The coordination between actin filaments and adhesion in mesenchymal migration

Mesenchymal cell motility is characterized by a polarized distribution of actin filaments, with a network of short branched actin filaments at the leading edge, and polymers of actin filaments arranged into distinct classes of actin stress fibres behind the leading edge. Importantly, the distinct actin filaments are characteristically associated with discrete adhesion structures and both the adhesions and the actin filaments are co-ordinately regulated during cell migration. While it has long been known that these macromolecular structures are intimately linked in cells, precisely how they are co-ordinately regulated is presently unknown. Live imaging data now suggests that the focal adhesions may act as sites of actin polymerization resulting in the generation of tension-bearing actin bundles of actin filaments (stress fibres). Moreover, a picture is emerging to suggest that the tropomyosin family of proteins that can determine actin filament dynamics may also play a key role in determining the transition between adhesion states. Molecules such as the tropomyosins are therefore tantalizing candidates to orchestrate the coordination of actin and adhesion dynamics during mesenchymal cell migration.     

Specification of actin filament function and molecular composition by 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 (hTM5(NM1)), to regulate actin filament function. We found that these Tms can differentially alter actin filament organization, cell size, and shape. hTm5(NM1) was 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.     

Discrete mechanical model of lamellipodial actin network implements molecular clutch mechanism and generates arcs and microspikes

Mechanical forces, actin filament turnover, and adhesion to the extracellular environment regulate lamellipodial protrusions. Computational and mathematical models at the continuum level have been used to investigate the molecular clutch mechanism, calculating the stress profile through the lamellipodium and around focal adhesions. However, the forces and deformations of individual actin filaments have not been considered while interactions between actin networks and actin bundles is not easily accounted with such methods. We develop a filament-level model of a lamellipodial actin network undergoing retrograde flow using 3D Brownian dynamics. Retrograde flow is promoted in simulations by pushing forces from the leading edge (due to actin polymerization), pulling forces (due to molecular motors), and opposed by viscous drag in cytoplasm and focal adhesions. Simulated networks have densities similar to measurements in prior electron micrographs. Connectivity between individual actin segments is maintained by permanent and dynamic crosslinkers. Remodeling of the network occurs via the addition of single actin filaments near the leading edge and via filament bond severing. We investigated how several parameters affect the stress distribution, network deformation and retrograde flow speed. The model captures the decrease in retrograde flow upon increase of focal adhesion strength. The stress profile changes from compression to extension across the leading edge, with regions of filament bending around focal adhesions. The model reproduces the observed reduction in retrograde flow speed upon exposure to cytochalasin D, which halts actin polymerization. Changes in crosslinker concentration and dynamics, as well as in the orientation pattern of newly added filaments demonstrate the model’s ability to generate bundles of filaments perpendicular (actin arcs) or parallel (microspikes) to the protruding direction.     

Tropomyosin Isoform Expression Regulates the Transition of Adhesions To Determine Cell Speed and Direction

