Cisplatin-induced activation of TGF-β signaling contributes to drug resistance

Growing evidence suggests an association between epithelial-mesenchymal transition (EMT), a hallmark of tumor malignancy, and chemoresistance to a number of anti-cancer drugs. However, the mechanism of EMT induction in the process of acquiring anti-cancer drug resistance remains unclear. To address this issue, we obtained a number of cisplatin-resistant clones from LoVo cells and found that almost all of them lost cell-cell contacts. In these clones, the epithelial marker E-cadherin was downregulated, whereas the mesenchymal marker N-cadherin was upregulated. Moreover, the expression of EMT-related transcription factors, including Slug, was elevated. On the other hand, the upregulation of other mesenchymal marker Vimentin was weak, suggesting that the mesenchymal-like phenotypic changes occurred in these cisplatin-resistant clones. These mesenchymal-like features of cisplatin-resistant clones were partially reversed to parental epithelial-like features by treatment with transforming growth factor-β (TGF-β) receptor kinase inhibitors, indicating that TGF-β signaling is involved in cisplatin-induced the mesenchymal-like phenotypic changes. Moreover, cisplatin was observed to enhance the secretion of TGF-β into the culture media without influencing TGF-β gene transcription. These results suggest that cisplatin may induce the mesenchymal-like phenotypic changes by enhancing TGF-β secretion, ultimately resulting in drug resistance.