title: Involvement of VDAC, Bax and ceramides in the efflux of AIF from mitochondria during curcumin-induced apoptosis.
abstract: BACKGROUND
  We previously identified curcumin as a potent inducer of fibroblast apoptosis, which could be used to treat hypertrophic scar formation. Here we investigated the underlying mechanism of this process.
  
  
  RESULTS
  Curcumin-induced apoptosis could not be blocked by caspase-inhibitors and we could not detect any caspase-3/7 activity. Curcumin predominantly induced mitochondria-mediated ROS formation and stimulated the expression of the redox-sensitive pro-apoptotic factor p53. Inhibition of the pro-apoptotic signaling enzyme glycogen synthase kinase-3beta (GSK-3beta) blocked curcumin-induced apoptosis. Apoptosis was associated with high molecular weight DNA damage, a possible indicator of apoptosis-inducing factor (AIF) activity. Indeed, curcumin caused nuclear translocation of AIF, which could be blocked by the antioxidant N-acetyl cysteine. We next investigated how AIF is effluxed from mitochondria in more detail. The permeability transition pore complex (PTPC), of which the voltage-dependent anion channel (VDAC) is a component, could be involved since the VDAC-inhibitor DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) efficiently blocked AIF translocation. However, PTPC is not involved in AIF release since cyclosporine A, a specific inhibitor of the complex did not block apoptosis. Alternatively, the pro-apoptotic protein Bax could have formed mitochondrial channels and interacted with VDAC. Curcumin caused mitochondrial translocation of Bax, which was blocked by DIDS, suggesting a Bax-VDAC interaction. Interestingly, ceramide channels can also release apoptogenic factors from mitochondria and we found that addition of ceramide induced caspase-independent apoptosis. Surprisingly, this process could also be blocked by DIDS, suggesting the concerted action of Bax, VDAC and ceramide in the efflux of AIF from the mitochondrion.
  
  
  CONCLUSIONS
  Curcumin-induced fibroblast apoptosis is totally caspase-independent and relies on the mitochondrial formation of ROS and the subsequent nuclear translocation of AIF, which is released from a mitochondrial pore that involves VDAC, Bax and possibly ceramides. The composition of the AIF-releasing channel seems to be much more complex than previously thought.
authors.affiliation: Department of Pharmacology and Toxicology, Radboud University Nijmegen Medical Centre, Nijmegen Centre for Molecular Life Sciences, Nijmegen, The Netherlands.
authors.forename: Alwin
authors.initials: A
authors.lastname: Scharstuhl
authors.forename: Henricus A M
authors.initials: HA
authors.lastname: Mutsaers
authors.forename: Sebastiaan W C
authors.initials: SW
authors.lastname: Pennings
authors.forename: Frans G M
authors.initials: FG
authors.lastname: Russel
authors.forename: Frank A D T G
authors.initials: FA
authors.lastname: Wagener
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D002518:Ceramides / Q000502:physiology*; D003474:Curcumin / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D008970:Molecular Weight; D021381:Protein Transport; D017382:Reactive Oxygen Species / Q000378:metabolism; D050994:Voltage-Dependent Anion Channels / Q000502:physiology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism / Q000502:physiology*
chemical_list: D051033:Apoptosis Inducing Factor; D002518:Ceramides; D004791:Enzyme Inhibitors; D018840:HSP70 Heat-Shock Proteins; D017382:Reactive Oxygen Species; D050994:Voltage-Dependent Anion Channels; D051028:bcl-2-Associated X Protein; D004247:DNA; D020169:Caspases; D003474:Curcumin
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