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Altmaier S, Le Harzic R, Stracke F, Speicher AM, Uhl D, Ehrlich J, Gerlach T, Schmidt K, Lemmer K, Lautenschläger F, Böse H, Neubauer JC, Zimmermann H, Meiser I. Cytoskeleton adaptation to stretchable surface relaxation improves adherent cryopreservation of human mesenchymal stem cells. Cryobiology 2024; 117:104958. [PMID: 39243925 DOI: 10.1016/j.cryobiol.2024.104958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2024] [Revised: 07/29/2024] [Accepted: 08/22/2024] [Indexed: 09/09/2024]
Abstract
Adherent cell systems are usually dissociated before being cryopreserved, as standard protocols are established for cells in suspension. The application of standard procedures to more complex systems, sensitive to dissociation, such as adherent monolayers, especially comprising mature cell types or tissues remains unsatisfactory. Uncontrolled cell detachment due to intracellular tensile stress, membrane ruptures and damages of adhesion proteins are common during freezing and thawing of cell monolayers. However, many therapeutically relevant cell systems grow adherently to develop their native morphology and functionality, but lose their integrity after dissociation. The hypothesis is that cells on stretchable substrates have a more adaptable cytoskeleton and membrane, reducing cryopreservation-induced stress. Our studies investigate the influence of stretchable surfaces on the cryopreservation of adherent cells to avoid harmful dissociation and expedite post-thawing cultivation of functional cells. A stretching apparatus for defined radial stretching, consisting of silicone vessels and films with specific surface textures for cell culture, was developed. Adherent human umbilical cord mesenchymal stem cells (hUC-MSCs) were cultivated on a stretched silicone film within the vessel, forming a monolayer that was compressed by relaxation, while remaining attached to the relaxed film. Compressed hUC-MSCs, which were cryopreserved adherently showed higher viability and less detachment after thawing compared to control cells without compression. Within three to seven days post-thawing, the hUC-MSCs recovered, and the monolayer reformed. These experiments support the hypothesis that cryopreservation success of adherent cell systems is enhanced by improved adaptability of the cytoskeleton and cell membrane, opening up new approaches in cryobiotechnology.
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Affiliation(s)
- Saskia Altmaier
- Department of Molecular and Cellular Biotechnology, Saarland University, 66123, Saarbrücken, Germany; Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Ronan Le Harzic
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Frank Stracke
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Anna Martina Speicher
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Detlev Uhl
- Center Smart Materials and Adaptive Systems (CeSMA), Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082, Würzburg, Germany
| | - Johannes Ehrlich
- Center Smart Materials and Adaptive Systems (CeSMA), Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082, Würzburg, Germany
| | - Thomas Gerlach
- Center Smart Materials and Adaptive Systems (CeSMA), Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082, Würzburg, Germany
| | - Katharina Schmidt
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Katja Lemmer
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | | | - Holger Böse
- Center Smart Materials and Adaptive Systems (CeSMA), Fraunhofer Institute for Silicate Research ISC, Neunerplatz 2, 97082, Würzburg, Germany
| | - Julia C Neubauer
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany
| | - Heiko Zimmermann
- Department of Molecular and Cellular Biotechnology, Saarland University, 66123, Saarbrücken, Germany; Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany; Facultad de Ciencias del Mar, Universidad Católica del Norte, 1780000, Coquimbo, Chile
| | - Ina Meiser
- Department of Cryosensor Technology, Fraunhofer Institute for Biomedical Engineering (IBMT), Joseph-von-Fraunhofer-Weg 1, 66820, Sulzbach, Germany.
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Wang S, Zhang Y, Mandlaa, Sun Z, Chen Z. Properties and mechanism of the antimicrobial peptide APT produced by Lactobacillus ALAC-4. Lebensm Wiss Technol 2022. [DOI: 10.1016/j.lwt.2022.113713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Extracellular Signalling Modulates Scar/WAVE Complex Activity through Abi Phosphorylation. Cells 2021; 10:cells10123485. [PMID: 34943993 PMCID: PMC8700165 DOI: 10.3390/cells10123485] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 12/01/2021] [Accepted: 12/05/2021] [Indexed: 01/01/2023] Open
Abstract
The lamellipodia and pseudopodia of migrating cells are produced and maintained by the Scar/WAVE complex. Thus, actin-based cell migration is largely controlled through regulation of Scar/WAVE. Here, we report that the Abi subunit-but not Scar-is phosphorylated in response to extracellular signalling in Dictyostelium cells. Like Scar, Abi is phosphorylated after the complex has been activated, implying that Abi phosphorylation modulates pseudopodia, rather than causing new ones to be made. Consistent with this, Scar complex mutants that cannot bind Rac are also not phosphorylated. Several environmental cues also affect Abi phosphorylation-cell-substrate adhesion promotes it and increased extracellular osmolarity diminishes it. Both unphosphorylatable and phosphomimetic Abi efficiently rescue the chemotaxis of Abi KO cells and pseudopodia formation, confirming that Abi phosphorylation is not required for activation or inactivation of the Scar/WAVE complex. However, pseudopodia and Scar patches in the cells with unphosphorylatable Abi protrude for longer, altering pseudopod dynamics and cell speed. Dictyostelium, in which Scar and Abi are both unphosphorylatable, can still form pseudopods, but migrate substantially faster. We conclude that extracellular signals and environmental responses modulate cell migration by tuning the behaviour of the Scar/WAVE complex after it has been activated.
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Braun F, Recalde A, Bähre H, Seifert R, Albers SV. Putative Nucleotide-Based Second Messengers in the Archaeal Model Organisms Haloferax volcanii and Sulfolobus acidocaldarius. Front Microbiol 2021; 12:779012. [PMID: 34880846 PMCID: PMC8646023 DOI: 10.3389/fmicb.2021.779012] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 11/01/2021] [Indexed: 12/16/2022] Open
Abstract
Research on nucleotide-based second messengers began in 1956 with the discovery of cyclic adenosine monophosphate (3',5'-cAMP) by Earl Wilbur Sutherland and his co-workers. Since then, a broad variety of different signaling molecules composed of nucleotides has been discovered. These molecules fulfill crucial tasks in the context of intracellular signal transduction. The vast majority of the currently available knowledge about nucleotide-based second messengers originates from model organisms belonging either to the domain of eukaryotes or to the domain of bacteria, while the archaeal domain is significantly underrepresented in the field of nucleotide-based second messenger research. For several well-stablished eukaryotic and/or bacterial nucleotide-based second messengers, it is currently not clear whether these signaling molecules are present in archaea. In order to shed some light on this issue, this study analyzed cell extracts of two major archaeal model organisms, the euryarchaeon Haloferax volcanii and the crenarchaeon Sulfolobus acidocaldarius, using a modern mass spectrometry method to detect a broad variety of currently known nucleotide-based second messengers. The nucleotides 3',5'-cAMP, cyclic guanosine monophosphate (3',5'-cGMP), 5'-phosphoadenylyl-3',5'-adenosine (5'-pApA), diadenosine tetraphosphate (Ap4A) as well as the 2',3'-cyclic isomers of all four RNA building blocks (2',3'-cNMPs) were present in both species. In addition, H. volcanii cell extracts also contain cyclic cytosine monophosphate (3',5'-cCMP), cyclic uridine monophosphate (3',5'-cUMP) and cyclic diadenosine monophosphate (3',5'-c-di-AMP). The widely distributed bacterial second messengers cyclic diguanosine monophosphate (3',5'-c-di-GMP) and guanosine (penta-)/tetraphosphate [(p)ppGpp] could not be detected. In summary, this study gives a comprehensive overview on the presence of a large set of currently established or putative nucleotide-based second messengers in an eury- and a crenarchaeal model organism.
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Affiliation(s)
- Frank Braun
- Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Freiburg, Germany
| | - Alejandra Recalde
- Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Freiburg, Germany
| | - Heike Bähre
- Research Core Unit Metabolomics, Hannover Medical School, Hanover, Germany
| | - Roland Seifert
- Research Core Unit Metabolomics, Hannover Medical School, Hanover, Germany
| | - Sonja-Verena Albers
- Molecular Biology of Archaea, Institute of Biology, University of Freiburg, Freiburg, Germany
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O'Day DH, Mathavarajah S, Myre MA, Huber RJ. Calmodulin-mediated events during the life cycle of the amoebozoan Dictyostelium discoideum. Biol Rev Camb Philos Soc 2020; 95:472-490. [PMID: 31774219 PMCID: PMC7079120 DOI: 10.1111/brv.12573] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 10/30/2019] [Accepted: 11/11/2019] [Indexed: 12/14/2022]
Abstract
This review focusses on the functions of intracellular and extracellular calmodulin, its target proteins and their binding proteins during the asexual life cycle of Dictyostelium discoideum. Calmodulin is a primary regulatory protein of calcium signal transduction that functions throughout all stages. During growth, it mediates autophagy, the cell cycle, folic acid chemotaxis, phagocytosis, and other functions. During mitosis, specific calmodulin-binding proteins translocate to alternative locations. Translocation of at least one cell adhesion protein is calmodulin dependent. When starved, cells undergo calmodulin-dependent chemotaxis to cyclic AMP generating a multicellular pseudoplasmodium. Calmodulin-dependent signalling within the slug sets up a defined pattern and polarity that sets the stage for the final events of morphogenesis and cell differentiation. Transected slugs undergo calmodulin-dependent transdifferentiation to re-establish the disrupted pattern and polarity. Calmodulin function is critical for stalk cell differentiation but also functions in spore formation, events that begin in the pseudoplasmodium. The asexual life cycle restarts with the calmodulin-dependent germination of spores. Specific calmodulin-binding proteins as well as some of their binding partners have been linked to each of these events. The functions of extracellular calmodulin during growth and development are also discussed. This overview brings to the forefront the central role of calmodulin, working through its numerous binding proteins, as a primary downstream regulator of the critical calcium signalling pathways that have been well established in this model eukaryote. This is the first time the function of calmodulin and its target proteins have been documented through the complete life cycle of any eukaryote.
