LC3, a mammalian homologue of yeast Apg8p, is localized in autophagosome membranes after processing

EMBO J. 2000 Nov 1;19(21):5720-8. doi: 10.1093/emboj/19.21.5720.

Abstract

Little is known about the protein constituents of autophagosome membranes in mammalian cells. Here we demonstrate that the rat microtubule-associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing. Two forms of LC3, called LC3-I and -II, were produced post-translationally in various cells. LC3-I is cytosolic, whereas LC3-II is membrane bound. The autophagic vacuole fraction prepared from starved rat liver was enriched with LC3-II. Immunoelectron microscopy on LC3 revealed specific labelling of autophagosome membranes in addition to the cytoplasmic labelling. LC3-II was present both inside and outside of autophagosomes. Mutational analyses suggest that LC3-I is formed by the removal of the C-terminal 22 amino acids from newly synthesized LC3, followed by the conversion of a fraction of LC3-I into LC3-II. The amount of LC3-II is correlated with the extent of autophagosome formation. LC3-II is the first mammalian protein identified that specifically associates with autophagosome membranes.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • DNA Primers / genetics
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • HeLa Cells
  • Humans
  • Intracellular Membranes / metabolism
  • Microscopy, Immunoelectron
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism*
  • Molecular Sequence Data
  • Phagosomes / metabolism*
  • Phagosomes / ultrastructure
  • Protein Processing, Post-Translational
  • Rats
  • Sequence Homology, Amino Acid
  • Subcellular Fractions / metabolism
  • Transfection

Substances

  • DNA Primers
  • Fungal Proteins
  • Microtubule-Associated Proteins