Prostaglandin E₂ couples through EP₄ prostanoid receptors to induce IL‐8 production in human colonic epithelial cell lines

Abstract

Background and purpose: Prostaglandin (PG) E2 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. PGE2 signals principally through prostanoid receptors of the EP2 and/or EP4 subtypes to promote cAMP-dependent cellular functions. The aim of this study was to identify the role of the EP2 and EP4 receptor subtype(s) on two human colonic epithelial cell lines (Caco-2 and T84), in regulating PGE2-induced IL-8 production.Experimental approach: To identify the causative receptor, we knocked-down and over-expressed EP2 and EP4 receptor subtypes in colonic epithelial cells and studied the effect of several selective EP2/EP4 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 PGE2 and Bmax values for the EP2 and EP4 receptor on colonic epithelial cells were determined by radioligandbinding assays with [ 3 H]PGE2. Key results: PGE2 had the highest affinity for the EP4 receptor subtype and promoted a robust stimulation of cAMP-dependent IL-8 synthesis. This effect was mimicked by a selective EP4 receptor agonist, ONO-AE1-329, and abolished by silencing the EP4 receptor gene by using siRNA techniques, a selective EP4 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 PGE2 acting via the EP4 receptor subtype.

Prostaglandin E2 modulates IL‐8 expression through formation of a multiprotein enhanceosome in human colonic epithelial cells

“…However, upon induction, its production can increase by more than 100-fold [9] showing highly controlled regulation. We have previously shown that PGE 2 signals through the EP4 receptor to activate cAMP and upregulated IL-8 expression [10], but the mechanistic details are unknown. cAMP can activate the transcription factor CREB to promote binding to cAMP response element (CRE) or similar DNA binding sites in several gene promoters [11].…”

“…The two receptors also differ in the rate of desensitization and internalization [23] and affinity to metabolites of the primary ligand PGE 2 . These observations suggest that the subtle differences in EP2 and EP4 receptor expression and signalling may help in fine tuning cellular responses to PGE 2 .In this study, we used colonic epithelial cells which overexpress either the EP2 or EP4 receptor in Caco2 human colonic epithelial cells [10]. PGE 2 was found to drive the activation of CREB and increase IL-8 expression when it preferentially coupled through EP4 receptor.…”

Prostaglandin E receptor 4 (PTGER4) involved in host protection against immune challenge in oyster, Crassostrea hongkongensis

“…In response to PGN stimulation, PTGER4 could increase cAMP levels and induce IL-6 production in RAW 264.7 macrophages [24]. In colonic inflammation, IL-8, an important mediator of the acute host inflammatory response, was induced by PGE2-PTGER4 signaling via a cAMP-dependent mechanism [25]. Additionally, the activation of PTGER4 may also regulate anti-inflammatory responses in certain cell types by inhibiting stimulus-induced expression of proinflammatory genes, including TNF-a, IFN-b, IL-1b and iNOS [14,17e19].…”

“…It has been reported that PTGER4-induced NF-kB activation plays a key role in diverse biological processes, including the pro-inflammatory and pro-survival responses [25,41]. For example, the activation of the NF-kB signaling pathway mediated by PGERT4, as well as PTGER2, could induce IL-6 production in PGN-treated RAW 264.7 macrophages [25]. Additionally, PGERT4 was also shown to promote survival pathways and impair intrinsic apoptotic pathways by activating the NF-kB signaling pathway in human endometriotic cells [41].…”

“…A previous study in RAW 264.7 macrophages demonstrated that activation of PTGER4 and PTGER2 by peptidoglycan (PGN) stimulation resulted in increased cAMP levels and activation of protein kinase A (PKA), which in turn increased NF-kB activation and finally induced IL-6 production [24]. Recently, it was reported that IL-8 is an important mediator of the acute host inflammatory response and is produced in response to PGE2 via the activation of a cAMP-dependent mechanism that is mediated exclusively by activation of PTGER4 in colonic inflammation [25].…”