1
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Wirshing ACE, Goode BL. Improved tools for live imaging of F-actin structures in yeast. Mol Biol Cell 2024; 35:mr7. [PMID: 39024291 DOI: 10.1091/mbc.e24-05-0212-t] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/20/2024] Open
Abstract
For over 20 years, the most effective probe for live imaging of yeast actin cables has been Abp140-GFP. Here, we report that endogenously-tagged Abp140-GFP poorly decorates actin patches and cables in the bud compartment of yeast cells, while robustly decorating these structures in the mother cell. Using mutagenesis, we found that asymmetric decoration by Abp140 requires F-actin binding. By expressing integrated Bni1-Bnr1 and Bnr1-Bni1 chimeras, we demonstrate that asymmetric cable decoration by Abp140 also does not depend on which formin assembles the cables in each compartment. In contrast, the short actin-binding fragment of Abp140 (known as "Lifeact"), fused to 1x or 3xmNeonGreen and expressed from the endogenous ABP140 promoter, uniformly decorates patches and cables in both compartments. Further, this probe dramatically improves live imaging detection of cables (and patches) without altering their in vivo dynamics or cell growth. Improved detection allows us to visualize cables growing inward from the cell cortex and dynamically interacting with the vacuole. This probe also robustly decorates the cytokinetic actomyosin ring. Because Lifeact-3xmNeon expressed at relatively low levels provides intense labeling of cellular F-actin structures, this tool may improve live imaging in other organisms where higher levels of Lifeact expression are detrimental.
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Affiliation(s)
- Alison C E Wirshing
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
| | - Bruce L Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
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2
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O'Brien MJ, Ansari A. Protein interaction network revealed by quantitative proteomic analysis links TFIIB to multiple aspects of the transcription cycle. BIOCHIMICA ET BIOPHYSICA ACTA. PROTEINS AND PROTEOMICS 2024; 1872:140968. [PMID: 37863410 PMCID: PMC10872477 DOI: 10.1016/j.bbapap.2023.140968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 10/11/2023] [Accepted: 10/12/2023] [Indexed: 10/22/2023]
Abstract
Although TFIIB is widely regarded as an initiation factor, recent reports have implicated it in multiple aspects of eukaryotic transcription. To investigate the broader role of TFIIB in transcription, we performed quantitative proteomic analysis of yeast TFIIB. We purified two different populations of TFIIB; one from soluble cell lysate, which is not engaged in transcription, and the other from the chromatin fraction which yields the transcriptionally active form of the protein. TFIIB purified from the chromatin exhibits several interactions that explain its non-canonical roles in transcription. RNAPII, TFIIF and TFIIH were the only components of the preinitiation complex with a significant presence in chromatin TFIIB. A notable feature was enrichment of all subunits of CF1 and Rat1 3' end processing-termination complexes in chromatin-TFIIB preparation. Subunits of the CPF termination complex were also detected in both chromatin and soluble derived TFIIB preparations. These results may explain the presence of TFIIB at the 3' end of genes during transcription as well as its role in promoter-termination interaction.
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Affiliation(s)
- Michael J O'Brien
- Department of Biological Science, 5047 Gullen Mall, Wayne State University, Detroit, MI 48202, United States of America
| | - Athar Ansari
- Department of Biological Science, 5047 Gullen Mall, Wayne State University, Detroit, MI 48202, United States of America.
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3
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Enshoji M, Miyano Y, Yoshida N, Nagano M, Watanabe M, Kunihiro M, Siekhaus DE, Toshima JY, Toshima J. Eps15/Pan1p is a master regulator of the late stages of the endocytic pathway. J Cell Biol 2022; 221:213415. [PMID: 35984332 PMCID: PMC9396825 DOI: 10.1083/jcb.202112138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 06/30/2022] [Accepted: 08/03/2022] [Indexed: 11/22/2022] Open
Abstract
Endocytosis is a multistep process involving the sequential recruitment and action of numerous proteins. This process can be divided into two phases: an early phase, in which sites of endocytosis are formed, and a late phase in which clathrin-coated vesicles are formed and internalized into the cytosol, but how these phases link to each other remains unclear. In this study, we demonstrate that anchoring the yeast Eps15-like protein Pan1p to the peroxisome triggers most of the events occurring during the late phase at the peroxisome. At this ectopic location, Pan1p recruits most proteins that function in the late phases-including actin nucleation promoting factors-and then initiates actin polymerization. Pan1p also recruited Prk1 kinase and actin depolymerizing factors, thereby triggering disassembly immediately after actin assembly and inducing dissociation of endocytic proteins from the peroxisome. These observations suggest that Pan1p is a key regulator for initiating, processing, and completing the late phase of endocytosis.
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Affiliation(s)
- Mariko Enshoji
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Yoshiko Miyano
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Nao Yoshida
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Makoto Nagano
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Minami Watanabe
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Mayumi Kunihiro
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan
| | - Daria E. Siekhaus
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Junko Y. Toshima
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan,School of Health Science, Tokyo University of Technology, Ota-ku, Tokyo, Japan,Junko Y. Toshima:
| | - Jiro Toshima
- Department of Biological Science and Technology, Tokyo University of Science, Katsushika-ku, Tokyo, Japan,Correspondence to Jiro Toshima:
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4
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Tyler JJ, Smaczynska-de Rooij II, Abugharsa L, Palmer JS, Hancock LP, Allwood EG, Ayscough KR. Phosphorylation of the WH2 domain in yeast Las17/WASP regulates G-actin binding and protein function during endocytosis. Sci Rep 2021; 11:9718. [PMID: 33958621 PMCID: PMC8102491 DOI: 10.1038/s41598-021-88826-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 04/12/2021] [Indexed: 11/29/2022] Open
Abstract
Actin nucleation is the key rate limiting step in the process of actin polymerization, and tight regulation of this process is critical to ensure actin filaments form only at specific times and at defined regions of the cell. WH2 domains are short sequence motifs found in many different actin binding proteins including WASP family proteins which regulate the actin nucleating complex Arp2/3. In this study we reveal a phosphorylation site, Serine 554, within the WH2 domain of the yeast WASP homologue Las17. Both phosphorylation and a phospho-mimetic mutation reduce actin monomer binding affinity while an alanine mutation, generated to mimic the non-phosphorylated state, increases actin binding affinity. The effect of these mutations on the Las17-dependent process of endocytosis in vivo was analysed and leads us to propose that switching of Las17 phosphorylation states may allow progression through distinct phases of endocytosis from site assembly through to the final scission stage. While the study is focused on Las17, the sole WASP family protein in yeast, our results have broad implications for our understanding of how a key residue in this conserved motif can underpin the many different actin regulatory roles with which WH2 domains have been associated.
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Affiliation(s)
- J J Tyler
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - I I Smaczynska-de Rooij
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - L Abugharsa
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - J S Palmer
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - L P Hancock
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - E G Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK
| | - K R Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, S10 2TN, UK.
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5
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Pollard TD. Cell Motility and Cytokinesis: From Mysteries to Molecular Mechanisms in Five Decades. Annu Rev Cell Dev Biol 2019; 35:1-28. [PMID: 31394047 DOI: 10.1146/annurev-cellbio-100818-125427] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This is the story of someone who has been fortunate to work in a field of research where essentially nothing was known at the outset but that blossomed with the discovery of profound insights about two basic biological processes: cell motility and cytokinesis. The field started with no molecules, just a few people, and primitive methods. Over time, technological advances in biophysics, biochemistry, and microscopy allowed the combined efforts of scientists in hundreds of laboratories to explain mysterious processes with molecular mechanisms that can be embodied in mathematical equations and simulated by computers. The success of this field is a tribute to the power of the reductionist strategy for understanding biology.
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Affiliation(s)
- Thomas D Pollard
- Departments of Molecular, Cellular and Developmental Biology; Molecular Biophysics and Biochemistry; and Cell Biology, Yale University, New Haven, Connecticut 06520-8103, USA;
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6
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Higgs HN. A fruitful tree: developing the dendritic nucleation model of actin-based cell motility. Mol Biol Cell 2018. [PMCID: PMC6333179 DOI: 10.1091/mbc.e18-07-0426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
A fundamental question in cell biology concerns how cells move, and this has been the subject of intense research for decades. In the 1990s, a major leap forward was made in our understanding of cell motility, with the proposal of the dendritic nucleation model. This essay describes the events leading to the development of the model, including findings from many laboratories and scientific disciplines. The story is an excellent example of the scientific process in action, with the combination of multiple perspectives leading to robust conclusions.
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Affiliation(s)
- Henry N. Higgs
- Department of Biochemistry and Cell Biology, Geisel School of Medicine at Dartmouth, Hanover, NH 03755
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7
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Epstein AE, Espinoza-Sanchez S, Pollard TD. Phosphorylation of Arp2 is not essential for Arp2/3 complex activity in fission yeast. Life Sci Alliance 2018; 1:e201800202. [PMID: 30456391 PMCID: PMC6238581 DOI: 10.26508/lsa.201800202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 10/12/2018] [Accepted: 10/12/2018] [Indexed: 12/23/2022] Open
Abstract
LeClaire et al presented evidence that phosphorylation of three sites on the Arp2 subunit activates the Arp2/3 complex to nucleate actin filaments. We mutated the homologous residues of Arp2 (Y198, T233, and T234) in the fission yeast genome to amino acids that preclude or mimic phosphorylation. Arp2/3 complex is essential for the viability of fission yeast, yet strains unable to phosphorylate these sites grew normally. Y198F/T233A/T234A Arp2 was only nonfunctional if GFP-tagged, as observed by LeClaire et al in Drosophila cells. Replacing both T233 and T234 with aspartic acid was lethal, suggesting that phosphorylation might be inhibitory. Nevertheless, blocking phosphorylation at these sites had the same effect as mimicking it: slowing assembly of endocytic actin patches. Mass spectrometry revealed phosphorylation at a fourth conserved Arp2 residue, Y218, but both blocking and mimicking phosphorylation of Y218 only slowed actin patch assembly slightly. Therefore, phosphorylation of Y198, T233, T234, and Y218 is not required for the activity of fission yeast Arp2/3 complex.
