TP53 and hepatocellular carcinoma: Furthermore, it has been found that ATRA upregulates p53 and thereby activates several apoptosis-related molecules, including Bax, p53 upregulated modulator of apoptosis (PUMA), caspase-9, Bid, caspase-8, caspase-3, and poly (ADP-ribose) polymerase (PARP), which leads to apoptosis in human hepatoma cells [19].