1
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Gonzalez Rodriguez S, Wirshing AC, Goodman AL, Goode BL. Cytosolic concentrations of actin binding proteins and the implications for in vivo F-actin turnover. J Cell Biol 2023; 222:e202306036. [PMID: 37801069 PMCID: PMC10558290 DOI: 10.1083/jcb.202306036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 08/31/2023] [Accepted: 09/21/2023] [Indexed: 10/07/2023] Open
Abstract
Understanding how numerous actin-binding proteins (ABPs) work in concert to control the assembly, organization, and turnover of the actin cytoskeleton requires quantitative information about the levels of each component. Here, we measured the cellular concentrations of actin and the majority of the conserved ABPs in Saccharomyces cerevisiae, as well as the free (cytosolic) fractions of each ABP. The cellular concentration of actin is estimated to be 13.2 µM, with approximately two-thirds in the F-actin form and one-third in the G-actin form. Cellular concentrations of ABPs range from 12.4 to 0.85 µM (Tpm1> Pfy1> Cof1> Abp1> Srv2> Abp140> Tpm2> Aip1> Cap1/2> Crn1> Sac6> Twf1> Arp2/3> Scp1). The cytosolic fractions of all ABPs are unexpectedly high (0.6-0.9) and remain so throughout the cell cycle. Based on these numbers, we speculate that F-actin binding sites are limited in vivo, which leads to high cytosolic levels of ABPs, and in turn helps drive the rapid assembly and turnover of cellular F-actin structures.
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Affiliation(s)
- Sofia Gonzalez Rodriguez
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Alison C.E. Wirshing
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
| | - Anya L. Goodman
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
- Department of Chemistry and Biochemistry, California Polytechnic State University SLO, San Luis Obispo, CA, USA
| | - Bruce L. Goode
- Department of Biology, Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA, USA
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2
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Guo S, Hoeprich GJ, Magliozzi JO, Gelles J, Goode BL. Dynamic remodeling of actin networks by cyclase-associated protein and CAP-Abp1 complexes. Curr Biol 2023; 33:4484-4495.e5. [PMID: 37797614 DOI: 10.1016/j.cub.2023.09.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 07/20/2023] [Accepted: 09/13/2023] [Indexed: 10/07/2023]
Abstract
How actin filaments are spatially organized and remodeled into diverse higher-order networks in vivo is still not well understood. Here, we report an unexpected F-actin "coalescence" activity driven by cyclase-associated protein (CAP) and enhanced by its interactions with actin-binding protein 1 (Abp1). We directly observe S. cerevisiae CAP and Abp1 rapidly transforming branched or linear actin networks by bundling and sliding filaments past each other, maximizing filament overlap, and promoting compaction into bundles. This activity does not require ATP and is conserved, as similar behaviors are observed for the mammalian homologs of CAP and Abp1. Coalescence depends on the CAP oligomerization domain but not the helical folded domain (HFD) that mediates its functions in F-actin severing and depolymerization. Coalescence by CAP-Abp1 further depends on interactions between CAP and Abp1 and interactions between Abp1 and F-actin. Our results are consistent with a mechanism in which the formation of energetically favorable sliding CAP and CAP-Abp1 crosslinks drives F-actin bundle compaction. Roles for CAP and CAP-Abp1 in actin remodeling in vivo are supported by strong phenotypes arising from deletion of the CAP oligomerization domain and by genetic interactions between sac6Δ and an srv2-301 mutant that does not bind Abp1. Together, these observations identify a new actin filament remodeling function for CAP, which is further enhanced by its direct interactions with Abp1.
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Affiliation(s)
- Siyang Guo
- Department of Biology, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Gregory J Hoeprich
- Department of Biology, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Joseph O Magliozzi
- Department of Biology, Brandeis University, 415 South Street, Waltham, MA 02454, USA
| | - Jeff Gelles
- Department of Biochemistry, Brandeis University, 415 South Street, Waltham, MA 02454, USA.
| | - Bruce L Goode
- Department of Biology, Brandeis University, 415 South Street, Waltham, MA 02454, USA.
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3
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Ishida H, Woodman AG, Kitada N, Aizawa T, Vogel HJ. The Dictyostelium discoideum FimA protein, unlike yeast and plant fimbrins, is regulated by calcium similar to mammalian plastins. Sci Rep 2023; 13:16208. [PMID: 37758724 PMCID: PMC10533516 DOI: 10.1038/s41598-023-42682-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 09/13/2023] [Indexed: 09/29/2023] Open
Abstract
Plastins, also known as fimbrins, are highly conserved eukaryotic multidomain proteins that are involved in actin-bundling. They all contain four independently folded Calponin Homology-domains and an N-terminal headpiece that is comprised of two calcium-binding EF-hand motifs. Since calcium-binding has been shown to be integral to regulating the activity of the three mammalian plastin proteins, we decided to study the properties of the headpiece regions of fimbrins from the model plant Arabidopsis thaliana, the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe and the amoeba Dictyostelium discoideum. Of these protein domains only the FimA headpiece from the amoeba protein possesses calcium binding properties. Structural characterization of this protein domain by multidimensional NMR and site-directed mutagenesis studies indicates that this EF-hand region of FimA also contains a regulatory 'switch helix' that is essential to regulating the activity of the human L-plastin protein. Interestingly this regulatory helical region seems to be lacking in the plant and yeast proteins and in fimbrins from all other nonmotile systems. Typical calmodulin antagonists can displace the switch-helix from the FimA headpiece, suggesting that such drugs can deregulate the Ca2+-regulation of the actin-bunding in the amoeba, thereby making it a useful organism for drug screening against mammalian plastins.
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Affiliation(s)
- Hiroaki Ishida
- Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada
| | - Andrew G Woodman
- Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada
| | - Naoya Kitada
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Tomoyasu Aizawa
- Faculty of Advanced Life Science, Hokkaido University, Sapporo, 060-0810, Japan
| | - Hans J Vogel
- Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada.
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4
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Stephan OOH. Effects of environmental stress factors on the actin cytoskeleton of fungi and plants: Ionizing radiation and ROS. Cytoskeleton (Hoboken) 2023; 80:330-355. [PMID: 37066976 DOI: 10.1002/cm.21758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 03/20/2023] [Accepted: 03/29/2023] [Indexed: 04/18/2023]
Abstract
Actin is an abundant and multifaceted protein in eukaryotic cells that has been detected in the cytoplasm as well as in the nucleus. In cooperation with numerous interacting accessory-proteins, monomeric actin (G-actin) polymerizes into microfilaments (F-actin) which constitute ubiquitous subcellular higher order structures. Considering the extensive spatial dimensions and multifunctionality of actin superarrays, the present study analyses the issue if and to what extent environmental stress factors, specifically ionizing radiation (IR) and reactive oxygen species (ROS), affect the cellular actin-entity. In that context, this review particularly surveys IR-response of fungi and plants. It examines in detail which actin-related cellular constituents and molecular pathways are influenced by IR and related ROS. This comprehensive survey concludes that the general integrity of the total cellular actin cytoskeleton is a requirement for IR-tolerance. Actin's functions in genome organization and nuclear events like chromatin remodeling, DNA-repair, and transcription play a key role. Beyond that, it is highly significant that the macromolecular cytoplasmic and cortical actin-frameworks are affected by IR as well. In response to IR, actin-filament bundling proteins (fimbrins) are required to stabilize cables or patches. In addition, the actin-associated factors mediating cellular polarity are essential for IR-survivability. Moreover, it is concluded that a cellular homeostasis system comprising ROS, ROS-scavengers, NADPH-oxidases, and the actin cytoskeleton plays an essential role here. Consequently, besides the actin-fraction which controls crucial genome-integrity, also the portion which facilitates orderly cellular transport and polarized growth has to be maintained in order to survive IR.
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Affiliation(s)
- Octavian O H Stephan
- Department of Biology, Friedrich-Alexander University of Erlangen-Nuremberg, Erlangen, Bavaria, 91058, Germany
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5
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Azar B. Profile of David G. Drubin. Proc Natl Acad Sci U S A 2023; 120:e2308153120. [PMID: 37399409 PMCID: PMC10334723 DOI: 10.1073/pnas.2308153120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2023] Open
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6
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Wang X, Pai CY, Stone DE. Gradient tracking in mating yeast depends on Bud1 inactivation and actin-independent vesicle delivery. J Biophys Biochem Cytol 2022; 221:213500. [PMID: 36156058 PMCID: PMC9516845 DOI: 10.1083/jcb.202203004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 08/06/2022] [Accepted: 09/06/2022] [Indexed: 12/13/2022] Open
Abstract
The mating of budding yeast depends on chemotropism, a fundamental cellular process. Haploid yeast cells of opposite mating type signal their positions to one another through mating pheromones. We have proposed a deterministic gradient sensing model that explains how these cells orient toward their mating partners. Using the cell-cycle determined default polarity site (DS), cells assemble a gradient tracking machine (GTM) composed of signaling, polarity, and trafficking proteins. After assembly, the GTM redistributes up the gradient, aligns with the pheromone source, and triggers polarized growth toward the partner. Since positive feedback mechanisms drive polarized growth at the DS, it is unclear how the GTM is released for tracking. What prevents the GTM from triggering polarized growth at the DS? Here, we describe two mechanisms that are essential for tracking: inactivation of the Ras GTPase Bud1 and positioning of actin-independent vesicle delivery upgradient.
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Affiliation(s)
- Xin Wang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL,Howard Hughes Medical Institute, Department of Developmental Biology, Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA
| | - Chih-Yu Pai
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL
| | - David E. Stone
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL,Correspondence to David E. Stone:
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7
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ER-phagy requires the assembly of actin at sites of contact between the cortical ER and endocytic pits. Proc Natl Acad Sci U S A 2022; 119:2117554119. [PMID: 35101986 PMCID: PMC8833162 DOI: 10.1073/pnas.2117554119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/24/2021] [Indexed: 01/03/2023] Open
Abstract
Portions of the endoplasmic reticulum (ER) are degraded by autophagy (ER-phagy) in response to starvation or the accumulation of misfolded proteins. We show that ER-phagy requires assembly of actin at sites of contact between the edges of ER sheets and endocytic pits on the plasma membrane. Actin assembly may help to bring an element of the ER carrying the selective autophagy receptor Atg40 into the cell interior, where it associates with Atg11, a scaffold needed to recruit components for autophagosome assembly. Understanding the mechanism by which regions of the ER are selected for degradation and sequestered within autophagosomes may help in the development of novel approaches to treat diseases that result from the accumulation of misfolded proteins within the ER. Fragments of the endoplasmic reticulum (ER) are selectively delivered to the lysosome (mammals) or vacuole (yeast) in response to starvation or the accumulation of misfolded proteins through an autophagic process known as ER-phagy. A screen of the Saccharomyces cerevisiae deletion library identified end3Δ as a candidate knockout strain that is defective in ER-phagy during starvation conditions, but not bulk autophagy. We find that loss of End3 and its stable binding partner Pan1, or inhibition of the Arp2/3 complex that is coupled by the End3-Pan1 complex to endocytic pits, blocks the association of the cortical ER autophagy receptor, Atg40, with the autophagosomal assembly scaffold protein Atg11. The membrane contact site module linking the rim of cortical ER sheets and endocytic pits, consisting of Scs2 or Scs22, Osh2 or Osh3, and Myo3 or Myo5, is also needed for ER-phagy. Both Atg40 and Scs2 are concentrated at the edges of ER sheets and can be cross-linked to each other. Our results are consistent with a model in which actin assembly at sites of contact between the cortical ER and endocytic pits contributes to ER sequestration into autophagosomes.
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8
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Gihana GM, Cross-Najafi AA, Lacefield S. The mitotic exit network regulates the spatiotemporal activity of Cdc42 to maintain cell size. J Cell Biol 2021; 220:211575. [PMID: 33284320 PMCID: PMC7721911 DOI: 10.1083/jcb.202001016] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2020] [Revised: 09/29/2020] [Accepted: 10/29/2020] [Indexed: 12/29/2022] Open
Abstract
During G1 in budding yeast, the Cdc42 GTPase establishes a polar front, along which actin is recruited to direct secretion for bud formation. Cdc42 localizes at the bud cortex and then redistributes between mother and daughter in anaphase. The molecular mechanisms that terminate Cdc42 bud-localized activity during mitosis are poorly understood. We demonstrate that the activity of the Cdc14 phosphatase, released through the mitotic exit network, is required for Cdc42 redistribution between mother and bud. Induced Cdc14 nucleolar release results in premature Cdc42 redistribution between mother and bud. Inhibition of Cdc14 causes persistence of Cdc42 bud localization, which perturbs normal cell size and spindle positioning. Bem3, a Cdc42 GAP, binds Cdc14 and is dephosphorylated at late anaphase in a Cdc14-dependent manner. We propose that Cdc14 dephosphorylates and activates Bem3 to allow Cdc42 inactivation and redistribution. Our results uncover a mechanism through which Cdc14 regulates the spatiotemporal activity of Cdc42 to maintain normal cell size at cytokinesis.
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Affiliation(s)
| | | | - Soni Lacefield
- Department of Biology, Indiana University, Bloomington, IN
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9
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Pollard LW, Garabedian MV, Alioto SL, Shekhar S, Goode BL. Genetically inspired in vitro reconstitution of Saccharomyces cerevisiae actin cables from seven purified proteins. Mol Biol Cell 2020; 31:335-347. [PMID: 31913750 PMCID: PMC7183793 DOI: 10.1091/mbc.e19-10-0576] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
A major goal of synthetic biology is to define the minimal cellular machinery required to assemble a biological structure in its simplest form. Here, we focused on Saccharomyces cerevisiae actin cables, which provide polarized tracks for intracellular transport and maintain defined lengths while continuously undergoing rapid assembly and turnover. Guided by the genetic requirements for proper cable assembly and dynamics, we show that seven evolutionarily conserved S. cerevisiae proteins (actin, formin, profilin, tropomyosin, capping protein, cofilin, and AIP1) are sufficient to reconstitute the formation of cables that undergo polarized turnover and maintain steady-state lengths similar to actin cables in vivo. Further, the removal of individual proteins from this simple in vitro reconstitution system leads to cable defects that closely approximate in vivo cable phenotypes caused by disrupting the corresponding genes. Thus, a limited set of molecular components is capable of self-organizing into dynamic, micron-scale actin structures with features similar to cables in living cells.
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Affiliation(s)
| | | | | | | | - Bruce L Goode
- Department of Biology, Brandeis University, Waltham, MA 02454
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10
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Li L, Zhang S, Liu X, Yu R, Li X, Liu M, Zhang H, Zheng X, Wang P, Zhang Z. Magnaporthe oryzae Abp1, a MoArk1 Kinase-Interacting Actin Binding Protein, Links Actin Cytoskeleton Regulation to Growth, Endocytosis, and Pathogenesis. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2019; 32:437-451. [PMID: 30451565 DOI: 10.1094/mpmi-10-18-0281-r] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The actin cytoskeleton and actin-coupled endocytosis are conserved cellular processes required for the normal growth and pathogenesis of the rice blast fungus Magnaporthe oryzae. We have previously shown that actin regulating kinase MoArk1 regulates actin dynamics and endocytosis to play a key role in virulence of the fungus. To understand the underlying mechanism, we have characterized the actin-binding protein MoAbp1 that interacts with MoArk1 from M. oryzae. The ΔMoabp1 mutant exhibited delayed endocytosis and defects in growth, host penetration, and invasive growth. Consistent with its putative function associated with actin-binding, MoAbp1 regulates the localization of actin patches and plays a role in MoArk1 phosphorylation. In addition, MoAbp1 interacts with MoCap (adenylyl cyclase-associated protein) affecting its normal patch localization pattern and the actin protein MoAct1 through its conserved domains. Taken together, our results support a notion that MoAbp1 functions as a protein scaffold linking MoArk1, MoCap1, and MoAct1 to regulate actin cytoskeleton dynamics critical in growth and pathogenicity of the blast fungus.
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Affiliation(s)
- Lianwei Li
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Shengpei Zhang
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Xinyu Liu
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Rui Yu
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Xinrui Li
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Muxing Liu
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Haifeng Zhang
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Xiaobo Zheng
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
| | - Ping Wang
- 2 Departments of Pediatrics, and Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, U.S.A
| | - Zhengguang Zhang
- 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, and Key Laboratory of Integrated Management of Crop Diseases and Pests, Ministry of Education, Nanjing 210095, China; and
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11
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Abp1 promotes Arp2/3 complex-dependent actin nucleation and stabilizes branch junctions by antagonizing GMF. Nat Commun 2018; 9:2895. [PMID: 30042427 PMCID: PMC6057921 DOI: 10.1038/s41467-018-05260-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 06/22/2018] [Indexed: 12/26/2022] Open
Abstract
Formation and turnover of branched actin networks underlies cell migration and other essential force-driven processes. Type I nucleation-promoting factors (NPFs) such as WASP recruit actin monomers to Arp2/3 complex to stimulate nucleation. In contrast, mechanisms of type II NPFs such as Abp1 (also known as HIP55 and Drebrin-like protein) are less well understood. Here, we use single-molecule analysis to investigate yeast Abp1 effects on Arp2/3 complex, and find that Abp1 strongly enhances Arp2/3-dependent branch nucleation by stabilizing Arp2/3 on sides of mother filaments. Abp1 binds dynamically to filament sides, with sub-second lifetimes, yet associates stably with branch junctions. Further, we uncover a role for Abp1 in protecting filament junctions from GMF-induced debranching by competing with GMF for Arp2/3 binding. These data, combined with EM structures of Abp1 dimers bound to Arp2/3 complex in two different conformations, expand our mechanistic understanding of type II NPFs. Abp1, a type II actin nucleation promoting factor, is a known component of branched actin networks but its mechanism remains poorly understood. Here, the authors find that Abp1 enhances Arp2/3-mediated actin branch formation, and blocks ‘debranching’ by GMF, making it a pro-branching factor.
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12
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Antsotegi-Uskola M, Markina-Iñarrairaegui A, Ugalde U. Copper Resistance in Aspergillus nidulans Relies on the P I-Type ATPase CrpA, Regulated by the Transcription Factor AceA. Front Microbiol 2017; 8:912. [PMID: 28611736 PMCID: PMC5447758 DOI: 10.3389/fmicb.2017.00912] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 05/04/2017] [Indexed: 01/17/2023] Open
Abstract
Copper homeostasis has been extensively studied in mammals, bacteria, and yeast, but it has not been well-documented in filamentous fungi. In this report, we investigated the basis of copper tolerance in the model fungus Aspergillus nidulans. Three genes involved in copper homeostasis have been characterized. First, crpA the A. nidulans ortholog of Candida albicans CaCRP1 gene encoding a PI-type ATPase was identified. The phenotype of crpA deletion led to a severe sensitivity to Cu+2 toxicity and a characteristic morphological growth defect in the presence of high copper concentration. CrpA displayed some promiscuity regarding metal species response. The expression pattern of crpA showed an initial strong elevation of mRNA and a low continuous gene expression in response to long term toxic copper levels. Coinciding with maximum protein expression level, CrpA was localized close to the cellular surface, however protein distribution across diverse organelles suggests a complex regulated trafficking process. Secondly, aceA gene, encoding a transcription factor was identified and deleted, resulting in an even more extreme copper sensitivity than the ΔcrpA mutant. Protein expression assays corroborated that AceA was necessary for metal inducible expression of CrpA, but not CrdA, a putative metallothionein the function of which has yet to be elucidated.
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Affiliation(s)
- Martzel Antsotegi-Uskola
- Microbial Biochemistry Laboratory, Department of Applied Chemistry, Faculty of Chemistry, University of the Basque CountrySan Sebastian, Spain
| | - Ane Markina-Iñarrairaegui
- Microbial Biochemistry Laboratory, Department of Applied Chemistry, Faculty of Chemistry, University of the Basque CountrySan Sebastian, Spain
| | - Unai Ugalde
- Microbial Biochemistry Laboratory, Department of Applied Chemistry, Faculty of Chemistry, University of the Basque CountrySan Sebastian, Spain
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13
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Kojima N. Molecular Cloning of Drebrin: Progress and Perspectives. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1006:25-36. [DOI: 10.1007/978-4-431-56550-5_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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14
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Vasicova P, Rinnerthaler M, Haskova D, Novakova L, Malcova I, Breitenbach M, Hasek J. Formaldehyde fixation is detrimental to actin cables in glucose-depleted S. cerevisiae cells. MICROBIAL CELL 2016; 3:206-214. [PMID: 28357356 PMCID: PMC5349148 DOI: 10.15698/mic2016.05.499] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Actin filaments form cortical patches and emanating cables in fermenting cells of
Saccharomyces cerevisiae. This pattern has been shown to be
depolarized in glucose-depleted cells after formaldehyde fixation and staining
with rhodamine-tagged phalloidin. Loss of actin cables in mother cells was
remarkable. Here we extend our knowledge on actin in live glucose-depleted cells
co-expressing the marker of actin patches (Abp1-RFP) with the marker of actin
cables (Abp140-GFP). Glucose depletion resulted in appearance of actin patches
also in mother cells. However, even after 80 min of glucose deprivation these
cells showed a clear network of actin cables labeled with Abp140-GFP in contrast
to previously published data. In live cells with a mitochondrial dysfunction
(rho0 cells), glucose depletion resulted in almost immediate
appearance of Abp140-GFP foci partially overlapping with Abp1-RFP patches in
mother cells. Residual actin cables were clustered in patch-associated bundles.
A similar overlapping “patchy” pattern of both actin markers was observed upon
treatment of glucose-deprived rho+ cells with FCCP (the inhibitor of
oxidative phosphorylation) and upon treatment with formaldehyde. While the
formaldehyde-targeted process stays unknown, our results indicate that published
data on yeast actin cytoskeleton obtained from glucose-depleted cells after
fixation should be considered with caution.
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Affiliation(s)
- Pavla Vasicova
- Laboratory of Cell Reproduction, Institute of Microbiology of the CAS, v.v.i., Prague, Czech Republic
| | - Mark Rinnerthaler
- Department of Cell Biology, Division of Genetics, University of Salzburg, Salzburg, Austria
| | - Danusa Haskova
- Laboratory of Cell Reproduction, Institute of Microbiology of the CAS, v.v.i., Prague, Czech Republic
| | - Lenka Novakova
- Laboratory of Cell Reproduction, Institute of Microbiology of the CAS, v.v.i., Prague, Czech Republic
| | - Ivana Malcova
- Laboratory of Cell Reproduction, Institute of Microbiology of the CAS, v.v.i., Prague, Czech Republic
| | - Michael Breitenbach
- Department of Cell Biology, Division of Genetics, University of Salzburg, Salzburg, Austria
| | - Jiri Hasek
- Laboratory of Cell Reproduction, Institute of Microbiology of the CAS, v.v.i., Prague, Czech Republic
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15
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Miao Y, Han X, Zheng L, Xie Y, Mu Y, Yates JR, Drubin DG. Fimbrin phosphorylation by metaphase Cdk1 regulates actin cable dynamics in budding yeast. Nat Commun 2016; 7:11265. [PMID: 27068241 PMCID: PMC4832064 DOI: 10.1038/ncomms11265] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 03/07/2016] [Indexed: 12/15/2022] Open
Abstract
Actin cables, composed of actin filament bundles nucleated by formins, mediate intracellular transport for cell polarity establishment and maintenance. We previously observed that metaphase cells preferentially promote actin cable assembly through cyclin-dependent kinase 1 (Cdk1) activity. However, the relevant metaphase Cdk1 targets were not known. Here we show that the highly conserved actin filament crosslinking protein fimbrin is a critical Cdk1 target for actin cable assembly regulation in budding yeast. Fimbrin is specifically phosphorylated on threonine 103 by the metaphase cyclin–Cdk1 complex, in vivo and in vitro. On the basis of conformational simulations, we suggest that this phosphorylation stabilizes fimbrin's N-terminal domain, and modulates actin filament binding to regulate actin cable assembly and stability in cells. Overall, this work identifies fimbrin as a key target for cell cycle regulation of actin cable assembly in budding yeast, and suggests an underlying mechanism. Metaphase cells preferentially promote actin cable assembly through cyclin-dependent kinase 1 (Cdk1) activity. Here the authors identify fimbrin as one of the main metaphase Cdk1 targets for cell cycle regulation of actin cable assembly in budding yeast.
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Affiliation(s)
- Yansong Miao
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202, USA.,School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.,School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore
| | - Xuemei Han
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - Liangzhen Zheng
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - Ying Xie
- School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore
| | - Yuguang Mu
- School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore
| | - John R Yates
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, California 92037, USA
| | - David G Drubin
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202, USA
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16
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Møller HD, Bojsen RK, Tachibana C, Parsons L, Botstein D, Regenberg B. Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells. J Vis Exp 2016:e54239 |. [PMID: 27077531 DOI: 10.3791/54239] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs contribute to genetic variation among somatic cells in multicellular organisms and to evolution of unicellular eukaryotes. Sensitive methods for detecting eccDNA are needed to clarify how these elements affect genome stability and how environmental and biological factors induce their formation in eukaryotic cells. This video presents a sensitive eccDNA-purification method called Circle-Seq. The method encompasses column purification of circular DNA, removal of remaining linear chromosomal DNA, rolling-circle amplification of eccDNA, deep sequencing, and mapping. Extensive exonuclease treatment was required for sufficient linear chromosomal DNA degradation. The rolling-circle amplification step by φ29 polymerase enriched for circular DNA over linear DNA. Validation of the Circle-Seq method on three S. cerevisiae CEN.PK populations of 10(10) cells detected hundreds of eccDNA profiles in sizes larger than 1 kilobase. Repeated findings of ASP3-1, COS111, CUP1, RSC30, HXT6, HXT7 genes on circular DNA in both S288c and CEN.PK suggests that DNA circularization is conserved between strains at these loci. In sum, the Circle-Seq method has broad applicability for genome-scale screening for eccDNA in eukaryotes as well as for detecting specific eccDNA types.
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Affiliation(s)
| | - Rasmus K Bojsen
- National Veterinary Institute, Technical University of Denmark
| | | | - Lance Parsons
- Lewis-Sigler Institute for Integrative Genomics, Princeton University
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17
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Schultzhaus Z, Quintanilla L, Hilton A, Shaw BD. Live Cell Imaging of Actin Dynamics in the Filamentous Fungus Aspergillus nidulans. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2016; 22:264-274. [PMID: 26879694 DOI: 10.1017/s1431927616000131] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Hyphal cells of filamentous fungi grow at their tips in a method analogous to pollen tube and root hair elongation. This process, generally referred to as tip growth, requires precise regulation of the actin cytoskeleton, and characterizing the various actin structures in these cell types is currently an active area of research. Here, the actin marker Lifeact was used to document actin dynamics in the filamentous fungus Aspergillus nidulans. Contractile double rings were observed at septa, and annular clusters of puncta were seen subtending growing hyphal tips, corresponding to the well-characterized subapical endocytic collar. However, Lifeact also revealed two additional structures. One, an apical array, was dynamic on the face opposite the tip, while a subapical web was dynamic on the apical face and was located several microns behind the growth site. Each was observed turning into the other over time, implying that they could represent different localizations of the same structure, although hyphae with a subapical web grew faster than those exhibiting an apical array. The subapical web has not been documented in any filamentous fungus to date, and is separate from the networks of F-actin seen in other tip-growing organisms surrounding septa or stationary along the plasmalemma.
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Affiliation(s)
- Zachary Schultzhaus
- Department of Plant Pathology and Microbiology,Texas A&M University,College Station,TX 77843,USA
| | - Laura Quintanilla
- Department of Plant Pathology and Microbiology,Texas A&M University,College Station,TX 77843,USA
| | - Angelyn Hilton
- Department of Plant Pathology and Microbiology,Texas A&M University,College Station,TX 77843,USA
| | - Brian D Shaw
- Department of Plant Pathology and Microbiology,Texas A&M University,College Station,TX 77843,USA
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18
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Feliziani C, Valdez Taubas J, Moyano S, Quassollo G, Poprawski JE, Wendland B, Touz MC. Vestiges of Ent3p/Ent5p function in the giardial epsin homolog. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:749-59. [PMID: 26851076 DOI: 10.1016/j.bbamcr.2016.02.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 01/12/2016] [Accepted: 02/01/2016] [Indexed: 11/29/2022]
Abstract
An accurate way to characterize the functional potential of a protein is to analyze recognized protein domains encoded by the genes in a given group. The epsin N-terminal homology (ENTH) domain is an evolutionarily conserved protein module found primarily in proteins that participate in clathrin-mediated trafficking. In this work, we investigate the function of the single ENTH-containing protein from the protist Giardia lamblia by testing its function in Saccharomyces cerevisiae. This protein, named GlENTHp (for G. lamblia ENTH protein), is involved in Giardia in endocytosis and in protein trafficking from the ER to the vacuoles, fulfilling the function of the ENTH proteins epsin and epsinR, respectively. There are two orthologs of epsin, Ent1p and Ent2p, and two orthologs of epsinR, Ent3p and Ent5p in S. cerevisiae. Although the expression of GlENTHp neither complemented growth in the ent1Δent2Δ mutant nor restored the GFP-Cps1 vacuolar trafficking defect in ent3Δent5Δ, it interfered with the normal function of Ent3/5 in the wild-type strain. The phenotype observed is linked to a defect in Cps1 localization and α-factor mating pheromone maturation. The finding that GlENTHp acts as dominant negative epsinR in yeast cells reinforces the phylogenetic data showing that GlENTHp belongs to the epsinR subfamily present in eukaryotes prior to their evolution into different taxa.
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Affiliation(s)
- Constanza Feliziani
- Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Friuli, 2434, Córdoba, Argentina
| | - Javier Valdez Taubas
- Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC (UNC-CONICET), Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, X5000HUA Córdoba, Argentina
| | - Sofía Moyano
- Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Friuli, 2434, Córdoba, Argentina
| | - Gonzalo Quassollo
- Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Friuli, 2434, Córdoba, Argentina
| | - Joanna E Poprawski
- Department of Biology, Johns Hopkins University, 3400 N. Charles St., Mudd Hall Room 35, Baltimore, USA
| | - Beverly Wendland
- Department of Biology, Johns Hopkins University, 3400 N. Charles St., Mudd Hall Room 35, Baltimore, USA
| | - Maria C Touz
- Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC-CONICET, Universidad Nacional de Córdoba, Friuli, 2434, Córdoba, Argentina.
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19
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Lee SJ, Seo BR, Koh JY. Metallothionein-3 modulates the amyloid β endocytosis of astrocytes through its effects on actin polymerization. Mol Brain 2015; 8:84. [PMID: 26637294 PMCID: PMC4670512 DOI: 10.1186/s13041-015-0173-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 11/30/2015] [Indexed: 12/30/2022] Open
Abstract
Background Astrocytes may play important roles in the pathogenesis of Alzheimer’s disease (AD) by clearing extracellular amyloid beta (Aβ) through endocytosis and degradation. We recently showed that metallothionein 3 (Mt3), a zinc-binding metallothionein that is enriched in the central nervous system, contributes to actin polymerization in astrocytes. Because actin is likely involved in the endocytosis of Aβ, we investigated the possible role of Mt3 in Aβ endocytosis by cortical astrocytes in this study. Results To assess the route of Aβ uptake, we exposed cultured astrocytes to fluorescently labeled Aβ1–40 or Aβ1–42 together with chloropromazine (CP) or methyl-beta-cyclodextrin (MβCD), inhibitors of clathrin- and caveolin-dependent endocytosis, respectively. CP treatment almost completely blocked Aβ1–40 and Aβ1–42 endocytosis, whereas exposure to MβCD had no significant effect. Actin disruption with cytochalasin D (CytD) or latrunculin B also completely blocked Aβ1–40 and Aβ1–42 endocytosis. Because the absence of Mt3 also results in actin disruption, we examined Aβ1–40 and Aβ1–42 uptake and expression in Mt3−/− astrocytes. Compared with wild-type (WT) cells, Mt3−/− cells exhibited markedly reduced Aβ1–40 and Aβ1–42 endocytosis and expression of Aβ1-42 monomers and oligomers. A similar reduction was observed in CytD-treated WT cells. Finally, actin disruption and Mt3 knockout each increased the overall levels of clathrin and the associated protein phosphatidylinositol-binding clathrin assembly protein (PICALM) in astrocytes. Conclusions Our results suggest that the absence of Mt3 reduces Aβ uptake in astrocytes through an abnormality in actin polymerization. In light of evidence that Mt3 is downregulated in AD, our findings indicate that this mechanism may contribute to the extracellular accumulation of Aβ in this disease.
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Affiliation(s)
- Sook-Jeong Lee
- Neural Injury Research Center, Asan Institute for Life Sciences, University of Ulsan College of Medicine, Seoul, South Korea. .,Present address: Department of New Drug Discovery and Development, Chungnam National University, 99 Daehak-ro, Yuseong, Daejeon, 34134, South Korea.
| | - Bo-Ra Seo
- Neural Injury Research Center, Asan Institute for Life Sciences, University of Ulsan College of Medicine, Seoul, South Korea.
| | - Jae-Young Koh
- Neural Injury Research Center, Asan Institute for Life Sciences, University of Ulsan College of Medicine, Seoul, South Korea. .,Department of Neurology, Asan Medical Center, University of Ulsan College of Medicine, 88, Olympic-ro 43-Gil, Songpa-Gu, Seoul, 05505, South Korea.
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20
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Wu CF, Chiou JG, Minakova M, Woods B, Tsygankov D, Zyla TR, Savage NS, Elston TC, Lew DJ. Role of competition between polarity sites in establishing a unique front. eLife 2015; 4:e11611. [PMID: 26523396 PMCID: PMC4728132 DOI: 10.7554/elife.11611] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 11/01/2015] [Indexed: 01/15/2023] Open
Abstract
Polarity establishment in many cells is thought to occur via positive feedback that reinforces even tiny asymmetries in polarity protein distribution. Cdc42 and related GTPases are activated and accumulate in a patch of the cortex that defines the front of the cell. Positive feedback enables spontaneous polarization triggered by stochastic fluctuations, but as such fluctuations can occur at multiple locations, how do cells ensure that they make only one front? In polarizing cells of the model yeast Saccharomyces cerevisiae, positive feedback can trigger growth of several Cdc42 clusters at the same time, but this multi-cluster stage rapidly evolves to a single-cluster state, which then promotes bud emergence. By manipulating polarity protein dynamics, we show that resolution of multi-cluster intermediates occurs through a greedy competition between clusters to recruit and retain polarity proteins from a shared intracellular pool.
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Affiliation(s)
- Chi-Fang Wu
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, United States
| | - Jian-Geng Chiou
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, United States
| | - Maria Minakova
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, United States
| | - Benjamin Woods
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, United States
| | - Denis Tsygankov
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, United States
| | - Trevin R Zyla
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, United States
| | - Natasha S Savage
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Timothy C Elston
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, United States
| | - Daniel J Lew
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, United States
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21
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The Stationary-Phase Cells of Saccharomyces cerevisiae Display Dynamic Actin Filaments Required for Processes Extending Chronological Life Span. Mol Cell Biol 2015; 35:3892-908. [PMID: 26351139 DOI: 10.1128/mcb.00811-15] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 08/31/2015] [Indexed: 11/20/2022] Open
Abstract
Stationary-growth-phase Saccharomyces cerevisiae yeast cultures consist of nondividing cells that undergo chronological aging. For their successful survival, the turnover of proteins and organelles, ensured by autophagy and the activation of mitochondria, is performed. Some of these processes are engaged in by the actin cytoskeleton. In S. cerevisiae stationary-phase cells, F actin has been shown to form static aggregates named actin bodies, subsequently cited to be markers of quiescence. Our in vivo analyses revealed that stationary-phase cultures contain cells with dynamic actin filaments, besides the cells with static actin bodies. The cells with dynamic actin displayed active endocytosis and autophagy and well-developed mitochondrial networks. Even more, stationary-phase cell cultures grown under calorie restriction predominantly contained cells with actin cables, confirming that the presence of actin cables is linked to successful adaptation to stationary phase. Cells with actin bodies were inactive in endocytosis and autophagy and displayed aberrations in mitochondrial networks. Notably, cells of the respiratory activity-deficient cox4Δ strain displayed the same mitochondrial aberrations and actin bodies only. Additionally, our results indicate that mitochondrial dysfunction precedes the formation of actin bodies and the appearance of actin bodies corresponds to decreased cell fitness. We conclude that the F-actin status reflects the extent of damage that arises from exponential growth.
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22
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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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23
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Zheng Z, Gao T, Zhang Y, Hou Y, Wang J, Zhou M. FgFim, a key protein regulating resistance to the fungicide JS399-19, asexual and sexual development, stress responses and virulence in Fusarium graminearum. MOLECULAR PLANT PATHOLOGY 2014; 15:488-99. [PMID: 24299032 PMCID: PMC6638886 DOI: 10.1111/mpp.12108] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Fimbrin is an actin-bundling protein found in intestinal microvilli, hair cell stereocilia and fibroblast filopodia. Its homologue Sac6p has been shown to play a critical role in endocytosis and diverse cellular processes in Saccharomyces cerevisiae. FgFim from the wheat scab pathogenic fungus Fusarium graminearum strain Y2021A, which is highly resistant to the fungicide JS399-19, was identified by screening a mutant library generated by HPH-HSV-tk cassette-mediated integration. The functions of FgFim were evaluated by constructing a deletion mutant of FgFim, designated ΔFgFim-15. The deletion mutant exhibited a reduced rate of mycelial growth, reduced conidiation, delayed conidium germination, irregularly shaped hyphae, a lack of sexual reproduction on autoclaved wheat kernels and a dramatic decrease in resistance to JS399-19. ΔFgFim-15 also exhibited increased sensitivity to diverse metal cations, to agents that induce osmotic stress and oxidative stress, and to agents that damage the cell membrane and cell wall. Pathogenicity assays showed that the virulence of the FgFim deletion mutant on flowering wheat heads was impaired, which was consistent with its reduced production of the toxin deoxynivalenol in host tissue. All of these defects were restored by genetic complementation of the mutant with the parental FgFim gene. Quantitative real-time polymerase chain reaction (PCR) assays showed that the basal expression of three Cyp51 genes, which encode sterol 14α-demethylase, was significantly lower in the mutant than in the parental strain. The results of this study indicate that FgFim plays a critical role in the regulation of resistance to JS399-19 and in various cellular processes in F. graminearum.
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Affiliation(s)
- Zhitian Zheng
- College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Pesticide, Jiangsu Province, Nanjing, 210095, China
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24
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Michelot A, Grassart A, Okreglak V, Costanzo M, Boone C, Drubin DG. Actin filament elongation in Arp2/3-derived networks is controlled by three distinct mechanisms. Dev Cell 2013; 24:182-95. [PMID: 23333351 DOI: 10.1016/j.devcel.2012.12.008] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Revised: 11/20/2012] [Accepted: 12/11/2012] [Indexed: 10/27/2022]
Abstract
Spatial and temporal control of actin filament barbed end elongation is crucial for force generation by actin networks. In this study, genetics, cell biology, and biochemistry were used to reveal three complementary mechanisms that regulate actin filament barbed end elongation in Arp2/3-derived networks. Aip1 inhibits elongation of aged ADP-actin filaments decorated with cofilin and, together with capping protein (CP), maintains a high level of assembly-competent actin species. We identified Abp1 and Aim3 as two additional proteins that work together to inhibit barbed end elongation. Abp1/Aim3 collaborates with CP to control elongation of newly assembled ATP-actin filaments to organize filament polarity within actin networks. Thus, three distinct mechanisms control filament elongation in different regions of Arp2/3 networks, maintaining pools of assembly-competent actin species while ensuring proper filament polarity and facilitating force production.
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Affiliation(s)
- Alphée Michelot
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA
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25
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Kaminskyj SGW, Jackson SL, Heath IB. Fixation induces differential polarized translocations of organelles in hyphae ofSaprolegnia ferax. J Microsc 2012. [DOI: 10.1111/j.1365-2818.1992.tb03226.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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26
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The importance of conserved features of yeast actin-binding protein 1 (Abp1p): the conditional nature of essentiality. Genetics 2012; 191:1199-211. [PMID: 22661326 DOI: 10.1534/genetics.112.141739] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Saccharomyces cerevisiae Actin-Binding Protein 1 (Abp1p) is a member of the Abp1 family of proteins, which are in diverse organisms including fungi, nematodes, flies, and mammals. All proteins in this family possess an N-terminal Actin Depolymerizing Factor Homology (ADF-H) domain, a central Proline-Rich Region (PRR), and a C-terminal SH3 domain. In this study, we employed sequence analysis to identify additional conserved features of the family, including sequences rich in proline, glutamic acid, serine, and threonine amino acids (PEST), which are found in all family members examined, and two motifs, Conserved Fungal Motifs 1 and 2 (CFM1 and CFM2), that are conserved in fungi. We also discovered that, similar to its mammalian homologs, Abp1p is phosphorylated in its PRR. This phosphorylation is mediated by the Cdc28p and Pho85p kinases, and it protects Abp1p from proteolysis mediated by the conserved PEST sequences. We provide evidence for an intramolecular interaction between the PRR region and SH3 domain that may be affected by phosphorylation. Although deletion of CFM1 alone caused no detectable phenotype in any genetic backgrounds or conditions tested, deletion of this motif resulted in a significant reduction of growth when it was combined with a deletion of the ADF-H domain. Importantly, this result demonstrates that deletion of highly conserved domains on its own may produce no phenotype unless the domains are assayed in conjunction with deletions of other functionally important elements within the same protein. Detection of this type of intragenic synthetic lethality provides an important approach for understanding the function of individual protein domains or motifs.
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27
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Role of actin-bundling protein Sac6 in growth of Cryptococcus neoformans at low oxygen concentration. EUKARYOTIC CELL 2012; 11:943-51. [PMID: 22562467 DOI: 10.1128/ec.00120-12] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Cryptococcus neoformans, the etiologic agent of cryptococcosis, is an obligately aerobic yeast that inhabits an environmental niche exposed to ambient air. The cell doubling time was significantly prolonged under 1% O(2) relative to that under normoxic conditions. No apparent cell cycle arrest occurred following a shift from ambient air to 1% O(2). However, yeast cells became hypersensitive to the actin monomer-sequestering agent latrunculin A at 1% O(2), indicating that proper actin function is critical for growth at low oxygen concentrations. We showed that Sac6, an actin-binding protein, played an important role in cell growth under low oxygen conditions. Sac6 colocalized with cortical actin patches and with the ring structures between mother cells and buds. Under low oxygen conditions, the sac6 deletion mutant grew poorly, and accumulation of the actin capping protein Cap1 was observed in the vacuole of the sac6Δ strain. Furthermore, endocytic processes were hampered in the sac6Δ mutant, but cell polarity and cytokinesis were not visibly disturbed. The deficiency of endocytosis in the sac6Δ strain could be rescued by 1 M sorbitol under 1% O(2), but growth remained retarded. These results suggest an absence of a direct link in C. neoformans between endocytosis and coping with the stress of low oxygen conditions. This interpretation is further supported by the observation that deletion of three conserved genes, ABP1, CRN1, and SLA2, which play important roles in endocytosis, had no effect on growth under 1% O(2). Interestingly, deletion of SAC6 in C. neoformans had no effect on virulence in mice.
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28
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Koch N, Dharmalingam E, Westermann M, Qualmann B, Thomas U, Kessels MM. Abp1 utilizes the Arp2/3 complex activator Scar/WAVE in bristle development. J Cell Sci 2012; 125:3578-89. [PMID: 22467854 DOI: 10.1242/jcs.101451] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many developmental processes rely on cortical actin dynamics; however, the mechanisms of its fine control at the cell cortex are still largely unknown. Our analyses demonstrate that the lipid- and F-actin-binding protein Abp1 is crucial for actin-driven bristle development in Drosophila melanogaster. Combined genetic, cell biological and biochemical analyses reveal that Abp1 triggers cortical Arp2/3-mediated actin nucleation by complex formation with Scar in bristle development. The role of the plasma-membrane-associated Abp1 subpool was highlighted by constitutively membrane-anchored Abp1. Such gain-of-function experiments led to a severe split-bristle phenotype, which was negatively correlated with bristle length. This phenotype was dependent on Scar but not on WASP and required the Scar-interacting SH3 domain of Abp1. Strikingly, knockout of abp1 led to defects in both microchaete and macrochaete bristle integrity. Importantly, Arp2- and Scar-deficient flies displayed similar bristle phenotypes. Microchaetes of flies deficient for Abp1, Arp2 and Scar functions had kinks, whereas those of wasp heterozygous flies did not. Electron microscopy analyses revealed that abp1 knockout, Arp2 RNAi and Scar RNAi all led to distorted macrochaetes with an excessive number of ridges. Interestingly, despite the physical association of Abp1 with Scar and its ability to use the Arp2/3 complex activator as an effector, abp1 knockout did not affect Scar stability. This is in contrast to classical Scar complex components, such as Kette or Sra-1. Our work reveals that Abp1 is an important, Scar-interacting factor controlling cortical Arp2/3-mediated actin nucleation and unravels a novel layer of complexity in the scrupulous control of cortical actin nucleation during sensory organ formation.
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Affiliation(s)
- Nicole Koch
- Institute for Biochemistry I, Jena University Hospital - Friedrich Schiller University Jena, 07743 Jena, Germany
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29
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Poukkula M, Kremneva E, Serlachius M, Lappalainen P. Actin-depolymerizing factor homology domain: a conserved fold performing diverse roles in cytoskeletal dynamics. Cytoskeleton (Hoboken) 2011; 68:471-90. [PMID: 21850706 DOI: 10.1002/cm.20530] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2011] [Revised: 06/29/2011] [Accepted: 08/05/2011] [Indexed: 11/09/2022]
Abstract
Actin filaments form contractile and protrusive structures that play central roles in many processes such as cell migration, morphogenesis, endocytosis, and cytokinesis. During these processes, the dynamics of the actin filaments are precisely regulated by a large array of actin-binding proteins. The actin-depolymerizing factor homology (ADF-H) domain is a structurally conserved protein motif, which promotes cytoskeletal dynamics by interacting with monomeric and/or filamentous actin, and with the Arp2/3 complex. Despite their structural homology, the five classes of ADF-H domain proteins display distinct biochemical activities and cellular roles, only parts of which are currently understood. ADF/cofilin promotes disassembly of aged actin filaments, whereas twinfilin inhibits actin filament assembly via sequestering actin monomers and interacting with filament barbed ends. GMF does not interact with actin, but instead binds Arp2/3 complex and promotes dissociation of Arp2/3-mediated filament branches. Abp1 and drebrin are multidomain proteins that interact with actin filaments and regulate the activities of other proteins during various actin-dependent processes. The exact function of coactosin is currently incompletely understood. In this review article, we discuss the biochemical functions, cellular roles, and regulation of the five groups of ADF-H domain proteins.
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Affiliation(s)
- Minna Poukkula
- Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, Finland
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Jorde S, Walther A, Wendland J. The Ashbya gossypii fimbrin SAC6 is required for fast polarized hyphal tip growth and endocytosis. Microbiol Res 2011; 166:137-45. [PMID: 21237627 DOI: 10.1016/j.micres.2010.09.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Revised: 09/15/2010] [Accepted: 09/25/2010] [Indexed: 11/16/2022]
Abstract
Ashbya gossypii has been an ideal system to study filamentous hyphal growth. Previously, we identified a link between polarized hyphal growth, the organization of the actin cytoskeleton and endocytosis with our analysis of the A. gossypii Wiskott-Aldrich Syndrome Protein (WASP)-homolog encoded by the AgWAL1 gene. Here, we studied the role of AgSAC6, encoding a fimbrin in polarized hyphal growth and endocytosis, and based on our functional analysis identified genetic interactions between AgSAC6 and AgWAL1. SAC6 mutants show severely reduced polarized growth. This growth phenotype is temperature dependent and sac6 spores do not germinate at elevated temperatures. Spores germinated at 30°C generate slow growing mycelia without displaying polarity establishment defects at the hyphal tip. Several phenotypic characteristics of sac6 hyphae resemble those found in wal1 mutants. First, tips of sac6 hyphae shifted to 37°C swell and produce subapical bulges. Second, actin patches are mislocalized subapically. And third, the rate of endocytotic uptake of the vital dye FM4-64 was reduced. This indicates that actin filament bundling, a conserved function of fimbrins, is required for fast polarized hyphal growth, polarity maintenance, and endocytosis in filamentous fungi.
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Affiliation(s)
- Sigyn Jorde
- Carlsberg Laboratory, Yeast Biology, Gamle Carlsberg Vej 10, DK-2500 Valby, Copenhagen, Denmark
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Wu Y, Yan J, Zhang R, Qu X, Ren S, Chen N, Huang S. Arabidopsis FIMBRIN5, an actin bundling factor, is required for pollen germination and pollen tube growth. THE PLANT CELL 2010; 22:3745-63. [PMID: 21098731 PMCID: PMC3015131 DOI: 10.1105/tpc.110.080283] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2010] [Revised: 10/09/2010] [Accepted: 11/08/2010] [Indexed: 05/18/2023]
Abstract
Actin cables in pollen tubes serve as molecular tracks for cytoplasmic streaming and organelle movement and are formed by actin bundling factors like villins and fimbrins. However, the precise mechanisms by which actin cables are generated and maintained remain largely unknown. Fimbrins comprise a family of five members in Arabidopsis thaliana. Here, we characterized a fimbrin isoform, Arabidopsis FIMBRIN5 (FIM5). Our results show that FIM5 is required for the organization of actin cytoskeleton in pollen grains and pollen tubes, and FIM5 loss-of-function associates with a delay of pollen germination and inhibition of pollen tube growth. FIM5 decorates actin filaments throughout pollen grains and tubes. Actin filaments become redistributed in fim5 pollen grains and disorganized in fim5 pollen tubes. Specifically, actin cables protrude into the extreme tips, and their longitudinal arrangement is disrupted in the shank of fim5 pollen tubes. Consequently, the pattern and velocity of cytoplasmic streaming were altered in fim5 pollen tubes. Additionally, loss of FIM5 function rendered pollen germination and tube growth hypersensitive to the actin-depolymerizing drug latrunculin B. In vitro biochemical analyses indicated that FIM5 exhibits actin bundling activity and stabilizes actin filaments. Thus, we propose that FIM5 regulates actin dynamics and organization during pollen germination and tube growth via stabilizing actin filaments and organizing them into higher-order structures.
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Affiliation(s)
- Youjun Wu
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Graduate School of Chinese Academy of Sciences, Beijing 100049, China
| | - Jin Yan
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Graduate School of Chinese Academy of Sciences, Beijing 100049, China
| | - Ruihui Zhang
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Graduate School of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaolu Qu
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Graduate School of Chinese Academy of Sciences, Beijing 100049, China
| | - Sulin Ren
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Graduate School of Chinese Academy of Sciences, Beijing 100049, China
| | - Naizhi Chen
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Shanjin Huang
- Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- Address correspondence to
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Abstract
Tropomyosins were discovered as regulators of actomyosin contractility in muscle cells, making yeasts and other fungi seem unlikely to harbor such proteins. Fungal cells are encased in a rigid cell wall and do not engage in the same sorts of contractile shape changes of animal cells. However, discovery of actin and myosin in yeast raised the possibility for a role for tropomyosin in regulating their interaction. Through a biochemical search, fungal tropomyosins were identified with strong similarities to their animal counterparts in terms ofprotein structure and physical properties. Two particular fungi, the buddingyeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe, have provided powerful genetic systems for studying tropomyosins in nonmetazoans. In these yeasts, tropomyosins associate with subsets ofactin filamentous structures. Mutational studies oftropomyosin genes and biochemical assays of purified proteins point to roles for these proteins as factors that stabilize actin filaments, promote actin-based structures of particular architecture and help maintain distinct biochemical identities among different filament populations. Tropomyosin-enriched filaments are the cytoskeletal structures that promote the major cell shape changes of these organisms: polarized growth and cell division.
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Affiliation(s)
- David Pruyne
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA.
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Intrinsic capability of budding yeast cofilin to promote turnover of tropomyosin-bound actin filaments. PLoS One 2008; 3:e3641. [PMID: 18982060 PMCID: PMC2572843 DOI: 10.1371/journal.pone.0003641] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 10/14/2008] [Indexed: 11/19/2022] Open
Abstract
The ability of actin filaments to function in cell morphogenesis and motility is closely coupled to their dynamic properties. Yeast cells contain two prominent actin structures, cables and patches, both of which are rapidly assembled and disassembled. Although genetic studies have shown that rapid actin turnover in patches and cables depends on cofilin, how cofilin might control cable disassembly remains unclear, because tropomyosin, a component of actin cables, is thought to protect actin filaments against the depolymerizing activity of ADF/cofilin. We have identified cofilin as a yeast tropomyosin (Tpm1) binding protein through Tpm1 affinity column and mass spectrometry. Using a variety of assays, we show that yeast cofilin can efficiently depolymerize and sever yeast actin filaments decorated with either Tpm1 or mouse tropomyosins TM1 and TM4. Our results suggest that yeast cofilin has the intrinsic ability to promote actin cable turnover, and that the severing activity may rely on its ability to bind Tpm1.
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The effect of temperature on Natural Antisense Transcript (NAT) expression in Aspergillus flavus. Curr Genet 2008; 54:241-69. [PMID: 18813928 DOI: 10.1007/s00294-008-0215-9] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2008] [Revised: 09/02/2008] [Accepted: 09/03/2008] [Indexed: 12/25/2022]
Abstract
Naturally occurring Antisense Transcripts (NATs) compose an emerging group of regulatory RNAs. These regulatory elements appear in all organisms examined, but little is known about global expression of NATs in fungi. Analysis of currently available EST sequences suggests that 352 cis NATs are present in Aspergillus flavus. An Affymetrix GeneChip microarray containing probes for these cis NATs, as well as all predicted genes in A. flavus, allowed a whole genome expression analysis of these elements in response to two ecologically important temperatures for the fungus. RNA expression analysis showed that 32 NATs and 2,709 genes were differentially expressed between 37 degrees C, the optimum temperature for growth, and 28 degrees C, the conducive temperature for the biosynthesis of aflatoxin (AF) and many other secondary metabolites. These NATs correspond to sense genes with diverse functions including transcription initiation, carbohydrate processing and binding, temperature sensitive morphogenesis, and secondary metabolism. This is the first report of a whole genome transcriptional analysis of NAT expression in a fungus.
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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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Onabajo OO, Seeley MK, Kale A, Qualmann B, Kessels M, Han J, Tan TH, Song W. Actin-binding protein 1 regulates B cell receptor-mediated antigen processing and presentation in response to B cell receptor activation. THE JOURNAL OF IMMUNOLOGY 2008; 180:6685-95. [PMID: 18453588 DOI: 10.4049/jimmunol.180.10.6685] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The BCR serves as both signal transducer and Ag transporter. Binding of Ags to the BCR induces signaling cascades and Ag processing and presentation, two essential cellular events for B cell activation. BCR-initiated signaling increases BCR-mediated Ag-processing efficiency by increasing the rate and specificity of Ag transport. Previous studies showed a critical role for the actin cytoskeleton in these two processes. In this study, we found that actin-binding protein 1 (Abp1/HIP-55/SH3P7) functioned as an actin-binding adaptor protein, coupling BCR signaling and Ag-processing pathways with the actin cytoskeleton. Gene knockout of Abp1 and overexpression of the Src homology 3 domain of Abp1 inhibited BCR-mediated Ag internalization, consequently reducing the rate of Ag transport to processing compartments and the efficiency of BCR-mediated Ag processing and presentation. BCR activation induced tyrosine phosphorylation of Abp1 and translocation of both Abp1 and dynamin 2 from the cytoplasm to plasma membrane, where they colocalized with the BCR and cortical F-actin. Mutations of the two tyrosine phosphorylation sites of Abp1 and depolymerization of the actin cytoskeleton interfered with BCR-induced Abp1 recruitment to the plasma membrane. The inhibitory effect of a dynamin proline-rich domain deletion mutant on the recruitment of Abp1 to the plasma membrane, coimmunoprecipitation of dynamin with Abp1, and coprecipitation of Abp1 with GST fusion of the dyanmin proline-rich domain demonstrate the interaction of Abp1 with dynamin 2. These results demonstrate that the BCR regulates the function of Abp1 by inducing Abp1 phosphorylation and actin cytoskeleton rearrangement, and that Abp1 facilitates BCR-mediated Ag processing by simultaneously interacting with dynamin and the actin cytoskeleton.
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Affiliation(s)
- Olusegun O Onabajo
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
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Gheorghe DM, Aghamohammadzadeh S, Smaczynska-de Rooij II, Allwood EG, Winder SJ, Ayscough KR. Interactions between the yeast SM22 homologue Scp1 and actin demonstrate the importance of actin bundling in endocytosis. J Biol Chem 2008; 283:15037-46. [PMID: 18400761 PMCID: PMC2397485 DOI: 10.1074/jbc.m710332200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The yeast SM22 homologue Scp1 has previously been shown to act as an actin-bundling protein in vitro. In cells, Scp1 localizes to the cortical actin patches that form as part of the invagination process during endocytosis, and its function overlaps with that of the well characterized yeast fimbrin homologue Sac6p. In this work we have used live cell imaging to demonstrate the importance of key residues in the Scp1 actin interface. We have defined two actin binding domains within Scp1 that allow the protein to both bind and bundle actin without the need for dimerization. Green fluorescent protein-tagged mutants of Scp1 also indicate that actin localization does not require the putative phosphorylation site Ser-185 to be functional. Deletion of SCP1 has few discernable effects on cell growth and morphology. However, we reveal that scp1 deletion is compensated for by up-regulation of Sac6. Furthermore, Scp1 levels are increased in the absence of sac6. The presence of compensatory pathways to up-regulate Sac6 or Scp1 levels in the absence of the other suggest that maintenance of sufficient bundling activity is critical within the cell. Analysis of cortical patch assembly and movement during endocytosis reveals a previously undetected role for Scp1 in movement of patches away from the plasma membrane. Additionally, we observe a dramatic increase in patch lifetime in a strain lacking both sac6 and scp1, demonstrating the central role played by actin-bundling proteins in the endocytic process.
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Affiliation(s)
- Dana M Gheorghe
- Departments of Molecular Biology and Biotechnology, Biomedical Science, University of Sheffield, Sheffield, S10 2TN, United Kingdom
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Upadhyay S, Shaw BD. The role of actin, fimbrin and endocytosis in growth of hyphae in Aspergillus nidulans. Mol Microbiol 2008; 68:690-705. [PMID: 18331474 DOI: 10.1111/j.1365-2958.2008.06178.x] [Citation(s) in RCA: 141] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Filamentous fungi are ideal systems to study the process of polarized growth, as their life cycle is dominated by hyphal growth exclusively at the cell apex. The actin cytoskeleton plays an important role in this growth. Until now, there have been no tools to visualize actin or the actin-binding protein fimbrin in live cells of a filamentous fungus. We investigated the roles of actin (ActA) and fimbrin (FimA) in hyphal growth in Aspergillus nidulans. We examined the localization of ActA::GFP and FimA::GFP in live cells, and each displayed a similar localization pattern. In actively growing hyphae, cortical ActA::GFP and FimA::GFP patches were highly mobile throughout the hypha and were concentrated near hyphal apices. A patch-depleted zone occupied the apical 0.5 microm of growing hypha. Both FimA::GFP and Act::GFP also localize transiently to septa. Movement and later localization of both was compromised after cytochalasin treatment. Disruption of fimA resulted in delayed polarity establishment during conidium germination, abnormal hyphal growth and endocytosis defects in apolar cells. Endocytosis was severely impaired in apolar fimA disruption cells. Our data support a novel apical recycling model which indicates a critical role for actin patch-mediated endocytosis to maintain polarized growth at the apex.
