FAK alters invadopodia and focal adhesion composition and dynamics to regulate breast cancer invasion

Podocalyxin-like 1 promotes invadopodia formation and metastasis through activation of Rac1/Cdc42/cortactin signaling in breast cancer cells

Metastatic disease is the leading cause of cancer mortality. Identifying biomarkers and regulatory mechanisms is important toward developing diagnostic and therapeutic tools against metastatic cancer. In this study, we demonstrated that podocalyxin-like 1 (PODXL) is overexpressed in breast tumor cells and increased in lymph node metastatic cancer. Mechanistically, we found that the expression of PODXL was associated with cell motility and invasiveness. Suppression of PODXL in MDA-MB-231 cells reduced lamellipodia formation and focal adhesion kinase (FAK) and paxillin phosphorylation. PODXL knockdown reduced the formation of invadopodia, such as inhibiting the colocalization of F-actin with cortactin and suppressing phosphorylation of cortactin and neural Wiskott-Aldrich syndrome protein. Conversely, overexpression of PODXL in MCF7 cells induced F-actin/cortactin colocalization and enhanced invadopodia formation and activation. Invadopodia activity and tumor invasion in PODXL-knockdown cells are similar to that in cortactin-knockdown cells. We further found that the DTHL motif in PODXL is crucial for regulating cortactin phosphorylation and Rac1/Cdc42 activation. Inhibition of Rac1/Cdc42 impeded PODXL-mediated cortactin activation and FAK and paxillin phosphorylation. Moreover, inhibition of PODXL in MDA-MB-231 cells significantly suppressed tumor colonization in the lungs and distant metastases, similar to those in cortactin-knockdown cells. These findings show that overexpression of PODXL enhanced invadopodia formation and tumor metastasis by inducing Rac1/Cdc42/cortactin signaling network.

Invadopodia, regulation, and assembly in cancer cell invasion

The occurrence of invadopodia has been, since its characterization, a hallmark of cancerous cell invasion and metastasis. These structures are now the subject of a controversy concerning their cellular function, molecular regulation, and assembly. The terms invadopodia and podosomes have been used interchangeably since their discovery back in 1980. Since then, these phenotypes are now more established and accepted by the scientific community as vital structures for 3D cancer cell motility. Many characteristics relating to invadopodia and podosomes have been elucidated, which might prove these structures as good targets for metastasis treatment. In this review, we briefly review the actin reorganization process needed in most types of cancer cell motility. We also review the important characteristics of invadopodia, including molecular components, assembly, markers, and the signaling pathways, providing a comprehensive model for invadopodia regulation.

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.

A Trio-Rac1-Pak1 signalling axis drives invadopodia disassembly

Rho family GTPases control cell migration and participate in the regulation of cancer metastasis. Invadopodia, associated with invasive tumor cells, are crucial for cellular invasion and metastasis. To study Rac1 GTPase in invadopodia dynamics, we developed a genetically-encoded, single-chain Rac1 Fluorescence Resonance Energy Transfer (FRET) biosensor.

The biosensor shows Rac1 activity exclusion from the core of invadopodia, and higher activity when invadopodia disappear, suggesting that reduced Rac1 activity is necessary for their stability, and Rac1 activation is involved in disassembly. Photoactivating Rac1 at invadopodia confirmed this previously-unknown Rac1 function.

We built an invadopodia disassembly model, where a signaling axis involving TrioGEF, Rac1, PAK1, and phosphorylation of cortactin, causing invadopodia dissolution. This mechanism is critical for the proper turnover of invasive structures during tumor cell invasion, where a balance of proteolytic activity and locomotory protrusions must be carefully coordinated to achieve a maximally invasive phenotype.

Retinoic acid reduces migration of human breast cancer cells: role of retinoic acid receptor beta

Breast cancer is the most common malignancy in women and the appearance of distant metastases produces the death in 98% of cases. The retinoic acid receptor β (RARβ) is not expressed in 50% of invasive breast carcinoma compared with normal tissue and it has been associated with lymph node metastasis. Our hypothesis is that RARβ protein participates in the metastatic process. T47D and MCF7 breast cancer cell lines were used to perform viability assay, immunobloting, migration assays, RNA interference and immunofluorescence. Administration of retinoic acid (RA) in breast cancer cells induced RARβ gene expression that was greatest after 72 hrs with a concentration 1 μM. High concentrations of RA increased the expression of RARβ causing an inhibition of the 60% in cell migration and significantly decreased the expression of migration-related proteins [moesin, c-Src and focal adhesion kinase (FAK)]. The treatment with RARα and RARγ agonists did not affect the cell migration. On the contrary, the addition of the selective retinoid RARβ-agonist (BMS453) significantly reduced cell migration comparable to RA inhibition. When RARβ gene silencing was performed, the RA failed to significantly inhibit migration and resulted ineffective to reduce moesin, c-Src and FAK expressions. RARβ is necessary to inhibit migration induced by RA in breast cancer cells modulating the expression of proteins involved in cell migration.

Non-thermal atmospheric pressure plasma inhibits thyroid papillary cancer cell invasion via cytoskeletal modulation, altered MMP-2/-9/uPA activity

Plasma, the fourth state of matter, is defined as a partially or completely ionized gas that includes a mixture of electrons and ions. Advances in plasma physics have made it possible to use non-thermal atmospheric pressure plasma (NTP) in cancer research. However, previous studies have focused mainly on apoptotic cancer cell death mediated by NTP as a potential cancer therapy. In this study, we investigated the effect of NTP on invasion or metastasis, as well as the mechanism by which plasma induces anti-migration and anti-invasion properties in human thyroid papillary cancer cell lines (BHP10-3 and TPC1). Wound healing, pull-down, and Transwell assays demonstrated that NTP reduced cell migration and invasion. In addition, NTP induced morphological changes and cytoskeletal rearrangements, as detected by scanning electron microscopy and immunocytochemistry. We also examined matrix metalloproteinase (MMP)-2/-9 and urokinase-type plasminogen activator (uPA) activity using gelatin zymography, uPA assays and RT-PCR. FAK, Src, and paxillin expression was detected using Western blot analyses and immunocytochemistry. NTP decreased FAK, Src, and paxillin expression as well as MMP/uPA activity. In conclusion, NTP inhibited the invasion and metastasis of BHP10-3 and TPC1 cells by decreasing MMP-2/-9 and uPA activities and rearranging the cytoskeleton, which is regulated by the FAK/Src complex. These findings suggest novel actions for NTP and may aid in the development of new therapeutic strategies for locally invasive and metastatic cancers.

