title: The pro-apoptotic BH3-only protein Bim interacts with components of the translocase of the outer mitochondrial membrane (TOM).
abstract: The pro-apoptotic Bcl-2-family protein Bim belongs to the BH3-only proteins known as initiators of apoptosis. Recent data show that Bim is constitutively inserted in the outer mitochondrial membrane via a C-terminal transmembrane anchor from where it can activate the effector of cytochrome c-release, Bax. To identify regulators of Bim-activity, we conducted a search for proteins interacting with Bim at mitochondria. We found an interaction of Bim with Tom70, Tom20 and more weakly with Tom40, all components of the Translocase of the Outer Membrane (TOM). In vitro import assays performed on tryptically digested yeast mitochondria showed reduced Bim insertion into the outer mitochondrial membrane (OMM) indicating that protein receptors may be involved in the import process. However, RNAi against components of TOM (Tom40, Tom70, Tom22 or Tom20) by siRNA, individually or in combination, did not consistently change the amount of Bim on HeLa mitochondria, either at steady state or upon de novo-induction. In support of this, the individual or combined knock-downs of TOM receptors also failed to alter the susceptibility of HeLa cells to Bim-induced apoptosis. In isolated yeast mitochondria, lack of Tom70 or the TOM-components Tom20 or Tom22 alone did not affect the import of Bim into the outer mitochondrial membrane. In yeast, expression of Bim can sensitize the cells to Bax-dependent killing. This sensitization was unaffected by the absence of Tom70 or by an experimental reduction in Tom40. Although thus the physiological role of the Bim-TOM-interaction remains unclear, TOM complex components do not seem to be essential for Bim insertion into the OMM. Nevertheless, this association should be noted and considered when the regulation of Bim in other cells and situations is investigated.
authors: Institute of Medical Microbiology and Hygiene, University Medical Center Freiburg, Freiburg, Germany; Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, Germany; Faculty of Biology, University of Freiburg, Freiburg, Germany.
authors: Daniel O
authors: DO
authors: Frank
authors: Department of Dermatology, Medical Center; Center for Biological Systems Analysis (ZBSA), Freiburg Institute for Advanced Studies (FRIAS), University of Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
authors: Jörn
authors: J
authors: Dengjel
authors: Department of Molecular Cell Biology, Max Planck Institute of Biochemistry, Martinsried, Germany.
authors: Florian
authors: F
authors: Wilfling
authors: Department of Microbiology, Biocenter, University of Würzburg, Würzburg, Germany.
authors: Vera
authors: V
authors: Kozjak-Pavlovic
authors: Institute of Medical Microbiology and Hygiene, University Medical Center Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.
authors: Georg
authors: G
authors: Häcker
authors: Institute of Medical Microbiology and Hygiene, University Medical Center Freiburg, Freiburg, Germany.
authors: Arnim
authors: A
authors: Weber
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D015153:Blotting, Western; D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011485:Protein Binding; D021381:Protein Transport / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; C000606775:BCL2L11 protein, human; C000606776:Bcl2l11 protein, mouse; C084008:TOMM20 protein, human; C489971:TOMM22 protein, human; C402118:TOMM70 protein, human; C400783:TOMM40 protein, human