MEK1/2 inhibitors promote Ara-C-induced apoptosis but not loss of Deltapsi(m) in HL-60 cells.
The effects of pharmacologic MEK1/2 inhibitors on ara-C-mediated mitochondrial injury, caspase activation, and apoptosis have been examined in HL-60 leukemic cells. Coadministration of subtoxic concentrations of the MEK1/2 inhibitors U0126 (20 microM), PD98059 (40 microM), or PD184352 (10 microM) with 10-100 microM ara-C (6 h) potentiated apoptosis (i.e., by approx twofold), and pro-caspase 3, pro-caspase 8, Bid, and PARP cleavage. Unexpectedly, MEK1/2 inhibitors failed to enhance ara-C-mediated loss of mitochondrial membrane potential (DeltaPsi(m)), but instead induced substantial increases in cytosolic release of cytochrome c and Smac/DIABLO. U0126/ara-C-mediated apoptosis and pro-caspase 3 activation, but not cytochrome c or Smac/DIABLO release, were blocked by the pan-caspase inhibitor ZVAD-fmk. Together, these findings indicate that potentiation of ara-C-mediated lethality in HL-60 cells by MEK1/2 inhibitors involves enhanced cytosolic release of cytochrome c and Smac/DIABLO but not discharge of DeltaPsi(m), implicating activation of an apoptotic pathway that differs, at least with respect to the nature of the accompanying mitochondrial injury, from that triggered by ara-C alone.
Yu
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Department of Medicine, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Wang
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Dent
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D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D051777:AraC Transcription Factor; D001426:Bacterial Proteins; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002352:Carrier Proteins; D003574:Cytochrome c Group / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D008564:Membrane Potentials / Q000187:drug effects*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors*; D009570:Nitriles / Q000494:pharmacology; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011506:Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism* / Q000494:pharmacology; D009418:S100 Proteins / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors
C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; D051017:Apoptosis Regulatory Proteins; D051777:AraC Transcription Factor; D001426:Bacterial Proteins; D001549:Benzamides; D002070:Butadienes; D002352:Carrier Proteins; D003574:Cytochrome c Group; C412403:DIABLO protein, human; D004791:Enzyme Inhibitors; D005419:Flavonoids; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D009570:Nitriles; D011506:Proteins; D012097:Repressor Proteins; D009418:S100 Proteins; D014157:Transcription Factors; C113580:U 0126; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one