Nestin regulates prostate cancer cell invasion by influencing the localisation and functions of FAK and integrins

Nestin, an intermediate filament protein and marker of undifferentiated cells, is expressed in several cancers. Nestin is important for neuronal survival and is a regulator of myogenesis but its function in malignancy is ambiguous. We show that nestin downregulation leads to a redistribution of phosphorylated focal adhesion kinase (pFAK, also known as PTK2) to focal adhesions and alterations in focal adhesion turnover. Nestin downregulation also leads to an increase in the protein levels of integrin α5β1 at the cell membrane, activation of integrin β1 and an increase in integrin clustering. These effects have striking consequences for cell invasion, as nestin downregulation leads to a significant increase in pFAK- and integrin-dependent matrix degradation and cell invasion. Our results indicate that nestin regulates the localisation and functions of FAK and integrin. Because nestin has been shown to be prevalent in a number of specific cancers, our observations have broad ramifications for the roles of nestin in malignant transformation.

Down-regulation of Gli transcription factor leads to the inhibition of migration and invasion of ovarian cancer cells via integrin β4-mediated FAK signaling

Background

Recent evidence suggests that aberrant activation of Hedgehog (Hh) signaling by Gli transcription factors is characteristic of a variety of aggressive human carcinomas including ovarian cancer. Therefore, chemotherapeutic agents that inhibit activation of Gli transcription factors have emerged as promising novel therapeutic drugs for ovarian cancer.

Results

In this study, we show that activation of Hh signaling promoted cellular migration and invasion, whereas blockade of Hh signaling with GANT61 suppressed cellular migration and invasion in ovarian cancer cells. After treatment with GANT61, cDNA microarray analyses revealed changes in many genes such as Integrin β4 subunit (ITGB4), focal adhesion kinase (FAK), etc. Furthermore, ITGB4 expression was up-regulated by Sonic Hedgehog (Shh) ligand and down-regulated by Hh signaling inhibitor. The Shh-mediated ovarian cell migration and invasion was blocked by neutralizing antibodies to ITGB4. In addition, phosphorylations of FAK were increased by Shh and decreased by Hh signaling inhibitor. Inhibition of Gli1 expression using siRNA mimicked the effects of GANT61 treatment, supporting the specificity of GANT61. Further investigations showed that activation of FAK was required for Shh-mediated cell migration and invasion. Finally, we found that down-regulation of Gli reduced the expression of ITGB4 and the phosphorylated FAK, resulting in the inhibition of tumor growth in vivo.

Conclusions

The Hh signaling pathway induces cell migration and invasion through ITGB4-mediated activation of FAK in ovarian cancer. Our findings suggest that the diminishment of crosstalk between phosphorylated FAK and ITGB4 due to the down-regulation of Gli family transcription factors might play a pivotal role for inhibiting ovarian cancer progression.

Mechanotransduction of fluid stresses governs 3D cell migration

Solid tumors are characterized by high interstitial fluid pressure, which drives fluid efflux from the tumor core. Tumor-associated interstitial flow (IF) at a rate of ∼3 µm/s has been shown to induce cell migration in the upstream direction (rheotaxis). However, the molecular biophysical mechanism that underlies upstream cell polarization and rheotaxis remains unclear. We developed a microfluidic platform to investigate the effects of IF fluid stresses imparted on cells embedded within a collagen type I hydrogel, and we demonstrate that IF stresses result in a transcellular gradient in β1-integrin activation with vinculin, focal adhesion kinase (FAK), FAK(PY397), F actin, and paxillin-dependent protrusion formation localizing to the upstream side of the cell, where matrix adhesions are under maximum tension. This previously unknown mechanism is the result of a force balance between fluid drag on the cell and matrix adhesion tension and is therefore a fundamental, but previously unknown, stimulus for directing cell movement within porous extracellular matrix.

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.

Inhibition of tumour spheroid-induced prometastatic intravasation gates in the lymph endothelial cell barrier by carbamazepine: drug testing in a 3D model

Metastatic breast cancer is linked to an undesired prognosis. One early and crucial metastatic step is the interaction of cancer emboli with adjacent stroma or endothelial cells, and understanding the mechanisms of this interaction provides the basis to define new targets as well as drugs for therapy and disease management. A three-dimensional (3D) co-culture model allowing the examination of lymphogenic dissemination of breast cancer cells was recently developed which facilitates not only the study of metastatic processes but also the testing of therapeutic concepts. This 3D setting consists of MCF-7 breast cancer cell spheroids (representing a ductal and hormone-dependent subtype) and of hTERT-immortalised lymph endothelial cell (LEC; derived from foreskin) monolayers. Tumour spheroids repel the continuous LEC layer, thereby generating "circular chemorepellent-induced defects" (CCIDs) that are reminiscent to the entry gates through which tumour emboli intravasate lymphatics. We found that the ion channel blocker carbamazepine (which is clinically used to treat epilepsy, schizophrenia and other neurological disorders) inhibited CCID formation significantly. This effect correlated with the inhibition of the activities of NF-κB, which contributes to cell motility, and with the inactivation of the mobility proteins MLC2, MYPT1 and FAK which are necessary for LEC migration. NF-κB activity and cell movement are prerequisites of CCID formation. On the other hand, the expression of the motility protein paxillin and of the NF-κB-dependent adhesion mediator ICAM-1 was unchanged. Also the activity of ALOX12 was unaffected. ALOX12 is the main enzyme synthesising 12(S)-HETE, which then triggers CCID formation. The relevance of the inhibition of CYP1A1, which is also involved in the generation of mid-chain HETEs such as 12(S)-HETE, by carbamazepine remains to be established, because the constitutive level of 12(S)-HETE did not change upon carbamazepine treatment. Nevertheless, the effect of carbamazepine on the inhibition of CCID formation as an early step of breast cancer metastasis was significant and substantial (~30 %) and achieved at concentrations that are found in the plasma of carbamazepine-treated adults (40-60 μM). The fact that carbamazepine is a drug approved by the US Food and Drug Administration facilitates a "from-bench-to-bedside" perspective. Therefore, the here presented data should undergo scrutiny in vivo.

Soft matrix is a natural stimulator for cellular invasiveness

ECM softness (low stiffness comparable to soft tissues) alone is sufficient to prevent cell-to-cell adherens junction formation, up-regulate MMP secretion, promote MMP activity, and induce invadosome-like protrusion formation. Such findings suggest that cell invasion in vivo is a spontaneous cell behavior in response to ECM stiffness.

Directional mesenchymal cell invasion in vivo is understood to be a stimulated event and to be regulated by cytokines, chemokines, and types of extracellular matrix (ECM). Instead, by focusing on the cellular response to ECM stiffness, we found that soft ECM (low stiffness) itself is sufficient to prevent stable cell-to-cell adherens junction formation, up-regulate matrix metalloproteinase (MMP) secretion, promote MMP activity, and induce invadosome-like protrusion (ILP) formation. Consistently, similar ILP formation was also detected in a three-dimensional directional invasion assay in soft matrix. Primary human fibroblasts spontaneously form ILPs in a very narrow range of ECM stiffness (0.1–0.4 kPa), and such ILP formation is Src family kinase dependent. In contrast, spontaneous ILP formation in malignant cancer cells and fibrosarcoma cells occurs across a much wider range of ECM stiffness, and these tumor cell ILPs are also more prominent at lower stiffness. These findings suggest that ECM softness is a natural stimulator for cellular invasiveness.