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Affiliation(s)
- Srijana Upadhyay
- Program for the Biology of Filamentous Fungi, Department of Plant Pathology and Microbiology, Texas A&M University, 2132 TAMU, College Station, TX 77843, USA
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Araujo-Bazán L, Peñalva MA, Espeso EA. Preferential localization of the endocytic internalization machinery to hyphal tips underlies polarization of the actin cytoskeleton in Aspergillus nidulans. Mol Microbiol 2008; 67:891-905. [DOI: 10.1111/j.1365-2958.2007.06102.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Haynes J, Garcia B, Stollar EJ, Rath A, Andrews BJ, Davidson AR. The biologically relevant targets and binding affinity requirements for the function of the yeast actin-binding protein 1 Src-homology 3 domain vary with genetic context. Genetics 2007; 176:193-208. [PMID: 17409071 PMCID: PMC1893037 DOI: 10.1534/genetics.106.070300] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Many protein-protein interaction domains bind to multiple targets. However, little is known about how the interactions of a single domain with many proteins are controlled and modulated under varying cellular conditions. In this study, we investigated the in vivo effects of Abp1p SH3 domain mutants that incrementally reduce target-binding affinity in four different yeast mutant backgrounds in which Abp1p activity is essential for growth. Although the severity of the phenotypic defects observed generally increased as binding affinity was reduced, some genetic backgrounds (prk1 Delta and sla1 Delta) tolerated large affinity reductions while others (sac6 Delta and sla2 Delta) were much more sensitive to these reductions. To elucidate the mechanisms behind these observations, we determined that Ark1p is the most important Abp1p SH3 domain interactor in prk1 Delta cells, but that interactions with multiple targets, including Ark1p and Scp1p, are required in the sac6 Delta background. We establish that the Abp1p SH3 domain makes different, functionally important interactions under different genetic conditions, and these changes in function are reflected by changes in the binding affinity requirement of the domain. These data provide the first evidence of biological relevance for any Abp1p SH3 domain-mediated interaction. We also find that considerable reductions in binding affinity are tolerated by the cell with little effect on growth rate, even when the actin cytoskeletal morphology is significantly perturbed.
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Affiliation(s)
- Jennifer Haynes
- Department of Moledular and Medical Genetics, University of Toronto, Toronto, Ontario, Canada
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41
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Gross SR, Kinzy TG. Improper organization of the actin cytoskeleton affects protein synthesis at initiation. Mol Cell Biol 2007; 27:1974-89. [PMID: 17178834 PMCID: PMC1820457 DOI: 10.1128/mcb.00832-06] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 06/14/2006] [Accepted: 12/07/2006] [Indexed: 11/20/2022] Open
Abstract
Although the actin cytoskeleton and the translation machinery are considered to be separate cellular complexes, growing evidence supports overlapping regulation of the two systems. Because of its interaction with actin, the eukaryotic translation elongation factor 1A (eEF1A) is proposed to be a regulator or link between these processes. Using a genetic approach with the yeast Saccharomyces cerevisiae, specific regions of eEF1A responsible for actin interactions and bundling were identified. Five new mutations were identified along one face of eEF1A. Dramatic changes in cell growth, cell morphology, and actin cable and patch formation as well as a unique effect on total translation in strains expressing the F308L or S405P eEF1A mutant form were observed. The translation effects do not correlate with reduced translation elongation but instead include an initiation defect. Biochemical analysis of the eEF1A mutant forms demonstrated reduced actin-bundling activity in vitro. Reduced total translation and/or the accumulation of 80S ribosomes in strains with either a mutation or a null allele of genes encoding actin itself or actin-regulating proteins Tpm1p, Mdm20p, and Bnirp/Bni1p was observed. Our data demonstrate that eEF1A, other actin binding proteins, and actin mutants affect translation initiation through the actin cytoskeleton.
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Affiliation(s)
- Stephane R Gross
- Department of Molecular Genetics, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854, USA
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Park HO, Bi E. Central roles of small GTPases in the development of cell polarity in yeast and beyond. Microbiol Mol Biol Rev 2007; 71:48-96. [PMID: 17347519 PMCID: PMC1847380 DOI: 10.1128/mmbr.00028-06] [Citation(s) in RCA: 323] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
SUMMARY The establishment of cell polarity is critical for the development of many organisms and for the function of many cell types. A large number of studies of diverse organisms from yeast to humans indicate that the conserved, small-molecular-weight GTPases function as key signaling proteins involved in cell polarization. The budding yeast Saccharomyces cerevisiae is a particularly attractive model because it displays pronounced cell polarity in response to intracellular and extracellular cues. Cells of S. cerevisiae undergo polarized growth during various phases of their life cycle, such as during vegetative growth, mating between haploid cells of opposite mating types, and filamentous growth upon deprivation of nutrition such as nitrogen. Substantial progress has been made in deciphering the molecular basis of cell polarity in budding yeast. In particular, it becomes increasingly clear how small GTPases regulate polarized cytoskeletal organization, cell wall assembly, and exocytosis at the molecular level and how these GTPases are regulated. In this review, we discuss the key signaling pathways that regulate cell polarization during the mitotic cell cycle and during mating.
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Affiliation(s)
- Hay-Oak Park
- Department of Molecular Genetics, The Ohio State University, 484 West 12th Avenue, Columbus, OH 43210-1292, USA.
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Huckaba TM, Lipkin T, Pon LA. Roles of type II myosin and a tropomyosin isoform in retrograde actin flow in budding yeast. ACTA ACUST UNITED AC 2007; 175:957-69. [PMID: 17178912 PMCID: PMC2064705 DOI: 10.1083/jcb.200609155] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Retrograde flow of cortical actin networks and bundles is essential for cell motility and retrograde intracellular movement, and for the formation and maintenance of microvilli, stereocilia, and filopodia. Actin cables, which are F-actin bundles that serve as tracks for anterograde and retrograde cargo movement in budding yeast, undergo retrograde flow that is driven, in part, by actin polymerization and assembly. We find that the actin cable retrograde flow rate is reduced by deletion or delocalization of the type II myosin Myo1p, and by deletion or conditional mutation of the Myo1p motor domain. Deletion of the tropomyosin isoform Tpm2p, but not the Tpm1p isoform, increases the rate of actin cable retrograde flow. Pretreatment of F-actin with Tpm2p, but not Tpm1p, inhibits Myo1p binding to F-actin and Myo1p-dependent F-actin gliding. These data support novel, opposing roles of Myo1p and Tpm2 in regulating retrograde actin flow in budding yeast and an isoform-specific function of Tpm1p in promoting actin cable function in myosin-driven anterograde cargo transport.
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Affiliation(s)
- Thomas M Huckaba
- Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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Moseley JB, Goode BL. The yeast actin cytoskeleton: from cellular function to biochemical mechanism. Microbiol Mol Biol Rev 2006; 70:605-45. [PMID: 16959963 PMCID: PMC1594590 DOI: 10.1128/mmbr.00013-06] [Citation(s) in RCA: 287] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
All cells undergo rapid remodeling of their actin networks to regulate such critical processes as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. These events are driven by the coordinated activities of a set of 20 to 30 highly conserved actin-associated proteins, in addition to many cell-specific actin-associated proteins and numerous upstream signaling molecules. The combined activities of these factors control with exquisite precision the spatial and temporal assembly of actin structures and ensure dynamic turnover of actin structures such that cells can rapidly alter their cytoskeletons in response to internal and external cues. One of the most exciting principles to emerge from the last decade of research on actin is that the assembly of architecturally diverse actin structures is governed by highly conserved machinery and mechanisms. With this realization, it has become apparent that pioneering efforts in budding yeast have contributed substantially to defining the universal mechanisms regulating actin dynamics in eukaryotes. In this review, we first describe the filamentous actin structures found in Saccharomyces cerevisiae (patches, cables, and rings) and their physiological functions, and then we discuss in detail the specific roles of actin-associated proteins and their biochemical mechanisms of action.
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Affiliation(s)
- James B Moseley
- Department of Biology and The Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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45
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Sagot I, Pinson B, Salin B, Daignan-Fornier B. Actin bodies in yeast quiescent cells: an immediately available actin reserve? Mol Biol Cell 2006; 17:4645-55. [PMID: 16914523 PMCID: PMC1635378 DOI: 10.1091/mbc.e06-04-0282] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Most eukaryotic cells spend most of their life in a quiescent state, poised to respond to specific signals to proliferate. In Saccharomyces cerevisiae, entry into and exit from quiescence are dependent only on the availability of nutrients in the environment. The transition from quiescence to proliferation requires not only drastic metabolic changes but also a complete remodeling of various cellular structures. Here, we describe an actin cytoskeleton organization specific of the yeast quiescent state. When cells cease to divide, actin is reorganized into structures that we named "actin bodies." We show that actin bodies contain F-actin and several actin-binding proteins such as fimbrin and capping protein. Furthermore, by contrast to actin patches or cables, actin bodies are mostly immobile, and we could not detect any actin filament turnover. Finally, we show that upon cells refeeding, actin bodies rapidly disappear and actin cables and patches can be assembled in the absence of de novo protein synthesis. This led us to propose that actin bodies are a reserve of actin that can be immediately mobilized for actin cables and patches formation upon reentry into a proliferation cycle.
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Affiliation(s)
- Isabelle Sagot
- Institut de Biochimie et Génétique Cellulaires, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5095, Université Victor Segalen/Bordeaux II, F-33077 Bordeaux Cedex, France.
