title: Apoptosis induced by TGF-beta 1 in Burkitt's lymphoma cells is caspase 8 dependent but is death receptor independent.
abstract: TGF-beta is a potent inducer of apoptosis in many Burkitt's lymphoma (BL) cell lines. In this study, we characterize this apoptotic process in the EBV-negative BL41 cell line. Induction of apoptosis was detected as early as 8 h after TGF-beta treatment, as assayed by TUNEL and poly(ADP-ribose) polymerase cleavage. FACS analysis demonstrates that this proceeds predominately from the G1, but also from the G2/M phases of the cell cycle. We observed no early detectable changes in the steady-state levels of Bcl-2 and several of its family members after TGF-beta treatment. We detected cleavage of caspases 2, 3, 7, 8, and 9 into their active subunits. Consistent with the involvement of these enzymes in TGF-beta-mediated apoptosis, the broad spectrum caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(Ome)-flouromethylketone (ZVAD-fmk) blocked TGF-beta-induced apoptosis and revealed a G1 arrest in treated cells. Use of specific caspase inhibitors revealed that the induction of apoptosis is caspase 8 dependent, but caspase 3 independent. Activation of caspase 8 has been shown to be a critical event in death receptor-mediated apoptosis. However, TGF-beta treatment of BL41 cells was found not to affect the cell surface expression of Fas, TNF-R1, DR3, DR4, or DR5, or the steady-state expression levels of Fas ligand, TNF-R1, DR3, DR4, and DR5. Furthermore, blocking experiments indicated that TGF-beta-mediated apoptosis is not dependent on Fas ligand, TNF-alpha, tumor necrosis-like apoptosis-inducing ligand, or TNF-like weak inducer of apoptosis signaling. Therefore, it appears that TGF-beta induces apoptosis in BL cell lines via caspase 8 in a death receptor-independent fashion.
authors.affiliation: Section of Virology and Cell Biology and the Ludwig Institute for Cancer Research, Imperial College of Science, Technology and Medicine, St. Mary's Campus, London, United Kingdom.
authors.forename: G J
authors.initials: GJ
authors.lastname: Inman
authors.forename: M J
authors.initials: MJ
authors.lastname: Allday
mesh_terms: D015703:Antigens, CD / Q000502:physiology; D017209:Apoptosis / Q000276:immunology*; D051017:Apoptosis Regulatory Proteins; D002051:Burkitt Lymphoma / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism / Q000502:physiology*; D002461:Cell Line, Transformed; D004789:Enzyme Activation / Q000276:immunology; D016193:G1 Phase / Q000276:immunology; D016195:G2 Phase / Q000276:immunology; D006801:Humans; D006868:Hydrolysis; D008024:Ligands; D008562:Membrane Glycoproteins / Q000502:physiology; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D053219:Receptors, Tumor Necrosis Factor, Member 25; D047888:Receptors, Tumor Necrosis Factor, Type I; D016160:Retinoblastoma Protein / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000502:physiology; D019014:fas Receptor / Q000502:physiology
chemical_list: D015703:Antigens, CD; D051017:Apoptosis Regulatory Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053219:Receptors, Tumor Necrosis Factor, Member 25; D047888:Receptors, Tumor Necrosis Factor, Type I; D016160:Retinoblastoma Protein; D053221:TNF-Related Apoptosis-Inducing Ligand; C105190:TNFRSF10A protein, human; C505639:TNFRSF10B protein, human; C506033:TNFRSF25 protein, human; C505653:TNFSF10 protein, human; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; 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