Epidermal growth factor receptor overexpression results in increased tumor cell motility in vivo coordinately with enhanced intravasation and metastasis

EGFRvIII mediates hepatocellular carcinoma cell invasion by promoting S100 calcium binding protein A11 expression

Epidermal growth factor receptor (EGFR) is frequently aberrantly expressed in cancer, and abnormal signalling downstream of this receptor contributes to tumour growth. EGFR variant III (EGFRvIII) is the most commonly altered form of EGFR and contains a truncated ligand-binding domain. Aberrant signalling downstream of this receptor contributes to tumour invasion. We previously reported that EGFRvIII can promote hepatocellular carcinoma (HCC) invasion. However, little is known concerning the mechanisms underlying EGFRvIII-mediated increases in cell motility and invasion in HCC. In this study, we observed that S100A11 was significantly upregulated in Huh-7 cells that overexpressed EGFRvIII. Moreover, S100A11 expression was elevated in HCC tissue samples (68.6%; 35/51), and this elevation was correlated with EGFRvIII expression (p = 0.0020; n = 20). Furthermore, the overexpression of S100A11 can promote HCC cell invasiveness, whereas siRNA against S100A11 can suppress the invasiveness of HCC cells stably transfected with EGFRvIII. Additionally, STAT3 inhibitors can block S100A11 expression and S100A11 promoter activity in HCC cells with stable overexpression of EGFRvIII. Furthermore, mutation in STATx binding sites could abolish the S1000A11 promoter activity stimulation by EGFRvIII. Taken together, the results demonstrate that the EGFRvIII-STAT3 pathway promotes cell migration and invasion by upregulating S100A11.

Radiation- and anthracycline-induced cardiac toxicity and the influence of ErbB2 blocking agents

In Her2-positive breast cancer patients, inhibition of epidermal growth factor receptor 2 (ErbB2)-signaling is often combined with chemotherapy and radiotherapy. The risk of cardiac toxicity after anthracyclines and radiotherapy is recognized, but little is known about increased risk when these treatments are combined with ErbB2 inhibition. This study investigated whether ErbB2 inhibition increased radiation or anthracycline-induced toxicity. In an in vitro study, human cardiomyocytes were treated with irradiation or doxorubicin, alone or in combination with trastuzumab, and evaluated for cell survival and growth. Groups of mice received 0 or 14 Gy to the heart, alone or in combination with lapatinib, or 3 × 4 mg/kg doxorubicin alone or in combination with lapatinib. Mice were evaluated 40 weeks after treatment for cardiac damage. Changes in cardiac function ((99m)Tc-Myoview gated SPECT) were related to histomorphology and microvascular damage. Radiation or doxorubicin-induced cardiomyocyte toxicity (in vitro) were not exacerbated by trastuzumab. Cardiac irradiation of mice decreased microvascular density (MVD) and increased endothelial damage in surviving capillaries (decrease alkaline phosphatase expression and increased von Willebrand factor), but these changes were not exacerbated by lapatinib. Inflammatory responses in the irradiated epicardium (CD45+ and F4/80+ cells) were significantly reduced in combination with lapatinib. Irradiation, doxorubicin, and lapatinib each induced cardiac fibrosis but this was not further enhanced when treatments were combined. At the ultra-structural level, both lapatinib and doxorubicin induced mitochondrial damage, which was enhanced in combined treatments. Lapatinib alone also induced mild changes in cardiac function but this was not enhanced in the combined treatments. Trastuzumab did not enhance direct radiation or anthracycline toxicity of cardiomyocytes in vitro. Lapatinib did not enhance the risk of radiation or anthracycline-induced cardiac toxicity in mice up to 40 weeks after treatment, but mitochondrial damage was more severe after doxorubicin combined with lapatinib.

Review: molecular mechanism of microglia stimulated glioblastoma invasion

Glioblastoma multiforme is one of the deadliest human cancers and is characterized by a high degree of microglia and macrophage infiltration. The role of these glioma infiltrating macrophages (GIMs) in disease progression has been the subject of recent investigation. While initially thought to reflect an immune response to the tumor, the balance of evidence clearly suggests GIMs can have potent tumor-tropic functions and assist in glioma cell growth and infiltration into normal brain. In this review, we focus on the evidence for GIMs aiding mediating glioblastoma motility and invasion. We survey the literature for molecular pathways that are involved in paracrine interaction between glioma cells and GIMs and assess which of these might serve as attractive targets for therapeutic intervention.

Autocrine HBEGF expression promotes breast cancer intravasation, metastasis and macrophage-independent invasion in vivo

Increased expression of HBEGF in ER negative breast tumors is correlated with enhanced metastasis to distant organ sites and more rapid disease recurrence upon removal of the primary tumor. Our previous work has demonstrated a paracrine loop between breast cancer cells and macrophages in which the tumor cells are capable of stimulating macrophages through the secretion of CSF-1 while the tumor associated macrophages (TAMs) in turn aid in tumor cell invasion by secreting EGF. To determine how the autocrine expression of EGFR ligands by carcinoma cells would affect this paracrine loop mechanism, and in particular whether tumor cell invasion depends on spatial ligand gradients generated by TAMs, we generated cell lines with increased HBEGF expression. We find that autocrine HBEGF expression enhanced in vivo intravasation and metastasis, and resulted in a novel phenomenon in which macrophages were no longer required for in vivo invasion of breast cancer cells. In vitro studies revealed that expression of HBEGF enhanced invadopodium formation, thus providing a mechanism for cell autonomous invasion. The increased invadopodium formation was directly dependent on EGFR signaling, as demonstrated by a rapid decrease in invadopodia upon inhibition of autocrine HBEGF/EGFR signaling as well as inhibition of signaling downstream of EGFR activation. HBEGF expression also resulted in enhanced invadopodium function via upregulation of MMP2 and MMP9 expression. We conclude that high levels of HBEGF expression can short-circuit the tumor cell/macrophage paracrine invasion loop, resulting in enhanced tumor invasion that is independent of macrophage signaling.

Expression of metastasis suppressor BRMS1 in breast cancer cells results in a marked delay in cellular adhesion to matrix

Metastatic dissemination is a multi-step process that depends on cancer cells' ability to respond to microenvironmental cues by adapting adhesion abilities and undergoing cytoskeletal rearrangement. Breast Cancer Metastasis Suppressor 1 (BRMS1) affects several steps of the metastatic cascade: it decreases survival in circulation, increases susceptibility to anoikis, and reduces capacity to colonize secondary organs. In this report, BRMS1 expression is shown to not significantly alter expression levels of integrin monomers, while time-lapse and confocal microscopy revealed that BRMS1-expressing cells exhibited reduced activation of both β1 integrin and focal adhesion kinase, and decreased localization of these molecules to sites of focal adhesions. Short-term plating of BRMS1-expressing cells onto collagen or fibronectin markedly decreased cytoskeletal reorganization and formation of cellular adhesion projections. Under 3D culture conditions, BRMS1-expressing cells remained rounded and failed to reorganize their cytoskeleton and form invasive colonies. Taken together, BRMS1-expressing breast cancer cells are greatly attenuated in their ability to respond to microenvironment changes. © 2013 Wiley Periodicals, Inc.

GRP78-targeting subtilase cytotoxin sensitizes cancer cells to photodynamic therapy

Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER)-resident chaperone and a major regulator of the unfolded protein response (UPR). Accumulating evidence indicate that GRP78 is overexpressed in many cancer cell lines, and contributes to the invasion and metastasis in many human tumors. Besides, GRP78 upregulation is detected in response to different ER stress-inducing anticancer therapies, including photodynamic therapy (PDT). This study demonstrates that GRP78 mRNA and protein levels are elevated in response to PDT in various cancer cell lines. Stable overexpression of GRP78 confers resistance to PDT substantiating its cytoprotective role. Moreover, GRP78-targeting subtilase cytotoxin catalytic subunit fused with epidermal growth factor (EGF-SubA) sensitizes various cancer cells to Photofrin-mediated PDT. The combination treatment is cytotoxic to apoptosis-competent SW-900 lung cancer cells, as well as to Bax-deficient and apoptosis-resistant DU-145 prostate cancer cells. In these cells, PDT and EGF-SubA cytotoxin induce protein kinase R-like ER kinase and inositol-requiring enzyme 1 branches of UPR and also increase the level of C/EBP (CCAAT/enhancer-binding protein) homologous protein, an ER stress-associated apoptosis-promoting transcription factor. Although some apoptotic events such as disruption of mitochondrial membrane and caspase activation are detected after PDT, there is no phosphatidylserine plasma membrane externalization or DNA fragmentation, suggesting that in DU-145 cells the late apoptotic events are missing. Moreover, in SW-900 cells, EGF-SubA cytotoxin potentiates PDT-mediated cell death but attenuates PDT-induced apoptosis. In addition, the cell death cannot be reversed by caspase inhibitor z-VAD, confirming that apoptosis is not a major cell death mode triggered by the combination therapy. Moreover, no typical features of necrotic or autophagic cell death are recognized. Instead, an extensive cellular vacuolation of ER origin is observed. Altogether, these findings indicate that PDT and GRP78-targeting cytotoxin treatment can efficiently kill cancer cells independent on their apoptotic competence and triggers an atypical, non-apoptotic cell death.

Cooperative roles of SDF-1α and EGF gradients on tumor cell migration revealed by a robust 3D microfluidic model

Chemokine-mediated directed tumor cell migration within a three dimensional (3D) matrix, or chemoinvasion, is an important early step in cancer metastasis. Despite its clinical importance, it is largely unknown how cytokine and growth factor gradients within the tumor microenvironment regulate chemoinvasion. We studied tumor cell chemoinvasion in well-defined and stable chemical gradients using a robust 3D microfluidic model. We used CXCL12 (also known as SDF-1α) and epidermal growth factor (EGF), two well-known extracellular signaling molecules that co-exist in the tumor microenvironment (e.g. lymph nodes or intravasation sites), and a malignant breast tumor cell line, MDA-MB-231, embedded in type I collagen. When subjected to SDF-1α gradients alone, MDA-MB-231 cells migrated up the gradient, and the measured chemosensitivity (defined as the average cell velocity along the direction of the gradient) followed the ligand - receptor (SDF-1α - CXCR4) binding kinetics. On the other hand, when subjected to EGF gradients alone, tumor cells increased their overall motility, but without statistically significant chemotactic (directed) migration, in contrast to previous reports using 2D chemotaxis assays. Interestingly, we found that the chemoinvasive behavior to SDF-1α gradients was abrogated or even reversed in the presence of uniform concentrations of EGF; however, the presence of SDF-1α and EGF together modulated tumor cell motility cooperatively. These findings demonstrate the capabilities of our microfluidic model in re-creating complex microenvironments for cells, and the importance of cooperative roles of multiple cytokine and growth factor gradients in regulating cell migration in 3D environments.

-216G/T (rs712829), a functional variant of the EGFR promoter, is associated with the pleural metastasis of lung adenocarcinoma

Numerous mutations and variants in the epidermal growth factor receptor (EGFR) gene have been demonstrated to be associated with the occurrence, metastasis and prognosis of various types of tumors, including lung cancer. Thus, the present study aimed to investigate whether -216G/T (rs712829), a functional polymorphism of the EGFR promoter that is able to induce EGFR activation and overexpression, is associated with the pleural metastasis of lung adenocarcinoma. The study subjects were comprised of 326 patients with primary lung adenocarcinoma and 312 matched cases with pleural metastasis. The -216G/T genotypes were determined in all subjects by PCR amplification and direct DNA sequencing, and EGFR expression was also evaluated by immunohistochemical staining in the primary tumor tissues with various -216G/T genotype backgrounds. The results showed that the frequencies of allele T and genotypes G/T and T/T in the pleural metastasis group were significantly higher compared with those in the non-metastasis group, with adjusted ORs of 1.46 (95% CI, 1.015–1.963) for G/T and 1.97 (95% CI, 1.051–3.152) for T/T. Furthermore, the expression of the EGFR protein was higher in the primary lung adenocarcinoma tissues with -216T/T and -216G/T compared with those with -216G/G (P<0.05). These results collectively indicate that the -216G/T polymorphism in the EGFR promoter is associated with the risk of the pleural metastasis of lung adenocarcinoma and that this effect may be associated with -216G/T-induced overexpression of the EGFR protein.

Specific inhibition of PI3K p110δ inhibits CSF-1-induced macrophage spreading and invasive capacity

Colony stimulating factor-1 (CSF-1) stimulates mononuclear phagocytic cell survival, growth and differentiation into macrophages through activation and autophosphorylation of the CSF-1 receptor (CSF-1R). We have previously demonstrated that CSF-1-induced phosphorylation of Y721 (pY721) in the receptor kinase insert triggers its association with the p85 regulatory subunit of phosphoinositide 3'-kinase (PI3K). Binding of p85 PI3K to the CSF-1R pY721 motif activates the associated p110 PI3K catalytic subunit and stimulates spreading and motility in macrophages and enhancement of tumor cell invasion. Here we show that pY721-based signaling is necessary for CSF-1-stimulated PtdIns(3,4,5)P production. While primary bone marrow-derived macrophages and the immortalized bone marrow-derived macrophage cell line M-/-.WT express all three class IA PI3K isoforms, p110δ predominates in the cell line. Treatment with p110δ-specific inhibitors demonstrates that the hematopoietically enriched isoform, p110δ, mediates CSF-1-regulated spreading and invasion in macrophages. Thus GS-1101, a potent and selective p110δ inhibitor, may have therapeutic potential by targeting the infiltrative capacity of tumor-associated macrophages that is critical for their enhancement of tumor invasion and metastasis.

