title: The Ppz protein phosphatases are key regulators of K+ and pH homeostasis: implications for salt tolerance, cell wall integrity and cell cycle progression.
abstract: The yeast Ppz protein phosphatases and the Hal3p inhibitory subunit are important determinants of salt tolerance, cell wall integrity and cell cycle progression. We present several lines of evidence showing that these disparate phenotypes are connected by the fact that Ppz regulates K+ transport. First, salt tolerance, cell wall integrity and cell cycle phenotypes of Ppz mutants are dependent on the Trk K+ transporters. Secondly, Ppz mutants exhibit altered activity of the Trk system, as measured by rubidium uptake. Thirdly, Ppz mutants exhibit altered intracellular K+ and pH, as expected from H+ efflux providing electrical balance during K+ uptake. Our unifying picture of Ppz phenotypes contends that activation of Trk by decreased Ppz activity results in plasma membrane depolarization (reducing uptake of toxic cations), increased intracellular K+ and turgor (compromising cell integrity), and increased intracellular pH (augmenting the expression of pH-regulated genes and facilitating alpha-factor recovery). In addition to providing a coherent explanation for all Ppz-dependent phenotypes, our results provide evidence for a causal relationship between intracellular cation homeostasis and a potential cell cycle checkpoint.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, Camino de Vera s/n, E-46022 Valencia, Spain. serrano@ibmcp.upv.es
authors.forename: Lynne
authors.initials: L
authors.lastname: Yenush
authors.forename: José M
authors.initials: JM
authors.lastname: Mulet
authors.forename: Joaquín
authors.initials: J
authors.lastname: Ariño
authors.forename: Ramón
authors.initials: R
authors.lastname: Serrano
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology; D027682:Cation Transport Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002473:Cell Wall / Q000502:physiology*; D005656:Fungal Proteins; D016193:G1 Phase; D006706:Homeostasis; D017136:Ion Transport / Q000502:physiology; D000072235:Mating Factor; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D009996:Osmotic Fragility / Q000502:physiology; D010455:Peptides / Q000502:physiology; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D006180:Proton-Translocating ATPases / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D018797:Cell Cycle Proteins; C086375:ENA1 protein, S cerevisiae; D005656:Fungal Proteins; D008565:Membrane Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; C092936:SIS2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D000072235:Mating Factor; D011189:Potassium Chloride; C075119:PPZ1 protein, S cerevisiae; C082731:PPZ2 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D000251:Adenosine Triphosphatases; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium