Eicosanoid formation by a cytochrome P450 isoform expressed in the pharynx of Caenorhabditis elegans
Résumé
Caenorhabditis elegans harbors several cytochrome P450 (CYP) genes that are homologous to mammalian CYP isoforms important to the production of physiologically active arachidonic acid (AA) metabolites. We tested the hypothesis that mammals and C. elegans may share similar basic mechanisms of CYP-dependent eicosanoid formation and action. We focused on CYP33E2, an isoform related to the human AA-epoxygenases CYP2C8 and CYP2J2. Co-expression of CYP33E2 with the human NADPH-CYP-reductase in insect cells resulted in the reconstitution of an active microsomal monooxygenase system that metabolized eicosapentaenoic acid (EPA) and, with lower activity, also AA to specific sets of regioisomeric epoxy- and hydroxy-derivatives. Main products included 17,18-epoxyeicosatetraenoic acid from EPA and 19-hydroxyeicosatetraenoic acid from AA. Using worms carrying a cyp33E2 promoter::GFP-reporter construct, we found that CYP33E2 is exclusively expressed in the pharynx, where it is predominantly localized in the marginal cells. RNAi-mediated CYP33E2 expression silencing as well as treatments with inhibitors of mammalian AA-metabolizing CYP enzymes, significantly reduced the pharyngeal pumping frequency of adult worms. These results demonstrate that EPA and AA are efficient CYP33E2 substrates and suggest that CYP-eicosanoids, influencing in mammals the contractility of cardiomyocytes and vascular smooth muscle cells, may function in C. elegans as regulators of the pharyngeal pumping activity.
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