title: tBID Homooligomerizes in the mitochondrial membrane to induce apoptosis.
abstract: Activation of the tumor necrosis factor R1/Fas receptor results in the cleavage of cytosolic BID to truncated tBID. tBID translocates to the mitochondria to induce the oligomerization of BAX or BAK, resulting in the release of cytochrome c (Cyt c). Here we demonstrate that in tumor necrosis factor alpha-activated FL5.12 cells, tBID becomes part of a 45-kDa cross-linkable mitochondrial complex that does not include BAX or BAK. Using fluorescence resonance energy transfer analysis and co-immunoprecipitation, we demonstrate that tBID-tBID interactions occur in the mitochondria of living cells. Cross-linking experiments using a tBID-GST chimera indicated that tBID forms homotrimers in the mitochondrial membrane. To test the functional consequence of tBID oligomerization, we expressed a chimeric FKBP-tBID molecule. Enforced dimerization of FKBP-tBID by the bivalent ligand FK1012 resulted in Cyt c release, caspase activation, and apoptosis. Surprisingly, enforced dimerization of tBID did not result in the dimerization of either BAX or BAK. Moreover, a tBID BH3 mutant (G94E), which does not interact with or induce the dimerization of either BAX or BAK, formed the 45-kDa complex and induced both Cyt c release and apoptosis. Thus, tBID oligomerization may represent an alternative mechanism for inducing mitochondrial dysfunction and apoptosis.
authors.affiliation: Department of Biological Regulation and Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Grinberg
authors.forename: Rachel
authors.initials: R
authors.lastname: Sarig
authors.forename: Yehudit
authors.initials: Y
authors.lastname: Zaltsman
authors.forename: Dan
authors.initials: D
authors.lastname: Frumkin
authors.forename: Nicholas
authors.initials: N
authors.lastname: Grammatikakis
authors.forename: Eitan
authors.initials: E
authors.lastname: Reuveny
authors.forename: Atan
authors.initials: A
authors.lastname: Gross
mesh_terms: D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D015153:Blotting, Western; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013347:Subcellular Fractions; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D008024:Ligands; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases