Urokinase-type plasminogen activator stimulates the Ras/Extracellular signal-regulated kinase (ERK) signaling pathway and MCF-7 cell migration by a mechanism that requires focal adhesion kinase, Src, and Shc. Rapid dissociation of GRB2/Sps-Shc complex is associated with the transient phosphorylation of ERK in urokinase-treated cells

CD87-targeted BiTE and CAR-T cells potently inhibit invasive nonfunctional pituitary adenomas

Recently, bispecific T-cell engagers (BiTEs) and chimeric antigen receptor-modified T cells (CAR-Ts) have been shown to have high therapeutic efficacy in hematological tumors. CD87 is highly expressed in solid tumors with an oncogenic function. To assess their cytotoxic effects on invasive nonfunctioning pituitary adenomas (iNFPAs), we first examined CD87 expression and its effects on the metabolism of iNFPA cells. We generated CD87-specific BiTE and CAR/IL-12 T cells, and their cytotoxic effects on iNFPAs cells and in mouse models were determined. CD87 had high expression in iNFPA tissue and cell samples but was undetected in noncancerous brain samples. CD87×CD3 BiTE and CD87 CAR/IL-12 T-cells showed antigenic specificity and exerted satisfactory cytotoxic effects, decreasing tumor cell proliferation in vitro and reducing existing tumors in experimental mice. Overall, the above findings suggest that CD87 is a promising target for the immunotherapeutic management of iNFPAs using anti-CD87 BiTE and CD87-specific CAR/IL-12 T cells.

SERPINA11 Inhibits Metastasis in Hepatocellular Carcinoma by Suppressing MEK/ERK Signaling Pathway

Purpose

By using integrative RNA sequencing analysis, we identified a novel tumor suppressor, serpin family A member 11 (SERPINA11), which is a serine proteinase inhibitor that belongs to the serpin superfamily. However, the function of SERPINA11 in hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to investigate the role and molecular mechanism of SERPINA11 in HCC.

Methods

Gene expression patterns of SERPINA11 were analyzed in tissue samples of HCC patients by qRT-PCR. In vitro and in vivo experiments were performed to characterize the function and molecular mechanism of SERPINA11 in the tumor metastasis capacity.

Results

SERPINA11 was downregulated in approximately 50% of HCC and significantly associated with metastasis and poor outcome of patients. Functional study demonstrated that SERPINA11 could inhibit cell growth, cell migration and tumor metastasis. Mechanistic investigations suggested that SERPINA11 accelerated urokinase-type plasminogen activator (uPA) degradation to suppress extracellular signal-regulated kinase (ERK1/2) phosphorylation, and thereby subdued metastatic capabilities of HCC cells.

Conclusion

SERPINA11 plays an important tumor suppressive role in HCC, with possible use as a biomarker and an intervention point for new therapeutic strategies.

Plasminogen Activator Urokinase Receptor Implies Immunosuppressive Features and Acts as an Unfavorable Prognostic Biomarker in Glioma

BACKGROUND

Clinical outcomes of patients with glioma are still poor, even after standard treatments, including surgery combined with radiotherapy and chemotherapy. New therapeutic strategies and targets for glioma are urgently needed. Plasminogen activator urokinase receptor (PLAUR), a highly glycosylated integral membrane protein, is reported to modulate plasminogen activation and extracellular matrix degradation in many malignant cancers, but its role in gliomas remains unclear.

METHODS

Glioma samples with mRNA sequencing data and clinical information from the Chinese Glioma Genome Atlas (n = 310) data set and The Cancer Genome Atlas (n = 611) data set were collected for this study. Analyses using Kaplan-Meier plots, time-dependent receiver operating characteristic curves, Cox regression, and nomograms were conducted to evaluate the prognostic performance of PLAUR expression. Analyses using Metascape, ESTIMATE, EPIC, and immunohistochemical staining were performed to reveal the potential biological mechanism. The statistical analysis and graphical work were completed using SPSS, R language, and GraphPad Prism.

RESULTS

PLAUR was highly expressed in phenotypes associated with glioma malignancy and could serve as an independent prognostic indicator. Functional analysis revealed the correlation between PLAUR and immune response. Further studies found that samples with higher PLAUR expression were infiltrated with fewer CD8 T cells and many more M2 macrophages. Strong positive correlation was demonstrated between PLAUR expression and some immunosuppressive markers, including immune checkpoints and cytokines. These findings were also confirmed in patient samples.

CONCLUSION

Our results elucidated the clinical significance and immunosuppressive effect of PLAUR in gliomas, which might provide some clues in glioma immunotherapy.

IMPLICATIONS FOR PRACTICE

Although the efficacy of immunotherapy has been verified in other tumors, its application in glioma is impeded because of the unique microenvironment. Tumor-associated macrophages, which are particularly abundant in a glioma mass, contribute much to the immunosuppressive microenvironment and offer new opportunities in glioma immunotherapy. The results of this study identified plasminogen activator urokinase receptor (PLAUR) expression as a potential marker to predict the infiltration of macrophages and the status of immune microenvironment in patients with glioma, suggesting that treatment decisions could be based on PLAUR level when administering immunotherapeutics. The soluble PLAUR in blood and other body fluids would make this approach easy to implement in the clinic.

Microfluidic devices for studying coagulation biology

The ability to study the behavior of cells, proteins, and cell-cell or cell-protein interactions under dynamic forces such as shear stress under fluid flow, provides a more accurate understanding of the physiopathology of hemostasis. This review touches upon the traditional methods for studying blood coagulation and platelet aggregation and provides an overview on cellular and protein response to shear stress. We also elaborate on the biological aspects of how cells recognize mechanical forces and convert them into biochemical signals that can drive various signaling pathways. We give a detailed description of the various types of microfluidic devices that are employed to study the complex processes of platelet aggregation and blood coagulation under flow conditions as well as to investigate endothelial shear-response. We also highlight works mimicking artificial vessels as platforms to study the mechanisms of coagulation, and finish our review by describing anticipated clinical uses of microfluidics devices and their standardization.

SerpinB2 inhibits migration and promotes a resolution phase signature in large peritoneal macrophages

SerpinB2 (plasminogen activator inhibitor type 2) has been called the "undecided serpin" with no clear consensus on its physiological role, although it is well described as an inhibitor of urokinase plasminogen activator (uPA). In macrophages, pro-inflammatory stimuli usually induce SerpinB2; however, expression is constitutive in Gata6+ large peritoneal macrophages (LPM). Interrogation of expression data from human macrophages treated with a range of stimuli using a new bioinformatics tool, CEMiTool, suggested that SerpinB2 is most tightly co- and counter-regulated with genes associated with cell movement. Using LPM from SerpinB2-/- and SerpinB2R380A (active site mutant) mice, we show that migration on Matrigel was faster than for their wild-type controls. Confocal microscopy illustrated that SerpinB2 and F-actin staining overlapped in focal adhesions and lamellipodia. Genes associated with migration and extracellular matrix interactions were also identified by RNA-Seq analysis of migrating RPM from wild-type and SerpinB2R380A mice. Subsequent gene set enrichment analyses (GSEA) suggested SerpinB2 counter-regulates many Gata6-regulated genes associated with migration. These data argue that the role of SerpinB2 in macrophages is inhibition of uPA-mediated plasmin generation during cell migration. GSEA also suggested that SerpinB2 expression (likely via ensuing modulation of uPA-receptor/integrin signaling) promotes the adoption of a resolution phase signature.

Selenium-isotopic signature toward mass spectrometric identification and enzyme activity assay

The unraveling of enzymatic reactions, especially identification of enzymatic substrates or products, is important to elucidate biological processes. Here a selenium-isotopic signature for mass spectrometric identification of enzymatic-related species is demonstrated by using selenium-containing peptides (SePeps) as substrates. Thus a strategy is proposed for rapid and precise assay of multiple enzyme activity. These SePeps can be synthesized by introduction of one selenomethionine residue in the sequence and simply identified in the full-scan mode with the feature of distinctive selenium-isotopic distribution without MS/MS verifications, which proposes a novel solution to the specific identification of enzyme-related species, allows to exclude the interferences of species with tiny mass differences in bio-samples, and meanwhile can offer a judgement on data accuracy for the analysis of enzyme activities. As a proof-of-concept, a method for multiple analysis of two representative enzymes in MCF-7 cell lysate has been developed with the isotopic peak areas of either SePep substrates or enzymatic products with the top intensities. These results could be the foundation to extend the method for more complicated enzyme systems. The selenium-isotopic signature provides a powerful protocol for high-throughput assays of peptide-metabolizing enzymes with enhanced confidence and can be extended to screen enzymatic reaction-related substrates.

The prognostic relevance of urokinase-type plasminogen activator (uPA) in the blood of patients with metastatic breast cancer

In breast cancer (BC), elevated levels of urokinase-type plasminogen activator (uPA) in tumor tissue have been confirmed as a strong prognostic factor in level-of-evidence-1 studies. The aim of the present study was to evaluate the clinical relevance of uPA levels in serum of metastatic BC patients and to compare uPA with other blood-based biomarkers. 252 patients were enrolled in this prospective, multicentre study. Blood samples were collected before begin of first-line or later-line systemic treatment. Serum uPA was quantified by a commercially available ELISA. Circulating tumor cells (CTCs) were detected using CellSearch; other biomarkers (EGFR, VEGF, HER2, RAS p21, TIMP1, CAIX) by ELISA. Using the ROC analysis, the optimal cut-off value (determined by the Youden index) of serum uPA was 2.52 ng/ml. Using this value, 26% of patients had elevated uPA levels. Patients with visceral metastasis and more than one metastatic site were significantly more likely to present with elevated uPA levels. CTC status, serum HER2, RAS p21, CAIX, TIMP1 and VEGF correlated significantly with uPA levels. Elevated uPA levels predicted shorter overall and progression-free survival in univariate analysis (median OS: 7.5 months [95%-CI 4.5–10.5 months] vs. not reached, p < 0.001; PFS: 4.8 [95%-CI: 3.1–6.5] vs. 9.1 [7.4–10.8] months, p < 0.001). In multivariate analysis, elevated uPA, presence of ≥5 CTCs, elevated RAS p21, higher grading and higher line of therapy were independent predictors of shorter OS, while elevated CTC counts, higher line of therapy and negative estrogen receptor status were independent predictors of shorter PFS. In conclusion, elevated uPA levels independently predict reduced overall survival and improved prognostication in patients with known CTC status. Whether high serum uPA might identify patients most likely to benefit from therapies targeting uPA, remains to be evaluated in future trials.

(-)-Epigallocatechin gallate derivatives reduce the expression of both urokinase plasminogen activator and plasminogen activator inhibitor-1 to inhibit migration, adhesion, and invasion of MDA-MB-231 cells

Urokinase plasminogen activator (uPA) and its inhibitor plasminogen activator inhibitor-1 (PAI-1) are established independent biomarkers for high metastasis risk in breast cancer. In this study, we investigated the regulatory activity of (-)-epigallocatechin-3-gallate (EGCG) and its derivatives on uPA and PAI-1 expression and thereby their anti-metastatic potential. EGCG showed only marginal effects on the uPA system and on the metastatic behavior of breast cancer cells (MDA-MB-231). However, the EGCG derivative 3e with a methyl-substituted carbonate substituent at the 4″-position showed potent inhibition of PAI-1 (62%) and uPA (50%) expression. The Ras-extracellular-signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), and phosphatidylinositol-3-kinase (PI3K)/Akt/NF-κB pathways, which regulate uPA and PAI-1 expression, were also affected by 3e (25%, 45%, and 25% reduction, respectively). In line with these findings, substantial reduction in metastatic behavior of MDA-MB-231 cells, such as adhesion (40%), invasion (56%), and migration (40%), was observed in the presence of 3e. It is also noteworthy that, in MDA-MB-231 cells, 3e did not exert any beneficial effect on the expression of matric metalloprotein (MMP) 2 and 9, which indicates that the anti-metastatic activity of 3e in MDA-MB-231 cells is not related to its regulation of the expression of MMPs. Taken together, we have shown that the EGCG derivative 3e could suppress the metastatic behavior of MDA-MB-231 cells through regulation of uPA and PAI-1.

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.

Integrin α5 triggers the metastatic potential in renal cell carcinoma

The therapy of advanced renal cell carcinoma (RCC) is still a major challenge. To intervene therapeutically a deeper comprehension of the particular steps of metastasis is necessary. In this context membrane bound receptors like integrins play a decisive role. We analyzed the integrin α5 expression in 141 clear cell RCC patients by Western blot. Patients with RCC expressed a significant higher level of integrin α5 in tumor than in normal tissue. The integrin α5 expression correlated with tumor grade, the development of distant metastases within five years after tumor nephrectomy and reduced survival. The RCC cell lines Caki-1 and CCF-RC1, which highly express integrin α5, were treated with fibronectin in combination with or without an inhibiting anti-integrin α5 antibody. Afterwards the migration, adhesion, viability and prominent signaling molecules were analyzed. Both cell lines showed a significant reduced migration potential as well as a decreased adhesion potential to fibronectin after treatment with an integrin α5 blocking antibody. A contribution of the AKT and ERK1/2 signaling pathways could be demonstrated. The results indicate integrin α5 as a potent marker to discriminate patients’ tumor prognosis. Consequently the integrin subunit α5 can be considered as a target for individual therapy of advanced RCC.

mTORC2 activation is regulated by the urokinase receptor (uPAR) in bladder cancer

Mammalian target of rapamycin complex 2 (mTORC2) has been identified as a major regulator of bladder cancer cell migration and invasion. Upstream pathways that mediate mTORC2 activation remain poorly defined. Urokinase-type plasminogen activator receptor (uPAR) is a GPI-anchored membrane protein and known activator of cell-signaling. We identified increased uPAR expression in 94% of invasive human bladder cancers and in 54-71% of non-invasive bladder cancers, depending on grade. Normal urothelium was uPAR-immunonegative. Analysis of publicly available datasets identified uPAR gene amplification or mRNA upregulation in a subset of bladder cancer patients with reduced overall survival. Using biochemical approaches, we showed that uPAR activates mTORC2 in bladder cancer cells. Highly invasive bladder cancer cell lines, including T24, J82 and UM-UC-3 cells, showed increased uPAR mRNA expression and protein levels compared with the less aggressive cell lines, UROtsa and RT4. uPAR gene-silencing significantly reduced phosphorylation of Serine-473 in Akt, an mTORC2 target. uPAR gene-silencing also reduced bladder cancer cell migration and Matrigel invasion. S473 phosphorylation was observed by immunohistochemistry in human bladder cancers only when the tumors expressed high levels of uPAR. S473 phosphorylation was not controlled by uPAR in bladder cancer cell lines that are PTEN-negative; however, this result probably did not reflect altered mTORC2 regulation. Instead, PTEN deficiency de-repressed alternative kinases that phosphorylate S473. Our results suggest that uPAR and mTORC2 are components of a single cell-signaling pathway. Targeting uPAR or mTORC2 may be beneficial in patients with bladder cancer.

