Chiang et al. reported that ATF4 contributed to the suppression of basal and chemical hypoxia-induced (CoCl2; 100 μM) transcription of EPO and that downregulation of PERK expression by siRNA enhanced EPO mRNA levels in association with reduction of ATF4 in the human hepatoma cell line HepG2 [46]. Here, EPO is linked to hepatocellular carcinoma.