Role of cadherins in the transendothelial migration of melanoma cells in culture

MARCH family E3 ubiquitin ligases selectively target and degrade cadherin family proteins

Cadherin family proteins play a central role in epithelial and endothelial cell-cell adhesion. The dynamic regulation of cell adhesion is achieved in part through endocytic membrane trafficking pathways that modulate cadherin cell surface levels. Here, we define the role for various MARCH family ubiquitin ligases in the regulation of cadherin degradation. We find that MARCH2 selectively downregulates VE-cadherin, resulting in loss of adherens junction proteins at cell borders and a loss of endothelial barrier function. Interestingly, N-cadherin is refractory to MARCH ligase expression, demonstrating that different classical cadherin family proteins are differentially regulated by MARCH family ligases. Using chimeric cadherins, we find that the specificity of different MARCH family ligases for different cadherins is conferred by the cadherin transmembrane domain. Further, juxta-membrane lysine residues are required for cadherin degradation by MARCH proteins. These findings expand our understanding of cadherin regulation and highlight a new role for mammalian MARCH family ubiquitin ligases in differentially regulating cadherin turnover.

MARCH family E3 ubiquitin ligases selectively target and degrade cadherin family proteins

Cadherin family proteins play a central role in epithelial and endothelial cell-cell adhesion. The dynamic regulation of cell adhesion is achieved in part through endocytic membrane trafficking pathways that modulate cadherin cell surface levels. Here, we define the role for various MARCH family ubiquitin ligases in the regulation of cadherin degradation. We find that MARCH2 selectively downregulates VE-cadherin, resulting in loss of adherens junction proteins at cell borders and a loss of endothelial barrier function. Interestingly, N-cadherin is refractory to MARCH ligase expression, demonstrating that different classical cadherin family proteins are differentially regulated by MARCH family ligases. Using chimeric cadherins, we find that the specificity of different MARCH family ligases for different cadherins is conferred by the cadherin transmembrane domain. Further, juxta-membrane lysine residues are required for cadherin degradation by MARCH proteins. These findings expand our understanding of cadherin regulation and highlight a new role for mammalian MARCH family ubiquitin ligases in differentially regulating cadherin turnover.

Interaction of Drug-Sensitive and -Resistant Human Melanoma Cells with HUVEC Cells: A Label-Free Cell-Based Impedance Study

Cancer cell extravasation is a crucial step in cancer metastasis. However, many of the mechanisms involved in this process are only now being elucidated. Thus, in the present study we analysed the trans-endothelial invasion of melanoma cells by a high throughput label-free cell impedance assay applied to transwell chamber invasion assay. This technique monitors and quantifies in real-time the invasion of endothelial cells by malignant tumour cells, for a long time, avoiding artefacts due to preparation of the end point measurements. Results obtained by impedance analysis were compared with endpoint measurements. In this study, we used human melanoma M14 wild type (WT) cells and their drug resistant counterparts, M14 multidrug resistant (ADR) melanoma cells, selected by prolonged exposure to doxorubicin (DOX). Tumour cells were co-cultured with monolayers of human umbilical vein endothelial cells (HUVEC). Results herein reported demonstrated that: (i) the trans-endothelial migration of resistant melanoma cells was faster than sensitive ones; (ii) the endothelial cells appeared to be strongly affected by the transmigration of melanoma cells which showed the ability to degrade their cytoplasm; (iii) resistant cells preferentially adopted the transcellular invasion vs. the paracellular one; (iv) the endothelial damage mediated by tumour metalloproteinases seemed to be reversible.

Small interfering RNA targeting N-cadherin regulates cell proliferation and migration in enzalutamide-resistant prostate cancer

Enzalutamide is one of the options for treating patients with castration-resistant or metastatic prostate cancer. However, a substantial proportion of patients become resistant to enzalutamide after a period of treatment. Cells in these tumors typically exhibit increased proliferative and migratory capabilities, in which N-cadherin (CDH2) appear to serve an important role. In the present study, by up- and downregulating the expression of CDH2, the possible effects of CDH2 on the prostate cancer cell line LNCaP were investigated. Male sex hormone-sensitive LNCaP cells treated with 10 µM enzalutamide were named LNCaP enzalutamide-resistant (EnzaR) cells. Reverse transcription-PCR, western blotting and immunofluorescence staining were used to measure CDH2, E-cadherin, α-SMA, Snail and Slug expression. Transfection with the pCMV-CDH2 plasmid was performed for CDH2 upregulation, whilst transfection with small interfering RNA (siRNA)-CDH2 was performed for CDH2 downregulation. MTT and Cell Counting Kit-4 assays were used to evaluate the proportion of viable cancer cells. Subsequently, gap closure assay was performed to evaluate the migratory capability of both LNCaP and LNCaP EnzaR cell lines. CDH2 expression was found to be increased in LNCaP EnzaR cells compared with that in LNCaP cells. CDH2 overexpression increased cell viability and migration in both LNCaP and LNCaP EnzaR cell lines. By contrast, the opposite trend was observed after CDH2 expression was knocked down. CDH2 expression also showed a high association with that of four epithelial-mesenchymal transition markers, which was confirmed by western blotting. Based on these results, it was concluded that knocking down CDH2 expression using siRNA transfection mediated significant influence on LNCaP EnzaR cell physiology, which may be a potential therapeutic option for prostate cancer treatment.

Spheroids of Endothelial Cells and Vascular Smooth Muscle Cells Promote Cell Migration in Hyaluronic Acid and Fibrinogen Composite Hydrogels

Cell migration plays a pivotal role in many pathological and physiological processes. So far, most of the studies have been focused on 2-dimensional cell adhesion and migration. Herein, the migration behaviors of cell spheroids in 3D hydrogels obtained by polymerization of methacrylated hyaluronic acid (HA-MA) and fibrinogen (Fg) with different ratios were studied. The Fg could be released to the medium gradually along with time prolongation, achieving the dynamic change of hydrogel structures and properties. Three types of cell spheroids, i.e., endothelial cell (EC), smooth muscle cell (SMC), and EC-SMC spheroids, were prepared with 10,000 cells in each, whose diameters were about 343, 108, and 224 μm, respectively. The composite hydrogels with an intermediate ratio of Fg allowed the fastest 3D migration of cell spheroids. The ECs-SMCs migrated longest up to 3200 μm at day 14, whereas the SMC spheroids migrated slowest with a distance of only ~400 μm at the same period of time. The addition of free RGD or anti-CD44 could significantly reduce the migration distance, revealing that the cell-substrate interactions take the major roles and the migration is mesenchymal dependent. Moreover, addition of anti-N-cadherin and MMP inhibitors also slowed down the migration rate, demonstrating that the degradation of hydrogels and cell-cell interactions are also largely involved in the cell migration. RT-PCR measurement showed that expression of genes related to cell adhesion and antiapoptosis, and angiogenesis was all upregulated in the EC-SMC spheroids than single EC or SMC spheroids, suggesting that the use of composite cell spheroids is more promising to promote cell-substrate interactions and maintenance of cell functions.

HIV-1 proteins gp120 and tat induce the epithelial-mesenchymal transition in oral and genital mucosal epithelial cells

The oral, cervical, and genital mucosa, covered by stratified squamous epithelia with polarized organization and strong tight and adherens junctions, play a critical role in preventing transmission of viral pathogens, including human immunodeficiency virus (HIV). HIV-1 interaction with mucosal epithelial cells may depolarize epithelia and disrupt their tight and adherens junctions; however, the molecular mechanism of HIV-induced epithelial disruption has not been completely understood. We showed that prolonged interaction of cell-free HIV-1 virions, and viral envelope and transactivator proteins gp120 and tat, respectively, with tonsil, cervical, and foreskin epithelial cells induces an epithelial-mesenchymal transition (EMT). EMT is an epigenetic process leading to the disruption of mucosal epithelia and allowing the paracellular spread of viral and other pathogens. Interaction of cell-free virions and gp120 and tat proteins with epithelial cells substantially reduced E-cadherin expression and activated vimentin and N-cadherin expression, which are well-known mesenchymal markers. HIV gp120- and tat-induced EMT was mediated by SMAD2 phosphorylation and activation of transcription factors Slug, Snail, Twist1 and ZEB1. Activation of TGF-β and MAPK signaling by gp120, tat, and cell-free HIV virions revealed the critical roles of these signaling pathways in EMT induction. gp120- and tat-induced EMT cells were highly migratory via collagen-coated membranes, which is one of the main features of mesenchymal cells. Inhibitors of TGF-β1 and MAPK signaling reduced HIV-induced EMT, suggesting that inactivation of these signaling pathways may restore the normal barrier function of mucosal epithelia.

How many cadherins do human endothelial cells express?

The vasculature is the paradigm of a compartment generated by parallel cellular barriers that aims to transport oxygen, nutrients and immune cells in complex organisms. Vascular barrier dysfunction leads to fatal acute and chronic inflammatory diseases. The endothelial barrier lines the inner side of vessels and is the main regulator of vascular permeability. Cadherins comprise a superfamily of 114 calcium-dependent adhesion proteins that contain conserved cadherin motifs and form cell-cell junctions in metazoans. In mature human endothelial cells, only VE (vascular endothelial)-cadherin and N (neural)-cadherin have been investigated in detail. Although both cadherins are essential for regulating endothelial permeability, no comprehensive expression studies to identify which other family members could play a relevant role in endothelial cells has so far been performed. Here, we have reviewed gene and protein expression databases to analyze cadherin expression in mature human endothelium and found that at least 24 cadherin superfamily members are significantly expressed. Based on data obtained from other cell types, organisms and experimental models, we discuss their potential functions, many of them unrelated to the formation of endothelial cell-cell junctions. The expression of this new set of endothelial cadherins highlights the important but still poorly defined roles of planar cell polarity, the Hippo pathway and mitochondria metabolism in human vascular homeostasis.

N-cadherin in cancer metastasis, its emerging role in haematological malignancies and potential as a therapeutic target in cancer

In many types of solid tumours, the aberrant expression of the cell adhesion molecule N-cadherin is a hallmark of epithelial-to-mesenchymal transition, resulting in the acquisition of an aggressive tumour phenotype. This transition endows tumour cells with the capacity to escape from the confines of the primary tumour and metastasise to secondary sites. In this review, we will discuss how N-cadherin actively promotes the metastatic behaviour of tumour cells, including its involvement in critical signalling pathways which mediate these events. In addition, we will explore the emerging role of N-cadherin in haematological malignancies, including bone marrow homing and microenvironmental protection to anti-cancer agents. Finally, we will discuss the evidence that N-cadherin may be a viable therapeutic target to inhibit cancer metastasis and increase tumour cell sensitivity to existing anti-cancer therapies.

Bioengineered Submucosal Organoids for In Vitro Modeling of Colorectal Cancer

The physical nature of the tumor microenvironment significantly impacts tumor growth, invasion, and response to drugs. Most in vitro tumor models are designed to study the effects of extracellular matrix (ECM) stiffness on tumor cells, while not addressing the effects of ECM's specific topography. In this study, we bioengineered submucosal organoids, using primary smooth muscle cells embedded in collagen I hydrogel, which produce aligned and parallel fiber topography similar to those found in vivo. The fiber organization in the submucosal organoids induced an epithelial phenotype in spheroids of colorectal carcinoma cells (HCT-116), which were embedded within the organoids. Conversely, unorganized fibers drove a mesenchymal phenotype in the tumor cells. HCT-116 cells in organoids with aligned fibers showed no WNT signaling activation, and conversely, WNT signaling activation was observed in organoids with disrupted fibers. Consequently, HCT-116 cells in the aligned condition exhibited decreased cellular proliferation and reduced sensitivity to 5-fluorouracil chemotherapeutic treatment compared to cells in the unorganized construct. Collectively, the results establish a unique colorectal tumor organoid model to study the effects of stromal topography on cancer cell phenotype, proliferation, and ultimately, chemotherapeutic susceptibility. In the future, such organoids can utilize patient-derived cells for precision medicine applications.

A microfluidic platform for modeling metastatic cancer cell matrix invasion

Invasion of the extracellular matrix is a critical step in the colonization of metastatic tumors. The invasion process is thought to be driven by both chemokine signaling and interactions between invading cancer cells and physical components of the metastatic niche, including endothelial cells that line capillary walls and serve as a barrier to both diffusion and invasion of the underlying tissue. Transwell chambers, a tool for generating artificial chemokine gradients to induce cell migration, have facilitated recent work to investigate the chemokine contributions to matrix invasion. These chambers, however, are poorly designed for imaging, which limits their use in investigating the physical cell-cell and cell-matrix interactions driving matrix invasion. Microfluidic devices offer a promising model in which the invasion process can be imaged. Many current designs, however, have limited surface areas and possess intricate geometries that preclude the use of standard staining protocols to visualize cells and matrix proteins. In this work, we present a novel microfluidic platform for imaging cell-cell and cell-matrix interactions driving metastatic cancer cell matrix invasion. Our model is applied to investigate how endothelial cell-secreted matrix proteins and the physical endothelial monolayer itself interact with invading metastatic breast cancer cells to facilitate invasion of an underlying type I collagen gel. The results show that matrix invasion of metastatic breast cancer cells is significantly enhanced in the presence of live endothelial cells. Probing this interaction further, our platform revealed that, while the fibronectin-rich matrix deposited by endothelial cells was not sufficient to drive invasion alone, metastatic breast cancer cells were able to exploit components of energetically inactivated endothelial cells to gain entry into the underlying matrix. These findings reveal novel cell-cell interactions driving a key step in the colonization of metastatic tumors and have important implications for designing drugs targeted at preventing cancer metastasis.

Protein kinase C inhibitor Gö6976 but not Gö6983 induces the reversion of E- to N-cadherin switch and metastatic phenotype in melanoma: identification of the role of protein kinase D1

Background

Melanoma is a highly metastatic type of cancer that is resistant to all standard anticancer therapies and thus has a poor prognosis. Therefore, metastatic melanoma represents a significant clinical problem and requires novel and effective targeted therapies. The protein kinase C (PKC) family comprises multiple isoforms of serine/threonine kinases that possess distinct roles in cancer development and progression. In this study, we determined whether inhibition of PKC could revert a major process required for melanoma progression and metastasis; i.e. the E- to N-cadherin switch.

Methods

The cadherin switch was analyzed in different patient-derived primary tumors and their respective metastatic melanoma cells to determine the appropriate cellular model (aggressive E-cadherin-negative/N-cadherin-positive metastasis-derived melanoma cells). Next, PKC inhibition in two selected metastatic melanoma cell lines, was performed by using either pharmacological inhibitors (Gö6976 and Gö6983) or stable lentiviral shRNA transduction. The expression of E-cadherin and N-cadherin was determined by western blot. The consequences of cadherin switch reversion were analyzed: cell morphology, intercellular interactions, and β-catenin subcellular localization were analyzed by immunofluorescence labeling and confocal microscopy; cyclin D1 expression was analyzed by western blot; cell metastatic potential was determined by anchorage-independent growth assay using methylcellulose as semi-solid medium and cell migration potential by wound healing and transwell assays.

Results

Gö6976 but not Gö6983 reversed the E- to N-cadherin switch and as a consequence induced intercellular interactions, profound morphological changes from elongated mesenchymal-like to cuboidal epithelial-like shape, β-catenin translocation from the nucleus to the plasma membrane inhibiting its oncogenic function, and reverting the metastatic potential of the aggressive melanoma cells. Comparison of the target spectrum of these inhibitors indicated that these observations were not the consequence of the inhibition of conventional PKCs (cPKCs), but allowed the identification of a novel serine/threonine kinase, i.e. protein kinase Cμ, also known as protein kinase D1 (PKD1), whose specific inhibition allows the reversion of the metastatic phenotype in aggressive melanoma.

Conclusion

In conclusion, our study suggests, for the first time, that while cPKCs don’t embody a pertinent therapeutic target, inhibition of PKD1 represents a novel attractive approach for the treatment of metastatic melanoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-3007-5) contains supplementary material, which is available to authorized users.

Prognostic significance of immunohistochemical epithelial–mesenchymal transition markers in skin melanoma patients

Aim: To investigate secreted protein acidic and rich in cystein (SPARC) and neural cadherin (NCAD), which are associated with epithelial–mesenchymal transition in primary skin melanoma and nodal metastases and their prognostic impact in melanoma patients. Methods: Expression of proteins was assessed by immunochemistry in archival paraffin samples from 103 primary melanoma tumors and 16 nodal metastases. Results: Increased expression of SPARC and NCAD in primary skin melanoma was associated with decreased overall survival, adverse clinicopathological features and particularly with microsatellitosis (SPARC) and ulceration (NCAD). In univariate Cox regression analysis, both biomarkers were significantly associated with the risk of death; the multivariate Cox regression analysis identified no significance. Conclusion: The most important result of our study was that we confirmed the strict correlation between SPARC and NCAD expression and clinicopathological parameters related with melanoma progression, which is a specific clinical equivalent of the molecular mechanisms of epithelial–mesenchymal transition process and confirms its key role in the disease outcome.

N-Cadherin and Fibroblast Growth Factor Receptors crosstalk in the control of developmental and cancer cell migrations

Cell migrations are diverse. They constitutemajor morphogenetic driving forces during embryogenesis, but they contribute also to the loss of tissue homeostasis and cancer growth. Capabilities of cells to migrate as single cells or as collectives are controlled by internal and external signalling, leading to the reorganisation of their cytoskeleton as well as by the rebalancing of cell-matrix and cell-cell adhesions. Among the genes altered in numerous cancers, cadherins and growth factor receptors are of particular interest for cell migration regulation. In particular, cadherins such as N-cadherin and a class of growth factor receptors, namely FGFRs cooperate to regulate embryonic and cancer cell behaviours. In this review, we discuss on reciprocal crosstalk between N-cadherin and FGFRs during cell migration. Finally, we aim at clarifying the synergy between N-cadherin and FGFR signalling that ensure cellular reorganization during cell movements, mainly during cancer cell migration and metastasis but also during developmental processes.

Therapeutic targeting of N-cadherin is an effective treatment for multiple myeloma

Elevated expression of the cell adhesion molecule N-cadherin (cadherin 2, type 1, N-cadherin (neuronal); CDH2) is associated with poor prognosis in newly-diagnosed multiple myeloma (MM) patients. In this study, we investigated whether targeting of N-cadherin represents a potential treatment for the ~50% of MM patients with elevated N-cadherin. Initially, we stably knocked-down N-cadherin in the mouse MM plasma cell (PC) line 5TGM1 to assess the functional role of N-cadherin in MM pathogenesis. When compared with 5TGM1-scramble-shRNA cells, 5TGM1-Cdh2-shRNA cells had significantly reduced adhesion to bone marrow endothelial cells. However, N-cadherin knock-down did not affect 5TGM1 cell proliferation or adhesion to bone marrow stromal cells. In the C57BL/KaLwRij murine MM model, mice intravenously inoculated with 5TGM1-Cdh2-shRNA cells showed significantly decreased tumour burden after 4 weeks, compared with animals bearing 5TGM1-scramble-shRNA cells. Finally, the N-cadherin antagonist ADH-1 had no effect on tumour burden in the established disease setting, whereas up-front ADH-1 treatment resulted in significantly reduced tumour burden after 4 weeks. Our findings demonstrate that N-cadherin may play a key role in the extravasation of circulating MM PCs promoting bone marrow homing. Moreover, these studies suggest that N-cadherin may represent a viable therapeutic target to prevent the dissemination of MM PCs and delay MM disease progression.

Actinomyosin contraction, phosphorylation of VE-cadherin, and actin remodeling enable melanoma-induced endothelial cell-cell junction disassembly

During melanoma cell extravasation through the vascular endothelium, melanoma cells interact with endothelial cells through secretion of cytokines and by adhesion between proteins displayed on opposing cell surfaces. How these tumor cell associated signals together regulate the dynamics of intracellular signaling pathways within endothelial cells leading to endothelial cell-cell junction disruption is not well understood. Here, we used a combination of experimental and computational approaches to examine the individual and combined effects of activation of the vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-8, and IL-1β signaling pathways on the integrity of vascular junctions. Our simulations predict a multifaceted interplay of signaling resulting from individual activation of VCAM-1, IL-8 and IL-1β pathways that is neither synergistic nor additive compared to all inputs turned on simultaneously. Furthermore, we show that the levels of phosphorylated proteins associated with actinomyosin contractility and junction disassembly peak prior to those related to actin remodeling. The results of this work provide insight into the dynamics of tumor-mediated endothelial junction disassembly and suggest that targeting proteins downstream of several interaction pathways may be the most effective therapeutic approach to reduce melanoma extravasation.

The biological and clinical importance of epithelial-mesenchymal transition in circulating tumor cells

Movement of tumor cells from a primary tumor to a nonadjacent or distant site is a contiguous and complex process. Among the multiple natural cellular programs that promote initiation and progression of tumor metastasis, epithelial-mesenchymal transition (EMT) may play a key role in the ultimate generation of a metastatic foci. Acquisition of the EMT phenotype by tumor cells not only increases their migration and invasion potentials, thereby facilitating their ability to infiltrate blood vessels and to produce circulating tumor cells (CTCs), but also promotes survival of CTCs in the bloodstream and their ability to extravasate out of the circulatory system and invade proximal tissues. In organs distal to the primary tumor, the phenotypic switching mechanism of mesenchymal-epithelial transition (MET) enables CTCs to grow and colonize, enhancing the likelihood of establishing metastasis. In addition, CTCs that have undergone EMT attain increased resistance to chemotherapy and targeted therapy. CTCs with the EMT phenotype have become recognized as an active source of metastases, and targeting EMT/MET processes during the individual steps of tumor metastasis represents a promising new approach for alleviating cancer metastasis and recurrence. In this article, we focus on the biological and clinical importance of EMT and/or MET in CTCs during the individual steps of tumor metastasis, summarizing the recent findings of the regulatory roles played by EMT and/or MET in the generation, survival, and recolonization of CTCs and discussing the EMT-targeting strategies developed for tumor diagnosis as well as their potential for management of metastatic malignant diseases.

Notch ligand Delta-like 1 promotes the metastasis of melanoma by enhancing tumor adhesion

Notch signaling plays a vital role in tumorigenicity and tumor progression by regulating proliferation, invasion, and the tumor microenvironment. Previous research by our group indicated that Notch ligand Delta-like 1 (Dll1) is involved in angiogenesis in melanoma, and we noticed that it took a longer time to trypsinize Dll1-expressing B16 melanoma cells than the control cells. In this article, we extended our study to investigate the effects of Dll1 on tumor cell adhesion and metastasis. Dll1 overexpression activated Notch signaling in B16 tumor cells and significantly enhanced the adhering capacity of B16 tumor cells both in vitro and in vivo. B16-Dll1 cells also had a higher metastatic potential than their counterpart in the mouse model of lung metastasis. Along with increased Dll1 expression, N-cadherin, but not E-cadherin, was upregulated in B16-Dll1 cells. These data suggested that Notch ligand Dll1 may enhance the adhesion and metastasis of melanoma cells by upregulation of N-cadherin.

Why is melanoma so metastatic?

Malignant melanoma is one of the most aggressive cancers and can disseminate from a relatively small primary tumor and metastasize to multiple sites, including the lung, liver, brain, bone, and lymph nodes. Elucidating the molecular and genetic changes that take place during the metastatic process has led to a better understanding of why melanoma is so metastatic. Herein, we describe the unique features that distinguish melanoma from other solid tumors and contribute to the malignant phenotype of melanoma cells. For example, although melanoma cells are highly antigenic, they are extremely efficient at evading host immune response. Melanoma cells share numerous cell surface molecules with vascular cells, are highly angiogenic, are mesenchymal in nature, and possess a higher degree of 'stemness' than do other solid tumors. Finally, analysis of melanoma mutations has revealed that the gene expression profile of malignant melanoma is different from that of other cancers. Elucidating these molecular and genetic processes in highly metastatic melanoma can lead to the development of improved treatment and individualized therapy options.

Proteolysis during tumor cell extravasation in vitro: metalloproteinase involvement across tumor cell types

To test if proteolysis is involved in tumor cell extravasation, we developed an in vitro model where tumor cells cross an endothelial monolayer cultured on a basement membrane. Using this model we classified the ability of the cells to transmigrate through the endothelial cell barrier onto the underlying matrix, and scored this invasion according to the stage of passage through the endothelium. Metalloproteinase inhibitors reduced tumor cell extravasation by at least 35%. Visualization of protease and cell adhesion molecules by confocal microscopy demonstrated the cell surface localization of MMP-2, MMP-9, MT1-MMP, furin, CD44 and αvβ3, during the process of transendothelial migration. By the addition of inhibitors and bio-modulators we assessed the functional requirement of the aforementioned molecules for efficient migration. Proteolytic digestion occurred at the cell-matrix interface and was most evident during the migratory stage. All of the inhibitors and biomodulators affected the transition of the tumor cells into the migratory stage, highlighting the most prevalent use of proteolysis at this particular step of tumor cell extravasation. These data suggest that a proteolytic interface operates at the tumor cell surface within the tumor-endothelial cell microenvironment.

T-cadherin loss promotes experimental metastasis of squamous cell carcinoma

T-cadherin is gaining recognition as a determinant for the development of incipient invasive squamous cell carcinoma (SCC). However, effects of T-cadherin expression on the metastatic potential of SCC have not been studied. Here, using a murine model of experimental metastasis following tail vein injection of A431 SCC cells we report that loss of T-cadherin increased both the incidence and rate of appearance of lung metastases. T-cadherin-silenced SCC metastases were highly disordered with evidence of single cell dissemination away from main foci whereas SCC metastases overexpressing T-cadherin developed as compact, tightly organised sheets. SCC cell adhesion to vascular endothelial cells (EC) in culture was increased for T-cadherin-silenced SCC and decreased for T-cadherin-overexpressing SCC. Confocal microscopy showed that T-cadherin-silenced SCC adherent on EC display an elongated morphology with long thin extensions and a high degree of intercalation within the EC monolayer, whereas SCC overexpressing T-cadherin formed poorly-spread multicellular aggregates that remain on the outer surface of the EC monolayer. T-cadherin-deficient SCC or human keratinocyte cells exhibited increased transendothelial migration in vitro which could be attenuated in the presence of EGFR inhibitor gefitinib. Our data suggest that loss of T-cadherin can increase metastatic potential and aggressiveness of SCC, possibly due to facilitating arrest and extravasation through the vascular wall and/or more efficient establishment of metastases in the new microenvironment.

Mutant B-RAF regulates a Rac-dependent cadherin switch in melanoma

The ability of cells to invade into the dermis is a critical event in the development of cutaneous melanoma and ultimately an indicator of poor prognosis. However, the molecular events surrounding the acquisition of this invasive phenotype remain incompletely understood. Mutations in B-RAF are frequent in melanoma and are known to regulate the invasive phenotype. In this study, we sought to determine the molecular mechanisms controlling melanoma invasion. We found that mutant B-RAF signaling regulates a cadherin switch. In melanoma cells expressing mutant B-RAF we observed high levels of N-cadherin and low levels of E-cadherin. Depletion of mutant B-RAF, by siRNA, caused a decrease in the levels of N-cadherin and an increase in the levels of E-cadherin. Mechanistically, we found that this cadherin switch required the activity of Rac1 and its GEF, Tiam1, both of which show suppressed activity in the presence of mutant B-RAF. Consistent with the work of others, we found that depletion of mutant B-RAF decreased the invasive capacity of the melanoma cells. However, simultaneous depletion of B-RAF and Rac or Tiam1 resulted in invasive capacity similar to that of control cells. Taken together, our results suggest that mutant B-RAF signaling downregulates Tiam1/Rac activity resulting in an increase in N-cadherin levels and a decrease in E-cadherin levels and ultimately enhanced invasion.

Notch-mediated induction of N-cadherin and α9-integrin confers higher invasive phenotype on rhabdomyosarcoma cells

Background:

Rhabdomyosarcoma (RMS) is the commonest type of soft-tissue sarcoma in children. Patients with metastatic RMS continue to have very poor prognosis. Recently, several works have demonstrated a connection between Notch pathway activation and the regulation of cell motility and invasiveness. However, the molecular mechanisms of this possible relationship remain unclear.

Methods:

The Notch pathway was manipulated pharmacologically and genetically. The mRNA changes were analysed by quantitative PCR and protein variations by western blot and immunofluorescence. Finally, the capabilities of RMS cells to adhere, heal a wound and invade were assessed in the presence of neuronal cadherin (N-cadherin)- and α9-integrin-blocking antibodies.

Results:

Cells treated with γ-secretase inhibitor showed lower adhesion capability and downregulation of N-cadherin and α9-integrin. Genetic manipulation of the Notch pathway led to concomitant variations in N-cadherin and α9-integrin. Treatment with anti-N-cadherin-blocking antibody rendered marked inhibition of cell adhesion and motility, while anti-α9-integrin-blocking antibody exerted a remarkable effect on cell adhesion and invasiveness.

Conclusion:

Neuronal cadherin and α9-integrin are postulated as leading actors in the association between the Notch pathway and promotion of cell adhesion, motility and invasion, pointing to these proteins and the Notch pathway itself as interesting putative targets for new molecular therapies against metastases in RMS.