The balance of transition between distinct adhesion types contributes to the regulation of mesenchymal cell migration, and the characteristic association of adhesions with actin filaments led us to question the role of actin filament-associating proteins in the transition between adhesive states. Tropomyosin isoform association with actin filaments imparts distinct filament structures, and we have thus investigated the role for tropomyosins in determining the formation of distinct adhesion structures. Using combinations of overexpression, knockdown, and knockout approaches, we establish that Tm5NM1 preferentially stabilizes focal adhesions and drives the transition to fibrillar adhesions via stabilization of actin filaments. Moreover, our data suggest that the expression of Tm5NM1 is a critical determinant of paxillin phosphorylation, a signaling event that is necessary for focal adhesion disassembly. Thus, we propose that Tm5NM1 can regulate the feedback loop between focal adhesion disassembly and focal complex formation at the leading edge that is required for productive and directed cell movement.Among the different modes of migration that cells adopt, mesenchymal cell migration is dependent on integrin-based adhesion to the extracellular matrix (14), and the cellular mechanisms regulating integrin adhesion formation and turnover (adhesion dynamics) are integral to this process. The fate of integrin adhesions is intimately linked with filaments of polymerized actin (4). At the molecular level, actin filaments are highly dynamic, and this aspect of actin polymer biology provides an important control mechanism by which cells can organize filaments into structures with distinct properties. Tropomyosins are a multi-isoform family of actin-associating proteins that confer isoform-specific regulation of diverse actin filaments (3, 16, 34, 35). The interdependence of integrin adhesions and actin filaments suggests that expression of actin-associated proteins such as the tropomyosins may represent a mechanism for the regulation of adhesion dynamics that determine cell migration.In migrating cells small integrin-based focal complexes form at the periphery of lamellipodial extensions (32). These complexes are characterized by their subcellular distribution, dot-like shape, dependence on Rac activity, phosphorylated paxillin, and association with the network of short, branched actin filaments at the leading edge. The focal complexes are short lived (43) but provide strong traction forces at the leading edge (2) and most likely regulate directional migration (19). Subsets of focal complexes mature into focal adhesions, structures characterized by: Rho GTPase and Rho kinase dependence, dash-like shape, high levels of paxillin and phosphorylated paxillin, and low levels of the actin-binding molecule tensin (43, 44). The focal adhesions play an important role in anchoring bundles of polymerized actin stress fibers, providing the contractile force necessary for the translocation of the cell body during migration. There are at least three distinct classes of stress fibers observed in migrating cells (20, 27). Dorsal stress fibers are inserted into focal adhesions at the ventral surface of the cell. The distal end of the dorsal fibers can associate with a second type of actin fiber, the transverse arcs that run parallel to the leading edge and are not directly connected to focal adhesions. Ventral stress fibers have focal adhesions at either end and can be established following the contraction of two dorsal stress fibers and the associated transverse arc to form one actin bundle (20).Increased ventral stress fibers and focal adhesions are characteristic of nonmotile cells, in contrast, cell migration depends on focal adhesion turnover at the leading edge, allowing the formation of newly protruding regions of membrane and focal complex formation (28, 39). While the precise mechanism of focal adhesion turnover is incompletely understood, activation and phosphorylation of Src kinase, p130Cas, and paxillin (13, 39, 45) have all been implicated in focal adhesion turnover. A biphasic relationship between cell adhesion and cell speed suggests that conditions that alter the turnover rate of focal adhesions (either too much or too little) can reduce cell speed (18, 22).In cells with a fibroblastic phenotype, increased levels of acto-myosin contractility promote focal adhesion transition to fibrillar adhesions (also known as ECM contacts) (6, 7): elongated, thin, central arrays of dots or elongated fibrils that characteristically contain tensin but low levels of phosphorylated paxillin (29, 44, 45) and bind fibrils of fibronectin parallel to actin bundles (23, 29). These adhesions are formed by ligand-occupied fibronectin integrin receptor translocation from focal adhesions along bundles of actin filaments toward the cell center, and the process is dependent on an intact actin cytoskeleton and myosin activity (29). Receptor translocation stimulates matrix reorganization by transmitting cytoskeleton-generated tension through the integrin receptors onto the surrounding matrix (25, 29). The rate of receptor translocation is apparently independent from the rate of cell migration (29). However, the cytoskeletal tension that causes the fibrillar adhesion formation is also reported to decrease paxillin phosphorylation (45). Since phosphorylated paxillin is required for the generation of new focal complexes (45), conditions which switch the balance of adhesion in favor of fibrillar adhesion should presumably result in significantly reduced paxillin phosphorylation, leading to reduced focal adhesion turnover and correspondingly decreased cell migration.The cytoskeletal tropomyosin Tm5NM1 is a broadly distributed isoform (37) that alters cell shape (34), localizes to and promotes stress fibers that are resistant to actin depolymerizing drugs (9), enhances myosin IIA activation and recruitment to stress fibers, and inhibits cell migration (3). Therefore, we hypothesized that Tm5NM1 expression might determine cell migration by coordinating actin-dependent transition toward a predominance of focal adhesions and fibrillar adhesions. Using overexpression, knockdown, and genetic knockout models, we demonstrate that Tm5NM1 inhibits cell migration by promoting selective stabilization of focal adhesions and transition to fibrillar adhesions via the regulation of paxillin phosphorylation.     

