Urokinase-receptor/integrin complexes are functionally involved in adhesion and progression of human breast cancer in vivo

Urokinase-type plasminogen activator receptor (uPAR) as a therapeutic target in cancer

Urokinase-type plasminogen activator receptor (uPAR) is an attractive target for the treatment of cancer, because it is expressed at low levels in healthy tissues but at high levels in malignant tumours. uPAR is closely related to the invasion and metastasis of malignant tumours, plays important roles in the degradation of extracellular matrix (ECM), tumour angiogenesis, cell proliferation and apoptosis, and is associated with the multidrug resistance (MDR) of tumour cells, which has important guiding significance for the judgement of tumor malignancy and prognosis. Several uPAR-targeted antitumour therapeutic agents have been developed to suppress tumour growth, metastatic processes and drug resistance. Here, we review the recent advances in the development of uPAR-targeted antitumor therapeutic strategies, including nanoplatforms carrying therapeutic agents, photodynamic therapy (PDT)/photothermal therapy (PTT) platforms, oncolytic virotherapy, gene therapy technologies, monoclonal antibody therapy and tumour immunotherapy, to promote the translation of these therapeutic agents to clinical applications.

Therapeutic Strategies Targeting Urokinase and Its Receptor in Cancer

Several studies have ascertained that uPA and uPAR do participate in tumor progression and metastasis and are involved in cell adhesion, migration, invasion and survival, as well as angiogenesis. Increased levels of uPA and uPAR in tumor tissues, stroma and biological fluids correlate with adverse clinic-pathologic features and poor patient outcomes. After binding to uPAR, uPA activates plasminogen to plasmin, a broad-spectrum matrix- and fibrin-degrading enzyme able to facilitate tumor cell invasion and dissemination to distant sites. Moreover, uPAR activated by uPA regulates most cancer cell activities by interacting with a broad range of cell membrane receptors. These findings make uPA and uPAR not only promising diagnostic and prognostic markers but also attractive targets for developing anticancer therapies. In this review, we debate the uPA/uPAR structure-function relationship as well as give an update on the molecules that interfere with or inhibit uPA/uPAR functions. Additionally, the possible clinical development of these compounds is discussed.

Fibrinolytic System and Cancer: Diagnostic and Therapeutic Applications

Fibrinolysis is a crucial physiological process that helps to maintain a hemostatic balance by counteracting excessive thrombosis. The components of the fibrinolytic system are well established and are associated with a wide array of physiological and pathophysiological processes. The aberrant expression of several components, especially urokinase-type plasminogen activator (uPA), its cognate receptor uPAR, and plasminogen activator inhibitor-1 (PAI-1), has shown a direct correlation with increased tumor growth, invasiveness, and metastasis. As a result, targeting the fibrinolytic system has been of great interest in the field of cancer biology. Even though there is a plethora of encouraging preclinical evidence on the potential therapeutic benefits of targeting the key oncogenic components of the fibrinolytic system, none of them made it from “bench to bedside” due to a limited number of clinical trials on them. This review summarizes our existing understanding of the various diagnostic and therapeutic strategies targeting the fibrinolytic system during cancer.

The Urokinase Receptor: A Multifunctional Receptor in Cancer Cell Biology. Therapeutic Implications

Proteolysis is a key event in several biological processes; proteolysis must be tightly controlled because its improper activation leads to dramatic consequences. Deregulation of proteolytic activity characterizes many pathological conditions, including cancer. The plasminogen activation (PA) system plays a key role in cancer; it includes the serine-protease urokinase-type plasminogen activator (uPA). uPA binds to a specific cellular receptor (uPAR), which concentrates proteolytic activity at the cell surface, thus supporting cell migration. However, a large body of evidence clearly showed uPAR involvement in the biology of cancer cell independently of the proteolytic activity of its ligand. In this review we will first describe this multifunctional molecule and then we will discuss how uPAR can sustain most of cancer hallmarks, which represent the biological capabilities acquired during the multistep cancer development. Finally, we will illustrate the main data available in the literature on uPAR as a cancer biomarker and a molecular target in anti-cancer therapy.

Development of inhibitors for uPAR: blocking the interaction of uPAR with its partners

Urokinase-type plasminogen activator receptor (uPAR) mediates a multitude of biological activities, has key roles in several clinical indications, including malignancies and inflammation, and, thus, has attracted intensive research over the past few decades. The pleiotropic functions of uPAR can be attributed to its interaction with an array of partners. Many inhibitors have been developed to intervene with the interaction of uPAR with these partners. Here, we review the development of these classes of uPAR inhibitor and their inhibitory mechanisms to promote the translation of these inhibitors to clinical applications.

Small-Molecule Inhibition of the uPAR ⋅ uPA Interaction by Conformational Selection

The urokinase receptor (uPAR) is a cell surface receptor that binds to the serine protease urokinase-type plasminogen activator (uPA) with high affinity. This interaction is beneficial for extravascular fibrin clearance, but it has also been associated with a broad range of pathological conditions including cancer, atherosclerosis, and kidney disease. Here, starting with a small molecule that we previously discovered by virtual screening and cheminformatics analysis, we design and synthesize several derivatives that were tested for binding and inhibition of the uPAR ⋅ uPA interaction. To confirm the binding site and establish a binding mode of the compounds, we carried out biophysical studies using uPAR mutants, among them uPAR^H47C-N259C , a mutant previously developed to mimic the structure of uPA-bound uPAR. Remarkably, a substantial increase in potency is observed for inhibition of uPAR^H47C-N259C binding to uPA compared to wild-type uPAR, consistent with our use of the structure of uPAR in its uPA-bound state to design small-molecule uPAR ⋅ uPA antagonists. Combined with the biophysical studies, molecular docking followed by extensive explicit-solvent molecular dynamics simulations and MM-GBSA free energy calculations yielded the most favorable binding pose of the compound. Collectively, these results suggest that potent inhibition of uPAR binding to uPA with small molecules will likely only be achieved by developing small molecules that exhibit high-affinity to solution apo structures of uPAR, rather than uPA-bound structures of the receptor.

Urokinase-type plasminogen activator receptor (uPAR) expression enhances invasion and metastasis in RAS mutated tumors

The urokinase-type plasminogen activator receptor (uPAR) is a GPI-anchored cell membrane receptor that focuses urokinase (uPA) proteolytic activity on the cell surface. Its expression is increased in many human cancers, including non-small cell lung cancer (NSCLC) and colorectal cancer (CRC), and correlates with a poor prognosis and early invasion and metastasis. uPAR is able to control, through a cross-talk with tyrosine kinase receptors, the shift between tumor dormancy and proliferation, that usually precedes metastasis formation. Therefore, we investigated the role of uPAR expression in RAS mutated NSCLC and CRC cells. In this study we provided evidence, for the first time, that RAS mutational condition is functionally correlated to uPAR overexpression in NSCLC and CRC cancer cell lines and patient-derived tissue samples. Moreover, oncogenic features related to uPAR overexpression in RAS mutated NSCLC and CRC, such as adhesion, migration and metastatic process may be targeted, in vitro and in vivo, by new anti-uPAR small molecules, specific inhibitors of uPAR-vitronectin interaction. Therefore, anti-uPAR drugs could represent an effective pharmacological strategy for NSCLC and CRC patients carrying RAS mutations.

Serum levels of urokinase-type plasminogen activator in healthy dogs and oncologic canine patients

Aim:

Urokinase plasminogen activator (uPA) has been scarcely studied in veterinary oncology. The aim of this study was to determine the uPA serum concentrations in healthy and oncologic canine patients and to investigate its potential value as a tumor biomarker.

Materials and Methods:

Serum uPA concentrations of healthy and oncologic canine patients were measured by enzyme-linked immunosorbent assay. Their relationships with the dogs’ health status and tumor characteristics were analyzed through ANOVA and independent t-test.

Results:

There were no significant differences between mean serum values (±standard deviation) of healthy dogs (0.19±0.13 ng/ml) and oncologic canine patients (0.22±0.33 ng/ml), or between dogs with benign or malignant tumors, and with or without metastases, although the latter tended to show higher uPA serum levels.

Conclusion:

This is the first study describing the uPA serum levels in dogs. Although its results do not support uPA as a tumor biomarker, higher uPA levels in dogs with metastatic neoplasms may reflect the role of the enzyme in tumor progression.

Avβ3 integrin: Pathogenetic role in osteotropic tumors

The interplay of cancer cells and accessory cells within the microenvironment drives signals regulating the proliferation, migration and skeleton colonization. Osteotropism of tumor cells depends on chemokine activation, production of soluble factors and defective gene expression that cooperate within the metastatic niche to the bone resorbing functions of osteoclasts. Adhesion of cancer cells to the extracellular matrix is regulated by integrins as αvβ3 that enhances their invasiveness, pro-tumor angiogenesis and skeleton invasion. Therefore, αvβ3 signaling is implicated in enhancing osteotropism of breast and prostate cancers as well as of multiple myeloma. Targeting of αvβ3 has been adopted to restrain the tumor progression in several cancer models leading to improvement of overall survival as effect of the reduction of both tumor burden and osteotropism by malignant cells. Here, we review both the role of αvβ3 in malignant osteoclastogenesis and its potential targeting to restrain the bone colonization by skeleton invading cancers.

In vitro microenvironments to study breast cancer bone colonisation

Bone metastasis occurs frequently in patients with advanced breast cancer and is a major cause of morbidity and mortality in these patients. In order to advance current therapies, the mechanisms leading to the formation of bone metastases and their pathophysiology have to be better understood. Several in vitro models have been developed for systematic studies of interactions between breast cancer cells and the bone microenvironment. Such models can provide insights into the molecular basis of bone metastatic colonisation and also may provide a useful platform to design more physiologically relevant drug testing assays. This review describes different in vitro approaches and discusses their advantages and disadvantages.

Involvement of urokinase-type plasminogen activator system in cancer: an overview

Currently, there are several studies supporting the role of urokinase-type plasminogen activator (uPA) system in cancer. The association of uPA to its receptor triggers the conversion of plasminogen into plasmin. This process is regulated by the uPA inhibitors (PAI-1 and PAI-2). Plasmin promotes degradation of basement membrane and extracellular matrix (ECM) components as well as activation of ECM latent matrix metalloproteases. Degradation and remodeling of the surrounding tissues is crucial in the early steps of tumor progression by facilitating expansion of the tumor mass, release of tumor growth factors, activation of cytokines as well as induction of tumor cell proliferation, migration, and invasion. Hence, many tumors showed a correlation between uPA system component levels and tumor aggressiveness and survival. Therefore, this review summarizes the structure of the uPA system, its contribution to cancer progression, and the clinical relevance of uPA family members in cancer diagnosis. In addition, the review evaluates the significance of uPA system in the development of cancer-targeted therapies.

Probing binding and cellular activity of pyrrolidinone and piperidinone small molecules targeting the urokinase receptor

The urokinase receptor (uPAR) is a cell-surface protein that is part of an intricate web of transient and tight protein interactions that promote cancer cell invasion and metastasis. Here, we evaluate the binding and biological activity of a new class of pyrrolidinone and piperidinone compounds, along with derivatives of previously-identified pyrazole and propylamine compounds. Competition assays revealed that the compounds displace a fluorescently labeled peptide (AE147-FAM) with inhibition constant (Ki ) values ranging from 6 to 63 μM. Structure-based computational pharmacophore analysis followed by extensive explicit-solvent molecular dynamics (MD) simulations and free energy calculations suggested the pyrazole-based and piperidinone-based compounds adopt different binding modes, despite their similar two-dimensional structures. In cells, pyrazole-based compounds showed significant inhibition of breast adenocarcinoma (MDA-MB-231) and pancreatic ductal adenocarcinoma (PDAC) cell proliferation, but piperidinone-containing compounds exhibited no cytotoxicity even at concentrations of 100 μM. One pyrazole-based compound impaired MDA-MB-231 invasion, adhesion, and migration in a concentration-dependent manner, while the piperidinone inhibited only invasion. The pyrazole derivative inhibited matrix metalloprotease-9 (gelatinase) activity in a concentration-dependent manner, while the piperidinone showed no effect suggesting different mechanisms for inhibition of cell invasion. Signaling studies further highlighted these differences, showing that pyrazole compounds completely inhibited ERK phosphorylation and impaired HIF1α and NF-κB signaling, while pyrrolidinones and piperidinones had no effect. Annexin V staining suggested that the effect of the pyrazole-based compound on proliferation was due to cell killing through an apoptotic mechanism. The compounds identified represent valuable leads in the design of further derivatives with higher affinities and potential probes to unravel the protein-protein interactions of uPAR.

Discovery of new small molecules targeting the vitronectin-binding site of the urokinase receptor that block cancer cell invasion

Besides focusing urokinase (uPA) proteolytic activity on the cell membrane, the uPA receptor (uPAR) is able to bind vitronectin, via a direct binding site. Furthermore, uPAR interacts with other cell surface receptors, such as integrins, receptor tyrosine kinases, and chemotaxis receptors, triggering cell-signaling pathways that promote tumor progression. The ability of uPAR to coordinate binding and degradation of extracellular matrix (ECM) and cell signaling makes it an attractive therapeutic target in cancer. We used structure-based virtual screening (SB-VS) to search for small molecules targeting the uPAR-binding site for vitronectin. Forty-one compounds were identified and tested on uPAR-negative HEK-293 epithelial cells transfected with uPAR (uPAR-293 cells), using the parental cell line transfected with the empty vector (V-293 cells) as a control. Compounds 6 and 37 selectively inhibited uPAR-293 cell adhesion to vitronectin and the resulting changes in cell morphology and signal transduction, without exerting any effect on V-293 cells. Compounds 6 and 37 inhibited uPAR-293 cell binding to vitronectin with IC50 values of 3.6 and 1.2 μmol/L, respectively. Compounds 6 and 37 targeted S88 and R91, key residues for uPAR binding to vitronectin but also for uPAR interaction with the fMLF family of chemotaxis receptors (fMLF-Rs). As a consequence, compounds 6 and 37 impaired uPAR-293 cell migration toward fetal calf serum (FCS), uPA, and fMLF, likely by inhibiting the interaction between uPAR and FPR1, the high affinity fMLF-R. Both compounds blocked in vitro ECM invasion of several cancer cell types, thus representing new promising leads for pharmaceuticals in cancer.

Deacetylated GM3 promotes uPAR-associated membrane molecular complex to activate p38 MAPK in metastatic melanoma

GM3, the simplest ganglioside, regulates cell proliferation, migration, and invasion by influencing cell signaling at the membrane level. Although the classic N-acetylated form of GM3 (NeuAcLacCer) is commonly expressed and has been well studied, deacetylated GM3 (NeuNH2LacCer, d-GM3) has been poorly investigated, despite its presence in metastatic tumors but not in noninvasive melanomas or benign nevi. We have recently found that d-GM3 stimulates cell migration and invasion by activating urokinase plasminogen activator receptor (uPAR) signaling to augment matrix metalloproteinase-2 (MMP-2) function. However, the mechanisms by which d-GM3/uPAR increase MMP-2 expression and activation are not clear. By modifying the expression of d-GM3 genetically and biochemically, we found that decreasing d-GM3 expression inhibits, whereas overexpressing d-GM3 stimulates, p38 mitogen-activated protein kinase (MAPK) activity to influence MMP-2 expression and activation. p38 MAPK (p38) activation requires the formation of a membrane complex that contains uPAR, caveolin-1, and integrin α5β1 in membrane lipid rafts. In addition, knocking down or inhibiting focal adhesion kinase (FAK), phosphoinositide 3-kinase (PI3K), or Src kinase significantly reduces d-GM3-induced p38 phosphorylation and activation. Taken together, these results suggest that d-GM3 enhances the metastatic phenotype by activating p38 signaling through uPAR/integrin signaling with FAK, PI3K, and Src kinase as intermediates. Elucidation of the mechanisms by which d-GM3, a newly discovered, potential biomarker of metastatic melanomas, promotes cell metastasis will help us to understand the function of d-GM3 in metastatic melanomas and may lead to novel GM3-based cancer therapies.

Wounds that will not heal: pervasive cellular reprogramming in cancer

There has been an explosion of articles on epithelial-mesenchymal transition and other modes of cellular reprogramming that influence the tumor microenvironment. Many controversies exist and remain to be resolved. The interest of the pathologists in the molecular and functional parallels between wound healing and the developing tumor stroma has its earliest origin in the writings of Rudolph Virchow in the 19(th) century. Since then, most of the focus has been primarily on the dynamics of the extracellular matrix; however, new interest has been redirected toward deciphering and understanding the enigmatic, yet elegant, plasticity of the cellular components of the proliferating epithelia and stroma and how they are reciprocally influenced. Citing several examples from breast cancer research, we will trace how these perspectives have unfolded in the pages of The American Journal of Pathology and other investigative journals during the past century, their impact, and where the field is headed.

Compensatory redistribution of neuroligins and N-cadherin following deletion of synaptic β1-integrin

β1-containing integrins are required for persistent synaptic potentiation in hippocampus and regulate hippocampal-dependent learning. Based largely on indirect evidence, there is a prevailing assumption that β1-integrins are localized at synapses, where they contribute to synapse adhesion and signaling, but this has not been examined directly. Here we investigate the fine localization of β1-integrin in adult mouse hippocampus using high-resolution immunogold labeling, with a particular emphasis on synaptic labeling patterns. We find that β1-integrins localize to synapses in CA1 and are concentrated postsynaptically. At the postsynaptic membrane, β1-integrins are found more commonly clustered near active zone centers rather than at the peripheral edges. In mice harboring a conditional deletion of β1-integrins, labeling for N-cadherin and neuroligins increases. Western blots show increased levels of N-cadherin in total lysates and neuroligins increase selectively in synaptosomes. These data suggest there is a dynamic, compensatory adjustment of synaptic adhesion. Such adjustment is specific only for certain cell adhesion molecules (CAMs), because labeling for SynCAM is unchanged. Together, our findings demonstrate unequivocally that β1-integrin is an integral synaptic adhesion protein, and suggest that adhesive function at the synapse reflects a cooperative and dynamic network of multiple CAM families.

Development of novel therapeutics targeting the urokinase plasminogen activator receptor (uPAR) and their translation toward the clinic

The urokinase plasminogen activator receptor (uPAR) mediates cell motility and tissue remodeling. Although uPAR may be expressed transiently in many tissues during development and wound healing, its constitutive expression appears to be associated with several pathological conditions, including cancer. uPAR expression has been demonstrated in most solid tumors and several hematologic malignancies including multiple myeloma and acute leukemias.Unlike many tumor antigens, uPAR is present not only in tumor cells but also in a number of tumor-associated cells including angiogenic endothelial cells and macrophages. The expression of uPAR has been shown to be fairly high in tumor compared to normal, quiescent tissues, which has led to uPAR being proposed as a therapeutic target, as well as a targeting agent, for the treatment of cancer. The majority of therapeutic approaches that have been investigated to date have focused on inhibiting the urokinase plasminogen activator (uPA)-uPAR interaction but these have not led to the development of a viable uPAR targeted clinical candidate. Genetic knockdown approaches e.g. siRNA, shRNA focused on decreasing uPAR expression have demonstrated robust antitumor activity in pre-clinical studies but have been hampered by the obstacles of stability and drug delivery that have limited the field of RNA nucleic acid based therapeutics. More recently, novel approaches that target interactions of uPAR that are downstream of uPA binding e.g. with integrins or that exploit observations describing the biology of uPAR such as mediating uPA internalization and signaling have generated novel uPAR targeted candidates that are now advancing towards clinic evaluation. This review will discuss some of the pitfalls that have delayed progress on uPAR-targeted interventions and will summarize recent progress in the development of uPAR-targeted therapeutics.

Integrin α3β1 as a breast cancer target

INTRODUCTION

Integrin receptors for cell adhesion to the extracellular matrix have important roles in all stages of cancer progression and metastasis. Since the integrin family was discovered in the early 1980's, many studies have identified critical adhesion and signaling functions for integrins expressed on tumor cells, endothelial cells and other cell types of the tumor microenvironment, in controlling proliferation, survival, migration and angiogenesis. In recent years, the laminin-binding integrin α3β1 has emerged as a potentially promising anti-cancer target on breast cancer cells.

AREAS COVERED

Studies from the past decade that implicate integrins as promising anti-cancer targets and the development of integrin antagonists as anti-cancer therapeutics. Recent preclinical studies that have identified the laminin-binding integrin α3β1 as an appealing anti-cancer target and the knowledge gaps that must be closed to fully exploit this integrin as a therapeutic target for breast cancer.

EXPERT OPINION

Although the tumor-promoting functions of α3β1 implicate this integrin as a promising therapeutic target on breast cancer cells, successful exploitation of this integrin as an anti-cancer target will require a better understanding of the molecular mechanisms whereby it regulates specific tumor cell behaviors and the identification of the most appropriate α3β1 functions to antagonize on breast cancer cells.

Antagonistic anti-urokinase plasminogen activator receptor (uPAR) antibodies significantly inhibit uPAR-mediated cellular signaling and migration

Interactions between urokinase plasminogen activator receptor (uPAR) and its various ligands regulate tumor growth, invasion, and metastasis. Antibodies that bind specific uPAR epitopes may disrupt these interactions, thereby inhibiting these processes. Using a highly diverse and naïve human fragment of the antigen binding (Fab) phage display library, we identified 12 unique human Fabs that bind uPAR. Two of these antibodies compete against urokinase plasminogen activator (uPA) for uPAR binding, whereas a third competes with beta1 integrins for uPAR binding. These competitive antibodies inhibit uPAR-dependent cell signaling and invasion in the non-small cell lung cancer cell line, H1299. Additionally, the integrin-blocking antibody abrogates uPAR/beta1 integrin-mediated H1299 cell adhesion to fibronectin and vitronectin. This antibody and one of the uPAR/uPA antagonist antibodies shows a significant combined effect in inhibiting cell invasion through Matrigel/Collagen I or Collagen I matrices. Our results indicate that these antagonistic antibodies have potential for the detection and treatment of uPAR-expressing tumors.

Plasminogen activator inhibitor-1 is an aggregate response factor with pleiotropic effects on cell signaling in vascular disease and the tumor microenvironment

In hemostasis, the serine protease inhibitor (serpin) plasminogen activator inhibitor-1 (PAI-1) functions to stabilize clots via inhibition of tissue plasminogen activator (tPA) with subsequent inhibition of fibrinolysis. In tissues, PAI-1 functions to inhibit extracellular matrix degradation via inhibition of urokinase plasminogen activator (uPA). Elevated levels of PAI-1 in the vasculature and in tissues have long been known to be associated with thrombosis and fibrosis, respectively. However, there is emerging evidence that PAI-1 may participate in the pathophysiology of a number of diseases such as atherosclerosis, restenosis, and cancer. In many of these disease states, the canonical view of PAI-1 as an inhibitor of tPA and uPA cannot fully account for a mechanism whereby PAI-1 contributes to the disease. In these cases, one must consider recent data, which indicates PAI-1 can directly promote pro-proliferative and anti-apoptotic signaling in a variety of cell types. Given the wide variety of inflammatory, hormonal, and metabolic signals that increase PAI-1 expression, it is important to consider mechanisms by which PAI-1 can directly participate in disease etiology.

De-N-acetyl GM3 promotes melanoma cell migration and invasion through urokinase plasminogen activator receptor signaling-dependent MMP-2 activation

We have recently discovered that de-N-acetyl GM3 [NeuNH(2)LacCer, d-GM3], a derivative of ganglioside GM3, is specifically expressed in metastatic tumor cells and that its expression correlates with an enhanced metastatic phenotype. Although the classic N-acetylated form of GM3 (NeuAcLacCer, c-GM3) is found in both normal and tumor cells, metastatic tumor cells (but not other cells) predominantly express d-GM3 (82-95% of total GM3). d-GM3 expression is mainly found in metastatic melanomas, but not in benign nevi or the majority of primary melanomas. Using metastatic (d-GM3-positive) and poorly invasive (d-GM3-negative) human melanoma cell lines, we found that d-GM3 stimulates cell migration and invasion by increasing the expression and activation of urokinase-like plasminogen activator (uPA). Further studies showed that d-GM3 activates matrix metalloproteinase-2 (MMP-2), but not MMP-9, when uPA receptor signaling is activated. These results implicate d-GM3 as a specific marker for metastatic melanoma and a novel therapeutic target for neoplastic diseases.

Urokinase plasminogen activator system as a potential target for cancer therapy

Proteolysis of extracellular matrix (ECM) and basement membrane is an essential mechanism used by cancer cells for their invasion and metastasis. The ECM proteinases are divided into three groups: metalloproteinases, cysteine proteinases and serine proteinases. The urokinase plasminogen activator (uPA) system is one of the serine proteinase systems involved in ECM degradation. Members of this system, including uPA and its receptor (uPAR), are overexpressed in several malignant tumors. This system plays a major role in adhesion, migration, invasion and metastasis of cancer cells, thus making it an important target for anticancer drug therapy. Several strategies, including the use of antisense oligodeoxynucleotides, ribozymes, DNAzyme, RNAi, uPA inhibitors, soluble uPAR, catalytically inactive uPA fragments, synthetic peptides and synthetic hybrids are under study, as they interfere with the expression and/or activity of uPA or uPAR in tumor cells. Herein, we discuss the various pharmaceutical strategies under investigation to combat the uPA activity in cancer.

The urokinase receptor promotes cancer metastasis independently of urokinase-type plasminogen activator in mice

The urokinase receptor (uPAR) promotes metastasis of human malignancies; however, its mechanism of action remains incompletely understood. Established models focus on the ability of uPAR to bind urokinase-type plasminogen activator (uPA) and promote protease activation in the tumor cell microenvironment; however, uPAR also regulates cell signaling and migration by both uPA-dependent and -independent mechanisms in vitro. The significance of uPAR as a cell-signaling receptor in vivo remains unclear. In this study, we expressed either human or mouse uPAR in human embryonic kidney (HEK-293) cells. We selected HEK-293 cells because, unlike most cancer cells, they do not express uPA or uPAR endogenously. Both mouse and human uPAR increased cell adhesion and migration on vitronectin. Rac1 was activated and responsible for the increase in cell migration. HEK-293 cells that did not express uPAR formed palpable tumors in severe combined immunodeficient mice; however, metastases were exceedingly rare. The xenografts contained abundant mouse uPA, produced by infiltrating mouse cells, but no human uPA. Mouse uPA bound only to mouse uPAR and not human uPAR and, thus, could not interact with human uPAR-expressing HEK-293 cells in xenografts. Nevertheless, both mouse and human uPAR significantly increased HEK-293 cell metastasis into the lungs. The activity of human uPAR suggests that uPAR may promote cancer metastasis independent of uPA. Candidate mechanisms include its effects on adhesion, migration, and Rac1 activation.

Sphingosine-1-phosphate regulates glioblastoma cell invasiveness through the urokinase plasminogen activator system and CCN1/Cyr61

Glioblastoma multiforme (GBM) is an aggressively invasive brain neoplasm with poor patient prognosis. We have previously shown that the bioactive lipid sphingosine-1-phosphate (S1P) stimulates in vitro invasiveness of GBM cells and that high expression levels of the enzyme that forms S1P, sphingosine kinase-1 (SphK1), correlate with shorter survival time of GBM patients. We also recently showed that S1P induces expression of CCN1 (also known as Cyr61), a matricellular protein known to correlate with poor patient prognosis, in GBM cells. In this study, we further explored the role of CCN1 as well as the urokinase plasminogen activator (uPA), a protein known to stimulate GBM cell invasiveness, in S1P-induced invasion using a spheroid invasion assay. We also investigated the roles of various S1P receptors in stimulating invasiveness through these pathways. S1P induced expression of uPA and its receptor, uPAR, in GBM cells. Whereas S1P(1), S1P(2), and S1P(3) receptors all contribute, at least partially, S1P(1) overexpression led to the most dramatic induction of the uPA system and of spheroid invasion, even in the absence of added S1P. Furthermore, neutralizing antibodies directed against uPA or CCN1 significantly decreased both basal and S1P-stimulated GBM cell invasiveness. Inhibition of SphK blocked basal expression of uPA and uPAR, as well as glioma cell invasion; however, overexpression of SphK did not augment S1P receptor-mediated enhancement of uPA activity or invasion. Thus, SphK is necessary for basal activity of the uPA system and glioma cell invasion, whereas S1P receptor signaling enhances invasion, partially through uPA and CCN1.

Inhibition of bone resorption and growth of breast cancer in the bone microenvironment

Breast cancer frequently metastasizes to bone, where tumor cells induce osteoclasts to locally destroy bone. During bone resorption, growth factors are locally released that may support bone metastatic growth. Differently from most other tissues, drugs that can limit local turnover, such as bisphosphonates and osteoprotegerin (OPG), are available for bone. We examined the hypothesis that inhibition of bone resorption by two different mechanisms may also affect the growth of cancer cells in bone. For this, we tested the effects of high doses of OPG and zoledronic acid (ZOL) on progression of MDA-231-B/Luc+ breast cancer cells in the bone microenvironment using whole body bioluminescent reporter imaging (BLI). Both treatments significantly inhibited the development of radiographically detectable osteolytic lesions. Histologic examination corroborated the radiographic findings, showing that both treatments preserved the integrity of bone trabeculae and prevented bone destruction (significantly higher trabecular bone volumes vs. vehicle). However, whereas practically no TRAcP-positive osteoclasts were observed in tibiae preparations of animals treated with Fc-OPG, TRAcP-positive osteoclasts were still present in the animals treated with ZOL. Intra-bone tumor burden was reduced with ZOL and Fc-OPG treatment. Although there appeared to be a trend for less overall total tumor burden upon treatment with both compounds, this was not significant as assessed by BLI and histomorphometric analysis due to the extramedullary growth of cancer cells which was not affected by these treatments. Collectively, anti-resorptive agents with different mechanisms of action - ZOL and OPG - significantly reduced cancer-induced osteolysis and intra-osseous tumor burden, but failed to restrain local tumor growth. However, interference with the bone micro-environmental growth support could still be of therapeutic relevance when given to patients early in the course of bone metastatic disease.

A dual role for caveolin-1 in the regulation of fibronectin matrix assembly by uPAR

The relationship between the plasminogen activator system and integrin function is well documented but incompletely understood. The mechanism of uPAR-mediated signaling across the membrane and the molecular basis of uPAR-dependent activation of integrins remain important issues. The present study was undertaken to identify the molecular intermediates involved in the uPAR signaling pathway controlling alpha5beta1-integrin activation and fibronectin polymerization. Disruption of lipid rafts with MbetaCD or depletion of caveolin-1 by siRNA led to the inhibition of uPAR-dependent integrin activation and stimulation of fibronectin polymerization in human dermal fibroblasts. The data indicate a dual role for caveolin-1 in the uPAR signaling pathway, leading to integrin activation. Caveolin-1 functions initially as a membrane adaptor or scaffold to mediate uPAR-dependent activation of Src and EGFR. Subsequently, in its phosphorylated form, caveolin-1 acts as an accessory molecule to direct trafficking of activated EGFR to focal adhesions. These studies provide a novel paradigm for the regulation of crosstalk among integrins, growth-factor receptors and uPAR.

Simultaneous downregulation of uPAR and MMP-9 induces overexpression of the FADD-associated protein RIP and activates caspase 9-mediated apoptosis in gliomas

We have previously demonstrated the effectiveness of simultaneous RNA interference (RNAi)-mediated downregulation of urokinase-type plasminogen activator receptor (uPAR) and matrix metalloproteinase-9 (MMP-9) in inhibiting tumor invasion in vitro and in vivo. In particular, we have shown that the downregulation of uPAR and MMP-9 inhibits intracranial tumor growth. The mechanism of the inhibition of tumor growth has not yet been determined. In this study, we have attempted to explain the mechanisms involved in the inhibition of invasiveness and tumor growth in vitro. SNB19 glioma cells were transfected with scrambled vector plasmid (pSV) and a siRNA-expressing plasmid targeting either uPAR (pU) or MMP-9 (pM) singly or in combination (pUM). Untransfected cells were also used as a control. Western blotting and RT-PCR analyses showed the downregulation of uPAR in pU-transfected cells and MMP-9 in pM-transfected cells. In cells transfected with pUM, we observed down-regulation of both uPAR and MMP-9, thereby indicating the specificity of the siRNA-expressing plasmids. An increase in caspase 9 expression was observed in cells transfected with pUM whereas no change in the level of caspase 9 was observed in pU or pM-transfected cells. Additionally, no change in the expression level of caspase 8 was observed. However, an increase in the expression level of cleaved PARP was observed in the case of cells transfected with pU, pM and pUM. Cells transfected with pUM showed the highest levels of cleaved PARP expression. Expression levels of APAF-1 were also higher in pUM-transfected cells with no change in expression levels of controls and in pU and pM-transfected cells. Total CAD expression levels did not change under any of the transfection conditions. However, immunohistochemical studies demonstrated that CAD was translocated to the nucleus, thereby indicating DNA damage. As determined by Western blot analysis of subcellular fractions, cytoplasmic levels of cytochrome c were also increased. We determined the extent of DNA damage using the TUNEL assay (poly-A termination of free -OH ends of degraded nuclear DNA). Based on our results we conclude that the simultaneous downregulation of uPAR and MMP-9 induces apoptosome-mediated apoptosis.

Differential proteome expression associated with urokinase plasminogen activator receptor (uPAR) suppression in malignant epithelial cancer

Dysregulation of the plasminogen activation cascade is a prototypic feature in many malignant epithelial cancers. Principally, this is thought to occur through activation of overexpressed urokinase plasminogen activator (uPA) concomitant with binding to its high specificity cell surface receptor urokinase plasminogen activator receptor (uPAR). Up-regulation of uPA and uPAR in cancer appears to potentiate the malignant phenotype, either (i) directly by triggering plasmin-mediated degradation or activation of uPA's or plasmin's proteolytic targets (e.g., extracellular matrix zymogen proteases or nascent growth factors) or indirectly by simultaneously altering a range of downstream functions including signal transduction pathways ( Romer, J. ; Nielsen, B. S. ; Ploug, M. The urokinase receptor as a potential target in cancer therapy Curr. Pharm. Des. 2004, 10 ( 19), 235976 ). Because many malignant epithelial cancers express high levels of uPAR, uPA or other components of the plasminogen activation cascade and because these are often associated with poor prognosis, characterizing how uPAR changes the downstream cellular "proteome" is fundamental to understanding any role in cancer. This study describes a carefully designed proteomic study of the effects of antisense uPAR suppression in a previously studied colon cancer cell line (HCT116). The study utilized replicate 2DE gels and two independent gel image analysis software packages to confidently identify 64 proteins whose expression levels changed (by > or =2 fold) coincident with a moderate ( approximately 40%) suppression of cell-surface uPAR. Not surprisingly, many of the altered proteins have previously been implicated in the regulation of tumor progression (e.g., p53 tumor suppressor protein and c-myc oncogene protein among many others). In addition, through a combination of proteomics and immunological methods, this study demonstrates that stathmin 1alpha, a cytoskeletal protein implicated in tumor progression, undergoes a basic isoelectric point shift (p I) following uPAR suppression, suggesting that post-translational modification of stathmin occur secondary to uPAR suppression. Overall, these results shed new light on the molecular mechanisms involved in uPAR signaling and how it may promulgate the malignant phenotype.

A convenient clinically relevant model of human breast cancer bone metastasis

Breast cancer patients with advanced disease exhibit bone metastases, leading to the formation of osteolytic lesions for which the only currently available treatments are palliative. Here, we describe how we refined a mouse model of human breast cancer metastasis into bone, characterized its transcriptome and demonstrated its clinical relevance. Cells were selected from bone metastases caused by MDA-MB-231 cells after several in vivo passages, and engineered to express luciferase. Whole body bioluminescence live imaging indicated that the selected isogenic B02 clone was unique in its ability to form rapidly growing osteolytic bone metastases. B02 cells were detected as early as 10 days after tail vein injection, as opposed to 1 month after cardiac injection in other haematogenous models. Whole transcriptomic analysis identified 114 upregulated and 247 downregulated genes in B02 cells compared to the parental cells, several of which represent novel targets. In addition, there was a 50% overlap between the B02 signature and a recently described signature obtained from human breast cancer bone metastases. Consistent with the plasticity of an aggressive metastatic variant, 10% of the regulated genes are involved in proliferation, migration, invasion and angiogenesis. Strikingly, B02 cells also express osteoblast-specific genes, thus mimicking a process referred to as osteomimicry in the clinic. The B02 cells "human bone metastatic signature", the expression of bone-specific genes, as well as the live imaging of this convenient model highlight its clinical relevance and usefulness during drug development.

RNA interference-mediated targeting of urokinase plasminogen activator receptor and matrix metalloproteinase-9 gene expression in the IOMM-lee malignant meningioma cell line inhibits tumor growth, tumor cell invasion and angiogenesis

Meningiomas are the most commonly occurring tumors of the central nervous system including the brain and spinal cord. Malignant meningiomas are highly aggressive and frequently recur after surgical resection of the tumor. Our previous studies have reported that urokinase plasminogen activator receptor (uPAR) and matrix metalloproteinase-9 (MMP-9) play important roles in tumor progression. In the present study, we have attempted to evaluate the roles of these molecules in the malignant meningioma tumor microenvironment and to determine the effectiveness of using single or bicistronic small interfering RNA constructs for uPAR and MMP-9 on tumor cell proliferation, migration, invasion, angiogenesis and regression of pre-established orthotopic tumors. Transfection of single or bicistronic constructs downregulated uPAR and MMP-9 in meningioma cells compared to controls. A significant reduction in tumor invasion was determined with matrigel gel and spheroid invasion assays in meningioma cells after transfection of these plasmids. Furthermore, downregulation of uPAR and MMP-9 reduced migration of tumor spheroids on vitronectin-coated plates. uPAR and MMP-9 downregulation suppressed capillary network formation, in both in vitro and in vivo models. Also, it is well known that tumor cells manipulate intracellular signaling pathways to aid in various processes involved in tumor progression. Our study revealed that downregulation of uPAR and MMP-9 leads to a decrease in the activation of some of the important enzymes participating in the MAPK and PI3 kinase pathways, which in turn, might decrease cell survival and proliferation. In addition, we analyzed the efficiency of RNAi-mediated targeting of uPAR and MMP-9 in pre-established tumor growth in vivo. We observed a significant regression of pre-established orthotopic tumors upon RNAi-mediated targeting of uPAR and MMP-9. In addition, the present study indicated that targeting both the proteins simultaneously augmented the therapeutic treatment of human meningiomas.

RNA interference-mediated targeting of urokinase plasminogen activator receptor and matrix metalloproteinase-9 gene expression in the IOMM-lee malignant meningioma cell line inhibits tumor growth, tumor cell invasion and angiogenesis

Meningiomas are the most commonly occurring tumors of the central nervous system including the brain and spinal cord. Malignant meningiomas are highly aggressive and frequently recur after surgical resection of the tumor. Our previous studies have reported that urokinase plasminogen activator receptor (uPAR) and matrix metalloproteinase-9 (MMP-9) play important roles in tumor progression. In the present study, we have attempted to evaluate the roles of these molecules in the malignant meningioma tumor microenvironment and to determine the effectiveness of using single or bicistronic small interfering RNA constructs for uPAR and MMP-9 on tumor cell proliferation, migration, invasion, angiogenesis and regression of pre-established orthotopic tumors. Transfection of single or bicistronic constructs downregulated uPAR and MMP-9 in meningioma cells compared to controls. A significant reduction in tumor invasion was determined with matrigel gel and spheroid invasion assays in meningioma cells after transfection of these plasmids. Furthermore, downregulation of uPAR and MMP-9 reduced migration of tumor spheroids on vitronectin-coated plates. uPAR and MMP-9 downregulation suppressed capillary network formation, in both in vitro and in vivo models. Also, it is well known that tumor cells manipulate intracellular signaling pathways to aid in various processes involved in tumor progression. Our study revealed that downregulation of uPAR and MMP-9 leads to a decrease in the activation of some of the important enzymes participating in the MAPK and PI3 kinase pathways, which in turn, might decrease cell survival and proliferation. In addition, we analyzed the efficiency of RNAi-mediated targeting of uPAR and MMP-9 in pre-established tumor growth in vivo. We observed a significant regression of pre-established orthotopic tumors upon RNAi-mediated targeting of uPAR and MMP-9. In addition, the present study indicated that targeting both the proteins simultaneously augmented the therapeutic treatment of human meningiomas.

The uPA receptor and the somatomedin B region of vitronectin direct the localization of uPA to focal adhesions in microvessel endothelial cells

Vitronectin is a plasma protein which can deposit into the extracellular matrix where it supports integrin and uPA dependent cell migration. In earlier studies, we have shown that the plasma protein, vitronectin, stimulates focal adhesion remodeling by recruiting urokinase-type plasminogen activator (uPA) to focal adhesion sites [Wilcox-Adelman, S. A., Wilkins-Port, C. E., McKeown-Longo, P. J., 2000. Localization of urokinase-type plasminogen activator to focal adhesions requires ligation of vitronectin integrin receptors. Cell. Adhes. Commun.7, 477-490]. In the present study, we used a variety of vitronectin constructs to demonstrate that the localization of uPA to adhesion sites requires the binding of both vitronectin integrin receptors and the uPA receptor (uPAR) to vitronectin. A recombinant fragment of vitronectin containing the connecting sequence (VN(CS)) was able to support integrin-dependent adhesion, spreading and focal adhesion assembly by human microvessel endothelial cells. Cells adherent to this fragment were not able to localize uPA to focal adhesions. A second recombinant fragment containing both the amino-terminal SMB domain and the CS domain was able to restore the localization of uPA to adhesion sites. This fragment, which contains a uPAR binding site, also resulted in the localization of uPAR to adhesion sites. uPAR blocking antibodies as well as phospholipase C treatment of cells inhibited uPA localization to adhesion sites confirming a role for uPAR in this process. The SMB domain alone was unable to direct either uPAR or uPA to adhesion sites in the absence of the CS domain. Our results indicate that vitronectin-dependent localization of uPA to adhesion sites requires the sequential binding of vitronectin integrins and uPAR to vitronectin.

Targeting urokinase-type plasminogen activator and its receptor for cancer therapy

Cancer invasion and metastasis are highly complex processes and a serine protease urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system has been postulated to play a central role in the mediation of cancer progression. Of note, malignant tumor urokinase-type plasminogen activator and urokinase-type plasminogen activator receptor levels have been found to vary considerably, and to be related to patient prognosis. In mouse models, the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system has been studied extensively as a target for anticancer therapy using a variety of approaches. In this review, we discuss the advances in the various modalities that have been used to target the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system, including protein-based and peptide-based drugs, antisense therapy, and RNA interference technology. In particular, preclinical mouse model studies that used human tumor xenografts are reviewed.

Ability of breast cancer cell lines to stimulate bone resorbing activity of mature osteoclasts correlates with an anti-apoptotic effect mediated by macrophage colony stimulating factor

We compared the effect of conditioned medium (CM) from several human breast carcinoma cell lines on osteoclast bone resorbing activity and osteoclast apoptosis. Our findings indicate that ability of cancer cell line to increase the in vitro bone resorbing activity is linked to their potential to inhibit osteoclast apoptosis. Cancer cells producing the higher level of M-CSF have the higher osteolytic activity, suggesting that M-CSF originating from cancer cells may contribute, at least in part, to the osteoclast activity at the metastatic site by enhancing their survival. Given that M-CSF plays an important role in the anti-apoptotic effect, we speculated that blocking M-CSF pathway would prevent the CM effects. Small interfering RNA (siRNA) targeting M-CSF and imatinib, a protein tyrosine kinase inhibitor targeting M-CSF receptor, almost completely reversed the CM effect on both osteoclast apoptosis and bone resorption. Blockade of M-CSF pathway could be thus of clinical value in the treatment of breast cancer related bone destruction.

Coordinate regulation of fibronectin matrix assembly by the plasminogen activator system and vitronectin in human osteosarcoma cells

Background

Plasminogen activators are known to play a key role in the remodeling of bone matrix which occurs during tumor progression, bone metastasis and bone growth. Dysfunctional remodeling of bone matrix gives rise to the osteoblastic and osteolytic lesions seen in association with metastatic cancers. The molecular mechanisms responsible for the development of these lesions are not well understood. Studies were undertaken to address the role of the plasminogen activator system in the regulation of fibronectin matrix assembly in the osteoblast-like cell line, MG-63.

Results

Treatment of MG-63 cells with P25, a peptide ligand for uPAR, resulted in an increase in assembly of fibronectin matrix which was associated with an increase in the number of activated β1 integrins on the cell surface. Overexpression of uPAR in MG-63 cells increased the effect of P25 on fibronectin matrix assembly and β₁ integrin activation. P25 had no effect on uPAR null fibroblasts, confirming a role for uPAR in this process. The addition of plasminogen activator inhibitor Type I (PAI-1) to cells increased the P25-induced fibronectin polymerization, as well as the number of activated integrins. This positive regulation of PAI-1 on fibronectin assembly was independent of PAI-1's anti-proteinase activity, but acted through PAI-1 binding to the somatomedin B domain of vitronectin.

Conclusion

These results indicate that vitronectin modulates fibronectin matrix assembly in osteosarcoma cells through a novel mechanism involving cross-talk through the plasminogen activator system.

Antiprotease therapy in cancer: hot or not?

The activity of a set of peptidases (proteases) involved in cancer progression is collectively known as the cancer 'degradome'. Invasion and metastasis were initially considered as late events in cancer development and the processes in which proteases were involved. However, recent studies indicate that invasion and metastasis are not late events, but can occur during early stages as well. Moreover, other processes occurring in various stages of cancer progression are also protease-dependent, such as (upregulation of) cell proliferation, (downregulation of) apoptosis, involvement of white blood cells, angiogenesis and induction of multi-drug resistance. Proteolytic activity in tumours is regulated in a complex manner, as both genetically unstable cancer cells and stable stromal cells, such as fibroblasts, endothelial cells and inflammatory cells, are involved. In vitro studies and studies using animal models have clearly shown protease dependency of many processes in carcinogenesis. However, clinical trials using protease inhibitors have thus far been unsuccessful except for a few applications of matrix metalloprotease (MMP) inhibitors when used in combination with cytostatic anticancer agents and/or in the early stages of cancer. Antithrombotics, such as low-molecular-weight heparin and warfarin, were also successful in clinical trials, probably by interfering with proteases of the coagulation cascade. The two-way association between cancer and thrombosis has long been recognised in the clinic. The poor outcome of other clinical trials of protease inhibitors is probably due to the late stages of cancer of the patient populations included, and the limited understanding of the complex regulation and effects of the activity of the various proteases in tumours depending on, among others, tumour type and stage, interactions between the cancer cells, other cells and the extracellular matrix in tumours. Therefore, a better fundamental understanding of the proteolytic complexity in tumours is essential before clinical trials can be rationally designed. At present, antithrombotics, the urokinase-type plasminogen activator system, the membrane-bound membrane-type 1-MMP, cathepsin L and the proteasome seem the most promising candidates as targets for anticancer strategies in early stages of cancer in combination with cytotoxic drugs. Moreover, metronomic therapy is an attractive approach using low doses of inhibitors for prolonged periods of time without interruption to specifically target endothelial cells that are involved in angiogenesis.

Interleukin-1alpha enhances the aggressive behavior of pancreatic cancer cells by regulating the alpha6beta1-integrin and urokinase plasminogen activator receptor expression

Background

In human pancreatic cancer progression, the α₆β₁-integrin is expressed on cancer cell surface during invasion and metastasis formation. In this study, we investigated whether interleukin (IL)-1α induces the alterations of integrin subunits and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) expression in pancreatic cancer cells. We hypothesize that the alterations of integrin subunits and uPA/uPAR expression make an important role in signaling pathways responsible for biological behavior of pancreatic cancer cells.

Results

IL-1α upregulated the expression of α₆ and β₁ integrins without any alterations of α₅ and α_v integrins expression. IL-1α also induced enhancement in the expression of uPA/uPAR in pancreatic cancer cells. IL-1α enhanced the proliferation, adhesion, and migration in pancreatic cancer cells, and IL-1α-induced alterations of uPA/uPAR expression correlated with the increased the migration of pancreatic cancer cells. Upregulation of α₆ integrin subunit and uPA/uPAR correlated with the activation of Ras and downstream extracellular signal-regulated kinase (ERK) pathways. IL-1α-induced activation of Ras and downstream ERK can be inhibited by using inhibitory antibodies against α₆ and β₁ integrin and uPAR, consistent with the inhibition of proliferation, adhesion and migration of pancreatic cancer cells. Immunohistochemical analysis demonstrated a significant association between strong expressions of α₆ integrin with uPAR in pancreatic cancer specimens. Furthermore, the strong expression of α₆ integrin and uPAR was found to be independent prognosticator in pancreatic cancer patients.

Conclusion

Based on these findings, we conclude that IL-1α can induce selective upregulation of α₆β₁-integrin and uPA/uPAR in pancreatic cancer cells and these changes may modulate the aggressive functions of pancreatic cancer.

Urokinase-type plasminogen activator receptor regulates a novel pathway of fibronectin matrix assembly requiring Src-dependent transactivation of epidermal growth factor receptor

Previous studies have indicated that the urokinase-type plasminogen activator receptor (uPAR) can functionally interact with integrins thereby modulating integrin activity. We have previously demonstrated that treatment of fibroblasts with the uPAR ligand, P25, results in an increase in the activation of the beta1 integrin and a 35-fold increase in fibronectin matrix assembly (Monaghan, E., Gueorguiev, V., Wilkins-Port, C., and McKeown-Longo, P. J. (2004) J. Biol. Chem. 279, 1400-1407). Experiments were conducted to address the mechanism of uPAR regulation of matrix assembly. Treatment of fibroblasts with P25 led to an increase in the activation of the epidermal growth factor receptor (EGFR) and a colocalization of activated EGFR with beta1 integrins in cell matrix contacts. The effects of P25 on matrix assembly and beta1 integrin activation were inhibited by pretreatment with EGFR or Src kinase inhibitors, suggesting a role for both Src and EGFR in integrin activation by uPAR. Phosphorylation of EGFR in response to P25 occurred on Tyr-845, an Src-dependent phosphorylation site and was inhibited by PP2, the Src kinase inhibitor, consistent with Src kinase lying upstream of EGFR and integrin activation. Cells null for Src kinases also showed a loss of P25-induced matrix assembly, integrin activation, and EGFR phosphorylation. These P25-induced effects were restored following Src re-expression. The effects of P25 were specific for uPAR as enhanced matrix assembly by P25 was not seen in uPAR-/- cells, but was restored upon uPAR re-expression. These data provide evidence for a novel pathway of fibronectin matrix assembly through the uPAR-dependent sequential activation of Src kinase, EGFR, and beta1 integrin.

Proteases and glioma angiogenesis

Angiogenesis, the process by which new branches sprout from existing vessels, requires the degradation of the vascular basement membrane and remodeling of the ECM in order to allow endothelial cells to migrate and invade into the surrounding tissues. Serine, metallo, and cysteine proteinases are 3 types of a family of enzymes that proteolytically degrade various components of extracellular matrix. These proteases release various growth factors and also increase adhesive molecules and signaling pathway molecules upon their activation, which plays a significant role in angiogenesis. Downregulation of these molecules by antisense/siRNA or synthetic inhibitors decreases the levels of these molecules, inhibits the release of growth factors, and decreases the levels of various signaling pathway molecules, thereby leading to the inhibition of angiogenesis. Furthermore, MMPs degrade specific substrates and release angiogenic inhibitors which inhibit angiogenesis. Downregulation of 2 molecules, such as uPA and uPAR, uPAR and MMP-9, or Cathepsin B and MMP-9, are more effective to inhibit angiogenesis rather than downregulation of single molecules. However, careful testing of these combinations are most important because multiple effects of these combinations play a significant role in angiogenesis.

DNA microarray analysis of gene expression in eutopic endometrium from patients with deep endometriosis using laser capture microdissection

OBJECTIVE

To investigate differentially expressed genes in epithelial and stromal cells of eutopic endometrium from patients with deep endometriosis and women with normal pelvic cavities using laser capture microdissection and complementary DNA microarrays.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENT(S)

Patients with deep endometriosis and fertile women who underwent laparoscopic tubal ligation or reversal of tubal sterilization.

INTERVENTION(S)

Endometrial tissue biopsies during the late proliferative phase and early, mid-, and late secretory phases.

MAIN OUTCOME MEASURE(S)

Genes that were regulated with a change greater than threefold were selected as differentially expressed genes. Validation was performed with real-time reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULT(S)

Microarray analysis identified up-regulation during the late secretory phase (patients with endometriosis vs. controls) of several genes in two important signaling pathways: RAS/RAF/MAPK and PI3K. This included the genes RON, SOS, 14-3-3 protein eta, and uPAR in epithelial cells and KSR and PI3K p85 regulatory subunit alpha in stromal cells; real-time RT-PCR analysis validated up-regulation of all six genes.

CONCLUSION(S)

The RAS/RAF/MAPK and PI3K pathways may be involved in initial development of endometriosis.

