Silibinin attenuates TGF-β1-induced migration and invasion via EMT suppression and is associated with COX-2 downregulation in bladder transitional cell carcinoma

Transforming growth factor (TGF)-1 is highly expressed in bladder transitional cell carcinoma (TCC) and is positively associated with tumor grade. TGF-1 signaling promotes cell metastasis by inducing epithelial-mesenchymal transition (EMT), however, the underlying mechanisms are not fully understood. Our previous study demonstrated the anti-metastatic effects of silibinin, a natural flavonoid derived from milk thistle, against TCC. The present study investigated the effects of silibinin on TGF-1-induced EMT in TCC, focusing on the role of prostaglandin-endoperoxide synthase 2 (COX-2). Cell migration was determined by a wound healing assay and Transwell migration assay, and cell invasion was investigated using a Transwell invasion assay. Cell morphology was observed using an inverted microscope. Cell viability was evaluated by an MTT and cell counting assays. EMT markers were detected by reverse transcription-quantitative polymerase chain reaction and western blotting. Specific small interfering RNA was used to knockdown COX-2 gene expression. TGF-1 promoted cell migration and invasion, induced EMT and upregulated the expression of COX-2. COX-2 knockdown attenuated TGF-1-induced EMT, indicating that COX-2 upregulation was essential for TGF-1-induced EMT. Silibinin attenuated TGF-1-induced migration and invasion by inhibiting EMT, and was associated with COX-2 downregulation. TGF-1-induced COX-2 upregulation, which was inhibited by silibinin. In addition, TGF-1-induced EMT was further inhibited when silibinin treatment was combined with COX-2-knockdown. The results suggested that silibinin may be a potential future treatment for metastatic TCC.