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Affiliation(s)
- Danton H. O'Day
- Cell and Systems BiologyUniversity of TorontoTorontoOntarioM5S 3G5Canada
- Department of BiologyUniversity of Toronto MississaugaMississaugaOntarioL5L 1C6Canada
| | | | - Michael A. Myre
- Department of Biological Sciences, Kennedy College of SciencesUniversity of Massachusetts LowellLowellMassachusetts01854USA
| | - Robert J. Huber
- Department of BiologyTrent UniversityPeterboroughOntarioK9L 0G2Canada
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Unfolding the Endoplasmic Reticulum of a Social Amoeba: Dictyostelium discoideum as a New Model for the Study of Endoplasmic Reticulum Stress. Cells 2018; 7:cells7060056. [PMID: 29890774 PMCID: PMC6025073 DOI: 10.3390/cells7060056] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 05/28/2018] [Accepted: 06/05/2018] [Indexed: 01/19/2023] Open
Abstract
The endoplasmic reticulum (ER) is a membranous network with an intricate dynamic architecture necessary for various essential cellular processes. Nearly one third of the proteins trafficking through the secretory pathway are folded and matured in the ER. Additionally, it acts as calcium storage, and it is a main source for lipid biosynthesis. The ER is highly connected with other organelles through regions of membrane apposition that allow organelle remodeling, as well as lipid and calcium traffic. Cells are under constant changes due to metabolic requirements and environmental conditions that challenge the ER network’s maintenance. The unfolded protein response (UPR) is a signaling pathway that restores homeostasis of this intracellular compartment upon ER stress conditions by reducing the load of proteins, and by increasing the processes of protein folding and degradation. Significant progress on the study of the mechanisms that restore ER homeostasis was achieved using model organisms such as yeast, Arabidopsis, and mammalian cells. In this review, we address the current knowledge on ER architecture and ER stress response in Dictyostelium discoideum. This social amoeba alternates between unicellular and multicellular phases and is recognized as a valuable biomedical model organism and an alternative to yeast, particularly for the presence of traits conserved in animal cells that were lost in fungi.
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Ren Y, West-Foyle H, Surcel A, Miller C, Robinson DN. Genetic suppression of a phosphomimic myosin II identifies system-level factors that promote myosin II cleavage furrow accumulation. Mol Biol Cell 2014; 25:4150-65. [PMID: 25318674 PMCID: PMC4263456 DOI: 10.1091/mbc.e14-08-1322] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
How myosin II localizes to the cleavage furrow in Dictyostelium and metazoan cells remains largely unknown despite significant advances in understanding its regulation. We designed a genetic selection using cDNA library suppression of 3xAsp myosin II to identify factors involved in myosin cleavage furrow accumulation. The 3xAsp mutant is deficient in bipolar thick filament assembly, fails to accumulate at the cleavage furrow, cannot rescue myoII-null cytokinesis, and has impaired mechanosensitive accumulation. Eleven genes suppressed this dominant cytokinesis deficiency when 3xAsp was expressed in wild-type cells. 3xAsp myosin II's localization to the cleavage furrow was rescued by constructs encoding rcdBB, mmsdh, RMD1, actin, one novel protein, and a 14-3-3 hairpin. Further characterization showed that RMD1 is required for myosin II cleavage furrow accumulation, acting in parallel with mechanical stress. Analysis of several mutant strains revealed that different thresholds of myosin II activity are required for daughter cell symmetry than for furrow ingression dynamics. Finally, an engineered myosin II with a longer lever arm (2xELC), producing a highly mechanosensitive motor, could also partially suppress the intragenic 3xAsp. Overall, myosin II accumulation is the result of multiple parallel and partially redundant pathways that comprise a cellular contractility control system.
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Affiliation(s)
- Yixin Ren
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Hoku West-Foyle
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Alexandra Surcel
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Christopher Miller
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205 Summer Academic Research Experience, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Douglas N Robinson
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205 Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205 Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD 21218
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8
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Araki T, Vu LH, Sasaki N, Kawata T, Eichinger L, Williams JG. Two Dictyostelium tyrosine kinase-like kinases function in parallel, stress-induced STAT activation pathways. Mol Biol Cell 2014; 25:3222-33. [PMID: 25143406 PMCID: PMC4196871 DOI: 10.1091/mbc.e14-07-1182] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/04/2014] [Accepted: 08/07/2014] [Indexed: 01/07/2023] Open
Abstract
When Dictyostelium cells are hyperosmotically stressed, STATc is activated by tyrosine phosphorylation. Unusually, activation is regulated by serine phosphorylation and consequent inhibition of a tyrosine phosphatase: PTP3. The identity of the cognate tyrosine kinase is unknown, and we show that two tyrosine kinase-like (TKL) enzymes, Pyk2 and Pyk3, share this function; thus, for stress-induced STATc activation, single null mutants are only marginally impaired, but the double mutant is nonactivatable. When cells are stressed, Pyk2 and Pyk3 undergo increased autocatalytic tyrosine phosphorylation. The site(s) that are generated bind the SH2 domain of STATc, and then STATc becomes the target of further kinase action. The signaling pathways that activate Pyk2 and Pyk3 are only partially overlapping, and there may be a structural basis for this difference because Pyk3 contains both a TKL domain and a pseudokinase domain. The latter functions, like the JH2 domain of metazoan JAKs, as a negative regulator of the kinase domain. The fact that two differently regulated kinases catalyze the same phosphorylation event may facilitate specific targeting because under stress, Pyk3 and Pyk2 accumulate in different parts of the cell; Pyk3 moves from the cytosol to the cortex, whereas Pyk2 accumulates in cytosolic granules that colocalize with PTP3.
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Affiliation(s)
- Tsuyoshi Araki
- College of Life Sciences, Welcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Linh Hai Vu
- Center for Biochemistry, Institute of Biochemistry I, 50931 Cologne, Germany
| | - Norimitsu Sasaki
- Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
| | - Takefumi Kawata
- Department of Biology, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
| | - Ludwig Eichinger
- Center for Biochemistry, Institute of Biochemistry I, 50931 Cologne, Germany
| | - Jeffrey G Williams
- College of Life Sciences, Welcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom
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Pfannes EKB, Anielski A, Gerhardt M, Beta C. Intracellular photoactivation of caged cGMP induces myosin II and actin responses in motile cells. Integr Biol (Camb) 2014; 5:1456-63. [PMID: 24136144 DOI: 10.1039/c3ib40109j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Cyclic GMP (cGMP) is a ubiquitous second messenger in eukaryotic cells. It is assumed to regulate the association of myosin II with the cytoskeleton of motile cells. When cells of the social amoeba Dictyostelium discoideum are exposed to chemoattractants or to increased osmotic stress, intracellular cGMP levels rise, preceding the accumulation of myosin II in the cell cortex. To directly investigate the impact of intracellular cGMP on cytoskeletal dynamics in a living cell, we released cGMP inside the cell by laser-induced photo-cleavage of a caged precursor. With this approach, we could directly show in a live cell experiment that an increase in intracellular cGMP indeed induces myosin II to accumulate in the cortex. Unexpectedly, we observed for the first time that also the amount of filamentous actin in the cell cortex increases upon a rise in the cGMP concentration, independently of cAMP receptor activation and signaling. We discuss our results in the light of recent work on the cGMP signaling pathway and suggest possible links between cGMP signaling and the actin system.
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Affiliation(s)
- Eva K B Pfannes
- Biological Physics, Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany.
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Habourdin C, Klein G, Araki T, Williams JG, Aubry L. The arrestin-domain containing protein AdcA is a response element to stress. Cell Commun Signal 2013; 11:91. [PMID: 24267687 PMCID: PMC3879092 DOI: 10.1186/1478-811x-11-91] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 11/06/2013] [Indexed: 01/01/2023] Open
Abstract
Background Cell behaviour is tightly determined by sensing and integration of extracellular changes through membrane detectors such as receptors and transporters and activation of downstream signalling cascades. Arrestin proteins act as scaffolds at the plasma membrane and along the endocytic pathway, where they regulate the activity and the fate of some of these detectors. Members of the arrestin clan are widely present from unicellular to metazoa, with roles in signal transduction and metabolism. As a soil amoeba, Dictyostelium is frequently confronted with environmental changes likely to compromise survival. Here, we investigated whether the recently described arrestin-related protein AdcA is part of the cell response to stresses. Results Our data provide evidence that AdcA responds to a variety of stresses including hyperosmolarity by a transient phosphorylation. Analysis in different mutant backgrounds revealed that AdcA phosphorylation involves pathways other than the DokA and cGMP-dependent osmostress pathways, respectively known to regulate PKA and STATc, key actors in the cellular response to conditions of hyperosmolarity. Interestingly, however, both AdcA and STATc are sensitive to changes in the F-actin polymerization status, suggesting a common primary sensor/trigger and linking the stress-sensitive kinase responsive for AdcA phosphorylation to the actin cytoskeleton. We also show that STATc-dependent transcriptional activity is involved for the timely dephosphorylation of AdcA in cells under stress. Conclusion Under osmotic stress, AdcA undergoes a phosphorylation-dephosphorylation cycle involving a stress-sensitive kinase and the transcription regulator STATc. This transient post-transcriptional modification may allow a regulation of AdcA function possibly to optimize the cellular stress response.
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Affiliation(s)
| | | | | | | | - Laurence Aubry
- CEA, iRTSV, Laboratoire Biologie à Grande Echelle, F-38054 Grenoble, France.
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11
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Ly DL, Waheed F, Lodyga M, Speight P, Masszi A, Nakano H, Hersom M, Pedersen SF, Szászi K, Kapus A. Hyperosmotic stress regulates the distribution and stability of myocardin-related transcription factor, a key modulator of the cytoskeleton. Am J Physiol Cell Physiol 2012; 304:C115-27. [PMID: 23054059 DOI: 10.1152/ajpcell.00290.2012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Hyperosmotic stress initiates several adaptive responses, including the remodeling of the cytoskeleton. Besides maintaining structural integrity, the cytoskeleton has emerged as an important regulator of gene transcription. Myocardin-related transcription factor (MRTF), an actin-regulated coactivator of serum response factor, is a major link between the actin skeleton and transcriptional control. We therefore investigated whether MRTF is regulated by hyperosmotic stress. Here we show that hypertonicity induces robust, rapid, and transient translocation of MRTF from the cytosol to the nucleus in kidney tubular cells. We found that the hyperosmolarity-triggered MRTF translocation is mediated by the RhoA/Rho kinase (ROK) pathway. Moreover, the Rho guanine nucleotide exchange factor GEF-H1 is activated by hyperosmotic stress, and it is a key contributor to the ensuing RhoA activation and MRTF translocation, since siRNA-mediated GEF-H1 downregulation suppresses these responses. While the osmotically induced RhoA activation promotes nuclear MRTF accumulation, the concomitant activation of p38 MAP kinase mitigates this effect. Moderate hyperosmotic stress (600 mosM) drives MRTF-dependent transcription through the cis-element CArG box. Silencing or pharmacological inhibition of MRTF prevents the osmotic stimulation of CArG-dependent transcription and renders the cells susceptible to osmotic shock-induced structural damage. Interestingly, strong hyperosmolarity promotes proteasomal degradation of MRTF, concomitant with apoptosis. Thus, MRTF is an osmosensitive and osmoprotective transcription factor, whose intracellular distribution is regulated by the GEF-H1/RhoA/ROK and p38 pathways. However, strong osmotic stress destabilizes MRTF, concomitant with apoptosis, implying that hyperosmotically induced cell death takes precedence over epithelial-myofibroblast transition, a potential consequence of MRTF-mediated phenotypic reprogramming.
