1
|
Körber S, Junemann A, Litschko C, Winterhoff M, Faix J. Convergence of Ras- and Rac-regulated formin pathways is pivotal for phagosome formation and particle uptake in Dictyostelium. Proc Natl Acad Sci U S A 2023; 120:e2220825120. [PMID: 36897976 PMCID: PMC10243128 DOI: 10.1073/pnas.2220825120] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Accepted: 02/03/2023] [Indexed: 03/12/2023] Open
Abstract
Macroendocytosis comprising phagocytosis and macropinocytosis is an actin-driven process regulated by small GTPases that depend on the dynamic reorganization of the membrane that protrudes and internalizes extracellular material by cup-shaped structures. To effectively capture, enwrap, and internalize their targets, these cups are arranged into a peripheral ring or ruffle of protruding actin sheets emerging from an actin-rich, nonprotrusive zone at its base. Despite extensive knowledge of the mechanism driving actin assembly of the branched network at the protrusive cup edge, which is initiated by the actin-related protein (Arp) 2/3 complex downstream of Rac signaling, our understanding of actin assembly in the base is still incomplete. In the Dictyostelium model system, the Ras-regulated formin ForG was previously shown to specifically contribute to actin assembly at the cup base. Loss of ForG is associated with a strongly impaired macroendocytosis and a 50% reduction in F-actin content at the base of phagocytic cups, in turn indicating the presence of additional factors that specifically contribute to actin formation at the base. Here, we show that ForG synergizes with the Rac-regulated formin ForB to form the bulk of linear filaments at the cup base. Consistently, combined loss of both formins virtually abolishes cup formation and leads to severe defects of macroendocytosis, emphasizing the relevance of converging Ras- and Rac-regulated formin pathways in assembly of linear filaments in the cup base, which apparently provide mechanical support to the entire structure. Remarkably, we finally show that active ForB, unlike ForG, additionally drives phagosome rocketing to aid particle internalization.
Collapse
Affiliation(s)
- Sarah Körber
- Institute for Biophysical Chemistry, Hannover Medical School, 30625Hannover, Germany
| | - Alexander Junemann
- Institute for Biophysical Chemistry, Hannover Medical School, 30625Hannover, Germany
| | - Christof Litschko
- Institute for Biophysical Chemistry, Hannover Medical School, 30625Hannover, Germany
| | - Moritz Winterhoff
- Institute for Biophysical Chemistry, Hannover Medical School, 30625Hannover, Germany
| | - Jan Faix
- Institute for Biophysical Chemistry, Hannover Medical School, 30625Hannover, Germany
| |
Collapse
|
2
|
Ecke M, Prassler J, Gerisch G. Genetic Instability Due to Spindle Anomalies Visualized in Mutants of Dictyostelium. Cells 2021; 10:cells10092240. [PMID: 34571889 PMCID: PMC8469108 DOI: 10.3390/cells10092240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 08/20/2021] [Accepted: 08/24/2021] [Indexed: 11/24/2022] Open
Abstract
Aberrant centrosome activities in mutants of Dictyostelium discoideum result in anomalies of mitotic spindles that affect the reliability of chromosome segregation. Genetic instabilities caused by these deficiencies are tolerated in multinucleate cells, which can be produced by electric-pulse induced cell fusion as a source for aberrations in the mitotic apparatus of the mutant cells. Dual-color fluorescence labeling of the microtubule system and the chromosomes in live cells revealed the variability of spindle arrangements, of centrosome-nuclear interactions, and of chromosome segregation in the atypical mitoses observed.
Collapse
|
3
|
Filić V, Mijanović L, Putar D, Talajić A, Ćetković H, Weber I. Regulation of the Actin Cytoskeleton via Rho GTPase Signalling in Dictyostelium and Mammalian Cells: A Parallel Slalom. Cells 2021; 10:1592. [PMID: 34202767 PMCID: PMC8305917 DOI: 10.3390/cells10071592] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 06/16/2021] [Accepted: 06/16/2021] [Indexed: 01/15/2023] Open
Abstract
Both Dictyostelium amoebae and mammalian cells are endowed with an elaborate actin cytoskeleton that enables them to perform a multitude of tasks essential for survival. Although these organisms diverged more than a billion years ago, their cells share the capability of chemotactic migration, large-scale endocytosis, binary division effected by actomyosin contraction, and various types of adhesions to other cells and to the extracellular environment. The composition and dynamics of the transient actin-based structures that are engaged in these processes are also astonishingly similar in these evolutionary distant organisms. The question arises whether this remarkable resemblance in the cellular motility hardware is accompanied by a similar correspondence in matching software, the signalling networks that govern the assembly of the actin cytoskeleton. Small GTPases from the Rho family play pivotal roles in the control of the actin cytoskeleton dynamics. Indicatively, Dictyostelium matches mammals in the number of these proteins. We give an overview of the Rho signalling pathways that regulate the actin dynamics in Dictyostelium and compare them with similar signalling networks in mammals. We also provide a phylogeny of Rho GTPases in Amoebozoa, which shows a variability of the Rho inventories across different clades found also in Metazoa.
Collapse
Affiliation(s)
- Vedrana Filić
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia; (L.M.); (D.P.); (A.T.); (H.Ć.)
| | | | | | | | | | - Igor Weber
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia; (L.M.); (D.P.); (A.T.); (H.Ć.)
| |
Collapse
|
4
|
Williams TD, Paschke PI, Kay RR. Function of small GTPases in Dictyostelium macropinocytosis. Philos Trans R Soc Lond B Biol Sci 2019; 374:20180150. [PMID: 30967009 PMCID: PMC6304742 DOI: 10.1098/rstb.2018.0150] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/31/2018] [Indexed: 12/17/2022] Open
Abstract
Macropinocytosis-the large-scale, non-specific uptake of fluid by cells-is used by Dictyostelium discoideum amoebae to obtain nutrients. These cells form circular ruffles around regions of membrane defined by a patch of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) and the activated forms of the small G-proteins Ras and Rac. When this ruffle closes, a vesicle of the medium is delivered to the cell interior for further processing. It is accepted that PIP3 is required for efficient macropinocytosis. Here, we assess the roles of Ras and Rac in Dictyostelium macropinocytosis. Gain-of-function experiments show that macropinocytosis is stimulated by persistent Ras activation and genetic analysis suggests that RasG and RasS are the key Ras proteins involved. Among the activating guanine exchange factors (GEFs), GefF is implicated in macropinocytosis by an insertional mutant. The individual roles of Rho family proteins are little understood but activation of at least some may be independent of PIP3. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.
Collapse
Affiliation(s)
| | | | - Robert R. Kay
- MRC-Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| |
Collapse
|
5
|
Williams TD, Peak-Chew SY, Paschke P, Kay RR. Akt and SGK protein kinases are required for efficient feeding by macropinocytosis. J Cell Sci 2019; 132:jcs.224998. [PMID: 30617109 DOI: 10.1242/jcs.224998] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 12/19/2018] [Indexed: 12/20/2022] Open
Abstract
Macropinocytosis is an actin-driven process of large-scale and non-specific fluid uptake used for feeding by some cancer cells and the macropinocytosis model organism Dictyostelium discoideum In Dictyostelium, macropinocytic cups are organized by 'macropinocytic patches' in the plasma membrane. These contain activated Ras, Rac and phospholipid PIP3, and direct actin polymerization to their periphery. We show that a Dictyostelium Akt (PkbA) and an SGK (PkbR1) protein kinase act downstream of PIP3 and, together, are nearly essential for fluid uptake. This pathway enables the formation of larger macropinocytic patches and macropinosomes, thereby dramatically increasing fluid uptake. Through phosphoproteomics, we identify a RhoGAP, GacG, as a PkbA and PkbR1 target, and show that it is required for efficient macropinocytosis and expansion of macropinocytic patches. The function of Akt and SGK in cell feeding through control of macropinosome size has implications for cancer cell biology.
Collapse
Affiliation(s)
| | | | - Peggy Paschke
- MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK
| | - Robert R Kay
- MRC Laboratory of Molecular Biology, Cambridge, CB2 0QH, UK
| |
Collapse
|
6
|
Veltman DM, Williams TD, Bloomfield G, Chen BC, Betzig E, Insall RH, Kay RR. A plasma membrane template for macropinocytic cups. eLife 2016; 5:e20085. [PMID: 27960076 PMCID: PMC5154761 DOI: 10.7554/elife.20085] [Citation(s) in RCA: 126] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Accepted: 11/14/2016] [Indexed: 12/18/2022] Open
Abstract
Macropinocytosis is a fundamental mechanism that allows cells to take up extracellular liquid into large vesicles. It critically depends on the formation of a ring of protrusive actin beneath the plasma membrane, which develops into the macropinocytic cup. We show that macropinocytic cups in Dictyostelium are organised around coincident intense patches of PIP3, active Ras and active Rac. These signalling patches are invariably associated with a ring of active SCAR/WAVE at their periphery, as are all examined structures based on PIP3 patches, including phagocytic cups and basal waves. Patch formation does not depend on the enclosing F-actin ring, and patches become enlarged when the RasGAP NF1 is mutated, showing that Ras plays an instructive role. New macropinocytic cups predominantly form by splitting from existing ones. We propose that cup-shaped plasma membrane structures form from self-organizing patches of active Ras/PIP3, which recruit a ring of actin nucleators to their periphery.
Collapse
Affiliation(s)
- Douwe M Veltman
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
- Beatson Institute for Cancer Research, Glasgow, United Kingdom
| | | | | | - Bi-Chang Chen
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - Eric Betzig
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, United States
| | - Robert H Insall
- Beatson Institute for Cancer Research, Glasgow, United Kingdom
| | - Robert R Kay
- MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| |
Collapse
|
7
|
Rho Signaling in Dictyostelium discoideum. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 322:61-181. [DOI: 10.1016/bs.ircmb.2015.10.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
8
|
Khajah MA, Luqmani YA. Involvement of Membrane Blebbing in Immunological Disorders and Cancer. Med Princ Pract 2016; 25 Suppl 2:18-27. [PMID: 26488882 PMCID: PMC5588526 DOI: 10.1159/000441848] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Accepted: 10/20/2015] [Indexed: 12/17/2022] Open
Abstract
Cellular blebbing is a unique form of dynamic protrusion emanating from the plasma membrane which can be either apoptotic or nonapoptotic in nature. Blebs have been observed in a wide variety of cell types and in response to multiple mechanical and chemical stimuli. They have been linked to various physiological and pathological processes including tumor motility and invasion, as well as to various immunological disorders. They can form and retract extremely rapidly in seconds or minutes, or slowly over hours or days. This review focuses on recent evidence regarding the role of blebbing in cell locomotion with particular emphasis on its role in tumor metastasis, indicating the role of specific causative molecules. The phenomenon of blebbing has been observed in endocrine-resistant breast cancer cells in response to brief exposure to extracellular alkaline pH, which leads to enhanced invasive capacity. Genetic or pharmacological targeting of cellular blebs could serve as a potential therapeutic option to control tumor metastasis.
Collapse
Affiliation(s)
| | - Yunus A. Luqmani
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Kuwait University, Safat, Kuwait
- *Yunus A. Luqmani, Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Kuwait University, PO Box 24923, Safat 13110 (Kuwait), E-Mail
| |
Collapse
|
9
|
Vlahou G, Schmidt O, Wagner B, Uenlue H, Dersch P, Rivero F, Weissenmayer BA. Yersinia outer protein YopE affects the actin cytoskeleton in Dictyostelium discoideum through targeting of multiple Rho family GTPases. BMC Microbiol 2009; 9:138. [PMID: 19602247 PMCID: PMC2724381 DOI: 10.1186/1471-2180-9-138] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Accepted: 07/14/2009] [Indexed: 01/31/2023] Open
Abstract
Background All human pathogenic Yersinia species share a virulence-associated type III secretion system that translocates Yersinia effector proteins into host cells to counteract infection-induced signaling responses and prevent phagocytosis. Dictyostelium discoideum has been recently used to study the effects of bacterial virulence factors produced by internalized pathogens. In this study we explored the potential of Dictyostelium as model organism for analyzing the effects of ectopically expressed Yersinia outer proteins (Yops). Results The Yersinia pseudotuberculosis virulence factors YopE, YopH, YopM and YopJ were expressed de novo within Dictyostelium and their effects on growth in axenic medium and on bacterial lawns were analyzed. No severe effect was observed for YopH, YopJ and YopM, but expression of YopE, which is a GTPase activating protein for Rho GTPases, was found to be highly detrimental. GFP-tagged YopE expressing cells had less conspicuous cortical actin accumulation and decreased amounts of F-actin. The actin polymerization response upon cAMP stimulation was impaired, although chemotaxis was unaffected. YopE also caused reduced uptake of yeast particles. These alterations are probably due to impaired Rac1 activation. We also found that YopE predominantly associates with intracellular membranes including the Golgi apparatus and inhibits the function of moderately overexpressed RacH. Conclusion The phenotype elicited by YopE in Dictyostelium can be explained, at least in part, by inactivation of one or more Rho family GTPases. It further demonstrates that the social amoeba Dictyostelium discoideum can be used as an efficient and easy-to-handle model organism in order to analyze the function of a translocated GAP protein of a human pathogen.
