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KRH1 and KRH2 are functionally non-redundant in signaling for pseudohyphal differentiation in Saccharomyces cerevisiae. Curr Genet 2017; 63:851-859. [PMID: 28247024 DOI: 10.1007/s00294-017-0684-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/31/2017] [Accepted: 02/11/2017] [Indexed: 10/20/2022]
Abstract
Diploid cells of Saccharomyces cerevisiae undergo pseudohyphal differentiation in response to nutrient depletion. Although this dimorphic transition occurs due to signals originating from carbon and nitrogen limitation, how these signals are coordinated and integrated is not understood. Results of this study indicate that the pseudohyphal defect of the mep2∆ mutant is overcome upon disruption of KRH2/GPB1 but not KRH1/GPB2. Further, the agar invasion defect observed in a mep2 mutant strain is suppressed only by deleting KRH2 and not KRH1. Thus, the results presented indicate that MEP2 functions by inhibiting KRH2 to trigger filamentation response when glucose becomes limiting. Biochemical data and phenotypic response to glucose replenishment reveal that KRH1 and KRH2 are differentially regulated by glucose and ammonium to induce pseudohyphae formation via the cAMP-PKA pathway. In contrast to the current view, this study clearly demonstrates that, KRH1 and KRH2 are not functionally redundant.
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2
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A Gβ protein and the TupA Co-Regulator Bind to Protein Kinase A Tpk2 to Act as Antagonistic Molecular Switches of Fungal Morphological Changes. PLoS One 2015; 10:e0136866. [PMID: 26334875 PMCID: PMC4559445 DOI: 10.1371/journal.pone.0136866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 08/09/2015] [Indexed: 11/19/2022] Open
Abstract
The human pathogenic fungus Paracoccidioides brasiliensis (Pb) undergoes a morphological transition from a saprobic mycelium to pathogenic yeast that is controlled by the cAMP-signaling pathway. There is a change in the expression of the Gβ-protein PbGpb1, which interacts with adenylate cyclase, during this morphological transition. We exploited the fact that the cAMP-signaling pathway of Saccharomyces cerevisiae does not include a Gβ-protein to probe the functional role of PbGpb1. We present data that indicates that PbGpb1 and the transcriptional regulator PbTupA both bind to the PKA protein PbTpk2. PbTPK2 was able to complement a TPK2Δ strain of S. cerevisiae, XPY5a/α, which was defective in pseudohyphal growth. Whilst PbGPB1 had no effect on the parent S. cerevisiae strain, MLY61a/α, it repressed the filamentous growth of XPY5a/α transformed with PbTPK2, behaviour that correlated with a reduced expression of the floculin FLO11. In vitro, PbGpb1 reduced the kinase activity of PbTpk2, suggesting that inhibition of PbTpk2 by PbGpb1 reduces the level of expression of Flo11, antagonizing the filamentous growth of the cells. In contrast, expressing the co-regulator PbTUPA in XPY5a/α cells transformed with PbTPK2, but not untransformed cells, induced hyperfilamentous growth, which could be antagonized by co-transforming the cells with PbGPB1. PbTUPA was unable to induce the hyperfilamentous growth of a FLO8Δ strain, suggesting that PbTupA functions in conjunction with the transcription factor Flo8 to control Flo11 expression. Our data indicates that P. brasiliensis PbGpb1 and PbTupA, both of which have WD/β-propeller structures, bind to PbTpk2 to act as antagonistic molecular switches of cell morphology, with PbTupA and PbGpb1 inducing and repressing filamentous growth, respectively. Our findings define a potential mechanism for controlling the morphological switch that underpins the virulence of dimorphic fungi.
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Conrad M, Schothorst J, Kankipati HN, Van Zeebroeck G, Rubio-Texeira M, Thevelein JM. Nutrient sensing and signaling in the yeast Saccharomyces cerevisiae. FEMS Microbiol Rev 2014; 38:254-99. [PMID: 24483210 PMCID: PMC4238866 DOI: 10.1111/1574-6976.12065] [Citation(s) in RCA: 414] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 12/23/2013] [Accepted: 01/22/2014] [Indexed: 02/04/2023] Open
Abstract
The yeast Saccharomyces cerevisiae has been a favorite organism for pioneering studies on nutrient-sensing and signaling mechanisms. Many specific nutrient responses have been elucidated in great detail. This has led to important new concepts and insight into nutrient-controlled cellular regulation. Major highlights include the central role of the Snf1 protein kinase in the glucose repression pathway, galactose induction, the discovery of a G-protein-coupled receptor system, and role of Ras in glucose-induced cAMP signaling, the role of the protein synthesis initiation machinery in general control of nitrogen metabolism, the cyclin-controlled protein kinase Pho85 in phosphate regulation, nitrogen catabolite repression and the nitrogen-sensing target of rapamycin pathway, and the discovery of transporter-like proteins acting as nutrient sensors. In addition, a number of cellular targets, like carbohydrate stores, stress tolerance, and ribosomal gene expression, are controlled by the presence of multiple nutrients. The protein kinase A signaling pathway plays a major role in this general nutrient response. It has led to the discovery of nutrient transceptors (transporter receptors) as nutrient sensors. Major shortcomings in our knowledge are the relationship between rapid and steady-state nutrient signaling, the role of metabolic intermediates in intracellular nutrient sensing, and the identity of the nutrient sensors controlling cellular growth.
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Affiliation(s)
- Michaela Conrad
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
| | - Joep Schothorst
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
| | - Harish Nag Kankipati
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
| | - Griet Van Zeebroeck
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
| | - Marta Rubio-Texeira
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
| | - Johan M Thevelein
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, KU LeuvenLeuven-Heverlee, Flanders, Belgium
- Department of Molecular Microbiology, VIBLeuven-Heverlee, Flanders, Belgium
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4
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Abstract
For centuries yeast species have been popular hosts for classical biotechnology processes, such as baking, brewing, and wine making, and more recently for recombinant proteins production, thanks to the advantages of unicellular organisms (i.e., ease of genetic manipulation and rapid growth) together with the ability to perform eukaryotic posttranslational modifications. Moreover, yeast cells have been used for few decades as a tool for identifying the genes and pathways involved in basic cellular processes such as the cell cycle, aging, and stress response. In the budding yeast S. cerevisiae the Ras/cAMP/PKA pathway is directly involved in the regulation of metabolism, cell growth, stress resistance, and proliferation in response to the availability of nutrients and in the adaptation to glucose, controlling cytosolic cAMP levels and consequently the cAMP-dependent protein kinase (PKA) activity. Moreover, Ras signalling has been identified in several pathogenic yeasts as a key controller for virulence, due to its involvement in yeast morphogenesis. Nowadays, yeasts are still useful for Ras-like proteins investigation, both as model organisms and as a test tube to study variants of heterologous Ras-like proteins.
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Affiliation(s)
- Renata Tisi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milan, Italy
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5
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The role of the RACK1 ortholog Cpc2p in modulating pheromone-induced cell cycle arrest in fission yeast. PLoS One 2013; 8:e65927. [PMID: 23843946 PMCID: PMC3701009 DOI: 10.1371/journal.pone.0065927] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Accepted: 05/04/2013] [Indexed: 11/24/2022] Open
Abstract
The detection and amplification of extracellular signals requires the involvement of multiple protein components. In mammalian cells the receptor of activated C kinase (RACK1) is an important scaffolding protein for signal transduction networks. Further, it also performs a critical function in regulating the cell cycle by modulating the G1/S transition. Many eukaryotic cells express RACK1 orthologs, with one example being Cpc2p in the fission yeast Schizosaccharomyces pombe. In contrast to RACK1, Cpc2p has been described to positively regulate, at the ribosomal level, cells entry into M phase. In addition, Cpc2p controls the stress response pathways through an interaction with Msa2p, and sexual development by modulating Ran1p/Pat1p. Here we describe investigations into the role, which Cpc2p performs in controlling the G protein-mediated mating response pathway. Despite structural similarity to Gβ-like subunits, Cpc2p appears not to function at the G protein level. However, upon pheromone stimulation, cells overexpressing Cpc2p display substantial cell morphology defects, disorientation of septum formation and a significantly protracted G1 arrest. Cpc2p has the potential to function at multiple positions within the pheromone response pathway. We provide a mechanistic interpretation of this novel data by linking Cpc2p function, during the mating response, with its previous described interactions with Ran1p/Pat1p. We suggest that overexpressing Cpc2p prolongs the stimulated state of pheromone-induced cells by increasing ste11 gene expression. These data indicate that Cpc2p regulates the pheromone-induced cell cycle arrest in fission yeast by delaying cells entry into S phase.
