Tumour-stromal interactions. Integrins and cell adhesions as modulators of mammary cell survival and transformation

Clinical significance of integrin αV and β superfamily members and focal adhesion kinase activity in oral squamous cell carcinoma: a retrospective observational study

Objectives: Integrins are heterodimeric transmembrane plasma membrane proteins composed of α- and β-chains. They bind to extracellular matrix (ECM) and cytoskeletal proteins as ECM protein receptors. Upon ECM protein binding, integrins activate focal adhesion kinase (FAK) and transduce various signals. Despite their importance, integrin and FAK expression in oral squamous cell carcinoma (OSCC) tissue and the prognosis of patients with OSCC remains elusive. Methods: In a retrospective observational study, we immunohistochemically evaluated integrin αV, β1, β3, β5, β6, FAK, and phosphorylated-FAK (pFAK) expressions as prognostic predictors in 96 patients with OSCC. Patients were classified as positive or negative based on staining intensity, and clinicopathologic characteristics and survival rates of the two groups were compared. The association between above integrin-related proteins and PD-1 or PD-L1 in OSCC tissues was investigated. Results: We observed immunohistochemical integrin αV, β1, β6, β8, and FAK expressions in the cell membrane and cytoplasm but not integrin β3 and β5 in the OSCC tissues. pFAK was expressed in the cytoplasm of OSCC cells. The overall survival rate significantly decreased in pFAK-positive OSCC patients compared to the negative group, and cervical lymph node metastasis significantly increased in integrin β8-positive patients with OSCC (p < 0.05). No association between integrin-related proteins and PD-1 or PD-L1 in OSCC tissues was observed. Conclusion: Our results indicate that pFAK and integrin β8 are prognostic factors for OSCC. Therefore, pFAK- and integrin β8-targeting new oral cancer diagnostic and therapeutic methods hold a promising potential.

Fast ICCD-based temperature modulated fluorescence tomography

Fluorescence tomography (FT) has become a powerful preclinical imaging modality with a great potential for several clinical applications. Although it has superior sensitivity and utilizes low-cost instrumentation, the highly scattering nature of bio-tissue makes FT in thick samples challenging, resulting in poor resolution and low quantitative accuracy. To overcome the limitations of FT, we previously introduced a novel method, termed temperature modulated fluorescence tomography (TMFT), which is based on two key elements: (1) temperature-sensitive fluorescent agents (ThermoDots) and (2) high-intensity focused ultrasound (HIFU). The fluorescence emission of ThermoDots increases up to hundredfold with only several degree temperature elevation. The exceptional and reversible response of these ThermoDots enables their modulation, which effectively allows their localization using the HIFU. Their localization is then used as functional a priori during the FT image reconstruction process to resolve their distribution with higher spatial resolution. The last version of the TMFT system was based on a cooled CCD camera utilizing a step-and-shoot mode, which necessitated long total imaging time only for a small selected region of interest (ROI). In this paper, we present the latest version of our TMFT technology, which uses a much faster continuous HIFU scanning mode based on an intensified CCD (ICCD) camera. This new, to the best of our knowledge, version can capture the whole field-of-view (FOV) of 50×30m m 2 at once and reduces the total imaging time down to 30 min, while preserving the same high resolution (∼1.3m m) and superior quantitative accuracy (<7% error) as the previous versions. Therefore, this new method is an important step toward utilization of TMFT for preclinical imaging.

Extracellular Matrices and Cancer-Associated Fibroblasts: Targets for Cancer Diagnosis and Therapy?

Solid cancer progression is dictated by neoplastic cell features and pro-tumoral crosstalks with their microenvironment. Stroma modifications, such as fibroblast activation into cancer-associated fibroblasts (CAFs) and extracellular matrix (ECM) remodeling, are now recognized as critical events for cancer progression and as potential therapeutic or diagnostic targets. The recent appreciation of the key, complex and multiple roles of the ECM in cancer and of the CAF diversity, has revolutionized the field and raised innovative but challenging questions. Here, we rapidly present CAF heterogeneity in link with their specific ECM remodeling features observed in cancer, before developing each of the impacts of such ECM modifications on tumor progression (survival, angiogenesis, pre-metastatic niche, chemoresistance, etc.), and on patient prognosis. Finally, based on preclinical studies and recent results obtained from clinical trials, we highlight key mechanisms or proteins that are, or may be, used as potential therapeutic or diagnostic targets, and we report and discuss benefits, disappointments, or even failures, of recently reported stroma-targeting strategies.

The Physical Microenvironment of Tumors: Characterization and Clinical Impact

The tumor microenvironment plays a critical role in tumorigenesis and metastasis. As tightly controlled extracellular matrix homeostasis is lost during tumor progression, a dysregulated extracellular matrix can significantly alter cellular phenotype and drive malignancy. Altered physical properties of the tumor microenvironment alter cancer cell behavior, limit delivery and efficacy of therapies, and correlate with tumorigenesis and patient prognosis. The physical features of the extracellular matrix during tumor progression have been characterized; however, a wide range of methods have been used between studies and cancer types resulting in a large range of reported values. Here, we discuss the significant mechanical and structural properties of the tumor microenvironment, summarizing their reported values and clinical impact across cancer type and grade. We attempt to integrate the values in the literature to identify sources of reported differences and commonalities to better understand how aberrant extracellular matrix dynamics contribute to cancer progression. An intimate understanding of altered matrix properties during malignant transformation will be crucial in effectively detecting, monitoring, and treating cancer.

Upregulation of annexin A1 protein expression in the intratumoral vasculature of human non-small-cell lung carcinoma and rodent tumor models

Annexin A1 (anxA1) is an immunomodulatory protein that has been proposed as a tumor vascular target for antitumor biologic agents, yet to date the vascular expression of anxA1 in specific tumor indications has not been systematically assessed. Attempts to evaluate vascular anxA1 expression by immunohistochemistry are complicated by a lack of available antibodies that are both specific for anxA1 and bind the N-terminal–truncated form of anxA1 that has previously been identified in tumor vasculature. To study the vascular expression pattern of anxA1 in non–small-cell lung carcinoma (NSCLC), we isolated an antibody capable of binding N-terminal–truncated anxA1_27-346 and employed it in immunohistochemical studies of human lung specimens. Lung tumor specimens evaluated with this antibody revealed vascular (endothelial) anxA1 expression in five of eight tumor samples studied, but no vascular anxA1 expression was observed in normal lung tissue. Tumor microarray analysis further demonstrated positive vascular staining for anxA1 in 30 of 80 NSCLC samples, and positive staining of neoplastic cells was observed in 54 of 80 samples. No correlation was observed between vascular and parenchymal anxA1 expression. Two rodent tumor models, B16-F10 and Py230, were determined to have upregulated anxA1 expression in the intratumoral vasculature. These data validate anxA1 as a potential vascular anti-tumor target in a subset of human lung tumors and identify rodent models which demonstrate anxA1 expression in tumor vasculature.

