title: Sphingosine contributes to glucocorticoid-induced apoptosis of thymocytes independently of the mitochondrial pathway.
abstract: During the selection process in the thymus, most thymocytes are eliminated by apoptosis through signaling via TCR or glucocorticoids. The involvement of ceramide (Cer) and sphingosine (SP), important apoptotic mediators, remains poorly defined in glucocorticoid-induced apoptosis. We report that, in mouse thymocytes, apoptosis triggered by 10(-6) M dexamethasone (DX) was preceded by a caspase-dependent Cer and SP generation, together with activation of acidic and neutral ceramidases. Apoptosis was drastically reduced by blocking either sphingolipid production (by acid sphingomyelinase inhibitor) or SP production (by ceramidase inhibitors), but not by inhibition of de novo Cer synthesis. Thus, SP generated through acid sphingomyelinase and ceramidase activity would contribute to the apoptotic effect of DX. Consistent with this hypothesis, SP addition or inhibition of SP kinase induced thymocyte apoptosis. DX induced a proteasome-dependent loss of mitochondrial membrane potential (Deltapsim) and caspase-8, -3, and -9 processing. Apoptosis was abolished by inhibition of Deltapsim loss or caspase-8 or -3, but not caspase-9. Deltapsim loss was independent of SP production and caspase-8, -3, and -9 activation. However, inhibition of SP production reduced caspase-8 and -3, but not caspase-9 processing. Proteasome inhibition impaired activation of the three caspases, whereas inhibition of Deltapsim loss solely blocked caspase-9 activation. These data indicate that DX-induced apoptosis is mediated in part by SP, which contributes, together with proteasome activity, to caspase-8-3 processing independently of mitochondria, and in part by the proteasome/mitochondria pathway, although independently of caspase-9 activation.
authors.affiliation: Biomembranes et Messagers Cellulaires, Centre National de la Recherche Scientifique, Université Paris XI, Orsay, France.
authors.forename: Sandrine
authors.initials: S
authors.lastname: Lépine
authors.forename: Boris
authors.initials: B
authors.lastname: Lakatos
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Courageot
authors.forename: Hervé
authors.initials: H
authors.lastname: Le Stunff
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Sulpice
authors.forename: Françoise
authors.initials: F
authors.lastname: Giraud
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D055572:Ceramidases; D002518:Ceramides / Q000096:biosynthesis; D003546:Cysteine Endopeptidases / Q000378:metabolism / Q000502:physiology; D003907:Dexamethasone / Q000494:pharmacology*; D004789:Enzyme Activation / Q000276:immunology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D009097:Multienzyme Complexes / Q000378:metabolism / Q000502:physiology; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013110:Sphingosine / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*
chemical_list: D002518:Ceramides; D009097:Multienzyme Complexes; D003907:Dexamethasone; D013108:Sphingomyelin Phosphodiesterase; C505409:Casp3 protein, mouse; C505526:Casp8 protein, mouse; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000581:Amidohydrolases; D055572:Ceramidases; D013110:Sphingosine