Targeting focal adhesion turnover in invasive breast cancer cells by the purine derivative reversine

Background:

The dynamics of focal adhesion (FA) turnover is a key determinant for the regulation of cancer cell migration. Here we investigated FA turnover in a panel of breast cancer models with distinct invasive properties and evaluated the impact of reversine on this turnover in relation to cancer cell invasion in in vitro and in vivo conditions.

Methods:

Live imaging and immunofluorescence assays were used to investigate FA turnover in breast cancer cells. Biochemical studies were used to investigate the impact of reversine on FA signalling and turnover. In vivo activity was investigated using orthotopic breast cancer mouse models.

Results:

Accelerated FA disassembly from plasma membrane protrusions was observed in invasive compared with non-invasive breast cancer cells or non-immortalised mammary epithelial cells. Reversine significantly inhibited FA disassembly leading to stable FAs, which was associated with reduced cell motility and invasion. The inhibitory effect of reversine on FA turnover accounted for a large part on its capacity to interfere with FAK function on regulating its downstream targets. In orthotopic breast cancer mouse models, reversine revealed a potent inhibitory activity on tumour progression to metastasis.

Conclusion:

These results support the utility of targeting FA turnover as a therapeutic approach for invasive breast cancer.

CDK5 is essential for TGF-β1-induced epithelial-mesenchymal transition and breast cancer progression

Epithelial-mesenchymal transition is a change of cellular plasticity critical for embryonic development and tumor metastasis. CDK5 is a proline-directed serine/threonine kinase playing important roles in cancer progression. Here we show that CDK5 is commonly overexpressed and significantly correlated with several poor prognostic parameters of breast cancer. We found that CDK5 participated in TGF-β1-induced EMT. In MCF10A, TGF-β1 upregulated the CDK5 and p35 expression, and CDK5 knockdown inhibited TGF-β1-induced EMT. CDK5 overexpression also exhibited a potential synergy in promoting TGF-β1-induced EMT. In mesenchymal breast cancer cells MDA-MB-231 and BT549, CDK5 knockdown suppressed cell motility and tumorigenesis. We further demonstrated that CDK5 modulated cancer cell migration and tumor formation by regulating the phosphorylation of FAK at Ser-732. Therefore, CDK5-FAK pathway, as a downstream step of TGF-β1 signaling, is essential for EMT and motility in breast cancer cells. This study implicates the potential value of CDK5 as a molecular marker for breast cancer.

Integrin-specific control of focal adhesion kinase and RhoA regulates membrane protrusion and invasion

Cell invasion through extracellular matrix (ECM) is a hallmark of the metastatic cascade. Cancer cells require adhesion to surrounding tissues for efficient migration to occur, which is mediated through the integrin family of receptors. Alterations in expression levels of β1 and β3 integrins have previously been reported in a number of human cancers. However, whether there are specific roles for these ubiquitous receptors in mediating cell invasion remains unclear. Here we demonstrate that loss of β1 but not β3 integrins leads to increased spread cell area and focal adhesion number in cells on 2D immobilized fibronectin. Increased adhesion numbers in β1 knockdown cells correlated with decreased cell migration on 2D surfaces. Conversely, cells depleted of β1 integrins showed increased migration speed on 3D cell-derived matrix as well as in 3D organotypic cultures and inverted invasion assays. This increased invasive potential was also seen in cells lacking β3 integrin but only in 3D cultures containing fibroblasts. Mechanistically, in situ analysis using FRET biosensors revealed that enhanced invasion in cells lacking β1 integrins was directly coupled with reduced activation of focal adhesion kinase (FAK) and the small GTPase RhoA resulting in formation of enhanced dynamic protrusions and increased invasion. These reductions in FAK-RhoA signal activationwere not detected in β3 knockdown cells under the same conditions. This data demonstrates a specific role for β1 integrins in the modulation of a FAK-RhoA-actomyosin signaling axis to regulate cell invasion through complex ECM environments.

Cell invasion through basement membrane: The netrin receptor DCC guides the way

Cell invasion through basement membrane is an essential part of normal development and physiology, and occurs during the pathological progression of human inflammatory diseases and cancer. F-actin-rich membrane protrusions, called invadopodia, have been hypothesized to be the “drill bits” of invasive cells, mediating invasion through the dense, highly cross-linked basement membrane matrix. Though studied in vitro for over 30 y, invadopodia function in vivo has remained elusive. We have recently discovered that invadopodia breach basement membrane during anchor cell invasion in C. elegans, a genetically and visually tractable in vivo invasion event. Further, we found that the netrin receptor DCC localizes to the initial site of basement membrane breach and directs invasion through a single gap in the matrix. In this commentary, we examine how the dynamics and structure of AC-invadopodia compare with in vitro invadopodia and how the netrin receptor guides invasion through a single basement membrane breach. We end with a discussion of our surprising result that the anchor cell pushes the basement membrane aside, instead of completely dissolving it through proteolysis, and provide some ideas for how proteases and physical displacement may work together to ensure efficient and robust invasion.

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.

Guiding cell migration by tugging

The ability of cells to move directionally toward areas of stiffer extracellular matrix (ECM) via a process known as 'durotaxis' is thought to be critical for development and wound healing, but durotaxis can also drive cancer metastasis. Migration is driven by integrin-mediated focal adhesions (FAs), protein assemblies that couple contractile actomyosin bundles to the plasma membrane, transmit force generated by the cytoskeleton to the ECM, and convert the mechanical properties of the microenvironment into biochemical signals. To probe the stiffness of the ECM, motile fibroblasts modulate FA mechanics on the nanoscale and exert forces that are reminiscent of repeated tugging on the ECM. Within a single cell, all FAs tug autonomously and thus act as local rigidity sensors, allowing discernment of differences in the extracellular matrix rigidity at high spatial resolution. In this article, we review current advances that may shed light on the mechanism of traction force fluctuations within FAs. We also examine plausible downstream effectors of tugging forces which may regulate cytoskeletal and FA dynamics to guide cell migration in response to ECM stiffness gradients.

Down expression of LRP1B promotes cell migration via RhoA/Cdc42 pathway and actin cytoskeleton remodeling in renal cell cancer

The low-density lipoprotein receptor-related protein 1B (LRP1B) is known as a putative tumor suppressor. The decreased expression of LRP1B has been involved in multiple primary cancers in several studies. However, its expression and function in the carcinogenesis of renal cell cancer (RCC) remain unclear. In this study, we investigated the expression of LRP1B in RCC by in situ hybridization (ISH) and real-time polymerase chain reaction (qRT-PCR). Our results indicated that LRP1B was frequently downexpressed in human RCC tissue and cell lines, which involved both epigenetic events (DNA methylation and histone deacetylation) and N-terminal deletion of LRP1B. Moreover, we testified that knockdown of LRP1B by shRNA significantly promoted anchorage-independent growth, cell migration and invasion in HEK293 cells and renal cancer cells 127 in vitro. We further found that silencing of LRP1B altered the expression of focal adhesion complex-associated proteins, and Cdc42/RhoA activities, which regulate the cytoskeleton dynamics. Taken together, these results strongly support that LRP1B may function as a tumor suppressor against renal cell cancer, and may regulate cell motility via RhoA/Cdc42 pathway and actin cytoskeleton reorganization in RCC.

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.

Stiff collagen matrices increase tumorigenic prolactin signaling in breast cancer cells

Clinically, circulating prolactin levels and density of the extracellular matrix (ECM) are individual risk factors for breast cancer. As tumors develop, the surrounding stroma responds with increased deposition and cross-linking of the collagen matrix (desmoplasia). In mouse models, prolactin promotes mammary carcinomas that resemble luminal breast cancers in women, and increased collagen density promotes tumor metastasis and progression. Although the contributions of the ECM to the physiologic actions of prolactin are increasingly understood, little is known about the functional relationship between the ECM and prolactin signaling in breast cancer. Here, we examined consequences of increased ECM stiffness on prolactin signals to luminal breast cancer cells in three-dimensional collagen I matrices in vitro. We showed that matrix stiffness potently regulates a switch in prolactin signals from physiologic to protumorigenic outcomes. Compliant matrices promoted physiological prolactin actions and activation of STAT5, whereas stiff matrices promoted protumorigenic outcomes, including increased matrix metalloproteinase-dependent invasion and collagen scaffold realignment. In stiff matrices, prolactin increased SRC family kinase-dependent phosphorylation of focal adhesion kinase (FAK) at tyrosine 925, FAK association with the mitogen-activated protein kinase mediator GRB2, and pERK1/2. Stiff matrices also increased co-localization of prolactin receptors and integrin-activated FAK, implicating altered spatial relationships. Together, these results demonstrate that ECM stiffness is a powerful regulator of the spectrum of prolactin signals and that stiff matrices and prolactin interact in a feed-forward loop in breast cancer progression. Our study is the first reported evidence of altered ECM-prolactin interactions in breast cancer, suggesting the potential for new therapeutic approaches.

Prostaglandin E₂ receptor EP1-mediated phosphorylation of focal adhesion kinase enhances cell adhesion and migration in hepatocellular carcinoma cells

The prostaglandin E₂ (PGE₂) EP1 receptor has been implicated in hepatocellular carcinoma (HCC) cell invasion. However, little is known about the mechanisms of EP1 receptor-mediated cell adhesion and migration. We previously showed that PGE₂ promotes cell adhesion and migration by activating focal adhesion kinase (FAK). The present study was designed to elucidate the association between the EP1 receptor and FAK activation in HCC cells and to investigate the related signaling pathways. The effects of PGE₂, EP1 agonist 17-phenyl trinor-PGE₂ (17-PT-PGE₂), PKC and EGFR inhibitors on FAK activation were investigated by treatment of Huh-7 cells. Phosphorylation of FAK Y397 and c-Src Y416 was investigated by western blotting. Cell adhesion and migration were analyzed by WST and transwell assays, respectively. Protein kinase C (PKC) activity was measured with a PKC assay kit. The results showed that 17-PT-PGE₂ (3 µM) increased FAK Y397 phosphorylation by more than 2-fold and promoted cell adhesion and migration in Huh-7 cells. In transfected 293 cells, expression of the EP1 receptor was confirmed to upregulate FAK phosphorylation, while the EP1 receptor antagonist sc-19220 decreased PGE₂-mediated FAK activation. PKC activity and c-Src Y416 phosphorylation were enhanced after 17-PT-PGE₂ treatment. Both PKC and c-Src inhibitor suppressed the 17-PT-PGE₂-upregulated FAK phosphorylation, as well as 17-PT-PGE₂-induced cell adhesion and migration. In addition, exogenous epidermal growth factor (EGF) treatment increased FAK phosphorylation. The EGF receptor (EGFR) inhibitor also suppressed 17-PT-PGE₂-upregulated FAK phosphorylation. Our study suggests that the PGE₂ EP1 receptor regulates FAK phosphorylation by activating the PKC/c-Src and EGFR signal pathways, which may coordinately regulate adhesion and migration in HCC.

WIP: WASP-interacting proteins at invadopodia and podosomes

Regulated cell invasion resulting from migratory and matrix-degrading events is an essential step in physiological processes such as the inflammatory response and tissue repair. Cell invasion is also thought to be a critical parameter in pathological conditions such as cancer metastasis. The migration of normal and cancer cells is largely driven by the actin cytoskeleton, which controls cell shape, adhesion and contractility. Podosomes and invadopodia are actin-rich protrusions that drive invasion in normal and cancer cells. These structures protrude from the basal region of the cell facing the extracellular matrix, where they adhere to and degrade the matrix, thus facilitating invasive migration. WASP (Wiskott-Aldrich syndrome protein) and WIP (WASP-interacting protein) localise to the actin rich core of podosomes and play a critical role in their formation. More recently, studies performed on microarray data sets from cancer patients of several tumour categories show a strong correlation between reduced WIP expression and improved prognosis. In this article, we identify endogenous WIP at the distal tips of cancer cell invasive protrusions and we summarise recent advances in the study of the roles of WIP- and WASP-protein families during migration and invasion of normal and cancer cells related to podosome and invadopodium generation.

Repulsive guidance molecule B (RGMB) plays negative roles in breast cancer by coordinating BMP signaling

Repulsive guidance molecules (RGMs) coordinate axon formation and iron homestasis. These molecules are also known as co-receptors of bone morphogenetic proteins (BMPs). However, the role played by RGMs in breast cancer remains unclear. The present study investigated the impact of RGMB on functions of breast cancer cells and corresponding mechanisms. RGMB was knocked down in breast cancer cells by way of an anti-RGMB ribozyme transgene. Knockdown of RGMB resulted in enhanced capacities of proliferation, adhesion, and migration in breast cancer cells. Further investigations demonstrated RGMB knockdown resulted in a reduced expression and activity of Caspase-3, accompanied with better survival in RGMB knockdown cells under serum starvation, which might be induced by its repression on MAPK JNK pathway. Up-regulations of Snai1, Twist, FAK, and Paxillin via enhanced Smad dependent sigaling led to increased capacities of adhesion and migration. Our current data firstly revealed that RGMB may act as a negative regulator in breast cancer through BMP signaling.