ALCAM regulates motility, invasiveness, and adherens junction formation in uveal melanoma cells

ALCAM, a member of the immunoglobulin superfamily, has been implicated in numerous developmental events and has been repeatedly identified as a marker for cancer metastasis. Previous studies addressing ALCAM's role in cancer have, however, yielded conflicting results. Depending on the tumor cell type, ALCAM expression has been reported to be both positively and negatively correlated with cancer progression and metastasis in the literature. To better understand how ALCAM might regulate cancer cell behavior, we utilized a panel of defined uveal melanoma cell lines with high or low ALCAM levels, and directly tested the effects of manipulating these levels on cell motility, invasiveness, and adhesion using multiple assays. ALCAM expression was stably silenced by shRNA knockdown in a high-ALCAM cell line (MUM-2B); the resulting cells displayed reduced motility in gap-closure assays and a reduction in invasiveness as measured by a transwell migration assay. Immunostaining revealed that the silenced cells were defective in the formation of adherens junctions, at which ALCAM colocalizes with N-cadherin and ß-catenin in native cells. Additionally, we stably overexpressed ALCAM in a low-ALCAM cell line (MUM-2C); intriguingly, these cells did not exhibit any increase in motility or invasiveness, indicating that ALCAM is necessary but not sufficient to promote metastasis-associated cell behaviors. In these ALCAM-overexpressing cells, however, recruitment of ß-catenin and N-cadherin to adherens junctions was enhanced. These data confirm a previously suggested role for ALCAM in the regulation of adherens junctions, and also suggest a mechanism by which ALCAM might differentially enhance or decrease invasiveness, depending on the type of cadherin adhesion complexes present in tissues surrounding the primary tumor, and on the cadherin status of the tumor cells themselves.

Ethanol disrupts vascular endothelial barrier: implication in cancer metastasis

Both epidemiological and experimental studies indicate that ethanol exposure enhances tumor progression. Ethanol exposure promotes cancer cell invasion and is implicated in tumor metastasis. Metastasis consists of multiple processes involving intravasation and extravasation of cancer cells across the blood vessel walls. The integrity of the vascular endothelial barrier that lines the inner surface of blood vessels plays a critical role in cancer cell intravasation/extravasation. We examined the effects of ethanol on the endothelial integrity in vitro. Ethanol at physiologically relevant concentrations did not alter cell viability but disrupted the endothelial monolayer integrity, which was evident by a decrease in the electric resistance and the appearance of intercellular gaps in the endothelial monolayer. The effect of ethanol was reversible once ethanol was removed. The disruption of the endothelial monolayer integrity was associated with an increased invasion of cancer cells through the endothelial monolayer. Ethanol induced the formation of stress fibers; stabilization of actin filaments by jasplakinolide prevented ethanol-induced disruption of endothelial integrity and cancer cell invasion. VE-cadherin is a critical component of the adherens junctions, which regulates vascular endothelial integrity. Ethanol induced the endocytosis of VE-cadherin and the effect was blocked by jasplakinolide. Our results indicate that ethanol may facilitate cancer metastasis by disrupting the vascular endothelial barrier.

Channel-independent influence of connexin 43 on cell migration

In this review we focus on the role of connexins, especially of Cx43, as modulators of migration - a fundamental process in embryogenesis and in physiologic functions of the adult organism. This impact of connexins is partly mediated by their function as intercellular channels but an increasing number of studies support the view that at least part of the effects are truly independent of the channel function. The channel-independent function comprises extrinsic guidance of migrating cells due to connexin mediated cell adhesion as well as intracellular processes. Cx43 has been shown to exert effects on migration by interfering with receptor signalling, cytoskeletal remodelling and tubulin dynamics. These effects are mainly dependent on the presence of the carboxyl tail of Cx43. The molecular basis of this channel-independent connexin function is still not yet fully understood but early results open an exciting view towards new functions of connexins in the cell. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Intercellular adhesion: mechanisms for growth and metastasis of epithelial cancers

Cell-cell adhesion molecules (CAMs) comprise a broad class of linker proteins that are crucial for the development of multicellular organisms, and for the continued maintenance of organ and tissue structure. Because of its pivotal function in tissue homeostasis, the deregulation of intercellular adhesion is linked to the onset of most solid tumors. The breakdown of homeostatic cell adhesions in highly ordered epithelial sheets is directly implicated in carcinogenesis, while continued changes in the adhesion profile of the primary tumor mass facilitate growth and expansion into adjacent tissue. Intercellular adhesion molecules are also involved in each subsequent phase of metastasis, including transendothelial migration, transit through the bloodstream or lymphatics, and renewed proliferation in secondary sites. This review addresses various roles of cadherin- and selectin-mediated intercellular adhesion in tumor initiation and malignant transformation, and discusses the mechanisms for the arrest and adhesion of circulating tumor cells to the vessel endothelium. Considering the contributions of these CAMs to cancer progression in the context of a systematic biological framework may prove valuable in identifying new ways to diagnose and treat cancer.

N-cadherin mediates angiogenesis by regulating monocyte chemoattractant protein-1 expression via PI3K/Akt signaling in prostate cancer cells

Over the past decade, evidence continues to mount showing that N-cadherin is a critical protein in cancer progression and metastasis. In the present study, we evaluated the expression of N-cadherin in human prostate cancer tissue specimens and cell lines. Enhanced expression of N-cadherin was observed in both the malignant and bone-metastasized prostate tissue specimens compared to the healthy prostate tissues. Consistent with the tissue array data, N-cadherin was highly expressed in PC3, but not in Du145 and LNCaP human prostate cell lines. Based on cell to cell binding assay, we found that N-cadherin expression facilitates homotypic interaction between human prostate cancer cells and human microvascular endothelial cells (HMEC). Human angiogenesis antibody array and in vitro angiogenesis assay showed that siRNA-mediated knockdown of N-cadherin reduced the secretion of monocyte chemoattractant protein-1 (MCP-1), which played a potential role in stimulating capillary network formation of HMEC. Additionally, culture supernatant of Du145 cells transfected with full-length N-cadherin expressing plasmid showed increased MCP-1 expression and chemoattractant ability compared to normal Du145 cells. Further, we noticed that blocking PI3K activity inhibited N-cadherin mediated MCP-1 expression. Our data demonstrated that N-cadherin in prostate cancer cell mediates cell-cell adhesion and regulates MCP-1 expression via the PI3K/Akt signaling pathway.

Cell communication networks in cancer invasion

The invasion of cancer is a major clinical problem. It is now apparent that invasion is not a simply a cancer cell autonomous process but relies on a complex network of paracrine interactions. Furthermore, this network can change as cancer cells disseminate. Here we summarise the key components of the network and their mechanisms of communication. Finally, we discuss the difficulties and opportunities that this complex network of interactions presents during cancer therapy.

Surface expression of precursor N-cadherin promotes tumor cell invasion

The expression of N-cadherin (NCAD) has been shown to correlate with increased tumor cell motility and metastasis. However, NCAD-mediated adhesion is a robust phenomenon and therefore seems to be inconsistent with the "release" from intercellular adhesion required for invasion. We show that in the most invasive melanoma and brain tumor cells, altered posttranslational processing results in abundant nonadhesive precursor N-cadherin (proNCAD) at the cell surface, although total NCAD levels remain constant. We demonstrate that aberrantly processed proNCAD promotes cell migration and invasion in vitro. Furthermore, in human tumor specimens, we find high levels of proNCAD as well, supporting an overall conclusion that proNCAD and mature NCAD coexist on these tumor cell surfaces and that it is the ratio between these functionally antagonistic moieties that directly correlates with invasion potential. Our work provides insight into what may be a widespread mechanism for invasion and metastasis and challenges the current dogma of the functional roles played by classic cadherins in tumor progression.

