Plasminogen activator inhibitor type 1 in cancer: therapeutic and prognostic implications

Plasminogen activator inhibitor 1 is associated with high-grade serous ovarian cancer metastasis and is reduced in patients who have received neoadjuvant chemotherapy

Introduction: High-grade serous ovarian cancer (HGSOC) is the most prevalent and deadliest subtype of epithelial ovarian cancer (EOC), killing over 140,000 people annually. Morbidity and mortality are compounded by a lack of screening methods, and recurrence is common. Plasminogen-activator-inhibitor 1 (PAI-1, the protein product of SERPIN E1) is involved in hemostasis, extracellular matrix (ECM) remodeling, and tumor cell migration and invasion. Overexpression is associated with poor prognosis in EOC. Platelets significantly increase PAI-1 in cancer cells in vitro, and may contribute to the hematogenous metastasis of circulating tumor cells (CTCs). CTCs are viable tumor cells that intravasate and travel through the circulation-often aided by platelets - with the potential to form secondary metastases. Here, we provide evidence that PAI-1 is central to the platelet-cancer cell interactome, and plays a role in the metastatic cascade. Methods: SK-OV-3 cells where PAI-1 had been silenced, treated with healthy donor platelets, and treated with platelet-conditioned medium were used as an in vitro model of metastatic EOC. Gene expression analysis was performed using RNA-Seq data from untreated cells and cells treated with PAI-1 siRNA or negative control, each with and without platelets. Four cohorts of banked patient plasma samples (n = 239) were assayed for PAI-1 by ELISA. Treatment-naïve (TN) whole blood (WB) samples were evaluated for CTCs in conjunction with PAI-1 evaluation in matched plasma. Results and discussion: Significant phenotypic changes occurring when PAI-1 was silenced and when platelets were added to cells were reflected by RNA-seq data, with PAI-1 observed to be central to molecular mechanisms of EOC metastasis. Increased proliferation was observed in cells treated with platelets. Plasma PAI-1 significantly correlated with advanced disease in a TN cohort, and was significantly reduced in a neoadjuvant chemotherapy (NACT) cohort. PAI-1 demonstrated a trend towards significance in overall survival (OS) in the late-stage TN cohort, and correlation between PAI-1 and neutrophils in this cohort was significant. 72.7% (16/22) of TN patients with plasma PAI-1 levels higher than OS cutoff were CTC-positive. These data support a central role for PAI-1 in EOC metastasis, and highlight PAI-1's potential as a biomarker, prognostic indicator, or gauge of treatment response in HGSOC.

The Perspective of Vitamin D on suPAR-Related AKI in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has claimed the lives of millions of people around the world. Severe vitamin D deficiency can increase the risk of death in people with COVID-19. There is growing evidence that acute kidney injury (AKI) is common in COVID-19 patients and is associated with poorer clinical outcomes. The kidney effects of SARS-CoV-2 are directly mediated by angiotensin 2-converting enzyme (ACE2) receptors. AKI is also caused by indirect causes such as the hypercoagulable state and microvascular thrombosis. The increased release of soluble urokinase-type plasminogen activator receptor (suPAR) from immature myeloid cells reduces plasminogen activation by the competitive inhibition of urokinase-type plasminogen activator, which results in low plasmin levels and a fibrinolytic state in COVID-19. Frequent hypercoagulability in critically ill patients with COVID-19 may exacerbate the severity of thrombosis. Versican expression in proximal tubular cells leads to the proliferation of interstitial fibroblasts through the C3a and suPAR pathways. Vitamin D attenuates the local expression of podocyte uPAR and decreases elevated circulating suPAR levels caused by systemic inflammation. This decrease preserves the function and structure of the glomerular barrier, thereby maintaining renal function. The attenuated hyperinflammatory state reduces complement activation, resulting in lower serum C3a levels. Vitamin D can also protect against COVID-19 by modulating innate and adaptive immunity, increasing ACE2 expression, and inhibiting the renin–angiotensin–aldosterone system. We hypothesized that by reducing suPAR levels, appropriate vitamin D supplementation could prevent the progression and reduce the severity of AKI in COVID-19 patients, although the data available require further elucidation.

Cooperation between monocytes and breast cancer cells promotes factors involved in cancer aggressiveness

In breast cancers, clinical symptoms of inflammation localised around the tumour at the time of diagnosis have been considered to have poor prognosis significance. In this study, the biological mechanisms responsible for the deleterious action of monocytes in cancer were investigated. The incubation of the breast-cancer-derived MDA-MB231 cells with monocytes resulted in an increase in factors involved in cell invasion (i.e. both cancer cells and monocytes-associated urokinase and Tissue Factor, and PAI-1 and MMP-9 secretion). Moreover, the functions of monocytes were also modified. Incubation of monocytes with MDA-MB231 cancer cells resulted in a downregulation in the secretion of the antiproliferative cytokine Oncostatin M, while the apoptotic factor TNF alpha was dramatically increased. However, MDA-MB231 cancer cells have been shown to be resistant towards the apoptotic action of TNF alpha. These findings demonstrate that incubation of MDA-MB231 cancer cells with monocytes induced a crosstalk, which resulted in an increased expression of factors involved in cancer cell invasiveness and in a modification of monocytes function against cancer cells, while inflammatory effects were increased.

