Coupling between cyclooxygenase, terminal prostanoid synthase, and phospholipase A(2)

We have recently shown that two distinct prostaglandin (PG) E-2 synthases s how preferential functional coupling with upstream cyclooxygenase (COX)-1 a nd COX-2 in PGE(2) biosynthesis. To investigate whether other lineage-speci fic PG synthases also show preferential coupling with either COX isozyme, w e introduced these enzymes alone or in combination into 293 cells to recons titute their functional interrelationship. As did the membrane-bound PGE2 s ynthase, the perinuclear enzymes thromboxane synthase and PGI(2) synthase g enerated their respective products via COX-2 in preference to COX-1 in both the A23187-induced immediate and interleukin-1-induced delayed responses. Hematopoietic PGD(2) synthase preferentially used COX-1 and COX-2 in the A2 3187-induced immediate and interleukin-1-induced delayed PGD(2)-biosyntheti c responses, respectively. This enzyme underwent stimulus-dependent translo cation from the cytosol to perinuclear compartments, where COX-1 or COX-2 e xists. COX selectivity of these lineage-specific PG synthases was also sign ificantly affected by the concentrations of arachidonate, which was added e xogenously to the cells or supplied endogenously by the action of cytosolic or secretory phospholipase A(2). Collectively, the efficiency of coupling between COXs and specific PG synthases may be crucially influenced by their spatial and temporal compartmentalization and by the amount of arachidonat e supplied by PLA(2)s at a moment when PG production takes place.