Thermodynamic consideration of tensional homeostasis in stress fibers

Cyclic stretching of endothelial cells (ECs), such as occurs in arteries during the cardiac cycle, induces ECs and their actin stress fibers to orient perpendicular to the direction of maximum stretch. This perpendicular alignment response is strengthened by increasing the magnitudes of stretch and cell contractility (1). The actin cytoskeleton is a dynamic structure that regulates cell shape changes and mechanical properties. It has been shown that actin stress fibers are ‘prestretched’ under normal, non-perturbed, conditions (2), consistent with the ideas of ‘prestress’ that have motivated tensegrity cell models (3). It has also been shown that ‘tractional forces’ generated by cells at focal adhesions tend to increase proportionately with increasing focal adhesion area, thus suggesting that cells tend to maintain constant the stress borne by a focal adhesion (4). By implication, this suggests that cells try to maintain constant the stress in actin stress fibers. Thus, it seems that cells reorganize or turnover cytoskeletal proteins and adhesion complexes so as to maintain constant a preferred mechanical state. Mizutani et al. (5) referred to this as cellular tensional homeostasis, although they did not suggest a model or theory to account for this dynamic process.

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Faculty Opinions recommendation of Stress fibers are generated by two distinct actin assembly mechanisms in motile cells.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1032232.373970 ◽

2006 ◽

Author(s):

Matthew Welch

Keyword(s):

Stress Fibers ◽

Actin Assembly ◽

Motile Cells

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Faculty Opinions recommendation of Nox1 redox signaling mediates oncogenic Ras-induced disruption of stress fibers and focal adhesions by down-regulating Rho.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1088398.541446 ◽

2007 ◽

Author(s):

Paola Chiarugi

Keyword(s):

Focal Adhesions ◽

Redox Signaling ◽

Stress Fibers ◽

Oncogenic Ras

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Calcium-Sensing Receptor Stimulation in Cultured Glomerular Podocytes Induces TRPC6-Dependent Calcium Entry and RhoA Activation

Cellular Physiology and Biochemistry ◽

10.1159/000484064 ◽

2017 ◽

Vol 43 (5) ◽

pp. 1777-1789 ◽

Cited By ~ 7

Author(s):

Lei Zhang ◽

Tianrong Ji ◽

Qin Wang ◽

Kexin Meng ◽

Rui Zhang ◽

...

Keyword(s):

Protective Action ◽

Focal Adhesions ◽

Stress Fiber ◽

Fiber Formation ◽

Stress Fibers ◽

Dependent Manner ◽

Calcium Sensing Receptor ◽

Rhoa Activity ◽

Rhoa Activation ◽

Calcium Sensing

Background/Aims: Recent studies provided compelling evidence that stimulation of the calcium sensing receptor (CaSR) exerts direct renoprotective action at the glomerular podocyte level. This protective action may be attributed to the RhoA-dependent stabilization of the actin cytoskeleton. However, the underlying mechanisms remain unclear. Methods: In the present study, an immortalized human podocyte cell line was used. Fluo-3 fluorescence was utilized to determine intracellular Ca2+ concentration ([Ca2+]i), and western blotting was used to measure canonical transient receptor potential 6 (TRPC6) protein expression and RhoA activity. Stress fibers were detected by FITC-phalloidin. Results: Activating CaSR with a high extracellular Ca2+ concentration ([Ca2+]o) or R-568 (a type II CaSR agonist) induces an increase in the [Ca2+]i in a dose-dependent manner. This increase in [Ca2+]i is phospholipase C (PLC)-dependent and is smaller in the absence of extracellular Ca2+ than in the presence of 0.5 mM [Ca2+]o. The CaSR activation-induced [Ca2+]i increase is attenuated by the pharmacological blockage of TRPC6 channels or siRNA targeting TRPC6. These data suggest that TRPC6 is involved in CaSR activation-induced Ca2+ influx. Consistent with a previous study, CaSR stimulation results in an increase in RhoA activity. However, the knockdown of TRPC6 significantly abolished the RhoA activity increase induced by CaSR stimulation, suggesting that TRPC6-dependent Ca2+ entry is required for RhoA activation. The activated RhoA is involved in the formation of stress fibers and focal adhesions in response to CaSR stimulation because siRNA targeting RhoA attenuated the increase in the stress fiber mediated by CaSR stimulation. Moreover, this effect of CaSR activation on the formation of stress fibers is also abolished by the knockdown of TRPC6. Conclusion: TRPC6 is involved in the regulation of stress fiber formation and focal adhesions via the RhoA pathway in response to CaSR activation. This may explain the direct protective action of CaSR agonists.

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The atypical structure and function of newborn arterial endothelium is mediated by Rho/Rho kinase signaling

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00327.2014 ◽

2014 ◽

Vol 307 (4) ◽

pp. H628-H632 ◽

Cited By ~ 10

Author(s):

Sheila Flavahan ◽

Nicholas A. Flavahan

Keyword(s):

