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 key step. In order to identify the enzymes that are linked to IL-1-mediated arachidonate availability and subsequent PGE(2) production, we have 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 forms of cyclooxygenase in human synoviocytes after stimulation with recombinant IL-1 beta. Northern-blot analysis revealed that both cPLA(2) and cyclooxygenase-2 mRNA were progressively upregulated upon exposure to IL-1 for 5 hours and the glucocorticoid, dexamethasone, blocked the increased expression of these two genes. In contrast, IL-1-induced sPLA(2) gene expression determined in the same cell samples was weak and most often rapid, and dexamethasone further stimulated it. In addition, 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-induced production of PGE(2) in human synoviocytes can be attributed to the stimulation of both cPLA(2) and cyclooxygenase-2. These enzymes may represent appropriate targets for selective blockade of prostanoid production in the inflammed joints.