Focal adhesion kinase overexpression and its impact on human osteosarcoma

Focal adhesion kinase (FAK) has been implicated in tumorigenesis in various malignancies. We sought to examine the expression patterns of FAK and the activated form, phosphorylated FAK (pFAK), in human osteosarcoma and to investigate the correlation of FAK expression with clinicopathologic parameters and prognosis. In addition, the functional consequence of manipulating the FAK protein level was investigated in human osteosarcoma cell lines. Immunohistochemical staining was used to detect FAK and pFAK in pathologic archived materials from 113 patients with primary osteosarcoma. Kaplan-Meier survival and Cox regression analyses were performed to evaluate the prognoses. The role of FAK in the cytological behavior of MG63 and 143B human osteosarcoma cell lines was studied via FAK protein knock down with siRNA. Cell proliferation, migration, invasiveness and apoptosis were assessed using the CCK8, Transwell and Annexin V/PI staining methods. Both FAK and pFAK were overexpressed in osteosarcoma. There were significant differences in overall survival between the FAK-/pFAK- and FAK+/pFAK- groups (P = 0.016), the FAK+/pFAK- and FAK+/pFAK+ groups (P = 0.012) and the FAK-/pFAK- and FAK+/pFAK+ groups (P < 0.001). There were similar differences in metastasis-free survival between groups. The Cox proportional hazards analysis showed that the FAK expression profile was an independent indicator of both overall and metastasis-free survival. SiRNA-based knockdown of FAK not only dramatically reduced the migration and invasion of MG63 and 143B cells, but also had a distinct effect on osteosarcoma cell proliferation and apoptosis. These results collectively suggest that FAK overexpression and phosphorylation might predict more aggressive biologic behavior in osteosarcoma and may be an independent predictor of poor prognosis.

Mechanism of Focal Adhesion Kinase Mechanosensing

Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP₂ binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP₂ concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP₂-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments.

Focal adhesions integrate external mechanical signals into biochemical circuits allowing cellular mechanosensing. Although the zoo of mechanosensing proteins at focal adhesions is steadily growing, force-induced enzymatic mechanisms, as those uncovered for autoinhibited kinases in muscle, remain to be identified for focal adhesion downstream signaling. Here, we provide evidence that focal adhesion kinase (FAK) can act as a direct mechano-enzyme at focal adhesions, using molecular dynamics simulations and kinetic modelling. We show that anchorage of FAK to the membrane via PIP-2 is critical for this mechanical activation. Our results suggest similar mechanisms to be at play for other membrane-bound autoinhibited kinases.

Urokinase receptor and resistance to targeted anticancer agents

The urokinase receptor (uPAR) is a GPI-anchored membrane protein, which regulates protease activity at the cell surface and, in collaboration with a system of co-receptors, triggers cell-signaling and regulates gene expression within the cell. In normal tissues, uPAR gene expression is limited; however, in cancer, uPAR is frequently over-expressed and the gene may be amplified. Hypoxia, which often develops in tumors, further increases uPAR expression by cancer cells. uPAR-initiated cell-signaling promotes cancer cell migration, invasion, metastasis, epithelial-mesenchymal transition, stem cell-like properties, survival, and release from states of dormancy. Newly emerging data suggest that the pro-survival cell-signaling activity of uPAR may allow cancer cells to "escape" from the cytotoxic effects of targeted anticancer drugs. Herein, we review the molecular properties of uPAR that are responsible for its activity in cancer cells and its ability to counteract the activity of anticancer drugs.

A8, an anti-uPA agonistic antibody, promotes metastasis of cancer cells via ERK pathway

Urokinase-type plasminogen activator (uPA) and uPA receptor (uPAR) are expressed in many tumors and have been reported to be correlated to protein expression and poor prognosis in malignant tumors. In a previous study, we reported on the selection of human single-chain variable fragment (scFv) A8 specific to uPA from phage-displayed human naïve scFv library. In this study, scFv A8 was converted to minibody form and evaluated for its functional ability on the uPA system involved in cellular signaling and cancer cell metastasis. A8 minibody increased enzyme activity of uPA and enhanced the migration and invasion of HT1080 colon cancer cells in a dose-dependent manner. A8 increased ERK phosphorylation, and enhanced migration was blocked by U0126, but not by LY0294002, SB2203580, and SP600125. A8 minibody also enhanced migration of MDA-MB231 by mediated expressing surface uPA, but not that of MCF-7 non-expressing surface uPA. Taken together, the A8 anti-uPA antibody is a uPA agonistic antibody, enhancing migration and invasion of cancer cells that express uPA via activation of ERK pathway.

Diallyl disulfide suppresses SRC/Ras/ERK signaling-mediated proliferation and metastasis in human breast cancer by up-regulating miR-34a

Diallyl disulfide (DADS) is one of the major volatile components of garlic oil. DADS has various biological properties, including anticancer, antiangiogenic, and antioxidant effects. However, the anticancer mechanisms of DADS in human breast cancer have not been elucidated, particularly in vivo. In this study, we demonstrated that the expression of miR-34a was up-regulated in DADS-treated MDA-MB-231 cells. miR-34a not only inhibited breast cancer growth but also enhanced the antitumor effect of DADS, both in vitro and in vivo. Furthermore, Src was identified as a target of miR-34a, with miR-34a inhibiting SRC expression and consequently triggering the suppression of the SRC/Ras/ERK pathway. These results suggest that DADS could be a promising anticancer agent for breast cancer. miR-34a may also demonstrate a potential gene therapy agent that could enhance the antitumor effects of DADS.

Neutralizing the EGF receptor in glioblastoma cells stimulates cell migration by activating uPAR-initiated cell signaling

In glioblastoma (GBM), the EGF receptor (EGFR) and Src family kinases (SFKs) contribute to an aggressive phenotype. EGFR may be targeted therapeutically; however, resistance to EGFR-targeting drugs such as Erlotinib and Gefitinib develops quickly. In many GBMs, a truncated form of the EGFR (EGFRvIII) is expressed. Although EGFRvIII is constitutively active and promotes cancer progression, its activity is attenuated compared with EGF-ligated wild-type EGFR, suggesting that EGFRvIII may function together with other signaling receptors in cancer cells to induce an aggressive phenotype. In this study, we demonstrate that in EGFRvIII-expressing GBM cells, the urokinase receptor (uPAR) functions as a major activator of SFKs, controlling phosphorylation of downstream targets, such as p130Cas and Tyr-845 in the EGFR in vitro and in vivo. When EGFRvIII expression in GBM cells was neutralized, either genetically or by treating the cells with Gefitinib, paradoxically, the cells demonstrated increased cell migration. The increase in cell migration was explained by a compensatory increase in expression of urokinase-type plasminogen activator, which activates uPAR-dependent cell signaling. GBM cells that were selected for their ability to grow in vivo in the absence of EGFRvIII also demonstrated increased cell migration, due to activation of the uPAR signaling system. The increase in GBM cell migration, induced by genetic or pharmacologic targeting of the EGFR, was blocked by Dasatinib, highlighting the central role of SFKs in uPAR-promoted cell migration. These results suggest that compensatory activation of uPAR-dependent cell signaling, in GBM cells treated with targeted therapeutics, may adversely affect the course of the disease by promoting cell migration, which may be associated with tumor progression.

