N-WASP-mediated invadopodium formation is involved in intravasation and lung metastasis of mammary tumors

Active invadopodia of mesenchymally migrating cancer cells contain both β and γ cytoplasmic actin isoforms

Invadopodia are actin-rich protrusions formed by mesenchymally migrating cancer cells. They are mainly composed of actin, actin-associated proteins, integrins and proteins of signaling machineries. These protrusions display focalized proteolytic activity towards the extracellular matrix. It is well known that polymerized (F-)actin is present in these structures, but the nature of the actin isoform has not been studied before. We here show that both cytoplasmic actin isoforms, β- and γ-actin, are present in the invadopodia of MDA-MB-231 breast cancer cells cultured on a 2D-surface, where they colocalize with the invadopodial marker cortactin. Invadopodial structures formed by the cells in a 3D-collagen matrix also contain β- and γ-actin. We demonstrate this using isoform-specific antibodies and expression of fluorescently-tagged actin isoforms. Additionally, using simultaneous expression of differentially tagged β- and γ-actin in cells, we show that the actin isoforms are present together in a single invadopodium. Cells with an increased level of β- or γ-actin, display a similar increase in the number and size of invadopodia in comparison to control cells. Moreover, increasing the level of either actin isoforms also increases invasion velocity.

Endothelin A receptor drives invadopodia function and cell motility through the β-arrestin/PDZ-RhoGEF pathway in ovarian carcinoma

The endothelin-1 (ET-1)/ET A receptor (ETAR) signalling pathway is a well-established driver of epithelial ovarian cancer (EOC) progression. One key process promoted by ET-1 is tumor cell invasion, which requires the scaffolding functions of β-arrestin-1 (β-arr1) downstream of the receptor; however, the potential role of ET-1 in inducing invadopodia, which are crucial for cellular invasion and tumor metastasis, is completely unknown. We describe here that ET-1/ETAR, through β-arr1, activates RhoA and RhoC GTPase and downstream ROCK (Rho-associated coiled coil-forming kinase) kinase activity, promoting actin-based dynamic remodelling and enhanced cell invasion. This is accomplished by the direct interaction of β-arr1 with PDZ-RhoGEF (postsynaptic density protein 95/disc-large/zonula occludens-RhoGEF). Interestingly, ETAR-mediated invasive properties are related to the regulation of invadopodia, as evaluated by colocalization of actin with cortactin, as well as with TKS5 and MT1-MMP (membrane type 1-matrix metalloproteinase) with areas of matrix degradation, and activation of cofilin pathway, which is crucial for regulating invadopodia activity. Depletion of PDZ-RhoGEF, or β-arr1, or RhoC, as well as the treatment with the dual ET-1 receptor antagonist macitentan, significantly impairs invadopodia function, MMP activity and invasion, demonstrating that β-arr1/PDZ-RhoGEF interaction mediates ETAR-driven ROCK-LIMK-cofilin pathway through the control of RhoC activity. In vivo, macitentan is able to inhibit metastatic dissemination and cofilin phosphorylation. Collectively, our data unveil a noncanonical activation of the RhoC/ROCK pathway through the β-arr1/PDZ-RhoGEF complex as a regulator of ETAR-induced motility and metastasis, establishing ET-1 axis as a novel regulator of invadopodia protrusions through the RhoC/ROCK/LIMK/cofilin pathway during the initial steps of EOC invasion.

In vivo fluorescence microscopy: lessons from observing cell behavior in their native environment

Microscopic imaging techniques to visualize cellular behaviors in their natural environment play a pivotal role in biomedical research. Here, we review how recent technical advances in intravital microscopy have enabled unprecedented access to cellular physiology in various organs of mice in normal and diseased states.

In vivo subcellular resolution optical imaging in the lung reveals early metastatic proliferation and motility

To better understand breast cancer metastatic cell seeding, we have employed multiphoton microscopy and a vacuum stabilized window which eliminates the need for complex registration software, video rate microscopy or specialized gating electronics to observe the initial steps of tumor cell seeding within the living, breathing lung. We observe that upon arrival to the lung, tumor cells are found exclusively in capillary vessels, completely fill their volume and display an initial high level of protrusive activity that dramatically reduces over time. Further, we observe a concomitant increase in positional stability during this same period. We employ several techniques accessible to most imaging labs for optimizing signal to noise and resolution which enable us to report the first direct observation, with subcellular resolution, of the arrival, proliferation, and motility of metastatic tumor cells within the lung.

N-wasp in pancreatic ductal adenocarcinoma: associations with perineural invasion and poor prognosis

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has long been acknowledged to have a dismal prognosis. Therefore, prognostic markers, especially molecular ones, are of interest. So far, expression of Neural Wiskott-Aldrich syndrome protein (N-WASP) and its associations with clinicopathologic variables and prognosis for patients with PDAC remain unknown.

METHODS

N-WASP expression was detected by immunohistochemical staining in a tissue microarray consisted of tumor and nontumor samples from 86 patients with PDAC. The correlations of N-WASP expression with clinicopathologic features and overall survival were evaluated. In addition, risk factors of perineural invasion (PNI) were identified.

RESULTS

High expression of N-WASP was more frequent in tumor than in nontumor tissues of PDAC patients (45.3 vs. 19.8%, p < 0.001). The rank of N-WASP grading was significantly higher in tumor tissues than in nontumor tissues (p = 0.048). Also, high expression of N-WASP in tumor tissues was significantly associated with PNI, and lymph node status had a marginally significant relation to tumoral N-WASP expression. Univariate analyses showed that, in addition to conventional clinicopathologic variables, including sex, histologic grade, PNI and lymph node metastasis, high tumoral N-WASP expression was an independent marker of PNI and served as a significant predictor of poor overall survival. The prognostic implication of N-WASP expression was not proven In the multivariate analysis.

CONCLUSIONS

Our data showed highly up-regulated expression of N-WASP in PDAC tissues, its correlations with PNI, and its association with an unfavorable prognosis.

Coupling between acto-adhesive machinery and ECM degradation in invadosomes

Invadosomes have two main functions represented by their actin-rich and adhesive components and their polarized secretory pathways controlling the delivery of metalloproteases necessary to degrade extracellular matrix (ECM). Invadosomes include invadopodia and podosomes, which have subtle differences in molecular composition, dynamics, and structure. These differences could reflect different stages of invadosome maturation. This review will outline current knowledge on the coupling between the acto-adhesive machinery and the ECM degradation activity in invadosome diversity. Multiple works support that these two functions are not automatically linked but seem to be finely regulated to allow different functions of invadosomes. We will explore the paradigmatic aspect of invadosomes, which are able to interact with ECM to degrade it so as to better control their own dynamics. Understanding the fine-tuning between these two functions could serve to understand the link between the different types of invadosomes from invadopodia to podosomes.

Invadopodia and basement membrane invasion in vivo

Over 20 years ago, protrusive, F-actin-based membrane structures, termed invadopodia, were identified in highly metastatic cancer cell lines. Invadopodia penetrate artificial or explanted extracellular matrices in 2D culture conditions and have been hypothesized to facilitate the migration of cancer cells through basement membrane, a thin, dense, barrier-like matrix surrounding most tissues. Despite intensive study, the identification of invadopodia in vivo has remained elusive and until now their possible roles during invasion or even existence have remained unclear. Studies in remarkably different cellular contexts-mouse tumor models, zebrafish intestinal epithelia, and C. elegans organogenesis-have recently identified invadopodia structures associated with basement membrane invasion. These studies are providing the first in vivo insight into the regulation, function, and role of these fascinating subcellular devices with critical importance to both development and human disease.

The interplay between the proteolytic, invasive, and adhesive domains of invadopodia and their roles in cancer invasion

Invadopodia are actin-based protrusions of the plasma membrane that penetrate into the extracellular matrix (ECM), and enzymatically degrade it. Invadopodia and podosomes, often referred to, collectively, as "invadosomes," are actin-based membrane protrusions that facilitate matrix remodeling and cell invasion across tissues, processes that occur under specific physiological conditions such as bone remodeling, as well as under pathological states such as bone, immune disorders, and cancer metastasis. In this review, we specifically focus on the functional architecture of invadopodia in cancer cells; we discuss here three functional domains of invadopodia responsible for the metalloproteinase-based degradation of the ECM, the cytoskeleton-based mechanical penetration into the matrix, and the integrin adhesome-based adhesion to the ECM. We will describe the structural and molecular organization of each domain and the cross-talk between them during the invasion process.

Regulation of invadopodia by the tumor microenvironment

The tumor microenvironment consists of stromal cells, extracellular matrix (ECM), and signaling molecules that communicate with cancer cells. As tumors grow and develop, the tumor microenvironment changes. In addition, the tumor microenvironment is not only influenced by signals from tumor cells, but also stromal components contribute to tumor progression and metastasis by affecting cancer cell function. One of the mechanisms that cancer cells use to invade and metastasize is mediated by actin-rich, proteolytic structures called invadopodia. Here, we discuss how signals from the tumor environment, including growth factors, hypoxia, pH, metabolism, and stromal cell interactions, affect the formation and function of invadopodia to regulate cancer cell invasion and metastasis. Understanding how the tumor microenvironment affects invadopodia biology could aid in the development of effective therapeutics to target cancer cell invasion and metastasis.

Role of the WASP and WAVE family proteins in breast cancer invasion and metastasis

The Wiskott–Aldrich syndrome protein (WASP) and WASP family verprolin-homologous protein (WAVE) family are a group of molecules that form a key link between GTPases and the actin cytoskeleton. The role of WASP/WAVE family proteins in the control of actin polymerization through activation of the actin-related protein 2/3 complex is critical in the formation of the actin-based membrane protrusions seen in cell migration and invasion. For this reason, the activity of the WASP/WAVE family in cancer cell invasion and migration has been of great interest in recent years. Many reports have highlighted the potential of targeting the WASP/WAVE family as a therapy for the prevention of cancer progression, in particular breast cancer. This review focuses on the role of the WASP/WAVE family in breast cancer cell invasion and migration and how this relates to the molecular mechanisms of WASP/WAVE activity, their exact contributions to the stages of cancer progression, and how this can lead to the development of anticancer drugs that target the WASP/WAVE family and related pathways.

CD147: regulator of hyaluronan signaling in invasiveness and chemoresistance

Major determinants that influence negative outcome in cancer patients are the abilities of cancer cells to resist current therapies and to invade surrounding host tissue, consequently leading to local and metastatic dissemination. Hyaluronan (HA), a prominent constituent of the tumor microenvironment, not only provides structural support but also interacts with cell surface receptors, especially CD44, that influence cooperative signaling pathways leading to chemoresistance and invasiveness. CD147 (emmprin; basigin) is a member of the Ig superfamily that has also been strongly implicated in chemoresistance and invasiveness. CD147 both regulates HA synthesis and interacts with the HA receptors, CD44, and LYVE-1. Increased CD147 expression induces formation of multiprotein complexes containing CD44 (or LYVE-1) as well as members of the membrane-type matrix metalloproteinase, receptor tyrosine kinase, ABC drug transporter, or monocarboxylate transporter families, which become assembled in specialized lipid raft domains along with CD147 itself. In each case, multivalent HA-receptor interactions are essential for formation or stabilization of the lipid raft complexes and for downstream signaling pathways or transporter activities that are driven by these complexes. We conclude that cooperativity between HA, HA receptors, and CD147 may be a major driver of the interconnected pathways of invasiveness and chemoresistance widely critical to malignancy.

Mechanical interplay between invadopodia and the nucleus in cultured cancer cells

Invadopodia are actin-rich membrane protrusions through which cells adhere to the extracellular matrix and degrade it. In this study, we explored the mechanical interactions of invadopodia in melanoma cells, using a combination of correlative light and electron microscopy. We show here that the core actin bundle of most invadopodia interacts with integrin-containing matrix adhesions at its basal end, extends through a microtubule-rich cytoplasm, and at its apical end, interacts with the nuclear envelope and indents it. Abolishment of invadopodia by microtubules or src inhibitors leads to the disappearance of these nuclear indentations. Based on the indentation profile and the viscoelastic properties of the nucleus, the force applied by invadopodia is estimated to be in the nanoNewton range. We further show that knockdown of the LINC complex components nesprin 2 or SUN1 leads to a substantial increase in the prominence of the adhesion domains at the opposite end of the invadopodia. We discuss this unexpected, long-range mechanical interplay between the apical and basal domains of invadopodia, and its possible involvement in the penetration of invadopodia into the matrix.

Dense fibrillar collagen is a potent inducer of invadopodia via a specific signaling network

High-density fibrillar collagen matrix induces invadopodia formation in both fibroblasts and carcinoma cell lines through a kindlin2-dependent mechanism that drives local ECM remodeling.

Cell interactions with the extracellular matrix (ECM) can regulate multiple cellular activities and the matrix itself in dynamic, bidirectional processes. One such process is local proteolytic modification of the ECM. Invadopodia of tumor cells are actin-rich proteolytic protrusions that locally degrade matrix molecules and mediate invasion. We report that a novel high-density fibrillar collagen (HDFC) matrix is a potent inducer of invadopodia, both in carcinoma cell lines and in primary human fibroblasts. In carcinoma cells, HDFC matrix induced formation of invadopodia via a specific integrin signaling pathway that did not require growth factors or even altered gene and protein expression. In contrast, phosphoproteomics identified major changes in a complex phosphosignaling network with kindlin2 serine phosphorylation as a key regulatory element. This kindlin2-dependent signal transduction network was required for efficient induction of invadopodia on dense fibrillar collagen and for local degradation of collagen. This novel phosphosignaling mechanism regulates cell surface invadopodia via kindlin2 for local proteolytic remodeling of the ECM.

A journey to uncharted territory: new technical frontiers in studying tumor-stromal cell interactions

The crosstalk between tumor cells and cells of the tumor stroma dictate malignant progression and represent an intriguing and viable anticancer therapeutic target. The successful development of therapeutics targeting tumor-stroma interactions is tied to the insight provided by basic research on such crosstalk. Tumor-stroma interactions can be transient and dynamic, and they occur within defined spatiotemporal contexts among genetically and compositionally heterogeneous populations of cells, yet methods currently applied to study the said crosstalk do not sufficiently address these features. Emerging imaging and genetic methods, however, can overcome limitations of traditional approaches and provide unprecedented insight into tumor-stroma crosstalk with unparalleled accuracy. The comprehensive data obtained by applying emerging methods will require processing and analysis by multidisciplinary teams, but the efforts will ultimately rejuvenate hope in developing novel therapies against pro-tumorigenic tumor-stroma crosstalk.

Profilin1 regulates invadopodium maturation in human breast cancer cells

Invadopodia are actin-driven membrane protrusions that show oscillatory assembly and disassembly causing matrix degradation to support invasion and dissemination of cancer cells in vitro and in vivo. Profilin1, an actin and phosphoinositide binding protein, is downregulated in several adenocarcinomas and it is been shown that its depletion enhances invasiveness and motility of breast cancer cells by increasing PI(3,4)P2 levels at the leading edge. In this study, we show for the first time that depletion of profilin1 leads to an increase in the number of mature invadopodia and these assemble and disassemble more rapidly than in control cells. Previous work by Sharma et al. (2013a), has shown that the binding of the protein Tks5 with PI(3,4)P2 confers stability to the invadopodium precursor causing it to mature into a degradation-competent structure. We found that loss of profilin1 expression increases the levels of PI(3,4)P2 at the invadopodium and as a result, enhances recruitment of the interacting adaptor Tks5. The increased PI(3,4)P2-Tks5 interaction accelerates the rate of invadopodium anchorage, maturation, and turnover. Our results indicate that profilin1 acts as a molecular regulator of the levels of PI(3,4)P2 and Tks5 recruitment in invadopodia to control the invasion efficiency of invadopodia.

Toca-1 is suppressed by p53 to limit breast cancer cell invasion and tumor metastasis

Introduction

Transducer of Cdc42-dependent actin assembly-1 (Toca-1) recruits actin regulatory proteins to invadopodia, and promotes breast tumor metastasis. Since metastatic breast tumors frequently harbor mutations in the tumor suppressor p53, we tested whether p53 regulates Toca-1 expression.

Methods

Normal mammary epithelial cells (HBL-100, MCF10A) and breast cancer cell lines expressing wild-type (WT) p53 (DU4475, MTLn3) were treated with camptothecin or Nutlin-3 to stabilize p53 to test effects on Toca-1 mRNA and protein levels. Chromatin immunoprecipitation (ChIP) assays were performed to identify p53 binding site in Toca-1 gene. Stable silencing of p53 and Toca-1 were performed in MTLn3 cells to test effects on invadopodia and cell invasion in vitro, and tumor metastasis in vivo.

Results

We observed that breast cancer cell lines with mutant p53 have high levels of Toca-1 compared to those with WT p53. Stabilization of WT p53 led to further reduction in Toca-1 mRNA and protein levels in normal breast epithelial cells and breast cancer cells. ChIP assays revealed p53 binding within intron 2 of toca1, and reduced histone acetylation within its promoter region upon p53 upregulation or activation. Stable silencing of WT p53 in MTLn3 cells led to increased extracellular matrix degradation and cell invasion compared to control cells. Interestingly, the combined silencing of p53 and Toca-1 led to a partial rescue of these effects of p53 silencing in vitro and reduced lung metastases in mice. In human breast tumors, Toca-1 levels were high in subtypes with frequent p53 mutations, and high Toca-1 transcript levels correlated with increased risk of relapse.

Conclusions

Based on these findings, we conclude that loss of p53 tumor suppressor function in breast cancers leads to upregulation of Toca-1, and results in enhanced risk of developing metastatic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0503-x) contains supplementary material, which is available to authorized users.

Multiparametric classification links tumor microenvironments with tumor cell phenotype

Tumor microenvironment features are established as predictors of tumor cell behavior and fate.

While it has been established that a number of microenvironment components can affect the likelihood of metastasis, the link between microenvironment and tumor cell phenotypes is poorly understood. Here we have examined microenvironment control over two different tumor cell motility phenotypes required for metastasis. By high-resolution multiphoton microscopy of mammary carcinoma in mice, we detected two phenotypes of motile tumor cells, different in locomotion speed. Only slower tumor cells exhibited protrusions with molecular, morphological, and functional characteristics associated with invadopodia. Each region in the primary tumor exhibited either fast- or slow-locomotion. To understand how the tumor microenvironment controls invadopodium formation and tumor cell locomotion, we systematically analyzed components of the microenvironment previously associated with cell invasion and migration. No single microenvironmental property was able to predict the locations of tumor cell phenotypes in the tumor if used in isolation or combined linearly. To solve this, we utilized the support vector machine (SVM) algorithm to classify phenotypes in a nonlinear fashion. This approach identified conditions that promoted either motility phenotype. We then demonstrated that varying one of the conditions may change tumor cell behavior only in a context-dependent manner. In addition, to establish the link between phenotypes and cell fates, we photoconverted and monitored the fate of tumor cells in different microenvironments, finding that only tumor cells in the invadopodium-rich microenvironments degraded extracellular matrix (ECM) and disseminated. The number of invadopodia positively correlated with degradation, while the inhibiting metalloproteases eliminated degradation and lung metastasis, consistent with a direct link among invadopodia, ECM degradation, and metastasis. We have detected and characterized two phenotypes of motile tumor cells in vivo, which occurred in spatially distinct microenvironments of primary tumors. We show how machine-learning analysis can classify heterogeneous microenvironments in vivo to enable prediction of motility phenotypes and tumor cell fate. The ability to predict the locations of tumor cell behavior leading to metastasis in breast cancer models may lead towards understanding the heterogeneity of response to treatment.

A large proportion of cancer deaths are due to metastasis—the spread of cancer from the primary tumor to other parts of the body. Movement of cells may require the formation of protrusions called invadopodia, which degrade extracellular matrix. Although some studies have reported on locomotion in primary tumors, the presence of invadopodia was not tested. Here, we show that single cells from mouse mammary carcinoma can move using a fast- or slow-locomotion mode depending on different levels of cues present in the tumor microenvironment. Using multiphoton microscopy in vivo combined with a machine-learning algorithm we show how manipulation of microenvironmental conditions can induce predictable changes in the number of locomoting cells or switch between the two locomotion modes. We also demonstrate that only the slower moving cells are associated with invadopodia in vivo, and that only tumor cells from regions rich in invadopodia degrade the surrounding extracellular matrix and disseminate. Specific targeting of invadopodia results in inhibition of lung metastasis. This work proposes a systems biology view of how tumor microenvironments regulate tumor progression and presents insight into the heterogeneity of the treatment response. The ability to define and predict conditions under which tumor cells disseminate offers potential therapeutic benefits in regulating tumor progression.

Invadosomes in their natural habitat

Podosomes and invadopodia (collectively known as invadosomes) are small, F-actin-rich protrusions that are located at points of cell-ECM contacts and endow cells with invasive capabilities. So far, they have been identified in human or murine immune (myelomonocytic), vascular and cancer cells. The overarching reason for studying invadosomes is their connection to human disease. For example, macrophages and osteoclasts lacking Wiskott-Aldrich syndrome protein (WASp) are not able to form podosomes, and this leads to altered macrophage chemotaxis and defective bone resorption by osteoclasts. In contrast, the ability of cancer cells to form invadopodia is associated with high invasive and metastatic potentials. While invadosome composition, dynamics and signaling cascades leading to their assembly can be followed easily in in vitro assays, studying their contribution to pathophysiological processes in situ remains challenging. A number of recent papers have started to address this issue and describe invadosomes in situ in mouse models of cancer, cardiovascular disease and angiogenesis. In addition, in vivo invadosome homologs have been reported in developmental model systems such as C. elegans, zebrafish and sea squirt. Comparative analyses among different invasion mechanisms as they happen in their natural habitats, i.e., in situ, may provide an outline of the invadosome evolutionary history, and guide our understanding of the roles of the invasion process in pathophysiology versus development.

Intravital multiphoton imaging reveals multicellular streaming as a crucial component of in vivo cell migration in human breast tumors

Metastasis is the main cause of death in breast cancer patients. Cell migration is an essential component of almost every step of the metastatic cascade, especially the early step of invasion inside the primary tumor. In this report, we have used intravital multiphoton microscopy to visualize the different migration patterns of human breast tumor cells in live primary tumors. We used xenograft tumors of MDA-MB-231 cells as well as a low passage xenograft tumor from orthotopically injected patient-derived breast tumor cells. Direct visualization of human tumor cells in vivo shows two patterns of high-speed migration inside primary tumors: (1) single cells and (2) multicellular streams (i.e., cells following each other in a single file but without cohesive cell junctions). Critically, we found that only streaming and not random migration of single cells was significantly correlated with proximity to vessels, with intravasation and with numbers of elevated circulating tumor cells in the bloodstream. Finally, although the two human tumors were derived from diverse genetic backgrounds, we found that their migratory tumor cells exhibited coordinated gene expression changes that led to the same end-phenotype of enhanced migration involving activating actin polymerization and myosin contraction. Our data are the first direct visualization and assessment of in vivo migration within a live patient-derived breast xenograft tumor.

Microfabricated Systems and Assays for Studying the Cytoskeletal Organization, Micromechanics, and Motility Patterns of Cancerous Cells

Cell motions are driven by coordinated actions of the intracellular cytoskeleton - actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cells types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.

Invadopodia are required for cancer cell extravasation and are a therapeutic target for metastasis

Tumor cell extravasation is a key step during cancer metastasis, yet the precise mechanisms that regulate this dynamic process are unclear. We utilized a high-resolution time-lapse intravital imaging approach to visualize the dynamics of cancer cell extravasation in vivo. During intravascular migration, cancer cells form protrusive structures identified as invadopodia by their enrichment of MT1-MMP, cortactin, Tks4, and importantly Tks5, which localizes exclusively to invadopodia. Cancer cells extend invadopodia through the endothelium into the extravascular stroma prior to their extravasation at endothelial junctions. Genetic or pharmacological inhibition of invadopodia initiation (cortactin), maturation (Tks5), or function (Tks4) resulted in an abrogation of cancer cell extravasation and metastatic colony formation in an experimental mouse lung metastasis model. This provides direct evidence of a functional role for invadopodia during cancer cell extravasation and distant metastasis and reveals an opportunity for therapeutic intervention in this clinically important process.

Invading one step at a time: the role of invadopodia in tumor metastasis

The ability to degrade extracellular matrix is critical for tumor cells to invade and metastasize. Recent studies show that tumor cells use specialized actin-based membrane protrusions termed invadopodia to perform matrix degradation. Invadopodia provide an elegant way for tumor cells to precisely couple focal matrix degradation with directional movement. Here we discuss several key components and regulators of invadopodia that have been uniquely implicated in tumor invasion and metastasis. Furthermore, we discuss existing and new therapeutic opportunities to target invadopodia for anti-metastasis treatment.

Expression of Neural Wiskott-Aldrich Syndrome Protein in Clear Cell Renal Cell Carcinoma and Its Correlation with Clinicopathological Features

INTRODUCTION

Neural Wiskott-Aldrich syndrome protein (N-WASP) expression is associated with tumor cell invasion and migration. However, its expression status in clear cell renal cell carcinoma (CCRCC) remains unclear. We examined the level of N-WASP in CCRCC and its association with clinicopathological features characteristic.

MATERIALS AND METHODS

73 CCRCC patients who underwent radical nephrectomy or partial nephrectomy were enrolled. Immunohistochemical staining for N-WASP was performed on tissue microarrays constructed from tumor and para-tumor tissue obtained from these patients. The difference in N-WASP expression between tumor tissue and adjacent normal renal tissue was examined. Correlations between N-WASP expression in the tumor and clinicopathological parameters were analyzed and the relationship between N-WASP expression and overall survival also assessed. Uni- and multivariate survival analyses were performed.

RESULTS

N-WASP expression was significantly reduced in tumor tissues and was significantly related to the histological grade of CCRCC. A higher level of N-WASP expression in the tumor was associated with relatively poor survival in CCRCC patients. The level of N-WASP expression, age at time of surgery, and histological grade were all responsible for clinical outcome in CCRCC patients. N-WASP was an independent predictor for overall survival.

