CDKN1B and hepatocellular carcinoma: Several of these miRNAs have been shown to target specific genes directly in liver tissue—that is, miR-21 regulates PTEN,52 miR-122a regulates cyclin G1,53 while miR-221 controls p57/CDKN1C and p27/CDKN1B.54 It is also important to note that some miRNA genes (such as miR-1) undergo methylation-mediated regulation in HCC cell lines,55 suggesting a strong link between the DNA methylome and the miRNAome.