Epithelial and mesenchymal phenotypic switchings modulate cell motility in metastasis

The most ominous stage of cancer progression is metastasis, or the dissemination of carcinoma cells from the primary site into distant organs. Metastases are often resistant to current extirpative therapies and even the newest biological agents cure only a small subset of patients. Therefore a greater understanding of tumor biology that integrates properties intrinsic to carcinomas with tissue environmental modulators of behavior is needed. In no aspect of tumor progression is this more evident than the acquisition of cell motility that is critical for both escape from the primary tumor and colonization. In this overview, we discuss how this behavior is modified by carcinoma cell phenotypic plasticity that is evidenced by reversible switching between epithelial and mesenchymal phenotypes. The presence or absence of intercellular adhesions mediate these switches and dictate the receptivity towards signals from the extracellular milieu. These signals, which include soluble growth factors, cytokines, and extracellular matrix embedded with matrikines and matricryptines will be discussed in depth. Finally, we will describe a new mode of discerning the balance between epithelioid and mesenchymal movement.

CXCL9 induces chemotaxis, chemorepulsion and endothelial barrier disruption through CXCR3-mediated activation of melanoma cells

Background:

Metastasis is associated with poor prognosis for melanoma. The formation of metastases is a multi-step process, in which cancer cells can subsequently acquire the potential to intravasate into the blood or lymph vessels, disseminate through the circulation, extravasate through the endothelium and invade the connective tissue. There is increasing evidence that chemokines have a pivotal role in the dissemination and establishment of melanoma metastasis.

Methods:

We isolated melanoma cells from melanoma metastasis and performed different migration assays and transendothelial resistance measurements of endothelial monolayers co-cultured with melanoma cells, in order to monitor barrier function and diapedesis and confirmed these results by confocal microscopy.

Results:

We observed that tumour endothelial cells (ECs) secrete high levels of CXCL9 in all, and CXCL10 in most melanoma metastases. Migration studies revealed that low concentrations of these chemokines induce chemotaxis, whereas high concentrations induce spontaneous migration of melanoma cells (chemokinesis/chemorepulsion) and the disruption of the endothelial barrier, resulting in an accelerated transendothelial migration (TEM). Addition of anti-CXCL9 or anti-CXCR3 antibodies to the co-cultures delayed the TEM of melanoma cells.

Conclusion:

Our data represent novel mechanisms by which tumour cells in melanoma metastases might use the chemokine-expressing endothelium to leave the tumour and eventually to form additional metastases at distinct sites.

Interplay of cadherin-mediated cell adhesion and canonical Wnt signaling

The epithelial-mesenchymal transition is essential in both embryonic development and the progression of carcinomas. Wnt signaling and cadherin-mediated adhesion have been implicated in both processes; clarifying their role will depend on linking them to rearrangements of cellular structure and behavior. beta-Catenin is an essential molecule both in cadherin-mediated cell adhesion and in canonical Wnt signaling. Numerous experiments have shown that the loss of cadherin-mediated cell adhesion can promote beta-catenin release and signaling; this is accomplished by proteases, protein kinases and other molecules. Cadherin loss can also signal to several other regulatory pathways. Additionally, many target genes of Wnt signaling influence cadherin adhesion. The most conspicuous of these Wnt target genes encode the transcription factors Twist and Slug, which directly inhibit the E-cadherin gene promoter. Other Wnt/beta-catenin target genes encode metalloproteases or the cell adhesion molecule L1, which favor the degradation of E-cadherin. These factors provide a mechanism whereby cadherin loss and increased Wnt signaling induce epithelial-mesenchymal transition in both carcinomas and development.

P-cadherin counteracts myosin II-B function: implications in melanoma progression

BACKGROUND

Malignant transformation of melanocytes is frequently attended by a switch in cadherin expression profile as shown for E- and N-cadherin. For P-cadherin, downregulation in metastasizing melanoma has been demonstrated, and over-expression of P-cadherin in melanoma cell lines has been shown to inhibit invasion. The strong invasive and metastatic nature of cutaneous melanoma implies a deregulated interplay between intercellular adhesion and migration-related molecules

RESULTS

In this study we performed a microarray analysis to compare the mRNA expression profile of an invasive BLM melanoma cell line (BLM LIE) and the non-invasive P-cadherin over-expression variant (BLM P-cad). Results indicate that nonmuscle myosin II-B is downregulated in BLM P-cad. Moreover, myosin II-B plays a major role in melanoma migration and invasiveness by retracting the tail during the migratory cycle, as shown by the localization of myosin II-B stress fibers relative to Golgi and the higher levels of phosphorylated myosin light chain. Analysis of P-cadherin and myosin II-B in nodular melanoma sections and in a panel of melanoma cell lines further confirmed that there is an inverse relationship between both molecules.

CONCLUSIONS

Therefore, we conclude that P-cadherin counteracts the expression and function of myosin II-B, resulting in the suppression of the invasive and migratory behaviour of BLM melanoma cells.

The role of the tissue microenvironment in the regulation of cancer cell motility and invasion

During malignant neoplastic progression the cells undergo genetic and epigenetic cancer-specific alterations that finally lead to a loss of tissue homeostasis and restructuring of the microenvironment. The invasion of cancer cells through connective tissue is a crucial prerequisite for metastasis formation. Although cell invasion is foremost a mechanical process, cancer research has focused largely on gene regulation and signaling that underlie uncontrolled cell growth. More recently, the genes and signals involved in the invasion and transendothelial migration of cancer cells, such as the role of adhesion molecules and matrix degrading enzymes, have become the focus of research. In this review we discuss how the structural and biomechanical properties of extracellular matrix and surrounding cells such as endothelial cells influence cancer cell motility and invasion. We conclude that the microenvironment is a critical determinant of the migration strategy and the efficiency of cancer cell invasion.

p38 MAP kinase is necessary for melanoma-mediated regulation of VE-cadherin disassembly

Vascular endothelial (VE)-cadherin is localized to the endothelial borders and the adherens junctions, which are regulated by changes in mitogen-activated protein (MAP) kinases, GTPases, and intracellular calcium. We previously showed that melanoma cells induce VE-cadherin disassembly through contact with human umbilical vein endothelial cells in coculture. However, the exact mechanism by which melanoma cells signal endothelial cells to induce VE-cadherin junction disassembly is not well understood. In this study, VE-cadherin junction disassembly was further examined under fluorescence microscopy. We found that melanoma-induced VE-cadherin junction disassembly and upregulation of p38 MAP kinase in endothelial cells is regulated by both soluble factors from melanomas, particularly interleukin (IL)-8, IL-6, and IL-1beta, and through vascular cell adhesion molecule-1. Neutralizing melanoma-secreted soluble factors reduced endothelial gap formation. Endothelial cells transfected with MAP kinase kinase 6, a direct activator of p38 MAP kinase, increased VE-cadherin-mediated gap formation, facilitating melanoma transendothelial migration. In contrast, endothelial cells transfected with small-interfering RNA against p38 MAP kinase expression largely prevented melanoma transendothelial migration in Boyden chamber experiments. These findings indicate that p38 MAP kinase proteins regulate VE-cadherin junction disassembly, facilitating melanoma migration across endothelial cells.

