PGE2 Induces Macrophage IL-10 Production and a Regulatory-like Phenotype via a Protein Kinase A–SIK–CRTC3 Pathway

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Abstract
The polarization of macrophages into a regulatory-like phenotype and the production of IL-10 plays an important role in the resolution of inflammation. We show in this study that PGE2, in combination with LPS, is able to promote an anti-inflammatory phenotype in macrophages characterized by high expression of IL-10 and the regulatory markers SPHK1 and LIGHT via a protein kinase A–dependent pathway. Both TLR agonists and PGE2 promote the phosphorylation of the transcription factor CREB on Ser133. However, although CREB regulates IL-10 transcription, the mutation of Ser133 to Ala in the endogenous CREB gene did not prevent the ability of PGE2 to promote IL-10 transcription. Instead, we demonstrate that protein kinase A regulates the phosphorylation of salt-inducible kinase 2 on Ser343, inhibiting its ability to phosphorylate CREB-regulated transcription coactivator 3 in cells. This in turn allows CREB-regulated transcription coactivator 3 to translocate to the nucleus where it serves as a coactivator with the transcription factor CREB to induce IL-10 transcription. In line with this, we find that either genetic or pharmacological inhibition of salt-inducible kinases mimics the effect of PGE2 on IL-10 production.