CONCLUSIONS

N-WASP was downregulated in CCRCC and could serve as a prognostic biomarker for predicting clinical outcome of CCRCC.

Autocrine CSF1R signaling mediates switching between invasion and proliferation downstream of TGFβ in claudin-low breast tumor cells

Patient data suggest that colony stimulating factor-1 (CSF1) and its receptor (CSF1R) play critical roles during breast cancer progression. We have previously shown that in human breast tumors expressing both CSF1 and CSF1R, invasion in vivo is dependent both on a paracrine interaction with tumor-associated macrophages and an autocrine regulation of CSF1R in the tumor cells themselves. Although the role of the paracrine interaction between tumor cells and macrophages has been extensively studied, very little is known about the mechanism by which the autocrine CSF1R signaling contributes to tumor progression. We show here that breast cancer patients of the claudin-low subtype have significantly increased expression of CSF1R. Using a panel of breast cancer cells lines, we confirm that CSF1R expression is elevated and regulated by TGFβ specifically in claudin-low cell lines. Abrogation of autocrine CSF1R signaling in MDA-MB-231 xenografts (a claudin-low cell line) leads to increased tumor size by enhanced proliferation, but significantly reduced invasion, dissemination and metastasis. Indeed, we show that proliferation and invasion are oppositely regulated by CSF1R downstream of TGFβ only in claudin-low cells lines. Intravital multiphoton imaging revealed that inhibition of CSF1R in the tumor cells leads to decreased in vivo motility and a more cohesive morphology. We show that, both in vitro and in vivo, CSF1R inhibition results in a reversal of claudin-low marker expression by significant upregulation of luminal keratins and tight junction proteins such as claudins. Finally, we show that artificial overexpression of claudins in MDA-MB-231 cells is sufficient to tip the cells from an invasive state to a proliferative state. Our results suggest that autocrine CSF1R signaling is essential in maintaining low claudin expression and that it mediates a switch between the proliferative and the invasive state in claudin-low tumor cells downstream of TGFβ.

The impact of hypoxia in pancreatic cancer invasion and metastasis

Intratumoral hypoxia is a common feature of solid tumors. Recent advances in cancer biology indicate that hypoxia is not only a consequence of unrestrained tumor growth, but also plays an active role in promoting tumor progression, malignancy, and resistance to therapy. Hypoxia signaling is mediated by the hypoxia-inducible factors (HIFs), which are not only stabilized under hypoxia, but also by activated oncogenes or inactivated tumor suppressors under normoxia. Hypoxia is a prominent feature of the tumor microenvironment of pancreatic tumors, also characterized by the presence of a fibrotic reaction that promotes, and is also modulated by, hypoxia. As the mechanisms by which hypoxia signaling impacts invasion and metastasis in pancreatic cancer are being elucidated, hypoxia is emerging as a key determinant of pancreatic cancer malignancy as well as an important target for therapy. Herein we present an overview of recent advances in the understanding of the impact that hypoxia has in pancreatic cancer invasion and metastasis.

Talin regulates moesin-NHE-1 recruitment to invadopodia and promotes mammary tumor metastasis

Invadopodia are actin-rich protrusions that degrade the extracellular matrix and are required for stromal invasion, intravasation, and metastasis. The role of the focal adhesion protein talin in regulating these structures is not known. Here, we demonstrate that talin is required for invadopodial matrix degradation and three-dimensional extracellular matrix invasion in metastatic breast cancer cells. The sodium/hydrogen exchanger 1 (NHE-1) is linked to the cytoskeleton by ezrin/radixin/moesin family proteins and is known to regulate invadopodium-mediated matrix degradation. We show that the talin C terminus binds directly to the moesin band 4.1 ERM (FERM) domain to recruit a moesin-NHE-1 complex to invadopodia. Silencing talin resulted in a decrease in cytosolic pH at invadopodia and blocked cofilin-dependent actin polymerization, leading to impaired invadopodium stability and matrix degradation. Furthermore, talin is required for mammary tumor cell motility, intravasation, and spontaneous lung metastasis in vivo. Thus, our findings provide a novel understanding of how intracellular pH is regulated and a molecular mechanism by which talin enhances tumor cell invasion and metastasis.

Three-dimensional cancer models mimic cell-matrix interactions in the tumour microenvironment

Basic in vitro systems can be used to model and assess complex diseases, such as cancer. Recent advances in this field include the incorporation of multiple cell types and extracellular matrix proteins into three-dimensional (3D) models to recapitulate the structure, organization and functionality of live tissue in situ. Cells within such a 3D environment behave very differently from cells on two-dimensional (2D) substrates, as cell-matrix interactions trigger signalling pathways and cellular responses in 3D, which may not be observed in 2D. Thus, the use of 3D systems can be advantageous for the assessment of disease progression over 2D set-ups alone. Here, we highlight the current advantages and challenges of employing 3D systems in the study of cancer and provide an overview to guide the appropriate use of distinct models in cancer research.

Imaging hallmarks of cancer in living mice

To comprehend the complexity of cancer, the biological characteristics acquired during the initiation and progression of tumours were classified as the 'hallmarks of cancer'. Intravital microscopy techniques have been developed to study individual cells that acquire these crucial traits, by visualizing tissues with cellular or subcellular resolution in living animals. In this Review, we highlight the latest intravital microscopy techniques that have been used in living animals (predominantly mice) to unravel fundamental and dynamic aspects of various hallmarks of cancer. In addition, we discuss the application of intravital microscopy techniques to cancer therapy, as well as limitations and future perspectives for these techniques.

Vimentin intermediate filament and plectin provide a scaffold for invadopodia, facilitating cancer cell invasion and extravasation for metastasis

To investigate the molecular mechanisms of cancer metastasis, we have isolated a high-metastatic bladder cancer cell subpopulation from a low-metastatic cell line by using an in vivo selection system. Cells in the subpopulation showed a high ability to form invadopodia, the filamentous actin (F-actin)-based membrane protrusions that play an essential role in cancer cell invasion. Analysis of the gene expression profile revealed that the expression of an intermediate filament (IF) protein, vimentin and a cytoskeletal linker protein, plectin was up-regulated in the high-metastatic subpopulation compared with the low metastatic cell line. Here we report a novel role of vimentin IF and plectin in metastasis. In invasive bladder cancer cells, the vimentin IF-plectin-invadopodia F-actin link was formed. Disruption of this link severely impaired invadopodia formation, reducing the capacities of extracellular matrix degradation, transendothelial migration and metastasis. In addition, the vimentin assembly into the filaments was required for invadopodia formation. Our results suggest that plectin anchoring invadopodia to vimentin IF scaffolds and stabilizes invadopodia, which is a critical molecular process for cancer cell invasion and extravasation for metastasis.

Traversing the basement membrane in vivo: a diversity of strategies

The basement membrane is a dense, highly cross-linked, sheet-like extracellular matrix that underlies all epithelia and endothelia in multicellular animals. During development, leukocyte trafficking, and metastatic disease, cells cross the basement membrane to disperse and enter new tissues. Based largely on in vitro studies, cells have been thought to use proteases to dissolve and traverse this formidable obstacle. Surprisingly, recent in vivo studies have uncovered a remarkably diverse range of cellular- and tissue-level strategies beyond proteolysis that cells use to navigate through the basement membrane. These fascinating and unexpected mechanisms have increased our understanding of how cells cross this matrix barrier in physiological and disease settings.

Cytoskeleton targeting value in prostate cancer treatment

Prostate cancer is a disease that affects hundreds of thousands of men in the United States each year. In the early stages of advanced prostate cancer, the disease can be suppressed by androgen deprivation therapy (ADT). Eventually, however, most patients experience resistance to androgen deprivation, and their treatment transitions to alternative targeting of the androgen axis with abiraterone and enzalutamide, as well as taxane-based chemotherapy. Development of advanced castration-resistant prostate cancer (CRPC) is a consequence of lack of an apoptotic response by the tumor cells to treatment. Understanding the mechanisms contributing to prostate tumor therapeutic resistance and progression to metastasis requires dissection of the signaling mechanisms navigating tumor invasion and metastasis as mediated by cell-matrix interactions engaging components of the extracellular matrix (ECM), to form adhesion complexes. For a tumor call to metastasize from the primary tumor, it requires disruption of cell-cell interactions from the surrounding cells, as well as detachment from the ECM and resistance to anoikis (apoptosis upon cell detachment from ECM). Attachment, movement and invasion of cancer cells are functionally facilitated by the actin cytoskeleton and tubulin as the structural component of microtubules. Transforming growth factor (TGF)-β has tumor-inhibitory activity in the early stages of tumorigenesis, but it promotes tumor invasive characteristics in metastatic disease. Recent evidence implicates active (dephosphorylated) cofilin, an F-actin severing protein required for cytoskeleton reorganization, as an important contributor to switching TGF-β characteristics from a growth suppressor to a promoter of prostate cancer invasion and metastasis. Cancer cells eventually lose the ability to adhere to adjacent neighboring cells as well as ECM proteins, and via epithelial-mesenchymal transition (EMT), acquire invasive and metastatic characteristics. Microtubule-targeting chemotherapeutic agents, taxanes, are used in combination with antiandrogen strategies to increase the survival rate in patients with CRPC. This review addresses the development of therapeutic platform for targeting the integrity of actin cytoskeleton to impair prostate cancer progression.

Extravasation during bladder cancer metastasis requires cortactin‑mediated invadopodia formation

Invasive cancer cells form the filamentous actin‑based membrane protrusions known as invadopodia. Invadopodia are thought to play a critical role in cancer cell invasion and metastasis due to their ability to degrade the extracellular matrix. The present study assessed whether invadopodia formation is essential in extravasation of circulating bladder cancer cells and lung metastasis. To analyze the importance of invadopodia, bladder cancer cell lines with reduced invadopodia formation were established by silencing the expression of cortactin, an essential component of invadopodia, using cortactin short hairpin RNA. Bladder cancer cells with cortactin knockdown demonstrated a markedly decreased ability to form invadopodia, secrete matrix metalloproteinases and invade the extracellular matrix. In addition, the knockdown cells exhibited a reduced transendothelial invasion capacity and decreased formation of metastatic foci in the lungs. The present study demonstrated that bladder cancer cells with cortactin knockdown have a reduced capacity to extravasate into the lung from the circulation, due to the decreased invasive character of invadopodia. This suggests that invadopodia formation is a critical process for cancer cell extravasation.

Invadopodia in context

Invadopodia are dynamic protrusions in motile tumor cells whose function is to degrade extracellular matrix so that cells can enter into new environments. Invadopodia are specifically identified by microscopy as proteolytic invasive protrusions containing TKS5 and cortactin. The increasing complexity in models for the study of invadopodia, including engineered 3D environments, explants, or animal models in vivo, entails a higher level of microenvironment complexity as well as cancer cell heterogeneity. Such experimental setups are rich in information and offer the possibility of contextualizing invadopodia and other motility-related structures. That is, they hold the promise of revealing more realistic microenvironmental conditions under which the invadopodium assembles and functions or in which tumor cells switch to a different cellular phenotype (focal adhesion, lamellipodia, proliferation, and apoptosis). For such an effort, we need a systemic approach to microscopy, which will integrate information from multiple modalities. While the individual technologies needed to achieve this are mostly available, data integration and standardization is not a trivial process. In a systems microscopy approach, microscopy is used to extract information on cell phenotypes and the microenvironment while -omics technologies assess profiles of cancer cell and microenvironment genetic, transcription, translation, and protein makeups. Data are classified and linked via in silico modeling (including statistical and mathematical models and bioinformatics). Computational considerations create predictions to be validated experimentally by perturbing the system through use of genetic manipulations and molecular biology. With such a holistic approach, a deeper understanding of function of invadopodia in vivo will be reached, opening the potential for personalized diagnostics and therapies.

Crossing the endothelial barrier during metastasis

During metastasis, cancer cells disseminate to other parts of the body by entering the bloodstream in a process that is called intravasation. They then extravasate at metastatic sites by attaching to endothelial cells that line blood vessels and crossing the vessel walls of tissues or organs. This Review describes how cancer cells cross the endothelial barrier during extravasation and how different receptors, signalling pathways and circulating cells such as leukocytes and platelets contribute to this process. Identification of the mechanisms that underlie cancer cell extravasation could lead to the development of new therapies to reduce metastasis.

Exosome secretion is enhanced by invadopodia and drives invasive behavior

Unconventional secretion of exosome vesicles from multivesicular endosomes (MVEs) occurs across a broad set of systems and is reported to be upregulated in cancer, where it promotes aggressive behavior. However, regulatory control of exosome secretion is poorly understood. Using cancer cells, we identified specialized invasive actin structures called invadopodia as specific and critical docking and secretion sites for CD63- and Rab27a-positive MVEs. Thus, inhibition of invadopodia formation greatly reduced exosome secretion into conditioned media. Functionally, addition of purified exosomes or inhibition of exosome biogenesis or secretion greatly affected multiple invadopodia life cycle steps, including invadopodia formation, stabilization, and exocytosis of proteinases, indicating a key role for exosome cargoes in promoting invasive activity and providing in situ signaling feedback. Exosome secretion also controlled cellular invasion through three-dimensional matrix. These data identify a synergistic interaction between invadopodia biogenesis and exosome secretion and reveal a fundamental role for exosomes in promoting cancer cell invasiveness.

Caught in the act: revealing the metastatic process by live imaging

The prognosis of metastatic cancer in patients is poor. Interfering with metastatic spread is therefore important for achieving better survival from cancer. Metastatic disease is established through a series of steps, including breaching of the basement membrane, intravasation and survival in lymphatic or blood vessels, extravasation, and growth at distant sites. Yet, although we know the steps involved in metastasis, the cellular and molecular mechanisms of dissemination and colonization of distant organs are incompletely understood. Here, we review the important insights into the metastatic process that have been gained specifically through the use of imaging technologies in murine, chicken embryo and zebrafish model systems, including high-resolution two-photon microscopy and bioluminescence. We further discuss how imaging technologies are beginning to allow researchers to address the role of regional activation of specific molecular pathways in the metastatic process. These technologies are shedding light, literally, on almost every step of the metastatic process, particularly with regards to the dynamics and plasticity of the disseminating cancer cells and the active participation of the microenvironment in the processes.

Oncogenic alternative splicing switches: role in cancer progression and prospects for therapy

Alterations in the abundance or activities of alternative splicing regulators generate alternatively spliced variants that contribute to multiple aspects of tumor establishment, progression and resistance to therapeutic treatments. Notably, many cancer-associated genes are regulated through alternative splicing suggesting a significant role of this post-transcriptional regulatory mechanism in the production of oncogenes and tumor suppressors. Thus, the study of alternative splicing in cancer might provide a better understanding of the malignant transformation and identify novel pathways that are uniquely relevant to tumorigenesis. Understanding the molecular underpinnings of cancer-associated alternative splicing isoforms will not only help to explain many fundamental hallmarks of cancer, but will also offer unprecedented opportunities to improve the efficacy of anti-cancer treatments.

Tks5 and SHIP2 regulate invadopodium maturation, but not initiation, in breast carcinoma cells

BACKGROUND

Tks5 regulates invadopodium formation, but the precise timing during invadopodium lifetime (initiation, stabilization, maturation) when Tks5 plays a role is not known.

RESULTS

We report new findings based on high-resolution spatiotemporal live-cell imaging of invadopodium precursor assembly. Cortactin, N-WASP, cofilin, and actin arrive together to form the invadopodium precursor, followed by Tks5 recruitment. Tks5 is not required for precursor initiation but is needed for precursor stabilization, which requires the interaction of the phox homology (PX) domain of Tks5 with PI(3,4)P2. During precursor formation, PI(3,4)P2 is uniformly distributed but subsequently starts accumulating at the precursor core 3-4 min after core initiation, and conversely, PI(3,4,5)P3 gets enriched in a ring around the precursor core. SHIP2, a 5'-inositol phosphatase, localizes at the invadopodium core and regulates PI(3,4)P2 levels locally at the invadopodium. The timing of SHIP2 arrival at the invadopodium precursor coincides with the onset of PI(3,4)P2 accumulation. Consistent with its late arrival, we found that SHIP2 inhibition does not affect precursor formation but does cause decreases in mature invadopodia and matrix degradation, whereas SHIP2 overexpression increases matrix degradation.

CONCLUSIONS

Together, these findings lead us to propose a new sequential model that provides novel insights into molecular mechanisms underlying invadopodium precursor initiation, stabilization, and maturation into a functional invadopodium.

Macrophage contact induces RhoA GTPase signaling to trigger tumor cell intravasation

Most cancer patients die as a result of metastasis, thus it is important to understand the molecular mechanisms of dissemination, including intra- and extravasation. Although the mechanisms of extravasation have been vastly studied in vitro and in vivo, the process of intravasation is still unclear. Furthermore, how cells in the tumor microenvironment facilitate tumor cell intravasation is still unknown. Using high-resolution imaging, we found that macrophages enhance tumor cell intravasation upon physical contact. Macrophage and tumor cell contact induce RhoA activity in tumor cells, triggering the formation of actin-rich degradative protrusions called invadopodia, enabling tumor cells to degrade and break through matrix barriers during tumor cell transendothelial migration. Interestingly, we show that macrophage-induced invadopodium formation and tumor cell intravasation also occur in patient-derived tumor cells and in vivo models, revealing a conserved mechanism of tumor cell intravasation. Our results illustrate a novel heterotypic cell contact mediated signaling role for RhoA, as well as yield mechanistic insight into the ability of cells within the tumor microenvironment to facilitate steps of the metastatic cascade.

Differential Tks5 isoform expression contributes to metastatic invasion of lung adenocarcinoma

Metastasis accounts for the vast majority of cancer-related deaths, yet the molecular mechanisms that drive metastatic spread remain poorly understood. Here we report that Tks5, which has been linked to the formation of proteolytic cellular protrusions known as invadopodia, undergoes an isoform switch during metastatic progression in a genetically engineered mouse model of lung adenocarcinoma. Nonmetastatic primary tumor-derived cells predominantly expressed a short isoform, Tks5short, while metastatic primary tumor- and metastasis-derived cells acquired increased expression of the full-length isoform Tks5long. This elevation of Tks5long to Tks5short ratio correlated with a commensurate increase in invadopodia activity in metastatic cells compared with nonmetastatic cells. Further characterization of these isoforms by knockdown and overexpression experiments demonstrated that Tks5long promoted invadopodia in vitro and increased metastasis in transplant models and an autochthonous model of lung adenocarcinoma. Conversely, Tks5short decreased invadopodia stability and proteolysis, acting as a natural dominant-negative inhibitor to Tks5long. Importantly, high Tks5long and low Tks5short expressions in human lung adenocarcinomas correlated with metastatic disease and predicted worse survival of early stage patients. These data indicate that tipping the Tks5 isoform balance to a high Tks5long to Tks5short ratio promotes invadopodia-mediated invasion and metastasis.

Signaling inputs to invadopodia and podosomes

Remodeling of extracellular matrix (ECM) is a fundamental cell property that allows cells to alter their microenvironment and move through tissues. Invadopodia and podosomes are subcellular actin-rich structures that are specialized for matrix degradation and are formed by cancer and normal cells, respectively. Although initial studies focused on defining the core machinery of these two structures, recent studies have identified inputs from both growth factor and adhesion signaling as crucial for invasive activity. This Commentary will outline the current knowledge on the upstream signaling inputs to invadopodia and podosomes and their role in governing distinct stages of these invasive structures. We discuss invadopodia and podosomes as adhesion structures and highlight new data showing that invadopodia-associated adhesion rings promote the maturation of already-formed invadopodia. We present a model in which growth factor stimulation leads to phosphoinositide 3-kinase (PI3K) activity and formation of invadopodia, whereas adhesion signaling promotes exocytosis of proteinases at invadopodia.

