title: Mechanism and functional role of XIAP and Mcl-1 down-regulation in flavopiridol/vorinostat antileukemic interactions.
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.
authors.affiliation: Massey Cancer Center, Virginia Commonwealth University, Medical College of Virginia Campus, MCV Station Box 980035, Richmond, VA 23298. stgrant@hsc.vcu.edu.
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Rosato
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Almenara
authors.forename: Sarah S
authors.initials: SS
authors.lastname: Kolla
authors.forename: Sonia C
authors.initials: SC
authors.lastname: Maggio
authors.forename: Stefanie
authors.initials: S
authors.lastname: Coe
authors.forename: Maria S
authors.initials: MS
authors.lastname: Giménez
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D001752:Blast Crisis; D015153:Blotting, Western; D002087:Butyrates / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D045304:Cytochromes c / Q000378:metabolism; D015536:Down-Regulation; D004347:Drug Interactions; D005419:Flavonoids / Q000494:pharmacology*; D056572:Histone Deacetylase Inhibitors; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects; D014410:Tumor Stem Cell Assay; D020298:U937 Cells / Q000187:drug effects; D000077337:Vorinostat; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: C494829:AIFM1 protein, human; D000970:Antineoplastic Agents; D051033:Apoptosis Inducing Factor; D002087:Butyrates; D005419:Flavonoids; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D010880:Piperidines; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C077990:alvocidib; D000077337:Vorinostat; D045304:Cytochromes c; D018844:Cyclin-Dependent Kinases; D020169:Caspases