Abstract
The mechanism and functional significance of XIAP and Mcl-1 down-regulation in human leukemia cells exposed to the histone deacetylase inhibitor vorinostat and the cyclin-dependent kinase inhibitor flavopiridol was investigated. Combined exposure of U937 leukemia cells to marginally toxic concentrations of vorinostat and flavopiridol resulted in a marked increase in mitochondrial damage and apoptosis accompanied by pronounced reductions in XIAP and Mcl-1 mRNA and protein. Down-regulation of Mcl-1 and XIAP expression by vorinostat/flavopiridol was associated with enhanced inhibition of phosphorylation of RNA polymerase II and was amplified by caspase-mediated protein degradation. Chromatin immunoprecipitation analysis revealed that XIAP and Mcl-1 down-regulation were also accompanied by both decreased association of nuclear factor-kappaB (XIAP) and increased E2F1 association (Mcl-1) with their promoter regions, respectively. Ectopic expression of Mcl-1 but not XIAP partially protected cells from flavopiridol/vorinostat-mediated mitochondrial injury at 48 h, but both did not significantly restored clonogenic potential. Flavopiridol/vorinostat-mediated transcriptional repression of XIAP, Mcl-1-enhanced apoptosis, and loss of clonogenic potential also occurred in primary acute myelogenous leukemia (AML) blasts. Together, these findings indicate that transcriptional repression of XIAP and Mcl-1 by flavopiridol/vorinostat contributes functionally to apoptosis induction at early exposure intervals and raise the possibility that expression levels may be a useful surrogate marker for activity in current trials.
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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Antineoplastic Agents / pharmacology*
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Apoptosis / drug effects
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Apoptosis Inducing Factor / metabolism
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Blast Crisis
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Blotting, Western
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Butyrates / pharmacology
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Caspases / metabolism
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Chromatin Immunoprecipitation
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Cyclin-Dependent Kinases / antagonists & inhibitors
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Cytochromes c / metabolism
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Down-Regulation
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Drug Interactions
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Flavonoids / pharmacology*
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Histone Deacetylase Inhibitors
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Humans
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Hydroxamic Acids / pharmacology*
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Leukemia, Myeloid, Acute / drug therapy
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Leukemia, Myeloid, Acute / metabolism
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Membrane Potential, Mitochondrial / drug effects
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins / antagonists & inhibitors
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Neoplasm Proteins / metabolism*
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Piperidines / pharmacology*
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Proto-Oncogene Proteins c-bcl-2 / antagonists & inhibitors
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Proto-Oncogene Proteins c-bcl-2 / metabolism*
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Transcription, Genetic / drug effects
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Tumor Stem Cell Assay
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U937 Cells / drug effects
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Vorinostat
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X-Linked Inhibitor of Apoptosis Protein / antagonists & inhibitors
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X-Linked Inhibitor of Apoptosis Protein / genetics
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X-Linked Inhibitor of Apoptosis Protein / metabolism*
Substances
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AIFM1 protein, human
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Antineoplastic Agents
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Apoptosis Inducing Factor
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Butyrates
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Flavonoids
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Histone Deacetylase Inhibitors
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Hydroxamic Acids
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins
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Piperidines
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Proto-Oncogene Proteins c-bcl-2
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RNA, Messenger
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X-Linked Inhibitor of Apoptosis Protein
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XIAP protein, human
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alvocidib
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Vorinostat
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Cytochromes c
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Cyclin-Dependent Kinases
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Caspases