As shown in Fig 2C, TGF-β1 treatment (10 ng/mL, 72 hours) significantly decreased the activity of MMPs in L6, RSC-364 and RC cells (P < 0.05), which was reversed by Lv-shRNA-Smad4 (P < 0.05) but not Lv-NC infection, suggesting that Smad4 gene knockdown offset the decrease of MMP activity in the three cell lines induced by TGF-β1. This evidence concerns the gene SMAD4 and infection.