Endothelin-1 promotes epithelial-to-mesenchymal transition in human ovarian cancer cells

Despite considerable efforts to improve early detection and advances in chemotherapy, metastatic relapses remain a major challenge in the management of ovarian cancer. The endothelin A receptor (ET_AR)/endothelin-1 (ET-1) axis has been shown to have a significant role in ovarian carcinoma by promoting tumorigenesis. Here we show that the ET-1/ET_AR autocrine pathway drives epithelial-to-mesenchymal transition (EMT) in ovarian tumor cells by inducing a fibroblastoid and invasive phenotype, down-regulation of E-cadherin, increased levels of β-catenin, Snail, and other mesenchymal markers, and suppression of E-cadherin promoter activity. Activation of ET_AR by ET-1 triggers an integrin-linked kinase (ILK)-mediated signaling pathway leading to glycogen synthase kinase-3β (GSK-3β) inhibition, Snail and β-catenin stabilization, and regulation of transcriptional programs that control EMT. Transfection of dominant negative ILK or exposure to an ILK inhibitor suppresses the ET-1-induced phosphorylation of GSK-3β as well as Snail and β-catenin protein stability, activity, and invasiveness, indicating that ET-1/ET_AR-induced EMT-promoting effects depend on ILK. ET_AR blockade by specific antagonists or reduction by ET _AR RNA interference reverses EMT and cell invasion by inhibiting autocrine signaling pathways. In ovarian carcinoma xenografts, ABT-627, a specific ET_AR antagonist, suppresses EMT determinants and tumor growth. In human ovarian cancers, ET_AR expression is associated with E-cadherin downregulation, N-cadherin expression, and tumor grade. Collectively, these findings provide evidence of a critical role for the ET-1/ET_AR axis during distinct steps of ovarian carcinoma progression and identify novel targets of therapeutic intervention.