Laser Scanning ◽

Rho Kinase ◽

Laser Scanning Microscopy ◽

Scanning Microscopy ◽

Stress Fibers ◽

Light Chains ◽

Myosin Light Chains ◽

Kinase Signaling ◽

No Donor ◽

Kinase Inhibition

Endothelium of fetal or newborn arteries is atypical, displaying actin stress fibers and reduced nitric oxide (NO)-mediated dilatation. This study tested the hypothesis that Rho/Rho kinase signaling, which promotes endothelial stress fibers and inhibits endothelial dilatation, contributed to this phenotype. Carotid arteries were isolated from newborn [ postnatal day 1 (P1)], P7, and P21 mice. Endothelial dilatation to acetylcholine (pressure myograph) was minimal at P1, increased at P7, and further increased at P21. Inhibition of Rho (C3 transferase) or Rho kinase (Y27632, fasudil) significantly increased dilatation to acetylcholine in P1 arteries but had no effect in P7 or P21 arteries. After inhibition of NO synthase ( NG-nitro-l-arginine methyl ester), Rho kinase inhibition no longer increased acetylcholine responses in P1 arteries. Rho kinase inhibition did not affect dilatation to the NO donor DEA-NONOate. The endothelial actin cytoskeleton was labeled with phalloidin and visualized by laser-scanning microscopy. In P1 arteries, the endothelium had prominent transcytoplasmic stress fibers, whereas in P7 and P21 arteries, the actin fibers had a significantly reduced intensity and were restricted to cell borders. Phosphorylation of myosin light chains, a Rho kinase substrate, was highest in P1 endothelium and significantly reduced in P7 and P21 endothelium (laser-scanning microscopy). In P1 arteries, inhibition of Rho (C3 transferase) or Rho kinase (Y27632) significantly reduced the intensity of actin fibers, which were restricted to cell borders. Similarly, in P1 arteries, Rho inhibition significantly reduced endothelial levels of phosphorylated myosin light chains. These results indicate that the atypical function and morphology of newborn endothelium is mediated by Rho/Rho kinase signaling.

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The inner workings of stress fibers − from contractile machinery to focal adhesions and back

Journal of Cell Science ◽

10.1242/jcs.180927 ◽

2016 ◽

Vol 129 (7) ◽

pp. 1293-1304 ◽

Cited By ~ 81

Author(s):

Ariel Livne ◽

Benjamin Geiger

Keyword(s):

Focal Adhesions ◽

Stress Fibers

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ROCK and mDia1 antagonize in Rho-dependent Rac activation in Swiss 3T3 fibroblasts

The Journal of Cell Biology ◽

10.1083/jcb.200112107 ◽

2002 ◽

Vol 157 (5) ◽

pp. 819-830 ◽

Cited By ~ 146

Author(s):

Takahiro Tsuji ◽

Toshimasa Ishizaki ◽

Muneo Okamoto ◽

Chiharu Higashida ◽

Kazuhiro Kimura ◽

...

Keyword(s):

Focal Adhesions ◽

Small Gtpase ◽

Dominant Negative ◽

Stress Fibers ◽

Induced Membrane ◽

3T3 Fibroblasts ◽

C3 Exoenzyme ◽

Swiss 3T3 ◽

Swiss 3T3 Fibroblasts ◽

Membrane Ruffle

The small GTPase Rho acts on two effectors, ROCK and mDia1, and induces stress fibers and focal adhesions. However, how ROCK and mDia1 individually regulate signals and dynamics of these structures remains unknown. We stimulated serum-starved Swiss 3T3 fibroblasts with LPA and compared the effects of C3 exoenzyme, a Rho inhibitor, with those of Y-27632, a ROCK inhibitor. Y-27632 treatment suppressed LPA-induced formation of stress fibers and focal adhesions as did C3 exoenzyme but induced membrane ruffles and focal complexes, which were absent in the C3 exoenzyme-treated cells. This phenotype was suppressed by expression of N17Rac. Consistently, the amount of GTP-Rac increased significantly by Y-27632 in LPA-stimulated cells. Biochemically, Y-27632 suppressed tyrosine phosphorylation of paxillin and focal adhesion kinase and not that of Cas. Inhibition of Cas phosphorylation with PP1 or expression of a dominant negative Cas mutant inhibited Y-27632–induced membrane ruffle formation. Moreover, Crk-II mutants lacking in binding to either phosphorylated Cas or DOCK180 suppressed the Y-27632–induced membrane ruffle formation. Finally, expression of a dominant negative mDia1 mutant also inhibited the membrane ruffle formation by Y-27632. Thus, these results have revealed the Rho-dependent Rac activation signaling that is mediated by mDia1 through Cas phosphorylation and antagonized by the action of ROCK.

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Specification of Actin Filament Function and Molecular Composition by Tropomyosin Isoforms

Molecular Biology of the Cell ◽

10.1091/mbc.e02-04-0244 ◽

2003 ◽

Vol 14 (3) ◽

pp. 1002-1016 ◽

Cited By ~ 180

Author(s):

Nicole S. Bryce ◽

Galina Schevzov ◽

Vicki Ferguson ◽

Justin M. Percival ◽

Jim J.-C. Lin ◽

...

Keyword(s):

Cell Size ◽

Functional Properties ◽

Actin Filament ◽

Actin Filaments ◽

Myosin Ii ◽

Molecular Composition ◽

Cellular Migration ◽

Stress Fibers ◽

Human Homologue ◽

Tropomyosin Isoforms

The specific functions of greater than 40 vertebrate nonmuscle tropomyosins (Tms) are poorly understood. In this article we have tested the ability of two Tm isoforms, TmBr3 and the human homologue of Tm5 (hTM5NM1), to regulate actin filament function. We found that these Tms can differentially alter actin filament organization, cell size, and shape. hTm5NM1was able to recruit myosin II into stress fibers, which resulted in decreased lamellipodia and cellular migration. In contrast, TmBr3 transfection induced lamellipodial formation, increased cellular migration, and reduced stress fibers. Based on coimmunoprecipitation and colocalization studies, TmBr3 appeared to be associated with actin-depolymerizing factor/cofilin (ADF)-bound actin filaments. Additionally, the Tms can specifically regulate the incorporation of other Tms into actin filaments, suggesting that selective dimerization may also be involved in the control of actin filament organization. We conclude that Tm isoforms can be used to specify the functional properties and molecular composition of actin filaments and that spatial segregation of isoforms may lead to localized specialization of actin filament function.

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