The receptor for urokinase type plasminogen activator polarizes expression of the protease to the leading edge of migrating monocytes and promotes degradation of enzyme inhibitor complexes

Remodeling of the extracellular matrix by serine proteases as a prerequisite for cancer initiation and progression

The extracellular matrix (ECM) serves as a physical scaffold for tissues that is composed of structural proteins such as laminins, collagens, proteoglycans and fibronectin, forming a three dimensional network, and a wide variety of other matrix proteins with ECM-remodeling and signaling functions. The activity of ECM-associated signaling proteins is tightly regulated. Thus, the ECM serves as a reservoir for water and growth regulatory signals. The ECM architecture is dynamically modulated by multiple serine proteases that process both structural and signaling proteins to regulate physiological processes such as organogenesis and tissue homeostasis but they also contribute to pathological events, especially cancer progression. Here, we review the current literature regarding the role of ECM remodeling by serine proteases (KLKs, uPA, furin, HtrAs, granzymes, matriptase, hepsin) in tumorigenesis.

Protein lipidation in health and disease: molecular basis, physiological function and pathological implication

Posttranslational modifications increase the complexity and functional diversity of proteins in response to complex external stimuli and internal changes. Among these, protein lipidations which refer to lipid attachment to proteins are prominent, which primarily encompassing five types including S-palmitoylation, N-myristoylation, S-prenylation, glycosylphosphatidylinositol (GPI) anchor and cholesterylation. Lipid attachment to proteins plays an essential role in the regulation of protein trafficking, localisation, stability, conformation, interactions and signal transduction by enhancing hydrophobicity. Accumulating evidence from genetic, structural, and biomedical studies has consistently shown that protein lipidation is pivotal in the regulation of broad physiological functions and is inextricably linked to a variety of diseases. Decades of dedicated research have driven the development of a wide range of drugs targeting protein lipidation, and several agents have been developed and tested in preclinical and clinical studies, some of which, such as asciminib and lonafarnib are FDA-approved for therapeutic use, indicating that targeting protein lipidations represents a promising therapeutic strategy. Here, we comprehensively review the known regulatory enzymes and catalytic mechanisms of various protein lipidation types, outline the impact of protein lipidations on physiology and disease, and highlight potential therapeutic targets and clinical research progress, aiming to provide a comprehensive reference for future protein lipidation research.

Concentrations of urinary neopterin, but not suPAR, positively correlate with age in rhesus macaques

Identifying biomarkers of age-related changes in immune system functioning that can be measured non-invasively is a significant step in progressing research on immunosenescence and inflammaging in free-ranging and wild animal populations. In the present study, we aimed to investigate the suitability of two urinary compounds, neopterin and suPAR, as biomarkers of age-related changes in immune activation and inflammation in a free-ranging rhesus macaque (Macaca mulatta) population. We also investigated age-associated variation in gene transcription from blood samples to understand the underlying proximate mechanisms that drive age-related changes in urinary neopterin or suPAR. Neopterin was significantly positively correlated with age, and had a moderate within-individual repeatability, indicating it is applicable as a biomarker of age-related changes. The age-related changes in urinary neopterin are not apparently driven by an age-related increase in the primary signaler of neopterin, IFN-y, but may be driven instead by an age-related increase in both CD14+ and CD14− monocytes. suPAR was not correlated with age, and had low repeatability within-individuals, indicating that it is likely better suited to measure acute inflammation rather than chronic age-related increases in inflammation (i.e., “inflammaging”). Neopterin and suPAR had a correlation of 25%, indicating that they likely often signal different processes, which if disentangled could provide a nuanced picture of immune-system function and inflammation when measured in tandem.

Urokinase-Type Plasminogen Activator Triggers Wingless/Int1-Independent Phosphorylation of the Low-Density Lipoprotein Receptor-Related Protein-6 in Cerebral Cortical Neurons

BACKGROUND

Urokinase-type plasminogen activator (uPA) is a serine proteinase found in excitatory synapses located in the II/III and V cortical layers. The synaptic release of uPA promotes the formation of synaptic contacts and the repair of synapses damaged by various forms of injury, and its abundance is decreased in the synapse of Alzheimer's disease (AD) patients. Inactivation of the Wingless/Int1 (Wnt)-β-catenin pathway plays a central role in the pathogenesis of AD. Soluble amyloid-β (Aβ) prevents the phosphorylation of the low-density lipoprotein receptor-related protein-6 (LRP6), and the resultant inactivation of the Wnt-β-catenin pathway prompts the amyloidogenic processing of the amyloid-β protein precursor (AβPP) and causes synaptic loss.

OBJECTIVE

To study the role of neuronal uPA in the pathogenesis of AD.

METHODS

We used in vitro cultures of murine cerebral cortical neurons, a murine neuroblastoma cell line transfected with the APP-695 Swedish mutation (N2asw), and mice deficient on either plasminogen, or uPA, or its receptor (uPAR).

RESULTS

We show that uPA activates the Wnt-β-catenin pathway in cerebral cortical neurons by triggering the phosphorylation of LRP6 via a plasmin-independent mechanism that does not require binding of Wnt ligands (Wnts). Our data indicate that uPA-induced activation of the Wnt-β-catenin pathway protects the synapse from the harmful effects of soluble Aβ and prevents the amyloidogenic processing of AβPP by inhibiting the expression of β-secretase 1 (BACE1) and the ensuing generation of Aβ 40 and Aβ 42 peptides.

CONCLUSION

uPA protects the synapse and antagonizes the inhibitory effect of soluble Aβ on the Wnt-β-catenin pathway by providing an alternative pathway for LRP6 phosphorylation and β-catenin stabilization.

suPAR to Risk-Stratify Patients With Malaria

Severe malaria (SM) is a leading cause of global morbidity and mortality, particularly in children in sub-Saharan Africa. However, existing malaria diagnostic tests do not reliably identify children at risk of severe and fatal outcomes. Dysregulated host immune and endothelial activation contributes to the pathogenesis of SM. Current research suggests that measuring markers of these pathways at presentation may have clinical utility as prognostic indicators of disease progression and risk of death. In this review, we focus on the available evidence implicating soluble urokinase-type plasminogen activator receptor (suPAR) as a novel and early predictor of severe and fatal malaria and discuss its potential utility for malaria triage and management.

Soluble Urokinase Plasminogen Activator Receptor Levels Correlation with Other Inflammatory Factors in Prognosis of Disability and Death in Patients with Ischemic Stroke

Soluble urokinase plasminogen activator receptor (suPAR) is an inflammatory biomarker elevated in cardiovascular diseases. The aim of this 3-year follow-up prospective study was to evaluate suPAR levels in patients with a first ischemic stroke in correlation with CRP, PCT, NT-proCNP and endothelin 1-21 and to investigate the impact of suPAR on the outcome. Fifty-one patients (mean age 73.7+ = 11.9 years, 26 female and 25 male) were included. Samples were collected on the first (suPAR 1), third (suPAR 3) and seventh days after stroke onset (suPAR 7). Plasma samples were analyzed using ELISA. A phone interview was conducted to collect follow-up information after 24 and 36 months (modified Rankin Scale, mRS). A positive correlation between suPAR levels and other inflammatory biomarkers (except endothelin 3) was observed. A positive correlation between suPAR 3 and mRS score at 24 months was observed (p = 0.042). The logistic regression model revealed no significant effect of suPAR on death occurrence in the first 24 months: suPAR 1 (p = 0.8794), suPAR 3 (p = 0.2757), and suPAR 7 (p = 0.3652). The suPAR level is a potential inflammatory marker in ischemic stroke, and there is a correlation with other markers. There is no major impact on mortality. However, the suPAR level is associated with a degree of disability or dependence in daily activities 2 years after a stroke.

THE ROLE OF THE UROKINASE SYSTEM IN LYMPHOGENOUS METASTASIS OF COLORECTAL CANCER

The aim of this work was to study the role and relationship of the levels of the components of the urokinase system with lymphogenous metastasis in patients with colorectal cancer.Materials and methods: the study was carried out on the basis of the Medical Scientific and Educational Center of the Moscow State University named after M.V. Lomonosov from 2019 to 2021. The study included healthy donors (control group) and patients with a verified diagnosis of stage I-III colorectal cancer in accordance with the inclusion criteria; all patients underwent surgical resection of the primary tumor with lymphadenectomy of the appropriate level. All patients underwent determination of the level of uPA and uPAR in blood serum before surgery. We also analyzed the clinical and demographic data of the patients, as well as the pathomorphological characteristics of the tumor.Results. The study included 7 healthy donors and 49 patients with stage I-III colorectal cancer. The average level of serum urokinase in the control group was 2.7±1.04 ng / ml, in the study group – 4, 15±1.9 ng / ml (p = 0.071), the level of the urokinase receptor in the control and study groups was 1.36 ±0.8 ng / ml vs 3.22±2.06 ng / ml (p = 0.05). The average level of serum urokinase in patients without and with lesions of lymph nodes was 3.4±1.4 ng / ml and 4.4±2.3 ng / ml (p = 0.068).Conclusion. There is a tendency to an increase in the level of components of the urokinase system in the peripheral blood in patients with colon neoplasms in the preoperative period, depending on the presence of metastatic lesions of regional lymph nodes, which indicates the need for further research in this area.

Mesenchymal stromal cells enhance self-assembly of a HUVEC tubular network through uPA-uPAR/VEGFR2/integrin/NOTCH crosstalk

Endothelial cells (ECs) degrade the extracellular matrix of vessel walls and contact surrounding cells to facilitate migration during angiogenesis, leading to formation of an EC-tubular network (ETN). Mesenchymal stromal cells (MSC) support ETN formation when co-cultured with ECs, but the mechanism is incompletely understood. We examined the role of the urokinase-type plasminogen activator (uPA) system, i.e. the serine protease uPA, its inhibitor PAI-1, receptor uPAR/CD87, clearance by the low-density lipoprotein receptor-related protein (LRP1) and their molecular partners, in the formation of ETNs supported by adipose tissue-derived MSC. Co-culture of human umbilical vein ECs (HUVEC) with MSC increased mRNA expression levels of uPAR, MMP14, VEGFR2, TGFβ1, integrin β₃ and Notch pathway components (Notch1 receptor and ligands: Dll1, Dll4, Jag1) in HUVECs and uPA, uPAR, TGFβ1, integrin β₃, Jag1, Notch3 receptor in MSC. Inhibition at several steps in the activation process indicates that uPA, uPAR and LRP1 cross-talk with α_v-integrins, VEGFR2 and Notch receptors/ligands to mediate ETN formation in HUVEC-MSC co-culture. The urokinase system mediates ETN formation through the coordinated action of uPAR, uPA's catalytic activity, its binding to uPAR and its nuclear translocation. These studies identify potential targets to help control aberrant angiogenesis with minimal impact on healthy vasculature.

Targeting the Urokinase-Type Plasminogen Activator Receptor (uPAR) in Human Diseases With a View to Non-invasive Imaging and Therapeutic Intervention

The interaction between the serine protease urokinase-type plasminogen activator (uPA) and its glycolipid-anchored receptor (uPAR) focalizes plasminogen activation to cell surfaces, thereby regulating extravascular fibrinolysis, cell adhesion, and migration. uPAR belongs to the Ly6/uPAR (LU) gene superfamily and the high-affinity binding site for uPA is assembled by a dynamic association of its three consecutive LU domains. In most human solid cancers, uPAR is expressed at the invasive areas of the tumor-stromal microenvironment. High levels of uPAR in resected tumors or shed to the plasma of cancer patients are robustly associated with poor prognosis and increased risk of relapse and metastasis. Over the years, a plethora of different strategies to inhibit uPA and uPAR function have been designed and investigated in vitro and in vivo in mouse models, but so far none have been implemented in the clinics. In recent years, uPAR-targeting with the intent of cytotoxic eradication of uPAR-expressing cells have nonetheless gained increasing momentum. Another avenue that is currently being explored is non-invasive imaging with specific uPAR-targeted reporter-molecules containing positron emitting radionuclides or near-infrared (NIR) florescence probes with the overarching aim of being able to: (i) localize disease dissemination using positron emission tomography (PET) and (ii) assist fluorescence guided surgery using optical imaging. In this review, we will discuss these advancements with special emphasis on applications using a small 9-mer peptide antagonist that targets uPAR with high affinity.

Downregulation of uPAR promotes urokinase translocation into the nucleus and epithelial to mesenchymal transition in neuroblastoma

The urokinase system is involved in a variety of physiological processes, such as fibrinolysis, matrix remodeling, wound healing, and regeneration. Upon binding to its cognate receptor urokinase‐type plasminogen activator receptor (uPAR), urokinase‐type plasminogen activator (uPA) catalyzes the conversion of plasminogen to plasmin and the activation of matrix metalloproteases. Apart from this, uPA–uPAR interaction can lead to the activation of transcription factors, mitogen‐activated protein kinase signaling pathways and RTK cascades. Elevated expression of uPA and uPAR is markedly associated with cancer progression and metastasis and correlates with a poor prognosis in clinics. Targeting the urokinase system has proved to be effective in experimental models in vitro and in vivo, however, in clinics the inhibition of the uPA/uPAR system has fallen short of expectations, suggesting that the question of the functional relevance of uPA/uPAR system is far from being moot. Recently, using CRISPR/Cas9 technology, we have shown that uPAR knockout decreases the proliferation of neuroblastoma Neuro2a cells in vitro. In the present study we demonstrate that uPAR expression is essential for maintaining the epithelial phenotype in Neuro2a cells and that uPAR silencing promotes epithelial‐mesenchymal transition (EMT) and increased cell migration. Accordingly, uPAR knockout results in the downregulation of epithelial markers (E‐cadherin, occludin, and claudin‐5) and in the increase of mesenchymal markers (N‐cadherin, α‐smooth muscle actin, and interleukin‐6). In search of the molecular mechanism underlying these changes, we identified uPA as a key component. Two key insights emerged as a result of this work: in the absence of uPAR, uPA is translocated into the nucleus where it is presumably involved in the activation of transcription factors (nuclear factor κB and Snail) resulting in EMT. In uPAR‐expressing cells, uPAR functions as a uPA “trap” that binds uPA on the cell surface and promotes controlled uPA internalization and degradation in lysosomes.

Role of angiogenesis in melanoma progression: Update on key angiogenic mechanisms and other associated components

Angiogenesis, the formation of new blood vessels from existing blood vessels, is a complex and highly regulated process that plays a role in a wide variety of physiological and pathological processes. In malignancy, angiogenesis is essential for neoplastic cells to acquire the nutrients and oxygen critical for their continued proliferation. Angiogenesis requires a sequence of well-coordinated events mediated by a number of tightly regulated interactions between pro-angiogenic factors and their corresponding receptors expressed on various vascular components (e.g., endothelial cells and pericytes) and stromal components forming the extracellular matrix. In this review, we discuss the functional roles of key growth factors and cytokines known to promote angiogenesis in cutaneous melanoma and key factors implicated in the extracellular matrix remodeling that acts synergistically with angiogenesis to promote tumor progression in melanoma, incorporating some of the most up-to-date basic science knowledge from recently published in vivo and in vitro experimental studies.

