Cytosolic phospholipase A2 is required for cytokine-induced expression of type IIA secretory phospholipase A2 that mediates optimal cyclooxygenase-2-dependent delayed prostaglandin E2 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 prostaglandin (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, Studies using an anti-type IIA sPLA(2) antibody, sPLA(2) inhibitors, and a type IIA sPLA(2)-specific antisense oligonucleotide revealed that IL-1 beta/TNF alpha-induced delayed PGE(2) generation by these cells was largely dependent on inducible type IIA sPLA(2), which was functionally linked to inducible COX-2, Delayed PGE(2) generation was also suppressed markedly by the cPLA(2) inhibitor arachidonoyl trifluoromethyl ketone (AACOCF(3)), which attenuated induction of type IIA sPLA(2), but not COX-2, expression, AACOCF(3) inhibited the initial phase of cytokine-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 subsequent induction of type IIA sPLA(2) expression and attendant delayed PGE(2) generation, Some lipoxygenase-derived products might be involved in this event, since IL-1 beta/TNF alpha-induced type IIA sPLA(2) induction 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 enzymes cPLA(2) and COX-1, even when type IIA sPLA(2) and COX-2 were maximally induced after IL-1 beta/TNF alpha treatment, revealing functional segregation of the constitutive and inducible PG biosynthetic enzymes.