Modulation of substrate adhesion dynamics via microtubule targeting requires kinesin-1

Focal adhesions are controlled by microtubules through local contractility regulation

Microtubules regulate cell polarity and migration via local activation of focal adhesion turnover, but the mechanism of this process is insufficiently understood. Molecular complexes containing KANK family proteins connect microtubules with talin, the major component of focal adhesions. Here, local optogenetic activation of KANK1-mediated microtubule/talin linkage promoted microtubule targeting to an individual focal adhesion and subsequent withdrawal, resulting in focal adhesion centripetal sliding and rapid disassembly. This sliding is preceded by a local increase of traction force due to accumulation of myosin-II and actin in the proximity of the focal adhesion. Knockdown of the Rho activator GEF-H1 prevented development of traction force and abolished sliding and disassembly of focal adhesions upon KANK1 activation. Other players participating in microtubule-driven, KANK-dependent focal adhesion disassembly include kinases ROCK, PAK, and FAK, as well as microtubules/focal adhesion-associated proteins kinesin-1, APC, and αTAT. Based on these data, we develop a mathematical model for a microtubule-driven focal adhesion disruption involving local GEF-H1/RhoA/ROCK-dependent activation of contractility, which is consistent with experimental data.

Septins guide noncentrosomal microtubules to promote focal adhesion disassembly in migrating cells

Endothelial cell migration is critical for vascular angiogenesis and is compromised to facilitate tumor metastasis. The migratory process requires the coordinated assembly and disassembly of focal adhesions (FA), actin, and microtubules (MT). MT dynamics at FAs deliver vesicular cargoes and enhance actomyosin contractility to promote FA turnover and facilitate cell advance. Noncentrosomal (NC) MTs regulate FA dynamics and are sufficient to drive cell polarity, but how NC MTs target FAs to control FA turnover is not understood. Here, we show that Rac1 induces the assembly of FA-proximal septin filaments that promote NC MT growth into FAs and inhibit mitotic centromere-associated kinesin (MCAK)-associated MT disassembly, thereby maintaining intact MT plus ends proximal to FAs. Septin-associated MT rescue is coupled with accumulation of Aurora-A kinase and cytoplasmic linker-associated protein (CLASP) localization to the MT between septin and FAs. In this way, NC MTs are strategically positioned to undergo MCAK- and CLASP-regulated bouts of assembly and disassembly into FAs, thereby regulating FA turnover and cell migration.

Probing mechanobiological role of filamin A in migration and invasion of human U87 glioblastoma cells using submicron soft pillars

Filamin A (FLNa) belongs to an actin-binding protein family in binding and cross-linking actin filaments into a three-dimensional structure. However, little attention has been given to its mechanobiological role in cancer cells. Here, we quantitatively investigated the role of FLNa by analyzing the following parameters in negative control (NC) and FLNa-knockdown (KD) U87 glioma cells using submicron pillars (900 nm diameter and 2 μm height): traction force (TF), rigidity sensing ability, cell aspect ratio, migration speed, and invasiveness. During the initial phase of cell adhesion (< 1 h), FLNa-KD cells polarized more slowly than did NC cells, which can be explained by the loss of rigidity sensing in FLNa-KD cells. The higher motility of FLNa-KD cells relative to NC cells can be explained by the high TF exerted by FLNa-KD cells when compared to NC cells, while the higher invasiveness of FLNa-KD cells relative to NC cells can be explained by a greater number of filopodia in FLNa-KD cells than in NC cells. Our results suggest that FLNa plays important roles in suppressing motility and invasiveness of U87 cells.

LSP1-myosin1e bimolecular complex regulates focal adhesion dynamics and cell migration

Several cytoskeleton-associated proteins and signaling pathways work in concert to regulate actin cytoskeleton remodeling, cell adhesion, and migration. Although the leukocyte-specific protein 1 (LSP1) has been shown to interact with the actin cytoskeleton, its function in the regulation of actin cytoskeleton dynamics is, as yet, not fully understood. We have recently demonstrated that the bimolecular complex between LSP1 and myosin1e controls actin cytoskeleton remodeling during phagocytosis. In this study, we show that LSP1 downregulation severely impairs cell migration, lamellipodia formation, and focal adhesion dynamics in macrophages. Inhibition of the interaction between LSP1 and myosin1e also impairs these processes resulting in poorly motile cells, which are characterized by few and small lamellipodia. Furthermore, cells in which LSP1-myosin1e interaction is inhibited are typically associated with inefficient focal adhesion turnover. Collectively, our findings show that the LSP1-myosin1e bimolecular complex plays a pivotal role in the regulation of actin cytoskeleton remodeling and focal adhesion dynamics required for cell migration.

The Golgi microtubules regulate single cell durotaxis

Current understandings on cell motility and directionality rely heavily on accumulated investigations of the adhesion-actin cytoskeleton-actomyosin contractility cycles, while microtubules have been understudied in this context. Durotaxis, the ability of cells to migrate up gradients of substrate stiffness, plays a critical part in development and disease. Here, we identify the pivotal role of Golgi microtubules in durotactic migration of single cells. Using high-throughput analysis of microtubule plus ends/focal adhesion interactions, we uncover that these non-centrosomal microtubules actively impart leading edge focal adhesion (FA) dynamics. Furthermore, we designed a new system where islands of higher stiffness were patterned within RGD peptide coated polyacrylamide gels. We revealed that the positioning of the Golgi apparatus is responsive to external mechanical cues and that the Golgi-nucleus axis aligns with the stiffness gradient in durotaxis. Together, our work unveils the cytoskeletal underpinning for single cell durotaxis. We propose a model in which the Golgi-nucleus axis serves both as a compass and as a steering wheel for durotactic migration, dictating cell directionality through the interaction between non-centrosomal microtubules and the FA dynamics.

An IFT20 mechanotrafficking axis is required for integrin recycling, focal adhesion dynamics, and polarized cell migration

Directional cell migration drives embryonic development, cancer metastasis, and tissue repair and regeneration. Here, we examine the role of intraflagellar transport (IFT) 20 (Ift20) during polarized migration of epidermal cells. IFT20 is implicated in regulating cell migration independently of the primary cilium, but how IFT proteins integrate with the cell migration machinery is poorly understood. We show that genetic ablation of IFT20 in vitro slows keratinocyte migration during wound healing. We find that this phenotype is independent of the primary cilium and instead can be attributed to alterations in integrin-mediated mechanotransduction and focal adhesion (FA) dynamics. Loss of Ift20 resulted in smaller and less numerous FAs and reduced the levels of activated FA kinase. Studies of FA dynamics during microtubule-induced FA turnover demonstrated that Ift20 loss specifically impaired the reformation, but not the disassembly, of FAs. In the absence of Ift20 function, β1 integrins endocytosed during FA disassembly are not transferred out of Rab5 (+) endosomes. This defective transit from the early endosome disrupts eventual recycling of β1 integrins back to the cell surface, resulting in defective FA reformation. In vivo, conditional ablation of Ift20 in hair follicle stem cells (HF-SCs) similarly impairs their ability to invade and migrate during epidermal wound healing. Using explant studies, lineage tracing, and clonal analysis, we demonstrate that Ift20 is required for HF-SC migration and their contribution to epidermal regeneration. This work identifies a new Ift20 mechanotrafficking mechanism required for polarized cell migration and stem cell-driven tissue repair.

Microtubules in cell migration

Directed cell migration is critical for embryogenesis and organ development, wound healing and the immune response. Microtubules are dynamic polymers that control directional migration through a number of coordinated processes: microtubules are the tracks for long-distance intracellular transport, crucial for delivery of new membrane components and signalling molecules to the leading edge of a migrating cell and the recycling of adhesion receptors. Microtubules act as force generators and compressive elements to support sustained cell protrusions. The assembly and disassembly of microtubules is coupled to Rho GTPase signalling, thereby controlling actin polymerisation, myosin-driven contractility and the turnover of cellular adhesions locally. Cross-talk of actin and microtubule dynamics is mediated through a number of common binding proteins and regulators. Furthermore, cortical microtubule capture sites are physically linked to focal adhesions, facilitating the delivery of secretory vesicles and efficient cross-talk. Here we summarise the diverse functions of microtubules during cell migration, aiming to show how they contribute to the spatially and temporally coordinated sequence of events that permit efficient, directional and persistent migration.

Microtubule Motors in Establishment of Epithelial Cell Polarity

Epithelial cells play a key role in insuring physiological homeostasis by acting as a barrier between the outside environment and internal organs. They are also responsible for the vectorial transport of ions and fluid essential to the function of many organs. To accomplish these tasks, epithelial cells must generate an asymmetrically organized plasma membrane comprised of structurally and functionally distinct apical and basolateral membranes. Adherent and occluding junctions, respectively, anchor cells within a layer and prevent lateral diffusion of proteins in the outer leaflet of the plasma membrane and restrict passage of proteins and solutes through intercellular spaces. At a fundamental level, the establishment and maintenance of epithelial polarity requires that signals initiated at cell-substratum and cell-cell adhesions are transmitted appropriately and dynamically to the cytoskeleton, to the membrane-trafficking machinery, and to the regulation of occluding and adherent junctions. Rigorous descriptive and mechanistic studies published over the last 50 years have provided great detail to our understanding of epithelial polarization. Yet still, critical early steps in morphogenesis are not yet fully appreciated. In this review, we discuss how cytoskeletal motor proteins, primarily kinesins, contribute to coordinated modification of microtubule and actin arrays, formation and remodeling of cell adhesions to targeted membrane trafficking, and to initiating the formation and expansion of an apical lumen.

Adenomatous polyposis coli nucleates actin assembly to drive cell migration and microtubule-induced focal adhesion turnover

Cell motility depends on tight coordination between the microtubule (MT) and actin cytoskeletons, but the mechanisms underlying this MT-actin cross talk have remained poorly understood. Here, we show that the tumor suppressor protein adenomatous polyposis coli (APC), which is a known MT-associated protein, directly nucleates actin assembly to promote directed cell migration. By changing only two residues in APC, we generated a separation-of-function mutant, APC (m4), that abolishes actin nucleation activity without affecting MT interactions. Expression of full-length APC carrying the m4 mutation (APC (m4)) rescued cellular defects in MT organization, MT dynamics, and mitochondrial distribution caused by depletion of endogenous APC but failed to restore cell migration. Wild-type APC and APC (m4) localized to focal adhesions (FAs), and APC (m4) was defective in promoting actin assembly at FAs to facilitate MT-induced FA turnover. These results provide the first direct evidence for APC-mediated actin assembly in vivo and establish a role for APC in coordinating MTs and actin at FAs to direct cell migration.

Tubulin beta 3 and 4 are involved in the generation of early fibrotic stages

The endothelial-mesenchymal transition (EndMT) is a fundamental cellular mechanism that occurs under both physiological and pathological conditions and includes the fibrotic stages of numerous organs, namely, the skin, kidneys, heart, lungs and liver. Endothelial cells that undergo EndMT are one of the main source of (myo)fibroblasts in fibrotic tissues. A critical step in cellular transdifferentiation is morphological change, which is engineered by the reorganization of cytoskeletal elements such as microtubules. These dynamic structures consist of αβ-tubulin heterodimers that are also involved in cellular movement and intracellular trafficking, processes modulated during EndMT. One fundamental mechanism that underlies microtubule stabilization is the regulation of the levels of α and β-tubulin. However, little is known about the roles of specific tubulin isotypes in the development of EndMT-based diseases. This study provides the first evidence that the upregulation of TUBB3 and TUBB4 is coupled with increased cell migration in EndMT-induced HMEC-1 cells. Immunochemical analysis reveals that these tubulins are upregulated in the early stages of EndMT, and siRNA analysis indicates that they are engaged in the generation of mesenchymal behavior via the enhancement of cell migration. This modulation seems to be especially important in wound healing. Finally, cell surface analysis reveals that TUBB3 and TUBB4 are necessary for the transport and proper localization of N-cadherin within the plasma membrane. We believe that our results will be valuable for the development of effective new anti-fibrotic therapies.

The CAMSAP3-ACF7 Complex Couples Noncentrosomal Microtubules with Actin Filaments to Coordinate Their Dynamics

For adaptation to complex cellular functions, dynamic cytoskeletal networks are required. There are two major components of the cytoskeleton, microtubules and actin filaments, which form an intricate network maintaining an exquisite cooperation to build the physical basis for their cellular function. However, little is known about the molecular mechanism underlying their synergism. Here, we show that in Caco2 epithelial cells, noncentrosomal microtubules crosstalk with F-actin through their minus ends and contribute to the regulation of focal adhesion size and cell migration. We demonstrate that ACF7, a member of the spectraplakin family of cytoskeletal crosslinking proteins, interacts with Nezha (also called CAMSAP3) at the minus ends of noncentrosomal microtubules and anchors them to actin filaments. Those noncentrosomal microtubules cooperate with actin filaments through retrograde flow to keep their length and orientation perpendicular to the cell edge as well as regulate focal adhesion size and cell migration.

The ubiquitin-proteasome system regulates focal adhesions at the leading edge of migrating cells

Cell migration requires the cyclical assembly and disassembly of focal adhesions. Adhesion induces phosphorylation of focal adhesion proteins, including Cas (Crk-associated substrate/p130Cas/BCAR1). However, Cas phosphorylation stimulates adhesion turnover. This raises the question of how adhesion assembly occurs against opposition from phospho-Cas. Here we show that suppressor of cytokine signaling 6 (SOCS6) and Cullin 5, two components of the CRL5^SOCS6 ubiquitin ligase, inhibit Cas-dependent focal adhesion turnover at the front but not rear of migrating epithelial cells. The front focal adhesions contain phospho-Cas which recruits SOCS6. If SOCS6 cannot access focal adhesions, or if cullins or the proteasome are inhibited, adhesion disassembly is stimulated. This suggests that the localized targeting of phospho-Cas within adhesions by CRL5^SOCS6 and concurrent cullin and proteasome activity provide a negative feedback loop, ensuring that adhesion assembly predominates over disassembly at the leading edge. By this mechanism, ubiquitination provides a new level of spatio-temporal control over cell migration.

DOI:http://dx.doi.org/10.7554/eLife.17440.001

Animal cells can move in the body, for example to heal a wound, by protruding a leading edge forwards, attaching it to the surroundings and then pulling against these new attachments while disassembling the older ones. Mechanical forces regulate the assembly and disassembly of these attachments, known as focal adhesions, and so do signals from outside the cell that are transmitted to the adhesions via specialized proteins. However, it was not clear how the assembly and disassembly of adhesions is coordinated.

CRL5 is a ubiquitin ligase, an enzyme that can mark other proteins for destruction. Cells migrate more quickly if CRL5 is inhibited, and so Teckchandani and Cooper set out to uncover whether CRL5 affects the assembly and disassembly of focal adhesions. The experiments showed that human cells lacking a crucial component of the CRL5 complex, SOCS6, disassemble adhesions faster than normal cells, but only at their leading edge and not at the rear.

Teckchandani and Cooper also found that SOCS6 localizes to the leading edge by binding to a focal adhesion protein called Cas. Shortly after the attachments assemble, the Cas protein becomes tagged with a phosphate group and then acts to promote the adhesion to disassemble. Further experiments indicated that Cas was marked by the CRL5 complex and possibly destroyed while in or very close to the leading edge adhesions, slowing their disassembly.

Together, these findings suggest that by binding Cas, SOCS6 regulates the turnover of adhesions, specifically by inhibiting disassembly and allowing adhesions to grow at the leading edge. Since SOCS6 is not present in adhesions outside of the leading edge, this may help explain how the older adhesions are disassembled. Future studies could next focus on the exact sequence of events that occur in focal adhesions after the CRL5 complex binds to Cas as the cell migrates.

DOI:http://dx.doi.org/10.7554/eLife.17440.002

In vivo epidermal migration requires focal adhesion targeting of ACF7

Turnover of focal adhesions allows cell retraction, which is essential for cell migration. The mammalian spectraplakin protein, ACF7 (Actin-Crosslinking Factor 7), promotes focal adhesion dynamics by targeting of microtubule plus ends towards focal adhesions. However, it remains unclear how the activity of ACF7 is regulated spatiotemporally to achieve focal adhesion-specific guidance of microtubule. To explore the potential mechanisms, we resolve the crystal structure of ACF7’s NT (amino-terminal) domain, which mediates F-actin interactions. Structural analysis leads to identification of a key tyrosine residue at the calponin homology (CH) domain of ACF7, whose phosphorylation by Src/FAK (focal adhesion kinase) complex is essential for F-actin binding of ACF7. Using skin epidermis as a model system, we further demonstrate that the phosphorylation of ACF7 plays an indispensable role in focal adhesion dynamics and epidermal migration in vitro and in vivo. Together, our findings provide critical insights into the molecular mechanisms underlying coordinated cytoskeletal dynamics during cell movement.

The spectraplakin protein ACF7 binds to actin at focal adhesions and targets microtubule plus ends to focal adhesions, promoting their disassembly. Here the authors reveal that ACF7 is phosphorylated by Src/FAK, and this regulates actin binding and focal adhesion dynamics in vitro and in vivo.

A Unique Role for Endothelial Cell Kinesin Light Chain 1, Variant 1 in Leukocyte Transendothelial Migration

A reservoir of parajunctional membrane in endothelial cells, the lateral border recycling compartment (LBRC), is critical for transendothelial migration (TEM). We have previously shown that targeted recycling of the LBRC to the site of TEM requires microtubules and a kinesin molecular motor. However, the identity of the kinesin and mechanism of cargo binding were not known. We show that microinjection of endothelial cells with a monoclonal antibody specific for kinesin-1 significantly blocked LBRC-targeted recycling and TEM. In complementary experiments, knocking down KIF5B, a ubiquitous kinesin-1 isoform, in endothelial cells significantly decreased targeted recycling of the LBRC and leukocyte TEM. Kinesin heavy chains move cargo along microtubules by one of many kinesin light chains (KLCs), which directly bind the cargo. Knocking down KLC 1 isoform variant 1 (KLC1C) significantly decreased LBRC-targeted recycling and TEM, whereas knocking down other isoforms of KLC1 had no effect. Re-expression of KLC1C resistant to the knockdown shRNA restored targeted recycling and TEM. Thus kinesin-1 and KLC1C are specifically required for targeted recycling and TEM. These data suggest that of the many potential combinations of the 45 kinesin family members and multiple associated light chains, KLC1C links the LBRC to kinesin-1 (KIF5B) during targeted recycling and TEM. Thus, KLC1C can potentially be used as a target for anti-inflammatory therapy.

KIF17 regulates RhoA-dependent actin remodeling at epithelial cell-cell adhesions

The kinesin KIF17 localizes at microtubule plus-ends where it contributes to regulation of microtubule stabilization and epithelial polarization. We now show that KIF17 localizes at cell-cell adhesions and that KIF17 depletion inhibits accumulation of actin at the apical pole of cells grown in 3D organotypic cultures and alters the distribution of actin and E-cadherin in cells cultured in 2D on solid supports. Overexpression of full-length KIF17 constructs or truncation mutants containing the N-terminal motor domain resulted in accumulation of newly incorporated GFP-actin into junctional actin foci, cleared E-cadherin from cytoplasmic vesicles and stabilized cell-cell adhesions to challenge with calcium depletion. Expression of these KIF17 constructs also increased cellular levels of active RhoA, whereas active RhoA was diminished in KIF17-depleted cells. Inhibition of RhoA or its effector ROCK, or expression of LIMK1 kinase-dead or activated cofilin(S3A) inhibited KIF17-induced junctional actin accumulation. Interestingly, KIF17 activity toward actin depends on the motor domain but is independent of microtubule binding. Together, these data show that KIF17 can modify RhoA-GTPase signaling to influence junctional actin and the stability of the apical junctional complex of epithelial cells.

GAR22β regulates cell migration, sperm motility, and axoneme structure

Spatiotemporal cytoskeleton remodeling is crucial for several biological processes. GAR22β interacts with EB1 via a novel noncanonical amino acid sequence and is pivotal for cell motility and focal adhesion turnover. GAR22β is also crucial for generation, motility, and ultrastructural organization of spermatozoa.

Spatiotemporal cytoskeleton remodeling is pivotal for cell adhesion and migration. Here we investigated the function of Gas2-related protein on chromosome 22 (GAR22β), a poorly characterized protein that interacts with actin and microtubules. Primary and immortalized GAR22β^−/− Sertoli cells moved faster than wild-type cells. In addition, GAR22β^−/− cells showed a more prominent focal adhesion turnover. GAR22β overexpression or its reexpression in GAR22β^−/− cells reduced cell motility and focal adhesion turnover. GAR22β–actin interaction was stronger than GAR22β–microtubule interaction, resulting in GAR22β localization and dynamics that mirrored those of the actin cytoskeleton. Mechanistically, GAR22β interacted with the regulator of microtubule dynamics end-binding protein 1 (EB1) via a novel noncanonical amino acid sequence, and this GAR22β–EB1 interaction was required for the ability of GAR22β to modulate cell motility. We found that GAR22β is highly expressed in mouse testes, and its absence resulted in reduced spermatozoa generation, lower actin levels in testes, and impaired motility and ultrastructural disorganization of spermatozoa. Collectively our findings identify GAR22β as a novel regulator of cell adhesion and migration and provide a foundation for understanding the molecular basis of diverse cytoskeleton-dependent processes.

Regulation of Focal Adhesion Dynamics and Cell Motility by the EB2 and Hax1 Protein Complex

Cell migration is a fundamental cellular process requiring integrated activities of the cytoskeleton, membrane, and cell/extracellular matrix adhesions. Many cytoskeletal activities rely on microtubule filaments. It has been speculated that microtubules can serve as tracks to deliver proteins essential for focal adhesion turnover. Three microtubule end-binding proteins (EB1, EB2, and EB3) in mammalian cells can track the plus ends of growing microtubules. EB1 and EB3 together can regulate microtubule dynamics by promoting microtubule growth and suppressing catastrophe, whereas, in contrast, EB2 does not play a direct role in microtubule dynamic instability, and little is known about the cellular function of EB2. By quantitative proteomics, we identified mammalian HCLS1-associated protein X-1 (HAX1) as an EB2-specific interacting protein. Knockdown of HAX1 and EB2 in skin epidermal cells stabilizes focal adhesions and impairs epidermal migration in vitro and in vivo. Our results further demonstrate that cell motility and focal adhesion turnover require interaction between Hax1 and EB2. Together, our findings provide new insights for this critical cellular process, suggesting that EB2 association with Hax1 plays a significant role in focal adhesion turnover and epidermal migration.

Kinesins in cell migration

Human cells express 45 kinesins, microtubule motors that transport a variety of molecules and organelles within the cell. Many kinesins also modulate the tracks they move on by either bundling or sliding or regulating the dynamic assembly and disassembly of the microtubule polymer. In migrating cells, microtubules control the asymmetry between the front and rear of the cell by differentially regulating force generation processes and substrate adhesion. Many of these functions are mediated by kinesins, transporters as well as track modulators. In this review, we summarize the current knowledge on kinesin functions in cell migration.

A plastic relationship between vinculin-mediated tension and adhesion complex area defines adhesion size and lifetime

Cell-matrix adhesions are central mediators of mechanotransduction, yet the interplay between force and adhesion regulation remains unclear. Here we use live cell imaging to map time-dependent cross-correlations between vinculin-mediated tension and adhesion complex area, revealing a plastic, context-dependent relationship. Interestingly, while an expected positive cross-correlation dominated in mid-sized adhesions, small and large adhesions display negative cross-correlation. Furthermore, although large changes in adhesion complex area follow vinculin-mediated tension alterations, small increases in area precede vinculin-mediated tension dynamics. Modelling based on this mapping of the vinculin-mediated tension-adhesion complex area relationship confirms its biological validity, and indicates that this relationship explains adhesion size and lifetime limits, keeping adhesions focal and transient. We also identify a subpopulation of steady-state adhesions whose size and vinculin-mediated tension become stabilized, and whose disassembly may be selectively microtubule-mediated. In conclusion, we define a plastic relationship between vinculin-mediated tension and adhesion complex area that controls fundamental cell-matrix adhesion properties.

Cell-matrix adhesions may increase or decrease in size in response to tension; however, the factors determining which of these responses predominates remain unclear. Hernández-Varas et al. quantify the plastic relationship between adhesion size and tension and use modelling to explain this behaviour.

Ultraviolet B Inhibits Skin Wound Healing by Affecting Focal Adhesion Dynamics

As the most important interface between human body and external environment, skin acts as an essential barrier preventing various environmental damages, among which DNA-damaging UV radiation from the sun remains the major environmental risk factor causing various skin diseases. It has been well documented that wavelengths in the ultraviolet B (UVB) radiation range (290-320 nm) of the solar spectrum can be absorbed by skin and lead to cutaneous injury and various other deleterious effects. During process such as wound healing, the orchestrated movement of cells in a particular direction is essential and highly regulated, integrating signals controlling adhesion, polarity and the cytoskeleton. Cell adhesion and migration are modulated through both of actin and microtubule cytoskeletons. However, little was known about how UVB affects skin wound healing and migration of epidermal keratinocytes. Here, we demonstrate that UVB can delay the wound healing progress in vivo with a murine model of full-thickness skin wound. In addition, UVB significantly inhibited keratinocyte motility by altering focal adhesion turnover and cytoskeletal dynamics. Our results provide new insights into the etiology of UVB exposure-induced skin damages.

Microtubules regulate focal adhesion dynamics through MAP4K4

Disassembly of focal adhesions (FAs) allows cell retraction and integrin detachment from the extracellular matrix, processes critical for cell movement. Growth of microtubules (MTs) can promote FA turnover by serving as tracks to deliver proteins essential for FA disassembly. The molecular nature of this FA "disassembly factor," however, remains elusive. By quantitative proteomics, we identified mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4) as an FA regulator that associates with MTs. Knockout of MAP4K4 stabilizes FAs and impairs cell migration. By exploring underlying mechanisms, we further show that MAP4K4 associates with ending binding 2 (EB2) and IQ motif and SEC7 domain-containing protein 1 (IQSEC1), a guanine nucleotide exchange factor specific for Arf6, whose activation promotes integrin internalization. Together, our findings provide critical insight into FA disassembly, suggesting that MTs can deliver MAP4K4 toward FAs through EB2, where MAP4K4 can, in turn, activate Arf6 via IQSEC1 and enhance FA dissolution.

Hematopoietic PBX-interacting protein (HPIP) is over expressed in breast infiltrative ductal carcinoma and regulates cell adhesion and migration through modulation of focal adhesion dynamics

The scaffolding protein, hematopoietic PBX-interacting protein (HPIP/PBXIP1), regulates cell migration necessary for cancer cell dissemination. However, the mechanism that governs this process remains unknown. We show here that HPIP expression is associated with stages of breast cancer where cell dissemination results in poor patient outcome. Our investigation finds a novel association of HPIP with focal adhesion kinase (FAK) regulating FA dynamics. Interestingly, this interaction that led to activation of FAK protein was mediated by the C-terminal domain of HPIP and not the typical integrin-binding motif. Further, short hairpin RNA-mediated knockdown of FAK expression significantly reduced HPIP-induced cell migration indicating participation of FAK pathway. Live-cell time-lapse imaging and biochemical analysis further established the role of HPIP in microtubule-induced FA disassembly. We also found that HPIP-mediated MAPK activation led to phosphorylation and subsequent activation of calpain2, and the activated calpain2 in turn proteolyses FA protein, talin. Interestingly, HPIP is also proteolysed by calpain2 in breast cancer cells. The proteolysis of HPIP and talin by calpain2, and the activation of calapin2 by HPIP-mediated MAPK phosphorylation, is a novel regulatory axis to modulate the cell migration signal. Together, we have determined HPIP as a novel activator of FAK and a new substrate of calpain2. These molecular interactions between HPIP and FAK, and HPIP and calpain2 regulate cell adhesion and migration through modulation of FA dynamics.

