CYTOSOLIC PHOSPHOLIPASE A(2) IS REQUIRED FOR CYTOKINE-INDUCED EXPRESSION OF TYPE IIA SECRETORY PHOSPHOLIPASE A(2) THAT MEDIATES OPTIMAL CYCLOOXYGENASE-2-DEPENDENT DELAYED PROSTAGLANDIN E-2 GENERATION IN RAT 3Y1 FIBROBLASTS

Activation of rat fibroblastic 3Y1 cells with interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) induced delayed pro staglandin (PG) E-2 generation over 6-48 h, which occurred in parallel with de novo induction of type IIA secretory phospholipase A(2) (sPLA (2)) and cyclooxygenase (COX)-2, without accompanied by changes in the constitutive expression of type IV cytosolic PLA(2) (cPLA(2)) and COX -1, Types V and IIC sPLA(2)s were barely detectable in these cells, St udies using an anti-type IIA sPLA(2) antibody, sPLA(2) inhibitors, and a type IIA sPLA(2)-specific antisense oligonucleotide revealed that I L-1 beta/TNF alpha-induced delayed PGE(2) generation by these cells wa s largely dependent on inducible type IIA sPLA(2), which was functiona lly linked to inducible COX-2, Delayed PGE(2) generation was also supp ressed markedly by the cPLA(2) inhibitor arachidonoyl trifluoromethyl ketone (AACOCF(3)), which attenuated induction of type IIA sPLA(2), bu t not COX-2, expression, AACOCF(3) inhibited the initial phase of cyto kine-stimulated arachidonic acid release, and supplementing AACOCF(3)- treated cells with exogenous arachidonic acid partially restored type IIA sPLA(2) expression, These results suggest that certain metabolites produced by the cPLA(2)-dependent pathway are crucial for the subsequ ent induction of type IIA sPLA(2) expression and attendant delayed PGE (2) generation, Some lipoxygenase-derived products might be involved i n this event, since IL-1 beta/TNF alpha-induced type IIA sPLA(2) induc tion and PGE(2) generation were reduced markedly by lipoxygenase, but not COX, inhibitors, In contrast, Ca2+ ionophore-stimulated immediate PGE(2) generation was regulated predominantly by the constitutive enzy mes cPLA(2) and COX-1, even when type IIA sPLA(2) and COX-2 were maxim ally induced after IL-1 beta/TNF alpha treatment, revealing functional segregation of the constitutive and inducible PG biosynthetic enzymes .