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.

Urokinase-type plasminogen activator receptor signaling is critical in nasopharyngeal carcinoma cell growth and metastasis

Nasopharyngeal carcinoma (NPC) is one of the most common malignancies in southern China and Southeast Asia, with the highest metastasis rate among head and neck cancers. The mechanisms underlying NPC progression remain poorly understood. Genome-wide expression profiling on 18 NPC vs. 18 noncancerous nasopharyngeal tissues together with GeneGo pathway analysis and expression verification in NPC cells and tissues revealed a potential role of urokinase-type plasminogen activator receptor (uPAR) in NPC progression, which has not been investigated in NPC. We then observed that uPAR expression is increased in poorly differentiated, highly metastatic NPC cells compared with lowly metastatic cells or differentiated NPC cells. In vitro studies demonstrated that uPAR regulates NPC cell growth, colony formation, migration, and invasion and promotes the epithelial-mesenchymal transition (EMT). Additional tumor xenograft and spontaneous metastasis experiments revealed that uPAR promotes NPC cell growth and metastasis in vivo. The JAK-STAT pathway is involved in uPAR-regulated signaling in NPC cells as determined by immunoblotting. Moreover, uPAR-mediated growth and motility is partially abolished upon treatment with the Jak1/Jak2 inhibitor INCB018424. We suppressed uPA expression in uPAR-overexpressing NPC cells and found that uPAR-mediated cellular growth and motility is not exclusively dependent on uPA. In summary, uPAR is a significant regulator of NPC progression and could serve as a promising therapeutic target.

Plasminogen activator urokinase expression reveals TRAIL responsiveness and supports fractional survival of cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/TNFSF10/Apo2L) holds promise for cancer therapy as it induces apoptosis in a large variety of cancer cells while exerting negligible toxicity in normal ones. However, TRAIL can also induce proliferative and migratory signaling in cancer cells resistant to apoptosis induced by this cytokine. In that regard, the molecular mechanisms underlying the tumor selectivity of TRAIL and those balancing apoptosis versus survival remain largely elusive. We show here that high mRNA levels of PLAU, which encodes urokinase plasminogen activator (uPA), are characteristic of cancer cells with functional TRAIL signaling. Notably, decreasing uPA levels sensitized cancer cells to TRAIL, leading to markedly increased apoptosis. Mechanistic analyses revealed three molecular events taking place in uPA-depleted cells: reduced basal ERK1/2 prosurvival signaling, decreased preligand decoy receptor 2 (DcR2)-death receptor 5 (DR5) interaction and attenuated recruitment of DcR2 to the death-inducing signaling complex upon TRAIL challenge. These phenomena were accompanied by increased FADD and procaspase-8 recruitment and processing, thus guiding cells toward a caspase-dependent cell death that is largely independent of the intrinsic apoptosis pathway. Collectively, our results unveil PLAU mRNA levels as marker for the identification of TRAIL-responsive tumor cells and highlight a key role of uPA signaling in ‘apoptosis versus survival' decision-making processes upon TRAIL challenge.

High-throughput tyrosine kinase activity profiling identifies FAK as a candidate therapeutic target in Ewing sarcoma

Limited progress has been made in the treatment of advanced-stage pediatric solid tumors despite the accelerated pace of cancer discovery over the last decade. Tyrosine kinase inhibition is one tractable therapeutic modality for treating human malignancy. However, little is known about the kinases critical to the development or maintenance of many pediatric solid tumors such as Ewing sarcoma. Using a fluorescent, bead-based technology to profile activated tyrosine kinases, we identified focal adhesion kinase (FAK, PTK2) as a candidate target in Ewing sarcoma. FAK is a tyrosine kinase critical for cellular adhesion, growth, and survival. As such, it is a compelling target for cancer-based therapy. In this study, we have shown that FAK is highly phosphorylated in primary Ewing sarcoma tumor samples and that downregulation of FAK by short hairpin RNA and treatment with a FAK-selective kinase inhibitor, PF-562271, impaired growth and colony formation in Ewing sarcoma cell lines. Moreover, treatment of Ewing sarcoma cell lines with PF-562271 induced apoptosis and led to downregulation of AKT/mTOR and CAS activity. Finally, we showed that small-molecule inhibition of FAK attenuated Ewing sarcoma tumor growth in vivo. With FAK inhibitors currently in early-phase clinical trials for adult malignancies, these findings may bear immediate relevance to patients with Ewing sarcoma.

The urokinase plasminogen activator system in breast cancer invasion and metastasis

The urokinase plasminogen activator system, which is a serine protease family include urokinase-type plasminogen activator (uPA), the uPA receptor and plasminogen activator inhibitors (PAIs). uPA catalyzes the transformation of plasminogen to its active form plasmin, which is able to degrade the extracellular matrix (ECM) and basement membranes, directly or indirectly through activating pro-matrix metalloproteinases (pro-MMPs), promoting cancer cell metastasis and invasion. Both uPA and PAI-1 are poor prognosis markers in primary breast cancer. Evidence has been presented that the uPA system facilitates breast cancer metastasis by several different mechanisms, such as the Ras-ERK pathway and p38 MAPK pathway. This review focuses on uPA system, summarizes their biological effects, highlights the molecular mechanism and pathway, and discusses the role of uPA system in the prevention and treatment of human breast cancers.

Aggregated low-density lipoprotein induce impairment of the cytoskeleton dynamics through urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor in human vascular smooth muscle cell

BACKGROUND

Urokinase-type plasminogen activator (UPA) regulates vascular smooth muscle cell (VSMC) functions relevant in vascular remodeling by facilitating proteolysis at the cell surface and inducing cell signaling pathways. Our previous results demonstrated that aggregated low-density lipoprotein (agLDL) impair cytoskeleton dynamics, a key event contributing to VSMC behavior during progression of atherosclerotic plaques.

OBJECTIVES

To investigate whether mechanisms underlying inhibition of cytoskeleton dynamics in lipid-loaded VSMC occurs through a UPA-mediated process.

METHODS

Adhesion assay was performed in lipid-loaded human VSMC after 16-h exposition to agLDL (100 μg mL(-1)). Protein subcellular localization and actin-fiber formation were assessed by confocal microscopy. For analysis of protein expression western blots were carried out. Co-immunoprecipitates of UPAR were examined by one-dimensional- or two-dimensional electrophoresis (1-DE or 2-DE), mass spectrometry MALDI-TOF and western blot.

RESULTS

agLDL induced UPA subcellular delocalization and significantly decreased UPA levels during attachment of VSMC. UPA (enhanced endogenous-expression or exogenous added) acting as a urokinase-type plasminogen activator receptor (UPAR)-ligand restored actin-cytoskeleton organization and adhesion capacity of lipid-loaded cells to control levels. UPAR co-immunoprecipitated with the unphosphorylated form of myosin regulatory light chain (MRLC) in lipid-loaded cells. The detrimental effects of agLDL on MRLC phosphorylation were reversed by high levels of UPA. The UPA effects on VSMC exposed to agLDL involved FAK phosphorylation.

CONCLUSIONS

The detrimental effects of atherogenic LDL on VSMC are mediated by a decrease and delocalization of the UPA-UPAR interaction that result in an impairment of cytoskeleton dynamics and adhesion capacity affecting cell phenotype and function.

Role of plasminogen activator inhibitor-1 in urokinase's paradoxical in vivo tumor suppressing or promoting effects

Tumor proteases and inhibitors have been associated with paradoxical effects on tumor progression in preclinical and clinical settings. We previously reported that urokinase (uPA) overexpression delays tumor progression in mammary cancer. This study aimed to determine the role of plasminogen activator inhibitor-1 (PAI-1) on uPA's paradoxical in vivo effects. Using syngeneic murine models, we found that stable uPA overexpression promoted in vivo growth of colon tumors (MC-38) naturally expressing high PAI-1, whereas growth inhibition was observed in renal tumors (RENCA) expressing lower PAI-1 levels. In murine mammary carcinoma (4T1), uPA overexpression shifted the uPA/PAI-1 balance in favor of the protease, resulting in significantly reduced tumor growth and metastases in vivo. Conversely, increased tumor progression was observed in stable PAI-1 overexpressing 4T1 tumors as compared with uPA-overexpressing and control tumors. These effects were associated with downregulation of metastases promoting genes in uPA-overexpressing tumors, such as metalloproteinases, CXCL-1, c-Fos, integrin α-5, VEGF-A, PDGF-α, and IL-1β. In PAI-1-overexpressing tumors, many of the above genes were upregulated. PAI-1 overexpressing tumors had increased total and new tumor microvessels, and increased tumor cell proliferation, whereas the opposite effects were found in uPA-overexpressing tumors. Finally, PAI-1 downregulation led to significant inhibition of 4T1 tumor growth and metastases in vivo. In conclusion, uPA's dual effects on tumor progression occur in the context of its interactions with endogenous PAI-1 expression. Our studies uncover novel mechanisms of in vivo tumor control by modulation of the balance between tumor proteases and inhibitors, which may be exploited therapeutically.

Inhibition of Grb2-mediated activation of MAPK signal transduction suppresses NOR1/CB1954-induced cytotoxicity in the HepG2 cell line

The nitroreductase oxidored-nitro domain containing protein 1 (NOR₁) gene may be involved in the chemical carcinogenesis of hepatic cancer and nasopharyngeal carcinoma (NPC). We have previously demonstrated that NOR₁ overexpression is capable of converting the monofunctional alkylating agent 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB1954) into a toxic form by reducing the 4-nitro group of CB1954. Toxic CB1954 is able to enhance cell killing in the NPC cell line CNE₁; however, the underlying mechanisms remain unknown. Using cDNA microarrays and quantitative real-time PCR, we previously discovered that NOR₁ increases the expression of growth factor receptor-bound protein 2 (Grb2) mRNA by 4.8-fold in the human hepatocellular carcinoma cell line HepG2. In the present study, we revealed that NOR₁ increased Grb2 protein expression by 3-fold in HepG2 cells. Additionally, we demonstrated that NOR₁ enhanced CB1954-induced cell killing in HepG2 cells, and cell cytotoxicity was inhibited with the tyrosine kinase inhibitor genistein, or by stable transfection of Grb2 small hairpin RNA (shRNA) pU6⁺²⁷-shGrb2 to silence the expression of Grb2. Western blot analysis revealed that Grb2 downregulation may reduce the activity of the mitogen-activated protein kinase (MAPK). Inhibiting the activation of MAPK using the methyl ethyl ketone (MEK) inhibtor PD98059 suppressed CB1954-induced cell killing. These results suggested that the NOR₁ gene enhances CB1954-mediated cell cytotoxicity through the upregulation of Grb2 expression and the activation of MAPK signal transduction in the HepG2 cell line.

A transformation in the mechanism by which the urokinase receptor signals provides a selection advantage for estrogen receptor-expressing breast cancer cells in the absence of estrogen

Binding of urokinase-type plasminogen activator (uPA) to its receptor, uPAR, in estrogen receptor-α (ERα) expressing breast cancer cells, transiently activates ERK downstream of FAK, Src family kinases, and H-Ras. Herein, we show that when uPAR is over-expressed, in two separate ERα-positive breast cancer cell lines, ERK activation occurs autonomously of uPA and is sustained. Autonomous ERK activation by uPAR requires H-Ras and Rac1. A mutated form of uPAR, which does not bind vitronectin (uPAR-W32A), failed to induce autonomous ERK activation. Expression of human uPAR or mouse uPAR but not uPAR-W32A in MCF-7 cells provided a selection advantage when these cells were deprived of estrogen in cell culture for two weeks. Similarly, MCF-7 cells that express mouse uPAR formed xenografts in SCID mice that survived and increased in volume in the absence of estrogen supplementation, probably reflecting the pro-survival activity of phospho-ERK. Autonomous uPAR signaling to ERK was sensitive to the EGFR tyrosine kinase inhibitors, Erlotinib and Gefitinib. The transition in uPAR signaling from uPA-dependent and transient to autonomous and sustained is reminiscent of the transformation in ErbB2/HER2 signaling observed when this gene is amplified in breast cancer. uPAR over-expression may provide a pathway for escape of breast cancer cells from ERα-targeting therapeutics.

Crosstalk between the urokinase-type plasminogen activator receptor and EGF receptor variant III supports survival and growth of glioblastoma cells

A truncated and constitutively active form of the EGF receptor, variant III (EGFRvIII), is a major determinant of tumor growth and progression in glioblastoma multiforme (GBM). Extensive bidirectional crosstalk occurs in the cell-signaling pathways downstream of the EGFR and the urokinase-type plasminogen activator receptor (uPAR); however, crosstalk between EGFRvIII and uPAR has not been examined. Here, we show that uPAR does not regulate ERK activation in EGFRvIII-expressing GBM cells; however, in GBM cells isolated from four separate xenografts in which EGFRvIII expression was down-regulated in vivo, uPAR assumed a major role in sustaining ERK activation. Phosphorylation of Tyr-845 in the EGFR, which is mediated by Src family kinases, depended on uPAR in EGFRvIII-expressing GBM cells. Activation of the mitogenic and prosurvival transcription factor, STAT5b, downstream of EGFRvIII, also required uPAR. The EGFR-selective tyrosine kinase inhibitors, erlotinib and gefitinib, blocked not only EGFRvIII signaling to ERK but also uPAR-dependent STAT5b activation. uPAR gene silencing in EGFRvIII-expressing GBM cells and in cells from tumors that escaped dependency on EGFRvIII decreased cell survival and proliferation. Xenografts of EGFRvIII-expressing cancer cell lines and a human GBM, which was propagated as a xenograft, were robustly immunopositive for uPAR and phospho-Tyr-845 by immunohistochemistry. A human GBM in which the EGFR gene was amplified without truncation was immunonegative for both uPAR and phospho-Tyr-845. These studies identify distinct cell-signaling activities for uPAR in GBM cells that express EGFRvIII and in cells released from dormancy when EGFRvIII is neutralized. uPAR and its crosstalk pathways with EGFRvIII emerge as logical targets for therapeutics development in GBM.