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Affiliation(s)
- Donald L Ly
- Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael’s Hospital and Department of Surgery, University of Toronto, Ontario, Canada
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12
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Kuwayama H. Arachidonic acid enhances caffeine-induced cell death via caspase-independent cell death. Sci Rep 2012; 2:577. [PMID: 22896810 PMCID: PMC3419364 DOI: 10.1038/srep00577] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 07/30/2012] [Indexed: 01/05/2023] Open
Abstract
Caffeine is a globally consumed psychostimulant but can be fatal to cells at overdose exposures. Although caspase-dependent apoptosis plays a role in caffeine-induced cell death, the responsible intracellular signalling cascade remains incompletely understood. The cellular slime mould, Dictyostelium discoideum, does not possess caspase-dependent apoptotic machinery. Here, we observed that ablation of D. discoideumplaA, which encodes a phospholipase A2 (PLA₂) homolog, leads to a decreased rate of cell death under high caffeine concentrations and to enhanced cell death with the addition of arachidonic acid. Moreover, the inhibition of PLA₂ activity lead to a recovery of the survival rate in caspase-inhibited Hela cervical carcinoma cells under high caffeine concentrations, indicating that caffeine-induced cell death is enhanced via PLA₂-dependent signalling. Our results indicate that arachidonic acid may be a general second messenger that negatively regulates caffeine tolerance via a caspase-independent cell death cascade, which leads to multiple effects in eukaryotic cells.
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Affiliation(s)
- Hidekazu Kuwayama
- Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Tennodai 1-1-1, Ibaraki 305-8572, Japan.
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Kortholt A, van Egmond WN, Plak K, Bosgraaf L, Keizer-Gunnink I, van Haastert PJM. Multiple regulatory mechanisms for the Dictyostelium Roco protein GbpC. J Biol Chem 2011; 287:2749-58. [PMID: 22119747 DOI: 10.1074/jbc.m111.315739] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GbpC is a multidomain Roco protein in Dictyostelium, involved in transduction of intracellular cGMP that is produced by chemotactic signals. We have shown previously that cGMP binding to GbpC induces an intramolecular signaling cascade by activating subsequently the GEF, Ras, and kinase domains. In this study, we report on the cellular localization of GbpC. In resting cells, the protein is present in the cytoplasm, but GbpC rapidly translocates to the cell boundary upon stimulation with the chemoattractant cAMP. Also, during the formation of cell-cell streams and osmotic shock, the protein localizes toward the plasma membrane and actin cytoskeleton. The translocation upon cAMP stimulation occurs downstream of heterotrimeric G proteins but is independent of guanylyl cyclases and the previously identified cGMP-induced intramolecular signaling cascade in GbpC. Mutations in the GRAM domain of GbpC lead to disturbed membrane association and inactivation of GbpC function during chemotaxis in vivo. Furthermore, we show that the GRAM domain itself associates with cellular membranes and binds various phospholipids in vitro. Together, the results show that GbpC receives multiple input signals that are both required for functional activity in vivo. cAMP-stimulation induces a cGMP-dependent signaling cascade, leading to activation of kinase activity, and, independently, cAMP induces a GRAM-dependent translocation of GbpC toward the plasma membrane and cell cortex, where it may locally phosphorylate effector proteins, which are needed for proper biological activity.
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Affiliation(s)
- Arjan Kortholt
- Department of Cell Biochemistry, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
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Abstract
Signal transducers and activators of transcription (STAT) proteins are one of the important mediators of phosphotyrosine-regulated signaling in metazoan cells. These proteins are components of JAK/STAT signal transduction pathways, which regulate immune responses, cell fate, proliferation, cell migration, and programmed cell death in multicellular organisms. The cellular slime mould, Dictyostelium discoideum, is the simplest multicellular organism using molecules homologous to STATs, Dd-STATa-d. The Dd-STATa null mutant displays delayed aggregation, no phototaxis and fails culmination. Here, the functions of Dictyostelium STATs during development and their associated signaling molecules are discussed.
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Affiliation(s)
- Takefumi Kawata
- Department of Biology, Faculty of Science, Toho University, Funabashi 274-8510, Japan.
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15
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Pakes NK, Jayasinghe SN, Williams RSB. Bio-electrospraying and aerodynamically assisted bio-jetting the model eukaryotic Dictyostelium discoideum: assessing stress and developmental competency post treatment. J R Soc Interface 2011; 8:1185-91. [PMID: 21288957 PMCID: PMC3119884 DOI: 10.1098/rsif.2010.0696] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Bio-electrospraying (BES) and aerodynamically assisted bio-jetting (AABJ) have recently been established as important novel biospray technologies for directly manipulating living cells. To elucidate their potential in medical and clinical sciences, these bio-aerosol techniques have been subjected to increasingly rigorous investigations. In parallel to these studies, we wish to introduce these unique biotechnologies for use in the basic biological sciences, for handling a wide range of cell types and systems, thus increasing the range and the scope of these techniques for modern research. Here, the authors present the analysis of the new use of these biospray techniques for the direct handling of the simple eukaryotic biomedical model organism Dictyostelium discoideum. These cells are widely used as a model for immune cell chemotaxis and as a simple model for development. We demonstrate that AABJ of these cells did not cause cell stress, as defined by the stress-gene induction, nor affect cell development. Furthermore, although BES induced the increased expression of one stress-related gene (gapA), this was not a generalized stress response nor did it affect cell development. These data suggest that these biospray techniques can be used to directly manipulate single cells of this biomedical model without inducing a generalized stress response or perturbing later development.
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Affiliation(s)
- Nicholl K Pakes
- Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
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16
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Araki T, van Egmond WN, van Haastert PJM, Williams JG. Dual regulation of a Dictyostelium STAT by cGMP and Ca2+ signalling. J Cell Sci 2010; 123:837-41. [PMID: 20159963 DOI: 10.1242/jcs.064436] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When cells are exposed to hyperosmotic stress, the Dictyostelium STAT orthologue STATc is rapidly tyrosine phosphorylated. Previous observations suggest a non-paradigmatic mode of STAT activation, whereby stress-induced serine phosphorylation of the PTP3 protein tyrosine phosphatase inhibits its activity towards STATc. We show that two serine residues in PTP3, S448 and S747, are rapidly phosphorylated after osmotic stress. cGMP is a second messenger for hyperosmotic stress response and 8-bromo-cGMP, a membrane-permeable form of cGMP, is a known activator of STATc. GbpC, a cGMP-binding Ras guanine nucleotide exchange factor protein, is a founder member of a protein family that includes LRRK2, the gene commonly mutated in familial Parkinson's disease. Genetic ablation of gbpC prevents STATc activation by 8-bromo-cGMP. However, osmotic-stress-induced activation of STATc occurs normally in the gbpC null mutant. Moreover, 8-bromo-cGMP does not stimulate phosphorylation of S448 and S747 of PTP3 in a wild-type strain. These facts imply the occurrence of redundant activation pathways. We present evidence that intracellular Ca(2+) is a parallel second messenger, by showing that agents that elevate intracellular Ca(2+) levels are potent STATc activators that stimulate phosphorylation of S448 and S747. We propose that stress-induced cGMP signalling exerts its stimulatory effect by potentiating the activity of a semi-constitutive tyrosine kinase that phosphorylates STATc, whereas parallel, stress-induced Ca(2+) signalling represses STATc dephosphorylation through its inhibitory effect on PTP3.
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Affiliation(s)
- Tsuyoshi Araki
- University of Dundee, College of Life Sciences, Dow Street, Dundee DD1 5EH, UK
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17
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Betapudi V, Egelhoff TT. Roles of an unconventional protein kinase and myosin II in amoeba osmotic shock responses. Traffic 2009; 10:1773-84. [PMID: 19843280 DOI: 10.1111/j.1600-0854.2009.00992.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The contractile vacuole (CV) is a dynamic organelle that enables Dictyostelium amoeba and other protist to maintain osmotic homeostasis by expelling excess water. In the present study, we have uncovered a mechanism that coordinates the mechanics of the CV with myosin II, regulated by VwkA, an unconventional protein kinase that is conserved in an array of protozoa. Green fluorescent protein (GFP)-VwkA fusion proteins localize persistently to the CV during both filling and expulsion phases of water. In vwkA null cells, the established CV marker dajumin still localizes to the CV, but these structures are large, spherical and severely impaired for discharge. Furthermore, myosin II cortical localization and assembly are abnormal in vwkA null cells. Parallel analysis of wild-type cells treated with myosin II inhibitors or of myosin II null cells also results in enlarged CVs with impaired dynamics. We suggest that the myosin II cortical cytoskeleton, regulated by VwkA, serves a critical conserved role in the periodic contractions of the CV, as part of the osmotic protective mechanism of protozoa.
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Affiliation(s)
- Venkaiah Betapudi
- Department of Cell Biology, The Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
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18
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Thirone ACP, Speight P, Zulys M, Rotstein OD, Szászi K, Pedersen SF, Kapus A. Hyperosmotic stress induces Rho/Rho kinase/LIM kinase-mediated cofilin phosphorylation in tubular cells: key role in the osmotically triggered F-actin response. Am J Physiol Cell Physiol 2008; 296:C463-75. [PMID: 19109524 DOI: 10.1152/ajpcell.00467.2008] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Hyperosmotic stress induces cytoskeleton reorganization and a net increase in cellular F-actin, but the underlying mechanisms are incompletely understood. Whereas de novo F-actin polymerization likely contributes to the actin response, the role of F-actin severing is unknown. To address this problem, we investigated whether hyperosmolarity regulates cofilin, a key actin-severing protein, the activity of which is inhibited by phosphorylation. Since the small GTPases Rho and Rac are sensitive to cell volume changes and can regulate cofilin phosphorylation, we also asked whether they might link osmostress to cofilin. Here we show that hyperosmolarity induced rapid, sustained, and reversible phosphorylation of cofilin in kidney tubular (LLC-PK1 and Madin-Darby canine kidney) cells. Hyperosmolarity-provoked cofilin phosphorylation was mediated by the Rho/Rho kinase (ROCK)/LIM kinase (LIMK) but not the Rac/PAK/LIMK pathway, because 1) dominant negative (DN) Rho and DN-ROCK but not DN-Rac and DN-PAK inhibited cofilin phosphorylation; 2) constitutively active (CA) Rho and CA-ROCK but not CA-Rac and CA-PAK induced cofilin phosphorylation; 3) hyperosmolarity induced LIMK-2 phosphorylation, and 4) inhibition of ROCK by Y-27632 suppressed the hypertonicity-triggered LIMK-2 and cofilin phosphorylation.We thenexamined whether cofilin and its phosphorylation play a role in the hypertonicity-triggered F-actin changes. Downregulation of cofilin by small interfering RNA increased the resting F-actin level and eliminated any further rise upon hypertonic treatment. Inhibition of cofilin phosphorylation by Y-27632 prevented the hyperosmolarity-provoked F-actin increase. Taken together, cofilin is necessary for maintaining the osmotic responsiveness of the cytoskeleton in tubular cells, and the Rho/ROCK/LIMK-mediated cofilin phosphorylation is a key mechanism in the hyperosmotic stress-induced F-actin increase.
