USP22 and hepatocellular carcinoma: Given that SIRT1 is deubiquitinated by USP22 and stabilized at the protein level (Armour et al., 2013; Lin et al., 2012) and previous studies have reported that SIRT1 could negatively influence the chemosensitivity of HCC cells (Chen et al., 2012), our results supported the notion that USP22 increases SIRT1 protein levels in HCC cells.