title: Mcl-1 down-regulation potentiates ABT-737 lethality by cooperatively inducing Bak activation and Bax translocation.
abstract: The Bcl-2 antagonist ABT-737 targets Bcl-2/Bcl-xL but not Mcl-1, which may confer resistance to this novel agent. Here, we show that Mcl-1 down-regulation by the cyclin-dependent kinase (CDK) inhibitor roscovitine or Mcl-1-shRNA dramatically increases ABT-737 lethality in human leukemia cells. ABT-737 induces Bax conformational change but fails to activate Bak or trigger Bax translocation. Coadministration of roscovitine and ABT-737 untethers Bak from Mcl-1 and Bcl-xL, respectively, triggering Bak activation and Bax translocation. Studies employing Bax and/or Bak knockout mouse embryonic fibroblasts (MEFs) confirm that Bax is required for ABT-737+/-roscovitine lethality, whereas Bak is primarily involved in potentiation of ABT-737-induced apoptosis by Mcl-1 down-regulation. Ectopic Mcl-1 expression attenuates Bak activation and apoptosis by ABT-737+roscovitine, whereas cells overexpressing Bcl-2 or Bcl-xL remain fully sensitive. Finally, Mcl-1 knockout MEFs are extremely sensitive to Bak conformational change and apoptosis induced by ABT-737, effects that are not potentiated by roscovitine. Collectively, these findings suggest down-regulation of Mcl-1 by either CDK inhibitors or genetic approaches dramatically potentiate ABT-737 lethality through cooperative interactions at two distinct levels: unleashing of Bak from both Bcl-xL and Mcl-1 and simultaneous induction of Bak activation and Bax translocation. These findings provide a mechanistic basis for simultaneously targeting Mcl-1 and Bcl-2/Bcl-xL in leukemia.
authors.affiliation: Department of Medicine, Virginia Commonwealth University and Massey Cancer Center, Richmond, Virginia 23298, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Chen
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Hisashi
authors.initials: H
authors.lastname: Harada
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000008:administration & dosage / Q000494:pharmacology*; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D015536:Down-Regulation / Q000187:drug effects; D004357:Drug Synergism; D018922:HL-60 Cells; D006801:Humans; D019169:Jurkat Cells; D007938:Leukemia / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009596:Nitrophenols / Q000008:administration & dosage / Q000494:pharmacology*; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011687:Purines / Q000008:administration & dosage / Q000494:pharmacology*; D034622:RNA Interference; D000077546:Roscovitine; D013449:Sulfonamides / Q000008:administration & dosage / Q000494:pharmacology*; D020298:U937 Cells; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism*; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C501332:ABT-737; C494772:BAK1 protein, human; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D001713:Biphenyl Compounds; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D009596:Nitrophenols; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011687:Purines; D013449:Sulfonamides; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D000077546:Roscovitine; D018844:Cyclin-Dependent Kinases