Transforming growth factor-β1 enhances the invasion and metastasis ability of breast cancer cells by inducing epithelial-mesenchymal transition

Objective To investigate the effect of transforming growth factor-β1(TGF-β1) on the invasion and metastasis ability of breast cancer cells through inducing epithelial- mesenchymal transition(EMT), and explore its related molecular mechanism. Methods The breast cancer cells MDA- MB-435S were treated with recombinant human TGF-β1(5μg/L).Then the cells were transfected with small inference RNA(siRNA)against Smad2 or control siRNA using Lipfectamine 2000.Western blotting was used to detect the expression of some epithelial markers, mesenchymal markers, Smad2 and phosphorylated Smad2(p- Smad2).The Matrigel- coated Transwell was used to detect the invasion and metastasis ability of breast cancer cells. Results After TGF-β1 treatment for 72 h, MDA- MB- 435S cells showed more elongated shape, displaying firoblast- like appearance compared to the untreated cells.Compared with the control group, the expression ofα- smooth muscle actin and vimentin were increased by 3.86 and 1.17 times respectively(P<0.01), the expression of cytokeratin and E- adherin were decreased by 63% and 70% respectively(P<0.01)and the expression of p- Smad2 was increased by 1.2 times compared with before(P< 0.01).The number of invasion cells in TGF-β1 group(79.20±7.35) were markerly increased than non- treated group(48.93±5.43,P<0.05).After knockdown of the Smad2 gene partially, the expression of cytokeratin was increased by 44%(P<0.01), the expression of vimentin was decreased by 59%(P<0.01).The number of invasion cells in siRNA group(54.34±6.09)was decreased as compared with control group(75.09±4.98)(P< 0.05). Conclusion Our current data demonstrated that EMT of breast cancer cells induced by TGF-β1 promotes the migration and invasion of breast cancer cells. Smad2 signal transduction pathway may play an important role in the EMT process of breast cancer cells. Key words: Breast cancer; Epithelial- mesenchymal transition; Transforming growth factorβ1; Smad2; Invasion