The role of soluble urokinase plasminogen activator receptor (suPAR) in the diagnostics of diabetic foot infection

Background: To investigate the role of soluble urokinase plasminogen activator receptor (suPAR) in the diagnosis of diabetic foot infection and to determine whether it is superior to other infection markers like leukocyte, neutrophil, erythrocyte sedimentation rate, c-reactive protein and procalcitonin.Methods: The present prospective study consisted of four groups: Group 1, healthy volunteers (n = 38); Group 2, patients without diabetic foot ulcers (n = 40); Group 3, diabetic patients with uninfected foot ulcers (n = 33); and Group 4, patients who had diabetic foot infection (n = 48). In each group, the leukocyte, neutrophil, erythrocyte sedimentation rate, c-reactive protein and procalcitonin and suPAR levels were examined. The results were then statistically compared. In addition, the patients in Group 4 were further divided according to the presence of mild, moderate, and severe infection. Also osteomyelitis were evaluated in Group 4 and statistically compared.Results: All infection markers were significantly higher in group 4 patients than those in the other three groups (p < .05). Similarly, all infection markers in the severe diabetic foot infection group were statistically higher than mild diabetic foot infection group (p < .05); however, only suPAR and erythrocyte sedimentation rate were significantly high in cases with osteomyelitis (p < .05). In the receiver operating characteristic analysis, the optimal cut-off value for suPAR was determined to be 2.8 ng/ml, and the sensitivity and specificity above this value were 95.8% and 82.8%, respectively.Conclusions: The current study demonstrated that suPAR might be used as a supportive diagnostic method for the diagnosis of diabetic foot infections.

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

CD49b, CD87, and CD95 Are Markers for Activated Cancer-Associated Fibroblasts Whereas CD39 Marks Quiescent Normal Fibroblasts in Murine Tumor Models

Fibroblasts are thought to be key players in the tumor microenvironment. Means to identify and isolate fibroblasts as well as an understanding of their cancer-specific features are essential to dissect their role in tumor biology. To date, the identification of cancer-associated fibroblasts is widely based on generic markers for activated fibroblasts in combination with their origin in tumor tissue. This study was focused on a deep characterization of the cell surface marker profile of cancer-associated fibroblasts in widely used mouse tumor models and defining aberrant expression profiles by comparing them to their healthy counterparts. We established a generic workflow to isolate healthy and cancer-associated fibroblasts from solid tissues, thereby reducing bias, and background noise introduced by non-target cells. We identified CD87, CD44, CD49b, CD95, and Ly-6C as cancer-associated fibroblast cell surface markers, while CD39 was identified to mark normal fibroblasts from healthy tissues. In addition, we found a functional association of most cancer-related fibroblast markers to proliferation and a systemic upregulation of CD87, and CD49b in tumor-bearing mice, even in non-affected tissues. These novel markers will facilitate the characterization of fibroblasts and shed further light in their functions and implication in cancer progression.

Characterising the Subsite Specificity of Urokinase-Type Plasminogen Activator and Tissue-Type Plasminogen Activator using a Sequence-Defined Peptide Aldehyde Library

Urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) are two serine proteases that contribute to initiating fibrinolysis by activating plasminogen. uPA is also an important tumour-associated protease due to its role in extracellular matrix remodelling. Overexpression of uPA has been identified in several different cancers and uPA inhibition has been reported as a promising therapeutic strategy. Although several peptide-based uPA inhibitors have been developed, the extent to which uPA tolerates different tetrapeptide sequences that span the P1-P4 positions remains to be thoroughly explored. In this study, we screened a sequence-defined peptide aldehyde library against uPA and tPA. Preferred sequences from the library screen yielded potent inhibitors for uPA, led by Ac-GTAR-H (K_i =18 nm), but not for tPA. Additionally, synthetic peptide substrates corresponding to preferred inhibitor sequences were cleaved with high catalytic efficiency by uPA but not by tPA. These findings provide new insights into the binding specificity of uPA and tPA and the relative activity of tetrapeptide inhibitors and substrates against these enzymes.

6-Substituted Hexamethylene Amiloride (HMA) Derivatives as Potent and Selective Inhibitors of the Human Urokinase Plasminogen Activator for Use in Cancer

Metastasis is the cause of death in the majority (∼90%) of malignant cancers. The oral potassium-sparing diuretic amiloride and its 5-substituted derivative 5 -N, N-(hexamethylene)amiloride (HMA) reportedly show robust antitumor/metastasis effects in multiple in vitro and animal models. These effects are likely due, at least in part, to inhibition of the urokinase plasminogen activator (uPA), a key protease determinant of cell invasiveness and metastasis. This study reports the discovery of 6-substituted HMA analogs that show nanomolar potency against uPA, high selectivity over related trypsin-like serine proteases, and minimal inhibitory effects against epithelial sodium channels (ENaC), the diuretic and antikaliuretic target of amiloride. Reductions in lung metastases were demonstrated for two analogs in a late-stage experimental mouse metastasis model, and one analog completely inhibited formation of liver metastases in an orthotopic xenograft mouse model of pancreatic cancer. The results support further evaluation of 6-substituted HMA derivatives as uPA-targeting anticancer drugs.

Cell Receptor and Cofactor Interactions of the Contact Activation System and Factor XI

The contact activation system (CAS) or contact pathway is central to the crosstalk between coagulation and inflammation and contributes to diverse disorders affecting the cardiovascular system. CAS initiation contributes to thrombosis but is not required for hemostasis and can trigger plasma coagulation via the intrinsic pathway [through factor XI (FXI)] and inflammation via bradykinin release. Activation of factor XII (FXII) is the principal starting point for the cascade of proteolytic cleavages involving FXI, prekallikrein (PK), and cofactor high molecular weight kininogen (HK) but the precise location and cell receptor interactions controlling these reactions remains unclear. FXII, PK, FXI, and HK utilize key protein domains to mediate binding interactions to cognate cell receptors and diverse ligands, which regulates protease activation. The assembly of contact factors has been demonstrated on the cell membranes of a variety of cell types and microorganisms. The cooperation between the contact factors and endothelial cells, platelets, and leukocytes contributes to pathways driving thrombosis yet the basis of these interactions and the relationship with activation of the contact factors remains undefined. This review focuses on cell receptor interactions of contact proteins and FXI to develop a cell-based model for the regulation of contact activation.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

Diversity and functional evolution of the plasminogen activator system

The urokinase plasminogen activator system is a family of serine proteases which consists of uPA (urokinase plasminogen activator), uPAR (urokinase type plasminogen activator receptor) and PAI-1 (plasminogen activator inhibitor 1). In addition to their significant roles in activation, these proteases act as key regulators of the tumor microenvironment and are involved in the metastatic process in many cancers. High levels of uPA system proteases in many human cancer predicts poor patient prognosis and strongly indicated a key role of uPA system in cancer metastasis. Individual components of uPA system are found to be differentially expressed in cancer cells compared to normal cells and therefore are potential therapeutic targets. In this review, we present the molecular and cellular mechanisms underlying the role of uPA system in cancer progression. Epithelial to mesenchymal transitions (EMT) is the main cause of the cancer cell metastasis. We have also attempted to relate the role of uPA signaling in EMT of cancer cells.

