title: Anti-apoptotic Bcl-2 Family Proteins Disassemble Ceramide Channels.
abstract: Early in mitochondria-mediated apoptosis, the mitochondrial outer membrane becomes permeable to proteins that, when released into the cytosol, initiate the execution phase of apoptosis. Proteins in the Bcl-2 family regulate this permeabilization, but the molecular composition of the mitochondrial outer membrane pore is under debate. We reported previously that at physiologically relevant levels, ceramides form stable channels in mitochondrial outer membranes capable of passing the largest proteins known to exit mitochondria during apoptosis (Siskind, L. J., Kolesnick, R. N., and Colombini, M. (2006) Mitochondrion 6, 118-125). Here we show that Bcl-2 proteins are not required for ceramide to form protein-permeable channels in mitochondrial outer membranes. However, both recombinant human Bcl-x(L) and CED-9, the Caenorhabditis elegans Bcl-2 homologue, disassemble ceramide channels in the mitochondrial outer membranes of isolated mitochondria from rat liver and yeast. Importantly, Bcl-x L and CED-9 disassemble ceramide channels in the defined system of solvent-free planar phospholipid membranes. Thus, ceramide channel disassembly likely results from direct interaction with these anti-apoptotic proteins. Mutants of Bcl-x L act on ceramide channels as expected from their ability to be anti-apoptotic. Thus, ceramide channels may be one mechanism for releasing pro-apoptotic proteins from mitochondria during the induction phase of apoptosis.
authors.affiliation: Department of General Internal Medicine/Geriatrics, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Leah J
authors.initials: LJ
authors.lastname: Siskind
authors.forename: Laurence
authors.initials: L
authors.lastname: Feinstein
authors.forename: Tingxi
authors.initials: T
authors.lastname: Yu
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Davis
authors.forename: David
authors.initials: D
authors.lastname: Jones
authors.forename: Jinna
authors.initials: J
authors.lastname: Choi
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Zuckerman
authors.forename: Wenzhi
authors.initials: W
authors.lastname: Tan
authors.forename: R Blake
authors.initials: RB
authors.lastname: Hill
authors.forename: J Marie
authors.initials: JM
authors.lastname: Hardwick
authors.forename: Marco
authors.initials: M
authors.lastname: Colombini
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000494:pharmacology*; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002518:Ceramides / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008297:Male; D051379:Mice; D008930:Mitochondria, Liver / Q000378:metabolism; D008954:Models, Biological; D010743:Phospholipids / Q000737:chemistry; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D029742:Caenorhabditis elegans Proteins; C087233:Ced-9 protein, C elegans; D002518:Ceramides; D010743:Phospholipids; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein