Accumulation of Mcl-1 upon proteasome inhibition is in line with a previous study, demonstrating an increase of this protein in various malignant tumor cell lines (including CRC) upon MG132 treatment.31 Because of the accumulation of Mcl-1, proteasome inhibition might not under all circumstances have anti-tumoral activity. This evidence concerns the gene MCL1 and colorectal carcinoma.