Suppression of uPA and uPAR blocks radiation-induced MCP-1 mediated recruitment of endothelial cells in meningioma

Chemokines play a vital role in recruiting various cell types in the process of tissue repair. Radiation, a major therapeutic modality in cancer treatment, has been described to induce inflammatory response that might lead to the expression of several chemokines. In the present study, we investigated the mechanism of monocyte chemoattractant protein-1 (MCP-1) induction by radiation in meningioma cell lines and the paracrine effect on human microvascular endothelial cells (HMEC). After radiation, meningioma cell lines (IOMM Lee and SF-3061) showed an increased expression of MCP-1. In addition, irradiated meningioma cancer cell conditioned medium (CM) showed an increased ability to attract HMEC and to stimulate MCP-1-induced protein (MCPIP), VEGF and angiogenin expression in HMEC. This chemotactic activity and angiogenic stimulator effect on HMEC were almost abrogated by depleting MCP-1 from the irradiated cancer cell CM. Further, inhibition of either ERK activation/expression or NF-κB nuclear translocation hindered radiation-induced MCP-1 expression in both meningioma cell lines. Further, supplementing cancer cells with exogenous ATF-uPA (with and without radiation) activated ERK phosphorylation, nuclear translocation of the NF-κB p65 sub-unit (Rel-A), and MCP-1 expression. Downregulation of uPA and uPAR, simultaneously by transfecting the cancer cells with bi-cistronic siRNA-expressing plasmid (pU) inhibited radiation-induced ERK activation, nuclear translocation of Rel-A, NF-κB DNA binding activity, and MCP-1 expression. In addition, pU-transfected cancer cells (with or without radiation) reduced radiation-induced MCP-1 and blocked the recruitment of other cell types during the inflammatory process induced by radiation both in in vitro and in vivo conditions.

Epigenetic upregulation of urokinase plasminogen activator promotes the tropism of mesenchymal stem cells for tumor cells

A major obstacle for the effective treatment of cancer is the invasive capacity of the tumor cells. Previous studies have shown the capability of mesenchymal stem cells (MSC) to target these disseminated tumor cells and to serve as therapeutic delivery vehicles. However, the molecular mechanisms that would enhance the migration of MSCs toward tumor areas are not well understood. In particular, very little is known about the role that epigenetic mechanisms play in cell migration and tropism of MSCs. In this study, we investigated whether histone deacetylation was involved in the repression of urokinase plasminogen activator (uPA) expression in MSCs derived from umbilical cord blood (CB) and bone marrow (BM). Induction of uPA expression by histone deacetylase inhibitors trichostatin A and sodium butyrate was observed in CB- and BM-derived MSCs examined. In vitro migration assays showed that induction of uPA expression by histone deacetylase inhibitors in CB- and BM-derived MSCs significantly enhanced tumor tropism of these cells. Furthermore, overexpression of uPA in CB-MSCs induced migration capacity toward human cancer cells in vitro. In addition, our results showed that uPA-uPAR knockdown in PC3 prostate cancer cells significantly inhibited tumor-specific migration of uPA-overexpressing MSCs. These results have significant implications for the development of MSC-mediated, tumor-selective gene therapies.

Key signalling nodes in mammary gland development and cancer. Mitogen-activated protein kinase signalling in experimental models of breast cancer progression and in mammary gland development

Seven classes of mitogen-activated protein kinase (MAPK) intracellular signalling cascades exist, four of which are implicated in breast disease and function in mammary epithelial cells. These are the extracellular regulated kinase (ERK)1/2 pathway, the ERK5 pathway, the p38 pathway and the c-Jun N-terminal kinase (JNK) pathway. In some forms of human breast cancer and in many experimental models of breast cancer progression, signalling through the ERK1/2 pathway, in particular, has been implicated as being important. We review the influence of ERK1/2 activity on the organised three-dimensional association of mammary epithelial cells, and in models of breast cancer cell invasion. We assess the importance of epidermal growth factor receptor family signalling through ERK1/2 in models of breast cancer progression and the influence of ERK1/2 on its substrate, the oestrogen receptor, in this context. In parallel, we consider the importance of these MAPK-centred signalling cascades during the cycle of mammary gland development. Although less extensively studied, we highlight the instances of signalling through the p38, JNK and ERK5 pathways involved in breast cancer progression and mammary gland development.

Regulation of cell signalling by uPAR

Urokinase-type plasminogen activator receptor (uPAR) expression is elevated during inflammation and tissue remodelling and in many human cancers, in which it frequently indicates poor prognosis. uPAR regulates proteolysis by binding the extracellular protease urokinase-type plasminogen activator (uPA; also known as urokinase) and also activates many intracellular signalling pathways. Coordination of extracellular matrix (ECM) proteolysis and cell signalling by uPAR underlies its important function in cell migration, proliferation and survival and makes it an attractive therapeutic target in cancer and inflammatory diseases. uPAR lacks transmembrane and intracellular domains and so requires transmembrane co-receptors for signalling. Integrins are essential uPAR signalling co-receptors and a second uPAR ligand, the ECM protein vitronectin, is also crucial for this process.

Alpha2-macroglobulin inhibits the malignant properties of astrocytoma cells by impeding beta-catenin signaling

Targets that could improve the treatment of brain tumors remain important to define. This study of a transformation-associated isoform of alpha2-macroglobulin (A2M*) and its interaction with the low-density lipoprotein receptor-related protein-1 (LRP1) suggests a new mechanism for abrogating the malignant potential of astrocytoma cells. LRP1 bound A2M* found to be associated with an inhibition of tumor cell proliferation, migration, invasion, spheroid formation, and anchorage-independent growth. Transcriptional studies implicated effects on the Wnt/beta-catenin signaling pathway. Notably, LRP1 antibodies could phenocopy the effects of A2M*. Our findings suggest a pathway of tumor suppression in astrocytoma that might be tractable to therapeutic exploitation.

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.

Polymorphonuclear cells stimulate the migration and metastatic potential of rat sarcoma cells

The tumour microenvironment, which is largely composed of inflammatory cells, is a crucial participant in the neoplastic process through the promotion of cell proliferation, survival and migration. Neutrophil polymorphonuclear cells (PMNs) induce inflammatory reactions that can be either cytotoxic for tumour cells or can promote tumour growth and metastasis. Previously, we have reported a spontaneous metastasis tumour model that has tumour PMNs infiltration, and metastasis, to liver and spleen. The aim of this study was to evaluate the PMNs influences on the tumour cell invasion and metastatic properties. We analysed intercellular adhesion molecule-1 (ICAM-1), urokinase-type plasminogen activator receptor (uPAR), MT1-MMP (membrane type 1-matrix metalloproteinase) and MMP2 protein expression in TuE-t cells cultured with PMNs or PMNs-conditioned medium isolated from tumour bearing and normal rats. The interaction between tumour cells and PMNs induced a decrease in ICAM-1 expression in tumour cells as well as an increase in MMP2 and tumour cell motility. Besides, conserved expression of uPAR and MT1-MMP in tumour cells was also demonstrated. The up-regulation in MMP2 associated with uPAR and MT1-MMP conserved expression may be related to an increased extracellular matrix proteolysis. These results showed that the interaction of tumour cells with PMNs could favour tumour cell spreading through the promotion of a tumour invasive phenotype.