Real-time motion analysis reveals cell directionality as an indicator of breast cancer progression

Cancer cells alter their migratory properties during tumor progression to invade surrounding tissues and metastasize to distant sites. However, it remains unclear how migratory behaviors differ between tumor cells of different malignancy and whether these migratory behaviors can be utilized to assess the malignant potential of tumor cells. Here, we analyzed the migratory behaviors of cell lines representing different stages of breast cancer progression using conventional migration assays or time-lapse imaging and particle image velocimetry (PIV) to capture migration dynamics. We find that the number of migrating cells in transwell assays, and the distance and speed of migration in unconstrained 2D assays, show no correlation with malignant potential. However, the directionality of cell motion during 2D migration nicely distinguishes benign and tumorigenic cell lines, with tumorigenic cell lines harboring less directed, more random motion. Furthermore, the migratory behaviors of epithelial sheets observed under basal conditions and in response to stimulation with epidermal growth factor (EGF) or lysophosphatitic acid (LPA) are distinct for each cell line with regard to cell speed, directionality, and spatiotemporal motion patterns. Surprisingly, treatment with LPA promotes a more cohesive, directional sheet movement in lung colony forming MCF10CA1a cells compared to basal conditions or EGF stimulation, implying that the LPA signaling pathway may alter the invasive potential of MCF10CA1a cells. Together, our findings identify cell directionality as a promising indicator for assessing the tumorigenic potential of breast cancer cell lines and show that LPA induces more cohesive motility in a subset of metastatic breast cancer cells.

Imaging tumor cell movement in vivo

This unit describes the methods that we have been developing for analyzing tumor cell motility in mouse and rat models of breast cancer metastasis. Rodents are commonly used both to provide a mammalian system for studying human tumor cells (as xenografts in immunocompromised mice) as well as for following the development of tumors from a specific tissue type in transgenic lines. The Basic Protocol in this unit describes the standard methods used for generation of mammary tumors and imaging them. Additional protocols for labeling macrophages, blood vessel imaging, and image analysis are also included.

Apoptosis resistance and PKC signaling: distinguishing features of high and low metastatic cells

The complexity of the process of metastasis is widely recognized. We report herein on a recurrent feature of high compared to low metastatic cells that is linked to their ability to survive early after their arrival at secondary sites. Using novel fluorescent-based imaging strategies that assess tumor cell interaction with the lung microenvironment, we have determined that most high and low metastatic cells can be distinguished within 6 hours of their arrival in the lung and further that this difference is defined by the ability of high metastatic cells to resist apoptosis at the secondary site. Despite the complexity of the metastatic cascade, the performance of cells during this critical window is highly defining of their metastatic proclivity. To explore mechanisms, we next evaluated biochemical pathways that may be linked to this survival phenotype in highly metastatic cells. Interestingly, we found no association between the Akt survival pathway and this metastatic phenotype. Of all pathways examined, only protein kinase C (PKC) activation was significantly linked to survival of highly metastatic cells. These data provide a conceptual understanding of a defining difference between high and low metastatic cells. The connection to PKC activation may provide a biologic rationale for the use of PKC inhibition in the prevention of metastatic progression.

Althaea rosea Cavanil and Plantago major L. suppress neoplastic cell transformation through the inhibition of epidermal growth factor receptor kinase

For thousands of years in Asia, Althaea rosea Cavanil (ARC) and Plantago major L. (PML) have been used as powerful non-toxic therapeutic agents that inhibit inflammation. However, the anticancer mechanisms and molecular targets of ARC and PML are poorly understood, particularly in epidermal growth factor (EGF)-induced neoplastic cell transformation. The aim of this study was to evaluate the chemopreventive effects and mechanisms of the methanol extracts from ARC (MARC) and PML (MPML) in EGF-induced neoplastic cell transformation of JB6 P+ mouse epidermal cells using an MTS assay, anchorage-independent cell transformation assay and western blotting. Our results showed that MARC and MPML significantly suppressed neoplastic cell transformation by inhibiting the kinase activity of the EGF receptor (EGFR). The activation of EGFR by EGF was suppressed by MARC and MPML treatment in EGFR(+/+) cells, but not in EGFR(-/-) cells. In addition, MARC and MPML inhibited EGF-induced cell proliferation in EGFR-expressing murine embryonic fibroblasts (EGFR(+/+)). These results strongly indicate that EGFR targeting by MARC and MPML may be a good strategy for chemopreventive or chemotherapeutic applications.

EGFR-mediated carcinoma cell metastasis mediated by integrin αvβ5 depends on activation of c-Src and cleavage of MUC1

Receptor tyrosine kinases and integrins play an essential role in tumor cell invasion and metastasis. We previously showed that EGF and other growth factors induce human carcinoma cell invasion and metastasis mediated by integrin αvβ5 that is prevented by Src blockade [1]. MUC1, a transmembrane glycoprotein, is expressed in most epithelial tumors as a heterodimer consisting of an extracellular and a transmembrane subunit. The MUC1 cytoplasmic domain of the transmembrane subunit (MUC1.CD) translocates to the nucleus where it promotes the transcription of a metastatic gene signature associated with epithelial to mesenchymal transition. Here, we demonstrate a requirement for MUC1 in carcinoma cell metastasis dependent on EGFR and Src without affecting primary tumor growth. EGF stimulates Src-dependent MUC1 cleavage and nuclear localization leading to the expression of genes linked to metastasis. Moreover, expression of MUC1.CD results in its nuclear localization and is sufficient for transcription of the metastatic gene signature and tumor cell metastasis. These results demonstrate that EGFR and Src activity contribute to carcinoma cell invasion and metastasis mediated by integrin αvβ5 in part by promoting proteolytic cleavage of MUC1 and highlight the ability of MUC1.CD to promote metastasis in a context-dependent manner. Our findings may have implications for the use and future design of targeted therapies in cancers known to express EGFR, Src, or MUC1.

