SMAD3 and cancer: To determine the molecular mechanism of miR-615-3p in the regulation of breast cancer cell migration, we analyzed the effect of miR-615-3p on the TGF-β1 signal pathway which is a critical EMT inducer in a number of cancer cells including breast cancer cells [26, 27].TGF-β1 treatment induced phosphorylation of Smad2 and Smad3 in a time-dependent manner [28, 29].