The urokinase-type plasminogen activator system and its role in tumor progression

In the multistage process of carcinogenesis, the key link in the growth and progression of the tumor is the invasion of malignant cells into normal tissue and their distribution and the degree of destruction of tissues. The most important role in the development of these processes is played by the system of urokinase-type plasminogen activator (uPA system), which consists of several components: serine proteinase – uPA, its receptor – uPAR and its two endogenous inhibitors – PAI-1 and PAI-2. The components of the uPA system are expressed by cancer cells to a greater extent than normal tissue cells. uPA converts plasminogen into broad spectrum, polyfunctional protease plasmin, which, in addition to the regulation of fibrinolysis, can hydrolyze a number of components of the connective tissue matrix (СTM), as well as activate the zymogens of secreted matrix metalloproteinases (MMР) – pro-MMР. MMРs together can hydrolyze all the main components of the СTM, and thus play a key role in the development of invasive processes, as well as to perform regulatory functions by activating and releasing from STM a number of biologically active molecules that are involved in the regulation of the main processes of carcinogenesis. The uPA system promotes tumor progression not only through the proteolytic cascade, but also through uPAR, PAI-1 and PAI-2, which are involved in both the regulation of uPA/uPAR activity and are involved in proliferation, apoptosis, chemotaxis, adhesion, migration and activation of epithelial-mesenchymal transition pathways. All of the above processes are aimed at regulating invasion, metastasis and angiogenesis. The components of the uPA system are used as prognostic and diagnostic markers of many cancers, as well as serve as targets for anticancer therapy.

Platelets and matrix metalloproteinases

Matrix metalloproteinases (MMPs) and their inhibitors essentially contribute to a variety of pathophysiologies by modulating cell migration, tissue degradation and inflammation. Platelet-associated MMP activity appears to play a major role in these processes. First, platelets can concentrate leukocyte-derived MMP activity to sites of vascular injury by leukocyte recruitment. Second, platelets stimulate MMP production in e.g. leukocytes, endothelial cells, or tumour cells by direct receptor interaction or/and by paracrine pathways. Third, platelets synthesise and secrete a variety of MMPs including MMP-1, MMP-2, MMP-3, and MMP-14 (MT1-MMP), and potentially MMP-9 as well as the tissue inhibitors of metalloproteinase (TIMPs). This review focuses on platelet-derived and platelet-induced MMPs and their inhibitors.

Recent Treatment Advances and New Trials in Adult Nephrotic Syndrome

The etiology of nephrotic syndrome is complex and ranges from primary glomerulonephritis to secondary forms. Patients with nephrotic syndrome often need immunosuppressive treatment with its side effects and may progress to end stage renal disease. This review focuses on recent advances in the treatment of primary causes of nephrotic syndrome (idiopathic membranous nephropathy (iMN), minimal change disease (MCD), and focal segmental glomerulosclerosis (FSGS)) since the publication of the KDIGO guidelines in 2012. Current treatment recommendations are mostly based on randomized controlled trials (RCTs) in children, small RCTs, or case series in adults. Recently, only a few new RCTs have been published, such as the Gemritux trial evaluating rituximab treatment versus supportive antiproteinuric and antihypertensive therapy in iMN. Many RCTs are ongoing for iMN, MCD, and FSGS that will provide further information on the effectiveness of different treatment options for the causative disease. In addition to reviewing recent clinical studies, we provide insight into potential new targets for the treatment of nephrotic syndrome from recent basic science publications.

Cross Talk Pathways Between Coagulation and Inflammation

Anatomic pathology studies performed over 150 years ago revealed that excessive activation of coagulation occurs in the setting of inflammation. However, it has taken over a century since these seminal observations were made to delineate the molecular mechanisms by which these systems interact and the extent to which they participate in the pathogenesis of multiple diseases. There is, in fact, extensive cross talk between coagulation and inflammation, whereby activation of one system may amplify activation of the other, a situation that, if unopposed, may result in tissue damage or even multiorgan failure. Characterizing the common triggers and pathways are key for the strategic design of effective therapeutic interventions. In this review, we highlight some of the key molecular interactions, some of which are already showing promise as therapeutic targets for inflammatory and thrombotic disorders.

Plasma Level of Soluble Urokinase-type Plasminogen Activator Receptor Predicts the Severity of Acute Alcohol Pancreatitis

OBJECTIVES

Systemic levels of soluble urokinase-type plasminogen activator receptor (suPAR) are increased in various inflammatory and infectious diseases. We investigated the activation and prognostic value of plasma suPAR (P-suPAR) in patients experiencing their first acute alcohol pancreatitis (AAP).

METHODS

From prospectively collected data, we measured P-suPAR concentrations in 104 patients with AAP during hospitalization and again after discharge.

RESULTS

According to the revised Atlanta classification, pancreatitis was moderately severe in 29 (28%) and severe in 6 (6%) patients and these severities were combined for further analysis (non-mild AAP, n = 35; 34%). Median P-suPAR levels were significantly higher in patients with AAP during hospitalization than after discharge (4.8 vs 3.1 ng/mL; P < 0.001) and in non-mild compared to mild AAP (6.2 vs 4.2 ng/mL; P < 0.001). When the analysis was made 1 to 4 days after admission (n = 68), the area under the curve was 0.81 (95% confidence interval, 0.70-0.92). P-suPAR was found to be a better prognostic marker in AAP than C-reactive protein, hematocrit, or creatinine.

CONCLUSIONS

P-suPAR concentrations are elevated in AAP and correlate with the severity of the disease. These results suggest that P-suPAR may have potential to serve as a novel prognostic marker for AAP severity on admission.

Increased Urokinase-Type Plasminogen Activator Receptor Expression on Circulating Monocytes Is Correlated with Clinical Instability and Long-Term Adverse Cardiac Events in Patients with Coronary Artery Disease

OBJECTIVES

This study sought to investigate the clinical correlates and prognostic roles of urokinase-type plasminogen activator receptor (uPAR) on circulating monocytes in patients with coronary artery disease (CAD).

METHODS

263 angina patients were included in this study. The percentage of uPAR expressing monocytes (PUEM) and the mean fluorescence intensity (MFI) index of uPAR were measured using flow cytometry. Patient follow-up was on average 604 days. Major adverse cardiac events (MACE) were defined as a composite of cardiac death, reinfarction, acute heart failure and hospitalization for revascularization.

RESULTS

The PUEM and MFI index levels were significantly more elevated in acute coronary syndrome patients than in stable ones. uPAR expressions on circulating monocytes at admission were correlated to inflammatory biomarkers and myocardial necrosis. Logistic regression analysis revealed that PUEM ≥15% (OR 21.96, 95% CI 7.31-65.98, p < 0.001) and uPAR MFI index ≥3.00 (OR 3.54, 95% CI 1.18-10.59, p = 0.024) were independent determinants of clinical instability in patients with CAD. When followed up, a high PUEM level at admission was an independent prognostic parameter for long-term MACE (HR 3.99, 95% CI 1.31-12.11, p = 0.015).

CONCLUSIONS

uPAR expression on circulating monocytes is associated with clinical instability and myocardial necrosis and independently predicts the risk of MACE in patients with CAD.

Urokinase and urokinase receptor participate in regulation of neuronal migration, axon growth and branching

PURPOSE

Recent findings indicate the significant contribution of urokinase and urokinase receptor (uPA and uPAR) in the processes of nerve regeneration, however, their role in axonal growth and branching is unclear. Using a 3D model of mouse Dorsal Root Ganglia (DRG) explants, differentiated into neurons Neuro 2a cells and transgenic mice lacking the urokinase gene, we studied the involvement of the uPA/uPAR system in the neural cell migration, neurite outgrowth, elongation and branching.

RESULTS

uPA and uPAR are expressed in the growth cones of axons. Using an ex vivo model of DRG explants in Matrigel we have found that uPA inhibition attenuates neural cell migration and axonal growth, pointing to an important role of urokinase in these processes. Apparently, uPA mediates its effects through its specific receptor uPAR: anti-uPAR antibody, which blocks the uPA binding to uPAR, stimulates axon branching and attenuates neural cell migration from DRG explants. Simultaneous inhibition of uPA and uPAR almost completely prevents the axonal outgrowth from explants into the Matrigels. Experiments in vitro using Neuro 2a cells differentiated into neurons demonstrate that administration of exogenous uPA increases the neurite growth rate (elongation), most likely via the interaction of uPA with uPAR. Blocking of uPAR stimulates neurite formation and enhances branching of preexisting neurites. The results obtained on DRG explants from transgenic mice lacking uPA gene support the assumption that uPA stimulates neurite growth via uPA/uPAR interaction and uPAR role in axons branching and neural cell migration.

CONCLUSIONS

The uPA/uPAR system plays an essential role in neural cell migration, axonal growth and branching.

Urokinase-type Plasminogen Activator (uPA) Promotes Angiogenesis by Attenuating Proline-rich Homeodomain Protein (PRH) Transcription Factor Activity and De-repressing Vascular Endothelial Growth Factor (VEGF) Receptor Expression

Urokinase-type plasminogen activator (uPA) regulates angiogenesis and vascular permeability through proteolytic degradation of extracellular matrix and intracellular signaling initiated upon its binding to uPAR/CD87 and other cell surface receptors. Here, we describe an additional mechanism by which uPA regulates angiogenesis. Ex vivo VEGF-induced vascular sprouting from Matrigel-embedded aortic rings isolated from uPA knock-out (uPA(-/-)) mice was impaired compared with vessels emanating from wild-type mice. Endothelial cells isolated from uPA(-/-) mice show less proliferation and migration in response to VEGF than their wild type counterparts or uPA(-/-) endothelial cells in which expression of wild type uPA had been restored. We reported previously that uPA is transported from cell surface receptors to nuclei through a mechanism that requires its kringle domain. Intranuclear uPA modulates gene transcription by binding to a subset of transcription factors. Here we report that wild type single-chain uPA, but not uPA variants incapable of nuclear transport, increases the expression of cell surface VEGF receptor 1 (VEGFR1) and VEGF receptor 2 (VEGFR2) by translocating to the nuclei of ECs. Intranuclear single-chain uPA binds directly to and interferes with the function of the transcription factor hematopoietically expressed homeodomain protein or proline-rich homeodomain protein (HHEX/PRH), which thereby lose their physiologic capacity to repress the activity of vehgr1 and vegfr2 gene promoters. These studies identify uPA-dependent de-repression of vegfr1 and vegfr2 gene transcription through binding to HHEX/PRH as a novel mechanism by which uPA mediates the pro-angiogenic effects of VEGF and identifies a potential new target for control of pathologic angiogenesis.

Organization, evolution and functions of the human and mouse Ly6/uPAR family genes

Members of the lymphocyte antigen-6 (Ly6)/urokinase-type plasminogen activator receptor (uPAR) superfamily of proteins are cysteine-rich proteins characterized by a distinct disulfide bridge pattern that creates the three-finger Ly6/uPAR (LU) domain. Although the Ly6/uPAR family proteins share a common structure, their expression patterns and functions vary. To date, 35 human and 61 mouse Ly6/uPAR family members have been identified. Based on their subcellular localization, these proteins are further classified as GPI-anchored on the cell membrane, or secreted. The genes encoding Ly6/uPAR family proteins are conserved across different species and are clustered in syntenic regions on human chromosomes 8, 19, 6 and 11, and mouse Chromosomes 15, 7, 17, and 9, respectively. Here, we review the human and mouse Ly6/uPAR family gene and protein structure and genomic organization, expression, functions, and evolution, and introduce new names for novel family members.

Circulating Permeability Factors in Primary Focal Segmental Glomerulosclerosis: A Review of Proposed Candidates

Primary focal segmental glomerulosclerosis (FSGS) is a major cause of the nephrotic syndrome and often leads to end-stage renal disease. This review focuses on circulating permeability factors in primary FSGS that have been implicated in the pathogenesis for a long time, partly due to the potential recurrence in renal allografts within hours after transplantation. Recently, three molecules have been proposed as a potential permeability factor by different groups: the soluble urokinase plasminogen activator receptor (suPAR), cardiotrophin-like cytokine factor-1 (CLCF-1), and CD40 antibodies. Both CLCF-1 and CD40 antibodies have not been validated by independent research groups yet. Since the identification of suPAR, different studies have questioned the validity of suPAR as a biomarker to distinguish primary FSGS from other proteinuric kidney diseases as well as suPAR's pathogenic role in podocyte damage. Researchers have suggested that cleaved molecules of suPAR have a pathogenic role in FSGS but further studies are needed to determine this role. In future studies, proposed standards for the research of the permeability factor should be carefully followed. The identification of the permeability factor in primary FSGS would be of great clinical relevance as it could influence potential individual treatment regimen.

Serum uPAR as Biomarker in Breast Cancer Recurrence: A Mathematical Model

There are currently over 2.5 million breast cancer survivors in the United States and, according to the American Cancer Society, 10 to 20 percent of these women will develop recurrent breast cancer. Early detection of recurrence can avoid unnecessary radical treatment. However, self-examination or mammography screening may not discover a recurring cancer if the number of surviving cancer cells is small, while biopsy is too invasive and cannot be frequently repeated. It is therefore important to identify non-invasive biomarkers that can detect early recurrence. The present paper develops a mathematical model of cancer recurrence. The model, based on a system of partial differential equations, focuses on tissue biomarkers that include the plasminogen system. Among them, only uPAR is known to have significant correlation to its concentration in serum and could therefore be a good candidate for serum biomarker. The model includes uPAR and other associated cytokines and cells. It is assumed that the residual cancer cells that survived primary cancer therapy are concentrated in the same location within a region with a very small diameter. Model simulations establish a quantitative relation between the diameter of the growing cancer and the total uPAR mass in the cancer. This relation is used to identify uPAR as a potential serum biomarker for breast cancer recurrence.

Role of mesenchymal stem cell-derived fibrinolytic factor in tissue regeneration and cancer progression

Tissue regeneration during wound healing or cancer growth and progression depends on the establishment of a cellular microenvironment. Mesenchymal stem cells (MSC) are part of this cellular microenvironment, where they functionally modulate cell homing, angiogenesis, and immune modulation. MSC recruitment involves detachment of these cells from their niche, and finally MSC migration into their preferred niches; the wounded area, the tumor bed, and the BM, just to name a few. During this recruitment phase, focal proteolysis disrupts the extracellular matrix (ECM) architecture, breaks cell-matrix interactions with receptors, and integrins, and causes the release of bioactive fragments from ECM molecules. MSC produce a broad array of proteases, promoting remodeling of the surrounding ECM through proteolytic mechanisms. The fibrinolytic system, with its main player plasmin, plays a crucial role in cell migration, growth factor bioavailability, and the regulation of other protease systems during inflammation, tissue regeneration, and cancer. Key components of the fibrinolytic cascade, including the urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1), are expressed in MSC. This review will introduce general functional properties of the fibrinolytic system, which go beyond its known function of fibrin clot dissolution (fibrinolysis). We will focus on the role of the fibrinolytic system for MSC biology, summarizing our current understanding of the role of the fibrinolytic system for MSC recruitment and the functional consequences for tissue regeneration and cancer. Aspects of MSC origin, maintenance, and the mechanisms by which these cells contribute to altered protease activity in the microenvironment under normal and pathological conditions will also be discussed.