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Affiliation(s)
- Ana C P Thirone
- Keenan Research Centre in the Li Ka Shing Knowledge Institute of the St. Michael's Hospital, Toronto, ON, Canada
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19
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Visualizing myosin-actin interaction with a genetically-encoded fluorescent strain sensor. Proc Natl Acad Sci U S A 2008; 105:16882-7. [PMID: 18971336 DOI: 10.1073/pnas.0805513105] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many proteins have been shown to undergo conformational changes in response to externally applied force in vitro, but whether the force-induced protein conformational changes occur in vivo remains unclear. To reveal the force-induced conformational changes, or strains, within proteins in living cells, we have developed a genetically encoded fluorescent "strain sensor," by combining the proximity imaging (PRIM) technique, which uses spectral changes of 2 GFP molecules that are in direct contact, and myosin-actin as a model system. The developed PRIM-based strain sensor module (PriSSM) consists of the tandem fusion of a normal and circularly permuted GFP. To apply strain to PriSSM, it was inserted between 2 motor domains of Dictyostelium myosin II. In the absence of strain, the 2 GFP moieties in PriSSM are in contact, whereas when the motor domains are bound to F-actin, PriSSM has a strained conformation, leading to the loss of contact and a concomitant spectral change. Using the sensor system, we found that the position of the lever arm in the rigor state was affected by mutations within the motor domain. Moreover, the sensor was used to visualize the interaction between myosin II and F-actin in Dictyostelium cells. In normal cells, myosin was largely detached from F-actin, whereas ATP depletion or hyperosmotic stress increased the fraction of myosin bound to F-actin. The PRIM-based strain sensor may provide a general approach for studying force-induced protein conformational changes in cells.
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Calvo-Garrido J, Carilla-Latorre S, Lázaro-Diéguez F, Egea G, Escalante R. Vacuole membrane protein 1 is an endoplasmic reticulum protein required for organelle biogenesis, protein secretion, and development. Mol Biol Cell 2008; 19:3442-53. [PMID: 18550798 DOI: 10.1091/mbc.e08-01-0075] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Vacuole membrane protein 1 (Vmp1) is membrane protein of unknown molecular function that has been associated with pancreatitis and cancer. The social amoeba Dictyostelium discoideum has a vmp1-related gene that we identified previously in a functional genomic study. Loss-of-function of this gene leads to a severe phenotype that compromises Dictyostelium growth and development. The expression of mammalian Vmp1 in a vmp1(-) Dictyostelium mutant complemented the phenotype, suggesting a functional conservation of the protein among evolutionarily distant species and highlights Dictyostelium as a valid experimental system to address the function of this gene. Dictyostelium Vmp1 is an endoplasmic reticulum protein necessary for the integrity of this organelle. Cells deficient in Vmp1 display pleiotropic defects in the secretory pathway and organelle biogenesis. The contractile vacuole, which is necessary to survive under hypoosmotic conditions, is not functional in the mutant. The structure of the Golgi apparatus, the function of the endocytic pathway and conventional protein secretion are also affected in these cells. Transmission electron microscopy of vmp1(-) cells showed the accumulation of autophagic features that suggests a role of Vmp1 in macroautophagy. In addition to these defects observed at the vegetative stage, the onset of multicellular development and early developmental gene expression are also compromised.
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Affiliation(s)
- Javier Calvo-Garrido
- Instituto de Investigaciones Biomédicas Alberto Sols, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, 28029 Madrid, Spain
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21
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Ahsan N, Lee SH, Lee DG, Lee H, Lee SW, Bahk JD, Lee BH. Physiological and protein profiles alternation of germinating rice seedlings exposed to acute cadmium toxicity. C R Biol 2007; 330:735-46. [PMID: 17905393 DOI: 10.1016/j.crvi.2007.08.001] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 05/25/2007] [Accepted: 08/02/2007] [Indexed: 11/16/2022]
Abstract
Seed germination is a complex physiological process in plants that can be affected severely by heavy metals. The interference of germination by cadmium stress has not been well documented at the proteomic level. In the present study, in order to investigate the protein profile alternations during the germination stage following exposure to cadmium, a proteomic approach has been adopted in combination with morphological and physiological parameters. Seeds were exposed with a wide range of cadmium between 0.2 and 1.0 mM. Increases of cadmium concentration in the medium resulted in increased cadmium accumulation in seeds and TBARS content, whereas germination rate, shoot elongation, biomass, and water content were decreased significantly. Temporal changes of the total proteins were investigated by two-dimensional electrophoresis (2-DE). Twenty-one proteins were identified using MALDI-TOF mass spectrometry, which were upregulated at least 1.5-fold in response to cadmium stress. The identified proteins are involved in several processes, including defense and detoxification, antioxidant, protein biosynthesis, and germination processes. The identification of these proteins in the cadmium stress response provides new insight that can lead to a better understanding of the molecular basis of heavy metal responses of seeds at the germination stage.
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Affiliation(s)
- Nagib Ahsan
- Division of Applied Life Sciences (BK21 & EB-NCRC), Gyeongsang National University, Jinju 660-701, Republic of Korea
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22
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Dalous J, Burghardt E, Müller-Taubenberger A, Bruckert F, Gerisch G, Bretschneider T. Reversal of cell polarity and actin-myosin cytoskeleton reorganization under mechanical and chemical stimulation. Biophys J 2007; 94:1063-74. [PMID: 17905847 PMCID: PMC2186262 DOI: 10.1529/biophysj.107.114702] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
To study reorganization of the actin system in cells that invert their polarity, we stimulated Dictyostelium cells by mechanical forces from alternating directions. The cells oriented in a fluid flow by establishing a protruding front directed against the flow and a retracting tail. Labels for polymerized actin and filamentous myosin-II marked front and tail. At 2.1 Pa, actin first disassembled at the previous front before it began to polymerize at the newly induced front. In contrast, myosin-II slowly disappeared from the previous tail and continuously redistributed to the new tail. Front specification was myosin-II independent and accumulation of polymerized actin was even more focused in mutants lacking myosin-II heavy chains. We conclude that under mechanical stimulation, the inversion of cell polarity is initiated by a global internal signal that turns down actin polymerization in the entire cell. It is thought to be elicited at the most strongly stimulated site of the cell, the incipient front region, and to be counterbalanced by a slowly generated, short-range signal that locally activates actin polymerization at the front. Similar pattern of front and tail interconversion were observed in cells reorienting in strong gradients of the chemoattractant cyclic AMP.
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Affiliation(s)
- Jérémie Dalous
- CEA-Grenoble, Département Réponse et Dynamique Cellulaires, Laboratoire de Biochimie et Biophysique des Systèmes Intégrés, Grenoble, France
| | | | | | - Franz Bruckert
- CEA-Grenoble, Département Réponse et Dynamique Cellulaires, Laboratoire de Biochimie et Biophysique des Systèmes Intégrés, Grenoble, France
- Institut National Polytechnique de Grenoble, Laboratoire des Matériaux et du Génie Physique, Grenoble, France
| | | | - Till Bretschneider
- Max-Planck-Institut für Biochemie, Martinsried, Germany
- Address reprint requests to Till Bretschneider.
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STATc is a key regulator of the transcriptional response to hyperosmotic shock. BMC Genomics 2007; 8:123. [PMID: 17517120 PMCID: PMC1888708 DOI: 10.1186/1471-2164-8-123] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Accepted: 05/21/2007] [Indexed: 11/14/2022] Open
Abstract
Background Dictyostelium discoideum is frequently subjected to environmental changes in its natural habitat, the forest soil. In order to survive, the organism had to develop effective mechanisms to sense and respond to such changes. When cells are faced with a hypertonic environment a complex response is triggered. It starts with signal sensing and transduction and leads to changes in cell shape, the cytoskeleton, transport processes, metabolism and gene expression. Certain aspects of the Dictyostelium osmotic stress response have been elucidated, however, no comprehensive picture was available up to now. Results To better understand the D. discoideum response to hyperosmotic conditions, we performed gene expression profiling using DNA microarrays. The transcriptional profile of cells treated with 200 mM sorbitol during a 2-hour time course revealed a time-dependent induction or repression of 809 genes, more than 15% of the genes on the array, which peaked 45 to 60 minutes after the hyperosmotic shock. The differentially regulated genes were applied to cluster analysis and functional annotation using gene GO terms. Two main responses appear to be the down-regulation of the metabolic machinery and the up-regulation of the stress response system, including STATc. Further analysis of STATc revealed that it is a key regulator of the transcriptional response to hyperosmotic shock. Approximately 20% of the differentially regulated genes were dependent on the presence of STATc. Conclusion At least two signalling pathways are activated in Dictyostelium cells subjected to hypertonicity. STATc is responsible for the transcriptional changes of one of them.
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Bader S, Kortholt A, Van Haastert P. Seven Dictyostelium discoideum phosphodiesterases degrade three pools of cAMP and cGMP. Biochem J 2007; 402:153-61. [PMID: 17040207 PMCID: PMC1783984 DOI: 10.1042/bj20061153] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The Dictyostelium discoideum genome uncovers seven cyclic nucleotide PDEs (phosphodiesterases), of which six have been characterized previously and the seventh is characterized in the present paper. Three enzymes belong to the ubiquitous class I PDEs, common in all eukaryotes, whereas four enzymes belong to the rare class II PDEs that are present in bacteria and lower eukaryotes. Since all D. discoideum PDEs are now characterized we have calculated the contribution of each enzyme in the degradation of the three important pools of cyclic nucleotides: (i) extracellular cAMP that induces chemotaxis during aggregation and differentiation in slugs; (ii) intracellular cAMP that mediates development; and (iii) intracellular cGMP that mediates chemotaxis. It appears that each cyclic nucleotide pool is degraded by a combination of enzymes that have different affinities, allowing a broad range of substrate concentrations to be degraded with first-order kinetics. Extracellular cAMP is degraded predominantly by the class II high-affinity enzyme DdPDE1 and its close homologue DdPDE7, and in the multicellular stage also by the low-affinity transmembrane class I enzyme DdPDE4. Intracellular cAMP is degraded by the DdPDE2, a class I enzyme regulated by histidine kinase/phospho-relay, and by the cAMP-/cGMP-stimulated class II DdPDE6. Finally, basal intracellular cGMP is degraded predominantly by the high-affinity class I DdPDE3, while the elevated cGMP levels that arise after receptor stimulation are degraded predominantly by a cGMP-stimulated cGMP-specific class II DdPDE5. The analysis shows that the combination of enzymes is tuned to keep the concentration and lifetime of the substrate within a functional range.
