Differentiation-enhanced binding of the amino-terminal fragment of human urokinase plasminogen activator to a specific receptor on U937 monocytes

Improving our understanding on the clinical role of plasmin-mediated von Willebrand factor degradation

PURPOSE OF REVIEW

Von Willebrand factor (VWF) plays a pivotal role in primary hemostasis. A Disintegrin And Metalloproteinase with a ThromboSpondin type 1 motif, member 13 (ADAMTS13) is primarily responsible for cleaving ultra-large VWF multimers into smaller, less adhesive forms. However, plasmin has also been shown to cleave VWF multimers. This proteolytic cleavage of VWF results in a decreased multimer size and, hence, a lower VWF activity. This review aims to present a comprehensive overview of the involvement of plasmin-mediated VWF proteolysis in (micro)thrombosis.

RECENT FINDINGS

Plasmin-mediated VWF proteolysis has been suggested to play a role in various pathologies involving microthrombosis in combination with an imbalance in VWF antigen levels and ADAMTS13 activity, as well as activation of the fibrinolytic system, but quantitative assays to demonstrate this were lacking. Recently, a V H H-based bioassay was developed designed specifically to quantify plasmin-cleaved VWF (cVWF). The novel ELISA assay holds significant promise for gaining further insights into the clinical relevance of plasmin-mediated VWF proteolysis in several pathologies. Furthermore, local plasmin activation at the site of microthrombosis has been shown to be a promising treatment strategy by degrading VWF-rich microthrombi.

SUMMARY

Plasmin-mediated proteolysis of VWF is observed during microthrombosis; however, it remains unclear whether it impacts disease severity. A novel ELISA method to detect cVWF will improve our understanding of the clinical role of plasmin-mediated VWF degradation.

Urokinase-Type Plasminogen Activator Receptor (uPAR) in Inflammation and Disease: A Unique Inflammatory Pathway Activator

The urokinase-type plasminogen activator receptor (uPAR) is a unique protease binding receptor, now recognized as a key regulator of inflammation. Initially, uPA/uPAR was considered thrombolytic (clot-dissolving); however, recent studies have demonstrated its predominant immunomodulatory functions in inflammation and cancer. The uPA/uPAR complex has a multifaceted central role in both normal physiological and also pathological responses. uPAR is expressed as a glycophosphatidylinositol (GPI)-linked receptor interacting with vitronectin, integrins, G protein-coupled receptors, and growth factor receptors within a large lipid raft. Through protein-to-protein interactions, cell surface uPAR modulates intracellular signaling, altering cellular adhesion and migration. The uPA/uPAR also modifies extracellular activity, activating plasminogen to form plasmin, which breaks down fibrin, dissolving clots and activating matrix metalloproteinases that lyse connective tissue, allowing immune and cancer cell invasion and releasing growth factors. uPAR is now recognized as a biomarker for inflammatory diseases and cancer; uPAR and soluble uPAR fragments (suPAR) are increased in viral sepsis (COVID-19), inflammatory bowel disease, and metastasis. Here, we provide a comprehensive overview of the structure, function, and current studies examining uPAR and suPAR as diagnostic markers and therapeutic targets. Understanding uPAR is central to developing diagnostic markers and the ongoing development of antibody, small-molecule, nanogel, and virus-derived immune-modulating treatments that target uPAR.

Endothelial-specific Enhancer as a Cis Element of PLAUR Regulation by TNF-alpha, IL-1beta, and VEGF

The expression of human PLAUR gene, which encodes the urokinase plasminogen activator receptor (uPAR), is cell- and process-specific and elevated in inflammation, cancer and senescence. Its tight regulation is achieved by regulatory elements in the gene locus, such as the promoter and several enhancers. The promoter activity is not specific to a particular cell type and has been described earlier. The proximal enhancer is endothelial-specific and responsible for the PLAUR expression pattern in endothelial cells. In this study we described the enhancer activity and its cis-regulatory elements based on the published data. We showed a possible connection of the enhancer activity with known cellular phenotypes.

All tangled up: interactions of the fibrinolytic and innate immune systems

The hemostatic and innate immune system are intertwined processes. Inflammation within the vasculature promotes thrombus development, whilst fibrin forms part of the innate immune response to trap invading pathogens. The awareness of these interlinked process has resulted in the coining of the terms "thromboinflammation" and "immunothrombosis." Once a thrombus is formed it is up to the fibrinolytic system to resolve these clots and remove them from the vasculature. Immune cells contain an arsenal of fibrinolytic regulators and plasmin, the central fibrinolytic enzyme. The fibrinolytic proteins in turn have diverse roles in immunoregulation. Here, the intricate relationship between the fibrinolytic and innate immune system will be discussed.

Nafamostat Mesylate in Combination with the Mouse Amino-Terminal Fragment of Urokinase-Human Serum Albumin Improves the Treatment Outcome of Triple-Negative Breast Cancer Therapy

Triple-negative breast cancer (TNBC) is highly aggressive and causes a higher proportion of metastatic cases. However, therapies directed to specific molecular targets have rarely achieved clinically meaningful improvements in the outcome of TNBC therapy. A urokinase-type plasminogen activator (uPA), one of the best-validated biomarkers of breast cancer, is an extracellular proteolytic serine protease involved in many pathological and physiological processes, including tumor cell invasion and metastasis. Nafamostat mesylate (NM) is a synthetic compound that inhibits various serine proteases and has been used as a therapeutic agent for the treatment of TNBC. Nevertheless, NM has poor specificity for serine proteases and is easy be hydrolyzed; moreover, the inhibitory mechanism of TNBC therapy is unclear. In this study, we combine NM with a macromolecular drug delivery vehicle, mouse amino-terminal fragment of urokinase-human serum albumin (mATF-HSA), to form a complex (mATF-HSA:NM) using the dilution-incubation-purification method. mATF specifically targets uPAR overexpressed on the surface of TNBC cells; moreover, HSA prevents NM from being hydrolyzed by numerous serine proteases. mATF-HSA:NM showed stronger inhibitory effects on the proliferation and metastasis of TNBC in vitro and in vivo without significant cytotoxicity on normal cells and tissues. In addition, we demonstrated that NM mediates metastasis of TNBC cells through inhibition of uPA using a stable uPA knockdown cell line (MDA-MB231 shuPA). Overall, we have developed a macromolecular complex targeted to treat high uPAR-expressing tumor types, and mATF-HSA can potentially be used to load other types of drugs with tumor-targeting specificity for mouse tumor models and is a promising tool to study tumor biology in mouse tumor models.

"Going with the flow" in modeling fibrinolysis

The formation of thrombi is shaped by intravascular shear stress, influencing both fibrin architecture and the cellular composition which has downstream implications in terms of stability against mechanical and fibrinolytic forces. There have been many advancements in the development of models that incorporate flow rates akin to those found in vivo. Both thrombus formation and breakdown are simultaneous processes, the balance of which dictates the size, persistence and resolution of thrombi. Therefore, there is a requirement to have models which mimic the physiological shear experienced within the vasculature which in turn influences the fibrinolytic degradation of the thrombus. Here, we discuss various assays for fibrinolysis and importantly the development of novel models that incorporate physiological shear rates. These models are essential tools to untangle the molecular and cellular processes which govern fibrinolysis and can recreate the conditions within normal and diseased vessels to determine how these processes become perturbed in a pathophysiological setting. They also have utility to assess novel drug targets and antithrombotic drugs that influence thrombus stability.

Caspase-10 affects the pathogenesis of primary biliary cholangitis by regulating inflammatory cell death

Primary biliary cholangitis (PBC) is an autoimmune disease that involves chronic inflammation and injury to biliary epithelial cells. To identify critical genetic factor(s) in PBC patients, we performed whole-exome sequencing of five female siblings, including one unaffected and four affected sisters, in a multi-PBC family, and identified 61 rare heterozygote variants that segregated only within the affected sisters. Among them, we were particularly interested in caspase-10, for although several caspases are involved in cell death, inflammation and autoimmunity, caspase-10 is little known from this perspective. We generated caspase-10 knockout macrophages, and then investigated the obtained phenotypes in comparison to those of its structurally similar protein, caspase-8. Unlike caspase-8, caspase-10 does not play a role during differentiation into macrophages, but after differentiation, it regulates the process of inflammatory cell deaths such as necroptosis and pyroptosis more strongly. Interestingly, caspase-10 displays better protease activity than caspase-8 in the process of RIPK1 cleavage, and an enhanced ability to form a complex with RIPK1 and FADD in human macrophages. Higher inflammatory cell death affected the fibrotic response of hepatic stellate cells; this effect could be recovered by treatment with UDCA and OCA, which are currently approved for PBC patients. Our findings strongly indicate that the defective roles of caspase-10 in macrophages contribute to the pathogenesis of PBC, thereby suggesting a new therapeutic strategy for PBC treatment.

Modulation of Cellular Function by the Urokinase Receptor Signalling: A Mechanistic View

Urokinase-type plasminogen activator receptor (uPAR or CD87) is a glycosyl-phosphatidyl-inositol anchored (GPI) membrane protein. The uPAR primary ligand is the serine protease urokinase (uPA), converting plasminogen into plasmin, a broad spectrum protease, active on most extracellular matrix components. Besides uPA, the uPAR binds specifically also to the matrix protein vitronectin and, therefore, is regarded also as an adhesion receptor. Complex formation of the uPAR with diverse transmembrane proteins, including integrins, formyl peptide receptors, G protein-coupled receptors and epidermal growth factor receptor results in intracellular signalling. Thus, the uPAR is a multifunctional receptor coordinating surface-associated pericellular proteolysis and signal transduction, thereby affecting physiological and pathological mechanisms. The uPAR-initiated signalling leads to remarkable cellular effects, that include increased cell migration, adhesion, survival, proliferation and invasion. Although this is beyond the scope of this review, the uPA/uPAR system is of great interest to cancer research, as it is associated to aggressive cancers and poor patient survival. Increasing evidence links the uPA/uPAR axis to epithelial to mesenchymal transition, a highly dynamic process, by which epithelial cells can convert into a mesenchymal phenotype. Furthermore, many reports indicate that the uPAR is involved in the maintenance of the stem-like phenotype and in the differentiation process of different cell types. Moreover, the levels of anchor-less, soluble form of uPAR, respond to a variety of inflammatory stimuli, including tumorigenesis and viral infections. Finally, the role of uPAR in virus infection has received increasing attention, in view of the Covid-19 pandemics and new information is becoming available. In this review, we provide a mechanistic perspective, via the detailed examination of consolidated and recent studies on the cellular responses to the multiple uPAR activities.

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.

Association of the Circulating Supar Levels with Inflammation, Fibrinolysis, and Outcome in Severe Burn Patients

BACKGROUND

Hyperfibrinolysis and pro/anti-inflammatory imbalance usually occur in the early stage of severe burns. Soluble urokinase-type plasminogen activator receptor (suPAR) is involved in fibrinolysis and inflammation. To date, the levels of circulating suPAR in non-survivors with severe burns remain unknown. This study aimed to investigate the early association between circulating suPAR levels and biomarkers of fibrinolysis, pro/anti-inflammatory, and prognosis.

METHODS

Sixty-four consecutive Chinese patients with severe burns and 26 healthy volunteers were enrolled in a prospective observational cohort. Clinical characteristics and laboratory data were collected prospectively. Blood samples were collected at 48 h post-burn, and suPAR and biomarkers of pro/anti-inflammatory and fibrinolysis were detected by enzyme-linked immunosorbent assays. Important indicators between non-survivors and survivors were compared. Linear regression analysis was performed to screen variables associated with suPAR. Logistic regression analysis and receiver operating characteristic curve (ROC) analysis were performed to evaluate the prognostic value of suPAR.

RESULT

Compared with the control group, the circulating suPAR levels in the survivors (P < 0.001) and non-survivors (P = 0.017) were higher. Compared with survivors, non-survivors had lower circulating suPAR levels at 48 h post-burn, and they showed a higher degree of fibrinolysis (higher D-dimer) and a lower TNF-α/IL-10 ratio. According to linear regression analysis, the variables independently associated with a lower suPAR level were lower platelet factor 4 (PF-4), urokinase-type plasminogen activator (uPA), and TNF-α/IL-10 levels and a higher D-dimer level. Logistic regression and ROC analyses indicated that a suPAR level ≤ 4.70 μg/L was independently associated with 30-day mortality.

CONCLUSION

Low circulating suPAR levels at 48 h post-burn in severe burn patients may reflect decreased TNF-α/IL-10 ratio and increased hyperfibrinolysis. suPAR can predict 30-day mortality in patients with severe burn.

The Urokinase Receptor (uPAR) as a "Trojan Horse" in Targeted Cancer Therapy: Challenges and Opportunities

Simple Summary

Discovered more than three decades ago, the urokinase-type plasminogen activator receptor (uPAR) has now firmly established itself as a versatile molecular target holding promise for the treatment of aggressive malignancies. The copious abundance of uPAR in virtually all human cancerous tissues versus their healthy counterparts has fostered a gradual shift in the therapeutic landscape targeting this receptor from function inhibition to cytotoxic approaches to selectively eradicate the uPAR-expressing cells by delivering a targeted cytotoxic insult. Multiple avenues are being explored in a preclinical setting, including the more innovative immune- or stroma targeting therapies. This review discusses the current state of these strategies, their potentialities, and challenges, along with future directions in the field of uPAR targeting.

Abstract

One of the largest challenges to the implementation of precision oncology is identifying and validating selective tumor-driving targets to enhance the therapeutic efficacy while limiting off-target toxicity. In this context, the urokinase-type plasminogen activator receptor (uPAR) has progressively emerged as a promising therapeutic target in the management of aggressive malignancies. By focalizing the plasminogen activation cascade and subsequent extracellular proteolysis on the cell surface of migrating cells, uPAR endows malignant cells with a high proteolytic and migratory potential to dissolve the restraining extracellular matrix (ECM) barriers and metastasize to distant sites. uPAR is also assumed to choreograph multiple other neoplastic stages via a complex molecular interplay with distinct cancer-associated signaling pathways. Accordingly, high uPAR expression is observed in virtually all human cancers and is frequently associated with poor patient prognosis and survival. The promising therapeutic potential unveiled by the pleiotropic nature of this receptor has prompted the development of distinct targeted intervention strategies. The present review will focus on recently emerged cytotoxic approaches emphasizing the novel technologies and related limits hindering their application in the clinical setting. Finally, future research directions and emerging opportunities in the field of uPAR targeting are also discussed.

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.

CRISPR/Cas9 uPAR Gene Knockout Results in Tumor Growth Inhibition, EGFR Downregulation and Induction of Stemness Markers in Melanoma and Colon Carcinoma Cell Lines

uPAR is a globular protein, tethered to the cell membrane by a GPI-anchor involved in several cancer-related properties and its overexpression commonly correlates with poor prognosis and metastasis. We investigated the consequences of uPAR irreversible loss in human melanoma and colon cancer cell lines, knocking out its expression by CRISPR/Cas9. We analyzed through flow cytometry, western blotting and qPCR, the modulation of the most known cancer stem cells-associated genes and the EGFR while we observed the proliferation rate exploiting 2D and 3D cellular models. We also generated uPAR “rescue” expression cell lines as well as we promoted the expression of only its 3’UTR to demonstrate the involvement of uPAR mRNA in tumor progression. Knocking out PLAUR, uPAR-encoding gene, we observed an inhibited growth ratio unexpectedly coupled with a significant percentage of cells acquiring a stem-like phenotype. In vivo experiments demonstrated that uPAR loss completely abrogates tumorigenesis despite the gained stem-like profile. Nonetheless, we proved that the reintroduction of the 3’UTR of PLAUR gene was sufficient to restore the wild-type status validating the hypothesis that such a region may act as a “molecular sponge”. In particular miR146a, by binding PLAUR 3’ UTR region might be responsible for uPAR-dependent inhibition of EGFR expression.

Endogenous and Borrowed Proteolytic Activity in the Borrelia

The Borrelia spp. are tick-borne pathogenic spirochetes that include the agents of Lyme disease and relapsing fever. As part of their life cycle, the spirochetes traffic between the tick vector and the vertebrate host, which requires significant physiological changes and remodeling of their outer membranes and proteome. This crucial proteome resculpting is carried out by a diverse set of proteases, adaptor proteins, and related chaperones. Despite its small genome, Borrelia burgdorferi has dedicated a large percentage of its genome to proteolysis, including a full complement of ATP-dependent proteases. Energy-driven proteolysis appears to be an important physiological feature of this dual-life-cycle bacterium. The proteolytic arsenal of Borrelia is strategically deployed for disposal of proteins no longer required as they move from one stage to another or are transferred from one host to another. Likewise, the Borrelia spp. are systemic organisms that need to break down and move through host tissues and barriers, and so their unique proteolytic resources, both endogenous and borrowed, make movement more feasible. Both the Lyme disease and relapsing fever Borrelia spp. bind plasminogen as well as numerous components of the mammalian plasminogen-activating system. This recruitment capacity endows the spirochetes with a borrowed proteolytic competency that can lead to increased invasiveness.

Neuraminidase-associated plasminogen recruitment enables systemic spread of natural avian Influenza viruses H3N1

Repeated outbreaks due to H3N1 low pathogenicity avian influenza viruses (LPAIV) in Belgium were associated with unusually high mortality in chicken in 2019. Those events caused considerable economic losses and prompted restriction measures normally implemented for eradicating high pathogenicity avian influenza viruses (HPAIV). Initial pathology investigations and infection studies suggested this virus to be able to replicate systemically, being very atypical for H3 LPAIV. Here, we investigate the pathogenesis of this H3N1 virus and propose a mechanism explaining its unusual systemic replication capability. By intravenous and intracerebral inoculation in chicken, we demonstrate systemic spread of this virus, extending to the central nervous system. Endoproteolytic viral hemagglutinin (HA) protein activation by either tissue-restricted serine peptidases or ubiquitous subtilisin-like proteases is the functional hallmark distinguishing (H5 or H7) LPAIV from HPAIV. However, luciferase reporter assays show that HA cleavage in case of the H3N1 strain in contrast to the HPAIV is not processed by intracellular proteases. Yet the H3N1 virus replicates efficiently in cell culture without trypsin, unlike LPAIVs. Moreover, this trypsin-independent virus replication is inhibited by 6-aminohexanoic acid, a plasmin inhibitor. Correspondingly, in silico analysis indicates that plasminogen is recruitable by the viral neuraminidase for proteolytic activation due to the loss of a strongly conserved N-glycosylation site at position 130. This mutation was shown responsible for plasminogen recruitment and neurovirulence of the mouse brain-passaged laboratory strain A/WSN/33 (H1N1). In conclusion, our findings provide good evidence in natural chicken strains for N1 neuraminidase-operated recruitment of plasminogen, enabling systemic replication leading to an unusual high pathogenicity phenotype. Such a gain of function in naturally occurring AIVs representing an established human influenza HA-subtype raises concerns over potential zoonotic threats.

Hydrogen Nano-Bubble Water Suppresses ROS Generation, Adipogenesis, and Interleukin-6 Secretion in Hydrogen-Peroxide- or PMA-Stimulated Adipocytes and Three-Dimensional Subcutaneous Adipose Equivalents

Reactive oxygen species (ROS)-induced oxidative stress in adipose tissue is associated with inflammation and the development of obesity-related metabolic disorders. The aim of this study is to investigate the effects of hydrogen nano-bubble water (HW) on ROS generation, adipogenesis, and interleukin-6 (IL-6) secretion in hydrogen peroxide (H₂O₂) or phorbol 12-myristate 13-acetate (PMA)-stimulated OP9 adipocytes, and three-dimensional (3D) subcutaneous adipose equivalents. Nanoparticle tracking analysis showed that fresh HW contains 1.17 × 10⁸/mL of nano-sized hydrogen bubbles. Even after 8 to 13 months of storage, approximately half of the bubbles still remained in the water. CellROX^® staining showed that HW could diminish H₂O₂- or PMA-induced intracellular ROS generation in human keratinocytes HaCaT and OP9 cells. We discovered that PMA could markedly increase lipid accumulation to 180% and IL-6 secretion 2.7-fold in OP9 adipocytes. Similarly, H₂O₂ (5 µM) also significantly stimulated lipid accumulation in OP9 cells and the 3D adipose equivalents. HW treatment significantly repressed H₂O₂- or PMA-induced lipid accumulation and IL-6 secretion in OP9 adipocytes and the 3D adipose equivalents. In conclusion, HW showed a possibility of repressing oxidative stress, inflammatory response, and adipogenesis at cellular/tissue levels. It can be used for preventing the development of metabolic disorders amongst obese people.

Assessing Plasmin Generation in Health and Disease

Fibrinolysis is an important process in hemostasis responsible for dissolving the clot during wound healing. Plasmin is a central enzyme in this process via its capacity to cleave fibrin. The kinetics of plasmin generation (PG) and inhibition during fibrinolysis have been poorly understood until the recent development of assays to quantify these metrics. The assessment of plasmin kinetics allows for the identification of fibrinolytic dysfunction and better understanding of the relationships between abnormal fibrin dissolution and disease pathogenesis. Additionally, direct measurement of the inhibition of PG by antifibrinolytic medications, such as tranexamic acid, can be a useful tool to assess the risks and effectiveness of antifibrinolytic therapy in hemorrhagic diseases. This review provides an overview of available PG assays to directly measure the kinetics of plasmin formation and inhibition in human and mouse plasmas and focuses on their applications in defining the role of plasmin in diseases, including angioedema, hemophilia, rare bleeding disorders, COVID-19, or diet-induced obesity. Moreover, this review introduces the PG assay as a promising clinical and research method to monitor antifibrinolytic medications and screen for genetic or acquired fibrinolytic disorders.

uPA-mediated plasminogen activation is enhanced by polyphosphate

Tissue plasminogen activator (tPA) and urokinase (uPA) differ in their modes of action. Efficient tPA-mediated plasminogen activation requires binding to fibrin. In contrast, uPA is fibrin independent and activates plasminogen in solution or when associated with its cellular receptor uPAR. We have previously shown that polyphosphate (polyP), alters fibrin structure and attenuates tPA and plasminogen binding to fibrin, thereby down-regulating fibrinolysis. Here we investigate the impact of polyP on uPA-mediated fibrinolysis. As previously reported polyP of an average chain length of 65 (polyP65) delays tPA-mediated fibrinolysis. The rate of plasmin generation was also delayed and reduced 1.6-fold in polyP65-containing clots (0.74 ± 0.06 vs. 1.17 ± 0.14 pM/s in P < 0.05). Analysis of tPA-mediated fibrinolysis in real-time by confocal microscopy was significantly slower in polyP65-containing clots. In marked contrast, polyP65 augmented the rate of uPA-mediated plasmin generation 4.7-fold (3.96 ± 0.34 vs. 0.84 ± 0.08 pM/s; P < 0.001) and accelerated fibrinolysis (t1/2 64.5 ± 1.7 min vs. 108.2 ± 3.8 min; P < 0.001). Analysis of lysis in real-time confirmed that polyP65 enhanced uPA-mediated fibrinolysis. Varying the plasminogen concentration (0.125 to 1 μM) in clots dose-dependently enhanced uPA-mediated fibrinolysis, while negligible changes were observed on tPA-mediated fibrinolysis. The accelerating effect of polyP65 on uPA-mediated fibrinolysis was overcome by additional plasminogen, while the down-regulation of tPA-mediated lysis and plasmin generation was largely unaffected. PolyP65 exerts opposing effects on tPA- and uPA-mediated fibrinolysis, attenuating the fibrin cofactor function in tPA-mediated plasminogen activation. In contrast, polyP may facilitate the interaction between fibrin-independent uPA and plasminogen thereby accelerating plasmin generation and downstream fibrinolysis.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Inhibiting Monocyte Recruitment to Prevent the Pro-Tumoral Activity of Tumor-Associated Macrophages in Chondrosarcoma

Chondrosarcomas (CHS) are malignant cartilaginous neoplasms with diverse morphological features, characterized by resistance to chemo- and radiation therapies. In this study, we investigated the role of tumor-associated macrophages (TAM)s in tumor tissues from CHS patients by immunohistochemistry. Three-dimensional organotypic co-cultures were set up in order to evaluate the contribution of primary human CHS cells in driving an M2-like phenotype in monocyte-derived primary macrophages, and the capability of macrophages to promote growth and/or invasiveness of CHS cells. Finally, with an in vivo model of primary CHS cells engrafted in nude mice, we tested the ability of a potent peptide inhibitor of cell migration (Ac-d-Tyr-d-Arg-Aib-d-Arg-NH2, denoted RI-3) to reduce recruitment and infiltration of monocytes into CHS neoplastic lesions. We found a significant correlation between alternatively activated M2 macrophages and intratumor microvessel density in both conventional and dedifferentiated CHS human tissues, suggesting a link between TAM abundance and vascularization in CHS. In 3D and non-contact cu-culture models, soluble factors produced by CHS induced a M2-like phenotype in macrophages that, in turn, increased motility, invasion and matrix spreading of CHS cells. Finally, we present evidence that RI-3 successfully prevent both recruitment and infiltration of monocytes into CHS tissues, in nude mice.

The urokinase plasminogen activator binding to its receptor: a quantum biochemistry description within an in/homogeneous dielectric function framework with application to uPA–uPAR peptide inhibitors

DFT calculations using the MFCC fragment-based model considering a spatial-dependent dielectric function based on the Poisson–Boltzmann approximation were performed to describe the uPA–uPAR interactions.

Differential expression of Plg-RKT and its effects on migration of proinflammatory monocyte and macrophage subsets

Membrane-bound plasmin is used by immune cells to degrade extracellular matrices, which facilitates migration. The plasminogen receptor Plg-R_KT is expressed by immune cells, including monocytes and macrophages. Among monocytes and macrophages, distinct subsets can be distinguished based on cell surface markers and pathophysiological function. We investigated expression of Plg-R_KT by monocyte and macrophage subsets and whether potential differential expression might have functional consequences for cell migration. Proinflammatory CD14⁺⁺CD16⁺ human monocytes and Ly6C^high mouse monocytes expressed the highest levels of Plg-R_KT and bound significantly more plasminogen compared with the other respective subsets. Proinflammatory human macrophages, generated by polarization with lipopolysaccharide and interferon-γ, showed significantly higher expression of Plg-R_KT compared with alternatively activated macrophages, polarized with interleukin-4 and interleukin-13. Directional migration of proinflammatory monocytes was plasmin dependent and was abolished by anti-Plg-R_KT monoclonal antibody, ε-amino-caproic acid, aprotinin, and the aminoterminal fragment of urokinase-type plasminogen activator. In an in vivo peritonitis model, significantly less Ly6C^high monocyte recruitment was observed in Plg-R_KT ^-/- compared with Plg-R_KT ^+/+ mice. Immunohistochemical analysis of human carotid plaques and adipose tissue showed that proinflammatory macrophages also exhibited high levels of Plg-R_KT in vivo. Our data demonstrate higher expression of Plg-R_KT on proinflammatory monocyte and macrophage subsets that impacts their migratory capacity.

Designing tracers for PET imaging of the urokinase-type plasminogen activator receptor from a cyclic uPA-derived peptide: first in vitro evaluations

The treatment of cancer remains a major challenge, especially after tumour cell dissemination and metastases formation. Expression of the urokinase-type plasminogen activation system including urokinase (uPA) and its receptor (uPAR) has been associated with the complex process of cell migration, a tumour's invasive potential as well as a reduced overall and disease-free survival of patients with solid cancers and haematological disorders. A cyclic peptide cyclo[21,29][d-Cys²¹ ,Cys²⁹ ]-uPA_21-30 was designed from the growth factor-like domain (GFD) of urokinase whose binding to uPAR was found to inhibit tumour growth and spread of human ovarian cancer cells in mice. With the aim of visualising uPAR expression using PET imaging to attempt an estimate on the tumour's aggressiveness, the cyclic peptide was modified with an either C- or N-terminally attached variable spacer and chelator. The free ligands were evaluated for their binding affinities to the isolated human uPAR and labelled with ⁶⁸ Ga and ¹⁷⁷ Lu to assess their lipophilicities and stabilities in human serum. Although retaining the full binding potential displayed by cyclo[21,29][d-Cys²¹ ,Cys²⁹ ]-uPA_21-30 to its target was found to be a challenging task upon both C- and N-terminal modification, chelator-bearing ligands were identified that can serve as promising starting points in the development of uPAR-addressing PET tracers.

Correlation of Serum and Ascitic Fluid Soluble Form Urokinase Plasminogen Activator Receptor Levels With Patient Complications, Disease Severity, Inflammatory Markers, and Prognosis in Patients With Severe Acute Pancreatitis

Supplemental digital content is available in the text.

Objectives

The aim of the study was to investigate the correlation of serum and ascitic fluid soluble form urokinase plasminogen activator receptor (suPAR) levels with patients' complications, disease severity, inflammatory markers, and prognosis in patients with severe acute pancreatitis (SAP).

Methods

Fifty patients with SAP, 47 patients with mild acute pancreatitis, and 50 healthy controls were enrolled. Serum samples were obtained from all participants after enrollment; meanwhile, ascitic fluid samples were collected from 20 patients with SAP who developed ascites. Serum and ascitic fluid suPAR levels were determined by enzyme-linked immunosorbent assay.

Results

Serum suPAR level was greatly elevated in patients with SAP than patients with mild acute pancreatitis and healthy controls. Receiver operating characteristic curve showed that serum suPAR presented with good value in predicting risk of pancreatic necrosis, pancreatic infection, and multiple organ dysfunction syndrome, whereas serum suPAR did not predict mortality. Serum suPAR level was also positively correlated with Acute Physiology and Chronic Health Evaluation II score, Balthazar index, and Sequential Organ Failure Assessment score. As to ascitic fluid suPAR, it was positively correlated with serum suPAR level, Acute Physiology and Chronic Health Evaluation II score, Sequential Organ Failure Assessment score, risk of pancreatic infection, and multiple organ dysfunction syndrome.

Conclusions

Serum and ascetic fluid suPAR levels could be served as markers for disease severity and risk of severe complications in patients with SAP.

Multifaced Roles of the Urokinase System in the Regulation of Stem Cell Niches

Proliferation, subsequent migration to the damaged area, differentiation into appropriate cell types, and/or secretion of biologically active molecules and extracellular vesicles are important processes that underlie the involvement of stem/progenitor cells in the repair and regeneration of tissues and organs. All these functions are regulated through the interaction between stem cells and the microenvironment in the tissue cell niches that control these processes through direct cell-cell interactions, production of the extracellular matrix, release of extracellular vesicles, and secretion of growth factors, cytokines, chemokines, and proteases. One of the most important proteolytic systems involved in the regulation of cell migration and proliferation is the urokinase system represented by the urokinase plasminogen activator (uPA, urokinase), its receptor (uPAR), and inhibitors. This review addresses the issues of urokinase system involvement in the regulation of stem cell niches in various tissues and analyzes the possible effects of this system on the signaling pathways responsible for the proliferation, programmed cell death, phenotype modulation, and migration properties of stem cells.

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.

Biophysical Mechanisms Mediating Fibrin Fiber Lysis

The formation and dissolution of blood clots is both a biochemical and a biomechanical process. While much of the chemistry has been worked out for both processes, the influence of biophysical properties is less well understood. This review considers the impact of several structural and mechanical parameters on lytic rates of fibrin fibers. The influences of fiber and network architecture, fiber strain, FXIIIa cross-linking, and particle transport phenomena will be assessed. The importance of the mechanical aspects of fibrinolysis is emphasized, and future research avenues are discussed.

Differentiation-Associated Downregulation of Poly(ADP-Ribose) Polymerase-1 Expression in Myoblasts Serves to Increase Their Resistance to Oxidative Stress

Poly(ADP-ribose) polymerase 1 (PARP-1), the major isoform of the poly (ADP-ribose) polymerase family, is a constitutive nuclear and mitochondrial protein with well-recognized roles in various essential cellular functions such as DNA repair, signal transduction, apoptosis, as well as in a variety of pathophysiological conditions including sepsis, diabetes and cancer. Activation of PARP-1 in response to oxidative stress catalyzes the covalent attachment of the poly (ADP-ribose) (PAR) groups on itself and other acceptor proteins, utilizing NAD⁺ as a substrate. Overactivation of PARP-1 depletes intracellular NAD⁺ influencing mitochondrial electron transport, cellular ATP generation and, if persistent, can result in necrotic cell death. Due to their high metabolic activity, skeletal muscle cells are particularly exposed to constant oxidative stress insults. In this study, we investigated the role of PARP-1 in a well-defined model of murine skeletal muscle differentiation (C2C12) and compare the responses to oxidative stress of undifferentiated myoblasts and differentiated myotubes. We observed a marked reduction of PARP-1 expression as myoblasts differentiated into myotubes. This alteration correlated with an increased resistance to oxidative stress of the myotubes, as measured by MTT and LDH assays. Mitochondrial function, assessed by measuring mitochondrial membrane potential, was preserved under oxidative stress in myotubes compared to myoblasts. Moreover, basal respiration, ATP synthesis, and the maximal respiratory capacity of mitochondria were higher in myotubes than in myoblasts. Inhibition of the catalytic activity of PARP-1 by PJ34 (a phenanthridinone PARP inhibitor) exerted greater protective effects in undifferentiated myoblasts than in differentiated myotubes. The above observations in C2C12 cells were also confirmed in a rat-derived skeletal muscle cell line (L6). Forced overexpression of PARP1 in C2C12 myotubes sensitized the cells to oxidant-induced injury. Taken together, our data indicate that the reduction of PARP-1 expression during the process of the skeletal muscle differentiation serves as a protective mechanism to maintain the cellular functions of skeletal muscle during oxidative stress.

Porphyromonas gingivalis-derived RgpA-Kgp Complex Activates the Macrophage Urokinase Plasminogen Activator System: IMPLICATIONS FOR PERIODONTITIS

Urokinase plasminogen activator (uPA) converts plasminogen to plasmin, resulting in a proteolytic cascade that has been implicated in tissue destruction during inflammation. Periodontitis is a highly prevalent chronic inflammatory disease characterized by destruction of the tissue and bone that support the teeth. We demonstrate that stimulation of macrophages with the arginine- and lysine-specific cysteine protease complex (RgpA-Kgp complex), produced by the keystone pathogen Porphyromonas gingivalis, dramatically increased their ability to degrade matrix in a uPA-dependent manner. We show that the RgpA-Kgp complex cleaves the inactive zymogens, pro-uPA (at consensus sites Lys(158)-Ile(159) and Lys(135)-Lys(136)) and plasminogen, yielding active uPA and plasmin, respectively. These findings are consistent with activation of the uPA proteolytic cascade by P. gingivalis being required for the pathogen to induce alveolar bone loss in a model of periodontitis and reveal a new host-pathogen interaction in which P. gingivalis activates a critical host proteolytic pathway to promote tissue destruction and pathogen virulence.

Zinc phthalocyanine conjugated with the amino-terminal fragment of urokinase for tumor-targeting photodynamic therapy

Photodynamic therapy (PDT) has attracted much interest for the treatment of cancer due to the increased incidence of multidrug resistance and systemic toxicity in conventional chemotherapy. Phthalocyanine (Pc) is one of main classes of photosensitizers for PDT and possesses optimal photophysical and photochemical properties. A higher specificity can ideally be achieved when Pcs are targeted towards tumor-specific receptors, which may also facilitate specific drug delivery. Herein, we develop a simple and unique strategy to prepare a hydrophilic tumor-targeting photosensitizer ATF-ZnPc by covalently coupling zinc phthalocyanine (ZnPc) to the amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA), a fragment responsible for uPA receptor (uPAR, a biomarker overexpressed in cancer cells), through the carboxyl groups of ATF. We demonstrate the high efficacy of this tumor-targeting PDT agent for the inhibition of tumor growth both in vitro and in vivo. Our in vivo optical imaging results using H22 tumor-bearing mice show clearly the selective accumulation of ATF-ZnPc in tumor region, thereby revealing the great potential of ATF-ZnPc for clinical applications such as cancer detection and guidance of tumor resection in addition to photodynamic treatment.

Single nucleotide polymorphisms in the u-PA gene are related to susceptibility to oral tongue squamous cell carcinoma in the Northern Chinese Han population

AIM

The purpose of this study was to determine whether susceptibility to oral tongue squamous cell carcinoma (OSCC) is related to polymorphisms in the u-PA gene.

METHODS

We examined the rs2227564 C/T and rs2227562 G/A single nucleotide polymorphisms (SNPs) in 196 OSCC patients and 201 age- and gender- matched controls via direct sequencing and PCR-RFLP methods.

RESULTS

Significant differences were found in allelic and genotypic distributions of the rs2227564 and rs2227562 loci when comparing cases and controls. In addition, logistic analyses indicated that the rs2227564 C/T genotype was related to a 1.52-fold increased risk of developing OSCC (adjusted OR=1.521, 95%CI: 1.144~2.022, P=0.004). Linkage disequilibrium analysis was conducted and no association between the two loci was found (D'=0.031, r2=0.000).

CONCLUSIONS

Our findings provide evidence that the rs2227564 C/T SNP in the u-PA gene is associated with the development of OSCC.

Structure-driven design of radionuclide tracers for non-invasive imaging of uPAR and targeted radiotherapy. The tale of a synthetic peptide antagonist

Research performed during the last two decades has provided a wealth of information to highlight the role of the urokinase-type plasminogen activator receptor (uPAR) in the progression and dissemination of invasive and metastatic cancer. In parallel, our perception of the structure-function relationships in uPAR has been refined to such a level that a rational design of uPAR function as well as compounds specifically targeting defined functions of uPAR are now realistic options. This knowledge opens new avenues for developing therapeutic intervention regimens targeting uPAR as well as for monitoring the effects of such treatments by non-invasive imaging using e.g. positron emission tomography. This mini-review will focus on recent advancements in translational research devoted to non-invasive targeting of uPAR, with a view to molecular imaging of its expression in live individuals as well as specific eradication of these cells by targeted radiotherapy.

uPAR: a modulator of VEGF-induced angiogenesis

Vascular endothelial growth factor (VEGF)-initiated angiogenesis requires both coordinated proteolytic degradation of extracellular matrix provided by the urokinase plasminogen activator/urokinase receptor (uPA/uPAR) system and regulation of cell-migration provided by integrin-matrix interaction. Previously we have shown that stimulation of pericellular proteolysis induced by VEGF occurs via the VEGF receptor-2 leading to redistribution of uPAR to focal adhesions at the leading edge of endothelial cells. In our recent work published in Cardiovascular Research, we investigated the mechanisms underlying the uPAR-dependent modulation of VEGF-induced endothelial migration. By applying a micropatterning technique we described that VEGF stimulation results in complex formation between uPAR and α 5β 1-integrin on the cell surface. The subsequent internalization of this complex, important for receptor redistribution, was demonstrated by flow-cytometry and immunohistochemistry. Targeting of the interaction site between uPAR and α 5β 1 impairs receptor internalization and leads to the inhibition of endothelial cell migration in vitro and in an angiogenesis model in vivo. This proof-of-principle that the interface of uPAR and α 5β 1-integrin may represent a promising site to therapeutically target tumor angiogenesis raises hope for the development of an anti-angiogenic approach that is limited to only the mobilizing effect of VEGF to endothelial cells, and does not interfere with the inarguably positive effect of VEGF as survival factor.

RhoB regulates uPAR signalling

Urokinase-type plasminogen activator (uPA) and its receptor, uPAR, play important roles in promoting cancer cell adhesion, migration and invasion. Rho GTPases are key coordinators of these processes; the Rho GTPase Rac1 has previously been implicated in uPA- and/or uPAR-induced migratory or morphological cell responses. We used RNAi to deplete 12 different Rho GTPases to screen for effects on uPA-stimulated migration, and found that depletion of RhoB significantly reduces uPA-induced migration and invasion of prostate carcinoma cells. RhoB depletion did not affect the expression or surface levels of uPAR but reduced the uPAR-induced increase in levels of several integrins and inhibited uPAR signalling to the actin regulator cofilin, the cell-adhesion signal-transduction adaptor molecule paxillin and the serine/threonine kinase Akt. uPAR rapidly activated RhoB and increased RhoB expression. RhoB depletion also reduced cell adhesion to and spreading on vitronectin, which is a uPAR ligand. This correlated with decreased association between integrins and uPAR and reduced integrin β1 activity. Our results indicate that RhoB is a key regulator of uPAR signalling in cell adhesion, migration and invasion.

Nanoparticulate systems as drug carriers: the need

Development of nanoparticles for drug delivery has progressed by leaps and bounds over the last few decades, facilitating the possibility of an efficacious therapy for some fatal diseases. This development has stemmed from either the unsuitable physicochemical characteristics of the existing drug molecules, such as limited solubility and hence poor bioavailability, or the inadequacy of the conventional delivery systems to provide safe and efficient delivery. This chapter focuses on the precise need for the development of these novel nanoparticulate drug carriers and reasons for their popularity with the drug delivery scientists. The text also discusses the various strategies, including different formulation and targeting approaches, which have been adopted to overcome the challenges presented by the inherent properties of the drug molecules. Examples of nanoparticulate drug delivery systems which have already gained market approval have been cited in the discussion, wherever applicable.

Elevated urinary levels of urokinase-type plasminogen activator receptor (uPAR) in pancreatic ductal adenocarcinoma identify a clinically high-risk group

Background

The urokinase plasminogen activator receptor is highly expressed and its gene is amplified in about 50% of pancreatic ductal adenocarcinomas; this last feature is associated with worse prognosis. It is unknown whether the level of its soluble form (suPAR) in urine may be a diagnostic-prognostic marker in these patients.

Methods

The urinary level of suPAR was measured in 146 patients, 94 pancreatic ductal adenocarcinoma and 52 chronic pancreatitis. Urine from 104 healthy subjects with similar age and gender distribution served as controls. suPAR levels were normalized with creatinine levels (suPAR/creatinine, ng/mg) to remove urine dilution effect.

Results

Urinary suPAR/creatinine values of pancreatic ductal adenocarcinoma patients were significantly higher (median 9.8; 25^th-75^th percentiles 5.3-20.7) than those of either healthy donors (median 0; 0-0.5) or chronic pancreatitis patients (median 2.7; 0.9-4.7). The distribution of values among cancer patients was widespread and asymmetric, 53% subjects having values beyond the 95^th percentile of healthy donors. The values of suPAR/creatinine did not correlate with tumour stage, Ca19-9 or CEA levels. Higher values correlated with poor prognosis among non-resected patients at univariate analysis; multivariate Cox regression identified high urinary suPAR/creatinine as an independent predictor of poor survival among all cancer patients (odds ratio 2.10, p = 0.0023), together with tumour stage (stage III odds ratio 2.65, p = 0.0017; stage IV odds ratio 4.61, p < 0.0001) and female gender (odds ratio 1.85, p = 0.01).

Conclusions

A high urinary suPAR/creatinine ratio represents a useful marker for the identification of a subset of patients with poorer outcome.

A deficiency of uPAR alters endothelial angiogenic function and cell morphology

The angiogenic potential of a cell requires dynamic reorganization of the cytoskeletal architecture that involves the interaction of urokinase-type plasminogen activator receptor (uPAR) with the extracellular matrix. This study focuses on the effect of uPAR deficiency (uPAR^-/-) on angiogenic function and associated cytoskeletal organization. Utilizing murine endothelial cells, it was observed that adhesion, migration, proliferation, and capillary tube formation were altered in uPAR^-/- cells compared to wild-type (WT) cells. On a vitronectin (Vn) matrix, uPAR^-/- cells acquired a "fried egg" morphology characterized by circular actin organization and lack of lamellipodia formation. The up-regulation of β1 integrin, FAK(P-Tyr925), and paxillin (P-Tyr118), and decreased Rac1 activation, suggested increased focal adhesions, but delayed focal adhesion turnover in uPAR^-/- cells. This accounted for the enhanced adhesion, but attenuated migration, on Vn. VEGF-enriched Matrigel implants from uPAR^-/- mice demonstrated a lack of mature vessel formation compared to WT mice. Collectively, these results indicate that a uPAR deficiency leads to decreased angiogenic functions of endothelial cells.

Targeting the urokinase plasminogen activator receptor inhibits ovarian cancer metastasis

PURPOSE

To understand the functional and preclinical efficacy of targeting the urokinase plasminogen activator receptor (u-PAR) in ovarian cancer.

EXPERIMENTAL DESIGN

Expression of u-PAR was studied in 162 epithelial ovarian cancers, including 77 pairs of corresponding primary and metastatic tumors. The effect of an antibody against u-PAR (ATN-658) on proliferation, adhesion, invasion, apoptosis, and migration was assessed in 3 (SKOV3ip1, HeyA8, and CaOV3) ovarian cancer cell lines. The impact of the u-PAR antibody on tumor weight, number, and survival was examined in corresponding ovarian cancer xenograft models and the mechanism by which ATN-658 blocks metastasis was explored.

RESULTS

Only 8% of all ovarian tumors were negative for u-PAR expression. Treatment of SKOV3ip1, HeyA8, and CaOV3 ovarian cancer cell lines with the u-PAR antibody inhibited cell invasion, migration, and adhesion. In vivo, anti-u-PAR treatment reduced the number of tumors and tumor weight in CaOV3 and SKOV3ip1 xenografts and reduced tumor weight and increased survival in HeyA8 xenografts. Immunostaining of CaOV3 xenograft tumors and ovarian cancer cell lines showed an increase in active-caspase 3 and TUNEL staining. Treatment with u-PAR antibody inhibited α(5)-integrin and u-PAR colocalization on primary human omental extracellular matrix. Anti-u-PAR treatment also decreased the expression of urokinase, u-PAR, β(3)-integrin, and fibroblast growth factor receptor-1 both in vitro and in vivo.

CONCLUSIONS

This study shows that an antibody against u-PAR reduces metastasis, induces apoptosis, and reduces the interaction between u-PAR and α(5)-integrin. This provides a rationale for targeting the u-PAR pathway in patients with ovarian cancer and for further testing of ATN-658 in this indication.

A cleavage-resistant urokinase plasminogen activator receptor exhibits dysregulated cell-surface clearance

Urokinase plasminogen activator receptor (u-PAR) binds urokinase plasminogen activator (u-PA) and participates in plasminogen activation in addition to modulating several cellular processes such as adhesion, proliferation, and migration. u-PAR is susceptible to proteolysis by its cognate ligand and several other proteases. To elucidate the biological significance of receptor cleavage by u-PA, we engineered and expressed a two-chain urokinase plasminogen activator (tcu-PA) cleavage-resistant u-PAR (cr-u-PAR). This mutated receptor was similar to wild-type u-PAR in binding u-PA and initiating plasminogen activation. However, cr-u-PAR exhibited accelerated internalization and resurfacing due to direct association with the endocytic receptor alpha(2)-macroglobulin receptor/low density lipoprotein receptor-related protein in the absence of the enzyme x inhibitor complex of tcu-PA and plasminogen activator inhibitor-1 (tcu-PA.PAI-1). cr-u-PAR-expressing cells had enhanced migration compared with wild-type u-PAR-expressing cells, and cr-u-PAR was less sensitive to chymotrypsin cleavage as compared with wt u-PAR. Our studies suggest that these mutations in the linker region result in a rearrangement within the cr-u-PAR structure that makes it resemble its ligand-bound form. This constitutively active variant may mimic highly glycosylated cleavage-resistant u-PAR expressed in certain highly malignant cancer-cells.

Targeting nanoparticles to cancer

Nanotechnology applications in medicine, termed as nanomedicine, have introduced a number of nanoparticles of variable chemistry and architecture for cancer imaging and treatment. Nanotechnology involves engineering multifunctional devices with dimensions at the nanoscale, similar dimensions as those of large biological vesicles or molecules in our body. These devices typically have features just tens to hundred nanometers across and they can carry one or two detection signals and/or therapeutic cargo(s). One unique class of nanoparticles is designed to do both, providing this way the theragnostic nanoparticles (therapy and diagnosis). Being inspired by physiologically existing nanomachines, nanoparticles are designed to safely reach their target and specifically release their cargo at the site of the disease, this way increasing the drug's tissue bioavailability. Nanoparticles have the advantage of targeting cancer by simply being accumulated and entrapped in tumours (passive targeting). The phenomenon is called the enhanced permeation and retention effect, caused by leaky angiogenetic vessels and poor lymphatic drainage and has been used to explain why macromolecules and nanoparticles are found at higher ratios in tumours compared to normal tissues. Although accumulation in tumours is observed cell uptake and intracellular drug release have been questioned. Polyethyleneglycol (PEG) is used to protect the nanoparticles from the Reticulo-Endothelial System (RES), however, it prevents cell uptake and the required intracellular drug release. Grafting biorecognition molecules (ligands) onto the nanoparticles refers to active targeting and aims to increase specific cell uptake. Nanoparticles bearing these ligands are recognised by cell surface receptors and this leads to receptor-mediated endocytosis. Several materials are suggested for the design of nanoparticles for cancer. Polymers, linear and dendrimers, are associated with the drug in a covalent or non-covalent way and have been used with or without a targeting ligand. Stealth liposomes are suggested to carry the drug in the aqueous core, and they are usually decorated by recognition molecules, being widely studied and applied. Inorganic nanoparticles such as gold and iron oxide are usually coupled to the drug, PEG and the targeting ligand. It appears that the PEG coating and ligand decoration are common constituents in most types of nanoparticles for cancer. There are several examples of successful cancer diagnostic and therapeutic nanoparticles and many of them have rapidly moved to clinical trials. Nevertheless there is still a room for optimisation in the area of the nanoparticle kinetics such as improving their plasma circulation and tumour bioavailability and understanding the effect of targeting ligands on their efficiency to treat cancer. The need to develop novel and efficient ligands has never been greater, and the use of proper conjugation chemistry is mandatory.

Modulation of cellular migration and survival by c-Myc through the downregulation of urokinase (uPA) and uPA receptor

It has been proposed that c-Myc proapoptotic activity accounts for most of its restraint of tumor formation. We established a telomerase-immortalized human epithelial cell line expressing an activatable c-Myc protein. We found that c-Myc activation induces, in addition to increased sensitivity to apoptosis, reductions in cell motility and invasiveness. Transcriptome analysis revealed that urokinase (uPA) and uPA receptor (uPAR) were strongly downregulated by c-Myc. Evidence is provided that the repression of uPA and uPAR may account for most of the antimigratory and proapoptotic activities of c-Myc. c-Myc is known to cooperate with Ras in cellular transformation. We therefore investigated if this cooperation could converge in the control of uPA/uPAR expression. We found that Ras is able to block the effects of c-Myc activation on apoptosis and cellular motility but not on cell invasiveness. Accordingly, the activation of c-Myc in the context of Ras expression had only minor influence on uPAR expression but still had a profound repressive effect on uPA expression. Thus, the differential regulation of uPA and uPAR by c-Myc and Ras correlates with the effects of these two oncoproteins on cell motility, invasiveness, and survival. In conclusion, we have discovered a novel link between c-Myc and uPA/uPAR. We propose that reductions of cell motility and invasiveness could contribute to the inhibition of tumorigenesis by c-Myc and that the regulation of uPA and uPAR expression may be a component of the ability of c-Myc to reduce motility and invasiveness.

The urokinase receptor: focused cell surface proteolysis, cell adhesion and signaling

Plasma membrane urokinase-type plasminogen activator (uPA)-receptor (uPAR) is a GPI-anchored protein that binds with high-affinity and activates the serine protease uPA, thus regulating proteolytic activity at the cell surface. In addition, uPAR is a signaling receptor that often does not require its protease ligand or its proteolytic function. uPAR is highly expressed during tissue reorganization, inflammation, and in virtually all human cancers. Since its discovery, in vitro and in vivo models, as well as retrospective clinical studies have shown that over-expression of components of the uPA/uPAR-system correlates with increased proliferation, migration, and invasion affecting the malignant phenotype of cancer. uPAR regulates the cells-extracellular matrix interactions promoting its degradation and turnover through the plasminogen activation cascade.

Selective growth inhibition of cancer cells by L-methioninase-containing fusion protein targeted to the urokinase receptor

BACKGROUND

We have reported the development of a novel fusion protein (FP) consisting of an amino-terminal fragment of urokinase linked to the amino terminus of the enzyme L-methioninase (L-M). The present study compared the effect of this novel FP on the proliferation of human ovarian, skin, breast endometrial and pancreatic cancer cell lines.

METHODS

The FP, L-M and a mutated FP, with reduced L-M activity, were produced by recombinant methods. The effect of treatment with FP, L-M and mutated FP on the proliferation of the cancer cells was measured in vitro using an MTS assay.

RESULTS

The inhibitory effect of the FP was found to be significantly greater than that of L-M alone or the mutated FP. In addition, the FP produced a greater inhibitory effect on an ovarian cancer cell line than on comparable normal, non-cancerous cells. Further, the FP produced a dose-dependent inhibition of the proliferation of pancreatic cancer cell lines.

CONCLUSION

These results suggest that this FP is a potent and selective inhibitor of the proliferation of various cancer cell lines and has potential as a therapeutic agent for the treatment of various methionine-dependent cancers.