Tensile stress stimulates microtubule outgrowth in living cells (original) (raw)
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The kinetics of force-induced cell reorganization depend on microtubules and actin
Cytoskeleton, 2010
The cytoskeleton is an important factor in the functional and structural adaption of cells to mechanical forces. In this study we investigated the impact of microtubules and the acto-myosin machinery on the kinetics of force-induced reorientation of NIH3T3 fibroblasts. These cells were subjected to uniaxial stretching forces that are known to induce cellular reorientation perpendicular to the stretch direction. We found that disruption of filamentous actin using cytochalasin D and latrunculin B as well as an induction of a massive unpolarized actin polymerization by jasplakinolide, inhibited the stretch-induced reorientation. Similarly, blocking of myosin II activity abolished the stretch-induced reorientation of cells but, interestingly, increased their motility under stretching conditions in comparison to myosininhibited nonstretched cells. Investigating the contribution of microtubules to the cellular reorientation, we found that, although not playing a significant role in reorientation itself, microtubule stability had a significant impact on the kinetics of this event. Overall, we conclude that acto-myosin, together with microtubules, regulate the kinetics of force-induced cell reorientation. V C 2010 Wiley-Liss, Inc.
Microtubules tune mechanosensitive cell responses
Nature Materials, 2021
Mechanotransduction is a process by which cells sense the mechanical properties of their surrounding environment, and adapt accordingly to perform cellular functions such as adhesion, migration and differentiation. Integrin-mediated focal adhesions are major sites of mechanotransduction, and their connection with the actomyosin network is crucial for mechanosensing as well as the generation and transmission of forces onto the substrate. Despite having emerged as major regulators of cell adhesion and migration, the contribution of microtubules to mechanotransduction still remains elusive. Here, we show that Talin-and actomyosin-dependent mechanosensing of substrate rigidity controls microtubule acetylation (a tubulin post-translational modification) by promoting the recruitment of alpha-tubulin acetyl transferase (αTAT1) to focal adhesions. Microtubule acetylation tunes mechanosensitivity of focal adhesions and YAP translocation, and in turn, promotes GEF-H1-mediated RhoA activation, actomyosin contractility, and traction forces. Our results reveal a fundamental crosstalk between microtubules and actin in mechanotransduction that contributes to mechanosensitive cell adhesion and migration. Main Cells sense the physical properties of their environment, translate them into biochemical signals and adapt their behaviour accordingly. This process known as mechanotransduction is crucial during development and in the adult, during physiological and pathological conditions such as cell migration, wound healing and cancer 1,2. Integrin-mediated focal adhesions (FAs) sense the matrix rigidity, control the generation of actomyosin-dependent forces and the transmission of these traction forces onto the substrate as well as contribute to mechanosensitive cell responses such as migration 3,4. In addition to the actin cytoskeleton, microtubules are also key regulators of 2D and 3D cell migration 5-8. Several studies have demonstrated the role of the actomyosin cytoskeleton and FAs in mechanotransduction;
Conserved microtubule–actin interactions in cell movement and morphogenesis
Nature Cell Biology, 2003
Interactions between microtubules and actin are a basic phenomenon that underlies many fundamental processes in which dynamic cellular asymmetries need to be established and maintained. These are processes as diverse as cell motility, neuronal pathfinding, cellular wound healing, cell division and cortical flow. Microtubules and actin exhibit two mechanistic classes of interactions-regulatory and structural. These interactions comprise at least three conserved 'mechanochemical activity modules' that perform similar roles in these diverse cell functions. Over the past 35 years, great progress has been made towards understanding the roles of the microtubule and actin cytoskeletal filament systems in mechanical cellular processes such as dynamic shape change, shape maintenance and intracellular organelle movement. These functions are attributed to the ability of polarized cytoskeletal polymers to assemble and disassemble rapidly, and to interact with binding proteins and molecular motors that mediate their regulated movement and/or assembly into higher order structures, such as radial arrays or bundles. This allows, for example, microtubules to form a bipolar spindle that can move chromosomes into two daughter cells with high fidelity, and actin to mediate muscle contraction or promote protrusion at the leading edge of a migrating cell. Although it is certainly true that microtubules and actin have such distinct roles, it has been evident for some time that interactions between these seemingly distinct filament systems exist. Vasiliev 1 hinted at this years ago when he showed that an intact microtubule cytoskeleton was required to maintain the polarized distribution of actin-dependent protrusions at the leading edge of a migrating fibroblast. This suggested that the microtubule cytoskeleton somehow directs proper placement of actin polymerization-and contractionbased activities. Since then, it has become clear that similar microtubule/actin interactions are a basic phenomenon that underlie many fundamental cellular processes, including cell motility, growth cone guidance, cell division, wound healing and cortical flow. In general, such cytoskeletal crosstalk occurs in processes that require dynamic cellular asymmetries to be established or maintained to allow rapid intracellular reorganization or changes in shape or direction in response to stimuli. Furthermore, the widespread occurrence of these interactions underscores their importance for life, as they occur in diverse cell types including epithelia, neurons, fibroblasts, oocytes and early embryos, and across species from yeast to humans. Thus, defining the mechanisms by which actin and microtubules interact is key to understanding a basic organizing principle for dynamic morphogenesis, which, in turn, is a step towards understanding health-related processes such as cancer, wound healing and neuronal regeneration. Recent investigations that shed light on these elusive interactions shall be the focus of our review. 