Bufalin inhibits TGF-β-induced epithelial-to-mesenchymal transition and migration in human lung cancer A549 cells by downregulating TGF-β receptors

The epithelial-to-mesenchymal transition (EMT) is a well-known prerequisite for cancer cells to acquire the migratory and invasive capacity, and to subsequently metastasize. Bufalin is one of the major active components of the traditional Chinese medicine Chan Su, and accumulating evidence has shown its anticancer effect in multipe types of cancer. However, the role of bufalin in transforming growth factor-β (TGF-β)-induced EMT and migration remains unclear. In the present study, the effect of bufalin on TGF-β-induced EMT and migration was investigated in human lung cancer A549 cells. TGF-β induced EMT in A549 cells and increased their migratory ability, which were markedly suppressed by bufalin. Additionally, TGF-β-induced upregulation of Twist2 and zinc finger E-box binding homeobox 2 (ZEB2), as well as the phosphorylation of Smad2 and Smad3 were also inhibited by bufalin. However, the Smad-independent signaling pathways were not affected. Further analysis showed that the TGF-β receptor I (TβRI) and TGF-β receptor II (TβRII) were downregulated in the presence of bufalin. Pretreatment with SB431542, a potent inhibitor of the phosphorylation of TβRI, significantly attenuated TGF-β-induced EMT, mimicking the effect of bufalin on A549 cells. Taken together, these results suggest that bufalin suppresses TGF-β-induced EMT and migration by downregulating TβRI and TβRII in A549 cells.