PROSTAGLANDIN SYNTHASE-1 AND PROSTAGLANDIN SYNTHASE-2 ARE COUPLED TO DISTINCT PHOSPHOLIPASES FOR THE GENERATION OF PROSTAGLANDIN D-2 IN ACTIVATED MAST-CELLS

Aggregation of IgE cell surface receptors on MMC-34 cells, a murine ma st cell line, induces the synthesis and secretion of prostaglandin D-2 (PGD(2)). Synthesis and secretion of PGD(2) in activated MMC-34 cells occurs in two stages, an early phase that is complete within 30 min a fter activation and a late phase that reaches a maximum about 6 h afte r activation. The early and late phases of PGD(2) generation are media ted by prostaglandin synthase 1 (PGS1) and prostaglandin synthase 2 (P GS2), respectively. Arachidonic acid, the substrate for both PGS1 and PGS2, is released from membrane phospholipids by the activation of pho spholipases. We now demonstrate that in activated mast cells (i) secre tory phospholipase A(2) (PLA(2)) mediates the release of arachidonic a cid for early, PGS1-dependent synthesis of PGD(2); (ii) secretory PLA( 2) does not play a role in the late, PGS2-dependent synthesis of PGD(2 ); (iii) cytoplasmic PLA(2) mediates the release of arachidonic acid f or late, P0GS2-dependent synthesis of PGD(2); and (iv) a cytoplasmic P LA(2)-dependent step precedes secretory PLA(2) activation and is neces sary for optimal PGD(2) production by the secretory PLA(2)/PGS1-depend ent early pathway.