title: Inositol depletion restores vesicle transport in yeast phospholipid flippase mutants.
abstract: In eukaryotic cells, type 4 P-type ATPases function as phospholipid flippases, which translocate phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of the lipid bilayer. Flippases function in the formation of transport vesicles, but the mechanism remains unknown. Here, we isolate an arrestin-related trafficking adaptor, ART5, as a multicopy suppressor of the growth and endocytic recycling defects of flippase mutants in budding yeast. Consistent with a previous report that Art5p downregulates the inositol transporter Itr1p by endocytosis, we found that flippase mutations were also suppressed by the disruption of ITR1, as well as by depletion of inositol from the culture medium. Interestingly, inositol depletion suppressed the defects in all five flippase mutants. Inositol depletion also partially restored the formation of secretory vesicles in a flippase mutant. Inositol depletion caused changes in lipid composition, including a decrease in phosphatidylinositol and an increase in phosphatidylserine. A reduction in phosphatidylinositol levels caused by partially depleting the phosphatidylinositol synthase Pis1p also suppressed a flippase mutation. These results suggest that inositol depletion changes the lipid composition of the endosomal/TGN membranes, which results in vesicle formation from these membranes in the absence of flippases.
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
authors.forename: Kanako
authors.initials: K
authors.lastname: Yamagami
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
authors.forename: Takaharu
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Laboratory of Biomembrane and Biofunctional Chemistry, Graduate School of Advanced Life Science, and Frontier Research Center for Post-Genome Science and Technology, Hokkaido University, Sapporo, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Sakai
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Mioka
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Sano
authors.affiliation: Laboratory of Biomembrane and Biofunctional Chemistry, Graduate School of Advanced Life Science, and Frontier Research Center for Post-Genome Science and Technology, Hokkaido University, Sapporo, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Igarashi
authors.affiliation: Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
authors.forename: Kazuma
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D007294:Inositol / Q000172:deficiency / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D049294:Phospholipid Transfer Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017855:Transferases (Other Substituted Phosphate Groups) / Q000235:genetics / Q000378:metabolism
chemical_list: C547820:Art5 protein, S cerevisiae; D002352:Carrier Proteins; C069143:ITR1 protein, S cerevisiae; D009004:Monosaccharide Transport Proteins; D010716:Phosphatidylinositols; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D029701:Saccharomyces cerevisiae Proteins; D007294:Inositol; D017855:Transferases (Other Substituted Phosphate Groups); C478389:PIS1 protein, S cerevisiae