scholarly journals Profilin and Mical combine to impair F-actin assembly and promote disassembly and remodeling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Elena E. Grintsevich ◽  
Giasuddin Ahmed ◽  
Anush A. Ginosyan ◽  
Heng Wu ◽  
Shannon K. Rich ◽  
...  
Keyword(s):  
Actin Filament ◽  
Model System ◽  
Actin Assembly ◽  
Elongation Factors ◽  
Actin Nucleation ◽  
Site Specific ◽  
Cellular Events ◽  
Axon Repulsion

AbstractCellular events require the spatiotemporal interplay between actin assembly and actin disassembly. Yet, how different factors promote the integration of these two opposing processes is unclear. In particular, cellular monomeric (G)-actin is complexed with profilin, which inhibits spontaneous actin nucleation but fuels actin filament (F-actin) assembly by elongation-promoting factors (formins, Ena/VASP). In contrast, site-specific F-actin oxidation by Mical promotes F-actin disassembly and release of polymerization-impaired Mical-oxidized (Mox)-G-actin. Here we find that these two opposing processes connect with one another to orchestrate actin/cellular remodeling. Specifically, we find that profilin binds Mox-G-actin, yet these complexes do not fuel elongation factors’-mediated F-actin assembly, but instead inhibit polymerization and promote further Mox-F-actin disassembly. Using Drosophila as a model system, we show that similar profilin–Mical connections occur in vivo – where they underlie F-actin/cellular remodeling that accompanies Semaphorin–Plexin cellular/axon repulsion. Thus, profilin and Mical combine to impair F-actin assembly and promote F-actin disassembly, while concomitantly facilitating cellular remodeling and plasticity.

Actin Assembly Takes Off Like a Rocket!

2013 ◽  
Vol 21 (2) ◽  
pp. 8-9
Author(s):  
Stephen W. Carmichael ◽  
Jeffrey L. Salisbury
Keyword(s):  
Actin Filament ◽  
Eukaryotic Cells ◽  
Actin Assembly ◽  
Elongation Factors ◽  
Delicate Balance ◽  
Filament Assembly ◽  
Two Factors

Actin filament assembly occurs in all eukaryotic cells and involves a delicate balance between factors that promote assembly and factors that inhibit assembly. Filament assembly begins with a process of nucleation and then proceeds via elongation. Filament assembly in vivo requires nucleation and elongation factors to overcome barriers that could either bind actin monomers to inhibit nucleation or “cap” the ends of elongating filaments. The formation of most cellular actin structures depends on two or more such factors, which may interact directly. The interaction between two factors that initiate nucleation and promote assembly has recently been demonstrated by Dennis Breitsprecher, Richa Jaiswal, Jeffrey Bombardier, Christopher Gould, Jeff Gelles, and Bruce Goode. Interestingly, the model of these factors in action (Figure 1) resembles a rocket launcher!

Magnetic Microspheres: A Model System for Site Specific Drug Delivery in Vivo

1978 ◽  
Vol 158 (2) ◽  
pp. 141-146 ◽  
Author(s):  
K. J. Widder ◽  
A. E. Senyei ◽  
D. G. Scarpelli
Keyword(s):  
Drug Delivery ◽  
Model System ◽  
Magnetic Microspheres ◽  
Specific Drug ◽  
Site Specific

scholarly journals Activation of the Arp2/3 Complex by the Actin Filament Binding Protein Abp1p

2001 ◽  
Vol 153 (3) ◽  
pp. 627-634 ◽  
Author(s):  
Bruce L. Goode ◽  
Avital A. Rodal ◽  
Georjana Barnes ◽  
David G. Drubin
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Mammalian Cells ◽  
Actin Assembly ◽  
Related Protein ◽  
Genetic Studies ◽  
Actin Networks ◽  
Specific Step

The actin-related protein (Arp) 2/3 complex plays a central role in assembly of actin networks. Because distinct actin-based structures mediate diverse processes, many proteins are likely to make spatially and temporally regulated interactions with the Arp2/3 complex. We have isolated a new activator, Abp1p, which associates tightly with the yeast Arp2/3 complex. Abp1p contains two acidic sequences (DDW) similar to those found in SCAR/WASp proteins. We demonstrate that mutation of these sequences abolishes Arp2/3 complex activation in vitro. Genetic studies indicate that this activity is important for Abp1p functions in vivo. In contrast to SCAR/WASp proteins, Abp1p binds specifically to actin filaments, not monomers. Actin filament binding is mediated by the ADF/cofilin homology (ADF-H) domain of Abp1p and is required for Arp2/3 complex activation in vitro. We demonstrate that Abp1p recruits Arp2/3 complex to the sides of filaments, suggesting a novel mechanism of activation. Studies in yeast and mammalian cells indicate that Abp1p is involved functionally in endocytosis. Based on these results, we speculate that Abp1p may link Arp2/3-mediated actin assembly to a specific step in endocytosis.

scholarly journals Cofilin recruitment and function during actin-mediated endocytosis dictated by actin nucleotide state

2007 ◽  
Vol 178 (7) ◽  
pp. 1251-1264 ◽  
Author(s):  
Voytek Okreglak ◽  
David G. Drubin
Keyword(s):  
Actin Filament ◽  
Membrane Trafficking ◽  
Adenosine Diphosphate ◽  
Living Cells ◽  
Actin Assembly ◽  
Actin Networks ◽  
Actin Turnover ◽  
And Function

Cofilin is the major mediator of actin filament turnover in vivo. However, the molecular mechanism of cofilin recruitment to actin networks during dynamic actin-mediated processes in living cells and cofilin's precise in vivo functions have not been determined. In this study, we analyzed the dynamics of fluorescently tagged cofilin and the role of cofilin-mediated actin turnover during endocytosis in Saccharomyces cerevisiae. In living cells, cofilin is not necessary for actin assembly on endocytic membranes but is recruited to molecularly aged adenosine diphosphate actin filaments and is necessary for their rapid disassembly. Defects in cofilin function alter the morphology of actin networks in vivo and reduce the rate of actin flux through actin networks. The consequences of decreasing actin flux are manifested by decreased but not blocked endocytic internalization at the plasma membrane and defects in late steps of membrane trafficking to the vacuole. These results suggest that cofilin-mediated actin filament flux is required for the multiple steps of endocytic trafficking.

scholarly journals Ligand-induced activation of a formin–NPF pair leads to collaborative actin nucleation

2013 ◽  
Vol 201 (4) ◽  
pp. 595-611 ◽  
Author(s):  
Brian R. Graziano ◽  
Erin M. Jonasson ◽  
Jessica G. Pullen ◽  
Christopher J. Gould ◽  
Bruce L. Goode
Keyword(s):  
Regulatory Sequence ◽  
Actin Assembly ◽  
Actin Nucleation ◽  
Binding Partner ◽  
In Vivo Binding ◽  
Established Role

Formins associate with other nucleators and nucleation-promoting factors (NPFs) to stimulate collaborative actin assembly, but the mechanisms regulating these interactions have been unclear. Yeast Bud6 has an established role as an NPF for the formin Bni1, but whether it also directly regulates the formin Bnr1 has remained enigmatic. In this paper, we analyzed NPF-impaired alleles of bud6 in a bni1Δ background and found that Bud6 stimulated Bnr1 activity in vivo. Furthermore, Bud6 bound directly to Bnr1, but its NPF effects were masked by a short regulatory sequence, suggesting that additional factors may be required for activation. We isolated a novel in vivo binding partner of Bud6, Yor304c-a/Bil1, which colocalized with Bud6 and functioned in the Bnr1 pathway for actin assembly. Purified Bil1 bound to the regulatory sequence in Bud6 and triggered NPF effects on Bnr1. These observations define a new mode of formin regulation, which has important implications for understanding NPF-nucleator pairs in diverse systems.

scholarly journals WAVE binds Ena/VASP for enhanced Arp2/3 complex–based actin assembly

2015 ◽  
Vol 26 (1) ◽  
pp. 55-65 ◽  
Author(s):  
Svitlana Havrylenko ◽  
Philippe Noguera ◽  
Majdouline Abou-Ghali ◽  
John Manzi ◽  
Fahima Faqir ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Actin Filament ◽  
Motility Assay ◽  
Actin Assembly ◽  
Complex Activity ◽  
Actin Networks ◽  
Wave Complex

The WAVE complex is the main activator of the Arp2/3 complex for actin filament nucleation and assembly in the lamellipodia of moving cells. Other important players in lamellipodial protrusion are Ena/VASP proteins, which enhance actin filament elongation. Here we examine the molecular coordination between the nucleating activity of the Arp2/3 complex and the elongating activity of Ena/VASP proteins for the formation of actin networks. Using an in vitro bead motility assay, we show that WAVE directly binds VASP, resulting in an increase in Arp2/3 complex–based actin assembly. We show that this interaction is important in vivo as well, for the formation of lamellipodia during the ventral enclosure event of Caenorhabditis elegans embryogenesis. Ena/VASP's ability to bind F-actin and profilin-complexed G-actin are important for its effect, whereas Ena/VASP tetramerization is not necessary. Our data are consistent with the idea that binding of Ena/VASP to WAVE potentiates Arp2/3 complex activity and lamellipodial actin assembly.

scholarly journals A Conserved Mechanism for Bni1- and mDia1-induced Actin Assembly and Dual Regulation of Bni1 by Bud6 and Profilin

2004 ◽  
Vol 15 (2) ◽  
pp. 896-907 ◽  
Author(s):  
James B. Moseley ◽  
Isabelle Sagot ◽  
Amity L. Manning ◽  
Yingwu Xu ◽  
Michael J. Eck ◽  
...  
Keyword(s):  
Cell Polarity ◽  
Actin Filament ◽  
Genetic Interaction ◽  
Actin Assembly ◽  
Nucleotide Exchange ◽  
Synthetic Lethal ◽  
Capping Protein ◽  
Filament Assembly ◽  
Species Specific

Formins have conserved roles in cell polarity and cytokinesis and directly nucleate actin filament assembly through their FH2 domain. Here, we define the active region of the yeast formin Bni1 FH2 domain and show that it dimerizes. Mutations that disrupt dimerization abolish actin assembly activity, suggesting that dimers are the active state of FH2 domains. The Bni1 FH2 domain protects growing barbed ends of actin filaments from vast excesses of capping protein, suggesting that the dimer maintains a persistent association during elongation. This is not a species-specific mechanism, as the activities of purified mammalian formin mDia1 are identical to those of Bni1. Further, mDia1 partially complements BNI1 function in vivo, and expression of a dominant active mDia1 construct in yeast causes similar phenotypes to dominant active Bni1 constructs. In addition, we purified the Bni1-interacting half of the cell polarity factor Bud6 and found that it binds specifically to actin monomers and, like profilin, promotes rapid nucleotide exchange on actin. Bud6 and profilin show additive stimulatory effects on Bni1 activity and have a synthetic lethal genetic interaction in vivo. From these results, we propose a model in which Bni1 FH2 dimers nucleate and processively cap the elongating barbed end of the actin filament, and Bud6 and profilin generate a local flux of ATP-actin monomers to promote actin assembly.

scholarly journals Loss of Aip1 reveals a role in maintaining the actin monomer pool and an in vivo oligomer assembly pathway

2010 ◽  
Vol 188 (6) ◽  
pp. 769-777 ◽  
Author(s):  
Voytek Okreglak ◽  
David G. Drubin
Keyword(s):  
Actin Filament ◽  
Monomer Concentration ◽  
Actin Assembly ◽  
Actin Monomer ◽  
Filament Assembly ◽  
Assembly Pathway ◽  
Latrunculin A ◽  
Mutant Cells

Although actin filaments can form by oligomer annealing in vitro, they are assumed to assemble exclusively from actin monomers in vivo. In this study, we show that a pool of actin resistant to the monomer-sequestering drug latrunculin A (lat A) contributes to filament assembly in vivo. Furthermore, we show that the cofilin accessory protein Aip1 is important for establishment of normal actin monomer concentration in cells and efficiently converts cofilin-generated actin filament disassembly products into monomers and short oligomers in vitro. Additionally, in aip1Δ mutant cells, lat A–insensitive actin assembly is significantly enhanced. We conclude that actin oligomer annealing is a physiologically relevant actin filament assembly pathway in vivo and identify Aip1 as a crucial factor for shifting the distribution of short actin oligomers toward monomers during disassembly.

scholarly journals Spire stimulates nucleation by Cappuccino and binds both ends of actin filaments

2019 ◽  
Author(s):  
Alexander O. Bradley ◽  
Christina L. Vizcarra ◽  
Hannah M. Bailey ◽  
Margot E. Quinlan
Keyword(s):  
Actin Filaments ◽  
Major Part ◽  
Direct Interaction ◽  
Binding Domain ◽  
Actin Assembly ◽  
Loss Of Function ◽  
Actin Nucleation ◽  
Outstanding Question

AbstractAn actin mesh fills both mouse and fly oocytes. The meshes are built by a conserved mechanism and used to establish polarity. Two actin nucleators, Spire and Cappuccino, collaborate to build actin filaments that connect vesicles and the cortex. Direct interaction between Spire and Cappuccino is required for in vitro synergistic actin assembly; however, we understand little about why the interaction is necessary. To mimic the geometry of Spire and Cappuccino in vivo, we immobilized Spire on beads. We found that increased nucleation is a major part of synergy and that Spire alone binds both barbed- and pointed-ends of actin filaments. We identified Spire’s barbed-end binding domain. Partial rescue of fertility by a loss-of-function mutant indicates that barbed-end binding is not necessary for Spire’s in vivo function, but that it may play a role under normal circumstances. We propose that Spire stimulates nucleation by Cappuccino in a manner similar to the collaboration between APC and mDia1.SummaryActin nucleators Cappuccino and Spire collaborate to build an actin mesh in oocytes. Data demonstrate that the collaboration leads to synergistic actin nucleation, as opposed to elongation. Further, Spire binds both ends of polar, actin filaments, resolving a long-outstanding question.

scholarly journals A Balance of Capping Protein and Profilin Functions Is Required to Regulate Actin Polymerization in Drosophila Bristle

2003 ◽  
Vol 14 (1) ◽  
pp. 118-128 ◽  
Author(s):  
Roberta Hopmann ◽  
Kathryn G. Miller
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Actin Polymerization ◽  
Genetic Interaction ◽  
Actin Binding ◽  
Actin Assembly ◽  
Loss Of Function ◽  
Capping Protein ◽  
Filament Dynamics

Profilin is a well-characterized protein known to be important for regulating actin filament assembly. Relatively few studies have addressed how profilin interacts with other actin-binding proteins in vivo to regulate assembly of complex actin structures. To investigate the function of profilin in the context of a differentiating cell, we have studied an instructive genetic interaction between mutations in profilin (chickadee) and capping protein (cpb). Capping protein is the principal protein in cells that caps actin filament barbed ends. When its function is reduced in the Drosophila bristle, F-actin levels increase and the actin cytoskeleton becomes disorganized, causing abnormal bristle morphology. chickadee mutations suppress the abnormal bristle phenotype and associated abnormalities of the actin cytoskeleton seen in cpb mutants. Furthermore, overexpression of profilin in the bristle mimics many features of thecpb loss-of-function phenotype. The interaction betweencpb and chickadee suggests that profilin promotes actin assembly in the bristle and that a balance between capping protein and profilin activities is important for the proper regulation of F-actin levels. Furthermore, this balance of activities affects the association of actin structures with the membrane, suggesting a link between actin filament dynamics and localization of actin structures within the cell.

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