Actin and microtubules in cell motility: which one is in control?

The WAVE Regulatory Complex Is Required to Balance Protrusion and Adhesion in Migration

Cells migrating over 2D substrates are required to polymerise actin at the leading edge to form lamellipodia protrusions and nascent adhesions to anchor the protrusion to the substrate. The major actin nucleator in lamellipodia formation is the Arp2/3 complex, which is activated by the WAVE regulatory complex (WRC). Using inducible Nckap1 floxed mouse embryonic fibroblasts (MEFs), we confirm that the WRC is required for lamellipodia formation, and importantly, for generating the retrograde flow of actin from the leading cell edge. The loss of NCKAP1 also affects cell spreading and focal adhesion dynamics. In the absence of lamellipodium, cells can become elongated and move with a single thin pseudopod, which appears devoid of N-WASP. This phenotype was more prevalent on collagen than fibronectin, where we observed an increase in migratory speed. Thus, 2D cell migration on collagen is less dependent on branched actin.

Dynamic and asymmetric fluctuations in the microtubule wall captured by high-resolution cryoelectron microscopy

Microtubules are tubular polymers with essential roles in numerous cellular activities. Structures of microtubules have been captured at increasing resolution by cryo-EM. However, dynamic properties of the microtubule are key to its function, and this behavior has proved difficult to characterize at a structural level due to limitations in existing structure determination methods. We developed a high-resolution cryo-EM refinement method that divides an imaged microtubule into its constituent protofilaments, enabling deviations from helicity and other sources of heterogeneity to be quantified and corrected for at the single-subunit level. We demonstrate that this method improves the resolution of microtubule 3D reconstructions and substantially reduces anisotropic blurring artifacts, compared with methods that utilize helical symmetry averaging. Moreover, we identified an unexpected, discrete behavior of the m-loop, which mediates lateral interactions between neighboring protofilaments and acts as a flexible hinge between them. The hinge angle adopts preferred values corresponding to distinct conformations of the m-loop that are incompatible with helical symmetry. These hinge angles fluctuate in a stochastic manner, and perfectly cylindrical microtubule conformations are thus energetically and entropically penalized. The hinge angle can diverge further from helical symmetry at the microtubule seam, generating a subpopulation of highly distorted microtubules. However, the seam-distorted subpopulation disappears in the presence of Taxol, a microtubule stabilizing agent. These observations provide clues into the structural origins of microtubule flexibility and dynamics and highlight the role of structural polymorphism in defining microtubule behavior.

Mitochondrial ROS accumulation inhibiting JAK2/STAT3 pathway is a critical modulator of CYT997-induced autophagy and apoptosis in gastric cancer

Background

Gastric cancer (GC) is a common form of malignant cancer in worldwide which has a poor prognosis. Despite recent improvements in the treatment of GC, the prognosis is not yet satisfactory for GC patients. CYT997, a novel microtubule-targeting agent, recently has been identified to be a promising anticancer candidate for the treatment of cancers; however, the effects of CYT997 in GC remain largely unknown.

Methods

Cell proliferation and apoptosis were detected by CCK8 assay and flow cytometry. The mitochondrial ROS were detected by confocal microscope and flow cytometry. Gastric cancer patient-derived xenograft (PDX) model was used to evaluate its antitumor activity of CYT997 in vivo.

Results

CYT997 inhibited gastric cancer cell proliferation and induced cell apoptosis and triggered autophagy. CYT997 induced apoptosis through triggering intracellular mitochondrial ROS generation in GC cells. ROS scavengers N-acetylcysteine (NAC) and Mitoquinone (MitoQ) distinctly weakened CYT997-induced cell cycle G2/M arrest and apoptosis in GC cells. Pretreatment with autophagy inhibitor 3-MA promoted the effect of CYT997 on cells apoptosis. Mechanistically, CYT997 performed its function through regulation of Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in GC cells. In addition, CYT997 inhibited growth of gastric cancer patient-derived xenograft (PDX) tumors.

Conclusions

CYT997 induces autophagy and apoptosis in gastric cancer by triggering mitochondrial ROS accumulation to silence JAK2/STAT3 pathway. CYT997 might be a potential antitumor drug candidate to treat GC.

What makes leader cells arise: Intrinsic properties and support from neighboring cells

Cancer cells collectively invading as a cohesive and polarized group is termed collective invasion, which is a fundamental property of many types of cancers. In this multicellular unit, cancer cells are heterogeneous, consisting of two morphologically and functionally distinct subpopulations, leader cells and follower cells. Leader cells at the invasive front are responsible for exploring the microenvironment, paving the way, and transmitting information to follower cells. Here, in this review, we will describe the important role of leader cells in collective invasion and the emerging underlying mechanisms of leader cell formation including intrinsic properties and the support from neighboring cells. It will help us to elucidate the essence of collective invasion and provide new anticancer therapeutic clues.

Paclitaxel Reduces Brain Injury from Repeated Head Trauma in Mice

Repetitive mild traumatic brain injury (rmTBI) is known to disturb axonal integrity and may play an important role in the pathogenic cascades leading to neurodegeneration. One critical approach to reduce the future onset of neurodegeneration is to intervene in this process at an early stage following a brain injury. Previously we showed that direct application of the microtubule-stabilizing drug, paclitaxel, on the brain following controlled cortical impact improved motor function and reduced lesion size. Herein, we extended these findings to a model of mild brain injury induced by repeated closed-skull impacts. Paclitaxel was administered intranasally to circumvent its poor transport across the blood-brain barrier. Mice received five mild closed-skull impacts (one per day for five days). Intranasal paclitaxel was administered once only, immediately after the first impact. We found that paclitaxel prevented injury-induced deficits in a spatial memory task in a water tread maze. In vivo magnetic resonance imaging (MRI) and positron emission tomography with 18F-flurodeoxyglucose (FDG-PET) revealed that paclitaxel prevented structural injury and hypometabolism. On MRI, apparent, injury-induced microbleeds were observed in 100% of vehicle-treated rmTBI mice, but not in paclitaxel-treated subjects. FDG-PET revealed a 42% increase in whole brain glucose metabolism in paclitaxel-treated mice as compared to vehicle-treated rmTBI. Immunohistochemistry found reduced evidence of axonal injury and synaptic loss. Our results indicate that intranasal paclitaxel administration imparts neuroprotection against brain injury and cognitive impairment in mice. The results from this study support the idea that microtubule-stabilization strategies hold therapeutic promise in mitigating traumatic brain injury.

Differential dynamics of early stages of platelet adhesion and spreading on collagen IV- and fibrinogen-coated surfaces

Background: Upon wound formation, platelets adhere to the neighboring extracellular matrix and spread on it, a process which is critical for physiological wound healing. Multiple external factors, such as the molecular composition of the environment and its mechanical properties, play a key role in this process and direct its speed and outcome. Methods: We combined live cell imaging, quantitative interference reflection microscopy and cryo-electron tomography to characterize, at a single platelet level, the differential spatiotemporal dynamics of the adhesion process to fibrinogen- and collagen IV-functionalized surfaces. Results: Initially, platelets sense both substrates by transient rapid extensions of filopodia. On collagen IV, a short-term phase of filopodial extension is followed by lamellipodia-based spreading. This transition is preceded by the extension of a single or couple of microtubules into the platelet's periphery and their apparent insertion into the core of the filopodia. On fibrinogen surfaces, the filopodia-to-lamellipodia transition was partial and microtubule extension was not observed leading to limited spreading, which could be restored by manganese or thrombin. Conclusions: Based on these results, we propose that interaction with collagen IV stimulate platelets to extend microtubules to peripheral filopodia, which in turn, enhances filopodial-to-lamellipodial transition and overall lamellipodia-based spreading. Fibrinogen, on the other hand, fails to induce these early microtubule extensions, leading to full lamellipodia spreading in only a fraction of the seeded platelets. We further suggest that activation of integrin αIIbβ3 is essential for filopodial-to-lamellipodial transition, based on the capacity of integrin activators to enhance lamellipodia spreading on fibrinogen.