A circulating permeability factor in focal segmental glomerulosclerosis: the hunt continues

Primary focal segmental glomerulosclerosis (FSGS) is one of the major causes of steroid-resistant nephrotic syndrome, and renal prognosis in patients with steroid-resistant FSGS is poor. It has been long speculated that a circulating permeability factor should be implicated in the pathogenesis of the disease because a substantial portion of the patients with primary FSGS experience recurrence shortly after transplantation. Although molecules such as cardiotrophin-like cytokine 1 (CLC-1) and anti-CD40 antibody have been proposed to be potential circulating permeability factors, a definitive factor remains to be discovered. Soluble urokinase-type plasminogen activator receptor (suPAR) has attracted substantial attention and garnered scrutiny by renal researchers since Reiser's group suggested that it was linked to the pathogenesis of primary FSGS and that it might be useful as a diagnostic biomarker. A number of different cohort studies have shown that serum suPAR levels are negatively associated with renal function and can scarcely differentiate FSGS from the other glomerular/renal diseases. In contrast to initial studies, several in vivo studies investigating the effects of forced suPAR upregulation could not show the induction of proteinuria or podocyte injury. Currently it is suggested that a different form of suPAR, which cannot be measured by presently available enzyme-linked immunosorbent assay, might be the culprit; however, it remains to be determined whether this is the case. Because a circulating permeability factor might be a useful biomarker for diagnosing FSGS as well as a potent therapeutic target for primary and recurrent FSGS, further dedicated work will be needed.

Interaction of spirochetes with the host fibrinolytic system and potential roles in pathogenesis

The pathogenic spirochetes Borrelia burgdorferi, B. hermsii, B. recurrentis, Treponema denticola and Leptospira spp. are the etiologic agents of Lyme disease, relapsing fever, periodontitis and leptospirosis, respectively. Lyme borreliosis is a multi-systemic disorder and the most prevalent tick-borne disease in the northern hemisphere. Tick-borne relapsing fever is persistent in endemic areas worldwide, representing a significant burden in some African regions. Periodontal disease, a chronic inflammatory disorder that often leads to tooth loss, is caused by several potential pathogens found in the oral cavity including T. denticola. Leptospirosis is considered the most widespread zoonosis, and the predominant human disease in tropical, undeveloped regions. What these diseases have in common is that they are a significant burden to healthcare costs in the absence of prophylactic measures. This review addresses the interaction of these spirochetes with the fibrinolytic system, plasminogen (Plg) binding to the surface of bacteria and the generation of plasmin (Pla) on their surface. The consequences on host-pathogen interactions when the spirochetes are endowed with this proteolytic activity are discussed on the basis of the results reported in the literature. Spirochetes equipped with Pla activity have been shown to degrade extracellular matrix (ECM) components, in addition to digesting fibrin, facilitating bacterial invasion and dissemination. Pla generation triggers the induction of matrix metalloproteases (MMPs) in a cascade of events that enhances the proteolytic capacity of the spirochetes. These activities in concert with the interference exerted by the Plg/Pla on the complement system - helping the bacteria to evade the immune system - should illuminate our understanding of the mechanisms involved in host infection.

Angiogenin interacts with the plasminogen activation system at the cell surface of breast cancer cells to regulate plasmin formation and cell migration

Angiogenin (ANG), a 14-kDa pro-angiogenic secreted protein, has been shown to play a role in cell migration and tumor invasion, which involve proteolytic cleavage of plasminogen to generate plasmin. However, the mechanism by which ANG regulates plasmin formation and cell migration was not known. Our studies here detected elevated levels of secreted and cell surface-bound ANG in highly invasive metastatic breast cancer cells. ANG was also detected at very high levels in the tumor cells in infiltrating ductal carcinomas. By immunofluorescence and immunoprecipitation analysis, ANG was detected at the leading edges of the cell surfaces where it colocalized and interacted with members of the plasminogen activation system (PAS) such as annexin A2 (A2), calpactin (S100-A10) and urokinase plasminogen activator receptor (uPAR). Analysis of lipid raft (LR) and non-lipid raft (NLR) regions of the cell membranes showed the predominance of ANG, A2 and S100-A10 in the LR regions. In contrast, uPAR was detected predominantly in the NLR fractions, suggesting that ANG interacts with uPAR at the junctions of LR and NLR regions. ANG knockdown in T47D and MDA-MB-231 breast cancer cell lines did not affect the cellular expression of A2, S100-A10 and uPAR but decreased cell migration and plasmin formation. Neutralization of ANG with monoclonal antibodies similarly decreased the migration of MDA-MB-231 cells. In the presence of ANG, uPAR was observed to interact with uPA, which is necessary for plasmin formation. Conversely, in the absence of ANG, uPAR did not interact with uPA and FAK and Src kinases were observed to be dephosphorylated. Exogenous addition of recombinant ANG to ANG knocked down MDA-MB-231 cells restored FAK phosphorylation, uPAR interactions with uPA, plasmin formation as well as migration of these cells. Taken together, our results identified a novel role for ANG as a member of the uPAR interactome that facilitates the interaction of uPAR with uPA, leading to plasmin formation and cell migration necessary for tumor invasion and metastasis of breast cancer cells.

Primary focal and segmental glomerulosclerosis and soluble factor urokinase-type plasminogen activator receptor

Primary focal and segmental glomerulosclerosis (FSGS) may be due to genetic or acquired etiologies and is a common cause of nephrotic syndrome with high morbidity that often leads to end-stage renal failure. The different available therapeutic approaches are unsuccessful, in part due to partially deciphered heterogeneous and complex pathophysiological mechanisms. Moreover, the term FSGS, even in its primary form, comprises a histological description shared by a number of different causes with completely different molecular pathways of disease. This review focuses on the latest developments regarding the pathophysiology of primary acquired FSGS caused by soluble factor urokinase type plasminogen activator receptor, a circulating permeability factor involved in proteinuria and edema formation, and describes recent advances with potential success in therapy.

Structural investigations of recombinant urokinase growth factor-like domain

Urokinase-type plasminogen activator (uPA) is a serine protease that converts the plasminogen zymogen into the enzymatically active plasmin. uPA is synthesized and secreted as the single-chain molecule (scuPA) composed of an N-terminal domain (GFD) and kringle (KD) and C-terminal proteolytic (PD) domains. Earlier, the structure of ATF (which consists of GFD and KD) was solved by NMR (A. P. Hansen et al. (1994) Biochemistry, 33, 4847-4864) and by X-ray crystallography alone and in a complex with the soluble form of the urokinase receptor (uPAR, CD87) lacking GPI (C. Barinka et al. (2006) J. Mol. Biol., 363, 482-495). According to these data, GFD contains two β-sheet regions oriented perpendicularly to each other. The area in the GFD responsible for binding to uPAR is localized in the flexible Ω-loop, which consists of seven amino acid residues connecting two strings of antiparallel β-sheet. It was shown by site-directed mutagenesis that shortening of the Ω-loop length by one amino acid residue leads to the inability of GFD to bind to uPAR (V. Magdolen et al. (1996) Eur. J. Biochem., 237, 743-751). Here we show that, in contrast to the above-mentioned studies, we found no sign of the β-sheet regions in GFD in our uPA preparations either free or in a complex with uPAR. The GFD seems to be a rather flexible and unstructured domain, demonstrating in spite of its apparent flexibility highly specific interaction with uPAR both in vitro and in cell culture experiments. Circular dichroism, tryptophan fluorescence during thermal denaturation of the protein, and heteronuclear NMR spectroscopy of ¹⁵N/¹³C-labeled ATF both free and in complex with urokinase receptor were used to judge the secondary structure of GFD of uPA.

