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

Abstract

. Since ICER lacks the transactivation domain, it functions as a transcription repressor as opposed to CREB. PGE 2 coupling through EP2/4 receptors can therefore acts in an opposing manner to either decrease (EP2) or promote IL-8 expression by recruiting CREB-binding protein (CBP) (EP4), which formed a multiprotein IL-8 enhanceosome. A novel half CRE (167CRE) and a composite NFAT1-AP1-like site in the IL-8 promoter participated in binding and complex formation as confirmed by mutagenesis and expression studies. These data unravel the mechanisms by which expression of IL-8 is controlled by different signalling pathways that are activated by PGE 2 but acting through different EP receptors. Keywords: CREB · Gene regulation · ICER · Inflammation · Promoter IntroductionProstaglandin E 2 (PGE 2 ) is a lipid mediator of inflammation, which was initially characterized as a pro-inflammatory molecule due to its role in inducing inflammatory changes. With increasing understanding of prostanoid physiology, it is now viewed as both a promoter and suppressor of inflammation depending on the complex regulatory network controlling its responses. The ultimate effect of PGE 2 depends on different factors such as the level of other immune cell activation, the cell physiology, and effect of Correspondence: Prof. Kris Chadee e-mail: kchadee@ucalgary.ca other mediators [1]. Prostaglandin levels increase during acute inflammation prior to lymphocyte recruitment [1]. With increasing infiltration of cells, there is further increase in PGE 2 levels. Mucosal tissue concentrations of PGE 2 are increased by more than threefold during inflammation [2]. Once produced from membrane phospholipids, PGE 2 is transported outside the cell by passive diffusion or active transport and may act both in an autocrine or paracrine fashion through cell surface receptors [3]. PGE 2 binds through four cell surface E-prostanoid (EP) receptors EP1 to EP4 to regulate downstream signalling pathway [4,5]. Binding of PGE 2 through EP2 and EP4 receptors couples to Gs to increase * These authors contributed equally to this work.C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 912-923 Immunomodulation 913 intracellular cyclic adenosine monophosphate (cAMP) which inhibits effector functions in some cells [4], while binding through EP3 can have opposing effects by blocking cAMP [6]. One cytokine that is strongly regulated by PGE 2 is interleukin-8 (IL-8), which is central to several inflammatory responses. IL-8 is a major pro-inflammatory cytokine belonging to the CXC chemokine family. IL-8 was originally identified as a neutrophil chemoattractant and activator which may cause non-specific tissue damage and promote inflammation [7]. Along with chemotaxis, it can also induce activation of target cells by increasing intracellular Ca 2+ and respiratory burst. In inflammatory bowel diseases (Crohn's disease and ulcerative colitis), the levels of IL-8 correspond to the active grade of inflammation [8]. IL-8 is remarkable in ...

Arsenic exposure causes epigenetic dysregulation of IL-8 expression leading to proneoplastic changes in kidney cells

“…Under normal condition, this site remains methylated, while upon arsenic induced demethylation, it may lead to IL-8 expression. Encompassing the À168 site is the binding site for CAAT/enhancer biding protein (C/EBP) transcription factor (NsiteMSoftBerry) and cAMP response element binding protein (CREB) (Srivastava et al, 2012). Srivastava et al (2012) had described the role of À168 site by using site directed mutagenesis.…”

“…Encompassing the À168 site is the binding site for CAAT/enhancer biding protein (C/EBP) transcription factor (NsiteMSoftBerry) and cAMP response element binding protein (CREB) (Srivastava et al, 2012). Srivastava et al (2012) had described the role of À168 site by using site directed mutagenesis. Mutation at À168 site was found to decrease the expression of IL-8 suggesting its crucial role.…”

The Prostanoid EP4 Receptor and Its Signaling Pathway

“…Among them, cAMP-response element-binding protein (CREB), a transcription factor, is one of the major downstream targets of PKA, which controls cellular functions via synthesis of a wide variety of proteins (Shaywitz and Greenberg, 1999). EP4-mediated CREB activation was reported in colon epithelial cells (Srivastava et al, 2012), dorsal root ganglion neurons (Cruz Duarte et al, 2012), Leydig tumor cells (Sirianni et al, 2009), and breast cancer cells (Subbaramaiah et al, 2008). Other signaling pathways in addition to CREB are activated via PKA.…”

“…Srivastava et al (2012) examined the mechanisms of differential regulation of IL-8 production by EP4 and demonstrated that PGE 2 -EP4 signaling activated CREB through both the PKA and PI3K pathways. Interestingly, they also demonstrated that EP2 activated the transcription factor-inducible cAMP early repressor (Srivastava et al, 2012). Because inducible cAMP early repressor lacks the transactivation domain, it functions as a transcription repressor, unlike CREB.…”

“…These data suggest that PGE 2 coupling through EP4 and EP2 receptors can therefore act in an opposing manner to either promote (EP4) or decrease (EP2) IL-8 expression, even though both receptors use the same second messenger, cAMP. Since Chadee's laboratory has reported that PGE 2 promotes IL-8 production in the human colonic epithelial cell lines Caco-2 and T84 through both the PKA and PI3K pathways (Dey and Chadee, 2008;Dey et al, 2009;Srivastava et al, 2012), it appears that EP4 contributes to IL-8 production.…”