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Haynes C, Oldfield CJ, Ji F, Klitgord N, Cusick ME, Radivojac P, Uversky VN, Vidal M, Iakoucheva LM. Intrinsic disorder is a common feature of hub proteins from four eukaryotic interactomes. PLoS Comput Biol 2006; 2:e100. [PMID: 16884331 PMCID: PMC1526461 DOI: 10.1371/journal.pcbi.0020100] [Citation(s) in RCA: 445] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Accepted: 06/23/2006] [Indexed: 12/13/2022] Open
Abstract
Recent proteome-wide screening approaches have provided a wealth of information about interacting proteins in various organisms. To test for a potential association between protein connectivity and the amount of predicted structural disorder, the disorder propensities of proteins with various numbers of interacting partners from four eukaryotic organisms (Caenorhabditis elegans, Saccharomyces cerevisiae, Drosophila melanogaster, and Homo sapiens) were investigated. The results of PONDR VL-XT disorder analysis show that for all four studied organisms, hub proteins, defined here as those that interact with ≥10 partners, are significantly more disordered than end proteins, defined here as those that interact with just one partner. The proportion of predicted disordered residues, the average disorder score, and the number of predicted disordered regions of various lengths were higher overall in hubs than in ends. A binary classification of hubs and ends into ordered and disordered subclasses using the consensus prediction method showed a significant enrichment of wholly disordered proteins and a significant depletion of wholly ordered proteins in hubs relative to ends in worm, fly, and human. The functional annotation of yeast hubs and ends using GO categories and the correlation of these annotations with disorder predictions demonstrate that proteins with regulation, transcription, and development annotations are enriched in disorder, whereas proteins with catalytic activity, transport, and membrane localization annotations are depleted in disorder. The results of this study demonstrate that intrinsic structural disorder is a distinctive and common characteristic of eukaryotic hub proteins, and that disorder may serve as a determinant of protein interactivity. From the formulation of Emil Fisher's lock-and-key hypothesis in 1894 until the early 1990s, a dominating and widely accepted concept in molecular biology was the protein structure–function paradigm. According to this concept, a protein can perform its biological function(s) only after folding into a specific rigid 3-D structure. Only recently has the validity of this structure–function paradigm been seriously challenged, primarily through the wealth of counterexamples that have gradually accumulated over the past 15 years. These counterexamples demonstrated that many proteins exist in a natively unfolded (or intrinsically disordered) state, and function without a prerequisite stably folded structure. In many cases, the lack of structure is required for biological function. Previous results have implicated intrinsic disorder as having an important role in protein interactions. The authors generalize this notion by comparing interaction networks from four eukaryotic organisms: yeast, worm, fly, and human. They have found that within these networks the proteins that interact with multiple protein partners (network hubs) are significantly more disordered than proteins that interact with a single protein partner (network ends). The results of this study demonstrate that intrinsic structural disorder is a distinctive and common characteristic of hub proteins, and that disorder may serve as a determinant of protein interactivity.
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Affiliation(s)
- Chad Haynes
- Laboratory of Statistical Genetics, The Rockefeller University, New York, New York, United States of America
| | - Christopher J Oldfield
- Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
| | - Fei Ji
- Laboratory of Statistical Genetics, The Rockefeller University, New York, New York, United States of America
| | - Niels Klitgord
- Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America
| | - Michael E Cusick
- Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America
| | - Predrag Radivojac
- Indiana University School of Informatics, Bloomington, Indiana, United States of America
| | - Vladimir N Uversky
- Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, Indianapolis, Indiana, United States of America
- Institute for Biological Instrumentation, Russian Academy of Sciences, Moscow, Russia
| | - Marc Vidal
- Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Lilia M Iakoucheva
- Laboratory of Statistical Genetics, The Rockefeller University, New York, New York, United States of America
- * To whom correspondence should be addressed. E-mail:
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Okada K, Ravi H, Smith EM, Goode BL. Aip1 and cofilin promote rapid turnover of yeast actin patches and cables: a coordinated mechanism for severing and capping filaments. Mol Biol Cell 2006; 17:2855-68. [PMID: 16611742 PMCID: PMC1483024 DOI: 10.1091/mbc.e06-02-0135] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Rapid turnover of actin structures is required for dynamic remodeling of the cytoskeleton and cell morphogenesis, but the mechanisms driving actin disassembly are poorly defined. Cofilin plays a central role in promoting actin turnover by severing/depolymerizing filaments. Here, we analyze the in vivo function of a ubiquitous actin-interacting protein, Aip1, suggested to work with cofilin. We provide the first demonstration that Aip1 promotes actin turnover in living cells. Further, we reveal an unanticipated role for Aip1 and cofilin in promoting rapid turnover of yeast actin cables, dynamic structures that are decorated and stabilized by tropomyosin. Through systematic mutagenesis of Aip1 surfaces, we identify two well-separated F-actin-binding sites, one of which contributes to actin filament binding and disassembly specifically in the presence of cofilin. We also observe a close correlation between mutations disrupting capping of severed filaments in vitro and reducing rates of actin turnover in vivo. We propose a model for balanced regulation of actin cable turnover, in which Aip1 and cofilin function together to "prune" tropomyosin-decorated cables along their lengths. Consistent with this model, deletion of AIP1 rescues the temperature-sensitive growth and loss of actin cable defects of tpm1Delta mutants.
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Affiliation(s)
- Kyoko Okada
- Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
| | - Harini Ravi
- Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
| | - Ellen M. Smith
- Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
| | - Bruce L. Goode
- Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
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Ren G, Vajjhala P, Lee JS, Winsor B, Munn AL. The BAR domain proteins: molding membranes in fission, fusion, and phagy. Microbiol Mol Biol Rev 2006; 70:37-120. [PMID: 16524918 PMCID: PMC1393252 DOI: 10.1128/mmbr.70.1.37-120.2006] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The Bin1/amphiphysin/Rvs167 (BAR) domain proteins are a ubiquitous protein family. Genes encoding members of this family have not yet been found in the genomes of prokaryotes, but within eukaryotes, BAR domain proteins are found universally from unicellular eukaryotes such as yeast through to plants, insects, and vertebrates. BAR domain proteins share an N-terminal BAR domain with a high propensity to adopt alpha-helical structure and engage in coiled-coil interactions with other proteins. BAR domain proteins are implicated in processes as fundamental and diverse as fission of synaptic vesicles, cell polarity, endocytosis, regulation of the actin cytoskeleton, transcriptional repression, cell-cell fusion, signal transduction, apoptosis, secretory vesicle fusion, excitation-contraction coupling, learning and memory, tissue differentiation, ion flux across membranes, and tumor suppression. What has been lacking is a molecular understanding of the role of the BAR domain protein in each process. The three-dimensional structure of the BAR domain has now been determined and valuable insight has been gained in understanding the interactions of BAR domains with membranes. The cellular roles of BAR domain proteins, characterized over the past decade in cells as distinct as yeasts, neurons, and myocytes, can now be understood in terms of a fundamental molecular function of all BAR domain proteins: to sense membrane curvature, to bind GTPases, and to mold a diversity of cellular membranes.
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Affiliation(s)
- Gang Ren
- Institute for Molecular Bioscience, University of Queensland, St. Lucia, Queensland 4072, Australia
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Wang Y, O'Halloran TJ. Abp1 regulates pseudopodium number in chemotaxing Dictyostelium cells. J Cell Sci 2006; 119:702-10. [PMID: 16449327 DOI: 10.1242/jcs.02742] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
When starved, Dictyostelium cells respond to extracellular signals, polarize, and move with strong persistence into aggregation centers. Actin and actin-associated proteins play key roles in regulating both the morphology and directed movements of cells during chemotactic aggregation. Recently, we identified an ortholog of Abp1 in Dictyostelium (Dabp1). The first actin binding protein identified in yeast, Abp1 functions in actin-based endocytosis in yeast and in receptor-mediated endocytosis in mammalian cells. To explore the functions for Abp1 in Dictyostelium, we examined the phenotypes of cells that overexpressed the Dabp1 protein and cells that eliminated Dabp1 expression. In these mutants, most actin-based processes were intact. However, cell motility was altered during early development. During chemotactic streaming, more than 90% of wild-type cells had a single leading pseudopodium and a single uropodium, whereas more than 27% of Dabp1 null cells projected multiple pseuodpodia. Similarly, ∼90% of cells that overexpressed Dabp1 projected multiple pseudopodia during chemotactic streaming, and displayed reduced rates of cell movement. Expression of the SH3 domain of Dabp1 showed this domain to be an important determinant in regulating pseudopodium number. These results suggest that Abp1 controls pseudopodium number and motility in early stages of chemotactic aggregation in Dictyostelium.
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Affiliation(s)
- Yanqin Wang
- Department of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA
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50
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Brinkworth RI, Munn AL, Kobe B. Protein kinases associated with the yeast phosphoproteome. BMC Bioinformatics 2006; 7:47. [PMID: 16445868 PMCID: PMC1373605 DOI: 10.1186/1471-2105-7-47] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2005] [Accepted: 01/31/2006] [Indexed: 02/08/2023] Open
Abstract
Background Protein phosphorylation is an extremely important mechanism of cellular regulation. A large-scale study of phosphoproteins in a whole-cell lysate of Saccharomyces cerevisiae has previously identified 383 phosphorylation sites in 216 peptide sequences. However, the protein kinases responsible for the phosphorylation of the identified proteins have not previously been assigned. Results We used Predikin in combination with other bioinformatic tools, to predict which of 116 unique protein kinases in yeast phosphorylates each experimentally determined site in the phosphoproteome. The prediction was based on the match between the phosphorylated 7-residue sequence and the predicted substrate specificity of each kinase, with the highest weight applied to the residues or positions that contribute most to the substrate specificity. We estimated the reliability of the predictions by performing a parallel prediction on phosphopeptides for which the kinase has been experimentally determined. Conclusion The results reveal that the functions of the protein kinases and their predicted phosphoprotein substrates are often correlated, for example in endocytosis, cytokinesis, transcription, replication, carbohydrate metabolism and stress response. The predictions link phosphoproteins of unknown function with protein kinases with known functions and vice versa, suggesting functions for the uncharacterized proteins. The study indicates that the phosphoproteins and the associated protein kinases represented in our dataset have housekeeping cellular roles; certain kinases are not represented because they may only be activated during specific cellular responses. Our results demonstrate the utility of our previously reported protein kinase substrate prediction approach (Predikin) as a tool for establishing links between kinases and phosphoproteins that can subsequently be tested experimentally.
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Affiliation(s)
- Ross I Brinkworth
- School of Molecular and Microbial Sciences, University of Queensland, Brisbane 4072, Australia
| | - Alan L Munn
- Institute for Molecular Bioscience and Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane 4072, Australia
- School of Biomedical Sciences, University of Queensland, Brisbane 4072, Australia
| | - Boštjan Kobe
- School of Molecular and Microbial Sciences, University of Queensland, Brisbane 4072, Australia
- Institute for Molecular Bioscience and Special Research Centre for Functional and Applied Genomics, University of Queensland, Brisbane 4072, Australia
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