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Affiliation(s)
- Alexander E Epstein
- Departments of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT, USA
| | - Sofia Espinoza-Sanchez
- Departments of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
| | - Thomas D Pollard
- Departments of Molecular Cellular and Developmental Biology, Yale University, New Haven, CT, USA
- Departments of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, USA
- Department of Cell Biology, Yale University, New Haven, CT, USA
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8
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Conformational changes in Arp2/3 complex induced by ATP, WASp-VCA, and actin filaments. Proc Natl Acad Sci U S A 2018; 115:E8642-E8651. [PMID: 30150414 DOI: 10.1073/pnas.1717594115] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
We used fluorescence spectroscopy and EM to determine how binding of ATP, nucleation-promoting factors, actin monomers, and actin filaments changes the conformation of Arp2/3 complex during the process that nucleates an actin filament branch. We mutated subunits of Schizosaccharomyces pombe Arp2/3 complex for labeling with fluorescent dyes at either the C termini of Arp2 and Arp3 or ArpC1 and ArpC3. We measured Förster resonance energy transfer (FRET) efficiency (ETeff) between the dyes in the presence of the various ligands. We also computed class averages from electron micrographs of negatively stained specimens. ATP binding made small conformational changes of the nucleotide-binding cleft of the Arp2 subunit. WASp-VCA, WASp-CA, and WASp-actin-VCA changed the ETeff between the dyes on the Arp2 and Arp3 subunits much more than between dyes on ArpC1 and ArpC3. Ensemble FRET detected an additional structural change that brought ArpC1 and ArpC3 closer together when Arp2/3 complex bound actin filaments. VCA binding to Arp2/3 complex causes a conformational change that favors binding to the side of an actin filament, which allows further changes required to nucleate a daughter filament.
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9
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A Flow Cytometry-Based Phenotypic Screen To Identify Novel Endocytic Factors in Saccharomyces cerevisiae. G3-GENES GENOMES GENETICS 2018. [PMID: 29540444 PMCID: PMC5940143 DOI: 10.1534/g3.118.200102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Endocytosis is a fundamental process for internalizing material from the plasma membrane, including many transmembrane proteins that are selectively internalized depending on environmental conditions. In most cells, the main route of entry is clathrin-mediated endocytosis (CME), a process that involves the coordinated activity of over 60 proteins; however, there are likely as-yet unidentified proteins involved in cargo selection and/or regulation of endocytosis. We performed a mutagenic screen to identify novel endocytic genes in Saccharomyces cerevisiae expressing the methionine permease Mup1 tagged with pHluorin (pHl), a pH-sensitive GFP variant whose fluorescence is quenched upon delivery to the acidic vacuole lumen. We used fluorescence-activated cell sorting to isolate mutagenized cells with elevated fluorescence, resulting from failure to traffic Mup1-pHl cargo to the vacuole, and further assessed subcellular localization of Mup1-pHl to characterize the endocytic defects in 256 mutants. A subset of mutant strains was classified as having general endocytic defects based on mislocalization of additional cargo proteins. Within this group, we identified mutations in four genes encoding proteins with known roles in endocytosis: the endocytic coat components SLA2, SLA1, and EDE1, and the ARP3 gene, whose product is involved in nucleating actin filaments to form branched networks. All four mutants demonstrated aberrant dynamics of the endocytic machinery at sites of CME; moreover, the arp3R346H mutation showed reduced actin nucleation activity in vitro. Finally, whole genome sequencing of two general endocytic mutants identified mutations in conserved genes not previously implicated in endocytosis, KRE33 and IQG1, demonstrating that our screening approach can be used to identify new components involved in endocytosis.
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10
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Picco A, Kukulski W, Manenschijn HE, Specht T, Briggs JAG, Kaksonen M. The contributions of the actin machinery to endocytic membrane bending and vesicle formation. Mol Biol Cell 2018; 29:1346-1358. [PMID: 29851558 PMCID: PMC5994895 DOI: 10.1091/mbc.e17-11-0688] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Branched and cross-linked actin networks mediate cellular processes that move and shape membranes. To understand how actin contributes during the different stages of endocytic membrane reshaping, we analyzed deletion mutants of yeast actin network components using a hybrid imaging approach that combines live imaging with correlative microscopy. We could thus temporally dissect the effects of different actin network perturbations, revealing distinct stages of actin-based membrane reshaping. Our data show that initiation of membrane bending requires the actin network to be physically linked to the plasma membrane and to be optimally cross-linked. Once initiated, the membrane invagination process is driven by nucleation and polymerization of new actin filaments, independent of the degree of cross-linking and unaffected by a surplus of actin network components. A key transition occurs 2 s before scission, when the filament nucleation rate drops. From that time point on, invagination growth and vesicle scission are driven by an expansion of the actin network without a proportional increase of net actin amounts. The expansion is sensitive to the amount of filamentous actin and its cross-linking. Our results suggest that the mechanism by which actin reshapes the membrane changes during the progress of endocytosis, possibly adapting to varying force requirements.
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Affiliation(s)
- Andrea Picco
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland
| | - Wanda Kukulski
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Cell Biology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Hetty E Manenschijn
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland.,Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Tanja Specht
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - John A G Briggs
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural and Computational Biology Unit, European Molecular Biology Laboratory, 69117 Heidelberg, Germany.,Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Marko Kaksonen
- Department of Biochemistry and NCCR Chemical Biology, University of Geneva, 1211 Geneva, Switzerland
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11
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Yamagishi Y, Abe H. Actin assembly mediated by a nucleation promoting factor WASH is involved in MTOC–TMA formation during
Xenopus
oocyte maturation. Cytoskeleton (Hoboken) 2018; 75:131-143. [DOI: 10.1002/cm.21428] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 11/16/2017] [Accepted: 12/18/2017] [Indexed: 12/20/2022]
Affiliation(s)
- Yuka Yamagishi
- Department of Nanobiology, Graduate School of Advanced Integration ScienceChiba University Chiba263‐8522 Japan
| | - Hiroshi Abe
- Department of Nanobiology, Graduate School of Advanced Integration ScienceChiba University Chiba263‐8522 Japan
- Department of Biology, Graduate School of ScienceChiba UniversityChiba, 263‐8522 Japan
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12
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Böttcher RT, Veelders M, Rombaut P, Faix J, Theodosiou M, Stradal TE, Rottner K, Zent R, Herzog F, Fässler R. Kindlin-2 recruits paxillin and Arp2/3 to promote membrane protrusions during initial cell spreading. J Cell Biol 2017; 216:3785-3798. [PMID: 28912124 PMCID: PMC5674885 DOI: 10.1083/jcb.201701176] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 07/14/2017] [Accepted: 08/08/2017] [Indexed: 12/18/2022] Open
Abstract
Cell spreading requires the coupling of actin-driven membrane protrusion and integrin-mediated adhesion to the extracellular matrix. The integrin-activating adaptor protein kindlin-2 plays a central role for cell adhesion and membrane protrusion by directly binding and recruiting paxillin to nascent adhesions. Here, we report that kindlin-2 has a dual role during initial cell spreading: it binds paxillin via the pleckstrin homology and F0 domains to activate Rac1, and it directly associates with the Arp2/3 complex to induce Rac1-mediated membrane protrusions. Consistently, abrogation of kindlin-2 binding to Arp2/3 impairs lamellipodia formation and cell spreading. Our findings identify kindlin-2 as a key protein that couples cell adhesion by activating integrins and the induction of membrane protrusions by activating Rac1 and supplying Rac1 with the Arp2/3 complex.
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Affiliation(s)
- Ralph T Böttcher
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
- German Centre for Cardiovascular Research (DZHK), partner site Munich Heart Alliance, Munich, Germany
| | - Maik Veelders
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Pascaline Rombaut
- Gene Center Munich, Ludwig Maximilians University Munich, Munich, Germany
| | - Jan Faix
- Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany
| | - Marina Theodosiou
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
| | | | - Klemens Rottner
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Zoological Institute, Technische Universität Braunschweig, Braunschweig, Germany
| | - Roy Zent
- Division of Nephrology, Department of Medicine, Vanderbilt University, Nashville, TN
- Department of Medicine, Veterans Affairs Medical Center, Nashville, TN
| | - Franz Herzog
- Gene Center Munich, Ludwig Maximilians University Munich, Munich, Germany
| | - Reinhard Fässler
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, Martinsried, Germany
- German Centre for Cardiovascular Research (DZHK), partner site Munich Heart Alliance, Munich, Germany
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13
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Disrupting the cortical actin cytoskeleton points to two distinct mechanisms of yeast [PSI+] prion formation. PLoS Genet 2017; 13:e1006708. [PMID: 28369054 PMCID: PMC5393896 DOI: 10.1371/journal.pgen.1006708] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Revised: 04/17/2017] [Accepted: 03/20/2017] [Indexed: 02/04/2023] Open
Abstract
Mammalian and fungal prions arise de novo; however, the mechanism is poorly understood in molecular terms. One strong possibility is that oxidative damage to the non-prion form of a protein may be an important trigger influencing the formation of its heritable prion conformation. We have examined the oxidative stress-induced formation of the yeast [PSI+] prion, which is the altered conformation of the Sup35 translation termination factor. We used tandem affinity purification (TAP) and mass spectrometry to identify the proteins which associate with Sup35 in a tsa1 tsa2 antioxidant mutant to address the mechanism by which Sup35 forms the [PSI+] prion during oxidative stress conditions. This analysis identified several components of the cortical actin cytoskeleton including the Abp1 actin nucleation promoting factor, and we show that deletion of the ABP1 gene abrogates oxidant-induced [PSI+] prion formation. The frequency of spontaneous [PSI+] prion formation can be increased by overexpression of Sup35 since the excess Sup35 increases the probability of forming prion seeds. In contrast to oxidant-induced [PSI+] prion formation, overexpression-induced [PSI+] prion formation was only modestly affected in an abp1 mutant. Furthermore, treating yeast cells with latrunculin A to disrupt the formation of actin cables and patches abrogated oxidant-induced, but not overexpression-induced [PSI+] prion formation, suggesting a mechanistic difference in prion formation. [PIN+], the prion form of Rnq1, localizes to the IPOD (insoluble protein deposit) and is thought to influence the aggregation of other proteins. We show Sup35 becomes oxidized and aggregates during oxidative stress conditions, but does not co-localize with Rnq1 in an abp1 mutant which may account for the reduced frequency of [PSI+] prion formation. Prions are infectious agents which are composed of misfolded proteins and have been implicated in progressive neurodegenerative diseases such as Creutzfeldt Jakob Disease (CJD). Most prion diseases occur sporadically and are then propagated in a protein-only mechanism via induced protein misfolding. Little is currently known regarding how normally soluble proteins spontaneously form their prion forms. Previous studies have implicated oxidative damage of the non-prion form of some proteins as an important trigger for the formation of their heritable prion conformation. Using a yeast prion model we found that the cortical actin cytoskeleton is required for the transition of an oxidized protein to its heritable infectious conformation. In mutants which disrupt the cortical actin cytoskeleton, the oxidized protein aggregates, but does not localize to its normal amyloid deposition site, termed the IPOD. The IPOD serves as a site where prion proteins undergo fragmentation and seeding and we show that preventing actin-mediated localization to this site prevents both spontaneous and oxidant-induced prion formation.
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14
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Qi T, Wang J, Sun Q, Day B, Guo J, Ma Q. TaARPC3, Contributes to Wheat Resistance against the Stripe Rust Fungus. FRONTIERS IN PLANT SCIENCE 2017; 8:1245. [PMID: 28769954 PMCID: PMC5513970 DOI: 10.3389/fpls.2017.01245] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Accepted: 06/30/2017] [Indexed: 05/19/2023]
Abstract
The actin cytoskeleton participates in numerous cellular processes, including less-characterized processes, such as nuclear organization, chromatin remodeling, transcription, and signal transduction. As a key regulator of actin cytoskeletal dynamics, the actin related protein 2/3 complex (Arp2/3 complex) controls multiple developmental processes in a variety of tissues and cell types. To date, the role of the Arp2/3 complex in plant disease resistance signaling is largely unknown. Herein, we identified and characterized wheat ARPC3, TaARPC3, which encodes the C3 subunit of the Arp2/3 complex. Expression of TaARPC3 in the arc18 mutant of Saccharomyces cerevisiae Δarc18 resulted in complementation of stress-induced phenotypes in S. cerevisiae, as well as restore wild-type cell shape malformations. TaARPC3 was found predominantly to be localized in the nucleus and cytoplasm when expressed transiently in wheat protoplast. TaARPC3 was significantly induced in response to avirulent race of Puccinia striiformis f. sp. tritici (Pst). Knock-down of TaARPC3 by virus-induced gene silencing resulted in a reduction of resistance against Pst through a specific reduction in actin cytoskeletal organization. Interestingly, this reduction was found to coincide with a block in reactive oxygen species (ROS) accumulation, the hypersensitive response (HR), an increase in TaCAT1 mRNA accumulation, and the growth of Pst. Taken together, these findings suggest that TaARPC3 is a key subunit of the Arp2/3 complex which is required for wheat resistance against Pst, a process that is associated with the regulation of the actin cytoskeleton.
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Affiliation(s)
- Tuo Qi
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F UniversityYangling, China
| | - Juan Wang
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F UniversityYangling, China
| | - Qixiong Sun
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F UniversityYangling, China
| | - Brad Day
- Department of Plant, Soil and Microbial Sciences, Michigan State University, East LansingMI, United States
- Plant Resilience Institute, Michigan State University, East LansingMI, United States
| | - Jun Guo
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F UniversityYangling, China
- *Correspondence: Qing Ma, Jun Guo,
| | - Qing Ma
- State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F UniversityYangling, China
- *Correspondence: Qing Ma, Jun Guo,
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15
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Wang X, Galletta BJ, Cooper JA, Carlsson AE. Actin-Regulator Feedback Interactions during Endocytosis. Biophys J 2016; 110:1430-43. [PMID: 27028652 DOI: 10.1016/j.bpj.2016.02.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Revised: 01/20/2016] [Accepted: 02/08/2016] [Indexed: 01/22/2023] Open
Abstract
Endocytosis mediated by clathrin, a cellular process by which cells internalize membrane receptors and their extracellular ligands, is an important component of cell signaling regulation. Actin polymerization is involved in endocytosis in varying degrees depending on the cellular context. In yeast, clathrin-mediated endocytosis requires a pulse of polymerized actin and its regulators, which recruit and activate the Arp2/3 complex. In this article, we seek to identify the main protein-protein interactions that 1) cause actin and its regulators to appear in pulses, and 2) determine the effects of key mutations and drug treatments on actin and regulator assembly. We perform a joint modeling/experimental study of actin and regulator dynamics during endocytosis in the budding yeast Saccharomyces cerevisiae. We treat both a stochastic model that grows an explicit three-dimensional actin network, and a simpler two-variable Fitzhugh-Nagumo type model. The models include a negative-feedback interaction of F-actin onto the Arp2/3 regulators. Both models explain the pulse time courses and the effects of interventions on actin polymerization: the surprising increase in the peak F-actin count caused by reduced regulator branching activity, the increase in F-actin resulting from slowing of actin disassembly, and the increased Arp2/3 regulator lifetime resulting from latrunculin treatment. In addition, they predict that decreases in the regulator branching activity lead to increases in accumulation of regulators, and we confirmed this prediction with experiments on yeast harboring mutations in the Arp2/3 regulators, using quantitative fluorescence microscopy. Our experimental measurements suggest that the regulators act quasi-independently, in the sense that accumulation of a particular regulator is most strongly affected by mutations of that regulator, as opposed to the others.
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Affiliation(s)
- Xinxin Wang
- Department of Physics, Washington University, St. Louis, Missouri
| | - Brian J Galletta
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
| | - John A Cooper
- Department of Cell Biology and Physiology, Washington University School of Medicine, St Louis, Missouri
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16
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The role of viral protein Ac34 in nuclear relocation of subunits of the actin-related protein 2/3 complex. Virol Sin 2016; 31:480-489. [PMID: 27900558 DOI: 10.1007/s12250-016-3912-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 11/28/2016] [Indexed: 12/31/2022] Open
Abstract
The actin nucleator actin-related protein complex (Arp2/3) is composed of seven subunits: Arp2, Arp3, p40/ARPC1 (P40), p34/ARPC2 (P34), p21/ARPC3 (P21), p20/ARPC4 (P20), and p16/ARPC5 (P16). Arp2/3 plays crucial roles in a variety of cellular activities through regulation of actin polymerization. Autographa californica multiple nucleopolyhedrovirus (AcMNPV), one of the beststudied alphabaculoviruses, induces Arp2/3 nuclear relocation and mediates nuclear actin polymerization to assist in virus replication. We have demonstrated that Ac34, a viral late-gene product, induces translocation of the P40 subunit of Arp2/3 to the nucleus during AcMNPV infection. However, it remains unknown whether Ac34 could relocate other Arp2/3 subunits to the nucleus. In this study, the effects of the viral protein Ac34 on the distribution of these subunits were studied by an immunofluorescence assay. Arp2, P34, P21, and P20 cloned from Spodoptera frugiperda (Sf9) cells showed mainly cytoplasmic localization and were relocated to the nucleus in the presence of Ac34. In addition, Arp3 was localized in the cytoplasm in both the presence and absence of Ac34, and P16 showed whole-cell localization. In contrast to Sf9 cells, all subunits of mammalian Arp2/3 showed no nuclear relocation in the presence of Ac34. Co-immunoprecipitation analysis of the interaction between Ac34 and Arp2/3 subunits revealed that Ac34 bound to P40, P34, and P20 of Sf9 cells. However, none of the subunits of mammalian Arp2/3 interacted with Ac34, indicating that protein-protein interaction is essential for Ac34 to relocate Arp2/3 subunits to the nucleus.
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Tyler JJ, Allwood EG, Ayscough KR. WASP family proteins, more than Arp2/3 activators. Biochem Soc Trans 2016; 44:1339-1345. [PMID: 27911716 PMCID: PMC5095904 DOI: 10.1042/bst20160176] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 07/14/2016] [Accepted: 07/21/2016] [Indexed: 01/19/2023]
Abstract
Wiskott-Aldrich syndrome protein (WASP) family proteins have been extensively characterized as factors that promote the nucleation of actin through the activation of the protein complex Arp2/3. While yeast mostly have a single member of the family, mammalian cells have at least six different members, often with multiple isoforms. Members of the family are characterized by a common structure. Their N-termini are varied and are considered to confer spatial and temporal regulation of Arp2/3-activating activity, whereas their C-terminal half contains a polyproline-rich region, one or more WASP homology-2 (WH2) actin-binding domains and motifs that bind directly to Arp2/3. Recent studies, however, indicate that the yeast WASP homologue Las17 is able to nucleate actin independently of Arp2/3 through the function of novel G-actin-binding activities in its polyproline region. This allows Las17 to generate the mother filaments that are needed for subsequent Arp2/3 recruitment and activation during the actin polymerization that drives endocytic invagination in yeast. In this review, we consider how motifs within the polyproline region of Las17 support nucleation of actin filaments, and whether similar mechanisms might exist among other family members.
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Affiliation(s)
- Joe J Tyler
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
| | - Ellen G Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
| | - Kathryn R Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, U.K
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18
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Allwood EG, Tyler JJ, Urbanek AN, Smaczynska-de Rooij II, Ayscough KR. Elucidating Key Motifs Required for Arp2/3-Dependent and Independent Actin Nucleation by Las17/WASP. PLoS One 2016; 11:e0163177. [PMID: 27637067 PMCID: PMC5026357 DOI: 10.1371/journal.pone.0163177] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 09/02/2016] [Indexed: 12/21/2022] Open
Abstract
Actin nucleation is the key rate limiting step in the process of actin polymerization, and tight regulation of this process is critical to ensure actin filaments form only at specific times and at defined regions of the cell. Arp2/3 is a well-characterised protein complex that can promote nucleation of new filaments, though its activity requires additional nucleation promotion factors (NPFs). The best recognized of these factors are the WASP family of proteins that contain binding motifs for both monomeric actin and for Arp2/3. Previously we demonstrated that the yeast WASP homologue, Las17, in addition to activating Arp2/3 can also nucleate actin filaments de novo, independently of Arp2/3. This activity is dependent on its polyproline rich region. Through biochemical and in vivo analysis we have now identified key motifs within the polyproline region that are required for nucleation and elongation of actin filaments, and have addressed the role of the WH2 domain in the context of actin nucleation without Arp2/3. We have also demonstrated that full length Las17 is able to bind liposomes giving rise to the possibility of direct linkage of nascent actin filaments to specific membrane sites to which Las17 has been recruited. Overall, we propose that Las17 functions as the key initiator of de novo actin filament formation at endocytic sites by nucleating, elongating and tethering nascent filaments which then serve as a platform for Arp2/3 recruitment and function.
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Affiliation(s)
- Ellen G. Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | - Joe J. Tyler
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | - Agnieszka N. Urbanek
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | | | - Kathryn R. Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield S10 2TN, United Kingdom
- * E-mail:
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19
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Hoshi HO, Zheng L, Ohta A, Horiuchi H. A Wiskott-Aldrich syndrome protein is involved in endocytosis in Aspergillus nidulans. Biosci Biotechnol Biochem 2016; 80:1802-12. [PMID: 26927610 DOI: 10.1080/09168451.2016.1148580] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Endocytosis is vital for hyphal tip growth in filamentous fungi and is involved in the tip localization of various membrane proteins. To investigate the function of a Wiskott-Aldrich syndrome protein (WASP) in endocytosis of filamentous fungi, we identified a WASP ortholog-encoding gene, wspA, in Aspergillus nidulans and characterized it. The wspA product, WspA, localized to the tips of germ tubes during germination and actin rings in the subapical regions of mature hyphae. wspA is essential for the growth and functioned in the polarity establishment and maintenance during germination of conidia. We also investigated its function in endocytosis and revealed that endocytosis of SynA, a synaptobrevin ortholog that is known to be endocytosed at the subapical regions of hyphal tips in A. nidulans, did not occur when wspA expression was repressed. These results suggest that WspA plays roles in endocytosis at hyphal tips and polarity establishment during germination.
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Affiliation(s)
- Hiro-Omi Hoshi
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
| | - Lu Zheng
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
| | - Akinori Ohta
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
| | - Hiroyuki Horiuchi
- a Department of Biotechnology , The University of Tokyo , Tokyo , Japan
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20
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Moosavi B, Mousavi B, Yang GF. Actin, Membrane Trafficking and the Control of Prion Induction, Propagation and Transmission in Yeast. Traffic 2015; 17:5-20. [PMID: 26503767 DOI: 10.1111/tra.12344] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/23/2015] [Accepted: 10/23/2015] [Indexed: 12/16/2022]
Abstract
The model eukaryotic yeast Saccharomyces cerevisiae has proven a useful model system in which prion biogenesis and elimination are studied. Several yeast prions exist in budding yeast and a number of studies now suggest that these alternate protein conformations may play important roles in the cell. During the last few years cellular factors affecting prion induction, propagation and elimination have been identified. Amongst these, proteins involved in the regulation of the actin cytoskeleton and dynamic membrane processes such as endocytosis have been found to play a critical role not only in facilitating de novo prion formation but also in prion propagation. Here we briefly review prion formation and maintenance with special attention given to the cellular processes that require the functionality of the actin cytoskeleton.
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Affiliation(s)
- Behrooz Moosavi
- Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, 430079, P.R. China
| | - Bibimaryam Mousavi
- Laboratory of Organometallics, Catalysis and Ordered Materials, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, P.R. China
| | - Guang-Fu Yang
- Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, 430079, P.R. China
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21
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Urbanek AN, Allwood EG, Smith AP, Booth WI, Ayscough KR. Distinct Actin and Lipid Binding Sites in Ysc84 Are Required during Early Stages of Yeast Endocytosis. PLoS One 2015; 10:e0136732. [PMID: 26312755 PMCID: PMC4552428 DOI: 10.1371/journal.pone.0136732] [Citation(s) in RCA: 7] [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: 05/29/2015] [Accepted: 08/08/2015] [Indexed: 11/18/2022] Open
Abstract
During endocytosis in S. cerevisiae, actin polymerization is proposed to provide the driving force for invagination against the effects of turgor pressure. In previous studies, Ysc84 was demonstrated to bind actin through a conserved N-terminal domain. However, full length Ysc84 could only bind actin when its C-terminal SH3 domain also bound to the yeast WASP homologue Las17. Live cell-imaging has revealed that Ysc84 localizes to endocytic sites after Las17/WASP but before other known actin binding proteins, suggesting it is likely to function at an early stage of membrane invagination. While there are homologues of Ysc84 in other organisms, including its human homologue SH3yl-1, little is known of its mode of interaction with actin or how this interaction affects actin filament dynamics. Here we identify key residues involved both in Ysc84 actin and lipid binding, and demonstrate that its actin binding activity is negatively regulated by PI(4,5)P2. Ysc84 mutants defective in their lipid or actin-binding interaction were characterized in vivo. The abilities of Ysc84 to bind Las17 through its C-terminal SH3 domain, or to actin and lipid through the N-terminal domain were all shown to be essential in order to rescue temperature sensitive growth in a strain requiring YSC84 expression. Live cell imaging in strains with fluorescently tagged endocytic reporter proteins revealed distinct phenotypes for the mutants indicating the importance of these interactions for regulating key stages of endocytosis.
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Affiliation(s)
- Agnieszka N. Urbanek
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, United Kingdom
| | - Ellen G. Allwood
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, United Kingdom
| | - Adam P. Smith
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, United Kingdom
| | - Wesley I. Booth
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, United Kingdom
| | - Kathryn R. Ayscough
- Department of Biomedical Science, Firth Court, University of Sheffield, Sheffield, United Kingdom
- * E-mail:
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22
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Picco A, Mund M, Ries J, Nédélec F, Kaksonen M. Visualizing the functional architecture of the endocytic machinery. eLife 2015; 4. [PMID: 25675087 PMCID: PMC4357291 DOI: 10.7554/elife.04535] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 02/10/2015] [Indexed: 01/08/2023] Open
Abstract
Clathrin-mediated endocytosis is an essential process that forms vesicles from the plasma membrane. Although most of the protein components of the endocytic protein machinery have been thoroughly characterized, their organization at the endocytic site is poorly understood. We developed a fluorescence microscopy method to track the average positions of yeast endocytic proteins in relation to each other with a time precision below 1 s and with a spatial precision of ∼10 nm. With these data, integrated with shapes of endocytic membrane intermediates and with superresolution imaging, we could visualize the dynamic architecture of the endocytic machinery. We showed how different coat proteins are distributed within the coat structure and how the assembly dynamics of N-BAR proteins relate to membrane shape changes. Moreover, we found that the region of actin polymerization is located at the base of the endocytic invagination, with the growing ends of filaments pointing toward the plasma membrane. DOI:http://dx.doi.org/10.7554/eLife.04535.001 Cells take up proteins and other useful material (called cargo) from their external environment through a process known as endocytosis. To start with, the cargo accumulates in a patch on the surface of the cell. On the inner side of the cell's membrane, a protein called clathrin gathers around the patch of cargo. Clathrin molecules and many other proteins bind together to make a lattice-like coat that causes the membrane to curve inwards and form a pocket that contains the cargo. This continues until the cargo is completely surrounded by membrane and eventually forms a bubble-like structure, or ‘vesicle’, that moves into the cell. More than 50 other proteins are involved in the endocytosis. These proteins arrive at the site of endocytosis in a particular order, complete their tasks and then move away to be used in further rounds of endocytosis. It is not clear how these proteins are organized to complete these steps because it is technically difficult to track the movements of many proteins at the same time. Here, Picco et al. developed a new fluorescence microscopy method that enabled them to track the positions of many of the proteins involved in endocytosis in yeast cells in real time. The experiments revealed when the proteins arrived at the site of endocytosis and how they assembled in relation to the membrane. For example, a group of proteins called N-BAR proteins formed an extended lattice covering the sides of the pocket that forms as the membrane curves inwards. To transform the flat membrane into a vesicle, a network of filaments made of a protein called actin needs to form at the site of endocytosis. The new method shows that the actin filaments grow in a small region at the base of the developing vesicle. By combining different types of microscopy data, Picco et al. were able to build a comprehensive model describing when the proteins involved in endocytosis move and assemble. The next challenge will be to understand the physics behind the molecular machine composed of these many proteins and the cell membrane. DOI:http://dx.doi.org/10.7554/eLife.04535.002
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Affiliation(s)
- Andrea Picco
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Markus Mund
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Jonas Ries
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - François Nédélec
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Marko Kaksonen
- Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Heidelberg, Germany
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23
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Abstract
Endocytosis, the process whereby the plasma membrane invaginates to form vesicles, is essential for bringing many substances into the cell and for membrane turnover. The mechanism driving clathrin-mediated endocytosis (CME) involves > 50 different protein components assembling at a single location on the plasma membrane in a temporally ordered and hierarchal pathway. These proteins perform precisely choreographed steps that promote receptor recognition and clustering, membrane remodeling, and force-generating actin-filament assembly and turnover to drive membrane invagination and vesicle scission. Many critical aspects of the CME mechanism are conserved from yeast to mammals and were first elucidated in yeast, demonstrating that it is a powerful system for studying endocytosis. In this review, we describe our current mechanistic understanding of each step in the process of yeast CME, and the essential roles played by actin polymerization at these sites, while providing a historical perspective of how the landscape has changed since the preceding version of the YeastBook was published 17 years ago (1997). Finally, we discuss the key unresolved issues and where future studies might be headed.
