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Rangarajan N, Gordy CL, Askew L, Bevill SM, Elston TC, Errede B, Hurst JH, Kelley JB, Sheetz JB, Suzuki SK, Valentin NH, Young E, Dohlman HG. Systematic analysis of F-box proteins reveals a new branch of the yeast mating pathway. J Biol Chem 2019; 294:14717-14731. [PMID: 31399514 DOI: 10.1074/jbc.ra119.010063] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 08/06/2019] [Indexed: 11/06/2022] Open
Abstract
The mating pathway in yeast Saccharomyces cerevisiae has long been used to reveal new mechanisms of signal transduction. The pathway comprises a pheromone receptor, a heterotrimeric G protein, and intracellular effectors of morphogenesis and transcription. Polarized cell growth, in the direction of a potential mating partner, is accomplished by the G-protein βγ subunits and the small G-protein Cdc42. Transcription induction, needed for cell-cell fusion, is mediated by Gβγ and the mitogen-activated protein kinase (MAPK) scaffold protein Ste5. A potential third pathway is initiated by the G-protein α subunit Gpa1. Gpa1 signaling was shown previously to involve the F-box adaptor protein Dia2 and an endosomal effector protein, the phosphatidylinositol 3-kinase Vps34. Vps34 is also required for proper vacuolar sorting and autophagy. Here, using a panel of reporter assays, we demonstrate that mating pheromone stimulates vacuolar targeting of a cytoplasmic reporter protein and that this process depends on Vps34. Through a systematic analysis of F-box deletion mutants, we show that Dia2 is required to sustain pheromone-induced vacuolar targeting. We also found that other F-box proteins selectively regulate morphogenesis (Ydr306, renamed Pfu1) and transcription (Ucc1). These findings point to the existence of a new and distinct branch of the pheromone-signaling pathway, one that likely leads to vacuolar engulfment of cytoplasmic proteins and recycling of cellular contents in preparation for mating.
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Affiliation(s)
- Nambirajan Rangarajan
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Claire L Gordy
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Lauren Askew
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Samantha M Bevill
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Timothy C Elston
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Beverly Errede
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Jillian H Hurst
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Joshua B Kelley
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Joshua B Sheetz
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Sara Kimiko Suzuki
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599.,Curriculum in Bioinformatics and Computational Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Natalie H Valentin
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Everett Young
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Henrik G Dohlman
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
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2
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Epigenetic control of pheromone MAPK signaling determines sexual fecundity in Candida albicans. Proc Natl Acad Sci U S A 2017; 114:13780-13785. [PMID: 29255038 DOI: 10.1073/pnas.1711141115] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Several pathogenic Candida species are capable of heritable and reversible switching between two epigenetic states, "white" and "opaque." In Candida albicans, white cells are essentially sterile, whereas opaque cells are mating-proficient. Here, we interrogate the mechanism by which the white-opaque switch regulates sexual fecundity and identify four genes in the pheromone MAPK pathway that are expressed at significantly higher levels in opaque cells than in white cells. These genes encode the β subunit of the G-protein complex (STE4), the pheromone MAPK scaffold (CST5), and the two terminal MAP kinases (CEK1/CEK2). To define the contribution of each factor to mating, C. albicans white cells were reverse-engineered to express elevated, opaque-like levels of these factors, either singly or in combination. We show that white cells co-overexpressing STE4, CST5, and CEK2 undergo mating four orders of magnitude more efficiently than control white cells and at a frequency approaching that of opaque cells. Moreover, engineered white cells recapitulate the transcriptional and morphological responses of opaque cells to pheromone. These results therefore reveal multiple bottlenecks in pheromone MAPK signaling in white cells and that alleviation of these bottlenecks enables efficient mating by these "sterile" cell types. Taken together, our findings establish that differential expression of several MAPK factors underlies the epigenetic control of mating in C. albicans We also discuss how fitness advantages could have driven the evolution of a toggle switch to regulate sexual reproduction in pathogenic Candida species.
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3
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Shellhammer JP, Morin-Kensicki E, Matson JP, Yin G, Isom DG, Campbell SL, Mohney RP, Dohlman HG. Amino acid metabolites that regulate G protein signaling during osmotic stress. PLoS Genet 2017; 13:e1006829. [PMID: 28558063 PMCID: PMC5469498 DOI: 10.1371/journal.pgen.1006829] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 06/13/2017] [Accepted: 05/17/2017] [Indexed: 12/29/2022] Open
Abstract
All cells respond to osmotic stress by implementing molecular signaling events to protect the organism. Failure to properly adapt can lead to pathologies such as hypertension and ischemia-reperfusion injury. Mitogen-activated protein kinases (MAPKs) are activated in response to osmotic stress, as well as by signals acting through G protein-coupled receptors (GPCRs). For proper adaptation, the action of these kinases must be coordinated. To identify second messengers of stress adaptation, we conducted a mass spectrometry-based global metabolomics profiling analysis, quantifying nearly 300 metabolites in the yeast S. cerevisiae. We show that three branched-chain amino acid (BCAA) metabolites increase in response to osmotic stress and require the MAPK Hog1. Ectopic addition of these BCAA derivatives promotes phosphorylation of the G protein α subunit and dampens G protein-dependent transcription, similar to that seen in response to osmotic stress. Conversely, genetic ablation of Hog1 activity or the BCAA-regulatory enzymes leads to diminished phosphorylation of Gα and increased transcription. Taken together, our results define a new class of candidate second messengers that mediate cross talk between osmotic stress and GPCR signaling pathways.
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Affiliation(s)
- James P. Shellhammer
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | | | - Jacob P. Matson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Guowei Yin
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Daniel G. Isom
- The University of Miami Miller School of Medicine, Miami, Florida, United States of America
| | - Sharon L. Campbell
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Robert P. Mohney
- Metabolon, Inc., Research Triangle Park, North Carolina, United States of America
| | - Henrik G. Dohlman
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail:
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4
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Dyjack N, Azeredo-Tseng C, Yildirim N. Mathematical modeling reveals differential regulation of MAPK activity by phosphatase proteins in the yeast pheromone response pathway. MOLECULAR BIOSYSTEMS 2017; 13:1323-1335. [DOI: 10.1039/c7mb00213k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To prevent indefinite cellular responses to external signals, cells utilize various adaptation mechanisms.
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Affiliation(s)
- Nathan Dyjack
- Division of Natural Sciences
- New College of Florida
- Sarasota
- USA
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5
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Bush A, Vasen G, Constantinou A, Dunayevich P, Patop IL, Blaustein M, Colman-Lerner A. Yeast GPCR signaling reflects the fraction of occupied receptors, not the number. Mol Syst Biol 2016; 12:898. [PMID: 28034910 PMCID: PMC5199120 DOI: 10.15252/msb.20166910] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
According to receptor theory, the effect of a ligand depends on the amount of agonist-receptor complex. Therefore, changes in receptor abundance should have quantitative effects. However, the response to pheromone in Saccharomyces cerevisiae is robust (unaltered) to increases or reductions in the abundance of the G-protein-coupled receptor (GPCR), Ste2, responding instead to the fraction of occupied receptor. We found experimentally that this robustness originates during G-protein activation. We developed a complete mathematical model of this step, which suggested the ability to compute fractional occupancy depends on the physical interaction between the inhibitory regulator of G-protein signaling (RGS), Sst2, and the receptor. Accordingly, replacing Sst2 by the heterologous hsRGS4, incapable of interacting with the receptor, abolished robustness. Conversely, forcing hsRGS4:Ste2 interaction restored robustness. Taken together with other results of our work, we conclude that this GPCR pathway computes fractional occupancy because ligand-bound GPCR-RGS complexes stimulate signaling while unoccupied complexes actively inhibit it. In eukaryotes, many RGSs bind to specific GPCRs, suggesting these complexes with opposing activities also detect fraction occupancy by a ratiometric measurement. Such complexes operate as push-pull devices, which we have recently described.
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Affiliation(s)
- Alan Bush
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Gustavo Vasen
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Andreas Constantinou
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Paula Dunayevich
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Inés Lucía Patop
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Matías Blaustein
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina.,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
| | - Alejandro Colman-Lerner
- Department of Physiology, Molecular and Cellular Biology, University of Buenos Aires, Buenos Aires, Argentina .,Institute of Physiology, Molecular Biology and Neurosciences, National Research Council (CONICET), Buenos Aires, Argentina
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6
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Jo MC, Qin L. Microfluidic Platforms for Yeast-Based Aging Studies. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2016; 12:5787-5801. [PMID: 27717149 PMCID: PMC5554731 DOI: 10.1002/smll.201602006] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 08/30/2016] [Indexed: 06/06/2023]
Abstract
The budding yeast Saccharomyces cerevisiae has been a powerful model for the study of aging and has enabled significant contributions to our understanding of basic mechanisms of aging in eukaryotic cells. However, the laborious low-throughput nature of conventional methods of performing aging assays limits the pace of discoveries in this field. Some of the technical challenges of conventional aging assay methods can be overcome by use of microfluidic systems coupled to time-lapse microscopy. One of the major advantages is the ability of a microfluidic system to perform long-term cell culture under well-defined environmental conditions while tracking individual yeast. Here, recent advancements in microfluidic platforms for various yeast-based studies including replicative lifespan assay, long-term culture and imaging, gene expression, and cell signaling are discussed. In addition, emerging problems and limitations of current microfluidic approaches are examined and perspectives on the future development of this dynamic field are presented.