EGF activates TTP expression by activation of ELK-1 and EGR-1 transcription factors

Background

Tristetraprolin (TTP) is a key mediator of processes such as inflammation resolution, the inhibition of autoimmunity and in cancer. It carries out this role by the binding and degradation of mRNA transcripts, thereby decreasing their half-life. Transcripts modulated by TTP encode proteins such as cytokines, pro-inflammatory agents and immediate-early response proteins. TTP can also modulate neoplastic phenotypes in many cancers. TTP is induced and functionally regulated by a spectrum of both pro- and anti-inflammatory cytokines, mitogens and drugs in a MAPK-dependent manner. So far the contribution of p38 MAPK to the regulation of TTP expression and function has been best described.

Results

Our results demonstrate the induction of the gene coding TTP (ZFP36) by EGF through the ERK1/2-dependent pathway and implicates the transcription factor ELK-1 in this process. We show that ELK-1 regulates ZFP36 expression by two mechanisms: by binding the ZFP36 promoter directly through ETS-binding site (+ 883 to +905 bp) and by inducing expression of EGR-1, which in turn increases ZFP36 expression through sequences located between -111 and -103 bp.

Conclusions

EGF activates TTP expression via ELK-1 and EGR-1 transcription factors.

Imaging molecular dynamics in vivo--from cell biology to animal models

Advances in fluorescence microscopy have enabled the study of membrane diffusion, cell adhesion and signal transduction at the molecular level in living cells grown in culture. By contrast, imaging in living organisms has primarily been restricted to the localization and dynamics of cells in tissues. Now, imaging of molecular dynamics is on the cusp of progressing from cell culture to living tissue. This transition has been driven by the understanding that the microenvironment critically determines many developmental and pathological processes. Here, we review recent progress in fluorescent protein imaging in vivo by drawing primarily on cancer-related studies in mice. We emphasize the need for techniques that can be easily combined with genetic models and complement fluorescent protein imaging by providing contextual information about the cellular environment. In this Commentary we will consider differences between in vitro and in vivo experimental design and argue for an approach to in vivo imaging that is built upon the use of intermediate systems, such as 3-D and explant culture models, which offer flexibility and control that is not always available in vivo. Collectively, these methods present a paradigm shift towards the molecular-level investigation of disease and therapy in animal models of disease.

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

Invadopodia are proteolytic membrane protrusions formed by highly invasive cancer cells, commonly observed on substrate(s) mimicking extracellular matrix. Although invadopodia are proposed to have roles in cancer invasion and metastasis, direct evidence has not been available. We previously reported that neural Wiskott-Aldrich syndrome protein (N-WASP), a member of WASP family proteins that regulate reorganization of the actin cytoskeleton, is an essential component of invadopodia. Here, we report that N-WASP-mediated invadopodium formation is essential in breast cancer invasion, intravasation and lung metastasis. We established stable cell lines based on MTLn3 rat mammary adenocarcinoma cells that either overexpressed a dominant-negative (DN) N-WASP construct or in which N-WASP expression was silenced by a pSuper N-WASP shRNA. Both the N-WASP shRNA and DN N-WASP cells showed a markedly decreased ability to form invadopodia and degrade extracellular matrix. In addition, formation of invadopodia in primary tumors and collagen I degradation were reduced in the areas of invasion (collagen-rich areas in the invasive edge of the tumor) and in the areas of intravasation (blood-vessel-rich areas). Our results suggest that tumor cells in vivo that have a decreased activity of N-WASP also have a reduced ability to form invadopodia, migrate, invade, intravasate and disseminate to lung compared with tumor cells with parental N-WASP levels.

Growth and metastasis suppression of glioma xenografts expressing exon 4-deletion variant of epidermal growth factor receptor by monoclonal antibody CH12-mediated receptor degradation

We recently isolated an exon-4-deleted epidermal growth factor receptor (EGFR) variant, termed de4 EGFR. Because the extracellular domain alteration of receptors often influences the antitumor effect of therapeutic antibodies, it is essential to test the sensitivity of de4 EGFR(+) tumors to anti-EGFR antibodies. Therefore, in this study, the antitumor activities of mAb CH12, an anti-EGFRvIII antibody developed in our laboratory, as well as a U.S. Food and Drug Administration-approved anti-EGFR antibody, cetuximab (C225), were characterized on de4 EGFR(+) models. The results of FACS assays showed that CH12 bound to de4 EGFR with a higher avidity than did C225. Interestingly, CH12, but not C225, significantly inhibited the metastasis and growth of U87MG-de4 EGFR xenografts, with a growth-inhibition ratio of 46.48% in vivo, and prolonged the survival of the tumor-bearing mice by 37.2%. Treatment with CH12 significantly suppressed tumor proliferation and angiogenesis with increased tumor apoptosis. Mechanistically, de4 EGFR protein expression was virtually undetectable in the U87MG-de4 EGFR xenografts treated with CH12. This may account for the observed reduction of Akt and Erk phosphorylation, cyclin D1, Bcl-2, and Bcl-x(L) expression and the increase of p27 and E-cadherin expression. Intriguingly, LAMP-1, a major component of the lysosome, was significantly up-regulated in the CH12-treated group but not in the C225-treated group, suggesting its contribution to the degradation of de4 EGFR. Taken together, our data demonstrated that mAb CH12 is a promising therapeutic agent for treating de4 EGFR(+) gliomas.

Identification of an exon 4-deletion variant of epidermal growth factor receptor with increased metastasis-promoting capacity

Several types of epidermal growth factor receptor (EGFR) gene alternations have been observed in human tumors. Here we present a novel EGFR variant with aberrant splicing of exon 4 (named as de4 EGFR). Variant-specific polymerase chain reaction showed that de4 EGFR was expressed in some glioma (4/40), prostate cancer (3/11), and ovarian cancer (3/9) tissues but not in tissues adjacent to tumors or normal tissues. de4 EGFR displayed an enhanced transformation and a higher metastasis-promoting capacity in comparison to wild-type EGFR. With minimal EGF-binding activity, de4 EGFR underwent ligand-independent autophosphorylation and self-dimerization. Moreover, in serum-starved condition, de4 EGFR expression in U87 MG cells significantly upregulated the extracellular signal-regulated kinase and AKT phosphorylation and expression of JUN and Src. Importantly, E-cadherin expression was barely detectable in the U87 MG cells expressing de4 EGFR and restored expression of E-cadherin in these cells inhibited their metastatic behaviors. Taken together, we identified a novel EGFR variant with increased metastasis-promoting activity that may become a promising new target for cancer therapy.

Apoptosis inhibitor ARC promotes breast tumorigenesis, metastasis, and chemoresistance

Apoptosis repressor with caspase recruitment domain (ARC) inhibits both death receptor- and mitochondrial/ER-mediated pathways of apoptosis. Although expressed mainly in terminally differentiated cells, ARC is markedly upregulated in a variety of human cancers, where its potential contributions have not yet been defined. In this study, we provide evidence of multiple critical pathophysiologic functions for ARC in breast carcinogenesis. In the polyoma middle T-antigen (PyMT) transgenic mouse model of breast cancer, in which endogenous ARC is strongly upregulated, deletion of the ARC-encoding gene nol3 decreased primary tumor burden without affecting tumor onset or multiplicity. More notably, ARC deficiency also limited tumor cell invasion and the number of circulating cancer cells, markedly reducing the number of lung metastases. Conversely, ectopic overexpression of ARC in a PyMT-derived metastatic breast cancer cell line increased invasion in vitro and lung metastasis in vivo. We confirmed these results in a humanized orthotopic model based on MDA-MB-231-derived LM2 metastatic breast cancer cells, in which RNAi-mediated knockdown of ARC levels was shown to reduce tumor volume, local invasion, and lung metastases. Lastly, we found that endogenous levels of ARC conferred chemoresistance in primary tumors and invading cell populations. Our results establish that ARC promotes breast carcinogenesis by driving primary tumor growth, invasion, and metastasis as well as by promoting chemoresistance in invasive cells.

Extracellular matrix determinants of proteolytic and non-proteolytic cell migration

Cell invasion into the 3D extracellular matrix (ECM) is a multistep biophysical process involved in inflammation, tissue repair, and metastatic cancer invasion. Migrating cells navigate through tissue structures of complex and often varying physicochemical properties, including molecular composition, porosity, alignment and stiffness, by adopting strategies that involve deformation of the cell and engagement of matrix-degrading proteases. We review how the ECM determines whether or not pericellular proteolysis is required for cell migration, ranging from protease-driven invasion and secondary tissue destruction, to non-proteolytic, non-destructive movement that solely depends on cell deformability and available tissue space. These concepts call for therapeutic targeting of proteases to prevent invasion-associated tissue destruction rather than the migration process per se.

High-resolution multiphoton imaging of tumors in vivo

Analysis of the individual steps in metastasis is crucial if insights at the molecular level are to be linked to the cell biology of cancer. A technical hurdle to achieving the analysis of the individual steps of metastasis is the fact that, at the gross level, tumors are heterogeneous in both animal models and patients. Human primary tumors show extensive variation in all properties ranging from growth and morphology of the tumor through tumor-cell density in the blood and formation and growth of metastases. Methods capable of the direct visualization and analysis of tumor-cell behavior at single-cell resolution in vivo have become crucial in advancing the understanding of mechanisms of metastasis, the definition of microenvironment, and the markers related to both. This article discusses the use of high-resolution multiphoton imaging of tumors (specifically breast tumors in mice) in vivo.

Dose Response of MTLn3 Cells to Serial Dilutions of Arsenic Trioxide and Ionizing Radiation

MTLn3 cells derived from mouse mammary epithelium are known to be highly malignant and are resistant to both radio- and chemo-therapy. We exposed MTLn3 cells to various doses of inorganic Arsenic trioxide (As2O3) in combination with ionizing radiation. Cells were treated with a series of As2O3 concentrations ranging from 20 μM to 1.22 nM for 8 hour, 24 hour and 48 hour periods. Post-treated cell proliferation was quantified by measuring mitochondrial activity and DNA analysis. Cells exposed to radiation and As2O3 at concentration greater than 1.25 μM showed apoptosis and radiations alone treated cells were statistically not different from the control. Hormesis was observed for As2O3 concentrations in the range of 0.078 μM to 0.625 μM while the combined chemo and radiation treatments of the cells did not affect the hormetic effect. We have demonstrated that As2O3 (in the presence and absence of ionizing radiation) in specific low concentrations induced apoptosis in the otherwise chemoresistant cancer cells. This low concentration-mediated cell death is immediately followed by a surge in cell survival. Low dosing dosimetry is highly desirable in metronomic therapy however, it has a narrow window since necrosis, hormesis, apoptosis and other dose-dependent biological processes take place in this region. Further quantifiable dosimetry is highly desired for routine clinical practice.

Illuminating epidermal growth factor receptor densities on filopodia through plasmon coupling

Filopodia have been hypothesized to act as remote sensors of the cell environment, but many details of the sensor function remain unclear. We investigated the distribution of the epidermal growth factor (EGF) receptor (EGFR) density on filopodia and on the dorsal cell membrane of A431 human epidermoid carcinoma cells using a nanoplasmonic enabled imaging tool. We targeted cell surface EGFR with 40 nm diameter Au nanoparticles (NPs) using a high affinity multivalent labeling strategy and determined relative NP binding affinities spatially resolved through plasmon coupling. Distance-dependent near-field interactions between the labels generated a NP density (ρ)-dependent spectral response that facilitated a spatial mapping of the EGFR density distribution on subcellular length scales in an optical microscope in solution. The measured ρ values were significantly higher on filopodia than on the cellular surface, which is indicative of an enrichment of EGFR on filopodia. A detailed characterization of the spatial distribution of the NP immunolabels through scanning electron microscopy (SEM) confirmed the findings of the all-optical plasmon coupling studies and provided additional structural details. The NPs exhibited a preferential association with the sides of the filopodia. We calibrated the ρ-dependent spectral response of the Au immunolabels through correlation of optical spectroscopy and SEM. The experimental dependence of the measured plasmon resonance wavelength (λ(res)) of the interacting immunolabels on ρ was well described by the fit λ(res) = 595.0 nm - 46.36 nm exp(-ρ/51.48) for ρ ≤ 476 NPs/μm(2). The performed correlated spectroscopic/SEM studies pave the way toward quantitative immunolabeling studies of EGFR and other important cell surface receptors in an optical microscope.

Mechanism of the mesenchymal-epithelial transition and its relationship with metastatic tumor formation

Cancer metastasis consists of a sequential series of events, and the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are recognized as critical events for metastasis of carcinomas. A current area of focus is the histopathological similarity between primary and metastatic tumors, and MET at sites of metastases has been postulated to be part of the process of metastatic tumor formation. Here, we summarize accumulating evidence from experimental studies that directly supports the role of MET in cancer metastasis, and we analyze the main mechanisms that regulate MET or reverse EMT in carcinomas. Given the critical role of MET in metastatic tumor formation, the potential to effectively target the MET process at sites of metastasis offers new hope for inhibiting metastatic tumor formation.

Simulating EGFR-ERK signaling control by scaffold proteins KSR and MP1 reveals differential ligand-sensitivity co-regulated by Cbl-CIN85 and endophilin

ERK activation is enhanced by the scaffolding proteins KSR and MP1, localized near the cell membrane and late endosomes respectively, but little is known about their dynamic interplay. We develop here a mathematical model with ordinary differential equations to describe the dynamic activation of EGFR-ERK signaling under a conventional pathway without scaffolds, a KSR-scaffolded pathway, and an MP1-scaffolded pathway, and their impacts were examined under the influence of the endosomal regulators, Cbl-CIN85 and Endophilin A1. This new integrated model, validated against experimental results and computational constraints, shows that changes of ERK activation and EGFR endocytosis in response to EGF concentrations (i.e ligand sensitivity) depend on these scaffold proteins and regulators. The KSR-scaffolded and the conventional pathways act synergistically and are sensitive to EGF stimulation. When the KSR level is high, the sensitivity of ERK activation from this combined pathway remains low when Cbl-CIN85 level is low. But, such sensitivity can be increased with increasing levels of Endophilin if Cbl-CIN85 level becomes high. However, reduced KSR levels already present high sensitivity independent of Endophilin levels. In contrast, ERK activation by MP1 is additive to that of KSR but it shows little ligand-sensitivity under high levels of EGF. This can be partly reversed by increasing level of Endophilin while keeping Cbl-CIN85 level low. Further analyses showed that high levels of KSR affect ligand-sensitivity of EGFR endocytosis whereas MP1 ensures the robustness of endosomal ERK activation. These simulations constitute a multi-dimensional exploration of how EGF-dependent EGFR endocytosis and ERK activation are dynamically affected by scaffolds KSR and MP1, co-regulated by Cbl-CIN85 and Endophilin A1. Together, these results provide a detailed and quantitative demonstration of how regulators and scaffolds can collaborate to fine-tune the ligand-dependent sensitivity of EGFR endocytosis and ERK activation which could underlie differences during normal physiology, disease states and drug responses.

Mena invasive (MenaINV) promotes multicellular streaming motility and transendothelial migration in a mouse model of breast cancer

We have shown previously that distinct Mena isoforms are expressed in invasive and migratory tumor cells in vivo and that the invasion isoform (Mena(INV)) potentiates carcinoma cell metastasis in murine models of breast cancer. However, the specific step of metastatic progression affected by this isoform and the effects on metastasis of the Mena11a isoform, expressed in primary tumor cells, are largely unknown. Here, we provide evidence that elevated Mena(INV) increases coordinated streaming motility, and enhances transendothelial migration and intravasation of tumor cells. We demonstrate that promotion of these early stages of metastasis by Mena(INV) is dependent on a macrophage-tumor cell paracrine loop. Our studies also show that increased Mena11a expression correlates with decreased expression of colony-stimulating factor 1 and a dramatically decreased ability to participate in paracrine-mediated invasion and intravasation. Our results illustrate the importance of paracrine-mediated cell streaming and intravasation on tumor cell dissemination, and demonstrate that the relative abundance of Mena(INV) and Mena11a helps to regulate these key stages of metastatic progression in breast cancer cells.

Two-photon intravital multicolor imaging combined with inducible gene expression to distinguish metastatic behavior of breast cancer cells in vivo

Purpose

The aim of this study is to use multicolor intravital imaging together with an inducible cell model to compare metastatic behavior of control and genetically modified breast cancer cell populations within the intact primary tumor of a mouse.

Procedure

GFP-MTLn3-ErbB1 cells were generated with doxycycline-regulated conditional transgene expression using lentiviral TREAutoR3-cyan fluorescent protein (CFP). CFP expression together with tumor cell motility is monitored in vitro and in vivo.

Results

Effective and tight control of doxycycline-induced CFP expression was observed both in vitro and in vivo. Intravital multiphoton microscopy on intact orthotopic tumors allowed a clear discrimination between GFP-only and (GFP + CFP) cell populations, which enables direct comparison of the motility behavior of two different cell populations in the same microenvironment in vivo.

Conclusions

This system is robust and versatile for conditional gene expression and can be used to study the role of individual candidate metastasis genes in vitro and in vivo. This technology will allow investigations of cellular events in cancer metastasis and in particular intravasation within a primary tumor.

Electronic supplementary material

The online version of this article (doi:10.1007/s11307-010-0307-z) contains supplementary material, which is available to authorized users.

A functional in vivo screen for regulators of tumor progression identifies HOXB2 as a regulator of tumor growth in breast cancer

Microarray profiling in breast cancer patients has identified genes correlated with prognosis whose functions are unknown. The purpose of this study was to develop an in vivo assay for functionally screening regulators of tumor progression using a mouse model. Transductant shRNA cell lines were made in the MDA-MB-231 breast cancer line. A pooled population of 25 transductants was injected into the mammary fat pads and tail veins of mice to evaluate tumor growth, and experimental metastasis. The proportions of transductants were evaluated in the tumor and metastases using barcodes specific to each shRNA transductant. We characterized the homeobox 2 transcription factor as a negative regulator, decreasing tumor growth in MDA-MB-231, T47D, and MTLn3 mammary adenocarcinoma cell lines. Homeobox genes have been correlated with cancer patient prognosis and tumorigenesis. Here we use a novel in vivo shRNA screen to identify a new role for a homeobox gene in human mammary adenocarcinoma.

Cdc42-interacting protein 4 is a Src substrate that regulates invadopodia and invasiveness of breast tumors by promoting MT1-MMP endocytosis

Invadopodia are actin-rich membrane protrusions that promote extracellular matrix degradation and invasiveness of tumor cells. Src protein-tyrosine kinase is a potent inducer of invadopodia and tumor metastases. Cdc42-interacting protein 4 (CIP4) adaptor protein interacts with actin regulatory proteins and regulates endocytosis. Here, we show that CIP4 is a Src substrate that localizes to invadopodia in MDA-MB-231 breast tumor cells expressing activated Src (MDA-SrcYF). To probe the function of CIP4 in invadopodia, we established stable CIP4 knockdown in MDA-SrcYF cell lines by RNA interference. Compared with control cells, CIP4 knockdown cells degrade more extracellular matrix (ECM), have increased numbers of mature invadopodia and are more invasive through matrigel. Similar results are observed with knockdown of CIP4 in EGF-treated MDA-MB-231 cells. This inhibitory role of CIP4 is explained by our finding that CIP4 limits surface expression of transmembrane type I matrix metalloprotease (MT1-MMP), by promoting MT1-MMP internalization. Ectopic expression of CIP4 reduces ECM digestion by MDA-SrcYF cells, and this activity is enhanced by mutation of the major Src phosphorylation site in CIP4 (Y471). Overall, our results identify CIP4 as a suppressor of Src-induced invadopodia and invasion in breast tumor cells by promoting endocytosis of MT1-MMP.

