title: Erythroid differentiation sensitizes K562 leukemia cells to TRAIL-induced apoptosis by downregulation of c-FLIP.
abstract: Regulation of the apoptotic threshold is of great importance in the homeostasis of both differentiating and fully developed organ systems. Triggering differentiation has been employed as a strategy to inhibit cell proliferation and accelerate apoptosis in malignant cells, in which the apoptotic threshold is often characteristically elevated. To better understand the mechanisms underlying differentiation-mediated regulation of apoptosis, we have studied death receptor responses during erythroid differentiation of K562 erythroleukemia cells, which normally are highly resistant to tumor necrosis factor (TNF) alpha-, FasL-, and TRAIL-induced apoptosis. However, upon hemin-mediated erythroid differentiation, K562 cells specifically lost their resistance to TNF-related apoptosis-inducing ligand (TRAIL), which efficiently killed the differentiating cells independently of mitochondrial apoptotic signaling. Concomitantly with the increased sensitivity, the expression of both c-FLIP splicing variants, c-FLIP(L) and c-FLIP(S), was downregulated, resulting in an altered caspase 8 recruitment and cleavage in the death-inducing signaling complex (DISC). Stable overexpression of both c-FLIP(L) and c-FLIP(S) rescued the cells from TRAIL-mediated apoptosis with isoform-specific effects on DISC-recruited caspase 8. Our results show that c-FLIP(L) and c-FLIP(S) potently control TRAIL responses, both by distinct regulatory features, and further imply that the differentiation state of malignant cells determines their sensitivity to death receptor signals.
authors.affiliation: Turku Centre for Biotechnology, University of Turku and Abo Akademi University, FIN-20521 Turku, Finland.
authors.forename: Ville
authors.initials: V
authors.lastname: Hietakangas
authors.forename: Minna
authors.initials: M
authors.lastname: Poukkula
authors.forename: Kaisa M
authors.initials: KM
authors.lastname: Heiskanen
authors.forename: Jarkko T
authors.initials: JT
authors.lastname: Karvinen
authors.forename: Lea
authors.initials: L
authors.lastname: Sistonen
authors.forename: John E
authors.initials: JE
authors.lastname: Eriksson
mesh_terms: D017398:Alternative Splicing; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D003574:Cytochrome c Group / Q000378:metabolism; D053418:Death Domain Receptor Signaling Adaptor Proteins; D015536:Down-Regulation; D018922:HL-60 Cells / Q000378:metabolism / Q000473:pathology; D006427:Hemin / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes; D047908:Intracellular Signaling Peptides and Proteins; D020014:K562 Cells / Q000378:metabolism / Q000473:pathology*; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D051020:bcl-X Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D003574:Cytochrome c Group; D053418:Death Domain Receptor Signaling Adaptor Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D006427:Hemin; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases