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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 TNFα. We established that the effect of PGE2 in conjunction with either LPS or TNFα 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 TNFα, we found that PKA-induced phosphorylation of cAMP-response element-binding protein ((P)CREB) and EPAC-induced phosphorylation of C/AATT enhancer-binding protein β ((P)C/EBPβ) mediate the stimulatory effect of PGE2 on IL-23p19 expression. This is the first report of CREB and C/EBPβ 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/EBPβ-induced IL-23p19 expression.

Dendritic Cells (DCs) play an important role in the initiation of the immune response by migrating to regional lymph nodes and presenting antigen processed at the inflammatory site to antigen-specific naïve T cells. Prostaglandin E2 (PGE2) has been reported to play an essential role in DC migration. We reported previously that PGE2 induces matrix metalloproteinase 9 (MMP-9) expression in DCs and that PGE2-induced MMP-9 is required for DC migration in vivo and in vitro. In this study, we investigated the signaling mechanisms involved in PGE2-induced MMP-9 expression in DCs. We show that PGE2-induced MMP-9 expression is mediated primarily through the EP2/EP4 → cAMP → protein kinase A (PKA)/PI3K → ERK signaling pathway, leading to c-Fos expression, and through JNK-mediated activation of c-Jun in a PKA/PI3K/ERK-independent manner. EP2 and EP4 receptor agonists, as well as cAMP analogs, mimic the up-regulation of MMP-9 by PGE2. PKA, PI3K, and ERK inhibitors abolished PGE2- and cAMP-induced c-Fos and MMP-9 up-regulation, and ERK activation was required for the binding of activator protein 1 (AP-1) transcription factor to the MMP-9 promoter. Our results describe a new molecular mechanism for the effect of PGE2 on MMP-9 production in DCs that could lead to future therapeutic approaches using ERK inhibitors to regulate DC migration.