Enzymatically active single chain caspase-8 maintains T-cell survival during clonal expansion

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Caspase-8 (casp8) regulates apoptosis via the extrinsic pathway.
• Non-apoptotic roles of casp8 include hematopoiesis, lymphocyte expansion, and T-cell autophagy modulation.
• The mechanisms underlying casp8's diverse cellular functions are not fully understood.

Purpose of the Study:

• To investigate the role of caspase-8 (casp8) catalytic activity in T-cell proliferation.
• To determine if casp8 self-processing is required for its non-apoptotic functions in T cells.

Main Methods:

• Utilized retroviral expression of enzymatically active or inactive casp8 in casp8-deficient T cells.
• Employed a biotinylated probe to detect active caspases in vivo.
• Assessed T-cell proliferation and survival following TCR ligation.
• Generated and tested a casp8 processing mutant (D387A).

Main Results:

• Enzymatically active casp8, but not inactive casp8, rescued proliferation in casp8-deficient T cells.
• Casp8 catalytic activity in proliferating T cells occurred independently of apoptosis signaling and did not require casp8 processing.
• Catalytically active full-length casp8 was detected in dividing T cells in vivo.
• A casp8 processing mutant (D387A) could rescue T-cell proliferation, indicating self-processing is dispensable for this function.
• Casp8 activity was most pronounced in CD8+ T cells, a rapidly proliferating subset.

Conclusions:

• The catalytically competent form of caspase-8 (casp8) is necessary for rapid T-cell proliferation upon TCR stimulation.
• Caspase-8 self-processing is essential for promoting apoptosis but not for its non-apoptotic role in T-cell proliferation.