TUBB Variants Underlying Different Phenotypes Result in Altered Vesicle Trafficking and Microtubule Dynamics

Tubulinopathies are rare neurological disorders caused by alterations in tubulin structure and function, giving rise to a wide range of brain abnormalities involving neuronal proliferation, migration, differentiation and axon guidance. TUBB is one of the ten β-tubulin encoding genes present in the human genome and is broadly expressed in the developing central nervous system and the skin. Mutations in TUBB are responsible for two distinct pathological conditions: the first is characterized by microcephaly and complex structural brain malformations and the second, also known as “circumferential skin creases Kunze type” (CSC-KT), is associated to neurological features, excess skin folding and growth retardation. We used a combination of immunocytochemical and cellular approaches to explore, on patients’ derived fibroblasts, the functional consequences of two TUBB variants: the novel mutation (p.N52S), associated with basal ganglia and cerebellar dysgenesis, and the previously reported variant (p.M73T), linked to microcephaly, corpus callosum agenesis and CSC-KT skin phenotype. Our results demonstrate that these variants impair microtubule (MT) function and dynamics. Most importantly, our studies show an altered epidermal growth factor (EGF) and transferrin (Tf) intracellular vesicle trafficking in both patients’ fibroblasts, suggesting a specific role of TUBB in MT-dependent vesicular transport.

Golgi-associated microtubules are fast cargo tracks and required for persistent cell migration

Microtubules derived from the Golgi (Golgi MTs) have been implicated to play critical roles in persistent cell migration, but the underlying mechanisms remain elusive, partially due to the lack of direct observation of Golgi MT-dependent vesicular trafficking. Here, using super-resolution stochastic optical reconstruction microscopy (STORM), we discovered that post-Golgi cargos are more enriched on Golgi MTs and also surprisingly move much faster than on non-Golgi MTs. We found that, compared to non-Golgi MTs, Golgi MTs are morphologically more polarized toward the cell leading edge with significantly fewer inter-MT intersections. In addition, Golgi MTs are more stable and contain fewer lattice repair sites than non-Golgi MTs. Our STORM/live-cell imaging demonstrates that cargos frequently pause at the sites of both MT intersections and MT defects. Furthermore, by optogenetic maneuvering of cell direction, we demonstrate that Golgi MTs are essential for persistent cell migration but not for cells to change direction. Together, our study unveils the role of Golgi MTs in serving as a group of "fast tracks" for anterograde trafficking of post-Golgi cargos.

Effect of tetracycline family of antibiotics on actin aggregation, resulting in the formation of Hirano bodies responsible for neuropathological disorders

Actin, an ATPase superfamily protein, regulates some vital biological functions like cell locomotion, cytokinesis, synaptic plasticity and cell signaling in higher eukaryotes, and is dependent on the dynamics of actin polymerization process. Impaired regulation of actin polymerization has been implicated in the formation and deposition of rod-like paracrystalline structures called as Hirano bodies in neuronal cells of patients suffering from Alzheimer's disease, Pick's disease, Guam amyotrophic lateral sclerosis and parkinsonism-dementia complex. Aggregation of actin forming amorphous deposition in the brain cells is also associated with chronic alcoholism and aging of the neurons. In the current article, we propose the breaking of the highly amorphous and dysregulated actin aggregates using generic compounds like tetracycline, oxytetracycline, doxycycline and minocycline which are used as antibiotics against tuberculosis and infection caused due to various Gram-negative bacteria. We have investigated the effect and affinity of binding of these four compounds to that of actin aggregates using 90° light scattering, size exclusion chromatography, dynamic light scattering, circular dichroism, scanning electron microscopy, transmission electron microscopy imaging and kinetic analysis. The isothermal calorimetric measurements showed that the binding constant for the cycline family molecules used in this study range from 9.8 E4 M^-1 to 1.3 E4 M^-1. To understand the in vivo effect, we also studied the effect of these drugs on Saccharomyces cerevisiae Δend3 mutant cells. Our data suggest that these generic compounds can plausibly be used for the treatment of various neurodegenerative diseases occurring due to Hirano body formation in brain cells.Communicated by Ramaswamy H. Sarma.

ARHGAP18: A Flow-Responsive Gene That Regulates Endothelial Cell Alignment and Protects Against Atherosclerosis

Background

Vascular endothelial cell (EC) alignment in the direction of flow is an adaptive response that protects against aortic diseases, such as atherosclerosis. The Rho GTPases are known to regulate this alignment. Herein, we analyze the effect of ARHGAP18 on the regulation of EC alignment and examine the effect of ARHGAP18 deficiency on the development of atherosclerosis in mice.

Methods and Results

We used in vitro analysis of ECs under flow conditions together with apolipoprotein E^−/−Arhgap18^−/− double‐mutant mice to study the function of ARHGAP18 in a high‐fat diet–induced model of atherosclerosis. Depletion of ARHGAP18 inhibited the alignment of ECs in the direction of flow and promoted inflammatory phenotype, as evidenced by disrupted junctions and increased expression of nuclear factor‐κB and intercellular adhesion molecule‐1 and decreased endothelial nitric oxide synthase. Mice with double deletion in ARHGAP18 and apolipoprotein E and fed a high‐fat diet show early onset of atherosclerosis, with lesions developing in atheroprotective regions.

Conclusions

ARHGAP18 is a protective gene that maintains EC alignments in the direction of flow. Deletion of ARHGAP18 led to loss of EC ability to align and promoted atherosclerosis development.

MoRBP9 Encoding a Ran-Binding Protein Microtubule-Organizing Center Is Required for Asexual Reproduction and Infection in the Rice Blast Pathogen Magnaporthe oryzae

Like many fungal pathogens, the conidium and appressorium play key roles during polycyclic dissemination and infection of Magnaporthe oryzae. Ran-binding protein microtubule-organizing center (RanBPM) is a highly conserved nucleocytoplasmic protein. In animalia, RanBPM has been implicated in apoptosis, cell morphology, and transcription. However, the functional roles of RanBPM, encoded by MGG_00753 (named MoRBP9) in M. oryzae, have not been elucidated. Here, the deletion mutant ΔMorbp9 for MoRBP9 was generated via homologous recombination to investigate the functions of this gene. The ΔMorbp9 exhibited normal conidial germination and vegetative growth but dramatically reduced conidiation compared with the wild type, suggesting that MoRBP9 is involved in conidial production. ΔMorbp9 conidia failed to produce appressoria on hydrophobic surfaces, whereas ΔMorbp9 still developed aberrantly shaped appressorium-like structures at hyphal tips on the same surface, suggesting that MoRBP9 is involved in the morphology of appressorium-like structures from hyphal tips and is critical for development of appressorium from germ tubes. Taken together, our results indicated that MoRBP9 played a pleiotropic role in polycyclic dissemination and infection-related morphogenesis of M. oryzae.

