P16INK4A sensitizes human leukemia cells to FAS- and glucocorticoid-induced apoptosis via induction of BBC3/Puma and repression of MCL1 and BCL2

Tyrolean Cancer Research Institute, Department of Pediatrics IV, Medical University Innsbruck, Innsbruck 6020, Austria.
Journal of Biological Chemistry (Impact Factor: 4.57). 10/2009; 284(45):30933-40. DOI: 10.1074/jbc.M109.051441
Source: PubMed

ABSTRACT Loss of CDKN2A/p16(INK4A) in hematopoietic stem cells is associated with enhanced self-renewal capacity and might facilitate progression of damaged stem cells into pre-cancerous cells that give rise to leukemia. This is also reflected by the frequent loss of the INK4A locus in acute lymphoblastic T-cell leukemia. T-cell acute lymphoblastic leukemia cells designed to conditionally express p16(INK4A) arrest in the G(0)/G(1) phase of the cell cycle and show increased sensitivity to glucocorticoid- and tumor necrosis factor receptor superfamily 6-induced apoptosis. To investigate the underlying molecular mechanism for increased death sensitivity, we interfered with specific steps of apoptosis signaling by expression of anti-apoptotic proteins. We found that alterations in cell death susceptibility resulted from changes in the composition of pro- and anti-apoptotic BCL2 proteins, i.e. repression of MCL1, BCL2, and PMAIP1/Noxa and the induction of pro-apoptotic BBC3/Puma. Interference with Puma induction by short hairpin RNA technology or retroviral expression of MCL1 or BCL2 significantly reduced both glucocorticoid- and FAS-induced cell death in p16(INK4A)-reconstituted leukemia cells. These results suggest that Puma, in concert with MCL1 and BCL2 repression, critically mediates p16(INK4A)-induced death sensitization and that in human T-cell leukemia the deletion of p16(INK4A) confers apoptosis resistance by shifting the balance of pro- and anti-apoptotic BCL2 proteins toward apoptosis protection.

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    • "This gene belongs to the BCL super-family, which is responsible for cell survival. It has been reported that down-regulation of MCL1 sensitizes T-cell leukemia cells to treatment with glucocorticoids [79]. In our system this gene appeared to be stable across all concentrations while, interestingly, it was up-regulated by the low prednisolone dose, confirming the anti-apoptotic effect observed previously by the low dose. "
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    ABSTRACT: It has been shown previously that glucocorticoids exert a dual mechanism of action, entailing cytotoxic, mitogenic as well as cell proliferative and anti-apoptotic responses, in a dose-dependent manner on CCRF-CEM cells at 72 h. Early gene expression response implies a dose-dependent dual mechanism of action of prednisolone too, something reflected on cell state upon 72 h of treatment. In this work, a generic, computational microarray data analysis framework is proposed, in order to examine the hypothesis, whether CCRF-CEM cells exhibit an intrinsic or acquired mechanism of resistance and investigate the molecular imprint of this, upon prednisolone treatment. The experimental design enables the examination of both the dose (0 nM, 10 nM, 22 uM, 700 uM) effect of glucocorticoid exposure and the dynamics (early and late, namely 4 h, 72 h) of the molecular response of the cells at the transcriptomic layer. In this work, we demonstrated that CCRF-CEM cells may attain a mixed mechanism of response to glucocorticoids, however, with a clear preference towards an intrinsic mechanism of resistance. Specifically, at 4 h, prednisolone appeared to down-regulate apoptotic genes. Also, low and high prednisolone concentrations up-regulates genes related to metabolism and signal-transduction in both time points, thus favoring cell proliferative actions. In addition, regulation of NF-κB-related genes implies an inherent mechanism of resistance through the established link of NF-κB inflammatory role and GC-induced resistance. The analysis framework applied here highlights prednisolone-activated regulatory mechanisms through identification of early responding sets of genes. On the other hand, study of the prolonged exposure to glucocorticoids (72 h exposure) highlights the effect of homeostatic feedback mechanisms of the treated cells. Overall, it appears that CCRF-CEM cells in this study exhibit a diversified, combined pattern of intrinsic and acquired resistance to prednisolone, with a tendency towards inherent resistant characteristics, through activation of different molecular courses of action.
    Journal of Clinical Bioinformatics 12/2011; 1(36). DOI:10.1186/2043-9113-1-36
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    • "Retrovirally transduced Survivin compensates for the loss of the endogenous protein in CEM/p16-Survivin cells. Re-expression of p16INK4A accelerates death-receptor-induced (anti-FAS anibody, 0.1 mg/ml, for four hours) and glucocorticoidinduced apoptosis (10 nM dexamethasone, 24 hours) as shown in B und C (Obexer et al, 2009a). Ectopic expression of Survivin did not change the sensitivity to dexamethasone (C), but prevents increased sensitivity to Fas-induced apoptosis (B). "
    T-Cell Leukemia, Edited by Olga Babusikova, Sinisa Dovat, Kimberly J. Payne, 01/2011; InTech., ISBN: 978-953-307-400-9
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    ABSTRACT: Neuroblastoma is the most frequent extracranial solid tumor in children. Here, we report that the proteasome inhibitor bortezomib (PS-341, Velcade) activated the pro-apoptotic BH3-only proteins PMAIP1/Noxa and BBC3/Puma and induced accumulation of anti-apoptotic MCL1 as well as repression of anti-apoptotic BCL2L1/Bcl-xL. Retroviral expression of Bcl-xL, but not of MCL1, prevented apoptosis by bortezomib. Gene knockdown of Noxa by shRNA technology significantly reduced apoptosis, whereas Puma knockdown did not affect cell death kinetics. Immunoprecipitation revealed that endogenous Noxa associated with both, Bcl-xL and MCL1, suggesting that in neuronal cells Noxa can neutralize Bcl-xL, explaining the pronounced protective effect of Bcl-xL. Tetracycline-regulated Noxa expression did not trigger cell death per se but sensitized to bortezomib treatment in a dose-dependent manner. This implies that the induction of Noxa is necessary but not sufficient for bortezomib-induced apoptosis. We conclude that MCL1 steady-state expression levels do not affect sensitivity to proteasome-inhibitor treatment in neuronal tumor cells, and that both the repression of Bcl-xL and the activation of Noxa are necessary for bortezomib-induced cell death.
    Journal of Biological Chemistry 03/2010; 285(10):6904-12. DOI:10.1074/jbc.M109.038331 · 4.57 Impact Factor
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