title: Calpain-mediated cleavage of Atg5 switches autophagy to apoptosis.
abstract: Autophagy-related gene (Atg) 5 is a gene product required for the formation of autophagosomes. Here, we report that Atg5, in addition to the promotion of autophagy, enhances susceptibility towards apoptotic stimuli. Enforced expression of Atg5-sensitized tumour cells to anticancer drug treatment both in vitro and in vivo. In contrast, silencing the Atg5 gene with short interfering RNA (siRNA) resulted in partial resistance to chemotherapy. Apoptosis was associated with calpain-mediated Atg5 cleavage, resulting in an amino-terminal cleavage product with a relative molecular mass of 24,000 (Mr 24K). Atg5 cleavage was observed independent of the cell type and the apoptotic stimulus, suggesting that calpain activation and Atg5 cleavage are general phenomena in apoptotic cells. Truncated Atg5 translocated from the cytosol to mitochondria, associated with the anti-apoptotic molecule Bcl-xL and triggered cytochrome c release and caspase activation. Taken together, calpain-mediated Atg5 cleavage provokes apoptotic cell death, therefore, represents a molecular link between autophagy and apoptosis--a finding with potential importance for clinical anticancer therapies.
authors.affiliation: Department of Pharmacology, University of Bern, CH-3010 Bern, Switzerland.
authors.forename: Shida
authors.initials: S
authors.lastname: Yousefi
authors.forename: Remo
authors.initials: R
authors.lastname: Perozzo
authors.forename: Inès
authors.initials: I
authors.lastname: Schmid
authors.forename: Andrew
authors.initials: A
authors.lastname: Ziemiecki
authors.forename: Thomas
authors.initials: T
authors.lastname: Schaffner
authors.forename: Leonardo
authors.initials: L
authors.lastname: Scapozza
authors.forename: Thomas
authors.initials: T
authors.lastname: Brunner
authors.forename: Hans-Uwe
authors.initials: HU
authors.lastname: Simon
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D002154:Calpain / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology
chemical_list: C502778:ATG5 protein, human; D000903:Antibiotics, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D000071187:Autophagy-Related Protein 5; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D005047:Etoposide; D004317:Doxorubicin; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D045304:Cytochromes c; D002154:Calpain; D020169:Caspases; D019311:Staurosporine