Molecular Determinants of the Caspase-promoting Activity of Smac/DIABLO and Its Role in the Death Receptor Pathway

• Published in: The Journal of biological chemistry 2000-11, Vol.275 (46), p.36152-36157
• Main Authors: Srinivasula, Srinivasa M., Datta, Pinaki, Fan, Xue-Jun, Fernandes-Alnemri, Teresa, Huang, Ziwei, Alnemri, Emad S.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Apoptosis - drug effects; Apoptosis Regulatory Proteins; Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - pharmacology; bcl-X Protein; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Caspase Inhibitors; Caspases - metabolism; Cell Differentiation; Cytosol - chemistry; Enzyme Activation; Humans; Inhibitor of Apoptosis Proteins; Insect Proteins; Intracellular Signaling Peptides and Proteins; Membrane Glycoproteins - metabolism; Mitochondria - metabolism; Mitochondrial Proteins; Molecular Sequence Data; Mutation - genetics; Protein Binding; Protein Isoforms - chemistry; Protein Isoforms - genetics; Protein Isoforms - metabolism; Proteins - chemistry; Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Receptors, Tumor Necrosis Factor - metabolism; Signal Transduction - drug effects; TNF-Related Apoptosis-Inducing Ligand; Transfection; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha - metabolism; X-Linked Inhibitor of Apoptosis Protein
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.C000533200

Smac/DIABLO is a mitochondrial protein that is released along with cytochrome c during apoptosis and promotes cytochrome c-dependent caspase activation by neutralizing inhibitor of apoptosis proteins (IAPs). We provide evidence that Smac/DIABLO functions at the levels of both the Apaf-1-caspase-9 apoptosome and effector caspases. The N terminus of Smac/DIABLO is absolutely required for its ability to interact with the baculovirus IAP repeat (BIR3) of XIAP and to promote cytochrome c-dependent caspase activation. However, it is less critical for its ability to interact with BIR1/BIR2 of XIAP and to promote the activity of the effector caspases. Consistent with the ability of Smac/DIABLO to function at the level of the effector caspases, expression of a cytosolic Smac/DIABLO in Type II cells allowed TRAIL to bypass Bcl-xL inhibition of death receptor-induced apoptosis. Combined, these data suggest that Smac/DIABLO plays a critical role in neutralizing IAP inhibition of the effector caspases in the death receptor pathway of Type II cells.