Thrombomodulin functions as a plasminogen receptor to modulate angiogenesis

Urokinase-type plasminogen activator (uPA) activates plasminogen (Plg) through a major pericellular proteolytic system involved in cell migration and angiogenesis; however, the Plg receptor that participates in uPA-mediated Plg activation has not yet been identified. In this study, we demonstrated that thrombomodulin (TM), a type I transmembrane glycoprotein, is a novel Plg receptor that plays a role in pericellular proteolysis and cell migration. Plg activation at the cell surface and the extent of its cell migration- and invasion-promoting effect are cellular TM expression dependent. Direct binding of Plg and the recombinant TM extracellular domain, with a KD of 0.1-0.3 μM, was determined through surface plasmon resonance analysis. Colocalization of TM, Plg, and the uPA receptor within plasma membrane lipid rafts, at the leading edge of migrating endothelial cells, was demonstrated and was also shown to overlap with areas of major pericellular proteolysis. Moreover, the roles of TM and Plg in neoangiogenesis were demonstrated in vivo through the skin wound-healing model. In conclusion, we propose that TM is a novel Plg receptor that regulates uPA/uPA receptor-mediated Plg activation and pericellular proteolysis within lipid rafts at the leading edge of migrating cells during angiogenesis.

Role of the AP-1 transcription factor FOSL1 in endothelial cells adhesion and migration

Vasculogenesis and angiogenesis, the fundamental processes by which new blood vessels are formed, involve the proliferation, migration, and remodeling of endothelial cells. Dynamic adhesion of endothelial cells to extracellular matrix plays a fundamental role in all these events. Key regulators of endothelial cells adhesion and migration are the αvβ3 and uPA-uPAR complexes. The αvβ3 integrin heterodimer is the receptor for extracellular matrix components such as vitronectin and is overexpressed on the cell surface of angiogenic endothelial cells, but not quiescent cells lining normal vessels. The uPA-uPAR complex contributes to extracellular matrix remodeling by mediating proteolytic activity at the leading edge of migrating cells. We recently reported that the FOSL1 transcription factor of the AP-1 family plays a pivotal role in the regulation of the level of the αvβ3 and uPA-uPAR complexes on the surface of endothelial cells. In this commentary, we review the current knowledge of αv and β3 transcriptional regulation in endothelial cells and discuss the role of FOSL1 in angiogenesis.

Transforming growth factor-Beta and urokinase-type plasminogen activator: dangerous partners in tumorigenesis-implications in skin cancer

Transforming growth factor-beta (TGF-β) is a pleiotropic factor, with several different roles in health and disease. TGF-β has been postulated as a dual factor in tumor progression, since it represses epithelial tumor development in early stages, whereas it stimulates tumor progression in advanced stages. During tumorigenesis, cancer cells acquire the capacity to migrate and invade surrounding tissues and to metastasize different organs. The urokinase-type plasminogen activator (uPA) system, comprising uPA, the uPA cell surface receptor, and plasminogen-plasmin, is involved in the proteolytic degradation of the extracellular matrix and regulates key cellular events by activating intracellular signal pathways, which together allow cancer cells to survive, thus, enhancing cell malignance during tumor progression. Due to their importance, uPA and its receptor are tightly transcriptionally regulated in normal development, but are deregulated in cancer, when their activity and expression are related to further development of cancer. TGF-β regulates uPA expression in cancer cells, while uPA, by plasminogen activation, may activate the secreted latent TGF-β, thus, producing a pernicious cycle which contributes to the enhancement of tumor progression. Here we review the specific roles and the interplay between TGF-β and uPA system in cancer cells and their implication in skin cancer.

Urokinase receptor orchestrates the plasminogen system in airway epithelial cell function

PURPOSE

The plasminogen system plays many roles in normal epithelial cell function, and components are elevated in diseases, such as cancer and asthma. The relative contribution of each component to epithelial function is unclear. We characterized normal cell function in airway epithelial cells with increased expression of selected pathway components.

METHODS

BEAS-2B R1 bronchial epithelial cells stably overexpressing membrane urokinase plasminogen activator receptor (muPAR), soluble spliced uPAR (ssuPAR), the ligand (uPA) or inhibitors (PAI1 or PAI2), were characterized for pathway expression. Cell function was examined using proliferation, apoptosis, and scratch wound assays. A549 alveolar epithelial cells overexpressing muPAR were similarly characterized and downstream plasmin activity, MMP-1, and MMP-9 measured.

RESULTS

Elevated expression of individual components led to changes in the plasminogen system expression profile, indicating coordinated regulation of the pathway. Increased muPAR expression augmented wound healing rate in BEAS-2B R1 and attenuated repair in A549 cells. Elevated expression of other system components had no effect on cell function in BEAS-2B R1 cells. This is the first study to investigate activity of the splice variant ssuPAR, with results suggesting that this variant plays a limited role in epithelial cell function in this model.

CONCLUSIONS

Our data highlight muPAR as the critical molecule orchestrating effects of the plasminogen system on airway epithelial cell function. These data have implications for diseases, such as cancer and asthma, and suggest uPAR as the key therapeutic target for the pathway in approaches to alter epithelial cell function.

Soluble urokinase plasminogen activator receptor is associated with inflammation in the vulnerable human atherosclerotic plaque

BACKGROUND AND PURPOSE

Recently, plasma soluble urokinase plasminogen activator receptor (suPAR) has gained interest as a marker of cardiovascular risk. suPAR is released through the cleavage of urokinase plasminogen activator receptor (uPAR), which is found in monocytes, activated T-lymphocytes and endothelial cells, all involved in atherosclerosis. suPAR levels have been well studied in plasma, but no studies have focused on suPAR in human atherosclerotic plaques. The aim of this study was to determine whether suPAR measured in the plaque is associated with symptomatic plaques and plaque inflammation.

METHODS

Plasma and carotid plaques from 162 patients were analyzed. Lipids, collagen, uPAR, and macrophages were measured histologically. Cytokines and suPAR were measured in homogenized plaque extracts using multiplex immunoassay and ELISA, respectively. Plasma levels of suPAR were analysed with ELISA. CD3, CD4, as well as uPAR mRNA expression were assessed with quantitative real-time polymerase chain reaction in plaque homogenates from 123 patients.

RESULTS

Plaque and plasma suPAR levels were higher in symptomatic patients compared with asymptomatic patients. Plaque suPAR levels correlated with plaque content of lipids and macrophages and with proinflammatory chemokines and cytokines monocyte chemoattractant protein 1, tumor necrosis factor α, interleukin 1β, interleukin 6, platelet-derived growth factor AB/BB, monocyte inflammatory protein 1β, regulated on activation normal T-cell expressed and secreted, and s-CD40L. uPAR mRNA and histological staining for uPAR correlated with plaque content of suPAR.

CONCLUSIONS

This study shows that suPAR in human carotid plaques and plasma is associated with the presence of symptoms and that plaque suPAR is associated with the vulnerable inflammatory plaque. These findings strengthen the hypothesis of suPAR as a future marker of vulnerable atherosclerotic plaques.

Differential roles of uPAR in peritoneal ovarian carcinomatosis

Epithelial ovarian cancer is the fourth leading cause of death from gynecologic malignancies in the United States. Most cases are diagnosed at late stages, with the solid tumor masses growing as peritoneal implants, or floating within the ascitic fluid (peritoneal ovarian carcinomatosis). Despite aggressive surgical "debulking," recurrence of recalcitrant disease is frequent with poor patient survival. Efforts to improve survival rates are hindered by lack of biomarkers that can detect and effectively treat ovarian cancer in its early stages. Urokinase plasminogen activator receptor (uPAR) is a multifunctional receptor involved in a myriad of tumor cell processes. However, the role of host uPAR in ovarian cancer is still elusive. To define the potential proinflammatory role of uPAR in ovarian cancer, first, using a syngeneic murine model in uPAR(-/-) mice, we found that ablation of uPAR restrained tumor take and peritoneal implants and prolonged the survival of uPAR(-/-) mice compared with their uPAR(+/+) counterparts. Ascitic fluid accumulation was significantly decreased in uPAR(-/-) mice with decreased macrophage infiltration. Second, in vitro mechanistic studies revealed that host uPAR is involved in the multiple steps of peritoneal metastatic cascade. Third, we evaluated the prognostic utility of tumor and stromal uPAR in human ovarian cancer tissue microarray. In summary, our studies indicated that uPAR plays a significant role in ovarian cancer cell-stromal crosstalk and contributes to increased vascular permeability and inflammatory ovarian cancer microenvironment. This provides a rationale for targeting the uPAR with either specific neutralizing antibodies or targeting its downstream inflammatory effectors in patients with ovarian cancer.