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Affiliation(s)
- Sonya Bader
- Department of Molecular Cell Biology, University of Groningen, Kerklaan 30, 9751NN, Haren, The Netherlands
| | - Arjan Kortholt
- Department of Molecular Cell Biology, University of Groningen, Kerklaan 30, 9751NN, Haren, The Netherlands
| | - Peter J. M. Van Haastert
- Department of Molecular Cell Biology, University of Groningen, Kerklaan 30, 9751NN, Haren, The Netherlands
- To whom correspondence should be addressed (email )
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Muramoto T, Kuwayama H, Kobayashi K, Urushihara H. A stress response kinase, KrsA, controls cAMP relay during the early development of Dictyostelium discoideum. Dev Biol 2007; 305:77-89. [PMID: 17362909 DOI: 10.1016/j.ydbio.2007.01.039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Revised: 01/29/2007] [Accepted: 01/31/2007] [Indexed: 11/19/2022]
Abstract
Solitary amoebae of Dictyostelium discoideum are frequently exposed to stressful conditions in nature, and their multicellular development is one response to environmental stress. Here we analyzed an aggregation stage abundant gene, krsA, homologous to human krs1 (kinase responsive to stress 1) to understand the mechanisms for the initiation of development and cell fate determination. The krsA- cells exhibited reduced viability under hyperosmotic conditions. They produced smaller aggregates on membrane filters and did not form aggregation streams on a plastic surface under submerged starvation conditions, but were normal in sexual development. During early asexual development, the expression of cAMP-related genes peaked earlier in the knockout mutants. Neither cAMP oscillation in starved cells nor an increase in the cAMP level following osmotic stress was observed in krsA-. The nuclear export signal, as well as the kinase domain, in KrsA was necessary for stream formation. These results strongly suggest that krsA is involved in cAMP relay, and that signaling pathways for multicellular development have evolved in unison with the stress response.
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Affiliation(s)
- Tetsuya Muramoto
- Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8572, Japan
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26
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Hoffmann EK, Pedersen SF. Shrinkage insensitivity of NKCC1 in myosin II-depleted cytoplasts from Ehrlich ascites tumor cells. Am J Physiol Cell Physiol 2007; 292:C1854-66. [PMID: 17229812 DOI: 10.1152/ajpcell.00474.2006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Protein phosphorylation/dephosphorylation and cytoskeletal reorganization regulate the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) during osmotic shrinkage; however, the mechanisms involved are unclear. We show that in cytoplasts, plasma membrane vesicles detached from Ehrlich ascites tumor cells (EATC) by cytochalasin treatment, NKCC1 activity evaluated as bumetanide-sensitive (86)Rb influx was increased compared with the basal level in intact cells yet could not be further increased by osmotic shrinkage. Accordingly, cytoplasts exhibited no regulatory volume increase after shrinkage. In cytoplasts, cortical F-actin organization was disrupted, and myosin II, which in shrunken EATC translocates to the cortical region, was absent. Moreover, NKCC1 activity was essentially insensitive to the myosin light chain kinase (MLCK) inhibitor ML-7, a potent blocker of shrinkage-induced NKCC1 activity in intact EATC. Cytoplast NKCC1 activity was potentiated by the Ser/Thr protein phosphatase inhibitor calyculin A, partially inhibited by the protein kinase A inhibitor H89, and blocked by the broad protein kinase inhibitor staurosporine. Cytoplasts exhibited increased protein levels of NKCC1, Ste20-related proline- and alanine-rich kinase (SPAK), and oxidative stress response kinase 1, yet they lacked the shrinkage-induced plasma membrane translocation of SPAK observed in intact cells. The basal phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was increased in cytoplasts compared with intact cells, yet in contrast to the substantial activation in shrunken intact cells, p38 MAPK could not be further activated by shrinkage of the cytoplasts. Together these findings indicate that shrinkage activation of NKCC1 in EATC is dependent on the cortical F-actin network, myosin II, and MLCK.
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Affiliation(s)
- Else K Hoffmann
- Department of Molecular Biology, University of Copenhagen, 13 Universitetsparken, Dk-2100 Copenhagen, Denmark.
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27
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Etzrodt M, Ishikawa HCF, Dalous J, Müller-Taubenberger A, Bretschneider T, Gerisch G. Time-resolved responses to chemoattractant, characteristic of the front and tail of Dictyostelium cells. FEBS Lett 2006; 580:6707-13. [PMID: 17126332 DOI: 10.1016/j.febslet.2006.11.031] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2006] [Revised: 11/06/2006] [Accepted: 11/13/2006] [Indexed: 11/26/2022]
Abstract
In a gradient of chemoattractant, Dictyostelium cells are orientated with their front directed toward the source and their tail pointing into the opposite direction. The front region is specified by the polymerization of actin and the tail by the recruitment of filamentous myosin-II. We have dissected these front and tail responses by exposing cells to an upshift of cyclic AMP. A sharp rise and fall of polymerized actin within 10s is accompanied by the recruitment of proteins involved in turning actin polymerization on or off. The cortical accumulation of myosin-II starts when the front response has declined, supporting the concept of divergent signal transmission and adaptation pathways.
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Affiliation(s)
- Martin Etzrodt
- Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany
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28
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Di Ciano-Oliveira C, Thirone ACP, Szászi K, Kapus A. Osmotic stress and the cytoskeleton: the R(h)ole of Rho GTPases. Acta Physiol (Oxf) 2006; 187:257-72. [PMID: 16734763 DOI: 10.1111/j.1748-1716.2006.01535.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Hyperosmotic stress initiates a variety of compensatory and adaptive responses, which either serve to restore near-normal volume or remodel and reinforce the cell structure to withstand the physical challenge. The latter response is brought about by the reorganization of the cytoskeleton; however, the underlying mechanisms are not well understood. Recent research has provided major breakthroughs in our knowledge about the link between message and structure, i.e. between signalling and cytoskeletal remodelling, predominantly in the context of cell migration. The major components of this progress are the in-depth characterization of Rho family small GTPases, master regulators of the cytoskeleton, and the discovery of the actin-related protein 2/3 complex, a signalling-sensitive structural element of the actin polymerization machinery. The primary aim of this review is to find the place of these novel and crucial players in osmotically induced (volume-dependent) remodelling of the cytoskeleton. We aim to address three questions: (1) What are the major structural changes in the cytoskeleton under hyperosmotic conditions? (2) Are the Rho family small GTPases (Rho, Rac and Cdc42) regulated by osmotic stress, and if so, by what mechanisms? (3) Are Rho GTPases involved, as mediators, in major adaptive responses, including cytoskeleton rearrangement, changes in ion transport and genetic reprogramming? Our answers will show how fragmentary our current knowledge is in these areas. Therefore, this overview has been written with the hardly disguised intention that it might foster further research in this field by highlighting some intriguing questions.
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Affiliation(s)
- C Di Ciano-Oliveira
- The St Michael's Hospital Research Institute, Department of Surgery, University of Toronto, Toronto, ON, Canada
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29
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Pikzack C, Prassler J, Furukawa R, Fechheimer M, Rivero F. Role of calcium-dependent actin-bundling proteins: characterization of Dictyostelium mutants lacking fimbrin and the 34-kilodalton protein. ACTA ACUST UNITED AC 2006; 62:210-31. [PMID: 16265631 DOI: 10.1002/cm.20098] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Actin-bundling proteins organize actin filaments into densely packed bundles. In Dictyostelium discoideum two abundant proteins display calcium-regulated bundling activity, fimbrin and the 34-kDa protein (ABP34). Using a GFP fusion we observed transient localization of fimbrin at the phagocytic cup and macropinosomes. The distribution of truncated constructs encompassing the EF hands and the first actin-binding domain (EA1) or both actin-binding domains devoid of EF hands (A1A2) was indistinguishable from that of the full length protein. The role of fimbrin and a possible functional overlap with ABP34 was investigated in fim- and double 34-/fim- mutants. Except for a moderate cell size defect, fim- mutants did not show defects in growth, endocytosis, exocytosis, and chemotaxis. Double mutants were characterized by a small cell size and a defect in morphogenesis resulting in small fruiting bodies and a low spore yield. The cell size defect could not be overcome by expression of fimbrin fragments EA1 or A1A2, suggesting that both bundling activity and regulation by calcium are important. Induction of filopod formation in 34-/fim- cells was not impaired, indicating that both proteins are dispensable for this process. We searched in the Dictyostelium genome database for fimbrin-like proteins that could compensate for the fimbrin defect and identified three unconventional fimbrins and two more proteins with actin-binding domains of the type present in fimbrins.
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Affiliation(s)
- Claudia Pikzack
- Zentrum für Biochemie, Medizinische Fakultät, Universität zu Köln, Köln, Germany
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Yamada Y, Sameshima M. Cell shape regulation and co-translocation of actin and adenosyl homocysteinase in response to intermediate hypertonicity. FEMS Microbiol Lett 2004. [DOI: 10.1111/j.1574-6968.2004.tb09784.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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31
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Sun B, Ma H, Firtel RA. Dictyostelium stress-activated protein kinase alpha, a novel stress-activated mitogen-activated protein kinase kinase kinase-like kinase, is important for the proper regulation of the cytoskeleton. Mol Biol Cell 2004; 14:4526-40. [PMID: 14593072 PMCID: PMC266770 DOI: 10.1091/mbc.e03-01-0039] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Mitogen-activated protein kinase cascades regulate various cellular functions, including growth, cell differentiation, development, and stress responses. We have identified a new Dictyostelium kinase (stress-activated protein kinase [SAPK]alpha), which is related to members of the mixed lineage kinase class of mitogen-activated protein kinase kinases. SAPKalpha is activated by osmotic stress, heat shock, and detachment from the substratum and by a membrane-permeable cGMP analog, a known regulator of stress responses in Dictyostelium. SAPKalpha is important for cellular resistance to stresses, because SAPKalpha null cells exhibit reduced viability in response to osmotic stress. We found that SAPKalpha mutants affect cellular processes requiring proper regulation of the actin cytoskeleton, including cell motility, morphogenesis, cytokinesis, and cell adhesion. Overexpression of SAPKalpha results in highly elevated basal and chemoattractant-stimulated F-actin levels and strong aggregation and developmental defects, including a failure to polarize and chemotax, and abnormal morphogenesis. These phenotypes require a kinase-active SAPKalpha. SAPKalpha null cells exhibit reduced chemoattractant-stimulated F-actin levels, cytokinesis, developmental and adhesion defects, and a motility defect that is less severe than that exhibited by SAPKalpha-overexpressing cells. SAPKalpha colocalizes with F-actin in F-actin-enriched structures, including membrane ruffles and pseudopodia during chemotaxis. Although SAPKalpha is required for these F-actin-mediated processes, it is not detectably activated in response to chemoattractant stimulation.
