Prostaglandin E2 inhibits the phospholipase D pathway stimulated by formyl-methionyl-leucyl-phenylalanine in human neutrophils.: Involvement of EP2 receptors and phosphatidylinositol 3-kinase γ

Prostaglandin E-2 (PGE(2)), originally discovered as a pro-inflammatory mediator, also inhibits several chemoattractant-elicited neutrophil functions, including adhesion, secretion of cytotoxic enzymes, production of superoxide anions, and chemotaxis. In this study, we have examined the effects of PGE(2) and prostaglandin E (EP) receptor-selective agonists/antagonists on several steps of the formyl-methionyl-leucyl-phenylalanine ( fMLP)induced phospholipase D (PLD) activation pathway in human neutrophils to elucidate the PGE(2) inhibitory mechanism. PGE(2) and EP2 receptor agonists inhibited the stimulation of the activity of PLD induced by fMLP in a concentration-dependent manner. The fMLP-stimulated translocation to membranes of protein kinase C alpha, Rho, and Arf GTPases was diminished in the presence of PGE(2) or EP2 agonists. Moreover, PGE(2) and EP2 agonists decreased the activation of phosphatidylinositol 3-kinase gamma (PI3Kgamma) and Tec kinases as well as the tyrosine phosphorylation of proteins stimulated by fMLP. These data provide strong evidence that 1) the inhibitory effects of PGE(2) on the fMLP-induced PLD activation pathway were mediated via EP2 receptors and that 2) the suppression of PI3Kgamma activity was the crucial step in the EP2-mediated inhibition of the fMLP-induced signaling cascade.