Fibulin-5 binds urokinase-type plasminogen activator and mediates urokinase-stimulated β1-integrin-dependent cell migration

uPA (urokinase-type plasminogen activator) stimulates cell migration through multiple pathways, including formation of plasmin and extracellular metalloproteinases, and binding to the uPAR (uPA receptor; also known as CD87), integrins and LRP1 (low-density lipoprotein receptor-related protein 1) which activate intracellular signalling pathways. In the present paper we report that uPA-mediated cell migration requires an interaction with fibulin-5. uPA stimulates migration of wild-type MEFs (mouse embryonic fibroblasts) (Fbln5+/+ MEFs), but has no effect on fibulin-5-deficient (Fbln5-/-) MEFs. Migration of MEFs in response to uPA requires an interaction of fibulin-5 with integrins, as MEFs expressing a mutant fibulin-5 incapable of binding integrins (Fbln(RGE/RGE) MEFs) do not migrate in response to uPA. Moreover, a blocking anti-(human β1-integrin) antibody inhibited the migration of PASMCs (pulmonary arterial smooth muscle cells) in response to uPA. Binding of uPA to fibulin-5 generates plasmin, which excises the integrin-binding N-terminal cbEGF (Ca2+-binding epidermal growth factor)-like domain, leading to loss of β1-integrin binding. We suggest that uPA promotes cell migration by binding to fibulin-5, initiating its cleavage by plasmin, which leads to its dissociation from β1-integrin and thereby unblocks the capacity of integrin to facilitate cell motility.

Role of epigenetics in cancer initiation and progression

The epigenome which comprises DNA methylation, histone modifications, chromatin structures and non-coding RNAs controls gene expression patterns. In cancer cells, there are aberrant changes in the epigenome. The question in cancer epigenetics is that whether these changes are the cause of cell transformation, or rather the consequence of it. We will discuss the epigenetic phenomenon in cancer, as well as the recent interests in the epigenetic reprogramming events, and their implications in the cancer stem cell theory. We will also look at the progression of cancers as they become more aggressive, with focus on the role of epigenetics in tumor metastases exemplified with the urokinase plasminogen activator (uPA) system. Last but not least, with therapeutics intervention in mind, we will highlight the importance of balance in the design of epigenetic based anti-cancer therapeutic strategies.

Role of integrins in regulating proteases to mediate extracellular matrix remodeling

The extracellular matrix (ECM) is an extracellular scaffold composed of complex mixtures of proteins that plays a pivotal role in tumor progression. ECM remodeling is crucial for tumor migration and invasion during the process of metastasis. ECM can be remodeled by several processes including synthesis, contraction and proteolytic degradation. In order to cross through the ECM barriers, malignant cells produce a spectrum of extracellular proteinases including matrix metalloproteinases (MMPs), serine proteases (mainly the urokinase plasminogen activator (uPA) system) and cysteine proteases to degrade ECM components. As major adhesion molecules to support cell attachment to ECM, integrins play critical roles in tumor progression by enhancing tumor cell survival, migration and invasion. Previous studies have shown that integrins can regulate the expression and activity of these proteases through different pathways. This review summarizes the roles of MMPs and uPA system in ECM remodeling and discusses the regulatory functions of integrins on these proteases in invasive tumors.

Matrix-bound PAI-1 supports cell blebbing via RhoA/ROCK1 signaling

The microenvironment of a tumor can influence both the morphology and the behavior of cancer cells which, in turn, can rapidly adapt to environmental changes. Increasing evidence points to the involvement of amoeboid cell migration and thus of cell blebbing in the metastatic process; however, the cues that promote amoeboid cell behavior in physiological and pathological conditions have not yet been clearly identified. Plasminogen Activator Inhibitor type-1 (PAI-1) is found in high amount in the microenvironment of aggressive tumors and is considered as an independent marker of bad prognosis. Here we show by immunoblotting, activity assay and immunofluorescence that, in SW620 human colorectal cancer cells, matrix-associated PAI-1 plays a role in the cell behavior needed for amoeboid migration by maintaining cell blebbing, localizing PDK1 and ROCK1 at the cell membrane and maintaining the RhoA/ROCK1/MLC-P pathway activation. The results obtained by modeling PAI-1 deposition around tumors indicate that matrix-bound PAI-1 is heterogeneously distributed at the tumor periphery and that, at certain spots, the elevated concentrations of matrix-bound PAI-1 needed for cancer cells to undergo the mesenchymal-amoeboid transition can be observed. Matrix-bound PAI-1, as a matricellular protein, could thus represent one of the physiopathological requirements to support metastatic formation.

Urokinase plasminogen activator receptor induced non-small cell lung cancer invasion and metastasis requires NHE1 transporter expression and transport activity

BACKGROUND: Non-small cell lung cancers (NSLC) are aggressive cancers that are insensitive to chemotherapies and accounts for nearly 33% of all cancer deaths in the United States. Two hallmarks of cancer that allow cells to invade and metastasize are sustained proliferation and enhanced motility. In this study we investigate the relationship between urokinase plasminogen activator (uPA)/uPA receptor (uPAR) signaling and Na(+)/H(+) exchanger isoform 1 (NHE1) expression and activity. METHODS AND RESULTS: The addition of 10nM uPA increased the carcinogenic potential of three NSCLC cell lines, NCI-H358, NCI-H460, and NCI-H1299. This included an increase in the rate of cell proliferation 1.6 to 1.9 fold; an increase in the percentage of cells displaying stress fibers 3.05 to 3.17 fold; and an increase in anchorage-independent growth from 1.64 to 2.0 fold. In each of these cases the increase was blocked when the experiments were performed with NHE1 inhibited by 10 μM EIPA (ethylisopropyl amiloride). To further evaluate the role of uPA/uPAR and NHE1 in tumor progression we assessed signaling events using full-length uPA compared to the uPA amino terminal fragment (ATF). Comparing uPA and ATF signaling in H460 cells, we found that both uPA and ATF increased stress fiber formation approximately 2 fold, while uPA increased matrix metalloproteinase 9 (MMP9) activity 5.44 fold compared to 2.81 fold for ATF. To expand this signaling study, two new cell lines were generated, one with reduced NHE1 expression (H460 NHE1 K/D) and one with reduced uPAR expression (H460 uPAR K/D). Using the K/D cell lines we found that neither uPA nor ATF could stimulate stress fiber formation or MMP9 activity in cells with dramatically decreased NHE1 or uPAR expression. Finally, using in vivo tumor formation studies in athymic mice we found that when mice were injected with H460 cells 80% of mice formed tumors with an average volume of 390 mm(3). This was compared to 20% of H460 uPAR K/D injected mice forming tumors with an average volume of 15 mm(3) and 10% of H460 NHE1 K/D injected mice forming tumors with an average volume of 5 mm(3). CONCLUSION: Taken together, these data demonstrate that uPA/uPAR-mediated tumor progression and metastasis requires NHE1 in NSCLC cells and suggests a potential therapeutic approach to blocking cancer progression.