title: Resistance to CD95-mediated apoptosis through constitutive c-FLIP expression in a non-Hodgkin's lymphoma B cell line.
abstract: CD95 (Fas/Apo-1) is a transmembrane molecule that induces apoptosis and plays a central role in the regulation of the immune response. The present study describes two new B lymphoid cell lines, B593 and BR97, derived from non-Hodgkin's lymphoma, which differ in susceptibility to CD95-mediated apoptosis. While B593 cells are sensitive to CD95mediated apoptosis, BR97 cells are completely resistant. Activation of caspase-8 and caspase-3 proteases plays an important role in the CD95 signalling pathway. CD95 stimulation induced caspase-8 and caspase-3 activation in B593, but not in BR97 cells. However, activation of both caspase-8 and caspase-3 was achieved in BR97 cells treated with staurosporine. Furthermore, protein synthesis inhibition by cycloheximide restored sensitivity to CD95-mediated apoptosis and allowed activation of both caspase-8 and caspase-3 in BR97 cells. These results indicate that, in BR97 cells, both caspases are functional and suggest that CD95-apoptosis resistance may result from the presence of inhibitory factor(s). Constitutive high level expression of the apoptotic inhibitor c-FLIP was observed in the CD95-resistant BR97 cell line compared to B593. Moreover, downregulation of c-FLIP expression level by protein synthesis inhibition strictly correlated with restored sensitivity to CD95-mediated apoptosis in BR97 cells. Furthermore, we demonstrate that c-FLIP is recruited to the CD95 DISC in BR97 cells together with caspase-8 and FADD. The data presented in this study strongly suggests that, in a B-NHL-derived cell line, resistance to CD95-mediated apoptosis results from endogenous high level expression of apoptotic inhibitor c-FLIP.
authors.affiliation: Research Group on Lymphoma, Albert Bonniot Institute, University Joseph Fourier, La Tronche, France.
authors.forename: M
authors.initials: M
authors.lastname: Irisarri
authors.forename: J
authors.initials: J
authors.lastname: Plumas
authors.forename: T
authors.initials: T
authors.lastname: Bonnefoix
authors.forename: M C
authors.initials: MC
authors.lastname: Jacob
authors.forename: C
authors.initials: C
authors.lastname: Roucard
authors.forename: M A
authors.initials: MA
authors.lastname: Pasquier
authors.forename: J J
authors.initials: JJ
authors.lastname: Sotto
authors.forename: A
authors.initials: A
authors.lastname: Lajmanovich
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D016393:Lymphoma, B-Cell / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000502:physiology*
chemical_list: D009363:Neoplasm Proteins; D019014:fas Receptor; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases