Group V Phospholipase A2-dependent Induction of Cyclooxygenase-2 in Macrophages*

When exposed for prolonged periods of time (up to 20 h) to bacterial lipopolysaccharide (LPS) murine P388D(1) macrophages exhibit a delayed prostaglandin biosynthetic response that is entirely mediated by cyclooxygenase-2 (COX-2). Both the constitutive Group IV cytosolic phospholipase A(2) (cPLA(2)) and the inducible Group V secretory phospholipase A(2) (sPLA(2)) are involved in the cyclooxygenase-2-dependent generation of prostaglandins in response to LPS. Using the selective sPLA(2) inhibitor 3-(3-acetamide-1-benzyl-2-ethylindolyl-5-oxy)propane sulfonic acid (LY311727) and an antisense oligonucleotide specific for Group V sPLA(2), we found that induction of COX-2 expression is strikingly dependent on Group V sPLA(2), which was further confirmed by experiments in which exogenous Group V sPLA(2) was added to the cells. Exogenous Group V sPLA(2) was able to induce significant arachidonate mobilization on its own and to induce expression of the COX-2. None of these effects was observed if inactive Group V sPLA(2) was utilized, implying that enzyme activity is crucial for these effects to take place. Therefore, not only delayed prostaglandin production but also COX-2 gene induction are dependent on a catalytically active Group V sPLA(2). COX-2 expression was also found to be blunted by the Group IV cPLA(2) inhibitor methyl arachidonyl fluorophosphonate, which we have previously found to block Group V sPLA(2) induction as well. Collectively, the results support a model whereby Group IV cPLA(2) activation regulates the expression of Group V sPLA(2), which in turn is responsible for delayed prostaglandin production by regulating COX-2 expression