Chemoresistance of Cancer Cells: Requirements of Tumor Microenvironment-mimicking In Vitro Models in Anti-Cancer Drug Development

For decades, scientists have been using two-dimensional cell culture platforms for high-throughput drug screening of anticancer drugs. Growing evidence indicates that the results of anti-cancer drug screening vary with the cell culture microenvironment, and this variation has been proposed as a reason for the high failure rate of clinical trials. Since the culture condition-dependent drug sensitivity of anti-cancer drugs may negatively impact the identification of clinically effective drug candidates, more reliable in vitro cancer platforms are urgently needed. In this review article, we provide an overview of how cell culture conditions can alter drug efficacy and highlight the importance of developing more reliable cancer drug testing platforms for use in the drug discovery process. The environmental factors that can alter drug delivery and efficacy are reviewed. Based on these observations of chemoresistant tumor physiology, we summarize the recent advances in the fabrication of in vitro cancer models and the model-dependent cytotoxicity of anti-cancer drugs, with a particular focus on engineered environmental factors in these platforms. It is believed that more physiologically relevant cancer models can revolutionize the drug discovery process.

From transformation to metastasis: deconstructing the extracellular matrix in breast cancer

The extracellular matrix (ECM) is a guiding force that regulates various developmental stages of the breast. In addition to providing structural support for the cells, it mediates epithelial-stromal communication and provides cues for cell survival, proliferation, and differentiation. Perturbations in ECM architecture profoundly influence breast tumor progression and metastasis. Understanding how a dysregulated ECM can facilitate malignant transformation is crucial to designing treatments to effectively target the tumor microenvironment. Here, we address the contribution of ECM mechanics to breast cancer progression, metastasis, and treatment resistance and discuss potential therapeutic strategies targeting the ECM.

In vitro cancer cell-ECM interactions inform in vivo cancer treatment

The general progression of cancer drug development involves in vitro testing followed by safety and efficacy evaluation in clinical trials. Due to the expense of bringing candidate drugs to trials, in vitro models of cancer cells and tumor biology are required to screen drugs. There are many examples of drugs exhibiting cytotoxic behavior in cancer cells in vitro but losing efficacy in vivo, and in many cases, this is the result of poorly understood chemoresistant effects conferred by the cancer microenvironment. To address this, improved methods for culturing cancer cells in biomimetic scaffolds have been developed; along the way, a great deal about the nature of cancer cell-extracellular matrix (ECM) interactions has been discovered. These discoveries will continue to be leveraged both in the development of novel drugs targeting these interactions and in the fabrication of biomimetic substrates for efficient cancer drug screening in vitro.

Overexpression of integrin αv facilitates proliferation and invasion of oral squamous cell carcinoma cells via MEK/ERK signaling pathway that is activated by interaction of integrin αvβ8 with type Ⅰ collagen

To examine the role of integrin αv subunit in the progression of squamous cell carcinoma (SCC), oral SCC cells were stably transfected with integrin αv cDNA. Integrin αv transfectants exhibited the enhancement of proliferation on type Ⅰ collagen, and seemed to have a high ability to invade type Ⅰ collagen gel. Overexpression of integrin αv led to rapid phosphorylation of focal adhesion kinase (FAK), mitogen‑activated protein kinase kinase 1/2 (MEK1/2) and extracellular signal‑regulated kinase 1/2 (ERK1/2) in SCC cells on type Ⅰ collagen. The downregulation of integrin β8 in integrin αv transfectants by its specific antisense oligonucleotide led to a decrease in type Ⅰ collagen‑stimulated activation of FAK and the MEK/ERK signaling pathway, and also suppressed the proliferation on type Ⅰ collagen and the invasiveness into type Ⅰ collagen gel. Moreover, the expression of integrin β8 was induced following transfection with integrin αv cDNA. These results indicated that the overexpression of integrin αv induces integrin αvβ8 heterodimer formation and the binding of integrin αvβ8 to type Ⅰ collagen might enhance the proliferation and invasion of SCC cells via the activation of the MEK/ERK signaling pathway.

Serum-free culture success of glial tumors is related to specific molecular profiles and expression of extracellular matrix-associated gene modules

BACKGROUND

Recent molecular characterization studies have identified clinically relevant molecular subtypes to coexist within the same histological entities of glioma. Comparative studies between serum-supplemented and serum-free (SF) culture conditions have demonstrated that SF conditions select for glioma stem-like cells, which superiorly conserve genomic alterations. However, neither the representation of molecular subtypes within SF culture assays nor the molecular distinctions between successful and nonsuccessful attempts have been elucidated.

METHODS

A cohort of 261 glioma samples from varying histological grades was documented for SF culture success and clinical outcome. Gene expression and single nucleotide polymorphism arrays were interrogated on a panel of tumors for comparative analysis of SF+ (successful cultures) and SF- (unsuccessful cultures).

RESULTS

SF culture outcome was correlated with tumor grade, while no relation was found between SF+ and patient overall survival. Copy number-based hierarchical clustering revealed an absolute separation between SF+ and SF- parental tumors. All SF+ cultures are derived from tumors that are isocitrate dehydrogenase 1 (IDH1) wild type, chromosome 7 amplified, and chromosome 10q deleted. SF- cultures derived from IDH1 mutant tumors demonstrated a fade-out of mutated cells during the first passages. SF+ tumors were enriched for The Cancer Genome Atlas Classical subtype and intrinsic glioma subtype-18. Comparative gene ontology analysis between SF+ and SF- tumors demonstrated enrichment for modules associated with extracellular matrix composition, Hox-gene signaling, and inflammation.

CONCLUSION

SF cultures are derived from a subset of parental tumors with a shared molecular background including enrichment for extracellular matrix-associated gene modules. These results provide leads to develop enhanced culture protocols for glioma samples not propagatable under current SF conditions.

Co-implanting orthotopic tissue creates stroma microenvironment enhancing growth and angiogenesis of multiple tumors

Tumor models are needed to study cancer. Noninvasive imaging of tumors under native conditions in vivo is critical but challenging. Intravital microscopy (IVM) of subcutaneous tumors provides dynamic, continuous, long-term imaging at high resolution. Although popular, subcutaneous tumor models are often criticized for being ectopic and lacking orthotopic tissue microenvironments critical for proper development. Similar IVM of orthotopic and especially spontaneous tumors is seldom possible. Here, we generate and characterize tumor models in mice for breast, lung, prostate and ovarian cancer by co-engrafting tumor spheroids with orthotopic tissue in dorsal skin window chambers for IVM. We use tumor cells and tissue, both genetically engineered to express distinct fluorescent proteins, in order to distinguish neoplastic cells from engrafted tissue. IVM of this new, two-colored model reveals classic tumor morphology with red tumor cell nests surrounded by green stromal elements. The co-implanted tissue forms the supportive stroma and vasculature of these tumors. Tumor growth and angiogenesis are more robust when tumor cells are co-implanted with orthotopic tissue versus other tissues, or in the skin alone. The orthotopic tissue promotes tumor cell mitosis over apoptosis. With time, tumor cells can adapt to new environments and ultimately even grow better in the non-orthotopic tissue over the original orthotopic tissue. These models offer a significant advance by recreating an orthotopic microenvironment in an ectopic location that is still easy to image by IVM. These "ectopic-orthotopic" models provide an exceptional way to study tumor and stroma cells in cancer, and directly show the critical importance of microenvironment in the development of multiple tumors.