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Affiliation(s)
- Binggang Sun
- Section of Cell and Developmental Biology, Division of Biological Sciences and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0634, USA
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De la Roche MA, Smith JL, Betapudi V, Egelhoff TT, Côté GP. Signaling pathways regulating Dictyostelium myosin II. J Muscle Res Cell Motil 2003; 23:703-18. [PMID: 12952069 DOI: 10.1023/a:1024467426244] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Dictyostelium myosin II is a conventional, two-headed myosin that consists of two copies each of a myosin heavy chain (MHC), an essential light chain (ELC) and a regulatory light chain (RLC). The MHC is comprised of an amino-terminal motor domain, a neck region that binds the RLC and ELC and a carboxyl-terminal alpha-helical coiled-coil tail. Electrostatic interactions between the tail domains mediate the self-assembly of myosin II into bipolar filaments that are capable of interacting with actin filaments to generate a contractile force. In this review we discuss the regulation of Dictyostelium myosin II by a myosin light chain kinase (MLCK-A) that phosphorylates the RLC and increases motor activity and by MHC kinases (MHCKs) that phosphorylate the tail and prevent filament assembly. Dictyostelium may express as many as four MHCKs (MHCK A-D) consisting of an atypical alpha-kinase catalytic domain and a carboxyl-terminal WD repeat domain that targets myosin II filaments. A previously reported MHCK, termed MHC-PKC, now seems more likely to be a diacylglycerol kinase (DgkA). The relationship of the MHCKs to the larger family of alpha-kinases is discussed and key features of the structure of the alpha-kinase catalytic domain are reviewed. Potential upstream regulators of myosin II are described, including DgkA, cGMP, cAMP and PAKa, a target for Rac GTPases. Recent results point to a complex network of signaling pathways responsible for controling the activity and localization of myosin II in the cell.
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Affiliation(s)
- Marc A De la Roche
- Department of Biochemistry, Botterell Hall, Queen's University, Kingston, Ontario, Canada K7L 3N6
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33
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Ehrenman K, Yang G, Hong WP, Gao T, Jang W, Brock DA, Hatton RD, Shoemaker JD, Gomer RH. Disruption of aldehyde reductase increases group size in dictyostelium. J Biol Chem 2003; 279:837-47. [PMID: 14551196 DOI: 10.1074/jbc.m310539200] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Developing Dictyostelium cells form structures containing approximately 20,000 cells. The size regulation mechanism involves a secreted counting factor (CF) repressing cytosolic glucose levels. Glucose or a glucose metabolite affects cell-cell adhesion and motility; these in turn affect whether a group stays together, loses cells, or even breaks up. NADPH-coupled aldehyde reductase reduces a wide variety of aldehydes to the corresponding alcohols, including converting glucose to sorbitol. The levels of this enzyme previously appeared to be regulated by CF. We find that disrupting alrA, the gene encoding aldehyde reductase, results in the loss of alrA mRNA and AlrA protein and a decrease in the ability of cell lysates to reduce both glyceraldehyde and glucose in an NADPH-coupled reaction. Counterintuitively, alrA- cells grow normally and have decreased glucose levels compared with parental cells. The alrA- cells form long unbroken streams and huge groups. Expression of AlrA in alrA- cells causes cells to form normal fruiting bodies, indicating that AlrA affects group size. alrA- cells have normal adhesion but a reduced motility, and computer simulations suggest that this could indeed result in the formation of large groups. alrA- cells secrete low levels of countin and CF50, two components of CF, and this could partially account for why alrA- cells form large groups. alrA- cells are responsive to CF and are partially responsive to recombinant countin and CF50, suggesting that disrupting alrA inhibits but does not completely block the CF signal transduction pathway. Gas chromatography/mass spectroscopy indicates that the concentrations of several metabolites are altered in alrA- cells, suggesting that the Dictyostelium aldehyde reductase affects several metabolic pathways in addition to converting glucose to sorbitol. Together, our data suggest that disrupting alrA affects CF secretion, causes many effects on cellular metabolism, and has a major effect on group size.
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Affiliation(s)
- Karen Ehrenman
- Howard Hughes Medical Institute and Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA
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Yumura S, Uyeda TQP. Myosins and cell dynamics in cellular slime molds. INTERNATIONAL REVIEW OF CYTOLOGY 2003; 224:173-225. [PMID: 12722951 DOI: 10.1016/s0074-7696(05)24005-6] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Myosin is a mechanochemical transducer and serves as a motor for various motile activities such as cell migration, cytokinesis, maintenance of cell shape, phagocytosis, and morphogenesis. Nonmuscle myosin in vivo does not either stay static at specific subcellular regions or construct highly organized structures, such as sarcomere in skeletal muscle cells. The cellular slime mold Dictyostelium discoideum is an ideal "model organism" for the investigation of cell movement and cytokinesis. The advantages of this organism prompted researchers to carry out pioneering cell biological, biochemical, and molecular genetic studies on myosin II, which resulted in elucidation of many fundamental features of function and regulation of this most abundant molecular motor. Furthermore, recent molecular biological research has revealed that many unconventional myosins play various functions in vivo. In this article, how myosins are organized and regulated in a dynamic manner in Dictyostelium cells is reviewed and discussed.
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Affiliation(s)
- Shigehiko Yumura
- Department of Biology, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan
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Eggermont J. Rho's role in cell volume: sensing, strutting, or signaling? Focus on "Hyperosmotic stress activates Rho: differential involvement in Rho kinase-dependent MLC phosphorylation and NKCC activation". Am J Physiol Cell Physiol 2003; 285:C509-11. [PMID: 12900385 DOI: 10.1152/ajpcell.00214.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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36
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Araki T, Tsujioka M, Abe T, Fukuzawa M, Meima M, Schaap P, Morio T, Urushihara H, Katoh M, Maeda M, Tanaka Y, Takeuchi I, Williams JG. A STAT-regulated, stress-induced signalling pathway in Dictyostelium. J Cell Sci 2003; 116:2907-15. [PMID: 12771188 DOI: 10.1242/jcs.00501] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Dictyostelium stalk cell inducer differentiation-inducing factor (DIF) directs tyrosine phosphorylation and nuclear accumulation of the STAT (signal transducer and activator of transcription) protein Dd-STATc. We show that hyperosmotic stress, heat shock and oxidative stress also activate Dd-STATc. Hyperosmotic stress is known to elevate intracellular cGMP and cAMP levels, and the membrane-permeant analogue 8-bromo-cGMP rapidly activates Dd-STATc, whereas 8-bromo-cAMP is a much less effective inducer. Surprisingly, however, Dd-STATc remains stress activatable in null mutants for components of the known cGMP-mediated and cAMP-mediated stress-response pathways and in a double mutant affecting both pathways. Also, Dd-STATc null cells are not abnormally sensitive to hyperosmotic stress. Microarray analysis identified two genes, gapA and rtoA, that are induced by hyperosmotic stress. Osmotic stress induction of gapA and rtoA is entirely dependent on Dd-STATc. Neither gene is inducible by DIF but both are rapidly inducible with 8-bromo-cGMP. Again, 8-bromo-cAMP is a much less potent inducer than 8-bromo-cGMP. These data show that Dd-STATc functions as a transcriptional activator in a stress-response pathway and the pharmacological evidence, at least, is consistent with cGMP acting as a second messenger.
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Affiliation(s)
- Tsuyoshi Araki
- School of Life Sciences, University of Dundee, Wellcome Trust Biocentre, Dow Street, Dundee, DD1 5EH, UK
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37
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Schreiner T, Mohrs MR, Blau-Wasser R, von Krempelhuber A, Steinert M, Schleicher M, Noegel AA. Loss of the F-actin binding and vesicle-associated protein comitin leads to a phagocytosis defect. EUKARYOTIC CELL 2002; 1:906-14. [PMID: 12477791 PMCID: PMC138752 DOI: 10.1128/ec.1.6.906-914.2002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Comitin is an F-actin binding and membrane-associated protein from Dictyostelium discoideum, which is present on Golgi and vesicle membranes and changes its localization in response to agents affecting the cytoskeleton. To investigate its in vivo functions we have generated knockout mutants by gene replacement. Based on comitin's in vitro functions we examined properties related to vesicular transport and microfilament function. Whereas cell growth, pinocytosis, secretion, chemotaxis, motility, and development were unaltered, comitin-lacking cells were impaired in the early steps of phagocytosis of Saccharomyces cerevisiae particles and of Escherichia coli, whereas uptake of latex beads was unaffected. Furthermore, the lack of comitin positively affected survival of pathogenic bacteria. Mutant cells also showed an altered response to hyperosmotic shock in comparison to the wild type. The redistribution of comitin during hyperosmotic shock in wild-type cells and its presence on early phagosomes suggest a direct involvement of comitin in these processes.
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Affiliation(s)
- Thomas Schreiner
- Center for Biochemistry, Medical Faculty, University of Cologne, 50931 Cologne, Germany
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38
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Bosgraaf L, Russcher H, Snippe H, Bader S, Wind J, Van Haastert PJM. Identification and characterization of two unusual cGMP-stimulated phoshodiesterases in dictyostelium. Mol Biol Cell 2002; 13:3878-89. [PMID: 12429832 PMCID: PMC133600 DOI: 10.1091/mbc.e02-05-0302] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Recently, we recognized two genes, gbpA and gbpB, encoding putative cGMP-binding proteins with a Zn(2+)-hydrolase domain and two cyclic nucleotide binding domains. The Zn(2+)-hydrolase domains belong to the superfamily of beta-lactamases, also harboring a small family of class II phosphodiesterases from bacteria and lower eukaryotes. Gene inactivation and overexpression studies demonstrate that gbpA encodes the cGMP-stimulated cGMP-phosphodiesterase that was characterized biochemically previously and was shown to be involved in chemotaxis. cAMP neither activates nor is a substrate of GbpA. The gbpB gene is expressed mainly in the multicellular stage and seems to encode a dual specificity phosphodiesterase with preference for cAMP. The enzyme hydrolyses cAMP approximately 9-fold faster than cGMP and is activated by cAMP and cGMP with a K(A) value of approximately 0.7 and 2.3 microM, respectively. Cells with a deletion of the gbpB gene have increased basal and receptor stimulated cAMP levels and are sporogeneous. We propose that GbpA and GbpB hydrolyze the substrate in the Zn(2+)-hydrolase domain, whereas the cyclic nucleotide binding domains mediate activation. The human cGMP-stimulated cAMP/cGMP phosphodiesterase has similar biochemical properties, but a completely different topology: hydrolysis takes place by a class I catalytic domain and GAF domains mediate cGMP activation.
