Binding of urokinase plasminogen activator to gp130 via a putative urokinase-binding consensus sequence

An engineered ultrahigh affinity bi-paratopic uPAR targeting agent confers enhanced tumor targeting

Urokinase-type plasminogen activator receptor (uPAR) is overexpressed on tumor cells in multiple types of cancer and contributes to disease progression and metastasis. In this work, we engineered a novel bi-paratopic uPAR targeting agent by fusing the binding domains of two native uPAR ligands: uPA and vitronectin, with a flexible peptide linker. The linker length was optimized to facilitate simultaneous engagement of both domains to their adjacent epitopes on uPAR, resulting in a high affinity and avid binding interaction. Furthermore, the individual domains were affinity-matured using yeast surface display and directed evolution, resulting in a bi-paratopic protein with affinity in the picomolar to femtomolar range. This engineered uPAR targeting agent demonstrated significantly enhanced tumor localization in mouse tumor models compared to the native uPAR ligand and warrants further investigation as a diagnostic and therapeutic agent for cancer.

Plasminogen activator receptor assemblies in cell signaling, innate immunity, and inflammation

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) are serine proteases and major activators of fibrinolysis in mammalian systems. Because fibrinolysis is an essential component of the response to tissue injury, diverse cells, including cells that participate in the response to injury, have evolved receptor systems to detect tPA and uPA and initiate appropriate cell-signaling responses. Formation of functional receptor systems for the plasminogen activators requires assembly of diverse plasma membrane proteins, including but not limited to: the urokinase receptor (uPAR); integrins; N-formyl peptide receptor-2 (FPR2), receptor tyrosine kinases (RTKs), the N-methyl-d-aspartate receptor (NMDA-R), and low-density lipoprotein receptor-related protein-1 (LRP1). The cell-signaling responses elicited by tPA and uPA impact diverse aspects of cell physiology. This review describes rapidly evolving knowledge regarding the structure and function of plasminogen activator receptor assemblies. How these receptor assemblies regulate innate immunity and inflammation is then considered.

Involvement of urokinase in cigarette smoke extract-induced epithelial-mesenchymal transition in human small airway epithelial cells

Urokinase-type plasminogen activator (uPA) augments inflammation and tissue remodeling during lung injury and repair. The uPA expression in small airway epithelium of chronic obstructive pulmonary disease (COPD) increases. Epithelial-mesenchymal transition (EMT) is important in the small airway fibrosis of COPD. This study shows the uPA regulation in cigarette smoke extract (CSE)-induced EMT in human small airway epithelial cell lines (HSAEpiCs). uPA is overexpressed in the small airway epithelium of COPD patients and CSE-treated cell lines. Furthermore, uPA expression correlated with vimentin expression in the small airway epithelium of COPD patients. uPA inhibition blocks CSE-induced EMT by reversing E-cadherin and α-catenin expression and retarding the induction of N-cadherin and vimentin, resulting in reduction in migration. uPA overexpression in HSAEpiC cells also promotes EMT and migration. EMT is partly reversed in uPA-overexpressing HSAEpiC cells through the silencing expression of uPA receptor. In conclusion, this study provides new insights into the contribution of uPA upregulation to EMT associated with small airway remodeling in COPD.

Vascular effects of glycoprotein130 ligands--part I: pathophysiological role

The vessel wall is no longer considered as only an anatomical barrier for blood cells but is recognized as an active endocrine organ. Dysfunction of the vessel wall occurs in various disease processes including atherosclerosis, hypertension, peripheral artery disease, aneurysms, and transplant and diabetic vasculopathies. Different cytokines were shown to modulate the behavior of the cells, which constitute the vessel wall such as immune cells, endothelial cells and smooth muscle cells. Glycoprotein 130 (gp130) is a common cytokine receptor that controls the activity of a group of cytokines, namely, interleukin (IL)-6, oncostatin M (OSM), IL-11, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), IL-27, and neuropoietin (NP). Gp130 and associated cytokines have abundantly diverse functions. Part I of this review focuses on the pathophysiological functions of gp130 ligands. We specifically describe vascular effects of these molecules and discuss the respective underlying molecular and cellular mechanisms.

