mTOR inhibits autophagy by controlling ULK1 ubiquitylation, self-association and function through AMBRA1 and TRAF6

• Published in: Nature cell biology Vol. 15; no. 4; pp. 406 - 416
• Main Authors: Nazio, Francesca, Strappazzon, Flavie, Antonioli, Manuela, Bielli, Pamela, Cianfanelli, Valentina, Bordi, Matteo, Gretzmeier, Christine, Dengjel, Joern, Piacentini, Mauro, Fimia, Gian Maria, Cecconi, Francesco
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2013; Nature Publishing Group
• Subjects: 631/80/39; 631/80/83/2359; Adaptor Proteins, Signal Transducing - antagonists & inhibitors; Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Autophagy; Autophagy (Cytology); Autophagy-Related Protein-1 Homolog; Binding proteins; Biology; Blotting, Western; Cancer Research; Cell Biology; Cells, Cultured; Developmental Biology; HeLa Cells; Humans; Immunoenzyme Techniques; Immunoprecipitation; Intracellular Signaling Peptides and Proteins - chemistry; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Kinases; Life Sciences; Mammals; Pathogens; Phosphorylation; Physiological aspects; Protein Binding; Protein kinases; Protein Serine-Threonine Kinases - chemistry; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Proteins; Real-Time Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Small Interfering - genetics; Stem Cells; TNF Receptor-Associated Factor 6 - genetics; TNF Receptor-Associated Factor 6 - metabolism; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism; Ubiquitin-proteasome system; Ubiquitination; Italy; Rome Italy; Germany
• ISSN: 1465-7392; 1476-4679; 1476-4679
• DOI: 10.1038/ncb2708

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. mTOR inhibition induces autophage-mediated degradation but few mTOR targets in the process have been identified so far. Cecconi and colleagues show that mTOR inhibits the autophagy regulator AMBRA1 by phosphorylation. Following autophagy induction, AMBRA1 is dephosphorylated and interacts with the E3 ligase TRAF6 to stabilize and activate ULK1 (a kinase required for autophagy) through its ubiquitylation.