title: Mechanisms of resistance to TRAIL-induced apoptosis in primary B cell chronic lymphocytic leukaemia.
abstract: Primary B cells from B cell chronic lymphocytic leukaemia (B-CLL) were resistant to the novel selective cytotoxic agent, TNF-related apoptosis-inducing ligand (TRAIL). Low levels of the death-inducing TRAIL receptors, TRAIL-R1 and TRAIL-R2 but not the putative 'decoy' receptors, TRAIL-R3 and TRAIL-R4, were expressed on the surface of B-CLL cells. Resistance to TRAIL was upstream of caspase-8 activation, as little or no caspase-8 was processed in TRAIL-treated B-CLL cells. Low levels of a TRAIL death-inducing signalling complex (DISC) were formed in these cells, accompanied by the recruitment of endogenous FADD, caspase-8 and c-FLIP(L) but not c-FLIP(S). Both caspase-8 and c-FLIP(L) were cleaved to form two stable intermediates of approximately 43 kDa, which remained associated with the DISC. Caspase-8 was not further processed to its active heterotetramer. Thus the resistance of B-CLL cells to TRAIL may be due partly to low surface expression of the death receptors resulting in low levels of DISC formation and also to the high ratio of c-FLIP(L) to caspase-8 within the DISC, which would prevent further activation of caspase-8. Our results highlight the possibility of sensitising B-CLL cells to TRAIL by modulation of c-FLIP levels or by upregulation of surface expression of death receptors.
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000032:analysis; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000032:analysis; D003513:Cycloheximide / Q000494:pharmacology; D053200:Fas-Associated Death Domain Protein; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D008875:Middle Aged; D011506:Proteins / Q000032:analysis; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D011506:Proteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D003513:Cycloheximide; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases