p38 kinase/cytosolic phospholipase A2/cyclooxygenase-2 pathway: A new signaling cascade for lipopolysaccharide-induced interleukin-1β 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 A2 (cPLA2), 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 cPLA2 in LPS-treated differentiated U937 cells. p38 MAPK inhibitor SB203580 suppressed interleukin-1β (IL-1β) and interleukin-6 (IL-6) release, as well as the activation of cPLA2. Transfection of cPLA2 antisense oligonucleotides or pre-treatment with cPLA2 inhibitor AACOCF3 abolished IL-1β and IL-6 release in a dose-dependent manner. These implied a potential role of cPLA2 in LPS-induced p38 pathways on interleukin release. As a downstream enzyme of cPLA2, cyclooxygenase-2 (COX-2) was down-regulated by SB203580 and/or AACOCF3, which precisely matched the levels of IL-1β and IL-6. Treatment with the COX-2 inhibitor (NS-398) or COX-2 antisense oligonucleotides also diminished IL-1β and IL-6 release. Given these findings, the p38 MAPK/cPLA2/COX-2 pathway was proposed to be implicated in the LPS-induced IL-1β and interleukin-6 production in differentiated U937 cells.