FIG. 2.

Effect of usnic acid on caspase-4 expression and the activity of caspase-3/7 in HepG2 cells with or without pre-treatment with 4-PBA. A, Total cellular proteins were extracted at 24 h after usnic acid treatment. The expression level of ER stress related caspase protein caspase-4 was determined by Western blotting. B, The HepG2 cells were pretreated with 1mM 4-PBA for 2h prior to 12.5 and 25 µM of usnic acid treatment for additional 24 h. Apoptosis was measured by caspase-3/7 activity. The bar graph shows the mean6SD from four independent experiments. *P<0.05 versus treatment of usnic acid alone. C, Cells were pretreated with 10 µM Z-VAD-FMK, a general caspase inhibitor, for 1h prior to 25 µM of usnic acid treatment for additional 24 h. The expression level of CHOP and ATF-4 was determined by Western blotting. n.s., no significant difference