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Affiliation(s)
- Bruce L Goode
- Brandeis University, Department of Biology, Rosenstiel Center, Waltham, Massachusetts 02454
| | - Julian A Eskin
- Brandeis University, Department of Biology, Rosenstiel Center, Waltham, Massachusetts 02454
| | - Beverly Wendland
- The Johns Hopkins University, Department of Biology, Baltimore, Maryland 21218
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24
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Exploration of the dynamic properties of protein complexes predicted from spatially constrained protein-protein interaction networks. PLoS Comput Biol 2014; 10:e1003654. [PMID: 24874694 PMCID: PMC4038459 DOI: 10.1371/journal.pcbi.1003654] [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: 11/22/2013] [Accepted: 04/19/2014] [Indexed: 11/19/2022] Open
Abstract
Protein complexes are not static, but rather highly dynamic with subunits that undergo 1-dimensional diffusion with respect to each other. Interactions within protein complexes are modulated through regulatory inputs that alter interactions and introduce new components and deplete existing components through exchange. While it is clear that the structure and function of any given protein complex is coupled to its dynamical properties, it remains a challenge to predict the possible conformations that complexes can adopt. Protein-fragment Complementation Assays detect physical interactions between protein pairs constrained to ≤8 nm from each other in living cells. This method has been used to build networks composed of 1000s of pair-wise interactions. Significantly, these networks contain a wealth of dynamic information, as the assay is fully reversible and the proteins are expressed in their natural context. In this study, we describe a method that extracts this valuable information in the form of predicted conformations, allowing the user to explore the conformational landscape, to search for structures that correlate with an activity state, and estimate the abundance of conformations in the living cell. The generator is based on a Markov Chain Monte Carlo simulation that uses the interaction dataset as input and is constrained by the physical resolution of the assay. We applied this method to an 18-member protein complex composed of the seven core proteins of the budding yeast Arp2/3 complex and 11 associated regulators and effector proteins. We generated 20,480 output structures and identified conformational states using principle component analysis. We interrogated the conformation landscape and found evidence of symmetry breaking, a mixture of likely active and inactive conformational states and dynamic exchange of the core protein Arc15 between core and regulatory components. Our method provides a novel tool for prediction and visualization of the hidden dynamics within protein interaction networks. Cells are complex dynamic systems, and a central challenge in modern cell biology is to capture information about interactions between the molecules underlying cellular processes. Proteins rarely act alone; more often they form functional partnerships that can specify the timing and/or location of activity. These partnerships are subject to dynamic changes, and thus protein interactions within complexes undergo continuous transitions. Genetic and biochemical evidence suggest that regulation or depletion of a single protein can alter the stability and activity of an entire protein complex. Experimental approaches that detect interactions within living cells provide critical information for the dynamical system that protein complexes represent; yet complexes are often depicted as static 2-dimensional networks. We have built a system that projects in vivo protein interaction datasets as 3-dimensional virtual protein complexes. By using this method to approximate the diffusion of complex components, we can predict transient conformational states and estimate their abundance in living cells. Our method offers biologists a framework to correlate experimental phenotypes with predicted complex dynamics such as short or long-range effects of a single perturbation to the function of the whole ensemble.
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25
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Idrissi FZ, Geli MI. Zooming in on the molecular mechanisms of endocytic budding by time-resolved electron microscopy. Cell Mol Life Sci 2014; 71:641-57. [PMID: 24002236 PMCID: PMC11113444 DOI: 10.1007/s00018-013-1452-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 07/17/2013] [Accepted: 08/08/2013] [Indexed: 12/31/2022]
Abstract
Endocytic budding implies the remodeling of a plasma membrane portion from a flat sheet to a closed vesicle. Clathrin- and actin-mediated endocytosis in yeast has proven a very powerful model to study this process, with more than 60 evolutionarily conserved proteins involved in fashioning primary endocytic vesicles. Major progress in the field has been made during the last decades by defining the sequential recruitment of the endocytic machinery at the cell cortex using live-cell fluorescence microscopy. Higher spatial resolution has been recently achieved by developing time-resolved electron microscopy methods, allowing for the first time the visualization of changes in the plasma membrane shape, coupled to the dynamics of the endocytic machinery. Here, we highlight these advances and review recent findings from yeast and mammals that have increased our understanding of where and how endocytic proteins may apply force to remodel the plasma membrane during different stages of the process.
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Affiliation(s)
- Fatima-Zahra Idrissi
- Department of Cell Biology, Instituto de Biología Molecular de Barcelona (CSIC), Baldiri i Reixac 15, 08028, Barcelona, Spain,
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26
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Abstract
Several bacterial pathogens, including Listeria monocytogenes, Shigella flexneri and Rickettsia spp., have evolved mechanisms to actively spread within human tissues. Spreading is initiated by the pathogen-induced recruitment of host filamentous (F)-actin. F-actin forms a tail behind the microbe, propelling it through the cytoplasm. The motile pathogen then encounters the host plasma membrane, forming a bacterium-containing protrusion that is engulfed by an adjacent cell. Over the past two decades, much progress has been made in elucidating mechanisms of F-actin tail formation. Listeria and Shigella produce tails of branched actin filaments by subverting the host Arp2/3 complex. By contrast, Rickettsia forms tails with linear actin filaments through a bacterial mimic of eukaryotic formins. Compared with F-actin tail formation, mechanisms controlling bacterial protrusions are less well understood. However, recent findings have highlighted the importance of pathogen manipulation of host cell–cell junctions in spread. Listeria produces a soluble protein that enhances bacterial protrusions by perturbing tight junctions. Shigella protrusions are engulfed through a clathrin-mediated pathway at ‘tricellular junctions’—specialized membrane regions at the intersection of three epithelial cells. This review summarizes key past findings in pathogen spread, and focuses on recent developments in actin-based motility and the formation and internalization of bacterial protrusions.
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Affiliation(s)
- Keith Ireton
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand.
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27
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A novel actin-binding motif in Las17/WASP nucleates actin filaments independently of Arp2/3. Curr Biol 2013; 23:196-203. [PMID: 23290554 DOI: 10.1016/j.cub.2012.12.024] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 10/24/2012] [Accepted: 12/13/2012] [Indexed: 11/22/2022]
Abstract
BACKGROUND Actin nucleation is the key rate-limiting step in actin polymerization, and tight regulation of this process is critical to ensure that actin filaments form only at specific regions of the cell. Las17 is the primary activator of Arp2/3-driven actin nucleation in yeast and is required for membrane invagination during endocytosis. Its mammalian homolog, WASP, has also been studied extensively as an activator of Arp2/3-driven actin polymerization. In both Las17 and WASP, actin nucleation activity is attributed to an ability to bind actin through a WH2 domain and to bind Arp2/3 through an acidic region. The central region of both Las17 and WASP is rich in proline residues and is generally considered to bind to SH3-domain-containing proteins. RESULTS We have identified a novel actin-binding activity in the polyproline domain of both yeast Las17 and mammalian WASP. The polyproline domain of Las17 is also able to nucleate actin filaments independently of Arp2/3. Mutational analysis reveals that proline residues are required for this nucleation activity and that the binding site on actin maps to a region distinct from those used by other nucleation activities. In vivo analysis of yeast strains expressing las17 mutated in the WH2 domain, one of its proline motifs, or both shows additive defects in actin organization and endocytosis, with the proline mutant conferring more severe phenotypes than the WH2 mutant. CONCLUSIONS Our data demonstrate a new actin-binding and nucleation mechanism in Las17/WASP that is required for its function in actin regulation during endocytosis.
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28
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Yanagisawa M, Zhang C, Szymanski DB. ARP2/3-dependent growth in the plant kingdom: SCARs for life. FRONTIERS IN PLANT SCIENCE 2013; 4:166. [PMID: 23802001 PMCID: PMC3689024 DOI: 10.3389/fpls.2013.00166] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Accepted: 05/12/2013] [Indexed: 05/18/2023]
Abstract
In the human experience SCARs (suppressor of cAMP receptors) are permanent reminders of past events, not always based on bad decisions, but always those in which an interplay of opposing forces leaves behind a clear record in the form of some permanent watery mark. During plant morphogenesis, SCARs are important proteins that reflect an unusual evolutionary outcome, in which the plant kingdom relies heavily on this single class of actin-related protein (ARP) 2/3 complex activator to dictate the time and place of actin filament nucleation. This unusually simple arrangement may serve as a permanent reminder that cell shape control in plants is fundamentally different from that of crawling cells in mammals that use the power of actin polymerization to define and maintain cell shape. In plant cells, actin filaments indirectly affect cell shape by determining the transport properties of organelles and cargo molecules that modulate the mechanical properties of the wall. It is becoming increasingly clear that polarized bundles of actin filaments operate at whole cell spatial scales to organize the cytoplasm and dictate the patterns of long-distance intracellular transport and secretion. The number of actin-binding proteins and actin filament nucleators that are known to participate in the process of actin network formation are rapidly increasing. In plants, formins and ARP2/3 are two important actin filament nucleators. This review will focus on ARP2/3, and the apparent reliance of most plant species on the SCAR/WAVE (WASP family verprolin homologous) regulatory complex as the sole pathway for ARP2/3 activation.
