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In cancer cells, epithelial-to-mesenchymal transition (EMT) is controlled by Snail1, a transcriptional factor also required for the activation of cancer-associated fibroblasts (CAF). Snail1 is short-lived in normal epithelial cells as a consequence of its coordinated and continuous ubiquitination by several F-box-specific E3 ligases, but its degradation is prevented in cancer cells and in activated fibroblasts. Here, we performed an siRNA screen and identified USP27X as a deubiquitinase that increases Snail1 stability. Expression of USP27X in breast and pancreatic cancer cell lines and tumors positively correlated with Snail1 expression levels. Accordingly, downregulation of USP27X decreased Snail1 protein in several tumor cell lines. USP27X depletion impaired Snail1-dependent cell migration and invasion and metastasis formation and increased cellular sensitivity to cisplatin. USP27X was upregulated by TGFβ during EMT and was required for TGFβ-induced expression of Snail1 and other mesenchymal markers in epithelial cells and CAF. In agreement with this, depletion of USP27X prevented TGFβ-induced EMT and fibroblast activation. Collectively, these results indicate that USP27X is an essential protein controlling Snail1 expression and function and may serve as a target for inhibition of Snail1-dependent tumoral invasion and chemoresistance. SIGNIFICANCE: These findings show that inhibition of USP27X destabilizes Snail1 to impair EMT and renders tumor cells sensitive to chemotherapy, thus opening new strategies for the inhibition of Snail1 expression and its protumoral actions.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/1/33/F1.large.jpg. This study was funded by grants awarded by Ministerio de Economía y Competitividad (MINECO) and Fondo Europeo de Desarrollo Regional-FEDER to A. García de Herreros (SAF2013-48849-C2-1-R and SAF2016-76461-R) and to V.M. Díaz (SAF2013-48849-C2-2-R). Research at the A. García de Herreros lab is supported by funds from the Fundación Científica de la Asociación Española contra el Cáncer and from the Instituto de Salud Carlos III (PIE15/00008). Research at the B.S. Atanassov lab is supported by the Rosswell Park Cancer Institute and NCI grant P30CA016056. Research at the J. Arribas lab is supported by funds from the Breast Cancer Research Foundation (BCRF-17-008) and Instituto de Salud Carlos III (PI16/00253).

Crosstalk between tumor and stromal cells in the tumor microenvironment alter its properties in ways that facilitate the invasive behavior of tumor cells. Here, we demonstrate that cancer-associated fibroblasts (CAF) increase the stiffness of the extracellular matrix (ECM) and promote anisotropic fiber orientation, two mechanical signals generated through a Snail1/RhoA/αSMA–dependent mechanism that sustains oriented tumor cell migration and invasiveness. Snail1-depleted CAF failed to acquire myofibroblastic traits in response to TGFβ, including RhoA activation, αSMA-positive stress fibers, increased fibronectin fibrillogenesis, and production of a stiff ECM with oriented fibers. Snail1 expression in human tumor–derived CAF was associated with an ability to organize the ECM. In coculture, a relatively smaller number of Snail1-expressing CAF were capable of imposing an anisotropic ECM architecture, compared with nonactivated fibroblasts. Pathologically, human breast cancers with Snail1+ CAF tended to exhibit desmoplastic areas with anisotropic fibers, lymph node involvement, and poorer outcomes. Snail1 involvement in driving an ordered ECM was further confirmed in wound-healing experiments in mice, with Snail1 depletion preventing the anisotropic organization of granulation tissue and delaying wound healing. Overall, our results showed that inhibiting Snail1 function in CAF could prevent tumor-driven ECM reorganization and cancer invasion. Cancer Res; 75(2); 284–95. ©2014 AACR.

40 p.-6 fig., Snail1 transcriptional factor is essential for triggering epithelial-to-mesenchymal transition (EMT) and inducing tumor cell invasion. We report here an additional, EMTindependent action of Snail1 on tumor invasion: its expression in cancer-associated fibroblasts is necessary for enhancement by these cells on epithelial cells tumor invasion. Snail1 expression in fibroblast requires signals derived from tumor cells such as TGF-; reciprocally, in fibroblasts Snail1 organizes a complex program that favors collective invasion of epithelial cells at least in part by the secretion of diffusible signaling molecules, such as prostaglandin E2. The capability of human or murine tumor-derived cancer associated fibroblasts to promote tumor invasion is associated to Snail1 expression and obliterated by Snail1 depletion. In vivo experiments show that Snail1 depletion in mice prevents the invasion of breast tumors and epithelial tumor cells co-xenografted with Snail1-depleted fibroblasts originate tumors with lower invasion than those transplanted with control fibroblasts. Therefore, these results demonstrate that the role of Snail1 in tumor invasion is not limited to EMT but dependent on its expression in stromal fibroblasts where it orchestrates its activation and the crosstalk with epithelial tumor cells. Moreover, they point to the interference of Snail expression as a promising target for preventing the action of stromal fibroblasts on tumor progression., This work was funded by grants from Fundación Científica de la Asociación Española contra el Cáncer to AGH, JIC and FB, and Ministerio de Economía(SAF2013-48849-C2-1-R) and Fundació La Marató de TV3 (120130) to AGH. We also thank the support from Instituto Carlos III (RD12/0036/005 and RD12/0036/004,1 part of the Plan Nacional I+D+I and cofounded by the ISCIII-Subdirección General de Evaluación and Fondo Europeo de Desarrollo Regional-FEDER) and Generalitat de Catalunya (2014 SGR 32).

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 (ETAR)/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/ETAR 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 ETAR 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/ETAR–induced EMT-promoting effects depend on ILK. ETAR blockade by specific antagonists or reduction by ETAR RNA interference reverses EMT and cell invasion by inhibiting autocrine signaling pathways. In ovarian carcinoma xenografts, ABT-627, a specific ETAR antagonist, suppresses EMT determinants and tumor growth. In human ovarian cancers, ETAR expression is associated with E-cadherin down-regulation, N-cadherin expression, and tumor grade. Collectively, these findings provide evidence of a critical role for the ET-1/ETAR axis during distinct steps of ovarian carcinoma progression and identify novel targets of therapeutic intervention. (Cancer Res 2005; 65(24): 11649-57)