in various kinds of PUFA-containing phospholipid species in ACSL4-deficient murine lung. We then examined the effects of ACSL4 gene deletion on lung injury by treating mice with two pulmonary toxic chemicals: paraquat (PQ) and methotrexate (MTX). The results showed that ACSL4 deficiency attenuated PQ-induced acute lung lesion and decreased mortality. PQ-induced lung inflammation and neutrophil migration were also suppressed in ACSL4-deficient mice. PQ administration increased the levels of phospholipid hydroperoxides in the lung, but ACSL4 gene deletion suppressed their increment. We further found that ACSL4 deficiency attenuated MTX-induced pulmonary fibrosis. These results suggested that ACSL4 gene deletion might confer protection against pulmonary toxic chemical-induced lung injury by reducing PUFA-containing membrane phospholipids, leading to the suppression of lipid peroxidation. Inhibition of ACSL4 may be promising for the prevention and treatment of chemical-induced lung injury.

Hepatic phosphatidylcholine catabolism driven by PNPLA7 and PNPLA8 supplies endogenous choline to replenish the methionine cycle with methyl groups.

Choline supplies methyl groups for regeneration of methionine and the methyl donor S-adenosylmethionine in the liver. Here, we report that the catabolism of membrane phosphatidylcholine (PC) into water-soluble glycerophosphocholine (GPC) by the phospholipase/lysophospholipase PNPLA8-PNPLA7 axis enables endogenous choline stored in hepatic PC to be utilized in methyl metabolism. PNPLA7-deficient mice show marked decreases in hepatic GPC, choline, and several metabolites related to the methionine cycle, accompanied by various signs of methionine insufficiency, including growth retardation, hypoglycemia, hypolipidemia, increased energy consumption, reduced adiposity, increased fibroblast growth factor 21 (FGF21), and an altered histone/DNA methylation landscape. Moreover, PNPLA8-deficient mice recapitulate most of these phenotypes. In contrast to wild-type mice fed a methionine/choline-deficient diet, both knockout strains display decreased hepatic triglyceride, likely via reductions of lipogenesis and GPC-derived glycerol flux. Collectively, our findings highlight the biological importance of phospholipid catabolism driven by PNPLA8/PNPLA7 in methyl group flux and triglyceride synthesis in the liver.

Prostacyclin Synthase as an Ambivalent Regulator of Inflammatory Reactions.

Prostacyclin (PGI2) synthase (PGIS) and microsomal prostaglandin (PG) E synthase-1 (PGES-1) are PG terminal synthases which functionally couple with inducible cyclooxygenase-2 (COX-2) as their upstream enzymes to produce PGI2 and PGE2, respectively. Non-steroidal anti-inflammatory drugs exert their pharmacological effects by the inhibition of COX-2 and thereby suppression of the biosynthesis of these PGs. PGIS is abundantly expressed in vascular endothelial and smooth muscle cells and has been shown to be critical for regulation of platelet aggregation and vascular tone. In addition to its role in vascular regulation, PGIS has been shown to be expressed in inflammatory cells including macrophages, and the proinflammatory roles of PGIS has been demonstrated. On the other hand, several investigators have recently reported that PGIS functions as an anti-inflammatory mediator by macrophage polarization and have indicated that PGIS is an ambivalent regulator of inflammatory reactions. In this review, we summarize the current understanding of proinflammatory and anti-inflammatory functions of PGIS and discuss its potential as a novel anti-inflammatory therapeutic target.

Role of ACSL4 in the chemical-induced cell death in human proximal tubule epithelial HK-2 cells.

