Prostaglandin H Synthase-2-catalyzed Oxygenation of 2-Arachidonoylglycerol Is More Sensitive to Peroxide Tone than Oxygenation of Arachidonic Acid
Vanderbilt University School of Medicine, United States. Journal of Biological Chemistry
(Impact Factor: 4.57).
09/2012; 287(44). DOI: 10.1074/jbc.M112.381202
The endocannabinoid, 2-arachidonoylglycerol (2-AG), is a selective substrate for the inducible isoform of prostaglandin H synthase (PGHS), PGHS-2. Its turnover leads to the formation of glyceryl esters of prostaglandins (PG-Gs), a subset of which elicit agonism at unique, as yet unidentified, receptors. The kcat/Kms for oxygenation of arachidonic acid (AA) and 2-AG by PGHS-2 are very similar, but the sensitivities of the two substrates to peroxide-dependent activation have not been compared. 15-Hydroperoxy derivatives of AA and 2-AG were found to be comparable in their ability to serve as substrates for the peroxidase activities of PGHS-2, PGHS-1, and glutathione peroxidase (GPx). They also were comparable in the activation of AA oxygenation by cyanide-inhibited PGHS-2. However, oxygenation of 2-AG was significantly suppressed relative to AA by the presence of GPx and GSH. Furthermore, 2-AG oxygenation by peroxidase-deficient H388YmPGHS-2 was much less efficient than AA oxygenation. Wild-type rates of 2-AG oxygenation were restored by treatment of H388YmPGHS-2 with hydroperoxide derivatives of AA or 2-AG. RNAi silencing of phospholipid hydroperoxide-specific GPx (GPx4) in NIH3T3 cells led to increases in cellular peroxidation and in the levels of the isoprostane product, 8-epi-PGF2α. GPx4 silencing led to two- to four-fold increases in PG-G formation but no change in PG formation. Thus cellular peroxide tone may be an important determinant of the extent of endocannabinoid oxygenation by PGHS-2.
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