Multi-level control of actin dynamics by protein kinase D

Dynamic actin remodeling is fundamental to processes such as cell motility, vesicle trafficking, and cytokinesis. Protein kinase D (PKD) is a serine-threonine kinase known to be involved in diverse biological functions ranging from vesicle fission at the Golgi complex to regulation of cell motility and invasion. This review addresses the role of PKD in the organization of the actin cytoskeleton with a particular emphasis on the substrates associated with this function. We further highlight the multi-level control of actin dynamics by PKD and suggest that the tight spatio-temporal control of PKD activity is critical for the coordination of directed cell migration.

TGF-β signaling and epithelial-mesenchymal transition in cancer progression

PURPOSE OF REVIEW

TGF-β acts as a potent driver of cancer progression through the induction of epithelial-mesenchymal transition (EMT), in which epithelial cells acquire mesenchymal phenotype, leading to enhanced motility and invasion. Recent reports highlight the fundamental roles of TGF-β-induced EMT in multiple aspects of cancer progression. In this review, we focus on the novel insights into the roles of TGF-β-induced EMT in cancer progression and the underlying mechanisms that enable TGF-β to activate this epithelial plasticity response at transcription, translation, and posttranslational levels.

RECENT FINDINGS

Smad-mediated transcription regulation is known to activate TGF-β-induced EMT. More recently, novel mechanisms of epigenetic control, alternative splicing, miRNAs, translation control, and posttranslational modifications have been shown to play key roles in the control of EMT. In addition to initiating carcinoma cell invasion, TGF-β-induced EMT can guide cancer cells to de-differentiate and gain cancer stem-cell-like properties. EMT also allows the generation of stromal cells that support and instruct cancer progression.

SUMMARY

The differentiation plasticity of epithelial cells that mediates TGF-β-induced EMT and reversion from mesenchymal to epithelial phenotype are increasingly seen as integral aspects of cancer progression that contribute to survival and dissemination of cancer cells. Further mechanistic insights under physiological conditions may lead to new therapeutic or prognostic strategies in cancer treatment.

Mechanotransduction at focal adhesions: from physiology to cancer development

Living cells are continuously exposed to mechanical cues, and can translate these signals into biochemical information (e.g. mechanotransduction). This process is crucial in many normal cellular functions, e.g. cell adhesion, migration, proliferation, and survival, as well as the progression of diseases such as cancer. Focal adhesions are the major sites of interactions between extracellular mechanical environments and intracellular biochemical signalling molecules/cytoskeleton, and hence focal adhesion proteins have been suggested to play important roles in mechanotransduction. Here, we overview the current molecular understanding in mechanotransduction occurring at focal adhesions. We also introduce recent studies on how extracellular matrix and mechanical microenvironments contribute to the development of cancer.

β1 integrin regulates Arg to promote invadopodial maturation and matrix degradation

β1 integrin is a major regulator of invadopodium maturation. Studies reveal that β1 integrin–mediated adhesion is a key upstream switch that induces Arg-dependent cortactin phosphorylation, actin polymerization, and MMP recruitment to invadopodia for extracellular matrix degradation.

β1 integrin has been shown to promote metastasis in a number of tumor models, including breast, ovarian, pancreatic, and skin cancer; however, the mechanism by which it does so is poorly understood. Invasive membrane protrusions called invadopodia are believed to facilitate extracellular matrix degradation and intravasation during metastasis. Previous work showed that β1 integrin localizes to invadopodia, but its role in regulating invadopodial function has not been well characterized. We find that β1 integrin is required for the formation of mature, degradation-competent invadopodia in both two- and three-dimensional matrices but is dispensable for invadopodium precursor formation in metastatic human breast cancer cells. β1 integrin is activated during invadopodium precursor maturation, and forced β1 integrin activation enhances the rate of invadopodial matrix proteolysis. Furthermore, β1 integrin interacts with the tyrosine kinase Arg and stimulates Arg-dependent phosphorylation of cortactin on tyrosine 421. Silencing β1 integrin with small interfering RNA completely abrogates Arg-dependent cortactin phosphorylation and cofilin-dependent barbed-end formation at invadopodia, leading to a significant decrease in the number and stability of mature invadopodia. These results describe a fundamental role for β1 integrin in controlling actin polymerization–dependent invadopodial maturation and matrix degradation in metastatic tumor cells.

Genome-wide methylation profiling and the PI3K-AKT pathway analysis associated with smoking in urothelial cell carcinoma

Urothelial cell carcinoma (UCC) is the second most common genitourinary malignant disease in the USA, and tobacco smoking is the major known risk factor for UCC development. Exposure to carcinogens, such as those contained in tobacco smoke, is known to directly or indirectly damage DNA, causing mutations, chromosomal deletion events and epigenetic alterations in UCC. Molecular studies have shown that chromosome 9 alterations and P53, RAS, RB and PTEN mutations are among the most frequent events in UCC. Recent studies suggested that continuous tobacco carcinogen exposure drives and enhances the selection of epigenetically altered cells in UCC, predominantly in the invasive form of the disease. However, the sequence of molecular events that leads to UCC after exposure to tobacco smoke is not well understood. To elucidate molecular events that lead to UCC oncogenesis and progression after tobacco exposure, we developed an in vitro cellular model for smoking-induced UCC. SV-40 immortalized normal HUC1 human bladder epithelial cells were continuously exposed to 0.1% cigarette smoke extract (CSE) until transformation occurred. Morphological alterations and increased cell proliferation of non-malignant urothelial cells were observed after 4 months (mo) of treatment with CSE. Anchorage-independent growth assessed by soft agar assay and increase in the migratory and invasive potential was observed in urothelial cells after 6 mo of CSE treatment. By performing a PCR mRNA expression array specific to the PI3K-AKT pathway, we found that 26 genes were upregulated and 22 genes were downregulated after 6 mo of CSE exposure of HUC1 cells. Among the altered genes, PTEN, FOXO1, MAPK1 and PDK1 were downregulated in the transformed cells, while AKT1, AKT2, HRAS, RAC1 were upregulated. Validation by RT-PCR and western blot analysis was then performed. Furthermore, genome-wide methylation analysis revealed MCAM, DCC and HIC1 are hypermethylated in CSE-treated urothelial cells when compared with non-CSE exposed cells. The methylation status of these genes was validated using quantitative methylation-specific PCR (QMSP), confirming an increase in methylation of CSE-treated urothelial cells compared to untreated controls. Therefore, our findings suggest that a tobacco signature could emerge from distinctive patterns of genetic and epigenetic alterations and can be identified using an in vitro cellular model for the development of smoking-induced cancer.