Microtubule and Actin Differentially Regulate Synaptic Vesicle Cycling to Maintain High-Frequency Neurotransmission

Cytoskeletal filaments such as microtubules (MTs) and filamentous actin (F-actin) dynamically support cell structure and functions. In central presynaptic terminals, F-actin is expressed along the release edge and reportedly plays diverse functional roles, but whether axonal MTs extend deep into terminals and play any physiological role remains controversial.

Cytoskeletal filaments such as microtubules (MTs) and filamentous actin (F-actin) dynamically support cell structure and functions. In central presynaptic terminals, F-actin is expressed along the release edge and reportedly plays diverse functional roles, but whether axonal MTs extend deep into terminals and play any physiological role remains controversial. At the calyx of Held in rats of either sex, confocal and high-resolution microscopy revealed that MTs enter deep into presynaptic terminal swellings and partially colocalize with a subset of synaptic vesicles (SVs). Electrophysiological analysis demonstrated that depolymerization of MTs specifically prolonged the slow-recovery time component of EPSCs from short-term depression induced by a train of high-frequency stimulation, whereas depolymerization of F-actin specifically prolonged the fast-recovery component. In simultaneous presynaptic and postsynaptic action potential recordings, depolymerization of MTs or F-actin significantly impaired the fidelity of high-frequency neurotransmission. We conclude that MTs and F-actin differentially contribute to slow and fast SV replenishment, thereby maintaining high-frequency neurotransmission.

SIGNIFICANCE STATEMENT The presence and functional role of MTs in the presynaptic terminal are controversial. Here, we demonstrate that MTs are present near SVs in calyceal presynaptic terminals and that MT depolymerization specifically prolongs the slow-recovery component of EPSCs from short-term depression. In contrast, F-actin depolymerization specifically prolongs fast-recovery component. Depolymerization of MT or F-actin has no direct effect on SV exocytosis/endocytosis or basal transmission, but significantly impairs the fidelity of high-frequency transmission, suggesting that presynaptic cytoskeletal filaments play essential roles in SV replenishment for the maintenance of high-frequency neurotransmission.

Generation and regulation of microtubule network asymmetry to drive cell polarity

Microtubules control cell architecture by serving as a scaffold for intracellular transport, signaling, and organelle positioning. Microtubules are intrinsically polarized, and their orientation, density, and post-translational modifications both respond and contribute to cell polarity. Animal cells that can rapidly reorient their polarity axis, such as fibroblasts, immune cells, and cancer cells, contain radially organized microtubule arrays anchored at the centrosome and the Golgi apparatus, whereas stably polarized cells often acquire non-centrosomal microtubule networks attached to the cell cortex, nucleus, or other structures. Microtubule density, longevity, and post-translational modifications strongly depend on the dynamics of their plus ends. Factors controlling microtubule plus-end dynamics are often part of cortical assemblies that integrate cytoskeletal organization, cell adhesion, and secretion and are subject to microtubule-dependent feedback regulation. Finally, microtubules can mechanically contribute to cell asymmetry by promoting cell elongation, a property that might be important for cells with dense microtubule arrays growing in soft environments.

Interaction of microtubules and actin during the post-fusion phase of exocytosis

Exocytosis is the intracellular trafficking step where a secretory vesicle fuses with the plasma membrane to release vesicle content. Actin and microtubules both play a role in exocytosis; however, their interplay is not understood. Here we study the interaction of actin and microtubules during exocytosis in lung alveolar type II (ATII) cells that secrete surfactant from large secretory vesicles. Surfactant extrusion is facilitated by an actin coat that forms on the vesicle shortly after fusion pore opening. Actin coat compression allows hydrophobic surfactant to be released from the vesicle. We show that microtubules are localized close to actin coats and stay close to the coats during their compression. Inhibition of microtubule polymerization by colchicine and nocodazole affected the kinetics of actin coat formation and the extent of actin polymerisation on fused vesicles. In addition, microtubule and actin cross-linking protein IQGAP1 localized to fused secretory vesicles and IQGAP1 silencing influenced actin polymerisation after vesicle fusion. This study demonstrates that microtubules can influence actin coat formation and actin polymerization on secretory vesicles during exocytosis.

Spatiotemporal characterization of dynamic epithelial filopodia during zebrafish epiboly

BACKGROUND

During zebrafish epiboly, the embryonic cell mass, or blastoderm, spreads to enclose the yolk cell. The blastoderm consists of an outer epithelial sheet, the enveloping layer (EVL), and the underlying deep cell layer (DEL). Studies have provided insights into the mechanisms of EVL and deep cell epiboly, but little is known about the interactions between the two cell layers and what role they may play during epiboly.

RESULTS

We used live imaging to examine EVL basal protrusions. We identified them as filopodia based on f-actin content and localization of fluorescently tagged filopodial markers. A spatiotemporal analysis revealed that the largest number of EVL filopodia were present during early epiboly at the animal pole. In functional studies, expression of a constitutively active actin-bundling protein resulted in increased filopodial length and delayed gastrulation.

CONCLUSIONS

We identified protrusions on the basal surface of EVL cells as filopodia and showed that they are present throughout the EVL during epiboly. The largest number of filopodia was at the animal pole during early epiboly, which is when and where deep cell radial intercalations occur to the greatest extent. These findings suggest that EVL filopodia may function during epiboly to promote deep cell rearrangements during epiboly initiation.

Energy-Mediated Machinery Drives Cellular Mechanical Allostasis

Allostasis is a fundamental biological process through which living organisms achieve stability via physiological or behavioral changes to protect against internal and external stresses, and ultimately better adapt to the local environment. However, an full understanding of cellular-level allostasis is far from developed. By employing an integrated micromechanical tool capable of applying controlled mechanical stress on an individual cell and simultaneously reporting dynamic information of subcellular mechanics, individual cell allostasis is observed to occur through a biphasic process; cellular mechanics tends to restore to a stable state through a mechanoadaptative process with excitative biophysical activity followed by a decaying adaptive phase. Based on these observations, it is found that cellular allostasis occurs through a complex balance of subcellular energy and cellular mechanics; upon a transient and local physical stimulation, cells trigger an allostatic state that maximizes energy and overcomes a mechanical "energy barrier" followed by a relaxation state that reaches its mechanobiological stabilization and energy minimization. Discoveries of energy-driven cellular machinery and conserved mechanotransductive pathways underscore the critical role of force-sensitive cytoskeleton equilibrium in cellular allostasis. This highlight the biophysical origin of cellular mechanical allostasis, providing subcellular methods to understand the etiology and progression of certain diseases or aging.

Molecular Mechanisms of Microglial Motility: Changes in Ageing and Alzheimer's Disease

Microglia are the tissue-resident immune cells of the central nervous system, where they constitute the first line of defense against any pathogens or injury. Microglia are highly motile cells and in order to carry out their function, they constantly undergo changes in their morphology to adapt to their environment. The microglial motility and morphological versatility are the result of a complex molecular machinery, mainly composed of mechanisms of organization of the actin cytoskeleton, coupled with a “sensory” system of membrane receptors that allow the cells to perceive changes in their microenvironment and modulate their responses. Evidence points to microglia as accountable for some of the changes observed in the brain during ageing, and microglia have a role in the development of neurodegenerative diseases, such as Alzheimer’s disease. The present review describes in detail the main mechanisms driving microglial motility in physiological conditions, namely, the cytoskeletal actin dynamics, with emphasis in proteins highly expressed in microglia, and the role of chemotactic membrane proteins, such as the fractalkine and purinergic receptors. The review further delves into the changes occurring to the involved proteins and pathways specifically during ageing and in Alzheimer’s disease, analyzing how these changes might participate in the development of this disease.

What makes cells move: Requirements and obstacles for leader cells in collective invasion

Most recently, mounting evidence has shown that cancer cells can invade as a cohesive and multicellular group with coordinated movement, which is called collective invasion. In this cohesive cancer cell group, cancer cells at the front of collective invasion are defined as leader cell that are responsible for many aspects of collective invasion, including sensing the microenvironment, determining the invasion direction, modifying the path of invasion and transmitting information to other cells. To fulfill their dispensable roles, leader cells are required to embark on some specific phenotypes with unusual expression of some proteins and it's very important to investigate into these proteins as they may serve as potential therapeutic targets. Here, in this review we will summarize current knowledge on four emerging proteins highly expressed in leader cells including K14, ΔNp63α, Dll4 and cysteine protease cathepsin B (CTSB), with a focus on their important roles in collective invasion and special mechanisms by which they promote collective invasion.

Live-cell Migration Assays to Study Motility of Neural andGlial (Oligodendrocyte) Progenitor Cells

Cell motility has been extensively studied in in vitro models using fibroblasts and keratocytes, but the cell type-specific mechanisms underlying migration of lineage- or disease-specific cells, such as neural and glial progenitor cells, remain an active field for investigation. The migrating neural and glial progenitor cells contribute to the development, tissue repair and tumor invasion in the central nervous system (CNS). Cell migration is a highly dynamic process which relies on membranous protrusions to assemble, extend, disassemble and retract. In the CNS, the motility of neural and glial progenitor cells is affected by various cell-autonomous and non-cell-autonomous mechanisms such as signaling molecules, actin and microtubule interactions, and environmental cues. Here, we described a live-cell migration assay for use in the assessment of neural and glial progenitor cell migration. We first will demonstrate the procedures for isolating and culturing neural and glial progenitor cells. Next, we will demonstrate the acquisition of time-lapse images using phase contrast microscopy, the methods for quantification and the analyses of various motility parameters including speed, velocity, straightness and leading-edge dynamics. This method allows researchers to dissect the mechanisms of cell motility in response to different environmental cues, such as chemoattractive and repulsive signals, matrix adhesiveness and stiffness. This assay also allows researchers to study migration of pharmacologically and genetically manipulated cells.

A Direct Podocalyxin-Dynamin-2 Interaction Regulates Cytoskeletal Dynamics to Promote Migration and Metastasis in Pancreatic Cancer Cells

The sialoglycoprotein podocalyxin is absent in normal pancreas but is overexpressed in pancreatic cancer and is associated with poor clinical outcome. Here, we investigate the role of podocalyxin in migration and metastasis of pancreatic adenocarcinomas using SW1990 and Pa03c as cell models. Although ezrin is regarded as a cytoplasmic binding partner of podocalyxin that regulates actin polymerization via Rac1 or RhoA, we did not detect podocalyxin-ezrin association in pancreatic cancer cells. Moreover, depletion of podocalyxin did not alter actin dynamics or modulate Rac1 and RhoA activities in pancreatic cancer cells. Using mass spectrometry, bioinformatics analysis, coimmunoprecipitation, and pull-down assays, we discovered a novel, direct binding interaction between the cytoplasmic tail of podocalyxin and the large GTPase dynamin-2 at its GTPase, middle, and pleckstrin homology domains. This podocalyxin-dynamin-2 interaction regulated microtubule growth rate, which in turn modulated focal adhesion dynamics and ultimately promoted efficient pancreatic cancer cell migration via microtubule- and Src-dependent pathways. Depletion of podocalyxin in a hemispleen mouse model of pancreatic cancer diminished liver metastasis without altering primary tumor size. Collectively, these findings reveal a novel mechanism by which podocalyxin facilitates pancreatic cancer cell migration and metastasis. SIGNIFICANCE: These findings reveal that a novel interaction between podocalyxin and dynamin-2 promotes migration and metastasis of pancreatic cancer cells by regulating microtubule and focal adhesion dynamics.

Microtubule acetylation but not detyrosination promotes focal adhesion dynamics and astrocyte migration

Microtubules play a crucial role in mesenchymal migration by controlling cell polarity and the turnover of cell adhesive structures on the extracellular matrix. The polarized functions of microtubules imply that microtubules are locally regulated. Here, we investigated the regulation and role of two major tubulin post-translational modifications, acetylation and detyrosination, which have been associated with stable microtubules. Using primary astrocytes in a wound healing assay, we show that these tubulin modifications are independently regulated during cell polarization and differently affect cell migration. In contrast to microtubule detyrosination, αTAT1 (ATAT1)-mediated microtubule acetylation increases in the vicinity of focal adhesions and promotes cell migration. We further demonstrate that αTAT1 increases focal adhesion turnover by promoting Rab6-positive vesicle fusion at focal adhesions. Our results highlight the specificity of microtubule post-translational modifications and bring new insight into the regulatory functions of tubulin acetylation.This article has an associated First Person interview with the first author of the paper.

Bio-Field Array: The Influence of Junction Mediating and Regulatory Protein Expression on Cytoskeletal Filament Behavior During Apoptosis in Triple-Negative Breast Cancer

Introduction:

The Bio-Field Array (BFA) is a device that generates a dielectrophoretic electromagnetic field (DEP-EMF) when placed in a hypotonic saline solution and a direct current (dc) of ~3 amperes is applied. Human triple-negative breast cancer (MDA-MB-231 cells) is known to have a high percentage of apoptotic (P53) deficient cells and some patients can have poor outcomes with current treatments.

Objectives:

Previously, we reported a strong upregulation of the apoptotic arm of the unfolded protein response, via reverse transcription–quantitative polymerase chain reaction (RT-qPCR), as well as positive annexin staining in this human breast carcinoma, when grown in media prepared with BFA’s dc DEP-EMF treated saline. Here we will examine and discuss cytoskeletal microtubule changes that were noted in the treated breast carcinoma that are strongly suggestive of apoptosis and the possible correlation of these microtubule changes to the upregulation of Junction Mediating and Regulatory Protein (JMY, a P53/TP53 cofactor) that is known to drive cytoskeleton microfilaments (actin) function.

Methods:

In addition to microarray and RT-qPCR analyses, we conducted 7 days of fluorescent microscopic analyses of tubulin assays in these treated versus control MDA-MB-231 cells.

Results:

These data suggest 2 possible forms of apoptosis, rounded and irregular, may be occurring and possibly facilitated by the significant upregulation (via microarray and RT-qPCR) of an important but poorly understood Nucleation-Promoting Factor (NPF), JMY.

Conclusions:

The ability of the BFA dc DEP-EMF to significantly upregulate JMY and possibly influence the regulation of unbranched (nucleation-microtubule spikes) and branched forms (autophagy) of actin in the cytoplasmic domains may facilitate a “two coffins” or round and irregular necrosis-like apoptosis for this highly aggressive and often apoptotic-deficient breast cancer cell line.

