CYTOKINE INDUCTION OF CYTOSOLIC PHOSPHOLIPASE A(2) AND CYCLOOXYGENASE-2 MESSENGER-RNA IS SUPPRESSED BY GLUCOCORTICOIDS IN HUMAN EPITHELIAL-CELLS

Prostaglandin (PG) release, which is increased in vivo by inflammatory conditions and in vitro by pro-inflammatory cytokines, is decreased b y glucocorticoids. Two phospholipase A(2) isoforms, secretory (sPLA(2) ) and cytosolic (cPLA(2,)), have been implicated in inflammation. Thes e enzymes catalyse the release of arachidonic acid which is then conve rted to prostaglandins by the cyclooxygenases (COX-1 and COX-2). Regul ation of these events at the mRNA level is poorly characterised in epi thelial cells. We have used a human epithelial-like cell line (A549) a s a model system to study mRNA expression of sPLA(2), cPLA(2), COX-1 a nd COX-2. Following treatment of cells and extraction of RNA, semi-qua ntitative reverse transcription polymerase chain reaction (RT-PCR) was used to examine expression of these genes. We show a coordinate induc tion of both cPLA(2) and COX-2 mRNA by pro-inflammatory cytokines whic h correlated with increased PGE(2) release. By contrast, sPLA(2) mRNA was undetectable and COX-1 was found to be expressed at a constant low level. In addition dexamethasone pretreatment significantly reduced b oth cPLA(2) and COX-2 mRNA levels as well as PGE(2) release following cytokine stimulation. These data indicate a major role for control of prostaglandin synthesis at the mRNA level of key synthetic genes in ep ithelial cells. Furthermore we show that a major mechanism of glucocor ticoid action in preventing prostaglandin release occurs by suppressio n of cPLA(2) and COX-2 mRNA levels.