Microtubule acetylation regulates dynamics of KIF1C-powered vesicles and contact of microtubule plus ends with podosomes

Microtubule dynamics are important for a variety of key cellular functions such as intracellular trafficking, adjustment of the cell surface proteome, or adhesion structure turnover. In the current study, we investigate the effects of altered microtubule acetylation levels on the subcellular distribution of kinesins and actin cytoskeletal architecture in primary human macrophages. Microtubule acetylation was altered by overexpression or siRNA-induced depletion of the acetylase MEC-17, or by blocking α-tubulin deacetylation by addition of the inhibitor tubacin. We show that microtubule acetylation influences the subcellular distribution of vesicles associated with the kinesin KIF1C, as well as their directionality, velocity and run length. Moreover, tubulin acetylation alters the targeting frequency of microtubule plus ends on podosomes and influences the number of podosomes per cell and thus the matrix-degrading capacity of macrophages. Collectively, our results point to α-tubulin acetylation as an important modification that impacts on kinesin vesicle dynamics, actin cytoskeletal architecture and cellular function of macrophages.

Paxillin inhibits HDAC6 to regulate microtubule acetylation, Golgi structure, and polarized migration

Polarized cell migration is essential for normal organism development and is also a critical component of cancer cell invasion and disease progression. Directional cell motility requires the coordination of dynamic cell-extracellular matrix interactions as well as repositioning of the Golgi apparatus, both of which can be controlled by the microtubule (MT) cytoskeleton. In this paper, we have identified a new and conserved role for the focal adhesion scaffold protein paxillin in regulating the posttranslational modification of the MT cytoskeleton through an inhibitory interaction with the α-tubulin deacetylase HDAC6. We also determined that through HDAC6-dependent regulation of the MT cytoskeleton, paxillin regulates both Golgi organelle integrity and polarized cell invasion and migration in both three-dimensional and two-dimensional matrix microenvironments. Importantly, these data reveal a fundamental role for paxillin in coordinating MT acetylation-dependent cell polarization and migration in both normal and transformed cells.

The late endosomal p14-MP1 (LAMTOR2/3) complex regulates focal adhesion dynamics during cell migration

Late endosomes locally regulate cell migration by transporting the p14–MP1 scaffold complex to the vicinity of focal adhesions.

Cell migration is mediated by the dynamic remodeling of focal adhesions (FAs). Recently, an important role of endosomal signaling in regulation of cell migration was recognized. Here, we show an essential function for late endosomes carrying the p14–MP1 (LAMTOR2/3) complex in FA dynamics. p14–MP1-positive endosomes move to the cell periphery along microtubules (MTs) in a kinesin1- and Arl8b-dependent manner. There they specifically target FAs to regulate FA turnover, which is required for cell migration. Using genetically modified fibroblasts from p14-deficient mice and Arl8b-depleted cells, we demonstrate that MT plus end–directed traffic of p14–MP1-positive endosomes triggered IQGAP1 disassociation from FAs. The release of IQGAP was required for FA dynamics. Taken together, our results suggest that late endosomes contribute to the regulation of cell migration by transporting the p14–MP1 scaffold complex to the vicinity of FAs.

Directional persistence of migrating cells requires Kif1C-mediated stabilization of trailing adhesions

Directional cell migration requires the establishment and maintenance of long-term differences in structure and function between the front and back of a cell. Here, we show that the microtubule motor Kif1C contributes to persistent cell migration primarily through stabilization of an extended cell rear. Kif1C-mediated transport of α5β1-integrins is required for the proper maturation of trailing focal adhesions and resistance to tail retraction. Tail retraction precedes and induces changes in migration direction. Stabilization of cell tails through inhibition of myosin II activity suppresses the Kif1C depletion phenotype and results in longer-lived tails and higher directional stability of migrating cells. Taken together, these findings indicate that the maintenance of an extended, tense cell tail facilitates directional migration. We propose a rear drag mechanism for directional persistence of migration whereby the counterforce originating from a well-anchored tail serves to maintain directionality of the force-generating leading edge of the cell.

Intermediate filament-associated cytolinker plectin 1c destabilizes microtubules in keratinocytes

The transition of microtubules (MTs) from an assembled to a disassembled state plays an essential role in several cellular functions. While MT dynamics are often linked to those of actin filaments, little is known about whether intermediate filaments (IFs) have an influence on MT dynamics. We show here that plectin 1c (P1c), one of the multiple isoforms of the IF-associated cytolinker protein plectin, acts as an MT destabilizer. We found that MTs in P1c-deficient (P1c(-/-)) keratinocytes are more resistant toward nocodazole-induced disassembly and display increased acetylation. In addition, live imaging of MTs in P1c(-/-), as well as in plectin-null, cells revealed decreased MT dynamics. Increased MT stability due to P1c deficiency led to changes in cell shape, increased velocity but loss of directionality of migration, smaller-sized focal adhesions, higher glucose uptake, and mitotic spindle aberrations combined with reduced growth rates of cells. On the basis of ex vivo and in vitro experimental approaches, we suggest a mechanism for MT destabilization in which isoform-specific binding of P1c to MTs antagonizes the MT-stabilizing and assembly-promoting function of MT-associated proteins through an inhibitory function exerted by plectin's SH3 domain. Our results open new perspectives on cytolinker-coordinated IF-MT interaction and its physiological significance.

KIF14 negatively regulates Rap1a-Radil signaling during breast cancer progression

The kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules.

The small GTPase Rap1 regulates inside-out integrin activation and thereby influences cell adhesion, migration, and polarity. Several Rap1 effectors have been described to mediate the cellular effects of Rap1 in a context-dependent manner. Radil is emerging as an important Rap effector implicated in cell spreading and migration, but the molecular mechanisms underlying its functions are unclear. We report here that the kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules. The depletion of KIF14 led to increased cell spreading, altered focal adhesion dynamics, and inhibition of cell migration and invasion. We also show that Radil is important for breast cancer cell proliferation and for metastasis in mice. Our findings provide evidence that the concurrent up-regulation of Rap1 activity and increased KIF14 levels in several cancers is needed to reach optimal levels of Rap1–Radil signaling, integrin activation, and cell–matrix adhesiveness required for tumor progression.

Targeting and transport: how microtubules control focal adhesion dynamics

Directional cell migration requires force generation that relies on the coordinated remodeling of interactions with the extracellular matrix (ECM), which is mediated by integrin-based focal adhesions (FAs). Normal FA turnover requires dynamic microtubules, and three members of the diverse group of microtubule plus-end-tracking proteins are principally involved in mediating microtubule interactions with FAs. Microtubules also alter the assembly state of FAs by modulating Rho GTPase signaling, and recent evidence suggests that microtubule-mediated clathrin-dependent and -independent endocytosis regulates FA dynamics. In addition, FA-associated microtubules may provide a polarized microtubule track for localized secretion of matrix metalloproteases (MMPs). Thus, different aspects of the molecular mechanisms by which microtubules control FA turnover in migrating cells are beginning to emerge.

Endoplasmic spreading requires coalescence of vimentin intermediate filaments at force-bearing adhesions

Interaction of vimentin filaments (vIFs) and force-bearing adhesions is essential for endoplasm spreading. For adhesions to be connected to a contractile network involved in endoplasm spreading, vIFs are needed. Thus endoplasm spreading and microtubule stabilization in the periphery require a multicomponent actin network anchored at adhesions.

For cells to develop long-range forces and carry materials to the periphery, the microtubule and organelle-rich region at the center of the cell—the endoplasm—needs to extend to near the cell edge. Depletion of the actin cross-linking protein filamin A (FlnA) causes a collapse of the endoplasm into a sphere around the nucleus of fibroblasts and disruption of matrix adhesions, indicating that FlnA is involved in endoplasmic spreading and adhesion growth. Here, we report that treatment with the calpain inhibitor N-[N-(N-acetyl-l-leucyl)-l-leucyl]-l-norleucine (ALLN) restores endoplasmic spreading as well as focal adhesion (FA) growth on fibronectin-coated surfaces in a Fln-depleted background. Addback of calpain-uncleavable talin, not full-length talin, achieves a similar effect in Fln-depleted cells and indicates a crucial role for talin in endoplasmic spreading. Because FA maturation involves the vimentin intermediate filament (vIF) network, we also examined the role of vIFs in endoplasmic spreading. Wild-type cells expressing a vimentin variant incapable of polymerization exhibit deficient endoplasmic spreading as well as defects in FA growth. ALLN treatment restores FA growth despite the lack of vIFs but does not restore endoplasmic spreading, implying that vIFs are essential for endoplasm spreading. Consistent with that hypothesis, vIFs are always displaced from adhesions when the endoplasm does not spread. In Fln-depleted cells, vIFs extend beyond adhesions, nearly to the cell edge. Finally, inhibiting myosin II–mediated contraction blocks endoplasmic spreading and adhesion growth. Thus we propose a model in which myosin II–mediated forces and coalescence of vIFs at mature FAs are required for endoplasmic spreading.

Binding of dynein intermediate chain 2 to paxillin controls focal adhesion dynamics and migration

In migrating NRK cells, aPKCs control the dynamics of turnover of paxillin-containing focal adhesions (FA) determining migration rate. Using a proteomic approach (two-dimensional fluorescence difference gel electrophoresis), dynein intermediate chain 2 (dynein IC2) was identified as a protein that is phosphorylated inducibly during cell migration in a PKC-regulated manner. By gene silencing and co-immunoprecipitation studies, we show that dynein IC2 regulates the speed of cell migration through its interaction with paxillin. This interaction is controlled by serine 84 phosphorylation, which lies on the aPKC pathway. The evidence presented thus links aPKC control of migration to the dynein control of FA turnover through paxillin.

Spectraplakins: master orchestrators of cytoskeletal dynamics

The dynamics of different cytoskeletal networks are coordinated to bring about many fundamental cellular processes, from neuronal pathfinding to cell division. Increasing evidence points to the importance of spectraplakins in integrating cytoskeletal networks. Spectraplakins are evolutionarily conserved giant cytoskeletal cross-linkers, which belong to the spectrin superfamily. Their genes consist of multiple promoters and many exons, yielding a vast array of differential splice forms with distinct functions. Spectraplakins are also unique in their ability to associate with all three elements of the cytoskeleton: F-actin, microtubules, and intermediate filaments. Recent studies have begun to unveil their role in a wide range of processes, from cell migration to tissue integrity.

Kinetic stabilization of microtubule dynamics by indanocine perturbs EB1 localization, induces defects in cell polarity and inhibits migration of MDA-MB-231 cells

Cell motility is an essential aspect of metastatic spread of cancer. Microtubule-targeted agents exhibit anti-metastatic properties, the underlying mechanism of which remains understudied. In this study, we have investigated the role of microtubule dynamics in migration of cancer cells using indanocine, a synthetic small molecule inhibitor of tubulin. We found that indanocine, at concentrations that did not visibly affect microtubule organization, suppressed dynamic instability of microtubules and reduced the rate of migration of highly metastatic MDA-MB-231 cells. Indanocine-treated cells were defective in lamellipodium formation and could not develop polarized morphology. The kinetic stabilization of microtubules was associated with a marked increase in their acetylation level and a perturbation in the localization of EB1, a microtubule plus end binding protein. Using standard scratch wound healing assay and immunofluorescence analysis; we found that microtubule acetylation occurred in the direction of migration in vehicle-treated cells, whereas indanocine treatment led to a global acetylation of microtubules. The results together suggested that selective stabilization of microtubules was perturbed in the presence of indanocine that possibly resulted in lack of cell polarization and a concurrent reduction in migration of cells. Moreover, microtubule stabilization by indanocine affected adhesion turnover and impaired the polarized pattern of adhesion sites in cells. Together the results indicated that the regulation of microtubule dynamics is required to coordinate cell polarization as well as adhesion asymmetry and support the hypothesis that the perturbation of microtubule dynamics by tubulin-targeted agents can be exploited to restrict the migration of tumor cells.

Turnover of focal adhesions and cancer cell migration

Cells are usually surrounded by the extracellular matrix (ECM), and adhesion of the cells to the ECM is a key step in their migration through tissues. Integrins are important receptors for the ECM and form structures called focal adhesions (FAs). Formation and disassembly of FAs are regulated dynamically during cell migration. Adhesion to the ECM has been studied mainly using cells cultured on an ECM-coated substratum, where the rate of cell migration is determined by the turnover of FAs. However, the molecular events underlying the disassembly of FAs are less well understood. We have recently identified both a new regulator of this disassembly process and its interaction partners. Here, we summarize our understanding of FA disassembly by focusing on the proteins implicated in this process.