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6
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Zhang Y, Kweon HK, Shively C, Kumar A, Andrews PC. Towards systematic discovery of signaling networks in budding yeast filamentous growth stress response using interventional phosphorylation data. PLoS Comput Biol 2013; 9:e1003077. [PMID: 23825934 PMCID: PMC3694812 DOI: 10.1371/journal.pcbi.1003077] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 04/17/2013] [Indexed: 11/19/2022] Open
Abstract
Reversible phosphorylation is one of the major mechanisms of signal transduction, and signaling networks are critical regulators of cell growth and development. However, few of these networks have been delineated completely. Towards this end, quantitative phosphoproteomics is emerging as a useful tool enabling large-scale determination of relative phosphorylation levels. However, phosphoproteomics differs from classical proteomics by a more extensive sampling limitation due to the limited number of detectable sites per protein. Here, we propose a comprehensive quantitative analysis pipeline customized for phosphoproteome data from interventional experiments for identifying key proteins in specific pathways, discovering the protein-protein interactions and inferring the signaling network. We also made an effort to partially compensate for the missing value problem, a chronic issue for proteomics studies. The dataset used for this study was generated using SILAC (Stable Isotope Labeling with Amino acids in Cell culture) technique with interventional experiments (kinase-dead mutations). The major components of the pipeline include phosphopeptide meta-analysis, correlation network analysis and causal relationship discovery. We have successfully applied our pipeline to interventional experiments identifying phosphorylation events underlying the transition to a filamentous growth form in Saccharomyces cerevisiae. We identified 5 high-confidence proteins from meta-analysis, and 19 hub proteins from correlation analysis (Pbi2p and Hsp42p were identified by both analyses). All these proteins are involved in stress responses. Nine of them have direct or indirect evidence of involvement in filamentous growth. In addition, we tested four of our predicted proteins, Nth1p, Pbi2p, Pdr12p and Rcn2p, by interventional phenotypic experiments and all of them present differential invasive growth, providing prospective validation of our approach. This comprehensive pipeline presents a systematic way for discovering signaling networks using interventional phosphoproteome data and can suggest candidate proteins for further investigation. We anticipate the methodology to be applicable as well to other interventional studies via different experimental platforms.
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Affiliation(s)
- Yan Zhang
- Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Hye Kyong Kweon
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Christian Shively
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Anuj Kumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Philip C. Andrews
- Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- * E-mail:
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7
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Abstract
Filamentous growth is a nutrient-regulated growth response that occurs in many fungal species. In pathogens, filamentous growth is critical for host-cell attachment, invasion into tissues, and virulence. The budding yeast Saccharomyces cerevisiae undergoes filamentous growth, which provides a genetically tractable system to study the molecular basis of the response. Filamentous growth is regulated by evolutionarily conserved signaling pathways. One of these pathways is a mitogen activated protein kinase (MAPK) pathway. A remarkable feature of the filamentous growth MAPK pathway is that it is composed of factors that also function in other pathways. An intriguing challenge therefore has been to understand how pathways that share components establish and maintain their identity. Other canonical signaling pathways-rat sarcoma/protein kinase A (RAS/PKA), sucrose nonfermentable (SNF), and target of rapamycin (TOR)-also regulate filamentous growth, which raises the question of how signals from multiple pathways become integrated into a coordinated response. Together, these pathways regulate cell differentiation to the filamentous type, which is characterized by changes in cell adhesion, cell polarity, and cell shape. How these changes are accomplished is also discussed. High-throughput genomics approaches have recently uncovered new connections to filamentous growth regulation. These connections suggest that filamentous growth is a more complex and globally regulated behavior than is currently appreciated, which may help to pave the way for future investigations into this eukaryotic cell differentiation behavior.
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8
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Brückner S, Mösch HU. Choosing the right lifestyle: adhesion and development in Saccharomyces cerevisiae. FEMS Microbiol Rev 2011; 36:25-58. [PMID: 21521246 DOI: 10.1111/j.1574-6976.2011.00275.x] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The budding yeast Saccharomyces cerevisiae is a eukaryotic microorganism that is able to choose between different unicellular and multicellular lifestyles. The potential of individual yeast cells to switch between different growth modes is advantageous for optimal dissemination, protection and substrate colonization at the population level. A crucial step in lifestyle adaptation is the control of self- and foreign adhesion. For this purpose, S. cerevisiae contains a set of cell wall-associated proteins, which confer adhesion to diverse biotic and abiotic surfaces. Here, we provide an overview of different aspects of S. cerevisiae adhesion, including a detailed description of known lifestyles, recent insights into adhesin structure and function and an outline of the complex regulatory network for adhesin gene regulation. Our review shows that S. cerevisiae is a model system suitable for studying not only the mechanisms and regulation of cell adhesion, but also the role of this process in microbial development, ecology and evolution.
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Affiliation(s)
- Stefan Brückner
- Department of Genetics, Philipps-Universität Marburg, Marburg, Germany
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9
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Budhwar R, Fang G, Hirsch JP. Kelch repeat proteins control yeast PKA activity in response to nutrient availability. Cell Cycle 2011; 10:767-70. [PMID: 21311222 DOI: 10.4161/cc.10.5.14828] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Regulation of protein kinase A (PKA) by binding of cAMP to the regulatory subunit and the resulting release of the active catalytic subunit is a very well established mechanism of kinase activation. We have shown recently that PKA in budding yeast is also subject to an additional level of regulation that that modulates its activity in response to nutrient availability. Nutrient regulation of PKA activity requires a pair of proteins, Gpb1 and Gpb2, that contain several kelch repeats, a sequence motif that predicts that they fold into a β-propeller structure. The regulatory process mediated by Gpb1 and Gpb2 causes an increase in the stability and phosphorylation of the PKA regulatory subunit Bcy1 in response to low extracellular glucose concentrations. Phosphorylation of serine-145 of Bcy1 controls its stability, and other phosphorylation events at the cluster of serines at positions 74-84 correlate with changes in nutrient availability. Here we present data consistent with a model in which the effects of Gpb1 and Gpb2 on Bcy1 are an indirect consequence of their primary effects on the PKA catalytic subunits.
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Affiliation(s)
- Roli Budhwar
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY, USA
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10
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Budhwar R, Lu A, Hirsch JP. Nutrient control of yeast PKA activity involves opposing effects on phosphorylation of the Bcy1 regulatory subunit. Mol Biol Cell 2010; 21:3749-58. [PMID: 20826609 PMCID: PMC2965690 DOI: 10.1091/mbc.e10-05-0388] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Kelch repeat proteins Gpb1 and Gpb2 control yeast PKA activity in response to nutrients by stimulating phosphorylation of the Bcy1 regulatory subunit. Gpb1 and Gpb2 function by blocking inhibition of Bcy1 phosphorylation by PKA catalytic subunits. Phosphorylated Bcy1 is more stable and is a more effective inhibitor of PKA activity. GPB1 and GPB2 encode kelch repeat-containing proteins that regulate protein kinase A (PKA) in yeast by a cAMP-independent process. Here we show that Gpb1 and Gpb2 stimulate phosphorylation of PKA regulatory subunit Bcy1 in low glucose concentrations, thereby promoting the inhibitory function of Bcy1 when nutrients are scarce and PKA activity is expected to be low. Gpb1 and Gpb2 stimulate Bcy1 phosphorylation at an unknown site, and this modification stabilizes Bcy1 that has been phosphorylated by PKA catalytic subunits at serine-145. The BCY1S145A mutation eliminates the effect of gpb1Δ gpb2Δ on Bcy1 stability but maintains their effect on phosphorylation and signaling, indicating that modulation of PKA activity by Gpb1 and Gpb2 is not solely due to increased levels of Bcy1. Inhibition of PKA catalytic subunits that are ATP analog-sensitive causes increased Bcy1 phosphorylation at the unknown site in high glucose. When PKA is inhibited, gpb1Δ gpb2Δ mutations have no effect on Bcy1 phosphorylation. Therefore, Gpb1 and Gpb2 oppose PKA activity by blocking the ability of PKA to inhibit Bcy1 phosphorylation at a site other than serine-145. Stimulation of Bcy1 phosphorylation by Gpb1 and Gpb2 produces a form of Bcy1 that is more stable and is a more effective PKA inhibitor.
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Affiliation(s)
- Roli Budhwar
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA
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11
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Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae. Curr Genet 2010; 56:1-32. [PMID: 20054690 DOI: 10.1007/s00294-009-0287-1] [Citation(s) in RCA: 163] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 12/18/2009] [Accepted: 12/19/2009] [Indexed: 12/27/2022]
Abstract
Cells of all living organisms contain complex signal transduction networks to ensure that a wide range of physiological properties are properly adapted to the environmental conditions. The fundamental concepts and individual building blocks of these signalling networks are generally well-conserved from yeast to man; yet, the central role that growth factors and hormones play in the regulation of signalling cascades in higher eukaryotes is executed by nutrients in yeast. Several nutrient-controlled pathways, which regulate cell growth and proliferation, metabolism and stress resistance, have been defined in yeast. These pathways are integrated into a signalling network, which ensures that yeast cells enter a quiescent, resting phase (G0) to survive periods of nutrient scarceness and that they rapidly resume growth and cell proliferation when nutrient conditions become favourable again. A series of well-conserved nutrient-sensory protein kinases perform key roles in this signalling network: i.e. Snf1, PKA, Tor1 and Tor2, Sch9 and Pho85-Pho80. In this review, we provide a comprehensive overview on the current understanding of the signalling processes mediated via these kinases with a particular focus on how these individual pathways converge to signalling networks that ultimately ensure the dynamic translation of extracellular nutrient signals into appropriate physiological responses.
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12
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cAMP signaling pathway controls glycogen metabolism in Neurospora crassa by regulating the glycogen synthase gene expression and phosphorylation. Fungal Genet Biol 2010; 47:43-52. [PMID: 19883780 DOI: 10.1016/j.fgb.2009.10.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 10/26/2009] [Accepted: 10/26/2009] [Indexed: 11/22/2022]
Abstract
The cAMP-PKA signaling pathway plays an important role in many biological processes including glycogen metabolism. In this work we investigated its role in the Neurospora crassa glycogen metabolism control using mutant strains affected in components of the pathway, the cr-1 strain deficient in adenylyl cyclase activity therefore has the PKA pathway not active, and the mcb strain a temperature-sensitive mutant defective in the regulatory subunit of PKA therefore is a strain with constitutively active PKA. We analyzed the expression of the gene encoding glycogen synthase (gsn), the regulatory enzyme in glycogen synthesis as a potential target of the regulation. The cr-1 strain accumulated, during vegetative growth, glycogen levels much higher than the wild type strain indicating a role of the PKA pathway in the glycogen accumulation. The gsn transcript was not increased in this strain but the GSN protein was less phosphorylated "in vitro", and therefore more active, suggesting that the post-translational modification of GSN is likely the main mechanism controlling glycogen accumulation during vegetative growth. Heat shock down-regulates gsn gene transcription in the two mutant strains, as well as in the wild type strain, suggesting that the PKA pathway may not be the only pathway having a direct role in gsn transcription under heat shock. DNA-protein complexes were formed between the STRE motif in the gsn promoter and nuclear proteins from heat-shocked mycelium. However STRE was not able to induce transcription of a reporter gene in Saccharomyces cerevisiae, suggesting that the motif might be involved in a different way of regulation in the N. crassa gene expression under heat shock. The CRE-like DNA elements present in the gsn promoter were shown to be bound by different proteins from the PKA mutant strains. The DNA-protein complexes were observed with proteins from the strains grown under normal condition and under heat shock indicating the functionality of this DNA element. In this work we presented some evidences that the PKA signaling pathway regulates glycogen metabolism in N. crassa in a different way when compared to the well-characterized model of regulation existent in S. cerevisiae.
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13
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Dijck PV. Nutrient sensing G protein-coupled receptors: interesting targets for antifungals? Med Mycol 2009; 47:671-80. [DOI: 10.3109/13693780802713349] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
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14
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Abstract
Yeast cells sense the amount and quality of external nutrients through multiple interconnected signaling networks, which allow them to adjust their metabolism, transcriptional profile and developmental program to adapt readily and appropriately to changing nutritional states. We present our current understanding of the nutritional sensing networks yeast cells rely on for perceiving the nutritional landscape, with particular emphasis on those sensitive to carbon and nitrogen sources. We describe the means by which these networks inform the cell's decision among the different developmental programs available to them-growth, quiescence, filamentous development, or meiosis/sporulation. We conclude that the highly interconnected signaling networks provide the cell with a highly nuanced view of the environment and that the cell can interpret that information through a sophisticated calculus to achieve optimum responses to any nutritional condition.
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Affiliation(s)
- Shadia Zaman
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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15
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Xue C, Hsueh YP, Heitman J. Magnificent seven: roles of G protein-coupled receptors in extracellular sensing in fungi. FEMS Microbiol Rev 2008; 32:1010-32. [PMID: 18811658 DOI: 10.1111/j.1574-6976.2008.00131.x] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
G protein-coupled receptors (GPCRs) represent the largest family of transmembrane receptors and are responsible for transducing extracellular signals into intracellular responses that involve complex intracellular-signaling networks. This review highlights recent research advances in fungal GPCRs, including classification, extracellular sensing, and G protein-signaling regulation. The involvement of GPCRs in pheromone and nutrient sensing has been studied extensively over the past decade. Following recent advances in fungal genome sequencing projects, a panoply of GPCR candidates has been revealed and some have been documented to play key roles sensing diverse extracellular signals, such as pheromones, sugars, amino acids, nitrogen sources, and even photons. Identification and deorphanization of additional putative GPCRs may require the development of new research tools. Here, we compare research on GPCRs in fungi with information derived from mammalian systems to provide a useful road map on how to better understand ligand-GPCR-G protein interactions in general. We also emphasize the utility of yeast as a discovery tool for systemic studies of GPCRs from other organisms.
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Affiliation(s)
- Chaoyang Xue
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, USA
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16
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Abstract
In the presence of glucose, yeast undergoes an important remodelling of its metabolism. There are changes in the concentration of intracellular metabolites and in the stability of proteins and mRNAs; modifications occur in the activity of enzymes as well as in the rate of transcription of a large number of genes, some of the genes being induced while others are repressed. Diverse combinations of input signals are required for glucose regulation of gene expression and of other cellular processes. This review focuses on the early elements in glucose signalling and discusses their relevance for the regulation of specific processes. Glucose sensing involves the plasma membrane proteins Snf3, Rgt2 and Gpr1 and the glucose-phosphorylating enzyme Hxk2, as well as other regulatory elements whose functions are still incompletely understood. The similarities and differences in the way in which yeasts and mammalian cells respond to glucose are also examined. It is shown that in Saccharomyces cerevisiae, sensing systems for other nutrients share some of the characteristics of the glucose-sensing pathways.
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Affiliation(s)
- Juana M Gancedo
- Department of Metabolism and Cell Signalling, Instituto de Investigaciones Biomédicas Alberto Sols, CSIC-UAM, Madrid, Spain.
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17
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Thevelein JM, Bonini BM, Castermans D, Haesendonckx S, Kriel J, Louwet W, Thayumanavan P, Popova Y, Rubio-Texeira M, Schepers W, Vandormael P, Van Zeebroeck G, Verhaert P, Versele M, Voordeckers K. Novel mechanisms in nutrient activation of the yeast protein kinase A pathway. Acta Microbiol Immunol Hung 2008; 55:75-89. [PMID: 18595314 DOI: 10.1556/amicr.55.2008.2.1] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In yeast the Protein Kinase A (PKA) pathway can be activated by a variety of nutrients. Fermentable sugars, like glucose and sucrose, trigger a spike in the cAMP level, followed by activation of PKA and phosphorylation of target proteins causing a.o. mobilization of reserve carbohydrates, repression of stress-related genes and induction of growth-related genes. Glucose and sucrose are sensed by a G-protein coupled receptor system that activates adenylate cyclase and also activates a bypass pathway causing direct activation of PKA. Addition of other essential nutrients, like nitrogen sources or phosphate, to glucose-repressed nitrogen- or phosphate-starved cells, also triggers rapid activation of the PKA pathway. In these cases cAMP is not involved as a second messenger. Amino acids are sensed by the Gap1 transceptor, previously considered only as an amino acid transporter. Recent results indicate that the amino acid ligand has to induce a specific conformational change for signaling. The same amino acid binding site is involved in transport and signaling. Similar results have been obtained for Pho84 which acts as a transceptor for phosphate activation of the PKA pathway. Ammonium activation of the PKA pathway in nitrogen-starved cells is mediated mainly by the Mep2 transceptor, which belongs to a different class of transporter proteins. Hence, different types of sensing systems are involved in control of the yeast PKA pathway by nutrients.
