High PGE2 Levels Inhibit the Migration of Dendritic Cells by Modulating the PKA-CREB Axis Instead of Epac1-Rap1.

Abstract

The inhibited migration of dendritic cells (DCs) from lesion tissue to draining lymph nodes is a possible way for tumors to achieve immune evasion. In a previous study, we demonstrated that high concentrations of Prostaglandin E2 (PGE₂), which were expressed in tumor microenvironments, inhibited DCs' migration. However, the specific mechanism is not yet clear. The current study aims to use the murine bone marrow-derived DCs (BMDCs) to demonstrate the possible signaling pathway of PGE₂. The mRNA and protein expressions of the Epac1-Rap1 axis and PKA-CREB axis were determined after administration of PGE₂ on DCs. Then, the agonist and antagonist of these molecules were used to treat DCs. The migration capability of DCs was detected as well as the RhoA activation levels. The mRNA and protein of Epac1 were barely undetectable in DCs. The use of Epac1 agonists showed no impact on DCs' migration capability and RhoA activation levels. The activation levels of Rap1 and protein expressions of Rap1a and Rap1b were not affected by PGE₂ administration. The using of Rap1a and Rap1b antagonists demonstrated no impact on DCs' migration capability and RhoA activation levels. Moreover, the PKA activation levels and phosphorylated CREB1 were increased by the administration of PGE₂ on DCs. The application of a PKA inhibitor attenuated the effect of PGE₂ in a 3D migration assay and in vivo experiment. These results suggest that the PKA-CREB axis, instead of Epac1-Rap1, probably associates with the intracellular signaling pathway induced by high PGE₂ levels, which demonstrates an inhibitory effect on DCs' migration. These findings can bring a different perspective on immunological surveillance of tumor progression.