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.
Leverrier
S
S
Department of Molecular Biology and Biochemistry, Institute for Immunology, University of California, Irvine, CA 92697-3900, USA.
Salvesen
G S
GS
Walsh
C M
CM
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