HDAC9 and hepatocellular carcinoma: The fact that HeLa cells induce p21 after treatment with an HDAC inhibitor and hTERT-RPE1 cells do not, in combination with the observation that HeLa cells induce apoptosis while hTERT-RPE1 cells do not, is in concordance with Papeleu et al., who report that hepatoma cells show an upregulation of p21, accompanied by increasing Caspase 3 activity and subsequent apoptosis induction, while primary hepatocytes do not show this p21 induction and they do not show an activation of Caspase 3 and no signs of cell death [42].