Activation of histone acetyltransferase p300 by MAPK pathway is required for optimal production of PGE2 in primary human monocytes activated with muramyl dipeptide adjuvant (MDP).

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Abstract Prostaglandin E2 (PGE2) is a proximal mediator of fever produced by human monocytes and macrophages activated by microbial pathogens and, in some cases, by adjuvants that contain analogues of microbial products. Here we studied the signaling pathway of PGE2 production in primary human monocytes activated with MDP, the minimal structure unit responsible for the adjuvant activity of peptidoglycans. MDP alone did not induce COX-2 mRNA expression and PGE2 protein production in monocytes. However, COX-2 mRNA and PGE2 were dramatically up-regulated when MDP was combined with T cell conditioned medium (TCM) prepared from CD3 bead-purified human T cells. MDP-induced nuclear NF-kB was not further increased by TCM. However, TCM induced increase in cytosolic Ca2+ and in phosphorylated ERK1/2 in monocytes, suggesting a role for MAPK signaling. In agreement with this, inhibition of Ca2+, of Ca2+-dependent PKC, and of MAPK kinase enzymes MEK1/2 suppressed PGE2 production in MDP/TCM-treated monocytes. Chromatin immunoprecipitation analysis showed that TCM alone or combined with MDP facilitated association of histone acetyltransferase p300 to the promoter regions of COX-2, IL-1b, and of IL-6 genes. Inhibition of p300 by C646 suppressed the recruitment of p300 and the acetylation of H3 and H4 histones at the COX-2 promoter, prevented COX-2 gene transcription, and PGE2 production. Taken together these results demonstrate that MDP-induced COX-2 gene transcription and PGE2 protein production in primary monocytes requires a second signal delivered by a TCM through a Ca2+-dependent activation of PKC/MEK1/2 signaling pathway followed by phosphorylation of ERK1/2 and p300-facilitated acetylation of histones H3 and H4 at the COX-2 promoter.