Role of the endothelium during tumor cell metastasis: is the endothelium a barrier or a promoter for cell invasion and metastasis?

The malignancy of cancer disease depends on the ability of the primary tumor to metastasize to distant organs. The process of the metastasis formation has largely been analyzed, but still main pathways regarding the extravasation step at the end of the metastasis formation process are controversially discussed. An agreement has been reached about the importance of the endothelium to promote metastasis formation either by enhancing the growth of the primary tumor or by homing (targeting) the tumor cells to blood or lymph vessels. The mechanical properties of the invading tumor cells become the focus of several studies, but the endothelial cell mechanical properties are still elusive. This paper describes the different roles of the endothelium in the process of metastasis formation and focuses on a novel role of the endothelium in promoting tumor cell invasion. It discusses how novel biophysical tools and in vivo animal models help to determine the role of the endothelium in the process of tumor cell invasion. Evidence is provided that cell mechanical properties, for example, contractile force generation of tumor cells, are involved in the process of tumor cell invasion.

Subtypes of melanocytes and melanoma cells distinguished by their intercellular contacts: heterotypic adherens junctions, adhesive associations, and dispersed desmoglein 2 glycoproteins

In the tissue integration of melanocytes and melanoma cells, an important role is attributed to cell adhesion molecules, notably the cadherins. In cultured melanoma cells, we have previously described a more heterogeneous repertoire of cadherins than normal, including some melanoma subtypes synthesizing the desmosomal cadherin, desmoglein 2, out of the desmosomal context. Using biochemical and immunological characterization of junctional molecules, confocal laser scanning, and electron and immunoelectron microscopy, we now demonstrate homo- and heterotypic cell-cell adhesions of normal epidermal melanocytes. In human epidermis, both in situ and in cell culture, melanocytes and keratinocytes are connected by closely aligned membranes that are interspersed by small puncta adhaerentia containing heterotypic complexes of E- and P-cadherin. Moreover, melanocytes growing in culture often begin to synthesize desmoglein 2, which is dispersed over extended areas of intimate adhesive cell-cell associations. As desmoglein 2 is not found in melanocytes in situ, we hypothesize that its synthesis is correlated with cell proliferation. Indeed, in tissue microarrays, desmoglein 2 has been demonstrated in a sizable subset of nevi and primary melanomas. The biological meanings of these cell-cell adhesion molecule arrangements, the possible diagnostic and prognostic significance of these findings, and the implications of the heterogeneity types of melanomas are discussed.

Cadherin switching

The cadherin molecules at adherens junctions have multiple isoforms. Cadherin isoform switching (cadherin switching) occurs during normal developmental processes to allow cell types to segregate from one another. Tumor cells often recapitulate this activity and the result is an aggressive tumor cell that gains the ability to leave the site of the tumor and metastasize. At present, we understand some of the mechanisms that promote cadherin switching and some of the pathways downstream of this process that influence cell behavior. Specific cadherin family members influence growth-factor-receptor signaling and Rho GTPases to promote cell motility and invasion. In addition, p120-catenin probably plays multiple roles in cadherin switching, regulating Rho GTPases and stabilizing cadherins.

Extracellular matrix protein betaig-h3/TGFBI promotes metastasis of colon cancer by enhancing cell extravasation

Metastasis, the major cause of cancer death, is a multistep process that requires interactions between cancer cells and stromal cells and between cancer cells and extracellular matrix. Molecular alterations of the extracellular matrix in the tumor microenvironment have a considerable impact on the metastatic process during tumorigenesis. Here we report that elevated expression of betaig-h3/TGFBI (transforming growth factor, beta-induced), an extracellular matrix protein secreted by colon cancer cells, is associated with high-grade human colon cancers. Ectopic expression of the betaig-h3 protein enhanced the aggressiveness and altered the metastatic properties of colon cancer cells in vivo. Inhibition of betaig-h3 expression dramatically reduced metastasis. Mechanistically, betaig-h3 appears to promote extravasation, a critical step in the metastatic dissemination of cancer cells, by inducing the dissociation of VE-cadherin junctions between endothelial cells via activation of the integrin alphavbeta5-Src signaling pathway. Thus, cancers associated with overexpression of betaig-h3 may have an increased metastatic potential, leading to poor prognosis in cancer patients.

Breakdown of the endothelial barrier function in tumor cell transmigration

The ability of tumor cells to metastasize is associated with a poor prognosis for cancer. During the process of metastasis, tumor cells circulating in the blood or lymph vessels can adhere to, and potentially transmigrate through, the endothelium and invade the connective tissue. We studied the effectiveness of the endothelium as a barrier against the invasion of 51 tumor cell lines into a three-dimensional collagen matrix. Only nine tumor cell lines showed attenuated invasion in the presence of an endothelial cell monolayer, whereas 17 cell lines became invasive or showed a significantly increased invasion. Endothelial cells cocultured with invasive tumor cells increased chemokine gene expression of IL-8 and Gro-β. Expression of the IL-8 and Gro-β receptor, CXCR2, was upregulated in invasive tumor cells. Addition of IL-8 or Gro-β increased tumor cell invasiveness by more than twofold. Tumor cell variants selected for high CXCR2 expression were fourfold more invasive in the presence of an endothelial cell layer, whereas CXCR2 siRNA knock-down cells were fivefold less invasive. We demonstrate that Gro-β and IL-8 secreted by endothelial cells, together with CXCR2 receptor expression on invasive tumor cells, contribute to the breakdown of the endothelial barrier by enhancing tumor cell force generation and cytoskeletal remodeling dynamics.

Expression profiling reveals genes associated with transendothelial migration of tumor cells: a functional role for alphavbeta3 integrin

Transendothelial migration is a key step in the extravasation of tumor cells during metastasis formation. Here, we have classified 45 human tumor cell lines derived from various tissues according to their capacity for transendothelial migration in vitro. We could distinguish cell lines showing strong transmigration (TEM+ cell lines) from others that did not transmigrate (TEM- cell lines). By DNA microarray analysis we could cluster TEM+ and TEM- cell lines according to their gene expression pattern and identify genes differentially expressed between the 2 groups. Among these we found the integrin beta3 subunit to be highly expressed in TEM+ cell lines as compared to TEM- cell lines. Cell surface localization of alphavbeta3 integrin receptors was exclusively found in TEM+ cell lines. Transendothelial migration of TEM+ cells but not their adhesion to the endothelial cells, or invasion into collagen gels could be blocked with an antibody against alphavbeta3 integrin and by RNAi mediated knock-down of the integrin beta3 subunit. These data establishes alphavbeta3 integrin as one key component of the transendothelial migration process of tumor cells, and as a potential target for anti-metastatic therapy. Our gene expression analysis of a defined collection of tumor cell lines can be used as a starting point to identify further genes functionally involved in transendothelial migration.

