Effect of usnic acid on apoptosis and AKT/mTOR. (A) Cellular caspase-3/7 activity was expressed as fold change compared with DMSO control cells (***p < 0.001). (B) HepG2 cells were pretreated with 10μM Z-VAD-FMK, general caspase inhibitor, for 1 h prior to treatment of usnic acid for 24 h, and then the cell viability was determined. (C) Total cell lysates were isolated at 24 and 48 h after usnic acid treatment. The expression levels of proteins of AKT signaling pathway including p-PDK1 (S241), Akt, p-Akt (T308), p-Akt (S473), mTOR, p-mTOR (S2448), p-p70 S6 kinase (S371), and p-4E-BP1 (T37/46) were determined by Western blotting. GAPDH was used as internal control.