Western blotting analysis was conducted with 20 μg of protein as described previously 14 (link)-16 (link). Primary antibodies were rabbit anti-TRAM2 antibody (dilute concentration, 1:1000, Thermo Fisher Scientific), mouse anti-GAPDH antibody (dilute concentration, 1:1000, Santa Cruz Biotechnology, Dallas, TX, USA), mouse anti-protein kinase RNA(PKR) - like ER kinase (PERK) antibody (dilute concentration, 1:1000, Santa Cruz Biotechnology), rabbit anti-MT1-MMP antibody (dilute concentration, 1:1000, Cell Signaling Technology, Danvers, MA, USA), rabbit anti-MMP2 antibody (dilute concentration, 1:500, Merck KGaA, Darmstadt, Germany), and rabbit anti-MMP9 antibody (dilute concentration, 1:3000, GeneTex Inc., Irvine, CA, USA). Horseradish peroxidase-conjugated anti-rabbit or anti-mouse IgG (Promega, Madison, WI, USA) was used as secondary antibodies.