Cleavage of Atg3 protein by caspase-8 regulates autophagy during receptor-activated cell death

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Autophagy is a crucial cellular process for survival during stress.
• The interplay between cell death pathways and autophagy is an active area of research.
• Receptor-mediated cell death pathways, like those involving TNFα and TRAIL, are critical for cellular homeostasis.

Purpose of the Study:

• To investigate the role of Atg3, a key regulator of autophagosome biogenesis, in receptor-mediated cell death.
• To determine if Atg3 is a substrate for caspases during apoptosis.
• To elucidate the functional consequences of Atg3 cleavage on autophagy and cell survival.

Main Methods:

• Utilized cell death induction via tumor necrosis factor α (TNFα) and TNF-related apoptosis-inducing ligand (TRAIL).
• Employed caspase inhibitors (zVAD, zIETD) and caspase-8 overexpression to assess Atg3 cleavage.
• Performed in vitro and in vivo cleavage assays using wild-type and mutated Atg3 proteins.
• Assessed autophagic activity and cell viability under various experimental conditions.

Main Results:

• Identified Atg3 as a direct substrate of caspase-8 during TNFα and TRAIL-induced cell death.
• Demonstrated that caspase-8 directly cleaves Atg3, leading to its degradation.
• Showed that Atg3 cleavage inhibits autophagy, and blocking caspases or using a non-cleavable Atg3 mutant restores autophagic activity.
• Confirmed that autophagy plays a pro-survival role, as its inhibition exacerbates cell death.

Conclusions:

• Atg3 is a novel substrate of caspase-8, linking apoptosis and autophagy.
• Caspase-8-mediated cleavage of Atg3 is a mechanism to suppress autophagy during receptor-activated cell death.
• Restoring autophagy, by preventing Atg3 cleavage, enhances cell survival in this context.