Abstract
The inhibitor of apoptosis (IAP) proteins bind and inhibit caspases via their baculovirus IAP repeat domains. Some of these IAPs are capable of ubiquitinating themselves and their interacting proteins through the ubiquitin-protein isopeptide ligase activity of their RING domain. The Drosophila IAP antagonists Reaper, Hid, and Grim can accelerate the degradation of Drosophila IAP1 and some mammalian IAPs by promoting their ubiquitin-protein isopeptide ligase activity. Here we show that Smac/DIABLO, a mammalian functional homolog of Reaper/Hid/Grim, selectively causes the rapid degradation of c-IAP1 and c-IAP2 but not XIAP and Livin in HeLa cells, although it efficiently promotes the auto-ubiquitination of them all. Smac binding to c-IAP via its N-terminal IAP-binding motif is the prerequisite for this effect, which is further supported by the findings that Smac N-terminal peptide is sufficient to enhance c-IAP1 ubiquitination, and Smac no longer promotes the ubiquitination of mutant c-IAP1 lacking all three baculovirus IAP repeat domains. In addition, different IAPs require the same ubiquitin-conjugating enzymes UbcH5a and UbcH6 for their ubiquitination. Taken together, Smac may serve as a key molecule in vivo to selectively reduce the protein level of c-IAPs through the ubiquitin/proteasome pathway.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing*
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Amino Acid Motifs
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Apoptosis Regulatory Proteins
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Blotting, Western
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Carrier Proteins / biosynthesis*
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Carrier Proteins / metabolism
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Carrier Proteins / physiology*
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Cysteine Endopeptidases / metabolism
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Escherichia coli / metabolism
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Glutathione Transferase / metabolism
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HeLa Cells
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Humans
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Inhibitor of Apoptosis Proteins
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Intracellular Signaling Peptides and Proteins
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Iron-Binding Proteins*
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Mitochondrial Proteins / metabolism
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Mitochondrial Proteins / physiology*
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Multienzyme Complexes / metabolism
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Mutation
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Neoplasm Proteins / biosynthesis*
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Plasmids / metabolism
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Proteasome Endopeptidase Complex
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Protein Binding
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Protein Biosynthesis*
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Protein Structure, Tertiary
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Proteins*
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Transfection
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Ubiquitin / metabolism
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Ubiquitin-Conjugating Enzymes / chemistry
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Ubiquitin-Protein Ligases
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X-Linked Inhibitor of Apoptosis Protein
Substances
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Adaptor Proteins, Signal Transducing
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Apoptosis Regulatory Proteins
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BIRC7 protein, human
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Carrier Proteins
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DIABLO protein, human
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Inhibitor of Apoptosis Proteins
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Intracellular Signaling Peptides and Proteins
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Iron-Binding Proteins
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Mitochondrial Proteins
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Multienzyme Complexes
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Neoplasm Proteins
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Proteins
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Ubiquitin
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X-Linked Inhibitor of Apoptosis Protein
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XIAP protein, human
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UBE2D1 protein, human
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UBE2J1 protein, human
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Ubiquitin-Conjugating Enzymes
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BIRC2 protein, human
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Ubiquitin-Protein Ligases
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Glutathione Transferase
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex