Spatial and temporal control of cofilin activity is required for directional sensing during chemotaxis

Intratumoral CXCL12 Gradients Contextualize Tumor Cell Invasion, Migration and Immune Suppression in Breast Cancer

Although the CXCL12/CXCR4 pathway has been prior investigated for its prometastatic and immuno- suppressive roles in the tumor microenvironment, evidence on the spatiotemporal regulation of these hallmarks has been lacking. Here, we demonstrate that CXCL12 forms a gradient specifically around cancer cell intravasation doorways, also known as Tumor Microenvironment of Metastasis (TMEM) doorways, thus facilitating the chemotactic translocation of prometastatic tumor cells expressing CXCR4 toward the perivascular TMEM doorways for subsequent entry into peripheral circulation. Fur- thermore, we demonstrate that the CXCL12-rich micro-environment around TMEM doorways may cre- ate immunosuppressive niches, whereby CD8 + T cells, despite being attracted to these regions, often exhibit reduced effector functions, limiting their efficacy. While the CXCL12/CXCR4 pathway can mini- mally influence the overall composition of immune cell populations, it biases the distribution of CD8 + T cells away from TMEM doorways, justifying its prior-established role as immunosuppressive factor for CD8 + T cells. Our research suggests that the complex interactions between CXCL12 and the various tumor and immune cell types contributes not only to the completion of the initial steps of the metastatic cascade, but also offers an immunological "sanctuary" to prometastatic tumor cells homed around TMEM doorways. Overall, our study enhances our current understanding on the mechanisms, via which CXCL12 orchestrates tumor cell behavior and immune dynamics, potentially guiding future thera- peutic strategies to combat breast cancer metastasis and improve anti-tumor immunity.

Decoding the tumour-modulatory roles of LIMK2

LIM domains kinase 2 (LIMK2) is a 72 kDa protein that regulates actin and cytoskeleton reorganization. Once phosphorylated by its upstream activator (ROCK1), LIMK2 can phosphorylate cofilin to inactivate it. This relieves the levering stress on actin and allows polymerization to occur. Actin rearrangement is essential in regulating cell cycle progression, apoptosis, and migration. Dysregulation of the ROCK1/LIMK2/cofilin pathway has been reported to link to the development of various solid cancers such as breast, lung, and prostate cancer and liquid cancer like leukemia. This review aims to assess the findings from multiple reported in vitro, in vivo, and clinical studies on the potential tumour-regulatory role of LIMK2 in different human cancers. The findings of the selected literature unraveled that activated AKT, EGF, and TGF-β pathways can upregulate the activities of the ROCK1/LIMK2/cofilin pathway. Besides cofilin, LIMK2 can modulate the cellular levels of other proteins, such as TPPP1, to promote microtubule polymerization. The tumour suppressor protein p53 can transactivate LIMK2b, a splice variant of LIMK2, to induce cell cycle arrest and allow DNA repair to occur before the cell enters the next phase of the cell cycle. Additionally, several non-coding RNAs, such as miR-135a and miR-939-5p, could also epigenetically regulate the expression of LIMK2. Since the expression of LIMK2 is dysregulated in several human cancers, measuring the tissue expression of LIMK2 could potentially help diagnose cancer and predict patient prognosis. As LIMK2 could play tumour-promoting and tumour-inhibiting roles in cancer development, more investigation should be conducted to carefully evaluate whether introducing a LIMK2 inhibitor in cancer patients could slow cancer progression without posing clinical harms.

Simvastatin Downregulates Cofilin and Stathmin to Inhibit Skeletal Muscle Cells Migration

Statins are the most effective therapeutic agents for reducing cholesterol synthesis. Given their widespread use, many adverse effects from statins have been reported; of these, musculoskeletal complications occurred in 15% of patients after receiving statins for 6 months, and simvastatin was the most commonly administered statin among these cases. This study investigated the negative effects of simvastatin on skeletal muscle cells. We performed RNA sequencing analysis to determine gene expression in simvastatin-treated cells. Cell proliferation and migration were examined through cell cycle analysis and the transwell filter migration assay, respectively. Cytoskeleton rearrangement was examined through F-actin and tubulin staining. Western blot analysis was performed to determine the expression of cell cycle-regulated and cytoskeleton-related proteins. Transfection of small interfering RNAs (siRNAs) was performed to validate the role of cofilin and stathmin in the simvastatin-mediated inhibition of cell migration. The results revealed that simvastatin inhibited the proliferation and migration of skeletal muscle cells and affected the rearrangement of F-actin and tubulin. Simvastatin reduced the expression of cofilin and stathmin. The knockdown of both cofilin and stathmin by specific siRNA synergistically impaired cell migration. In conclusion, our results indicated that simvastatin inhibited skeletal muscle cell migration by reducing the expressions of cofilin and stathmin.

A chemorepellent inhibits local Ras activation to inhibit pseudopod formation to bias cell movement away from the chemorepellent

The ability of cells to sense chemical gradients is essential during development, morphogenesis, and immune responses. Although much is known about chemoattraction, chemorepulsion remains poorly understood. Proliferating Dictyostelium cells secrete a chemorepellent protein called AprA. AprA prevents pseudopod formation at the region of the cell closest to the source of AprA, causing the random movement of cells to be biased away from the AprA. Activation of Ras proteins in a localized sector of a cell cortex helps to induce pseudopod formation, and Ras proteins are needed for AprA chemorepulsion. Here we show that AprA locally inhibits Ras cortical activation through the G protein–coupled receptor GrlH, the G protein subunits Gβ and Gα8, Ras protein RasG, protein kinase B, the p21-activated kinase PakD, and the extracellular signal–regulated kinase Erk1. Diffusion calculations and experiments indicate that in a colony of cells, high extracellular concentrations of AprA in the center can globally inhibit Ras activation, while a gradient of AprA that naturally forms at the edge of the colony allows cells to activate Ras at sectors of the cell other than the sector of the cell closest to the center of the colony, effectively inducing both repulsion from the colony and cell differentiation. Together, these results suggest that a pathway that inhibits local Ras activation can mediate chemorepulsion.

The principles of directed cell migration

Cells have the ability to respond to various types of environmental cues, and in many cases these cues induce directed cell migration towards or away from these signals. How cells sense these cues and how they transmit that information to the cytoskeletal machinery governing cell translocation is one of the oldest and most challenging problems in biology. Chemotaxis, or migration towards diffusible chemical cues, has been studied for more than a century, but information is just now beginning to emerge about how cells respond to other cues, such as substrate-associated cues during haptotaxis (chemical cues on the surface), durotaxis (mechanical substrate compliance) and topotaxis (geometric features of substrate). Here we propose four common principles, or pillars, that underlie all forms of directed migration. First, a signal must be generated, a process that in physiological environments is much more nuanced than early studies suggested. Second, the signal must be sensed, sometimes by cell surface receptors, but also in ways that are not entirely clear, such as in the case of mechanical cues. Third, the signal has to be transmitted from the sensing modules to the machinery that executes the actual movement, a step that often requires amplification. Fourth, the signal has to be converted into the application of asymmetric force relative to the substrate, which involves mostly the cytoskeleton, but perhaps other players as well. Use of these four pillars has allowed us to compare some of the similarities between different types of directed migration, but also to highlight the remarkable diversity in the mechanisms that cells use to respond to different cues provided by their environment.

