MMP9 and hepatocellular carcinoma: Another study demonstrated that HCC cells secreted exosomal miRNA-21, which promoted activation of pyruvate dehydrogenase kinase 1 (PDK1)/AKT signaling in HSCs by directly targeting PTEN; PDK1/AKT signaling activation, and promoted cancer progression by causing HCC cells to secrete angiogenic molecules including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), matrix metallopeptidase 2 (MMP2), MMP9, and TGF-β [185].