Phospholipid metabolite production in human urothelial cells after protease-activated receptor cleavage

Our laboratory demonstrated previously that stimulation of protease-activated receptors (PARs) on the human urothelial carcinoma cell line RT4 results in activation of a calcium-independent phospholipase A(2) (iPLA(2)), leading to arachidonic acid and PGE(2) release. In this study, we have examined PAR activation in normal human urothelial cells (HUR) leading to the production of inflammatory or cytoprotective phospholipid metabolites. The presence of both PAR-1 and PAR-2 on HUR was confirmed by immunoblotting. Stimulation of PAR-1 with thrombin or PAR-2 by tryptase leads to activation of a membrane-associated iPLA(2) and the production of platelet-activating factor, arachidonic acid, and PGE(2). These responses were all blocked by pretreatment with the iPLA(2)-selective inhibitor bromoenol lactone. Thus stimulation of PAR-1 or PAR-2 on HUR leads to iPLA(2)-catalyzed phospholipid hydrolysis, resulting in the production of metabolites that may mediate inflammation or provide cytoprotection to the bladder.