Acyl-CoA synthetase long-chain family member 4 (ACSL4) activates polyunsaturated fatty acids (PUFAs) to produce PUFA-derived acyl-CoAs, which are utilised for the synthesis of various biological components, including phospholipids (PLs). Although the roles of ACSL4 in non-apoptotic programmed cell death ferroptosis are well-characterised, its role in the other types of cell death is not fully understood. In the present study, we investigated the effects of ACSL4 knockdown on the levels of acyl-CoA, PL, and ferroptosis in the human normal kidney proximal tubule epithelial (HK-2) cells. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses revealed that the knockdown of ACSL4 markedly reduced the levels of PUFA-derived acyl-CoA, but not those of other acyl-CoAs. In contrast with acyl-CoA levels, the docosahexaenoic acid (DHA)-containing PL levels were preferentially decreased in the ACSL4-knockdown cells compared with the control cells. Cell death induced by the ferroptosis inducers RSL3 and FIN56 was significantly suppressed by treatment with ferrostatin-1 or ACSL4 knockdown, and, unexpectedly, upon treating with a necroptosis inhibitor. In contrast, ACSL4 knockdown failed to suppress the other oxidative stress-induced cell deaths initiated by cadmium chloride and sodium arsenite. In conclusion, ACSL4 is involved in the biosynthesis of DHA-containing PLs in HK-2 cells and is specifically involved in the cell death induced by ferroptosis inducers.

Substrate Specificity of Human Long-Chain Acyl-CoA Synthetase ACSL6 Variants.

Long-chain acyl-CoA synthetases (ACSLs) are a family of enzymes that convert long-chain free fatty acids into their active form, acyl-CoAs. Recent knock-out mouse studies revealed that among ACSL isoenzymes, ACSL6 plays an important role in the maintenance of docosahexaenoic acid (DHA)-containing glycerophospholipids. Several transcript variants of the human ACSL6 gene have been found; the two major ACSL6 variants, ACSL6V1 and V2, encode slightly different short motifs that both contain a conserved structural domain, the fatty acid Gate domain. In the present study, we expressed recombinant human ACSL6V1 and V2 in Spodoptera frugiperda 9 (Sf9) cells using the baculovirus expression system, and then, using our novel ACSL assay system with liquid chromatography-tandem mass spectrometry (LC-MS/MS), we examined the substrate specificities of the recombinant human ACSL6V1 and V2 proteins. The results showed that both ACSL6V1 and V2 could convert various kinds of long-chain fatty acids into their acyl-CoAs. Oleic acid was a good common substrate and eicosapolyenoic acids were poor common substrates for both variants. However, ACSL6V1 and V2 differed considerably in their preferences for octadecapolyenoic acids, such as linoleic acid, and docosapolyenoic acids, such as DHA and docosapentaenoic acid (DPA): ACSL6V1 preferred octadecapolyenoic acids, whereas V2 strongly preferred docosapolyenoic acids. Moreover, our kinetic studies revealed that ACSL6V2 had a much higher affinity for DHA than ACSL6V1. Our results suggested that ACSL6V1 and V2 might exert different physiological functions and indicated that ACSL6V2 might be critical for the maintenance of membrane phospholipids bearing docosapolyenoic acids such as DHA.

Absence of prostacyclin greatly relieves cyclophosphamide-induced cystitis and bladder pain in mice.

Cyclophosphamide (CP) has been widely used in the treatment of various malignancies and autoimmune diseases, but acrolein, a byproduct of CP, causes severe hemorrhagic cystitis as the major side effect of CP. On the other hand, a large amount of prostacyclin (PGI2 ) is produced in bladder tissues, and PGI2 has been shown to play a critical role in bladder homeostasis. PGI2 is biosynthesized from prostaglandin (PG) H2 , the common precursor of PGs, by PGI2 synthase (PTGIS) and is known to also be involved in inflammatory responses. However, little is known about the roles of PTGIS-derived PGI2 in bladder inflammation including CP-induced hemorrhagic cystitis. Using both genetic and pharmacological approaches, we here revealed that PTGIS-derived PGI2 -IP (PGI2 receptor) signaling exacerbated CP-induced bladder inflammatory reactions. Ptgis deficiency attenuated CP-induced vascular permeability and chemokine-mediated neutrophil migration into bladder tissues and then suppressed hemorrhagic cystitis. Treatment with RO1138452, an IP selective antagonist, also suppressed CP-induced cystitis. We further found that cystitis-related nociceptive behavior was also relieved in both Ptgis-/- mice and RO1138452-treated mice. Our findings may provide new drug targets for bladder inflammation and inflammatory pain in CP-induced hemorrhagic cystitis.

Gene Deletion of Microsomal Prostaglandin E Synthase-1 Suppresses Chemically Induced Skin Carcinogenesis.

BACKGROUND/AIM: Microsomal prostaglandin (PG) E synthase-1 (mPGES-1) is a terminal enzyme in PGE2 synthesis and highly expressed in several cancers. In this study, to reveal the involvement of mPGES-1 in skin carcinogenesis, the effect of mPGES-1 deficiency on two-stage skin carcinogenesis in mice was investigated. MATERIALS AND METHODS: A two-stage skin carcinogenesis model using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter was applied on mPGES-1 knockout (KO) mice and littermate wild-type mice of a Balb/c genetic background. RESULTS: DMBA/TPA-induced skin carcinogenesis was suppressed in mPGES-1 KO mice. The induction of IL-17 and other inflammatory cytokines by TPA was also suppressed by mPGES-1 deficiency, although DMBA-induced apoptosis was not affected. CONCLUSION: mPGES-1 promotes chemically induced skin carcinogenesis and might play an important role in the TPA-induced promotion phase of the two-stage skin carcinogenesis model. mPGES-1 inhibition may be a therapeutic target for skin cancer.

Coordinated action of microsomal prostaglandin E synthase-1 and prostacyclin synthase on contact hypersensitivity.

Microsomal prostaglandin (PG) E synthase-1 (mPGES-1) and prostacyclin (PGI2) synthase (PGIS) are PG terminal synthases that work downstream of cyclooxygenase and synthesize PGE2 and PGI2, respectively. Although the involvement of PG receptors in acquired cutaneous immune responses was recently shown, the roles of these PG terminal synthases remain unclear. To identify the pathophysiological roles of mPGES-1 and PGIS in cutaneous immune systems, we applied contact hypersensitivity (CHS) to mPGES-1 and PGIS knockout (KO) mice as a model of acquired immune responses. Mice were treated with 1-fluoro-2,4-dinitrobenzene (DNFB) and evaluated for ear thickness and histopathological features. The results showed that the severity of ear swelling in both gene-deficient mice was much lower than that in wild-type (WT) mice. Histological examination of DNFB-treated ears showed that inflammatory cell infiltration and edema in the dermis were also less apparent in both genotypic mice. LC-MS analysis further showed that the increment in PGE2 levels in DNFB-treated ear tissue was reduced in mPGES-1 KO mice, and that 6-keto PGF1α (a stable metabolite of PGI2) was not detected in PGIS KO mice. Furthermore, we made bone marrow (BM) chimera and found that transplantation of WT mouse-derived BM cells restored the impaired CHS response in mPGES-1 KO mice but did not restore the response in PGIS KO mice. These results indicated that mPGES-1 in BM-derived cells and PGIS in non-BM-derived cells might play critical roles in DNFB-induced CHS. mPGES-1-derived PGE2 and PGIS-derived PGI2 might coordinately promote acquired cutaneous immune responses.

Involvement of prostacyclin synthase in high-fat-diet-induced obesity.

Prostacyclin (PGI2) synthase (PGIS) functions downstream of inducible cyclooxygenase COX-2 in the PGI2 biosynthetic pathway. Although COX-2 and PGI2 receptor (IP) are known to be involved in adipogenesis and obesity, the involvement of PGIS has not been fully elucidated. In this study, we examined the role of PGIS in adiposity by using PGIS-deficient mice. Although PGIS deficiency did not affect in vitro adipocyte differentiation, when fed a high-fat diet (HFD), PGIS knockout (KO) mice showed reductions in both body weight gain and epididymal fat mass relative to wild-type (WT) mice. PGIS deficiency might reduce HFD-induced obesity by suppressing PGI2 production. We further found that additional gene deletion of microsomal prostaglandin (PG) E synthase-1 (mPGES-1), one of the other PG terminal synthases that also functions downstream of COX-2, emphasized the metabolic phenotypes of PGIS-deficient mice. More marked reduction in obesity and improved insulin resistance were observed in PGIS/mPGES-1 double KO (DKO) mice. Since an additive increase in PGF2α level in epididymal fat was observed in DKO mice, mPGES-1 deficiency might affect adiposity by enhancing the production of PGF2α. Our immunohistochemical analysis further revealed that in adipose tissues, PGIS was expressed in vascular and stromal cells but not in adipocytes. These results suggested that PGI2 produced from PGIS-expressed stromal tissues might enhance HFD-induced obesity by acting on IP expressed in adipocytes. The balance of expressions of PG terminal synthases and the subsequent production of prostanoids might be critical for adiposity.

