title: Caspases and mitochondria in c-Myc-induced apoptosis: identification of ATM as a new target of caspases.
abstract: The mechanism(s) of c-Myc transcription factor-induced apoptosis is still obscure. The activation of c-Myc has been found to lead into the processing/activation of caspases (caspase-3), but the significance of this for the cell demise is debatable. Here we report that several targets of caspases (PKCdelta, MDM2, PARP, replication factor C, 70 kDa U1snRNP, fodrin and lamins) are cleaved during c-Myc-induced apoptosis in Rat-1 MycER cells, indicating an important role for caspases in the apoptotic process. We further found that the ATM (ataxia telangiectasia mutated)--protein is a novel key substrate of caspases. In in vitro assays, purified recombinant ATM protein was found to be cleaved by the effector caspases 3 and 7. The functional significance of the ATM cleavage is supported by the finding that ectopic expression of ATM protected in part against apoptosis. We also show that c-Myc-induced apoptosis involves loss of mitochondrial transmembrane potential, release of cytochrome c from mitochondria into the cytosol and subsequent processing of caspase-9. The cleavage of caspase-9 is, however, minimal and a much later event than the processing/activation of caspase-3, suggesting that it is not the apical caspase. Evidence is provided that there is, nevertheless, an upstream caspase(s) regulating the functions of caspase-3 and mitochondria. Additionally, it was found that p53 becomes upregulated, together with its transcriptional targets MDM2 and p21, upon c-Myc induction, but this occurs also at a later time than the activation of caspase-3.
authors.affiliation: Haartman Institute, Department of Pathology, University of Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Hotti
authors.forename: K
authors.initials: K
authors.lastname: Järvinen
authors.forename: P
authors.initials: P
authors.lastname: Siivola
authors.forename: E
authors.initials: E
authors.lastname: Hölttä
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D064007:Ataxia Telangiectasia Mutated Proteins; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D016259:Genes, myc; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D034882:Lamins; D008564:Membrane Potentials; D008840:Microfilament Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051745:Protein Kinase C-delta; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D013049:Spectrin
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D064007:Ataxia Telangiectasia Mutated Proteins; D002352:Carrier Proteins; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D020169:Caspases; D018797:Cell Cycle Proteins; D015853:Cysteine Proteinase Inhibitors; D003574:Cytochrome c Group; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D034882:Lamins; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D009842:Oligopeptides; D011065:Poly(ADP-ribose) Polymerases; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D017346:Protein Serine-Threonine Kinases; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D013049:Spectrin; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C497260:Prkcd protein, rat; C576324:ATM protein, human; C497258:PRKCD protein, human; C505407:CASP3 protein, human; C505520:CASP7 protein, human; C505410:Casp3 protein, rat