MycN sensitizes neuroblastoma cells for drug-induced apoptosis.
Amplification of the MYCN gene is found in a large proportion of neuroblastoma and considered as an adverse prognostic factor. To investigate the effect of ectopic MycN expression on the susceptibility of neuroblastoma cells to cytotoxic drugs we used a human neuroblastoma cell line harboring tetracycline-controlled expression of MycN. Neither conditional expression of MycN alone nor low drug concentrations triggered apoptosis. However, when acting in concert, MycN and cytotoxic drugs efficiently induced cell death. Apoptosis depended on mitochondrial permeability transition and activation of caspases, since the mitochondrion-specific inhibitor bongkrekic acid and the caspase inhibitor zVAD-fmk almost completely abrogated apoptosis. Loss of mitochondrial transmembrane potential and release of cytochrome c from mitochondria preceded activation of caspase-8 and caspase-3 and cleavage of PARP. CD95 expression was upregulated by treatment with cytotoxic drugs, while MycN cooperated with cytotoxic drugs to increase sensitivity to CD95-induced apoptosis and enhancing CD95-L expression. MycN overexpression and cytotoxic drugs also synergized to induce p53 and Bax protein expression, while Bcl-2 and Bcl-X(L) protein levels remained unchanged. Since amplification of MYCN is usually associated with a poor prognosis, these findings suggest that dysfunctions in apoptosis pathways may be a mechanism by which MycN-induced apoptosis of neuroblastoma cells is inhibited.
University Children's Hospital, Ulm, Germany.
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Fulda
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Lutz
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Schwab
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Debatin
D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002945:Cisplatin / Q000633:toxicity; D004317:Doxorubicin / Q000633:toxicity; D004789:Enzyme Activation; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D009447:Neuroblastoma / Q000473:pathology*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000378:metabolism
C494826:BAX protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D004317:Doxorubicin; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D002945:Cisplatin