Granzyme A cleaves a mitochondrial complex I protein to initiate caspase-independent cell death

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Granzyme A (GzmA) is a cytotoxic protease released by killer lymphocytes.
• GzmA induces caspase-independent cell death with apoptotic features.
• Previous studies indicated GzmA targets mitochondria, generating reactive oxygen species (ROS) and disrupting mitochondrial membrane potential, but not outer membrane permeabilization.

Purpose of the Study:

• To elucidate the precise mechanism by which GzmA induces mitochondrial damage and cell death.
• To identify the specific mitochondrial target of GzmA.
• To investigate the role of mitochondrial complex I in GzmA-mediated cytotoxicity.

Main Methods:

• Mitochondrial isolation and biochemical assays.
• Mass spectrometry to identify GzmA cleavage targets.
• Site-directed mutagenesis of NDUFS3.
• Cell viability assays in response to GzmA treatment.

Main Results:

• GzmA directly accesses the mitochondrial matrix.
• GzmA cleaves the mitochondrial complex I subunit NDUFS3 at Lys56.
• Cleavage of NDUFS3 impairs NADH oxidation and enhances superoxide anion generation.
• Cells expressing a mutated NDUFS3 cleavage site are resistant to GzmA-induced cell death.

Conclusions:

• GzmA-mediated cell death relies on the cleavage of mitochondrial complex I subunit NDUFS3.
• This cleavage event disrupts mitochondrial function, leading to ROS production and cytotoxicity.
• GzmA's targeting of complex I provides a specific mechanism for initiating apoptosis-like cell death.