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Affiliation(s)
| | - Chunhua Zhang
- Department of Botany and Plant Sciences, University of CaliforniaRiverside, CA, USA
| | - Daniel B. Szymanski
- Department of Agronomy, Purdue UniversityWest Lafayette, IN, USA
- Department of Biological Sciences, Purdue UniversityWest Lafayette, IN, USA
- *Correspondence: Daniel B. Szymanski, Department of Agronomy, Purdue University, 1150 Lilly Hall of Life Sciences, West Lafayette, IN 47907-1150, USA e-mail:
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29
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30
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Abstract
Many forms of cellular motility are driven by the growth of branched networks of actin filaments, which push against a membrane. In the dendritic nucleation model, Arp2/3 complex is critical, binding to the side of an existing mother filament, nucleating a new daughter filament, and thus creating a branch. Spatial and temporal regulation of Arp2/3 activity is critical for efficient generation of force and movement. A diverse collection of Arp2/3 regulatory proteins has been identified. They bind to and/or activate Arp2/3 complex via an acidic motif with a conserved tryptophan residue. We tested this model for Arp2/3 regulator function in vivo, by examining the roles of multiple Arp2/3 regulators in endocytosis in living yeast cells. We measured the molecular composition of the actin network in cells with mutations that removed the acidic motifs of the four Arp2/3 regulators previously shown to influence the proper function of the actin network. Unexpectedly, we did not find a simple or direct correlation between defects in patch assembly and movement and changes in the composition and dynamics of dendritic nucleation proteins. Taken together our data does not support the simple hypothesis that the primary role for Arp2/3 regulators is to recruit and activate Arp2/3. Rather our data suggests that these regulators may be playing more subtle roles in establishing functional networks in vivo.
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Affiliation(s)
- Brian J Galletta
- Department of Cell Biology and Physiology, Washington University, Saint Louis, MO, USA
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31
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Zeng G, Wang YM, Wang Y. Cdc28-Cln3 phosphorylation of Sla1 regulates actin patch dynamics in different modes of fungal growth. Mol Biol Cell 2012; 23:3485-97. [PMID: 22787279 PMCID: PMC3431942 DOI: 10.1091/mbc.e12-03-0231] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
A dynamic balance between targeted transport and endocytosis is critical for polarized cell growth. However, how actin-mediated endocytosis is regulated in different growth modes remains unclear. Here we report differential regulation of cortical actin patch dynamics between the yeast and hyphal growth in Candida albicans. The mechanism involves phosphoregulation of the endocytic protein Sla1 by the cyclin-dependent kinase (CDK) Cdc28-Cln3 and the actin-regulating kinase Prk1. Mutational studies of the CDK phosphorylation sites of Sla1 revealed that Cdc28-Cln3 phosphorylation of Sla1 enhances its further phosphorylation by Prk1, weakening Sla1 association with Pan1, an activator of the actin-nucleating Arp2/3 complex. Sla1 is rapidly dephosphorylated upon hyphal induction and remains so throughout hyphal growth. Consistently, cells expressing a phosphomimetic version of Sla1 exhibited markedly reduced actin patch dynamics, impaired endocytosis, and defective hyphal development, whereas a nonphosphorylatable Sla1 had the opposite effect. Taken together, our findings establish a molecular link between CDK and a key component of the endocytic machinery, revealing a novel mechanism by which endocytosis contributes to cell morphogenesis.
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Affiliation(s)
- Guisheng Zeng
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Singapore 138673
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32
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Kruth KA, Rubenstein PA. Two deafness-causing (DFNA20/26) actin mutations affect Arp2/3-dependent actin regulation. J Biol Chem 2012; 287:27217-26. [PMID: 22718764 DOI: 10.1074/jbc.m112.377283] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Hearing requires proper function of the auditory hair cell, which is critically dependent upon its actin-based cytoskeletal structure. Currently, ten point mutations in nonmuscle γ-actin have been identified as causing progressive autosomal dominant nonsyndromic hearing loss (DFNA20/26), highlighting these ten residues as functionally important to actin structure and/or regulation. Two of the mutations, K118M and K118N, are located near the putative binding site for the ubiquitously expressed Arp2/3 complex. We therefore hypothesized that these mutations may affect Arp2/3-dependent regulation of the actin cytoskeleton. Using in vitro bulk polymerization assays, we show that the Lys-118 mutations notably reduce actin + Arp2/3 polymerization rates compared with WT. Further in vitro analysis of the K118M mutant using TIRF microscopy indicates the actual number of branches formed per filament is reduced compared with WT and, surprisingly, branch location is altered such that the majority of K118M branches form near the pointed end of the filament. These results highlight a previously unknown role for the Lys-118 residue in the actin-Arp2/3 interaction and also further suggest that Lys-118 may play a more significant role in intra- and intermonomer interactions than was initially hypothesized.
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Affiliation(s)
- Karina A Kruth
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1109, USA
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Bi E, Park HO. Cell polarization and cytokinesis in budding yeast. Genetics 2012; 191:347-87. [PMID: 22701052 PMCID: PMC3374305 DOI: 10.1534/genetics.111.132886] [Citation(s) in RCA: 217] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2011] [Accepted: 11/04/2011] [Indexed: 12/26/2022] Open
Abstract
Asymmetric cell division, which includes cell polarization and cytokinesis, is essential for generating cell diversity during development. The budding yeast Saccharomyces cerevisiae reproduces by asymmetric cell division, and has thus served as an attractive model for unraveling the general principles of eukaryotic cell polarization and cytokinesis. Polarity development requires G-protein signaling, cytoskeletal polarization, and exocytosis, whereas cytokinesis requires concerted actions of a contractile actomyosin ring and targeted membrane deposition. In this chapter, we discuss the mechanics and spatial control of polarity development and cytokinesis, emphasizing the key concepts, mechanisms, and emerging questions in the field.
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Affiliation(s)
- Erfei Bi
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6058, USA.
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Casolari JM, Thompson MA, Salzman J, Champion LM, Moerner WE, Brown PO. Widespread mRNA association with cytoskeletal motor proteins and identification and dynamics of myosin-associated mRNAs in S. cerevisiae. PLoS One 2012; 7:e31912. [PMID: 22359641 PMCID: PMC3281097 DOI: 10.1371/journal.pone.0031912] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Accepted: 01/15/2012] [Indexed: 01/08/2023] Open
Abstract
Programmed mRNA localization to specific subcellular compartments for localized translation is a fundamental mechanism of post-transcriptional regulation that affects many, and possibly all, mRNAs in eukaryotes. We describe here a systematic approach to identify the RNA cargoes associated with the cytoskeletal motor proteins of Saccharomyces cerevisiae in combination with live-cell 3D super-localization microscopy of endogenously tagged mRNAs. Our analysis identified widespread association of mRNAs with cytoskeletal motor proteins, including association of Myo3 with mRNAs encoding key regulators of actin branching and endocytosis such as WASP and WIP. Using conventional fluorescence microscopy and expression of MS2-tagged mRNAs from endogenous loci, we observed a strong bias for actin patch nucleator mRNAs to localize to the cell cortex and the actin patch in a Myo3- and F-actin dependent manner. Use of a double-helix point spread function (DH-PSF) microscope allowed super-localization measurements of single mRNPs at a spatial precision of 25 nm in x and y and 50 nm in z in live cells with 50 ms exposure times, allowing quantitative profiling of mRNP dynamics. The actin patch mRNA exhibited distinct and characteristic diffusion coefficients when compared to a control mRNA. In addition, disruption of F-actin significantly expanded the 3D confinement radius of an actin patch nucleator mRNA, providing a quantitative assessment of the contribution of the actin cytoskeleton to mRNP dynamic localization. Our results provide evidence for specific association of mRNAs with cytoskeletal motor proteins in yeast, suggest that different mRNPs have distinct and characteristic dynamics, and lend insight into the mechanism of actin patch nucleator mRNA localization to actin patches.
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Affiliation(s)
- Jason M. Casolari
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
| | - Michael A. Thompson
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Julia Salzman
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Statistics, Stanford University, Stanford, California, United States of America
| | - Lowry M. Champion
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
| | - W. E. Moerner
- Department of Chemistry, Stanford University, Stanford, California, United States of America
| | - Patrick O. Brown
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California, United States of America
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35
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Kaminska J, Spiess M, Stawiecka-Mirota M, Monkaityte R, Haguenauer-Tsapis R, Urban-Grimal D, Winsor B, Zoladek T. Yeast Rsp5 ubiquitin ligase affects the actin cytoskeleton in vivo and in vitro. Eur J Cell Biol 2011; 90:1016-28. [DOI: 10.1016/j.ejcb.2011.08.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 08/11/2011] [Accepted: 08/17/2011] [Indexed: 10/16/2022] Open
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Narayanan A, LeClaire LL, Barber DL, Jacobson MP. Phosphorylation of the Arp2 subunit relieves auto-inhibitory interactions for Arp2/3 complex activation. PLoS Comput Biol 2011; 7:e1002226. [PMID: 22125478 PMCID: PMC3220268 DOI: 10.1371/journal.pcbi.1002226] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2010] [Accepted: 08/27/2011] [Indexed: 11/18/2022] Open
Abstract
Actin filament assembly by the actin-related protein (Arp) 2/3 complex is necessary to build many cellular structures, including lamellipodia at the leading edge of motile cells and phagocytic cups, and to move endosomes and intracellular pathogens. The crucial role of the Arp2/3 complex in cellular processes requires precise spatiotemporal regulation of its activity. While binding of nucleation-promoting factors (NPFs) has long been considered essential to Arp2/3 complex activity, we recently showed that phosphorylation of the Arp2 subunit is also necessary for Arp2/3 complex activation. Using molecular dynamics simulations and biochemical assays with recombinant Arp2/3 complex, we now show how phosphorylation of Arp2 induces conformational changes permitting activation. The simulations suggest that phosphorylation causes reorientation of Arp2 relative to Arp3 by destabilizing a network of salt-bridge interactions at the interface of the Arp2, Arp3, and ARPC4 subunits. Simulations also suggest a gain-of-function ARPC4 mutant that we show experimentally to have substantial activity in the absence of NPFs. We propose a model in which a network of auto-inhibitory salt-bridge interactions holds the Arp2 subunit in an inactive orientation. These auto-inhibitory interactions are destabilized upon phosphorylation of Arp2, allowing Arp2 to reorient to an activation-competent state.
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Affiliation(s)
- Arjun Narayanan
- Graduate Group in Biophysics, University of California, San Francisco, San Francisco, California, USA.
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37
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Xu XP, Rouiller I, Slaughter BD, Egile C, Kim E, Unruh JR, Fan X, Pollard TD, Li R, Hanein D, Volkmann N. Three-dimensional reconstructions of Arp2/3 complex with bound nucleation promoting factors. EMBO J 2011; 31:236-47. [PMID: 21934650 DOI: 10.1038/emboj.2011.343] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 08/30/2011] [Indexed: 11/09/2022] Open
Abstract
Arp2/3 complex initiates the growth of branched actin-filament networks by inducing actin polymerization from the sides of pre-existing filaments. Nucleation promoting factors (NPFs) are essential for the branching reaction through interactions with the Arp2/3 complex prior to branch formation. The modes by which NPFs bind Arp2/3 complex and associated conformational changes have remained elusive. Here, we used electron microscopy to determine three-dimensional structures at ~2 nm resolution of Arp2/3 complex with three different bound NPFs: N-WASp, Scar-VCA and cortactin. All of these structures adopt a conformation with the two actin-related proteins in an actin-filament-like dimer and the NPF bound to the pointed end. Distance constraints derived by fluorescence resonance energy transfer independently verified the NPF location. Furthermore, all bound NPFs partially occlude the actin-filament binding site, suggesting that additional local structural rearrangements are required in the pathway of Arp2/3 complex activation to allow branch formation.
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Affiliation(s)
- Xiao-Ping Xu
- Bioinformatics and Systems Biology Program, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA
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38
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Boettner DR, Friesen H, Andrews B, Lemmon SK. Clathrin light chain directs endocytosis by influencing the binding of the yeast Hip1R homologue, Sla2, to F-actin. Mol Biol Cell 2011; 22:3699-714. [PMID: 21849475 PMCID: PMC3183023 DOI: 10.1091/mbc.e11-07-0628] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The clathrin light-chain (LC) N-terminal region interacts with the Sla2/Hip1/Hip1R family of ANTH/talin–like proteins. In vivo evidence shows that LC–Sla2 binding is important for releasing Sla2 attachments to actin in the endocytic coat. Loss of this regulation can suppress major actin defects during endocytosis. The role of clathrin light chain (CLC) in clathrin-mediated endocytosis is not completely understood. Previous studies showed that the CLC N-terminus (CLC-NT) binds the Hip1/Hip1R/Sla2 family of membrane/actin–binding factors and that overexpression of the CLC-NT in yeast suppresses endocytic defects of clathrin heavy-chain mutants. To elucidate the mechanistic basis for this suppression, we performed synthetic genetic array analysis with a clathrin CLC-NT deletion mutation (clc1-Δ19-76). clc1-Δ19-76 suppressed the internalization defects of null mutations in three late endocytic factors: amphiphysins (rvs161 and rvs167) and verprolin (vrp1). In actin sedimentation assays, CLC binding to Sla2 inhibited Sla2 interaction with F-actin. Furthermore, clc1-Δ19-76 suppression of the rvs and vrp phenotypes required the Sla2 actin-binding talin-Hip1/R/Sla2 actin-tethering C-terminal homology domain, suggesting that clc1-Δ19-76 promotes internalization by prolonging actin engagement by Sla2. We propose that CLC directs endocytic progression by pruning the Sla2-actin attachments in the clathrin lattice, providing direction for membrane internalization.
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Affiliation(s)
- Douglas R Boettner
- Department of Molecular and Cellular Pharmacology, University of Miami, Miami, FL 33101, USA
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Wong MH, Meng L, Rajmohan R, Yu S, Thanabalu T. Vrp1p-Las17p interaction is critical for actin patch polarization but is not essential for growth or fluid phase endocytosis in S. cerevisiae. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:1332-46. [PMID: 20816901 DOI: 10.1016/j.bbamcr.2010.08.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2010] [Revised: 08/26/2010] [Accepted: 08/26/2010] [Indexed: 11/24/2022]
Abstract
Vrp1p (yeast WIP) forms a protein complex with Las17p (yeast WASP), however the physiological significance of the interaction has not been fully characterized. Vrp1p residues, (788)MPKPR(792) are essential for Vrp1p-Las17p interaction. While C-Vrp1p(364-817) complements all the defects of the vrp1Δ strain, C-Vrp1p(364-817)(5A) ((788)AAAAA(792)) does not complement any of the defects, due to its inability to localize to cortical patches. Targeting C-Vrp1p(364-817)(5A) to membranes using CAAX motif (C-Vrp1p(364-817)(5A)-CAAX) rescued the growth and endocytosis defect but not the actin patch polarization defect of vrp1Δ. Vrp1p can localize to cortical patches, either by binding to Las17p through LBD (Las17 Binding Domain, Vrp1p(760-817)) or independent of Las17p through residues in N-Vrp1p(1-364). Unlike Vrp1p, Vrp1p(5A) localizes poorly to cortical patches and complements all the defects of vrp1Δ strain except actin patch polarization at elevated temperature. N-Vrp1p(1-364) complements all the defects of vrp1Δ strain except the actin patch polarization defect while N-Vrp1p(1-364)-LBD fusion protein complements all the defects. Thus our results show that while both Vrp1p and Las17p are essential for many cellular processes, the two proteins do not necessarily have to bind to each other to carry out these cellular functions. However, Las17p-Vrp1p interaction is essential for actin patch polarization at elevated temperature.
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Affiliation(s)
- Ming Hwa Wong
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Republic of Singapore
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40
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Yamamoto T, Mochida J, Kadota J, Takeda M, Bi E, Tanaka K. Initial polarized bud growth by endocytic recycling in the absence of actin cable-dependent vesicle transport in yeast. Mol Biol Cell 2010; 21:1237-52. [PMID: 20147449 PMCID: PMC2847527 DOI: 10.1091/mbc.e09-05-0412] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Budding yeast mutants in assembly of actin cables, which are thought to be the only actin structures essential for budding, still could form a small bud. Mutations in actin patch endocytic machineries/endocytic recycling factors inhibited this budding, suggesting a mechanism that promotes polarized growth by local recycling of endocytic vesicles. The assembly of filamentous actin is essential for polarized bud growth in budding yeast. Actin cables, which are assembled by the formins Bni1p and Bnr1p, are thought to be the only actin structures that are essential for budding. However, we found that formin or tropomyosin mutants, which lack actin cables, are still able to form a small bud. Additional mutations in components for cortical actin patches, which are assembled by the Arp2/3 complex to play a pivotal role in endocytic vesicle formation, inhibited this budding. Genes involved in endocytic recycling were also required for small-bud formation in actin cable-less mutants. These results suggest that budding yeast possesses a mechanism that promotes polarized growth by local recycling of endocytic vesicles. Interestingly, the type V myosin Myo2p, which was thought to use only actin cables to track, also contributed to budding in the absence of actin cables. These results suggest that some actin network may serve as the track for Myo2p-driven vesicle transport in the absence of actin cables or that Myo2p can function independent of actin filaments. Our results also show that polarity regulators including Cdc42p were still polarized in mutants defective in both actin cables and cortical actin patches, suggesting that the actin cytoskeleton does not play a major role in cortical assembly of polarity regulators in budding yeast.
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Affiliation(s)
- Takaharu Yamamoto
- Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University, Sapporo, Japan
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42
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Dominguez R. Structural insights into de novo actin polymerization. Curr Opin Struct Biol 2010; 20:217-25. [PMID: 20096561 DOI: 10.1016/j.sbi.2009.12.012] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Revised: 12/18/2009] [Accepted: 12/23/2009] [Indexed: 01/05/2023]
Abstract
Many cellular functions depend on rapid and localized actin polymerization/depolymerization. Yet, the de novo polymerization of actin in cells is kinetically unfavorable because of the instability of polymerization intermediates (small actin oligomers) and the actions of actin monomer binding proteins. Cells use filament nucleation and elongation factors to initiate and sustain polymerization. Structural biology is beginning to shed light on the diverse mechanisms by which these unrelated proteins initiate polymerization, undergo regulation, and mediate the transition of monomeric actin onto actin filaments. A prominent role is played by the W domain, which in some of these proteins occurs in tandem repeats that recruit multiple actin subunits. Pro-rich regions are also abundant and mediate the binding of profilin-actin complexes, which are the main source of polymerization competent actin in cells. Filament nucleation and elongation factors frequently interact with Rho-family GTPases, which relay signals from membrane receptors to regulate actin cytoskeleton remodeling.
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Affiliation(s)
- Roberto Dominguez
- Department of Physiology, 3700 Hamilton Walk, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
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43
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Dominguez R. Actin filament nucleation and elongation factors--structure-function relationships. Crit Rev Biochem Mol Biol 2009; 44:351-66. [PMID: 19874150 DOI: 10.3109/10409230903277340] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The spontaneous and unregulated polymerization of actin filaments is inhibited in cells by actin monomer-binding proteins such as profilin and Tbeta4. Eukaryotic cells and certain pathogens use filament nucleators to stabilize actin polymerization nuclei, whose formation is rate-limiting. Known filament nucleators include the Arp2/3 complex and its large family of nucleation promoting factors (NPFs), formins, Spire, Cobl, VopL/VopF, TARP and Lmod. These molecules control the time and location for polymerization, and additionally influence the structures of the actin networks that they generate. Filament nucleators are generally unrelated, but with the exception of formins they all use the WASP-Homology 2 domain (WH2 or W), a small and versatile actin-binding motif, for interaction with actin. A common architecture, found in Spire, Cobl and VopL/VopF, consists of tandem W domains that bind three to four actin subunits to form a nucleus. Structural considerations suggest that NPFs-Arp2/3 complex can also be viewed as a specialized form of tandem W-based nucleator. Formins are unique in that they use the formin-homology 2 (FH2) domain for interaction with actin and promote not only nucleation, but also processive barbed end elongation. In contrast, the elongation function among W-based nucleators has been "outsourced" to a dedicated family of proteins, Eva/VASP, which are related to WASP-family NPFs.
