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.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Animals
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Antineoplastic Combined Chemotherapy Protocols / pharmacology*
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Apoptosis / drug effects
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Biphenyl Compounds / administration & dosage
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Biphenyl Compounds / pharmacology*
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Cyclin-Dependent Kinases / antagonists & inhibitors
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Down-Regulation / drug effects
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Drug Synergism
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HL-60 Cells
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Humans
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Jurkat Cells
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Leukemia / drug therapy*
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Leukemia / genetics
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Leukemia / metabolism
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Mice
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Mice, Knockout
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins / biosynthesis
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism*
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Nitrophenols / administration & dosage
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Nitrophenols / pharmacology*
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Piperazines / administration & dosage
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Piperazines / pharmacology
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Protein Kinase Inhibitors / pharmacology
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Proto-Oncogene Proteins c-bcl-2 / biosynthesis
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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Purines / administration & dosage
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Purines / pharmacology*
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RNA Interference
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Roscovitine
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Sulfonamides / administration & dosage
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Sulfonamides / pharmacology*
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U937 Cells
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bcl-2 Homologous Antagonist-Killer Protein / metabolism*
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bcl-2-Associated X Protein / metabolism*
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bcl-X Protein / metabolism
Substances
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ABT-737
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BAK1 protein, human
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BAX protein, human
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BCL2L1 protein, human
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Biphenyl Compounds
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Mcl1 protein, mouse
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins
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Nitrophenols
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Piperazines
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Protein Kinase Inhibitors
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Proto-Oncogene Proteins c-bcl-2
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Purines
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Sulfonamides
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bcl-2 Homologous Antagonist-Killer Protein
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bcl-2-Associated X Protein
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bcl-X Protein
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Roscovitine
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Cyclin-Dependent Kinases