Neither caspase nor c-Jun N-terminal kinase inhibitors block bortezomib-induced IκBα down-regulation. (A) RPMI 8226 cells were cultured with bortezomib (20 nM for 8 hours and 12 hours) in the presence of control media (lane 2), Z-VAD-FMK (lane 3), or Z-DEVD-FMK (lane 4). Whole-cell lysates were subjected to immunoblotting with indicated Abs (A), and nuclear extracts were subjected to EMSA (B).