title: Ionizing radiation but not anticancer drugs causes cell cycle arrest and failure to activate the mitochondrial death pathway in MCF-7 breast carcinoma cells.
abstract: There is considerable evidence that ionizing radiation (IR) and chemotherapeutic drugs mediate apoptosis through the intrinsic death pathway via the release of mitochondrial cytochrome c and activation of caspases -9 and -3. Here we show that MCF-7 cells that lack caspase-3 undergo a caspase-dependent apoptotic cell death in the absence of DNA fragmentation and alpha-fodrin cleavage following treatment with etoposide or doxorubicin, but not after exposure to IR. Re-expression of caspase-3 restored DNA fragmentation and alpha-fodrin cleavage following drug treatment, but it did not alter the radiation-resistant phenotype of these cells. In contrast to the anticancer drugs, IR failed to induce the intrinsic death pathway in MCF-7/casp-3 cells, an event readily observed in IR-induced apoptosis of HeLa cells. Although IR-induced DNA double-strand breaks were repaired with similar efficiencies in all cell lines, cell cycle analyses revealed a persistent G2/M arrest in the two MCF-7 cell lines, but not in HeLa cells. Together, our data demonstrate that caspase-3 is required for DNA fragmentation and alpha-fodrin cleavage in drug-induced apoptosis and that the intrinsic death pathway is fully functional in MCF-7 cells. Furthermore, they show that the radiation-resistant phenotype of MCF-7 cells is not due to the lack of caspase-3, but is caused by the failure of IR to activate the intrinsic death pathway. We propose (1) different signaling pathways are induced by anticancer drugs and IR, and (2) IR-induced G2/M arrest prevents the generation of an apoptotic signal required for the activation of the intrinsic death pathway.
authors.affiliation: Department of Immunology and Cell Biology, University of Münster, Röntgenstrasse 21, 48149 Münster, Germany. r.janicke@uni-muenster.de
authors.forename: R U
authors.initials: RU
authors.lastname: Jänicke
authors.forename: I H
authors.initials: IH
authors.lastname: Engels
authors.forename: T
authors.initials: T
authors.lastname: Dunkern
authors.forename: B
authors.initials: B
authors.lastname: Kaina
authors.forename: K
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: A G
authors.initials: AG
authors.lastname: Porter
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000628:therapy; D002277:Carcinoma; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002453:Cell Cycle; D004249:DNA Damage; D053938:DNA Fragmentation; D004273:DNA, Neoplasm / Q000528:radiation effects; D004317:Doxorubicin / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D011839:Radiation, Ionizing; D014170:Transformation, Genetic; D014407:Tumor Cells, Cultured; D013049:Spectrin
chemical_list: D000970:Antineoplastic Agents; D002352:Carrier Proteins; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D004273:DNA, Neoplasm; D004317:Doxorubicin; D005047:Etoposide; D008840:Microfilament Proteins; D013049:Spectrin; C505407:CASP3 protein, human; C506433:CASP9 protein, human