Collapse
Affiliation(s)
- Georgia Vlahou
- Zentrum für Biochemie und Zentrum für Molekulare Medizin, Medizinische Fakultät, Universität Köln, Joseph-Stelzmann-Strasse 52, 50931 Köln, Germany.
| | | | | | | | | | | | | |
Collapse
|
10
|
Maeda YT, Inose J, Matsuo MY, Iwaya S, Sano M. Ordered patterns of cell shape and orientational correlation during spontaneous cell migration. PLoS One 2008; 3:e3734. [PMID: 19011688 PMCID: PMC2581918 DOI: 10.1371/journal.pone.0003734] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Accepted: 10/27/2008] [Indexed: 12/27/2022] Open
Abstract
Background In the absence of stimuli, most motile eukaryotic cells move by
spontaneously coordinating cell deformation with cell movement in the
absence of stimuli. Yet little is known about how cells change their own
shape and how cells coordinate the deformation and movement. Here, we
investigated the mechanism of spontaneous cell migration by using
computational analyses. Methodology We observed spontaneously migrating Dictyostelium cells
in both a vegetative state (round cell shape and slow motion) and
starved one (elongated cell shape and fast motion). We then extracted
regular patterns of morphological dynamics and the pattern-dependent
systematic coordination with filamentous actin (F-actin) and cell
movement by statistical dynamic analyses. Conclusions/Significance We found that Dictyostelium cells in both vegetative and
starved states commonly organize their own shape into three ordered
patterns, elongation, rotation, and oscillation, in the absence of
external stimuli. Further, cells inactivated for PI3-kinase (PI3K)
and/or PTEN did not show ordered patterns due to the lack of spatial
control in pseudopodial formation in both the vegetative and starved
states. We also found that spontaneous polarization was achieved in
starved cells by asymmetric localization of PTEN and F-actin. This
breaking of the symmetry of protein localization maintained the leading
edge and considerably enhanced the persistence of directed migration,
and overall random exploration was ensured by switching among the
different ordered patterns. Our findings suggest that
Dictyostelium cells spontaneously create the
ordered patterns of cell shape mediated by PI3K/PTEN/F-actin and control
the direction of cell movement by coordination with these patterns even
in the absence of external stimuli.
Collapse
Affiliation(s)
- Yusuke T Maeda
- Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
| | | | | | | | | |
Collapse
|
11
|
Abstract
Plasma membrane blebs are dynamic cytoskeleton-regulated cell protrusions that have been implicated in apoptosis, cytokinesis, and cell movement. Influencing Rho–guanosine triphosphatase activities and subsequent actomyosin dynamics appears to constitute a core component for bleb formation. In this paper, we discuss recent evidence in support of a central role of nonapoptotic membrane blebbing for cell migration and cancer cell invasion as well as advances in our understanding of the underlying molecular mechanisms. Based on these studies, we propose that in a physiological context, bleb-associated cell motility reflects a cell's response to reduced substratum adhesion. The importance of blebbing as a functional protrusion is underscored by the existence of multiple molecular mechanisms that govern actin-mediated bleb retraction.
