Current evidence suggests that two forms of prostaglandin (PG) E synthase (PGES), cytosolic PGES and membrane-bound PGES (mPGES) -1, preferentially lie downstream of cyclooxygenase (COX) -1 and -2, respectively, in the PGE 2 biosynthetic pathway. In this study, we examined the expression and functional aspects of the third PGES enzyme, mPGES-2, in mammalian cells and tissues. mPGES-2 was synthesized as a Golgi membrane-associated protein, and spontaneous cleavage of the N-terminal hydrophobic domain led to the formation of a truncated mature protein that was distributed in the cytosol with a trend to be enriched in the perinuclear region. In several cell lines, mPGES-2 promoted PGE 2 production via both COX-1 and COX-2 in the immediate and delayed responses with modest COX-2 preference. In contrast to the marked inducibility of mPGES-1, mPGES-2 was constitutively expressed in various cells and tissues and was not increased appreciably during tissue inflammation or damage. Interestingly, a considerable elevation of mPGES-2 expression was observed in human colorectal cancer. Collectively, mPGES-2 is a unique PGES that can be coupled with both COXs and may play a role in the production of the PGE 2 involved in both tissue homeostasis and disease.Biosynthesis of prostaglandin (PG) 1 E 2 , which is produced by a variety of cells and tissues and exhibits diverse bioactivities, is mediated by three enzymatic reactions involving phospholipase A 2 (PLA 2 ), cyclooxygenase (COX), and PGE synthase (PGES). In this biosynthetic pathway, arachidonic acid (AA) released from membrane phospholipids by cytosolic or secretory PLA 2 s is converted to PGH 2 by COX-1 or COX-2 and is then isomerized to PGE 2 by terminal PGES enzymes.The constitutive COX-1 mainly promotes immediate PG production elicited by agonists promptly mobilizing intracellular Ca 2ϩ , a situation in which a burst release of AA occurs (1-5).The inducible COX-2 is essential for delayed PG generation induced by proinflammatory stimuli, during which AA is gradually supplied over long periods, and also promotes immediate PG production if it already exists in cells primed by particular stimuli (1-5). Current studies employing isozyme-specific inhibitors and knockout mice have revealed that the two COXs play distinct roles in vivo (6 -10), and segregated utilization of these enzymes at the cellular level has been explained not only by their distinct expression profiles but also by subtle differences in their AA requirement, hydroperoxide sensitivity, and subcellular localization (4, 11-13). In addition, selective coupling with various terminal PG synthases has also been shown to influence crucially the utilization of the two COX isoforms during the different phases of cell activation (14 -16). PGES enzymes, which lie downstream of COXs, occur in multiple forms in mammalian cells (1). Among them, a perinuclear membrane-bound form of PGES belonging to the MAPEG (for membrane-associated proteins involved in eicosanoid and glutathione metabolism) family, which we herein cal...

We examined the in vivo role of membrane-bound prostaglandin E synthase (mPGES)-1, a terminal enzyme in the PGE 2 -biosynthetic pathway, using mPGES-1 knockout (KO) mice. Comparison of PGES activity in the membrane fraction of tissues from mPGES-1 KO and wild-type (WT) mice indicated that mPGES-1 accounted for the majority of lipopolysaccharide (LPS)-inducible PGES in WT mice. LPS-stimulated production of PGE 2 , but not other PGs, was impaired markedly in mPGES-1-null macrophages, although a low level of cyclooxygenase-2-dependent PGE 2 production still remained. Pain nociception, as assessed by the acetic acid writhing response, was reduced significantly in KO mice relative to WT mice. This phenotype was particularly evident when these mice were primed with LPS, where the stretching behavior and the peritoneal PGE 2 level of KO mice were far less than those of WT mice. Formation of inflammatory granulation tissue and attendant angiogenesis in the dorsum induced by subcutaneous implantation of a cotton thread were reduced significantly in KO mice compared with WT mice. Moreover, collagen antibody-induced arthritis, a model for human rheumatoid arthritis, was milder in KO mice than in WT mice. Collectively, our present results provide unequivocal evidence that mPGES-1 contributes to the formation of PGE 2 involved in pain hypersensitivity and inflammation.

PLA2G2D ameliorates skin inflammation through mobilizing pro-resolving lipid mediators.

Microsomal prostaglandin E 2 synthase-1 (mPGES-1) is a stimulus-inducible enzyme that functions downstream of cyclooxygenase (COX)-2 in the PGE 2 -biosynthetic pathway. Given the accumulating evidence that COX-2-derived PGE 2 participates in the development of various tumors, including colorectal cancer, we herein examined the potential involvement of mPGES-1 in tumorigenesis. Immunohistochemical analyses demonstrated the expression of both COX-2 and mPGES-1 in human colon cancer tissues. HCA-7, a human colorectal adenocarcinoma cell line that displays COX-2-and PGE 2 -dependent proliferation, expressed both COX-2 and mPGES-1 constitutively. Treatment of HCA-7 cells with an mPGES-1 inhibitor or antisense oligonucleotide attenuated, whereas overexpression of mPGES-1 accelerated, PGE 2 production and cell proliferation. Moreover, cotransfection of COX-2 and mPGES-1 into HEK293 cells resulted in cellular transformation manifested by colony formation in soft agar culture and tumor formation when implanted subcutaneously into nude mice. cDNA array analyses revealed that this mPGES-1-directed cellular transformation was accompanied by changes in the expression of a variety of genes related to proliferation, morphology, adhesion, and the cell cycle. These results collectively suggest that aberrant expression of mPGES-1 in combination with COX-2 can contribute to tumorigenesis.Clinical, genetic, and biochemical evidence has suggested that prostaglandin (PG) 1 E 2 produced via the cyclooxygenase (COX)-2-dependent pathway plays a crucial role in the development of colorectal cancer and possibly other cancers (1). Non-steroidal anti-inflammatory drugs, which inhibit COX-2, reduce the incidence of colorectal cancer (2-4). The major prostanoid produced by several types of cancer is PGE 2 , which is produced by three biosynthetic reactions involving phospholipase A 2 (PLA 2 ), COX, and terminal PGE 2 synthase (PGES). PGE 2 promotes survival and motility of colon cancer cells in vitro and promotes tumorigenesis and angiogenesis in vivo (5-7). High levels of constitutive expression of COX-2 have been found in various cancer cells and tissues (8,9), and studies employing overexpression, antisense suppression, and specific inhibitors of COX-2 have demonstrated that COX-2 contributes to the progression of several types of cancer (10 -12).More direct evidence for the role of COX-2 and its product PGE 2 in colorectal tumorigenesis has been provided by gene targeting studies. Gene disruption of either COX-2 (13) or the PGE receptor EP2 (14) results in reduction of the number and size of intestinal polyps in Apc mutant mice, a model for human familial adenomatous polyposis. In another model, disruption of the genes for the PGE receptors EP1 (15) or EP4 (16) suppresses the development of colorectal cancer induced by carcinogen. Moreover, gene knockout of cytosolic PLA 2 ␣ (cPLA 2 ␣), which supplies the substrate arachidonic acid to COX-2, also leads to reduced polyposis in Apc mutant mice (17,18).PGES catalyzes the conversion of PGH 2 ...

No abstract