Prostaglandin D2 inhibits TGF-β1-induced epithelial-to-mesenchymal transition in MDCK cells

In a separate study, we identified PGE(2) as a potent inhibitor of TGF-beta 1-induced epithelial-mesenchymal transition (EMT) in cultured Madin-Darby canine kidney (MDCK) cells (Zhang A, Wang M-H, Dong Z, and Yang T. Am J Physiol Renal Physiol 291: F1323 - F1331, 2006). This finding prompted us to examine the roles of other prostanoids: PGD(2), PGF(2 alpha), PGI(2), and thromboxane A(2) (TXA(2)). Treatment with 10 ng/ml TGF-beta(1) for 3 days induced EMT as reflected by conversion to the spindle-like morphology, loss of E-cadherin, and activation of alpha-smooth muscle actin (alpha-SMA). Treatment with PGD(2) remarkably preserved the epithelial-like morphology, restored the expression of E-cadherin, and abolished the activation of alpha-SMA. In contrast, PGF(2 alpha), carbocyclic thromboxane A(2), PGI(2) and its stable analog beraprost were without an effect. MDCK cells expressed DP1 and DP2 receptors; however, the effect of PGD(2) was neither prevented by DP1 antagonist BW-A868C or DP2 antagonist BAY-u3405 nor was mimicked by DP1 agonist BW-245C. cAMP-elevating agents forskolin and 8-Br-cAMP blocked EMT. However, cAMP blockers H89 and Rp-cAMP failed to block the effect of PGD(2). PGD2 did not seem to act via its metabolites as 15-deoxy- Delta(12,14)prostaglandin J(2) (15d-PGJ(2)) levels in the medium following incubation with 3 mu M PGD(2) were well below the values predicted from the cross activity of the assay. Exposure to TGF-beta(1) induced a threefold increase in reactive oxygen species production that was completely abolished by PGD(2). We conclude that 1) PGD(2), but not PGI(2), PGF(2 alpha), and TXA(2) inhibit EMT, 2) PGD(2) inhibits EMT independently of DP1 and DP2 receptors, and 3) PGD(2) exhibits antioxidant property which may, in part, account for the antifibrotic action of this PG.