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Affiliation(s)
- Myeong Chan Jo
- Department of Nanomedicine, Houston Methodist Research Institute, Houston, TX, 77030, USA
- Department of Cell and Developmental Biology, Weill Medical College of Cornell University, New York, NY, 10065, USA
| | - Lidong Qin
- Department of Nanomedicine, Houston Methodist Research Institute, Houston, TX, 77030, USA
- Department of Cell and Developmental Biology, Weill Medical College of Cornell University, New York, NY, 10065, USA
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7
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Shi HB, Chen GQ, Chen YP, Dong B, Lu JP, Liu XH, Lin FC. MoRad6-mediated ubiquitination pathways are essential for development and pathogenicity in Magnaporthe oryzae. Environ Microbiol 2016; 18:4170-4187. [PMID: 27581713 DOI: 10.1111/1462-2920.13515] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Accepted: 08/28/2016] [Indexed: 01/19/2023]
Abstract
The ubiquitin system modulates protein functions through targeting substrates for ubiquitination. Here, E2 conjugating enzyme MoRad6-related ubiquitination pathways are identified and analyzed in Magnaporthe oryzae, the causal agent of rice blast disease. Disruption of MoRad6 leads to severe defects in growth, sporulation, conidial germination, appressorium formation, and plant infection. To depict the functions of MoRad6, three putative ubiquitin ligases, MoRad18, MoBre1 and MoUbr1, are also characterized. Deletion of MoRad18 causes minor phenotypic changes, while MoBre1 is required for growth, conidiation and pathogenicity in M. oryzae. Defects in ΔMobre1 likely resulted from the reduction in di- and tri-methylation level of Histone 3 lysine 4 (H3K4). Notably, MoUbr1 is crucial for conidial adhesion and germination, possibly by degrading components of cAMP/PKA and mitogen-activated protein kinase (MAPK) Pmk1 signaling pathways via the N-end rule pathway. Germination failure of ΔMoubr1 conidia could be rescued by elevation of cAMP level or enhanced Pmk1 phosphorylation resulting from further deletion of MoIra1, the M. oryzae homolog of yeast Ira1/2. These reveal vital effects of cAMP/PKA and MAPK Pmk1 signaling on conidial germination in M. oryzae. Altogether, our results suggest that MoRad6-mediated ubiquitination pathways are essential for the infection-related development and pathogenicity of M. oryzae.
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Affiliation(s)
- Huan-Bin Shi
- State Key Laboratory for Rice Biology, Biotechnology Institute, Zhejiang University, Hangzhou, 310058, China
| | - Guo-Qing Chen
- State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006, China
| | - Ya-Ping Chen
- State Key Laboratory for Rice Biology, Biotechnology Institute, Zhejiang University, Hangzhou, 310058, China
| | - Bo Dong
- Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Science, Hangzhou, 310021, China
| | - Jian-Ping Lu
- College of Life Sciences, Zhejiang University, Hangzhou, 310058, China
| | - Xiao-Hong Liu
- State Key Laboratory for Rice Biology, Biotechnology Institute, Zhejiang University, Hangzhou, 310058, China
| | - Fu-Cheng Lin
- State Key Laboratory for Rice Biology, Biotechnology Institute, Zhejiang University, Hangzhou, 310058, China
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8
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Sridharan R, Connelly SM, Naider F, Dumont ME. Variable Dependence of Signaling Output on Agonist Occupancy of Ste2p, a G Protein-coupled Receptor in Yeast. J Biol Chem 2016; 291:24261-24279. [PMID: 27646004 DOI: 10.1074/jbc.m116.733006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 09/04/2016] [Indexed: 12/22/2022] Open
Abstract
We report here on the relationship between ligand binding and signaling responses in the yeast pheromone response pathway, a well characterized G protein-coupled receptor system. Responses to agonist (α-factor) by cells expressing widely varying numbers of receptors depend primarily on fractional occupancy, not the absolute number of agonist-bound receptors. Furthermore, the concentration of competitive antagonist required to inhibit α-factor-dependent signaling is more than 10-fold higher than predicted based on the known ligand affinities. Thus, responses to a particular number of agonist-bound receptors can vary greatly, depending on whether there are unoccupied or antagonist-bound receptors present on the same cell surface. This behavior does not appear to be due to pre-coupling of receptors to G protein or to the Sst2p regulator of G protein signaling. The results are consistent with a signaling response that is determined by the integration of positive signals from agonist-occupied receptors and inhibitory signals from unoccupied receptors, where the inhibitory signals can be diminished by antagonist binding.
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Affiliation(s)
- Rajashri Sridharan
- From the Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642
| | - Sara M Connelly
- From the Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642
| | - Fred Naider
- the Department of Chemistry and Macromolecular Assembly Institute, College of Staten Island of the City University of New York, Staten Island, New York 10314, and.,the Ph.D. Programs in Biochemistry and Chemistry, Graduate Center of the City University of New York, New York, New York 10016
| | - Mark E Dumont
- From the Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642,
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9
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Di Roberto RB, Chang B, Trusina A, Peisajovich SG. Evolution of a G protein-coupled receptor response by mutations in regulatory network interactions. Nat Commun 2016; 7:12344. [PMID: 27487915 PMCID: PMC4976203 DOI: 10.1038/ncomms12344] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 06/24/2016] [Indexed: 12/17/2022] Open
Abstract
All cellular functions depend on the concerted action of multiple proteins organized in complex networks. To understand how selection acts on protein networks, we used the yeast mating receptor Ste2, a pheromone-activated G protein-coupled receptor, as a model system. In Saccharomyces cerevisiae, Ste2 is a hub in a network of interactions controlling both signal transduction and signal suppression. Through laboratory evolution, we obtained 21 mutant receptors sensitive to the pheromone of a related yeast species and investigated the molecular mechanisms behind this newfound sensitivity. While some mutants show enhanced binding affinity to the foreign pheromone, others only display weakened interactions with the network's negative regulators. Importantly, the latter changes have a limited impact on overall pathway regulation, despite their considerable effect on sensitivity. Our results demonstrate that a new receptor–ligand pair can evolve through network-altering mutations independently of receptor–ligand binding, and suggest a potential role for such mutations in disease. Co-evolution of a new receptor-ligand pair will affect the downstream signal transduction network. Here, the authors use experimental evolution of yeast mating receptor Ste2 to show the effect of enhanced binding affinity and weakened interactions with the network's negative regulators on protein evolution.
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Affiliation(s)
- Raphaël B Di Roberto
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
| | - Belinda Chang
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
| | - Ala Trusina
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen Ø 2100, Denmark
| | - Sergio G Peisajovich
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
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10
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Chen W, Nie Q, Yi TM, Chou CS. Modelling of Yeast Mating Reveals Robustness Strategies for Cell-Cell Interactions. PLoS Comput Biol 2016; 12:e1004988. [PMID: 27404800 PMCID: PMC4942089 DOI: 10.1371/journal.pcbi.1004988] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Accepted: 05/16/2016] [Indexed: 11/18/2022] Open
Abstract
Mating of budding yeast cells is a model system for studying cell-cell interactions. Haploid yeast cells secrete mating pheromones that are sensed by the partner which responds by growing a mating projection toward the source. The two projections meet and fuse to form the diploid. Successful mating relies on precise coordination of dynamic extracellular signals, signaling pathways, and cell shape changes in a noisy background. It remains elusive how cells mate accurately and efficiently in a natural multi-cell environment. Here we present the first stochastic model of multiple mating cells whose morphologies are driven by pheromone gradients and intracellular signals. Our novel computational framework encompassed a moving boundary method for modeling both a-cells and α-cells and their cell shape changes, the extracellular diffusion of mating pheromones dynamically coupled with cell polarization, and both external and internal noise. Quantification of mating efficiency was developed and tested for different model parameters. Computer simulations revealed important robustness strategies for mating in the presence of noise. These strategies included the polarized secretion of pheromone, the presence of the α-factor protease Bar1, and the regulation of sensing sensitivity; all were consistent with data in the literature. In addition, we investigated mating discrimination, the ability of an a-cell to distinguish between α-cells either making or not making α-factor, and mating competition, in which multiple a-cells compete to mate with one α-cell. Our simulations were consistent with previous experimental results. Moreover, we performed a combination of simulations and experiments to estimate the diffusion rate of the pheromone a-factor. In summary, we constructed a framework for simulating yeast mating with multiple cells in a noisy environment, and used this framework to reproduce mating behaviors and to identify strategies for robust cell-cell interactions. One of the riddles of Nature is how cells interact with one another to create complex cellular networks such as the neural networks in the brain. Forming precise connections between irregularly shaped cells is a challenge for biology. We developed computational methods for simulating these complex cell-cell interactions. We applied these methods to investigate yeast mating in which two yeast cells grow projections that meet and fuse guided by pheromone attractants. The simulations described molecules both inside and outside of the cell, and represented the continually changing shapes of the cells. We found that positioning the secretion and sensing of pheromones at the same location on the cell surface was important. Other key factors for robust mating included secreting a protein that removed excess pheromone from outside of the cell so that the signal would not be too strong. An important advance was being able to simulate as many as five cells in complex mating arrangements. Taken together we used our novel computational methods to describe in greater detail the yeast mating process, and more generally, interactions among cells changing their shapes in response to their neighbors.
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Affiliation(s)
- Weitao Chen
- Department of Mathematics, University of California, Irvine, Irvine, California, United States of America
| | - Qing Nie
- Department of Mathematics, University of California, Irvine, Irvine, California, United States of America
| | - Tau-Mu Yi
- Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, United States of America
- * E-mail: (TMY); (CSC)
| | - Ching-Shan Chou
- Department of Mathematics, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail: (TMY); (CSC)
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11
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Torres M. Chapter Two - Heterotrimeric G Protein Ubiquitination as a Regulator of G Protein Signaling. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2016; 141:57-83. [PMID: 27378755 DOI: 10.1016/bs.pmbts.2016.03.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Ubiquitin-mediated regulation of G proteins has been known for over 20 years as a result of discoveries made independently in yeast and vertebrate model systems for pheromone and photoreception, respectively. Since that time, several details underlying the cause and effect of G protein ubiquitination have been determined-including the initiating signals, responsible enzymes, trafficking pathways, and their effects on protein structure, function, interactions, and cell signaling. The collective body of evidence suggests that Gα subunits are the primary targets of ubiquitination. However, longstanding and recent results suggest that Gβ and Gγ subunits are also ubiquitinated, in some cases impacting cell polarization-a process essential for chemotaxis and polarized cell growth. More recently, evidence from mass spectrometry (MS)-based proteomics coupled with advances in PTM bioinformatics have revealed that protein families representing G protein subunits contain several structural hotspots for ubiquitination-most of which have not been investigated for a functional role in signal transduction. Taken together, our knowledge and understanding of heterotrimeric G protein ubiquitination as a regulator of G protein signaling-despite 20 years of research-is still emerging.
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Affiliation(s)
- M Torres
- Georgia Institute of Technology, School of Biology, Atlanta, GA, United States.
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12
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Nagiec MJ, McCarter PC, Kelley JB, Dixit G, Elston TC, Dohlman HG. Signal inhibition by a dynamically regulated pool of monophosphorylated MAPK. Mol Biol Cell 2015; 26:3359-71. [PMID: 26179917 PMCID: PMC4569323 DOI: 10.1091/mbc.e15-01-0037] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Accepted: 07/08/2015] [Indexed: 12/21/2022] Open
Abstract
MAPKs are activated by dual phosphorylation. Much of the MAPK Fus3 is monophosphorylated and acts to inhibit signaling in vivo. Computational models reveal how a kinase scaffold and phosphatase act together to dynamically regulate dual-phosphorylated and monophosphorylated MAPKs and the downstream signal. Protein kinases regulate a broad array of cellular processes and do so through the phosphorylation of one or more sites within a given substrate. Many protein kinases are themselves regulated through multisite phosphorylation, and the addition or removal of phosphates can occur in a sequential (processive) or a stepwise (distributive) manner. Here we measured the relative abundance of the monophosphorylated and dual-phosphorylated forms of Fus3, a member of the mitogen-activated protein kinase (MAPK) family in yeast. We found that upon activation with pheromone, a substantial proportion of Fus3 accumulates in the monophosphorylated state. Introduction of an additional copy of Fus3 lacking either phosphorylation site leads to dampened signaling. Conversely, cells lacking the dual-specificity phosphatase (msg5Δ) or that are deficient in docking to the MAPK-scaffold (Ste5ND) accumulate a greater proportion of dual-phosphorylated Fus3. The double mutant exhibits a synergistic, or “synthetic,” supersensitivity to pheromone. Finally, we present a predictive computational model that combines MAPK scaffold and phosphatase activities and is sufficient to account for the observed MAPK profiles. These results indicate that the monophosphorylated and dual-phosphorylated forms of the MAPK act in opposition to one another. Moreover, they reveal a new mechanism by which the MAPK scaffold acts dynamically to regulate signaling.
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Affiliation(s)
- Michal J Nagiec
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Patrick C McCarter
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 Bioinformatics and Computational Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Joshua B Kelley
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Gauri Dixit
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Timothy C Elston
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Henrik G Dohlman
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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13
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Sridharan R, Zuber J, Connelly SM, Mathew E, Dumont ME. Fluorescent approaches for understanding interactions of ligands with G protein coupled receptors. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1838:15-33. [PMID: 24055822 PMCID: PMC3926105 DOI: 10.1016/j.bbamem.2013.09.005] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 09/03/2013] [Accepted: 09/08/2013] [Indexed: 11/18/2022]
Abstract
G protein coupled receptors are responsible for a wide variety of signaling responses in diverse cell types. Despite major advances in the determination of structures of this class of receptors, the underlying mechanisms by which binding of different types of ligands specifically elicits particular signaling responses remain unclear. The use of fluorescence spectroscopy can provide important information about the process of ligand binding and ligand dependent conformational changes in receptors, especially kinetic aspects of these processes that can be difficult to extract from X-ray structures. We present an overview of the extensive array of fluorescent ligands that have been used in studies of G protein coupled receptors and describe spectroscopic approaches for assaying binding and probing the environment of receptor-bound ligands with particular attention to examples involving yeast pheromone receptors. In addition, we discuss the use of fluorescence spectroscopy for detecting and characterizing conformational changes in receptors induced by the binding of ligands. Such studies have provided strong evidence for diversity of receptor conformations elicited by different ligands, consistent with the idea that GPCRs are not simple on and off switches. This diversity of states constitutes an underlying mechanistic basis for biased agonism, the observation that different stimuli can produce different responses from a single receptor. It is likely that continued technical advances will allow fluorescence spectroscopy to play an important role in continued probing of structural transitions in G protein coupled receptors. This article is part of a Special Issue entitled: Structural and biophysical characterisation of membrane protein-ligand binding.
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Affiliation(s)
- Rajashri Sridharan
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Jeffrey Zuber
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Sara M. Connelly
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Elizabeth Mathew
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
| | - Mark E. Dumont
- Department of Biochemistry and Biophysics, P.O. Box 712, University of Rochester Medical Center, Rochester, NY 14642
- Department of Pediatrics, P.O. Box 777, University of Rochester Medical Center, Rochester, NY 14642
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14
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Yang Y, Wang Z, Yang H, Wang L, Gillespie SR, Wolosin JM, Bernstein AM, Reinach PS. TRPV1 potentiates TGFβ-induction of corneal myofibroblast development through an oxidative stress-mediated p38-SMAD2 signaling loop. PLoS One 2013; 8:e77300. [PMID: 24098582 PMCID: PMC3788725 DOI: 10.1371/journal.pone.0077300] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Accepted: 08/30/2013] [Indexed: 01/02/2023] Open
Abstract
Injuring mouse corneas with alkali causes myofibroblast expression leading to tissue opacification. However, in transient receptor potential vanilloid 1 channel (TRPV1-/-) knockout mice healing results in transparency restoration. Since TGFβ is the primary inducer of the myofibroblast phenotype, we examined the mechanism by which TRPV1 affects TGFβ-induced myofibroblast development. Experiments were performed in pig corneas and human corneal fibroblasts (HCFs). Immunohistochemical staining of α-smooth muscle actin (α-SMA) stress fibers was used to visualize myofibroblasts. Protein and phosphoprotein were determined by Western blotting. siRNA transfection silenced TRPV1 gene expression. Flow cytometry with a reactive oxygen species (ROS) reporting dye analyzed intracellular ROS. [Ca2+]I was measured by loading HCF with fura2. In organ cultured corneas, the TRPV1 antagonist capsazepine drastically reduced by 75% wound-induced myofibroblast development. In HCF cell culture, TGF-β1 elicited rapid increases in Ca2+ influx, phosphorylation of SMAD2 and MAPKs (ERK1/2, JNK1/2 and p38), ROS generation and, after 72 hrs myofibroblast development. SMAD2 and p38 activation continued for more than 16 h, whereas p-ERK1/2 and p-JNK1/2 waned within 90 min. The long-lived SMAD2 activation was dependent on activated p38 and vice versa, and it was essential to generate a > 13-fold increase in α-SMA protein and a fully developed myofibroblast phenotype. These later changes were markedly reduced by inhibition of TRPV1 or reduction of the ROS generation rate. Taken together our results indicate that in corneal derived fibroblasts, TGFβ- induced myofibroblast development is highly dependent on a positive feedback loop where p-SMAD2-induced ROS activates TRPV1, TRPV1 causes activation of p38, the latter in turn further enhances the activation of SMAD2 to establish a recurrent loop that greatly extends the residency of the activated state of SMAD2 that drives myofibroblast development.
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Affiliation(s)
- Yuanquan Yang
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, New York, United States of America
| | - Zheng Wang
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
| | - Hua Yang
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, New York, United States of America
| | - Lingyan Wang
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
| | - Stephanie R. Gillespie
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
| | - J. Mario Wolosin
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
| | - Audrey M. Bernstein
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
- * E-mail: (PSR); (AMB)
| | - Peter S. Reinach
- Department of Biological Sciences, State University of New York, State College of Optometry, New York, New York, United States of America
- * E-mail: (PSR); (AMB)
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15
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Croft W, Hill C, McCann E, Bond M, Esparza-Franco M, Bennett J, Rand D, Davey J, Ladds G. A physiologically required G protein-coupled receptor (GPCR)-regulator of G protein signaling (RGS) interaction that compartmentalizes RGS activity. J Biol Chem 2013; 288:27327-27342. [PMID: 23900842 DOI: 10.1074/jbc.m113.497826] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors (GPCRs) can interact with regulator of G protein signaling (RGS) proteins. However, the effects of such interactions on signal transduction and their physiological relevance have been largely undetermined. Ligand-bound GPCRs initiate by promoting exchange of GDP for GTP on the Gα subunit of heterotrimeric G proteins. Signaling is terminated by hydrolysis of GTP to GDP through intrinsic GTPase activity of the Gα subunit, a reaction catalyzed by RGS proteins. Using yeast as a tool to study GPCR signaling in isolation, we define an interaction between the cognate GPCR (Mam2) and RGS (Rgs1), mapping the interaction domains. This reaction tethers Rgs1 at the plasma membrane and is essential for physiological signaling response. In vivo quantitative data inform the development of a kinetic model of the GTPase cycle, which extends previous attempts by including GPCR-RGS interactions. In vivo and in silico data confirm that GPCR-RGS interactions can impose an additional layer of regulation through mediating RGS subcellular localization to compartmentalize RGS activity within a cell, thus highlighting their importance as potential targets to modulate GPCR signaling pathways.
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Affiliation(s)
- Wayne Croft
- Division of Biomedical Cell Biology, Warwick Medical School
| | | | - Eilish McCann
- Division of Biomedical Cell Biology, Warwick Medical School
| | - Michael Bond
- Division of Biomedical Cell Biology, Warwick Medical School
| | | | | | - David Rand
- Systems Biology Centre, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - John Davey
- Division of Biomedical Cell Biology, Warwick Medical School
| | - Graham Ladds
- Division of Biomedical Cell Biology, Warwick Medical School.
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16
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Hurst JH, Dohlman HG. Dynamic ubiquitination of the mitogen-activated protein kinase kinase (MAPKK) Ste7 determines mitogen-activated protein kinase (MAPK) specificity. J Biol Chem 2013; 288:18660-71. [PMID: 23645675 DOI: 10.1074/jbc.m113.475707] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Ubiquitination is a post-translational modification that tags proteins for proteasomal degradation. In addition, there is a growing appreciation that ubiquitination can influence protein activity and localization. Ste7 is a prototype MAPKK in yeast that participates in both the pheromone signaling and nutrient deprivation/invasive growth pathways. We have shown previously that Ste7 is ubiquitinated upon pheromone stimulation. Here, we show that the Skp1/Cullin/F-box ubiquitin ligase SCF(Cdc4) and the ubiquitin protease Ubp3 regulate Ste7 ubiquitination and signal specificity. Using purified components, we demonstrate that SCF(Cdc4) ubiquitinates Ste7 directly. Using gene deletion mutants, we show that SCF(Cdc4) and Ubp3 have opposing effects on Ste7 ubiquitination. Although SCF(Cdc4) is necessary for proper activation of the pheromone MAPK Fus3, Ubp3 is needed to limit activation of the invasive growth MAPK Kss1. Finally, we show that Fus3 phosphorylates Ubp3 directly and that phosphorylation of Ubp3 is necessary to limit Kss1 activation. These results reveal a feedback loop wherein one MAPK limits the ubiquitination of an upstream MAPKK and thereby prevents spurious activation of a second competing MAPK.
