Notch1 antiapoptotic activity is abrogated by caspase cleavage in dying T lymphocytes

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Notch1 receptor signaling plays a critical role in T lymphocyte survival.
• Excessive Notch1 signaling can inhibit apoptosis, but its regulation during programmed cell death is not fully understood.

Purpose of the Study:

• To investigate whether the intracellular domain of Notch1 (NICD) is a substrate for caspases during T lymphocyte apoptosis.
• To elucidate the functional consequences of Notch1 cleavage on its antiapoptotic activity.

Main Methods:

• Apoptosis was induced in Jurkat cells and primary T lymphocytes.
• Cleavage of NICD was assessed using caspase inhibitors (DEVD-fmk, VEID-fmk) and by analyzing protein fragments.
• The role of specific caspases (caspase-3, caspase-6) in NICD cleavage was determined.
• Expression of HES-1 and antagonism of Nur77 activity by Notch1 were evaluated.
• Functional assays were performed in a T-cell hybridoma to assess activation-induced cell death.

Main Results:

• The intracellular domain of Notch1 (NICD) is cleaved into six fragments during T lymphocyte apoptosis.
• Notch1 cleavage is inhibited by caspase inhibitors and Bcl-2 expression.
• Caspase-3 and caspase-6 were identified as the caspases responsible for cleaving NICD at specific sites.
• Notch1 cleavage correlates with decreased HES-1 expression and loss of its antiapoptotic function, as evidenced by its inability to inhibit activation-induced cell death and antagonize Nur77 activity.

Conclusions:

• The Notch1 receptor is a caspase substrate during T lymphocyte apoptosis.
• Caspase-mediated cleavage inactivates the antiapoptotic function of Notch1, contributing to T cell death.
• These findings reveal a novel mechanism for regulating T cell survival pathways during apoptosis.