Activation of arachidonate release and cytosolic phospholipase A2 via extracellular signal-regulated kinase and p38 mitogen-activated protein kinase in macrophages stimulated by bacteria or zymosan.

The mitogen-activated protein kinases (MAP kinases), extracellular signal-regulated kinase (ERK) and p38, can both contribute to the activation of cytosolic phospholipase A2 (cPLA2). We have investigated the hypothesis that ERK and p38 together or independent of one another play roles in the regulation of cPLA2 in macrophages responding to the oral bacterium Prevotella intermedia or zymosan. Stimulation with bacteria or zymosan beads caused arachidonate release and enhanced in vitro cPLA2 activity of cell lysate by 1.5- and 1.7-fold, respectively, as well as activation of ERK and p38. The specific inhibitor of MAP kinase kinase, PD 98059, and the inhibitor of p38, SB 203580, both partially inhibited cPLA2 activation and arachidonate release induced by bacteria and zymosan. Together, the two inhibitors had additive effects and completely blocked cPLA2 activation and arachidonate release. The present results demonstrate that ERK and p38 both have important roles in the regulation of cPLA2 and together account for its activation in P. intermedia and zymosan-stimulated mouse macrophages.