Dimerization and processing of procaspase-9 by redox stress in mitochondria

Area of Science:

• Mitochondrial biology
• Cell death pathways
• Redox signaling

Background:

• Mitochondria play a crucial role in apoptosis initiation.
• Caspase-9 activation is a key step in the intrinsic apoptosis pathway.
• The precise mechanism of caspase-9 activation under redox stress is not fully understood.

Purpose of the Study:

• To elucidate the mechanism of intra-mitochondrial caspase-9 activation by redox stress.
• To investigate the role of hydrogen peroxide (H(2)O(2)) in initiating apoptosis.
• To determine the involvement of thiol-disulfide reactions in caspase-9 activation.

Main Methods:

• Studied H(2)O(2)-induced changes in mitochondrial membrane potential and cytochrome c release.
• Analyzed procaspase-9 processing and activation within isolated mitochondria.
• Investigated the effect of Bcl-2 overexpression and thioredoxin treatment on caspase-9 activation and cell death.

Main Results:

• H(2)O(2) caused a decrease in mitochondrial membrane potential with minimal cytochrome c release.
• Procaspase-9 autocleavage and activation occurred within mitochondria prior to cytosolic caspase cascade induction.
• Disulfide-bonded caspase-9 dimers were detected in mitochondria, and their formation was inhibited by thioredoxin.
• Bcl-2 overexpression prevented mitochondrial caspase-9 activation and conferred resistance to redox stress.

Conclusions:

• Mitochondrial redox stress triggers caspase-9 activation through thiol-disulfide reactions, independent of cytochrome c release.
• The cytochrome c-Apaf-1 complex is involved in caspase amplification, not initiation.
• This mechanism explains apoptosis execution in Apaf-1-null cells and highlights Bcl-2's role in blocking mitochondrial caspase activation.