Urokinase links plasminogen activation and cell adhesion by cleavage of the RGD motif in vitronectin

Induction of epithelial cell senescence by SERPINE1 derived from fibroblasts in the amnion at parturition

Senescence of amnion epithelial cells not only disrupts the fetal membrane structure, but also becomes a source of proinflammatory signals contributing to membrane inflammation at parturition. However, the trigger initiating their senescence awaits identification. In this study, we found that SERPINE1 abundance was significantly increased in the amnion at parturition, where SERPINE1 was found predominantly expressed in amnion fibroblasts. SERPINE1 from amnion fibroblasts induced amnion epithelial cell senescence by causing vitronectin shedding from the cells thereby interrupting the association of vitronectin with integrin subunit αV, which led to the inhibition of the cell survival-associated focal adhesion pathway. In turn, proinflammatory cytokines such as interleukin-1β from senescent amnion epithelial cells enhanced SERPINE1 expression in amnion fibroblasts, thus forming a feed-forward loop between SERPINE1 production in amnion fibroblasts and epithelial cell senescence at parturition. Studies in the pregnant mice showed that intra-amniotic injection of SERPINE1 induced preterm birth with increased cellular senescence in the fetal membranes, which could be reversed by co-administration of vitronectin. Our findings indicate that SERPINE1 derived from amnion fibroblasts participates in the induction of amnion epithelial cell senescence at parturition. Intervening in the interaction of SERPINE1 with vitronectin may have therapeutic benefit in the treatment of preterm birth.

Urokinase Plasminogen Activation System Modulation in Transformed Cell Lines

The role of the plasminogen activation system is to regulate the activity of the extracellular protease plasmin. It comprises the urokinase plasminogen activator (uPA), a specific extracellular protease which activates plasminogen, its inhibitor PAI1, and the urokinase plasminogen activator receptor, uPAR, which localizes the urokinase activity. The plasminogen activation system is involved in tissue remodeling through extracellular matrix degradation, and therefore participates in numerous physiological and pathological processes, which make it a potential biomarker. To investigate the role of these molecules in the cellular processes, we cloned human uPA, PAI1, and uPAR and overexpressed them in two cell lines, the glioblastoma line A1235 and the transformed human embryonal kidney cells HEK 293. We analyzed the urokinase activity and the expression of plasminogen activation system elements on the protein and RNA level by Western blot analysis and RTqPCR. Cell proliferation was followed up by cell counting, cell migration and invasion by wound-healing and the transwell assays, respectively, and cell adhesion and dispersal by spheroid formation. The cells transfected with urokinase sequence had increased urokinase activity and uPA expression, while the PAI1-transfected cells decreased urokinase activity, increased PAI1 expression, and decreased cell migration. HEK 293 cells expressing PAI formed only small spheroids. The effects of the uPA system molecules depended on their interactions with each other and with other molecules in the microenvironment, as well as on the cell-type-specific signaling.

Mesenchymal stem/stromal cells alleviate early-stage pulmonary fibrosis in a uPAR-dependent manner

Pulmonary fibrosis, a debilitating lung disorder characterised by excessive fibrous tissue accumulation in lung parenchyma, compromises respiratory function leading to a life-threatening respiratory failure. While its origins are multifaceted and poorly understood, the urokinase system, including urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plays a significant role in regulating fibrotic response, extracellular matrix remodelling, and tissue repair. Mesenchymal stem/stromal cells (MSCs) hold promise in regenerative medicine for treating pulmonary fibrosis. Our study aimed to investigate the potential of MSCs to inhibit pulmonary fibrosis as well as the contribution of uPAR expression to this effect. We found that intravenous MSC administration significantly reduced lung fibrosis in the bleomycin-induced pulmonary fibrosis model in mice as revealed by MRI and histological evaluations. Notably, administering the MSCs isolated from adipose tissue of uPAR knockout mice (Plaur-/- MSCs) attenuated lung fibrosis to a lesser extent as compared to WT MSCs. Collagen deposition, a hallmark of fibrosis, was markedly reduced in lungs treated with WT MSCs versus Plaur-/- MSCs. Along with that, endogenous uPA levels were affected differently; after Plaur-/- MSCs were administered, the uPA content was specifically decreased within the blood vessels. Our findings support the potential of MSC treatment in attenuating pulmonary fibrosis. We provide evidence that the observed anti-fibrotic effect depends on uPAR expression in MSCs, suggesting that uPAR might counteract the uPA accumulation in lungs.

SERPINE1: Role in Cholangiocarcinoma Progression and a Therapeutic Target in the Desmoplastic Microenvironment

A heterogenous population of inflammatory elements, other immune and nonimmune cells and cancer-associated fibroblasts (CAFs) are evident in solid malignancies where they coexist with the growing tumor mass. In highly desmoplastic malignancies, CAFs are the prominent mesenchymal cell type in the tumor microenvironment (TME), where their presence and abundance signal a poor prognosis. CAFs play a major role in the progression of various cancers by remodeling the supporting stroma into a dense, fibrotic matrix while secreting factors that promote the maintenance of cancer stem-like characteristics, tumor cell survival, aggressive growth and metastasis and reduced sensitivity to chemotherapeutics. Tumors with high stromal fibrotic signatures are more likely to be associated with drug resistance and eventual relapse. Identifying the molecular underpinnings for such multidirectional crosstalk among the various normal and neoplastic cell types in the TME may provide new targets and novel opportunities for therapeutic intervention. This review highlights recent concepts regarding the complexity of CAF biology in cholangiocarcinoma, a highly desmoplastic cancer. The discussion focuses on CAF heterogeneity, functionality in drug resistance, contributions to a progressively fibrotic tumor stroma, the involved signaling pathways and the participating genes.

Targeted imaging of uPAR expression in vivo with cyclic AE105 variants

A comprehensive literature reports on the correlation between elevated levels of urokinase-type plasminogen activator receptor (uPAR) and the severity of diseases with chronic inflammation including solid cancers. Molecular imaging is widely used as a non-invasive method to locate disease dissemination via full body scans and to stratify patients for targeted treatment. To date, the only imaging probe targeting uPAR that has reached clinical phase-II testing relies on a high-affinity 9-mer peptide (AE105), and several studies by positron emission tomography (PET) scanning or near-infra red (NIR) fluorescence imaging have validated its utility and specificity in vivo. While our previous studies focused on applying various reporter groups, the current study aims to improve uPAR-targeting properties of AE105. We successfully stabilized the small uPAR-targeting core of AE105 by constraining its conformational landscape by disulfide-mediated cyclization. Importantly, this modification mitigated the penalty on uPAR-affinity typically observed after conjugation to macrocyclic chelators. Cyclization did not impair tumor targeting efficiency of AE105 in vivo as assessed by PET imaging and a trend towards increased tracer uptake was observed. In future studies, we predict that this knowledge will aid development of new fluorescent AE105 derivatives with a view to optical imaging of uPAR to assist precision guided cancer surgery.

Bioinformatics and computational analyses of kidney stone modulatory proteins lead to solid experimental evidence and therapeutic potential

In recent biomedical research, bioinformatics and computational analyses have played essential roles for examining experimental findings and database information. Several bioinformatic tools have been developed and made publicly available for analyzing protein sequence, structure, functional motif/domain, and interactions network. Such properties are very helpful to define biochemical and functional roles of the protein(s) of interest. During the past few decades, bioinformatics and computational biotechnology have been widely applied to kidney stone research. This review summarizes commonly used tools and evidence of bioinformatics and computational biotechnology applied to kidney stone disease (KSD) with special emphasis on analyses of the stone modulatory proteins that play critical roles in kidney stone formation. Such analyses lead to solid experimental evidence to demonstrate mechanisms underlying their stone modulatory activities. The findings obtained from such analyses may also lead to better understanding of KSD pathogenesis and to further development of new therapeutic and preventive strategies.

Urokinase System in Pathogenesis of Pulmonary Fibrosis: A Hidden Threat of COVID-19

Pulmonary fibrosis is a common and threatening post-COVID-19 complication with poorly resolved molecular mechanisms and no established treatment. The plasminogen activator system, including urokinase (uPA) and urokinase receptor (uPAR), is involved in the pathogenesis of COVID-19 and contributes to the development of lung injury and post-COVID-19 pulmonary fibrosis, although their cellular and molecular underpinnings still remain obscure. The aim of the current study was to assess the role of uPA and uPAR in the pathogenesis of pulmonary fibrosis. We analyzed uPA and uPAR expression in human lung tissues from COVID-19 patients with pulmonary fibrosis using single-cell RNA-seq and immunohistochemistry. We modeled lung fibrosis in Plau-/- and Plaur-/- mice upon bleomycin instillation and explored the effect of uPAR downregulation in A549 and BEAS-2B lung epithelial cells. We found that uPAR expression drastically decreased in the epithelial airway basal cells and monocyte/macrophage cells, whereas uPA accumulation significantly increased in tissue samples of COVID-19 patients. Lung injury and fibrosis in Plaur-/- vs. WT mice upon bleomycin instillation revealed that uPAR deficiency resulted in pro-fibrogenic uPA accumulation, IL-6 and ACE2 upregulation in lung tissues and was associated with severe fibrosis, weight loss and poor survival. uPAR downregulation in A549 and BEAS-2B was linked to an increased N-cadherin expression, indicating the onset of epithelial-mesenchymal transition and potentially contributing to pulmonary fibrosis. Here for the first time, we demonstrate that plasminogen treatment reversed lung fibrosis in Plaur-/- mice: the intravenous injection of 1 mg of plasminogen on the 21st day of bleomycin-induced fibrosis resulted in a more than a two-fold decrease in the area of lung fibrosis as compared to non-treated mice as evaluated by the 42nd day. The expression and function of the plasminogen activator system are dysregulated upon COVID-19 infection, leading to excessive pulmonary fibrosis and worsening the prognosis. The potential of plasminogen as a life-saving treatment for non-resolving post-COVID-19 pulmonary fibrosis warrants further investigation.

The Association of PLAUR Genotype and Soluble suPAR Serum Level with COVID-19-Related Lung Damage Severity

Uncovering the risk factors for acute respiratory disease coronavirus 2019 (COVID-19) severity may help to provide a valuable tool for early patient stratification and proper treatment implementation, improving the patient outcome and lowering the burden on the healthcare system. Here we report the results of a single-center retrospective cohort study on 151 severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-infected symptomatic hospitalized adult patients. We assessed the association of several blood test measurements, soluble urokinase receptor (uPAR) serum level and specific single nucleotide polymorphisms of ACE (I/D), NOS3 (rs2070744, rs1799983), SERPINE1 (rs1799768), PLAU (rs2227564) and PLAUR (rs344781, rs2302524) genes, with the disease severity classified by the percentage of lung involvement on computerized tomography scans. Our findings reveal that the T/C genotype of PLAUR rs2302524 was independently associated with a less severe lung damage (odds ratio 0.258 [0.071-0.811]). Along with high C-reactive protein, fibrinogen and soluble uPAR serum levels turned out to be independently associated with more severe lung damage in COVID-19 patients. The identified factors may be further employed as predictors of a possibly severe COVID-19 clinical course.

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.

Personalised Approach to Diagnosing and Managing Ischemic Stroke with a Plasma-Soluble Urokinase-Type Plasminogen Activator Receptor

Background: The increasing incidence of ischemic stroke has led to the search for a novel biomarker to predict the course of disease and the risk of mortality. Recently, the role of the soluble urokinase plasminogen activator receptor (suPAR) as a biomarker and indicator of immune system activation has been widely examined. Therefore, the aim of the current study was to assess the dynamics of changes in serum levels of suPAR in ischemic stroke and to evaluate the prognostic value of suPAR in determining mortality risk. Methods: Eighty patients from the Department of Neurology, diagnosed with ischemic stroke, were enrolled in the study. Residual blood was obtained from all the patients on the first, third and seventh days after their ischemic stroke and the concentrations of suPAR and C-reactive protein (CRP), as well as the number of leukocytes and National Institute of Health’s Stroke Scale (NIHSS) scores, were evaluated. Results: On the first day of ischemic stroke, the average suPAR concentration was 6.55 ng/mL; on the third day, it was 8.29 ng/mL; on the seventh day, it was 9.16 ng/mL. The average CRP concentration on the first day of ischemic stroke was 4.96 mg/L; on the third day, it was 11.76 mg/L; on the seventh day, it was 17.17 mg/L. The number of leukocytes on the first day of ischemic stroke was 7.32 × 103/mm3; on the third day, it was 9.27 × 103/mm3; on the seventh day, it was 10.41 × 103/mm3. Neurological condition, which was assessed via the NIHSS, on the first day of ischemic stroke, was scored at 10.71 points; on the third day, it was scored at 12.34 points; on the seventh day, it was scored at 13.75 points. An increase in the values of all the evaluated parameters on the first, third and seventh days of hospitalisation was observed. The patients with hypertension, ischemic heart disease and type 2 diabetes showed higher suPAR and CRP concentrations at the baseline as well as on subsequent days of hospitalisation. The greatest sensitivity and specificity were characterised by suPAR-3, where a value above 10.5 ng/mL resulted in a significant increase in mortality risk. Moreover, an NIHSS-1 score above 12 points and a CRP-3 concentration above 15.6 mg/L significantly increased the risk of death in the course of the disease. Conclusions: The plasma suPAR concentration after ischemic stroke is strongly related to the patient’s clinical status, with a higher concentration on the first and third days of stroke resulting in a poorer prognosis at a later stage of treatment. Therefore, assessing the concentration of this parameter has important prognostic value.

uPAR: An Essential Factor for Tumor Development

Tumorigenesis is closely related to the loss of control of many genes. Urokinase-type plasminogen activator receptor (uPAR), a glycolipid-anchored protein on the cell surface, is controlled by many factors in tumorigenesis and is expressed in many tumor tissues. In this review, we summarize the regulatory effects of the uPAR signaling pathway on processes and factors related to tumor progression, such as tumor cell proliferation, adhesion, metastasis, glycolysis, tumor microenvironment and angiogenesis. Overall, the evidence accumulated to date suggests that uPAR induction by tumor progression may be one of the most important factors affecting therapeutic efficacy. An improved understanding of the interactions between uPAR and its coreceptors in cancer will provide critical biomolecular information that may help to better predict the disease course and response to therapy.

Vitronectin stabilizes intravascular adhesion of neutrophils by coordinating β2 integrin clustering

The recruitment of neutrophils from the microvasculature to the site of injury or infection represents a key event in the inflammatory response. Vitronectin (VN) is a multifunctional macromolecule abundantly present in blood and extracellular matrix. The role of this glycoprotein in the extravasation process of circulating neutrophils remains elusive. Employing advanced in vivo/ex vivo imaging techniques in different mouse models as well as in vitro methods, we uncovered a previously unrecognized function of VN in the transition of dynamic to static intravascular interactions of neutrophils with microvascular endothelial cells. These distinct properties of VN require the heteromerization of this glycoprotein with plasminogen activator inhibitor-1 (PAI- 1) on the activated venular endothelium and subsequent interactions of this protein complex with the scavenger receptor low-density lipoprotein receptor-related protein-1 on intravascularly adhering neutrophils. This induces p38 mitogen-activated protein kinases-dependent intracellular signaling events which, in turn, regulates the proper clustering of the b2 integrin lymphocyte function associated antigen-1 on the surface of these immune cells. As a consequence of this molecular interplay, neutrophils become able to stabilize their adhesion to the microvascular endothelium and, subsequently, to extravasate to the perivascular tissue. Hence, endothelial-bound VN-PAI-1 heteromers stabilize intravascular adhesion of neutrophils by coordinating b2 integrin clustering on the surface of these immune cells, thereby effectively controlling neutrophil trafficking to inflamed tissue. Targeting this protein complex might be beneficial for the prevention and treatment of inflammatory pathologies.

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.

Insight into vitronectin structural evolution on material surface chemistries: The mediation for cell adhesion

Biomaterial surface chemistry engenders profound consequences on cell adhesion and the ultimate tissue response by adsorbing proteins from extracellular matrix, where vitronectin (Vn) is involved as one of the crucial mediator proteins. Deciphering the adsorption behaviors of Vn in molecular scale provides a useful account of how to design biomaterial surfaces. But the details of structural dynamics and consequential biological effect remain elusive. Herein, both experimental and computational approaches were applied to delineate the conformational and orientational evolution of Vn during adsorption onto self-assembled monolayers (SAMs) terminating with -COOH, -NH₂, -CH₃ and -OH. To unravel the interplay between cell binding and the charge and wettability of material surface, somatomedin-B (SMB) domain of Vn holding the RGD cell-binding motif was employed in molecular dynamics (MD) simulations, with orientation initialized by Monte Carlo (MC) method. Experimental evidences including protein adsorption, cell adhesion and integrin gene expressions were thoroughly investigated. The adsorption of Vn on different surface chemistries showed very complex profiles. Cell adhesion was enabled on all Vn-adsorbed surfaces but with distinct mechanisms mostly determined by conformational change induced reorientation. Higher amount of Vn was observed on negatively charged surface (COOH) and hydrophobic surface (CH₃). However, advantageous orientations defined by RGD loop conditions were only obtained on the charged surfaces (COOH and NH₂). Specifically, COOH surface straightened up the Vn molecules and accumulated them into a higher density, whereas CH₃ surface squashed Vn and stacked them into higher density multilayer by tracking adsorption but with the RGD loops restrained. These findings may have a broad implication on the understanding of Vn functionality and would help develop new strategies for designing advanced biomaterials.

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Unfolded straighten structure of Vn unbinds RGD loop on negatively charged surface.

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Unfolded Vn forms compact multilayers by tracking adsorption on hydrophobic surface.

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Accessible RGD loop of adsorbed Vn endows better cell affinity for charged surface.

Novel LRAP-binding partner revealing the plasminogen activation system as a regulator of cementoblast differentiation and mineral nodule formation in vitro

Amelogenin isoforms, including full-length amelogenin (AMEL) and leucine-rich amelogenin peptide (LRAP), are major components of the enamel matrix, and are considered as signaling molecules in epithelial-mesenchymal interactions regulating tooth development and periodontal regeneration. Nevertheless, the molecular mechanisms involved are still poorly understood. The aim of the present study was to identify novel binding partners for amelogenin isoforms in the cementoblast (OCCM-30), using an affinity purification assay (GST pull-down) followed by mass spectrometry and immunoblotting. Protein-protein interaction analysis for AMEL and LRAP evidenced the plasminogen activation system (PAS) as a potential player regulating OCCM-30 response to amelogenin isoforms. For functional assays, PAS was either activated (plasmin) or inhibited (ε-aminocaproic acid [aminocaproic]) in OCCM-30 cells and the cell morphology, mineral nodule formation, and gene expression were assessed. PAS inhibition (EACA 100 mM) dramatically decreased mineral nodule formation and expression of OCCM-30 differentiation markers, including osteocalcin (Bglap), bone sialoprotein (Ibsp), osteopontin (Spp1), tissue-nonspecific alkaline phosphatase (Alpl) and collagen type I (Col1a1), and had no effect on runt-related transcription factor 2 (Runx2) and Osterix (Osx) mRNA levels. PAS activation (plasmin 5 µg/µl) significantly increased Col1a1 and decreased Bglap mRNA levels (p < .05). Together, our findings shed new light on the potential role of plasminogen signaling pathway in the control of the amelogenin isoform-mediated response in cementoblasts and provide new insights into the development of targeted therapies.

Structural Biology and Protein Engineering of Thrombolytics

Myocardial infarction and ischemic stroke are the most frequent causes of death or disability worldwide. Due to their ability to dissolve blood clots, the thrombolytics are frequently used for their treatment. Improving the effectiveness of thrombolytics for clinical uses is of great interest. The knowledge of the multiple roles of the endogenous thrombolytics and the fibrinolytic system grows continuously. The effects of thrombolytics on the alteration of the nervous system and the regulation of the cell migration offer promising novel uses for treating neurodegenerative disorders or targeting cancer metastasis. However, secondary activities of thrombolytics may lead to life-threatening side-effects such as intracranial bleeding and neurotoxicity. Here we provide a structural biology perspective on various thrombolytic enzymes and their key properties: (i) effectiveness of clot lysis, (ii) affinity and specificity towards fibrin, (iii) biological half-life, (iv) mechanisms of activation/inhibition, and (v) risks of side effects. This information needs to be carefully considered while establishing protein engineering strategies aiming at the development of novel thrombolytics. Current trends and perspectives are discussed, including the screening for novel enzymes and small molecules, the enhancement of fibrin specificity by protein engineering, the suppression of interactions with native receptors, liposomal encapsulation and targeted release, the application of adjuvants, and the development of improved production systems.

Did evolution create a flexible ligand-binding cavity in the urokinase receptor through deletion of a plesiotypic disulfide bond?

The urokinase receptor (uPAR) is a founding member of a small protein family with multiple Ly6/uPAR (LU) domains. The motif defining these LU domains contains five plesiotypic disulfide bonds stabilizing its prototypical three-fingered fold having three protruding loops. Notwithstanding the detailed knowledge on structure-function relationships in uPAR, one puzzling enigma remains unexplored. Why does the first LU domain in uPAR (DI) lack one of its consensus disulfide bonds, when the absence of this particular disulfide bond impairs the correct folding of other single LU domain-containing proteins? Here, using a variety of contemporary biophysical methods, we found that reintroducing the two missing half-cystines in uPAR DI caused the spontaneous formation of the corresponding consensus 7-8 LU domain disulfide bond. Importantly, constraints due to this cross-link impaired (i) the binding of uPAR to its primary ligand urokinase and (ii) the flexible interdomain assembly of the three LU domains in uPAR. We conclude that the evolutionary deletion of this particular disulfide bond in uPAR DI may have enabled the assembly of a high-affinity urokinase-binding cavity involving all three LU domains in uPAR. Of note, an analogous neofunctionalization occurred in snake venom α-neurotoxins upon loss of another pair of the plesiotypic LU domain half-cystines. In summary, elimination of the 7-8 consensus disulfide bond in the first LU domain of uPAR did have significant functional and structural consequences.

Podocytopathy in the mesangial proliferative immunoglobulin A nephropathy: new insights into the mechanisms of damage and progression

Immunoglobulin A nephropathy (IgAN) was defined as a mesangiopathic disease, since the primary site of deposition of IgA immune material is the mesangium, and proliferation of mesangial cells and matrix excess deposition are the first histopathologic lesions. However, the relentless silent progression of IgAN is mostly due to the development of persistent proteinuria, and recent studies indicate that a major role is played by previous damage of function and anatomy of podocytes. In IgAN, the podocytopathic changes are the consequence of initial alterations in the mesangial area with accumulation of IgA containing immune material. Podocytes are therefore affected by interactions of messages originally driven from the mesangium. After continuous insult, podocytes detach from the glomerular basement membrane. This podocytopathy favours not only the development of glomerular focal and segmental sclerosis, but also the progressive renal function loss. It is still debated whether these lesions can be prevented or cured by corticosteroid/immunosuppressive treatment. We aimed to review recent data on the mechanisms implicated in the podocytopathy present in IgAN, showing new molecular risk factors for progression of this disease. Moreover, these observations may indicate that the target for new drugs is not only focused on decreasing the activity of mesangial cells and inflammatory reactions in IgAN, but also on improving podocyte function and survival.

Increased soluble urokinase plasminogen activator receptor (suPAR) levels in neovascular age-related macular degeneration: a role for inflammation in the pathogenesis of the disease?

PURPOSE

To evaluate the plasma concentration of the soluble form of the urokinase-type plasminogen activator receptor ((s)uPAR), an established biomarker of chronic inflammation, in patients affected by neovascular age-related macular degeneration.

METHODS

Forty consecutive patients affected by age-related macular degeneration and 52 subjects with no history of the disease were included in this case-control study. The two groups of individuals considered for the study were matched for age, sex, and class of medications taken. Plasma concentration of suPAR was measured using a specific ELISA assay (suPARnostic, Birkeroed, Denmark).

RESULTS

The case and control groups were similar for age, gender distribution, weight, height, and systolic and diastolic blood pressure, as well as for dyslipidemia and high blood pressure medication (P > 0.28). The plasma concentrations of suPAR were significantly increased in patients with neovascular age-related macular degeneration when compared to controls (6.19 ± 2.2 ng/ml, vs 5.21 ± 1.5, respectively, mean ± SD P = 0.01).

CONCLUSIONS

Patients with neovascular age-related macular degeneration display increased plasma levels of suPAR, suggesting that chronic inflammation may be involved in the pathogenesis of the disease.

Arms race: diverse effector proteins with conserved motifs

Effector proteins play important roles in the infection by pathogenic oomycetes and fungi or the colonization by endophytic and mycorrhizal fungi. They are either translocated into the host plant cells via specific translocation mechanisms and function in the host's cytoplasm or nucleus, or they reside in the apoplast of the plant cells and act at the extracellular host-microbe interface. Many effector proteins possess conserved motifs (such as the RXLR, CRN, LysM, RGD, DELD, EAR, RYWT, Y/F/WXC or CFEM motifs) localized in their N- or C-terminal regions. Analysis of the functions of effector proteins, especially so-called "core effectors", is crucial for the understanding of pathogenicity/symbiosis mechanisms and plant defense strategies, and helps to develop breeding strategies for pathogen-resistant cultivars, and to increase crop yield and quality as well as abiotic stress resistance. This review summarizes current knowledge about these effector proteins with the conversed motifs and their involvement in pathogenic or mutualistic plant/fungal interactions.

Fibronectin Facilitates Enterovirus 71 Infection by Mediating Viral Entry

Fibronectin (FN) is a high-molecular-weight extracellular matrix protein that contains the RGDS motif, which is required to bind to integrins. Synthetic RGDS peptides have been reported to compete with FN to bind to the cell surface and inhibit the function of FN. Here, we identified that synthetic RGDS peptides significantly inhibit human enterovirus 71 (EV71) infection in cell cultures. In addition, mice treated with RGDS peptides and infected with EV71 had a significantly higher survival rate and a lower viral load than the control group. Because RGDS peptides affect the function of FN, we questioned whether FN may play a role in virus infection. Our study indicates that overexpression of FN enhanced EV71 infection. In contrast, knockout of FN significantly reduced viral yield and decreased the viral binding to host cells. Furthermore, EV71 entry, rather than intracellular viral replication, was blocked by FN inhibitor pretreatment. Next, we found that FN could interact with the EV71 capsid protein VP1, and further truncated-mutation assays indicated that the D2 domain of FN could interact with the N-terminal fragment of VP1. Taken together, our results demonstrate that the host factor FN binds to EV71 particles and facilitates EV71 entry, providing a potential therapy target for EV71 infection.IMPORTANCE Hand, foot, and mouth disease outbreaks have occurred frequently in recent years, sometimes causing severe neurological complications and even death in infants and young children worldwide. Unfortunately, no effective antiviral drugs are available for human enterovirus 71 (EV71), one of the viruses that cause hand, foot, and mouth disease. The infection process and the host factors involved remain unknown, although several receptors have been identified. In this study, we found that the host factor fibronectin (FN) facilitated EV71 replication by interacting with EV71 particles and further mediated their entry. The RGDS peptide, an FN inhibitor, significantly inhibited EV71 replication in both RD cells and mice. In conclusion, our research identified a new host factor involved in EV71 infection, providing a new potential antiviral target for EV71 treatment.

Collagen structure regulates MSCs behavior by MMPs involved cell–matrix interactions

Various scaffolds have been studied in the formation of cell niches and regulation of mesenchymal stem cells (MSCs) behaviors.

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.

Vitronectin and Urokinase-Type Plasminogen Activator Gene Expression Levels Are Increased in Patients with Coronary Artery In-Stent Restenosis

Neointimal hyperplasia is known as a main factor contributing to in-stent restenosis (ISR). Monocytes may play a central role in vessel restenosis process after stent implantation. The aim of this study was to investigate the relationships between the urokinase-type plasminogen activator (PLAU) and vitronectin (Vtn) gene expression levels in peripheral blood mononuclear cell samples isolated from whole blood of 66 patients undergoing coronary artery angiography (22 controls, stenosis < 0.05%; 22 with stent no-restenosis and stenosis < 70%; and 22 with ISR and stenosis > 70%). The Vtn and PLAU gene expression levels were measured by real-time quantitative polymerase chain reaction technique. The age- and gender-independent increases in the expression levels of Vtn (17-fold; p  < 0.001) and PLAU (27-fold; p  < 0.0001) genes were found in the patients with ISR as compared with the control group. The results suggested that the Vtn and PLAU genes may be involved in the coronary artery ISR.

Mechanisms of plasminogen activator inhibitor 1 action in stromal remodeling and related diseases

Plasminogen activator inhibitor type 1 (PAI-1) is the main physiologic inhibitor of fibrinolysis. However, it is also involved in many physiological processes such as extracellular matrix (ECM) proteolysis and remodeling, cell adhesion, motility, and apoptosis, angiogenesis, etc. The aim of the study was to summarize current knowledge and gain insights into the mechanisms of PAI-1 action in the processes of stromal remodeling and diseases with considerable matrix pathologies (atherosclerosis, tissue fibrosis, cancer metastasis, pregnancy related complications, etc). As a component of an early cellular response to injury, PAI-1 reacts with membrane surface proteins and participates in the initiation of intracellular signaling, specifically cytoskeletal reorganization and motility. Complexity of ECM homeostasis resides in varying relation of the plasminogen system components and other matrix constituents. Inflammatory mediators (transforming growth factor-β and interferon-γ) and hormones (angiotensin II) are in the close interdependent relation with PAI-1. Also, special attention is devoted to the role of increased PAI-1 concentrations due to the common 4G/5G polymorphism. Some of the novel mechanisms of ECM modification consider PAI-1 dependent stabilization of urokinase mediated cell adhesion, control of the vascular endothelial cadherin trafficking and interaction with endothelial cells proteasome, its relation to matrix metalloproteinase 2 and osteopontin, and oxidative inhibition by myeloperoxidase. Targeting and/or alteration of PAI-1 functions might bring benefit to the future therapeutic approaches in diseases where ECM undergoes substantial remodeling.

Plasminogen activator inhibitor-1 is an independent prognostic factor of ovarian cancer and IMD-4482, a novel plasminogen activator inhibitor-1 inhibitor, inhibits ovarian cancer peritoneal dissemination

In the present study, the therapeutic potential of targeting plasminogen activator inhibitor-1 (PAI-1) in ovarian cancer was tested. Tissues samples from 154 cases of ovarian carcinoma were immunostained with anti-PAI-1 antibody, and the prognostic value was analyzed. Among the samples, 67% (104/154) showed strong PAI-1 expression; this was significantly associated with poor prognosis (progression-free survival: 20 vs. 31 months, P = 0.0033). In particular, among patients with stage II-IV serous adenocarcinoma, PAI-1 expression was an independent prognostic factor. The effect of a novel PAI-1 inhibitor, IMD-4482, on ovarian cancer cell lines was assessed and its therapeutic potential was examined using a xenograft mouse model of ovarian cancer. IMD-4482 inhibited in vitro cell adhesion to vitronectin in PAI-1-positive ovarian cancer cells, followed by the inhibition of extracellular signal-regulated kinase and focal adhesion kinase phosphorylation through dissociation of the PAI-urokinase receptor complex from integrin αVβ3. IMD-4482 caused G0/G1 cell arrest and inhibited the proliferation of PAI-1-positive ovarian cancer cells. In the xenograft model, IMD-4482 significantly inhibited peritoneal dissemination with the reduction of PAI-1 expression and the inhibition of focal adhesion kinase phosphorylation. Collectively, the functional inhibition of PAI-1 significantly inhibited ovarian cancer progression, and targeting PAI-1 may be a potential therapeutic strategy in ovarian cancer.

Systems biology-opportunities and challenges: the application of proteomics to study the cardiovascular extracellular matrix

Systems biology approaches including proteomics are becoming more widely used in cardiovascular research. In this review article, we focus on the application of proteomics to the cardiac extracellular matrix (ECM). ECM remodelling is a hallmark of many cardiovascular diseases. Proteomic techniques using mass spectrometry (MS) provide a platform for the comprehensive analysis of ECM proteins without a priori assumptions. Proteomics overcomes various constraints inherent to conventional antibody detection. On the other hand, studies that use whole tissue lysates for proteomic analysis mask the identification of the less abundant ECM constituents. In this review, we first discuss decellularization-based methods that enrich for ECM proteins in cardiac tissue, and how targeted MS allows for accurate protein quantification. The second part of the review will focus on post-translational modifications including hydroxylation and glycosylation and on the release of matrix fragments with biological activity (matrikines), all of which can be interrogated by proteomic techniques.

Urokinase links plasminogen activation and cell adhesion by cleavage of the RGD motif in vitronectin

Components of the plasminogen activation system including urokinase (uPA), its inhibitor (PAI-1) and its cell surface receptor (uPAR) have been implicated in a wide variety of biological processes related to tissue homoeostasis. Firstly, the binding of uPA to uPAR favours extracellular proteolysis by enhancing cell surface plasminogen activation. Secondly, it promotes cell adhesion and signalling through binding of the provisional matrix protein vitronectin. We now report that uPA and plasmin induces a potent negative feedback on cell adhesion through specific cleavage of the RGD motif in vitronectin. Cleavage of vitronectin by uPA displays a remarkable receptor dependence and requires concomitant binding of both uPA and vitronectin to uPAR Moreover, we show that PAI-1 counteracts the negative feedback and behaves as a proteolysis-triggered stabilizer of uPAR-mediated cell adhesion to vitronectin. These findings identify a novel and highly specific function for the plasminogen activation system in the regulation of cell adhesion to vitronectin. The cleavage of vitronectin by uPA and plasmin results in the release of N-terminal vitronectin fragments that can be detected in vivo, underscoring the potential physiological relevance of the process.