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Affiliation(s)
- Jillian H Hurst
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA
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17
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Fernandez-Piñar P, Alemán A, Sondek J, Dohlman HG, Molina M, Martín H. The Salmonella Typhimurium effector SteC inhibits Cdc42-mediated signaling through binding to the exchange factor Cdc24 in Saccharomyces cerevisiae. Mol Biol Cell 2012; 23:4430-43. [PMID: 23015760 PMCID: PMC3496616 DOI: 10.1091/mbc.e12-03-0243] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Expression of the Salmonella effector SteC in yeast leads to down-regulation of the mating and HOG pathways by Cdc42 inhibition. This is mediated by the SteC N-terminal domain through binding to the GEF Cdc24. SteC alters Cdc24 localization and also interacts with human GEF Vav1, suggesting that SteC could target Cdc42 function in host cells. Intracellular survival of Salmonella relies on the activity of proteins translocated into the host cell by type III secretion systems (T3SS). The protein kinase activity of the T3SS effector SteC is required for F-actin remodeling in host cells, although no SteC target has been identified so far. Here we show that expression of the N-terminal non-kinase domain of SteC down-regulates the mating and HOG pathways in Saccharomyces cerevisiae. Epistasis analyses using constitutively active components of these pathways indicate that SteC inhibits signaling at the level of the GTPase Cdc42. We demonstrate that SteC interacts through its N-terminal domain with the catalytic domain of Cdc24, the sole S. cerevisiae Cdc42 guanine nucleotide exchange factor (GEF). SteC also binds to the human Cdc24-like GEF protein Vav1. Moreover, expression of human Cdc42 suppresses growth inhibition caused by SteC. Of interest, the N-terminal SteC domain alters Cdc24 cellular localization, preventing its nuclear accumulation. These data reveal a novel functional domain within SteC, raising the possibility that this effector could also target GTPase function in mammalian cells. Our results also highlight the key role of the Cdc42 switch in yeast mating and HOG pathways and provide a new tool to study the functional consequences of Cdc24 localization.
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Affiliation(s)
- Pablo Fernandez-Piñar
- Departamento de Microbiología II, Facultad de Farmacia, Universidad Complutense de Madrid, and Instituto Ramón y Cajal de Investigaciones Sanitarias, 28040 Madrid, Spain
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18
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Functional and physical interactions among Saccharomyces cerevisiae α-factor receptors. EUKARYOTIC CELL 2012; 11:1276-88. [PMID: 22923047 DOI: 10.1128/ec.00172-12] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The α-factor receptor Ste2p is a G protein-coupled receptor (GPCR) expressed on the surface of MATa haploid cells of the yeast Saccharomyces cerevisiae. Binding of α-factor to Ste2p results in activation of a heterotrimeric G protein and of the pheromone response pathway. Functional interactions between α-factor receptors, such as dominant-negative effects and recessive behavior of constitutive and hypersensitive mutant receptors, have been reported previously. We show here that dominant-negative effects of mutant receptors persist over a wide range of ratios of the abundances of G protein to receptor and that such effects are not blocked by covalent fusion of G protein α subunits to normal receptors. In addition, we detected dominant effects of mutant C-terminally truncated receptors, which had not been previously reported to act in a dominant manner. Furthermore, coexpression of C-terminally truncated receptors with constitutively active mutant receptors results in enhancement of constitutive signaling. Together with previous evidence for oligomerization of Ste2p receptors, these results are consistent with the idea that functional interactions between coexpressed receptors arise from physical interactions between them rather than from competition for limiting downstream components, such as G proteins.
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19
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Hao N, Yildirim N, Nagiec MJ, Parnell SC, Errede B, Dohlman HG, Elston TC. Combined computational and experimental analysis reveals mitogen-activated protein kinase-mediated feedback phosphorylation as a mechanism for signaling specificity. Mol Biol Cell 2012; 23:3899-910. [PMID: 22875986 PMCID: PMC3459865 DOI: 10.1091/mbc.e12-04-0333] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
A series of mathematical models was used to quantitatively characterize pheromone-stimulated kinase activation and determine how mitogen-activated protein (MAP) kinase specificity is achieved. The findings reveal how feedback phosphorylation of a common pathway component can limit the activity of a competing MAP kinase through feedback phosphorylation of a common activator, and thereby promote signal fidelity. Different environmental stimuli often use the same set of signaling proteins to achieve very different physiological outcomes. The mating and invasive growth pathways in yeast each employ a mitogen-activated protein (MAP) kinase cascade that includes Ste20, Ste11, and Ste7. Whereas proper mating requires Ste7 activation of the MAP kinase Fus3, invasive growth requires activation of the alternate MAP kinase Kss1. To determine how MAP kinase specificity is achieved, we used a series of mathematical models to quantitatively characterize pheromone-stimulated kinase activation. In accordance with the computational analysis, MAP kinase feedback phosphorylation of Ste7 results in diminished activation of Kss1, but not Fus3. These findings reveal how feedback phosphorylation of a common pathway component can limit the activity of a competing MAP kinase through feedback phosphorylation of a common activator, and thereby promote signal fidelity.
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Affiliation(s)
- Nan Hao
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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20
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Scaffold number in yeast signaling system sets tradeoff between system output and dynamic range. Proc Natl Acad Sci U S A 2011; 108:20265-70. [PMID: 22114196 DOI: 10.1073/pnas.1004042108] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Although the proteins comprising many signaling systems are known, less is known about their numbers per cell. Existing measurements often vary by more than 10-fold. Here, we devised improved quantification methods to measure protein abundances in the Saccharomyces cerevisiae pheromone response pathway, an archetypical signaling system. These methods limited variation between independent measurements of protein abundance to a factor of two. We used these measurements together with quantitative models to identify and investigate behaviors of the pheromone response system sensitive to precise abundances. The difference between the maximum and basal signaling output (dynamic range) of the pheromone response MAPK cascade was strongly sensitive to the abundance of Ste5, the MAPK scaffold protein, and absolute system output depended on the amount of Fus3, the MAPK. Additional analysis and experiment suggest that scaffold abundance sets a tradeoff between maximum system output and system dynamic range, a prediction supported by recent experiments.
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21
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Zhu M, Torres MP, Kelley JB, Dohlman HG, Wang Y. Pheromone- and RSP5-dependent ubiquitination of the G protein beta subunit Ste4 in yeast. J Biol Chem 2011; 286:27147-55. [PMID: 21685393 DOI: 10.1074/jbc.m111.254193] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ste4 is the β subunit of a heterotrimeric G protein that mediates mating responses in Saccharomyces cerevisiae. Here we show that Ste4 undergoes ubiquitination in response to pheromone stimulation. Ubiquitination of Ste4 is dependent on the E3 ligase Rsp5. Disrupting the activity of Rsp5 abolishes ubiquitination of Ste4 in vivo, and recombinant Rsp5 is capable of ubiquitinating Ste4 in vitro. We find also that Lys-340 is a major ubiquitination site on Ste4, as pheromone-induced ubiquitination of the protein is prevented when this residue is mutated to an arginine. Functionally, ubiquitination does not appear to regulate the stability of Ste4, as blocking ubiquitination has no apparent effect on either the abundance or the half-life of the protein. However, when presented with a concentration gradient of pheromone, Ste4(K340R) mutant cells polarize significantly faster than wild-type cells, indicating that ubiquitination limits pheromone-directed polarized growth. Together, these findings reveal a novel stimulus-dependent posttranslational modification of a Gβ subunit, establish Ste4 as a new substrate of the E3 ligase Rsp5, and demonstrate a role for G protein ubiquitination in cell polarization.
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Affiliation(s)
- Ming Zhu
- Department of Biology, Saint Louis University, St. Louis, Missouri 63103, USA
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22
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Torres MP, Clement ST, Cappell SD, Dohlman HG. Cell cycle-dependent phosphorylation and ubiquitination of a G protein alpha subunit. J Biol Chem 2011; 286:20208-16. [PMID: 21521692 DOI: 10.1074/jbc.m111.239343] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A diverse array of external stimuli, including most hormones and neurotransmitters, bind to cell surface receptors that activate G proteins. Mating pheromones in yeast Saccharomyces cerevisiae activate G protein-coupled receptors and initiate events leading to cell cycle arrest in G(1) phase. Here, we show that the Gα subunit (Gpa1) is phosphorylated and ubiquitinated in response to changes in the cell cycle. We systematically screened 109 gene deletion strains representing the non-essential yeast kinome and identified a single kinase gene, ELM1, as necessary and sufficient for Gpa1 phosphorylation. Elm1 is expressed in a cell cycle-dependent manner, primarily at S and G(2)/M. Accordingly, phosphorylation of Gpa1 in G(2)/M phase leads to polyubiquitination in G(1) phase. These findings demonstrate that Gpa1 is dynamically regulated. More broadly, they reveal how G proteins can simultaneously regulate, and become regulated by, progression through the cell cycle.
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Affiliation(s)
- Matthew P Torres
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7260, USA
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23
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Chung BG, Choo J. Microfluidic gradient platforms for controlling cellular behavior. Electrophoresis 2010; 31:3014-27. [PMID: 20734372 DOI: 10.1002/elps.201000137] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Concentration gradients play an important role in controlling biological and pathological processes, such as metastasis, embryogenesis, axon guidance, and wound healing. Microfluidic devices fabricated by photo- and soft lithography techniques can manipulate the fluidic flow and diffusion profile to create biomolecular gradients in a temporal and spatial manner. Furthermore, microfluidic devices enable the control of cell-extracellular microenvironment interactions, including cell-cell, cell-matrix, and cell-soluble factor interaction. In this paper, we review the development of microfluidic-based gradient devices and highlight their biological applications.
