Coordinated up-regulation of cyclooxygenase-2 and microsomal prostaglandin E synthase 1 transcription by nuclear factor kappa B and early growth response-1 in macrophages

Prostaglandin (PG) E2 is a potent lipid mediator that plays an essential role in inflammation, fever and pain. It is produced from arachidonic acid (AA) by a cascade of enzymatic reactions involving cyclooxygenases (COX-1 and -2) and prostaglandin E synthases (cPGES, mPGES-1 and -2). Functional coupling of the inducible enzymes COX-2 and mPGES-1 has been proposed for increased production of PGE2 in different cell types. PGE2 produced by macrophages plays an essential role in the pathogenesis of inflammatory diseases. Here, we have investigated the mechanisms involved in the regulation of COX-2 and mPGES-1 expressions in murine macrophages upon bacterial lipopolysaccharide (LPS) treatment. LPS stimulation induced the coordinated synthesis of COX-2 and mPGES-1 that resulted in an enhanced production of PGE2 in RAW 264.7 macrophages. Furthermore, we show the involvement of NF-κB and Egr-1 transcription factors in the transcriptional induction of these enzymes. LPS treatment promoted specific binding of NF-κB to both COX-2 and mPGES-1 promoters. Site-directed mutagenesis, electrophoretic mobility shift assays and ChIP assays allowed the identification of a sequence acting as a NF-κB recognition site in the murine mPGES-1 promoter. Furthermore, LPS induced the expression of Egr-1 that cooperated with NF-κB in the up-regulation of COX-2 and mPGES-1. Inhibition of Egr-1 expression reduced substantially LPS-mediated induction of COX-2 and mPGES-1 expression, resulting in a decrease in PGE2 production. Our findings point out to Egr-1 and NF-κB cooperation as determinant for PGE2 synthesis by macrophages in inflammatory processes through the coordinated regulation of COX-2 and mPGES-1.