Force-induced cell polarisation is linked to RhoA-driven microtubule-independent focal-adhesion sliding

111

Cyclic stretch is an artificial model of mechanical force loading, which induces the reorientation of vascular endothelial cells and their stress fibers in a direction perpendicular to the stretch axis. Rho family GTPases are crucial for cyclic-stretch-induced endothelial cell reorientation; however, the mechanism underlying stretch-induced activation of Rho family GTPases is unknown. A screen of short hairpin RNAs targeting 63 Rho guanine nucleotide exchange factors (Rho-GEFs) revealed that at least 11 Rho-GEFs -Abr, alsin, ARHGEF10, Bcr, GEF-H1 (also known as ARHGEF2), LARG (also known as ARHGEF12), p190RhoGEF (also known as ARHGEF28), PLEKHG1, P-REX2, Solo (also known as ARHGEF40) and a-PIX (also known as ARHGEF6) -which specifically or broadly target RhoA, Rac1 and/or Cdc42, are involved in cyclic-stretch-induced perpendicular reorientation of endothelial cells. Overexpression of Solo induced RhoA activation and F-actin accumulation at cell-cell and cell-substrate adhesion sites. Knockdown of Solo suppressed cyclic-stretch-or tensile-force-induced RhoA activation. Moreover, knockdown of Solo significantly reduced cyclic-stretch-induced perpendicular reorientation of endothelial cells when cells were cultured at high density, but not when they were cultured at low density or pretreated with EGTA or VE-cadherin-targeting small interfering RNAs. These results suggest that Solo is involved in cellcell-adhesion-mediated mechanical signal transduction during cyclicstretch-induced endothelial cell reorientation.

Section: Solo Is Involved In Cyclic-stretch-induced Rhoa Activationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Rho-guanine nucleotide exchange factors involved in cyclic stretch-induced reorientation of vascular endothelial cells

Abiko¹,

Fujiwara²,

Ohashi³

et al. 2015

111

“…Quantitative analysis of the orientation of myoblasts relative to the 3D fibrin gel axis was performed by measuring the orientation parameter cos 2h (Goldyn et al, 2009), where h is the angle formed between the long axis of the cell and that of the gel (Fig. 2B).…”

Section: Image Analysismentioning

confidence: 99%

“…2B). A mean value of cos 2h51 indicates a perfect parallel orientation of cells, whereas the value cos 2h50 corresponds to a random orientation of cells relative to the gel axis (Goldyn et al, 2009). Localization of nuclear envelope proteins were determined from a stack of 9-10 consecutive images (total thickness51 mm) centered on the middle of the nucleus.…”

Section: Image Analysismentioning

confidence: 99%

Cellular micro-environments reveal defective mechanosensing responses and elevated YAP signaling in LMNA-mutated muscle precursors

Bertrand

Ziaei

Ehret

et al. 2014

101

111

The mechanisms underlying the cell response to mechanical forces are crucial for muscle development and functionality. We aim to determine whether mutations of the LMNA gene (which encodes lamin A/C) causing congenital muscular dystrophy impair the ability of muscle precursors to sense tissue stiffness and to respond to mechanical challenge. We found that LMNA-mutated myoblasts embedded in soft matrix did not align along the gel axis, whereas control myoblasts did. LMNA-mutated myoblasts were unable to tune their cytoskeletal tension to the tissue stiffness as attested by inappropriate cell-matrix adhesion sites and cytoskeletal tension in soft versus rigid substrates or after mechanical challenge. Importantly, in soft two-dimensional (2D) and/or static threedimensional (3D) conditions, LMNA-mutated myoblasts showed enhanced activation of the yes-associated protein (YAP) signaling pathway that was paradoxically reduced after cyclic stretch. siRNAmediated downregulation of YAP reduced adhesion and actin stress fibers in LMNA myoblasts. This is the first demonstration that human myoblasts with LMNA mutations have mechanosensing defects through a YAP-dependent pathway. In addition, our data emphasize the crucial role of biophysical attributes of cellular microenvironment to the response of mechanosensing pathways in LMNA-mutated myoblasts.

“…However, this still does not explain the mechanism of stress fiber remodeling during reorientation. It remains to be elucidated whether stress fiber turnover or stress fiber rotation and associated FA sliding (Chen et al, 2012;Goldyn et al, 2009) is the cause of fiber reorientation. Based on our observations, we propose that, in the actin cap, the rapid remodeling of stress fibers is caused by stress fiber rotation and FA sliding.…”

Section: Discussionmentioning

confidence: 99%

Cellular strain avoidance is mediated by a functional actin cap – observations in an Lmna-deficient cell model

Tamiello

Halder

Kamps

et al. 2017

In adherent cells, the relevance of a physical mechanotransduction pathway provided by the perinuclear actin cap stress fibers has recently emerged. Here, we investigate the impact of a functional actin cap on the cellular adaptive response to topographical cues and uniaxial cyclic strain. Lmna-deficient fibroblasts are used as a model system because they do not develop an intact actin cap, but predominantly form a basal layer of actin stress fibers underneath the nucleus. We observe that topographical cues induce alignment in both normal and Lmna-deficient fibroblasts, suggesting that the topographical signal transmission occurs independently of the integrity of the actin cap. By contrast, in response to cyclic uniaxial strain, Lmna-deficient cells show a compromised strain avoidance response, which is completely abolished when topographical cues and uniaxial strain are applied along the same direction. These findings point to the importance of an intact and functional actin cap in mediating cellular strain avoidance.