title: Consequences of loss of Vph1 protein-containing vacuolar ATPases (V-ATPases) for overall cellular pH homeostasis.
abstract: In yeast cells, subunit a of the vacuolar proton pump (V-ATPase) is encoded by two organelle-specific isoforms, VPH1 and STV1. V-ATPases containing Vph1 and Stv1 localize predominantly to the vacuole and the Golgi apparatus/endosomes, respectively. Ratiometric measurements of vacuolar pH confirm that loss of STV1 has little effect on vacuolar pH. Loss of VPH1 results in vacuolar alkalinization that is even more rapid and pronounced than in vma mutants, which lack all V-ATPase activity. Cytosolic pH responses to glucose addition in the vph1Δ mutant are similar to those in vma mutants. The extended cytosolic acidification in these mutants arises from reduced activity of the plasma membrane proton pump, Pma1p. Pma1p is mislocalized in vma mutants but remains at the plasma membrane in both vph1Δ and stv1Δ mutants, suggesting multiple mechanisms for limiting Pma1 activity when organelle acidification is compromised. pH measurements in early prevacuolar compartments via a pHluorin fusion to the Golgi protein Gef1 demonstrate that pH responses of these compartments parallel cytosolic pH changes. Surprisingly, these compartments remain acidic even in the absence of V-ATPase function, possibly as a result of cytosolic acidification. These results emphasize that loss of a single subunit isoform may have effects far beyond the organelle where it resides.
authors.affiliation: Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, New York 13210, USA.
authors.forename: Maureen
authors.initials: M
authors.lastname: Tarsio
authors.forename: Huimei
authors.initials: H
authors.lastname: Zheng
authors.forename: Anne M
authors.initials: AM
authors.lastname: Smardon
authors.forename: Gloria A
authors.initials: GA
authors.lastname: Martínez-Muñoz
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Kane
mesh_terms: D020134:Catalytic Domain / Q000502:physiology*; D018118:Chloride Channels / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D005947:Glucose / Q000494:pharmacology; D006056:Golgi Apparatus / Q000201:enzymology / Q000235:genetics; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D013549:Sweetening Agents / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000201:enzymology* / Q000235:genetics
chemical_list: D018118:Chloride Channels; C089713:GEF1 protein, S cerevisiae; D007527:Isoenzymes; D029701:Saccharomyces cerevisiae Proteins; D013549:Sweetening Agents; D025262:Vacuolar Proton-Translocating ATPases; D005947:Glucose