title: Ca(2+)-induced inhibition of apoptosis in human SH-SY5Y neuroblastoma cells: degradation of apoptotic protease activating factor-1 (APAF-1).
abstract: During apoptotic and excitotoxic neuron death, challenged mitochondria release the pro-apoptotic factor cytochrome c. In the cytosol, cytochrome c is capable of binding to the apoptotic protease-activating factor-1 (APAF-1). This complex activates procaspase-9 in the presence of dATP, resulting in caspase-mediated execution of apoptotic neuron death. Many forms of Ca(2+)-mediated neuron death, however, do not lead to prominent activation of the caspase cascade despite significant release of cytochrome c from mitochondria. We demonstrate that elevation of cytosolic Ca(2+) induced prominent degradation of APAF-1 in human SH-SY5Y neuroblastoma cells and in a neuronal cell-free apoptosis system. Loss of APAF-1 correlated with a reduced ability of cytochrome c to activate caspase-3-like proteases. Ca(2+) induced the activation of calpains, monitored by the cleavage of full-length alpha-spectrin into a calpain-specific 150-kDa breakdown product. However, pharmacological inhibition of calpain activity indicated that APAF-1 degradation also occurred via calpain-independent pathways. Our data suggest that Ca(2+) inhibits caspase activation during Ca(2+)-mediated neuron death by triggering the degradation of the cytochrome c-binding protein APAF-1.
authors.affiliation: Interdisciplinary Center for Clinical Research (IZKF), Research Group Apoptosis and Cell Death, Westphalian Wilhelms-University, Münster, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Reimertz
authors.forename: D
authors.initials: D
authors.lastname: Kögel
authors.forename: S
authors.initials: S
authors.lastname: Lankiewicz
authors.forename: M
authors.initials: M
authors.lastname: Poppe
authors.forename: J H
authors.initials: JH
authors.lastname: Prehn
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053477:Apoptotic Protease-Activating Factor 1; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D002154:Calpain / Q000494:pharmacology / Q000502:physiology; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000502:physiology; D002474:Cell-Free System; D003574:Cytochrome c Group / Q000494:pharmacology; D003593:Cytoplasm / Q000201:enzymology; D004789:Enzyme Activation; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D009336:Necrosis; D009474:Neurons / Q000201:enzymology; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000473:pathology
chemical_list: C506592:APAF1 protein, human; D053477:Apoptotic Protease-Activating Factor 1; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D007476:Ionophores; D011506:Proteins; D000001:Calcimycin; C505407:CASP3 protein, human; D002154:Calpain; D053148:Caspase 3; D020169:Caspases; D002118:Calcium