Molecular mechanisms of lipopolysaccharide-induced cyclooxygenase-2 expression in human neutrophils: Involvement of the mitogen-activated protein kinase pathway and regulation by anti-inflammatory cytokines

Neutrophils are an important cellular source of proinflammatory mediators, whose regulation may be of potential benefit for the treatment of a number of inflammatory diseases. However, the mechanisms of lipopolysaccharide (LPS)-induced neutrophil activation and its regulation by anti-inflammatory cytokines have not yet been fully elucidated. Recent studies have revealed that mitogen-activated protein kinases (MAPK) play a crucial role in the generation of proinflammatory mediators in some cell types. Therefore, we conducted this study to determine whether MAPK activation could be involved in prostaglandin E₂ (PGE₂) production and cyclooxygenase (COX)-2 expression in LPS-stimulated human neutrophils. PD98059 (MEK1 inhibitor) and SB203580 (p38^MAPK inhibitor) reduced PGE₂ production as well as COX-2 expression in LPS-stimulated neutrophils. In addition, both extracellular signal-regulated protein kinase (ERK) and p38^MAPK were phosphorylated and activated in time- and dose-dependent manners. Since we previously showed that IL-10 and IL-4 similarly inhibited COX-2 expression in LPS-stimulated neutrophils, we next tested the effects of IL-10 and IL-4 on the phosphorylation and activation of both kinases. IL-10 inhibited the phosphorylation and activation of p38^MAPK, but not ERK. In addition, IL-4 caused a marginal inhibition in the activation of p38^MAPK. Taken together, these results suggest that both ERK and p38^MAPK pathways are involved in LPS-induced COX-2 expression and PGE₂ production in neutrophils, and IL-10 and IL-4 inhibit neutrophil prostanoid synthesis by down-regulating the activation of p38^MAPK.