Plasmin and plasminogen activator inhibitor type 1 promote cellular motility by regulating the interaction between the urokinase receptor and vitronectin

Neutrophil extracellular traps-related signature predicts the prognosis and immune infiltration in gastric cancer

Introduction

Gastric cancer (GC) is the fifth most prevalent cancer globally, with the third highest case fatality rate. Neutrophil extracellular traps (NETs) are a reticulated structure of DNA, histones, and antimicrobial peptides produced by active neutrophils that trap pathogens. Even though NETs are associated with poorer recurrence-free survival (RFS) and overall survival (OS), the specifics of this interaction between NETs and cancer cells are yet unknown.

Methods

The keywords "neutrophil extracellular traps and gastric cancer" were used in the GEO database for retrieval, and the GSE188741 dataset was selected to obtain the NETs-related gene. 27 NETs-related genes were screened by univariate Cox regression analysis (p < 0.05). 27 NETs-related genes were employed to identify and categorize NETs-subgroups of GC patients under the Consensus clustering analysis. 808 GC patients in TCGA-STAD combined with GES84437 were randomly divided into a training group (n = 403) and a test group (n = 403) at a ratio of 1:1 to validate the NETs-related signature.

Results

Based on Multivariate Cox regression and LASSO regression analysis to develop a NETs-related prognosis model. We developed a very specific nomogram to improve the NETs-clinical score's usefulness. Similarly, we also performed a great result in pan-cancer study with NETs-score. Low NETs scores were linked to higher MSI-H (microsatellite instability-high), mutation load, and immune activity. The cancer stem cell (CSC) index and chemotherapeutic treatment sensitivity were also connected to the NET score. Our comprehensive analysis of NETs in GC suggests that NETs have a role in the tumor microenvironment, clinicopathological features, and prognosis.

Discussion

The NETs-score risk model provides a basis for better prognosis and therapy outcomes in GC patients.

Identifying new molecular players in extracellular proteostasis

Proteostasis refers to a delicately tuned balance between the processes of protein synthesis, folding, localization, and the degradation of proteins found inside and outside cells. Our understanding of extracellular proteostasis is rather limited and largely restricted to knowledge of 11 currently established extracellular chaperones (ECs). This review will briefly outline what is known of the established ECs, before moving on to discuss experimental strategies used to identify new members of this growing family, and an examination of a group of putative new ECs identified using one of these approaches. An observation that emerges from an analysis of the expanding number of ECs is that all of these proteins are multifunctional. Strikingly, the armory of activities each possess uniquely suit them as a group to act together at sites of tissue damage, infection, and inflammation to restore homeostasis. Lastly, we highlight outstanding questions to guide future research in this field.

Soluble CD95L in cancers and chronic inflammatory disorders, a new therapeutic target?

Although CD95L (also known as FasL) is still predominantly considered as a death ligand that induces apoptosis in infected and transformed cells, substantial evidence indicate that it can also trigger non-apoptotic signaling pathways whose pathophysiological roles remain to be fully elucidated. The transmembrane ligand CD95L belongs to the tumor necrosis factor (TNF) superfamily. After cleavage by metalloprotease, its soluble form (s-CD95L) fails to trigger the apoptotic program but instead induces signaling pathways promoting the aggressiveness of certain inflammatory disorders such as autoimmune diseases and cancers. We propose to evaluate the various pathologies in which the metalloprotease-cleaved CD95L is accumulated and analyze whether this soluble ligand may play a significant role in the pathology progression. Based on the TNFα-targeting therapeutics, we envision that targeting the soluble form of CD95L may represent a very attractive therapeutic option in the pathologies depicted herein.

The Fibrinolytic System: Mysteries and Opportunities

The deposition and removal of fibrin has been the primary role of coagulation and fibrinolysis, respectively. There is also little doubt that these 2 enzyme cascades influence each other given they share the same serine protease family ancestry and changes to 1 arm of the hemostatic pathway would influence the other. The fibrinolytic system in particular has also been known for its capacity to clear various non-fibrin proteins and to activate other enzyme systems, including complement and the contact pathway. Furthermore, it can also convert a number of growth factors into their mature, active forms. More recent findings have extended the reach of this system even further. Here we will review some of these developments and also provide an account of the influence of individual players of the fibrinolytic (plasminogen activating) pathway in relation to physiological and pathophysiological events, including aging and metabolism.

LncRNA NKX2-1-AS1 promotes tumor progression and angiogenesis via upregulation of SERPINE1 expression and activation of the VEGFR-2 signaling pathway in gastric cancer

Long noncoding RNAs (lncRNAs) can compete with endogenous RNAs to modulate the gene expression and contribute to oncogenesis and tumor metastasis. lncRNA NKX2-1-AS1 (NKX2-1 antisense RNA 1) plays a pivotal role in cancer progression and metastasis; however, the contribution of aberrant expression of NKX2-1-AS1 and the mechanism by which it functions as a competing endogenous RNA (ceRNA) in gastric cancer (GC) remains elusive. NKX2-1-AS1 expression was detected in paired tumor and nontumor tissues of 178 GC patients by quantitative reverse transcription PCR (qRT-PCR). Using loss-of-function and gain-of-function experiments, the biological functions of NKX2-1-AS1 were evaluated both in vitro and in vivo. Further, to assess that NKX2-1-AS1 regulates angiogenic processes, tube formation and co-culture assays were performed. RNA binding protein immunoprecipitation (RIP) assay, a dual-luciferase reporter assay, quantitative PCR, Western blot, and fluorescence in situ hybridization (FISH) assays were performed to determine the potential molecular mechanism underlying this ceRNA. The results indicated that NKX2-1-AS1 expression was upregulated in GC cell lines and tumor tissues. Overexpression of NKX2-1-AS1 was significantly associated with tumor progression and enhanced angiogenesis. Functionally, NKX2-1-AS1 overexpression promoted GC cell proliferation, metastasis, invasion, and angiogenesis, while NKX2-1-AS1 knockdown restored these effects, both in vitro and in vivo. RIP and dual-luciferase assays revealed that the microRNA miR-145-5p is a direct target of NKX2-1-AS1 and that NKX2-1-AS1 serves as a ceRNA to sponge miRNA and regulate angiogenesis in GC. Moreover, serpin family E member 1 (SERPINE1) is an explicit target for miR-145-5p; besides, the NKX2-1-AS1/miR-145-5p axis induces the translation of SERPINE1, thus activating the VEGFR-2 signaling pathway to promote tumor progression and angiogenesis. NKX2-1-AS1 overexpression is associated with enhanced tumor cell proliferation, angiogenesis, and poor prognosis in GC. Collectively, NKX2-1-AS1 functions as a ceRNA to miR-145-5p and promotes tumor progression and angiogenesis by activating the VEGFR-2 signaling pathway via SERPINE1.

MAPKAP Kinase-2 Drives Expression of Angiogenic Factors by Tumor-Associated Macrophages in a Model of Inflammation-Induced Colon Cancer

Chronic inflammation increases the risk for colorectal cancer through a variety of mechanisms involving the tumor microenvironment. MAPK-activated protein kinase 2 (MK2), a major effector of the p38 MAPK stress and DNA damage response signaling pathway, and a critical regulator of pro-inflammatory cytokine production, has been identified as a key contributor to colon tumorigenesis under conditions of chronic inflammation. We have previously described how genetic inactivation of MK2 in an inflammatory model of colon cancer results in delayed tumor progression, decreased tumor angiogenesis, and impaired macrophage differentiation into a pro-tumorigenic M2-like state. The molecular mechanism responsible for the impaired angiogenesis and tumor progression, however, has remained contentious and poorly defined. Here, using RNA expression analysis, assays of angiogenesis factors, genetic models, in vivo macrophage depletion and reconstitution of macrophage MK2 function using adoptive cell transfer, we demonstrate that MK2 activity in macrophages is necessary and sufficient for tumor angiogenesis during inflammation-induced cancer progression. We identify a critical and previously unappreciated role for MK2-dependent regulation of the well-known pro-angiogenesis factor CXCL-12/SDF-1 secreted by tumor associated-macrophages, in addition to MK2-dependent regulation of Serpin-E1/PAI-1 by several cell types within the tumor microenvironment.

Altered Protein Function Caused by AMD-associated Variant rs704 Links Vitronectin to Disease Pathology

Purpose

Vitronectin, a cell adhesion and spreading factor, is suspected to play a role in the pathogenesis of age-related macular degeneration (AMD), as it is a major component of AMD-specific extracellular deposits (e.g., soft drusen, subretinal drusenoid deposits). The present study addressed the impact of AMD-associated non-synonymous variant rs704 in the vitronectin-encoding gene VTN on vitronectin functionality.

Methods

Effects of rs704 on vitronectin expression and processing were analyzed by semi-quantitative sequencing of VTN transcripts from retinal pigment epithelium (RPE) cells generated from human induced pluripotent stem cells (hiPSCs) and from human neural retina, as well as by western blot analyses on heterologously expressed vitronectin isoforms. Binding of vitronectin isoforms to retinal and endothelial cells was analyzed by western blot. Immunofluorescence staining followed extracellular matrix (ECM) deposition in cultured RPE cells heterologously expressing the vitronectin isoforms. Adhesion of fluorescently labeled RPE or endothelial cells in dependence of recombinant vitronectin or vitronectin-containing ECM was investigated fluorometrically or microscopically. Tube formation and migration assays addressed effects of vitronectin on angiogenesis-related processes.

Results

Variant rs704 affected expression, secretion, and processing but not oligomerization of vitronectin. Cell binding and influence on RPE-mediated ECM deposition differed between AMD-risk-associated and non-AMD-risk-associated protein isoforms. Finally, vitronectin affected adhesion and endothelial tube formation.

Conclusions

The AMD-risk-associated vitronectin isoform exhibits increased expression and altered functionality in cellular processes related to the sub-RPE aspects of AMD pathology. Although further research is required to address the subretinal disease aspects, this initial study supports an involvement of vitronectin in AMD pathogenesis.

Indirect Contributions to Tumor Dynamics in the First Stage of the Avascular Phase

A continuum model for tumor invasion in a two-dimensional spatial domain based on the interaction of the urokinase plasminogen activation system with a model for cancer cell dynamics is proposed. The arising system of partial differential equations is numerically solved using the finite element method. We simulated a portion of biological tissue imposing no flux boundary conditions. We monitored the cancer cell dynamics, as well the degradation of an extra cellular matrix representative, vitronectin, and the evolution of a specific degrading enzyme, plasmin, inside the biological tissue. The computations were parameterized as a function of the indirect cell proliferation induced by a plasminogen activator inhibitor binding to vitronectin and of the indirect plasmin deactivation due to the plasminogen activator inhibitor binding to the urokinase plasminogen activator. Their role during the cancer dynamical evolution was identified, together with a possible marker helping the mapping of the cancer invasive front. Our results indicate that indirect cancer cell proliferation biases the speed of the tumor invasive front as well as the heterogeneity of the cancer cell clustering and networking, as it ultimately acts on the proteolytic activity supporting cancer formation. Because of the initial conditions imposed, the numerical solutions of the model show a symmetrical dynamical evolution of heterogeneities inside the simulated domain. Moreover, an increase of up to about 12% in the invasion speed was observed, increasing the rate of indirect cancer cell proliferation, while increasing the plasmin deactivation rate inhibits heterogeneities and networking. As cancer cell proliferation causes vitronectin consumption and plasmin formation, the intensities of the concentration maps of both vitronectin and plasmin are superimposable to the cancer cell concentration maps. The qualitative imprinting that cancer cells leave on the extra cellular matrix during the time evolution as well their activity area is identified, framing the numerical results in the context of a methodology aimed at diagnostic and therapeutic improvement.

Medulloblastoma cancer stem cells: molecular signatures and therapeutic targets

Medulloblastoma (MB) is the most common malignant primary intracranial neoplasm diagnosed in childhood. Although numerous efforts have been made during the past few years to exploit novel targeted therapies for this aggressive neoplasm, there still exist substantial hitches hindering successful management of MB. Lately, progress in cancer biology has shown evidence that a subpopulation of cells within the tumour, namely cancer stem cells (CSCs), are thought to be responsible for the resistance to most chemotherapeutic agents and radiation therapy, accounting for cancer recurrence. Hence, it is crucial to identify the molecular signatures and genetic aberrations that characterise those CSCs and develop therapies that specifically target them. In this review, we aim to give an overview of the main genetic and molecular cues that depict MB-CSCs and provide a synopsis of the novel therapeutic approaches that specifically target this population of cells to attain enhanced antitumorous effects and therefore overcome resistance to therapy.

Circulating miR-30c as a predictive biomarker of type 2 diabetes mellitus with coronary heart disease by regulating PAI-1/VN interactions

AIMS

Type 2 diabetes mellitus (DM2) is associated with coronary heart disease (CHD) and is characterized by high levels of plasminogen activator inhibitor (PAI)-1. Circulating microRNAs have been reported as potential diagnostic biomarkers for DM2 and CHD. However, the underlying mechanisms have largely remained unclear.

MAIN METHODS

The changes of circulating miR-30c, PAI-1 and vitronetin (VN) in plasma from CHD, noncomplicated (NC) + DM2, CHD + DM2 subjects and control individuals were assessed by quantitative reverse transcription PCR (qRT-PCR) and ELISA assays, respectively. The effects of miR-30c on VN expression by targeting PAI-1 were assessed in vitro SMC and in ex vivo plasma, using bioinformatic analysis, miRNA transfection, luciferase assays, qRT-PCR and western blot, respectively.

KEY FINDINGS

We found that decreased circulating miR-30c was negatively correlated with the severity of coronary lesions and the resulting elevated PAI-1 and VN levels. Circulating miR-30c significantly distinguished between patients with CHD + DM2, NC + DM2, CHD and control subjects, and that were significantly associated with certain risk factors for progression from a normal individual to one with CHD + DM2. Furthermore, we also showed that miR-30c plays a previously unrecognized role in regulating the expression of VN levels via regulating PAI-1 levels in vitro SMC and in ex vivo plasma.

SIGNIFICANCE

These findings provide a novel regulatory mechanism of miR-30c in regulating PAI-1/VN interactions and that may serve as a diagnostic biomarker of DM2 that is complicated with CHD.

Identification of a PAI-1-binding site within an intrinsically disordered region of vitronectin

The serine protease inhibitor, plasminogen activator inhibitor Type-1 (PAI-1) is a metastable protein that undergoes an unusual transition to an inactive conformation with a short half-life of only 1-2 hr. Circulating PAI-1 is bound to a cofactor vitronectin, which stabilizes PAI-1 by slowing this latency conversion. A well-characterized PAI-1-binding site on vitronectin is located within the somatomedin B (SMB) domain, corresponding to the first 44 residues of the protein. Another PAI-1 recognition site has been identified with an engineered form of vitronectin lacking the SMB domain, yet retaining PAI-1 binding capacity (Schar, Blouse, Minor, Peterson. J Biol Chem. 2008;283:28487-28496). This additional binding site is hypothesized to lie within an intrinsically disordered domain (IDD) of vitronectin. To localize the putative binding site, we constructed a truncated form of vitronectin containing 71 amino acids from the N-terminus, including the SMB domain and an additional 24 amino acids from the IDD region. This portion of the IDD is rich in acidic amino acids, which are hypothesized to be complementary to several basic residues identified within an extensive vitronectin-binding site mapped on PAI-1 (Schar, Jensen, Christensen, Blouse, Andreasen, Peterson. J Biol Chem. 2008;283:10297-10309). Steady-state and stopped-flow fluorescence measurements demonstrate that the truncated form of vitronectin exhibits the same rapid biphasic association as full-length vitronectin and that the IDD hosts the elusive second PAI-1 binding site that lies external to the SMB domain of vitronectin.

Proteases in Pemphigoid Diseases

Pemphigoid diseases are a subgroup of autoimmune skin diseases characterized by widespread tense blisters. Standard of care typically involves immunosuppressive treatments, which may be insufficient and are often associated with significant adverse events. As such, a deeper understanding of the pathomechanism(s) of pemphigoid diseases is necessary in order to identify improved therapeutic approaches. A major initiator of pemphigoid diseases is the accumulation of autoantibodies against proteins at the dermal-epidermal junction (DEJ), followed by protease activation at the lesion. The contribution of proteases to pemphigoid disease pathogenesis has been investigated using a combination of in vitro and in vivo models. These studies suggest proteolytic degradation of anchoring proteins proximal to the DEJ is crucial for dermal-epidermal separation and blister formation. In addition, proteases can also augment inflammation, expose autoantigenic cryptic epitopes, and/or provoke autoantigen spreading, which are all important in pemphigoid disease pathology. The present review summarizes and critically evaluates the current understanding with respect to the role of proteases in pemphigoid diseases.

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.

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

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

The NC11 domain of human collagen XVI induces vasculogenic mimicry in oral squamous cell carcinoma cells

Collagen XVI, a fibril-associated collagen with interrupted triple helix (FACIT) collagen, is involved in oral squamous cell carcinoma (OSCC) and glioblastoma progression. The NC11 domain of collagen XVI has been described previously with a strong implication in physiological processes. We detected the non-collagenous (NC) 11-domain in supernatants of OSCC cells after recombinant expression of full-length collagen XVI and in sera from OSCC patients and healthy individuals. Stable expression of NC11-green fluorescent protein (GFP) fusion protein in OSCC cells initiated proliferation control and block of anchorage-independent growth. Moreover, the NC11 domain triggered the generation of tubular-like net structures on laminin-rich matrix in contrast to mock-GFP control cells and cells expressing full-length collagen XVI. Taqman® quantitative PCR and diaminobenzidine staining in 2D- and 3D cell culture revealed a significantly increased gene and protein expression of VEGFR1, VEGFR2 and uPAR in recombinant NC11-GFP-expressing cells. Specific VEGF receptor inhibition with Axitinib or fetal calf serum heat inactivation prevented formation of tubular-like net structures. Accordantly, NC11-GFP coated culture slides led to an increase of focal adhesion contact formation and the upregulation of VEGFR1 and uPAR in three different non-transfected OSCC cell lines. In summary, we suggest that the NC11 domain of collagen XVI is a potential biomarker for OSCC and triggers vasculogenic mimicry via upregulation of endothelial receptors VEGFR1, VEGFR2 and uPAR in 2D- and 3D OSCC cell culture conditions.

Directional migration and transcriptional analysis of oligodendrocyte precursors subjected to stimulation of electrical signal

Loss of oligodendrocytes as the result of central nervous system disease causes demyelination that impairs axon function. Effective directional migration of endogenous or grafted oligodendrocyte precursor cells (OPCs) to a lesion is crucial in the neural remyelination process. In this study, the migration of OPCs in electric fields (EFs) was investigated. We found that OPCs migrated anodally in applied EFs, and the directedness and displacement of anodal migration increased significantly when the EF strength increased from 50 to 200 mV/mm. However, EFs did not significantly affect the cell migration speed. The transcriptome of OPCs subjected to EF stimulation (100 and 200 mV/mm) was analyzed using RNA sequencing (RNA-Seq), and results were verified by the reverse transcription quantitative polymerase chain reaction. A Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that the mitogen-activated protein kinase pathway that signals cell migration was significantly upregulated in cells treated with an EF of 200 mV/mm compared with control cells. Gene ontology enrichment analysis showed the downregulation of differentially expressed genes in chemotaxis. This study suggests that an applied EF is an effective cue to guiding OPC migration in neural regeneration and that transcriptional analysis contributes to the understanding of the mechanism of EF-guided cell migration.

Macrophages of M1 phenotype have properties that influence lung cancer cell progression

Stromal macrophages of different phenotypes can contribute to the expression of proteins that affects metastasis such as urokinase-type plasminogen activator (uPA), its receptor uPAR, and plasminogen activator inhibitor-1 (PAI-1), but knowledge of how essential their contribution is in comparison to the cancer cells in small cell lung cancer (SCLC) and lung squamous cell carcinoma (SCC) is lacking. The expression of uPA, uPAR, and PAI-1 and of the matrix metalloproteinases (MMP)-2 and MMP-9 were studied in human macrophages of M1 and M2 phenotype and compared to a lung SCC (NCI-H520) and a SCLC (NCI-H69) cell line. Effects of treatment with conditioned media (CM) from M1 and M2 macrophages on the expression of these genes in H520 and H69 cells as well as effects on the cell growth were investigated. In addition, data on the stromal macrophages immunoreactivity of uPAR, MMP-2, and MMP-9 in a few SCC and SCLC biopsies was included. uPAR, MMP-2, and MMP-9 were confirmed in stromal cells including macrophages in the SCC and SCLC biopsies. In vitro, both macrophage phenotypes expressed considerably higher mRNA levels of uPA, uPAR, PAI-1, and MMP-9 compared to the cancer cell lines, and regarding uPAR, the highest level was found in the M1 macrophage phenotype. Furthermore, M1 CM treatment not only induced an upregulation of PAI-1 in both H520 and H69 cells but also inhibited cell growth in both cell lines, giving M1 macrophages both tumor-promoting and tumor-killing potential.

Pre-eclampsia has an adverse impact on maternal and fetal health

Pre-eclampsia (preE) is a multifaceted complication found uniquely in the pregnant patient and one that has puzzled scientists for years. PreE is not a single disorder, but a complex syndrome that is produced by various pathophysiological triggers and mechanisms affecting about 5% of obstetrical patients. PreE is a major cause of premature delivery and maternal and fetal morbidity and mortality. PreE is characterized by de novo development of hypertension and proteinuria after 20 weeks of gestation and affects nearly every organ system, with the most severe consequences being eclampsia, pulmonary edema, intrauterine growth restriction, and thrombocytopenia. PreE alters the intrauterine environment by modulating the pattern of hormonal signals and activating the detrimental cellular signaling that has been transported to the fetus. The fetus has to adapt to this intrauterine environment with detrimental signals. The adaptive changes increase the risk of disease later in life. This review defines the predisposition and causes of preE and the cellular signaling detrimental to maternal health during preE. Moreover, the risk factors for diseases that are transmitted to the offspring have been addressed in this review. The detrimental signaling molecules that have been overexpressed in preE patients raises the possibility that those signals could be therapeutically blocked one day.

Hyperglycemia impairs cytotrophoblast function via stress signaling

OBJECTIVE

Diabetes mellitus is a risk factor for preeclampsia. Cytotrophoblast (CTB) invasion is facilitated from the conversion of plasminogen to plasmin by urokinase plasminogen activator (uPA), regulated by plasminogen activator inhibitor 1 (PAI-1), and may be inhibited in preeclampsia. This study assessed signaling mechanisms of hyperglycemia-induced CTB dysfunction.

STUDY DESIGN

Human CTBs were treated with 45, 135, 225, 495, or 945 mg/dL glucose for 48 hours. Some cells were pretreated with a p38 inhibitor (SB203580) or a peroxisome proliferator-activated receptor-gamma (PPAR-γ) ligand (rosiglitazone). Expression of uPA, PAI-1, and PPAR-γ levels and p38 mitogen-activated protein kinase phosphorylation were measured by Western blot in cell lysates. Messenger ribonucleic acid of uPA and PAI-1 was measured by quantitative polymerase chain reaction. Levels of interleukin-6, angiogenic (vascular endothelial growth factor [VEGF], placenta growth factor [PlGF]) and antiangiogenic factors (soluble fms-like tyrosine kinase-1 [sFlt-1], soluble endoglin [sEng]) were measured in the media by enzyme-linked immunosorbent assay kits. Statistical comparisons were performed using analysis of variance with a Duncan's post-hoc test.

RESULTS

Both uPA and PAI-1 protein and messenger ribonucleic acid were down-regulated (P < .05) in CTBs treated with 135 mg/dL glucose or greater compared with basal (45 mg/dL). The sEng, sFlt-1, and interleukin-6 were up-regulated, whereas the VEGF and PlGF were down-regulated by 135 mg/dL glucose or greater. p38 phosphorylation and PPAR-γ were up-regulated (P < .05) in hyperglycemia-treated CTBs. The SB203580 or rosiglitazone pretreatment showed an attenuation of glucose-induced down-regulation of uPA and PAI-1.

CONCLUSION

Hyperglycemia disrupts the invasive profile of CTB by decreasing uPA and PAI-1 expression; down-regulating VEGF and PlGF; and up-regulating sEng, sFlt-1, and interleukin-6. Attenuation of CTB dysfunction by SB203580 or rosiglitazone pretreatment suggests the involvement of stress signaling.

Heat shock proteins HSP70 and MRJ cooperatively regulate cell adhesion and migration through urokinase receptor

Background

The urokinase-type plasminogen activator receptor (uPAR) is an important regulator of ECM proteolysis, cell-ECM interactions and cell signaling. uPAR and heat shock proteins HSP70 and MRJ (DNAJB6) have been implicated in tumor growth and metastasis. We have reported recently that MRJ (DNAJB6, a heat shock protein) can interact with uPAR and enhance cell adhesion. Here, we identified another heat shock protein HSP70 as a novel uPAR-interacting protein.

Methods

We performed co-immunoprecipitation in human embryonic kidney (HEK) 293 and colon cancer HCT116 cells as well as immunofluorence assays in HEK293 cells stably transfected with uPAR to investigate the association of suPAR with HSP70/MRJ. To understand the biological functions of the triple complex of suPAR/HSP70/MRJ, we determined whether HSP70 and/or MRJ regulated uPAR-mediated cell invasion, migration, adhesion to vitronectin and MAPK pathway in two pair of human tumor cells (uPAR negative HEK293 cells vs HEK293 cells stably transfected with uPAR and HCT116 cells stably transfected with antisense-uPAR vs HCT116 mock cells transfected with vector only) using transwell assay, wound healing assay, quantitative RT-PCR analyzing mmp2 and mmp9 transcription levels, cell adhesion assay and Western blotting assay.

Results

HSP70 and MRJ formed a triple complex with uPAR and over-expression of MRJ enhanced the interaction between HSP70 and uPAR, while knockdown of MRJ decreased soluble uPAR in HCT116 cells (P < 0.05) and reduced the formation of the triple complex, suggesting that MRJ may act as an uPAR-specific adaptor protein to link uPAR to HSP70. Further experiments showed that knockdown of HSP70 and/or MRJ by siRNA inhibited uPAR-mediated cell adhesion to vitronectin as well as suppressed cell invasion and migration. Knockdown of HSP70 and/or MRJ inhibited expression of invasion related genes mmp2 and mmp9. Finally, HSP70 and/or MRJ up-regulated phosphorylation levels of ERK1/2 and FAK suggesting MAPK pathway was involved. All the biological function experiments in cell level showed an additive effect when HSP70 and MRJ were regulated simultaneously indicating their collaborated regulation effects on uPAR.

Conclusions

These findings may offer a novel insight into the interactions between uPAR and HSP70/MRJ and their functions in cell adhesion and migration may provide more understanding of the roles in regulating cancer metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-639) contains supplementary material, which is available to authorized users.

Vitronectin-binding PAI-1 protects against the development of cardiac fibrosis through interaction with fibroblasts

Plasminogen activator inhibitor-1 (PAI-1) promotes or abates fibrotic processes occurring in different organs. Binding of PAI-1 to vitronectin, an extracellular matrix component, may inhibit vitronectin-integrin complex-mediated cellular responses in pathophysiological conditions. To investigate the importance of plasmin suppression vs vitronectin-binding pathways of PAI-1 in cardiac fibrosis, we studied uninephrectomized mice fed a high salt diet and infused with angiotensin II (Ang II) together with different PAI-1 variants, including PAI-1AK (AK) that inhibits plasminogen activators but does not bind vitronectin, PAI-1RR (RR) that binds vitronectin but does not have protease inhibitory effects or control PAI-1 (CPAI), the control mutant that has similar molecular backbone and half-life as AK and RR while retaining all functions of native PAI-1. Compared with RR and CPAI, non-vitronectin-binding AK significantly increased expression of cardiac fibroblast marker, periostin (Ang+AK 8.40±3.55 vs Ang+RR 2.23±0.44 and Ang+CPAI 2.33±0.12% positive area, both P<0.05) and cardiac fibrosis (Ang+AK 1.79±0.26% vs Ang+RR 0.91±0.18% and Ang+CPAI 0.81±0.12% fibrotic area, both P<0.05), as well as Col1 mRNA (Ang+AK 12.81±1.84 vs Ang+RR 4.04±1.06 and Ang+CPAI 5.23±1.21 fold increase, both P<0.05). To elucidate mechanisms underlying the protective effects of vitronectin-binding PAI-1 against fibrosis, fibroblasts from normal adult human ventricles were stimulated with Ang and different PAI-1 variants. Protease inhibitory AK and CPAI increased supernatant fibronectin, while decreasing plasminogen activator/plasmin activities and matrix metalloproteinase. RR and CPAI variants significantly reduced fibroblast expression of integrin β3, vitronectin level in the supernatant and fibroblast adhesion to vitronectin compared with the non-vitronectin-binding AK. Further, RR and CPAI preserved apoptotic, decreased anti-apoptotic and proliferative activities in fibroblasts. Thus, PAI-1 promotes or protects against development of cardiac fibrosis differentially through the protease inhibitory pathway or through its binding to vitronectin.

Urokinase plasminogen activator is a central regulator of macrophage three-dimensional invasion, matrix degradation, and adhesion

Urokinase plasminogen activator (uPA) and its receptor (uPAR) coordinate a plasmin-mediated proteolytic cascade that has been implicated in cell adhesion, cell motility, and matrix breakdown, for example, during inflammation. As part of their function during inflammatory responses, macrophages move through tissues and encounter both two-dimensional (2D) surfaces and more complex three-dimensional (3D) interstitial matrices. Based on approaches employing uPA gene-deficient macrophages, plasminogen supplementation, and neutralization with specific protease inhibitors, it is reported in this study that uPA activity is a central component of the invasion of macrophages through a 3D Matrigel barrier; it also has a nonredundant role in macrophage-mediated matrix degradation. For murine macrophages, matrix metalloproteinase-9 activity was found to be required for these uPA-mediated effects. Evidence for a unique role for uPA in the inverse relationship between macrophage adhesion and 2D migration was also noted: macrophage adhesion to vitronectin was enhanced by uPA and blocked by plasminogen activator inhibitor-1, the latter approach also able to enhance in turn the 2D migration on this matrix protein. It is therefore proposed that uPA can have a key role in the inflammatory response at several levels as a central regulator of macrophage 3D invasion, matrix remodeling, and adhesion.

SERPINE1: A Molecular Switch in the Proliferation-Migration Dichotomy in Wound-"Activated" Keratinocytes

Significance: A highly interactive serine protease/plasmin/matrix metalloproteinase axis regulates stromal remodeling in the wound microenvironment. Current findings highlight the importance of stringent controls on protease expression and their topographic activities in cell proliferation, migration, and tissue homeostasis. Targeting elements in this cascading network may lead to novel therapeutic approaches for fibrotic diseases and chronic wounds. Recent Advances: Matrix-active proteases and their inhibitors orchestrate wound site tissue remodeling, cell migration, and proliferation. Indeed, the serine proteases urokinase plasminogen activator and tissue-type plasminogen activator (uPA/tPA) and their major phsyiological inhibitor, plasminogen activator inhibitor-1 (PAI-1; serine protease inhibitor clade E member 1 [SERPINE1]), are upregulated in several cell types during injury repair. Coordinate expression of proteolytic enzymes and their inhibitors in the wound bed provides a mechanism for fine control of focal proteolysis to facilitate matrix restructuring and cell motility in complex environments. Critical Issues: Cosmetic and tissue functional consequences of wound repair anomalies affect the quality of life of millions of patients in the United States alone. The development of novel therapeutics to manage individuals most affected by healing anomalies will likely derive from the identification of critical, translationally accessible, control elements in the wound site microenvironment. Future Directions: Activation of the PAI-1 gene early after wounding, its prominence in the repair transcriptome and varied functions suggest a key role in the global cutaneous injury response program. Targeting PAI-1 gene expression and/or PAI-1 function with molecular genetic constructs, neutralizing antibodies or small molecule inhibitors may provide a novel, therapeutically relevant approach, to manage the pathophysiology of wound healing disorders associated with deficient or excessive PAI-1 levels.

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

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

Identification of a new epitope in uPAR as a target for the cancer therapeutic monoclonal antibody ATN-658, a structural homolog of the uPAR binding integrin CD11b (αM)

The urokinase plasminogen activator receptor (uPAR) plays a role in tumor progression and has been proposed as a target for the treatment of cancer. We recently described the development of a novel humanized monoclonal antibody that targets uPAR and has anti-tumor activity in multiple xenograft animal tumor models. This antibody, ATN-658, does not inhibit ligand binding (i.e. uPA and vitronectin) to uPAR and its mechanism of action remains unclear. As a first step in understanding the anti-tumor activity of ATN-658, we set out to identify the epitope on uPAR to which ATN-658 binds. Guided by comparisons between primate and human uPAR, epitope mapping studies were performed using several orthogonal techniques. Systematic site directed and alanine scanning mutagenesis identified the region of aa 268–275 of uPAR as the epitope for ATN-658. No known function has previously been attributed to this epitope Structural insights into epitope recognition were obtained from structural studies of the Fab fragment of ATN-658 bound to uPAR. The structure shows that the ATN-658 binds to the DIII domain of uPAR, close to the C-terminus of the receptor, corroborating the epitope mapping results. Intriguingly, when bound to uPAR, the complementarity determining region (CDR) regions of ATN-658 closely mimic the binding regions of the integrin CD11b (αM), a previously identified uPAR ligand thought to be involved in leukocyte rolling, migration and complement fixation with no known role in tumor progression of solid tumors. These studies reveal a new functional epitope on uPAR involved in tumor progression and demonstrate a previously unrecognized strategy for the therapeutic targeting of uPAR.

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

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

Plasminogen activator inhibitor-1 is increased in colonic epithelial cells from patients with colitis-associated cancer

BACKGROUND

Patients with long-term ulcerative colitis are at risk for developing colorectal cancer.

METHODS

Archival formalin-fixed paraffin-embedded tissue from ulcerative colitis patients who underwent a colectomy for high-grade dysplasia or carcinoma was examined for changes in expression of plasminogen activator inhibitor-1 (PAI-1) as well as other mediators of inflammation-associated cancer. Epithelia from areas of colons that showed histologic evidence of carcinoma, high-grade dysplasia, and epithelia that were not dysplastic or malignant but did contain evidence of prior inflammation (quiescent colitis) was microdissected using laser capture microscopy. mRNA was extracted from the microdissected tissue and PCR array analysis was performed. To extend our findings, PAI-1 protein levels were determined using immunohistochemistry.

RESULTS

The mRNA expression of PAI-1 is increased 6-fold (p=0.02) when comparing the carcinoma group to the quiescent colitis group; increases were also observed in NFKB2, REL, SRC, and VEGFA. The protein levels of PAI-1 are increased by 50% (p<0.001) in high-grade dysplasia and by 60% (p<0.001) in carcinoma when compared to the quiescent colitis group.

CONCLUSIONS

The increase in PAI-1 in high-grade dysplasia and carcinoma suggests a functional role for PAI-1 in malignant transformation in colitis-associated cancer. PAI-1 could also prove a useful diagnostic marker to identify patients at risk for neoplasia and it may be a useful therapeutic target to treat colitis-associated cancer.

Progesterone receptor isoforms PRA and PRB differentially contribute to breast cancer cell migration through interaction with focal adhesion kinase complexes

Conditionally expressed progesterone receptor isoforms PRA and PRB enhance breast cancer cell migration through interaction with focal adhesion kinase (FAK) and differential regulation of FAK phosphorylation and turnover. PRB-stimulated migration is reduced by progestins, which is prevented by PR antagonists or agonist-bound PRA.

Progesterone receptor (PR) and progestins affect mammary tumorigenesis; however, the relative contributions of PR isoforms A and B (PRA and PRB, respectively) in cancer cell migration remains elusive. By using a bi-inducible MDA-MB-231 breast cancer cell line expressing PRA and/or PRB, we analyzed the effect of conditional PR isoform expression. Surprisingly, unliganded PRB but not PRA strongly enhanced cell migration as compared with PR(–) cells. 17,21-Dimethyl-19-norpregna-4,9-dien-3,20-dione (R5020) progestin limited this effect and was counteracted by the antagonist 11β-(4-dimethyl­amino)­phenyl-17β-hydroxy-17-(1-propynyl)­estra-4,9-dien-3-one (RU486). Of importance, PRA coexpression potentiated PRB-mediated migration, whereas PRA alone was ineffective. PR isoforms differentially regulated expressions of major players of cell migration, such as urokinase plasminogen activator (uPA), its inhibitor plasminogen activator inhibitor type 1, uPA receptor (uPAR), and β1-integrin, which affect focal adhesion kinase (FAK) signaling. Moreover, unliganded PRB but not PRA enhanced FAK Tyr397 phosphorylation and colocalized with activated FAK in cell protrusions. Because PRB, as well as PRA, coimmunoprecipitated with FAK, both isoforms can interact with FAK complexes, depending on their respective nucleocytoplasmic trafficking. In addition, FAK degradation was coupled to R5020-dependent turnovers of PRA and PRB. Such an effect of PRB/PRA expression on FAK signaling might thus affect adhesion/motility, underscoring the implication of PR isoforms in breast cancer invasiveness and metastatic evolution with underlying therapeutic outcomes.

Biological significance of a thyroid hormone-regulated secretome

The thyroid hormone, 3,3,5-triiodo-L-thyronine (T3), modulates several physiological processes, including cellular growth, differentiation, metabolism and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Several intracellular and extracellular protein candidates are regulated by T3. Moreover, T3-regulated secreted proteins participate in physiological processes or cellular transformation. T3 has been employed as a marker in several disorders, such as cardiovascular disorder in chronic kidney disease, as well as diseases of the liver, immune system, endocrine hormone metabolism and coronary artery. Our group subsequently showed that T3 regulates several tumor-related secretory proteins, leading to cancer progression via alterations in extracellular matrix proteases and tumor-associated signaling pathways in hepatocellular carcinomas. Therefore, elucidation of T3/thyroid hormone receptor-regulated secretory proteins and their underlying mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a detailed summary on the known secretory proteins regulated by T3 and their physiological significance. This article is part of a Special Issue entitled: An Updated Secretome.

Cell surface remodeling by plasmin: a new function for an old enzyme

Plasmin, one of the most potent and reactive serine proteases, is involved in various physiological processes, including embryo development, thrombolysis, wound healing and cancer progression. The proteolytic activity of plasmin is tightly regulated through activation of its precursor, plasminogen, only at specific times and in defined locales as well as through inhibition of active plasmin by its abundant natural inhibitors. By exploiting the plasminogen activating system and overexpressing distinct components of the plasminogen activation cascade, such as pro-uPA, uPAR and plasminogen receptors, malignant cells can enhance the generation of plasmin which in turn, modifies the tumor microenvironment to sustain cancer progression. While plasmin-mediated degradation and modification of extracellular matrix proteins, release of growth factors and cytokines from the stroma as well as activation of several matrix metalloproteinase zymogens, all have been a focus of cancer research studies for decades, the ability of plasmin to cleave transmembrane molecules and thereby to generate functionally important cleaved products which induce outside-in signal transduction, has just begun to receive sufficient attention. Herein, we highlight this relatively understudied, but important function of the plasmin enzyme as it is generated de novo at the interface between cross-talking cancer and host cells.

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

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

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

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

Stable isotope labeling with amino acids in cell culture (SILAC)-based quantitative proteomics study of a thyroid hormone-regulated secretome in human hepatoma cells

The thyroid hormone, 3, 3',5-triiodo-l-thyronine (T(3)), regulates cell growth, development, differentiation, and metabolism via interactions with thyroid hormone receptors (TRs). However, the secreted proteins that are regulated by T(3) are yet to be characterized. In this study, we used the quantitative proteomic approach of stable isotope labeling with amino acids in cell culture coupled with nano-liquid chromatography-tandem MS performed on a LTQ-Orbitrap instrument to identify and characterize the T(3)-regulated proteins secreted in human hepatocellular carcinoma cell lines overexpressing TRα1 (HepG2-TRα1). In total, 1742 and 1714 proteins were identified and quantified, respectively, in three independent experiments. Among these, 61 up-regulated twofold and 11 down-regulated twofold proteins were identified. Eight proteins displaying increased expression and one with decreased expression in conditioned media were validated using Western blotting. Real-time quantitative RT-PCR further disclosed induction of plasminogen activator inhibitor-1 (PAI-1), a T(3) target, in a time-course and dose-dependent manner. Serial deletions of the PAI-1 promoter region and subsequent chromatin immunoprecipitation assays revealed that the thyroid hormone response element on the promoter is localized at positions -327/-312. PAI-1 overexpression enhanced tumor growth and migration in a manner similar to what was seen when T(3) induced PAI-1 expression in J7-TRα1 cells, both in vitro and in vivo. An in vitro neutralizing assay further supported a crucial role of secreted PAI-1 in T(3)/TR-regulated cell migration. To our knowledge, these results demonstrate for the first time that proteins involved in the urokinase plasminogen activator system, including PAI-1, uPAR, and BSSP4, are augmented in the extra- and intracellular space of T(3)-treated HepG2-TRα1 cells. The T(3)-regulated secretome generated in the current study may provide an opportunity to establish the mechanisms underlying T(3)-associated tumor progression and prognosis.

uPAR regulates bronchial epithelial repair in vitro and is elevated in asthmatic epithelium

Background

The asthma-associated gene urokinase plasminogen activator receptor (uPAR) may be involved in epithelial repair and airway remodelling. These processes are not adequately targeted by existing asthma therapies. A fuller understanding of the pathways involved in remodelling may lead to development of new therapeutic opportunities. uPAR expression in the lung epithelium of normal subjects and patients with asthma was investigated and the contribution of uPAR to epithelial wound repair in vitro was studied using primary bronchial epithelial cells (NHBECs).

Methods

Bronchial biopsy sections from normal subjects and patients with asthma were immunostained for uPAR. NHBECs were used in a scratch wound model to investigate the contribution of the plasminogen pathway to repair. The pathway was targeted via blocking of the interaction between urokinase plasminogen activator (uPA) and uPAR and overexpression of uPAR. The rate of wound closure and activation of intracellular signalling pathways and matrix metalloproteinases (MMPs) were measured.

Results

uPAR expression was significantly increased in the bronchial epithelium of patients with asthma compared with controls. uPAR expression was increased during wound repair in monolayer and air-liquid interface-differentiated NHBEC models. Blocking the uPA–uPAR interaction led to attenuated wound repair via changes in Erk1/2, Akt and p38MAPK signalling. Cells engineered to have raised levels of uPAR showed attenuated repair via sequestration of uPA by soluble uPAR.

Conclusions

The uPAR pathway is required for efficient epithelial wound repair. Increased uPAR expression, as seen in the bronchial epithelium of patients with asthma, leads to attenuated wound repair which may contribute to the development and progression of airway remodelling in asthma. This pathway may therefore represent a potential novel therapeutic target for the treatment of asthma.

Effects of plasminogen activator inhibitor-1-specific RNA aptamers on cell adhesion, motility, and tube formation

The serine protease inhibitor (serpin) plasminogen activator inhibitor-1 (PAI-1) is associated with the pathophysiology of several diseases, including cancer and cardiovascular disease. The extracellular matrix protein vitronectin increases at sites of vessel injury and is also present in fibrin clots. Integrins present on the cell surface bind to vitronectin and anchor the cell to the extracellular matrix. However, the binding of PAI-1 to vitronectin prevents this interaction, thereby decreasing both cell adhesion and migration. We previously developed PAI-1-specific RNA aptamers that bind to (or in the vicinity of) the vitronectin binding site of PAI-1. These aptamers prevented cancer cells from detaching from vitronectin in the presence of PAI-1, resulting in an increase in cell adhesion. In the current study, we used in vitro assays to investigate the effects that these aptamers have on human aortic smooth muscle cell (HASMC) and human umbilical vein endothelial cell (HUVEC) migration, adhesion, and proliferation. The PAI-1-specific aptamers (SM20 and WT15) increased attachment of HASMCs and HUVECs to vitronectin in the presence of PAI-1 in a dose-dependent manner. Whereas PAI-1 significantly inhibited cell migration through its interaction with vitronectin, both SM20 and WT15 restored cell migration. The PAI-1 vitronectin binding mutant (PAI-1AK) did not facilitate cell detachment or have an effect on cell migration. The effect on cell proliferation was minimal. Additionally, both SM20 and WT15 promoted tube formation on matrigel that was supplemented with vitronectin, thereby reversing the PAI-1's inhibition of tube formation. Collectively, results from this study show that SM20 and WT15 bind to the PAI-1's vitronectin binding site and interfere with its effect on cell migration, adhesion, and tube formation. By promoting smooth muscle and endothelial cell migration, these aptamers can potentially eliminate the adverse effects of elevated PAI-1 levels in the pathogenesis of vascular disease.

PAI-1: An Integrator of Cell Signaling and Migration

Cellular migration, over simple surfaces or through complex stromal barriers, requires coordination between detachment/re-adhesion cycles, involving structural components of the extracellular matrix and their surface-binding elements (integrins), and the precise regulation of the pericellular proteolytic microenvironment. It is now apparent that several proteases and protease inhibitors, most notably urokinase plasminogen activator (uPA) and plasminogen activator inhibitor type-1 (PAI-1), also interact with several cell surface receptors transducing intracellular signals that significantly affect both motile and proliferative programs. These events appear distinct from the original function of uPA/PAI-1 as modulators of the plasmin-based proteolytic cascade. The multifaceted interactions of PAI-1 with specific matrix components (i.e., vitronectin), the low-density lipoprotein receptor-related protein-1 (LRP1), and the uPA/uPA receptor complex have dramatic consequences on the migratory phenotype and may underlie the pathophysiologic sequalae of PAI-1 deficiency and overexpression. This paper focuses on the increasingly intricate role of PAI-1 as a major mechanistic determinant of the cellular migratory phenotype.

