title: Stress conditions promote yeast Gap1 permease ubiquitylation and down-regulation via the arrestin-like Bul and Aly proteins.
abstract: Gap1, the yeast general amino acid permease, is a convenient model for studying how the intracellular traffic of membrane transporters is regulated. Present at the plasma membrane under poor nitrogen supply conditions, it undergoes ubiquitylation, endocytosis, and degradation upon activation of the TORC1 kinase complex in response to an increase in internal amino acids. This down-regulation is stimulated by TORC1-dependent phosphoinhibition of the Npr1 kinase, resulting in activation by dephosphorylation of the arrestin-like Bul1 and Bul2 adaptors recruiting the Rsp5 ubiquitin ligase to Gap1. We report here that Gap1 is also down-regulated when cells are treated with the TORC1 inhibitor rapamycin or subjected to various stresses and that a lack of the Tco89 subunit of TORC1 causes constitutive Gap1 down-regulation. Both the Bul1 and Bul2 and the Aly1 and Aly2 arrestin-like adaptors of Rsp5 promote this down-regulation without undergoing dephosphorylation. Furthermore, they act via the C-terminal regions of Gap1 not involved in ubiquitylation in response to internal amino acids, whereas a Gap1 mutant altered in the N-terminal tail and resistant to ubiquitylation by internal amino acids is efficiently down-regulated under stress via the Bul and Aly adaptors. Although the Bul proteins mediate Gap1 ubiquitylation of two possible lysines, Lys-9 and Lys-16, the Aly proteins promote ubiquitylation of the Lys-16 residue only. This stress-induced pathway of Gap1 down-regulation targets other permeases as well, and it likely allows cells facing adverse conditions to retrieve amino acids from permease degradation.
authors.affiliation: From Molecular Physiology of the Cell, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, 6041 Gosselies, Belgium.
authors.forename: Myriam
authors.initials: M
authors.lastname: Crapeau
authors.affiliation: From Molecular Physiology of the Cell, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, 6041 Gosselies, Belgium.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Merhi
authors.affiliation: From Molecular Physiology of the Cell, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, 6041 Gosselies, Belgium bran@ulb.ac.be.
authors.forename: Bruno
authors.initials: B
authors.lastname: André
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D026905:Amino Acid Transport Systems / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D019390:Arrestins / Q000378:metabolism; D001665:Binding Sites; D015536:Down-Regulation / Q000187:drug effects; D008239:Lysine / Q000737:chemistry; D008954:Models, Biological; D008958:Models, Molecular; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D013312:Stress, Physiological; D014157:Transcription Factors / Q000037:antagonists & inhibitors; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D048948:14-3-3 Proteins; D048868:Adaptor Proteins, Signal Transducing; C554942:Aly1 protein, S cerevisiae; C554941:Aly2 protein, S cerevisiae; D026905:Amino Acid Transport Systems; D000596:Amino Acids; D019390:Arrestins; C099939:BUL1 protein, S cerevisiae; C117205:BUL2 protein, S cerevisiae; C491145:GAP1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C561842:TORC1 protein complex, S cerevisiae; D014157:Transcription Factors; D044767:Ubiquitin-Protein Ligases; D008239:Lysine; D020123:Sirolimus
keywords: Amino Acid Transport; Arrestin; Endocytosis; Stress; TOR Complex (TORC); Ubiquitin; Yeast