In a separate study, we identified PGE2 as a potent inhibitor of TGF-β1-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: PGD2, PGF 2α, PGI2, and thromboxane A2 (TXA 2). Treatment with 10 ng/ml TGF-β1 for 3 days induced EMT as reflected by conversion to the spindle-like morphology, loss of E-cadherin, and activation of α-smooth muscle actin (α-SMA). Treatment with PGD2 remarkably preserved the epithelial-like morphology, restored the expression of E-cadherin, and abolished the activation of α-SMA. In contrast, PGF2α, carbocyclic thromboxane A2, PGI2 and its stable analog beraprost were without an effect. MDCK cells expressed DP1 and DP2 receptors; however, the effect of PGD2 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 PGD2. PGD2 did not seem to act via its metabolites as 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) levels in the medium following incubation with 3 μM PGD2 were well below the values predicted from the cross activity of the assay. Exposure to TGF-β1 induced a threefold increase in reactive oxygen species production that was completely abolished by PGD2. We conclude that 1) PGD2, but not PGI2, PGF2α, and TXA 2 inhibit EMT, 2) PGD2 inhibits EMT independently of DP1 and DP2 receptors, and 3) PGD2 exhibits antioxidant property which may, in part, account for the antifibrotic action of this PG.
- Madin-Darby canine kidney cells
- Reactive oxygen species
- Transforming growth factor-β
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