Cyclooxygenase-2 induction by bradykinin in human pulmonary artery smooth muscle cells is mediated by the cyclic AMP response element through a novel autocrine loop involving endogenous prostaglandin E2, E-prostanoid 2 (EP2), and EP4 receptors

Abstract

Bradykinin (BK) is an important mediator in several inflammatory and vascular diseases that acts in part via induction of cyclooxygenase-2 (COX-2). The mechanisms involved in BK-mediated COX-2 induction are unclear. Here we characterized the transcriptional mechanisms involved in human pulmonary artery smooth muscle cells. BK stimulated the activity of a transiently transfected 966-bp (-917 to + 49) COX-2 promoter luciferase reporter construct. There was no reduction in BK-induced luciferase activity in cells transfected with COX-2 promoter constructs of 674, 407, 239, and 135 bp or constructs with mutated CCAAT/enhancer-binding protein- or NF-kappaB-binding sites. In contrast luciferase activity was reduced in cells transfected with a 407-bp COX-2 promoter fragment containing a mutated cAMP response element (CRE)-binding site, suggesting that the CRE binding site is critical. Electrophoretic mobility shift assays using oligonucleotides specific for the CRE-binding region of the COX-2 promoter and consensus oligonucleotides showed strong specific binding. Furthermore BK increased consensus cAMP-responsive luciferase reporter (p6CRE/luc)-mediated luciferase expression. CRE activation occurred by BK inducing cytosolic phospholipase A2-mediated arachidonic acid release and rapid prostaglandin E2 (PGE2) production, thereby increasing cAMP. Indomethacin inhibited BK-induced PGE2 production, cAMP accumulation, and CRE/luc reporter and COX-2 promoter luciferase activity. Exogenous PGE2 and EP2 (ONO-AE1 259) and EP4 (ONO-AE1 329) PGE2 receptor agonists mimicked the effect of BK. Collectively these studies indicate that COX-2 induction by BK in human pulmonary artery smooth muscle cells is mediated by the CRE through a novel autocrine loop involving endogenous PGE2.