title: The antiproliferative activity of kinase inhibitors in chronic myeloid leukemia cells is mediated by FOXO transcription factors.
abstract: Chronic myeloid leukemia (CML) is initiated and maintained by the tyrosine kinase BCR-ABL which activates a number of signal transduction pathways, including PI3K/AKT signaling and consequently inactivates FOXO transcription factors. ABL-specific tyrosine kinase inhibitors (TKIs) induce minimal apoptosis in CML progenitor cells, yet exert potent antiproliferative effects, through as yet poorly understood mechanisms. Here, we demonstrate that in CD34+ CML cells, FOXO1 and 3a are inactivated and relocalized to the cytoplasm by BCR-ABL activity. TKIs caused a decrease in phosphorylation of FOXOs, leading to their relocalization from cytoplasm (inactive) to nucleus (active), where they modulated the expression of key FOXO target genes, such as Cyclin D1, ATM, CDKN1C, and BCL6 and induced G1 arrest. Activation of FOXO1 and 3a and a decreased expression of their target gene Cyclin D1 were also observed after 6 days of in vivo treatment with dasatinib in a CML transgenic mouse model. The over-expression of FOXO3a in CML cells combined with TKIs to reduce proliferation, with similar results seen for inhibitors of PI3K/AKT/mTOR signaling. While stable expression of an active FOXO3a mutant induced a similar level of quiescence to TKIs alone, shRNA-mediated knockdown of FOXO3a drove CML cells into cell cycle and potentiated TKI-induced apoptosis. These data demonstrate that TKI-induced G1 arrest in CML cells is mediated through inhibition of the PI3K/AKT pathway and reactivation of FOXOs. This enhanced understanding of TKI activity and induced progenitor cell quiescence suggests that new therapeutic strategies for CML should focus on manipulation of this signaling network.
authors.affiliation: Paul O'Gorman Leukaemia Research Centre, College of Medical, Veterinary & Life Sciences, Institute of Cancer Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Francesca
authors.initials: F
authors.lastname: Pellicano
authors.forename: Mary T
authors.initials: MT
authors.lastname: Scott
authors.forename: G Vignir
authors.initials: GV
authors.lastname: Helgason
authors.forename: Lisa E M
authors.initials: LE
authors.lastname: Hopcroft
authors.forename: Elaine K
authors.initials: EK
authors.lastname: Allan
authors.forename: Mark
authors.initials: M
authors.lastname: Aspinall-O'Dea
authors.forename: Mhairi
authors.initials: M
authors.lastname: Copland
authors.forename: Andrew
authors.initials: A
authors.lastname: Pierce
authors.forename: Brian J P
authors.initials: BJ
authors.lastname: Huntly
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Whetton
authors.forename: Tessa L
authors.initials: TL
authors.lastname: Holyoake
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor; D000069439:Dasatinib / Q000494:pharmacology; D051858:Forkhead Transcription Factors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects; D020869:Gene Expression Profiling; D006801:Humans; D020014:K562 Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000473:pathology; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D051858:Forkhead Transcription Factors; D047428:Protein Kinase Inhibitors; D000069439:Dasatinib
keywords: BCR-ABL; CD34+ progenitor cells; Chronic myeloid leukemia; FOXO transcription factors; Quiescence; Tyrosine kinase inhibitors