DDIT3 and hepatocellular carcinoma: Moreover, western blot assays further indicated that p-PERK, PERK, ATF4 and CHOP protein levels showed no significant difference in the KGM or 5-FU treatment groups compared with the control, while their cotreatment significantly increased the protein expression of p-PERK, ATF4 and CHOP in HCC cells with 5-FU resistance.