Gene Deletion of Calcium-Independent Phospholipase A2γ (iPLA2γ) Suppresses Adipogenic Differentiation of Mouse Embryonic Fibroblasts.

Adipogenic differentiation is a complex process by which fibroblast-like undifferentiated cells are converted into cells that accumulate lipid droplets. We here investigated the effect of gene deletion of calcium-independent phospholipase A2γ (iPLA2γ), a membrane-bound PLA2 enzyme, on adipogenic differentiation in mice. Since iPLA2γ knockout (KO) mice showed reduced fat volume and weight, we prepared mouse embryonic fibroblasts (MEF) from wild-type (WT) and iPLA2γ KO mice and examined the effect of iPLA2γ deletion on in vitro adipogenic differentiation. iPLA2γ increased during adipogenic differentiation in WT mouse-derived MEFs, and the differentiation was partially abolished in iPLA2γ KO-derived MEFs. In KO-derived MEFs, the inductions of peroxisome proliferator activator receptor γ (PPARγ) and CAAT/enhancer-binding protein α (C/EBPα) were also reduced during adipogenic differentiation, and the reductions in PPARγ and C/EBPα expressions and the defect in adipogenesis were restored by treatment with troglitazone, a PPARγ ligand. These results indicate that iPLA2γ might play a critical role in adipogenic differentiation by regulating PPARγ expression.

Ferroptosis driven by radical oxidation of n-6 polyunsaturated fatty acids mediates acetaminophen-induced acute liver failure.

Acetaminophen (APAP) overdose is a common cause of drug-induced acute liver failure. Although hepatocyte cell death is considered to be the critical event in APAP-induced hepatotoxicity, the underlying mechanism remains unclear. Ferroptosis is a newly discovered type of cell death that is caused by a loss of cellular redox homeostasis. As glutathione (GSH) depletion triggers APAP-induced hepatotoxicity, we investigated the role of ferroptosis in a murine model of APAP-induced acute liver failure. APAP-induced hepatotoxicity (evaluated in terms of ALT, AST, and the histopathological score), lipid peroxidation (4-HNE and MDA), and upregulation of the ferroptosis maker PTGS2 mRNA were markedly prevented by the ferroptosis-specific inhibitor ferrostatin-1 (Fer-1). Fer-1 treatment also completely prevented mortality induced by high-dose APAP. Similarly, APAP-induced hepatotoxicity and lipid peroxidation were prevented by the iron chelator deferoxamine. Using mass spectrometry, we found that lipid peroxides derived from n-6 fatty acids, mainly arachidonic acid, were elevated by APAP, and that auto-oxidation is the predominant mechanism of APAP-derived lipid oxidation. APAP-induced hepatotoxicity was also prevented by genetic inhibition of acyl-CoA synthetase long-chain family member 4 or α-tocopherol supplementation. We found that ferroptosis is responsible for APAP-induced hepatocyte cell death. Our findings provide new insights into the mechanism of APAP-induced hepatotoxicity and suggest that ferroptosis is a potential therapeutic target for APAP-induced acute liver failure.

Long-chain acyl-CoA synthetase 4 participates in the formation of highly unsaturated fatty acid-containing phospholipids in murine macrophages.

Long-chain acyl-coenzyme A synthetases (ACSLs) are a family of enzymes that convert free long-chain fatty acids into their acyl-coenzyme A (CoA) forms. ACSL4, belonging to the ACSL family, shows a preferential use of arachidonic acid (AA) as its substrate and plays a role in the remodeling of AA-containing phospholipids by incorporating free AA. However, little is known about the roles of ACSL4 in inflammatory responses. Here, we assessed the roles of ACSL4 on the effector functions of bone marrow-derived macrophages (BMDMs) obtained from mice lacking ACSL4. Liquid chromatography-tandem mass spectrometry analysis revealed that various highly unsaturated fatty acid (HUFA)-derived fatty acyl-CoA species were markedly decreased in the BMDMs obtained from ACSL4-deficient mice compared with those in the BMDMs obtained from wild-type mice. BMDMs from ACSL4-deficient mice also showed a reduced incorporation of HUFA into phosphatidylcholines. The stimulation of BMDMs with lipopolysaccharide (LPS) elicited the release of prostaglandins (PGs), such as PGE2, PGD2 and PGF2α, and the production of these mediators was significantly enhanced by ACSL4 deficiency. In contrast, neither the LPS-induced release of cytokines, such as IL-6 and IL-10, nor the endocytosis of zymosan or dextran was affected by ACSL4 deficiency. These results suggest that ACSL4 has a crucial role in the maintenance of HUFA composition of certain phospholipid species and in the incorporation of free AA into the phospholipids in LPS-stimulated macrophages. ACSL4 dysfunction may facilitate inflammatory responses by an enhanced eicosanoid storm.

