scholarly journals Osmotic Stress Signaling and Osmoadaptation in Yeasts

2002 ◽  
Vol 66 (2) ◽  
pp. 300-372 ◽  
Author(s):  
Stefan Hohmann
Keyword(s):  
Cell Surface ◽  
Map Kinase ◽  
Surface Properties ◽  
Transcriptional Response ◽  
Yeast Cells ◽  
Hog Pathway ◽  
Cell Surface Properties ◽  
High Osmolarity ◽  
Map Kinase Cascade ◽  
Kinase Cascade

SUMMARY The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.

scholarly journals The Stress-activated Mitogen-activated Protein Kinase Signaling Cascade Promotes Exit from Mitosis

2006 ◽  
Vol 17 (7) ◽  
pp. 3136-3146 ◽  
Author(s):  
Vladimír Reiser ◽  
Katharine E. D’Aquino ◽  
Ly-Sha Ee ◽  
Angelika Amon
Keyword(s):  
Map Kinase ◽  
Mitogen Activated Protein Kinase ◽  
Hog Pathway ◽  
Hypertonic Stress ◽  
Map Kinase Cascade ◽  
Protein Map ◽  
Mitogen Activated Protein ◽  
Early Anaphase ◽  
Kinase Cascade ◽  
Protein Kinase Signaling

In budding yeast, a signaling network known as the mitotic exit network (MEN) triggers exit from mitosis. We find that hypertonic stress allows MEN mutants to exit from mitosis in a manner dependent on the high osmolarity glycerol (HOG) mitogen-activated protein (MAP) kinase cascade. The HOG pathway drives exit from mitosis in MEN mutants by promoting the activation of the MEN effector, the protein phosphatase Cdc14. Activation of Cdc14 depends on the Cdc14 early anaphase release network, a group of proteins that functions in parallel to the MEN to promote Cdc14 function. Notably, exit from mitosis is promoted by the signaling branch defined by the Sho1 osmosensing system, but not by the Sln1 osmosensor of the HOG pathway. Our results suggest that the stress MAP kinase pathway mobilizes programs to promote completion of the cell cycle and entry into G1 under unfavorable conditions.

scholarly journals Expression of a Fungal Hydrophobin in the Saccharomyces cerevisiae Cell Wall: Effect on Cell Surface Properties and Immobilization

2002 ◽  
Vol 68 (7) ◽  
pp. 3385-3391 ◽  
Author(s):  
Tiina Nakari-Setälä ◽  
Joana Azeredo ◽  
Mariana Henriques ◽  
Rosário Oliveira ◽  
José Teixeira ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Wall ◽  
Cell Surface ◽  
Surface Properties ◽  
Hydrophobic Interactions ◽  
Surface Characteristics ◽  
Yeast Cells ◽  
Phase System ◽  
Two Phase ◽  
Cell Surface Properties

ABSTRACT The aim of this work was to modify the cell surface properties of Saccharomyces cerevisiae by expression of the HFBI hydrophobin of the filamentous fungus Trichoderma reesei on the yeast cell surface. The second aim was to study the immobilization capacity of the modified cells. Fusion to the Flo1p flocculin was used to target the HFBI moiety to the cell wall. Determination of cell surface characteristics with contact angle and zeta potential measurements indicated that HFBI-producing cells are more apolar and slightly less negatively charged than the parent cells. Adsorption of the yeast cells to different commercial supports was studied. A twofold increase in the binding affinity of the hydrophobin-producing yeast to hydrophobic silicone-based materials was observed, while no improvement in the interaction with hydrophilic carriers could be seen compared to that of the parent cells. Hydrophobic interactions between the yeast cells and the support are suggested to play a major role in attachment. Also, a slight increase in the initial adsorption rate of the hydrophobin yeast was observed. Furthermore, due to the engineered cell surface, hydrophobin-producing yeast cells were efficiently separated in an aqueous two-phase system by using a nonionic polyoxyethylene detergent, C12-18EO5.

scholarly journals A Third Osmosensing Branch in Saccharomyces cerevisiae Requires the Msb2 Protein and Functions in Parallel with the Sho1 Branch

2002 ◽  
Vol 22 (13) ◽  
pp. 4739-4749 ◽  
Author(s):  
Sean M. O'Rourke ◽  
Ira Herskowitz
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Map Kinase ◽  
Cross Talk ◽  
Dna Microarrays ◽  
Hog Pathway ◽  
Gene Sets ◽  
Map Kinase Cascade ◽  
Mitogen Activated Protein ◽  
Kinase Cascade ◽  
Membrane Spanning

ABSTRACT Two Saccharomyces cerevisiae plasma membrane-spanning proteins, Sho1 and Sln1, function during increased osmolarity to activate a mitogen-activated protein (MAP) kinase cascade. One of these proteins, Sho1, utilizes the MAP kinase kinase kinase Ste11 to activate Pbs2. We previously used the FUS1 gene of the pheromone response pathway as a reporter to monitor cross talk in hog1 mutants. Cross talk requires the Sho1-Ste11 branch of the HOG pathway, but some residual signaling, which is STE11 dependent, still occurs in the absence of Sho1. These observations led us to propose the existence of another osmosensor upstream of Ste11. To identify such an osmosensor, we screened for mutants in which the residual signaling in a hog1 sho1 mutant was further reduced. We identified the MSB2 gene, which encodes a protein with a single membrane-spanning domain and a large presumptive extracellular domain. Assay of the FUS1-lacZ reporter (in a hog1 mutant background) showed that sho1 and msb2 mutations both reduced the expression of the reporter partially and that the hog1 sho1 msb2 mutant was severely defective in the expression of the reporter. The use of DNA microarrays to monitor gene expression revealed that Sho1 and Msb2 regulate identical gene sets in hog1 mutants. A role for MSB2 in HOG1 strains was also seen in strains defective in the two known branches that activate Pbs2: an ssk1 sho1 msb2 strain was more osmosensitive than an ssk1 sho1 MSB2 strain. These observations indicate that Msb2 is partially redundant with the Sho1 osmosensing branch for the activation of Ste11.

scholarly journals Isolation and Characterization of High-Osmolarity-Sensitive Mutants of Fission Yeast

1998 ◽  
Vol 180 (19) ◽  
pp. 5038-5043 ◽  
Author(s):  
Hirofumi Aiba ◽  
Ryosuke Kawaura ◽  
Eiji Yamamoto ◽  
Hisami Yamada ◽  
Kaoru Takegawa ◽  
...  
Keyword(s):  
Map Kinase ◽  
Fission Yeast ◽  
High Osmolarity ◽  
Downstream Target ◽  
Isolation And Characterization ◽  
Map Kinase Cascade ◽  
Mitogen Activated Protein ◽  
Downstream Target Gene ◽  
Kinase Cascade ◽  
Glycerol 3 Phosphate Dehydrogenase

ABSTRACT For the fission yeast Schizosaccharomyces pombe, adaptation to high-osmolarity medium is mediated by a mitogen-activated protein (MAP) kinase cascade, involving the Wis1 MAP kinase kinase and the Sty1 MAP kinase. The MAP kinase pathway transduces an osmotic signal and accordingly regulates the expression of the downstream target gene (gpd1 +) that encodes NADH-dependent glycerol-3-phosphate dehydrogenase, in order to adaptively accumulate glycerol inside the cells as an osmoprotectant. We previously characterized a set of high-osmolarity-sensitive S. pombemutants, including wis1, sty1, andgpd1. In this study, we attempted to further isolate novel osmolarity-sensitive mutants. For some of the mutants isolated, profiles of glycerol production in response to the osmolarity of the growth medium were indistinguishable from that of the wild-type cells, suggesting that they are novel types. They were classified into three distinct types genetically and, thus, were designated hos1,hos2, and hos3 (high osmolarity sensitive) mutants. One of them, the hos1 mutant, was characterized in detail. The hos1 mutant was demonstrated to have a mutational lesion in the known ryh1 + gene, which encodes a small GTP-binding protein. Disruption of theryh1 + gene results not only in osmosensitivity but also in temperature sensitivity for growth. It was also found that the Δryh1 mutant is severely sterile. These results are discussed with special reference to the osmoadaptation of S. pombe.

scholarly journals Requirement of STE50 for Osmostress-Induced Activation of the STE11 Mitogen-Activated Protein Kinase Kinase Kinase in the High-Osmolarity Glycerol Response Pathway

1998 ◽  
Vol 18 (10) ◽  
pp. 5788-5796 ◽  
Author(s):  
Francesc Posas ◽  
Elizabeth A. Witten ◽  
Haruo Saito
Keyword(s):  
Osmotic Stress ◽  
Map Kinase ◽  
Kinase Activation ◽  
High Osmolarity ◽  
High Osmolarity Glycerol ◽  
Terminal Domain ◽  
Map Kinase Cascade ◽  
Two Component ◽  
Mitogen Activated Protein ◽  
Kinase Cascade

ABSTRACT Exposure of yeast cells to increases in extracellular osmolarity activates the HOG1 mitogen-activated protein (MAP) kinase cascade, which is composed of three tiers of protein kinases: (i) the SSK2, SSK22, and STE11 MAP kinase kinase kinases (MAPKKKs), (ii) the PBS2 MAPKK, and (iii) the HOG1 MAP kinase. Activation of the MAP kinase cascade is mediated by two upstream mechanisms. The SLN1-YPD1-SSK1 two-component osmosensor activates the SSK2 and SSK22 MAPKKKs by direct interaction of the SSK1 response regulator with these MAPKKKs. The second mechanism of HOG1 MAP kinase activation is independent of the two-component osmosensor and involves the SHO1 transmembrane protein and the STE11 MAPKKK. Only PBS2 and HOG1 are common to the two mechanisms. We conducted an exhaustive mutant screening to identify additional elements required for activation of STE11 by osmotic stress. We found that strains with mutations in the STE50 gene, in combination with ssk2Δ ssk22Δ mutations, were unable to induce HOG1 phosphorylation after osmotic stress. Both two-hybrid analyses and coprecipitation assays demonstrated that the N-terminal domain of STE50 binds strongly to the N-terminal domain of STE11. The binding of STE50 to STE11 is constitutive and is not affected by osmotic stress. Furthermore, the two proteins relocalize similarly after osmotic shock. It was concluded that STE50 fulfills an essential role in the activation of the high-osmolarity glycerol response pathway by acting as an integral subunit of the STE11 MAPKKK.

scholarly journals Phosphorelay-Regulated Degradation of the Yeast Ssk1p Response Regulator by the Ubiquitin-Proteasome System

2003 ◽  
Vol 23 (18) ◽  
pp. 6662-6671 ◽  
Author(s):  
Naoto Sato ◽  
Hiroyuki Kawahara ◽  
Akio Toh-e ◽  
Tatsuya Maeda
Keyword(s):  
Map Kinase ◽  
Response Regulator ◽  
Signal Transduction Pathway ◽  
Ubiquitin Proteasome System ◽  
Hog Pathway ◽  
High Osmolarity ◽  
Mitogen Activated Protein ◽  
Inactivation Mechanism ◽  
Kinase Cascade ◽  
Ubiquitin Proteasome

ABSTRACT In Saccharomyces cerevisiae, a phosphorelay signal transduction pathway composed of Sln1p, Ypd1p, and Ssk1p, which are homologous to bacterial two-component signal transducers, is involved in the osmosensing mechanism. In response to high osmolarity, the phosphorelay system is inactivated and Ssk1p remains unphosphorylated. Unphosphorylated Ssk1p binds to and activates the Ssk2p mitogen-activated protein (MAP) kinase kinase kinase, which in turn activates the downstream components of the high-osmolarity glycerol response (HOG) MAP kinase cascade. Here, we report a novel inactivation mechanism for Ssk1p involving degradation by the ubiquitin-proteasome system. Degradation is regulated by the phosphotransfer from Ypd1p to Ssk1p, insofar as unphosphorylated Ssk1p is degraded more rapidly than phosphorylated Ssk1p. Ubc7p/Qri8p, an endoplasmic reticulum-associated ubiquitin-conjugating enzyme, is involved in the phosphorelay-regulated degradation of Ssk1p. In ubc7Δ cells in which the degradation is hampered, the dephosphorylation and/or inactivation process of the Hog1p MAP kinase is delayed compared with wild-type cells after the hyperosmotic treatment. Our results indicate that unphosphorylated Ssk1p is selectively degraded by the Ubc7p-dependent ubiquitin-proteasome system and that this mechanism downregulates the HOG pathway after the completion of the osmotic adaptation.

scholarly journals Mating in Saccharomyces cerevisiae: The Role of the Pheromone Signal Transduction Pathway in the Chemotropic Response to Pheromone

Genetics ◽  
1997 ◽  
Vol 147 (1) ◽  
pp. 19-32 ◽  
Author(s):  
Kathrin Schrick ◽  
Barbara Garvik ◽  
Leland H Hartwell
Keyword(s):  
Signal Transduction ◽  
Map Kinase ◽  
Transcriptional Activation ◽  
Signal Transduction Pathway ◽  
Transduction Pathway ◽  
Wild Type ◽  
Mating Partner ◽  
Map Kinase Cascade ◽  
Kinase Cascade ◽  
Wild Type Control

Abstract The mating process in yeast has two distinct aspects. One is the induction and activation of proteins required for cell fusion in response to a pheromone signal; the other is chemotropism, i.e., detection of a pheromone gradient and construction of a fusion site available to the signaling cell. To determine whether components of the signal transduction pathway necessary for transcriptional activation also play a role in chemotropism, we examined strains with null mutations in components of the signal transduction pathway for diploid formation, prezygote formation and the chemotropic process of mating partner discrimination when transcription was induced downstream of the mutation. Cells mutant for components of the mitogen-activated protein (MAP) kinase cascade (ste5, ste20, ste11, ste7 or fus3 kss1) formed diploids at a frequency 1% that of the wild-type control, but formed prezygotes as efficiently as the wild-type control and showed good mating partner discrimination, suggesting that the MAP kinase cascade is not essential for chemotropism. In contrast, cells mutant for the receptor (ste2) or the β or γ subunit (ste4 and stel8) of the G protein were extremely defective in both diploid and prezygote formation and discriminated poorly between signaling and nonsignaling mating partners, implying that these components are important for chemotropism.

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