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

Jesús Balsinde, Hiroyuki Shinohara, Lee J. Lefkowitz, Christina A. Johnson, Marı́a A. Balboa, Edward A. Dennis
1999 Journal of Biological Chemistry  
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
more » ... -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. Phospholipase A 2 (PLA 2 ) 1 plays a key role in numerous cellular processes by regulating the release of arachidonic acid (AA) from membrane phospholipids. In turn, free AA can be converted into the prostaglandin (PG) precursor PGH 2 by the action of cyclooxygenases (COX). These two reactions constitute the regulatory checkpoints of the pathway leading to PG biosynthesis in mammalian cells. A considerable body of evidence suggests that specific coupling between certain PLA 2 and COX forms accounts for the differential regulation of the immediate and delayed responses (1-11). We have shown that the immediate platelet-activating factor-receptor-mediated phase of PGE 2 production in LPSprimed P388D 1 macrophages involves Group V sPLA 2 coupling to COX-2 (3). More recently, we have discovered that the exact same coupling of Group V sPLA 2 to COX-2 also regulates the delayed PGE 2 response of P388D 1 macrophages to LPS alone (4). Under the latter conditions, expression of both Group V sPLA 2 and COX-2 was markedly induced and correlated with ongoing AA release and PG biosynthesis, respectively (4), suggesting that the AA produced by Group V sPLA 2 was used by COX-2 to produce PGE 2 . Importantly, sPLA 2 expression could be abolished by pretreating the cells with the cPLA 2 inhibitor methyl arachidonyl fluorophosphonate, implying that a functionally active cPLA 2 is required for the delayed PGE 2 response to occur (4). In the current study we extend our previous observations on the delayed phase of PGE 2 in P388D 1 macrophages to further investigate the regulatory relationships between the three effectors of the response (i.e. cPLA 2 , sPLA 2 , and COX-2). We now demonstrate tight coupling between sPLA 2 and COX-2 for the delayed phase of PGE 2 generation by showing that COX-2 induction by LPS is dependent upon a catalytically active Group V sPLA 2 .
doi:10.1074/jbc.274.37.25967 pmid:10473537 fatcat:yjjd2sh6gjcodg3wrasezjlbl4