Involvement of Mitogen-Activated Protein Kinase Homologues in the Regulation of Lipopolysaccharide-Mediated Induction of Cyclo-oxygenase-2 but not Nitric Oxide Synthase in RAW 264.7 Macrophages

Abstract

In RAW 264.7 macrophages lipopolysaccharide (LPS) stimulated the activation of p42 and p44 MAP kinases and their upstream activator mitogen-activated protein (MAP) kinase kinase (MAPKK), and induced the 69-kDa isoform of cyclo-oxygenase-2 (COX-2) and the 130-kDa isoform of nitric oxide synthase (iNOS). PD 098059, a specific inhibitor of the activation of MAPKK, prevented LPS-mediated activation of MAPKK IC 50 = 3.0 ± 0.1 μM, n = 3 and p42/44 MAP kinases and substantially reduced the induction of COX-2 by approximately 40%–70%, but was without effect upon the induction of iNOS. In parallel, LPS also stimulated the activation of p38 MAP kinase and the MAPKAP kinase-2, a downstream target of p38 MAP kinase. SB 203580, a specific inhibitor of p38 MAP kinase prevented the activation of p38 MAP kinase IC 50 = 3.3 ± 1.4 μM, n = 3 and MAPKAP kinase-2 by LPS and reduced the induction of COX-2 by approximately 50–90%, with no significant effect upon iNOS expression. These studies indicate the involvement of both the classical p42/44 MAP kinases and p38 MAP kinase in the regulation of COX-2 but not iNOS induction following exposure to LPS.