title: Identification of Ypk1 as a novel selective substrate for nitrogen starvation-triggered proteolysis requiring autophagy system and endosomal sorting complex required for transport (ESCRT) machinery components.
abstract: Nitrogen starvation-mediated reduction of Ypk1 is suggested to suppress translational initiation, possibly in parallel with the target of rapamycin complex 1 (TORC1) signaling. However, the molecular mechanism that regulates Ypk1 in nitrogen-starved cells is poorly understood. Here we report that Ypk1 is a novel selective substrate for nitrogen starvation-triggered proteolysis requiring autophagy system. Among various nutrient starvation methods used to elicit autophagy, rapid Ypk1 degradation was specific to nitrogen starvation. In screening genes required for such nitrogen starvation-specific vacuolar proteolysis, we found that autophagy-related degradation of Ypk1 depended on the endosomal sorting complex required for transport (ESCRT) machinery, which is conventionally thought to function in endosomal trafficking. In microscopic analyses, the disruption of ESCRT subunits resulted in the accumulation of both Ypk1 and autophagosomal Atg8 at a perivacuolar site that was distinct from conventional endosomes. ESCRT machinery was not involved in autophagic flux induced by the TORC1 inhibitor rapamycin, thus suggesting that ESCRT represents an exclusive mechanism of nitrogen starvation-specific proteolysis of Ypk1. Overall, we propose a novel regulation of Ypk1 that is specific to nitrogen limitation.
authors.affiliation: Laboratory of Membrane Biochemistry and Biophysics, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Mitsugu
authors.initials: M
authors.lastname: Shimobayashi
authors.forename: Hiromu
authors.initials: H
authors.lastname: Takematsu
authors.forename: Kazuo
authors.initials: K
authors.lastname: Eiho
authors.forename: Yukari
authors.initials: Y
authors.lastname: Yamane
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kozutsumi
mesh_terms: D001343:Autophagy / Q000502:physiology*; D015153:Blotting, Western; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009584:Nitrogen / Q000172:deficiency*; D010447:Peptide Hydrolases / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013217:Starvation; D014617:Vacuoles / Q000378:metabolism
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D038362:Glycogen Synthase Kinase 3; C068124:MCK1 protein, S cerevisiae; D010447:Peptide Hydrolases; D009584:Nitrogen