Post-transcriptional regulation of gene expression in the plasminogen activation system

Relationship between systemic inflammation and lung injury induced by chromate exposure: A cross-sectional study in workers

Hexavalent chromium [Cr(VI)] compounds, known as "Group I Human Carcinogen" and "Category I Respiratory Sensitizer", posed great challenges to the respiratory system. A cross-sectional study was undertaken among chromate workers. Serum club cell protein 16 (CC16) and soluble urokinase-type plasminogen activator receptor (suPAR) were measured using ELISA. Thirteen macrophage-related mediators were tested using cytometric bead array. After controlling for sex, age, smoking status, drinking status and BMI, each increase of one-unit of Ln-transformed blood Cr was related to the increase of IL-1beta [Beta (95% CI), 7.22(1.14, 13.29)%, P = 0.021], IL-23 [8.5(1.15, 15.85)%, P = 0.021], IFN-gamma [3.14(0.15, 6.13)%, P = 0.040], and suPAR [9.31(2.5, 16.12) %, P = 0.008], as well as the increase of CC16 by 3.88(0.42, 7.34) % (P = 0.029). Moreover, these inflammatory mediators played an mediation role in the rise of CC16 caused by Cr(VI). The exposure-response curve analysis revealed a substantial nonlinear association of IFN-gamma and suPAR with CC16, thus the mediation effect of INF-gamma and suPAR required cautious interpretation. The positive connection between macrophage-related mediators was stronger in the high exposure group than in the low exposure group, suggesting that high concentration of chromate might promote a complex interplay within the immune system.

Posttranscriptional Regulation of the Plasminogen Activation System by Non-Coding RNA in Cancer

Various species of non-coding RNAs (ncRNAs) may act as functional molecules regulating diverse biological processes. In cancer cell biology, ncRNAs include RNAs that regulate the expression of oncogenes and tumor suppressor genes through various mechanisms. The urokinase (uPA)-mediated plasminogen activation system (PAS) includes uPA, its inhibitors PAI-1 and PAI-2 and its specific cellular receptor uPAR; their increased expression represents a negative prognostic factor in several cancers. Here, we will briefly describe the main uPA-mediated PAS components and ncRNA species; then, we will review more recent evidence of the roles that ncRNAs may play in regulating the expression and functions of uPA-mediated PAS components in cancer.

Metastatic phenotype and immunosuppressive tumour microenvironment in pancreatic ductal adenocarcinoma: Key role of the urokinase plasminogen activator (PLAU)

BACKGROUND

Previous studies have revealed the role of dysregulated urokinase plasminogen activator (encoded by PLAU) expression and activity in several pathways associated with cancer progression. However, systematic investigation into the association of PLAU expression with factors that modulate PDAC (pancreatic ductal adenocarcinoma) progression is lacking, such as those affecting stromal (pancreatic stellate cell, PSC)-cancer cell interactions, tumour immunity, PDAC subtypes and clinical outcomes from potential PLAU inhibition.

METHODS

This study used an integrated bioinformatics approach to identify prognostic markers correlated with PLAU expression using different transcriptomics, proteomics, and clinical data sets. We then determined the association of dysregulated PLAU and correlated signatures with oncogenic pathways, metastatic phenotypes, stroma, immunosuppressive tumour microenvironment (TME) and clinical outcome. Finally, using an in vivo orthotopic model of pancreatic cancer, we confirmed the predicted effect of inhibiting PLAU on tumour growth and metastasis.

RESULTS

Our analyses revealed that PLAU upregulation is not only associated with numerous other prognostic markers but also associated with the activation of various oncogenic signalling pathways, aggressive phenotypes relevant to PDAC growth and metastasis, such as proliferation, epithelial-mesenchymal transition (EMT), stemness, hypoxia, extracellular cell matrix (ECM) degradation, upregulation of stromal signatures, and immune suppression in the tumour microenvironment (TME). Moreover, the upregulation of PLAU was directly connected with signalling pathways known to mediate PSC-cancer cell interactions. Furthermore, PLAU upregulation was associated with the aggressive basal/squamous phenotype of PDAC and significantly reduced overall survival, indicating that this subset of patients may benefit from therapeutic interventions to inhibit PLAU activity. Our studies with a clinically relevant orthotopic pancreatic model showed that even short-term PLAU inhibition is sufficient to significantly halt tumour growth and, importantly, eliminate visible metastasis.

CONCLUSION

Elevated PLAU correlates with increased aggressive phenotypes, stromal score, and immune suppression in PDAC. PLAU upregulation is also closely associated with the basal subtype type of PDAC; patients with this subtype are at high risk of mortality from the disease and may benefit from therapeutic targeting of PLAU.

