Antagonism between PKA and Epac signaling is involved in the regulation of PGE2-induced ICAM-1 expression in bEnd.3 cells

Abstract

Increased leukocyte adhesion and infiltration under various pathological conditions is accompanied by increased expression of endothelial ICAM-1 and the blockade of ICAM-1 ligation limits leukocyte infiltration and brain damage. PGE2 is known to be the principal pro-inflammatory prostanoid and play important roles in brain diseases through binding to EP1-4 receptors. However, there have been contradictory reports on its actions during inflammation processes, especially in vascular endothelial cells. In this study, we investigated the roles of PGE2 in the expression of ICAM-1 in bEnd.3 cells and therein involved signaling pathways. We investigated that elevation of cAMP is necessary for PGE2-induced ICAM-1 expression in bEnd.3 cells. We determined effect of PGE2 on Epac activation using Rap1-GTP pull down assay and effect of Epac on PI3K/Akt activation as well as ICAM-1 expression. Next, we showed that loss of Akt activity results in inhibition of PGE2-induced NF-κB activation. On the other hand, interestingly enough, PKA inhibitor stimulated Akt phosphorylation and ICAM-1 expression and specific activator inhibited PGE2-induced ICAM-1 expression and Akt phosphorylation. Taken together, these data suggest that this antagonism between PKA and Epac signaling is importantly involved in the regulation of PI3K/Akt signaling axis, and thereby ICAM-1 expression in cerebrovascular endothelial cells.