title: Ceramide and activated Bax act synergistically to permeabilize the mitochondrial outer membrane.
abstract: A critical step in apoptosis is mitochondrial outer membrane permeabilization (MOMP), releasing proteins critical to downstream events. While the regulation of this process by Bcl-2 family proteins is known, the role of ceramide, which is known to be involved at the mitochondrial level, is not well-understood. Here, we demonstrate that Bax and ceramide induce MOMP synergistically. Experiments were performed on mitochondria isolated from both rat liver and yeast (lack mammalian apoptotic machinery) using both a protein release assay and real-time measurements of MOMP. The interaction between activated Bax and ceramide was also studied in a defined isolated system: planar phospholipid membranes. At concentrations where ceramide and activated Bax have little effects on their own, the combination induces substantial MOMP. Direct interaction between ceramide and activated Bax was demonstrated both by using yeast mitochondria and phospholipid membranes. The apparent affinity of activated Bax for ceramide increases with ceramide content indicating that activated Bax shows enhanced propensity to permeabilize in the presence of ceramide. An agent that inhibits ceramide-induced but not activated Bax induced permeabilization blocked the enhanced MOMP, suggesting that ceramide is the key permeabilizing entity, at least when ceramide is present. These and previous findings that anti-apoptotic proteins disassemble ceramide channels suggest that ceramide channels, regulated by Bcl-2-family proteins, may be responsible for the MOMP during apoptosis.
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
authors.forename: Vidyaramanan
authors.initials: V
authors.lastname: Ganesan
authors.forename: Meenu N
authors.initials: MN
authors.lastname: Perera
authors.forename: David
authors.initials: D
authors.lastname: Colombini
authors.forename: Debra
authors.initials: D
authors.lastname: Datskovskiy
authors.forename: Kirti
authors.initials: K
authors.lastname: Chadha
authors.forename: Marco
authors.initials: M
authors.lastname: Colombini
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism; D002518:Ceramides / Q000494:pharmacology*; D004594:Electrophysiology; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D008930:Mitochondria, Liver / Q000378:metabolism / Q000648:ultrastructure; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000378:metabolism; D008958:Models, Molecular; D010539:Permeability; D051381:Rats; D014199:Trehalose / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; D002518:Ceramides; D008051:Lipid Bilayers; D051028:bcl-2-Associated X Protein; D014199:Trehalose