Filopodial initiation and a novel filament-organizing center, the focal ring

This study examines filopodial initiation and implicates a putative actin filament organizer, the focal ring. Filopodia were optically recorded as they emerged from veils, the active lamellar extensions of growth cones. Motile histories revealed three events that consistently preceded filopodial emergence: an influx of cytoplasm into adjacent filopodia, a focal increase in phase density at veil margins, and protrusion of nubs that transform into filopodia. The cytoplasmic influx probably supplies materials needed for initiation. In correlated time lapse-immunocytochemistry, these focal phase densities corresponded to adhesions. These adhesions persisted at filopodial bases, regardless of subsequent movements. In correlated time lapse-electron microscopy, these adhesion sites contained a focal ring (an oblate, donut-shaped structure approximately 120 nm in diameter) with radiating actin filaments. Filament geometry may explain filopodial emergence at 30 degree angles relative to adjacent filopodia. A model is proposed in which focal rings play a vital role in initiating and stabilizing filopodia: 1) they anchor actin filaments at adhesions, thereby facilitating tension development and filopodial emergence; 2) "axial" filaments connect focal rings to nub tips, thereby organizing filament bundling and ensuring the bundle intersects an adhesion; and 3) "lateral" filaments interconnect focal rings and filament bundles, thereby helping stabilize lamellar margins and filopodia.     

Calpain mediates integrin-induced signaling at a point upstream of Rho family members.

Integrin-induced adhesion leads to cytoskeletal reorganizations, cell migration, spreading, proliferation, and differentiation. The details of the signaling events that induce these changes in cell behavior are not well understood but they appear to involve activation of Rho family members which activate signaling molecules such as tyrosine kinases, serine/threonine kinases, and lipid kinases. The result is the formation of focal complexes, focal adhesions, and bundles and networks of actin filaments that allow the cell to spread. The present study shows that mu-calpain is active in adherent cells, that it cleaves proteins known to be present in focal complexes and focal adhesions, and that overexpression of mu-calpain increased the cleavage of these proteins, induced an overspread morphology and induced an increased number of stress fibers and focal adhesions. Inhibition of calpain with membrane permeable inhibitors or by expression of a dominant negative form of mu-calpain resulted in an inability of cells to spread or to form focal adhesions, actin filament networks, or stress fibers. Cells expressing constitutively active Rac1 could still form focal complexes and actin filament networks (but not focal adhesions or stress fibers) in the presence of calpain inhibitors; cells expressing constitutively active RhoA could form focal adhesions and stress fibers. Taken together, these data indicate that calpain plays an important role in regulating the formation of focal adhesions and Rac- and Rho-induced cytoskeletal reorganizations and that it does so by acting at sites upstream of both Rac1 and RhoA.     

Reorganization of myosin and focal adhesion proteins in Swiss 3T3 fibroblasts induced by transforming growth factor beta

Certain types of cells show a dramatic change in cell morphology cultured in the presence of transforming growth factor beta (TGF-beta). To identify cellular components or factors leading to morphological changes, we investigated if any members of cytoskeletal proteins and cell-adhesion molecules were redistributed in TGF-beta-treated Swiss 3T3 fibroblasts by indirect immunofluorescence and Western-blot analysis. Changes in cell morphology became apparent within 12 h of the addition of TGF-beta and new RNA and protein synthesis was necessitated by the changes. While TGF-beta induced reorganization of microfilaments as reported in earlier studies, one of the actin isoforms, alpha actin of smooth muscle, was induced to form stress fibers in Swiss 3T3 cells. It was observed that myosin light chain was relocated from cell periphery to cytoplasmic filamentous structures by TGF-beta treatment, with an increased amount. In addition, the cell-shape change was accompanied by an increase in the level of vinculin and tyrosine phosphorylation at focal adhesions. These results suggest that new protein synthesis is required for the cell-shape change, and acto-myosin filaments and focal adhesion proteins are involved in the alteration of cell morphology induced by TGF-beta in Swiss 3T3 fibroblasts.     

Tropomyosin assembly intermediates in the control of microfilament system turnover

Tropomyosin is a coiled-coil alpha-helical protein, which self-associates in a head-to-tail fashion along polymers of actin to produce thin filaments. Mammalian non-muscle cells express a large number of tropomyosin isoforms, which are differentially regulated during embryogenesis and associated with specialized actin microfilament ensembles in cells. The function of tropomyosin in specifying form and localization of these subcellular structures, and the precise mechanism(s) by which they carry out their functions, is unclear. This paper reports that, while the major fraction of non-muscle cell tropomyosin resides in actin thin filaments of the cytomatrix, the soluble part of the cytoplasm contains tropomyosins in the form of actin-free multimers, which are isoform specific and of high molecular weight (MW(app) 180,000-250,000). Stimulation of motile cells with growth factors induces a rapid, actin polymerization-dependent outgrowth of lamellipodia and filopodia. Concomitantly, the levels of tropomyosin isoform-specific multimers decrease, suggesting their involvement in actin thin filament formation. Malignant tumor cells have drastically altered levels and composition of tropomyosin isoform-specific multimers as well as tropomyosin in the cytomatrix.     

Tropomyosin isoforms: divining rods for actin cytoskeleton function

Actin filament functional diversity is paralleled by variation in the composition of isoforms of tropomyosin in these filaments. Although the role of tropomyosin is well understood in skeletal muscle, where it regulates the actin-myosin interaction, its role in the cytoskeleton has been obscure. The intracellular sorting of tropomyosin isoforms indicated a role in spatial specialization of actin filament function. Genetic manipulation and protein chemistry studies have confirmed that these isoforms are functionally distinct. Tropomyosins differ in their recruitment of myosin motors and their interaction with actin filament regulators such as ADF-cofilin. Tropomyosin isoforms have therefore provided a powerful mechanism to diversify actin filament function in different intracellular compartments.     

Study of reciprocal effects of cardiac myosin and tropomyosin isoforms on actin-myosin interaction with in vitro motility assay

Interaction of myosin with actin in striated muscle is controlled by Ca²⁺ via thin filament associated proteins: troponin and tropomyosin. In cardiac muscle there is a whole pattern of myosin and tropomyosin isoforms. The aim of the current work is to study regulatory effect of tropomyosin on sliding velocity of actin filaments in the in vitro motility assay over cardiac isomyosins. It was found that tropomyosins of different content of α- and β-chains being added to actin filament effects the sliding velocity of filaments in different ways. On the other hand the velocity of filaments with the same tropomyosins depends on both heavy and light chains isoforms of cardiac myosin.     

ROCK1 and 2 differentially regulate actomyosin organization to drive cell and synaptic polarity

RhoGTPases organize the actin cytoskeleton to generate diverse polarities, from front–back polarity in migrating cells to dendritic spine morphology in neurons. For example, RhoA through its effector kinase, RhoA kinase (ROCK), activates myosin II to form actomyosin filament bundles and large adhesions that locally inhibit and thereby polarize Rac1-driven actin polymerization to the protrusions of migratory fibroblasts and the head of dendritic spines. We have found that the two ROCK isoforms, ROCK1 and ROCK2, differentially regulate distinct molecular pathways downstream of RhoA, and their coordinated activities drive polarity in both cell migration and synapse formation. In particular, ROCK1 forms the stable actomyosin filament bundles that initiate front–back and dendritic spine polarity. In contrast, ROCK2 regulates contractile force and Rac1 activity at the leading edge of migratory cells and the spine head of neurons; it also specifically regulates cofilin-mediated actin remodeling that underlies the maturation of adhesions and the postsynaptic density of dendritic spines.     

Tropomyosin Tm5NM1 Spatially Restricts Src Kinase Activity through Perturbation of Rab11 Vesicle Trafficking

In order for cells to stop moving, they must synchronously stabilize actin filaments and their associated focal adhesions. How these two structures are coordinated in time and space is not known. We show here that the actin association protein Tm5NM1, which induces stable actin filaments, concurrently suppresses the trafficking of focal-adhesion-regulatory molecules. Using combinations of fluorescent biosensors and fluorescence recovery after photobleaching (FRAP), we demonstrate that Tm5NM1 reduces the level of delivery of Src kinase to focal adhesions, resulting in reduced phosphorylation of adhesion-resident Src substrates. Live imaging of Rab11-positive recycling endosomes that carry Src to focal adhesions reveals disruption of this pathway. We propose that tropomyosin synchronizes adhesion dynamics with the cytoskeleton by regulating actin-dependent trafficking of essential focal-adhesion molecules.     

