. 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 ...