scholarly journals Socius Is a Novel Rnd GTPase-Interacting Protein Involved in Disassembly of Actin Stress Fibers

2002 ◽  
Vol 22 (9) ◽  
pp. 2952-2964 ◽  
Author(s):  
Hironori Katoh ◽  
Amane Harada ◽  
Kazutoshi Mori ◽  
Manabu Negishi
Keyword(s):  
Actin Cytoskeleton ◽  
Cell Body ◽  
Inhibitory Effect ◽  
Small Gtpases ◽  
Fiber Formation ◽  
Stress Fibers ◽  
Cell Periphery ◽  
Cellular Processes ◽  
Rho Family ◽  
Actin Stress Fibers

ABSTRACT Rho family small GTPases are key regulators of the actin cytoskeleton in various cell types. The Rnd proteins, Rnd1, Rnd2, and Rnd3/RhoE, have been recently identified as new members of the Rho family of GTPases, and expression of Rnd1 or Rnd3 in fibroblasts causes the disassembly of actin stress fibers and the retraction of the cell body to produce extensively branching cellular processes. Here we have performed a yeast two-hybrid screening by using Rnd1 as bait and identified a novel protein that specifically binds to Rnd GTPases. We named this protein Socius. Socius directly binds to Rnd GTPases through its COOH-terminal region. When transfected into COS-7 cells, Socius is translocated to the cell periphery in response to Rnd1 and Rnd3 and colocalized with the GTPases. While expression of wild-type Socius in Swiss 3T3 fibroblasts has little effect on the actin cytoskeleton, the expression of a membrane-targeted form of Socius, containing a COOH-terminal farnesylation motif (Socius-CAAX), induces a dramatic loss of stress fibers. The inhibitory effect of Socius-CAAX on stress fiber formation is enhanced by truncation of its NH2 terminus. On the other hand, the expression of Socius-CAAX or its NH2 terminus-truncated form suppresses the Rnd-induced retraction of the cell body and the production of extensively branching cellular processes, although the disassembly of stress fibers is observed. We propose that Socius participates in the Rnd GTPase-induced signal transduction pathways, leading to reorganization of the actin cytoskeleton.

scholarly journals RhoE Regulates Actin Cytoskeleton Organization and Cell Migration

1998 ◽  
Vol 18 (8) ◽  
pp. 4761-4771 ◽  
Author(s):  
Rosa M. Guasch ◽  
Peter Scambler ◽  
Gareth E. Jones ◽  
Anne J. Ridley
Keyword(s):  
Actin Cytoskeleton ◽  
Mdck Cells ◽  
Fiber Formation ◽  
Stress Fibers ◽  
Complete Disappearance ◽  
Actin Organization ◽  
Cytoskeleton Organization ◽  
Actin Cytoskeleton Organization ◽  
Rho Family ◽  
As Stress

ABSTRACT The actin cytoskeleton is regulated by Rho family proteins: in fibroblasts, Rho mediates the formation of actin stress fibers, whereas Rac regulates lamellipodium formation and Cdc42 controls filopodium formation. We have cloned the mouse RhoE gene, whose product is a member of the Rho family that shares (except in one amino acid) the conserved effector domain of RhoA, RhoB, and RhoC. RhoE is able to bind GTP but does not detectably bind GDP and has low intrinsic GTPase activity compared with Rac. The role of RhoE in regulating actin organization was investigated by microinjection in Bac1.2F5 macrophages and MDCK cells. In macrophages, RhoE induced actin reorganization, leading to the formation of extensions resembling filopodia and pseudopodia. In MDCK cells, RhoE induced the complete disappearance of stress fibers, together with cell spreading. However, RhoE did not detectably affect the actin bundles that run parallel to the outer membranes of cells at the periphery of colonies, which are known to be dependent on RhoA. In addition, RhoE induced an increase in the speed of migration of hepatocyte growth factor/scatter factor-stimulated MDCK cells, in contrast to the previously reported inhibition produced by activated RhoA. The subcellular localization of RhoE at the lateral membranes of MDCK cells suggests a role in cell-cell adhesion, as has been shown for RhoA. These results suggest that RhoE may act to inhibit signalling downstream of RhoA, altering some RhoA-regulated responses, such as stress fiber formation, but not affecting others, such as peripheral actin bundle formation.

scholarly journals Primary Cilia, Ciliogenesis and the Actin Cytoskeleton: A Little Less Resorption, A Little More Actin Please

2020 ◽  
Vol 8 ◽  
Author(s):  
Claire E. L. Smith ◽  
Alice V. R. Lake ◽  
Colin A. Johnson
Keyword(s):  
Cell Membrane ◽  
Actin Cytoskeleton ◽  
Actin Polymerization ◽  
Primary Cilia ◽  
Fiber Formation ◽  
Stress Fibers ◽  
Apical Surface ◽  
Apical Cell Membrane ◽  
Cellular Processes ◽  
Filament Bundles

Primary cilia are microtubule-based organelles that extend from the apical surface of most mammalian cells, forming when the basal body (derived from the mother centriole) docks at the apical cell membrane. They act as universal cellular “antennae” in vertebrates that receive and integrate mechanical and chemical signals from the extracellular environment, serving diverse roles in chemo-, mechano- and photo-sensation that control developmental signaling, cell polarity and cell proliferation. Mutations in ciliary genes cause a major group of inherited developmental disorders called ciliopathies. There are very few preventative treatments or new therapeutic interventions that modify disease progression or the long-term outlook of patients with these conditions. Recent work has identified at least four distinct but interrelated cellular processes that regulate cilia formation and maintenance, comprising the cell cycle, cellular proteostasis, signaling pathways and structural influences of the actin cytoskeleton. The actin cytoskeleton is composed of microfilaments that are formed from filamentous (F) polymers of globular G-actin subunits. Actin filaments are organized into bundles and networks, and are attached to the cell membrane, by diverse cross-linking proteins. During cell migration, actin filament bundles form either radially at the leading edge or as axial stress fibers. Early studies demonstrated that loss-of-function mutations in ciliopathy genes increased stress fiber formation and impaired ciliogenesis whereas pharmacological inhibition of actin polymerization promoted ciliogenesis. These studies suggest that polymerization of the actin cytoskeleton, F-actin branching and the formation of stress fibers all inhibit primary cilium formation, whereas depolymerization or depletion of actin enhance ciliogenesis. Here, we review the mechanistic basis for these effects on ciliogenesis, which comprise several cellular processes acting in concert at different timescales. Actin polymerization is both a physical barrier to both cilia-targeted vesicle transport and to the membrane remodeling required for ciliogenesis. In contrast, actin may cause cilia loss by localizing disassembly factors at the ciliary base, and F-actin branching may itself activate the YAP/TAZ pathway to promote cilia disassembly. The fundamental role of actin polymerization in the control of ciliogenesis may present potential new targets for disease-modifying therapeutic approaches in treating ciliopathies.

scholarly journals Delayed stress fiber formation mediates pulmonary myofibroblast differentiation in response to TGF-β

2011 ◽  
Vol 301 (5) ◽  
pp. L656-L666 ◽  
Author(s):  
Nathan Sandbo ◽  
Andrew Lau ◽  
Jacob Kach ◽  
Caitlyn Ngam ◽  
Douglas Yau ◽  
...  
Keyword(s):  
Rho Kinase ◽  
Stress Fiber ◽  
Fiber Formation ◽  
Stress Fibers ◽  
Nuclear Accumulation ◽  
Myofibroblast Differentiation ◽  
Latrunculin B ◽  
Stress Fiber Formation ◽  
Actin Expression ◽  
Actin Stress Fibers

Myofibroblast differentiation induced by transforming growth factor-β (TGF-β) and characterized by de novo expression of smooth muscle (SM)-specific proteins is a key process in wound healing and in the pathogenesis of fibrosis. We have previously shown that TGF-β-induced expression and activation of serum response factor (SRF) is required for this process. In this study, we examined the signaling mechanism for SRF activation by TGF-β as it relates to pulmonary myofibroblast differentiation. TGF-β stimulated a profound, but delayed (18–24 h), activation of Rho kinase and formation of actin stress fibers, which paralleled SM α-actin expression. The translational inhibitor cycloheximide blocked these processes without affecting Smad-dependent gene transcription. Inhibition of Rho kinase by Y-27632 or depolymerization of actin by latrunculin B resulted in inhibition TGF-β-induced SRF activation and SM α-actin expression, having no effect on Smad signaling. Conversely, stabilization of actin stress fibers by jasplakinolide was sufficient to drive these processes in the absence of TGF-β. TGF-β promoted a delayed nuclear accumulation of the SRF coactivator megakaryoblastic leukemia-1 (MKL1)/myocardin-related transcription factor-A, which was inhibited by latrunculin B. Furthermore, TGF-β also induced MKL1 expression, which was inhibited by latrunculin B, by SRF inhibitor CCG-1423, or by SRF knockdown. Together, these data suggest a triphasic model for myofibroblast differentiation in response to TGF-β that involves 1) initial Smad-dependent expression of intermediate signaling molecules driving Rho activation and stress fiber formation, 2) nuclear accumulation of MKL1 and activation of SRF as a result of actin polymerization, and 3) SRF-dependent expression of MKL1, driving further myofibroblast differentiation.

Vascular-endothelial-cadherin modulates endothelial monolayer permeability

1999 ◽  
Vol 112 (12) ◽  
pp. 1915-1923 ◽  
Author(s):  
P.L. Hordijk ◽  
E. Anthony ◽  
F.P. Mul ◽  
R. Rientsma ◽  
L.C. Oomen ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Actin Cytoskeleton ◽  
Adhesion Molecule ◽  
Cell Adhesion Molecule ◽  
Transendothelial Migration ◽  
Stress Fibers ◽  
Vascular Endothelial ◽  
Monolayer Permeability ◽  
Actin Stress Fibers ◽  
Cell Cell

Vascular endothelial (VE)-cadherin is the endothelium-specific member of the cadherin family of homotypic cell adhesion molecules. VE-cadherin, but not the cell adhesion molecule platelet/endothelial cell adhesion molecule (PECAM-1), markedly colocalizes with actin stress fibers at cell-cell junctions between human umbilical vein endothelial cells. Inhibition of VE-cadherin-mediated, but not PECAM-1-mediated, adhesion induced reorganization of the actin cytoskeleton, loss of junctional VE-cadherin staining and loss of cell-cell adhesion. In functional assays, inhibition of VE-cadherin caused increased monolayer permeability and enhanced neutrophil transendothelial migration. In a complementary set of experiments, modulation of the actin cytoskeleton was found to strongly affect VE-cadherin distribution. Brief stimulation of the beta2-adrenergic receptor with isoproterenol induced a loss of actin stress fibers resulting in a linear, rather than ‘jagged’, VE-cadherin distribution. The concomitant, isoproterenol-induced, reduction in monolayer permeability was alleviated by a VE-cadherin-blocking antibody. Finally, cytoskeletal reorganization resulting from the inactivation of p21Rho caused a diffuse localization of VE-cadherin, which was accompanied by reduced cell-cell adhesion. Together, these data show that monolayer permeability and neutrophil transendothelial migration are modulated by VE-cadherin-mediated cell-cell adhesion, which is in turn controlled by the dynamics of the actin cytoskeleton.

Rho-kinase regulates myosin II activation in MDCK cells during recovery after ATP depletion

2001 ◽  
Vol 281 (5) ◽  
pp. F810-F818 ◽  
Author(s):  
Timothy A. Sutton ◽  
Henry E. Mang ◽  
Simon J. Atkinson
Keyword(s):  
Epithelial Cells ◽  
Actin Cytoskeleton ◽  
Mdck Cells ◽  
Myosin Ii ◽  
Atp Depletion ◽  
Stress Fibers ◽  
Tubular Epithelial Cells ◽  
Renal Tubular Epithelial Cells ◽  
Renal Tubular ◽  
Actin Stress Fibers

Alterations in the actin cytoskeleton of renal tubular epithelial cells during periods of ischemic injury and recovery have important consequences for normal cell and kidney function. Myosin II has been demonstrated to be an important effector in organizing basal actin structures in some cell types. ATP depletion in vitro has been demonstrated to recapitulate alterations of the actin cytoskeleton in renal tubular epithelial cells observed during renal ischemia in vivo. We utilized this reversible cell culture model of ischemia to examine the correlation of the activation state and cellular distribution of myosin II with disruption of actin stress fibers in Madin-Darby canine kidney (MDCK) cells during ATP depletion and recovery from ATP depletion. We found that myosin II inactivation occurs rapidly and precedes dissociation of myosin II from actin stress fibers during ATP depletion. Myosin II activation temporally correlates with colocalization of myosin II to reorganizing stress fibers during recovery from ATP depletion. Furthermore, myosin activation and actin stress fiber formation were found to be Rho-associated Ser/Thr protein kinase dependent during recovery from ATP depletion.

