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).