Chemokine-triggered microtubule polymerization promotes neutrophil chemotaxis and invasion but not transendothelial migration

Microtubules (MTs) are critically involved in the transport of material within cells, but their roles in chemotactic leukocyte motility and effector functions are still obscure. Resting neutrophils contain few MTs assembled in an MT organizing center (MTOC) behind their multilobular nuclei. Using a probe of real-time tubulin polymerization, SiR-tubulin, we found that neutrophils elongated their MTs within minutes in response to signals from the two prototypic chemotactic peptides, CXCL1 and fMLP. Taxol, a beta-tubulin binding and MT stabilizing drug, was found to abolish this CXCL1- and fMLP-stimulated MT polymerization. Nevertheless, taxol treatment as well as disruption of existing and de novo generated MTs did not impair neutrophil protrusion and squeezing through IL-1β-stimulated endothelial monolayers mediated by endothelial deposited CXCL1 and neutrophil CXCR2. Notably, CXCL1-dependent neutrophil TEM was not associated with neutrophil MT polymerization. Chemokinetic neutrophil motility on immobilized CXCL1 was also not associated with MT polymerization, and taxol treatment did not interfere with this motility. Nevertheless, and consistent with its ability to suppress MT polymerization induced by soluble CXCL1 and fMLP, taxol treatment inhibited neutrophil chemotaxis toward both chemotactic peptides. Taxol treatment also suppressed CXCL1- and fMLP-triggered elastase-dependent neutrophil invasion through collagen I barriers. Collectively, our results highlight de novo chemoattractant-triggered MT polymerization as key for neutrophil chemotaxis and elastase-dependent invasion but not for chemotactic neutrophil crossing of inflamed endothelial barriers.

An Introduction to LFA-1/ICAM-1 Interactions in T-Cell Motility

The inherent ability of T-cells to migrate is critical for a fully functional immune system, both in normal immune surveillance and for mounting an adaptive immune response. At the same time, inappropriate trafficking of T-cells can be a pathological factor for immune-mediated or chronic inflammatory diseases. T-cell motility is critically dependent on a series of ligand-receptor interactions, a precisely regulated intracellular signaling, an involvement of adaptor proteins, and dynamic remodeling of the cytoskeletal systems. The leukocyte integrin LFA-1 receptor present on T-cells binds to the ligand intercellular adhesion molecule 1 (ICAM-1) and this LFA-1/ICAM-1 contact acts as a trigger for T-cell motility. In this book, we present a collection of methods and protocols that are frequently used by researchers to better understand T-cell motility in health and diseases.

Intracellular reduction in ATP levels contributes to CYT997-induced suppression of metastasis of head and neck squamous carcinoma

The incidence rate of head and neck squamous cell carcinoma (HNSCC) has steadily increased over the past decade. However, treatment options for metastatic HNSCC are often limited and the 5‐year survival rate has remained static. Therefore, the development and assessment of more efficient but less toxic therapeutic strategies is an unmet need for treatment of more extensive HNSCC. Here, we report that CYT997, a novel microtubule‐disrupting agent, exerts strong activity in inhibiting HNSCC cell invasion and metastasis. The loss of invasion capacity by CYT997 was accompanied by an associated increase in cell adhesion and the reversal of epithelial‐mesenchymal transition (EMT). Increased expression of E‐cadherin protein and decreased expression of Vimentin protein became evident in HNSCC cells following CYT997 exposure, which were consistently observed in HNSCC xenografts from the mice receiving CYT997. Moreover, the capacity of invasive HNSCC cells to form pulmonary metastases was significantly blocked with CYT997 treatment, indicating that the diminishment of EMT traits contributes to CYT997‐suppressed metastasis. Intriguingly, CYT997 impaired intracellular ATP levels in HNSCC cells, at least in part, through its inhibitory effect on the mitochondrial protein IF1. The addition of ATP attenuated CYT997‐induced suppression of cell invasion, coupled with down‐regulation of E‐Cadherin and up‐regulation of Vimentin. These findings support a critical role of ATP levels in cell invasion and metastasis under the influence of CYT997. Collectively, our data unveil the mechanism involved in mediating CYT997 action, and provide preclinical rationale for possible clinical application of CYT997 as a novel therapeutic strategy against aggressive HNSCC.

The Role of Melanoma Cell-Stroma Interaction in Cell Motility, Invasion, and Metastasis

The importance of studying cancer cell invasion is highlighted by the fact that 90% of all cancer-related mortalities are due to metastatic disease. Melanoma metastasis is driven fundamentally by aberrant cell motility within three-dimensional or confined environments. Within this realm of cell motility, cytokines, growth factors, and their receptors are crucial for engaging signaling pathways, which both mediate crosstalk between cancer, stromal, and immune cells in addition to interactions with the surrounding microenvironment. Recently, the study of the mechanical biology of tumor cells, stromal cells and the mechanics of the microenvironment have emerged as important themes in driving invasion and metastasis. While current anti-melanoma therapies target either the MAPK signaling pathway or immune checkpoints, there are no drugs available that specifically inhibit motility and thus invasion and dissemination of melanoma cells during metastasis. One of the reasons for the lack of so-called "migrastatics" is that, despite decades of research, the precise biology of metastatic disease is still not fully understood. Metastatic disease has been traditionally lumped into a single classification, however what is now emergent is that the biology of melanoma metastasis is highly diverse, heterogeneous and exceedingly dynamic-suggesting that not all cases are created equal. The following mini-review discusses melanoma heterogeneity in the context of the emergent theme of mechanobiology and how it influences the tumor-stroma crosstalk during metastasis. Thus, highlighting future therapeutic options for migrastatics and mechanomedicines in the prevention and treatment of metastatic melanoma.

Human dermal fibroblast proliferation controlled by surface roughness of two-component nanostructured latex polymer coatings

In this study hierarchically-structured latex polymer coatings and self-supporting films were characterised and their suitability for cell growth studies was tested with Human Dermal Fibroblasts (HDF). Latex can be coated or printed on rigid or flexible substrates thus enabling high-throughput fabrication. Here, coverslip glass substrates were coated with blends of two different aqueous latex dispersions: hydrophobic polystyrene (PS) and hydrophilic carboxylated acrylonitrile butadiene styrene (ABS). The nanostructured morphology and topography of the latex films was controlled by varying the mixing ratio of the components in the latex blend. Thin latex-coatings retain high transparency on glass allowing optical and high resolution imaging of cell growth and morphology. Compared to coverslip glass surfaces and commercial well-plates HDF cell growth was enhanced up to 150-250 % on latex surfaces with specific nanostructure. Growth rates were correlated with selected roughness parameters such as effective surface area (S_q), RMS-roughness (S_dr) and correlation length (S_cl37). High-resolution confocal microscopy clearly indicated less actin stress-fibre development in cells on the latex surface compared to coverslip glass. The results show that surface nanotopography can, by itself, passively modulate HDF cell proliferation and cytoskeletal architecture.

Ethanol Enhances Estrogen Mediated Angiogenesis in Breast Cancer

Angiogenesis, a highly regulated process, is exploited by tumors like breast cancer to ensure a constant supply of oxygen and nutrients and is key for tumor survival and progression. Estrogen and alcohol independently have been observed to contribute to angiogenesis in breast cancer but their combinatorial effects have never been evaluated. The exact mechanism by which estrogen and alcohol contribute to breast cancer angiogenesis remains to be elucidated. In this study, we defined the in vitro effects of the combination of estrogen and alcohol in breast cancer angiogenesis using the tubulogenesis and scratch wound assays. Conditioned media, generated by culturing the murine mammary cancer cell line, TG1-1, in estrogen and ethanol, enhanced tubule formation and migration as well as modulated the MAP Kinase pathway in the murine endothelial cell line, SVEC4-10. Additionally, estrogen and ethanol in combination enhanced the expression of the pro-angiogenic factors VEGF, MMP-9, and eNOS, and modulated Akt activation. These observations suggest that TG1-1 cells secrete pro-angiogenic molecules in response to the combination of estrogen and ethanol that modulate the morphological and migratory properties of endothelial cells. The data presented in this study, is the first in attempting to link the cooperative activity between estrogen and ethanol in breast cancer progression, underscoring correlations first made by epidemiological observations linking the two.

Estramustine Phosphate Inhibits TGF-β-Induced Mouse Macrophage Migration and Urokinase-Type Plasminogen Activator Production

Transforming growth factor-beta (TGF-β) has been demonstrated as a key regulator of immune responses including monocyte/macrophage functions. TGF-β regulates macrophage cell migration and polarization, as well as it is shown to modulate macrophage urokinase-type plasminogen activator (uPA) production, which also contributes to macrophage chemotaxis and migration toward damaged or inflamed tissues. Microtubule (MT) cytoskeleton dynamic plays a key role during the cell motility, and any interference on the MT network profoundly affects cell migration. In this study, by using estramustine phosphate (EP), which modifies MT stability, we analysed whether tubulin cytoskeleton contributes to TGF-β-induced macrophage cell migration and uPA expression. We found out that, in the murine macrophage cell line RAW 264.7, EP at noncytotoxic concentrations inhibited cell migration and uPA expression induced by TGF-β. Moreover, EP greatly reduced the capacity of TGF-β to trigger the phosphorylation and activation of its downstream Smad3 effector. Furthermore, Smad3 activation seems to be critical for the increased cell motility. Thus, our data suggest that EP, by interfering with MT dynamics, inhibits TGF-β-induced RAW 264.7 cell migration paralleled with reduction of uPA induction, in part by disabling Smad3 activation by TGF-β.

Oncoprotein Stathmin Modulates Sensitivity to Apoptosis in Hepatocellular Carcinoma Cells During Hepatitis C Viral Replication

Patients with chronic hepatitis C virus (HCV) infection risk complications of cirrhosis, liver failure, and hepatocellular carcinoma (HCC). Previously, our proteomic examination of hepatocytes carrying a HCV-replicon revealed that deregulation of cytoskeletal dynamics may be a potential mechanism of viral-induced HCC growth. Here, we demonstrate the effect of HCV replication on the microtubule regulator stathmin (STMN1) in HCC cells. We further explore how the altered activity or synthesis of stathmin affects cellular proliferation and sensitivity to apoptosis in control HCC cells (Huh7.5) and experimental HCV-replicon harboring HCC cells (R-Huh7.5). The HCV-replicon harboring HCC cells (R-Huh 7.5) lack viral structural genes/proteins for acute infectivity and thus is the standard model for in vitro chronic infection study. Knockdown of endogenous stathmin reduced sensitivity to apoptosis in replicon cells. Meanwhile, constitutively active stathmin increased sensitivity to apoptosis in replicon cells. In addition, overexpression of constitutively active stathmin reduced cell proliferation in both control and replicon cells. These findings implicate, for the first time, a novel role for stathmin in viral replication–related apoptosis. Stathmin’s potential role in HCV replication and HCC make it a candidate for the future study of viral-induced malignancies.

SIRT2 reduces actin polymerization and cell migration through deacetylation and degradation of HSP90

SIRT2, a member of the class III histone deacetylase family, has been identified as a tumor suppressor, which is associated with various cellular processes including metabolism and proliferation. However, the effects of SIRT2 on cancer cell migration caused by cytoskeletal rearrangement remain uncertain. Here we show that SIRT2 inhibits cell motility by suppressing actin polymerization. SIRT2 regulates actin dynamics through HSP90 destabilization and subsequent repression of LIM kinase (LIMK) 1/cofilin pathway. SIRT2 directly interacts with HSP90 and regulates its acetylation and ubiquitination. In addition, the deacetylase activity of SIRT2 is required for the regulation of actin polymerization and the ubiquitin-mediated proteasomal degradation of HSP90 induced by SIRT2.

KIAA0100 Modulates Cancer Cell Aggression Behavior of MDA-MB-231 through Microtubule and Heat Shock Proteins

The KIAA0100 gene was identified in the human immature myeloid cell line cDNA library. Recent studies have shown that its expression is elevated in breast cancer and associated with more aggressive cancer types as well as poor outcomes. However, its cellular and molecular function is yet to be understood. Here we show that silencing KIAA0100 by siRNA in the breast cancer cell line MDA-MB-231 significantly reduced the cancer cells’ aggressive behavior, including cell aggregation, reattachment, cell metastasis and invasion. Most importantly, silencing the expression of KIAA0100 particularly sensitized the quiescent cancer cells in suspension culture to anoikis. Immunoprecipitation, mass spectrometry and immunofluorescence analysis revealed that KIAA0100 may play multiple roles in the cancer cells, including stabilizing microtubule structure as a microtubule binding protein, and contributing to MDA-MB-231 cells Anoikis resistance by the interaction with stress protein HSPA1A. Our study also implies that the interaction between KIAA0100 and HSPA1A may be targeted for new drug development to specifically induce anoikis cell death in the cancer cell.

Nanoparticle-Cell Interaction: A Cell Mechanics Perspective

Progress in the field of nanoparticles has enabled the rapid development of multiple products and technologies; however, some nanoparticles can pose both a threat to the environment and human health. To enable their safe implementation, a comprehensive knowledge of nanoparticles and their biological interactions is needed. In vitro and in vivo toxicity tests have been considered the gold standard to evaluate nanoparticle safety, but it is becoming necessary to understand the impact of nanosystems on cell mechanics. Here, the interaction between particles and cells, from the point of view of cell mechanics (i.e., bionanomechanics), is highlighted and put in perspective. Specifically, the ability of intracellular and extracellular nanoparticles to impair cell adhesion, cytoskeletal organization, stiffness, and migration are discussed. Furthermore, the development of cutting-edge, nanotechnology-driven tools based on the use of particles allowing the determination of cell mechanics is emphasized. These include traction force microscopy, colloidal probe atomic force microscopy, optical tweezers, magnetic manipulation, and particle tracking microrheology.

Unraveling the molecular mechanism of interactions of the Rho GTPases Cdc42 and Rac1 with the scaffolding protein IQGAP2

IQ motif-containing GTPase-activating proteins (IQGAPs) are scaffolding proteins playing central roles in cell-cell adhesion, polarity, and motility. The Rho GTPases Cdc42 and Rac1, in their GTP-bound active forms, interact with all three human IQGAPs. The IQGAP-Cdc42 interaction promotes metastasis by enhancing actin polymerization. However, despite their high sequence identity, Cdc42 and Rac1 differ in their interactions with IQGAP. Two Cdc42 molecules can bind to the Ex-domain and the RasGAP site of the GTPase-activating protein (GAP)-related domain (GRD) of IQGAP and promote IQGAP dimerization. Only one Rac1 molecule might bind to the RasGAP site of GRD and may not facilitate the dimerization, and the exact mechanism of Cdc42 and Rac1 binding to IQGAP is unclear. Using all-atom molecular dynamics simulations, site-directed mutagenesis, and Western blotting, we unraveled the detailed mechanisms of Cdc42 and Rac1 interactions with IQGAP2. We observed that Cdc42 binding to the Ex-domain of GRD of IQGAP2 (GRD2) releases the Ex-domain at the C-terminal region of GRD2, facilitating IQGAP2 dimerization. Cdc42 binding to the Ex-domain promoted allosteric changes in the RasGAP site, providing a binding site for the second Cdc42 in the RasGAP site. Of note, the Cdc42 "insert loop" was important for the interaction of the first Cdc42 with the Ex-domain. By contrast, differences in Rac1 insert-loop sequence and structure precluded its interaction with the Ex-domain. Rac1 could bind only to the RasGAP site of apo-GRD2 and could not facilitate IQGAP2 dimerization. Our detailed mechanistic insights help decipher how Cdc42 can stimulate actin polymerization in metastasis.

Binary Clostridium difficile toxin (CDT) - A virulence factor disturbing the cytoskeleton

Clostridium difficile infection causes antibiotics-associated diarrhea and pseudomembranous colitis. Major virulence factors of C. difficile are the Rho-glucosylating toxins TcdA and TcdB. In addition, many, so-called hypervirulent C. difficile strains produce the binary actin-ADP-ribosylating toxin CDT. CDT causes depolymerization of F-actin and rearrangement of the actin cytoskeleton. Thereby, many cellular functions, which depend on actin, are altered. CDT disturbs the dynamic balance between actin and microtubules in target cells. The toxin increases microtubule polymerization and induces the formation of microtubule-based protrusions at the plasma membrane of target cells. Moreover, CDT causes a redistribution of vesicles from the basolateral side to the apical side, where extracellular matrix proteins are released. These processes may increase the adherence of clostridia to target cells. Here, we review the effects of the action of CDT on the actin cytoskeleton and on the microtubule system.

Dynamic Tracking of Osteoblastic Cell Traction Force during Guided Migration

Introduction

Continuous development of cell traction force can regulate cell migration on various extracellular matrixes in vivo. However, the topographical effect on traction force is still not fully understood.

Methods

Micropost sensors with parallel guiding gratings were fabricated in polydimethylsiloxane to track the cell traction force during topographical guidance in real time. The force distributions along MC3T3-E1 mouse osteoblasts were captured every minute. The traction force in the leading, middle, and trailing regions was monitored during forward and reversed cell migration.

Results

The traction force showed periodic changes during cell migration when the cell changed from elongated to contracted shape. For cell migration without guiding pattern, the leading region showed the largest traction force among the three regions, typically 5.8 ± 0.8 nanonewton (nN) when the cell contracted and 7.1 ± 0.5 nN when it elongated. During guided cell migration, a lower traction force was obtained. When a cell contracted, the trailing traction force was 4.1 ± 0.4 for non-guided migration and 2.2 ± 0.2 nN for guided migration. As a cell became elongated, the trailing traction force was 6.0 ± 0.5 nN during non-guided migration and 4.8 ± 0.3 nN under guidance. When a cell reversed its migration direction, the magnitudes of the traction force from the leading to the trailing regions also flipped.

Conclusion

The cell traction force is continuously influenced by topographical guidance, which determines cell migration speed and direction. These results of cell traction force development on various topographies could lead to better cell migration control using topotaxis.

Investigation of fullerenol-induced changes in poroelasticity of human hepatocellular carcinoma by AFM-based creep tests

In this study, atomic force microscopy (AFM) is used to investigate the alterations of the poroelastic properties of hepatocellular carcinoma (SMMC-7721) cells treated with fullerenol. The SMMC-7721 cells were subject to AFM-based creep tests, and a corresponding poroelastic indentation model was used to determine the poroelastic parameters by curve fitting. Comparative analyses indicated that the both permeability and diffusion of fullerenol-treated cells increased significantly while their elastic modulus decreased by a small amount. From the change in the trend of the determined parameter, we verified the corresponding alternations of cytoskeleton (mainly filaments actin), which was reported by the previous study using confocal imaging method. Our investigation on SMMC-7721 cell reveals that the poroelastic properties could provide a better understanding how the cancer cells are affected by fullerenol or potentially other drugs which could find possible applications in drug efficacy test, cancer diagnosis and secure therapies.

Visualizing the spatiotemporal map of Rac activation in bovine aortic endothelial cells under laminar and disturbed flows

Disturbed flow can eliminate the alignment of endothelial cells in the direction of laminar flow, and significantly impacts on atherosclerosis in collateral arteries near the bifurcation and high curvature regions. While shear stress induced Rac polarity has been shown to play crucial roles in cell polarity and migration, little is known about the spatiotemporal map of Rac under disturbed flow, and the mechanism of flow-induced cell polarity still needs to be elucidated. In this paper, disturbed flow or laminar flow with 15 dyn/cm2 of average shear stress was applied on bovine aortic endothelial cells (BAECs) for 30 minutes. A genetically-encoded PAK-PBD-GFP reporter was transfected into BAECs to visualize the real-time activation of Rac in living cell under fluorescence microscope. The imaging of the fluorescence intensity was analyzed by Matlab and the normalized data was converted into 3D spatiotemporal map. Then the changes of data upon chemical interference were fitted with logistic curve to explore the rule and mechanism of Rac polarity under laminar or disturbed flow. A polarized Rac activation was observed at the downstream edge along the laminar flow, which was enhanced by benzol alcohol-enhanced membrane fluidity but inhibited by nocodazole-disrupted microtubules or cholesterol-inhibited membrane fluidity, while no obvious polarized Rac activation could be found upon disturbed flow application. It is concluded that disturbed flow inhibits the flow-induced Rac polarized activation, which is related to the interaction of cell membrane and cytoskeleton, especially the microtubules.

mDia1 senses both force and torque during F-actin filament polymerization

Formins, an important family of force-bearing actin-polymerizing factors, function as homodimers that bind with the barbed end of actin filaments through a ring-like structure assembled from dimerized FH2 domains. It has been hypothesized that force applied to formin may facilitate transition of the FH2 ring from an inhibitory closed conformation to a permissive open conformation, speeding up actin polymerization. We confirm this hypothesis for mDia1 dependent actin polymerization by stretching a single-actin filament in the absence of profilin using magnetic tweezers, and observe that increasing force from 0.5 to 10 pN can drastically speed up the actin polymerization rate. Further, we find that this force-promoted actin polymerization requires torsionally unconstrained actin filament, suggesting that mDia1 also senses torque. As actin filaments are subject to complex mechanical constraints in living cells, these results provide important insights into how formin senses these mechanical constraints and regulates actin organization accordingly.

Mechanical plasticity during oligodendrocyte differentiation and myelination

In the central nervous system, oligodendrocyte precursor cells are exclusive in their potential to differentiate into myelinating oligodendrocytes. Oligodendrocyte precursor cells migrate within the parenchyma and extend cell membrane protrusions that ultimately evolve into myelinating sheaths able to wrap neuronal axons and significantly increase their electrical conductivity. The subcellular force generating mechanisms driving morphological and functional transformations during oligodendrocyte differentiation and myelination remain elusive. In this review, we highlight the mechanical processes governing oligodendrocyte plasticity in a dynamic interaction with the extracellular matrix.