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Affiliation(s)
- Bong Geun Chung
- Department of Bionano Engineering, Hanyang University, Ansan, Korea.
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24
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Tanaka H, Yi TM. The effects of replacing Sst2 with the heterologous RGS4 on polarization and mating in yeast. Biophys J 2010; 99:1007-17. [PMID: 20712983 DOI: 10.1016/j.bpj.2010.04.078] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Revised: 04/16/2010] [Accepted: 04/30/2010] [Indexed: 11/30/2022] Open
Abstract
RGS proteins stimulate the deactivation of heterotrimeric G-proteins. The yeast RGS protein Sst2 is regulated at both the transcriptional and posttranscriptional levels. We replaced the SST2 gene with the distantly related human RGS4 gene, which consists of the catalytic domain and an N-terminal membrane attachment peptide, and replaced the native promoter (P(SST2)) with the heterologous tetracycline-repressible promoter (P(TET)). We then measured the effect of the substitutions on pheromone sensitivity, mating, and polarization. Although the pheromone sensitivity was essentially normal, there were differences in mating and polarization. In particular, the RGS4-substituted strains did not form multiple mating projections at high levels of alpha-factor, but instead formed a single malformed projection, which frequently gave rise to a bud. We provide evidence that this phenotype arose because unlike Sst2, RGS4 did not localize to the projection. We use mathematical modeling to argue that localization of Sst2 to the projection prevents excess G-protein activation during the pheromone response. In addition, modeling and experiments demonstrate that the dose of Sst2 influences the frequency of mating projection formation.
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Affiliation(s)
- Hiromasa Tanaka
- Department of Developmental and Cell Biology, University of California, Irvine, California, USA
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25
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Cappell SD, Baker R, Skowyra D, Dohlman HG. Systematic analysis of essential genes reveals important regulators of G protein signaling. Mol Cell 2010; 38:746-57. [PMID: 20542006 DOI: 10.1016/j.molcel.2010.05.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 01/30/2010] [Accepted: 04/02/2010] [Indexed: 10/19/2022]
Abstract
The yeast pheromone pathway consists of a canonical heterotrimeric G protein and MAP kinase cascade. To identify additional signaling components, we systematically evaluated 870 essential genes using a library of repressible-promoter strains. Quantitative transcription-reporter and MAPK activity assays were used to identify strains that exhibit altered pheromone sensitivity. Of the 92 newly identified essential genes required for proper G protein signaling, those involved with protein degradation were most highly represented. Included in this group are members of the Skp, Cullin, F box (SCF) ubiquitin ligase complex. Further genetic and biochemical analysis reveals that SCF(Cdc4) acts together with the Cdc34 ubiquitin-conjugating enzyme at the level of the G protein; promotes degradation of the G protein alpha subunit, Gpa1, in vivo; and catalyzes Gpa1 ubiquitination in vitro. These insights to the G protein signaling network reveal the essential genome as an untapped resource for identifying new components and regulators of signal transduction pathways.
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Affiliation(s)
- Steven D Cappell
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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26
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Murakami S, Suzuki S, Ishii M, Inanobe A, Kurachi Y. Cellular modelling: experiments and simulation to develop a physiological model of G-protein control of muscarinic K+ channels in mammalian atrial cells. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2010; 368:2983-3000. [PMID: 20478917 DOI: 10.1098/rsta.2010.0093] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The first model of G-protein-K(ACh) channel interaction was developed 14 years ago and then expanded to include both the receptor-G-protein cycle and G-protein-K(ACh) channel interaction. The G-protein-K(ACh) channel interaction used the Monod-Wyman-Changeux allosteric model with the idea that one K(ACh) channel is composed of four subunits, each of which binds one active G-protein subunit (G(betagamma)). The receptor-G-protein cycle used a previous model to account for the steady-state relationship between K(ACh) current and intracellular guanosine-5-triphosphate at various extracellular concentrations of acetylcholine (ACh). However, simulations of the activation and deactivation of K(ACh) current upon ACh application or removal were much slower than experimental results. This clearly indicates some essential elements were absent from the model. We recently found that regulators of G-protein signalling are involved in the control of K(ACh) channel activity. They are responsible for the voltage-dependent relaxation behaviour of K(ACh) channels. Based on this finding, we have improved the receptor-G-protein cycle model to reproduce the relaxation behaviour. With this modification, the activation and deactivation of K(ACh) current in the model are much faster and now fall within physiological ranges.
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Affiliation(s)
- Shingo Murakami
- Division of Molecular and Cellular Pharmacology, Department of Pharmacology, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
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27
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Molina M, Cid VJ, Martín H. Fine regulation of Saccharomyces cerevisiae MAPK pathways by post-translational modifications. Yeast 2010; 27:503-11. [DOI: 10.1002/yea.1791] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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28
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Hwang IY, Park C, Harrision KA, Huang NN, Kehrl JH. Variations in Gnai2 and Rgs1 expression affect chemokine receptor signaling and the organization of secondary lymphoid organs. Genes Immun 2010; 11:384-96. [PMID: 20508603 PMCID: PMC2908210 DOI: 10.1038/gene.2010.27] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Ligand bound chemoattractant receptors activate the heterotrimeric G protein Gi to stimulate downstream signaling pathways to properly position lymphocytes in lymphoid organs. Here we show how variations the expression of a chemokine receptor and in two components in the signaling pathway, Gαi2 and RGS1, affects the output fidelity of the signaling pathway. Examination of B cells from mice with varying numbers of intact alleles of Ccr7, Rgs1, Gnai2, and Gnai3 provided the basis for these results. Loss of a single allele of either Gnai2 or Rgs1 affected CCL19 triggered chemotaxis, while loss of a single allele of Ccr7, which encodes the cognate CCL19 receptor, had little effect. Emphasizing the importance of Gnai2, B cells lacking Gnai3 expression responded to chemokines better than did wild type B cells. At an organismal level, variations in Rgs1 and Gnai2 expression affected marginal zone B cell development, splenic architecture, lymphoid follicle size, and germinal center morphology. Gnai2 expression was also needed for the proper alignment of MOMA-1+ macrophages and MAdCAM-1+ endothelial cells along marginal zone sinuses in the spleen. These data indicate that chemoattractant receptors, heterotrimeric G-proteins, and RGS protein expression levels have a complex inter-relationship that affects the responses to chemoattractant exposure.
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Affiliation(s)
- I Y Hwang
- B-Cell Molecular Immunology Section, Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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29
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Falkenburger BH, Jensen JB, Hille B. Kinetics of M1 muscarinic receptor and G protein signaling to phospholipase C in living cells. ACTA ACUST UNITED AC 2010; 135:81-97. [PMID: 20100890 PMCID: PMC2812500 DOI: 10.1085/jgp.200910344] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
G protein-coupled receptors (GPCRs) mediate responses to external stimuli in various cell types. Early events, such as the binding of ligand and G proteins to the receptor, nucleotide exchange (NX), and GTPase activity at the Galpha subunit, are common for many different GPCRs. For G(q)-coupled M(1) muscarinic (acetylcholine) receptors (M(1)Rs), we recently measured time courses of intermediate steps in the signaling cascade using Förster resonance energy transfer (FRET). The expression of FRET probes changes the density of signaling molecules. To provide a full quantitative description of M(1)R signaling that includes a simulation of kinetics in native (tsA201) cells, we now determine the density of FRET probes and construct a kinetic model of M(1)R signaling through G(q) to activation of phospholipase C (PLC). Downstream effects on the trace membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP(2)) and PIP(2)-dependent KCNQ2/3 current are considered in our companion paper in this issue (Falkenburger et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.200910345). By calibrating their fluorescence intensity, we found that we selected transfected cells for our experiments with approximately 3,000 fluorescently labeled receptors, G proteins, or PLC molecules per microm(2) of plasma membrane. Endogenous levels are much lower, 1-40 per microm(2). Our kinetic model reproduces the time courses and concentration-response relationships measured by FRET and explains observed delays. It predicts affinities and rate constants that align well with literature values. In native tsA201 cells, much of the delay between ligand binding and PLC activation reflects slow binding of G proteins to receptors. With M(1)R and Gbeta FRET probes overexpressed, 10% of receptors have G proteins bound at rest, rising to 73% in the presence of agonist. In agreement with previous work, the model suggests that binding of PLC to Galpha(q) greatly speeds up NX and GTPase activity, and that PLC is maintained in the active state by cycles of rapid GTP hydrolysis and NX on Galpha(q) subunits bound to PLC.
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Affiliation(s)
- Björn H Falkenburger
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA
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Rateitschak K, Wolkenhauer O. Thresholds in transient dynamics of signal transduction pathways. J Theor Biol 2010; 264:334-46. [PMID: 20144619 DOI: 10.1016/j.jtbi.2010.02.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 02/01/2010] [Accepted: 02/02/2010] [Indexed: 10/19/2022]
Abstract
Transient dynamics of signal transduction pathways play an important role in many biological processes, including cell differentiation, apoptosis, metabolism and DNA damage response. Recent examples of quantitative methods to characterize transient signals include transient metabolic control coefficients and finite time Lyapunov exponents. In our work we compare these quantitative methods to characterize transient phenomena and specifically discuss their predictive power for three examples. We focus on the identification of thresholds that separate different transient dynamic behaviors. Our investigation leads to the following results: The spectrum of the finite-time Lyapunov exponents unambiguously and reliably identifies putative thresholds in transient dynamics. Metabolic control coefficients do not reliably detect all thresholds and suffer from false positives.
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Affiliation(s)
- Katja Rateitschak
- Systems Biology and Bioinformatics Group, University of Rostock, 18051 Rostock, Germany.
