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Atg4D at the interface between autophagy and apoptosis

Virginie M S Betin1, Jon D Lane

  • 1Cell Biology Laboratories, Department of Biochemistry, University of Bristol, Bristol, UK.

Autophagy
|August 29, 2009
PubMed

Insights

Human Atg4D, an endopeptidase regulating autophagy, is activated by caspase-3 during apoptosis. This cleavage enhances its activity and induces cytotoxicity via a BH3 domain, not enhanced autophagy.

Area of Science:

  • Cellular biology
  • Molecular mechanisms of autophagy
  • Apoptosis signaling pathways

Background:

  • The Atg4 family of endopeptidases is essential for autophagosome biogenesis, controlling Atg8 lipidation and delipidation.
  • Regulation of Atg4 activity in living cells remains largely uncharacterized.
  • Autophagy and apoptosis are critical cellular processes with complex regulatory networks.

Purpose of the Study:

  • To investigate the regulation of the human Atg4D endopeptidase.
  • To determine the functional consequences of Atg4D cleavage by caspases during apoptosis.
  • To elucidate the mechanism underlying the cytotoxicity of cleaved Atg4D.

Main Methods:

  • Biochemical assays to assess Atg4D enzymatic activity.
  • Apoptosis induction and cell-based assays.
  • Analysis of protein cleavage and localization using molecular biology techniques.
  • Assessment of cytotoxicity and its correlation with cellular events.

Main Results:

  • Human Atg4D is cleaved by caspase-3 at the DEVD(63)K site during apoptosis.
  • Native Atg4D is enzymatically inactive; caspase cleavage activates its GABARAP-L1 priming and delipidation activity.
  • Caspase-cleaved Atg4D exhibits significant cytotoxicity, independent of enhanced autophagy.
  • The cytotoxicity is mediated by a C-terminal BH3-like domain and involves transient mitochondrial recruitment of Atg4D.

Conclusions:

  • Caspase-3-mediated cleavage activates the Atg4D endopeptidase.
  • Activated Atg4D contributes to apoptosis-induced cytotoxicity through a mechanism involving its BH3 domain and mitochondrial localization.
  • This study reveals a novel regulatory mechanism for Atg4D and its role in linking autophagy machinery to apoptotic pathways.

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