Melatonin, a novel selective ATF-6 inhibitor, induces human hepatoma cell apoptosis through COX-2 downregulation

Figure 2 Selection of the proper melatonin concentration. The effects of melatonin (MT) on the three unfolded protein response (UPR) pathways of HepG2 cells induced by tunicamycin (TM). HepG2 cells were exposed to different concentrations of melatonin (10^-9, 10^-7, 10^-5 and 10^-3 mol/L) for 24 h. A: Equal protein amounts of cell lysates were subjected to western blot assay using anti-ATF-6, anti-IRE-1 and anti-PERK. β-actin in the same HepG2 cells extract was used as an internal reference; B: Optical density reading values of specific proteins are represented as fold differences relative to the loading control protein, β-actin. ^aP < 0.01 vs negative control (NC); ^bP < 0.05 vs positive control (TM); ^cP < 0.01 vs positive control (TM). ATF-6: Activating transcription factor 6; IRE: Inositol-requiring enzyme; PERK: Protein kinase RNA-like endoplasmic reticulum kinase.