Bortezomib-induced Mcl-1 accumulation in different cancer cell lines. Cells were treated with 1 mM bortezomib (+) for 6 h and harvested for Western blotting. Control cells (-) received no bortezomib. Data represent one of two independent experiments with similar results. Fold of Mcl-1 accumulation represents the value of accumulated Mcl-1 normalized with its endogenous product.