Metals affect the structure and activity of human plasminogen activator inhibitor-1. II. Binding affinity and conformational changes

Human plasminogen activator inhibitor type 1 (PAI-1) is a serine protease inhibitor with a metastable active conformation. The lifespan of the active form of PAI-1 is modulated via interaction with the plasma protein, vitronectin, and various metal ions. These metal ions fall into two categories: Type I metals, including calcium, magnesium, and manganese, stabilize PAI-1 in the absence of vitronectin, whereas Type II metals, including cobalt, copper, and nickel, destabilize PAI-1 in the absence of vitronectin, but stabilize PAI-1 in its presence. To provide a mechanistic basis for understanding the unusual modulation of PAI-1 structure and activity, the binding characteristics and conformational effects of these two types of metals were further evaluated. Steady-state binding measurements using surface plasmon resonance indicated that both active and latent PAI-1 exhibit a dissociation constant in the low micromolar range for binding to immobilized nickel. Stopped-flow measurements of approach-to-equilibrium changes in intrinsic protein fluorescence indicated that the Type I and Type II metals bind in different modes that induce distinct conformational effects on PAI-1. Changes in the observed rate constants with varying concentrations of metal allowed accurate determination of binding affinities for cobalt, nickel, and copper, yielding dissociation constants of ∼40, 30, and 0.09 μM, respectively. Competition experiments that tested effects on PAI-1 stability were consistent with these measurements of affinity and indicate that copper binds tightly to PAI-1.

Insulin-like growth factor-I:vitronectin complex-induced changes in gene expression effect breast cell survival and migration

Recent studies have demonstrated that IGF-I associates with vitronectin (VN) through IGF-binding proteins (IGFBP), which in turn modulate IGF-stimulated biological functions such as cell proliferation, attachment, and migration. Because IGFs play important roles in transformation and progression of breast tumors, we aimed to describe the effects of IGF-I:IGFBP:VN complexes on breast cell function and to dissect mechanisms underlying these responses. In this study we demonstrate that substrate-bound IGF-I:IGFBP:VN complexes are potent stimulators of MCF-7 breast cell survival, which is mediated by a transient activation of ERK/MAPK and sustained activation of phosphoinositide 3-kinase/AKT pathways. Furthermore, use of pharmacological inhibitors of the MAPK and phosphoinositide 3-kinase pathways confirms that both pathways are involved in IGF-I:IGFBP:VN complex-mediated increased cell survival. Microarray analysis of cells stimulated to migrate in response to IGF-I:IGFBP:VN complexes identified differential expression of genes with previously reported roles in migration, invasion, and survival (Ephrin-B2, Sharp-2, Tissue-factor, Stratifin, PAI-1, IRS-1). These changes were not detected when the IGF-I analogue ([L(24)][A(31)]-IGF-I), which fails to bind to the IGF-I receptor, was substituted; confirming the IGF-I-dependent differential expression of genes associated with enhanced cell migration. Taken together, these studies have established that IGF-I:IGFBP:VN complexes enhance breast cell migration and survival, processes central to facilitating metastasis. This study highlights the interdependence of extracellular matrix and growth factor interactions in biological functions critical for metastasis and identifies potential novel therapeutic targets directed at preventing breast cancer progression.

Vitronectin accumulates in the interstitium but minimally impacts fibrogenesis in experimental chronic kidney disease

Vitronectin (Vtn) is a glycoprotein found in normal serum and pathological extracellular matrix. Given its known interactions with plasminogen activator inhibitor-1 (PAI-1) and Vtn cellular receptors, especially αvβ3 integrin and the urokinase receptor (uPAR), this study was designed to investigate its role in renal fibrogenesis in the mouse model of unilateral ureteral obstruction (UUO). Kidney Vtn mRNA levels were increased ×1.8-5.1 and Vtn protein levels ×1.9-3 on days 7, 14, and 21 after UUO compared with sham kidney levels. Groups of age-matched C57BL/6 wild-type (Vtn+/+) and Vtn-/- mice (n = 10-11/group) were killed 7, 14, or 21 days after UUO. Absence of Vtn resulted in the following significant differences, but only on day 14: fewer αSMA+ interstitial myofibroblasts (×0.53), lower procollagen III mRNA levels (×0.41), lower PAI-1 protein (×0.23), higher uPA activity (×1.1), and lower αv protein (×0.32). The number of CD68+ macrophages did not differ between the genotypes. Despite these transient differences on day 14, the absence of Vtn had no effect on fibrosis severity based on both picrosirius red-positive interstitial area and total kidney collagen measured by the hydroxyproline assay. These findings suggest that despite significant interstitial Vtn deposition in the UUO model of chronic kidney disease, its fibrogenic role is either nonessential or redundant. These data are remarkable given Vtn's strong affinity for the potent fibrogenic molecule PAI-1.

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.

Plasminogen activator inhibitors regulate cell adhesion through a uPAR-dependent mechanism

Binding of type-1 plasminogen activator inhibitor (PAI-1) to cell surface urokinase (uPA) promotes inactivation and internalization of adhesion receptors (e.g., urokinase receptor (uPAR), integrins) and leads to cell detachment from a variety of extracellular matrices. In this report, we begin to examine the mechanism of this process. We show that neither specific antibodies to uPA, nor active site inhibitors of uPA, can detach the cells. Thus, cell detachment is not simply the result of the binding of macromolecules to uPA and/or of the inactivation of uPA. We further demonstrate that another uPA inhibitor, protease nexin-1 (PN-1), also stimulates cell detachment in a uPA/uPAR-dependent manner. The binding of both inhibitors to uPA leads to the specific inactivation of the matrix-engaged integrins and the subsequent detachment of these integrins from the underlying extracellular matrix (ECM). This inhibitor-mediated inactivation of integrins requires direct interaction between uPAR and those integrins since cells attached to the ECM through integrins incapable of binding uPAR do not respond to the presence of either PAI-1 of PN-1. Although both inhibitors initiate the clearance of uPAR, only PAI-1 triggers the internalization of integrins. However, cell detachment by PAI-1 or PN-1 does not depend on the endocytosis of these integrins since cell detachment was also observed when clearance of these integrins was blocked. Thus, PAI-1 and PN-1 induce cell detachment through two slightly different mechanisms that affect integrin metabolism. These differences may be important for distinct cellular processes that require controlled changes in the subcellular localization of these receptors.