The role of tumour-stromal interactions in modifying drug response: challenges and opportunities

The role of stromal cells and the tumour microenvironment in general in modulating tumour sensitivity is increasingly becoming a key consideration for the development of active anticancer therapeutics. Here, we discuss how these tumour-stromal interactions affect tumour cell signalling, survival, proliferation and drug sensitivity. Particular emphasis is placed on the ability of stromal cells to confer - to tumour cells - resistance or sensitization to different classes of therapeutics, depending on the specific microenvironmental context. The mechanistic understanding of these microenvironmental interactions can influence the evaluation and selection of candidate agents for various cancers, in both the primary site as well as the metastatic setting. Progress in in vitro screening platforms as well as orthotopic and 'orthometastatic' xenograft mouse models has enabled comprehensive characterization of the impact of the tumour microenvironment on therapeutic efficacy. These recent advances can hopefully bridge the gap between preclinical studies and clinical trials of anticancer agents.

Mammary fibroblasts regulate morphogenesis of normal and tumorigenic breast epithelial cells by mechanical and paracrine signals

Stromal factors play a critical role in the development of the mammary gland. Using a three dimensional-coculture model we demonstrate a significant role for stromal fibroblasts in the regulation of normal mammary epithelial morphogenesis and the control of tumor growth. Both soluble factors secreted by fibroblasts and fibroblast-derived modifications of the matrix compliance contribute to the regulation of epithelial cell morphogenesis. Readjustment of matrix tension by fibroblasts can even induce a phenotypic reversion of breast carcinoma cells. These data offer a basis to develop new strategies for the normalization of the tumor stroma as an innovative target in cancer therapy.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

β1 integrin mediates an alternative survival pathway in breast cancer cells resistant to lapatinib

INTRODUCTION

The overexpression of human epidermal growth factor receptor (HER)-2 in 20% of human breast cancers and its association with aggressive growth has led to widespread use of HER2-targeted therapies, such as trastuzumab (T) and lapatinib (L). Despite the success of these drugs, their efficacy is limited in patients whose tumors demonstrate de novo or acquired resistance to treatment. The β1 integrin resides on the membrane of the breast cancer cell, activating several elements of breast tumor progression including proliferation and survival.

METHODS

We developed a panel of HER2-overexpressing cell lines resistant to L, T, and the potent LT combination through long-term exposure and validated these models in 3D culture. Parental and L/T/LT-resistant cells were subject to HER2 and β1 integrin inhibitors in 3D and monitored for 12 days, followed by quantification of colony number. Parallel experiments were conducted where cells were either stained for Ki-67 and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) or harvested for protein and analyzed by immunoblot. Results were subjected to statistical testing using analysis of variance and linear contrasts, followed by adjustment with the Sidak method.

RESULTS

Using multiple cell lines including BT474 and HCC1954, we reveal that in L and LT resistance, where phosphorylation of EGFR/HER1, HER2, and HER3 are strongly inhibited, kinases downstream of β1 integrin--including focal adhesion kinase (FAK) and Src--are up-regulated. Blockade of β1 by the antibody AIIB2 abrogates this up-regulation and functionally achieves significant growth inhibition of L and LT resistant cells in 3D, without dramatically affecting the parental cells. SiRNA against β1 as well as pharmacologic inhibition of FAK achieve the same growth inhibitory effect. In contrast, trastuzumab-resistant cells, which retain high levels of phosphorylated EGFR/HER1, HER2, and HER3, are only modestly growth-inhibited by AIIB2.

CONCLUSIONS

Our data suggest that HER2 activity, which is suppressed in resistance involving L but not T alone, dictates whether β1 mediates an alternative pathway driving resistance. Our findings justify clinical studies investigating the inhibition of β1 or its downstream signaling moieties as strategies to overcome acquired L and LT resistance.

Epigenetic regulation of cellular adhesion in cancer

Epigenetics describes the development and maintenance of stable heritable gene expression patterns, which allow cells to show different phenotypes despite of a commonly shared genetic code. The increasing knowledge in this field during the last decades reveals its importance for many physiological processes like differentiation, embryogenesis and parental imprinting, but also for some diseases such as cancer. Recent data have shown that the complexity of carcinogenesis can no longer be explained solely on the basis of genetic changes, but epigenomic alterations such as changes of the DNA methylation pattern and/or post-translational histone modifications and changes of microRNA expression need to be equally considered. Such epigenetic alterations may cause permanent changes in gene expression patterns and may therefore essentially contribute to some of the known phenotypic characteristics of cancer cells like the loss of growth control, altered intercellular communication and enhanced motility. The two latter may essentially be associated with the downregulation of cellular adhesion molecules, which may therefore be relevant in the context of cancer invasiveness and prognosis. The targeted modification of the epigenome may therefore open new horizons within the increasingly important field of epigenetic therapeutics-particularly in view of the regulation of cellular adhesion with particular attention to tumor cell invasion and metastasis.

Carcinoma matrix controls resistance to cisplatin through talin regulation of NF-kB

Extracellular matrix factors within the tumor microenvironment that control resistance to chemotherapeutics are poorly understood. This study focused on understanding matrix adhesion pathways that control the oral carcinoma response to cisplatin. Our studies revealed that adhesion of HN12 and JHU012 oral carcinomas to carcinoma matrix supported tumor cell proliferation in response to treatment with cisplatin. Proliferation in response to 30 µM cisplatin was not observed in HN12 cells adherent to other purified extracellular matrices such as Matrigel, collagen I, fibronectin or laminin I. Integrin β₁ was important for adhesion to carcinoma matrix to trigger proliferation after treatment with cisplatin. Disruption of talin expression in HN12 cells adherent to carcinoma matrix increased cisplatin induced proliferation. Pharmacological inhibitors were used to determine signaling events required for talin deficiency to regulate cisplatin induced proliferation. Pharmacological inhibition of NF-kB reduced proliferation of talin-deficient HN12 cells treated with 30 µM cisplatin. Nuclear NF-kB activity was assayed in HN12 cells using a luciferase reporter of NF-kB transcriptional activity. Nuclear NF-kB activity was similar in HN12 cells adherent to carcinoma matrix and collagen I when treated with vehicle DMSO. Following treatment with 30 µM cisplatin, NF-kB activity is maintained in cells adherent to carcinoma matrix whereas NF-kB activity is reduced in collagen I adherent cells. Expression of talin was sufficient to trigger proliferation of HN12 cells adherent to collagen I following treatment with 1 and 30 µM cisplatin. Talin overexpression was sufficient to trigger NF-kB activity following treatment with cisplatin in carcinoma matrix adherent HN12 cells in a process disrupted by FAK siRNA. Thus, adhesions within the carcinoma matrix create a matrix environment in which exposure to cisplatin induces proliferation through the function of integrin β₁, talin and FAK pathways that regulate NF-kB nuclear activity.

[Implication of integrin alpha5beta1 in human breast carcinoma apoptosis and drug resistance]

Doxorubicin-resistant MCF-7Dox line, which is a derivative of the drug-sensitive MCF-7 human breast carcinoma line, differs from the latter by a strongly reduced expression of the alpha2beta1 integrin and a highly increased expression of the alpha5beta1 receptor. Silencing of this integrin in the MCF-7Dox cells by transfection with alpha5-specific siRNA markedly stimulated anoikis and increased sensitivity of the cells to doxorubicin. Alpha5beta1 silencing also leads to significant inhibition of the activity of kinases Akt and Erk2 in MCF-7Dox cells. Our results suggest that integrins alpha5beta1-induced signals, controlling distinct aspects of cell behavior, are conducted through the common signal pathways.

Reduction of lung metastasis, cell invasion, and adhesion in mouse melanoma by statin-induced blockade of the Rho/Rho-associated coiled-coil-containing protein kinase pathway

Background

Melanomas are highly malignant and have high metastatic potential; hence, there is a need for new therapeutic strategies to prevent cell metastasis. In the present study, we investigated whether statins inhibit tumor cell migration, invasion, adhesion, and metastasis in the B16BL6 mouse melanoma cell line.

Methods

The cytotoxicity of statins toward the B16BL6 cells were evaluated using a cell viability assay. As an experimental model, B16BL6 cells were intravenously injected into C57BL/6 mice. Cell migration and invasion were assessed using Boyden chamber assays. Cell adhesion analysis was performed using type I collagen-, type IV collagen-, fibronectin-, and laminin-coated plates. The mRNA levels, enzyme activities and protein levels of matrix metalloproteinases (MMPs) were determined using RT-PCR, activity assay kits, and Western blot analysis, respectively; the mRNA and protein levels of vary late antigens (VLAs) were also determined. The effects of statins on signal transduction molecules were determined by western blot analyses.

Results

We found that statins significantly inhibited lung metastasis, cell migration, invasion, and adhesion at concentrations that did not have cytotoxic effects on B16BL6 cells. Statins also inhibited the mRNA expressions and enzymatic activities of matrix metalloproteinases (MMPs). Moreover, they suppressed the mRNA and protein expressions of integrin α₂, integrin α₄, and integrin α₅ and decreased the membrane localization of Rho, and phosphorylated LIM kinase (LIMK) and myosin light chain (MLC).

Conclusions

The results indicated that statins suppressed the Rho/Rho-associated coiled-coil-containing protein kinase (ROCK) pathways, thereby inhibiting B16BL6 cell migration, invasion, adhesion, and metastasis. Furthermore, they markedly inhibited clinically evident metastasis. Thus, these findings suggest that statins have potential clinical applications for the treatment of tumor cell metastasis.

Investigation of integrin expression on the surface of osteoblast-like cells by atomic force microscopy

The transforming growth factor beta1 (TGF-beta1) is a human cytokine which has been demonstrated to modulate cell surface integrin repertoire. In this work integrin expression in response to TGF-beta1 stimulation has been investigated on the surface of human osteoblast-like cells. We used atomic force microscopy (AFM) and confocal laser scanning microscopy to assess integrin expression and to evaluate their distribution over the dorsal side of the plasma membrane. AFM probes have been covalently functionalized with monoclonal antibodies specific to the beta1 integrin subunit. Force curves have been collected in order to obtain maps of the interaction between the immobilized antibody and the respective cell membrane receptors. Adhesion peaks have been automatically detected by means of an ad hoc developed data analysis software. The specificity of the detected interactions has been assessed by adding free antibody in the solution and monitoring the dramatic decrease in the recorded interactions. In addition, the effect of TGF-beta1 treatment on both the fluorescence signal and the adhesion events has been tested. The level of expression of the beta1 integrin subunit was enhanced by TGF-beta1. As a further analysis, the adhesion force of the single living cells to the substrate was measured by laterally pushing the cell with the AFM tip and measuring the force necessary to displace it. The treatment with TGF-beta1 resulted in a decrease of the cell/substrate adhesion force. Results obtained by AFM have been validated by confocal laser scanning microscopy thus demonstrating the high potential of the AFM technique for the investigation of cell surface receptors distribution and trafficking at the nanoscale.

Lysyl oxidase-like 2 promotes migration in noninvasive breast cancer cells but not in normal breast epithelial cells

A growing number of studies indicate the importance of the lysyl oxidase family in the promotion of epithelial neoplasms towards their more aggressive forms. However, the role of individual family members in carcinoma progression has yet to be ascertained. In this study, we analyzed LOXL2 expression in malignantly transformed MCF-7 and normal MCF-10A mammary epithelial cell line clones stably transduced with LOXL2 in vitro, and in normal and cancerous breast tissue samples in vivo. We found LOXL2 to be catalytically active in both MCF-7 and MCF-10 clones. LOXL2 overexpression promoted a more mesenchymal morphology in both cell types, but LOXL2-induced increase in migratory ability could only be established in MCF-7 clones. We demonstrated altered localization of the LOXL2 protein in breast cancer tissue compared to normal mammary tissue, and altered localization and processing of LOXL2 protein in breast cancer cell lines compared to normal cell lines, which may allow LOXL2 to interact with different intra and extracellular components during tumor progression. Results support the role of LOXL2 in selectively promoting a metastatic phenotype in breast tumor cells. Additional data suggest epigenetic molecular mechanisms in tumor specific regulation of LOXL2 expression that could be explored as a molecular target in the prevention of breast cancer progression.

Biomechanical regulation of cell orientation and fate

Biomechanical regulation of tumor phenotypes have been noted for several decades, yet the function of mechanics in the co-evolution of the tumor epithelium and altered cancer extracellular matrix has not been appreciated until fairly recently. In this review, we examine the dynamic interaction between the developing epithelia and the extracellular matrix, and discuss how similar interactions are exploited by the genetically modified epithelium during tumor progression. We emphasize the process of mechanoreciprocity, which is a phenomenon observed during epithelial transformation, in which tension generated within the extracellular microenvironment induce and cooperate with opposing reactive forces within transformed epithelium to drive tumor progression and metastasis. We highlight the importance of matrix remodeling, and present a new, emerging paradigm that underscores the importance of tissue morphology as a key regulator of epithelial cell invasion and metastasis.

Tumor-stroma interactions of metastatic prostate cancer cell lines: analyses using microarrays

Tumor-stroma interactions are of great importance not only for the development and progression of primary prostate carcinoma but probably also for the establishment of metastasis. Fibroblasts are an important stromal cell type encountered by metastatic tumor cells at different sites. In previous investigations, we had found that media conditioned by three metastatic prostate cancer cell lines (LNCaP, PC-3, and DU-145) induced cultured nonprostatic fibroblasts to proliferate or to express matrix-metalloproteinase-1 considered important for tumor invasion. Fibroblast-conditioned media in turn stimulate proliferation of DU-145 cells and migration of PC-3 cells. Both tumor cells and fibroblasts secrete VEGF suggesting that not only metastatic but also stromal cells at metastatic sites contribute to the vascularization of metastasis necessary for continuous growth. In order to better understand the reciprocal tumor-stroma cross-talk in molecular terms we used the mRNA extracted from stimulated and unstimulated neoplastic and fibroblastic stromal cells for cDNA array hybridization using Affymetrix chips. The three prostate cell lines influenced the fibroblasts nearly in the same manner. In particular proteins involved in cell adhesion, cell-cell contact, and cell cycle regulation were downregulated in stimulated fibroblasts. In contrast, fibroblasts affected every prostate cancer cell line in different ways, which may be because of the different origin of the metastatic prostate cancer cell lines.

Prenatal bisphenol A exposure induces preneoplastic lesions in the mammary gland in Wistar rats

BACKGROUND

Humans are routinely exposed to bisphenol A (BPA), an estrogenic compound that leaches from dental materials, food and beverage containers, and other consumer products. Prenatal exposure to BPA has produced long-lasting and profound effects on rodent hormone-dependent tissues that are manifested 1-6 months after the end of exposure.

OBJECTIVE

The aim of the present work was to examine whether in utero exposure to BPA alters mammary gland development and increases its susceptibility to the carcinogen N-nitroso-N-methylurea (NMU).

METHODS

Pregnant Wistar rats were exposed to BPA (25 pg/kg body weight per day) or to vehicle. Female offspring were sacrificed on postnatal day (PND) 30, 50, 110, or 180. On PND50 a group of rats received a single subcarcinogenic dose of NMU (25 mg/kg) and they were sacrificed on either PND110 or PND180.

RESULTS

At puberty, animals exposed prenatally to BPA showed an increased proliferation/apoptosis ratio in both the epithelial and stromal compartments. During adulthood (PND110 and PND180), BPA-exposed animals showed an increased number of hyperplastic ducts and augmented stromal nuclear density. Moreover, the stroma associated with hyperplastic ducts showed signs of desmoplasia and contained an increased number of mast cells, suggesting a heightened risk of neoplastic transformation. Administration of a subcarcinogenic dose of NMU to animals exposed prenatally to BPA increased the percentage of hyperplastic ducts and induced the development of neoplastic lesions.

CONCLUSIONS

Our results demonstrate that the prenatal exposure to low doses of BPA perturbs mammary gland histoarchitecture and increases the carcinogenic susceptibility to a chemical challenge administered 50 days after the end of BPA exposure.

Altered expression pattern of topoisomerase IIalpha in ovarian tumor epithelial and stromal cells after platinum-based chemotherapy

OBJECTIVE

The aim of this study was to evaluate the expression of topoisomerase IIalpha (TOP2A) in epithelial and stromal cells of ovarian cancer.

METHODS

TOP2A expression was analyzed prospectively in normal and tumor epithelial and adjacent stromal cells using quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) after laser microdissection (n = 38), RNA in situ hybridization (n = 13), and immunohistochemistry (n = 69).

RESULTS

TOP2A mRNA was detected by RNA in situ hybridization in all ovarian cancer samples, with stronger hybridization signals in tumor epithelial cells compared to adjacent stromal cells. The same expression pattern was found by immunohistochemistry (P = .0001). Very interestingly, specific change was found in recurrent ovarian cancer after platinum-based chemotherapy: TOP2A expression decreased in tumor epithelial cells of recurrent ovarian cancer compared to primary ovarian cancer (P = .056), whereas it increased in tumor-adjacent stromal cells in carboplatin-treated recurrent tumors compared to primary ovarian cancer (P = .023).

CONCLUSION

TOP2A mRNA and protein expression in ovarian cancer exhibits specific patterns in tumor epithelial and adjacent stromal cells, which are differentially modulated after platinum-based chemotherapy. These data support the recently discovered importance of the stromal compartment in tumor progression and suggest that tumor stromal cells might be relevant to the development of chemotherapy resistance in ovarian cancer.

The role of beta1 integrin subfamily in anchorage-dependent apoptosis of breast carcinoma cells differing in multidrug resistance

Integrin expression was investigated in MCF-7 human breast adenocarcinoma line and in the MCF-7Dox line, which was selected from MCF-7 by a resistance to multiple antitumor drugs (MDR). We have shown that acquisition of MDR was accompanied by a drastically reduced expression of some integrins of the beta1-subfamily (alpha2beta1, alpha3beta1, alpha6beta1) and of alpha vbeta5 intergin in the adenocarcinoma cells. In contrast, expression of alpha5beta1 integrin was markedly increased in the MDR cells. Along with multiple antitumor drug resistance, MCF-7Dox cells demonstrate elevated resistance to anchorage-dependent apoptosis (anoikis) and enhanced in vitro invasive activity. To elucidate the implication of beta1-integrins in the above phenotypic modifications, the effect of beta1-integrin signaling was assayed. Stimulation of beta1-mediated signaling was accomplished by treating of the cells with antibodies to the beta1-subunit common for members of the beta1-subfamily. These data show that activation of beta1-integrin signaling markedly upregulated anoikis of the adenocarcinoma cells.

Separation, cultivation and biological characteristics of oral carcinoma-associated fibroblasts

OBJECTIVES

Carcinoma-associated fibroblasts (CAFs) have been suggested to regulate the initiation and progression of many types of solid tumors. The aim of the study was to separate, cultivate, identify oral CAFs, and to investigate their biological characteristics.

MATERIALS AND METHODS

The primary CAFs and normal fibroblasts (NFs) of the tongue were obtained by tissue culture. Then cells were dissociated by 0.25% trypsin and purified by curettage method combining with trypsinization. The cells were verified according to morphological observation and immunohistochemical staining of certain proteins. Multiple proliferation indexes and karyotype of the cells were assayed.

RESULTS

Third passage purified oral CAFs and NFs were attained successfully. The morphological characteristics of the CAFs changed significantly comparing to the NFs. The CAFs showed positive staining for vimentin, alpha-smooth muscle actin and matrix metalloproteinases-2. The proliferation and mitosis ability of the CAFs were significantly increased compared with the NFs (P < 0.05). No karyotypic abnormalities were found in the CAFs.

CONCLUSIONS

There were obvious differences in the biological characteristics between oral CAFs and NFs. The results may provide us an experimental foundation for further studies on the roles of CAFs in the initiation and progression of oral cancer.

Resensitization of breast cancer cells to anoikis by Tropomyosin-1: role of Rho kinase-dependent cytoskeleton and adhesion

Two most common properties of malignant cells are the presence of aberrant actin cytoskeleton and resistance to anoikis. Suppression of several key cytoskeletal proteins, including tropomyosin-1 (TM1), during neoplastic transformation is hypothesized to contribute to the altered cytoskeleton and neoplastic phenotype. Using TM1 as a paradigm, we have shown that cytoskeletal proteins induce anoikis in breast cancer (MCF-7 and MDA MB 231) cells. Here, we have tested the hypothesis that TM1-mediated cytoskeletal changes regulate integrin activity and the sensitivity to anoikis. TM1 expression in MDA MB 231 cells promotes the assembly of stress fibers, induces rapid anoikis via caspase-dependent pathways involving the release of cytochrome c. Further, TM1 inhibits binding of MDA MB 231 cells to collagen I, but promotes adhesion to laminin. Inhibition of Rho kinase disrupts TM1-mediated cytoskeletal reorganization and adhesion to the extracellular matrix components, whereas the parental cells attach to collagen I, spread and form extensive actin meshwork in the presence of Rho kinase inhibitor, underscoring the differences in parental and TM1-transduced breast cancer cells. Further, treatment with the cytoskeletal disrupting drugs rescues the cells from TM1-induced anoikis. These new findings demonstrate that the aberrant cytoskeleton contributes to neoplastic transformation by conferring resistance to anoikis. Restoration of stress fiber network through enhanced expression of key cytoskeletal proteins may modulate the activity of focal adhesions and sensitize the neoplastic cells to anoikis.

A novel in vitro model of human mesothelioma for studying tumor biology and apoptotic resistance

Like many tumors, malignant mesothelioma exhibits significant chemoresistance and resistance to apoptosis in vivo that is not seen in current in vitro models. To study the mechanisms of this multicellular resistance, biologically relevant in vitro models are necessary. Therefore, we characterized and tested human mesothelioma tissue grown in vitro as tumor fragment spheroids. After 5-10 d in culture, fragments from each of 15 human mesothelioma tumors rounded into spheroids. The tumor fragment spheroids maintained multiple characteristics of the original tumors for up to 3 mo including the presence of viable mesothelioma cells, macrophages, and a collagen-rich stroma. In 14-d-old spheroids, mesothelioma cells showed the same proliferation rate and expression of a death receptor, DR5, as in the original tumor. To determine responses to treatment, we treated tumor fragment spheroids grown from three separate tumors with agents, TNF-related apoptosis-inducing ligand (TRAIL) plus cycloheximide, that induced near total apoptosis in three human mesothelioma cell lines (M28, REN, MS-1) grown as monolayers (94 +/- 6% apoptosis; mean +/- SEM). Compared with mesothelioma cells in monolayers, mesothelioma cells in the spheroids were resistant to TRAIL plus cycloheximide (32 +/- 4% apoptosis; mean +/- SEM). Apoptotic resistance of mesothelioma cells was significantly reduced by inhibiting either the PI3K/Akt pathway with LY294002 (47 +/- 6% apoptosis) or the mTOR pathway with rapamycin (50 +/- 17% apoptosis). We conclude that human mesothelioma can be maintained in vitro in a biologically relevant model that exhibits apoptotic resistance, thereby permitting study of its tumor biology and of novel approaches to therapy.

Aging, tumor suppression and cancer: high wire-act!

Evolutionary theory holds that aging is a consequence of the declining force of natural selection with age. We discuss here the evidence that among the causes of aging in complex multicellular organisms, such as mammals, is the antagonistically pleiotropic effects of the cellular responses that protect the organism from cancer. Cancer is relatively rare in young mammals, owing in large measure to the activity of tumor suppressor mechanisms. These mechanisms either protect the genome from damage and/or mutations, or they elicit cellular responses-apoptosis or senescence--that eliminate or prevent the proliferation of somatic cells at risk for neoplastic transformation. We focus here on the senescence response, reviewing its causes, regulation and effects. In addition, we describe recent data that support the idea that both senescence and apoptosis may indeed be the double-edged swords predicted by the evolutionary hypothesis of antagonistic pleiotropy-protecting organisms from cancer early in life, but promoting aging phenotypes, including late life cancer, in older organisms.

Mammary ECM composition and function are altered by reproductive state

To address whether reproductive state alters mammary gland extracellular matrix (ECM) composition and function, ECM was isolated from nulliparous, pregnant, lactating, involuting, and regressed rat mammary glands. The ECM composition of fibronectin, tenascin, laminin, clusterin, and MMPs was found to vary dramatically with reproductive state. In 3-dimensional (3-D) culture, we identified novel effects of these endogenous mammary matrices on mammary epithelial cells. Specifically we found that (1) matrix isolated from nulliparous animals promoted the formation of epithelial ducts with bifurcation, (2) matrix isolated from mid-involuting mammary glands induced cell death, (3) matrix isolated from late-stage involuting glands restored glandular development, while (4) matrix isolated from parous animals restricted glandular morphogenesis. Our data were consistent with mammary gland ECM facilitating epithelial cell proliferation, differentiation, death, and glandular reorganization that occur during the pregnancy and involution cycle. Further, we show that the parous gland has persistent changes in ECM function. Cumulatively, our data demonstrated that the microenvironment of the normal adult mammary gland is highly plastic, which has important implications for mammary tumor cell progression and dormancy. These data also raised the possibility of targeting mammary matrix production with preventive or therapeutic interventions.

A visual-quantitative analysis of fibroblastic stromagenesis in breast cancer progression

One fundamental difference between normal and transformed cells is the way they interact with their immediate environment. Exploring this difference is crucial for understanding the pathobiology of cancer progression. Benign epithelial tumors are constrained by a surrounding stroma consisting, among other cells, of fibroblasts embedded within fibrillar three-dimensional matrices. However, at a critical point in tumor progression, tumor cells become altered and overcome the barrier, inducing changes in the stroma, which promote, rather than impede, tumor progression. Inherited or acquired genetic aberrations affecting mammary gland epithelia are usually blamed for promoting neoplasia in individuals at "high risk" for breast cancer. However, in addition to these epithelial aberrations certain individuals possess permissive breast stroma. The occurrence of this permissive stroma results in a predisposition for cancer initiation or progression. Here we review stromagenic stages, experimental 3D systems, and discuss digital imaging analyses suitable for uncovering the mechanisms behind fibroblastic breast stromagenesis.

The tension mounts: mechanics meets morphogenesis and malignancy

The tissue microenvironment regulates mammary gland development and tissue homeostasis through soluble, insoluble and cellular cues that operate within the three dimensional architecture of the gland. Disruption of these critical cues and loss of tissue architecture characterize breast tumors. The developing and lactating mammary gland are also subject to a plethora of tensional forces that shape the morphology of the gland and orchestrate its functionally differentiated state. Moreover, malignant transformation of the breast is associated with dramatic changes in gland tension that include elevated compression forces, high tensional resistance stresses and increased extracellular matrix stiffness. Chronically increased mammary gland tension may influence tumor growth, perturb tissue morphogenesis, facilitate tumor invasion, and alter tumor survival and treatment responsiveness. Because mammary tissue differentiation is compromised by high mechanical force and transformed cells exhibit altered mechanoresponsiveness, malignant transformation of the breast may be functionally linked to perturbed tensional-homeostasis. Accordingly, it will be important to define the role of tensional force in mammary gland development and tumorigenesis. Additionally, it will be critical to identify the key molecular elements regulating tensional-homeostasis of the mammary gland and thereafter to characterize their associated mechanotransduction pathways.

