Proteasome activities in HSPC cells. CD34⁺ cells were treated as indicated, lysed, and tested for proteasome peptidase activities. Peptidase activities were assayed by monitoring the production of 7-amino-4-methylcoumarin (amc) from fluorogenic peptides: Suc-LLVY-amc for the chymotrypsin-like activity, Boc-LRR-amc for the trypsin-like activity, and Ac-YVAD-amc for the caspase-like activity. (A) Peptidase activities of cells exposed to cytokines (+cyt) or not (–cyt) for 24 hours. (B-D) Chymotrypsin-like activity of cells kept in culture for the indicated times with (+cyt) or without (–cyt) cytokines (B); exposed to cytokines (+cyt), to MG132 (MG132), or to both treatments (+cyt MG132) for 24 hours (C); and exposed to the indicated cytokine for 24 hours (D). Values in panels A-C are mean ± SD of 3 measurements from 1 of 2 experiments with similar results, performed with different cell preparations. Values in panel D are the average of 2 experiments and are expressed as percentage of the proteasome activity of unstimulated cells.