title: c-Myc potentiates the mitochondrial pathway of apoptosis by acting upstream of apoptosis signal-regulating kinase 1 (Ask1) in the p38 signalling cascade.
abstract: Cell transformation by growth-promoting oncoproteins renders cells extremely sensitive to apoptosis through an unknown mechanism affecting the mitochondrial pathway of apoptosis. We have shown previously that sensitization to apoptosis also correlated with the activation of the stress-activated protein kinase p38. In the present study, we investigated the role of p38 in c-Myc-dependent apoptosis induced by the anticancer agent cisplatin. Cisplatin treatment of Rat1 cells with deregulated expression of c-Myc resulted in nuclear fragmentation that was accompanied in all cells by the activation of Bax and the translocation of cytochrome c from the mitochondria to the cytoplasm. None of these features of apoptosis was induced in control Rat-1 cells. p38 was also activated by cisplatin only in cells with deregulated expression of c-Myc, but, in contrast with all features of apoptosis, this activation was not affected by Bcl-2. Remarkably, overexpression of an interfering mutant of the p38alpha isoform, but not p38beta, blocked cisplatin-induced Bax activation or cytochrome c release and nuclear fragmentation. Analysis of the kinase cascade upstream of p38 revealed a c-Myc-dependent activation by cisplatin of mitogen-activated protein kinase kinase (MKK) 3/6 and apoptosis signal-regulating kinase 1 (Ask1). Inhibition of Ask1 blocked p38 activation by cisplatin and all features of apoptosis. Several of these data were confirmed using other DNA-damaging agents. The findings indicated that c-Myc potentiation of the mitochondrial pathway of apoptosis results, at least in part, from a sensitization of Ask1 activation, allowing DNA-damaging agents to induce in cascade Ask1, p38alpha and Bax.
authors.affiliation: Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, 9 rue McMahon, Québec, Canada G1R 2J6.
authors.forename: Katia M
authors.initials: KM
authors.lastname: Desbiens
authors.forename: Réna G
authors.initials: RG
authors.lastname: Deschesnes
authors.forename: Mireille M
authors.initials: MM
authors.lastname: Labrie
authors.forename: Yan
authors.initials: Y
authors.lastname: Desfossés
authors.forename: Herman
authors.initials: H
authors.lastname: Lambert
authors.forename: Jacques
authors.initials: J
authors.lastname: Landry
authors.forename: Kerstin
authors.initials: K
authors.lastname: Bellmann
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D002945:Cisplatin / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D048848:MAP Kinase Kinase Kinase 5; D020930:MAP Kinase Kinase Kinases / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D048290:Mitogen-Activated Protein Kinase 11; D048308:Mitogen-Activated Protein Kinase 14; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013347:Subcellular Fractions; D014162:Transfection; D051028:bcl-2-Associated X Protein
chemical_list: D000970:Antineoplastic Agents; C494828:Bax protein, rat; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D051028:bcl-2-Associated X Protein; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048290:Mitogen-Activated Protein Kinase 11; D048308:Mitogen-Activated Protein Kinase 14; D020928:Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5; D020930:MAP Kinase Kinase Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases; D002945:Cisplatin