Cyclooxygenase-2 Expression in Macrophages: Modulation by Protein Kinase C-α

Abstract

Cyclooxygenase-2 (COX-2) is an inducible enzyme responsible for high levels of PG production during inflammation and immune responses. Previous studies with pharmacological inhibitors suggested a role for protein kinase C (PKC) in PG production possibly by regulating COX-2 expression. In this study, we addressed the role of PKC-α in the modulation of COX-2 expression and PGE2 synthesis by the overexpressing of a dominant-negative (DN) mutant of this isoenzyme in the mouse macrophage cell line RAW 264.7. We investigated the effect of various stimuli on COX-2 expression, namely, LPS, IFN-γ, and the intracellular parasite Leishmania donovani. Whereas LPS-induced COX-2 mRNA and protein expression were down-regulated in DN PKC-α-overexpressing clones, IFN-γ-induced COX-2 expression was up-regulated in DN PKC-α-overexpressing clones with respect to normal RAW 264.7 cells. Measurements of PGE2 levels revealed a strong correlation between PGE2 secretion and IFN-γ-induced COX-2 mRNA and protein levels in DN PKC-α-overexpressing clones. Taken together, these results suggest a role for PKC-α in the modulation of LPS- and IFN-γ-induced COX-2 expression, as well as in IFN-γ-induced PGE2 secretion.