Tumor necrosis factor α sensitizes primary murine hepatocytes to Fas/CD95-induced apoptosis in a Bim- and Bid-dependent manner.
Fas/CD95 is a critical mediator of cell death in many chronic and acute liver diseases and induces apoptosis in primary hepatocytes in vitro. In contrast, the proinflammatory cytokine tumor necrosis factor α (TNFα) fails to provoke cell death in isolated hepatocytes but has been implicated in hepatocyte apoptosis during liver diseases associated with chronic inflammation. Here we report that TNFα sensitizes primary murine hepatocytes cultured on collagen to Fas ligand (FasL)-induced apoptosis. This synergism is time-dependent and is specifically mediated by TNFα. Fas itself is essential for the sensitization, but neither Fas up-regulation nor endogenous FasL is responsible for this effect. Although FasL is shown to induce Bid-independent apoptosis in hepatocytes cultured on collagen, the sensitizing effect of TNFα is clearly dependent on Bid. Moreover, both c-Jun N-terminal kinase activation and Bim, another B cell lymphoma 2 homology domain 3 (BH3)-only protein, are crucial mediators of TNFα-induced apoptosis sensitization. Bim and Bid activate the mitochondrial amplification loop and induce cytochrome c release, a hallmark of type II apoptosis. The mechanism of TNFα-induced sensitization is supported by a mathematical model that correctly reproduces the biological findings. Finally, our results are physiologically relevant because TNFα also induces sensitivity to agonistic anti-Fas-induced liver damage.


CONCLUSIONS
Our data suggest that TNFα can cooperate with FasL to induce hepatocyte apoptosis by activating the BH3-only proteins Bim and Bid.
Schmich
Kathrin
K
Department of Pharmaceutical Biology and Biotechnology, Albert Ludwigs University of Freiburg, Freiburg, Germany.
Schlatter
Rebekka
R
Corazza
Nadia
N
Sá Ferreira
Karine
K
Ederer
Michael
M
Brunner
Thomas
T
Borner
Christoph
C
Merfort
Irmgard
I
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000502:physiology*; D000072224:Bcl-2-Like Protein 11; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002478:Cells, Cultured; D053222:Fas Ligand Protein / Q000502:physiology; D022781:Hepatocytes / Q000473:pathology; D008107:Liver Diseases / Q000209:etiology*; D048670:MAP Kinase Kinase 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology*; D015854:Up-Regulation; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000502:physiology; D019014:fas Receptor / Q000276:immunology
D000906:Antibodies; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C494815:Bid protein, mouse; D053222:Fas Ligand Protein; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor; D048670:MAP Kinase Kinase 4; C505409:Casp3 protein, mouse; C505524:Casp7 protein, mouse; D053148:Caspase 3; D053179:Caspase 7