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Affiliation(s)
- Johan M Thevelein
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Belgium.
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18
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Saccharomyces cerevisiae phospholipase C regulates transcription of Msn2p-dependent stress-responsive genes. EUKARYOTIC CELL 2008; 7:967-79. [PMID: 18375619 DOI: 10.1128/ec.00438-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Phosphatidylinositol phosphates are involved in signal transduction, cytoskeletal organization, and membrane trafficking. Inositol polyphosphates, produced from phosphatidylinositol phosphates by the phospholipase C-dependent pathway, regulate chromatin remodeling. We used genome-wide expression analysis to further investigate the roles of Plc1p (phosphoinositide-specific phospholipase C in Saccharomyces cerevisiae) and inositol polyphosphates in transcriptional regulation. Plc1p contributes to the regulation of approximately 2% of yeast genes in cells grown in rich medium. Most of these genes are induced by nutrient limitation and other environmental stresses and are derepressed in plc1 Delta cells. Surprisingly, genes regulated by Plc1p do not correlate with gene sets regulated by Swi/Snf or RSC chromatin remodeling complexes but show correlation with genes controlled by Msn2p. Our results suggest that the increased expression of stress-responsive genes in plc1 Delta cells is mediated by decreased cyclic AMP synthesis and protein kinase A (PKA)-mediated phosphorylation of Msn2p and increased binding of Msn2p to stress-responsive promoters. Accordingly, plc1 Delta cells display other phenotypes characteristic of cells with decreased PKA activity. Our results are consistent with a model in which Plc1p acts together with the membrane receptor Gpr1p and associated G(alpha) protein Gpa2p in a pathway separate from Ras1p/Ras2p and converging on PKA.
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Vinod PK, Sengupta N, Bhat PJ, Venkatesh KV. Integration of global signaling pathways, cAMP-PKA, MAPK and TOR in the regulation of FLO11. PLoS One 2008; 3:e1663. [PMID: 18301741 PMCID: PMC2246015 DOI: 10.1371/journal.pone.0001663] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Accepted: 01/22/2008] [Indexed: 11/19/2022] Open
Abstract
The budding yeast, Saccharomyces cerevisiae, responds to various environmental cues by invoking specific adaptive mechanisms for their survival. Under nitrogen limitation, S. cerevisiae undergoes a dimorphic filamentous transition called pseudohyphae, which helps the cell to forage for nutrients and reach an environment conducive for growth. This transition is governed by a complex network of signaling pathways, namely cAMP-PKA, MAPK and TOR, which controls the transcriptional activation of FLO11, a flocculin gene that encodes a cell wall protein. However, little is known about how these pathways co-ordinate to govern the conversion of nutritional availability into gene expression. Here, we have analyzed an integrative network comprised of cAMP-PKA, MAPK and TOR pathways with respect to the availability of nitrogen source using experimental and steady state modeling approach. Our experiments demonstrate that the steady state expression of FLO11 was bistable over a range of inducing ammonium sulphate concentration based on the preculturing condition. We also show that yeast switched from FLO11 expression to accumulation of trehalose, a STRE response controlled by a transcriptional activator Msn2/4, with decrease in the inducing concentration to complete starvation. Steady state analysis of the integrative network revealed the relationship between the environment, signaling cascades and the expression of FLO11. We demonstrate that the double negative feedback loop in TOR pathway can elicit a bistable response, to differentiate between vegetative growth, filamentous growth and STRE response. Negative feedback on TOR pathway function to restrict the expression of FLO11 under nitrogen starved condition and also with re-addition of nitrogen to starved cells. In general, we show that these global signaling pathways respond with specific sensitivity to regulate the expression of FLO11 under nitrogen limitation. The holistic steady state modeling approach of the integrative network revealed how the global signaling pathways could differentiate between multiple phenotypes.
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Affiliation(s)
- P. K. Vinod
- School of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, India
| | - Neelanjan Sengupta
- Department of Chemical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai, India
| | - P. J. Bhat
- School of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, India
| | - K. V. Venkatesh
- School of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, India
- Department of Chemical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai, India
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20
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Shpakov AO, Pertseva MN. Chapter 4 Signaling Systems of Lower Eukaryotes and Their Evolution. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 269:151-282. [DOI: 10.1016/s1937-6448(08)01004-6] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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21
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Tamaki H. Glucose-stimulated cAMP-protein kinase A pathway in yeast Saccharomyces cerevisiae. J Biosci Bioeng 2007; 104:245-50. [PMID: 18023794 DOI: 10.1263/jbb.104.245] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Accepted: 07/09/2007] [Indexed: 11/17/2022]
Abstract
In the yeast Saccharomyces cerevisiae, glucose signals activate the production of cellular cAMP. This signaling pathway is called the cAMP-protein kinase A (PKA) pathway, which plays a major role in the regulation of cell growth, metabolism, and stress resistance. Extensive studies have been carried out to clarify the mechanism of this pathway, and many factors involved in the pathway have been identified such as small G proteins, the GDP-GTP exchange factor, adenylate cyclase, and PKA. Also, additional elements involved in this pathway have been evaluated in the last decade. A heterotrimeric G protein alpha subunit was identified as a mammalian Galpha homologue, and a G-protein-coupled receptor (GPCR), which initiates the signaling pathway in response to glucose addition, was identified. GPCR-Galpha was shown to function in a signaling pathway that acts parallel to small G proteins. These signaling pathways regulate cell growth and differentiation in response to nutrients.
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Affiliation(s)
- Hisanori Tamaki
- Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
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22
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Chen D, Janganan TK, Chen G, Marques ER, Kress MR, Goldman GH, Walmsley AR, Borges-Walmsley MI. The cAMP pathway is important for controlling the morphological switch to the pathogenic yeast form of Paracoccidioides brasiliensis. Mol Microbiol 2007; 65:761-79. [PMID: 17635191 PMCID: PMC2064555 DOI: 10.1111/j.1365-2958.2007.05824.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Paracoccidioides brasiliensis is a human pathogenic fungus that switches from a saprobic mycelium to a pathogenic yeast. Consistent with the morphological transition being regulated by the cAMP-signalling pathway, there is an increase in cellular cAMP levels both transiently at the onset (< 24 h) and progressively in the later stages (> 120 h) of the transition to the yeast form, and this transition can be modulated by exogenous cAMP. We have cloned the cyr1 gene encoding adenylate cyclase (AC) and established that its transcript levels correlate with cAMP levels. In addition, we have cloned the genes encoding three Gα (Gpa1–3), Gβ (Gpb1) and Gγ (Gpg1) G proteins. Gpa1 and Gpb1 interact with one another and the N-terminus of AC, but neither Gpa2 nor Gpa3 interacted with Gpb1 or AC. The interaction of Gpa1 with Gpb1 was blocked by GTP, but its interaction with AC was independent of bound nucleotide. The transcript levels for gpa1, gpb1 and gpg1 were similar in mycelium, but there was a transient excess of gpb1 during the transition, and an excess of gpa1 in yeast. We have interpreted our findings in terms of a novel signalling mechanism in which the activity of AC is differentially modulated by Gpa1 and Gpb1 to maintain the signal over the 10 days needed for the morphological switch.
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Affiliation(s)
- Daliang Chen
- Centre for Infectious Diseases, Wolfson Research Institute, School of Biological and Biomedical Sciences, University of Durham – Queen's CampusStockton-on-Tees TS17 6BH, UK.
| | - Thamarai K Janganan
- Centre for Infectious Diseases, Wolfson Research Institute, School of Biological and Biomedical Sciences, University of Durham – Queen's CampusStockton-on-Tees TS17 6BH, UK.
| | - Gongyou Chen
- Centre for Infectious Diseases, Wolfson Research Institute, School of Biological and Biomedical Sciences, University of Durham – Queen's CampusStockton-on-Tees TS17 6BH, UK.
| | - Everaldo R Marques
- Departamento de Ciencias Farmaceuticas, Faculdade de Ciencias Farmaceuticas de Ribeirao Preto, Universidade de Sao Paulo, Av. do Cafe S/NCEP 14040-903, Ribeirao Preto, Sao Paulo, Brazil.
| | - Marcia R Kress
- Departamento de Ciencias Farmaceuticas, Faculdade de Ciencias Farmaceuticas de Ribeirao Preto, Universidade de Sao Paulo, Av. do Cafe S/NCEP 14040-903, Ribeirao Preto, Sao Paulo, Brazil.
| | - Gustavo H Goldman
- Departamento de Ciencias Farmaceuticas, Faculdade de Ciencias Farmaceuticas de Ribeirao Preto, Universidade de Sao Paulo, Av. do Cafe S/NCEP 14040-903, Ribeirao Preto, Sao Paulo, Brazil.
| | - Adrian R Walmsley
- Centre for Infectious Diseases, Wolfson Research Institute, School of Biological and Biomedical Sciences, University of Durham – Queen's CampusStockton-on-Tees TS17 6BH, UK.