Tropomyosin isoform 3 promotes the formation of filopodia by regulating the recruitment of actin-binding proteins to actin filaments

Tropomyosins are believed to function in part by stabilizing actin filaments. However, accumulating evidence suggests that fundamental differences in function exist between tropomyosin isoforms, which contributes to the formation of functionally distinct filament populations. We investigated the functions of the high-molecular-weight isoform Tm3 and examined the molecular properties of Tm3-containing actin filament populations. Overexpression of the Tm3 isoform specifically induced the formation of filopodia and changes in actin solubility. We observed alterations in actin-binding protein recruitment to filaments, co-incident with changes in expression levels, which can account for this functional outcome. Tm3-associated filaments recruit active actin depolymerizing factor and are bundled into filopodia by fascin, which is both up-regulated and preferentially associated with Tm3-containing filaments in the Tm3 overexpressing cells. This study provides further insight into the isoform-specific roles of different tropomyosin isoforms. We conclude that variation in the tropomyosin isoform composition of microfilaments provides a mechanism to generate functionally distinct filament populations.     

Integrating actin dynamics,mechanotransduction and integrin activation: The multiple functions of actin binding proteins in focal adhesions

Focal adhesions are clusters of integrin transmembrane receptors that mechanically couple the extracellular matrix to the actin cytoskeleton during cell migration. Focal adhesions sense and respond to variations in force transmission along a chain of protein-protein interactions linking successively actin filaments, actin binding proteins, integrins and the extracellular matrix to adapt cell-matrix adhesion to the composition and mechanical properties of the extracellular matrix. This review focuses on the molecular mechanisms by which actin binding proteins integrate actin dynamics, mechanotransduction and integrin activation to control force transmission in focal adhesions.     

Dynamic actin remodeling during epithelial-mesenchymal transition depends on increased moesin expression

Remodeling of actin filaments is necessary for epithelial-mesenchymal transition (EMT); however, understanding of how this is regulated in real time is limited. We used an actin filament reporter and high-resolution live-cell imaging to analyze the regulated dynamics of actin filaments during transforming growth factor-β-induced EMT of mammary epithelial cells. Progressive changes in cell morphology were accompanied by reorganization of actin filaments from thin cortical bundles in epithelial cells to thick, parallel, contractile bundles that disassembled more slowly but remained dynamic in transdifferentiated cells. We show that efficient actin filament remodeling during EMT depends on increased expression of the ezrin/radixin/moesin (ERM) protein moesin. Cells suppressed for moesin expression by short hairpin RNA had fewer, thinner, and less stable actin bundles, incomplete morphological transition, and decreased invasive capacity. These cells also had less α-smooth muscle actin and phosphorylated myosin light chain in cortical patches, decreased abundance of the adhesion receptor CD44 at membrane protrusions, and attenuated autophosphorylation of focal adhesion kinase. Our findings suggest that increased moesin expression promotes EMT by regulating adhesion and contractile elements for changes in actin filament organization. We propose that the transciptional program driving EMT controls progressive remodeling of actin filament architectures.     

Coronin 1C negatively regulates cell-matrix adhesion and motility of intestinal epithelial cells

Coronins, WD-repeat actin-binding proteins, are known to regulate cell motility by coordinating actin filament turnover in lamellipodia of migrating cell. Here we report a novel mechanism of Coronin 1C-mediated cell motility that involves regulation of cell-matrix adhesion. RNAi silencing of Coronin 1C in intestinal epithelial cells enhanced cell migration and modulated lamellipodia dynamics by increasing the persistence of lamellipodial protrusion. Coronin 1C-depleted cells showed increased cell-matrix adhesions and enhanced cell spreading compared to control cells, while over-expression of Coronin 1C antagonized cell adhesion and spreading. Enhanced cell-matrix adhesion of coronin-deficient cells correlated with hyperphosphorylation of focal adhesion kinase (FAK) and paxillin, and an increase in number of focal adhesions and their redistribution at the cell periphery. siRNA depletion of FAK in coronin-deficient cells rescued the effects of Coronin 1C depletion on motility, cell-matrix adhesion, and spreading. Thus, our findings provide the first evidence that Coronin 1C negatively regulates epithelial cell migration via FAK-mediated inhibition of cell-matrix adhesion.     