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Seibel C, Gremel G, do Nascimento Silva R, Schuster A, Kubicek CP, Schmoll M. Light-dependent roles of the G-protein alpha subunit GNA1 of Hypocrea jecorina (anamorph Trichoderma reesei). BMC Biol 2009; 7:58. [PMID: 19728862 PMCID: PMC2749820 DOI: 10.1186/1741-7007-7-58] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Accepted: 09/03/2009] [Indexed: 02/02/2023] Open
Abstract
Background The filamentous ascomycete Hypocrea jecorina (anamorph Trichoderma reesei) is primarily known for its efficient enzymatic machinery that it utilizes to decompose cellulosic substrates. Nevertheless, the nature and transmission of the signals initiating and modulating this machinery are largely unknown. Heterotrimeric G-protein signaling represents one of the best studied signal transduction pathways in fungi. Results Analysis of the regulatory targets of the G-protein α subunit GNA1 in H. jecorina revealed a carbon source and light-dependent role in signal transduction. Deletion of gna1 led to significantly decreased biomass formation in darkness in submersed culture but had only minor effects on morphology and hyphal apical extension rates on solid medium. Cellulase gene transcription was abolished in Δgna1 on cellulose in light and enhanced in darkness. However, analysis of strains expressing a constitutively activated GNA1 revealed that GNA1 does not transmit the essential inducing signal. Instead, it relates a modulating signal with light-dependent significance, since induction still required the presence of an inducer. We show that regulation of transcription and activity of GNA1 involves a carbon source-dependent feedback cycle. Additionally we found a function of GNA1 in hydrophobin regulation as well as effects on conidiation and tolerance of osmotic and oxidative stress. Conclusion We conclude that GNA1 transmits a signal the physiological relevance of which is dependent on both the carbon source as well as the light status. The widespread consequences of mutations in GNA1 indicate a broad function of this Gα subunit in appropriation of intracellular resources to environmental (especially nutritional) conditions.
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Affiliation(s)
- Christian Seibel
- Research Area Gene Technology and Applied Biochemistry, Institute of Chemical Engineering, Vienna University of Technology, Wien, Austria.
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Smith B, Hill C, Godfrey EL, Rand D, van den Berg H, Thornton S, Hodgkin M, Davey J, Ladds G. Dual positive and negative regulation of GPCR signaling by GTP hydrolysis. Cell Signal 2009; 21:1151-60. [PMID: 19285552 DOI: 10.1016/j.cellsig.2009.03.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2009] [Accepted: 03/04/2009] [Indexed: 10/21/2022]
Abstract
G protein-coupled receptors (GPCRs) regulate a variety of intracellular pathways through their ability to promote the binding of GTP to heterotrimeric G proteins. Regulator of G protein signaling (RGS) proteins increases the intrinsic GTPase activity of Galpha-subunits and are widely regarded as negative regulators of G protein signaling. Using yeast we demonstrate that GTP hydrolysis is not only required for desensitization, but is essential for achieving a high maximal (saturated level) response. Thus RGS-mediated GTP hydrolysis acts as both a negative (low stimulation) and positive (high stimulation) regulator of signaling. To account for this we generated a new kinetic model of the G protein cycle where Galpha(GTP) enters an inactive GTP-bound state following effector activation. Furthermore, in vivo and in silico experimentation demonstrates that maximum signaling output first increases and then decreases with RGS concentration. This unimodal, non-monotone dependence on RGS concentration is novel. Analysis of the kinetic model has revealed a dynamic network motif that shows precisely how inclusion of the inactive GTP-bound state for the Galpha produces this unimodal relationship.
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Affiliation(s)
- Benjamin Smith
- Molecular Organization and Assembly of Cells Centre, University of Warwick, Coventry, UK
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Torres MP, Lee MJ, Ding F, Purbeck C, Kuhlman B, Dokholyan NV, Dohlman HG. G Protein Mono-ubiquitination by the Rsp5 Ubiquitin Ligase. J Biol Chem 2009; 284:8940-50. [PMID: 19176477 DOI: 10.1074/jbc.m809058200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Emerging evidence suggests that ubiquitination serves as a protein trafficking signal in addition to its well characterized role in promoting protein degradation. The yeast G protein alpha subunit Gpa1 represents a rare example of a protein that undergoes both mono- and poly-ubiquitination. Whereas mono-ubiquitinated Gpa1 is targeted to the vacuole, poly-ubiquitinated Gpa1 is directed instead to the proteasome. Here we investigate the structural requirements for mono- and poly-ubiquitination of Gpa1. We find that variants of Gpa1 engineered to be unstable are more likely to be poly-ubiquitinated and less likely to be mono-ubiquitinated. In addition, mutants that cannot be myristoylated are no longer mono-ubiquitinated but are still polyubiquitinated. Finally, we show that the ubiquitin ligase Rsp5 is necessary for Gpa1 mono-ubiquitination in vivo and that the purified enzyme is sufficient to catalyze Gpa1 mono-ubiquitination in vitro. Taken together, these data indicate that mono- and poly-ubiquitination have distinct enzyme and substrate recognition requirements; whereas poly-ubiquitination targets misfolded protein for degradation, a distinct ubiquitination apparatus targets the fully mature, fully myristoylated G protein for mono-ubiquitination and delivery to the vacuole.
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Affiliation(s)
- Matthew P Torres
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA
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Moore TI, Chou CS, Nie Q, Jeon NL, Yi TM. Robust spatial sensing of mating pheromone gradients by yeast cells. PLoS One 2008; 3:e3865. [PMID: 19052645 PMCID: PMC2586657 DOI: 10.1371/journal.pone.0003865] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 10/29/2008] [Indexed: 01/27/2023] Open
Abstract
Projecting or moving up a chemical gradient is a universal behavior of living organisms. We tested the ability of S. cerevisiaea-cells to sense and respond to spatial gradients of the mating pheromone α-factor produced in a microfluidics chamber; the focus was on bar1Δ strains, which do not degrade the pheromone input. The yeast cells exhibited good accuracy with the mating projection typically pointing in the correct direction up the gradient (∼80% under certain conditions), excellent sensitivity to shallow gradients, and broad dynamic range so that gradient-sensing was relatively robust over a 1000-fold range of average α-factor concentrations. Optimal directional sensing occurred at lower concentrations (5 nM) close to the Kd of the receptor and with steeper gradient slopes. Pheromone supersensitive mutations (sst2Δ and ste2300Δ) that disrupt the down-regulation of heterotrimeric G-protein signaling caused defects in both sensing and response. Interestingly, yeast cells employed adaptive mechanisms to increase the robustness of the process including filamentous growth (i.e. directional distal budding) up the gradient at low pheromone concentrations, bending of the projection to be more aligned with the gradient, and forming a more accurate second projection when the first projection was in the wrong direction. Finally, the cells were able to amplify a shallow external gradient signal of α-factor to produce a dramatic polarization of signaling proteins at the front of the cell. Mathematical modeling revealed insights into the mechanism of this amplification and how the supersensitive mutants can disrupt accurate polarization. Together, these data help to specify and elucidate the abilities of yeast cells to sense and respond to spatial gradients of pheromone.
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Affiliation(s)
- Travis I. Moore
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
| | - Ching-Shan Chou
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Qing Nie
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Mathematics, University of California Irvine, Irvine, California, United States of America
| | - Noo Li Jeon
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- Department of Biomedical Engineering, University of California Irvine, Irvine, California, United States of America
| | - Tau-Mu Yi
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, California, United States of America
- Center for Complex Biological Systems, University of California Irvine, Irvine, California, United States of America
- * E-mail:
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Oscillatory phosphorylation of yeast Fus3 MAP kinase controls periodic gene expression and morphogenesis. Curr Biol 2008; 18:1700-6. [PMID: 18976914 DOI: 10.1016/j.cub.2008.09.027] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2008] [Revised: 09/05/2008] [Accepted: 09/05/2008] [Indexed: 11/22/2022]
Abstract
Signal-transduction networks can display complex dynamic behavior such as oscillations in the activity of key components [1-6], but it is often unclear whether such dynamic complexity is actually important for the network's regulatory functions [7, 8]. Here, we found that the mitogen-activated protein kinase (MAPK) Fus3, a key regulator of the yeast mating-pheromone response, undergoes sustained oscillations in its phosphorylation and activation state during continuous pheromone exposure. These MAPK activity oscillations led to corresponding oscillations in mating-gene expression. Oscillations in MAPK activity and gene expression required the negative regulator of G protein signaling Sst2 and partially required the MAPK phosphatase Msg5. Peaks in Fus3 activation correlated with periodic rounds of cell morphogenesis, with each peak preceding the formation of an additional mating projection. Preventing projection formation did not eliminate MAPK oscillation, but preventing MAPK oscillation blocked the formation of additional projections. A mathematical model was developed that reproduced several features of the observed oscillatory dynamics. These observations demonstrate a role for MAPK activity oscillation in driving a periodic downstream response and explain how the pheromone signaling pathway, previously thought to desensitize after 1-3 hr, controls morphology changes that continue for a much longer time.
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Dose-to-duration encoding and signaling beyond saturation in intracellular signaling networks. PLoS Comput Biol 2008; 4:e1000197. [PMID: 18846202 PMCID: PMC2543107 DOI: 10.1371/journal.pcbi.1000197] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2008] [Accepted: 09/02/2008] [Indexed: 11/27/2022] Open
Abstract
The cellular response elicited by an environmental cue typically varies with the strength of the stimulus. For example, in the yeast Saccharomyces cerevisiae, the concentration of mating pheromone determines whether cells undergo vegetative growth, chemotropic growth, or mating. This implies that the signaling pathways responsible for detecting the stimulus and initiating a response must transmit quantitative information about the intensity of the signal. Our previous experimental results suggest that yeast encode pheromone concentration as the duration of the transmitted signal. Here we use mathematical modeling to analyze possible biochemical mechanisms for performing this “dose-to-duration” conversion. We demonstrate that modulation of signal duration increases the range of stimulus concentrations for which dose-dependent responses are possible; this increased dynamic range produces the counterintuitive result of “signaling beyond saturation” in which dose-dependent responses are still possible after apparent saturation of the receptors. We propose a mechanism for dose-to-duration encoding in the yeast pheromone pathway that is consistent with current experimental observations. Most previous investigations of information processing by signaling pathways have focused on amplitude encoding without considering temporal aspects of signal transduction. Here we demonstrate that dose-to-duration encoding provides cells with an alternative mechanism for processing and transmitting quantitative information about their surrounding environment. The ability of signaling pathways to convert stimulus strength into signal duration results directly from the nonlinear nature of these systems and emphasizes the importance of considering the dynamic properties of signaling pathways when characterizing their behavior. Understanding how signaling pathways encode and transmit quantitative information about the external environment will not only deepen our understanding of these systems but also provide insight into how to reestablish proper function of pathways that have become dysregulated by disease. Cells must be able to detect and respond to changes in their surroundings. Often environmental cues, such as hormones or growth factors, are received by membrane receptors that in turn activate intracellular signaling pathways. These pathways then transmit information about the stimulus to the cellular components required to elicit an appropriate response. In many cases, the nature of the response depends on the dose of the stimulus. Thus, in addition to relaying qualitative information (e.g., the presence or absence of a stimulus), signaling pathways must also transmit quantitative information about the intensity of the stimulus. Here we introduce “dose-to-duration” encoding as an effective strategy for relaying such information. We demonstrate that by providing a mechanism for overcoming saturation effects, modulation of signal duration increases the range of stimulus concentrations for which dose-dependent responses are possible. This increased dynamic range produces the counterintuitive result of “signaling beyond saturation” in which dose-dependent responses are still possible after apparent saturation of the receptors. Finally, we demonstrate that dose-to-duration encoding is used in the yeast mating response pathway and presents a simple mechanism that can account for current experimental observations.
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Turcotte M, Tang W, Ross EM. Coordinate regulation of G protein signaling via dynamic interactions of receptor and GAP. PLoS Comput Biol 2008; 4:e1000148. [PMID: 18716678 PMCID: PMC2518520 DOI: 10.1371/journal.pcbi.1000148] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Accepted: 07/01/2008] [Indexed: 11/28/2022] Open
Abstract
Signal output from receptor–G-protein–effector modules is a dynamic function of the nucleotide exchange activity of the receptor, the GTPase-accelerating activity of GTPase-activating proteins (GAPs), and their interactions. GAPs may inhibit steady-state signaling but may also accelerate deactivation upon removal of stimulus without significantly inhibiting output when the receptor is active. Further, some effectors (e.g., phospholipase C-β) are themselves GAPs, and it is unclear how such effectors can be stimulated by G proteins at the same time as they accelerate G protein deactivation. The multiple combinations of protein–protein associations and interacting regulatory effects that allow such complex behaviors in this system do not permit the usual simplifying assumptions of traditional enzyme kinetics and are uniquely subject to systems-level analysis. We developed a kinetic model for G protein signaling that permits analysis of both interactive and independent G protein binding and regulation by receptor and GAP. We evaluated parameters of the model (all forward and reverse rate constants) by global least-squares fitting to a diverse set of steady-state GTPase measurements in an m1 muscarinic receptor–Gq–phospholipase C-β1 module in which GTPase activities were varied by ∼104-fold. We provide multiple tests to validate the fitted parameter set, which is consistent with results from the few previous pre-steady-state kinetic measurements. Results indicate that (1) GAP potentiates the GDP/GTP exchange activity of the receptor, an activity never before reported; (2) exchange activity of the receptor is biased toward replacement of GDP by GTP; (3) receptor and GAP bind G protein with negative cooperativity when G protein is bound to either GTP or GDP, promoting rapid GAP binding and dissociation; (4) GAP indirectly stabilizes the continuous binding of receptor to G protein during steady-state GTPase hydrolysis, thus further enhancing receptor activity; and (5) receptor accelerates GDP/GTP exchange primarily by opening an otherwise closed nucleotide binding site on the G protein but has minimal effect on affinity (Kassoc = kassoc/kdissoc) of G protein for nucleotide. Model-based simulation explains how GAP activity can accelerate deactivation >10-fold upon removal of agonist but still allow high signal output while the receptor is active. Analysis of GTPase flux through distinct reaction pathways and consequent accumulation of specific GTPase cycle intermediates indicate that, in the presence of a GAP, the receptor remains bound to G protein throughout the GTPase cycle and that GAP binds primarily during the GTP-bound phase. The analysis explains these behaviors and relates them to the specific regulatory phenomena described above. The work also demonstrates the applicability of appropriately data-constrained system-level analysis to signaling networks of this scale. Throughout the eukaryotes, G proteins convey information from receptors for diverse stimuli—neurotransmitters, hormones, light, odors, and pheromones—to intracellular regulatory proteins collectively known as effectors. G proteins function by transiting a dynamic cycle of activation and deactivation. Receptors accelerate activation, which allows G proteins to regulate effectors, and receptors thus increase signal output. GTPase-activating proteins, GAPs, accelerate deactivation. GAPs can thus attenuate signaling, but GAPs can also accelerate signal termination when stimulus is removed without inhibiting signal output while stimulus is present. Surprisingly, some effectors are also GAPs for the G proteins that activate them, essentially turning off their activator. We developed a mathematical model that describes control of G protein signaling by receptor and GAP and used experimental data to determine its important parameters. We show that GAPs actually potentiate G protein activation by receptor, a previously unsuspected effect. Further, GAPs indirectly stabilize receptor–G protein binding during stimulation, which we had previously predicted based on inconsistencies among other experimental results. The present results elucidate how GAPs can independently control signaling kinetics and amplitude and thus clarify how effectors can both respond to G proteins and act as G protein GAPs.
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Affiliation(s)
- Marc Turcotte
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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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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Hooks SB, Martemyanov K, Zachariou V. A role of RGS proteins in drug addiction. Biochem Pharmacol 2007; 75:76-84. [PMID: 17880927 DOI: 10.1016/j.bcp.2007.07.045] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2007] [Revised: 07/24/2007] [Accepted: 07/26/2007] [Indexed: 11/22/2022]
Abstract
The diverse family of Regulators of G protein signaling (RGS) proteins are widely distributed proteins with multiple functions, including GAP activity for heterotrimeric G protein alpha subunits. Three members of the RGS family, RGS9-2, RGS4 and RGSz, have been shown to play an essential modulatory role in psychostimulant and opiate drug actions. Interestingly, these proteins show distinct structure, distribution pattern and cellular localization. In addition, each of these proteins is differentially regulated by drugs of abuse in particular brain networks and appears to modulate distinct signal transduction events. The striatal enriched RGS9 plays a prominent role in opiate and psychostimulant drug reward; RGS4 appears to modulate opiate dependence via actions in the locus coeruleus, whereas RGSz modulates analgesia via activation of the PKC pathway.
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Affiliation(s)
- Shelley B Hooks
- University of Georgia, Department of Pharmaceutical and Biomedical Sciences, Athens, GA, USA
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Hao N, Behar M, Elston TC, Dohlman HG. Systems biology analysis of G protein and MAP kinase signaling in yeast. Oncogene 2007; 26:3254-66. [PMID: 17496920 DOI: 10.1038/sj.onc.1210416] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Approximately a third of all drugs act by binding directly to cell surface receptors coupled to G proteins. Other drugs act indirectly on these same pathways, for example, by inhibiting neurotransmitter reuptake or by blocking the inactivation of intracellular second messengers. These drugs have revolutionized the treatment of human disease. However, the complexity of G protein signaling mechanisms has significantly hampered our ability to identify additional new drug targets. Moreover, today's molecular pharmacologists are accustomed to working on narrowly focused problems centered on a single protein or enzymatic process. Here we describe emerging efforts in yeast aimed at identifying proteins and processes that modulate the function of receptors, G proteins and MAP kinase effectors. The scope of these efforts is far more systematic, comprehensive and quantitative than anything attempted previously, and includes integrated approaches in genetics, proteomics and computational biology.
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Affiliation(s)
- N Hao
- Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599-7365, USA
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Abstract
The majority of intracellular signalling cascades in higher eukaryotes are initiated by GPCRs (G-protein-coupled receptors). Hundreds of GPCRs signal through a handful of trimeric G-proteins, raising the issue of signal specificity. In the present paper, we illustrate a simple kinetic model of G-protein signalling. This model shows that stable production of significant amounts of free Galpha(GTP) (GTP-bound Galpha subunit) and betagamma is only one of multiple modes of behaviour of the G-protein system upon activation. Other modes, previously uncharacterized, are sustained production of betagamma without significant levels of Galpha(GTP) and transient production of Galpha(GTP) with sustained betagamma. The system can flip between different modes upon changes in conditions. This model demonstrates further that the negative feedback of receptor uncoupling or internalization, when combined with a positive feedback within the G-protein cycle, under a broad range of conditions results not in termination of the response but in relaxed oscillations in GPCR signalling. This variety of G-protein responses may serve to encode signal specificity in GPCR signal transduction.
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Affiliation(s)
- Vladimir L Katanaev
- University of Konstanz, Department of Biology, Universitätstrasse 10, Box M643, Konstanz 78457, Germany.
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Wang Y, Dohlman HG. Regulation of G protein and mitogen-activated protein kinase signaling by ubiquitination: insights from model organisms. Circ Res 2007; 99:1305-14. [PMID: 17158346 DOI: 10.1161/01.res.0000251641.57410.81] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Guanine nucleotide binding proteins (G proteins) and mitogen-activated protein kinases are highly conserved signaling molecules engaged in a wide variety of cellular processes. The strength and duration of signaling mediated by G proteins and mitogen-activated protein kinases are well known to be regulated via phosphorylation of pathway components. Over the past few years, it has become evident that many of the same signaling proteins also undergo ubiquitination, a posttranslational modification that typically leads to protein degradation. Consequently the strength and duration of signaling can also be modulated by regulating the abundance of signaling proteins. This article describes G protein- and mitogen-activated protein kinase-mediated signaling pathways that are known to be regulated by ubiquitination. The focus is on studies performed in the budding yeast Saccharomyces cerevisiae, as many principles governing this new regulatory mechanism were initially discovered in this model organism. Similar mechanisms uncovered in other model systems are also briefly discussed to illustrate the importance and universality of signaling regulation by ubiquitination.
