Prostaglandin E2 is a potent inhibitor of epithelial-to-mesenchymal transition: interaction with hepatocyte growth factor

Eicosanoid lipid mediators in fibrotic lung diseases: ready for prime time?

Recognition of a pivotal role for eicosanoids in both normal and pathologic fibroproliferation is long overdue. These lipid mediators have the ability to regulate all cell types and nearly all pathways relevant to fibrotic lung disorders. Abnormal fibroproliferation is characterized by an excess of profibrotic leukotrienes and a deficiency of antifibrotic prostaglandins. The relevance of an eicosanoid imbalance is pertinent to diseases involving the parenchymal, airway, and vascular compartments of the lung, and is supported by studies conducted both in humans and animal models. Given the lack of effective alternatives, and the existing and emerging options for therapeutic targeting of eicosanoids, such treatments are ready for prime time.

Hepatocyte growth factor regulates cyclooxygenase-2 expression via beta-catenin, Akt, and p42/p44 MAPK in human bronchial epithelial cells

Hepatocyte growth factor (HGF) is upregulated in response to lung injury and has been implicated in tissue repair through its antiapoptotic and proliferative activities. Cyclooxygenase-2 (COX-2) is an inducible enzyme in the biosynthetic pathway of prostaglandins, and its activation has been shown to play a role in cell growth. Here, we report that HGF induces gene transcription of COX-2 in human bronchial epithelial cells (HBEpC). Treatment of HBEpC with HGF resulted in phosphorylation of the HGF receptor (c-Met), activation of Akt, and upregulation of COX-2 mRNA. Adenovirus-mediated gene transfer of a dominant negative (DN) Akt mutant revealed that HGF increased COX-2 mRNA in an Akt-dependent manner. COX-2 promoter analysis in luciferase reporter constructs showed that HGF regulation required the beta-catenin-responsive T cell factor-4 binding element (TBE). The HGF activation of the COX-2 gene transcription was blocked by DN mutant of beta-catenin or by inhibitors that blocked activation of Akt. Inhibition of p42/p44 MAPK pathway blocked HGF-mediated activation of beta-catenin gene transcription but not Akt activation, suggesting that p42/p44 MAPK acts in a parallel mechanism for beta-catenin activation. We also found that inhibition of COX-2 with NS-398 blocked HGF-induced growth in HBEpC. Together, the results show that the HGF increases COX-2 gene expression via an Akt-, MAPK-, and beta-catenin-dependent pathway in HBEpC.

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

ANG II induces c-Jun NH2-terminal kinase activation and proliferation of human mesangial cells via redox-sensitive transactivation of the EGFR

We previously showed that ANG II induces mesangial cell (MC) proliferation via the JNK-activator protein-1 pathway. The present study attempted to determine the upstream mediators of JNK activation, with emphasis on reactive oxygen species (ROS) and the epidermal growth factor (EGF) receptor (EGFR). In cultured human MCs (HMCs), as early as 3 min, ANG II time dependently increased intracellular ROS production, which was sensitive to 10 microM diphenyleneiodonium sulfate and 500 microM apocynin, two structurally distinct NADPH oxidase inhibitors. In contrast, inhibitors of other oxidant-producing enzymes, including the mitochondrial complex I inhibitor rotenone, the xanthine oxidase inhibitor allopurinol, the cyclooxygenase inhibitor indomethacin, the lipoxygenase inhibitor nordihydroguiaretic acid, the cytochrome P-450 oxygenase inhibitor ketoconazole, and the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester, were without effect. ANG II-induced ROS generation was inhibited by the angiotensin type 1 receptor antagonist losartan (10 muM) but not the angiotensin type 2 receptor antagonist PD-123319 (10 microM). ANG II induced translocation of p47(phox) and p67(phox) from the cytosol to the membrane. The antioxidants almost abolished the ANG II mitogenic response, as assessed by [(3)H]thymidine incorporation and cell number, associated with a remarkable blockade of the activation of EGFR (90% inhibition) and JNK (83% inhibition). The EGFR inhibitor AG-1478 was able to mimic the effect of antioxidants, in that it inhibited the mitogenic response and the JNK activation following ANG II treatment. Together, these data suggest that the ROS-EGFR-JNK pathway is involved in transducing the proliferative effect of ANG II in cultured HMCs.

Prostaglandin D2 inhibits TGF-beta1-induced epithelial-to-mesenchymal transition in MDCK cells

In a separate study, we identified PGE2 as a potent inhibitor of TGF-beta1induced 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(2alpha), PGI2, and thromboxane A2 (TXA2). Treatment with 10 ng/ml TGF-beta1 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 PGD2 remarkably preserved the epithelial-like morphology, restored the expression of E-cadherin, and abolished the activation of alpha-SMA. In contrast, PGF(2alpha), 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 microM PGD2 were well below the values predicted from the cross activity of the assay. Exposure to TGF-beta1 induced a threefold increase in reactive oxygen species production that was completely abolished by PGD2. We conclude that 1) PGD2, but not PGI2, PGF(2alpha), and TXA2 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.