EGF-induced urokinase plasminogen activator receptor promotes epithelial to mesenchymal transition in human gastric cancer cells

The uPA/uPAR System Orchestrates the Inflammatory Response, Vascular Homeostasis, and Immune System in Fibrosis Progression

Fibrotic diseases, such as systemic sclerosis (SSc), idiopathic pulmonary fibrosis, renal fibrosis and liver cirrhosis are characterized by tissue overgrowth due to excessive extracellular matrix (ECM) deposition. Fibrosis progression is caused by ECM overproduction and the inhibition of ECM degradation due to several events, including inflammation, vascular endothelial dysfunction, and immune abnormalities. Recently, it has been reported that urokinase plasminogen activator (uPA) and its receptor (uPAR), known to be fibrinolytic factors, orchestrate the inflammatory response, vascular homeostasis, and immune homeostasis system. The uPA/uPAR system may show promise as a potential therapeutic target for fibrotic diseases. This review considers the role of the uPA/uPAR system in the progression of fibrotic diseases.

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.

Experimental and Clinical Evidence Supports the Use of Urokinase Plasminogen Activation System Components as Clinically Relevant Biomarkers in Gastroesophageal Adenocarcinoma

Simple Summary

Patients with gastric and oesophageal adenocarcinomas (GOCs) have short life expectancies as their tumours spread to other sites early. This is facilitated by the increased expression of the urokinase plasminogen activation system (uPAS); a feature of the majority of GOCs. There is increasing appreciation of the importance of uPAS expression in a range of cell types within the tumour microenvironment. Abundant clinical evidence indicates that altered expression of uPAS proteins is associated with worse outcomes, including time to tumour recurrence and patient survival. Emerging technologies, including liquid biopsy, suggest a role of uPAS for the detection of circulating tumour cells, which are responsible for the dissemination of cancers. We review and summarise pre-clinical and clinical data that supports the use of uPAS as a biomarker in GOC.

Abstract

Gastric and oesophageal cancers (GOCs) are lethal cancers which metastasise early and recur frequently, even after definitive surgery. The urokinase plasminogen activator system (uPAS) is strongly implicated in the invasion and metastasis of many aggressive tumours including GOCs. Urokinase plasminogen activator (uPA) interaction with its receptor, urokinase plasminogen activator receptor (uPAR), leads to proteolytic activation of plasminogen to plasmin, a broad-spectrum protease which enables tumour cell invasion and dissemination to distant sites. uPA, uPAR and the plasminogen activator inhibitor type 1 (PAI-1) are overexpressed in some GOCs. Accumulating evidence points to a causal role of activated receptor tyrosine kinase pathways enhancing uPAS expression in GOCs. Expression of these components are associated with poorer clinicopathological features and patient survival. Stromal cells, including tumour-associated macrophages and myofibroblasts, also express the key uPAS proteins, supporting the argument of stromal involvement in GOC progression and adverse effect on patient survival. uPAS proteins can be detected on circulating leucocytes, circulating tumour cells and within the serum; all have the potential to be developed into circulating biomarkers of GOC. Herein, we review the experimental and clinical evidence supporting uPAS expression as clinical biomarker in GOC, with the goal of developing targeted therapeutics against the uPAS.

Prognostic significance of uPA and uPAR expression in patients with cervical cancer undergoing radiotherapy

Cervical cancer remains a major health threat. Urokinase serves as a marker of metastatic tumors. The present study aimed to determine whether the expression levels of urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR), before and during the course of radiotherapy, serve as prognostic markers for patients with cervical cancer. Cervical tumor tissue biopsies were collected from 72 patients before radiotherapy and after the completion of external beam radiotherapy (EBRT) before intracavitary brachytherapy. The levels of uPA and uPAR were determined using ELISA assays. The significance of the associations between the protein expression levels and the clinical outcomes of patients was determined. Although irradiation enhanced uPA and uPAR expression in cervical cancer cell lines, average uPA levels significantly decreased in tumors, and uPAR levels significantly increased after EBRT. The levels of uPA increased in 12 patients and decreased in 26 patients; and those of uPAR increased in 13 patients and decreased in two patients. Cox regression analysis revealed that increased expression of uPAR was significantly associated with 5-year overall survival rate [hazard ratio (HR), 3.65; 95% confidence interval (CI), 1.18-11.30]. However, the levels of both proteins before radiotherapy failed to predict clinical outcomes. Other significant predictive factors were partial response (HR 7.22; 95% CI 1.17-44.73) and disease progression (HR, 13.41; 95% CI, 1.17-153.07). These findings indicated that increased expression of uPAR in cervical tumor tissue during radiotherapy may serve as a prognostic marker for patients with cervical cancer.

