Dynamics of proteasome subunit expression in bortezomib-resistant cells after exposure and removal of bortezomib. (A) Effect of 1- to 7-day removal of bortezomib-selective pressure from THP1/BTZ₁₀₀ cells on proteasome subunit β5 protein expression and (B) β5 proteasome subunit mRNA expression. Results are the means (± SD) of 3 separate experiments. (C) Protein expression of β1-, β2-, β5- and α/β-core proteasome subunits in THP1/WT cells, THP1/BTZ_(-100) cells, and THP1/BTZ₂₀₀ cells after 4-day bortezomib washout (control/0) and 24-hour exposure to the indicated concentrations of bortezomib. (D) Protein expression of β1, β2, β5- and α/β-core proteasome subunits for THP1/WT cells, THP1/BTZ_(-100) cells, and THP1/BTZ₂₀₀ cells after a 4-day bortezomib washout period (control) and after 24-hour incubation with the indicated concentrations of bor-tezomib. Results of scanning of protein band intensities are presented as the mean ± SD of 3 separate experiments. (E) Effect of short-term (0-24 hours) exposure of THP1/BTZ_(-100) cells to 100 nM bortezomib on proteasome subunit β5 protein expression and (F) β5 proteasome subunit mRNA expression. Results are the means of duplicate experiments (E) and 3 separate experiments (± SD; F).