Regulation of cytosolic phospholipase A_2, cyclooxygenase-1 and -2 expression by PMA, TNFα, LPS and M-CSF in human monocytes and macrophages

摘要

Cytosolic phospholipase A_2 (cPLA_2) and cyclooxygenases-1 and -2 (COX-1 and -2) play a pivotal role in the metabolism of arachidonic acid (AA) and in eicosanoid production. The coordinate regulation and expression of these enzymes is not well defined. In this study, the effect of phorbol 12-myristate 13-acetate (PMA), tumor necrosis factor α (TNFα), lipopolysaccharide (LPS) and macrophage-coloy stimulating factor (M-CSF) on AA release and prostaglandin E_2 (PGE_2) production and the expression of cPLA_2 and COX-1 and -2 were investigated in U937 human pre-monocytic cells and fully differentiated macrophages. Treatment of U937 cells with PMA or macrophages with LPS increased AA release and PGE_2 production. Incubation of U937 cells or macrophages for 8 h with all stimuli elevated cPLA_2 expression. In contrast, cPLA_2 expression was reduced upon further incubation of U937 cells or macrophages for 24 h with all stimuli indicating a bi-phasic expression pattern of this enzyme. PMA induced COX-1 expression in U937 cells whereas LPS induced COX-2 expression in macrophages. Although TNFα and M-CSF induced a significant amount of AA release in both cell models, they failed to induce a comparable production of PGE_2 since they were unable to induce the coordinate expression of the downstream key enzymes, COX-1 or COX-2. The results suggest that the enhancement of AA release in both U937 cells and macrophages may be caused by both increased cPLA_2 activity and elevated cPLA_2 protein expression. In addition, PMA stimulate PGE_2 production via up-regulation of COX-1, and likely COX-2, expression in U937 cells whereas LPS stimulates PGE_2 production via induction of COX-2 expression in macrophages.