Zhu et al. also confirmed that miR-21 could modulate PDCD4 expression at the translational and post-transcriptional levels in HepG2 cells, enhance phosphorylation of c-Jun protein, and activate AP-1-dependent transcription of MMP-2 as well as MMP-9, thus promoting migration and invasion of hepatocellular carcinoma cell lines [41]. Here, MMP9 is linked to hepatocellular carcinoma.