title: Dynamic and transient interactions of Atg9 with autophagosomes, but not membrane integration, are required for autophagy.
abstract: Autophagy is a catabolic process essential for cell homeostasis, at the core of which is the formation of double-membrane organelles called autophagosomes. Atg9 is the only known transmembrane protein required for autophagy and is proposed to deliver membrane to the preautophagosome structures and autophagosomes. We show here that mammalian Atg9 (mAtg9) is required for the formation of DFCP1-positive autophagosome precursors called phagophores. mAtg9 is recruited to phagophores independent of early autophagy proteins, such as ULK1 and WIPI2, but does not become a stable component of the autophagosome membrane. In fact, mAtg9-positive structures interact dynamically with phagophores and autophagosomes without being incorporated into them. The membrane compartment enriched in mAtg9 displays a unique sedimentation profile, which is unaltered upon starvation-induced autophagy. Correlative light electron microscopy reveals that mAtg9 is present on tubular-vesicular membranes emanating from vacuolar structures. We show that mAtg9 resides in a unique endosomal-like compartment and on endosomes, including recycling endosomes, where it interacts with the transferrin receptor. We propose that mAtg9 trafficking through multiple organelles, including recycling endosomes, is essential for the initiation and progression of autophagy; however, rather than acting as a structural component of the autophagosome, it is required for the expansion of the autophagosome precursor.
authors.affiliation: London Research Institute, Cancer Research UK, London, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Orsi
authors.forename: M
authors.initials: M
authors.lastname: Razi
authors.forename: H C
authors.initials: HC
authors.lastname: Dooley
authors.forename: D
authors.initials: D
authors.lastname: Robinson
authors.forename: A E
authors.initials: AE
authors.lastname: Weston
authors.forename: L M
authors.initials: LM
authors.lastname: Collinson
authors.forename: S A
authors.initials: SA
authors.lastname: Tooze
mesh_terms: D000818:Animals; D001343:Autophagy; D000071189:Autophagy-Related Protein-1 Homolog; D000071183:Autophagy-Related Proteins; D015415:Biomarkers / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure; D028044:Phosphate-Binding Proteins; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034622:RNA Interference; D011990:Receptors, Transferrin / Q000378:metabolism; D033921:Vesicular Transport Proteins
chemical_list: C574794:ATG9A protein, human; D000071183:Autophagy-Related Proteins; D015415:Biomarkers; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D028044:Phosphate-Binding Proteins; D011990:Receptors, Transferrin; D033921:Vesicular Transport Proteins; C569007:WIPI2 protein, human; C426003:ZFYVE1 protein, human; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; C484754:ULK1 protein, human