'Structural' versus 'regulatory' interactions What are the cellular and molecular bases of microtubule-actin cooperation? One popular viewpoint is the 'tensegrity model 2,3 , in which actomyosin generates tension against stiff microtubule 'struts' and adhesions to the substrate to stabilize or change cell shape. Although these principles may be applicable, we propose an alternative, not necessarily exclusive, hypothesis, in which the interactions between actin and microtubules may be classified as either 'regulatory' or 'structural'. Regulatory interactions are those in which the two systems indirectly control each other through their effects on signalling cascades (Fig. 1a). The best understood example of regulatory interactions is provided by the Rho family of small GTPases, which regulate both microtubules and actin 4. For example, RhoA mediates formation of contractile actin structures, such as stress fibres 5 , and at the same time promotes stabilization of a sub-population of microtubules 6. Two key factors are known to function downstream of RhoA: Rho kinase, which promotes contractility by increasing phosphorylation of the regulatory light chain of myosin-2 (ref. 7), and the formin, mDia, which regulates actin polymerization into bundles 8,9 and also mediates microtubule stabilization 10. Similarly, Rac1 activity regulates the
Biophysical Journal, 2008
We investigate both theoretically and experimentally how stress is propagated through the actin cytoskeleton of adherent cells and consequentially distributed at sites of focal adhesions (FAs). The actin cytoskeleton is modeled as a twodimensional cable network with different lattice geometries. Both prestrain, resulting from actomyosin contractility, and central application of external force, lead to finite forces at the FAs that are largely independent of the lattice geometry, but strongly depend on the exact spatial distribution of the FAs. The simulation results compare favorably with experiments with adherent fibroblasts onto which lateral force is exerted using a microfabricated pillar. For elliptical cells, central application of external force along the long axis leads to two large stress regions located obliquely opposite to the pulling direction. For elliptical cells pulled along the short axis as well as for circular cells, there is only one region of large stress opposite to the direction of pull. If in the computer simulations FAs are allowed to rupture under force for elliptically elongated and circular cell shapes, then morphologies arise which are typical for migrating fibroblasts and keratocytes, respectively. The same effect can be obtained also by internally generated force, suggesting a mechanism by which cells can control their migration morphologies.
Buckling of actin stress fibers: A new wrinkle in the cytoskeletal tapestry
Cell Motility and The Cytoskeleton, 2002
Intracellular tension is considered an important determinant of cytoskeletal architecture and cell function. However, many details about cytoskeletal tension remain poorly understood because these forces cannot be directly measured in living cells. Therefore, we have developed a method to characterize the magnitude and distribution of pre-extension of actin stress fibers (SFs) due to resting tension in the cytoskeleton. Using a custom apparatus, human aortic endothelial cells (HAECs) were cultured on a pre-stretched silicone substrate coated with a fibronectin-like polymer. Release of the substrate caused SFs aligned in the shortening direction in adhered cells to buckle when compressed rapidly (5% shortening per second or greater) beyond their unloaded slack length. Subsequently, the actin cytoskeleton completely disassembled in 5 sec and reassembled within 60 sec. Quantification of buckling in digital fluorescent micrographs of cells fixed and stained with rhodamine phalloidin indicated a nonuniform distribution of 0–26% pre-extension of SFs in non-locomoting HAECs. Local variability suggests heterogeneity of cytoskeletal tension and/or stiffness within individual cells. These findings provide new information about the magnitude and distribution of cytoskeletal tension and the dynamics of actin stress fibers, and the approach offers a novel method to elucidate the role of specific cytoskeletal elements and crosslinking proteins in the force generating apparatus of non-muscle cells. Cell Motil. Cytoskeleton 52:266–274, 2002. © 2002 Wiley-Liss, Inc.
PLoS ONE, 2013
The actin cytoskeleton plays a crucial role for the spreading of cells, but is also a key element for the structural integrity and internal tension in cells. In fact, adhesive cells and their actin stress fiber-adhesion system show a remarkable reorganization and adaptation when subjected to external mechanical forces. Less is known about how mechanical forces alter the spreading of cells and the development of the actin-cell-matrix adhesion apparatus. We investigated these processes in fibroblasts, exposed to uniaxial cyclic tensile strain (CTS) and demonstrate that initial cell spreading is stretch-independent while it is directed by the mechanical signals in a later phase. The total temporal spreading characteristic was not changed and cell protrusions are initially formed uniformly around the cells. Analyzing the actin network, we observed that during the first phase the cells developed a circumferential arc-like actin network, not affected by the CTS. In the following orientation phase the cells elongated perpendicular to the stretch direction. This occurred simultaneously with the de novo formation of perpendicular mainly ventral actin stress fibers and concurrent realignment of cell-matrix adhesions during their maturation. The stretch-induced perpendicular cell elongation is microtubule-independent but myosin II-dependent. In summary, a CTS-induced cell orientation of spreading cells correlates temporary with the development of the actomyosin system as well as contact to the underlying substrate by cell-matrix adhesions.