title: Regulation of yeast nutrient permease endocytosis by ATP-binding cassette transporters and a seven-transmembrane protein, RSB1.
abstract: Ceramide is produced by the condensation of a long chain base with a very long chain fatty acid. In Saccharomyces cerevisiae, one of the two major long chain bases is called phytosphingosine (PHS). PHS has been shown to cause toxicity in tryptophan auxotrophic strains of yeast because this bioactive ceramide precursor causes diversion of the high affinity tryptophan permease Tat2 to the vacuole rather than the plasma membrane. Loss of the integral membrane protein Rsb1 increased PHS sensitivity, which was suggested to be due to this protein acting as an ATP-dependent long chain base efflux protein. More recent experiments demonstrated that loss of the genes encoding the ATP-binding cassette transporter proteins Pdr5 and Yor1 elevated PHS tolerance. This increased resistance was suggested to be due to increased expression of RSB1. Here, we provide an alternative view of PHS resistance influenced by Rsb1 and Pdr5/Yor1. Rsb1 has a seven-transmembrane domain topology more consistent with that of a regulatory protein like a G-protein-coupled receptor rather than a transporter. Importantly, an rsb1Δ cell does not exhibit higher internal levels of PHS compared with isogenic wild-type cells. However, tryptophan transport is increased in pdr5Δ yor1 strains and reduced in rsb1Δ cells. Localization and vacuolar degradation of Tat2 are affected in these genetic backgrounds. Finally, internalization of FM4-64 dye suggests that loss of Pdr5 and Yor1 slows normal endocytic rates. Together, these data argue that Rsb1, Pdr5, and Yor1 regulate the endocytosis of Tat2 and likely other membrane transporter proteins.
authors.affiliation: Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Soraya S
authors.initials: SS
authors.lastname: Johnson
authors.forename: Pamela K
authors.initials: PK
authors.lastname: Hanson
authors.forename: Raman
authors.initials: R
authors.lastname: Manoharlal
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Brice
authors.forename: L Ashley
authors.initials: LA
authors.lastname: Cowart
authors.forename: W Scott
authors.initials: WS
authors.lastname: Moye-Rowley
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009154:Mutation; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D026905:Amino Acid Transport Systems; D008565:Membrane Proteins; C092438:PDR5 protein, S cerevisiae; C465340:RSB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C429825:TAT2 protein, S cerevisiae; D049452:Green Fluorescent Proteins; D014364:Tryptophan; C012491:phytosphingosine; D013110:Sphingosine
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