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

Gastrointestinal inflammation is mediated by the pro-inflammatory mediators interleukin-8 (IL-8) and prostaglandin E2 (PGE2). PGE2 binding and coupling through EP2/4 receptor subtypes on colonic epithelial cells stimulates cyclic adenosine monophosphate (cAMP) and IL-8 production. Here we determined the mechanisms whereby PGE2 regu-lates IL-8 in Caco2 colonic epithelial cells and in cells over-expressing the EP2/4 receptors (EP2S/EP4S). PGE2 coupling through EP2 activated the transcription factor inducible cAMP early repressor (ICER), whereas coupling through EP4 receptors activated the cyclic AMP-responsive element-binding protein (CREB). Activation of CREB in Caco2/EP2S was protein kinase A (PKA) dependent, whereas in EP4S cells, activation of CREB occurred through the PKA and phosphatidylinositol 3-kinase pathways. Since ICER lacks the transactivation domain, it functions as a transcription repressor as opposed to CREB. PGE2 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 PGE2 but acting through different EP receptors.