Effects of Bcl-2 levels on Fas signaling-induced caspase-3 activation: molecular genetic tests of computational model predictions.
Fas-induced apoptosis is a critical process for normal immune system development and function. Although many molecular components in the Fas signaling pathway have been identified, a systematic understanding of how they work together to determine network dynamics and apoptosis itself has remained elusive. To address this, we generated a computational model for interpreting and predicting effects of pathway component properties. The model integrates current information concerning the signaling network downstream of Fas activation, through both type I and type II pathways, until activation of caspase-3. Unknown parameter values in the model were estimated using experimental data obtained from human Jurkat T cells. To elucidate critical signaling network properties, we examined the effects of altering the level of Bcl-2 on the kinetics of caspase-3 activation, using both overexpression and knockdown in the model and experimentally. Overexpression was used to distinguish among alternative hypotheses for inhibitory binding interactions of Bcl-2 with various components in the mitochondrial pathway. In comparing model simulations with experimental results, we find the best agreement when Bcl-2 blocks the release of cytochrome c by binding to both Bax and truncated Bid instead of Bax, truncated Bid, or Bid alone. Moreover, although Bcl-2 overexpression strongly reduces caspase-3 activation, Bcl-2 knockdown has a negligible effect, demonstrating a general model finding that varying the expression levels of signal molecules frequently has asymmetric effects on the outcome. Finally, we demonstrate that the relative dominance of type I vs type II pathways can be switched by varying particular signaling component levels without changing network structure.
Center for Cancer Research and Biological Engineering Division, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. fhua@mit.edu
Fei
F
Hua
Melanie G
MG
Cornejo
Michael H
MH
Cardone
Cynthia L
CL
Stokes
Douglas A
DA
Lauffenburger
D017209:Apoptosis / Q000235:genetics / Q000276:immunology; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D002461:Cell Line, Transformed; D019295:Computational Biology / Q000379:methods*; D003198:Computer Simulation; D004789:Enzyme Activation / Q000276:immunology; D053222:Fas Ligand Protein; D006801:Humans; D019169:Jurkat Cells; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D018448:Models, Immunological; D011237:Predictive Value of Tests; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference / Q000276:immunology; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014161:Transduction, Genetic / Q000379:methods*; D015854:Up-Regulation / Q000276:immunology*; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000502:physiology*
C494772:BAK1 protein, human; C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D061945:Caspase Inhibitors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases