After the protein extraction and quantification by the Radio Immunoprecipitation Assay (RIPA) lysis buffer (KeyGen, Nanjing, China) and BCA Protein Assay Kit (Takara) respectively, the mixture of proteins (40 µg per sample) and loading buffer (Takara) was loaded on 10% sodium dodecyl sulfate polyacrylamide gel to conduct the electrophoresis for 2 h. Then, the separated proteins on the gel were transferred onto the polyvinylidene fluoride membranes (Millipore, Billerica, MA, USA) and blocked using 5% non-fat milk (Beyotime). Afterwards, the membranes were incubated with primary antibodies at 4°C overnight and secondary antibody for 1 h at indoor temperature, followed by the detection of the SignalFire™ Plus ECL Reagent (Cell Signaling Technology (CST), Boston, MA, USA). The protein bands were observed by ImageLab software version 4.1 (Bio-Rad Laboratories, Hercules, CA, USA) and the signal levels were analyzed as described earlier.23 (link) The antibodies used in this report were listed as follows: anti-E-cadherin (CST, #3195, 1:1000), anti-N-cadherin (CST, #4061, 1:1000), anti-Vimentin (CST, #5741, 1:1000), anti-KLK4 (Abcam, Cambridge, UK, ab181402, 1:1000), internal control anti-β-actin (CST, #4970, 1:1000), and goat anti-rabbit IgG/HRP-linked secondary antibody (CST, #7074, 1:3000).