title: Autophagosomes form at ER-mitochondria contact sites.
abstract: Autophagy is a tightly regulated intracellular bulk degradation/recycling system that has fundamental roles in cellular homeostasis. Autophagy is initiated by isolation membranes, which form and elongate as they engulf portions of the cytoplasm and organelles. Eventually isolation membranes close to form double membrane-bound autophagosomes and fuse with lysosomes to degrade their contents. The physiological role of autophagy has been determined since its discovery, but the origin of autophagosomal membranes has remained unclear. At present, there is much controversy about the organelle from which the membranes originate--the endoplasmic reticulum (ER), mitochondria and plasma membrane. Here we show that autophagosomes form at the ER-mitochondria contact site in mammalian cells. Imaging data reveal that the pre-autophagosome/autophagosome marker ATG14 (also known as ATG14L) relocalizes to the ER-mitochondria contact site after starvation, and the autophagosome-formation marker ATG5 also localizes at the site until formation is complete. Subcellular fractionation showed that ATG14 co-fractionates in the mitochondria-associated ER membrane fraction under starvation conditions. Disruption of the ER-mitochondria contact site prevents the formation of ATG14 puncta. The ER-resident SNARE protein syntaxin 17 (STX17) binds ATG14 and recruits it to the ER-mitochondria contact site. These results provide new insight into organelle biogenesis by demonstrating that the ER-mitochondria contact site is important in autophagosome formation.
authors: Department of Genetics, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors: Maho
authors: M
authors: Hamasaki
authors: Nobumichi
authors: N
authors: Furuta
authors: Atsushi
authors: A
authors: Matsuda
authors: Akiko
authors: A
authors: Nezu
authors: Akitsugu
authors: A
authors: Yamamoto
authors: Naonobu
authors: N
authors: Fujita
authors: Hiroko
authors: H
authors: Oomori
authors: Takeshi
authors: T
authors: Noda
authors: Tokuko
authors: T
authors: Haraguchi
authors: Yasushi
authors: Y
authors: Hiraoka
authors: Atsuo
authors: A
authors: Amano
authors: Tamotsu
authors: T
authors: Yoshimori
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D001343:Autophagy; D000071183:Autophagy-Related Proteins; D019556:COS Cells; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C539000:ATG14 protein, human; D033942:Adaptor Proteins, Vesicular Transport; D000071183:Autophagy-Related Proteins; D050765:Qa-SNARE Proteins; C551267:STX17 protein, human