title: Evidence of a new role for the high-osmolarity glycerol mitogen-activated protein kinase pathway in yeast: regulating adaptation to citric acid stress.
abstract: Screening the Saccharomyces cerevisiae disruptome, profiling transcripts, and determining changes in protein expression have identified an important new role for the high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathway in the regulation of adaptation to citric acid stress. Deletion of HOG1, SSK1, PBS2, PTC2, PTP2, and PTP3 resulted in sensitivity to citric acid. Furthermore, citric acid resulted in the dual phosphorylation, and thus activation, of Hog1p. Despite minor activation of glycerol biosynthesis, the inhibitory effect of citric acid was not due to an osmotic shock. HOG1 negatively regulated the expression of a number of proteins in response to citric acid stress, including Bmh1p. Evidence suggests that BMH1 is induced by citric acid to counteract the effect of amino acid starvation. In addition, deletion of BMH2 rendered cells sensitive to citric acid. Deletion of the transcription factor MSN4, which is known to be regulated by Bmh1p and Hog1p, had a similar effect. HOG1 was also required for citric acid-induced up-regulation of Ssa1p and Eno2p. To counteract the cation chelating activity of citric acid, the plasma membrane Ca(2+) channel, CCH1, and a functional vacuolar membrane H(+)-ATPase were found to be essential for optimal adaptation. Also, the transcriptional regulator CYC8, which mediates glucose derepression, was required for adaptation to citric acid to allow cells to metabolize excess citrate via the tricarboxylic acid (TCA) cycle. Supporting this, Mdh1p and Idh1p, both TCA cycle enzymes, were up-regulated in response to citric acid.
authors.affiliation: Centre for Biomolecular Science, School of Biology, University of St. Andrews, St. Andrews, Fife KY16 9ST, United Kingdom.
authors.forename: Clare L
authors.initials: CL
authors.lastname: Lawrence
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Botting
authors.forename: Robin
authors.initials: R
authors.lastname: Antrobus
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Coote
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D004789:Enzyme Activation; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D016681:Genome, Fungal; D005990:Glycerol; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009994:Osmolar Concentration; D010641:Phenotype; D010766:Phosphorylation; D020543:Proteome / Q000032:analysis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D020543:Proteome; D029701:Saccharomyces cerevisiae Proteins; D019343:Citric Acid; C088589:HOG1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D000251:Adenosine Triphosphatases; D005990:Glycerol