Induction of autophagy-dependent necroptosis is required for childhood acute lymphoblastic leukemia cells to overcome glucocorticoid resistance
Laura Bonapace, Beat C. Bornhauser, Maike Schmitz, Gunnar Cario, Urs Ziegler, Felix K. Niggli, Beat W. Schäfer, Martin Schrappe, Martin Stanulla, Jean-Pierre Bourquin
Laura Bonapace, Beat C. Bornhauser, Maike Schmitz, Gunnar Cario, Urs Ziegler, Felix K. Niggli, Beat W. Schäfer, Martin Schrappe, Martin Stanulla, Jean-Pierre Bourquin
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Research Article Oncology

Induction of autophagy-dependent necroptosis is required for childhood acute lymphoblastic leukemia cells to overcome glucocorticoid resistance

Abstract

In vivo resistance to first-line chemotherapy, including to glucocorticoids, is a strong predictor of poor outcome in children with acute lymphoblastic leukemia (ALL). Modulation of cell death regulators represents an attractive strategy for subverting such drug resistance. Here we report complete resensitization of multidrug-resistant childhood ALL cells to glucocorticoids and other cytotoxic agents with subcytotoxic concentrations of obatoclax, a putative antagonist of BCL-2 family members. The reversal of glucocorticoid resistance occurred through rapid activation of autophagy-dependent necroptosis, which bypassed the block in mitochondrial apoptosis. This effect was associated with dissociation of the autophagy inducer beclin-1 from the antiapoptotic BCL-2 family member myeloid cell leukemia sequence 1 (MCL-1) and with a marked decrease in mammalian target of rapamycin (mTOR) activity. Consistent with a protective role for mTOR in glucocorticoid resistance in childhood ALL, combination of rapamycin with the glucocorticoid dexamethasone triggered autophagy-dependent cell death, with characteristic features of necroptosis. Execution of cell death, but not induction of autophagy, was strictly dependent on expression of receptor-interacting protein (RIP-1) kinase and cylindromatosis (turban tumor syndrome) (CYLD), two key regulators of necroptosis. Accordingly, both inhibition of RIP-1 and interference with CYLD restored glucocorticoid resistance completely. Together with evidence for a chemosensitizing activity of obatoclax in vivo, our data provide a compelling rationale for clinical translation of this pharmacological approach into treatments for patients with refractory ALL.

Authors

Laura Bonapace, Beat C. Bornhauser, Maike Schmitz, Gunnar Cario, Urs Ziegler, Felix K. Niggli, Beat W. Schäfer, Martin Schrappe, Martin Stanulla, Jean-Pierre Bourquin

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Figure 2

Obatoclax resensitizes GC-resistant ALL cells to dexamethasone without activation of mitochondrial apoptosis.

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Obatoclax resensitizes GC-resistant ALL cells to dexamethasone without a...
(A) ALL cells were treated as indicated for 48 hours, for controls STS or zVAD.fmk (80 nM) was used, and cell viability was assessed with the MTT assay. 697 cells served as GC-sensitive control. (B) Jurkat CASP9–/– and BAX–/–BAK–/– cells were treated for 72 hours as indicated, and clonogenic survival was assessed after incubation in methylcellulose for 7 days. (C) Percentages of cells with JC-1 monomers, corresponding to a loss of the mitochondrial potential, are shown for GC-resistant CEM-C1 and GC-sensitive CEM-C7 cells and in samples from PGR and PPR patients after treatment as indicated for 16 hours. (D) Cytochrome c release was induced in steroid-sensitive RS4;11 cells but not in the resistant CEM-C1 cell line upon treatment with dexamethasone or dexamethasone and obatoclax. STS was used as positive control. Cytochrome c release was detected by flow cytometry. ***P < 0.05.