Regulation of Arachidonic Acid Release and Prostaglandin E2Production in Thymic Epithelial Cells by ATPγS and Transforming Growth Factor-α

The arachidonic acid metabolites produced by thymic epithelial cells play a pivotal role in thymocyte development. We have discovered that ATP and TGF-α regulate the arachidonic acid metabolism in TEA3A1 rat thymic epithelial cells by activating phospholipase A2enzymatic activity. Our present study demonstrates that ATP and its nonhydrolyzable analog ATPγS stimulate both prostaglandin E2production and Ca2+influx in TEA3A1 cells. The stimulation of prostaglandin E2production and Ca2+influx by ATP is inhibited by pertussis toxin treatment, indicating that ATP mediates its effect by binding to a G-protein-coupled purinergic receptor. Treatment of cells with ATPγS and transforming growth factor-α results in a synergistic activation of phospholipase A2and stimulation of prostaglandin E2production. Results from experiments using an inhibitor of receptor-mediated Ca2+influx indicate that the synergistic stimulation of prostaglandin E2production by ATPγS and transforming growth factor-α requires ATPγS-mediated Ca2+influx. The inhibitor of tyrosine kinase genistein also blocked both ATPγS- and ATPγS plus transforming growth factor-α-mediated stimulation of prostaglandin E2production, indicating that the activation of phospholipase A2may involve a protein tyrosine phosphorylation step.