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Affiliation(s)
- Roberto Dominguez
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
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44
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Boettner DR, D'Agostino JL, Torres OT, Daugherty-Clarke K, Uygur A, Reider A, Wendland B, Lemmon SK, Goode BL. The F-BAR protein Syp1 negatively regulates WASp-Arp2/3 complex activity during endocytic patch formation. Curr Biol 2009; 19:1979-87. [PMID: 19962315 DOI: 10.1016/j.cub.2009.10.062] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Revised: 10/11/2009] [Accepted: 10/16/2009] [Indexed: 02/07/2023]
Abstract
BACKGROUND Actin polymerization by Arp2/3 complex must be tightly regulated to promote clathrin-mediated endocytosis. Although many Arp2/3 complex activators have been identified, mechanisms for its negative regulation have remained more elusive. To address this, we analyzed the yeast arp2-7 allele, which is biochemically unique in causing unregulated actin assembly in vitro in the absence of Arp2/3 activators. RESULTS We examined endocytosis in arp2-7 mutants by live-cell imaging of Sla1-GFP, a coat marker, and Abp1-RFP, which marks the later actin phase of endocytosis. Sla1-GFP and Abp1-RFP lifetimes were accelerated in arp2-7 mutants, which is opposite to actin nucleation-impaired arp2 alleles or deletions of Arp2/3 activators. We performed a screen for multicopy suppressors of arp2-7 and identified SYP1, an FCHO1 homolog, which contains F-BAR and AP-2micro homology domains. Overexpression of SYP1 in arp2-7 cells slowed Sla1-GFP lifetimes closer to wild-type cells. Further, purified Syp1 directly inhibited Las17/WASp stimulation of Arp2/3 complex-mediated actin assembly in vitro. This activity was mapped to a fragment of Syp1 located between its F-BAR and AP-2micro homology domains and depends on sequences in Las17/WASp outside of the VCA domain. CONCLUSIONS Together, these data identify Syp1 as a novel negative regulator of WASp-Arp2/3 complex that helps choreograph the precise timing of actin assembly during endocytosis.
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Affiliation(s)
- Douglas R Boettner
- Department of Molecular and Cellular Pharmacology, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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45
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Biochemical mechanisms for regulating protrusion by nematode major sperm protein. Biophys J 2009; 97:748-57. [PMID: 19651033 DOI: 10.1016/j.bpj.2009.05.038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2009] [Revised: 05/18/2009] [Accepted: 05/19/2009] [Indexed: 11/22/2022] Open
Abstract
Crawling motion is ubiquitous in eukaryotic cells and contributes to important processes such as immune response and tumor growth. To crawl, a cell must adhere to the substrate, while protruding at the front and retracting at the rear. In most crawling cells protrusion is driven by highly regulated polymerization of the actin cytoskeleton, and much of the biochemical network for this process is known. Nematode sperm utilize a cytoskeleton composed of Major Sperm Protein (MSP), which is considered to form a simpler, yet similar, crawling motility apparatus. Key components involved in the polymerization of MSP have been identified; however, little is known about the chemical kinetics for this system. Here we develop a model for MSP polymerization that takes into account the effects of several of the experimentally identified cytosolic and membrane-bound proteins. To account for some of the data, the model requires force-dependent polymerization, as is predicted by Brownian ratchet mechanisms. Using the tethered polymerization ratchet model with our biochemical kinetic model for MSP polymerization, we find good agreement with experimental data on MSP-driven protrusion. In addition, our model predicts the force-velocity relation that is expected for in vitro protrusion assays.
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46
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Rajmohan R, Wong MH, Meng L, Munn AL, Thanabalu T. Las17p-Vrp1p but not Las17p-Arp2/3 interaction is important for actin patch polarization in yeast. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:825-35. [PMID: 19272406 DOI: 10.1016/j.bbamcr.2009.02.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 02/25/2009] [Accepted: 02/26/2009] [Indexed: 11/18/2022]
Abstract
The actin cytoskeleton plays a central role in many important cellular processes such as cell polarization, cell division and endocytosis. The dynamic changes to the actin cytoskeleton that accompany these processes are regulated by actin-associated proteins Wiskott-Aldrich Syndrome Protein (WASP) (known as Las17p in yeast) and WASP-Interacting Protein (WIP) (known as Vrp1p in yeast). Both yeast and human WASP bind to and stimulate the Arp2/3 complex which in turn nucleates assembly of actin monomers into filaments at polarized sites at the cortex. WASP-WIP interaction in yeast and humans are important for Arp2/3 complex stimulation in vitro. It has been proposed that these interactions are also important for polarized actin assembly in vivo. However, the redundancy of actin-associated proteins has made it difficult to test this hypothesis. We have identified two point mutations (L80T and H94L) in yeast WASP that in combination abolish WASP-WIP interaction in yeast. We also identify an N-terminal fragment of Las17p (N-Las17p1-368) able to interact with Vrp1p but not Arp2/3. Using these mutant and truncated forms of yeast WASP we provide novel evidence that WASP interaction with WIP is more important than interaction with Arp2/3 for polarized actin assembly and endocytosis in yeast.
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Affiliation(s)
- Rajamuthiah Rajmohan
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Republic of Singapore
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Robertson AS, Allwood EG, Smith APC, Gardiner FC, Costa R, Winder SJ, Ayscough KR. The WASP homologue Las17 activates the novel actin-regulatory activity of Ysc84 to promote endocytosis in yeast. Mol Biol Cell 2009; 20:1618-28. [PMID: 19158382 PMCID: PMC2655254 DOI: 10.1091/mbc.e08-09-0982] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Actin plays an essential role in many eukaryotic cellular processes, including motility, generation of polarity, and membrane trafficking. Actin function in these roles is regulated by association with proteins that affect its polymerization state, dynamics, and organization. Numerous proteins have been shown to localize with cortical patches of yeast actin during endocytosis, but the role of many of these proteins remains poorly understood. Here, we reveal that the yeast protein Ysc84 represents a new class of actin-binding proteins, conserved from yeast to humans. It contains a novel N-terminal actin-binding domain termed Ysc84 actin binding (YAB), which can bind and bundle actin filaments. Intriguingly, full-length Ysc84 alone does not bind to actin, but binding can be activated by a specific motif within the polyproline region of the yeast WASP homologue Las17. We also identify a new monomeric actin-binding site on Las17. Together, the polyproline region of Las17 and Ysc84 can promote actin polymerization. Using live cell imaging, kinetics of assembly and disassembly of proteins at the endocytic site were analyzed and reveal that loss of Ysc84 and its homologue Lsb3 decrease inward movement of vesicles consistent with a role in actin polymerization during endocytosis.
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Affiliation(s)
- Alastair S Robertson
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom
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Stawiecka-Mirota M, Kamińska J, Urban-Grimal D, Haines DS, Żołądek T. Nedd4, a human ubiquitin ligase, affects actin cytoskeleton in yeast cells. Exp Cell Res 2008; 314:3318-25. [DOI: 10.1016/j.yexcr.2008.08.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Revised: 08/25/2008] [Accepted: 08/25/2008] [Indexed: 11/29/2022]
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Qi Y, Suhail Y, Lin YY, Boeke JD, Bader JS. Finding friends and enemies in an enemies-only network: a graph diffusion kernel for predicting novel genetic interactions and co-complex membership from yeast genetic interactions. Genome Res 2008; 18:1991-2004. [PMID: 18832443 DOI: 10.1101/gr.077693.108] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The yeast synthetic lethal genetic interaction network contains rich information about underlying pathways and protein complexes as well as new genetic interactions yet to be discovered. We have developed a graph diffusion kernel as a unified framework for inferring complex/pathway membership analogous to "friends" and genetic interactions analogous to "enemies" from the genetic interaction network. When applied to the Saccharomyces cerevisiae synthetic lethal genetic interaction network, we can achieve a precision around 50% with 20% to 50% recall in the genome-wide prediction of new genetic interactions, supported by experimental validation. The kernels show significant improvement over previous best methods for predicting genetic interactions and protein co-complex membership from genetic interaction data.
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Affiliation(s)
- Yan Qi
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Sinitsina N, Orshansky I, Sokolova O. Actin-binding proteins: how to reveal the conformational changes. J Bioinform Comput Biol 2008; 6:869-84. [PMID: 18763747 DOI: 10.1142/s0219720008003667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2007] [Revised: 12/31/2007] [Accepted: 01/04/2008] [Indexed: 11/18/2022]
Abstract
Actin is the most abundant protein in eukaryotes. Under physiological conditions, it can polymerize into polarized filaments. At the heart of these processes are actin-binding proteins that stimulate actin assembly. Most of them are composed of multiple domains that perform both regulatory and signaling functions. Many actin-binding proteins, including WASP and formin family proteins, are auto-inhibited through intramolecular interactions that mask the actin-regulating sites of these proteins. The large flexible molecules of formins have so far eluded crystallization, and have been crystallized only partially. The information from the available crystal structures is valuable, but somewhat difficult to interpret without a larger framework on which to pose the actin-binding mechanism. Single-particle electron microscopy and electron tomography could provide such a large framework with the full-length structures of protein complexes. The recent advances in determining the molecular interactions in protein complexes predict that the molecular modeling and molecular dynamics methods could be employed to study conformational changes in molecules.
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Affiliation(s)
- Natalia Sinitsina
- Faculty of Biology, Moscow State University, GSP-1, 1 Leninskie Gory, Bld 12, 119991 Moscow, Russia
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