Nutrient-regulated Phosphorylation of ATG13 Inhibits Starvation-induced Autophagy

J Biol Chem. 2016 Mar 11;291(11):6026-6035. doi: 10.1074/jbc.M115.689646. Epub 2016 Jan 22.


Autophagy is a conserved catabolic process that utilizes a defined series of membrane trafficking events to generate a de novo double-membrane vesicle termed the autophagosome, which matures by fusing to the lysosome. Subsequently, the lysosome facilitates the degradation and recycling of the cytoplasmic cargo. In yeast, the upstream signals that regulate the induction of starvation-induced autophagy are clearly defined. The nutrient-sensing kinase Tor inhibits the activation of autophagy by regulating the formation of the Atg1-Atg13-Atg17 complex, through hyperphosphorylation of Atg13. However, in mammals, the ortholog complex ULK1-ATG13-FIP200 is constitutively formed. As such, the molecular mechanism by which mTOR regulates mammalian autophagy is unknown. Here we report the identification and characterization of novel nutrient-regulated phosphorylation sites on ATG13: Ser-224 and Ser-258. mTOR directly phosphorylates ATG13 on Ser-258 while Ser-224 is modulated by the AMPK pathway. In ATG13 knock-out cells reconstituted with an unphosphorylatable mutant of ATG13, ULK1 kinase activity is more potent, and amino acid starvation induced more rapid ATG13 and ULK1 translocation. These events culminated in a more rapid starvation-induced autophagy response. Therefore, ATG13 phosphorylation plays a crucial role in autophagy regulation.

Keywords: AMP-activated kinase (AMPK); Macroautophagy; TOR complex (TORC); ULK1; autophagy; mammalian target of rapamycin (mTOR); phosphorylation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • AMP-Activated Protein Kinases / metabolism
  • Amino Acid Sequence
  • Amino Acids / metabolism
  • Animals
  • Apoptosis Regulatory Proteins / chemistry
  • Apoptosis Regulatory Proteins / metabolism*
  • Autophagy*
  • Cell Line
  • HEK293 Cells
  • Humans
  • Mice
  • Molecular Sequence Data
  • Phosphorylation
  • Sequence Alignment
  • Starvation / metabolism*
  • TOR Serine-Threonine Kinases / metabolism


  • ATG13 protein, mouse
  • Amino Acids
  • Apoptosis Regulatory Proteins
  • TOR Serine-Threonine Kinases
  • AMP-Activated Protein Kinases