INTERLEUKIN-1-INDUCED PROSTAGLANDIN E(2) BIOSYNTHESIS IN HUMAN SYNOVIAL-CELLS INVOLVES THE ACTIVATION OF CYTOSOLIC PHOSPHOLIPASE A(2) AND CYCLOOXYGENASE-2

Treatment of human synovial cells with interleukin-1 (IL-1) results in a large increase in the production of prostaglandin E(2) (PGE(2)), a function in which the activation of phospholipase A(2) (PLA(2)) is a k ey step. In order to identify the enzymes that are linked to IL-1-medi ated arachidonate availability and subsequent PGE(2) production, we ha ve investigated the changes in gene expression of the 85-kDa cytosolic PLA(2) (cPLA(2)), the 14-kDa secretory PLA(2) (sPLA(2)) and the two f orms of cyclooxygenase in human synoviocytes after stimulation with re combinant IL-1 beta. Northern-blot analysis revealed that both cPLA(2) and cyclooxygenase-2 mRNA were progressively upregulated upon exposur e to IL-1 for 5 hours and the glucocorticoid, dexamethasone, blocked t he increased expression of these two genes. In contrast, IL-1-induced sPLA(2) gene expression determined in the same cell samples was weak a nd most often rapid, and dexamethasone further stimulated it. In addit ion, IL-1 did not modify the levels of the constitutive cyclooxygenase -1. The cPLA(2) and cyclooxygenase-2 enzymic activities are dependent upon de novo synthesis of mRNA and protein, since they were inhibited by actinomycin D and cycloheximide. Our data suggest that the IL-1-ind uced production of PGE(2) in human synoviocytes can be attributed to t he stimulation of both cPLA(2) and cyclooxygenase-2. These enzymes may represent appropriate targets for selective blockade of prostanoid pr oduction in the inflammed joints.