Introduction:
The microRNA-200 (miR-200) family and sex-determining region Y-box 4 (SOX4) could regulate epithelial-mesenchymal transition (EMT), which is important for the process of tumor pathology. This study explored the association of miR-200a with SOX4 in transforming growth factor (TGF)-β-induced EMT of ovarian carcinoma (OC) cells.

Material and methods:
For the in vitro experiments, human CO cells subjected to TGF-β were used to induce EMT; the activity of miR-200a was selectively inhibited or overexpressed by miR-200a inhibitor and mimics, respectively. Small interfering RNAs against SOX4 (si-SOX4) were used to inhibit SOX4 expression in human OC cell lines.

Results:
Decreased miR-200a and increased SOX4 levels were detected in patients with OC and these changes were closely related to the International Federation of Gynaecology and Obstetrics stage, ovarian tumor biomarker CA125 level, lymph node status and tumor size. The TGF-β-treated cells increased the miR-200a level, decreased the SOX4 level and prompted EMT properties, including a reduction in epithelial marker (E-cadherin), induction of interstitial markers (vimentin and n-cadherin), and enhancement of proliferation, migration and invasion. The OC cells were transduced with miR-200a mimic and the overexpression cells were subsequently treated with TGF-β; decreased SOX4 expression and EMT properties were detected. Also, in miR-200a inhibited cells, TGF-β increased SOX4 expression and EMT properties. Moreover, SOX4 silencing weakened the effect of the miR-200a inhibitor.

Conclusions:
Overall, these results provide a link between miR-200a and SOX4 in OC pathogenesis and indicate that miRNA-200a inhibits EMT by downregulating SOX4 expression in human OC cells.