title: Proteasome inhibitors potentiate etoposide-induced cell death in human astrocytoma cells bearing a mutated p53 isoform.
abstract: Resistance to anticancer agents is often due to defects of intracellular pathways of cell death. Thus, the identification of the apoptotic pathways that can still be recruited by chemotherapeutic agents in cancerous cells can disclose new opportunities to treat malignancies. Here we show that human astrocytoma ADF cells (which are resistant to "mitochondriotropic" agents as well as to the antineoplastic drug etoposide and to proteasome inhibitors when used alone) undergo dramatic apoptotic death when exposed to a combination protocol based on the use of etoposide in the presence of proteasome inhibitors. Sensitization to cell death involved an autoamplifying loop of caspase activation, where the "executioner" phase of apoptosis was sustained by cooperation of caspase-2, -9, -8, and -3. We also show that sensitization of cells to the combination protocol involved the nuclear relocalization of p53, despite the presence of a polymorphism in its DNA-binding domain, suggesting the likely induction of p53-dependent proapoptotic genes. Conversely, p53 phosphorylation on Ser-15 did not play any role in apoptosis. In conclusion, use of etoposide in combination with proteasome inhibitors may represent an effective strategy to restore sensitivity to apoptosis in human astrocytoma cells bearing multiple defects of intracellular apoptotic pathways.
authors.affiliation: Laboratory of Molecular and Cellular Pharmacology of Purinergic Transmission, Department of Pharmacological Sciences, School of Pharmacy, University of Milan, Milan, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Ceruti
authors.forename: Alessia
authors.initials: A
authors.lastname: Mazzola
authors.forename: Maria P
authors.initials: MP
authors.lastname: Abbracchio
mesh_terms: D000595:Amino Acid Sequence; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001254:Astrocytoma / Q000188:drug therapy* / Q000473:pathology; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology*; D016158:Genes, p53 / Q000235:genetics*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects*; D012334:RNA, Neoplasm / Q000096:biosynthesis / Q000302:isolation & purification; D015398:Signal Transduction / Q000187:drug effects; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D012334:RNA, Neoplasm; D005047:Etoposide; D020169:Caspases; D046988:Proteasome Endopeptidase Complex