Malignant mammary cells acquire independence from extracellular context for regulation of estrogen receptor alpha

Interactions between luminal epithelial cells and their surrounding microenvironment govern the normal development and function of the mammary gland. Alterations of these interactions can induce abnormal intracellular signaling pathways that affect the development and progression of breast tumors. One critical component of mammary gland development, as well as breast cancer progression, is the expression of estrogen receptors. In a previous study using cultured nonmalignant mammary epithelial cells, we found that the basement membrane molecules, laminin-1 and collagen-IV, were involved in maintenance of estrogen receptor (ER) alpha expression, and that this response could be interfered with by disrupting cell-extracellular matrix adhesion. Here we use phenotypically normal mammary epithelial SCp2 cells to dissect the promoter region of the ERalpha that is involved in the selective response to basement membrane. We also analyze the alteration of this response in SCg6 cells, a malignant cell line that shares a common lineage with the SCp2 cells, to provide insight into the relative overexpression of ERalpha and the unresponsiveness to basement membrane regulation found in those malignant cells. Evidence is presented to show the relevance of the cross-talk between different signaling pathways in the constitution of a functional tissue organization and how this integration may be disrupted in the malignant phenotype.

Extracellular matrix enhances heregulin-dependent BRCA1 phosphorylation and suppresses BRCA1 expression through its C terminus

Germ line mutations in the breast cancer susceptibility gene BRCA1 account for the increased risk of early onset of familial breast cancer, whereas overexpression of the ErbB family of receptor tyrosine kinases has been linked to the development of nonfamilial or sporadic breast cancer. To analyze whether there is a link between these two regulatory molecules, we studied the effects of ErbB-2 activation by heregulin (HRG) on BRCA1 function. It was previously demonstrated that HRG induced the phosphorylation of BRCA1, which was mediated by the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Since altered interaction between cells and the surrounding extracellular matrix (ECM) is a common feature in a variety of tumors and since ECM modulates intracellular signaling, we hypothesized that ECM may affect the expression and HRG-dependent phosphorylation of BRCA1. Following stimulation by HRG, a strong increase in [(3)H]thymidine incorporation was observed in human T47D breast cancer cells seeded on plastic (PL). When T47D cells were seeded on laminin (LAM) or Matrigel, HRG induced a significantly higher proliferation than it did in cells seeded on PL. T47D cells seeded on poly-L-lysine had an abrogated mitogenic response, indicating the involvement of integrins in this process. HRG treatment induced a transient phosphorylation of BRCA1 that was enhanced in T47D cells grown on LAM. LAM-enhanced BRCA1 phosphorylation was mediated through alpha(6) integrin upon HRG stimulation. Accordingly, T47D cells grown on LAM had the greatest increase in ErbB-2 activation, PI3K activity, and phosphorylation of Akt. A similar pattern of BRCA1 mRNA expression was observed when T47D cells were seeded on PL, LAM, or COL4. There was a significant decrease in the steady state of the BRCA1 mRNA level on both the LAM and COL4 matrices compared to that for cells seeded on PL. In addition, HRG stimulation caused a significant decrease in BRCA1 mRNA expression that was dependent on protein synthesis. Pretreatment with both the calpain inhibitor ALLN (N-acetyl-Leu-Leu-norleucinal) and the proteosome inhibitor lactacystin inhibited the HRG-induced down-regulation of BRCA1 mRNA expression. Likewise, there was a strong decrease in the protein level of BRCA1 in T47D cells 4 h after treatment with HRG compared to its level in control nontreated T47D cells. Pretreatment with the proteosome inhibitors ALLN, lactacystin, and PSI [N-benzyloxycarbonyl-Ile-Glu-(O-t-butyl)-Ala-leucinal] inhibited also the HRG-induced down-regulation of BRCA1 protein in breast cancer cells. Interestingly, BRCA1 mRNA expression in HCC-1937 breast cancer cells, which express C-terminally truncated BRCA1, was not affected by either LAM or CL4. No phosphorylation of BRCA1 from HCC-1937 cells was observed in response to HRG. While Cdk4 phosphorylated wild-type BRCA1 in response to HRG in T47D cells, Cdk4 failed to phosphorylate the truncated form of BRCA1 in HCC-1937 cells. Furthermore, overexpression of wild-type BRCA1 in HCC-1937 cells resulted in the phosphorylation of BRCA1 and decreased BRCA1 expression upon HRG stimulation while overexpression of truncated BRCA1 in T47D cells resulted in a lack of BRCA1 phosphorylation and restoration of BRCA1 expression. These findings suggest that ECM enhances HRG-dependent BRCA1 phosphorylation and that ECM and HRG down-regulate BRCA1 expression in breast cancer cells. Furthermore, ECM suppresses BRCA1 expression through the C terminus of BRCA1.

Cancer and aging: a model for the cancer promoting effects of the aging stroma

The incidence of cancer rises exponentially with age in humans and many other mammalian species. Malignant tumors are caused by an accumulation of oncogenic mutations. In addition, malignant tumorigenesis requires a permissive tissue environment in which mutant cells can survive, proliferate, and express their neoplastic phenotype. We propose that the age-related increase in cancer results from a synergy between the accumulation of mutations and age-related, pro-oncogenic changes in the tissue milieu. Most age-related cancers derive from the epithelial cells of renewable tissues. An important element of epithelial tissues is the stroma, the sub-epithelial layer composed of extracellular matrix and several cell types. The stroma is maintained, remodeled and repaired by resident fibroblasts, supports and instructs the epithelium, and is essential for epithelial function. One change that occurs in tissues during aging is the accumulation of epithelial cells and fibroblasts that have undergone cellular senescence. Cellular senescence irreversibly arrests proliferation in response to damage or stimuli that put cells at risk for neoplastic transformation. Senescent cells secrete factors that can disrupt tissue architecture and/or stimulate nearby cells to proliferate. We therefore speculate that their presence may create a pro-oncogenic tissue environment that synergizes with oncogenic mutations to drive the rise in cancer incidence with age. Recent evidence lends support to this idea, and suggests that senescent stromal fibroblasts may be particularly adept at creating a tissue environment that can promote the development of age-related epithelial cancers.

