Time-course study of U937 cells exposed to 17-AAG and UCN-01. (A) U937 cells were exposed to 400 nM 17-AAG with or without 75 nM UCN-01 for the designated interval, after which the percentage of apoptotic cells was determined as described in “Materials and methods.” (B) U937 cells were exposed to 75 nM UCN-01 plus 400 nM 17-AAG for 30 hours in the presence or absence of 1 μM cycloheximide (CHX), after which the extent of apoptosis was evaluated as described. (C) U937 cells were exposed for 30 hours to 400 nM 17-AAG in the presence or absence of 1 μM bisindolylmaleimide (GFX), after which apoptosis was evaluated as above. In each case, values represent the means ± SD for 3 separate experiments performed in triplicate.