Phosphorylation of Glycogen Synthase Kinase-3 and Stimulation of T-cell Factor Signaling following Activation of EP2 and EP4 Prostanoid Receptors by Prostaglandin E2

Abstract

Recently we have shown that the FP(B) prostanoid receptor, a G-protein-coupled receptor that couples to Galpha(q), activates T-cell factor (Tcf)/lymphoid enhancer factor (Lef)-mediated transcriptional activation (Fujino, H., and Regan, J. W. (2001) J. Biol. Chem. 276, 12489-12492). We now report that the EP(2) and EP(4) prostanoid receptors, which couple to Galpha(s), also activate Tcf/Lef signaling. By using a Tcf/Lef-responsive luciferase reporter gene, transcriptional activity was stimulated approximately 10-fold over basal by 1 h of treatment with prostaglandin E(2) (PGE(2)) in HEK cells that were stably transfected with the human EP(2) and EP(4) receptors. This stimulation of reporter gene activity was accompanied by a PGE(2)-dependent increase in the phosphorylation of both glycogen synthase kinase-3 (GSK-3) and Akt kinase. H-89, an inhibitor of protein kinase A (PKA), completely blocked the agonist-dependent phosphorylation of GSK-3 in both EP(2)- and EP(4)-expressing cells. However, H-89 pretreatment only blocked PGE(2)-stimulated Lef/Tcf reporter gene activity by 20% in EP(4)-expressing cells compared with 65% inhibition in EP(2)-expressing cells. On the other hand wortmannin, an inhibitor of phosphatidylinositol 3-kinase, had the opposite effect and inhibited PGE(2)-stimulated reporter gene activity to a much greater extent in EP(4)-expressing cells as compared with EP(2)-expressing cells. These findings indicate that the activation of Tcf/Lef signaling by EP(2) receptors occurs primarily through a PKA-dependent pathway, whereas EP(4) receptors activate Tcf/Lef signaling mainly through a phosphatidylinositol 3-kinase-dependent pathway. This is the first indication of a fundamental difference in the signaling potential of EP(2) and EP(4) prostanoid receptors.

Prostaglandin E2 Mediates IL-1β-Related Fibroblast Mitogenic Effects in Acute Lung Injury through Differential Utilization of Prostanoid Receptors

“…Furthermore, mice deficient in EP2 receptors exhibit a greater profibrotic response to bleomycin than wild-type mice, suggesting that changes in EP receptor profile can control in vivo fibrotic responses (36). Although we have clearly shown that EP2 and EP3 receptors are coupled to increases and decreases in cAMP, respectively, it remains possible that cross-talk among other downstream signaling intermediates, and/or transactivation of other receptors, may condition the response to PGE 2 and/or changes in cAMP (65)(66)(67)(68). Future studies will be directed at defining the precise explanation for our novel observations.…”

Potential cross-talk between (pro)renin receptors and Wnt/frizzled receptors in cardiovascular and renal disorders

“…9,43 It is worth mentioning that the transcriptional activity of b-catenin may also occur independent of the activation of Wnt and Fz. Activation of G protein-coupled receptors such as prostanoid (EP2, EP4), 44 lysophosphatidic acid (LPA2, LPA3), 18,45 gonadotrophin releasing hormone 46 and parathyroid 47 can also turn on b-cateninmediated gene transcriptional programs. In a recent study, it has been shown that the free G a and G bg subunits released from an activated G protein act co-operatively to inhibit b-catenin degradation and subsequently activate b-catenin-mediated transcriptional program.…”

Protein Kinase A-mediated 14-3-3 Association Impedes Human Dapper1 to Promote Dishevelled Degradation

“…Cyclooxygenase-2 (COX-2) is involved in prostaglandin E 2 (PGE 2 ) synthesis and highly expressed in colon cancer (42,43). PGE 2 , through PKA and protein kinase B (PKB/AKT) activation, has also been shown to promote ␤-catenin signaling (44,45).…”