N-WASP coordinates the delivery and F-actin-mediated capture of MT1-MMP at invasive pseudopods

Metastasizing tumor cells use matrix metalloproteases, such as the transmembrane collagenase MT1-MMP, together with actin-based protrusions, to break through extracellular matrix barriers and migrate in dense matrix. Here we show that the actin nucleation-promoting protein N-WASP (Neural Wiskott-Aldrich syndrome protein) is up-regulated in breast cancer, and has a pivotal role in mediating the assembly of elongated pseudopodia that are instrumental in matrix degradation. Although a role for N-WASP in invadopodia was known, we now show how N-WASP regulates invasive protrusion in 3D matrices. In actively invading cells, N-WASP promoted trafficking of MT1-MMP into invasive pseudopodia, primarily from late endosomes, from which it was delivered to the plasma membrane. Upon MT1-MMP's arrival at the plasma membrane in pseudopodia, N-WASP stabilized MT1-MMP via direct tethering of its cytoplasmic tail to F-actin. Thus, N-WASP is crucial for extension of invasive pseudopods into which MT1-MMP traffics and for providing the correct cytoskeletal framework to couple matrix remodeling with protrusive invasion.

Beta2-adaptin binds actopaxin and regulates cell spreading, migration and matrix degradation

Cell adhesion to the extracellular matrix is a key event in cell migration and invasion and endocytic trafficking of adhesion receptors and signaling proteins plays a major role in regulating these processes. Beta2-adaptin is a subunit of the AP-2 complex and is involved in clathrin-mediated endocytosis. Herein, β2-adaptin is shown to bind to the focal adhesion protein actopaxin and localize to focal adhesions during cells spreading in an actopaxin dependent manner. Furthermore, β2-adaptin is enriched in adhesions at the leading edge of migrating cells and depletion of β2-adaptin by RNAi increases cell spreading and inhibits directional cell migration via a loss of cellular polarity. Knockdown of β2-adaptin in both U2OS osteosarcoma cells and MCF10A normal breast epithelial cells promotes the formation of matrix degrading invadopodia, adhesion structures linked to invasive migration in cancer cells. These data therefore suggest that actopaxin-dependent recruitment of the AP-2 complex, via an interaction with β2-adaptin, to focal adhesions mediates cell polarity and migration and that β2-adaptin may control the balance between the formation of normal cell adhesions and invasive adhesion structures.

Network analysis of the focal adhesion to invadopodia transition identifies a PI3K-PKCα invasive signaling axis

In cancer, deregulated signaling can produce an invasive cellular phenotype. We modeled the invasive transition as a theoretical switch between two cytoskeletal structures: focal adhesions and extracellular matrix-degrading invadopodia. We constructed molecular interaction networks of each structure and identified upstream regulatory hubs through computational analyses. We compared these regulatory hubs to the status of signaling components from head and neck carcinomas, which led us to analyze phosphatidylinositol 3-kinase (PI3K) and protein kinase C α (PKCα). Consistent with previous studies, PI3K activity promoted both the formation and the activity of invadopodia. We found that PI3K induction of invadopodia was increased by overexpression of SH2 (Src homology 2) domain-containing inositol 5'-phosphatase 2 (SHIP2), which converts the phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] that is produced by PI3K activity to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], which is believed to promote invadopodia formation. Knockdown of PKCα had divergent effects on invadopodia formation, depending on the status of PI3K. Loss of PKCα inhibited invadopodia formation in cells with wild-type PI3K pathway status. Conversely, in cells with constitutively active PI3K (through activating PI3K mutants or lacking the endogenous opposing enzyme PTEN), PKCα knockdown increased invadopodia formation. Mechanistic studies revealed a negative feedback loop from PKCα that dampened PI3K activity and invasive behavior in cells with genetic hyperactivation of the PI3K pathway. These studies demonstrated the potential of network modeling as a discovery tool and identified PI3K and PKCα as interacting regulators of invasive behavior.

Tumor cell migration in complex microenvironments

Tumor cell migration is essential for invasion and dissemination from primary solid tumors and for the establishment of lethal secondary metastases at distant organs. In vivo and in vitro models enabled identification of different factors in the tumor microenvironment that regulate tumor progression and metastasis. However, the mechanisms by which tumor cells integrate these chemical and mechanical signals from multiple sources to navigate the complex microenvironment remain poorly understood. In this review, we discuss the factors that influence tumor cell migration with a focus on the migration of transformed carcinoma cells. We provide an overview of the experimental and computational methods that allow the investigation of tumor cell migration, and we highlight the benefits and shortcomings of the various assays. We emphasize that the chemical and mechanical stimulus paradigms are not independent and that crosstalk between them motivates the development of new assays capable of applying multiple, simultaneous stimuli and imaging the cellular migratory response in real-time. These next-generation assays will more closely mimic the in vivo microenvironment to provide new insights into tumor progression, inform techniques to control tumor cell migration, and render cancer more treatable.

Spatiotemporal regulation of Src and its substrates at invadosomes

In the past decade, substantial progress has been made in understanding how Src family kinases regulate the formation and function of invadosomes. Invadosomes are organized actin-rich structures that contain an F-actin core surrounded by an adhesive ring and mediate invasive migration. Src kinases orchestrate, either directly or indirectly, each phase of the invadosome life cycle including invadosome assembly, maturation and matrix degradation and disassembly. Complex arrays of Src effector proteins are involved at different stages of invadosome maturation and their spatiotemporal activity must be tightly regulated to achieve effective invasive migration. In this review, we highlight some recent progress and the challenges of understanding how Src is regulated temporally and spatially to orchestrate the dynamics of invadosomes and mediate cell invasion.

Focal adhesion kinases in adhesion structures and disease

Cell adhesion to the extracellular matrix (ECM) is essential for cell migration, proliferation, and embryonic development. Cells can contact the ECM through a wide range of matrix contact structures such as focal adhesions, podosomes, and invadopodia. Although they are different in structural design and basic function, they share common remodeling proteins such as integrins, talin, paxillin, and the tyrosine kinases FAK, Pyk2, and Src. In this paper, we compare and contrast the basic organization and role of focal adhesions, podosomes, and invadopodia in different cells. In addition, we discuss the role of the tyrosine kinases, FAK, Pyk2, and Src, which are critical for the function of the different adhesion structures. Finally, we discuss the essential role of these tyrosine kinases from the perspective of human diseases.

Oncogenic signaling by tyrosine kinases of the SRC family in advanced colorectal cancer

The non-receptor tyrosine kinases of the SRC family (SFK) play important roles in signal transduction induced by a large variety of extracellular stimuli, including growth factors and Integrins. When deregulated, SFKs show oncogenic activity, as originally reported for v-Src, the transforming product of the avian retrovirus RSV, and then, in many human cancers, particularly colorectal cancer (CRC). In CRC, SFK deregulation largely occurs in the absence of mutations of the corresponding genes, but the underlying molecular mechanisms involved are still unclear. In addition to a role in early tumor progression, SFK deregulation may also be important in advanced CRC, as suggested by the association between increased SFK activity and poor clinical outcome. However, SFK contribution to CRC metastasis formation is still poorly documented. Here, we will review recent findings that broaden our understanding of the mechanisms underlying SFK deregulation and signaling in advanced CRC. We will also discuss the implication of these observations for SFK-based therapy in metastatic CRC.