- For correspondence. E-mail , ; Tel. (+44) (0)191 334 0465 or 0467; Fax (+44) (0)191 334 0468
| | - M Inês Borges-Walmsley
- Centre for Infectious Diseases, Wolfson Research Institute, School of Biological and Biomedical Sciences, University of Durham – Queen's CampusStockton-on-Tees TS17 6BH, UK.
- For correspondence. E-mail , ; Tel. (+44) (0)191 334 0465 or 0467; Fax (+44) (0)191 334 0468
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Dranginis AM, Rauceo JM, Coronado JE, Lipke PN. A biochemical guide to yeast adhesins: glycoproteins for social and antisocial occasions. Microbiol Mol Biol Rev 2007; 71:282-94. [PMID: 17554046 PMCID: PMC1899881 DOI: 10.1128/mmbr.00037-06] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fungi are nonmotile eukaryotes that rely on their adhesins for selective interaction with the environment and with other fungal cells. Glycosylphosphatidylinositol (GPI)-cross-linked adhesins have essential roles in mating, colony morphology, host-pathogen interactions, and biofilm formation. We review the structure and binding properties of cell wall-bound adhesins of ascomycetous yeasts and relate them to their effects on cellular interactions, with particular emphasis on the agglutinins and flocculins of Saccharomyces and the Als proteins of Candida. These glycoproteins share common structural motifs tailored to surface activity and biological function. After being secreted to the outer face of the plasma membrane, they are covalently anchored in the wall through modified GPI anchors, with their binding domains elevated beyond the wall surface on highly glycosylated extended stalks. N-terminal globular domains bind peptide or sugar ligands, with between millimolar and nanomolar affinities. These affinities and the high density of adhesins and ligands at the cell surface determine microscopic and macroscopic characteristics of cell-cell associations. Central domains often include Thr-rich tandemly repeated sequences that are highly glycosylated. These domains potentiate cell-to-cell binding, but the molecular mechanism of such an association is not yet clear. These repeats also mediate recombination between repeats and between genes. The high levels of recombination and epigenetic regulation are sources of variation which enable the population to continually exploit new niches and resources.
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Affiliation(s)
- Anne M Dranginis
- Department of Biological Science, St John's University, Queens, New York, USA
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24
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Biswas S, Van Dijck P, Datta A. Environmental sensing and signal transduction pathways regulating morphopathogenic determinants of Candida albicans. Microbiol Mol Biol Rev 2007; 71:348-76. [PMID: 17554048 PMCID: PMC1899878 DOI: 10.1128/mmbr.00009-06] [Citation(s) in RCA: 392] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Candida albicans is an opportunistic fungal pathogen that is found in the normal gastrointestinal flora of most healthy humans. However, under certain environmental conditions, it can become a life-threatening pathogen. The shift from commensal organism to pathogen is often correlated with the capacity to undergo morphogenesis. Indeed, under certain conditions, including growth at ambient temperature, the presence of serum or N-acetylglucosamine, neutral pH, and nutrient starvation, C. albicans can undergo reversible transitions from the yeast form to the mycelial form. This morphological plasticity reflects the interplay of various signal transduction pathways, either stimulating or repressing hyphal formation. In this review, we provide an overview of the different sensing and signaling pathways involved in the morphogenesis and pathogenesis of C. albicans. Where appropriate, we compare the analogous pathways/genes in Saccharomyces cerevisiae in an attempt to highlight the evolution of the different components of the two organisms. The downstream components of these pathways, some of which may be interesting antifungal targets, are also discussed.
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Affiliation(s)
- Subhrajit Biswas
- National Centre for Plant Genome Research, New Delhi 110 067, India
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25
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Zeller CE, Parnell SC, Dohlman HG. The RACK1 ortholog Asc1 functions as a G-protein beta subunit coupled to glucose responsiveness in yeast. J Biol Chem 2007; 282:25168-76. [PMID: 17591772 DOI: 10.1074/jbc.m702569200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
According to the prevailing paradigm, G-proteins are composed of three subunits, an alpha subunit with GTPase activity and a tightly associated betagamma subunit complex. In the yeast Saccharomyces cerevisiae there are two known Galpha proteins (Gpa1 and Gpa2) but only one Gbetagamma, which binds only to Gpa1. Here we show that the yeast ortholog of RACK1 (receptor for activated protein kinase C1) Asc1 functions as the Gbeta for Gpa2. As with other known Gbeta proteins, Asc1 has a 7-WD domain structure, interacts directly with the Galpha in a guanine nucleotide-dependent manner, and inhibits Galpha guanine nucleotide exchange activity. In addition, Asc1 binds to the effector enzyme adenylyl cyclase (Cyr1), and diminishes the production of cAMP in response to glucose stimulation. Thus, whereas Gpa2 promotes glucose signaling through elevated production of cAMP, Asc1 has opposing effects on these same processes. Our findings reveal the existence of an unusual Gbeta subunit, one having multiple functions within the cell in addition to serving as a signal transducer for cell surface receptors and intracellular effectors.
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Affiliation(s)
- Corinne E Zeller
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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26
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Niranjan T, Guo X, Victor J, Lu A, Hirsch JP. Kelch repeat protein interacts with the yeast Galpha subunit Gpa2p at a site that couples receptor binding to guanine nucleotide exchange. J Biol Chem 2007; 282:24231-8. [PMID: 17584745 DOI: 10.1074/jbc.m702595200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The kelch repeat-containing proteins Krh1p and Krh2p are negative regulators of the Gpa2p signaling pathway that directly interact with the G protein alpha-subunit Gpa2p in the yeast Saccharomyces cerevisiae. A screen was carried out to identify Gpa2p variants that are defective in their ability to bind Krh1p but retain the ability to bind another Gpa2p-interacting protein, Ime2p. This screen identified amino acids Gln-419 and Asn-425 as being important for the interaction between Gpa2p and Krh1p. Gpa2p variants with changes at these positions are defective for Krh1p binding in vivo. Cells containing these forms of Gpa2p display decreased heat shock resistance and increased expression of a gene required for pseudohyphal growth. These findings indicate that the substitutions at positions 419 and 425 confer a degree of constitutive activity to the Gpa2p alpha-subunit. Residues Gln-419 and Asn-425 are located in the beta6-alpha5 loop and alpha5 helix of Gpa2p, which is the region that couples receptor binding to guanine nucleotide exchange. The results suggest that binding of Gpa2p to Krh1p does not resemble the binding of Galpha subunits to either Gbeta subunits or effectors, but it instead represents a novel type of functional interaction.
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Affiliation(s)
- Thiruvur Niranjan
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York 10029, USA
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27
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Li L, Borkovich KA. GPR-4 is a predicted G-protein-coupled receptor required for carbon source-dependent asexual growth and development in Neurospora crassa. EUKARYOTIC CELL 2007; 5:1287-300. [PMID: 16896213 PMCID: PMC1539153 DOI: 10.1128/ec.00109-06] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The filamentous fungus Neurospora crassa is able to utilize a wide variety of carbon sources. Here, we examine the involvement of a predicted G-protein-coupled receptor (GPCR), GPR-4, during growth and development in the presence of different carbon sources in N. crassa. Deltagpr-4 mutants have reduced mass accumulation compared to the wild type when cultured on high levels of glycerol, mannitol, or arabinose. The defect is most severe on glycerol and is cell density dependent. The genetic and physical relationship between GPR-4 and the three N. crassa Galpha subunits (GNA-1, GNA-2, and GNA-3) was explored. All three Galpha mutants are defective in mass accumulation when cultured on glycerol. However, the phenotypes of Deltagna-1 and Deltagpr-4 Deltagna-1 mutants are identical, introduction of a constitutively activated gna-1 allele suppresses the defects of the Deltagpr-4 mutation, and the carboxy terminus of GPR-4 interacts most strongly with GNA-1 in the yeast two-hybrid assay. Although steady-state cyclic AMP (cAMP) levels are normal in Deltagpr-4 strains, exogenous cAMP partially remediates the dry mass defects of Deltagpr-4 mutants on glycerol medium and Deltagpr-4 strains lack the transient increase in cAMP levels observed in the wild type after addition of glucose to glycerol-grown liquid cultures. Our results support the hypothesis that GPR-4 is coupled to GNA-1 in a cAMP signaling pathway that regulates the response to carbon source in N. crassa. GPR-4-related GPCRs are present in the genomes of several filamentous ascomycete fungal pathogens, raising the possibility that a similar pathway regulates carbon sensing in these organisms.
