Prostaglandin E 2 couples through EP 4 prostanoid receptors to induce IL-8 production in human colonic epithelial cell lines

Abstract

Background and purpose: Prostaglandin (PG) E 2 and interleukin (IL)-8 are simultaneously increased during the inflammation that characterizes numerous pathologies such as inflammatory bowel disease. IL-8 is a potent neutrophil chemo-attractant and activator, and can initiate and/or exacerbate tissue injury. PGE 2 signals principally through prostanoid receptors of the EP 2 and/or EP 4 subtypes to promote cAMP-dependent cellular functions. The aim of this study was to identify the role of the EP 2 and EP 4 receptor subtype(s) on two human colonic epithelial cell lines (Caco-2 and T84), in regulating PGE 2-induced IL-8 production. Experimental approach: To identify the causative receptor, we knocked-down and over-expressed EP 2 and EP 4 receptor subtypes in colonic epithelial cells and studied the effect of several selective EP 2/EP 4 receptor agonists and antagonists. The inductions of IL-8 and EP receptor mRNA and protein expression were determined by real-time PCR and western blot analysis. The affinity of PGE 2 and Bmax values for the EP 2 and EP 4 receptor on colonic epithelial cells were determined by radioligand-binding assays with [ 3H]PGE 2. Key results: PGE 2 had the highest affinity for the EP 4 receptor subtype and promoted a robust stimulation of cAMP-dependent IL-8 synthesis. This effect was mimicked by a selective EP 4 receptor agonist, ONO-AE1-329, and abolished by silencing the EP 4 receptor gene by using siRNA techniques, a selective EP 4 receptor antagonist (ONO-AE3-208) and a selective inhibitor (Rp-cAMP) of cAMP-dependent protein kinase. Conclusions and implications: These findings suggest that initiation and progression of colonic inflammation induced by IL-8 could be mediated, at least in part, by PGE 2 acting via the EP 4 receptor subtype. © 2009 The British Pharmacological Society.