Involvement of phospholipid hydroperoxide glutathione peroxidase in the modulation of prostaglandin D2 synthesis

Antigenic cross-linking of the high affinity IgE receptors on mast cells induced the synthesis of prostaglandin D-2 (PGD(2)). The production of PGD(2) in L9 cells, which overexpressed non-mitochondrial phospholipid glutathione peroxidase (PHGPx), was only one-third that in the control line of cells (S1 cells). The reduction in the formation of PGD, in L9 cells was reversed upon inhibition of PHGPx activity by buthionine sulfoximine. Experiments with inhibitors demonstrated that prostaglandin H synthase-a (PGHS-2) was the isozyme responsible for the production of PGD, upon cross-linking of IgE receptors. The conversion of radiolabeled arachidonic acid to prostaglandin H, (PGH,) was strongly inhibited in L9 cells, whereas the rate of conversion of PGH, to PGD, was the same in L9 cells and S1 cells, indicating that PGHS was inactivated in L9 cells. The PGHS activity in L9 cells was about half that in S1 cells. However, PGHS activity in L9 cells increased to the level in S1 cells upon the addition of the hydroperoxide 15-hydroperoxyeicosatetraenoic acid or of 3-chloroperoxy-benzoic acid. These results suggest that non-mitochondrial PHGPx might be involved in the inactivation of PGHS-2 in nucleus and endoplasmic reticulum via reductions in levels of the hydroperoxides that are required for full activation of PGHS. Therefore, it appears that PHGPx might function as a modulator of the production of prostanoids, in addition to its role as an antioxidant enzyme.