Adhesion rings surround invadopodia and promote maturation

Invasion and metastasis are aggressive cancer phenotypes that are highly related to the ability of cancer cells to degrade extracellular matrix (ECM). At the cellular level, specialized actin-rich structures called invadopodia mediate focal matrix degradation by serving as exocytic sites for ECM-degrading proteinases. Adhesion signaling is likely to be a critical regulatory input to invadopodia, but the mechanism and location of such adhesion signaling events are poorly understood. Here, we report that adhesion rings surround invadopodia shortly after formation and correlate strongly with invadopodium activity on a cell-by-cell basis. By contrast, there was little correlation of focal adhesion number or size with cellular invadopodium activity. Prevention of adhesion ring formation by inhibition of RGD-binding integrins or knockdown (KD) of integrin-linked kinase (ILK) reduced the number of ECM-degrading invadopodia and reduced recruitment of IQGAP to invadopodium actin puncta. Furthermore, live cell imaging revealed that the rate of extracellular MT1-MMP accumulation at invadopodia was greatly reduced in both integrin-inhibited and ILK-KD cells. Conversely, KD of MT1-MMP reduced invadopodium activity and dynamics but not the number of adhesion-ringed invadopodia. These results suggest a model in which adhesion rings are recruited to invadopodia shortly after formation and promote invadopodium maturation by enhancing proteinase secretion. Since adhesion rings are a defining characteristic of podosomes, similar structures formed by normal cells, our data also suggest further similarities between invadopodia and podosomes.

Src-mediated phosphorylation of mammalian Abp1 (DBNL) regulates podosome rosette formation in transformed fibroblasts

Podosomes are dynamic actin-based structures that mediate adhesion to the extracellular matrix and localize matrix degradation to facilitate cell motility and invasion. Drebrin-like protein (DBNL), which is homologous to yeast mAbp1 and is therefore known as mammalian actin-binding protein 1 (mAbp1), has been implicated in receptor-mediated endocytosis, vesicle recycling and dorsal ruffle formation. However, it is not known whether mAbp1 regulates podosome formation or cell invasion. In this study, we found that mAbp1 localizes to podosomes and is necessary for the formation of podosome rosettes in Src-transformed fibroblasts. Despite their structural similarity, mAbp1 and cortactin play distinct roles in podosome regulation. Cortactin was necessary for the formation of podosome dots, whereas mAbp1 was necessary for the formation of organized podosome rosettes in Src-transformed cells. We identified specific Src phosphorylation sites, Tyr337 and Tyr347 of mAbp1, which mediate the formation of podosome rosettes and degradation of the ECM. In contrast to dorsal ruffles, the interaction of mAbp1 with WASP-interacting protein (WIP) was not necessary for the formation of podosome rosettes. Finally, we showed that depletion of mAbp1 increased invasive cell migration, suggesting that mAbp1 differentially regulates matrix degradation and cell invasion. Collectively, our findings identify a role for mAbp1 in podosome rosette formation and cell invasion downstream of Src.

Invasive matrix degradation at focal adhesions occurs via protease recruitment by a FAK-p130Cas complex

Tumor cell migration and the concomitant degradation of extracellular matrix (ECM) are two essential steps in the metastatic process. It is well established that focal adhesions (FAs) play an important role in regulating migration; however, whether these structures contribute to matrix degradation is not clear. In this study, we report that multiple cancer cell lines display degradation of ECM at FA sites that requires the targeted action of MT1-MMP. Importantly, we have found that this MT1-MMP targeting is dependent on an association with a FAK-p130Cas complex situated at FAs and is regulated by Src-mediated phosphorylation of Tyr 573 at the cytoplasmic tail of MT1. Disrupting the FAK-p130Cas-MT1 complex significantly impairs FA-mediated degradation and tumor cell invasion yet does not appear to affect invadopodia formation or function. These findings demonstrate a novel function for FAs and also provide molecular insights into MT1-MMP targeting and function.

Formation of atypical podosomes in extravillous trophoblasts regulates extracellular matrix degradation

Throughout pregnancy the cytotrophoblast, the stem cell of the placenta, gives rise to the differentiated forms of trophoblasts. The two main cell lineages are the syncytiotrophoblast and the invading extravillous trophoblast. A successful pregnancy requires extravillous trophoblasts to migrate and invade through the decidua and then remodel the maternal spiral arteries. Many invasive cells use specialised cellular structures called invadopodia or podosomes in order to degrade extracellular matrix. Despite being highly invasive cells, the presence of invadapodia or podosomes has not previously been investigated in trophoblasts. In this study these structures have been identified and characterised in extravillous trophoblasts. The role of specialised invasive structures in trophoblasts in the degradation of the extracellular matrix was compared with well characterised podosomes and invadopodia in other invasive cells and the trophoblast specific structures were characterised by using a sensitive matrix degradation assay which enabled visualisation of the structures and their dynamics. We show trophoblasts form actin rich protrusive structures which have the ability to degrade the extracellular matrix during invasion. The degradation ability and dynamics of the structures closely resemble podosomes, but have unique characteristics that have not previously been described in other cell types. The composition of these structures does not conform to the classic podosome structure, with no distinct ring of plaque proteins such as paxillin or vinculin. In addition, trophoblast podosomes protrude more deeply into the extracellular matrix than established podosomes, resembling invadopodia in this regard. We also show several significant pathways such as Src kinase, MAPK kinase and PKC along with MMP-2 and 9 as key regulators of extracellular matrix degradation activity in trophoblasts, while podosome activity was regulated by the rigidity of the extracellular matrix.

Focal adhesion kinase and tumour angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones, is essential for tumour development. It is initiated and regulated by growth factors via their surface receptors, which activate several intracellular signalling pathways in endothelial cells. Cell adhesion molecules, such as integrins, also regulate angiogenesis. Despite these facts, inhibitors of endothelial cell growth factor receptors or integrins have not been as effective as initially hoped in the long-term inhibition of angiogenesis in cancer patients. Signalling downstream of growth factor receptors and integrins converge on the ubiquitously expressed non-receptor tyrosine kinase focal adhesion kinase (FAK). FAK is involved in endothelial cell proliferation, migration and survival, is up-regulated in many cancers and has recently been shown to control tumour angiogenesis. Indeed, FAK inhibitors are presently being developed for the treatment of cancer. However, recent studies have indicated the complexities of understanding the precise role for FAK in angiogenesis. Here we have summarized some of the key features of FAK, addressed some of the apparently contradictory roles of this molecule in angiogenesis and provided some perspectives for future studies.