Identification of uPAR Variants Acting as ceRNAs in Leukaemia Cells

Simple Summary

The urokinase (uPA) receptor (uPAR) concentrates proteolytic activities on the cell surface and is an adhesion receptor for vitronectin. Urokinase/Vitronectin binding to uPAR activates intracellular signals promoting cell adhesion, migration, proliferation and survival. Thus, uPAR can sustain most activities of malignant cells and, accordingly, increased uPAR expression is associated with poor prognosis in several malignancies. We previously demonstrated that, in leukaemia cells, the uPAR 3′untranslated region (3′UTR) up-regulates the expression of pro-tumoral factors by recruiting microRNAs targeting their mRNAs, thus acting as competitive endogenous RNA (ceRNA). Here, we identify 3′UTR-containing variants of uPAR mRNA in leukaemia cells and demonstrate that the over-expression of uPAR Δ5-variant mRNA promotes expression of pro-tumoral factors and increase in biological activities, probably by its ceRNA activity. On this basis, we propose that uPAR may play a crucial role in cancer biology also at mRNA level, through the ceRNA activity of its variants.

Abstract

The 3′untranslated region (3′UTR) of the urokinase (uPA) receptor (uPAR) mRNA can act as a competitive endogenous RNA (ceRNA) in acute myeloid leukaemia (AML) cells, promoting the expression of pro-tumoral targets, including uPAR. Here, we identified three variants of uPAR mRNA containing the 3′UTR, in KG1 and U937 leukaemia cells expressing low and high uPAR levels, respectively. Identified variants lack exon 5 (uPAR Δ5) or exon 6 (uPAR Δ6) or part of exon 6, exon 7 and part of 3′UTR (uPAR Δ6/7). uPAR Δ5 and uPAR Δ6 transcript levels were higher in U937 cells compared to KG1 cells. Both uPAR variants were expressed also in AML blasts, at higher levels as compared to CD34 hematopoietic cells from healthy donors. The presence of the 3′UTR conferred high instability to the uPAR Δ5 variant transcript, preventing its translation in protein. Overexpression of the uPAR Δ5-3′UTR variant regulated the expression of some pro-tumoral factors previously reported to be regulated by the 3′UTR of uPAR and increased KG1 cell adhesion, migration and proliferation. These results demonstrate the expression of uPAR mRNA variants containing the 3′UTR in AML cells and the ceRNA activity and the biological effects of the uPAR Δ5-3′UTR variant.

A novel oncogenic role for urokinase receptor in leukemia cells: molecular sponge for oncosuppressor microRNAs

Urokinase receptor (uPAR) expression is up-regulated and represents a negative prognostic marker in most cancers. We previously reported that uPAR and CXCR4 can be regulated by common microRNAs in leukemia cells. Transcripts containing response elements for shared microRNAs in their 3’UTR may regulate their availability.

We investigated uPAR 3’UTR capability to recruit microRNAs, thus regulating the expression of their targets. uPAR 3’UTR transfection in KG1 leukemia cells up-regulates the expression of endogenous uPAR. Transfection of uPAR 3’UTR, inserted downstream a reporter gene, increases uPAR expression and simultaneously down-regulates the reporter gene expression. Transfection of uPAR 3’UTR also increases CXCR4 expression; accordingly, uPAR silencing induces down-regulation of CXCR4 expression, through a mechanism involving Dicer, the endoribonuclease required for microRNA maturation.

Transfection of uPAR 3’UTR also increases the expression of pro-tumoral factors and modulates cell adhesion and migration, consistently with the capability of uPAR3’UTR-recruited microRNAs to target several and different transcripts and, thus, functions.

Finally, we found 3’UTR-containing variants of uPAR transcript in U937 leukemia cells, which show higher levels of uPAR expression as compared to KG1 cells, in which these variants are not detected.

These results suggest that uPAR mRNA may recruit oncosuppressor microRNAs, allowing the expression of their targets.

Urokinase receptor and CXCR4 are regulated by common microRNAs in leukaemia cells

The urokinase-type plasminogen activator (uPA) receptor (uPAR) focuses uPA proteolytic activity on the cell membrane, promoting localized degradation of extracellular matrix (ECM), and binds vitronectin (VN), mediating cell adhesion to the ECM. uPAR-bound uPA and VN induce proteolysis-independent intracellular signalling, regulating cell adhesion, migration, survival and proliferation. uPAR cross-talks with CXCR4, the receptor for the stroma-derived factor 1 chemokine. CXCR4 is crucial in the trafficking of hematopoietic stem cells from/to the bone marrow, which involves also uPAR. Both uPAR and CXCR4 are expressed in acute myeloid leukaemia (AML), with a lower expression in undifferentiated and myeloid subsets, and higher expression in myelomonocytic and promyelocytic subsets. We hypothesized a microRNA (miR)-mediated co-regulation of uPAR and CXCR4 expression, which could allow their cross-talk at the cell surface. We identified three miRs, miR-146a, miR-335 and miR-622, regulating the expression of both uPAR and CXCR4 in AML cell lines. Indeed, these miRs directly target the 3'untranslated region of both uPAR- and CXCR4-mRNAs; accordingly, uPAR/CXCR4 expression is reduced by their overexpression in AML cells and increased by their specific inhibitors. Overexpression of all three miRs impairs migration, invasion and proliferation of myelomonocytic cells. Interestingly, we observed an inverse relationship between uPAR/CXCR4 expression and miR-146a and miR-335 levels in AML blasts, suggesting their possible role in the regulation of uPAR/CXCR4 expression also in vivo.

Transforming growth factor-Beta and urokinase-type plasminogen activator: dangerous partners in tumorigenesis-implications in skin cancer

Transforming growth factor-beta (TGF-β) is a pleiotropic factor, with several different roles in health and disease. TGF-β has been postulated as a dual factor in tumor progression, since it represses epithelial tumor development in early stages, whereas it stimulates tumor progression in advanced stages. During tumorigenesis, cancer cells acquire the capacity to migrate and invade surrounding tissues and to metastasize different organs. The urokinase-type plasminogen activator (uPA) system, comprising uPA, the uPA cell surface receptor, and plasminogen-plasmin, is involved in the proteolytic degradation of the extracellular matrix and regulates key cellular events by activating intracellular signal pathways, which together allow cancer cells to survive, thus, enhancing cell malignance during tumor progression. Due to their importance, uPA and its receptor are tightly transcriptionally regulated in normal development, but are deregulated in cancer, when their activity and expression are related to further development of cancer. TGF-β regulates uPA expression in cancer cells, while uPA, by plasminogen activation, may activate the secreted latent TGF-β, thus, producing a pernicious cycle which contributes to the enhancement of tumor progression. Here we review the specific roles and the interplay between TGF-β and uPA system in cancer cells and their implication in skin cancer.

uPAR regulates pericellular proteolysis through a mechanism involving integrins and fMLF-receptors

The expression of the urokinase-type plasminogen activator (uPA) and its receptor (uPAR) can be regulated by several hormones, cytokines, and tumour promoters. uPAR is a glycosyl-phosphatidyl inositol (GPI)-linked cell-surface protein; however, it is capable to transduce signals inside the cell by interacting with other cell-surface proteins, such as integrins and G-protein coupled (GPC) receptors. We previously reported that uPAR cell-surface expression can be positively regulated by its ligand, uPA, independently of its proteolytic activity. We now demonstrate that uPAR overexpression induces or increases uPA secretion both in uPAR-negative and in uPAR-expressing cells. Accordingly, uPAR depletion impairs uPA expression in cells which constitutively express both uPA and its receptor. uPAR exerts its regulatory effect through the activation of the ERK mitogen-activated protein kinases (MAPKs), whereas the p-38 MAPK is not involved. Overexpression of truncated forms of uPAR, lacking the N-terminal domain (DI) and not able to interact with membrane co-receptors, failed to increase uPA expression. Inhibition of uPAR-integrin interaction by the specific P-25 peptide, as well as Gi-protein inhibition by cholera pertussin toxin or depletion of the GPC receptors for fMLF (fMLF-Rs) also impaired uPAR capability to regulate uPA expression. These findings demonstrate that uPAR, whose expression is regulated by uPA, can, in turn, regulate uPA expression through a mechanism involving its functional interaction with integrins and fMLF-Rs.