Role of acyl-CoA synthetase ACSL4 in arachidonic acid metabolism.

The activation of long-chain free fatty acids is the first step reaction of their usage in the cells and tissues, which are catalyzed by a family of enzymes called acyl-coenzyme A synthetases long-chain isoform (ACSL). The five ACSL enzymes identified in mammals are thought to have specific and differing functions. Among them, ACSL4 is a unique isozyme that preferentially catalyzes several polyunsaturated fatty acids (PUFAs) such as arachidonic acid (AA), and ACSL4 is thought to be an important isozyme for PUFA metabolism. Recent studies revealed that ACSL4 is involved in biological responses including inflammation, steroidogenesis, cell death, female fertility, and cancer. ACSL4 and its substrate PUFAs are thus likely to contribute to these responses. However, the roles of ACSL4 in PUFA metabolism are not fully understood. In this review, we describe the recent progress in ACSL4 research including the involvement of this enzyme in AA metabolism.

Analysis on the Substrate Specificity of Recombinant Human Acyl-CoA Synthetase ACSL4 Variants.

Acyl-CoA synthetase long-chain family members (ACSLs) are a family of enzymes that convert long-chain free fatty acids into their acyl-CoAs. ACSL4 is an ACSL isozyme with a strong preference for arachidonic acid (AA) and has been hypothesized to modulate the metabolic fates of AA. There are two ACSL4 splice variants: ACSL4V1, which is the more abundant transcript, and ACSL4V2, which is believed to be restricted to the brain. In the present study, we expressed recombinant human ACSL4V1 and V2 in Spodoptera frugiperda 9 (Sf9) cells using the baculovirus expression system and then partially purified both variants by cobalt affinity column chromatography. We then established a novel ACSL assay system with LC-MS/MS, which is highly sensitive and applicable to various kinds of fatty acids, and used it to investigate the substrate specificity of recombinant human ACSL4V1 and V2. The results showed that both ACSL4 variants preferred various kinds of highly unsaturated fatty acids (HUFAs), including docosahexaenoic acid (DHA), adrenic acid (docosatetraenoic acid) and eicosapentaenoic acid (EPA), as well as AA as a substrate. Moreover, our kinetic studies revealed that the two variants had similar relative affinities for AA, EPA and DHA but different reaction rates for each HUFA. These results confirmed the importance of both of ACSL4 variants in the maintenance of membrane phospholipids bearing HUFAs. Structural analysis of these variants might reveal the molecular mechanism by which they maintain membrane phospholipids bearing HUFAs.

Calcium-independent phospholipase A2γ (iPLA2γ) and its roles in cellular functions and diseases.

Calcium-independent phospholipase A2γ (iPLA2γ)/patatin-like phospholipase domain-containing lipase 8 (PNPLA8) is one of the iPLA2 enzymes, which do not require Ca2+ ion for their activity. iPLA2γ is a membrane-bound enzyme with unique features, including the utilization of four distinct translation initiation sites and the presence of mitochondrial and peroxisomal localization signals. This enzyme is preferentially distributed in the mitochondria and peroxisomes and is thought to be responsible for the maintenance of lipid homeostasis in these organelles. Thus, both the overexpression and the deletion of iPLA2γ in vivo caused mitochondrial abnormalities and dysfunction. Roles of iPLA2γ in lipid mediator production and cytoprotection against oxidative stress have also been suggested by in vitro and in vivo studies. The dysregulation of iPLA2γ can therefore be a critical factor in the development of many diseases, including metabolic diseases and cancer. In this review, we provide an overview of the biochemical properties of iPLA2γ and then summarize the current understanding of the in vivo roles of iPLA2γ revealed by knockout mouse studies.

