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

Authors

  • Yukiko Kabeya,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
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  • Noboru Mizushima,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    2. PRESTO, Japan Science and Technology Corporation (JST), Kawaguchi, Japan
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  • Takashi Ueno,

    1. Department of Biochemistry, Juntendo University School of Medicine, Hongo, Tokyo, Japan
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  • Akitsugu Yamamoto,

    1. Department of Physiology, Kansai Medical University, Moriguchi, Japan
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  • Takayoshi Kirisako,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    2. Department of Molecular Biomechanics, School of Life Science, The Graduate University for Advanced Studies, Hayama, Japan
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  • Takeshi Noda,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    2. Department of Molecular Biomechanics, School of Life Science, The Graduate University for Advanced Studies, Hayama, Japan
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  • Eiki Kominami,

    1. Department of Biochemistry, Juntendo University School of Medicine, Hongo, Tokyo, Japan
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  • Yoshinori Ohsumi,

    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    2. Department of Molecular Biomechanics, School of Life Science, The Graduate University for Advanced Studies, Hayama, Japan
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  • Tamotsu Yoshimori

    Corresponding author
    1. Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan
    2. Department of Molecular Biomechanics, School of Life Science, The Graduate University for Advanced Studies, Hayama, Japan
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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.

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