Targeting cancer cell integrins using gold nanorods in photothermal therapy inhibits migration through affecting cytoskeletal proteins

Metastasis is responsible for most cancer-related deaths, but the current clinical treatments are not effective. Recently, gold nanoparticles (AuNPs) were discovered to inhibit cancer cell migration and prevent metastasis. Rationally designed AuNPs could greatly benefit their antimigration property, but the molecular mechanisms need to be explored. Cytoskeletons are cell structural proteins that closely relate to migration, and surface receptor integrins play critical roles in controlling the organization of cytoskeletons. Herein, we developed a strategy to inhibit cancer cell migration by targeting integrins, using Arg-Gly-Asp (RGD) peptide-functionalized gold nanorods. To enhance the effect, AuNRs were further activated with 808-nm near-infrared (NIR) light to generate heat for photothermal therapy (PPTT), where the temperature was adjusted not to affect the cell viability/proliferation. Our results demonstrate changes in cell morphology, observed as cytoskeleton protrusions-i.e., lamellipodia and filopodia-were reduced after treatment. The Western blot analysis indicates the downstream effectors of integrin were attracted toward the antimigration direction. Proteomics results indicated broad perturbations in four signaling pathways, Rho GTPases, actin, microtubule, and kinases-related pathways, which are the downstream regulators of integrins. Due to the dominant role of integrins in controlling cytoskeleton, focal adhesion, actomyosin contraction, and actin and microtubule assembly have been disrupted by targeting integrins. PPTT further enhanced the remodeling of cytoskeletal proteins and decreased migration. In summary, the ability of targeting AuNRs to cancer cell integrins and the introduction of PPTT stimulated broad regulation on the cytoskeleton, which provides the evidence for a potential medical application for controlling cancer metastasis.

The role of MACF1 in nervous system development and maintenance

Microtubule-actin crosslinking factor 1 (MACF1), also known as actin crosslinking factor 7 (ACF7), is essential for proper modulation of actin and microtubule cytoskeletal networks. Most MACF1 isoforms are expressed broadly in the body, but some are exclusively found in the nervous system. Consequentially, MACF1 is integrally involved in multiple neural processes during development and in adulthood, including neurite outgrowth and neuronal migration. Furthermore, MACF1 participates in several signaling pathways, including the Wnt/β-catenin and GSK-3 signaling pathways, which regulate key cellular processes, such as proliferation and cell migration. Genetic mutation or dysregulation of the MACF1 gene has been associated with neurodevelopmental and neurodegenerative diseases, specifically schizophrenia and Parkinson's disease. MACF1 may also play a part in neuromuscular disorders and have a neuroprotective role in the optic nerve. In this review, the authors seek to synthesize recent findings relating to the roles of MACF1 within the nervous system and explore potential novel functions of MACF1 not yet examined.

Correlative STED and Atomic Force Microscopy on Live Astrocytes Reveals Plasticity of Cytoskeletal Structure and Membrane Physical Properties during Polarized Migration

The plasticity of the cytoskeleton architecture and membrane properties is important for the establishment of cell polarity, adhesion and migration. Here, we present a method which combines stimulated emission depletion (STED) super-resolution imaging and atomic force microscopy (AFM) to correlate cytoskeletal structural information with membrane physical properties in live astrocytes. Using STED compatible dyes for live cell imaging of the cytoskeleton, and simultaneously mapping the cell surface topology with AFM, we obtain unprecedented detail of highly organized networks of actin and microtubules in astrocytes. Combining mechanical data from AFM with optical imaging of actin and tubulin further reveals links between cytoskeleton organization and membrane properties. Using this methodology we illustrate that scratch-induced migration induces cytoskeleton remodeling. The latter is caused by a polarization of actin and microtubule elements within astroglial cell processes, which correlates strongly with changes in cell stiffness. The method opens new avenues for the dynamic probing of the membrane structural and functional plasticity of living brain cells. It is a powerful tool for providing new insights into mechanisms of cell structural remodeling during physiological or pathological processes, such as brain development or tumorigenesis.

Intermediate filament reorganization dynamically influences cancer cell alignment and migration

The interactions between a cancer cell and its extracellular matrix (ECM) have been the focus of an increasing amount of investigation. The role of the intermediate filament keratin in cancer has also been coming into focus of late, but more research is needed to understand how this piece fits in the puzzle of cytoskeleton-mediated invasion and metastasis. In Panc-1 invasive pancreatic cancer cells, keratin phosphorylation in conjunction with actin inhibition was found to be sufficient to reduce cell area below either treatment alone. We then analyzed intersecting keratin and actin fibers in the cytoskeleton of cyclically stretched cells and found no directional correlation. The role of keratin organization in Panc-1 cellular morphological adaptation and directed migration was then analyzed by culturing cells on cyclically stretched polydimethylsiloxane (PDMS) substrates, nanoscale grates, and rigid pillars. In general, the reorganization of the keratin cytoskeleton allows the cell to become more ‘mobile’- exhibiting faster and more directed migration and orientation in response to external stimuli. By combining keratin network perturbation with a variety of physical ECM signals, we demonstrate the interconnected nature of the architecture inside the cell and the scaffolding outside of it, and highlight the key elements facilitating cancer cell-ECM interactions.

p49/STRAP, a Serum Response Factor Binding Protein (SRFBP1), Is Involved in the Redistribution of Cytoskeletal F-Actin Proteins during Glucose Deprivation

The functional decline that usually accompanies adult aging also encompasses cellular changes including cytoplasmic architecture. In addition to their role in cytoskeletal structure, actin microfilaments have important roles in various cellular processes, including cell-to-cell communication and intracellular signaling. Age-related diseases and late-stage cellular morphological appearances often correlate with altered f-actin structure, which has been observed most notably in cancer. What remains less clear are the molecular pathways that may be involved in normal and premature aging-induced f-actin changes. We report herein that p49/STRAP, a serum response factor binding protein (SRFBP1), is increased with normal aging and appears to be sensitive to low glucose-exposure. Our study results suggest that increased levels of p49/STRAP expression tend to correlate with f-actin redistribution genes, particularly cofilin, while siRNA-mediated knockdown of p49/STRAP resulted in a reduction of thymosin-β4. Furthermore, with the redistribution of f-actin, we observed an increase in the intermediate filament vimentin, compatible with the notion that vimentin may be increased due to its greater role in cytoskeletal dynamics during advancing population doubling levels (PDLs) and in response to a low-glucose exposure. Taken together, these data suggest that p49/STRAP may play a role in glucose-deprivation associated cytoskeletal changes.

TNF-alpha stimulation increases dental pulp stem cell migration in vitro through integrin alpha-6 subunit upregulation

OBJECTIVE

The dissemination of stem cells into tissues requiring inflammatory and reparative response is fundamentally dependent upon their chemotactic migration. Expression of TNF-α is up regulated in inflamed pulps. Dental pulp cells are also known to express integrin α6 subunit. Expression of integrin subunit α6 has been linked to the acquisition of migratory potential in a wide variety of cell types in both pathological and physiological capacities. Therefore, in this study we examined the effects of a pleiotropic cytokine TNF-α on the migration of hDPSCs and investigated its relationship with expression of integrin α6 in hDPSCs during chemotactic migration.

DESIGN

hDPSC cultures were established. Protein expression profile of α6 integrin subunit was determined. Effect of exogenous TNF-α (50ng/mL) on hDPSCs' migration potential was evaluated by transwell inserts and in vitro scratch assay. Upregulation/downregulation of TNF-α mediated migration was assayed in presence/absence of integrin α6 respectively. To suppress integrin α6 expression, cells were transfected with integrin α6 siRNA and then cell migration and cytoskeletal changes were evaluated.

RESULTS

Our results showed significant increase of hDPSCs' migration after stimulation with TNF-α. By knockdown of integrin α6, which is upregulated by TNF-α, we observed a decrease in the TNF-α directed chemotaxis of hDPSCs.

CONCLUSION

In this study, we show that activation of integrin α6 brought about by TNF-α led to an increase in migratory activity in DPSCs in vitro thus describing a novel association between a cytokine TNF-α and α6 chain of an adhesion receptor integrin in regulating migration of hDPSCs.