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Affiliation(s)
- Leonard Bosgraaf
- Department of Biochemistry, University of Groningen, 9747 AG Groningen, The Netherlands
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39
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Khurana B, Khurana T, Khaire N, Noegel AA. Functions of LIM proteins in cell polarity and chemotactic motility. EMBO J 2002; 21:5331-42. [PMID: 12374734 PMCID: PMC129082 DOI: 10.1093/emboj/cdf550] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
LimC and LimD are two novel LIM proteins of Dictyostelium, which are comprised of double and single LIM domains, respectively. Green fluorescent protein-fused LimC and LimD proteins preferentially accumulate at areas of the cell cortex where they co-localize with actin and associate transiently with cytoskeleton-dependent dynamic structures like phagosomes, macropinosomes and pseudopods. Furthermore, both LimC and LimD interact directly with F-actin in vitro. Mutant cells that lack either LimC or LimD, or both, exhibit normal growth. They are, however, significantly impaired in growth under stress conditions and are highly sensitive to osmotic shock, suggesting that LimC and LimD contribute towards the maintenance of cortical strength. Moreover, we noted an altered morphology and F-actin distribution in LimD(-) and LimC(-)/D(-) mutants, and changes in chemotactic motility associated with an increased pseudopod formation. Our results reveal both unique and overlapping roles for LimC and LimD, and suggest that both act directly on the actin cytoskeleton and provide rigidity to the cortex.
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Affiliation(s)
- Bharat Khurana
- Center for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Cologne, Germany
Present address: Laboratory of Viral Diseases, Building 4, Room 131, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health, Bethesda, MD 20892-8028, USA Present address: Laboratory of Cellular and Developmental Biology, Building 50, Room 3345, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health, Bethesda, MD 20892-8028, USA Corresponding author e-mail: B.Khurana and T.Khurana contributed equally to this work
| | - Taruna Khurana
- Center for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Cologne, Germany
Present address: Laboratory of Viral Diseases, Building 4, Room 131, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health, Bethesda, MD 20892-8028, USA Present address: Laboratory of Cellular and Developmental Biology, Building 50, Room 3345, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health, Bethesda, MD 20892-8028, USA Corresponding author e-mail: B.Khurana and T.Khurana contributed equally to this work
| | | | - Angelika A. Noegel
- Center for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Cologne, Germany
Present address: Laboratory of Viral Diseases, Building 4, Room 131, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health, Bethesda, MD 20892-8028, USA Present address: Laboratory of Cellular and Developmental Biology, Building 50, Room 3345, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health, Bethesda, MD 20892-8028, USA Corresponding author e-mail: B.Khurana and T.Khurana contributed equally to this work
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Kang R, Kae H, Ip H, Spiegelman GB, Weeks G. Evidence for a role for the Dictyostelium Rap1 in cell viability and the response to osmotic stress. J Cell Sci 2002; 115:3675-82. [PMID: 12186953 DOI: 10.1242/jcs.00039] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Dictyostelium genome contains a single rapA gene, which encodes a Rap1 monomeric G protein. As attempts at generating rapA-null Dictyostelium cells had been unsuccessful, expression of antisense RNA from the rapA gene under control of the folate repressible discoidin promoter was used to reduce cellular levels of the Rap1 protein. As Rap1 levels gradually decreased following antisense rapA RNA induction, growth rate and cell viability also decreased, a result consistent with the idea that rapA is an essential gene. The Rap1-depleted cells exhibited reduced viability in response to osmotic shock. The accumulation of cGMP in response to 0.4 M sorbitol was reduced after rapA antisense RNA induction and was enhanced in cells expressing the constitutively activated Rap1(G12V) protein, suggesting a role for Rap1 in the generation of cGMP. Dictyostelium Rap1 formed a complex with the Ras-binding domain of RalGDS only when it was in a GTP-bound state. This assay was used to demonstrate that activation of Rap1 in response to 0.4 M sorbitol occurred with initial kinetics similar to those observed for the accumulation of cGMP. Furthermore, the addition of 2 mM EDTA to osmotically shocked cells, a treatment that enhances cGMP accumulation, also enhanced Rap1 activation. These results suggest a direct role for Rap1 in the activation of guanylyl cyclase during the response to hyperosmotic conditions. Rap1 was also activated in response to low temperature but not in response to low osmolarity or high temperature.
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Affiliation(s)
- Rujun Kang
- Department of Microbiology and Immunology, University of British Columbia, 300-6174 University Blvd., Vancouver, BC V6T 1Z3, Canada
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Di Ciano C, Nie Z, Szászi K, Lewis A, Uruno T, Zhan X, Rotstein OD, Mak A, Kapus A. Osmotic stress-induced remodeling of the cortical cytoskeleton. Am J Physiol Cell Physiol 2002; 283:C850-65. [PMID: 12176742 DOI: 10.1152/ajpcell.00018.2002] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Osmotic stress is known to affect the cytoskeleton; however, this adaptive response has remained poorly characterized, and the underlying signaling pathways are unexplored. Here we show that hypertonicity induces submembranous de novo F-actin assembly concomitant with the peripheral translocation and colocalization of cortactin and the actin-related protein 2/3 (Arp2/3) complex, which are key components of the actin nucleation machinery. Additionally, hyperosmolarity promotes the association of cortactin with Arp2/3 as revealed by coimmunoprecipitation. Using various truncation or phosphorylation-incompetent mutants, we show that cortactin translocation requires the Arp2/3- or the F-actin binding domain, but the process is independent of the shrinkage-induced tyrosine phosphorylation of cortactin. Looking for an alternative signaling mechanism, we found that hypertonicity stimulates Rac and Cdc42. This appears to be a key event in the osmotically triggered cytoskeletal reorganization, because 1) constitutively active small GTPases translocate cortactin, 2) Rac and cortactin colocalize at the periphery of hypertonically challenged cells, and 3) dominant-negative Rac and Cdc42 inhibit the hypertonicity-provoked cortactin and Arp3 translocation. The Rho family-dependent cytoskeleton remodeling may be an important osmoprotective response that reinforces the cell cortex.
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Affiliation(s)
- Caterina Di Ciano
- Department of Surgery, Toronto General Hospital, University Health Network and University of Toronto, Ontario, Canada
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42
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Pedersen SF, Hoffmann EK. Possible interrelationship between changes in F-actin and myosin II, protein phosphorylation, and cell volume regulation in Ehrlich ascites tumor cells. Exp Cell Res 2002; 277:57-73. [PMID: 12061817 DOI: 10.1006/excr.2002.5529] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Osmotic shrinkage of Ehrlich ascites tumor cells (EATC) elicited translocation of myosin II from the cytosol to the cortical region, and swelling elicits concentration of myosin II in the Golgi region. Rho kinase and p38 both appeared to be involved in shrinkage-induced myosin II reorganization. In contrast, the previously reported shrinkage-induced actin polymerization [Pedersen et al. (1999) Exp. Cell Res. 252, 63-74] was independent of Rho kinase, p38, myosin light chain kinase (MLCK), and protein kinase C (PKC), which thus do not exert their effects on the shrinkage-activated transporters via effects on F-actin. The subsequent F-actin depolymerization, however, appeared MLCK- and PKC-dependent, and the initial swelling-induced F-actin depolymerization was MLCK-dependent; both effects were apparently secondary to kinase-mediated effects on cell volume changes. NHE1 in EATC is activated both by osmotic shrinkage and by the serine/threonine phosphatase inhibitor Calyculin A (CL-A). Both stimuli caused Rho kinase-dependent myosin II relocation to the cortical cytoplasm, but in contrast to the shrinkage-induced F-actin polymerization, CL-A treatment elicited a slight F-actin depolymerization. Moreover, Rho kinase inhibition did not significantly affect NHE1 activation, neither by shrinkage nor by CL-A. Implications for the possible interrelationship between changes in F-actin and myosin II, protein phosphorylation, and cell volume regulation are discussed.
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Affiliation(s)
- S F Pedersen
- Department of Biochemistry, August Krogh Institute, University of Copenhagen, Denmark.
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43
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Taminato A, Bagattini R, Gorjão R, Chen G, Kuspa A, Souza GM. Role for YakA, cAMP, and protein kinase A in regulation of stress responses of Dictyostelium discoideum cells. Mol Biol Cell 2002; 13:2266-75. [PMID: 12134067 PMCID: PMC117311 DOI: 10.1091/mbc.01-11-0555] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The Dictyostelium protein kinase YakA is required for the growth-to-development transition. During growth YakA controls the cell cycle, regulating the intervals between cell divisions. When starved for nutrients Dictyostelium cells arrest growth and undergo changes in gene expression, decreasing vegetative mRNAs and inducing the expression of pkaC. YakA is an effector of these changes, being necessary for the decrease of vegetative mRNA expression and the increase of protein kinase A (PKA) activity that will ultimately regulate expression of adenylyl cyclase, cAMP synthesis, and the induction of development. We report a role for this kinase in the response to nitrosoative or oxidative stress of Dictyostelium cells. Hydrogen peroxide and sodium nitroprusside arrest the growth of cells and trigger cAMP synthesis and activation of PKA in a manner similar to the well-established response to nutrient starvation. We have found that yakA null cells are hypersensitive to nitrosoative/oxidative stress and that a second-site mutation in pkaC suppresses this sensitivity. The response to different stresses has been investigated and YakA, cAMP, and PKA have been identified as components of the pathway that regulate the growth arrest that follows treatment with compounds that generate reactive oxygen species. The effect of different types of stress was evaluated in Dictyostelium and the YakA/PKA pathway was also implicated in the response to heat stress.
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Affiliation(s)
- Alexandre Taminato
- Instituto de Química, Departamento de Bioquímica, Universidade de São Paulo, São Paulo, Brazil 05508-900
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Kaitna S, Schnabel H, Schnabel R, Hyman AA, Glotzer M. A ubiquitin C-terminal hydrolase is required to maintain osmotic balance and execute actin-dependent processes in the early C. elegansembryo. J Cell Sci 2002; 115:2293-302. [PMID: 12006614 DOI: 10.1242/jcs.115.11.2293] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the early Caenorhabditis elegans embryo, establishment of cell polarity and cytokinesis are both dependent upon reorganization of the actin cytoskeleton. Mutations in the cyk-3 gene cause maternal effect embryonic lethality. Embryos produced by homozygous cyk-3 mutant animals become multinucleate. We have further analyzed the cyk-3mutant phenotype and have found that cyk-3 mutant embryos fail to properly polarize the actin cytoskeleton and fail to segregate germline determinants. In addition, they fail to assemble an intact cleavage furrow. However, we have found that cyk-3 mutant embryos are intrinsically defective in osmotic regulation and that the cytokinesis defects can be partially rescued by providing osmotic support. The cyk-3 gene has been identified and found to encode a ubiquitin C-terminal hydrolase that is active against model substrates. These data indicate that the deubiquitination of certain substrates by CYK-3 is crucial for cellular osmoregulation. Defects in osmoregulation appear to indirectly affect actin-dependent processes.