Involvement of miR-30c and miR-301a in immediate induction of plasminogen activator inhibitor-1 by placental growth factor in human pulmonary endothelial cells

PAI-1 (plasminogen activator inhibitor-1) is a key physiological inhibitor of fibrinolysis. Previously, we have reported PlGF (placental growth factor)-mediated transcriptional up-regulation of PAI-1 (SERPINE1) mRNA expression via activation of HIF-1α (hypoxia-inducible factor-1α) and AP-1 (activator protein-1) in HPMVECs (human pulmonary microvascular endothelial cells), which resulted in elevated PAI-1 in humans with SCA (sickle cell anaemia). In the present study, we have identified the role of post-transcriptional mechanism(s) of PlGF-mediated accumulation of PAI-1 mRNA in HPMVECs by examining the role of microRNAs (miRNAs/miRs) in PlGF-induced PAI-1 mRNA stability. Our results show reduced expression of miR-30c and miR-301a, but not of miR-99a, in response to PlGF, which have evolutionarily conserved binding sites in the 3'-UTR (3'-untranslated region) of PAI-1 mRNA. Transfection of anti-miR-30c or anti-miR-301a oligonucleotides resulted in increased PAI-1 mRNA levels, which were increased further with PlGF stimulation. Conversely, overexpression of pre-miR-30c or pre-miR-301a resulted in an attenuation of PlGF-induced PAI-1 mRNA and protein levels. Luciferase reporter assays using wild-type and mutant 3'-UTR constructs confirmed that the PAI-1 3'-UTR is indeed a direct target of miR-30c and miR-301a. Finally, plasma levels of miR-30c and miR-301a were significantly down-regulated in patients with SCA compared with normal controls. These results provide a post-transcriptional regulatory mechanism of PlGF-induced PAI-1 elevation.

Down-regulation of activity and expression of three transport-related proteins in the gills of the euryhaline green crab, Carcinus maenas, in response to high salinity acclimation

The euryhaline green crab, Carcinus maenas, undergoes an annual cycle of salinity exposure, having to adapt to low salinity during its annual spring migration into estuaries, and then having to re-adapt to high salinity when it moves off-shore at the end of summer. Most studies have focused on low salinity acclimation, the activation of osmoregulatory mechanisms, and the induction of transport protein and transport-related enzyme activity and gene expression. In this study we followed the changes in hemolymph osmolality, carbonic anhydrase activity, and mRNA expression of three proteins through a complete cycle of low (15 ppt) and high (32 ppt) salinity acclimation. One week of low salinity acclimation resulted in hemolymph osmoregulation and a four-fold induction of branchial carbonic anhydrase activity. Relative mRNA expression increased for two CA isoforms (CAc 100-fold, and CAg 7-fold) and the α-subunit of the Na/K-ATPase (8-fold). Upon re-exposure to high salinity, hemolymph osmolality increased to 32 ppt acclimated levels by 6 h, and mRNA levels returned to high salinity, baseline levels within 1 week. However, CA activity remained unchanged in response to high salinity exposure for the first week and then gradually declined to baseline levels over 4 weeks. The relative timing of these changes suggests that while whole-organism physiological adaptations and regulation at the gene level can be very rapid, changes at the level of protein expression and turnover are much slower. It is possible that the high metabolic cost of protein synthesis and/or processing could be the underlying reason for long biological life spans of physiologically important proteins.

Angiotensin II induces renal plasminogen activator inhibitor-1 and cyclooxygenase-2 expression post-transcriptionally via activation of the mRNA-stabilizing factor human-antigen R

Angiotensin (Ang) II-induced fibrosis of the kidney is characterized by the enhanced expression of profibrotic and proinflammatory genes, including the serine protease inhibitor plasminogen activator inhibitor-1 (PAI-1) and cyclooxygenase-2 (COX-2). In addition to transcriptional regulation, both genes are subject to post-transcriptional control by AU-rich destabilizing elements that reside within the 3' untranslated region of the mRNA. We demonstrated that the continuous infusion of AngII in rats induced fibrosis concomitant with a significant increase in glomerular PAI-1 and COX-2 expression levels. Using RNA pull-down assays and electromobility shift assays, we demonstrated the increased binding of the ubiquitous RNA-binding protein human-antigen R (HuR) to the mRNAs of both PAI-1 and COX-2 in the cytoplasmic fractions of renal homogenates from AngII-treated rats. Actinomycin D experiments in rat mesangial cells revealed that AngII stabilizes both mRNAs via HuR as proven by small interfering RNA. Mechanistically, AngII promotes an increase in nucleo-cytoplasmic HuR shuttling, which was blocked by the PKC inhibitor rottlerin and the type-I AngII (AT(1)) receptor antagonist valsartan but was unaffected by both AT(2) receptor antagonists PD123319 and CGP42112. Co-immunoprecipitation revealed that AngII treatment caused an increase in nuclear PKC-delta concomitant with binding to nuclear HuR both in vitro and in vivo. The post-transcriptional regulation of PAI-1 and COX-2 by PKC-delta-dependent HuR shuttling may contribute to the pathogenesis of hypertensive nephrosclerosis triggered by AngII.

