title: Restoration of TNF-alpha-induced ceramide generation and apoptosis in resistant human leukemia KG1a cells by the P-glycoprotein blocker PSC833.
abstract: Tumor necrosis factor (TNF-alpha) is a cytokine with antitumor activity against several cellular models. TNF-alpha-induced apoptosis seems to be mediated by a signaling pathway termed 'sphingomyelin-ceramide' pathway, which consists of the hydrolysis of sphingomyelin and the production of its breakdown product ceramide. Our study shows that KG1a cells, which are inherently resistant to TNF-alpha and do not produce ceramide upon cytokine stimulation, can be sensitized by the use of the P-glycoprotein inhibitor PSC833. Coincubation with 1 microM of this cyclosporin derivative restored the apoptotic potential of 10 ng/ml TNF-alpha. This effect was associated with the restoration of ceramide generation (315%) and activation of neutral, but not acid sphingomyelinase activity (143%). Furthermore, we demonstrate that treatment of KG1a cells with 1 microM PSC833 led to a threefold increase in inner plasma membrane sphingomyelin content and basal neutral sphingomyelinase activity. These results support the hypothesis whereby resistance to TNF-alpha-mediated apoptosis of certain leukemic cells is linked to the disposability of the sphingomyelin pool. These data also suggest a role for P-glycoprotein in sphingomyelin transverse plasma membrane asymmetry.
authors.affiliation: CJF INSERM 9503, Centre Claudius Régaud, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Bezombes
authors.forename: N
authors.initials: N
authors.lastname: Maestre
authors.forename: G
authors.initials: G
authors.lastname: Laurent
authors.forename: T
authors.initials: T
authors.lastname: Levade
authors.forename: A
authors.initials: A
authors.lastname: Bettaïeb
authors.forename: J P
authors.initials: JP
authors.lastname: Jaffrézou
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D003524:Cyclosporins / Q000494:pharmacology*; D006801:Humans; D007951:Leukemia, Myeloid / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013109:Sphingomyelins / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003524:Cyclosporins; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; D013108:Sphingomyelin Phosphodiesterase; C070272:valspodar