Bombesin-dependent pro-MMP-9 activation in prostatic cancer cells requires beta1 integrin engagement

Bombesin-like peptides, including the mammalian homologue gastrin-releasing peptide, are highly expressed and secreted by neuroendocrine cells in prostate carcinoma tissues and are likely to be related to the progression of this neoplastic disease. Previously, we demonstrated that bombesin increased migration and protease expression in androgen-independent cells. In this work we show that bombesin is able to activate pro-MMP-9 through a mechanism involving the beta1 integrin subunit. In fact, MMP-9 processing was evident only when beta1 integrin was engaged with specific adhesive substrates, such as type I collagen, or when cells were seeded on dishes coated with antibodies against beta1 integrin, resulting in activation of the surface ligand. When exogenous pro-MMP-9 was added to PC3 cells, MMP-9 active forms were produced within 30 min by bombesin-treated cultures while control cultures expressed activated forms only after a longer time and at lower levels. MMP-9 activation required cytoskeleton integrity since this effect was abolished by cytochalasin D. Engagement of beta1 integrin caused an increased membrane-linked uPA activity which was required for MMP-9 activation. The cross talk between bombesin- and beta1-integrin-engaged signals seems to be crucial for the modulation of both membrane-linked uPA activity and MMP-9 activation and triggers complex intracellular signaling pathways requiring activation of tyrosine kinase activity, including that of src and PI3K. The beta1 integrin may be considered an important mechanism by which bombesin induces MMP-9 activation. This finding supports the idea that cellular responses to growth factors may be driven by cell-matrix interactions and stresses the role of neuroendocrine factors in prostate carcinoma progression.

Quantification of epithelial cells in coculture with fibroblasts by fluorescence image analysis

BACKGROUND

To demonstrate that senescent fibroblasts stimulate the proliferation and neoplastic transformation of premalignant epithelial cells (Krtolica et al.: Proc Natl Acad Sci USA 98:12072-12077, 2001), we developed methods to quantify the proliferation of epithelial cells cocultured with fibroblasts.

METHODS

We stained epithelial-fibroblast cocultures with the fluorescent DNA-intercalating dye 4,6-diamidino-2-phenylindole (DAPI), or expressed green fluorescent protein (GFP) in the epithelial cells, and then cultured them with fibroblasts. The cocultures were photographed under an inverted microscope with appropriate filters, and the fluorescent images were captured with a digital camera. We modified an image analysis program to selectively recognize the smaller, more intensely fluorescent epithelial cell nuclei in DAPI-stained cultures and used the program to quantify areas with DAPI fluorescence generated by epithelial nuclei or GFP fluorescence generated by epithelial cells in each field.

RESULTS

Analysis of the image areas with DAPI and GFP fluorescences produced nearly identical quantification of epithelial cells in coculture with fibroblasts. We confirmed these results by manual counting. In addition, GFP labeling permitted kinetic studies of the same coculture over multiple time points.

CONCLUSIONS

The image analysis-based quantification method we describe here is an easy and reliable way to monitor cells in coculture and should be useful for a variety of cell biological studies.

Differential interactions between IGFBP-3 and transforming growth factor-beta (TGF-beta) in normal vs cancerous breast epithelial cells

In addition to modulating insulin-like growth factors action, it is now clear that insulin-like growth factor-binding protein-3 also has intrinsic effects on cell growth and survival. We have compared the effects of insulin-like growth factor-binding protein-3 and transforming growth factor-beta on cell proliferation and death of Hs578T cells and the normal breast epithelial cell line, MCF-10A. The growth of MCF-10A cells was inhibited at low concentrations of insulin-like growth factor-binding protein-3 but stimulated at high concentrations. These differential effects were unaffected in the presence of an insulin-like growth factor-I receptor antagonist. A synthetic peptide corresponding to the serine phosphorylation domain of insulin-like growth factor-binding protein-3 (that does not bind to insulin-like growth factors) also mimicked these differential actions. The growth of both cell lines was significantly inhibited by transforming growth factor-beta, this was associated with a 14-fold increase of insulin-like growth factor-binding protein-3 secreted by the Hs578T cells but a five-fold decrease of insulin-like growth factor-binding protein-3 secreted by MCF-10A cells. Replacement doses of exogenous insulin-like growth factor-binding protein-3 overcame the transforming growth factor-beta-induced growth inhibition in the MCF-10A cells. Cell death induced by ceramide was significantly reduced by insulin-like growth factor-binding protein-3 in the MCF-10A cells and depleting insulin-like growth factor-binding protein-3 with transforming growth factor-beta in these cells consequently increased their susceptibility to ceramide. In contrast, insulin-like growth factor-binding protein-3 enhanced apoptosis induced by ceramide in the Hs578T cells but transforming growth factor-beta treated Hs578T cells were resistant to apoptosis. The addition of anti-sense mRNA to insulin-like growth factor-binding protein-3 significantly abrogated this effect of transforming growth factor-beta. These data indicate that insulin-like growth factor-binding protein-3 has intrinsic activity capable of inhibiting or enhancing the growth and survival of breast epithelial cells depending on the cell line and exposure to other cytokines.

The macrophage growth factor CSF-1 in mammary gland development and tumor progression

Colony stimulating factor 1 (CSF-1), a major regulator of the mononuclear phagocytic lineage, is expressed in more than 70% of human breast cancers and its expression is correlated with poor prognosis. Studies of CSF-1 null mutant mice demonstrated that CSF-1 plays an important role in normal mammary ductal development as well as in mammary tumor progression to metastasis. CSF-1 regulates these processes through the recruitment and regulation of macrophages, cells that become associated with mammary tumors and the terminal end buds at the end of the growing ducts. This phenomenon suggests that the tumors subvert normal developmental processes to allow invasion into the surrounding stroma, a process that gives the tumor access to the vasculature and consequently the promotion of metastasis. In addition, soluble CSF-1 secreted from the tumor acts to divert antitumor macrophage responses and suppresses the differentiation of mature tumor-antigen-presenting dendritic cell This review discusses these observations in detail and attempts to fit them into a larger picture of CSF-1 and macrophage action in the regulation of normal mammary gland development and tumor progression.

Conformational effects of volatile anesthetics on the membrane-bound acetylcholine receptor protein: facilitation of the agonist-induced affinity conversion

The rate of the carbamylcholine-induced affinity conversion of the membrane-bound acetylcholine receptor protein from Torpedo californica is enhanced by pretreatment of the membranes under an atmosphere of 3% halothane or 1% chloroform. The enhancement is much more pronounced in the presence of low rather than high concentrations of carbamylcholine since the volatile anesthetics alter the apparent dissociation constant for carbamylcholine from 17 to 3 microM without affecting the first-order rate constant for the ligand-induced conversion (0.07 s-1). These results indicate that the acetylcholine receptor is assuming a conformational form with intermediate affinity for carbamylcholine in addition to the previously described low- and high-affinity forms. The dissociation constants for carbamylcholine obtained from kinetic studies of the carbamylcholine-induced transition are 3-15-fold lower than those obtained as inhibition constants from the rate of 125I-labeled alpha-bungarotoxin binding to the low-affinity conformer of the acetylcholine receptor protein. This pattern, observed in both the presence and absence of anesthetic, provides further evidence that the acetylcholine receptor has nonequivalent ligand binding sites for carbamylcholine.