title: mTOR inhibits autophagy by controlling ULK1 ubiquitylation, self-association and function through AMBRA1 and TRAF6.
abstract: Autophagy is important in the basal or stress-induced clearance of bulk cytosol, damaged organelles, pathogens and selected proteins by specific vesicles, the autophagosomes. Following mTOR (mammalian target of rapamycin) inhibition, autophagosome formation is primed by the ULK1 and the beclin-1-Vps34-AMBRA1 complexes, which are linked together by a scaffold platform, the exocyst. Although several regulative steps have been described along this pathway, few targets of mTOR are known, and the cross-talk between ULK1 and beclin 1 complexes is still not fully understood. We show that under non-autophagic conditions, mTOR inhibits AMBRA1 by phosphorylation, whereas on autophagy induction, AMBRA1 is dephosphorylated. In this condition, AMBRA1, interacting with the E3-ligase TRAF6, supports ULK1 ubiquitylation by LYS-63-linked chains, and its subsequent stabilization, self-association and function. As ULK1 has been shown to activate AMBRA1 by phosphorylation, the proposed pathway may act as a positive regulation loop, which may be targeted in human disorders linked to impaired autophagy.
authors.affiliation: Dulbecco Telethon Institute at the Department of Biology, University of Rome 'Tor Vergata', 00133 Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Nazio
authors.forename: Flavie
authors.initials: F
authors.lastname: Strappazzon
authors.forename: Manuela
authors.initials: M
authors.lastname: Antonioli
authors.forename: Pamela
authors.initials: P
authors.lastname: Bielli
authors.forename: Valentina
authors.initials: V
authors.lastname: Cianfanelli
authors.forename: Matteo
authors.initials: M
authors.lastname: Bordi
authors.forename: Christine
authors.initials: C
authors.lastname: Gretzmeier
authors.forename: Joern
authors.initials: J
authors.lastname: Dengjel
authors.forename: Mauro
authors.initials: M
authors.lastname: Piacentini
authors.forename: Gian Maria
authors.initials: GM
authors.lastname: Fimia
authors.forename: Francesco
authors.initials: F
authors.lastname: Cecconi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy; D000071189:Autophagy-Related Protein-1 Homolog; D015153:Blotting, Western; D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C553334:AMBRA1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D048029:TNF Receptor-Associated Factor 6; C546842:MTOR protein, human; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; C484754:ULK1 protein, human