p38 kinase/cytosolic phospholipase A2/cyclooxygenase-2 pathway: a new signaling cascade for lipopolysaccharide-induced interleukin-1beta and interleukin-6 release in differentiated U937 cells.

p38 Mitogen-activated protein kinase (p38 MAPK) activation is essential for lipopolysaccharide (LPS)-induced pro-inflammatory cytokines expression. Although the regulation results from combined effect of both transcription and translation levels, the precise mechanism by which p38 regulates still remains to be elucidated. Our previous work showed cytosolic phospholipase A(2) (cPLA(2)), a substrate of p38, was involved in this regulation. Further investigations were carried out to study the possible mechanisms of the interleukin expression modulated by cPLA(2) in LPS-treated differentiated U937 cells. p38 MAPK inhibitor SB203580 suppressed interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) release, as well as the activation of cPLA(2). Transfection of cPLA(2) antisense oligonucleotides or pre-treatment with cPLA(2) inhibitor AACOCF3 abolished IL-1beta and IL-6 release in a dose-dependent manner. These implied a potential role of cPLA(2) in LPS-induced p38 pathways on interleukin release. As a downstream enzyme of cPLA(2), cyclooxygenase-2 (COX-2) was down-regulated by SB203580 and/or AACOCF(3), which precisely matched the levels of IL-1beta and IL-6. Treatment with the COX-2 inhibitor (NS-398) or COX-2 antisense oligonucleotides also diminished IL-1beta and IL-6 release. Given these findings, the p38 MAPK/cPLA(2)/COX-2 pathway was proposed to be implicated in the LPS-induced IL-1beta and interleukin-6 production in differentiated U937 cells.