ATF4 and hepatocellular carcinoma: For instance, arginosuccinate synthase 1 treatment suppresses tumor progression and triggers pro-apoptotic ER stress responses in hepatocellular carcinoma through the hyperactivation of PERK-eukaryotic translation initiation factor 2α (eIF2α)-activating transcription factor 4 (ATF4)-C/EBP homologous protein (CHOP) arm of the UPR [18].