Promigratory effect of plasminogen activator inhibitor-1 on invasive breast cancer cell populations

The urokinase-type plasminogen activator (uPA) system is a dynamic complex in which the membrane receptor uPAR binds uPA that binds the plasminogen activator inhibitor (PAI)-1 localized in the extracellular matrix, resulting in endocytosis of the whole complex by the low-density lipoprotein receptor-related protein (LRP). High expression of PAI-1 is paradoxically associated with marked tumor spreading and poor prognosis. We previously reported a nonproteolytic role of the [uPAR:uPA:PAI-1:LRP] complex operative in cell migration. Here we explored whether matrix PAI-1 could be used as a migration support by human breast cancer cells. We showed that the uPA system and LRP are localized at filopodia of invasive cells, and that formation/internalization of the [uPAR:uPA:PAI-1:LRP] complex is required for attachment and migration of cancer cells on plastic and on a PAI-1 coat. PAI-1 increased both filopodia formation and migration of cancer cells suggesting a chemokine-like activity. Migration velocity, expression of the uPA system, use of the [uPAR:uPA:PAI-1:LRP] complex to migrate, and promigratory effects of PAI-1 paralleled cancer cell invasiveness. Phenotyping and functional analysis of invasive cancer cell subclones indicated that different cell subpopulations may use different strategies to migrate depending on both the environment and their expression of the uPA system, some of them taking advantage of abundant available PAI-1.

Clinical implications of elevated PAI-1 revisited: multiple arterial thrombosis in a patient with essential thrombocythemia and elevated plasminogen activator inhibitor-1 (PAI-1) levels: a case report and review of the literature

Plasminogen activator inhibitor (PAI-1), a member of the serine protein family, is the most active in vivo inhibitor of fibrinolysis induced by plasminogen, tissue plasminogen activator (tPA), and urokinase type plasminogen activator (uPA). While the association between elevated PAI-1 and thrombogenesis has been well studied for several disease processes, including coronary disease, postoperative deep vein thrombosis (DVT), myocardial infarction, malignancy, and diabetes, few studies have concentrated on the correlation between elevated PAI-1 levels and thrombogenesis in patients with myeloproliferative disorders. Essential thrombocythemia (ET), a chronic myeloproliferative disorder, characterized by the overproduction of poorly functioning platelets, is associated with both thrombotic and hemorrhagic life-threatening complications. Although the events resulting in thrombogenesis in such patients may be multifactorial in nature, an association between elevated PAI-1 levels and thrombus formation has been proposed. Herein we present a patient diagnosed with ET complicated by multiple episodes of arterial thrombosis. Elevations in PAI-1 levels were documented repeatedly. The role of elevated PAI-1 when associated with other disease processes is also discussed.

Inhibitory role of plasminogen activator inhibitor-1 in invasion and proliferation of HLE hepatocellular carcinoma cells

Plasminogen activator inhibitor (PAI)-1, a serine protease inhibitor, inactivates urokinase-type plasminogen activator (uPA) and regulates degradation of the extracellular matrix; whether it functions for or against tumor progression, however, has been the subject of controversy. To assess the role of PAI-1 in invasion and proliferation of hepatocellular carcinoma (HCC) cells, HLE cells were transfected with a vector capable of expressing an antisense PAI-1 transcript. Analysis of seven stably transfected clones (PAI-1-) showed reductions of 81% in PAI-1 mRNA by northern blot analysis and 63% in the cellular PAI-1 antigen level by enzyme-linked immunosorbent assay (ELISA). There was no change in the levels of secreted PAI-1 or PAI-2. The activity of cellular uPA increased by 54%, without change in the protein level or the secreted uPA activity evaluated by ELISA. Morphologically, PAI-1 antisense induced a spindle shape with narrower cytoplasmic processes in HLE cells. The forced inhibition of PAI-1 increased the invasion and the growth of PAI-1- cells by 75% and 82%, respectively. These results suggest that PAI-1 plays a role in inhibiting invasion and proliferation, and the balance between uPA and PAI-1 expression is important to assess the invasiveness of HCC cells.

Cisplatin resistant glioblastoma cells may have increased concentration of urokinase plasminogen activator and plasminogen activator inhibitor type 1

Gliomas are the most common form of intrinsic primary brain tumors, that extensively invade the surrounding normal brain tissue. The failure of chemotherapy treatment of these tumors is chiefly attributed to drug-resistance. From human glioblastoma we developed two cell sublines resistant to cisplatin due to acute (AT cells) or continuous (CT cells) treatment with clinically relevant doses of cisplatin. We examined their sensitivity to different cytostatics by colorimetric MTT assay. The concentrations of urokinase plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) were determined by the ELISA assay. The results reveal that both AT and CT cells became resistant to cisplatin and vincristine; AT cells became resistant also to etoposide. Both AT and CT cells did not significantly change their sensitivity to doxorubicin, 5-fluorouracil and chlorambucil. Concentrations of uPA and PAI-1 were increased in CT cells, with no change in AT cells. In the conditioned medium of both, AT and CT cells, the level of uPA were increased. No differences in concentrations of PAI-1 in the conditioned medium of these cells were found. Thus, our results show that drug-resistance of glioblastoma cells may be accompanied with the increased levels of markers for tumor invasion.