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Affiliation(s)
- Yuqi Wang
- Department of Biology, Saint Louis University, 128 Macelwane Hall, 3507 Laclede Ave, St Louis, MO 63103, USA.
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Maurya M, Bornheimer S, Venkatasubramanian V, Subramaniam S. Reduced-order modelling of biochemical networks: application to the GTPase-cycle signalling module. ACTA ACUST UNITED AC 2006; 152:229-42. [PMID: 16986265 PMCID: PMC3417759 DOI: 10.1049/ip-syb:20050014] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Biochemical systems embed complex networks and hence development and analysis of their detailed models pose a challenge for computation. Coarse-grained biochemical models, called reduced-order models (ROMs), consisting of essential biochemical mechanisms are more useful for computational analysis and for studying important features of a biochemical network. The authors present a novel method to model-reduction by identifying potentially important parameters using multidimensional sensitivity analysis. A ROM is generated for the GTPase-cycle module of m1 muscarinic acetylcholine receptor, Gq, and regulator of G-protein signalling 4 (a GTPase-activating protein or GAP) starting from a detailed model of 48 reactions. The resulting ROM has only 17 reactions. The ROM suggested that complexes of G-protein coupled receptor (GPCR) and GAP--which were proposed in the detailed model as a hypothesis--are required to fit the experimental data. Models previously published in the literature are also simulated and compared with the ROM. Through this comparison, a minimal ROM, that also requires complexes of GPCR and GAP, with just 15 parameters is generated. The proposed reduced-order modelling methodology is scalable to larger networks and provides a general framework for the reduction of models of biochemical systems.
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Affiliation(s)
- M.R. Maurya
- San Diego Supercomputer Center, 9500 Gilman Drive MC 0505, La Jolla, CA 92093, USA
| | - S.J. Bornheimer
- Departments of Chemistry and Biochemistry and Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive La Jolla, CA 92093, USA
| | - V. Venkatasubramanian
- Laboratory for Intelligent Process Systems, School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA
| | - S. Subramaniam
- San Diego Supercomputer Center, 9500 Gilman Drive MC 0505, La Jolla, CA 92093, USA, the Departments of Chemistry and Biochemistry and Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive La Jolla, CA 92093, USA and the Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive La Jolla, CA 92093, USA
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Esch RK, Wang Y, Errede B. Pheromone-induced degradation of Ste12 contributes to signal attenuation and the specificity of developmental fate. EUKARYOTIC CELL 2006; 5:2147-60. [PMID: 17041188 PMCID: PMC1694826 DOI: 10.1128/ec.00270-06] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Ste12 transcription factor of Saccharomyces cerevisiae regulates transcription programs controlling two different developmental fates. One is differentiation into a mating-competent form that occurs in response to mating pheromone. The other is the transition to a filamentous-growth form that occurs in response to nutrient deprivation. These two distinct roles for Ste12 make it a focus for studies into regulatory mechanisms that impart biological specificity. The transient signal characteristic of mating differentiation led us to test the hypothesis that regulation of Ste12 turnover might contribute to attenuation of the mating-specific transcription program and restrict activation of the filamentation program. We show that prolonged pheromone induction leads to ubiquitin-mediated destabilization and decreased amounts of Ste12. This depletion in pheromone-stimulated cultures is dependent on the mating-pathway-dedicated mitogen-activated protein kinase Fus3 and its target Cdc28 inhibitor, Far1. Attenuation of pheromone-induced mating-specific gene transcription (FUS1) temporally correlates with Ste12 depletion. This attenuation is abrogated in the deletion backgrounds (fus3Delta or far1Delta) where Ste12 is found to persist. Additionally, pheromone induces haploid invasion and filamentous-like growth instead of mating differentiation when Ste12 levels remain high. These observations indicate that loss of Ste12 reinforces the adaptive response to pheromone and contributes to the curtailing of a filamentation response.
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Affiliation(s)
- R Keith Esch
- Department of Biochemistry and Biophysics, CB 7260 512 ME Jones, University of North Carolina, Chapel Hill, NC 27599-7260, USA
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Goryachev AB, Pokhilko AV. Computational model explains high activity and rapid cycling of Rho GTPases within protein complexes. PLoS Comput Biol 2006; 2:e172. [PMID: 17140284 PMCID: PMC1676031 DOI: 10.1371/journal.pcbi.0020172] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Accepted: 10/09/2006] [Indexed: 01/01/2023] Open
Abstract
Formation of multiprotein complexes on cellular membranes is critically dependent on the cyclic activation of small GTPases. FRAP-based analyses demonstrate that within protein complexes, some small GTPases cycle nearly three orders of magnitude faster than they would spontaneously cycle in vitro. At the same time, experiments report concomitant excess of the activated, GTP-bound form of GTPases over their inactive form. Intuitively, high activity and rapid turnover are contradictory requirements. How the cells manage to maximize both remains poorly understood. Here, using GTPases of the Rab and Rho families as a prototype, we introduce a computational model of the GTPase cycle. We quantitatively investigate several plausible layouts of the cycling control module that consist of GEFs, GAPs, and GTPase effectors. We explain the existing experimental data and predict how the cycling of GTPases is controlled by the regulatory proteins in vivo. Our model explains distinct and separable roles that the activating GEFs and deactivating GAPs play in the GTPase cycling control. While the activity of GTPase is mainly defined by GEF, the turnover rate is a sole function of GAP. Maximization of the GTPase activity and turnover rate places conflicting requirements on the concentration of GAP. Therefore, to achieve a high activity and turnover rate at once, cells must carefully maintain concentrations of GEFs and GAPs within the optimal range. The values of these optimal concentrations indicate that efficient cycling can be achieved only within dense protein complexes typically assembled on the membrane surfaces. We show that the concentration requirement for GEF can be dramatically reduced by a GEF-activating GTPase effector that can also significantly boost the cycling efficiency. Interestingly, we find that the cycling regimes are only weakly dependent on the concentration of GTPase itself. A large variety of cellular processes, such as the formation of filopodia or transport vesicles, require that large protein complexes are precisely positioned on intracellular membranes to execute a specific task and then are promptly disassembled to perform their function elsewhere. Small GTPases play a major role in the spatiotemporal control of these complexes. Their function is based on the unique property of cycling between the active GTP-bound state, in which they enable complex formation, and the inactive GDP-bound state, which promotes complex dissolution. Recent experiments based on fluorescence recovery after photobleaching have found that some small GTPases rapidly cycle within protein complexes, causing continuous release and recruitment of the complex components. The seemingly futile cycling is accompanied by a large excess of the active form. This puzzling behavior challenges one's intuition and calls for the application of quantitative methods. Here, Goryachev and Pokhilko use computational modeling to identify regulatory mechanisms that could enable GTPases to cycle with the experimentally observed frequency and efficiency. They show that to achieve high activity and turnover simultaneously, the concentrations of the regulatory molecules that control GTPase cycling should be tightly maintained within the optimal range.
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Shao D, Zheng W, Qiu W, Ouyang Q, Tang C. Dynamic studies of scaffold-dependent mating pathway in yeast. Biophys J 2006; 91:3986-4001. [PMID: 16980360 PMCID: PMC1635675 DOI: 10.1529/biophysj.106.081661] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mating pathway in Saccharomyces cerevisiae is one of the best understood signal transduction pathways in eukaryotes. It transmits the mating signal from plasma membrane into the nucleus through the G-protein coupled receptor and the mitogen-activated protein kinase (MAPK) cascade. According to current understanding of the mating pathway, we construct a system of ordinary differential equations to describe the process. Our model is consistent with a wide range of experiments, indicating that it captures some main characteristics of the signal transduction along the pathway. Investigation with the model reveals that the shuttling of the scaffold protein and the dephosphorylation of kinases involved in the MAPK cascade cooperate to regulate the response upon pheromone induction and to help preserve the fidelity of the mating signaling. We explored factors affecting the dose-response curves of this pathway and found that both negative feedback and concentrations of the proteins involved in the MAPK cascade play crucial roles. Contrary to some other MAPK systems where signaling sensitivity is being amplified successively along the cascade, here the mating signal is transmitted through the cascade in an almost linear fashion.
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Affiliation(s)
- Danying Shao
- Center for Theoretical Biology, Peking University, Beijing, China
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48
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Abstract
Regulator of G protein signalling (RGS) proteins are vital in the adaptation of cells to stimulation via G protein-coupled receptors. Yeast have been integral in elucidating the important role that RGS proteins play within cellular processes. In addition to extensive characterisation of the endogenous RGS proteins, these organisms have enabled the identification and analysis of numerous mammalian homologues. The simplicity and plasticity of the yeast pheromone-response pathway has facilitated studies which would have been impossible in mammalian systems and it is certain that yeast will continue to have a great impact on this field of research in the future.
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Affiliation(s)
- Claire Hill
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
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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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Wang X, Hao N, Dohlman HG, Elston TC. Bistability, stochasticity, and oscillations in the mitogen-activated protein kinase cascade. Biophys J 2006; 90:1961-78. [PMID: 16361346 PMCID: PMC1386776 DOI: 10.1529/biophysj.105.073874] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2005] [Accepted: 11/21/2005] [Indexed: 11/18/2022] Open
Abstract
Signaling pathways respond to stimuli in a variety of ways, depending on the magnitude of the input and the physiological status of the cell. For instance, yeast can respond to pheromone stimulation in either a binary or graded fashion. Here we present single cell transcription data indicating that a transient binary response in which all cells eventually become activated is typical. Stochastic modeling of the biochemical steps that regulate activation of the mitogen-activated protein kinase Fus3 reveals that this portion of the pathway can account for the graded-to-binary conversion. To test the validity of the model, genetic approaches are used to alter expression levels of Msg5 and Ste7, two of the proteins that negatively and positively regulate Fus3, respectively. Single cell measurements of the genetically altered cells are shown to be consistent with predictions of the model. Finally, computational modeling is used to investigate the effects of protein turnover on the response of the pathway. We demonstrate that the inclusion of protein turnover can lead to sustained oscillations of protein concentrations in the absence of feedback regulation. Thus, protein turnover can profoundly influence the output of a signaling pathway.
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Affiliation(s)
- Xiao Wang
- Department of Statistics and Operations Research, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7365, USA
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