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EMBO J. 2017 Jun 14;36(12):1719-1735. doi: 10.15252/embj.201695189. Epub 2017 May 11.

Autophagosome formation is initiated at phosphatidylinositol synthase-enriched ER subdomains.

Author information

1
Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, The University of Tokyo, Tokyo, Japan t.nishimura@ucl.ac.uk nmizu@m.u-tokyo.ac.jp.
2
Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
3
Department of Developmental and Regenerative Biology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
4
Department of Health Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.
5
AMED-CREST, Japan Agency for Medical Research and Development, Tokyo, Japan.

Abstract

The autophagosome, a double-membrane structure mediating degradation of cytoplasmic materials by macroautophagy, is formed in close proximity to the endoplasmic reticulum (ER). However, how the ER membrane is involved in autophagy initiation and to which membrane structures the autophagy-initiation complex is localized have not been fully characterized. Here, we were able to biochemically analyze autophagic intermediate membranes and show that the autophagy-initiation complex containing ULK and FIP200 first associates with the ER membrane. To further characterize the ER subdomain, we screened phospholipid biosynthetic enzymes and found that the autophagy-initiation complex localizes to phosphatidylinositol synthase (PIS)-enriched ER subdomains. Then, the initiation complex translocates to the ATG9A-positive autophagosome precursors in a PI3P-dependent manner. Depletion of phosphatidylinositol (PI) by targeting bacterial PI-specific phospholipase C to the PIS domain impairs recruitment of downstream autophagy factors and autophagosome formation. These findings suggest that the autophagy-initiation complex, the PIS-enriched ER subdomain, and ATG9A vesicles together initiate autophagosome formation.

KEYWORDS:

ATG9A; FIP200; autophagy; phosphatidylinositol synthase; the ULK complex

PMID:
28495679
PMCID:
PMC5470044
DOI:
10.15252/embj.201695189
[Indexed for MEDLINE]
Free PMC Article

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