Dipeptidyl peptidase III in malignant and non-malignant gynaecological tissue

Exopeptidases, in contrast to endopeptidases (proteinases) have been much less studied in relation to cancer. The aim of this study was to investigate one such enzyme, dipeptidyl peptidase III (DPP III), in gynaecological tissues, by measuring both the enzyme activity and enzyme content. DPP III activity was assessed in normal (n = 65), benign (n = 9) and malignant (n = 51) gynaecological tissues. A statistically significant higher DPP III activity was observed in endometrial (n = 40, P = 4.6 x 10(-7)) and ovarian (n = 11, P = 8.1 x 10(-4)) malignant tumours, whereas no significant difference was detected for leiomyomas (n = 8), if compared to the activity in normal tissue. A matched pair analysis of normal and cancerous endometrial tissue confirmed the significance of the DPP III activity increase in the transformed tissue (n = 7, P = 0.022). Western blot analysis revealed a significantly (P = 0.014) increased level of DPP III in endometrial cancer. Further, regression analysis showed a positive correlation between the activity and the content of DPP III in normal tissue (r = 0.637, P = 0.047) and in endometrial cancer (r = 0.574, P < 0.007). The increase of the DPP III activity was observed in the endometrial carcinomas of various histological types, grade or the depth of myometrial invasion. The easy-to-perform determination of this exopeptidase activity may serve as a potential indicator of endometrial and ovarian malignancies.

Is plasminogen activator inhibitor-1 the molecular switch that governs urokinase receptor-mediated cell adhesion and release?

Induction of the urokinase type plasminogen activator receptor (uPAR) promotes cell adhesion through its interaction with vitronectin (VN) in the extracellular matrix, and facilitates cell migration and invasion by localizing uPA to the cell surface. We provide evidence that this balance between cell adhesion and cell detachment is governed by PA inhibitor-1 (PAI-1). First, we demonstrate that uPAR and PAI-1 bind to the same site in VN (i.e., the amino-terminal somatomedin B domain; SMB), and that PAI-1 competes with uPAR for binding to SMB. Domain swapping and mutagenesis studies indicate that the uPAR-binding sequence is located within the central region of the SMB domain, a region previously shown to contain the PAI-1-binding motif. Second, we show that PAI-1 dissociates bound VN from uPAR and detaches U937 cells from their VN substratum. This PAI-1 mediated release of cells from VN appears to occur independently of its ability to function as a protease inhibitor, and may help to explain why high PAI-1 levels indicate a poor prognosis for many cancers. Finally, we show that uPA can rapidly reverse this effect of PAI-1. Taken together, these results suggest a dynamic regulatory role for PAI-1 and uPA in uPAR-mediated cell adhesion and release.

Urokinase-type plasminogen activation in three human breast cancer cell lines correlates with their in vitro invasiveness

In order to invade and spread cancer cells must degrade extracellular matrix proteins. This degradation is catalysed by the concerted action of several enzymes, including the serine protease plasmin. Several experimental studies have shown that inhibition of plasmin formation reduces cancer cell invasion and metastasis, indicating a critical role of this proteolytic pathway in these processes. In order to further study the role of plasmin in cancer progression, we have characterized urokinase-type plasminogen activator (uPA) mediated plasmin formation in three human breast cancer cell lines. Using monoclonal antibodies against uPA and its receptor uPAR, we have investigated the contribution of uPA and uPAR to invasive capacity in an in vitro invasion assay. MDA-MB-231 BAG cells were found to express high protein levels of uPA, uPAR and PAI-1. MDA-MB 435 BAG cells produced low amounts of uPA, PAI-1 and moderate amounts of uPAR, whereas MCF-7 BAG cells showed low levels of uPA, uPAR and PAI-1 protein. In a plasmin generation assay MDA-MB-231 BAG cells were highly active in mediating plasmin formation, which could be abolished by adding either an anticatalytic monoclonal antibody to uPA (clone 5) or an anti-uPAR monoclonal antibody (clone R3), which blocks binding of uPA to uPAR. The two other cell lines lacked the capacity to mediate plasmin formation. In the Matrigel invasion assay the cells showed activity in this order: MCF-7 BAG < MDA-MB-435 BAG < MDA-MB-231 BAG. Testing MDA-MB-231 BAG cells in the Matrigel invasion assay revealed that invasion could be inhibited in a dose-dependent manner either by the clone 5 uPA antibody or by the clone R3 uPAR antibody, suggesting that the cell surface uPA system is actively involved in this invasive process. It is concluded that these three cell lines constitute a valuable model system for in vitro studies of the role of cell surface uPA in cancer cell invasion and has application in the search for novel compounds which inhibit mechanisms involved in uPA-mediated plasmin generation on cancer cells.