title: Glucose starvation-induced turnover of the yeast glucose transporter Hxt1.
abstract: BACKGROUND
  The budding yeast Saccharomyces cerevisiae possesses multiple glucose transporters with different affinities for glucose that enable it to respond to a wide range of glucose concentrations. The steady-state levels of glucose transporters are regulated in response to changes in the availability of glucose. This study investigates the glucose regulation of the low affinity, high capacity glucose transporter Hxt1.
  
  
  RESULTS
  Western blotting and confocal microscopy were performed to evaluate glucose regulation of the stability of Hxt1. Our results show that glucose starvation induces endocytosis and degradation of Hxt1 and that this event requires End3, a protein required for endocytosis, and the Doa4 deubiquitination enzyme. Mutational analysis of the lysine residues in the Hxt1 N-terminal domain demonstrates that the two lysine residues, K12 and K39, serve as the putative ubiquitin-acceptor sites by the Rsp5 ubiquitin ligase. We also demonstrate that inactivation of PKA (cAMP-dependent protein kinase A) is needed for Hxt1 turnover, implicating the role of the Ras/cAMP-PKA glucose signaling pathway in the stability of Hxt1.
  
  
  CONCLUSIONS
  Hxt1, most useful when glucose is abundant, is internalized and degraded when glucose becomes depleted. Of note, the stability of Hxt1 is regulated by PKA, known as a positive regulator for glucose induction of HXT1 gene expression, demonstrating a dual role of PKA in regulation of Hxt1.
authors.affiliation: Department of Biochemistry and Molecular Medicine, The George Washington University Medical Center, 2300 Eye Street, Washington, DC 20037, USA.
authors.forename: Adhiraj
authors.initials: A
authors.lastname: Roy
authors.affiliation: Department of Biochemistry and Molecular Medicine, The George Washington University Medical Center, 2300 Eye Street, Washington, DC 20037, USA.
authors.forename: Yong-Bae
authors.initials: YB
authors.lastname: Kim
authors.affiliation: Department of Microbiology, Southern Illinois University Carbondale, 1125 Lincoln Drive, Carbondale, IL 62901, USA.
authors.forename: Kyu Hong
authors.initials: KH
authors.lastname: Cho
authors.affiliation: Department of Biochemistry and Molecular Medicine, The George Washington University Medical Center, 2300 Eye Street, Washington, DC 20037, USA. Electronic address: jh_kim@gwu.edu.
authors.forename: Jeong-Ho
authors.initials: JH
authors.lastname: Kim
mesh_terms: D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D051246:Glucose Transport Proteins, Facilitative / Q000096:biosynthesis* / Q000235:genetics; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D043222:Ubiquitin Thiolesterase / Q000235:genetics / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; C084434:DOA4 protein, S cerevisiae; C091908:END3 protein, S cerevisiae; D056827:Endosomal Sorting Complexes Required for Transport; D051246:Glucose Transport Proteins, Facilitative; C090594:HXT1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D010450:Endopeptidases; D043222:Ubiquitin Thiolesterase; D005947:Glucose
keywords: Endocytosis; Glucose transporter; Hxt1; Yeast