The group VIA calcium-independent phospholipase A2 and NFATc4 pathway mediates IL-1ß-induced expression of chemokines CCL2 and CXCL10 in rat fibroblasts.

Chemokines are secreted proteins that regulate cell migration and are involved in inflammatory and immune responses. Here, we sought to define the functional crosstalk between the lipid signaling and chemokine signaling. We obtained evidence that the induction of some chemokines is regulated by group VIA calcium-independent phospholipase A2 ß (iPLA2 ß) in IL-1ß-stimulated rat fibroblastic 3Y1 cells. Treatment of 3Y1 cells with IL-1ß elicited an increased release of chemotactic factor(s) for monocytic THP-1 cells into culture medium in a time-dependent manner. Inhibitor studies revealed that an intracellular PLA2 inhibitor, arachidonoyl trifluoromethyl ketone (AACOCF3 ), but not the cyclooxygenase inhibitor indomethacin, attenuated the release of chemotactic factor(s). The chemotactic activity was inactivated by treatment with either heat or proteinase K, suggesting this chemotactic factor(s) is a proteinaceous factor(s). We purified the chemotactic factor(s) from the conditioned medium of IL-1ß-stimulated 3Y1 cells using a heparin column and identified several chemokines, including CCL2 and CXCL10. The inducible expressions of CCL2 and CXCL10 were significantly attenuated by pretreatment with AACOCF3 . Gene silencing using siRNA revealed that the inductions of CCL2 and CXCL10 were attenuated by iPLA2 ß knockdown. Additionally, the transcriptional activation of nuclear factor of activated T-cell proteins (NFATs), but not nuclear factor-κB, by IL-1ß stimulation was markedly attenuated by the iPLA2 inhibitor bromoenol lactone, and NFATc4 knockdown markedly attenuated the IL-1ß-induced expression of both CCL2 and CXCL10. Collectively, these results indicated that iPLA2 ß plays roles in IL-1ß-induced chemokine expression, in part via NFATc4 signaling.

Prostaglandin terminal synthases as novel therapeutic targets.

Non-steroidal anti-inflammatory drugs (NSAIDs) exert their anti-inflammatory and anti-tumor effects by reducing prostaglandin (PG) production via the inhibition of cyclooxygenase (COX). However, the gastrointestinal, renal and cardiovascular side effects associated with the pharmacological inhibition of the COX enzymes have focused renewed attention onto other potential targets for NSAIDs. PGH2, a COX metabolite, is converted to each PG species by species-specific PG terminal synthases. Because of their potential for more selective modulation of PG production, PG terminal synthases are now being investigated as a novel target for NSAIDs. In this review, I summarize the current understanding of PG terminal synthases, with a focus on microsomal PGE synthase-1 (mPGES-1) and PGI synthase (PGIS). mPGES-1 and PGIS cooperatively exacerbate inflammatory reactions but have opposing effects on carcinogenesis. mPGES-1 and PGIS are expected to be attractive alternatives to COX as therapeutic targets for several diseases, including inflammatory diseases and cancer.

Cytosolic Prostaglandin E Synthase Is Involved in c-Fos Expression in Rat Fibroblastic 3Y1 Cells.

Cytosolic prostaglandin (PG) E synthase (cPGES/p23) plays a role in the biosynthesis of PGE2 and in the molecular chaperone machinery. Studies of knockout mice lacking cPGES/p23 have demonstrated that cPGES/p23 is essential in fetal mouse development. A cDNA microarray analysis revealed that a lack of cPGES/p23 decreases the expression of some immediate early genes, such as c-fos and activating transcription factor 3 (ATF3). Here we report the involvement of cPGES/p23 in c-Fos expression. A stable knockdown of cPGES/p23 in cultured fibroblasts not only reduced serum-induced c-Fos expression, but also decreased the phosphorylation of extracellular signal regulated kinase (ERK). These results suggest that cPGES/p23 is involved in the activation of ERK to promote c-Fos expression.