Apoptosis after exposure to 17-AAG and UCN-01 for 10 hours. U937 cells were exposed to 400 nM 17-AAG with or without 75 nM UCN-01 for 10 hours, after which cells were lysed, proteins separated by SDS-PAGE, and Western analysis used to monitor expression of (A) Raf-1, total MEK, phospho-MEK, total ERK, phospho-ERK, and phospho-p38 MAPK, or (B) total Akt, phospho-Akt, phospho-GSK3α/β, p34^cdc2, phospho-p34^cdc2, and phospho-JNK. For each condition, lanes were loaded with 25 μg protein; blots were subsequently stripped and reprobed with antibodies to actin to ensure equivalent loading and transfer. The results of a representative experiment are shown; an additional study yielded equivalent results.