A novel signaling pathway: fibroblast nicotinic receptor alpha1 binds urokinase and promotes renal fibrosis

The nicotinic acetylcholine receptor alpha1 (nAChRalpha1) was investigated as a potential fibrogenic molecule in the kidney, given reports that it may be an alternative urokinase (urokinase plasminogen activator; uPA) receptor in addition to the classical receptor uPAR. In a mouse obstructive uropathy model of chronic kidney disease, interstitial fibroblasts were identified as the primary cell type that bears nAChRalpha1 during fibrogenesis. Silencing of the nAChRalpha1 gene led to significantly fewer interstitial alphaSMA(+) myofibroblasts (2.8 times decreased), reduced interstitial cell proliferation (2.6 times decreased), better tubular cell preservation (E-cadherin 14 times increased), and reduced fibrosis severity (24% decrease in total collagen). The myofibroblast-inhibiting effect of nAChRalpha1 silencing in uPA-sufficient mice disappeared in uPA-null mice, suggesting that a uPA-dependent fibroblastic nAChRalpha1 pathway promotes renal fibrosis. To further establish this possible ligand-receptor relationship and to identify downstream signaling pathways, in vitro studies were performed using primary cultures of renal fibroblasts. (35)S-Labeled uPA bound to nAChRalpha1 with a K(d) of 1.6 x 10(-8) m, which was displaced by the specific nAChRalpha1 inhibitor d-tubocurarine in a dose-dependent manner. Pre-exposure of uPA to the fibroblasts inhibited [(3)H]nicotine binding. The uPA binding induced a cellular calcium influx and an inward membrane current that was entirely prevented by d-tubocurarine preincubation or nAChRalpha1 silencing. By mass spectrometry phosphoproteome analyses, uPA stimulation phosphorylated nAChRalpha1 and a complex of signaling proteins, including calcium-binding proteins, cytoskeletal proteins, and a nucleoprotein. This signaling pathway appears to regulate the expression of a group of genes that transform renal fibroblasts into more active myofibroblasts characterized by enhanced proliferation and contractility. This new fibrosis-promoting pathway may also be relevant to disorders that extend beyond chronic kidney disease.

Urokinase and its receptors in chronic kidney disease

This review focuses on the role of the serine protease urokinase-type plasminogen activator and its high affinity receptor uPAR/CD87 in chronic kidney disease (CKD) progression. An emerging theme is their organ- and site-specific effects. In addition to tubules, uPA is produced by macrophages and fibroblasts in CKD. By activating hepatocyte growth factor and degrading fibrinogen uPA may have anti-fibrotic effects. However renal fibrosis was similar between uPA wild-type and knockout mice in experimental CKD. The uPAR is expressed by renal parenchymal cells and inflammatory cells in a variety of kidney diseases. Such expression appears anti-fibrotic based on studies in uPAR-deficient mice. In CKD uPAR expression is associated with higher uPA activity but its most important effect appears to be due to effects on cell recruitment and migration that involve interactions with a variety of co-receptors and chemoattractant effects of soluble uPAR. Vitronectin and high molecular weight kininogen are alternate uPAR ligands, and receptors in addition to uPAR may also bind directly to uPA and activate cell signaling pathways.

