Caspases are activated in a branched protease cascade and control distinct downstream processes in Fas-induced...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Caspases are key proteases orchestrating programmed cell death (apoptosis).
• Understanding the specific roles of individual caspases in apoptotic pathways is crucial for dissecting cell death mechanisms.

Purpose of the Study:

• To elucidate the caspase activation cascade in Fas-stimulated Jurkat cells.
• To delineate the distinct functions of caspase-3 and caspase-6 in executing apoptosis.

Main Methods:

• Utilized novel synthetic tetrapeptide inhibitors (VEID-CHO and DMQD-CHO) selective for caspase-6 and caspase-3.
• Employed affinity labeling techniques to map protease interactions.
• Analyzed specific substrate cleavages and morphological changes in Fas-stimulated Jurkat cells.

Main Results:

• Identified a branched protease cascade: caspase-8 activates caspase-3/-7, which then activates caspase-6.
• Demonstrated distinct roles: caspase-6 cleaves NuMA, mediating nuclear shrinkage/fragmentation; caspase-3 cleaves NuMA differently, causing DNA fragmentation and chromatin condensation.
• Showed caspase-3 also mediates extranuclear events (PAK2 cleavage, apoptotic body formation, phosphatidylserine exposure).
• Highlighted that mitochondrial disruption and cytoplasmic shrinkage are mediated by caspases other than -3 or -6.

Conclusions:

• Caspases are organized in a hierarchical protease cascade during Fas-induced apoptosis.
• Each activated caspase plays specific, non-redundant roles in the execution of cell death.
• Caspase-3 and -6 are major effectors of nuclear apoptosis, with distinct substrate specificities and functions.