Interference with the Microenvironmental Support Impairs the De novo Formation of Bone Metastases In vivo

Interference with the microenvironmental growth support is an attractive therapeutic strategy for repressing metastatic tumor growth. Bone is a highly dynamic tissue that is continuously remodeled by bone resorption and subsequent bone formation. Growth factors supporting bone metastatic growth are released especially during bone resorption. Differently from most other tissues, drugs that can limit local turnover, such as bisphosphonates, are available for bone. In the present study, we tested the hypothesis that inhibition of bone turnover can affect development and growth progression of experimental bone metastasis. Whole-body bioluminescent reporter imaging was used for the detection, monitoring, and quantification in vivo of the growth progression of bone metastases induced by intracardiac or intraosseous injection of luciferase-transfected breast cancer cells (MDA-231-B/luc+) to nude mice. Suppression of bone turnover by bisphosphonates, before bone colonization by cancer cells, inhibited by a great extent the number of developing bone metastasis. Tumor growth in the few, but still developing, bone metastases was affected only transiently. Reduction of bone turnover had no effect on growth progression of bone metastases, which were already established when bisphosphonate treatment was initiated, despite a substantial reduction in osteolysis. Therefore, cancer cells metastatic to bone, after an initial growth phase that depends on the interaction with the local stroma, become independent of microenvironmental growth factor support and progress autonomously. Inhibition of bone turnover may represent a useful adjuvant therapy especially for cancer patients at risk to develop bone metastasis.

The kringle domain of urokinase-type plasminogen activator potentiates LPS-induced neutrophil activation through interaction with {alpha}V{beta}3 integrins

Urokinase plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. In addition, uPA has been shown to have proinflammatory properties, particularly in potentiating lipopolysaccharide (LPS)-induced neutrophil responses. To explore the mechanisms by which uPA exerts these effects, we examined the ability of specific uPA domains to increase cytokine expression in murine and human neutrophils stimulated with LPS. Whereas the addition of intact uPA to neutrophils cultured with LPS increased mRNA and protein levels of interleukin-1beta, macrophage-inflammatory protein-2, and tumor necrosis factor alpha, deletion of the kringle domain (KD) from uPA resulted in loss of these potentiating effects. Addition of purified uPA KD to LPS-stimulated neutrophils increased cytokine expression to a degree comparable with that produced by single-chain uPA. Inclusion of the arginine-glycine-aspartic but not the arginine-glycine-glutamic peptide to neutrophil cultures blocked uPA kringle-induced potentiation of proinflammatory responses, demonstrating that interactions between the KD and integrins were involved. Antibodies to alpha(V) or beta(3) integrins or to the combination of alpha(V)beta(3) prevented uPA kringle-induced enhancement of expression of proinflammatory cytokines and also of adhesion of neutrophils to the uPA KD. These results demonstrate that the KD of uPA, through interaction with alpha(V)beta(3) integrins, potentiates neutrophil activation.

Ascites induces modulation of alpha6beta1 integrin and urokinase plasminogen activator receptor expression and associated functions in ovarian carcinoma

Interactions between cancer cells and the surrounding medium are not fully understood. In this study, we demonstrate that ascites induces selective changes in the expression of integrins and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) in ovarian cancer cells. We hypothesise that this change of integrin and uPA/uPAR expression triggers signalling pathways responsible for modulating phenotype-dependent functional changes in ovarian cancer cells. Human ovarian surface epithelial (HOSE) cell lines and epithelial ovarian cancer cell lines were treated with ascites for 48 h. Ascites induced upregulation of alpha6 integrin, without any change in the expression of alphav, beta1 and beta4 integrin subunits. Out of the four ovarian cancer cell lines studied, ascites induced enhancement in the expression of uPA/uPAR in the more invasive OVCA 433 and HEY cell lines without any change in the noninvasive OVHS1 and moderately invasive PEO.36 cell lines. On the other hand, no change in the expression of alpha6 integrin or uPAR, in response to ascites, was observed in HOSE cells. In response to ascites, enhancement in proliferation and in adhesion was observed in all four ovarian cancer cell lines studied. In contrast, no significant increase in proliferation or adhesion by ascites was observed in HOSE cells. Ascites-induced expression of uPA/uPAR correlated with the increased invasiveness of HEY and OVCA 433 cell lines but was not seen in OVHS1, PEO.36 and HOSE cell lines. Upregulation of alpha6 integrin and uPA/uPAR correlated with the activation of Ras and downstream Erk pathways. Ascites-induced activation of Ras and downstream Erk can be inhibited by using inhibitory antibodies against alpha6 and beta1 integrin and uPAR, consistent with the inhibition of proliferation, adhesion and invasive functions of ovarian cancer cell lines. Based on these findings, we conclude that ascites can induce selective upregulation of integrin and uPA/uPAR in ovarian cancer cells and these changes may modulate the functions of ovarian carcinomas.

Ascites induces modulation of alpha6beta1 integrin and urokinase plasminogen activator receptor expression and associated functions in ovarian carcinoma

Interactions between cancer cells and the surrounding medium are not fully understood. In this study, we demonstrate that ascites induces selective changes in the expression of integrins and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) in ovarian cancer cells. We hypothesise that this change of integrin and uPA/uPAR expression triggers signalling pathways responsible for modulating phenotype-dependent functional changes in ovarian cancer cells. Human ovarian surface epithelial (HOSE) cell lines and epithelial ovarian cancer cell lines were treated with ascites for 48 h. Ascites induced upregulation of alpha6 integrin, without any change in the expression of alphav, beta1 and beta4 integrin subunits. Out of the four ovarian cancer cell lines studied, ascites induced enhancement in the expression of uPA/uPAR in the more invasive OVCA 433 and HEY cell lines without any change in the noninvasive OVHS1 and moderately invasive PEO.36 cell lines. On the other hand, no change in the expression of alpha6 integrin or uPAR, in response to ascites, was observed in HOSE cells. In response to ascites, enhancement in proliferation and in adhesion was observed in all four ovarian cancer cell lines studied. In contrast, no significant increase in proliferation or adhesion by ascites was observed in HOSE cells. Ascites-induced expression of uPA/uPAR correlated with the increased invasiveness of HEY and OVCA 433 cell lines but was not seen in OVHS1, PEO.36 and HOSE cell lines. Upregulation of alpha6 integrin and uPA/uPAR correlated with the activation of Ras and downstream Erk pathways. Ascites-induced activation of Ras and downstream Erk can be inhibited by using inhibitory antibodies against alpha6 and beta1 integrin and uPAR, consistent with the inhibition of proliferation, adhesion and invasive functions of ovarian cancer cell lines. Based on these findings, we conclude that ascites can induce selective upregulation of integrin and uPA/uPAR in ovarian cancer cells and these changes may modulate the functions of ovarian carcinomas.

Expression of the urokinase receptor regulates focal adhesion assembly and cell migration in adenoid cystic carcinoma cells

Adenoid cystic carcinoma (AdCC) cell lines (ACCS and ACCT) showed higher migration responses and adhesion to the extracellular matrix (ECM), especially types I and IV collagen, than did the oral squamous cell carcinoma (SCC) lines (NA and TF). The response to collagens was largely and exclusively inhibited by anti-alpha(2) integrin antibody. Moreover, AdCC cell lines expressed higher surface levels of urokinase-type plasminogen activator receptor (uPAR) than did SCC cell lines. When AdCC cells were plated on collagen, the surface level of uPAR was increased, and numerous focal adhesions consisting of uPAR, vinculin, and paxillin were assembled; whereas collagen-stimulated SCC cell counterparts or AdCC cells plated on other types of ECM, such as fibronectin, failed to assemble such definite focal adhesions. In order to elucidate the association of uPAR with collagen-induced events, an ACCS-AS cell line transfected with a vector expressing antisense uPAR RNA was established and shown to have reduced uPAR (about 10% that of parental ACCS at both the protein and mRNA levels). ACCS-AS showed a strong reduction of collagen-stimulated migration and focal adhesion assembly of alpha(2) integrin, vinculin, and paxillin. These findings suggest that AdCC has a proclivity for migrating to types I and IV collagens due to the overexpression of uPAR, which plays a key role in focal adhesion assembly and migration.