Collapse
Affiliation(s)
- Oliver T Fackler
- Department of Virology, University of Heidelberg, 69120 Heidelberg, Germany.
| | | |
Collapse
|
12
|
Phagocytosis and host-pathogen interactions in Dictyostelium with a look at macrophages. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 271:253-300. [PMID: 19081545 DOI: 10.1016/s1937-6448(08)01206-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Research into phagocytosis and host-pathogen interactions in the lower eukaryote Dictyostelium discoideum has flourished in recent years. This chapter presents a glimpse of where this research stands, with emphasis on the cell biology of the phagocytic process and on the wealth of molecular genetic data that have been gathered. The basic mechanistic machinery and most of the underlying genes appear to be evolutionarily conserved, reflecting the fact that phagocytosis arose as an efficient way to ingest food in single protozoan cells devoid of a rigid cell wall. In spite of some differences, the signal transduction pathways regulating phagosome biogenesis are also emerging as ultimately similar between Dictyostelium and macrophages. Both cell types are hosts for many pathogenic invasive bacteria, which exploit phagocytosis to grow intracellularly. We present an overwiew, based on the analysis of mutants, on how Dictyostelium contributes as a genetic model system to decipher the complexity of host-pathogen interactions.
Collapse
|
13
|
Fang J, Brzostowski JA, Ou S, Isik N, Nair V, Jin T. A vesicle surface tyrosine kinase regulates phagosome maturation. ACTA ACUST UNITED AC 2007; 178:411-23. [PMID: 17664333 PMCID: PMC2064856 DOI: 10.1083/jcb.200701023] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phagocytosis is crucial for host defense against microbial pathogens and for obtaining nutrients in Dictyostelium discoideum. Phagocytosed particles are delivered via a complex route from phagosomes to lysosomes for degradation, but the molecular mechanisms involved in the phagosome maturation process are not well understood. Here, we identify a novel vesicle-associated receptor tyrosine kinase-like protein, VSK3, in D. discoideum. We demonstrate how VSK3 is involved in phagosome maturation. VSK3 resides on the membrane of late endosomes/lysosomes with its C-terminal kinase domain facing the cytoplasm. Inactivation of VSK3 by gene disruption reduces the rate of phagocytosis in cells, which is rescued by re-expression of VSK3. We found that the in vivo function of VSK3 depends on the presence of the kinase domain and vesicle localization. Furthermore, VSK3 is not essential for engulfment, but instead, is required for the fusion of phagosomes with late endosomes/lysosomes. Our findings suggest that localized tyrosine kinase signaling on the surface of endosome/lysosomes represents a control mechanism for phagosome maturation.
Collapse
Affiliation(s)
- Jun Fang
- Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH), Rockville, MD 20852, USA
| | | | | | | | | | | |
Collapse
|
14
|
Han JW, Leeper L, Rivero F, Chung CY. Role of RacC for the regulation of WASP and phosphatidylinositol 3-kinase during chemotaxis of Dictyostelium. J Biol Chem 2006; 281:35224-34. [PMID: 16968699 PMCID: PMC2853593 DOI: 10.1074/jbc.m605997200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
WASP family proteins are key players for connecting multiple signaling pathways to F-actin polymerization. To dissect the highly integrated signaling pathways controlling WASP activity, we identified a Rac protein that binds to the GTPase binding domain of WASP. Using two-hybrid and FRET-based functional assays, we identified RacC as a major regulator of WASP. RacC stimulates F-actin assembly in cell-free systems in a WASP-dependent manner. A FRET-based microscopy approach showed local activation of RacC at the leading edge of chemotaxing cells. Cells overexpressing RacC exhibit a significant increase in the level of F-actin polymerization upon cAMP stimulation, which can be blocked by a phosphatidylinositol (PI) 3-kinase inhibitor. Membrane translocation of PI 3-kinase and PI 3,4,5-trisphosphate reporter is absent in racC null cells. Cells overexpressing dominant negative RacC mutants and racC null cells move at a significantly slower speed and show a poor directionality during chemotaxis. Our results suggest that RacC plays an important role in PI 3-kinase activation and WASP activation for dynamic regulation of F-actin assembly during Dictyostelium chemotaxis.
Collapse
Affiliation(s)
- Ji W. Han
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600
| | - Laura Leeper
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600
| | - Francisco Rivero
- Zentrum für Biochemie and Zentrum für Molekulare Medizin, Medizinische Fakultät, Universität zu Köln, Joseph-Stelzmann-Strasse 52, 50931 Köln, Germany
| | - Chang Y. Chung
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600
- To whom correspondence should be addressed: 468 Robinson Research Bldg. (MRB I), 1215 21st Ave. South at Pierce, Nashville, TN 37232-6600. Tel.: 615-322-4956; Fax: 615-343-6532;
| |
Collapse
|
15
|
Somesh BP, Vlahou G, Iijima M, Insall RH, Devreotes P, Rivero F. RacG regulates morphology, phagocytosis, and chemotaxis. EUKARYOTIC CELL 2006; 5:1648-63. [PMID: 16950926 PMCID: PMC1595345 DOI: 10.1128/ec.00221-06] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
RacG is an unusual member of the complex family of Rho GTPases in Dictyostelium. We have generated a knockout (KO) strain, as well as strains that overexpress wild-type (WT), constitutively active (V12), or dominant negative (N17) RacG. The protein is targeted to the plasma membrane, apparently in a nucleotide-dependent manner, and induces the formation of abundant actin-driven filopods. RacG is enriched at the rim of the progressing phagocytic cup, and overexpression of RacG-WT or RacG-V12 induced an increased rate of particle uptake. The positive effect of RacG on phagocytosis was abolished in the presence of 50 microM LY294002, a phosphoinositide 3-kinase inhibitor, indicating that generation of phosphatidylinositol 3,4,5-trisphosphate is required for activation of RacG. RacG-KO cells showed a moderate chemotaxis defect that was stronger in the RacG-V12 and RacG-N17 mutants, in part because of interference with signaling through Rac1. The in vivo effects of RacG-V12 could not be reproduced by a mutant lacking the Rho insert region, indicating that this region is essential for interaction with downstream components. Processes like growth, pinocytosis, exocytosis, cytokinesis, and development were unaffected in Rac-KO cells and in the overexpressor mutants. In a cell-free system, RacG induced actin polymerization upon GTPgammaS stimulation, and this response could be blocked by an Arp3 antibody. While the mild phenotype of RacG-KO cells indicates some overlap with one or more Dictyostelium Rho GTPases, like Rac1 and RacB, the significant changes found in overexpressors show that RacG plays important roles. We hypothesize that RacG interacts with a subset of effectors, in particular those concerned with shape, motility, and phagocytosis.
Collapse
Affiliation(s)
- Baggavalli P Somesh
- Center for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Cologne, Germany
| | | | | | | | | | | |
Collapse
|
16
|
Strehle A, Schleicher M, Faix J. Trix, a novel Rac guanine-nucleotide exchange factor from Dictyostelium discoideum is an actin-binding protein and accumulates at endosomes. Eur J Cell Biol 2006; 85:1035-45. [PMID: 16781009 DOI: 10.1016/j.ejcb.2006.05.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Small Rho family GTPases are involved in regulation of actin cytoskeleton dynamics. These molecular switches are themselves mainly controlled by specific GTPase-activating proteins (GAPs) and guanine-nucleotide exchange factors (GEFs). We have cloned and initially characterized a novel putative RhoGEF from Dictyostelium discoideum. The predicted 135-kDa protein displays a unique domain organization in its N-terminus by harboring two type3 calponin homology (CH) domains followed by a single type1 CH domain. The C-terminal region encompasses a diffuse B-cell lymphoma homology/pleckstrin homology tandem domain that is typically found in RhoGEFs. We therefore refer to this protein as Trix (triple CH-domain array exchange factor). A recombinant N-terminal region of Trix carrying all three CH domains binds to F-actin and bundles actin filaments. Trix-null mutants are viable and display only subtle defects when compared to wild-type cells with the exception of a substantial decrease in exocytosis of a fluid-phase marker. GFP fusions with the full-length protein or the N-terminal part containing all three CH domains revealed that Trix localizes to the cortical region and strongly accumulates on late endosomes. Our results suggest that Trix is specifically involved in a Rho GTPase-signaling pathway that is required for regulation of the actin cytoskeleton during exocytosis.