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Affiliation(s)
- Liande Li
- Department of Plant Pathology, 1415 Boyce Hall, 900 University Avenue, University of California, Riverside, Riverside, CA 92521, USA.
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28
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Shpakov AO. Serpentine type receptors and heterotrimeric G-proteins in yeasts: Structural-functional organization and molecular mechanisms of action. J EVOL BIOCHEM PHYS+ 2007. [DOI: 10.1134/s0022093007010012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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29
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Hoffman CS. Propping up our knowledge of G protein signaling pathways: diverse functions of putative noncanonical Gbeta subunits in fungi. ACTA ACUST UNITED AC 2007; 2007:pe3. [PMID: 17244888 PMCID: PMC4417480 DOI: 10.1126/stke.3702007pe3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Heterotrimeric guanine nucleotide-binding proteins, composed of Galpha, Gbeta, and Ggamma subunits, are important mediators of fungal pheromone and nutrient signaling pathways. Most fungal genomes encode two or three functionally distinct Galpha subunits but only a single canonical Gbeta subunit, which does not bind multiple Galpha subunits. Studies in Saccharomyces cerevisiae, Cryptococcus neoformans, and Schizosaccharomyces pombe have identified binding partners for Galpha subunits, which are proposed to be "noncanonical Gbeta subunits." This Perspective reviews these studies, summarizing the strengths and weaknesses of the claims to this designation for these four fungal proteins.
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Palmer DA, Thompson JK, Li L, Prat A, Wang P. Gib2, a novel Gbeta-like/RACK1 homolog, functions as a Gbeta subunit in cAMP signaling and is essential in Cryptococcus neoformans. J Biol Chem 2006; 281:32596-605. [PMID: 16950773 DOI: 10.1074/jbc.m602768200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Canonical G proteins are heterotrimeric, consisting of alpha, beta, and gamma subunits. Despite multiple Galpha subunits functioning in fungi, only a single Gbeta subunit per species has been identified, suggesting that non-conventional G protein signaling exists in this diverse group of eukaryotic organisms. Using the Galpha subunit Gpa1 that functions in cAMP signaling as bait in a two-hybrid screen, we have identified a novel Gbeta-like/RACK1 protein homolog, Gib2, from the human pathogenic fungus Cryptococcus neoformans. Gib2 contains a seven WD-40 repeat motif and is predicted to form a seven-bladed beta propeller structure characteristic of beta transducins. Gib2 is also shown to interact, respectively, with two Ggamma subunit homologs, Gpg1 and Gpg2, similar to the conventional Gbeta subunit Gpb1. In contrast to Gpb1 whose overexpression promotes mating response, overproduction of Gib2 suppresses defects of gpa1 mutation in both melanization and capsule formation, the phenotypes regulated by cAMP signaling and associated with virulence. Furthermore, depletion of Gib2 by antisense suppression results in a severe growth defect, suggesting that Gib2 is essential. Finally, Gib2 is shown to also physically interact with a downstream target of Gpa1-cAMP signaling, Smg1, and the protein kinase C homolog Pkc1, indicating that Gib2 is also a multifunctional RACK1-like protein.
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Affiliation(s)
- Daniel A Palmer
- Research Institute for Children, Department of Pediatrics, Louisiana State University Health Sciences Center, 200 Henry Clay Avenue, New Orleans, LA 70118, USA
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31
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Harashima T, Anderson S, Yates JR, Heitman J. The kelch proteins Gpb1 and Gpb2 inhibit Ras activity via association with the yeast RasGAP neurofibromin homologs Ira1 and Ira2. Mol Cell 2006; 22:819-830. [PMID: 16793550 DOI: 10.1016/j.molcel.2006.05.011] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2005] [Revised: 03/14/2006] [Accepted: 05/08/2006] [Indexed: 11/26/2022]
Abstract
The G protein-coupled receptor Gpr1 and associated Galpha subunit Gpa2 govern dimorphic transitions in response to extracellular nutrients by signaling coordinately with Ras to activate adenylyl cyclase in the yeast Saccharomyces cerevisiae. Gpa2 forms a protein complex with the kelch Gbeta mimic subunits Gpb1/2, and previous studies demonstrate that Gpb1/2 negatively control cAMP-PKA signaling via Gpa2 and an unknown second target. Here, we define these targets of Gpb1/2 as the yeast neurofibromin homologs Ira1 and Ira2, which function as GTPase activating proteins of Ras. Gpb1/2 bind to a conserved C-terminal domain of Ira1/2, and loss of Gpb1/2 results in a destabilization of Ira1 and Ira2, leading to elevated levels of Ras2-GTP and unbridled cAMP-PKA signaling. Because the Gpb1/2 binding domain on Ira1/2 is conserved in the human neurofibromin protein, an analogous signaling network may contribute to the neoplastic development of neurofibromatosis type 1.
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Affiliation(s)
- Toshiaki Harashima
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710
| | - Scott Anderson
- The Scripps Research Institute, La Jolla, California 92037
| | - John R Yates
- The Scripps Research Institute, La Jolla, California 92037
| | - Joseph Heitman
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710.
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Peeters T, Louwet W, Geladé R, Nauwelaers D, Thevelein JM, Versele M. Kelch-repeat proteins interacting with the Galpha protein Gpa2 bypass adenylate cyclase for direct regulation of protein kinase A in yeast. Proc Natl Acad Sci U S A 2006; 103:13034-9. [PMID: 16924114 PMCID: PMC1559748 DOI: 10.1073/pnas.0509644103] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The cAMP-PKA pathway consists of an extracellular ligand-sensitive G protein-coupled receptor, a G protein signal transmitter, and the effector, adenylate cyclase, of which the product, cAMP, acts as an intracellular second messenger. cAMP activates PKA by dissociating the regulatory subunit from the catalytic subunit. Yeast cells (Saccharomyces cerevisiae) contain a glucose/sucrose-sensitive seven-transmembrane domain receptor, Gpr1, that was proposed to activate adenylate cyclase through the G(alpha) protein Gpa2. Consistently, we show here that adenylate cyclase binds only to active, GTP-bound Gpa2. Two related kelch-repeat proteins, Krh1/Gpb2 and Krh2/Gpb1, are associated with Gpa2 and were suggested to act as G(beta) mimics for Gpa2, based on their predicted seven-bladed beta-propeller structure. However, we find that although Krh1 associates with both GDP and GTP-bound Gpa2, it displays a preference for GTP-Gpa2. The strong down-regulation of PKA targets by Krh1 and Krh2 does not require Gpa2 but is strictly dependent on both the catalytic and the regulatory subunits of PKA. Krh1 directly interacts with PKA by means of the catalytic subunits, and Krh1/2 stimulate the association between the catalytic and regulatory subunits in vivo. Indeed, both a constitutively active GPA2 allele and deletion of KRH1/2 lower the cAMP requirement of PKA for growth. We propose that active Gpa2 relieves the inhibition imposed by the kelch-repeat proteins on PKA, thereby bypassing adenylate cyclase for direct regulation of PKA. Importantly, we show that Krh1/2 also enhance the association between mouse R and C subunits, suggesting that Krh control of PKA has been evolutionarily conserved.