Stepping out of the flow: capillary extravasation in cancer metastasis

In order for cancer cells to successfully colonize a metastatic site, they must detach from the primary tumor using extracellular matrix-degrading proteases, intravasate and survive in the circulation, evade the immune response, and extravasate the vasculature to invade the target tissue parenchyma, where metastatic foci are established. Though many of the steps of metastasis are widely studied, the precise cellular interactions and molecular alterations associated with extravasation are unknown, and further study is needed to elucidate the mechanisms inherent to this process. Studies of leukocytes localized to inflamed tissue during the immune response may be used to elucidate the process of cancer extravasation, since leukocyte diapedesis through the vasculature involves critical adhesive interactions with endothelial cells, and both leukocytes and cancer cells express similar surface receptors capable of binding endothelial adhesion molecules. Thus, leukocyte extravasation during the inflammatory response has provided a model for transendothelial migration (TEM) of cancer cells. Leukocyte extravasation is characterized by a process whereby rolling mediated by cytokine-activated endothelial selectins is followed by firmer adhesions with beta1 and beta2 integrin subunits to an activated endothelium and subsequent diapedesis, which most likely involves activation of Rho GTPases, regulators of cytoskeletal rearrangements and motility. It is controversial whether such selectin-mediated rolling is necessary for TEM of cancer cells. However, it has been established that similar stable adhesions between tumor and endothelial cells precede cancer cell transmigration through the endothelium. Additionally, there is support for the preferential attachment of tumor cells to the endothelium and, accordingly, site-specific metastasis of cancer cells. Rho GTPases are critical to TEM of cancer cells as well, and some progress has been made in understanding the specific roles of the Rho GTPase family, though much is still unknown. As the mechanisms of cancer TEM are elucidated, new approaches to study and target metastasis may be utilized and developed.

Differential cadherin expression: potential markers for epithelial to mesenchymal transformation during tumor progression

The cadherin family of adhesion molecules regulates cell-cell interactions during development and in tissues. The prototypical cadherin, E-cadherin, is responsible for maintaining interactions of epithelial cells and is frequently downregulated during tumor progression. N-cadherin, normally found in fibroblasts and neural cells, can be upregulated during tumor progression and can increase the invasiveness of tumor cells. The proinvasive effects of N-cadherin expression in tumor cells result from two possible mechanisms: promotion of tumor cell interactions with the N-cadherin-expressing microenvironment, or enhancement of signaling via the fibroblast growth factor receptor. The downregulation of E-cadherin and the upregulation of N-cadherin in tumors may be a result of an epithelial to mesenchymal transformation (EMT) of tumor cells, which is notoriously difficult to detect in vivo. Double labeling of individual tumors with specific E- and N-cadherin antibodies suggests that EMT can occur heterogeneously and/or transiently within an invasive tumor.

Rho/Rho-associated kinase-II signaling mediates disassembly of epithelial apical junctions

Apical junctional complex (AJC) plays a vital role in regulation of epithelial barrier function. Disassembly of the AJC is observed in diverse physiological and pathological states; however, mechanisms governing this process are not well understood. We previously reported that the AJC disassembly is driven by the formation of apical contractile acto-myosin rings. In the present study, we analyzed the signaling pathways regulating acto-myosin-dependent disruption of AJC by using a model of extracellular calcium depletion. Pharmacological inhibition analysis revealed a critical role of Rho-associated kinase (ROCK) in AJC disassembly in calcium-depleted epithelial cells. Furthermore, small interfering RNA (siRNA)-mediated knockdown of ROCK-II, but not ROCK-I, attenuated the disruption of the AJC. Interestingly, AJC disassembly was not dependent on myosin light chain kinase and myosin phosphatase. Calcium depletion resulted in activation of Rho GTPase and transient colocalization of Rho with internalized AJC proteins. Pharmacological inhibition of Rho prevented AJC disassembly. Additionally, Rho guanine nucleotide exchange factor (GEF)-H1 translocated to contractile F-actin rings after calcium depletion, and siRNA-mediated depletion of GEF-H1 inhibited AJC disassembly. Thus, our findings demonstrate a central role of the GEF-H1/Rho/ROCK-II signaling pathway in the disassembly of AJC in epithelial cells.

Homo- and heterotypic cell contacts in malignant melanoma cells and desmoglein 2 as a novel solitary surface glycoprotein

During progression of melanomas, a crucial role has been attributed to alterations of cell-cell adhesions, specifically, to a "cadherin switch" from E- to N-cadherin (cad). We have examined the adhesion of melanoma cells to each other and to keratinocytes. When different human melanoma cell lines were studied by protein analysis and immunofluorescence microscopy, six of eight lines contained N-cad, three E-cad, and five P-cad, and some lines had more than one cad. Surprisingly, two N-cad-positive lines, MeWo and C32, also contained desmoglein 2 (Dsg2), a desmosomal cad previously not reported for melanomas, whereas other desmosome-specific proteins were absent. This finding was confirmed by reverse transcriptase-PCR, immunoprecipitation, and matrix-assisted laser desorption ionization-time of flight analyses. Double-label confocal and immunoelectron microscopy showed N-cad, alpha- and beta-catenin in plaque-bearing puncta adhaerentia, whereas Dsg2 was distributed rather diffusely over the cell surface. In cocultures with HaCaT keratinocytes Dsg2 was found in heterotypic cell contact regions. Correspondingly, immunohistochemistry revealed Dsg2 in five of 10 melanoma metastases. Together, we show that melanoma cell adhesions are more heterogeneous than expected and that certain cells devoid of desmosomes contain Dsg2 in a non-junction-restricted form. Future studies will have to clarify the diagnostic and prognostic significance of these different adhesion protein subtypes.

Collagen I promotes metastasis in pancreatic cancer by activating c-Jun NH(2)-terminal kinase 1 and up-regulating N-cadherin expression

We have previously shown that N-cadherin expression is associated with tumor invasion, and that some cancer cells respond to specific extracellular matrix molecules by up-regulating N-cadherin. Pancreatic cancer is characterized by excessive deposition of type I collagen. Here, we show that human pancreatic cancer cells respond to collagen I, but not other matrices, by increasing motility and up-regulating mesenchymal markers, including N-cadherin. Both collagen I-mediated motility and metastasis in a mouse model for pancreatic cancer were inhibited by N-cadherin knockdown. Furthermore, inhibiting c-Jun NH(2)-terminal kinase (JNK) with chemical inhibitors or short hairpin RNA abrogated all collagen I-induced changes. We show that JNK1 is activated in response to collagen I, which increases tumorigenesis by up-regulating N-cadherin expression and by increasing motility.

Expression of T-cadherin in tumor cells influences invasive potential of human hepatocellular carcinoma

Overexpression of T-cadherin (T-cad) transcripts occurs in approximately 50% of human hepatocellular carcinomas (HCCs). To elucidate T-cad functions in HCC, we examined T-cad protein expression in normal and tumoral human livers and hepatoma cell lines and investigated its influence on invasive potential of HCC using RNA interference silencing of T-cad expression in Mahlavu cells. Whereas T-cad expression was restricted to endothelial cells (EC) from large blood vessels in normal livers, it was up-regulated in sinusoidal EC from 8/15 invasive HCCs. Importantly, in three of them (38%) T-cad was detected in tumor cells within regions in which E-cadherin expression was absent. Among six hepatoma cell lines, only Mahlavu expressed T-cad but not E-cadherin. T-cad exhibited a globally punctuate distribution in quiescent Mahlavu and additionally it concentrated at the leading edge of migrating cells. Matrigel invasion assay revealed that Mahlavu possess a high invasive potential that was significantly inhibited by T-cad silencing. Wound healing and random motility assays demonstrated that inhibition of T-cad expression in Mahlavu significantly reduced their motility. We propose that T-cad expression in tumor cells might occur by cadherin-switching during epithelial-mesenchymal transition and may represent an additional mechanism contributing to HCC metastasis.