Live cell in vitro and in vivo imaging applications: accelerating drug discovery

Dynamic regulation of specific molecular processes and cellular phenotypes in live cell systems reveal unique insights into cell fate and drug pharmacology that are not gained from traditional fixed endpoint assays. Recent advances in microscopic imaging platform technology combined with the development of novel optical biosensors and sophisticated image analysis solutions have increased the scope of live cell imaging applications in drug discovery. We highlight recent literature examples where live cell imaging has uncovered novel insight into biological mechanism or drug mode-of-action. We survey distinct types of optical biosensors and associated analytical methods for monitoring molecular dynamics, in vitro and in vivo. We describe the recent expansion of live cell imaging into automated target validation and drug screening activities through the development of dedicated brightfield and fluorescence kinetic imaging platforms. We provide specific examples of how temporal profiling of phenotypic response signatures using such kinetic imaging platforms can increase the value of in vitro high-content screening. Finally, we offer a prospective view of how further application and development of live cell imaging technology and reagents can accelerate preclinical lead optimization cycles and enhance the in vitro to in vivo translation of drug candidates.

Sorting nexin 6 interacts with breast cancer metastasis suppressor-1 and promotes transcriptional repression

Sorting nexin 6 (SNX6), a predominantly cytoplasmic protein involved in intracellular trafficking of membrane receptors, was identified as a TGF-β family interactor. However, apart from being a component of the Retromer, little is known about SNX6 cellular functions. Pim-1-dependent SNX6 nuclear translocation has been reported suggesting a putative nuclear role for SNX6. Here, we describe a previously non-reported association of SNX6 with breast cancer metastasis suppressor 1 (BRMS1) protein detected by a yeast two-hybrid screening. The interaction can be reconstituted in vitro and further FRET analysis confirmed the novel interaction. Additionally, we identified their coiled-coil domains as the minimal binding motives required for interaction. Since BRMS1 has been shown to repress transcription, we sought the ability of SNX6 to interfere with this nuclear activity. Using a standard gene reporter assay, we observed that SNX6 increases BRMS1-dependent transcriptional repression. Moreover, over-expression of SNX6 was capable of diminishing trans-activation in a dose-dependent manner.

Cell invasion of highly metastatic MTLn3 cancer cells is dependent on phospholipase D2 (PLD2) and Janus kinase 3 (JAK3)

MTLn3 cells are highly invasive breast adenoacarcinoma cells. The relative level of the epidermal-growth-factor-stimulated invasion of this cell line is greater than two other breast cancer cell lines (MDA-MB-231 and MCF-7) and one non-small cell lung cancer cell line (H1299). We have determined that the mechanism of cancer cell invasion involves the presence of an enzymatically active phospholipase D (PLD), with the PLD2 isoform being more relevant than PLD1. PLD2 silencing abrogated invasion, whereas ectopic expression of PLD2 augmented cell invasion in all four cell lines, with an efficacy (MTLn3±MDA-MB-231>H1299±MCF-7) that correlated well with their abilities to invade Matrigel in vitro. We also report that PLD2 is under the control of Janus kinase 3 (JAK3), with the kinase phosphorylating PLD2 at the Y415 residue, thus enabling its activation. Y415 is located downstream of a PH domain and upstream of the catalytic HKD-1 domain of PLD2. JAK3 knockdown abrogated lipase activity and epidermal-growth-factor-stimulated cell invasion directly. For the purposes of activating PLD2 for cell invasion, JAK3 operates via an alternative pathway that is independent of STAT, at least in MTLn3 cells. We also consistently found that JAK3 and PLD2 pathways are utilized at the maximum efficiency (phosphorylation and activity) in highly invasive MTLn3 cells versus a relatively low utilization in the less invasive MCF-7 cell line. In summary, a high level of cell invasiveness of cancer cells can be explained for the first time by combined high JAK3/PLD2 phosphorylation and activity involving PLD2's Y415 residue, which might constitute a novel target to inhibit cancer cell invasion.

Functional screening with a live cell imaging-based random cell migration assay

Cell migration, essential in cancer progression, is a complex process comprising a number of spatiotemporally regulated and well-coordinated mechanisms. In order to study (random) cell migration in the context of responses to various external cues (such as growth factors) or intrinsic cell signaling, a number of different tools and approaches have been developed. In order to unravel the key pathways and players involved in the regulation of (cancer) cell migration, a systematical mapping of the players/pathways is required. For this purpose, we developed a cell migration assay based on automatic high-throughput microscopy screen. This approach allows for screening of hundreds of genes, e.g., those encoding various kinases and phosphatases but can also be used for screening of drugs libraries. Moreover, we have developed an automatic analysis pipeline comprising of (a) automatic data acquisition (movie) and (b) automatic analysis of the acquired movies of the migrating cells. Here, we describe various facets of this approach. Since cell migration is essential in progression of cancer metastasis, we describe two examples of experiments performed on highly motile (metastatic) cancer cells.

Two-photon intravital multicolour imaging to study metastatic behaviour of cancer cells in vivo

In the last decade, intravital microscopy on breast tumours in mice at single-cell resolution has resulted in important new insight into mechanisms of metastatic behaviour such as migration, invasion, and intravasation of tumour cells; angiogenesis; and the response of immune cells. This chapter describes the methods that can be used for analysing tumour cell motility in a mouse model of breast cancer metastasis. It includes protocols for generation of a labelled primary tumour, its imaging with two-photon microscopy, and the processing of time-lapse image data. Furthermore, we present a methodology, recently developed in our laboratory that combines multicolour imaging with an inducible cell model to study the role of a specific gene of interest in tumour cell motility in vivo. This protocol can be used to image the metastatic behaviour of different individual tumour cells within the same tumour microenvironment and correlate it with metastasis formation. Additional protocols for labelling macrophages to visualise blood flow and image analysis are also included.

Tumor-stroma: In vivo assays and intravital imaging to study cell migration and metastasis

The development of metastatic disease is often correlated with poor patient outcome in a variety of different cancers. The metastatic cascade is a complex, multistep process that involves the growth of the primary tumor and angiogenesis, invasion into the local environment, intravasation into the vasculature, tumor cell survival in the circulation, extravasation from the vasculature and sustained growth at secondary organ sites to form metastases. Although in vitro assays of single cell types can provide information regarding cell autonomous mechanisms contributing to metastasis, the in vivo microenvironment entails a network of interactions between cells which is also important. Insight into the mechanisms underlying tumor cell migration, invasion and metastasis in vivo has been aided by development of multiphoton microscopy and in vivo assays, which we will review here.

