Rapid induction of mitochondrial events and caspase-independent apoptosis in Survivin-targeted melanoma cells.
The inhibitor of apoptosis (IAP) protein Survivin is expressed in most cancers and is a key factor in maintaining apoptosis resistance. Although several IAPs have been shown to act as direct inhibitors of caspases, the precise antiapoptotic function of Survivin remains controversial. To clarify the mechanism by which Survivin protects cells, we investigated the kinetics of apoptosis and apoptotic events following Survivin inhibition utilizing a melanoma cell line harboring a tetracycline-regulated Survivin dominant-negative mutant (Survivin-T34A). Blocking Survivin resulted in both caspase activation and apoptosis; however, the level of apoptosis was only partially reduced by caspase inhibition. Survivin blockade also resulted in mitochondrial events that preceded caspase activation, including depolarization and release of cytochrome c and Smac/DIABLO. Levels of other IAPs were not altered in Survivin-targeted cells, although modest cleavage of XIAP and Livin was observed. The earliest proapoptotic event observed in Survivin-targeted cells was nuclear translocation of mitochondrial apoptosis-inducing factor (AIF), known to trigger both apoptotic mitochondrial events and caspase-independent DNA fragmentation. These findings suggest that a key antiapoptotic function of Survivin relates to inhibition of mitochondrial and AIF-dependent apoptotic pathways, and its expression in melanoma and other cancers likely protects against both caspase-independent and -dependent apoptosis.
Liu
Tong
T
Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112, USA.
Brouha
Brook
B
Grossman
Douglas
D
D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D051033:Apoptosis Inducing Factor; D002352:Carrier Proteins / Q000378:metabolism; D020169:Caspases / Q000502:physiology*; D045744:Cell Line, Tumor; D005420:Flavoproteins / Q000378:metabolism; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008545:Melanoma / Q000473:pathology* / Q000628:therapy; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors*; D008928:Mitochondria / Q000502:physiology*; D009363:Neoplasm Proteins / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein
C494829:AIFM1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D051033:Apoptosis Inducing Factor; C107489:BIRC5 protein, human; C419866:BIRC7 protein, human; D002352:Carrier Proteins; D005420:Flavoproteins; D051034:Inhibitor of Apoptosis Proteins; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D011506:Proteins; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases