Prostaglandin E2-induced IL-23p19 Subunit Is Regulated by cAMP-responsive Element-binding Protein and C/AATT Enhancer-binding Protein β in Bone Marrow-derived Dendritic Cells

We reported previously that prostaglandin E2 (PGE2)up-regulates IL- 23 in vitro in bone marrow-derived dendritic cells and in vivo in models of collagen-induced arthritis and inflammatory bowel disease, leading to preferential Th17 development and activity. There is very little information on the molecular mechanisms involved in the PGE2-induced up-regulation of Il23a gene expression. In this study we investigated the signaling pathways and transcription factors involved in the stimulatory effect of PGE2. Although PGE2 does not induce IL-23p19 expression by itself, it synergizes with both extra- and intracellular Toll-like receptor ligands and with inflammatory cytokines such as TNF alpha. We established that the effect of PGE2 in conjunction with either LPS or TNF alpha is mediated through the EP4 receptor and the cAMP-dependent activation of both protein kinase A (PKA) and exchange protein activated by cAMP (EPAC). Using the EP4 agonist PGE(1)OH in conjunction with TNF alpha, we found that PKA-induced phosphorylation of cAMP-response element-binding protein ((CREB)-C-P) and EPAC-induced phosphorylation of C/AATT enhancer-binding protein beta (C-P/EBP beta) mediate the stimulatory effect of PGE2 on IL-23p19 expression. This is the first report of CREB and C/EBP beta involvement in Il23a promoter activation. Mutation within the putative CREB and C/EBP sites combined with in vivo DNA binding (ChIP) assays identified the distal CREB site (-1125) and the two proximal C/EBP sites (-274 and -232) as essential for PKA-activated CREB and EPAC-activated C/EBP beta-induced IL-23p19 expression.