In vivo imaging in cancer

Imaging has become an indispensable tool in the study of cancer biology and in clinical prognosis and treatment. The rapid advances in high resolution fluorescent imaging at single cell level and MR/PET/CT image registration, combined with new molecular probes of cell types and metabolic states, will allow the physical scales imaged by each to be bridged. This holds the promise of translation of basic science insights at the single cell level to clinical application. In this article, we describe the recent advances in imaging at the macro- and micro-scale and how these advances are synergistic with new imaging agents, reporters, and labeling schemes. Examples of new insights derived from the different scales of imaging and relevant probes are discussed in the context of cancer progression and metastasis.

Thyroid hormone induces cerebellar neuronal migration and Bergmann glia differentiation through epidermal growth factor/mitogen-activated protein kinase pathway

Cerebellar development in the postnatal period is mainly characterized by an intense cellular proliferation in the external granular layer, followed by migration of granular cells in the molecular layer along the Bergmann glia (BG) fibers. Cerebellar ontogenesis undergoes dramatic modulation by thyroid hormones (THs), although their mechanism of action in this organ is still largely unknown. We previously demonstrated that THs induce astrocytes to secrete epidermal growth factor (EGF), which thus promotes cerebellar neuronal proliferation and extracellular matrix remodeling in vitro. In the present study, we investigated the effect of the TH/EGF pathway on granule neuronal migration. By taking advantage of rat explant and dissociated culture assays, we showed that cerebellar astrocytes treated with TH promote granule cell migration. The addition of neutralizing antibodies against EGF or the pharmacological inhibitor of EGF signaling, bis-tyrphostin, completely inhibited TH-astrocyte-induced migration. Likewise, the addition of EGF itself greatly increased neuronal migration. Treatment of BG-dissociated cultures by EGF dramatically induced an alteration in cell morphology, characterized by an elongation in the glial process. Both neuronal migration and BG elongation were inhibited by the mitogen-activated protein kinase pathway inhibitor PD98059, suggesting that these events might be associated. Together, our results suggest that, by inducing EGF secretion, THs promote neuronal migration through BG elongation. Our data provide new clues to the molecular mechanism of THs in cerebellar development, and may contribute to a better understanding of some neuroendocrine disorders associated with migration deficits.

Metastasis: tumor cells becoming MENAcing

During breast cancer metastasis cells emigrate from the primary tumor to the bloodstream, and this carries them to distant sites where they infiltrate and sometimes form metastases within target organs. These cells must penetrate the dense extracellular matrix comprising the basement membrane of the mammary duct/acinus and migrate toward blood and lymphatic vessels, processes that mammary tumor cells execute primarily using epidermal growth factor (EGF)-dependent protrusive and migratory activity. Here, we focus on how the actin regulatory protein Mena affects EGF-elicited movement, invasion and metastasis. Recent findings indicate that, in invasive migratory tumor cells, Mena isoforms that endow heightened sensitivity to EGF and increased protrusive and migratory abilities are upregulated, whereas other isoforms are selectively downregulated. This change in Mena isoform expression enables tumor cells to invade in response to otherwise benign EGF stimulus levels and could offer an opportunity to identify metastatic risk in patients.

Endoglin suppresses human prostate cancer metastasis

Endoglin is a transmembrane receptor that suppresses human prostate cancer (PCa) cell invasion. Small molecule therapeutics now being tested in humans can activate endoglin signaling. It is not known whether endoglin can regulate metastatic behavior, PCa tumor growth, nor what signaling pathways are linked to these processes. This study sought to investigate the effect of endoglin on these parameters. We used a murine orthotopic model of human PCa metastasis, designed by us to measure effects at early steps in the metastatic cascade, and implanted PCa cells stably engineered to express differing levels of endoglin. We now extend this model to measure cancer cells circulating in the blood. Progressive endoglin loss led to progressive increases in the number of circulating PCa cells as well as to the formation of soft tissue metastases. Endoglin was known to suppress invasion by activating the Smad1 transcription factor. We now show that it selectively activates specific Smad1-responsive genes, including JUNB, STAT1, and SOX4. Increased tumor growth and increased Ki67 expression in tissue was seen only with complete endoglin loss. By showing that endoglin increased TGFβ-mediated suppression of cell growth in vitro and TGFβ-mediated signaling in tumor tissue, loss of this growth-suppressive pathway appears to be implicated at least in part for the increased size of endoglin-deficient tumors. Endoglin is shown for the first time to suppress cell movement out of primary tumor as well as the formation of distant metastasis. It is also shown to co-regulate tumor growth and metastatic behavior in human PCa.

Oncogenic Src requires a wild-type counterpart to regulate invadopodia maturation

The proto-oncogene Src tyrosine kinase (Src) is overexpressed in human cancers and is currently a target of anti-invasive therapies. Activation of Src is an essential catalyst of invadopodia production. Invadopodia are cellular structures that mediate extracellular matrix (ECM) proteolysis, allowing invasive cell types to breach confining tissue barriers. Invadopodia assembly and maturation is a multistep process, first requiring the targeting of actin-associated proteins to form pre-invadopodia, which subsequently mature by recruitment and activation of matrix metalloproteases (MMPs) that facilitate ECM degradation. We demonstrate that active, oncogenic Src alleles require the presence of a wild-type counterpart to induce ECM degradation at invadopodia sites. In addition, we identify the phosphorylation of the invadopodia regulatory protein cortactin as an important mediator of invadopodia maturation downstream of wild-type Src. Distinct phosphotyrosine-based protein-binding profiles in cells forming pre-invadopodia and mature invadopodia were identified by SH2-domain array analysis. These results indicate that although elevated Src kinase activity is required to target actin-associated proteins to pre-invadopodia, regulated Src activity is required for invadopodia maturation and matrix degradation activity. Our findings describe a previously unappreciated role for proto-oncogenic Src in enabling the invasive activity of constitutively active Src alleles.

Systems microscopy approaches to understand cancer cell migration and metastasis

Cell migration is essential in a number of processes, including wound healing, angiogenesis and cancer metastasis. Especially, invasion of cancer cells in the surrounding tissue is a crucial step that requires increased cell motility. Cell migration is a well-orchestrated process that involves the continuous formation and disassembly of matrix adhesions. Those structural anchor points interact with the extra-cellular matrix and also participate in adhesion-dependent signalling. Although these processes are essential for cancer metastasis, little is known about the molecular mechanisms that regulate adhesion dynamics during tumour cell migration. In this review, we provide an overview of recent advanced imaging strategies together with quantitative image analysis that can be implemented to understand the dynamics of matrix adhesions and its molecular components in relation to tumour cell migration. This dynamic cell imaging together with multiparametric image analysis will help in understanding the molecular mechanisms that define cancer cell migration.