Lyn is a redox sensor that mediates leukocyte wound attraction in vivo

Tissue wounding induces the rapid recruitment of leukocytes. Wounds and tumours--a type of 'unhealed wound'--generate hydrogen peroxide (H(2)O(2)) through an NADPH oxidase (NOX). This extracellular H(2)O(2) mediates recruitment of leukocytes, particularly the first responders of innate immunity, neutrophils, to injured tissue. However, the sensor that neutrophils use to detect the redox state at wounds is unknown. Here we identify the Src family kinase (SFK) Lyn as a redox sensor that mediates initial neutrophil recruitment to wounds in zebrafish larvae. Lyn activation in neutrophils is dependent on wound-derived H(2)O(2) after tissue injury, and inhibition of Lyn attenuates neutrophil wound recruitment. Inhibition of SFKs also disrupted H(2)O(2)-mediated chemotaxis of primary human neutrophils. In vitro analysis identified a single cysteine residue, C466, as being responsible for direct oxidation-mediated activation of Lyn. Furthermore, transgenic-tissue-specific reconstitution with wild-type Lyn and a cysteine mutant revealed that Lyn C466 is important for the neutrophil wound response and downstream signalling in vivo. This is the first identification, to our knowledge, of a physiological redox sensor that mediates leukocyte wound attraction in multicellular organisms.

FAK is required for the assembly of podosome rosettes

Podosomes are dynamic actin-enriched membrane structures that play an important role in invasive cell motility and extracellular matrix degradation. They are often found to assemble into large rosettelike structures in highly invasive cells. However, the mechanism of this assembly remains obscure. In this study, we identified focal adhesion kinase (FAK) as a key molecule necessary for assembly. Moreover, phosphorylation of p130Cas and suppression of Rho signaling by FAK were found to be important for FAK to induce the assembly of podosome rosettes. Finally, we found that suppression of vimentin intermediate filaments by FAK facilitates the assembly of podosome rosettes. Collectively, our results strongly suggest a link between FAK, podosome rosettes, and tumor invasion and unveil a negative role for Rho signaling and vimentin filaments in podosome rosette assembly.

Nck2 promotes human melanoma cell proliferation, migration and invasion in vitro and primary melanoma-derived tumor growth in vivo

Background

Nck1 and Nck2 adaptor proteins are involved in signaling pathways mediating proliferation, cytoskeleton organization and integrated stress response. Overexpression of Nck1 in fibroblasts has been shown to be oncogenic. Through the years this concept has been challenged and the consensus is now that overexpression of either Nck cooperates with strong oncogenes to transform cells. Therefore, variations in Nck expression levels in transformed cells could endorse cancer progression.

Methods

Expression of Nck1 and Nck2 proteins in various cancer cell lines at different stages of progression were analyzed by western blots. We created human primary melanoma cell lines overexpressing GFP-Nck2 and investigated their ability to proliferate along with metastatic characteristics such as migration and invasion. By western blot analysis, we compared levels of proteins phosphorylated on tyrosine as well as cadherins and integrins in human melanoma cells overexpressing or not Nck2. Finally, in mice we assessed tumor growth rate of human melanoma cells expressing increasing levels of Nck2.

Results

We found that expression of Nck2 is consistently increased in various metastatic cancer cell lines compared with primary counterparts. Particularly, we observed significant higher levels of Nck2 protein and mRNA, as opposed to no change in Nck1, in human metastatic melanoma cell lines compared with non-metastatic melanoma and normal melanocytes. We demonstrated the involvement of Nck2 in proliferation, migration and invasion in human melanoma cells. Moreover, we discovered that Nck2 overexpression in human primary melanoma cells correlates with higher levels of proteins phosphorylated on tyrosine residues, assembly of Nck2-dependent pY-proteins-containing molecular complexes and downregulation of cadherins and integrins. Importantly, we uncovered that injection of Nck2-overexpressing human primary melanoma cells into mice increases melanoma-derived tumor growth rate.

Conclusions

Collectively, our data indicate that Nck2 effectively influences human melanoma phenotype progression. At the molecular level, we propose that Nck2 in human primary melanoma promotes the formation of molecular complexes regulating proliferation and actin cytoskeleton dynamics by modulating kinases or phosphatases activities that results in increased levels of proteins phosphorylated on tyrosine residues. This study provides new insights regarding cancer progression that could impact on the therapeutic strategies targeting cancer.

Tyrosine phosphorylation within the SH3 domain regulates CAS subcellular localization, cell migration, and invasiveness

Crk-associated substrate (CAS) Tyr-12 phosphorylation has an important role in ligand binding, CAS localization, turnover of adhesion structures, migration, and invasiveness. CAS Tyr-12 phosphorylation thus possibly represents a novel regulatory mechanism by which CAS-mediated signaling could trigger different cellular responses.

Crk-associated substrate (CAS) is a major tyrosine-phosphorylated protein in cells transformed by v-crk and v-src oncogenes and plays an important role in invasiveness of Src-transformed cells. A novel phosphorylation site on CAS, Tyr-12 (Y12) within the ligand-binding hydrophobic pocket of the CAS SH3 domain, was identified and found to be enriched in Src-transformed cells and invasive human carcinoma cells. To study the biological significance of CAS Y12 phosphorylation, phosphomimicking Y12E and nonphosphorylatable Y12F mutants of CAS were studied. The phosphomimicking mutation decreased interaction of the CAS SH3 domain with focal adhesion kinase (FAK) and PTP-PEST and reduced tyrosine phosphorylation of FAK. Live-cell imaging showed that green fluorescent protein–tagged CAS Y12E mutant is, in contrast to wild-type or Y12F CAS, excluded from focal adhesions but retains its localization to podosome-type adhesions. Expression of CAS-Y12F in cas–/– mouse embryonic fibroblasts resulted in hyperphosphorylation of the CAS substrate domain, and this was associated with slower turnover of focal adhesions and decreased cell migration. Moreover, expression of CAS Y12F in Src-transformed cells greatly decreased invasiveness when compared to wild-type CAS expression. These findings reveal an important role of CAS Y12 phosphorylation in the regulation of focal adhesion assembly, cell migration, and invasiveness of Src-transformed cells.

Role of FAK in S1P-regulated endothelial permeability

The vascular endothelium serves as a semi-selective barrier between the circulating contents of the blood and the tissues through which they flow. Disruption of this barrier results in significant organ dysfunction during devastating inflammatory syndromes such as sepsis and acute lung injury (ALI). Sphingosine 1-phosphate (S1P) is an endogenous lipid regulator of endothelial permeability that produces potent barrier enhancement via actin and junctional protein rearrangement and resultant cytoskeletal changes. A key effector protein in this S1P response is focal adhesion kinase (FAK), a highly conserved cytoplasmic tyrosine kinase involved in the engagement of integrins and assembly of focal adhesions (FA) through the catalysis of multiple downstream signals. After stimulation by S1P, endothelial FAK undergoes specific tyrosine phosphorylation that results in activation of the kinase and dynamic interactions with other effector molecules to improve the endothelial barrier. FAK participates in peripheral actin cytoskeletal rearrangement as well as cell-matrix (FA) and cell-cell (adherens junction) junctional complex strengthening that combine to decrease vascular permeability. This review summarizes the current knowledge of the role of FAK in mediating enhanced endothelial barrier function by S1P.

