Coupling between Cyclooxygenase, Terminal Prostanoid Synthase, and Phospholipase A2 *

We have recently shown that two distinct prostaglandin (PG) E2 synthases show preferential functional coupling with upstream cyclooxygenase (COX)-1 and COX-2 in PGE2 biosynthesis. To investigate whether other lineage-specific PG synthases also show preferential coupling with either COX isozyme, we introduced these enzymes alone or in combination into 293 cells to reconstitute their functional interrelationship. As did the membrane-bound PGE2 synthase, the perinuclear enzymes thromboxane synthase and PGI2 synthase generated their respective products via COX-2 in preference to COX-1 in both theA23187-induced immediate and interleukin-1-induced delayed responses. Hematopoietic PGD2 synthase preferentially used COX-1 and COX-2 in the A23187-induced immediate and interleukin-1-induced delayed PGD2-biosynthetic responses, respectively. This enzyme underwent stimulus-dependent translocation from the cytosol to perinuclear compartments, where COX-1 or COX-2 exists. COX selectivity of these lineage-specific PG synthases was also significantly affected by the concentrations of arachidonate, which was added exogenously to the cells or supplied endogenously by the action of cytosolic or secretory phospholipase A2. 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 arachidonate supplied by PLA2s at a moment when PG production takes place.