FOXA2-Interacting FOXP2 Prevents Epithelial-Mesenchymal Transition of Breast Cancer Cells by Stimulating E-Cadherin and PHF2 Transcription

FOXP2, a member of forkhead box transcription factor family, was first identified as a language-related gene that played an important role in language learning and facial movement. In addition, FOXP2 was also suggested regulating the progression of cancer cells. In previous studies, we found that FOXA2 inhibited epithelial-mesenchymal transition (EMT) in breast cancer cells. In this study, by identifying FOXA2-interacting proteins from FOXA2-pull-down cell lysates with Mass Spectrometry Analysis, we found that FOXP2 interacted with FOXA2. After confirming the interaction between FOXP2 and FOXA2 through Co-IP and immunofluorescence assays, we showed a correlated expression of FOXP2 and FOXA2 existing in clinical breast cancer samples. The overexpression of FOXP2 attenuated the mesenchymal phenotype whereas the stable knockdown of FOXP2 promoted EMT in breast cancer cells. Even though FOXP2 was believed to act as a transcriptional repressor in most cases, we found that FOXP2 could activate the expression of tumor suppressor PHF2. Meanwhile, we also found that FOXP2 could endogenously bind to the promoter of E-cadherin and activate its transcription. This transcriptional activity of FOXP2 relied on its interaction with FOXA2. Furthermore, the stable knockdown of FOXP2 enhanced the metastatic capacity of breast cancer cells in vivo. Together, the results suggested that FOXP2 could inhibit EMT by activating the transcription of certain genes, such as E-cadherin and PHF2, in concert with FOXA2 in breast cancer cells.

Predictive value of EGF and uPAR for chemoradiotherapy response and survival in patients with esophageal squamous cell carcinoma

Background

Chemoradiotherapy (CRT) plays a central role in the treatment of esophageal squamous cell carcinoma (ESCC). However, no effective biomarkers have been identified for predict CRT sensitivity and prognosis of patients with ESCC. The aim of this study was to investigate cytokine profiles of epidermal growth factor (EGF) and urokinase plasminogen activator receptor (uPAR) in 68 ESCC patients, and to evaluate the clinical utility of these markers.

Methods

This pilot study enrolled 68 patients who received neoadjuvant CRT followed by radical surgery or definitive CRT between 2015 and 2017. Serum specimen was obtained from each patient before treatment and at the time of administration of total doses of 40 Gy. Cytokines expression analyses were performed in pre- and post-treatment serum using human cytokine antibody arrays which contained 120 known tumor-related cytokines.

Results

Seven differentially expressed cytokines identified by cytokine antibody arrays in pre- and post-treatment serum from 4 patients with CRT sensitivity and 4 patients with CRT resistance. Of these, up-regulation of EGF and uPAR in serum at the doses of 40 Gy were associated with adverse clinical outcomes. The predictive value of EGF and uPAR were further assessed in a second set of 60 ESCCs. A total of 68 patients enrolled in this study. The median follow-up duration of these patients was 15.87 months (range, 6.21–23.85 months). Cox multivariate survival analyses revealed that high uPAR ratio after CRT independently predicted progression-free survival (PFS) (HR =3.999, 95% CI: 1.503–10.639, P=0.006) and patients with elevated levels of EGF after CRT exhibited significantly worse overall survival (OS) (HR =2.574, 95% CI: 1.046–6.335, P=0.040). Of note, uPAR expression was significantly positive correlation with EGF expression in pre- and post-treatment serum (P=0.0001, P=0.0038). Patients with both high EGF and uPAR ratios had an inferior PFS and OS, compared to patients with a high EGF ratio only or uPAR ratio only or neither (1-year PFS rate 44.2% vs. 61.4%, 1-year OS rate 64.2% vs. 83.4%, P=0.033 and 0.029, respectively).

Conclusions

The levels of EGF and uPAR in serum are reliable and predictive biomarkers for survival in ESCC patients. Further prospective validation in larger independent cohorts is necessary to fully assess its predictive power. We present the following article in accordance with the REMARK reporting checklist.

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

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