Role of Rho and myosin phosphorylation in actin stress fiber assembly in mesangial cells

1997 ◽  
Vol 273 (2) ◽  
pp. F283-F288 ◽  
Author(s):  
J. I. Kreisberg ◽  
N. Ghosh-Choudhury ◽  
R. A. Radnik ◽  
M. A. Schwartz
Keyword(s):  
Cell Shape ◽  
Mesangial Cells ◽  
Stress Fiber ◽  
Fiber Formation ◽  
Stress Fibers ◽  
Actin Stress Fiber ◽  
Glomerular Mesangial Cells ◽  
Fiber Assembly ◽  
Camp Elevation ◽  
Actin Stress Fibers

Treatment of renal glomerular mesangial cells with adenosine 3',5'-cyclic monophosphate (cAMP)-elevating agents induces actin stress fiber disassembly, myosin light chain (MLC) dephosphorylation, loss of adhesion to the substratum and cell shape change [J. I. Kreisberg and M. A. Venkatachalam. Am. J. Physiol. 251 (Cell Physiol. 20): C505-C511, 1986]. Thrombin and vasopressin block the effects of cAMP. Because these agents are known to promote stress fiber formation via the small GTP-binding protein Rho, we investigated the effect of an activated variant of Rho on the response to cAMP elevation. Microinjecting V14-Rho completely blocked the effect of cAMP elevation on cell shape and the actin cytoskeleton, whereas inactivating Rho with botulinum C3 exoenzyme induced stress fiber disruption and cell retraction that was indistinguishable from that caused by elevations in intracellular levels of cAMP. Disruption of actin stress fibers by cAMP has previously been ascribed to MLC dephosphorylation; however, both C3 and cytochalasin D also caused dephosphorylation of MLC, whereas blocking MLC dephosphorylation failed to block the cAMP-induced loss of actin stress fibers. We conclude that Rho can modulate the effects of cAMP elevation and suggest that MLC dephosphorylation may be a consequence of actin stress fiber disassembly.

Rho GTPase signaling modulates cell shape and contractile phenotype in an isoactin-specific manner

2003 ◽  
Vol 285 (5) ◽  
pp. C1116-C1121 ◽  
Author(s):  
Alexey Y. Kolyada ◽  
Kathleen N. Riley ◽  
Ira M. Herman
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Actin Cytoskeleton ◽  
Cell Size ◽  
Rho Gtpase ◽  
Small Gtpases ◽  
Protein Isoforms ◽  
Stress Fibers ◽  
Contractile Phenotype ◽  
Specific Manner

Rho family small GTPases (Rho, Rac, and Cdc42) play an important role in cell motility, adhesion, and cell division by signaling reorganization of the actin cytoskeleton. Here, we report an isoactin-specific, Rho GTPase-dependent signaling cascade in cells simultaneously expressing smooth muscle and nonmuscle actin isoforms. We transfected primary cultures of microvascular pericytes, cells related to vascular smooth muscle cells, with various Rho-related and Rho-specific expression plasmids. Overexpression of dominant positive Rho resulted in the formation of nonmuscle actin-containing stress fibers. At the same time, α-vascular smooth muscle actin (αVSMactin) containing stress fibers were disassembled, resulting in a dramatic reduction in cell size. Rho activation also yielded a disassembly of smooth muscle myosin and nonmuscle myosin from stress fibers. Overexpression of wild-type Rho had similar but less dramatic effects. In contrast, dominant negative Rho and C3 exotransferase or dominant positive Rac and Cdc42 expression failed to alter the actin cytoskeleton in an isoform-specific manner. The loss of smooth muscle contractile protein isoforms in pericyte stress fibers, together with a concomitant decrease in cell size, suggests that Rho activation influences “contractile” phenotype in an isoactin-specific manner. This, in turn, should yield significant alteration in microvascular remodeling during developmental and pathologic angiogenesis.

scholarly journals Translocation of Src kinase to the cell periphery is mediated by the actin cytoskeleton under the control of the Rho family of small G proteins.

1996 ◽  
Vol 135 (6) ◽  
pp. 1551-1564 ◽  
Author(s):  
V J Fincham ◽  
M Unlu ◽  
V G Brunton ◽  
J D Pitts ◽  
J A Wyke ◽  
...  
Keyword(s):  
G Proteins ◽  
Focal Adhesions ◽  
Cytochalasin D ◽  
Mitogen Activated Protein Kinase ◽  
Stress Fibers ◽  
Cell Periphery ◽  
Double Labeling ◽  
Rho Family ◽  
Swiss 3T3 ◽  
Small G Proteins

We have isolated Swiss 3T3 subclones that are resistant to the mitogenic and morphological transforming effects of v-Src as a consequence of aberrant translocation of the oncoprotein under low serum conditions. In chicken embryo and NIH 3T3 fibroblasts under similar conditions, v-Src rapidly translocates from the perinuclear region to the focal adhesions upon activation of the tyrosine kinase, resulting in downstream activation of activator protein-1 and mitogen-activated protein kinase, which are required for the mitogenic and transforming activity of the oncoprotein. Since serum deprivation induces cytoskeletal disorganization in Swiss 3T3, we examined whether regulators of the cytoskeleton play a role in the translocation of v-Src, and also c-Src, in response to biological stimuli. Actin stress fibers and translocation of active v-Src to focal adhesions in quiescent Swiss 3T3 cells were restored by microinjection of activated Rho A and by serum. Double labeling with anti-Src and phalloidin demonstrated that v-Src localized along the reformed actin filaments in a pattern that would be consistent with trafficking in complexes along the stress fibers to focal adhesions. Furthermore, treatment with the actin-disrupting drug cytochalasin D, but not the microtubule-disrupting drug nocodazole, prevented v-Src translocation. In addition to v-Src, we observed that PDGF-induced, Rac-mediated membrane ruffling was accompanied by translocation of c-Src from the cytoplasm to the plasma membrane, an effect that was also blocked by cytochalasin D. Thus, we conclude that translocation of Src from its site of synthesis to its site of action at the cell membrane requires an intact cytoskeletal network and that the small G proteins of the Rho family may specify the peripheral localization in focal adhesions or along the membrane, mediated by their effects on the cytoskeleton.

scholarly journals Rho GTPases: molecular switches that control the organization and dynamics of the actin cytoskeleton

2000 ◽  
Vol 355 (1399) ◽  
pp. 965-970 ◽  
Author(s):  
Alan Hall ◽  
Catherine D. Nobes
Keyword(s):  
Actin Cytoskeleton ◽  
Rho Gtpases ◽  
Mammalian Cells ◽  
Fundamental Property ◽  
Small Gtpases ◽  
Membrane Receptors ◽  
Embryonic Cells ◽  
Filamentous Actin ◽  
Rho Family ◽  
Plasma Membrane Receptors

The actin cytoskeleton plays a fundamental role in all eukaryotic cells—it is a major determinant of cell morphology and polarity and the assembly and disassembly of filamentous actin structures provides a driving force for dynamic processes such as cell motility, phagocytosis, growth cone guidance and cytokinesis. The ability to reorganize actin filaments is a fundamental property of embryonic cells during development; the shape changes accompanying gastrulation and dorsal closure, for example, are dependent on the plasticity of the actin cytoskeleton, while the ability of cells or cell extensions, such as axons, to migrate within the developing embryo requires rapid and spatially organized changes to the actin cytoskeleton in response to the external environment. W ork in mammalian cells over the last decade has demonstrated the central role played by the highly conserved Rho family of small GTPases in signal transduction pathways that link plasma membrane receptors to the organization of the actin cytoskeleton.

scholarly journals The LD4 motif of paxillin regulates cell spreading and motility through an interaction with paxillin kinase linker (PKL)

2001 ◽  
Vol 154 (1) ◽  
pp. 161-176 ◽  
Author(s):  
Kip A. West ◽  
Huaye Zhang ◽  
Michael C. Brown ◽  
Sotiris N. Nikolopoulos ◽  
M.C. Riedy ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Focal Adhesion ◽  
Deletion Mutant ◽  
Morphological Changes ◽  
Cell Spreading ◽  
Small Gtpases ◽  
Random Motility ◽  
Phenotypic Changes ◽  
Rho Family ◽  
Mutant Cells

The small GTPases of the Rho family are intimately involved in integrin-mediated changes in the actin cytoskeleton that accompany cell spreading and motility. The exact means by which the Rho family members elicit these changes is unclear. Here, we demonstrate that the interaction of paxillin via its LD4 motif with the putative ARF-GAP paxillin kinase linker (PKL) (Turner et al., 1999), is critically involved in the regulation of Rac-dependent changes in the actin cytoskeleton that accompany cell spreading and motility. Overexpression of a paxillin LD4 deletion mutant (paxillinΔLD4) in CHO.K1 fibroblasts caused the generation of multiple broad lamellipodia. These morphological changes were accompanied by an increase in cell protrusiveness and random motility, which correlated with prolonged activation of Rac. In contrast, directional motility was inhibited. These alterations in morphology and motility were dependent on a paxillin–PKL interaction. In cells overexpressing paxillinΔLD4 mutants, PKL localization to focal contacts was disrupted, whereas that of focal adhesion kinase (FAK) and vinculin was not. In addition, FAK activity during spreading was not compromised by deletion of the paxillin LD4 motif. Furthermore, overexpression of PKL mutants lacking the paxillin-binding site (PKLΔPBS2) induced phenotypic changes reminiscent of paxillinΔLD4 mutant cells. These data suggest that the paxillin association with PKL is essential for normal integrin-mediated cell spreading, and locomotion and that this interaction is necessary for the regulation of Rac activity during these events.

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