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Affiliation(s)
- Tom Peeters
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
| | - Wendy Louwet
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
| | - Ruud Geladé
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
| | - David Nauwelaers
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
| | - Johan M. Thevelein
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
| | - Matthias Versele
- Laboratory of Molecular Cell Biology, Katholieke Universiteit Leuven, and Department of Molecular Microbiology, Flanders Interuniversity Institute of Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Belgium
- *To whom correspondence should be addressed. E-mail:
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33
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Chasse SA, Flanary P, Parnell SC, Hao N, Cha JY, Siderovski DP, Dohlman HG. Genome-scale analysis reveals Sst2 as the principal regulator of mating pheromone signaling in the yeast Saccharomyces cerevisiae. EUKARYOTIC CELL 2006; 5:330-46. [PMID: 16467474 PMCID: PMC1405904 DOI: 10.1128/ec.5.2.330-346.2006] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A common property of G protein-coupled receptors is that they become less responsive with prolonged stimulation. Regulators of G protein signaling (RGS proteins) are well known to accelerate G protein GTPase activity and do so by stabilizing the transition state conformation of the G protein alpha subunit. In the yeast Saccharomyces cerevisiae there are four RGS-homologous proteins (Sst2, Rgs2, Rax1, and Mdm1) and two Galpha proteins (Gpa1 and Gpa2). We show that Sst2 is the only RGS protein that binds selectively to the transition state conformation of Gpa1. The other RGS proteins also bind Gpa1 and modulate pheromone signaling, but to a lesser extent and in a manner clearly distinct from Sst2. To identify other candidate pathway regulators, we compared pheromone responses in 4,349 gene deletion mutants representing nearly all nonessential genes in yeast. A number of mutants produced an increase (sst2, bar1, asc1, and ygl024w) or decrease (cla4) in pheromone sensitivity or resulted in pheromone-independent signaling (sst2, pbs2, gas1, and ygl024w). These findings suggest that Sst2 is the principal regulator of Gpa1-mediated signaling in vivo but that other proteins also contribute in distinct ways to pathway regulation.
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Affiliation(s)
- Scott A Chasse
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599-7260, USA
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Van Nuland A, Vandormael P, Donaton M, Alenquer M, Lourenço A, Quintino E, Versele M, Thevelein JM. Ammonium permease-based sensing mechanism for rapid ammonium activation of the protein kinase A pathway in yeast. Mol Microbiol 2006; 59:1485-505. [PMID: 16468990 DOI: 10.1111/j.1365-2958.2005.05043.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the yeast Saccharomyces cerevisiae starvation for nitrogen on a glucose-containing medium causes entrance into G0 and downregulation of all targets of the PKA pathway. Re-addition of a nitrogen source in the presence of glucose causes rapid activation of trehalase and other PKA targets. Trehalase activation upon ammonium re-supplementation is dependent on PKA activity, but not on its regulatory subunit nor is it associated with an increase in cAMP. In nitrogen-starved cells, ammonium transport and activation of trehalase are most active in strains expressing either the Mep2 or Mep1 ammonium permease, as opposed to Mep3. The non-metabolizable ammonium analogue, methylamine, also triggers activation of trehalase when transported by Mep2 but not when taken up by diffusion. Inhibition of ammonium incorporation into metabolism did not prevent signalling. Extensive site-directed mutagenesis of Mep2 showed that transport and signalling were generally affected in a similar way, although they could be separated partially by specific mutations. Our results suggest an ammonium permease-based sensing mechanism for rapid activation of the PKA pathway. Mutagenesis of Asn246 to Ala in Mep2 abolished transport and signalling with methylamine but had no effect with ammonium. The plant AtAmt1;1, AtAmt1;2, AtAmt1;3 and AtAmt2 ammonium transporters sustained transport and trehalase activation to different extents. Specific mutations in Mep2 affected the activation of trehalase differently from induction of pseudohyphal differentiation. We also show that Mep permease involvement in PKA control is different from their role in haploid invasive growth, in which Mep1 sustains and Mep2 inhibits, in a way independent of the ammonium level in the medium.
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Affiliation(s)
- An Van Nuland
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium
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Lu A, Hirsch JP. Cyclic AMP-independent regulation of protein kinase A substrate phosphorylation by Kelch repeat proteins. EUKARYOTIC CELL 2006; 4:1794-800. [PMID: 16278446 PMCID: PMC1287861 DOI: 10.1128/ec.4.11.1794-1800.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pseudohyphal and invasive growth in the yeast Saccharomyces cerevisiae is regulated by the kelch repeat-containing proteins Gpb1p and Gpb2p, which act downstream of the G protein alpha-subunit Gpa2p. Here we show that deletion of GPB1 and GPB2 causes increased haploid invasive growth in cells containing any one of the three protein kinase A (PKA) catalytic subunits, suggesting that Gpb1p and Gpb2p are able to inhibit each of these kinases. Cells containing gpb1Delta gpb2Delta mutations also display increased phosphorylation of the PKA substrates Sfl1p and Msn2p, indicating that Gpb1p and Gpb2p are negative regulators of PKA substrate phosphorylation. Stimulation of PKA-dependent signaling by gpb1Delta gpb2Delta mutations occurs in cells that lack both adenylyl cyclase and the high-affinity cyclic AMP (cAMP) phosphodiesterase. This effect is also seen in cells that lack the low-affinity cAMP phosphodiesterase. Given that these three enzymes control the synthesis and degradation of cAMP, these results indicate that the effect of Gpb1p and Gpb2p on PKA substrate phosphorylation does not occur by regulating the intracellular cAMP concentration. These findings suggest that Gpb1p and Gpb2p mediate their effects on the cAMP/PKA signaling pathway either by inhibiting the activity of PKA in a cAMP-independent manner or by activating phosphatases that act on PKA substrates.
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Affiliation(s)
- Ailan Lu
- Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, Box 1603, 1 Gustave L. Levy Place, New York, NY 10029, USA
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Overton MC, Chinault SL, Blumer KJ. Oligomerization of G-protein-coupled receptors: lessons from the yeast Saccharomyces cerevisiae. EUKARYOTIC CELL 2006; 4:1963-70. [PMID: 16339714 PMCID: PMC1317502 DOI: 10.1128/ec.4.12.1963-1970.2005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Mark C Overton
- Department of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110-1010, USA
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Kao RS, Morreale E, Wang L, Ivey FD, Hoffman CS. Schizosaccharomyces pombe Git1 is a C2-domain protein required for glucose activation of adenylate cyclase. Genetics 2006; 173:49-61. [PMID: 16489217 PMCID: PMC1461440 DOI: 10.1534/genetics.106.055699] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Schizosaccharomyces pombe senses environmental glucose through a cAMP-signaling pathway, activating cAMP-dependent protein kinase A (PKA). This requires nine git (glucose insensitive transcription) genes that encode adenylate cyclase, the PKA catalytic subunit, and seven "upstream" proteins required for glucose-triggered adenylate cyclase activation, including three heterotrimeric G-protein subunits and its associated receptor. We describe here the cloning and characterization of the git1+ gene. Git1 is distantly related to a small group of uncharacterized fungal proteins, including a second S. pombe protein that is not functionally redundant with Git1, as well as to members of the UNC-13/Munc13 protein family. Mutations in git1+ demonstrate functional roles for the two most highly conserved regions of the protein, the C2 domain and the MHD2 Munc homology domain. Cells lacking Git1 are viable, but display phenotypes associated with cAMP-signaling defects, even in strains expressing a mutationally activated G alpha-subunit, which activates adenylate cyclase. These cells possess reduced basal cAMP levels and fail to mount a cAMP response to glucose. In addition, Git1 and adenylate cyclase physically interact and partially colocalize in the cell. Thus, Git1 is a critical component of the S. pombe glucose/cAMP pathway.
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Affiliation(s)
- Richard S Kao
- Biology Department, Boston College, Chestnut Hill, Massachusetts 02467, USA
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Hoffman CS. Except in every detail: comparing and contrasting G-protein signaling in Saccharomyces cerevisiae and Schizosaccharomyces pombe. EUKARYOTIC CELL 2005; 4:495-503. [PMID: 15755912 PMCID: PMC1087802 DOI: 10.1128/ec.4.3.495-503.2005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Charles S Hoffman
- Biology Department, Boston College, 140 Commonwealth Ave., Higgins Hall 401B, Chestnut Hill, MA 02467, USA.
