ANALYSIS OF THE SECRETORY PHOSPHOLIPASE A(2) THAT MEDIATES PROSTAGLANDIN PRODUCTION IN MAST-CELLS

Prostaglandin D-2 (PGD(2)) synthesis in activated mast cells occurs in two phases, an early phase that is dependent on prostaglandin synthas e 1 and a delayed phase that is dependent on activation-induced prosta glandin synthase 2 gene expression. Early phase PGD(2) synthesis in ac tivated mast cells also requires the activity of a secretory phospholi pase A(2) (PLA(2)). It has been thought that the secretory PLA(2) expr essed in mast cells is group IIa PLA(2), encoded by the Pla2 g2a gene. However, activated bone marrow-derived mast cells prepared from Pla2 g2a(+/+) mice and mast cells prepared from mice with a mutation in the Pla2 g2a gene both demonstrate early phase PGD(2) synthesis. Moreover , mast cells from both murine strains secrete PLA(2) activity followin g activation. Northern and reverse transcriptase/polymerase chain reac tion analyses demonstrate that mast cells from Pla2 g2a(+/+) and Pla2 g2a(-/-) mice do not express group IIa PLA(2) message. Instead, Northe rn and reverse transcriptase/polymerase chain reaction analyses demons trate that both Pla2 g2a(+/+) and Pla2 g2a(-/-) mast cells express mRN A for group V PLA(2), encoded by the Pla2gV gene, An antisense oligonu cleotide directed against group V PLA(2) is also able to inhibit both the early phase of PGD(2) production and the secretion of PLA(2) activ ity by activated mast cells, Our data suggest that (i) group IIa PLA(2 ) does not play a significant role in murine mast cell prostaglandin s ynthesis, (ii) group V PLA(2) mediates early mast cell PGD(2) producti on and transcellular PGE(2) production in murine mast cells, and (iii) much of the data, based on studies with chemical inhibitors and antib odies, suggesting that group IIa PLA(2) is responsible for arachidonic acid mobilization needs to be reevaluated.