Abeta1-42 stimulates actin polymerization in hippocampal neurons through Rac1 and Cdc42 Rho GTPases

Abstract Enhanced activity and overexpression of Pannexin 1 (PANX1) channels contribute to neuronal pathologies, such as epilepsy and Alzheimer’s disease (AD). In the hippocampus, the PANX1 channel ablation alters glutamatergic neurotransmission, synaptic plasticity, and memory flexibility. Nevertheless, PANX1-knockout (PANX1-KO) mice still preserve the ability to learn, suggesting that compensatory mechanisms work to stabilize neuronal activity. Here, we show that the absence of PANX1 in the adult brain promotes a series of structural and functional modifications in PANX1-KO CA1 hippocampal synapses, preserving spontaneous activity. Adult CA1 neurons of PANX1-KO mice exhibit enhanced excitability, a more complex dendritic branching, enhanced spine maturation, and multiple synaptic contacts compared to the WT condition. These modifications seem to rely on the actin-cytoskeleton dynamics as an increase in actin polymerization and an imbalance between Rac1 and RhoA GTPase activity is observed in the absence of PANX1. Our findings highlight a novel interaction between PANX1, actin, and small Rho GTPases, which appear to be relevant for synapse stability.

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Long-term Pannexin 1 ablation promotes structural and functional modifications in hippocampal neurons through the regulation of actin cytoskeleton and Rho GTPases activity.

10.1101/2021.11.03.467134 ◽

2021 ◽

Author(s):

Carolina Flores-Muñoz ◽

Francisca Garcia-Rojas ◽

MIguel A. Perez ◽

Odra Santander ◽

Elena Mery ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Rho Gtpases ◽

Hippocampal Neurons ◽

Actin Polymerization ◽

Adult Brain ◽

Compensatory Mechanism ◽

Compensatory Mechanisms ◽

Pannexin 1 ◽

Synapse Maintenance

Enhanced activity and overexpression of Pannexin 1 (PANX1) channels contribute to neuronal pathologies, such as epilepsy and Alzheimers disease (AD). In the hippocampus, the PANX1 channels ablation alters glutamatergic neurotransmission, synaptic plasticity, and memory flexibility. Nevertheless, PANX1-knockout (KO) mice still preserve the ability to learn, suggesting that compensatory mechanisms work to stabilize neuronal activity. Here, we show that the absence of PANX1 in the adult brain promotes a series of structural and functional modifications in KO hippocampal synapses, preserving spontaneous activity. Adult CA1 neurons of KO mice exhibit enhanced excitability, complex dendritic branching, spine maturation, and multiple synaptic contacts compared to the WT condition. These modifications seem to rely on the actin-cytoskeleton dynamics as an increase in actin polymerization and an imbalance between Rac1 and RhoA GTPase activity is observed in the absence of PANX1. Our findings highlight a novel interaction between PANX1, actin, and small Rho GTPases that appear to be relevant for synapse maintenance as a long-term compensatory mechanism for PANX1 deficiency.

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Distinct signals via Rho GTPases and Src drive shape changes by thrombin and sphingosine-1-phosphate in endothelial cells

Journal of Cell Science ◽

10.1242/jcs.115.12.2475 ◽

2002 ◽

Vol 115 (12) ◽

pp. 2475-2484 ◽

Cited By ~ 3

Author(s):

Valérie Vouret-Craviari ◽

Christine Bourcier ◽

Etienne Boulter ◽

Ellen Van Obberghen-Schilling

Keyword(s):

Endothelial Cells ◽

Rho Gtpases ◽

Actin Polymerization ◽

Morphological Changes ◽

Umbilical Vein ◽

Cell Spreading ◽

Actin Binding ◽

Sphingosine 1 Phosphate ◽

And Migration ◽

Umbilical Vein Endothelial Cells

Soluble mediators such as thrombin and sphingosine-1-phosphate regulate morphological changes in endothelial cells that affect vascular permeability and new blood vessel formation. Although these ligands activate a similar set of heterotrimeric G proteins, thrombin causes cell contraction and rounding whereas sphingosine-1-phosphate induces cell spreading and migration. A functional requirement for Rho family GTPases in the cytoskeletal responses to both ligands has been established, yet the dynamics of their regulation and additional signaling mechanisms that lead to such opposite effects remain poorly understood. Using a pull-down assay to monitor the activity of Rho GTPases in human umbilical vein endothelial cells, we find significant temporal and quantitative differences in RhoA and Rac1 activation. High levels of active RhoA rapidly accumulate in cells in response to thrombin whereas Rac1 is inhibited. In contrast, sphingosine-1-phosphate addition leads to comparatively weak and delayed activation of RhoA and it activates Rac1. In addition, we show here that sphingosine-1-phosphate treatment activates a Src family kinase and triggers recruitment of the F-actin-binding protein cortactin to sites of actin polymerization at the rim of membrane ruffles. Both Src and Rac pathways are essential for lamellipodia targeting of cortactin. Further, Src plays a determinant role in sphingosine-1-phosphate-induced cell spreading and migration. Taken together these data demonstrate that the thrombin-induced contractile and immobile phenotype in endothelial cells reflects both robust RhoA activation and Rac inhibition, whereas Src- and Rac-dependent events couple sphingosine-1-phosphate receptors to the actin polymerizing machinery that drives the extension of lamellipodia and cell migration.

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Tropomyosin Tpm3.1 is required to maintain the structure and function of the axon initial segment

10.1101/711614 ◽

2019 ◽

Cited By ~ 1

Author(s):

Amr Abouelezz ◽

Holly Stefen ◽

Mikael Segerstråle ◽

David Micinski ◽

Rimante Minkeviciene ◽

...

Keyword(s):

Actin Filaments ◽

Hippocampal Neurons ◽

Initial Segment ◽

Actin Polymerization ◽

Firing Frequency ◽

Axon Initial Segment ◽

Action Potential Initiation ◽

Sodium Ion Channels ◽

And Function ◽

Filament Network

ABSTRACTThe axon initial segment (AIS) is the site of action potential initiation and serves as a vesicular filter and diffusion barrier that help maintain neuronal polarity. Recent studies have revealed details about a specialized structural complex in the AIS. While an intact actin cytoskeleton is required for AIS formation, pharmacological disruption of actin polymerization compromises the AIS vesicle filter but does not affect overall AIS structure. In this study, we found that the tropomyosin isoform Tpm3.1 decorates a population of relatively stable actin filaments in the AIS. Inhibiting Tpm3.1 in cultured hippocampal neurons led to the loss of AIS structure, the AIS vesicle filter, the clustering of sodium ion channels, and reduced firing frequency. We propose that Tpm3.1-decorated actin filaments form a stable actin filament network under the AIS membrane which provides a scaffold for membrane organization and AIS proteins.

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RacG Regulates Morphology, Phagocytosis, and Chemotaxis

Eukaryotic Cell ◽

10.1128/ec.00221-06 ◽

2006 ◽

Vol 5 (10) ◽

pp. 1648-1663 ◽

Cited By ~ 20

Author(s):

Baggavalli P. Somesh ◽

Georgia Vlahou ◽

Miho Iijima ◽

Robert H. Insall ◽

Peter Devreotes ◽

...

Keyword(s):

Rho Gtpases ◽

Actin Polymerization ◽

Kinase Inhibitor ◽

Dominant Negative ◽

Dependent Manner ◽

Free System ◽

Mild Phenotype ◽

Particle Uptake ◽

Phosphoinositide 3 Kinase

ABSTRACTRacG is an unusual member of the complex family of Rho GTPases inDictyostelium. We have generated a knockout (KO) strain, as well as strains that overexpress wild-type (WT), constitutively active (V12), or dominant negative (N17) RacG. The protein is targeted to the plasma membrane, apparently in a nucleotide-dependent manner, and induces the formation of abundant actin-driven filopods. RacG is enriched at the rim of the progressing phagocytic cup, and overexpression of RacG-WT or RacG-V12 induced an increased rate of particle uptake. The positive effect of RacG on phagocytosis was abolished in the presence of 50 μM LY294002, a phosphoinositide 3-kinase inhibitor, indicating that generation of phosphatidylinositol 3,4,5-trisphosphate is required for activation of RacG. RacG-KO cells showed a moderate chemotaxis defect that was stronger in the RacG-V12 and RacG-N17 mutants, in part because of interference with signaling through Rac1. The in vivo effects of RacG-V12 could not be reproduced by a mutant lacking the Rho insert region, indicating that this region is essential for interaction with downstream components. Processes like growth, pinocytosis, exocytosis, cytokinesis, and development were unaffected in Rac-KO cells and in the overexpressor mutants. In a cell-free system, RacG induced actin polymerization upon GTPγS stimulation, and this response could be blocked by an Arp3 antibody. While the mild phenotype of RacG-KO cells indicates some overlap with one or moreDictyosteliumRho GTPases, like Rac1 and RacB, the significant changes found in overexpressors show that RacG plays important roles. We hypothesize that RacG interacts with a subset of effectors, in particular those concerned with shape, motility, and phagocytosis.

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Genetic dissection of active forgetting in labile and consolidated memories in Drosophila

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1903763116 ◽

2019 ◽

Vol 116 (42) ◽

pp. 21191-21197 ◽

Cited By ~ 2

Author(s):

Yang Gao ◽

Yichun Shuai ◽

Xuchen Zhang ◽

Yuwei Peng ◽

Lianzhang Wang ◽

...

Keyword(s):

Rho Gtpases ◽

Mushroom Body ◽

Actin Polymerization ◽

Molecular Mechanisms ◽

Genetic Dissection ◽

Actin Depolymerization ◽

Downstream Effector ◽

Different Types ◽

Wasp Family Proteins

Different memory components are forgotten through distinct molecular mechanisms. In Drosophila, the activation of 2 Rho GTPases (Rac1 and Cdc42), respectively, underlies the forgetting of an early labile memory (anesthesia-sensitive memory, ASM) and a form of consolidated memory (anesthesia-resistant memory, ARM). Here, we dissected the molecular mechanisms that tie Rac1 and Cdc42 to the different types of memory forgetting. We found that 2 WASP family proteins, SCAR/WAVE and WASp, act downstream of Rac1 and Cdc42 separately to regulate ASM and ARM forgetting in mushroom body neurons. Arp2/3 complex, which organizes branched actin polymerization, is a canonical downstream effector of WASP family proteins. However, we found that Arp2/3 complex is required in Cdc42/WASp-mediated ARM forgetting but not in Rac1/SCAR-mediated ASM forgetting. Instead, we identified that Rac1/SCAR may function with formin Diaphanous (Dia), a nucleator that facilitates linear actin polymerization, in ASM forgetting. The present study, complementing the previously identified Rac1/cofilin pathway that regulates actin depolymerization, suggests that Rho GTPases regulate forgetting by recruiting both actin polymerization and depolymerization pathways. Moreover, Rac1 and Cdc42 may regulate different types of memory forgetting by tapping into different actin polymerization mechanisms.

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Cdc42 and Phosphoinositide 3-Kinase Drive Rac-Mediated Actin Polymerization Downstream of c-Met in Distinct and Common Pathways

Molecular and Cellular Biology ◽

10.1128/mcb.00367-07 ◽

2007 ◽

Vol 27 (19) ◽

pp. 6615-6628 ◽

Cited By ~ 36

Author(s):

Tanja Bosse ◽

Julia Ehinger ◽

Aleksandra Czuchra ◽

Stefanie Benesch ◽

Anika Steffen ◽

...

Keyword(s):

Rho Gtpases ◽

Actin Polymerization ◽

Pi3 Kinase ◽

Actin Assembly ◽

Actin Reorganization ◽

Membrane Ruffling ◽

Internalin B ◽

Phosphoinositide 3 Kinase ◽

Hepatocyte Growth ◽

Wave Complex

ABSTRACT Activation of c-Met, the hepatocyte growth factor (HGF)/scatter factor receptor induces reorganization of the actin cytoskeleton, which drives epithelial cell scattering and motility and is exploited by pathogenic Listeria monocytogenes to invade nonepithelial cells. However, the precise contributions of distinct Rho-GTPases, the phosphatidylinositol 3-kinases, and actin assembly regulators to c-Met-mediated actin reorganization are still elusive. Here we report that HGF-induced membrane ruffling and Listeria invasion mediated by the bacterial c-Met ligand internalin B (InlB) were significantly impaired but not abrogated upon genetic removal of either Cdc42 or pharmacological inhibition of phosphoinositide 3-kinase (PI3-kinase). While loss of Cdc42 or PI3-kinase function correlated with reduced HGF- and InlB-triggered Rac activation, complete abolishment of actin reorganization and Rac activation required the simultaneous inactivation of both Cdc42 and PI3-kinase signaling. Moreover, Cdc42 activation was fully independent of PI3-kinase activity, whereas the latter partly depended on Cdc42. Finally, Cdc42 function did not require its interaction with the actin nucleation-promoting factor N-WASP. Instead, actin polymerization was driven by Arp2/3 complex activation through the WAVE complex downstream of Rac. Together, our data establish an intricate signaling network comprising as key molecules Cdc42 and PI3-kinase, which converge on Rac-mediated actin reorganization essential for Listeria invasion and membrane ruffling downstream of c-Met.

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Thromboxane-induced actin polymerization in hypoxic neonatal pulmonary arterial myocytes involves Cdc42 signaling

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00036.2014 ◽

2014 ◽

Vol 307 (11) ◽

pp. L877-L887 ◽

Cited By ~ 8

Author(s):

Jena Fediuk ◽

Anurag S. Sikarwar ◽

Nora Nolette ◽

Shyamala Dakshinamurti

Keyword(s):

Rho Gtpases ◽

Laser Scanning ◽

Actin Polymerization ◽

Filamentous Actin ◽

Actin Isoforms ◽

Pi3k Activity ◽

Laser Scanning Cytometry ◽

Pulmonary Arterial ◽

P21 Activated Kinase ◽

Syndrome Protein

In hypoxic pulmonary arterial (PA) myocytes, challenge with thromboxane mimetic U46619 induces marked actin polymerization and contraction, phenotypic features of persistent pulmonary hypertension of the newborn (PPHN). Rho GTPases regulate the actin cytoskeleton. We previously reported that U46619-induced actin polymerization in hypoxic PA myocytes occurs independently of the RhoA pathway and hypothesized involvement of the Cdc42 pathway. PA myocytes grown in normoxia or hypoxia for 72 h were stimulated with U46619, then analyzed for Rac/Cdc42 activation by affinity precipitation, phosphatidylinositide-3-kinase (PI3K) activity by phospho-Akt, phospho-p21-activated kinase (PAK) by immunoblot, and association of Cdc42 with neuronal Wiskott Aldrich Syndrome protein (N-WASp) by immunoprecipitation. The effect of Rac or PAK inhibition on filamentous actin was quantified by laser-scanning cytometry and by cytoskeletal fractionation; effects of actin-modifying agents were measured by isometric myography. Basal Cdc42 activity increased in hypoxia, whereas Rac activity decreased. U46619 challenge increased Cdc42 and Rac activity in hypoxic cells, independently of PI3K. Hypoxia increased phospho-PAK, unaltered by U46619. Association of Cdc42 with N-WASp decreased in hypoxia but increased after U46619 exposure. Hypoxia doubled filamentous-to-globular ratios of α- and γ-actin isoforms. Jasplakinolide stabilized γ-filaments, increasing force; cytochalasin D depolymerized all actin isoforms, decreasing force. Rac and PAK inhibition decreased filamentous actin in tissues although without decrease in force. Rho inhibition decreased myosin phosphorylation and force. Hypoxia induces actin polymerization in PA myocytes, particularly increasing filamentous α- and γ-actin, contributing to U46619-induced contraction. Hypoxic PA myocytes challenged with a thromboxane mimetic polymerize actin via the Cdc42 pathway, reflecting increased Cdc42 association with N-WASp. Mechanisms regulating thromboxane-mediated actin polymerization are potential targets for future PPHN pharmacotherapy.

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The TRE17 Oncogene Encodes a Component of a Novel Effector Pathway for Rho GTPases Cdc42 and Rac1 and Stimulates Actin Remodeling

Molecular and Cellular Biology ◽

10.1128/mcb.23.6.2151-2161.2003 ◽

2003 ◽

Vol 23 (6) ◽

pp. 2151-2161 ◽

Cited By ~ 36

Author(s):

Jeffrey M. Masuda-Robens ◽

Sara N. Kutney ◽

Hongwei Qi ◽

Margaret M. Chou

Keyword(s):

Plasma Membrane ◽

Rho Gtpases ◽

Actin Polymerization ◽

Dependent Manner ◽

Cortical Actin ◽

Actin Remodeling ◽

Membrane Recruitment ◽

Truncation Mutant ◽

Effector Pathway

ABSTRACT The Rho family GTPases Cdc42 and Rac1 play fundamental roles in transformation and actin remodeling. Here, we demonstrate that the TRE17 oncogene encodes a component of a novel effector pathway for these GTPases. TRE17 coprecipitated specifically with the active forms of Cdc42 and Rac1 in vivo. Furthermore, the subcellular localization of TRE17 was dramatically regulated by these GTPases and mitogens. Under serum-starved conditions, TRE17 localized predominantly to filamentous structures within the cell. Epidermal growth factor (EGF) induced relocalization of TRE17 to the plasma membrane in a Cdc42-/Rac1-dependent manner. Coexpression of activated alleles of Cdc42 or Rac1 also caused complete redistribution of TRE17 to the plasma membrane, where it partially colocalized with the GTPases in filopodia and ruffles, respectively. Membrane recruitment of TRE17 by EGF or the GTPases was dependent on actin polymerization. Finally, we found that a C-terminal truncation mutant of TRE17 induced the accumulation of cortical actin, mimicking the effects of activated Cdc42. Together, these results identify TRE17 as part of a novel effector complex for Cdc42 and Rac1, potentially contributing to their effects on actin remodeling. The present study provides insights into the regulation and cellular function of this previously uncharacterized oncogene.

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Syndecan-2 induces filopodia and dendritic spine formation via the neurofibromin–PKA–Ena/VASP pathway

The Journal of Cell Biology ◽

10.1083/jcb.200608121 ◽

2007 ◽

Vol 177 (5) ◽

pp. 829-841 ◽

Cited By ~ 94

Author(s):

Yi-Ling Lin ◽

Ya-Ting Lei ◽

Chen-Jei Hong ◽

Yi-Ping Hsueh

Keyword(s):

Hippocampal Neurons ◽

Actin Polymerization ◽

Kinase Inhibitors ◽

Cyclic Adenosine Monophosphate ◽

Adenosine Monophosphate ◽

Dominant Negative ◽

Dominant Negative Mutant ◽

Human Embryonic Kidney Cells ◽

Spine Formation ◽

Downstream Signaling

Syndecan-2 induced filopodia before spinogenesis; therefore, filopodia formation was used here as a model to study the early downstream signaling of syndecan-2 that leads to spinogenesis. Screening using kinase inhibitors indicated that protein kinase A (PKA) is required for syndecan-2–induced filopodia formation in both human embryonic kidney cells and hippocampal neurons. Because neurofibromin, a syndecan-2–binding partner, activates the cyclic adenosine monophosphate pathway, the role of neurofibromin in syndecan-2–induced filopodia formation was investigated by deletion mutant analysis, RNA interference, and dominant-negative mutant. The results showed that neurofibromin mediates the syndecan-2 signal to PKA. Among actin-associated proteins, Enabled (Ena)/vasodilator-stimulated phosphoprotein (VASP) were predicted as PKA effectors downstream of syndecan-2, as Ena/VASP, which is activated by PKA, induces actin polymerization. Indeed, when the activities of Ena/VASP were blocked, syndecan-2 no longer induced filopodia formation. Finally, in addition to filopodia formation, neurofibromin and Ena/VASP contributed to spinogenesis. This study reveals a novel signaling pathway in which syndecan-2 activates PKA via neurofibromin and PKA consequently phosphorylates Ena/VASP, promoting filopodia and spine formation.

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