Macromolecular substrates for the ICE-like proteases during apoptosis

Area of Science:

• Molecular Biology
• Cell Biology
• Immunology

Background:

• The interleukin-1 beta-converting enzyme (ICE) protease family plays a crucial role in apoptosis (programmed cell death).
• The precise physiological functions of individual ICE homologs during apoptosis are not fully understood.
• Identifying the specific substrates targeted by these proteases is key to elucidating their pro-apoptotic mechanisms.

Purpose of the Study:

• To identify distal substrates of ICE proteases involved in apoptosis.
• To understand the roles of specific proteolysis events in the apoptotic process.
• To investigate the significance of autoantibodies in systemic lupus erythematosus (SLE) for identifying apoptotic substrates.

Main Methods:

• Analysis of autoantibodies from SLE patients.
• Identification of autoantigens recognized by these antibodies.
• In vitro and in situ assays to determine substrate cleavage by CPP32, an ICE family protease.

Main Results:

• A subset of SLE autoantibodies recognized molecules cleaved early in apoptosis.
• Identified autoantigens included nuclear proteins like PARP, U1-70 kDa, and DNA-PKcs.
• These autoantigens were confirmed as substrates for CPP32 in both in vitro and apoptotic cell contexts.

Conclusions:

• The identified substrates (PARP, U1-70 kDa, DNA-PKcs) are critical catalytic proteins involved in cellular homeostasis.
• Cleavage of these homeostatic proteins suggests that disrupting homeostasis is a fundamental mechanism for irreversible apoptosis.
• Further identification of ICE protease substrates will enable a comprehensive assessment of their roles in apoptotic cell death.