Integrins in cell migration

Integrin-based adhesion has served as a model for studying the central role of adhesion in migration. In this article, we outline modes of migration, both integrin-dependent and -independent in vitro and in vivo. We next discuss the roles of adhesion contacts as signaling centers and linkages between the ECM and actin that allows adhesions to serve as traction sites. This includes signaling complexes that regulate migration and the interplay among adhesion, signaling, and pliability of the substratum. Finally, we address mechanisms of adhesion assembly and disassembly and the role of adhesion in cellular polarity.

Knockdown of Rab5a expression decreases cancer cell motility and invasion through integrin-mediated signaling pathway

BACKGROUND

Rab GTPases function as modulators in intracellular transport. Rab5a, a member of the Rab subfamily of small GTPases, is an important regulator of vesicle traffic from the plasma membrane to early endosomes. Recent findings have reported that Rab5a gene was involved in the progression of cancer. In the present study, we investigated the effect of Rab5a on cervical cancer invasion and metastasis and the molecular mechanism underlying the involvement of Rab5a.

METHODS

Rab5a expression was assessed by immunohistochemical analysis on a cervical cancer tissue microarray. RNA interference (RNAi) was performed to knock down the endogenous expression of Rab5a gene in HeLa and SiHa cells. Cell motility was evaluated using invasion assay and wound migration assay in vitro. The expression levels of integrin-associated molecules were detected by Western blot and immunofluorescence.

RESULTS

We found that Rab5a was expressed at a high level in cervical cancer tissues. Silencing of Rab5a expression significantly decreased cancer cell motility and invasiveness. The down-regulation of integrin-associated focal adhesion signaling molecules was further detected in Rab5a knockdown cells. Meanwhile, active GTP-bound Rac1, Cdc42, and RhoA were also down-regulated, accompanied with the reduction in the number and size of filopodia and lamellipodia.

CONCLUSIONS

Taken together, these data suggest that Rab5a functions in regulating the invasion phenotype, and we propose that this regulation may be via integrin-mediated signaling pathway in cervical cancer cells.

Detection of focal adhesion kinase activation at membrane microdomains by fluorescence resonance energy transfer

Proper subcellular localization of focal adhesion kinase (FAK) is crucial for many cellular processes. It remains, however, unclear how FAK activity is regulated at subcellular compartments. To visualize the FAK activity at different membrane microdomains, we develop a fluorescence resonance energy transfer (FRET)-based FAK biosensor, and target it into or outside of detergent-resistant membrane (DRM) regions at the plasma membrane. Here we show that, on cell adhesion to extracellular matrix proteins or stimulation by platelet-derived growth factor (PDGF), the FRET responses of DRM-targeting FAK biosensor are stronger than that at non-DRM regions, suggesting that FAK activation can occur at DRM microdomains. Further experiments reveal that the PDGF-induced FAK activation is mediated and maintained by Src activity, whereas FAK activation on cell adhesion is independent of, and in fact essential for the Src activation. Therefore, FAK is activated at membrane microdomains with distinct activation mechanisms in response to different physiological stimuli.

A Src-Tks5 pathway is required for neural crest cell migration during embryonic development

In the adult organism, cell migration is required for physiological processes such as angiogenesis and immune surveillance, as well as pathological events such as tumor metastasis. The adaptor protein and Src substrate Tks5 is necessary for cancer cell migration through extracellular matrix in vitro and tumorigenicity in vivo. However, a role for Tks5 during embryonic development, where cell migration is essential, has not been examined. We used morpholinos to reduce Tks5 expression in zebrafish embryos, and observed developmental defects, most prominently in neural crest-derived tissues such as craniofacial structures and pigmentation. The Tks5 morphant phenotype was rescued by expression of mammalian Tks5, but not by a variant of Tks5 in which the Src phosphorylation sites have been mutated. We further evaluated the role of Tks5 in neural crest cells and neural crest-derived tissues and found that loss of Tks5 impaired their ventral migration. Inhibition of Src family kinases also led to abnormal ventral patterning of neural crest cells and their derivatives. We confirmed that these effects were likely to be cell autonomous by shRNA-mediated knockdown of Tks5 in a murine neural crest stem cell line. Tks5 was required for neural crest cell migration in vitro, and both Src and Tks5 were required for the formation of actin-rich structures with similarity to podosomes. Additionally, we observed that neural crest cells formed Src-Tks5-dependent cell protrusions in 3-D culture conditions and in vivo. These results reveal an important and novel role for the Src-Tks5 pathway in neural crest cell migration during embryonic development. Furthermore, our data suggests that this pathway regulates neural crest cell migration through the generation of actin-rich pro-migratory structures, implying that similar mechanisms are used to control cell migration during embryogenesis and cancer metastasis.

Degrading devices: invadosomes in proteolytic cell invasion

Podosomes and invadopodia, collectively known as invadosomes, are cell-matrix contacts in a variety of cell types, such as monocytic cells or cancer cells, that have to cross tissue barriers. Both structures share an actin-rich core, which distinguishes them from other matrix contacts, and are regulated by a multitude of signaling pathways including RhoGTPases, kinases, actin-associated proteins, and microtubule-dependent transport. Invadosomes recruit and secrete proteinases and are thus able to lyse extracellular matrix components. They are therefore considered to be potential key structures in proteolytic cell invasion in both physiological and pathological settings. This review provides an overview of the field, with special focus on current developments such as intracellular transport processes, ultrastructural analysis, the possible involvement of invadosomes in disease, and the tentative identification of invadosomes in 3D environments and in vivo.

The SRC-associated protein CUB Domain-Containing Protein-1 regulates adhesion and motility

Multiple SRC-family kinases (SFKs) are commonly activated in carcinoma and appear to have a role in metastasis through incompletely understood mechanisms. Recent studies have shown that CDCP1 (CUB (complement C1r/C1s, Uegf, Bmp1) Domain-Containing Protein-1) is a transmembrane protein and an SRC substrate potentially involved in metastasis. Here we show that increased SFK and CDCP1 tyrosine phosphorylation is, surprisingly, associated with a decrease in FAK phosphorylation. This appears to be true in human tumors as shown by our correlation analysis of a mass spectrometric data set of affinity-purified phosphotyrosine peptides obtained from normal and cancer lung tissue samples. Induction of tyrosine phosphorylation of CDCP1 in cell culture, including by a mAb that binds to its extracellular domain, promoted changes in SFK and FAK tyrosine phosphorylation, as well as in PKC(TM), a protein known to associate with CDCP1, and these changes are accompanied by increases in adhesion and motility. Thus, signaling events that accompany the CDCP1 tyrosine phosphorylation observed in cell lines and human lung tumors may explain how the CDCP1/SFK complex regulates motility and adhesion.