MMP2 and hepatocellular carcinoma: miR-135a likely induced HCC cell metastasis and invasion by directly targeting the 3′ untranslated region (3′ UTR) of FOXO1 mRNA, consequently increasing Snail and matrix metalloproteinase-2 (MMP2) expression, inhibiting FOXO3a phosphorylation, and promoting AKT phosphorylation.