Smad7 maintains epithelial phenotype of ovarian cancer stem-like cells and supports tumor colonization by mesenchymal-epithelial transition.

Epithelial ovarian carcinoma (EOC) is a lethal gynecological malignancy. Epithelial-mesenchymal transition (EMT) has an important role in the tumorigenesis and progression of EOC. During the process of EMT, the transforming growth factor-β (TGF-β)-Smad signaling pathway has been indicated to regulate cell motility and tumor development. Among numerous EMT-associated transcripts, Smad7 is considered to be an inhibitor, however its involvement together with TGF-β1 in the progression of ovarian cancer remains to be elucidated. The present study demonstrated that Smad7 was overexpressed in SK-OV-3 and stem-like side populations of EOC cells, both of which grow in an epithelial pattern. The transformation of cells from an epithelial to a mesenchymal phenotype was stimulated by TGF-β1 with a corresponding increase in Smad7 expression in SK-OV-3 cells. These results indicate that Smad7 is a regulator in the maintenance of the epithelial phenotype in EOC cells, and may serve as an inhibitory element which targets TGF-β-stimulated EMT. Furthermore, inhibition of Smad7 resulted in cellular mesenchymal transformation, with an increased expression of N-cadherin and a decreased expression of E-cadherin. The invasiveness and migratory capabilities of Smad7 small hairpin RNA transduced EOC cells was also reduced. The findings of the present study have identified Smad7 as a fundamental factor in the maintenance of epithelial growth of EOC cells. Reversal of EMT results in a mesenchymal-epithelial transition, which is necessary for EOC cell colonization at metastatic sites.