Bortezomib activates the intrinsic pathway in MCL cells. Effect of caspase inhibition and ROS elimination on bortezomib-induced apoptosis in MCL. Jeko and Granta-519 cells were treated with 20 nM bortezomib for 18 hours in the absence or presence of z-VAD-fmk (50 μM) or glutathione-reduced ethyl ester (GSH, 2 mM). These inhibitors were preincubated for 1 hour before bortezomib addition. Cell viability was determined by annexin V/PI staining. ΔΨ_m was assessed by DiOC₆(3) staining, and ROS generation was quantified using DHE. Bax/Bak conformational changes and caspase-3 activation were determined by staining permeabilized cells with anti-Bax, anti-Bak, and anti-active caspase-3 antibodies. In treated cells, the histogram (black) is superimposed with the control (gray). The percentage of positive cells for each labeling is indicated inside the chart.