Dysferlin interacts with histone deacetylase 6 and increases alpha-tubulin acetylation

Dysferlin is a multi-C2 domain transmembrane protein involved in a plethora of cellular functions, most notably in skeletal muscle membrane repair, but also in myogenesis, cellular adhesion and intercellular calcium signaling. We previously showed that dysferlin interacts with alpha-tubulin and microtubules in muscle cells. Microtubules are heavily reorganized during myogenesis to sustain growth and elongation of the nascent muscle fiber. Microtubule function is regulated by post-translational modifications, such as acetylation of its alpha-tubulin subunit, which is modulated by the histone deacetylase 6 (HDAC6) enzyme. In this study, we identified HDAC6 as a novel dysferlin-binding partner. Dysferlin prevents HDAC6 from deacetylating alpha-tubulin by physically binding to both the enzyme, via its C2D domain, and to the substrate, alpha-tubulin, via its C2A and C2B domains. We further show that dysferlin expression promotes alpha-tubulin acetylation, as well as increased microtubule resistance to, and recovery from, Nocodazole- and cold-induced depolymerization. By selectively inhibiting HDAC6 using Tubastatin A, we demonstrate that myotube formation was impaired when alpha-tubulin was hyperacetylated early in the myogenic process; however, myotube elongation occurred when alpha-tubulin was hyperacetylated in myotubes. This study suggests a novel role for dysferlin in myogenesis and identifies HDAC6 as a novel dysferlin-interacting protein.

Regulation of cell migration by dynamic microtubules

Microtubules define the architecture and internal organization of cells by positioning organelles and activities, as well as by supporting cell shape and mechanics. One of the major functions of microtubules is the control of polarized cell motility. In order to support the asymmetry of polarized cells, microtubules have to be organized asymmetrically themselves. Asymmetry in microtubule distribution and stability is regulated by multiple molecular factors, most of which are microtubule-associated proteins that locally control microtubule nucleation and dynamics. At the same time, the dynamic state of microtubules is key to the regulatory mechanisms by which microtubules regulate cell polarity, modulate cell adhesion and control force-production by the actin cytoskeleton. Here, we propose that even small alterations in microtubule dynamics can influence cell migration via several different microtubule-dependent pathways. We discuss regulatory factors, potential feedback mechanisms due to functional microtubule-actin crosstalk and implications for cancer cell motility.

ZF21 protein, a regulator of the disassembly of focal adhesions and cancer metastasis, contains a novel noncanonical pleckstrin homology domain

Directional migration of adherent cells on an extracellular matrix requires repeated formation and disassembly of focal adhesions (FAs). Directional migration of adherent cells We have identified ZF21 as a regulator of disassembly of FAs and cell migration, and increased expression of the gene has been linked to metastatic colon cancer. ZF21 is a member of a protein family characterized by the presence of the FYVE domain, which is conserved among Fab1p, YOPB, Vps27p, and EEA1 proteins, and has been shown to mediate the binding of such proteins to phosphoinositides in the lipid layers of cell membranes. ZF21 binds multiple factors that promote disassembly of FAs such as FAK, β-tubulin, m-calpain, and SHP-2. ZF21 does not contain any other known protein motifs other than the FYVE domain, but a region of the protein C-terminal to the FYVE domain is sufficient to mediate binding to β-tubulin. In this study, we demonstrate that the C-terminal region is important for the ability of ZF21 to induce disassembly of FAs and cell migration, and to promote an early step of experimental metastasis to the lung in mice. In light of the importance of the C-terminal region, we analyzed its ternary structure using NMR spectroscopy. We demonstrate that this region exhibits a structure similar to that of a canonical pleckstrin homology domain, but that it lacks a positively charged interface to bind phosphatidylinositol phosphate. Thus, ZF21 contains a novel noncanonical PH-like domain that is a possible target to develop a therapeutic strategy to treat metastatic cancer.

Siva1 suppresses epithelial-mesenchymal transition and metastasis of tumor cells by inhibiting stathmin and stabilizing microtubules

Epithelial-mesenchymal transition (EMT) enables epithelial cells to acquire motility and invasiveness that are characteristic of mesenchymal cells. It plays an important role in development and tumor cell metastasis. However, the mechanisms of EMT and their dysfunction in cancer cells are still not well understood. Here we report that Siva1 interacts with stathmin, a microtubule destabilizer. Siva1 inhibits stathmin's activity directly as well as indirectly through Ca(2+)/calmodulin-dependent protein kinase II-mediated phosphorylation of stathmin at Ser16. Via the inhibition of stathmin, Siva1 enhances the formation of microtubules and impedes focal adhesion assembly, cell migration, and EMT. Low levels of Siva1 and Ser16-phosphorylated stathmin correlate with high metastatic states of human breast cancer cells. In mouse models, knockdown of Siva1 promotes cancer dissemination, whereas overexpression of Siva1 inhibits it. These results suggest that microtubule dynamics are critical for EMT. Furthermore, they reveal an important role for Siva1 in suppressing cell migration and EMT and indicate that down-regulation of Siva1 may contribute to tumor cell metastasis.

Kinesins and protein kinases: key players in the regulation of microtubule dynamics and organization

Microtubule dynamics is controlled and amplified in vivo by complex sets of regulators. Among these regulatory proteins, molecular motors from the kinesin superfamily are taking an increasing importance. Here we review how microtubule disassembly or assembly into interphase microtubules, mitotic spindle or cilia may involve kinesins and how protein kinases may participate in these kinesin-dependent regulations.

Filamin depletion blocks endoplasmic spreading and destabilizes force-bearing adhesions

Cells severely depleted of filamins were observed to have numerous motility-related defects, including a defect in endoplasmic spreading; smaller, more dynamic focal adhesions; and an inability to sustain high levels of traction force. The endoplasm as a separate mechanical unit spread by pulling forces is also discussed.

Cell motility is an essential process that depends on a coherent, cross-linked actin cytoskeleton that physically coordinates the actions of numerous structural and signaling molecules. The actin cross-linking protein, filamin (Fln), has been implicated in the support of three-dimensional cortical actin networks capable of both maintaining cellular integrity and withstanding large forces. Although numerous studies have examined cells lacking one of the multiple Fln isoforms, compensatory mechanisms can mask novel phenotypes only observable by further Fln depletion. Indeed, shRNA-mediated knockdown of FlnA in FlnB^–/– mouse embryonic fibroblasts (MEFs) causes a novel endoplasmic spreading deficiency as detected by endoplasmic reticulum markers. Microtubule (MT) extension rates are also decreased but not by peripheral actin flow, because this is also decreased in the Fln-depleted system. Additionally, Fln-depleted MEFs exhibit decreased adhesion stability that appears in increased ruffling of the cell edge, reduced adhesion size, transient traction forces, and decreased stress fibers. FlnA^–/– MEFs, but not FlnB^–/– MEFs, also show a moderate defect in endoplasm spreading, characterized by initial extension followed by abrupt retractions and stress fiber fracture. FlnA localizes to actin linkages surrounding the endoplasm, adhesions, and stress fibers. Thus we suggest that Flns have a major role in the maintenance of actin-based mechanical linkages that enable endoplasmic spreading and MT extension as well as sustained traction forces and mature focal adhesions.

