Knockdown of transmembrane protease serine 4 (TMPRSS4) regulated the expression of epithelial-mesenchymal transition (EMT) related genes. (A and B) RT-qPCR demonstrated that EMT markers of E-cadherin and vimentin were upregulated and downregulated respectively after TMPRSS4 knockdown in MDA-MB-468 and MDA-MB-231 cells. For the expression of key EMT transcriptional factors, claudin-1 and slug were upregulated and downregulated after transfection with siRNA, respectively. However, expression of ZEB1 did not show significant change. (C-F) Transfection efficiency and similar results were further observed in western blot analysis. β-actin was an internal control. *P<0.05, **P<0.01 and ***P<0.001. NC, negative control; EMT, epithelial-mesenchymal transition.