title: Tumor necrosis factor-alpha and Fas activate complementary Fas-associated death domain-dependent pathways that enhance apoptosis induced by gamma-irradiation.
abstract: Activation of either tumor necrosis factor receptor 1 or Fas induces a low level of programmed cell death in LNCaP human prostate cancer cells. We have shown that LNCaP cells are entirely resistant to gamma-radiation-induced apoptosis, but can be sensitized to irradiation by TNF-alpha. Fas activation also sensitized LNCaP cells to irradiation, causing nearly 40% cell death 72 h after irradiation. Caspase-8 was cleaved and activated after exposure to tumor necrosis factor (TNF)-alpha. However, after exposure to anti-Fas antibody caspase-8 cleavage occurred only between the 26-kDa N-terminal prodomain and the 28-kDa C-terminal region that contains the protease components. Although anti-Fas antibody plus irradiation induced apoptosis that could be blocked by the pancaspase inhibitor zVAD, there was no measurable caspase-8 activity after exposure to anti-Fas antibody. The effector caspases-6 and -7, and to a lesser extent caspase-3, were activated by TNF-alpha, but not by anti-Fas antibody. Anti-Fas antibody, like TNF-alpha also activated serine proteases that contributed to cell death. Exposure of LNCaP cells simultaneously to TNF-alpha and anti-Fas antibody CH-11 resulted in marked enhancement of apoptosis that occurred very rapidly and was still further augmented by irradiation. Rapid apoptosis that ensued from combined treatment with TNF-alpha, anti-Fas antibody, and irradiation was completely blocked either by zVAD or expression of dominant negative Fas-associated death domain. Our data shows that there are qualitative differences in caspase activation resulting from either TNF receptor 1 or Fas. Simultaneous activation of these receptors was synergistic and caused rapid epithelial cell apoptosis mediated by the caspase cascade.
authors.affiliation: Department of Oncology, Lombardi Cancer Center, Georgetown University, Washington, D.C. 20007-2197, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kimura
authors.forename: E P
authors.initials: EP
authors.lastname: Gelmann
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D015703:Antigens, CD / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D004357:Drug Synergism; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein; D005720:Gamma Rays / Q000009:adverse effects*; D006801:Humans; D008024:Ligands; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism*; D011836:Radiation Tolerance; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I; D015398:Signal Transduction; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D019014:fas Receptor / Q000276:immunology / Q000494:pharmacology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000590:Amino Acid Chloromethyl Ketones; D015703:Antigens, CD; D002352:Carrier Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D008024:Ligands; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D014409:Tumor Necrosis Factor-alpha; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D014107:Tosyllysine Chloromethyl Ketone; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases