TGF--mediated LEFTY/Akt/GSK-3/Snail axis modulates epithelial-mesenchymal transition and cancer stem cell properties in ovarian clear cell carcinomas

Advanced ovarian clear cell carcinoma (OCCCa) shows poor prognosis with chemoresistance, which is associated with epithelial-mesenchymal transition (EMT)/cancer stem cell (CSC) features. The left-right determination factor (LEFTY), a novel member of the TGF- superfamily, is a marker of stemness. Here we focused on the functional roles of LEFTY in OCCCas. OCCCa cell lines that were cultured in STK2, a serum-free medium for mesenchymal stem cells, or treated with TGF-1 underwent morphological changes toward an EMT appearance, along with increased expression of LEFTY and Snail. The cells also showed CSC properties, as demonstrated by increases in the aldehyde dehydrogenase (ALDH)1(high) activity population, number of spheroid formation, and expression of several CSC markers. Inhibition of LEFTY expression induced decreases in the number of spindle-shaped cells and CSC features, while cells stably overexpressing LEFTY exhibited enhancement of such EMT/CSC properties. Finally, treatment of cells with TGF-1 led to increased LEFTY expression and activation of Akt, which subsequently induced inactivation of GSK-3, while inhibition of GSK-3 resulted in increased expression of both LEFTY and Snail. In clinical samples, LEFTY expression showed a tendency for positive associations with expression of vimentin, as well as Sox2 and ALDH1, in OCCCas with epithelial-like morphology, indicating a possible relationship between LEFTY and the epithelial-mesenchymal hybrid stage of the tumors. In conclusion, TGF--mediated LEFTY/Akt/GSK-3/Snail axis may contribute to the establishment and maintenance of phenotypic characteristics of OCCCas through modulation of EMT/CSC properties.