Impact of IFN-γ exposure on proteasome catalytic activity in intact cells and cell extracts of bortezomib-resistant and bortezomib-sensitive 8226 (MM), THP1 (AML) and CEM (ALL) cells. (A) Chymotrypsin-like, caspase-like and trypsin-like proteasome activity in intact bortezomib-resistant and (B) bortezomib-sensitive 8226, THP1 and CEM cells before and after 6-72 hrs exposure 100 U/ml IFN-γ. Results are presented relative to untreated controls and represent the mean (± SD) of 3 individual experiments. (C) β5, β5i and β1i-associated catalytic activity in cell extracts of 8226/WT, 8226/BTZ100, THP1/WT, THP1/BTZ, CEM/WT, and CEM/BTZ200 cells after 24 hr and 48 hr exposure to 100 U/ml IFN-γ. Activity assays in cell extracts employed subunit-specific substrates. Results represent the mean (± SD) of 3 experiments.