Alpha-fetoprotein positively regulates cytochrome c-mediated caspase activation and apoptosome complex formation.
Previous results have shown that the oncoembryonic marker alpha-fetoprotein (AFP) is able to induce apoptosis in tumor cells through activation of caspase 3, bypassing Fas-dependent and tumor necrosis factor receptor-dependent signaling. In this study we further investigate the molecular interactions involved in the AFP-mediated signaling of apoptosis. We show that AFP treatment of tumor cells is accompanied by cytosolic translocation of mitochondrial cytochrome c. In a cell-free system, AFP mediates processing and activation of caspases 3 and 9 by synergistic enhancement of the low-dose cytochrome c-mediated signals. AFP was unable to regulate activity of caspase 3 in cell extracts depleted of cytochrome c or caspase 9. Using high-resolution chromatography, we show that AFP positively regulates cytochrome c/dATP-mediated apoptosome complex formation, enhances recruitment of caspases and Apaf-1 into the complex, and stimulates release of the active caspases 3 and 9 from the apoptosome. By using a direct protein-protein interaction assay, we show that pure human AFP almost completely disrupts the association between processed caspases 3 and 9 and the cellular inhibitor of apoptosis protein (cIAP-2), demonstrating its release from the complex. Our data suggest that AFP may regulate cell death by displacing cIAP-2 from the apoptosome, resulting in promotion of caspase 3 activation and its release from the complex.
Semenkova
Lidia
L
Institute of Immunological Engineering, Moscow, Russia.
Dudich
Elena
E
Dudich
Igor
I
Tokhtamisheva
Natalie
N
Tatulov
Edward
E
Okruzhnov
Yury
Y
Garcia-Foncillas
Jesus
J
Palop-Cubillo
Juan-Antonio
JA
Korpela
Timo
T
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D002474:Cell-Free System; D002853:Chromatography, Liquid; D045304:Cytochromes c / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D006801:Humans; D008928:Mitochondria / Q000201:enzymology; D013050:Spectrometry, Fluorescence; D000509:alpha-Fetoproteins / Q000502:physiology*
D000509:alpha-Fetoproteins; D045304:Cytochromes c; D020169:Caspases