Autophagy initiation by ULK complex assembly on ER tubulovesicular regions marked by ATG9 vesicles

Nat Commun. 2016 Aug 11;7:12420. doi: 10.1038/ncomms12420.

Abstract

Autophagosome formation requires sequential translocation of autophagy-specific proteins to membranes enriched in PI3P and connected to the ER. Preceding this, the earliest autophagy-specific structure forming de novo is a small punctum of the ULK1 complex. The provenance of this structure and its mode of formation are unknown. We show that the ULK1 structure emerges from regions, where ATG9 vesicles align with the ER and its formation requires ER exit and coatomer function. Super-resolution microscopy reveals that the ULK1 compartment consists of regularly assembled punctate elements that cluster in progressively larger spherical structures and associates uniquely with the early autophagy machinery. Correlative electron microscopy after live imaging shows tubulovesicular membranes present at the locus of this structure. We propose that the nucleation of autophagosomes occurs in regions, where the ULK1 complex coalesces with ER and the ATG9 compartment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Autophagosomes / metabolism
  • Autophagy*
  • Autophagy-Related Protein-1 Homolog / metabolism*
  • Autophagy-Related Proteins / metabolism*
  • Endoplasmic Reticulum / metabolism*
  • Green Fluorescent Proteins / metabolism
  • HEK293 Cells
  • Humans
  • Intracellular Membranes / metabolism
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Lysosomes / metabolism
  • Membrane Proteins / metabolism*
  • Microscopy, Confocal
  • Microscopy, Electron
  • Mitochondria / metabolism
  • Plasmids / metabolism
  • Protein Transport
  • Vesicular Transport Proteins / metabolism*

Substances

  • ATG13 protein, human
  • Adaptor Proteins, Signal Transducing
  • Atg9a protein, human
  • Autophagy-Related Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Vesicular Transport Proteins
  • Green Fluorescent Proteins
  • Autophagy-Related Protein-1 Homolog
  • ULK1 protein, human