scholarly journals Rho-GTPase–dependent filamentous actin dynamics coordinate vesicle targeting and exocytosis during tip growth

2008 ◽  
Vol 181 (7) ◽  
pp. 1155-1168 ◽  
Author(s):  
Yong Jik Lee ◽  
Amy Szumlanski ◽  
Erik Nielsen ◽  
Zhenbiao Yang
Keyword(s):  
Plasma Membrane ◽  
Tip Growth ◽  
Rho Gtpase ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Filamentous Actin ◽  
Latrunculin B ◽  
Dynamic Activity ◽  
Guanosine Triphosphatase ◽  
Spatiotemporal Coordination

The dynamic activity of tip-localized filamentous actin (F-actin) in pollen tubes is controlled by counteracting RIC4 and RIC3 pathways downstream of the ROP1 guanosine triphosphatase promoting actin assembly and disassembly, respectively. We show here that ROP1 activation is required for both the polar accumulation and the exocytosis of vesicles at the plasma membrane apex. The apical accumulation of exocytic vesicles oscillated in phase with, but slightly behind, apical actin assembly and was enhanced by overexpression of RIC4. However, RIC4 overexpression inhibited exocytosis, and this inhibition could be suppressed by latrunculin B treatment or RIC3 overexpression. We conclude that RIC4-dependent actin assembly is required for polar vesicle accumulation, whereas RIC3-mediated actin disassembly is required for exocytosis. Thus ROP1-dependent F-actin dynamics control tip growth through spatiotemporal coordination of vesicle targeting and exocytosis.

scholarly journals A Rho family GTPase controls actin dynamics and tip growth via two counteracting downstream pathways in pollen tubes

2005 ◽  
Vol 169 (1) ◽  
pp. 127-138 ◽  
Author(s):  
Ying Gu ◽  
Ying Fu ◽  
Peter Dowd ◽  
Shundai Li ◽  
Vanessa Vernoud ◽  
...  
Keyword(s):  
Pollen Tube ◽  
Tip Growth ◽  
Rho Gtpase ◽  
Plant Cells ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Filamentous Actin ◽  
Growth Defects ◽  
Spatiotemporal Regulation ◽  
Rho Family

Tip growth in neuronal cells, plant cells, and fungal hyphae is known to require tip-localized Rho GTPase, calcium, and filamentous actin (F-actin), but how they interact with each other is unclear. The pollen tube is an exciting model to study spatiotemporal regulation of tip growth and F-actin dynamics. An Arabidopsis thaliana Rho family GTPase, ROP1, controls pollen tube growth by regulating apical F-actin dynamics. This paper shows that ROP1 activates two counteracting pathways involving the direct targets of tip-localized ROP1: RIC3 and RIC4. RIC4 promotes F-actin assembly, whereas RIC3 activates Ca2+ signaling that leads to F-actin disassembly. Overproduction or depletion of either RIC4 or RIC3 causes tip growth defects that are rescued by overproduction or depletion of RIC3 or RIC4, respectively. Thus, ROP1 controls actin dynamics and tip growth through a check and balance between the two pathways. The dual and antagonistic roles of this GTPase may provide a unifying mechanism by which Rho modulates various processes dependent on actin dynamics in eukaryotic cells.

IgE alone-induced actin assembly modifies calcium signaling and degranulation in RBL-2H3 mast cells

2004 ◽  
Vol 286 (2) ◽  
pp. C256-C263 ◽  
Author(s):  
Tatsuya Oka ◽  
Masatoshi Hori ◽  
Akane Tanaka ◽  
Hiroshi Matsuda ◽  
Hideaki Karaki ◽  
...  
Keyword(s):  
Mast Cell ◽  
Mast Cells ◽  
Cell Activation ◽  
De Novo ◽  
Immunoglobulin E ◽  
Cytochalasin D ◽  
Mast Cell Activation ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Filamentous Actin

In the mast cell signaling pathways, the binding of immunoglobulin E (IgE) to FcϵRI, its high-affinity receptor, is generally thought to be a passive step. In this study, we examined the effect of IgE alone, that is, without antigen stimulation, on the degranulation in mast cells. Monomeric IgE (500–5,000 ng/ml) alone increased cytosolic Ca2+ level ([Ca2+]i) and induced degranulation in rat basophilic leukemia (RBL)-2H3 mast cells. Monomeric IgE (5,000 ng/ml) alone also increased [Ca2+]i and induced degranulation in bone marrow-derived mast cells. Interestingly, monomeric IgE (5–50 ng/ml) alone, in concentrations too low to induce degranulation, increased filamentous actin content in RBL-2H3 mast cells. We next examined whether actin dynamics affect the IgE alone-induced RBL-2H3 mast cell activation pathways. Cytochalasin D inhibited the ability of IgE alone (50 ng/ml) to induce de novo actin assembly. In cytochalasin D-treated cells, IgE (50 ng/ml) alone increased [Ca2+]i and induced degranulation. We have summarized the current findings into two points. First, IgE alone increases [Ca2+]i and induces degranulation in mast cells. Second, IgE, at concentrations too low to increase either [Ca2+]i or degranulation, significantly induces actin assembly, which serves as a negative feedback control in the mast cell Ca2+ signaling and degranulation.

scholarly journals The RhoGAP myosin 9/HUM-7 integrates membrane signals to modulate Rho/RHO-1 during embryonic morphogenesis in C. elegans

2018 ◽  
Author(s):  
Andre G. Wallace ◽  
Hamidah Raduwan ◽  
John Carlet ◽  
Martha C. Soto
Keyword(s):  
Plasma Membrane ◽  
Epidermal Cell ◽  
Rho Gtpase ◽  
Actin Dynamics ◽  
Rac Gtpase ◽  
Cell Behaviors ◽  
C Elegans ◽  
Embryonic Morphogenesis

AbstractDuring embryonic morphogenesis, cells and tissues undergo dramatic movements under the control of F-actin regulators. Our studies of epidermal cell migrations in developing C. elegans embryos have identified multiple plasma membrane signals that regulate the Rac GTPase, thus regulating WAVE and Arp2/3 complexes, to promote branched F-actin formation and polarized enrichment. We describe here a pathway that acts in parallel to Rac to transduce membrane signals to control epidermal F-actin through the GTPase Rho. Rho contributes to epidermal migrations through effects on underlying neuroblasts. Here we identify signals to regulate Rho in the epidermis. HUM-7, the C. elegans homolog of human Myo9A and Myo9B, regulates F-actin dynamics during epidermal migrations, by controlling Rho. Genetics and biochemistry support that HUM-7 behaves as GAP for the Rho GTPase, so that loss of HUM-7 enhances Rho-dependent epidermal cell behaviors. We identify SAX-3/ROBO as an upstream signal that contributes to attenuated Rho activation through its regulation of HUM-7/Myo9. These studies identify a new role for Rho during epidermal cell migrations, and suggest that Rho activity is regulated by SAX-3/ROBO acting on the RhoGAP HUM-7.

scholarly journals Type I myosins anchor actin assembly to the plasma membrane during clathrin-mediated endocytosis

2019 ◽  
Vol 218 (4) ◽  
pp. 1138-1147 ◽  
Author(s):  
Ross T.A. Pedersen ◽  
David G. Drubin
Keyword(s):  
Plasma Membrane ◽  
Membrane Trafficking ◽  
Force Generation ◽  
Type I ◽  
Actin Assembly ◽  
Filamentous Actin ◽  
Actin Networks ◽  
Wide Range ◽  
Assembly Factors ◽  
Myosin Motors

The actin cytoskeleton generates forces on membranes for a wide range of cellular and subcellular morphogenic events, from cell migration to cytokinesis and membrane trafficking. For each of these processes, filamentous actin (F-actin) interacts with membranes and exerts force through its assembly, its associated myosin motors, or both. These two modes of force generation are well studied in isolation, but how they are coordinated in cells is mysterious. During clathrin-mediated endocytosis, F-actin assembly initiated by the Arp2/3 complex and several proteins that compose the WASP/myosin complex generates the force necessary to deform the plasma membrane into a pit. Here we present evidence that type I myosin is the key membrane anchor for endocytic actin assembly factors in budding yeast. By mooring actin assembly factors to the plasma membrane, this myosin organizes endocytic actin networks and couples actin-generated forces to the plasma membrane to drive invagination and scission. Through this unexpected mechanism, myosin facilitates force generation independent of its motor activity.

scholarly journals Actin depolymerization is sufficient to induce programmed cell death in self-incompatible pollen

2006 ◽  
Vol 174 (2) ◽  
pp. 221-229 ◽  
Author(s):  
Steven G. Thomas ◽  
Shanjin Huang ◽  
Shutian Li ◽  
Christopher J. Staiger ◽  
Vernonica E. Franklin-Tong
Keyword(s):  
Cell Death ◽  
Programmed Cell Death ◽  
Actin Polymerization ◽  
Caspase 3 ◽  
Tip Growth ◽  
Causal Link ◽  
Actin Dynamics ◽  
Latrunculin B ◽  
Actin Depolymerization ◽  
Incompatible Pollen

Self-incompatibility (SI) prevents inbreeding through specific recognition and rejection of incompatible pollen. In incompatible Papaver rhoeas pollen, SI triggers a Ca2+ signaling cascade, resulting in the inhibition of tip growth, actin depolymerization, and programmed cell death (PCD). We investigated whether actin dynamics were implicated in regulating PCD. Using the actin-stabilizing and depolymerizing drugs jasplakinolide (Jasp) and latrunculin B, we demonstrate that changes in actin filament levels or dynamics play a functional role in initiating PCD in P. rhoeas pollen, triggering a caspase-3–like activity. Significantly, SI-induced PCD in incompatible pollen was alleviated by pretreatment with Jasp. This represents the first account of a specific causal link between actin polymerization status and initiation of PCD in a plant cell and significantly advances our understanding of the mechanisms involved in SI.

scholarly journals Plasma membrane nano-organization specifies phosphoinositide effects on Rho-GTPases and actin dynamics in tobacco pollen tubes

2020 ◽  
Author(s):  
Marta Fratini ◽  
Praveen Krishnamoorthy ◽  
Irene Stenzel ◽  
Mara Riechmann ◽  
Kirsten Bacia ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Trafficking ◽  
Rho Gtpases ◽  
Rho Gtpase ◽  
Pollen Tubes ◽  
Actin Dynamics ◽  
Tobacco Pollen ◽  
Dual Distribution ◽  
Cytoskeletal Dynamics

AbstractPollen tube growth requires coordination of cytoskeletal dynamics and apical secretion. The regulatory phospholipid, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) is enriched in the subapical plasma membrane of pollen tubes and can influence both actin dynamics and secretion. How alternative PtdIns(4,5)P2-effects are specified is unclear. Spinning disc microscopy (SD) reveals dual distribution of a fluorescent PtdIns(4,5)P2-reporter in dynamic plasma membrane nanodomains vs. apparent diffuse membrane labelling, consistent with spatially distinct coexisting pools of PtdIns(4,5)P2. Several PI4P 5-kinases (PIP5Ks) can generate PtdIns(4,5)P2 in pollen tubes. Despite localizing to one membrane region, AtPIP5K2 and NtPIP5K6 display distinctive overexpression effects on cell morphologies, respectively related to altered actin dynamics or membrane trafficking. When analyzed by SD, AtPIP5K2-EYFP associated with nanodomains, whereas NtPIP5K6-EYFP localized diffusely. Chimeric AtPIP5K2 and NtPIP5K6 variants with reciprocally swapped membrane-associating domains evoked reciprocally shifted effects on cell morphology upon overexpression. Overall, PI4P 5-kinase variants targeted to nanodomains stabilized actin, suggesting a specific function of PtdIns(4,5)P2-nanodomains. A distinct role of nanodomain-associated AtPIP5K2 in actin regulation is further supported by proximity to and interaction with the Rho-GTPase NtRac5, and by functional interplay with elements of ROP-signalling. Plasma membrane nano-organization may thus aid the specification of PtdIns(4,5)P2-functions to coordinate cytoskeletal dynamics and secretion in pollen tubes.

scholarly journals Actin dynamics in cell migration

2019 ◽  
Vol 63 (5) ◽  
pp. 483-495 ◽  
Author(s):  
Matthias Schaks ◽  
Grégory Giannone ◽  
Klemens Rottner
Keyword(s):  
Plasma Membrane ◽  
Cell Migration ◽  
Actin Filament ◽  
Rho Gtpases ◽  
Rho Gtpase ◽  
Actin Dynamics ◽  
Regulatory Complex ◽  
Membrane Protrusions ◽  
Filament Networks ◽  
Contractile Forces

Abstract Cell migration is an essential process, both in unicellular organisms such as amoeba and as individual or collective motility in highly developed multicellular organisms like mammals. It is controlled by a variety of activities combining protrusive and contractile forces, normally generated by actin filaments. Here, we summarize actin filament assembly and turnover processes, and how respective biochemical activities translate into different protrusion types engaged in migration. These actin-based plasma membrane protrusions include actin-related protein 2/3 complex-dependent structures such as lamellipodia and membrane ruffles, filopodia as well as plasma membrane blebs. We also address observed antagonisms between these protrusion types, and propose a model – also inspired by previous literature – in which a complex balance between specific Rho GTPase signaling pathways dictates the protrusion mechanism employed by cells. Furthermore, we revisit published work regarding the fascinating antagonism between Rac and Rho GTPases, and how this intricate signaling network can define cell behavior and modes of migration. Finally, we discuss how the assembly of actin filament networks can feed back onto their regulators, as exemplified for the lamellipodial factor WAVE regulatory complex, tightly controlling accumulation of this complex at specific subcellular locations as well as its turnover.

scholarly journals Adenovirus E4orf4 Hijacks Rho GTPase-dependent Actin Dynamics to Kill Cells: A Role for Endosome-associated Actin Assembly

2006 ◽  
Vol 17 (7) ◽  
pp. 3329-3344 ◽  
Author(s):  
Amélie Robert ◽  
Nicolas Smadja-Lamère ◽  
Marie-Claude Landry ◽  
Claudia Champagne ◽  
Ryan Petrie ◽  
...  
Keyword(s):  
Rho Gtpases ◽  
Actin Polymerization ◽  
Rho Gtpase ◽  
De Novo ◽  
Strong Support ◽  
Src Family Kinases ◽  
Actin Dynamics ◽  
Death Process ◽  
Actin Assembly ◽  
Orf4 Protein

The adenovirus early region 4 ORF4 protein (E4orf4) triggers a novel death program that bypasses classical apoptotic pathways in human cancer cells. Deregulation of the cell cytoskeleton is a hallmark of E4orf4 killing that relies on Src family kinases and E4orf4 phosphorylation. However, the cytoskeletal targets of E4orf4 and their role in the death process are unknown. Here, we show that E4orf4 translocates to cytoplasmic sites and triggers the assembly of a peculiar juxtanuclear actin–myosin network that drives polarized blebbing and nuclear shrinkage. We found that E4orf4 activates the myosin II motor and triggers de novo actin polymerization in the perinuclear region, promoting endosomes recruitment to the sites of actin assembly. E4orf4-induced actin dynamics requires interaction with Src family kinases and involves a spatial regulation of the Rho GTPases pathways Cdc42/N-Wasp, RhoA/Rho kinase, and Rac1, which make distinct contributions. Remarkably, activation of the Rho GTPases is required for induction of apoptotic-like cell death. Furthermore, inhibition of actin dynamics per se dramatically impairs E4orf4 killing. This work provides strong support for a causal role for endosome-associated actin dynamics in E4orf4 killing and in the regulation of cancer cell fate.

scholarly journals Expression of Actin-interacting Protein 1 Suppresses Impaired Chemotaxis of Dictyostelium Cells Lacking the Na+-H+ Exchanger NHE1

2010 ◽  
Vol 21 (18) ◽  
pp. 3162-3170 ◽  
Author(s):  
Chang-Hoon Choi ◽  
Hitesh Patel ◽  
Diane L. Barber
Keyword(s):  
Cell Migration ◽  
Mammalian Cells ◽  
Current Data ◽  
Full Length ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Filamentous Actin ◽  
Interacting Protein ◽  
Terminal Fragment ◽  
Ph Dependent

Increased intracellular pH is an evolutionarily conserved signal necessary for directed cell migration. We reported previously that in Dictyostelium cells lacking H+ efflux by a Na+-H+ exchanger (NHE; Ddnhe1−), chemotaxis is impaired and the assembly of filamentous actin (F-actin) is attenuated. We now describe a modifier screen that reveals the C-terminal fragment of actin-interacting protein 1 (Aip1) enhances the chemotaxis defect of Ddnhe1− cells but has no effect in wild-type Ax2 cells. However, expression of full-length Aip1 mostly suppresses chemotaxis defects of Ddnhe1− cells and restores F-actin assembly. Aip1 functions to promote cofilin-dependent actin remodeling, and we found that although full-length Aip1 binds cofilin and F-actin, the C-terminal fragment binds cofilin but not F-actin. Because pH-dependent cofilin activity is attenuated in mammalian cells lacking H+ efflux by NHE1, our current data suggest that full-length Aip1 facilitates F-actin assembly when cofilin activity is limited. We predict the C-terminus of Aip1 enhances defective chemotaxis of Ddnhe1− cells by sequestering the limited amount of active cofilin without promoting F-actin assembly. Our findings indicate a cooperative role of Aip1 and cofilin in pH-dependent cell migration, and they suggest defective chemotaxis in Ddnhe1− cells is determined primarily by loss of cofilin-dependent actin dynamics.

scholarly journals Enhanced Production of the Mical Redox Domain for Enzymology and F-actin Disassembly Assays

2021 ◽  
Vol 22 (4) ◽  
pp. 1991
Author(s):  
Jimok Yoon ◽  
Heng Wu ◽  
Ruei-Jiun Hung ◽  
Jonathan R. Terman
Keyword(s):  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Actin Dynamics ◽  
Specific Substrate ◽  
Actin Assembly ◽  
Redox Enzymes ◽  
Enhanced Production ◽  
Reversible Redox ◽  
Future Work ◽  
Signaling Process

To change their behaviors, cells require actin proteins to assemble together into long polymers/filaments—and so a critical goal is to understand the factors that control this actin filament (F-actin) assembly and stability. We have identified a family of unusual actin regulators, the MICALs, which are flavoprotein monooxygenase/hydroxylase enzymes that associate with flavin adenine dinucleotide (FAD) and use the co-enzyme nicotinamide adenine dinucleotide phosphate (NADPH) in Redox reactions. F-actin is a specific substrate for these MICAL Redox enzymes, which oxidize specific amino acids within actin to destabilize actin filaments. Furthermore, this MICAL-catalyzed reaction is reversed by another family of Redox enzymes (SelR/MsrB enzymes)—thereby revealing a reversible Redox signaling process and biochemical mechanism regulating actin dynamics. Interestingly, in addition to the MICALs’ Redox enzymatic portion through which MICALs covalently modify and affect actin, MICALs have multiple other domains. Less is known about the roles of these other MICAL domains. Here we provide approaches for obtaining high levels of recombinant protein for the Redox only portion of Mical and demonstrate its catalytic and F-actin disassembly activity. These results provide a ground state for future work aimed at defining the role of the other domains of Mical — including characterizing their effects on Mical’s Redox enzymatic and F-actin disassembly activity.

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