Fibronectin induces epithelial-mesenchymal transition in human breast cancer MCF-7 cells via activation of calpain.

Fibronectin (FN) is a primary component of the mammary mesenchymal compartment and undergoes dramatic changes during breast cancer development. Increased FN expression is associated with an invasive and metastatic breast cancer phenotype. The present study demonstrated that FN causes an epithelial-mesenchymal transition (EMT)-like morphological change in MCF-7 breast cancer cells. FN stimulation caused the downregulation of epithelial markers E-cadherin and tight junction protein ZO-1, and the upregulation of mesenchymal markers N-cadherin and vimentin. Additionally, FN promoted cell migration and invasion in MCF-7 cells, with increased expression of calpain-2 and proteolysis of focal adhesion kinase 1 (FAK), indicating calpain activation. Notably, the FN induced changes in morphology and EMT markers were reversed with the treatment of calpain-specific inhibitors, calpain inhibitor I (N-acetyl-L-leucyl-L-leucyl-L-norleucinal), calpeptin and calpain inhibitor IV. Meanwhile, the effects of FN on cell migration and invasion, as well as FAK proteolysis were markedly suppressed by calpain inhibitors. Taken together, the results of the present study indicate that calpain plays an essential role in FN-induced EMT response, and that targeting calpain signaling may be a potential strategy to reduce breast cancer metastasis.