Enzymatically active single chain caspase-8 maintains T-cell survival during clonal expansion.
The extrinsic, or death receptor, pathway integrates apoptotic signals through the protease caspase-8 (casp8). Beyond cell death regulation, non-apoptotic functions of casp8 include its essential requirement for hematopoiesis and lymphocyte clonal expansion, and tempering of autophagy in T cells. However, the mechanistic basis for the control of these disparate cellular processes remains elusive. Here, we show that casp8-deficient T-cell survival was rescued by enzymatically active, but not inactive, casp8-expressing retroviruses. The casp8 catalytic induction in proliferating T cell occurred independent of extrinsic and intrinsic apoptotic-signaling cascades and did not induce casp8 proteolytic processing. Using a biotinylated probe selectively targeting enzymatically active caspases, catalytically active full-length casp8 was found in vivo in dividing T cells. A casp8 D387A processing mutant was able to rescue casp8-deficient T-cell proliferation, validating that casp8 self-processing is not required for its non-apoptotic function(s). Finally, casp8 activity was highest in CD8(+) T cells, the most rapidly proliferating subset. These results show that the catalytically competent form of casp8 is required for rapid T-cell proliferation in response to TCR ligation, but that processing of the caspase is only necessary to promote apoptosis.
Department of Molecular Biology and Biochemistry, Institute for Immunology, University of California, Irvine, CA 92697-3900, USA.
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S
Leverrier
G S
GS
Salvesen
C M
CM
Walsh
D019943:Amino Acid Substitution; D000818:Animals; D017209:Apoptosis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D002470:Cell Survival; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D016297:Mutagenesis, Site-Directed; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000276:immunology
C505534:Fadd protein, mouse; D053200:Fas-Associated Death Domain Protein; D011948:Receptors, Antigen, T-Cell; D053181:Caspase 8