title: The serine/threonine kinase ULK1 is a target of multiple phosphorylation events.
abstract: Autophagy is a cellular degradation process that is up-regulated upon starvation. Nutrition-dependent regulation of mTOR (mammalian target of rapamycin) is a major determinant of autophagy. RTK (receptor tyrosine kinase) signalling and AMPK (AMP-activated protein kinase) converge upon mTOR to suppress or activate autophagy. Nutrition-dependent regulation of autophagy is mediated via mTOR phosphorylation of the serine/threonine kinase ULK1 (unc51-like kinase 1). In the present study, we also describe ULK1 as an mTOR-independent convergence point for AMPK and RTK signalling. We initially identified ULK1 as a 14-3-3-binding protein and this interaction was enhanced by treatment with AMPK agonists. AMPK interacted with ULK1 and phosphorylated ULK1 at Ser(555) in vitro. Mutation of this residue to alanine abrogated 14-3-3 binding to ULK1, and in vivo phosphorylation of ULK1 was blocked by a dominant-negative AMPK mutant. We next identified a high-stringency Akt site in ULK1 at Ser(774) and showed that phosphorylation at this site was increased by insulin. Finally, we found that the kinase-activation loop of ULK1 contains a consensus phosphorylation site at Thr(180) that is required for ULK1 autophosphorylation activity. Collectively, our results suggest that ULK1 may act as a major node for regulation by multiple kinases including AMPK and Akt that play both stimulatory and inhibitory roles in regulating autophagy.
authors.affiliation: Department of Biochemistry and Molecular Biology and Monash Micro Imaging, School of Biomedical Sciences, Monash University, Melbourne, VIC 3800, Australia.
authors.forename: Markus
authors.initials: M
authors.lastname: Bach
authors.forename: Mark
authors.initials: M
authors.lastname: Larance
authors.forename: David E
authors.initials: DE
authors.lastname: James
authors.forename: Georg
authors.initials: G
authors.lastname: Ramm
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000595:Amino Acid Sequence; D001343:Autophagy / Q000502:physiology; D000071189:Autophagy-Related Protein-1 Homolog; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D047908:Intracellular Signaling Peptides and Proteins; C546842:MTOR protein, human; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C484754:ULK1 protein, human; D055372:AMP-Activated Protein Kinases