Helicobacter pylori infection stimulates plasminogen activator inhibitor 1 production by gastric epithelial cells

Chronic infection with the gastric pathogen Helicobacter pylori significantly increases the risk of developing atrophic gastritis, peptic ulcer disease, and gastric adenocarcinoma. H. pylori strains that possess the cag pathogenicity island, which translocates CagA into the host cells, augment these risks. The aim of this study was to determine the molecular mechanisms through which H. pylori upregulates the expression of plasminogen activator inhibitor 1 (PAI-1), a member of the urokinase activator system that is involved in tumor metastasis and angiogenesis. Levels of PAI-1 mRNA and protein were examined in tissues from H. pylori-infected patients and in vitro using AGS gastric epithelial cells. In vitro, cells were infected with toxigenic cag-positive or nontoxigenic cag-negative strains of H. pylori or isogenic mutants. The amount of PAI-1 secretion was measured by enzyme-linked immunosorbent assay, and mRNA levels were determined using real-time PCR. The regulation of PAI-1 was examined using the extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitor and small interfering RNA. Analysis of human biopsy samples revealed an increase in both PAI-1 mRNA and protein levels in patients with H. pylori gastritis compared to those of uninfected controls. Infection of AGS cells with H. pylori significantly increased PAI-1 mRNA expression and the secretion of PAI-1 protein. Moreover, PAI-1 mRNA and protein production was more pronounced when AGS cells were infected by H. pylori strains carrying a functional cag secretion system than when cells were infected by strains lacking this system. PAI-1 secretion was also reduced when cells were infected with either cagE-negative or cagA-negative mutants. The ectopic overexpression of CagA significantly increased the levels of PAI-1 mRNA and protein, whereas blockade of the ERK1/2 pathway inhibited H. pylori-mediated PAI-1 upregulation. These findings suggest that the upregulation of PAI-1 in H. pylori-infected gastric epithelial cells may contribute to the carcinogenic process.

Purification of c-phycocyanin from Spirulina fusiformis and its effect on the induction of urokinase-type plasminogen activator from calf pulmonary endothelial cells

c-Phycocyanin (c-pc), a blue coloured, fluorescent protein was purified from blue-green alga, Spirulina fusiformis and its effect on fibrinolytic system in vascular endothelial cells was investigated. The c-pc consisted of two subunits, alpha and beta, whose molecular masses were 16 and 17 kDa, respectively. N-terminal sequences of both subunits were well conserved compared with other blue green algal phycobiliproteins. Fibrinolytic activity in the medium conditioned by calf pulmonary arterial endothelial cells was measured by the fibrin plate method. The c-pc increased the fibrinolytic activity in dose- and time-dependent manners. Fibrin zymographic studies indicated that c-pc-induced urokinase-type plasminogen activator in the cells. These in vitro results suggest that c-pc from S. fusiformis is a potent profibrinolytic protein in the vascular endothelial system.

E2F1 up-regulates the expression of the tumour suppressor axin2 both by activation of transcription and by mRNA stabilisation

Axin2 is a negative regulator of Wnt/beta-catenin signalling with roles in early development and tumour suppression. Axin2 is induced by E2F1 and therefore acts as a point of cross-talk between the pRb/E2F and Wnt/beta-catenin pathways: two of the most frequently deregulated pathways in human cancers. In this study, we show that E2F1 up-regulates axin2 by two independent mechanisms. The human axin2 gene allows transcription of messages with three different 5' untranslated regions and in the first mechanism E2F1 directly activates the transcription of only one of these species by acting at canonical E2F binding sites. Second, E2F1 induces stabilisation of axin2 mRNAs. We discuss this regulation with respect to other known E2F targets.

Iron-mediated stability of PAI-1 mRNA in adenocarcinoma cells—involvement of a mRNA-binding nuclear protein

This study reports the stability of mRNA of type-1 plasminogen activator inhibitor (PAI-1), the major physiologic inhibitor of plasminogen activation, by deferoxamine-aided iron deprivation, in PC3 adenocarcinoma cells. ELISA and Northern analyses studies revealed dose-dependent increase in PAI-1 expression by deferoxamine-treated cells. Co-treatment with ferric citrate quenched the effect of deferoxamine, confirming the role of iron in PAI-1 regulation. DRB-based RNA chase experiments suggested that post-transcriptional mechanism was involved in PAI-1 regulation. De-novo protein synthesis was necessary for this regulation. Electrophoretic mobility shift assay revealed the presence of a nuclear protein, binding to the 3'-UTR of PAI-1 mRNA in an iron-mediated manner. This is the first report of iron-mediated mRNA-protein interaction in PAI-1, involved in mRNA stability.