Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE(2) (prostaglandin E-2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE(2) terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-I (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1 beta (interleukin 1 beta) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near -8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBP beta (CCAAT/enhancer-binding protein beta) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBP beta binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBP beta in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBP beta highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.