DEPLETION OF HUMAN MONOCYTE 85-KDA PHOSPHOLIPASE A(2) DOES NOT ALTER LEUKOTRIENE FORMATION

Human monocytes possess several acylhydrolase activities and are capab le of producing both prostanoids (PG) and leukotriene (LT) products up on acute stimulation with calcium ionophore, A23187 or phagocytosis of zymosan particles. The cytosolic 85-kDa phospholipase (PLA) A(2) co e xists with the 14-kDa PLA(2) in the human monocyte, but their respecti ve roles in LT production are not well understood, Reduction in 85-kDa PLA(2) cellular protein levels by initiation site-directed antisense (SK 7111) or exposure to the 85-kDa PLA(2) inhibitor, arachidonyl trif luoromethyl ketone (AACOCF(3)), prevented A23187 or zymosan-stimulated monocyte prostanoid formation. In contrast, neither treatment altered stimulated LTC(4) production. This confirmed the important role of th e 85-kDa PLA(2) in prostanoid formation but suggests that it has less of a role in LT biosynthesis, Alternatively, treatment of monocytes wi th the selective, active site directed 14-kDa PLA(2) inhibitor, SB 203 347, prior to stimulation had no effect on prostanoid formation at con centrations that totally inhibited LT formation. Addition of 20 mu M e xogenous arachidonic acid to monocytes exposed to SK 7111 or SB 203347 did not alter A23187-induced PGE(2) or LTC(4) generation, respectivel y, indicating that these agents had no effect on downstream arachidoni c acid-metabolizing enzymes in this setting, Taken together, these res ults provide evidence that the 85-kDa PLA(2) may play a more significa nt role in the formation of PG than LT. Further, utilization of SB 203 347 provides intriguing data to form the hypothesis that a non-85-kDa PLA(2) sn-2 acyl hydrolase, possibly the 14-kDa PLA(2), may provide su bstrate for LT formation.