title: Regulation of 17-AAG-induced apoptosis: role of Bcl-2, Bcl-XL, and Bax downstream of 17-AAG-mediated down-regulation of Akt, Raf-1, and Src kinases.
abstract: 17-allylamino-demethoxy geldanamycin (17-AAG) inhibits the chaperone function of heat shock protein-90 (Hsp-90) and promotes the proteasomal degradation of its misfolded client proteins. Here, we demonstrate that treatment of the human acute myeloid leukemia HL-60 cells with 17-AAG attenuates the intracellular levels of a number of Hsp-90 client proteins, including Akt, c-Raf-1, and c-Src. Also, 17-AAG induced the mitochondrial release and cytosolic accumulation of cytochrome c (cyt c) and second mitochondria-derived activator of caspases (Smac)/DIABLO, resulting in the activation of caspase-9 and caspase-3 and apoptosis. Treatment with 17-AAG triggered the B-cell lymphoma-2 (Bcl-2)-associated X protein (Bax) conformational change associated with apoptosis, while Bax-deficient cells were resistant to 17-AAG-induced apoptosis. In addition, in HL-60/Bcl-2 and HL-60/Bcl-xL cells, which ectopically express Bcl-2 and Bcl-xL respectively, 17-AAG-induced Bax conformational change, cytosolic accumulation of cyt c and Smac/DIABLO, and apoptosis were markedly inhibited. Although the rate of 17-AAG-mediated decline in Akt, c-Raf-1, and c-Src levels was blunted, the total decline was not compromised in HL-60/Bcl-2 and HL-60/Bcl-xL cells. Cotreatment with HA14-1, a nonpeptidic ligand that can bind and inhibit the antiapoptotic activity of Bcl-2, significantly overcame the resistance to 17-AAG-induced apoptosis in HL-60/Bcl-2 cells. Together, these findings indicate that although 17-AAG treatment causes the levels of a number of survival-signaling protein kinases to decline, the downstream engagement of the mitochondrial pathway of apoptosis is regulated by the activity of the Bcl-2 family of proteins. Also, neutralizing the antiapoptotic effect of Bcl-2 would further enhance the antileukemia activity of 17-AAG.
authors.affiliation: Department of Interdisciplinary Oncology, Moffitt Cancer Center and Research Institute, University of South Florida, 12902 Magnolia Drive, MRC 3 East, Rm 3056, Tampa, FL 33612, USA.
authors.forename: Ramadevi
authors.initials: R
authors.lastname: Nimmanapalli
authors.forename: Erica
authors.initials: E
authors.lastname: O'Bryan
authors.forename: Deborah
authors.initials: D
authors.lastname: Kuhn
authors.forename: Hirohito
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: Hong-Gang
authors.initials: HG
authors.lastname: Wang
authors.forename: Kapil N
authors.initials: KN
authors.lastname: Bhalla
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones; D015153:Blotting, Western; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D047029:Lactams, Macrocyclic; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000096:biosynthesis / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf / Q000032:analysis / Q000096:biosynthesis; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D019061:src-Family Kinases / Q000032:analysis / Q000096:biosynthesis
chemical_list: C494826:BAX protein, human; C494811:BCL2L1 protein, human; D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D017828:Rifabutin; C112765:tanespimycin; D019061:src-Family Kinases; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf