title: Lipid Signaling via Pkh1/2 Regulates Fungal CO2 Sensing through the Kinase Sch9.
abstract: Adaptation to alternating CO2concentrations is crucial for all organisms. Carbonic anhydrases-metalloenzymes that have been found in all domains of life-enable fixation of scarce CO2by accelerating its conversion to bicarbonate and ensure maintenance of cellular metabolism. In fungi and other eukaryotes, the carbonic anhydrase Nce103 has been shown to be essential for growth in air (~0.04% CO2). Expression of NCE103 is regulated in response to CO2availability. In Saccharomyces cerevisiae, NCE103 is activated by the transcription factor ScCst6, and in Candida albicans and Candida glabrata, it is activated by its homologues CaRca1 and CgRca1, respectively. To identify the kinase controlling Cst6/Rca1, we screened an S. cerevisiae kinase/phosphatase mutant library for the ability to regulate NCE103 in a CO2-dependent manner. We identified ScSch9 as a potential ScCst6-specific kinase, as the sch9Δ mutant strain showed deregulated NCE103 expression on the RNA and protein levels. Immunoprecipitation revealed the binding capabilities of both proteins, and detection of ScCst6 phosphorylation by ScSch9 in vitro confirmed Sch9 as the Cst6 kinase. We could show that CO2-dependent activation of Sch9, which is part of a kinase cascade, is mediated by lipid/Pkh1/2 signaling but not TORC1. Finally, we tested conservation of the identified regulatory cascade in the pathogenic yeast species C. albicans and C. glabrata Deletion of SCH9 homologues of both species impaired CO2-dependent regulation of NCE103 expression, which indicates a conservation of the CO2adaptation mechanism among yeasts. Thus, Sch9 is a Cst6/Rca1 kinase that links CO2adaptation to lipid signaling via Pkh1/2 in fungi.
  
  
  
  All living organisms have to cope with alternating CO2concentrations as CO2levels range from very low in the atmosphere (0.04%) to high (5% and more) in other niches, including the human body. In fungi, CO2is sensed via two pathways. The first regulates virulence in pathogenic yeast by direct activation of adenylyl cyclase. The second pathway, although playing a fundamental role in fungal metabolism, is much less understood. Here the transcription factor Cst6/Rca1 controls carbon homeostasis by regulating carbonic anhydrase expression. Upstream signaling in this pathway remains elusive. We identify Sch9 as the kinase controlling Cst6/Rca1 activity in yeast and demonstrate that this pathway is conserved in pathogenic yeast species, which highlights identified key players as potential pharmacological targets. Furthermore, we provide a direct link between adaptation to changing CO2conditions and lipid/Pkh1/2 signaling in yeast, thus establishing a new signaling cascade central to metabolic adaptation.
authors.affiliation: Septomics Research Center, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Susann
authors.initials: S
authors.lastname: Pohlers
authors.affiliation: Septomics Research Center, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.|Friedrich Schiller University Jena, Jena, Germany.
authors.forename: Ronny
authors.initials: R
authors.lastname: Martin
authors.affiliation: Department of Molecular and Applied Microbiology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krüger
authors.affiliation: Septomics Research Center, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Hellwig
authors.affiliation: Department of Cell and Molecular Biology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Hänel
authors.affiliation: Friedrich Schiller University Jena, Jena, Germany.|Department of Molecular and Applied Microbiology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Olaf
authors.identifier: 0000-0002-9493-6402
authors.initials: O
authors.lastname: Kniemeyer
authors.affiliation: Friedrich Schiller University Jena, Jena, Germany.|Department of Cell and Molecular Biology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Saluz
authors.affiliation: VIB Department of Molecular Microbiology, KU Leuven, Leuven, Belgium.|Laboratory of Molecular Cell Biology, KU Leuven, Leuven, Belgium.
authors.forename: Patrick
authors.identifier: 0000-0002-1542-897X
authors.initials: P
authors.lastname: Van Dijck
authors.affiliation: Department Biologie, Molekulare Mykologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
authors.forename: Joachim F
authors.initials: JF
authors.lastname: Ernst
authors.affiliation: Friedrich Schiller University Jena, Jena, Germany.|Department of Molecular and Applied Microbiology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Brakhage
authors.affiliation: Kent Fungal Group, School of Biosciences, University of Kent, Canterbury, United Kingdom.|Clinical Microbiology Service, East Kent Hospitals University NHS Foundation Trust, The William Harvey Hospital, Ashford, United Kingdom.
authors.forename: Fritz A
authors.initials: FA
authors.lastname: Mühlschlegel
authors.affiliation: Septomics Research Center, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute (HKI), Jena, Germany oliver.kurzai@leibniz-hki.de.|Center for Sepsis Control and Care, University Hospital Jena, Jena, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kurzai
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases / Q000378:metabolism*; D051696:Activating Transcription Factors / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D002176:Candida albicans / Q000235:genetics; D041221:Candida glabrata / Q000235:genetics; D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D050356:Lipid Metabolism; D008666:Metalloendopeptidases / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D051696:Activating Transcription Factors; C410226:CST6 protein, S cerevisiae; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D002245:Carbon Dioxide; D064413:3-Phosphoinositide-Dependent Protein Kinases; C118385:PKH1 protein, S cerevisiae; C118386:PKH2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C530964:SCH9 protein, S cerevisiae; D008666:Metalloendopeptidases; D000251:Adenosine Triphosphatases; C102166:YTA12 protein, S cerevisiae; D002256:Carbonic Anhydrases