Caspase cleavage of Atg4D stimulates GABARAP-L1 processing and triggers mitochondrial targeting and apoptosis

J Cell Sci. 2009 Jul 15;122(Pt 14):2554-66. doi: 10.1242/jcs.046250. Epub 2009 Jun 23.

Abstract

Autophagy is an important catabolic process with roles in cell survival and cell death. It sequesters cytosol and organelles within double-membrane autophagosomes that deliver their contents to lysosomes for degradation. Autophagosome biogenesis is coordinated by the autophagy-related protein 4 (Atg4) family of C54 endopeptidases (Atg4A-Atg4D). These enzymes prime and then later delipidate the autophagosome marker, Atg8. Here, we show that one family member, Atg4D, is cleaved by caspase-3 in vitro and in apoptotic cells. Atg4D is a poor priming and delipidation enzyme in vitro, but truncated DeltaN63 Atg4D displays increased activity against the Atg8 paralogue, gamma-aminobutyric acid receptor-associated protein-like 1 (GABARAP-L1). In living cells, DeltaN63 Atg4D stimulates the delipidation of GABARAP-L1, whereas siRNA silencing of the gene expressing Atg4D abrogates GABARAP-L1 autophagosome formation and sensitises cells to starvation and staurosporine-induced cell death. Interestingly, Atg4D overexpression induces apoptosis, which is preceded by the caspase-independent recruitment of Atg4D to mitochondria and is facilitated by a putative C-terminal Bcl-2 homology 3 (BH3) domain. Atg4D also acquires affinity for damaged mitochondria in cells treated with hydrogen peroxide. These data suggest that Atg4D is an autophagy regulator that links mitochondrial dysfunction with apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Amino Acid Sequence
  • Apoptosis* / drug effects
  • Autophagy* / drug effects
  • Autophagy-Related Proteins
  • Caspase 3 / metabolism*
  • Cysteine Endopeptidases / genetics
  • Cysteine Endopeptidases / metabolism*
  • HeLa Cells
  • Humans
  • Hydrogen Peroxide / pharmacology
  • Lipid Metabolism
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism*
  • Mitochondria / drug effects
  • Mitochondria / enzymology*
  • Mitochondria / pathology
  • Molecular Sequence Data
  • Mutation
  • Oxidative Stress
  • Protein Structure, Tertiary
  • RNA Interference
  • Signal Transduction* / drug effects
  • Staurosporine / pharmacology
  • Stress, Physiological* / drug effects
  • Time Factors
  • Transfection

Substances

  • Adaptor Proteins, Signal Transducing
  • Autophagy-Related Proteins
  • GABARAPL1 protein, human
  • Microtubule-Associated Proteins
  • Hydrogen Peroxide
  • ATG4B protein, human
  • ATG4D protein, human
  • CASP3 protein, human
  • Caspase 3
  • Cysteine Endopeptidases
  • Staurosporine