Segregation and activation of myosin IIB creates a rear in migrating cells

We have found that MLC-dependent activation of myosin IIB in migrating cells is required to form an extended rear, which coincides with increased directional migration. Activated myosin IIB localizes prominently at the cell rear and produces large, stable actin filament bundles and adhesions, which locally inhibit protrusion and define the morphology of the tail. Myosin IIA forms de novo filaments away from the myosin IIB–enriched center and back to form regions that support protrusion. The positioning and dynamics of myosin IIA and IIB depend on the self-assembly regions in their coiled-coil C terminus. COS7 and B16 melanoma cells lack myosin IIA and IIB, respectively; and show isoform-specific front-back polarity in migrating cells. These studies demonstrate the role of MLC activation and myosin isoforms in creating a cell rear, the segregation of isoforms during filament assembly and their differential effects on adhesion and protrusion, and a key role for the noncontractile region of the isoforms in determining their localization and function.     

Stress fibers are generated by two distinct actin assembly mechanisms in motile cells

Stress fibers play a central role in adhesion, motility, and morphogenesis of eukaryotic cells, but the mechanism of how these and other contractile actomyosin structures are generated is not known. By analyzing stress fiber assembly pathways using live cell microscopy, we revealed that these structures are generated by two distinct mechanisms. Dorsal stress fibers, which are connected to the substrate via a focal adhesion at one end, are assembled through formin (mDia1/DRF1)-driven actin polymerization at focal adhesions. In contrast, transverse arcs, which are not directly anchored to substrate, are generated by endwise annealing of myosin bundles and Arp2/3-nucleated actin bundles at the lamella. Remarkably, dorsal stress fibers and transverse arcs can be converted to ventral stress fibers anchored to focal adhesions at both ends. Fluorescence recovery after photobleaching analysis revealed that actin filament cross-linking in stress fibers is highly dynamic, suggesting that the rapid association-dissociation kinetics of cross-linkers may be essential for the formation and contractility of stress fibers. Based on these data, we propose a general model for assembly and maintenance of contractile actin structures in cells.     

Actin cytoskeleton regulates functional anchorage-migration switch during T-cadherin-induced phenotype modulation of vascular smooth muscle cells

Vascular smooth muscle cell (SMC) switching between differentiated and dedifferentiated phenotypes is reversible and accompanied by morphological and functional alterations that require reconfiguration of cell-cell and cell-matrix adhesion networks. Studies attempting to explore changes in overall composition of the adhesion nexus during SMC phenotype transition are lacking. We have previously demonstrated that T-cadherin knockdown enforces SMC differentiation, whereas T-cadherin upregulation promotes SMC dedifferentiation. This study used human aortic SMCs ectopically modified with respect to T-cadherin expression to characterize phenotype-associated cell-matrix adhesion molecule expression, focal adhesions configuration and migration modes. Compared with dedifferentiated/migratory SMCs (expressing T-cadherin), the differentiated/contractile SMCs (T-cadherin-deficient) exhibited increased adhesion to several extracellular matrix substrata, decreased expression of several integrins, matrix metalloproteinases and collagens, and also distinct focal adhesion, adherens junction and intracellular tension network configurations. Differentiated and dedifferentiated phenotypes displayed distinct migrational velocity and directional persistence. The restricted migration efficiency of the differentiated phenotype was fully overcome by reducing actin polymerization with ROCK inhibitor Y-27632 whereas myosin II inhibitor blebbistatin was less effective. Migration efficiency of the dedifferentiated phenotype was diminished by promoting actin polymerization with lysophosphatidic acid. These findings held true in both 2D-monolayer and 3D-spheroid migration models. Thus, our data suggest that despite global differences in the cell adhesion nexus of the differentiated and dedifferentiated phenotypes, structural actin cytoskeleton characteristics per se play a crucial role in permissive regulation of cell-matrix adhesive interactions and cell migration behavior during T-cadherin-induced SMC phenotype transition.