To investigate the expression of TMPRSS4 in breast cancer (BC) cells and to analyze the relationship between TMPRSS4 expression and epithelial-mesenchymal transition (EMT) as well as the significance of TMPRSS4 expression in the development and progression of BC.

qRT-PCR and Western blot analysis were used to determine the expressions levels of TMPRSS4 mRNA and protein in five BC cell lines (MCF-7, ADM, T47D, MDA-MB-231, and MDA-MB-468). A plasmid expressing TMPRSS4 was transfected into MDA-MB-468 and MDA-MB-231cells, and transfection efficiency was evaluated. The MTS assay, EdU assay, and Transwell and Matrigel invasion assays were used to assess the proliferation, invasion, and metastasis of BC cells. Following transfection with the TMPRSS4 expressing plasmid, the mRNA and protein expression of key biomarkers of EMT (E-cadherin, Vimentin, Claudin-1, Slug, and ZEB1) was detected by qRT-PCR and Western blot analysis, respectively.

qRT-PCR and Western blot analysis showed that TMPRSS4 was differentially expressed in five BC cell lines, with MDA-MB-468 cells having the highest expression. MTS assay showed that the cell proliferation rate was significantly increased in TMPRSS4 overexpressing MDA-MB-468 cells (P=0.039) and MDA-MB-231 cells (P=0.038) than in non-transfected cells. EdU assay further confirmed that TMPRSS4 overexpression promoted BC cell proliferation. The proliferation of TMPRSS4 overexpressing MDA-MB-468 cells and MDA-MB-231 cells was significantly higher than that of the negative control group (P=0.001 and P=0.008, respectively). Transwell and Matrigel assays showed that the migration and infiltration capacities of TMPRSS4 overexpressing MDA-MB-468 cells and MDA-MB-231 cells were significantly increased compared with those of the negative control group (P=0.001, 0.001, 0.012, and 0.000, respectively). qRT-PCR and Western blot analysis revealed that the expression of E-cadherin and Claudin-1 was significantly decreased, while the expression of Vimentin and Slug was increased after the overexpression of TMPRSS4 (P=0.024, 0.003, 0.002, and 0.012, respectively).

TMPRSS4 participates in the occurrence of EMT in BC and promotes the proliferation, invasion, and metastasis of BC cells through regulating EMT.