MMP9 and hepatocellular carcinoma: MUC1 can promote the migration and invasion of HCC by increasing TGF-β levels via the MAPK/JNK/AP-1 signaling pathway (65, 66), and MUC1 can also promote TGF-β-related signaling molecules (Smads) or elevate other transcription factors, such as MMP-9, which supports the stimulating influence of MUC1 on the proliferation, migration and invasiveness of HCC cells (64, 74).