Endogenous urokinase lacks antifibrotic activity during progressive renal injury

Interstitial fibrosis is a universal feature of progressive kidney disease. Urokinase-type plasminogen activator (uPA) is thought to participate for several reasons: 1) uPA is produced predominantly in kidney, 2) its inhibitor plasminogen activator inhibitor-1 (PAI-1) is a strong promoter of interstitial fibrosis, whereas its receptor (uPAR) attenuates renal fibrosis, 3) uPA reduces fibrosis in liver and lung, and 4) uPA can activate hepatocyte growth factor (HGF), a potent antifibrotic growth factor. The present study tested the hypothesis that endogenous uPA reduces fibrosis severity by investigating the unilateral ureteral obstruction (UUO) model in wild-type (WT) and uPA-/- mice. Several outcomes were measured: renal collagen 3-21 days after UUO, macrophage accumulation (F4/80 Western blotting), interstitial myofibroblast density (alpha-smooth muscle actin immunostaining), and tubular injury (E-cadherin and Ksp-cadherin Western blotting). None of these measures differed significantly between WT and uPA-/- mice. uPA genetic deficiency was not associated with compensatory changes in renal uPAR mRNA levels, PAI-1 protein levels, or tissue plasminogen activator activity levels after UUO. Despite the known ability of uPA to activate latent HGF, immunoblotting failed to detect significant differences in levels of the active HGF alpha-chain and phosphorylated cMET (the activated HGF receptor) between the WT and uPA-/- groups. These findings suggest that the profibrotic actions of PAI-1 are uPA independent and that an alternative pathway must activate HGF in kidney. Finally, these results highlight a significant organ-specific difference in basic fibrogenic pathways, as enhanced uPA activity has been reported to attenuate pulmonary and hepatic fibrosis.

Designing scaffolds of peptides for phage display libraries

Phage display is a powerful method for the discovery of peptide ligands that are used for analytical tools, drug discovery, and target validations. Phage display technology can produce a huge number of peptides and generate novel peptide ligands. Recently, phage display technology has successfully managed to create peptide ligands that bind to pharmaceutically difficult targets such as the erythropoietin receptor. As a result of the structural analysis of their ligands, we found that the conformational design of peptides in library is important for selecting high-affinity ligands that bind to every target from a phage peptide library. Key issues concern constraints on the conformation of peptides on the phage and the development of chemically synthesized peptides derived from peptides on phage. This review discusses studies related to the conformation of peptides selected from phage display peptide libraries in addition to the conversion from peptides to non-peptides.

Significant overexpression of urokinase-type plasminogen activator in pancreatic adenocarcinoma using real-time quantitative reverse transcription polymerase chain reaction

BACKGROUND AND AIMS

Overexpression of urokinase-type plasminogen activator (uPA) has been shown to be strongly associated with an increased metastatic potential and poor prognosis in a variety of human malignancies. It was hypothesized that uPA would be overexpressed in highly metastatic pancreatic cancer. The aims of this study were to analyze uPA mRNA expression in pancreatic cancer and to correlate this to the expression of uPA protein and to the stage of the disease.

METHODS

Twenty-one pancreatic adenocarcinoma, six ampullary carcinoma and 10 benign mucinous cystadenoma samples, all with adjacent normal tissue, were collected. uPA mRNA was measured using real-time quantitative reverse transcription polymerase chain reaction. Localization of uPA within normal and pancreatic tumor sections was subsequently confirmed using immunohistochemistry.

RESULTS

The median and range of the ratios of uPA mRNA measures between tumor tissue and non-involved pancreatic tissue was 17.1 (1.4-653.6) for pancreatic adenocarcinoma (P < 0.001), 3.9 (0.7-7.7) for ampullary carcinoma (P = 0.055) and 1.9 (0.6-5.9) for mucinous cystadenoma tissue (P = 0.052). uPA low tumors were associated with an exuberant stromal reaction, whereas uPA high tumors showed little stromal response. Immunohistochemistry confirmed that uPA protein was more prevalent in pancreatic adenocarcinoma tissue than in normal tissue and that it was membrane-bound. uPA mRNA expression was significantly associated with poorly differentiated pancreatic cancers (P < 0.05) and positively associated with tumor stage.

CONCLUSIONS

These observations suggest that significant overexpression of uPA correlates closely to the rapid progression and invasiveness of pancreatic cancer and that uPA may provide a future therapeutic target for pancreatic cancer treatment.