title: Therapy-resistant acute lymphoblastic leukemia (ALL) cells inactivate FOXO3 to escape apoptosis induction by TRAIL and Noxa.
abstract: Forkhead transcription factors (FOXO) are downstream targets of the phosphoinositol-3-kinase (PI3K) protein kinase B (PKB) signaling cascade and play a pivotal role in cell differentiation, cell cycle and apoptosis. We found that cells from prednisone-resistant T-acute lymphoblastic leukemia (T-ALL) patients showed cytoplasmic localization of FOXO3 in comparison to prednisone-sensitive patients suggesting its inactivation. To determine the impact of FOXO3, T-ALL cells were infected with a 4OH-tamoxifen-regulated, phosphorylation-independent FOXO3(A3)ERtm allele. After FOXO3-activation these cells undergo caspase-dependent apoptosis. FOXO3 induces the death ligand TRAIL and the BH3-only protein Noxa implicating extrinsic as well as intrinsic death signaling. Whereas dnFADD partially inhibited cell death, CrmA and dnBID efficiently rescued ALL cells after FOXO3 activation, suggesting a caspase-8 amplifying feedback loop downstream of FADD. Knockdown of TRAIL and Noxa reduced FOXO3-induced apoptosis, implicating that mitochondrial destabilization amplifies TRAIL-signaling. The-reconstitution of the cell cycle inhibitor p16INK4A, which sensitizes ALL cells to mitochondria-induced cell death, represses FOXO3 protein levels and reduces the dependency of these leukemia cells on PI3K-PKB signaling. This suggests that if p16INK4A is deleted during leukemia development, FOXO3 levels elevate and FOXO3 has to be inactivated by deregulation of the PI3K-PKB pathway to prevent FOXO3-induced cell death.
authors.affiliation: Department of Pediatrics I, Medical University Innsbruck, Austria.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ausserlechner
authors.forename: Christina
authors.initials: C
authors.lastname: Salvador
authors.forename: Andrea
authors.initials: A
authors.lastname: Deutschmann
authors.forename: Martin
authors.initials: M
authors.lastname: Bodner
authors.forename: Giampietro
authors.initials: G
authors.lastname: Viola
authors.forename: Roberta
authors.initials: R
authors.lastname: Bortolozzi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Basso
authors.forename: Judith
authors.initials: J
authors.lastname: Hagenbuchner
authors.forename: Petra
authors.initials: P
authors.lastname: Obexer
mesh_terms: D000293:Adolescent; D017209:Apoptosis / Q000502:physiology; D002648:Child; D002675:Child, Preschool; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis / Q000235:genetics; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt