CASP9 and hepatocellular carcinoma: The upregulation of CYCS in the USP53-overexpressing cells was accompanied by increased cell apoptosis as well as higher expression levels of the pro-apoptotic cleaved-caspase-9, cleaved-caspase-3 and cleaved-PARP proteins, which was observed both in the sections of subcutaneous tumor tissues and in HCC cells (Fig. 6A, B).