Alkaloid derivative ION-31a inhibits breast cancer metastasis and angiogenesis by targeting HSP90α

Breast cancer has become the number one killer of women. In our previous study, an active compound, ION-31a, with potential anti-metastasis activity against breast cancer was identified through the synthesis of ionone alkaloid derivatives. In the present study, we aimed to identify the therapeutic target of ION-31a. We used a fluorescence tag labeled probe, molecular docking simulation, and surface plasmon resonance (SPR) analysis to identify the target of ION-31a. The main target of ION-31a was identified as heat shock protein 90 (HSP90). Thus, ION-31a is a novel HSP90 inhibiter that could suppress the metastasis of breast cancer and angiogenesis significantly in vitro and in vivo. ION-31a acts via inhibiting the HSP90/hypoxia inducible factor 1 alpha (HIF-1α)/vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR2) pathway and downregulating downstream signal pathways, including protein kinase B (AKT)/mammalian target of rapamycin (mTOR), AKT2/protein kinase C epsilon (PKCζ), extracellular regulated kinase 1/2 (ERK1/2), focal adhesion kinase (FAK), and mitogen-activated protein kinase 14 (p38MAPK) pathways. ION-31a affects multiple effectors implicated in tumor metastasis and has the potential to be developed as an anti-metastatic agent to treat patients with breast cancer.

Growth Factors as Axon Guidance Molecules: Lessons From in vitro Studies

Growth cones at the tips of extending axons navigate through developing organisms by probing extracellular cues, which guide them through intermediate steps and onto final synaptic target sites. Widespread focus on a few guidance cue families has historically overshadowed potentially crucial roles of less well-studied growth factors in axon guidance. In fact, recent evidence suggests that a variety of growth factors have the ability to guide axons, affecting the targeting and morphogenesis of growth cones in vitro. This review summarizes in vitro experiments identifying responses and signaling mechanisms underlying axon morphogenesis caused by underappreciated growth factors.

Deciphering molecular mechanisms of metastasis: novel insights into targets and therapeutics

BACKGROUND

The transition of a primary tumour to metastatic progression is driven by dynamic molecular changes, including genetic and epigenetic alterations. The metastatic cascade involves bidirectional interactions among extracellular and intracellular components leading to disintegration of cellular junctions, cytoskeleton reorganization and epithelial to mesenchymal transition. These events promote metastasis by reprogramming the primary cancer cell's molecular framework, enabling them to cause local invasion, anchorage-independent survival, cell death and immune resistance, extravasation and colonization of distant organs. Metastasis follows a site-specific pattern that is still poorly understood at the molecular level. Although various drugs have been tested clinically across different metastatic cancer types, it has remained difficult to develop efficacious therapeutics due to complex molecular layers involved in metastasis as well as experimental limitations.

CONCLUSIONS

In this review, a systemic evaluation of the molecular mechanisms of metastasis is outlined and the potential molecular components and their status as therapeutic targets and the associated pre-clinical and clinical agents available or under investigations are discussed. Integrative methods like pan-cancer data analysis, which can provide clinical insights into both targets and treatment decisions and help in the identification of crucial components driving metastasis such as mutational profiles, gene signatures, associated pathways, site specificities and disease-gene phenotypes, are discussed. A multi-level data integration of the metastasis signatures across multiple primary and metastatic cancer types may facilitate the development of precision medicine and open up new opportunities for future therapies.

Mechanical Cues Affect Migration and Invasion of Cells From Three Different Directions

Cell migration and invasion is a key driving factor for providing essential cellular functions under physiological conditions or the malignant progression of tumors following downward the metastatic cascade. Although there has been plentiful of molecules identified to support the migration and invasion of cells, the mechanical aspects have not yet been explored in a combined and systematic manner. In addition, the cellular environment has been classically and frequently assumed to be homogeneous for reasons of simplicity. However, motility assays have led to various models for migration covering only some aspects and supporting factors that in some cases also include mechanical factors. Instead of specific models, in this review, a more or less holistic model for cell motility in 3D is envisioned covering all these different aspects with a special emphasis on the mechanical cues from a biophysical perspective. After introducing the mechanical aspects of cell migration and invasion and presenting the heterogeneity of extracellular matrices, the three distinct directions of cell motility focusing on the mechanical aspects are presented. These three different directions are as follows: firstly, the commonly used invasion tests using structural and structure-based mechanical environmental signals; secondly, the mechano-invasion assay, in which cells are studied by mechanical forces to migrate and invade; and thirdly, cell mechanics, including cytoskeletal and nuclear mechanics, to influence cell migration and invasion. Since the interaction between the cell and the microenvironment is bi-directional in these assays, these should be accounted in migration and invasion approaches focusing on the mechanical aspects. Beyond this, there is also the interaction between the cytoskeleton of the cell and its other compartments, such as the cell nucleus. In specific, a three-element approach is presented for addressing the effect of mechanics on cell migration and invasion by including the effect of the mechano-phenotype of the cytoskeleton, nucleus and the cell's microenvironment into the analysis. In precise terms, the combination of these three research approaches including experimental techniques seems to be promising for revealing bi-directional impacts of mechanical alterations of the cellular microenvironment on cells and internal mechanical fluctuations or changes of cells on the surroundings. Finally, different approaches are discussed and thereby a model for the broad impact of mechanics on cell migration and invasion is evolved.

GPER1 Signaling Initiates Migration of Female V-SVZ-Derived Cells

In the rodent ventricular-subventricular zone (V-SVZ) neurons are generated throughout life. They migrate along the rostral migratory stream (RMS) into the olfactory bulb before their final differentiation into interneurons and integration into local circuits. Estrogen receptors (ERs) are steroid hormone receptors with important functions in neurogenesis and synaptic plasticity. In this study, we show that the ER GPER1 is expressed in subsets of cells within the V-SVZ of female animals and provide evidence for a potential local estrogen source from aromatase-positive astrocytes surrounding the RMS. Blocking of GPER1 in Matrigel cultures of female animals significantly impairs migration of V-SVZ-derived cells. This outgrowth is accompanied by regulation of phosphorylation of the actin-binding protein cofilin by GPER1 signaling including an involvement of the p21-Ras pathway. Our results point to a prominent role of GPER1 in the initiation of neuronal migration from the V-SVZ to the olfactory bulb.

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GPER1 is expressed within all cell types of the stem cell lineage in the V-SVZ

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Blocking of GPER1 leads to a decrease in migration of V-SVZ-derived neuroblasts

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GPER1 signaling in V-SVZ Matrigel cultures involves Ras-induced p21

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Blocking of GPER1 signaling leads to an increase in the ratio of p-cofilin/cofilin

Alcoholic-Hepatitis, Links to Brain and Microbiome: Mechanisms, Clinical and Experimental Research

The following review article presents clinical and experimental features of alcohol-induced liver disease (ALD). Basic aspects of alcohol metabolism leading to the development of liver hepatotoxicity are discussed. ALD includes fatty liver, acute alcoholic hepatitis with or without liver failure, alcoholic steatohepatitis (ASH) leading to fibrosis and cirrhosis, and hepatocellular cancer (HCC). ALD is fully attributable to alcohol consumption. However, only 10-20% of heavy drinkers (persons consuming more than 40 g of ethanol/day) develop clinical ALD. Moreover, there is a link between behaviour and environmental factors that determine the amount of alcohol misuse and their liver disease. The range of clinical presentation varies from reversible alcoholic hepatic steatosis to cirrhosis, hepatic failure, and hepatocellular carcinoma. We aimed to (1) describe the clinico-pathology of ALD, (2) examine the role of immune responses in the development of alcoholic hepatitis (ASH), (3) propose diagnostic markers of ASH, (4) analyze the experimental models of ALD, (5) study the role of alcohol in changing the microbiota, and (6) articulate how findings in the liver and/or intestine influence the brain (and/or vice versa) on ASH; (7) identify pathways in alcohol-induced organ damage and (8) to target new innovative experimental concepts modeling the experimental approaches. The present review includes evidence recognizing the key toxic role of alcohol in ALD severity. Cytochrome p450 CYP2E1 activation may change the severity of ASH. The microbiota is a key element in immune responses, being an inducer of proinflammatory T helper 17 cells and regulatory T cells in the intestine. Alcohol consumption changes the intestinal microbiota and influences liver steatosis and liver inflammation. Knowing how to exploit the microbiome to modulate the immune system might lead to a new form of personalized medicine in ALF and ASH.

Suppression of LIM Kinase 1 and LIM Kinase 2 Limits Glioblastoma Invasion

The aggressive brain tumor glioblastoma (GBM) is characterized by rapid cellular infiltration of brain tissue, raising the possibility that disease progression could potentially be slowed by disrupting the machinery of cell migration. The LIM kinase isoforms LIMK1 and LIMK2 (LIMK1/2) play important roles in cell polarization, migration, and invasion and are markedly upregulated in GBM and many other infiltrative cancers. Yet, it remains unclear whether LIMK suppression could serve as a viable basis for combating GBM infiltration. In this study, we investigated effects of LIMK1/2 suppression on GBM invasion by combining GBM culture models, engineered invasion paradigms, and mouse xenograft models. While knockdown of either LIMK1 or LIMK2 only minimally influenced invasion in culture, simultaneous knockdown of both isoforms strongly reduced the invasive motility of continuous culture models and human GBM tumor-initiating cells (TIC) in both Boyden chamber and 3D hyaluronic acid spheroid invasion assays. Furthermore, LIMK1/2 functionally regulated cell invasiveness, in part, by disrupting polarized cell motility under confinement and cell chemotaxis. In an orthotopic xenograft model, TICs stably transduced with LIMK1/2 shRNA were implanted intracranially in immunocompromised mice. Tumors derived from LIMK1/2 knockdown TICs were substantially smaller and showed delayed growth kinetics and more distinct margins than tumors derived from control TICs. Overall, LIMK1/2 suppression increased mean survival time by 30%. These findings indicate that LIMK1/2 strongly regulate GBM invasive motility and tumor progression and support further exploration of LIMK1/2 as druggable targets. SIGNIFICANCE: Targeting the actin-binding proteins LIMK1 and LIMK2 significantly diminishes glioblastoma invasion and spread, suggesting the potential value of these proteins as therapeutic targets.

Mechanosensing during directed cell migration requires dynamic actin polymerization at focal adhesions

The mechanical properties of a cell's microenvironment influence many aspects of cellular behavior, including cell migration. Durotaxis, the migration toward increasing matrix stiffness, has been implicated in processes ranging from development to cancer. During durotaxis, mechanical stimulation by matrix rigidity leads to directed migration. Studies suggest that cells sense mechanical stimuli, or mechanosense, through the acto-myosin cytoskeleton at focal adhesions (FAs); however, FA actin cytoskeletal remodeling and its role in mechanosensing are not fully understood. Here, we show that the Ena/VASP family member, Ena/VASP-like (EVL), polymerizes actin at FAs, which promotes cell-matrix adhesion and mechanosensing. Importantly, we show that EVL regulates mechanically directed motility, and that suppression of EVL expression impedes 3D durotactic invasion. We propose a model in which EVL-mediated actin polymerization at FAs promotes mechanosensing and durotaxis by maturing, and thus reinforcing, FAs. These findings establish dynamic FA actin polymerization as a central aspect of mechanosensing and identify EVL as a crucial regulator of this process.

Physical constraints on accuracy and persistence during breast cancer cell chemotaxis

Directed cell motion in response to an external chemical gradient occurs in many biological phenomena such as wound healing, angiogenesis, and cancer metastasis. Chemotaxis is often characterized by the accuracy, persistence, and speed of cell motion, but whether any of these quantities is physically constrained by the others is poorly understood. Using a combination of theory, simulations, and 3D chemotaxis assays on single metastatic breast cancer cells, we investigate the links among these different aspects of chemotactic performance. In particular, we observe in both experiments and simulations that the chemotactic accuracy, but not the persistence or speed, increases with the gradient strength. We use a random walk model to explain this result and to propose that cells’ chemotactic accuracy and persistence are mutually constrained. Our results suggest that key aspects of chemotactic performance are inherently limited regardless of how favorable the environmental conditions are.

One of the most ubiquitous and important cell behaviors is chemotaxis: the ability to move in the direction of a chemical gradient. Due to its importance, key aspects of chemotaxis have been quantified for a variety of cells, including the accuracy, persistence, and speed of cell motion. However, whether these aspects are mutually constrained is poorly understood. Can a cell be accurate but not persistent, or vice versa? Here we use theory, simulations, and experiments on cancer cells to uncover mutual constraints on the properties of chemotaxis. Our results suggest that accuracy and persistence are mutually constrained.

Cofilin and profilin: partners in cancer aggressiveness

This review covers aspects of cofilin and profilin regulations and their influence on actin polymerisation responsible for cell motility and metastasis. The regulation of their activity by phosphorylation and nitration, miRs, PI(4,5)P₂ binding, pH, oxidative stress and post-translational modification is described. In this review, we have highlighted selected similarities, complementarities and differences between the two proteins and how their interplay affects actin filament dynamics.

Semaphorin 3A as an inhibitive factor for migration of olfactory ensheathing cells through cofilin activation is involved in formation of olfactory nerve layer

Olfactory ensheathing cells (OECs) migrate from olfactory epithelium towards olfactory bulb (OB), contributing to formation of the presumptive olfactory nerve layer during development. However, it remains unclear that molecular mechanism of regulation of OEC migration in OB. In the present study, we found that OECs highly expressed the receptors of semaphorin 3A (Sema3A) in vitro and in vivo, whereas Sema3A displayed a gradient expression pattern with higher in inner layer of OB and lower in outer layer of OB. Furthermore, the collapse assays, Boyden chamber migration assays and single-cell migration assays showed that Sema3A induced the collapse of leading front of OECs and inhibited OEC migration. Thirdly, the leading front of OECs exhibited adaptation in a protein synthesis-independent manner, and endocytosis-dependent manner during Sema3A-induced OEC migration. Finally, Sema3A-induced collapse of leading front was required the decrease of focal adhesion and a retrograde F-actin flow in a cofilin activation-dependent manner. Taken together, these results demonstrate that Sema3A as an inhibitive migratory factor for OEC migration through cofilin activation is involved in the formation of olfactory nerve layer.

Inhibition of human prostate smooth muscle contraction by the LIM kinase inhibitors, SR7826 and LIMKi3

BACKGROUND AND PURPOSE

In men with benign prostatic hyperplasia, increased smooth muscle tone in the prostate may lead to bladder outlet obstruction and subsequent lower urinary tract symptoms. Consequently, medical treatment aims to inhibit prostate smooth muscle contraction. However, the efficacy of the treatment options available is limited, and improved understanding of mechanisms of prostate smooth muscle contraction and identification of new targets for medical intervention are mandatory. Several studies suggest that LIM kinases (LIMKs) promote smooth muscle contraction; however, this has not yet been examined. Here, we studied effects of the LIMK inhibitors on prostate smooth muscle contraction.

EXPERIMENTAL APPROACH

Human prostate tissues were obtained from radical prostatectomy. Phosphorylation of cofilin, a LIMK substrate, was examined using a phospho-specific antibody. Smooth muscle contractions were studied in organ bath experiments.

KEY RESULTS

Real-time PCR, Western blot and immunofluorescence suggested LIMKs are expressed in smooth muscle cells of prostate tissues. Two different LIMK inhibitors, SR7826 (1 μM) and LIMKi3 (1 μM), inhibited contractions of prostate strips, which were induced by electrical field stimulation, α₁ -adrenoceptor agonists phenylephrine and methoxamine and the TXA₂ analogue, U46619. LIMK inhibition in prostate tissues and cultured stromal cells (WPMY-1) was confirmed by cofilin phosphorylation, which was reduced by SR7826 and LIMKi3. In WPMY-1 cells, SR7826 and LIMKi3 caused breakdown of actin filaments and reduced viability.

CONCLUSIONS AND IMPLICATIONS

Smooth muscle tone in the hyperplastic human prostate may underlie the effects of LIMKs, which promote contraction. Contraction of prostate strips can be inhibited by small molecule LIMK inhibitors.

PKD regulates actin polymerization, neutrophil deformability, and transendothelial migration in response to fMLP and trauma

Neutrophils are important mediators of the innate immune defense and of the host response to a physical trauma. Because aberrant infiltration of injured sites by neutrophils was shown to cause adverse effects after trauma, we investigated how neutrophil infiltration could be modulated at the cellular level. Our data indicate that protein kinase D (PKD) is a vital regulator of neutrophil transmigration. PKD phosphorylates the Cofilin-phosphatase Slingshot-2L (SSH-2L). SSH-2L in turn dynamically regulates Cofilin activity and actin polymerization in response to a chemotactic stimulus for neutrophils, for example, fMLP. Here, we show that inhibition of PKD by two specific small molecule inhibitors results in broad, unrestricted activation of Cofilin and strongly increases the F-actin content of neutrophils even under basal conditions. This phenotype correlates with a significantly impaired neutrophil deformability as determined by optical stretcher analysis. Consequently, inhibition of PKD impaired chemotaxis as shown by reduced extravasation of neutrophils. Consequently, we demonstrate that transendothelial passage of both, neutrophil-like NB4 cells and primary PMNs recovered from a hemorrhagic shock trauma model was significantly reduced. Thus, inhibition of PKD may represent a promising modulator of the neutrophil response to trauma.

A Reaction-Diffusion Model Explains Amplification of the PLC/PKC Pathway in Fibroblast Chemotaxis

During the proliferative phase of cutaneous wound healing, dermal fibroblasts are recruited into the clotted wound by a concentration gradient of platelet-derived growth factor (PDGF), together with other spatial cues. Despite the importance of this chemotactic process, the mechanisms controlling the directed migration of slow-moving mesenchymal cells such as fibroblasts are not well understood. Here, we develop and analyze a reaction-diffusion model of phospholipase C/protein kinase C (PKC) signaling, which was recently identified as a requisite PDGF-gradient-sensing pathway, with the goal of identifying mechanisms that can amplify its sensitivity in the shallow external gradients typical of chemotaxis experiments. We show that phosphorylation of myristoylated alanine-rich C kinase substrate by membrane-localized PKC constitutes a positive feedback that is sufficient for local pathway amplification. The release of phosphorylated myristoylated alanine-rich C kinase substrate and its subsequent diffusion and dephosphorylation in the cytosol also serves to suppress the pathway in down-gradient regions of the cell. By itself, this mechanism only weakly amplifies signaling in a shallow PDGF gradient, but it synergizes with other feedback mechanisms to enhance amplification. This model offers a framework for a mechanistic understanding of phospholipase C/PKC signaling in chemotactic gradient sensing and can guide the design of experiments to assess the roles of putative feedback loops.

Overexpression of cofilin correlates with poor survival in breast cancer: A tissue microarray analysis

Cofilin, a key regulator of actin cytoskeleton dynamics, is considered to be involved in cellular migration, tumor invasion and mitosis, and its activity is increased in cancer cells. To address the association between cofilin and breast cancer prognosis, which is unclear at present, cofilin expression was analyzed in tissue microarrays of tumors from 310 patients with breast cancer via immunohistochemistry. In a multivariate Cox regression analysis, a high expression of cofilin in tumor cells correlated significantly with shorter overall survival (hazard ratio, 2.22; 95% confidence interval, 1.35–3.66, P=0.002, and with the Nottingham histologic grade, Ki-67 status and human epidermal growth factor receptor 2 status (P=0.031, 0.001, and 0.001, respectively). Cofilin expression was not observed as correlated with estrogen or progesterone receptor expression, tumor size or lymph node status. These data demonstrate that cofilin is associated with poor outcome, thereby suggesting that it is a potential prognostic factor in breast cancer.

Myosin phosphorylation on stress fibers predicts contact guidance behavior across diverse breast cancer cells

During cancer progression the extracellular matrix is remodeled, forming aligned collagen fibers that proceed radially from the tumor, resulting in invasion. We have recently shown that different invasive breast cancer cells respond to epitaxially grown, aligned collagen fibrils differently. This article develops insight into why these cells differ in their contact guidance fidelity. Small changes in contractility or adhesion dramatically alter directional persistence on aligned collagen fibrils, while migration speed remains constant. The directionality of highly contractile and adhesive MDA-MB-231 cells can be diminished by inhibiting Rho kinase or β1 integrin binding. Inversely, the directionality of less contractile and adhesive MTLn3 cells can be enhanced by activating contractility or integrins. Subtle, but quantifiable alterations in myosin II regulatory light chain phosphorylation on stress fibers explain the tuning of contact guidance fidelity, separate from migration per se indicating that the contractile and adhesive state of the cell in combination with collagen organization in the tumor microenvironment determine the efficiency of migration. Understanding how distinct cells respond to contact guidance cues will not only illuminate mechanisms for cancer invasion, but will also allow for the design of environments to separate specific subpopulations of cells from patient-derived tissues by leveraging differences in responses to directional migration cues.

Blood vessel endothelium-directed tumor cell streaming in breast tumors requires the HGF/C-Met signaling pathway

During metastasis to distant sites, tumor cells migrate to blood vessels. In vivo, breast tumor cells utilize a specialized mode of migration known as streaming, where a linear assembly of tumor cells migrate directionally towards blood vessels on fibronectin-collagen I-containing extracellular matrix (ECM) fibers in response to chemotactic signals. We have successfully reconstructed tumor cell streaming in vitro by co-plating tumors cells, macrophages and endothelial cells on 2.5 μm thick ECM-coated micro-patterned substrates. We found that tumor cells and macrophages, when plated together on the micro-patterned substrates, do not demonstrate sustained directional migration in only one direction (sustained directionality) but show random bi-directional walking. Sustained directionality of tumor cells as seen in vivo was established in vitro when beads coated with human umbilical vein endothelial cells were placed at one end of the micro-patterned 'ECM fibers' within the assay. We demonstrated that these endothelial cells supply the hepatocyte growth factor (HGF) required for the chemotactic gradient responsible for sustained directionality. Using this in vitro reconstituted streaming system, we found that directional streaming is dependent on, and most effectively blocked, by inhibiting the HGF/C-Met signaling pathway between endothelial cells and tumor cells. Key observations made with the in vitro reconstituted system implicating C-Met signaling were confirmed in vivo in mammary tumors using the in vivo invasion assay and intravital multiphoton imaging of tumor cell streaming. These results establish HGF/C-Met as a central organizing signal in blood vessel-directed tumor cell migration in vivo and highlight a promising role for C-Met inhibitors in blocking tumor cell streaming and metastasis in vivo, and for use in human trials.

Endothelial repair in stented arteries is accelerated by inhibition of Rho-associated protein kinase

Aims

Stent deployment causes endothelial cells (EC) denudation, which promotes in-stent restenosis and thrombosis. Thus endothelial regrowth in stented arteries is an important therapeutic goal. Stent struts modify local hemodynamics, however the effects of flow perturbation on EC injury and repair are incompletely understood. By studying the effects of stent struts on flow and EC migration, we identified an intervention that promotes endothelial repair in stented arteries.

Methods and Results

In vitro and in vivo models were developed to monitor endothelialization under flow and the influence of stent struts. A 2D parallel-plate flow chamber with 100 μm ridges arranged perpendicular to the flow was used. Live cell imaging coupled to computational fluid dynamic simulations revealed that EC migrate in the direction of flow upstream from the ridges but subsequently accumulate downstream from ridges at sites of bidirectional flow. The mechanism of EC trapping by bidirectional flow involved reduced migratory polarity associated with altered actin dynamics. Inhibition of Rho-associated protein kinase (ROCK) enhanced endothelialization of ridged surfaces by promoting migratory polarity under bidirectional flow (P < 0.01). To more closely mimic the in vivo situation, we cultured EC on the inner surface of polydimethylsiloxane tubing containing Coroflex Blue stents (65 μm struts) and monitored migration. ROCK inhibition significantly enhanced EC accumulation downstream from struts under flow (P < 0.05). We investigated the effects of ROCK inhibition on re-endothelialization in vivo using a porcine model of EC denudation and stent placement. En face staining and confocal microscopy revealed that inhibition of ROCK using fasudil (30 mg/day via osmotic minipump) significantly increased re-endothelialization of stented carotid arteries (P < 0.05).

Conclusions

Stent struts delay endothelial repair by generating localized bidirectional flow which traps migrating EC. ROCK inhibitors accelerate endothelial repair of stented arteries by enhancing EC polarity and migration through regions of bidirectional flow.

Cellular functions of the ADF/cofilin family at a glance

The actin depolymerizing factor (ADF)/cofilin family comprises small actin-binding proteins with crucial roles in development, tissue homeostasis and disease. They are best known for their roles in regulating actin dynamics by promoting actin treadmilling and thereby driving membrane protrusion and cell motility. However, recent discoveries have increased our understanding of the functions of these proteins beyond their well-characterized roles. This Cell Science at a Glance article and the accompanying poster serve as an introduction to the diverse roles of the ADF/cofilin family in cells. The first part of the article summarizes their actions in actin treadmilling and the main mechanisms for their intracellular regulation; the second part aims to provide an outline of the emerging cellular roles attributed to the ADF/cofilin family, besides their actions in actin turnover. The latter part discusses an array of diverse processes, which include regulation of intracellular contractility, maintenance of nuclear integrity, transcriptional regulation, nuclear actin monomer transfer, apoptosis and lipid metabolism. Some of these could, of course, be indirect consequences of actin treadmilling functions, and this is discussed.

Applied stretch initiates directional invasion through the action of Rap1 GTPase as a tension sensor

Although it is known that a stiffening of the stroma and the rearrangement of collagen fibers within the extracellular matrix facilitate the movement of tumor cells away from the primary lesion, the underlying mechanisms responsible are not fully understood. We now show that this invasion, which can be initiated by applying tensional loads to a three-dimensional collagen gel matrix in culture, is dependent on the Rap1 GTPases (Rap1a and Rap1b, referred to collectively as Rap1). Under these conditions Rap1 activity stimulates the formation of focal adhesion structures that align with the tensional axis as single tumor cells move into the matrix. These effects are mediated by the ability of Rap1 to induce the polarized polymerization and retrograde flow of actin, which stabilizes integrins and recruits vinculin to preformed adhesions, particularly those near the leading edge of invasive cells. Rap1 activity also contributes to the tension-induced collective invasive elongation of tumor cell clusters and it enhances tumor cell growth in vivo Thus, Rap1 mediates the effects of increased extracellular tension in multiple ways that are capable of contributing to tumor progression when dysregulated.

Cell polarity signaling in the plasticity of cancer cell invasiveness

Apico-basal polarity is typical of cells present in differentiated epithelium while front-rear polarity develops in motile cells. In cancer development, the transition from epithelial to migratory polarity may be seen as the hallmark of cancer progression to an invasive and metastatic disease. Despite the morphological and functional dissimilarity, both epithelial and migratory polarity are controlled by a common set of polarity complexes Par, Scribble and Crumbs, phosphoinositides, and small Rho GTPases Rac, Rho and Cdc42. In epithelial tissues, their mutual interplay ensures apico-basal and planar cell polarity. Accordingly, altered functions of these polarity determinants lead to disrupted cell-cell adhesions, cytoskeleton rearrangements and overall loss of epithelial homeostasis. Polarity proteins are further engaged in diverse interactions that promote the establishment of front-rear polarity, and they help cancer cells to adopt different invasion modes. Invading cancer cells can employ either the collective, mesenchymal or amoeboid invasion modes or actively switch between them and gain intermediate phenotypes. Elucidation of the role of polarity proteins during these invasion modes and the associated transitions is a necessary step towards understanding the complex problem of metastasis. In this review we summarize the current knowledge of the role of cell polarity signaling in the plasticity of cancer cell invasiveness.

Validation of a device for the active manipulation of the tumor microenvironment during intravital imaging

The tumor microenvironment is recognized as playing a significant role in the behavior of tumor cells and their progression to metastasis. However, tools to manipulate the tumor microenvironment directly, and image the consequences of this manipulation with single cell resolution in real time in vivo, are lacking. We describe here a method for the direct, local manipulation of microenvironmental parameters through the use of an implantable Induction Nano Intravital Device (iNANIVID) and simultaneous in vivo visualization of the results at single-cell resolution. As a proof of concept, we deliver both a sustained dose of EGF to tumor cells while intravital imaging their chemotactic response as well as locally induce hypoxia in defined microenvironments in solid tumors.

Lamellipodin promotes invasive 3D cancer cell migration via regulated interactions with Ena/VASP and SCAR/WAVE

Cancer invasion is a hallmark of metastasis. The mesenchymal mode of cancer cell invasion is mediated by elongated membrane protrusions driven by the assembly of branched F-actin networks. How deregulation of actin regulators promotes cancer cell invasion is still enigmatic. We report that increased expression and membrane localization of the actin regulator Lamellipodin correlate with reduced metastasis-free survival and poor prognosis in breast cancer patients. In agreement, we find that Lamellipodin depletion reduced lung metastasis in an orthotopic mouse breast cancer model. Invasive 3D cancer cell migration as well as invadopodia formation and matrix degradation was impaired upon Lamellipodin depletion. Mechanistically, we show that Lamellipodin promotes invasive 3D cancer cell migration via both actin-elongating Ena/VASP proteins and the Scar/WAVE complex, which stimulates actin branching. In contrast, Lamellipodin interaction with Scar/WAVE but not with Ena/VASP is required for random 2D cell migration. We identified a phosphorylation-dependent mechanism that regulates selective recruitment of these effectors to Lamellipodin: Abl-mediated Lamellipodin phosphorylation promotes its association with both Scar/WAVE and Ena/VASP, whereas Src-dependent phosphorylation enhances binding to Scar/WAVE but not to Ena/VASP. Through these selective, regulated interactions Lamellipodin mediates directional sensing of epidermal growth factor (EGF) gradients and invasive 3D migration of breast cancer cells. Our findings imply that increased Lamellipodin levels enhance Ena/VASP and Scar/WAVE activities at the plasma membrane to promote 3D invasion and metastasis.

ADF and Cofilin1 Control Actin Stress Fibers, Nuclear Integrity, and Cell Survival

Genetic co-depletion of the actin-severing proteins ADF and CFL1 triggers catastrophic loss of adult homeostasis in multiple tissues. There is impaired cell-cell adhesion in skin keratinocytes with dysregulation of E-cadherin, hyperproliferation of differentiated cells, and ultimately apoptosis. Mechanistically, the primary consequence of depleting both ADF and CFL1 is uncontrolled accumulation of contractile actin stress fibers associated with enlarged focal adhesions at the plasma membrane, as well as reduced rates of membrane protrusions. This generates increased intracellular acto-myosin tension that promotes nuclear deformation and physical disruption of the nuclear lamina via the LINC complex that normally connects regulated actin filaments to the nuclear envelope. We therefore describe a pathway involving the actin-severing proteins ADF and CFL1 in regulating the dynamic turnover of contractile actin stress fibers, and this is vital to prevent the nucleus from being damaged by actin contractility, in turn preserving cell survival and tissue homeostasis.

Profilin-1 overexpression in MDA-MB-231 breast cancer cells is associated with alterations in proteomics biomarkers of cell proliferation, survival, and motility as revealed by global proteomics analyses

Despite early screening programs and new therapeutic strategies, metastatic breast cancer is still the leading cause of cancer death in women in industrialized countries and regions. There is a need for novel biomarkers of susceptibility, progression, and therapeutic response. Global analyses or systems science approaches with omics technologies offer concrete ways forward in biomarker discovery for breast cancer. Previous studies have shown that expression of profilin-1 (PFN1), a ubiquitously expressed actin-binding protein, is downregulated in invasive and metastatic breast cancer. It has also been reported that PFN1 overexpression can suppress tumorigenic ability and motility/invasiveness of breast cancer cells. To obtain insights into the underlying molecular mechanisms of how elevating PFN1 level induces these phenotypic changes in breast cancer cells, we investigated the alteration in global protein expression profiles of breast cancer cells upon stable overexpression of PFN1 by a combination of three different proteome analysis methods (2-DE, iTRAQ, label-free). Using MDA-MB-231 as a model breast cancer cell line, we provide evidence that PFN1 overexpression is associated with alterations in the expression of proteins that have been functionally linked to cell proliferation (FKPB1A, HDGF, MIF, PRDX1, TXNRD1, LGALS1, STMN1, LASP1, S100A11, S100A6), survival (HSPE1, HSPB1, HSPD1, HSPA5 and PPIA, YWHAZ, CFL1, NME1) and motility (CFL1, CORO1B, PFN2, PLS3, FLNA, FLNB, NME2, ARHGDIB). In view of the pleotropic effects of PFN1 overexpression in breast cancer cells as suggested by these new findings, we propose that PFN1-induced phenotypic changes in cancer cells involve multiple mechanisms. Our data reported here might also offer innovative strategies for identification and validation of novel therapeutic targets and companion diagnostics for persons with, or susceptibility to, breast cancer.

Chronophin coordinates cell leading edge dynamics by controlling active cofilin levels

Cofilin, a critical player of actin dynamics, is spatially and temporally regulated to control the direction and force of membrane extension required for cell locomotion. In carcinoma cells, although the signaling pathways regulating cofilin activity to control cell direction have been established, the molecular machinery required to generate the force of the protrusion remains unclear. We show that the cofilin phosphatase chronophin (CIN) spatiotemporally regulates cofilin activity at the cell edge to generate persistent membrane extension. We show that CIN translocates to the leading edge in a PI3-kinase-, Rac1-, and cofilin-dependent manner after EGF stimulation to activate cofilin, promotes actin free barbed end formation, accelerates actin turnover, and enhances membrane protrusion. In addition, we establish that CIN is crucial for the balance of protrusion/retraction events during cell migration. Thus, CIN coordinates the leading edge dynamics by controlling active cofilin levels to promote MTLn3 cell protrusion.

Classic Ras Proteins Promote Proliferation and Survival via Distinct Phosphoproteome Alterations in Neurofibromin-Null Malignant Peripheral Nerve Sheath Tumor Cells

Neurofibromin, the tumor suppressor encoded by the neurofibromatosis type 1 (NF1) gene, potentially suppresses the activation of H-Ras, N-Ras, and K-Ras. However, it is not known whether these classic Ras proteins are hyperactivated in NF1-null nerve sheath tumors, how they contribute to tumorigenesis, and what signaling pathways mediate their effects. Here we show that H-Ras, N-Ras, and K-Ras are coexpressed with their activators (guanine nucleotide exchange factors) in neurofibromin-null malignant peripheral nerve sheath tumor (MPNST) cells, and that all 3 Ras proteins are activated. Dominant negative (DN) H-Ras, a pan-inhibitor of the classic Ras family, inhibited MPNST proliferation and survival, but not migration. However, NF1-null MPNST cells were variably dependent on individual Ras proteins. In some lines, ablation of H-Ras, N-Ras, and/or K-Ras inhibited mitogenesis. In others, ablation of a single Ras protein had no effect on proliferation; in these lines, ablation of a single Ras protein resulted in compensatory increases in the activation and/or expression of other Ras proteins. Using mass spectrometry-based phosphoproteomics, we identified 7 signaling networks affecting morphology, proliferation, and survival that are regulated by DN H-Ras. Thus, neurofibromin loss activates multiple classic Ras proteins that promote proliferation and survival by regulating several distinct signaling cascades.

JG6, a novel marine-derived oligosaccharide, suppresses breast cancer metastasis via binding to cofilin

Cofilin, an actin-binding protein which disassembles actin filaments, plays an important role in invasion and metastasis. Here, we discover that JG6, an oligomannurarate sulfate, binds to cofilin, suppresses the migration of human breast cancer cells and cancer metastasis in breast cancer xenograft model. Mechanistically, JG6 occupies actin-binding sites of cofilin, thereby disrupting cofilin modulated actin turnover. Our results highlight the significance of cofilin in cancer and suggest JG6, a cofilin inhibitor, to treat metastatic cancer.

Mesenchymal chemotaxis requires selective inactivation of myosin II at the leading edge via a noncanonical PLCγ/PKCα pathway

Chemotaxis, migration toward soluble chemical cues, is critical for processes such as wound healing and immune surveillance and is exhibited by various cell types, from rapidly migrating leukocytes to slow-moving mesenchymal cells. To study mesenchymal chemotaxis, we observed cell migration in microfluidic chambers that generate stable gradients of platelet-derived growth factor (PDGF). Surprisingly, we found that pathways implicated in amoeboid chemotaxis, such as PI3K and mammalian target of rapamycin signaling, are dispensable for PDGF chemotaxis. Instead, we find that local inactivation of Myosin IIA, through a noncanonical Ser1/2 phosphorylation of the regulatory light chain, is essential. This site is phosphorylated by PKCα, which is activated by an intracellular gradient of diacylglycerol generated by PLCγ. Using a combination of live imaging and gradients of activators/inhibitors in the microfluidic chambers, we demonstrate that this signaling pathway and subsequent inhibition of Myosin II activity at the leading edge are required for mesenchymal chemotaxis.

Invasive breast carcinoma cells from patients exhibit MenaINV- and macrophage-dependent transendothelial migration

Metastasis is a complex, multistep process of cancer progression that has few treatment options. A critical event is the invasion of cancer cells into blood vessels (intravasation), through which cancer cells disseminate to distant organs. Breast cancer cells with increased abundance of Mena [an epidermal growth factor (EGF)-responsive cell migration protein] are present with macrophages at sites of intravasation, called TMEM sites (for tumor microenvironment of metastasis), in patient tumor samples. Furthermore, the density of these intravasation sites correlates with metastatic risk in patients. We found that intravasation of breast cancer cells may be prevented by blocking the signaling between cancer cells and macrophages. We obtained invasive breast ductal carcinoma cells of various subtypes by fine-needle aspiration (FNA) biopsies from patients and found that, in an in vitro transendothelial migration assay, cells that migrated through a layer of human endothelial cells were enriched for the transcript encoding Mena(INV), an invasive isoform of Mena. This enhanced transendothelial migration required macrophages and occurred with all of the breast cancer subtypes. Using mouse macrophages and the human cancer cells from the FNAs, we identified paracrine and autocrine activation of colony-stimulating factor-1 receptor (CSF-1R). The paracrine or autocrine nature of the signal depended on the breast cancer cell subtype. Knocking down Mena(INV) or adding an antibody that blocks CSF-1R function prevented transendothelial migration. Our findings indicate that Mena(INV) and TMEM frequency are correlated prognostic markers and CSF-1 and Mena(INV) may be therapeutic targets to prevent metastasis of multiple breast cancer subtypes.

Movers and shakers: cell cytoskeleton in cancer metastasis

Metastasis is responsible for the greatest number of cancer deaths. Metastatic disease, or the movement of cancer cells from one site to another, is a complex process requiring dramatic remodelling of the cell cytoskeleton. The various components of the cytoskeleton, actin (microfilaments), microtubules (MTs) and intermediate filaments, are highly integrated and their functions are well orchestrated in normal cells. In contrast, mutations and abnormal expression of cytoskeletal and cytoskeletal-associated proteins play an important role in the ability of cancer cells to resist chemotherapy and metastasize. Studies on the role of actin and its interacting partners have highlighted key signalling pathways, such as the Rho GTPases, and downstream effector proteins that, through the cytoskeleton, mediate tumour cell migration, invasion and metastasis. An emerging role for MTs in tumour cell metastasis is being unravelled and there is increasing interest in the crosstalk between key MT interacting proteins and the actin cytoskeleton, which may provide novel treatment avenues for metastatic disease. Improved understanding of how the cytoskeleton and its interacting partners influence tumour cell migration and metastasis has led to the development of novel therapeutics against aggressive and metastatic disease.

LINKED ARTICLES

This article is part of a themed section on Cytoskeleton, Extracellular Matrix, Cell Migration, Wound Healing and Related Topics. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-24.

Protein kinase d isoforms differentially modulate cofilin-driven directed cell migration

Background

Protein kinase D (PKD) enzymes regulate cofilin-driven actin reorganization and directed cell migration through both p21-activated kinase 4 (PAK4) and the phosphatase slingshot 1L (SSH1L). The relative contributions of different endogenous PKD isoforms to both signaling pathways have not been elucidated, sufficiently.

Methodology/Principal Findings

We here analyzed two cell lines (HeLa and MDA-MB-468) that express the subtypes protein kinase D2 (PKD2) and protein kinase D3 (PKD3). We show that under normal growth conditions both isoforms can form a complex, in which PKD3 is basally-active and PKD2 is inactive. Basal activity of PKD3 mediates PAK4 activity and downstream signaling, but does not significantly inhibit SSH1L. This signaling constellation was required for facilitating directed cell migration. Activation of PKD2 and further increase of PKD3 activity leads to additional phosphorylation and inhibition of endogenous SSH1L. Net effect is a dramatic increase in phospho-cofilin and a decrease in cell migration, since now both PAK4 and SSH1L are regulated by the active PKD2/PKD3 complex.

Conclusions/Significance

Our data suggest that PKD complexes provide an interface for both cofilin regulatory pathways. Dependent on the activity of involved PKD enzymes signaling can be balanced to guarantee a functional cofilin activity cycle and increase cell migration, or imbalanced to decrease cell migration. Our data also provide an explanation of how PKD isoforms mediate different effects on directed cell migration.

Cofilin drives cell-invasive and metastatic responses to TGF-β in prostate cancer

Cofilin (CFL) is an F-actin-severing protein required for the cytoskeleton reorganization and filopodia formation, which drives cell migration. CFL binding and severing of F-actin is controlled by Ser3 phosphorylation, but the contributions of this step to cell migration during invasion and metastasis of cancer cells are unclear. In this study, we addressed the question in prostate cancer cells, including the response to TGF-β, a critical regulator of migration. In cells expressing wild-type CFL, TGF-β treatment increased LIMK-2 activity and cofilin phosphorylation, decreasing filopodia formation. Conversely, constitutively active CFL (SerAla) promoted filipodia formation and cell migration mediated by TGF-β. Notably, in cocultures of prostate cancer epithelial cells and cancer-associated fibroblasts, active CFL promoted invasive migration in response to TGF-β in the microenvironment. Further, constitutively active CFL elevated the metastatic ability of prostate cancer cells in vivo. We found that levels of active CFL correlated with metastasis in a mouse model of prostate tumor and that in human prostate cancer, CFL expression was increased significantly in metastatic tumors. Our findings show that the actin-severing protein CFL coordinates responses to TGF-β that are needed for invasive cancer migration and metastasis.

Swiprosin-1 modulates actin dynamics by regulating the F-actin accessibility to cofilin

Membrane protrusions, like lamellipodia, and cell movement are dependent on actin dynamics, which are regulated by a variety of actin-binding proteins acting cooperatively to reorganize actin filaments. Here, we provide evidence that Swiprosin-1, a newly identified actin-binding protein, modulates lamellipodial dynamics by regulating the accessibility of F-actin to cofilin. Overexpression of Swiprosin-1 increased lamellipodia formation in B16F10 melanoma cells, whereas knockdown of Swiprosin-1 inhibited EGF-induced lamellipodia formation, and led to a loss of actin stress fibers at the leading edges of cells but not in the cell cortex. Swiprosin-1 strongly facilitated the formation of entangled or clustered F-actin, which remodeled the structural organization of actin filaments making them in accessible to cofilin. EGF-induced phosphorylation of Swiprosin-1 at Ser183, a phosphorylation site newly identified using mass spectrometry, effectively inhibited clustering of actin filaments and permitted cofilin access to F-actin, resulting in actin depolymerization. Cells over expressing a Swiprosin-1 phosphorylation-mimicking mutant or a phosphorylation-deficient mutant exhibited irregular membrane dynamics during the protrusion and retraction cycles of lamellipodia. Taken together, these findings suggest that dynamic exchange of Swiprosin-1 phosphorylation and dephosphorylation is a novel mechanism that regulates actin dynamics by modulating the pattern of cofilin activity at the leading edges of cells.

Dynamic chemotactic response of fibroblasts to local stimulation using EGF-immobilized microbeads

Directional cellular migrations as a chemotactic response to spatially inhomogeneous growth factor stimulation play an important role in establishing physiological mechanisms and pathological events in cells. We developed epidermal growth factor (EGF)-immobilized microbeads by photoreaction and evaluated its local stimulatory effects on the dynamic chemotactic motility of fibroblasts. The local stimulation resulted in global activation of ERK 1/2 and directionality of cellular migration. The cellular migration by stimulation using 3-μm diameter EGF-immobilized microbeads persisted for a longer time, were involved a wider field and their number were further increased with stimulation. This effective technique allows cellular migration and biochemical analyses that will help elucidate the mechanisms involved in signal transduction by spatially inhomogeneous stimulation of the growth factor.

Protein kinase D-mediated phosphorylation at Ser99 regulates localization of p21-activated kinase 4

PAKs (p21-activated kinases) are effectors of RhoGTPases. PAK4 contributes to regulation of cofilin at the leading edge of migrating cells through activation of LIMK (Lin-11/Isl-1/Mec-3 kinase). PAK4 activity is regulated by an autoinhibitory domain that is released upon RhoGTPase binding as well as phosphorylation at Ser474 in the activation loop of the kinase domain. In the present study, we add another level of complexity to PAK4 regulation by showing that phosphorylation at Ser99 is required for its targeting to the leading edge. This phosphorylation is mediated by PKD1 (protein kinase D1). Phosphorylation of PAK4 at Ser99 also mediates binding to 14-3-3 protein, and is required for the formation of a PAK4-LIMK-PKD1 complex that regulates cofilin activity and directed cell migration.

O-GlcNAcylation of cofilin promotes breast cancer cell invasion

O-GlcNAcylation is a post-translational modification that regulates a broad range of nuclear and cytoplasmic proteins and is emerging as a key regulator of various biological processes. Previous studies have shown that increased levels of global O-GlcNAcylation and O-GlcNAc transferase (OGT) are linked to the incidence of metastasis in breast cancer patients, but the molecular basis behind this is not fully known. In this study, we have determined that the actin-binding protein cofilin is O-GlcNAcylated by OGT and mainly, if not completely, mediates OGT modulation of cell mobility. O-GlcNAcylation at Ser-108 of cofilin is required for its proper localization in invadopodia at the leading edge of breast cancer cells during three-dimensional cell invasion. Loss of O-GlcNAcylation of cofilin leads to destabilization of invadopodia and impairs cell invasion, although the actin-severing activity or lamellipodial localization is not affected. Our study provides insights into the mechanism of post-translational modification in fine-tuning the regulation of cofilin activity and suggests its important implications in cancer metastasis.

Cofilin: a redox sensitive mediator of actin dynamics during T-cell activation and migration

Cofilin is an actin-binding protein that depolymerizes and/or severs actin filaments. This dual function of cofilin makes it one of the major regulators of actin dynamics important for T-cell activation and migration. The activity of cofilin is spatio-temporally regulated. Its main control mechanisms comprise a molecular toolbox of phospho-, phospholipid, and redox regulation. Phosphorylated cofilin is inactive and represents the dominant cofilin fraction in the cytoplasm of resting human T cells. A fraction of dephosphorylated cofilin is kept inactive at the plasma membrane by binding to phosphatidylinositol 4,5-bisphosphate. Costimulation via the T-cell receptor/CD3 complex (signal 1) together with accessory receptors (signal 2) or triggering through the chemokine SDF1α (stromal cell-derived factor 1α) induce Ras-dependent dephosphorylation of cofilin, which is important for immune synapse formation, T-cell activation, and T-cell migration. Recently, it became evident that cofilin is also highly sensitive for microenvironmental changes, particularly for alterations in the redox milieu. Cofilin is inactivated by oxidation, provoking T-cell hyporesponsiveness or necrotic-like programmed cell death. In contrast, in a reducing environment, even phosphatidylinositol 4,5-bisphosphate-bound cofilin becomes active, leading to actin dynamics in the vicinity of the plasma membrane. In addition to the well-established three signals for T-cell activation, this microenvironmental control of cofilin delivers a modulating signal for T-cell-dependent immune reactions. This fourth modulating signal highly impacts both initial T-cell activation and the effector phase of T-cell-mediated immune responses.

The effect of carbonic anhydrase IX on focal contacts during cell spreading and migration

Carbonic anhydrase IX is a hypoxia-induced transmembrane enzyme linked with solid tumors. It catalyzes the reversible hydration of CO2 providing bicarbonate ions for intracellular neutralization and protons for extracellular acidosis, thereby supporting tumor cell survival and invasiveness. CA IX is the only human CA isoform containing the proteoglycan (PG) domain in its extracellular part. The PG domain appears to enhance the catalytic activity of CA IX and mediate its binding to the extracellular matrix. Moreover, manipulation of the CA IX level by siRNA or overexpression modulates cell adhesion pathway so that in the presence of CA IX, cells display an increased rate of adhesion and spreading. Here we show that deletion of the PG domain as well as treatment with the PG-binding monoclonal antibody M75 can impair this CA IX effect. Accordingly, CA IX-expressing cells show more prominent and elongated maturing paxillin-stained focal contacts (FC) than CA IX-negative controls, proving the role of CA IX in cell spreading. However, during active cell movement, CA IX is relocalized to lamellipodia and improves migration via its catalytic domain. Thus, we examined the influence of CA IX on FC turnover in these structures. While the lamellipodial regions lacking CA IX display dash-like adhesions, the CA IX-enriched neighboring regions exhibit dynamic dot-like FCs. These results suggest that CA IX can promote initial adhesion through its PG domain, but at the same time it facilitates formation of nascent adhesions at the leading edge of moving cells. Thereby it may allow for transmission of large forces and enhanced migration rate, presumably through catalytic activity and impact of pHe on FC dynamics. Thus, we provide the first evidence that CA IX protein localizes directly in focal adhesion (FA) structures and propose its functional relationship with the proteins involved in the regulation of FC turnover and maturation.

A reducing milieu renders cofilin insensitive to phosphatidylinositol 4,5-bisphosphate (PIP2) inhibition

Oxidative stress can lead to T cell hyporesponsiveness. A reducing micromilieu (e.g. provided by dendritic cells) can rescue T cells from such oxidant-induced dysfunction. However, the reducing effects on proteins leading to restored T cell activation remained unknown. One key molecule of T cell activation is the actin-remodeling protein cofilin, which is dephosphorylated on serine 3 upon T cell costimulation and has an essential role in formation of mature immune synapses between T cells and antigen-presenting cells. Cofilin is spatiotemporally regulated; at the plasma membrane, it can be inhibited by phosphatidylinositol 4,5-bisphosphate (PIP₂). Here, we show by NMR spectroscopy that a reducing milieu led to structural changes in the cofilin molecule predominantly located on the protein surface. They overlapped with the PIP₂- but not actin-binding sites. Accordingly, reduction of cofilin had no effect on F-actin binding and depolymerization and did not influence the cofilin phosphorylation state. However, it did prevent inhibition of cofilin activity through PIP₂. Therefore, a reducing milieu may generate an additional pool of active cofilin at the plasma membrane. Consistently, in-flow microscopy revealed increased actin dynamics in the immune synapse of untransformed human T cells under reducing conditions. Altogether, we introduce a novel mechanism of redox regulation: reduction of the actin-remodeling protein cofilin renders it insensitive to PIP₂ inhibition, resulting in enhanced actin dynamics.

PTTG1 promotes migration and invasion of human non-small cell lung cancer cells and is modulated by miR-186

Deeper mechanistic understanding of non-small cell lung cancer (NSCLC), a leading cause of total cancer-related deaths, may facilitate the establishment of more effective therapeutic strategies. In this study, pituitary tumor transforming gene (PTTG1) expression was associated with lymph node and distant metastasis in patients with NSCLC and was correlated with patient survival. Reduction of PTTG1 by small interfering RNA (siRNA) inhibits the migration and invasion of NSCLC cells by mediating matrix metalloproteinases expression. To the best of our knowledge, this study is the first to report that PTTG1 promotes epidermal growth factor (EGF) induced the phosphorylation of LIN-11, Isl1 and MEC-3 protein domain kinase and cofilin, a critical step in cofilin recycling and actin polymerization. Additionally, EGF-induced Akt phosphorylation was suppressed through knockdown of PTTG1. Interestingly, miR-186 can modulate PTTG1 protein expression. As observed from the animal experiment in this study, knockdown of PTTG1 through siRNA and overexpression of miR-186 inhibited invasive activity of NSCLC cells toward the SCID mice lung. In summary, our in vitro and in vivo results indicate that PTTG1 modulated by miR-186 has an important function in NSCLC invasion/metastasis. This study identified both PTTG1 and miR-186 as potential anti-invasion targets for therapeutic intervention in NSCLC.

The switch-associated protein 70 (SWAP-70) bundles actin filaments and contributes to the regulation of F-actin dynamics

Coordinated assembly and disassembly of actin into filaments and higher order structures such as stress fibers and lamellipodia are fundamental for cell migration and adhesion. However, the precise spatiotemporal regulation of F-actin structures is not completely understood. SWAP-70, a phosphatidylinositol 3,4,5-trisphosphate-interacting, F-actin-binding protein, participates in actin rearrangements through yet unknown mechanisms. Here, we show that SWAP-70 is an F-actin-bundling protein that oligomerizes through a Gln/Glu-rich stretch within a coiled-coil region. SWAP-70 bundles filaments in parallel and anti-parallel fashion through its C-terminal F-actin binding domain and delays dilution-induced F-actin depolymerization. We further demonstrate that SWAP-70 co-localizes and directly interacts with cofilin, an F-actin severing and depolymerization factor, and contributes to the regulation of cofilin activity in vivo. In line with these activities, upon stem cell factor stimulation, murine bone marrow-derived mast cells lacking SWAP-70 display aberrant regulation of F-actin and actin free barbed ends dynamics. Moreover, proper stem cell factor-dependent cofilin activation via dephosphorylation and subcellular redistribution into a detergent-resistant cytoskeletal compartment also require SWAP-70. Together, these findings reveal an important role of SWAP-70 in the dynamic spatiotemporal regulation of F-actin networks.