Response to high osmotic conditions and elevated temperature in Saccharomyces cerevisiae is controlled by intracellular glycerol and involves coordinate activity of MAP kinase pathways.
In the yeast Saccharomyces cerevisiae, response to an increase in external osmolarity is mediated by the HOG (high osmolarity glycerol) MAP kinase pathway. HOG pathway mutant strains display osmosensitive phenotypes. Recently evidence has been obtained that the osmosensitivity of HOG pathway mutants is reduced during growth at elevated temperature (37 degrees C). A notable exception is the ste11ssk2ssk22 mutant, which displays hypersensitivity to osmotic stress at 37 degrees C. This paper reports that overexpression of FPS1 or GPD1 (encoding the glycerol transport facilitator and glycerol-3-phosphate dehydrogenase, respectively, and both affecting intracellular glycerol levels) reduces the hypersensitivity to osmotic stress of ste11ssk2ssk22 at 37 degrees C. Although in this particular HOG pathway mutant a correlation between suppression of the phenotype and glycerol content could be demonstrated, the absolute level of intracellular glycerol per se does not determine whether a strain is osmosensitive or not. Rather, evidence was obtained that the glycerol level may have an indirect effect, viz. by influencing signalling through the PKC (protein kinase C) MAP kinase pathway, which plays an important role in maintenance of cellular integrity. In order to validate the data obtained with a HOG pathway mutant strain for wild-type yeast cells, MAP kinase signalling under different growth conditions was examined in wild-type strains. PKC pathway signalling, which is manifest at elevated growth temperature by phosphorylation of MAP kinase Mpk1p, is rapidly lost when cells are shifted to high external osmolarity conditions. Expression of bck1-20 or overexpression of WSC3 in wild-type cells resulted in restoration of PKC signalling. Both PKC and HOG signalling, cell wall phenotypes and high osmotic stress responses in wild-type cells were found to be influenced by the growth temperature. The data taken together indicate the intricate interdependence of growth temperature, intracellular glycerol, cell wall structure and MAP kinase signalling in the hyperosmotic stress response of yeast.
Maria Curie-Sklodowska University, Institute of Biology, Department of Invertebrate Immunology, Akademicka 19, 20-033 Lublin, Poland.
Iwona
I
Wojda
Department of Biochemistry and Molecular Biology, IMBW, Biocentrum Amsterdam, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Rebeca
R
Alonso-Monge
Department of Biochemistry and Molecular Biology, IMBW, Biocentrum Amsterdam, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Jan-Paul
JP
Bebelman
Department of Biochemistry and Molecular Biology, IMBW, Biocentrum Amsterdam, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Willem H
WH
Mager
Department of Biochemistry and Molecular Biology, IMBW, Biocentrum Amsterdam, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
Marco
M
Siderius
D002473:Cell Wall / Q000737:chemistry; D015966:Gene Expression Regulation, Fungal; D005990:Glycerol / Q000378:metabolism*; D018869:Heat-Shock Response; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009997:Osmotic Pressure; D011493:Protein Kinase C / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013696:Temperature
D029701:Saccharomyces cerevisiae Proteins; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D005990:Glycerol