Inhibition of Hsp90 by IPI-504 causes BCR-ABL protein degradation. (A) Structure of IPI-504. (B) IPI-504–induced disassociation of BCR-ABL and Hsp90, and subsequent degradation of BCR-ABL protein. BCR-ABL-T315I–expressing 32D cells were treated with IPI-504 (2 μM) for 30 minutes and 4 hours, respectively. Protein lysates were analyzed by Western blotting using antibodies indicated. WCL indicates whole cell lysate; IP, immunoprecipitation; and IB, immunoblotting. (C) The proteasome inhibitor PS-341 restored IPI-504–mediated depletion of BCR-ABL protein. BCR-ABL-T315I–expressing 32D cells were treated with IPI-504 (2 μM) alone or IPI-504 plus PS-341 (100 nM) for 4 or 8 hours, respectively. Protein lysates were analyzed by Western blotting using antibodies indicated. The well-described Hsp90 client, Akt, was evaluated as a positive control. Note that the cells were pretreated with PS-341 for 30 minutes prior to the cotreatment with IPI-504 and PS-341. The black lines indicate that the lanes that were not adjacent on the same original Western blotting gel were brought together to generate this figure.