TCR-mediated up-regulation of c-FLIPshort correlates with resistance toward CD95-mediated apoptosis by blocking death-inducing signaling complex activity.
To investigate apoptosis resistance upon restimulation in human peripheral blood T lymphocytes, we used the following in vitro model. This model represents the main features of T cell reactivity: freshly isolated PHA-activated T cells cultured in IL-2 for a prolonged period of time develop a CD95 (APO-1/Fas) apoptosis-sensitive phenotype. These T cells represent activation-induced cell death-sensitive T cells during the down phase of an immune response. A fraction of apoptosis-sensitive activated T cells becomes apoptosis resistant upon TCR/CD3 restimulation. CD95 apoptosis sensitivity requires formation of a functional receptor associated death-inducing signaling complex (DISC), i.e., a protein complex of CD95 receptors, the adaptor Fas-associated death domain protein (FADD)/MORT1 and caspase-8 (FADD-like IL-1ss-converting enzyme (FLICE), MACH, Mch5). We identified activation of procaspase-8 at the DISC as the main target for the protective activity of TCR/CD3 restimulation. We found that procaspase-8 cleavage is reduced in T cells after TCR/CD3 restimulation. In addition, we detected up-regulation of c-FLIP(S) (the short splice variant of the cellular FLICE inhibitory protein) and strongly enhanced recruitment of c-FLIP(S) into the DISC. These data suggest that the recruitment of c-FLIP(S) into the DISC results in reduced DISC and caspase-8 activity.
Kirchhoff
S
S
Tumor Immunology Program, German Cancer Research Center, Heidelberg, Germany.
Müller
W W
WW
Krueger
A
A
Schmitz
I
I
Krammer
P H
PH
D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000096:biosynthesis*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007111:Immunity, Cellular; D007113:Immunity, Innate; D007425:Intracellular Membranes / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology; D008564:Membrane Potentials / Q000276:immunology; D008928:Mitochondria / Q000276:immunology; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects / Q000276:immunology*; D019014:fas Receptor / Q000502:physiology*
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D019014:fas Receptor; D003513:Cycloheximide; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases