Phospholipase A2 is secreted by murine keratinocytes after stimulation with IL-1 alpha and TNF-alpha.

Phospholipase A2 (PLA2)-catalysed liberation of arachidonic acid is the rate-limiting step in the generation of the lipid mediators prostaglandins and leukotrienes. PLA2 regulation thus represents a pivotal mechanism in the pathogenesis of inflammation. In this study we investigated the effects of TNF alpha and IL-1 alpha on PLA2 activity in cultured murine keratinocytes. Starting 18 h after stimulation, PLA2 activity increased significantly by about 250-320%) in the supernatants and in the cell pellets. This effect was completely inhibited either by preincubation of the cells with dexamethasone 48 h before stimulation or by coincubation with actinomycin D. PLA2 activity detected in the supernatants was blocked by reduction with dithiothreitol, whereas the PLA2 activity in the pellets was dithiothreitol-resistant. We conclude that in murine keratinocytes IL-1 alpha induce de novo synthesis and release of a secretory PLA2 and the induction of a different PLA2 activity in the cytosol. These findings indicate a crucial link between early cytokine effects and the initiation of the lipid mediator cascade in keratinocytes. The observation that PLA2 induction could be completely inhibited by preincubation with dexamethasone allows new insights into the mechanism of steroid effects on epidermal inflammation and renders PLA2 regulation an interesting therapeutic target.