RT Journal Article SR Electronic T1 Mechanisms of Prostaglandin E2 Release by Intact Cells Expressing Cyclooxygenase-2: Evidence for a ‘Two-Component’ Model JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 1101 OP 1106 VO 288 IS 3 A1 Michael A. Saunders A1 Maria G. Belvisi A1 Guiseppe Cirino A1 P. J. Barnes A1 Timothy D. Warner A1 Jane A. Mitchell YR 1999 UL http://jpet.aspetjournals.org/content/288/3/1101.abstract AB Prostaglandin (PG) release in cells expressing constitutive cyclooxygenase-1 is known to be regulated by liberation of arachidonic acid by phospholipase A2 followed by metabolism by cyclooxygenase. However, the relative contribution of phospholipase A2 to the release of PGs in cells expressing cyclooxygenase-2 is not clear. We addressed this question by using radioimmunoassay to measure PGE2 release by human cells (A549) induced to express cyclooxygenase-2 (measured by Western blot analysis) by interleukin-1β. Cells were either unstimulated or stimulated with agents known to activate phospholipase A2(bradykinin, Des-Arg10-kallidin, or the calcium ionophore A23187) or treated with exogenous arachidonic acid. When cells were treated to express cyclooxygenase-2, the levels of PGE2released over 15 min were undetectable; however, in the same cells stimulated with bradykinin, A23187, or arachidonic acid, large amounts of prostanoid were produced. Using selective inhibitors/antagonists, we found that the effects of bradykinin were mediated by B2 receptor activation and that prostanoid release was due to cyclooxygenase-2, and not cyclooxygenase-1, activity. In addition, we show that the release of PGE2 stimulated by either bradykinin, A23187, or arachidonic acid was inhibited by the phospholipase A2 inhibitor arachidonate trifluoromethyl ketone. Hence, we have demonstrated that PGE2 is released by two components: induction of cyclooxygenase-2 and supply of substrate, probably via activation of phospholipase A2. This is illustrated in A549 cells by a clear synergy between the cytokine interleukin-1β and the kinin bradykinin. The American Society for Pharmacology and Experimental Therapeutics