ZF21 is a new regulator of focal adhesion disassembly and a potential member of the spreading initiation center

Adherent cells migrate on extracellular matrices (ECM) by repeated spreading and contraction of the cell body. Focal adhesions (FAs) play a major role in the adherence of cells to the ECM and in the generation of the cellular forces that maintain morphology and allow cells to move. FAs also mediate bidirectional transmembrane signals in conjunction with growth factor receptors and signaling molecules. Although the mechanisms that regulate cell migration are not yet fully understood, the regulation of the formation and turnover of FAs is a key factor determining the rate and direction of cell migration. We recently identified a component of FAs termed ZF21, which is a member of a family of proteins characterized by the presence of a conserved phosphoinositide-binding motif. ZF21 promotes dephosphorylation of FAK at Tyr ( 397) upon microtubule extension to FAs and thereby regulates the disassembly of FAs in a microtubules-dependent manner. To obtain further insight into the regulation of cell adhesion by ZF21, we analyzed proteins associating with ZF21 by proteomic analysis. We identified 45 proteins including FA-related proteins and multiple RNA binding proteins that have been shown recently to be components of the spreading initiation center (SIC). SICs are cell adherent structures that can be observed only in the early stages of cell spreading and have been implicated in regulating the rate of cell spreading. In this article, we report new ZF21-binding proteins identified by proteomic analysis and discuss the potential functions of ZF21 in regulating disassembly of FAs.

Local anesthetics inhibit kinesin motility and microtentacle protrusions in human epithelial and breast tumor cells

Detached breast tumor cells produce dynamic microtubule protrusions that promote reattachment of cells and are termed tubulin microtentacles (McTNs) due to their mechanistic distinctions from actin-based filopodia/invadopodia and tubulin-based cilia. McTNs are enriched with vimentin and detyrosinated α-tubulin, (Glu-tubulin). Evidence suggests that vimentin and Glu-tubulin are cross-linked by kinesin motor proteins. Using known kinesin inhibitors, Lidocaine and Tetracaine, the roles of kinesins in McTN formation and function were tested. Live-cell McTN counts, adhesion assays, immunofluorescence, and video microscopy were performed to visualize inhibitor effects on McTNs. Viability and apoptosis assays were used to confirm the non-toxicity of the inhibitors. Treatments of human non-tumorigenic mammary epithelial and breast tumor cells with Lidocaine or Tetracaine caused rapid collapse of vimentin filaments. Live-cell video microscopy demonstrated that Tetracaine reduces motility of intracellular GFP-kinesin and causes centripetal collapse of McTNs. Treatment with Tetracaine inhibited the extension of McTNs and their ability to promote tumor cell aggregation and reattachment. Lidocaine showed similar effects but to a lesser degree. Our current data support a model in which the inhibition of kinesin motor proteins by Tetracaine leads to the reductions in McTNs, and provides a novel mechanism for the ability of this anesthetic to decrease metastatic progression.

Kinectin-mediated endoplasmic reticulum dynamics supports focal adhesion growth in the cellular lamella

Focal adhesions (FAs) control cell shape and motility, which are important processes that underlie a wide range of physiological functions. FA dynamics is regulated by cytoskeleton, motor proteins and small GTPases. Kinectin is an integral endoplasmic reticulum (ER) membrane protein that extends the ER along microtubules. Here, we investigated the influence of the ER on FA dynamics within the cellular lamella by disrupting the kinectin-kinesin interaction by overexpressing the minimal kinectin-kinesin interaction domain on kinectin in cells. This perturbation resulted in a morphological change to a rounded cell shape and reduced cell spreading and migration. Immunofluorescence and live-cell imaging demonstrated a kinectin-dependent ER extension into the cellular lamella and ER colocalisation with FAs within the cellular lamella. FRAP experiments showed that ER contact with FAs was accompanied with an increase in FA protein recruitment to FAs. Disruption of the kinectin-kinesin interaction caused a reduction in FA protein recruitment to FAs. This suggests that the ER supports FA growth within the cellular lamella. Microtubule targeting to FAs is known to promote adhesion disassembly; however, ER contact increased FA size even in the presence of microtubules. Our results suggest a scenario whereby kinectin-kinesin interaction facilitates ER transport along microtubules to support FA growth.

Mechanical integration of actin and adhesion dynamics in cell migration

Directed cell migration is a physical process that requires dramatic changes in cell shape and adhesion to the extracellular matrix. For efficient movement, these processes must be spatiotemporally coordinated. To a large degree, the morphological changes and physical forces that occur during migration are generated by a dynamic filamentous actin (F-actin) cytoskeleton. Adhesion is regulated by dynamic assemblies of structural and signaling proteins that couple the F-actin cytoskeleton to the extracellular matrix. Here, we review current knowledge of the dynamic organization of the F-actin cytoskeleton in cell migration and the regulation of focal adhesion assembly and disassembly with an emphasis on how mechanical and biochemical signaling between these two systems regulate the coordination of physical processes in cell migration.

Methods for expressing and analyzing GFP-tubulin and GFP-microtubule-associated proteins

Important advances in our understanding of the organization and dynamics of the cytoskeleton have been made by direct observations of fluorescently tagged cytoskeletal proteins in living cells. In early experiments, the cytoskeletal protein of interest was purified, covalently modified with a fluorescent dye, and microinjected into living cells. In the mid-1990s, a powerful new technology arose: Researchers developed methods for expressing chimeric proteins consisting of the gene of interest fused to green fluorescent protein (GFP). This approach has become a standard method for characterizing protein localization and dynamics. More recently, a profusion of "XFP" (spectral variants of GFP) has been developed, allowing researchers straightforwardly to perform experiments ranging from simultaneous co-observation of protein dynamics to fluorescence recovery after photobleaching (FRAP), fluorescence resonance energy transfer (FRET), and subresolution techniques such as stimulated emission-depletion microscopy (STED) and photoactivated localization microscopy (PALM). In this article, the methods used to express and analyze GFP- and/or XFP-tagged tubulin and microtubule-associated proteins (MAPs) are discussed. Although some details may be system-specific, the methods and considerations outlined here can be adapted to a wide variety of proteins and organisms.

Mechanotransduction by endothelial cells is locally generated, direction-dependent, and ligand-specific

Vascular endothelial cells display a wide panel of responses to changes in the shear stress that is exerted on them by blood flow. How sensory mechanisms convey information about flow conditions and how this information is integrated remains poorly understood. The issue is confounded by: (1) a large number of potential force sensors, (2) difficulties in differentiating these sensors from downstream sites of signal integration, and (3) the complexities inherent in understanding how forces are transmitted from the apical surface of the cell via the cytoskeleton to intracellular sites. As a consequence, neither the structures that sense force nor the nature of the forces that loads them have been clearly defined. In this study, we employed magnetic microspheres coated with ligands that bind integrin subsets (RGD peptides or type I collagen) or PECAM-1 to discriminate the downstream signaling effects of different sensor molecules and mechanisms for how they are loaded. We found that application of force to these transmembrane molecules elicited biologically important signaling (ERK1/2, AKT, and GSK-3beta phosphorylation), and downstream biological responses that depended on the following two factors: (1) the ligand that transmitted force and (2) the direction in which force was applied. These findings indicate that ligands locally generate different shear-induced responses in endothelium that depend on how force is delivered.