Ligand binding to LRP1 transactivates Trk receptors by a Src family kinase-dependent pathway

Low-density lipoprotein receptor-related protein 1 (LRP1) functions in endocytosis and intracellular signaling for a variety of structurally diverse ligands. Although LRP1 has been implicated in several aspects of neuronal function, molecular mechanisms underlying the activity of neuronal LRP1 remain unclear. Here, we describe a signaling pathway whereby LRP1 transactivates Trk receptors. Binding of tissue-type plasminogen activator or alpha(2)-macroglobulin (alpha(2)M) to LRP1 resulted in Src family kinase (SFK) activation and SFK-dependent Trk receptor transactivation in PC12 cells and neurons. Trk receptor transactivation was necessary for activation of Akt and extracellular signal-regulated kinase and for neurite outgrowth downstream of LRP1. Injection of the LRP1-binding domain of alpha(2)M into rat dorsal root ganglia induced Trk receptor phosphorylation, which was blocked by receptor-associated protein, an antagonist of ligand binding to LRP1. Trk receptor transactivation provides a mechanism by which diverse LRP1 ligands may show neurotrophic activity.

uPAR-deficient mouse keratinocytes fail to produce EGFR-dependent laminin-5, affecting migration in vivo and in vitro

The urokinase receptor (uPAR) is involved in a series of pathological processes, from inflammation to cancer. We have analyzed in detail the role of uPAR and the mechanisms involved in keratinocyte behavior during wound healing by exploiting uPAR-knockout (KO) mice. In vivo, uPAR-KO mice showed delayed wound healing, with abnormal keratinocyte migration and proliferation. In vitro, unlike wild-type cells, primary uPAR-KO keratinocytes did not proliferate in response to epidermal growth factor (EGF), their growth and migration were not inhibited by EGF-receptor (EGFR) inhibitors, and they did not adhere to uncoated surfaces. Whereas EGFR levels in uPAR-KO keratinocytes were normal, there was no tyrosine phosphorylation upon addition of EGF, and its downstream targets, extracellular-signal-regulated kinases 1 and 2 (ERK1/2), were not activated. Re-introduction of mouse uPAR rescued all phenotypes. In vitro adhesion and migration defects were associated with the failure of uPAR-KO keratinocytes to normally produce and secrete laminin-5 (LN5), an event that requires EGFR signaling. These results were confirmed in vivo, with LN5 being upregulated during wound healing in wild-type but not in uPAR-KO epidermis.

A dual role for caveolin-1 in the regulation of fibronectin matrix assembly by uPAR

The relationship between the plasminogen activator system and integrin function is well documented but incompletely understood. The mechanism of uPAR-mediated signaling across the membrane and the molecular basis of uPAR-dependent activation of integrins remain important issues. The present study was undertaken to identify the molecular intermediates involved in the uPAR signaling pathway controlling alpha5beta1-integrin activation and fibronectin polymerization. Disruption of lipid rafts with MbetaCD or depletion of caveolin-1 by siRNA led to the inhibition of uPAR-dependent integrin activation and stimulation of fibronectin polymerization in human dermal fibroblasts. The data indicate a dual role for caveolin-1 in the uPAR signaling pathway, leading to integrin activation. Caveolin-1 functions initially as a membrane adaptor or scaffold to mediate uPAR-dependent activation of Src and EGFR. Subsequently, in its phosphorylated form, caveolin-1 acts as an accessory molecule to direct trafficking of activated EGFR to focal adhesions. These studies provide a novel paradigm for the regulation of crosstalk among integrins, growth-factor receptors and uPAR.

Revisiting the biological roles of PAI2 (SERPINB2) in cancer

Tumour expression of the urokinase plasminogen activator correlates with invasive capacity. Consequently, inhibition of this serine protease by physiological inhibitors should decrease invasion and metastasis. However, of the two main urokinase inhibitors, high tumour levels of the type 1 inhibitor actually promote tumour progression, whereas high levels of the type 2 inhibitor decrease tumour growth and metastasis. We propose that the basis of this apparently paradoxical action of two similar serine protease inhibitors lies in key structural differences controlling interactions with components of the extracellular matrix and endocytosis-signalling co-receptors.

The inhibitory effect of HKa in endothelial cell tube formation is mediated by disrupting the uPA-uPAR complex and inhibiting its signaling and internalization

In two-dimensional (2-D) culture systems, we have previously shown that cleaved two-chain high-molecular-weight kininogen (HKa) or its domain 5 induced apoptosis by disrupting urokinase plasminogen activator (uPA) receptor (uPAR)-integrin signal complex formation. In the present study, we used a three-dimensional (3-D) collagen-fibrinogen culture system to monitor the effects of HKa on tube formation. In a 3-D system, HKa significantly inhibited tube and vacuole formation as low as 10 nM, which represents 1.5% of the physiological concentration of high-molecular-weigh kininogen (660 nM), without apparent apoptosis. However, HKa (300 nM) completely inhibited tube formation and increased apoptotic cells about 2-fold by 20-24 h of incubation. uPA-dependent ERK activation and uPAR internalization regulate cell survival and migration. In a 2-D system, we found that exogenous uPA-induced ERK phosphorylation and uPAR internalization were blocked by HKa. In a 3-D system, we found that not only uPA-uPAR association but also the activation of ERK were inhibited by HKa. HKa disrupts the uPA-uPAR complex, inhibiting the signaling pathways, and also inhibits uPAR internalization and regeneration to the cell surface, thereby interfering with uPAR-mediated cell migration, proliferation, and survival. Thus, our data suggest that the suppression of ERK activation and uPAR internalization by HKa contributes to the inhibition of tube formation. We conclude that in this 3-D collagen-fibrinogen gel, HKa modulates the multiple functions of uPAR in endothelial cell tube formation, a process that is closely related to in vivo angiogenesis.

Deciphering the signaling events that promote melanoma tumor cell vasculogenic mimicry and their link to embryonic vasculogenesis: role of the Eph receptors

During embryogenesis, the primordial microcirculation is formed through a process known as vasculogenesis. The term "vasculogenic mimicry" has been used to describe the manner in which highly aggressive, but not poorly aggressive melanoma tumor cells express endothelial and epithelial markers and form vasculogenic-like networks similar to embryonic vasculogenesis. Vasculogenic mimicry is one example of the remarkable plasticity demonstrated by aggressive melanoma cells and suggests that these cells have acquired an embryonic-like phenotype. Since the initial discovery of tumor cell vasculogenic mimicry by our laboratory, we have been focusing on understanding the molecular mechanisms that regulate this process. This review will highlight recent findings identifying key signal transduction events that regulate melanoma vasculogenic mimicry and their similarity to the signal transduction events responsible for promoting embryonic vasculogenesis and angiogenesis. Specifically, this review will focus on the role of the Eph receptors and ligands in embryonic vasculogenesis, angiogenesis, and vasculogenic mimicry.

Urinary-type plasminogen activator (uPA) and its receptor (uPAR) in squamous cell carcinoma of the oral cavity

OSCC (oral squamous cell carcinoma) is the most common oral malignancy and is estimated to affect approx. 350000 new patients worldwide this year. OSCC is characterized by a high degree of morbidity and mortality, as most patients exhibit local, regional and distant metastasis at the time of diagnosis. Recent genome-wide screening efforts have identified the serine proteinase uPA (urinary-type plasminogen activator, also known as urokinase) as a strong biomarker for prediction of poor disease outcome and a key candidate for molecular classification of oral neoplasms using a 'gene signature' approach. The proteinase uPA binds a surface-anchored receptor designated uPAR (uPA receptor), focalizing proteolytic activity to the pericellular milieu. Furthermore, uPA-uPAR can interact with transmembrane proteins to modify multiple signal transduction pathways and influence a wide variety of cellular behaviours. Correlative clinical data show elevated uPA-uPAR in oral tumour tissues, with tumours exhibiting high levels of both uPA and uPAR as the most invasive. Combined in vitro, pre-clinical and clinical data support the need for further analysis of uPA-uPAR as a prognostic indicator as well as a potential therapeutic target in OSCC.