Collapse
Affiliation(s)
- Axel Strehle
- A. Butenandt-Institut/Zellbiologie, Ludwig-Maximilians-Universität, Schillerstr. 42, D-80336 München, Germany
| | | | | |
Collapse
|
17
|
Langridge PD, Kay RR. Blebbing of Dictyostelium cells in response to chemoattractant. Exp Cell Res 2006; 312:2009-17. [PMID: 16624291 DOI: 10.1016/j.yexcr.2006.03.007] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2006] [Revised: 03/01/2006] [Accepted: 03/06/2006] [Indexed: 11/21/2022]
Abstract
Stimulation of Dictyostelium cells with a high uniform concentration of the chemoattractant cyclic-AMP induces a series of morphological changes, including cell rounding and subsequent extension of pseudopodia in random directions. Here we report that cyclic-AMP also elicits blebs and analyse their mechanism of formation. The surface area and volume of cells remain constant during blebbing indicating that blebs form by the redistribution of cytoplasm and plasma membrane rather than the exocytosis of internal membrane coupled to a swelling of the cell. Blebbing occurs immediately after a rapid rise and fall in submembraneous F-actin, but the blebs themselves contain little F-actin as they expand. A mutant with a partially inactivated Arp2/3 complex has a greatly reduced rise in F-actin content, yet shows a large increase in blebbing. This suggests that bleb formation is not enhanced by the preceding actin dynamics, but is actually inhibited by them. In contrast, cells that lack myosin-II completely fail to bleb. We conclude that bleb expansion is likely to be driven by hydrostatic pressure produced by cortical contraction involving myosin-II. As blebs are induced by chemoattractant, we speculate that hydrostatic pressure is one of the forces driving pseudopod extension during movement up a gradient of cyclic-AMP.
Collapse
Affiliation(s)
- Paul D Langridge
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, UK.
| | | |
Collapse
|
18
|
Park KC, Rivero F, Meili R, Lee S, Apone F, Firtel RA. Rac regulation of chemotaxis and morphogenesis in Dictyostelium. EMBO J 2004; 23:4177-89. [PMID: 15470506 PMCID: PMC524383 DOI: 10.1038/sj.emboj.7600368] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2004] [Accepted: 07/27/2004] [Indexed: 12/22/2022] Open
Abstract
Chemotaxis requires localized F-actin polymerization at the site of the plasma membrane closest to the chemoattractant source, a process controlled by Rac/Cdc42 GTPases. We identify Dictyostelium RacB as an essential mediator of this process. RacB is activated upon chemoattractant stimulation, exhibiting biphasic kinetics paralleling F-actin polymerization. racB null cells have strong chemotaxis and morphogenesis defects and a severely reduced chemoattractant-mediated F-actin polymerization and PAKc activation. RacB activation is partly controlled by the PI3K pathway. pi3k1/2 null cells and wild-type cells treated with LY294002 exhibit a significantly reduced second peak of RacB activation, which is linked to pseudopod extension, whereas a PTEN hypomorph exhibits elevated RacB activation. We identify a RacGEF, RacGEF1, which has specificity for RacB in vitro. racgef1 null cells exhibit reduced RacB activation and cells expressing mutant RacGEF1 proteins display chemotaxis and morphogenesis defects. RacGEF1 localizes to sites of F-actin polymerization. Inhibition of this localization reduces RacB activation, suggesting a feedback loop from RacB via F-actin polymerization to RacGEF1. Our findings provide a critical linkage between chemoattractant stimulation, F-actin polymerization, and chemotaxis in Dictyostelium.
Collapse
Affiliation(s)
- Kyung Chan Park
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA, USA
| | - Francisco Rivero
- Zentrum für Biochemie der Medizinischen Fakultät, Universität zu Köln, Köln, Germany
| | - Ruedi Meili
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA, USA
| | - Susan Lee
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA, USA
| | - Fabio Apone
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA, USA
| | - Richard A Firtel
- Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA, USA
- University of California, Natural Sciences Building, Room 6316, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0380, USA. Tel.: +1 858 534 2788; Fax: +1 858 822 5900; E-mail:
| |
Collapse
|