title: Direct transcriptional regulation of Bim by FoxO3a mediates STI571-induced apoptosis in Bcr-Abl-expressing cells.
abstract: In this study, we have used the human BV173 and the mouse BaF3/Bcr-Abl-expressing cell lines as model systems to investigate the molecular mechanisms whereby STI571 and FoxO3a regulate Bim expression and apoptosis. FoxO3a lies downstream of Bcr-Abl signalling and is constitutively phosphorylated in the Bcr-Abl-positive BV173 and BaF3/Bcr-Abl cells. Inhibition of Bcr-Abl kinase by STI571 results in FoxO3a activation, induction of Bim expression and apoptosis. Using reporter gene assays, we demonstrate that STI571 and FoxO3a activate Bim transcription through a FoxO-binding site (FHRE) located within the promoter. This was verified by DNA pull-down and chromatin immunoprecipitation analyses. We find that conditional activation of FoxO3a leads to induction of Bim expression and apoptosis. Conversely, silencing of FoxO3a in Bcr-Abl-expressing cells abolishes STI571-mediated Bim induction and apoptosis. Together, the results presented clearly confirm FoxO3a as a key regulator of apoptosis induced by STI571, and show that Bim is a direct transcriptional target of FoxO3a that mediates the STI571-induced apoptosis. Thus, STI571 induces an accumulation of FoxO3a activity which in turn binds directly to an FHRE in the promoter to activate Bim expression and apoptosis.
authors.affiliation: Cancer Research-UK labs, Department of Cancer Medicine, MRC Cyclotron Building, Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK.
authors.forename: Abdelkader
authors.initials: A
authors.lastname: Essafi
authors.forename: Silvia
authors.initials: S
authors.lastname: Fernández de Mattos
authors.forename: Yasmin A M
authors.initials: YA
authors.lastname: Hassen
authors.forename: Inês
authors.initials: I
authors.lastname: Soeiro
authors.forename: Ghulam J
authors.initials: GJ
authors.lastname: Mufti
authors.forename: N Shaun B
authors.initials: NS
authors.lastname: Thomas
authors.forename: René H
authors.initials: RH
authors.lastname: Medema
authors.forename: Eric W-F
authors.initials: EW
authors.lastname: Lam
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides; D002352:Carrier Proteins / Q000235:genetics*; D002460:Cell Line; D045744:Cell Line, Tumor; D004247:DNA; D004268:DNA-Binding Proteins / Q000502:physiology*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D010879:Piperazines / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D011743:Pyrimidines / Q000494:pharmacology*; D034741:RNA, Small Interfering; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D001549:Benzamides; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D008565:Membrane Proteins; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D011743:Pyrimidines; D034741:RNA, Small Interfering; D014157:Transcription Factors; D000068877:Imatinib Mesylate; D004247:DNA; D016044:Fusion Proteins, bcr-abl