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Affiliation(s)
- Susanne Kaitna
- Research Institute for Molecular Pathology, Dr Bohr-Gasse 7, A-1030 Vienna, Austria
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45
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Tao GZ, Rott LS, Lowe AW, Omary MB. Hyposmotic stress induces cell growth arrest via proteasome activation and cyclin/cyclin-dependent kinase degradation. J Biol Chem 2002; 277:19295-303. [PMID: 11897780 DOI: 10.1074/jbc.m109654200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ordered cell cycle progression requires the expression and activation of several cyclins and cyclin-dependent kinases (Cdks). Hyperosmotic stress causes growth arrest possibly via proteasome-mediated degradation of cyclin D1. We studied the effect of hyposmotic conditions on three colonic (Caco2, HRT18, HT29) and two pancreatic (AsPC-1 and PaCa-2) cell lines. Hyposmosis caused reversible cell growth arrest of the five cell lines in a cell cycle-independent fashion, although some cell lines accumulated at the G(1)/S interface. Growth arrest was followed by apoptosis or by formation of multinucleated giant cells, which is consistent with cell cycle catastrophe. Hyposmosis dramatically decreased Cdc2, Cdk2, Cdk4, cyclin B1, and cyclin D3 expression in a time-dependent fashion, in association with an overall decrease in cellular protein synthesis. However, some protein levels remained unaltered, including cyclin E and keratin 8. Selective proteasome inhibition prevented Cdk and cyclin degradation and reversed hyposmotic stress-induced growth arrest, whereas calpain and lysosome enzyme inhibitors had no measurable effect on cell cycle protein degradation. Therefore, hyposmotic stress inhibits cell growth and, depending on the cell type, causes cell cycle catastrophe with or without apoptosis. The growth arrest is due to decreased protein synthesis and proteasome activation, with subsequent degradation of several cyclins and Cdks.
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Affiliation(s)
- Guo-Zhong Tao
- Department of Medicine, Palo Alto Veterans Affairs Medical Center, Palo Alto, California 94034, USA
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46
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Goldberg JM, Bosgraaf L, Van Haastert PJM, Smith JL. Identification of four candidate cGMP targets in Dictyostelium. Proc Natl Acad Sci U S A 2002; 99:6749-54. [PMID: 12011437 PMCID: PMC124474 DOI: 10.1073/pnas.102167299] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2001] [Accepted: 03/22/2002] [Indexed: 11/18/2022] Open
Abstract
In Dictyostelium, a transient increase in intracellular cGMP is important for cytoskeletal rearrangements during chemotaxis. There must be cGMP-binding proteins in Dictyostelium that regulate key cytoskeletal components after treatment with chemoattractants, but to date, no such proteins have been identified. Using a bioinformatics approach, we have found four candidate cGMP-binding proteins (GbpA-D). GbpA and -B have two tandem cGMP-binding sites downstream of a metallo beta-lactamase domain, a superfamily that includes cAMP phosphodiesterases. GbpC contains the following nine domains (in order): leucine-rich repeats, Ras, MEK kinase, Ras guanine nucleotide exchange factor N-terminal (RasGEF-N), DEP, RasGEF, cGMP-binding, GRAM, and a second cGMP-binding domain. GbpD is related to GbpC, but is much shorter; it begins with the RasGEF-N domain, and lacks the DEP domain. Disruption of the gbpC gene results in loss of all high-affinity cGMP-binding activity present in the soluble cellular fraction. GbpC mRNA levels increase dramatically 8 h after starvation is initiated. GbpA, -B, and -D mRNA levels show less dramatic changes, with gbpA mRNA levels highest 4 h into starvation, gbpB mRNA levels highest in vegetative cells, and gbpD levels highest at 8 h. The identification of these genes is the first step in a molecular approach to studying downstream effects of cGMP signaling in Dictyostelium.
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Affiliation(s)
- Jonathan M Goldberg
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472-2829, USA
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47
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Pintsch T, Zischka H, Schuster SC. Hisactophilin is involved in osmoprotection in Dictyostelium. BMC BIOCHEMISTRY 2002; 3:10. [PMID: 11996675 PMCID: PMC115871 DOI: 10.1186/1471-2091-3-10] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2001] [Accepted: 05/07/2002] [Indexed: 11/30/2022]
Abstract
BACKGROUND Dictyostelium cells exhibit an unusual stress response as they protect themselves against hyperosmotic stress. Cytoskeletal proteins are recruited from the cytosolic pool to the cell cortex, thereby reinforcing it. In order to gain more insight into the osmoprotective mechanisms of this amoeba, we used 1-D and 2-D gel electrophoresis to identify new proteins that are translocated during osmotic shock. RESULTS We identified hisactophilin as one of the proteins that are enriched in the cytoskeletal fraction during osmotic shock. In mutants lacking hisactophilin, viability is reduced under hyperosmotic stress conditions. In wild type cells, serine phosphorylation of hisactophilin was specifically induced by hypertonicity, but not when other stress conditions were imposed on cells. The phosphorylation kinetics reveals a slow accumulation of phosphorylated hisactophilin from 20-60 min after onset of the hyperosmotic shock condition. CONCLUSION In the present study, we identified hisactophilin as an essential protein for the osmoprotection of Dictyostelium cells. The observed phosphorylation kinetics suggest that hisactophilin regulation is involved in long-term osmoprotection and that phosphorylation occurs in parallel with inactivation of the dynamic actin cytoskeleton.
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Affiliation(s)
- Tanja Pintsch
- Max-Planck-Institute for Biochemistry, 82152 Martinsried, Germany
- SWITCH Biotech AG, Fraunhoferstr. 10, 82152 Martinsried, Germany
| | - Hans Zischka
- Max-Planck-Institute for Biochemistry, 82152 Martinsried, Germany
- GSF – Forschungszentrum für Umwelt und Gesundheit, GmbH Ingolstädter Landstraβe 1, D-85764 Neuherberg
| | - Stephan C Schuster
- Max-Planck-Institute for Biochemistry, 82152 Martinsried, Germany
- Max-Planck-Institute for Developmental Biology, Spemannstr. 35, 72076 Tübingen, Germany
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48
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Abstract
The plasmodium of Physarum polycephalum grows without cytokinesis and shows an active cytoplasmic streaming under wet and nutritious conditions. It can undergo reversible differentiation into several types of dormancy to survive in adverse environments. Temperature change or osmotic stress leads to cytoplasmic division of the plasmodium into cells containing one or more nuclei: these form a macrocyst, the spherule. Desiccation also induces cell division of the plasmodium followed by formation of a sclerotium, a dormant body resistant to dry stress. More than half of the actin in a sclerotium is phosphorylated at a single site, threonine 203, resulting in loss of its ability to polymerize into actin filaments. In the present study, actin phosphorylation was found in the sclerotium but not in either the plasmodium or in the spherule. This result suggests that phosphorylation of sclerotium actin may be related to the mechanism associated with desiccation resistance rather than morphological changes through cell compartmentalization in the macrocyst formation. Moreover. dephosphorylation of the phosphorylated form of sclerotium actin began within 5 min after addition of water. Dephosphorylation was not affected by sucrose and sorbitol sugars, but was inhibited by ammonium bicarbonate, ammonium phosphate, sodium phosphate, NaCl, and KCl in a dose-dependent manner. On the other hand, in germination of the sclerotium there was measurable sensitivity to both carbohydrates and salts. Actin dephosphorylation seems to be one of the important processes in the early phase of sclerotium germination.
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Affiliation(s)
- Kiyoshi Furuhashi
- Department of Biology, Faculty of Education, Shiga University, Otsu, Japan.
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49
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Tang L, Gao T, McCollum C, Jang W, Vicker MG, Ammann RR, Gomer RH. A cell number-counting factor regulates the cytoskeleton and cell motility in Dictyostelium. Proc Natl Acad Sci U S A 2002; 99:1371-6. [PMID: 11818526 PMCID: PMC122197 DOI: 10.1073/pnas.022516099] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Little is known about how a morphogenetic rearrangement of a tissue is affected by individual cells. Starving Dictyostelium discoideum cells aggregate to form dendritic streams, which then break up into groups of approximately 2 x 10(4) cells. Cell number is sensed at this developmental stage by using counting factor (CF), a secreted complex of polypeptides. A high extracellular concentration of CF indicates that there is a large number of cells, which then causes the aggregation stream to break up. Computer simulations indicated that stream breakup could be caused by CF decreasing cell-cell adhesion and/or increasing cell motility, and we observed that CF does indeed decrease cell-cell adhesion. We find here that CF increases cell motility. In Dictyostelium, motility is mediated by actin and myosin. CF increases the amounts of polymerized actin and the ABP-120 actin-crosslinking protein. Partially inhibiting motility by using drugs that interfere with actin polymerization reduces stream dissipation, resulting in fewer stream breaks and thus larger groups. CF also potentiates the phosphorylation and redistribution of myosin while repressing its basal level of assembly. The computer simulations indicated that a narrower distribution of group sizes results when a secreted factor modulates both adhesion and motility. CF thus seems to induce the morphogenesis of streams into evenly sized groups by increasing actin polymerization, ABP-120 levels, and myosin phosphorylation and decreasing adhesion and myosin polymerization.
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Affiliation(s)
- Lei Tang
- Department of Biochemistry and Cell Biology, MS-140, Rice University, Houston, TX 77005-1892, USA
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50
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Van Dijken P, Van Haastert PJM. Phospholipase Cdelta regulates germination of Dictyostelium spores. BMC Cell Biol 2001; 2:25. [PMID: 11737859 PMCID: PMC60988 DOI: 10.1186/1471-2121-2-25] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2001] [Accepted: 12/05/2001] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Many eukaryotes, including plants and fungi make spores that resist severe environmental stress. The micro-organism Dictyostelium contains a single phospholipase C gene (PLC); deletion of the gene has no effect on growth, cell movement and differentiation. In this report we show that PLC is essential to sense the environment of food-activated spores. RESULTS Plc-null spores germinate at alkaline pH, reduced temperature or increased osmolarity, conditions at which the emerging amoebae can not grow. In contrast, food-activated wild-type spores return to dormancy till conditions in the environment allow growth. The analysis of inositol 1,4,5-trisphosphate (IP3) levels and the effect of added IP3 uncover an unexpected mechanism how PLC regulates spore germination: i) deletion of PLC induces the enhanced activity of an IP5 phosphatase leading to high IP3 levels in plc-null cells; ii) in wild-type spores unfavourable conditions inhibit PLC leading to a reduction of IP3 levels; addition of exogenous IP3 to wild-type spores induces germination at unfavourable conditions; iii) in plc-null spores IP3 levels remain high, also at unfavourable environmental conditions. CONCLUSIONS The results imply that environmental conditions regulate PLC activity and that IP3 induces spore germination; the uncontrolled germination of plc-null spores is not due to a lack of PLC activity but to the constitutive activation of an alternative IP3-forming pathway.
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Affiliation(s)
- Peter Van Dijken
- Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Peter JM Van Haastert
- Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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