Stimulation of prostaglandin synthesis in WI-38 human lung fibroblasts following inhibition of phospholipid acylation by p-hydroxymercuribenzoate

Abstract

The release of arachidonic acid and its metabolites, prostaglandin E 2 and thromboxane A 2, from WI-38 human lung fibroblasts was modulated by p-hydroxymercuribenzoate. Exposure to the inhibitor resulted in a dose-dependent decrease in [1- 14C]arachidonic acid uptake and incorporation into phospholipids and neutral lipid pools. Activities of lung fibroblast arachidonyl-CoA synthetase and lysolecithin acyltransferase were inhibited by 100 μM p-hydroxymercuribenzoate. [ 14C]Arachidonic acid labelled fibroblasts exhibited an increased release of [ 14C]arachidonate and [ 14C]prostaglandin E 2 of 54% and 112%, respectively, when exposed to 100 μM of inhibitor. The stimulatory effects of 8.0 μM Δ 1-tetrahydrocannabinol on arachidonate release and prostaglandin E synthesis (Burstein S., Hunter S.A., Sedor C. and Shulman S. (1982) Biochem. Pharmacol. 31, 2361–2365) were modified by the inclusion of inhibiting agent, resulting in a 608% stimulation in arachidonic acid release, while prostaglandin E 2 and thromboxane A 2 synthesis increased 894% and 390%, respectively, over levels obtained by untreated cells. The levels of arachidonate metabolites were altered by inhibitor when compared to cells treated with cannabinoid alone. No significant inhibition by Δ 1-tetrahydrocannabinol was found on arachidonic uptake in these cells. In unlabelled studies, p-hydroxy-mercuribenzoate resulted in a profound, dose-dependent stimulation of prostaglandin E synthesis of 1490% at 150 μM inhibitor concentration. These results provide evidence that free arachidonate is reincorporated via acylation, thereby implicating this pathway as a possible control mechanism for the synthesis of arachidonic acid metabolites.