Abstract
The current study demonstrates a novel cross-talk mechanism between the TRAIL receptor death signaling pathway and the mitochondria. This newly identified pathway is regulated at the mitochondrial outer membrane by a complex between the prosurvival Bcl-2 member, Mcl-1 and the BH3-only protein, Bim. Under non-apoptotic conditions, Bim is sequestered by Mcl-1. Direct degradation of Mcl-1 by TRAIL-activated caspase-8 or caspase-3 produces Mcl-1-free Bim that mediates a Bax-dependent apoptotic cascade. Using Mcl-1 or Bim RNAi, we demonstrate that a loss in Mcl-1 expression significantly enhances the mitochondrial apoptotic response to TRAIL that is now mediated by freed Bim. Whereas overexpression of Mcl-1 contributes to the preservation of the mitochondrial membrane potential, Mcl-1 knockdown facilitates the Bim-mediated dissipation of this potential. Loss of Mcl-1 contributes to an increased level of caspase activity downstream of the mitochondrial response to TRAIL. Furthermore, the Mcl-1 expression level at the mitochondrial outer membrane determines the release efficiency for the apoptogenic proteins cytochrome c, Smac, and HtrA2 in response to Bim. These are the first findings to demonstrate the involvement of Bim in the TRAIL-mediated mitochondrial cascade. They also suggest that Mcl-1 may serve as a direct substrate for TRAIL-activated caspases implying the existence of a novel TRAIL/caspase-8/Mcl-1/Bim communication mechanism between the extrinsic and the intrinsic apoptotic pathways.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Apoptosis Regulatory Proteins / metabolism*
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Apoptosis Regulatory Proteins / physiology*
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Apoptosis*
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Bcl-2-Like Protein 11
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Blotting, Western
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Caspase 3
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Caspase 8
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Caspases / metabolism
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Cell Line
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Cloning, Molecular
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Cytochromes c / metabolism
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DNA, Complementary / metabolism
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Dose-Response Relationship, Drug
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Down-Regulation
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Flow Cytometry
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HeLa Cells
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Humans
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Intracellular Signaling Peptides and Proteins / metabolism
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Membrane Glycoproteins / metabolism*
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Membrane Proteins / metabolism
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Membrane Proteins / physiology*
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Mitochondria / metabolism*
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Mitochondrial Proteins / metabolism
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Mutation
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins / metabolism
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Neoplasm Proteins / physiology*
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Polymerase Chain Reaction
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Protein Binding
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Protein Biosynthesis
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins / physiology*
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Proto-Oncogene Proteins c-bcl-2 / physiology*
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RNA Interference
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TNF-Related Apoptosis-Inducing Ligand
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Transcription, Genetic
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Transfection
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Tumor Necrosis Factor-alpha / metabolism*
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bcl-2-Associated X Protein / metabolism
Substances
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Apoptosis Regulatory Proteins
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BCL2L11 protein, human
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Bcl-2-Like Protein 11
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DIABLO protein, human
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DNA, Complementary
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Intracellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Membrane Proteins
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Mitochondrial Proteins
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Myeloid Cell Leukemia Sequence 1 Protein
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Neoplasm Proteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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TNF-Related Apoptosis-Inducing Ligand
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TNFSF10 protein, human
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Tumor Necrosis Factor-alpha
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bcl-2-Associated X Protein
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Cytochromes c
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CASP3 protein, human
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CASP8 protein, human
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Caspase 3
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Caspase 8
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Caspases