Compound 5 induces the ER-mediated apoptosis. A) Representative Western blot showing the enhanced release of Smac/DIABLO but not cytochrome c from the mitochondria (MF) into the cytosol (CF) of compound 5-treated A549 lung cancer cells (GI50). Equal protein loading was controlled by staining membranes with Ponceau S (a representative section of the stained membrane is shown). The experiment was repeated three times and the corresponding quantification is shown in (B), B) Quantification of smac/DIABLO and cytochrome C levels in vehicle-treated control A549 cells and cells treated with GI50 amount of compound 5 or 5% DMSO as a negative control. M: mitochondria fraction; C: cytosol fraction. Scale bars: mean ± SEM of three independent experiments. ** p < 0.01 compared to vehicle-treated control cells, C) Representative Western blot showing the induction of phosphorylation of eukaryotic initiation factor-2 (eIF-2) in A549 cells treated with GI50 amounts of compound 5. For comparison purposes, thapsigargin (TG), an ER stress-causing drug was used (3 μM, 2 h) as a positive control. The experiment was repeated three times.