The plasma kallikrein-kinin system: its evolution from contact activation

The plasma kallikrein-kinin system consists of the proteins factor XII (FXII), prekallikrein (PK), and high molecular weight kininogen. It was first recognized as a surface-activated coagulation system that is activated when blood or plasma interacts with artificial surfaces. Although surface-activated contact activation occurs in vivo in the case of tissue destruction or a developing thrombus, the physiologic basis for the activation and function of this system has not been delineated. New investigations indicate that there is a proteolytic pathway on cells for PK activation independent of FXII. This pathway for PK with subsequent FXII activation indicates physiologic activities. These activities include blood pressure regulation and modulation of thrombosis risk independently of hemostasis. Furthermore, they include regulation of endothelial cell proliferation, angiogenesis and apoptosis through a cellular-based, outside-in signaling system. The present characterizations of this system, which incorrectly had been thought to initiate coagulation, represent an evolution of understanding in this field.

Breast cancer and metabolic syndrome linked through the plasminogen activator inhibitor-1 cycle

Plasminogen activator inhibitor-1 (PAI-1) is a physiological inhibitor of urokinase (uPA), a serine protease known to promote cell migration and invasion. Intuitively, increased levels of PAI-1 should be beneficial in downregulating uPA activity, particularly in cancer. By contrast, in vivo, increased levels of PAI-1 are associated with a poor prognosis in breast cancer. This phenomenon is termed the "PAI-1 paradox". Many factors are responsible for the upregulation of PAI-1 in the tumor microenvironment. We hypothesize that there is a breast cancer predisposition to a more aggressive stage when PAI-1 is upregulated as a consequence of Metabolic Syndrome (MetS). MetS exerts a detrimental effect on the breast tumor microenvironment that supports cancer invasion. People with MetS have an increased risk of coronary heart disease, stroke, peripheral vascular disease and hyperinsulinemia. Recently, MetS has also been identified as a risk factor for breast cancer. We hypothesize the existence of the "PAI-1 cycle". Sustained by MetS, adipocytokines alter PAI-1 expression to promote angiogenesis, tumor-cell migration and procoagulant microparticle formation from endothelial cells, which generates thrombin and further propagates PAI-1 synthesis. All of these factors culminate in a chemotherapy-resistant breast tumor microenvironment. The PAI-1 cycle may partly explain the PAI-1 paradox. In this hypothesis paper, we will discuss further how MetS upregulates PAI-1 and how an increased level of PAI-1 can be linked to a poor prognosis.

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: a perspective

Cell migration is critical for many physiological processes and is often misregulated in developmental disorders and pathological conditions including cancer and neurodegeneration. MAPK signaling and the Rho family of proteins are known regulators of cell migration that exert their influence on cellular cytoskeleton during cell adhesion and migration. Here we review data supporting the view that localized ERK signaling mediated through recently identified scaffold proteins may regulate cell migration.

Tissue plasminogen activator induces pancreatic cancer cell proliferation by a non-catalytic mechanism that requires extracellular signal-regulated kinase 1/2 activation through epidermal growth factor receptor and annexin A2

Tissue plasminogen activator (tPA) is overexpressed in pancreatic ductal carcinoma and is involved in tumor progression. This effect is probably mediated through the activation of angiogenesis, cell invasion, and cell proliferation. Previous studies support the notion that the effects of tPA on cell invasion require its proteolytic activity. Here, we report the molecular mechanism responsible for the proliferative effects of tPA on pancreatic tumor cells. tPA activates the extracellular signal-regulated kinase 1/2 signaling pathway in a manner that is independent of its catalytic activity. We also show that at least two membrane receptors, epidermal growth factor receptor and annexin A2, which are overexpressed in pancreatic cancer, are involved in the transduction of tPA signaling in pancreatic tumors. This observation suggests the establishment of an amplification loop in tumor cell proliferation. Double immunofluorescence experiments showed co-localization of tPA/epidermal growth factor receptor and tPA/annexin A2 in pancreas cancer cells. These results add novel insights into the non-catalytic functions of tPA in cancer and the molecular mechanisms behind the effects of this protease on cell proliferation, including a role for epidermal growth factor receptor.

A Src/Abl Kinase Inhibitor, SKI-606, Blocks Breast Cancer Invasion, Growth, and MetastasisIn vitroandIn vivo

The central role of Src in the development of several malignancies, including breast cancer, and the accumulating evidence of its interaction with receptor tyrosine kinases, integrins, and steroid receptors have identified it as an attractive therapeutic target. In the current study, we have evaluated the effect of a Src/Abl kinase inhibitor, SKI-606, on breast cancer growth, migration, invasion, and metastasis. Treatment of human breast cancer cells MDA-MB-231 with SKI-606 caused a marked inhibition of cell proliferation, invasion, and migration by inhibiting mitogen-activated protein kinase and Akt phosphorylation. For in vivo studies, MDA-MB-231 cells transfected with the plasmid encoding green fluorescent protein (GFP; MDA-MB-231-GFP) were inoculated into the mammary fat pads of female BALB/c nu/nu mice. Once tumor volume reached 30 to 50 mm(3), animals were randomized and treated with vehicle alone or 150 mg/kg SKI-606 by daily oral gavage. Experimental animals receiving SKI-606 developed tumors of significantly smaller volume (45-54%) compared with control animals receiving vehicle alone. Analysis of lungs, liver, and spleen of these animals showed a significant decrease in GFP-positive tumor metastasis in animals receiving SKI-606 at a dose that was well tolerated. Western blot analysis and immunohistochemical analysis of primary tumors showed that these effects were due to the ability of SKI-606 to block tumor cell proliferation, angiogenesis, growth factor expression, and inhibition of Src-mediated signaling pathways in vivo. Together, the results from these studies provide compelling evidence for the role of Src inhibitors as therapeutic agents for blocking breast cancer growth and metastasis.

Expression of urokinase-type plasminogen activator receptor is correlated with metastases of lingual squamous cell carcinoma

Lingual squamous cell carcinoma is common and the survival rate is relatively low. The invasion of cancer cells from the primary tumour into the surrounding tissue is an early step in the process of metastasis and urokinase-type plasminogen activator receptor (uPAR) is a vital mediator of cellular migration in some carcinomas. By binding urokinase-type plasminogen activator, uPAR localises proteolytic activity to the leading edge of the cells, thereby facilitating cellular migration and penetration through tissue boundaries. uPAR also binds directly to vitronectin and associates with integrins within the plasma membrane, which alters the strength of cellular adhesion. In this study we used reverse transcription polymerase chain reaction, immunocytochemistry, and Western-blot to examine the expression of uPAR mRNA and protein in Ts and Tca 8113 cell lines of lingual squamous cell carcinoma and in normal oral mucosal cells. uPAR mRNA and protein were expressed in Ts cells, but not in Tca 8113 cells or in normal oral epithelial cells. Ts cells have higher metastatic potential than Tca 8113 cells. The results suggest that uPAR has an important role in the aggressiveness of lingual squamous cell carcinoma.