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Harashima T, Heitman J. Galpha subunit Gpa2 recruits kelch repeat subunits that inhibit receptor-G protein coupling during cAMP-induced dimorphic transitions in Saccharomyces cerevisiae. Mol Biol Cell 2005; 16:4557-71. [PMID: 16030250 PMCID: PMC1237064 DOI: 10.1091/mbc.e05-05-0403] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 06/23/2005] [Accepted: 07/12/2005] [Indexed: 11/11/2022] Open
Abstract
All eukaryotic cells sense extracellular stimuli and activate intracellular signaling cascades via G protein-coupled receptors (GPCR) and associated heterotrimeric G proteins. The Saccharomyces cerevisiae GPCR Gpr1 and associated Galpha subunit Gpa2 sense extracellular carbon sources (including glucose) to govern filamentous growth. In contrast to conventional Galpha subunits, Gpa2 forms an atypical G protein complex with the kelch repeat Gbeta mimic proteins Gpb1 and Gpb2. Gpb1/2 negatively regulate cAMP signaling by inhibiting Gpa2 and an as yet unidentified target. Here we show that Gpa2 requires lipid modifications of its N-terminus for membrane localization but association with the Gpr1 receptor or Gpb1/2 subunits is dispensable for membrane targeting. Instead, Gpa2 promotes membrane localization of its associated Gbeta mimic subunit Gpb2. We also show that the Gpa2 N-terminus binds both to Gpb2 and to the C-terminal tail of the Gpr1 receptor and that Gpb1/2 binding interferes with Gpr1 receptor coupling to Gpa2. Our studies invoke novel mechanisms involving GPCR-G protein modules that may be conserved in multicellular eukaryotes.
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Affiliation(s)
- Toshiaki Harashima
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
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Schneper L, Düvel K, Broach JR. Sense and sensibility: nutritional response and signal integration in yeast. Curr Opin Microbiol 2005; 7:624-30. [PMID: 15556035 DOI: 10.1016/j.mib.2004.10.002] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Yeast cells respond to the quantity and quality of carbon and nitrogen sources in the environment both by adjusting their transcriptional and metabolic profiles to make optimum use of the available nutrients and by selecting a developmental program--budding, pseudohyphal differentiation, quiescence or sporulation--that maximizes their potential for survival under the existing nutrient conditions. Recent studies fueled by genomic tools have refined our knowledge of the components and connections within individual pathways and the interconnections between pathways. More significantly, these studies begin to paint an as yet inchoate portrait of the yeast cells' means of processing its environmental information, in which specific transcription factors and chromatin modifying activities coordinate input from several signaling pathways to yield an appropriate and coherent response of genes involved in mass accumulation and metabolism.
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Affiliation(s)
- Lisa Schneper
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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Wu YL, Hooks SB, Harden TK, Dohlman HG. Dominant-negative inhibition of pheromone receptor signaling by a single point mutation in the G protein alpha subunit. J Biol Chem 2004; 279:35287-97. [PMID: 15197187 DOI: 10.1074/jbc.m404896200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In yeast, two different constitutive mutants of the G protein alpha subunit have been reported. Gpa1(Q323L) cannot hydrolyze GTP and permanently activates the pheromone response pathway. Gpa1(N388D) was also proposed to lack GTPase activity, yet it has an inhibitory effect on pheromone responsiveness. We have characterized this inhibitory mutant (designated Galpha(ND)) and found that it binds GTP, interacts with G protein betagamma subunits, and exhibits full GTPase activity in vitro. Although pheromone leads to dissociation of the receptor from wild-type G protein, the same treatment promotes stable association of the receptor with Galpha(ND). We conclude that agonist binding to the receptor promotes the formation of a nondissociable complex with Galpha(ND), and in this manner prevents activation of the endogenous wild-type G protein. Dominant-negative mutants may be useful in matching specific receptors and their cognate G proteins and in determining mechanisms of G protein signaling specificity.
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Affiliation(s)
- Yuh-Lin Wu
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill 27599-7260, USA
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Rützler M, Reissaus A, Budzowska M, Bandlow W. SUT2 is a novel multicopy suppressor of low activity of the cAMP/protein kinase A pathway in yeast. ACTA ACUST UNITED AC 2004; 271:1284-91. [PMID: 15030478 DOI: 10.1111/j.1432-1033.2004.04034.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
SUT2 was found in a screen for multicopy suppressors of the synthetic slow growth phenotype of a Deltaras2Deltagpa2 double deletion mutant. It failed, however, to cure the lethal phenotype of a Deltaras1Deltaras2 mutant suggesting that it acts upstream of Ras or in a parallel pathway. By testing cAMP-dependent reactions including the accumulation of storage carbohydrates, pseudohyphal differentiation, entry of meiosis as well as the measurement of FLO11 reporter activity we show that Sut2p modulates the activity of protein kinase A (PKA). Additionally, we demonstrate that cellular levels of Ras2p are affected by Sut2p and that Sut2-GFPp accumulates significantly in the nucleus. Based on the observed influence of high SUT2 gene dosage on PKA activity as well as Sut2p's homology to the presumptive transcription factor Sut1p, we suggest that Sut2p contributes to regulation of PKA activity at the level of transcription.
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Affiliation(s)
- Michael Rützler
- Ludwig-Maximilians-Universität München, Department Biologie I, Bereich Genetik, Munich, Germany.
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Prag S, Adams JC. Molecular phylogeny of the kelch-repeat superfamily reveals an expansion of BTB/kelch proteins in animals. BMC Bioinformatics 2003; 4:42. [PMID: 13678422 PMCID: PMC222960 DOI: 10.1186/1471-2105-4-42] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Accepted: 09/17/2003] [Indexed: 12/15/2022] Open
Abstract
Background The kelch motif is an ancient and evolutionarily-widespread sequence motif of 44–56 amino acids in length. It occurs as five to seven repeats that form a β-propeller tertiary structure. Over 28 kelch-repeat proteins have been sequenced and functionally characterised from diverse organisms spanning from viruses, plants and fungi to mammals and it is evident from expressed sequence tag, domain and genome databases that many additional hypothetical proteins contain kelch-repeats. In general, kelch-repeat β-propellers are involved in protein-protein interactions, however the modest sequence identity between kelch motifs, the diversity of domain architectures, and the partial information on this protein family in any single species, all present difficulties to developing a coherent view of the kelch-repeat domain and the kelch-repeat protein superfamily. To understand the complexity of this superfamily of proteins, we have analysed by bioinformatics the complement of kelch-repeat proteins encoded in the human genome and have made comparisons to the kelch-repeat proteins encoded in other sequenced genomes. Results We identified 71 kelch-repeat proteins encoded in the human genome, whereas 5 or 8 members were identified in yeasts and around 18 in C. elegans, D. melanogaster and A. gambiae. Multiple domain architectures were identified in each organism, including previously unrecognised forms. The vast majority of kelch-repeat domains are predicted to form six-bladed β-propellers. The most prevalent domain architecture in the metazoan animal genomes studied was the BTB/kelch domain organisation and we uncovered 3 subgroups of human BTB/kelch proteins. Sequence analysis of the kelch-repeat domains of the most robustly-related subgroups identified differences in β-propeller organisation that could provide direction for experimental study of protein-binding characteristics. Conclusion The kelch-repeat superfamily constitutes a distinct and evolutionarily-widespread family of β-propeller domain-containing proteins. Expansion of the family during the evolution of multicellular animals is mainly accounted for by a major expansion of the BTB/kelch domain architecture. BTB/kelch proteins constitute 72 % of the kelch-repeat superfamily of H. sapiens and form three subgroups, one of which appears the most-conserved during evolution. Distinctions in propeller blade organisation between subgroups 1 and 2 were identified that could provide new direction for biochemical and functional studies of novel kelch-repeat proteins.
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Affiliation(s)
- Soren Prag
- Dept. of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195, USA
| | - Josephine C Adams
- Dept. of Cell Biology, Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, Ohio 44195, USA
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Gettemans J, Meerschaert K, Vandekerckhove J, De Corte V. A kelch beta propeller featuring as a G beta structural mimic: reinventing the wheel? SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2003; 2003:PE27. [PMID: 12865498 DOI: 10.1126/stke.2003.191.pe27] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
New genetic and protein interaction data suggest that G protein alpha subunits may have partners with primary sequences that are quite divergent. How this is achieved may be through the adoption of similar structures, the beta propeller, by both proteins containing WD-40 repeats and kelch domains. Gettemans et al. describe results in yeast that suggest that kelch-domain proteins may serve as previously unrecognized beta subunits in the heterotrimeric G protein complex.
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Affiliation(s)
- Jan Gettemans
- Department of Biochemistry, Faculty of Medicine and Health Sciences, Flanders Interuniversity Institute for Biotechnology, Ghent University, Rommelaere Institute, Albert Baertsoenkaai 3, B-9000 Ghent, Belgium.
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Gettemans J, Meerschaert K, Vandekerckhove J, De Corte V. A Kelch Propeller Featuring as a G Structural Mimic: Reinventing the Wheel? Sci Signal 2003. [DOI: 10.1126/scisignal.1912003pe27] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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