Metastasis of transgenic breast cancer in plasminogen activator inhibitor-1 gene-deficient mice

ADAM9 functions as a transcriptional regulator to drive angiogenesis in esophageal squamous cell carcinoma

Hypoxia and angiogenesis play key roles in the pathogenesis of esophageal squamous cell carcinoma (ESCC), but regulators linking these two pathways to drive tumor progression remain elusive. Here we provide evidence of ADAM9's novel function in ESCC progression. Increasing expression of ADAM9 was correlated with poor clinical outcomes in ESCC patients. Suppression of ADAM9 function diminished ESCC cell migration and in vivo metastasis in ESCC xenograft mouse models. Using cellular fractionation and imaging, we found a fraction of ADAM9 was present in the nucleus and was uniquely associated with gene loci known to be linked to the angiogenesis pathway demonstrated by genome-wide ChIP-seq. Mechanistically, nuclear ADAM9, triggered by hypoxia-induced translocation, functions as a transcriptional repressor by binding to promoters of genes involved in the negative regulation of angiogenesis, and thereby promotes tumor angiogenesis in plasminogen/plasmin pathway. Moreover, ADAM9 suppresses plasminogen activator inhibitor-1 gene transcription by interacting with its transcription factors at the promoter. Our findings uncover a novel regulatory mechanism of ADAM9 as a transcriptional regulator in angiogenesis and highlight ADAM9 as a promising therapeutic target for ESCC treatment.

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

Combined Genotype Effects of TP53 and PAI-1 Polymorphisms in Breast Cancer Susceptibility: Multifactor Dimensionality Reduction and in silico Analysis

INTRODUCTION

Breast cancer is a heterogeneous and multifactorial disease. TP53 and PAI-1 as important tumor suppressor genes are involved in the development, invasion, and metastasis of many cancers. This study's objective was to demonstrate the combined genotype effects of these 2 genes by investigating their single nucleotide polymorphisms.

METHODS

In this case-control study, 200 individuals with breast cancer and 179 healthy individuals were studied. The genotypes were determined using the tetra-ARMS method. For data analysis, MDR, online javstat statistics package, and SPSS v.24 software were used. Also, in silico studies on the estimated effects of each of these polymorphisms were performed.

RESULTS

We showed a novel gene-gene interaction of these 2 genes and demonstrated a strong synergistic interaction for TP53/PAI-1, moderate synergistic interaction for PAI-1/age, and correlation for TP53/age. On the other hand, there was no association between the allelic and genotype frequency alone and in combination, with case-control status, using the parametric method, between TP53 and PAI-1.

DISCUSSION/CONCLUSION

Our findings suggest that the polymorphism of codon 72 of the TP53 gene was significantly associated with tumor stage (p < 0.023). In conclusion, we showed a gene-gene interaction between TP53 and PAI-1, in combination, using the MDR method.

Metastasis of Breast Cancer Promoted by Circadian Rhythm Disruption due to Light/Dark Shift and its Prevention by Dietary Quercetin in Mice

Epidemiological studies have indicated that a disturbed circadian rhythm resulting from night-shift work is a potential risk factor for breast cancer. However, the mechanism of increased risk of breast cancer by night-shift work remains unclear, and there have been few in vivo studies conducted to definitively associate the two factors. In this study, BJMC3879Luc2 mouse breast cancer cells were transplanted into BALB/c mice. Mice were maintained under lighting conditions that modeled the two-shift system and were investigated for the effect of light/dark cycle disruption on tumor growth and lymph node metastasis. Circadian dysfunction, which was confirmed by measuring circadian locomotor activities using a nano tag device in our light/dark shift model, did not affect tumor growth. However, a significant increase in the number of lymph nodes with distant metastasis was observed. Neutrophil-to-lymphocyte ratio, which is an adverse prognostic factor of breast cancer and also indicator of inflammation, also increased. It has been demonstrated that a chronic inflammatory response is associated with cancer malignancy and poor prognosis in various cancers. These results suggest that night-shift work may also affect distant metastasis and prognosis. In addition, we investigated whether dietary quercetin has anti-metastatic activity against light/dark shift-induced metastasis. A diet containing 0.3 % quercetin significantly inhibited distant lymph node metastasis, particularly metastasis to the iliac and kidney lymph nodes. Our results contribute to our understandings of the effects of the external light environment on breast cancer metastasis and provide a glimpse into potential protective effects of dietary quercetin on light/dark disturbance-induced metastasis.

Dietary Selenium Supplementation Does Not Attenuate Mammary Tumorigenesis-Mediated Bone Loss in Male MMTV-PyMT Mice

Bone wasting occurs during the progression of breast cancer and contributes to breast cancer mortality. We evaluated the effect of methylseleninic acid (MSeA), an anti-carcinogenic form of selenium, on bone microstructural changes in the presence of mammary tumors in a male breast cancer model of mouse mammary tumor virus-polyomavirus middle T-antigen (MMTV-PyMT). In this study, we performed microcomputed tomographic analysis of femurs and vertebrae collected from a study showing that dietary supplementation with MSeA reduces mammary tumorigenesis in male mice. Compared to age-matched, non-tumor-bearing mice (MMTV-PyMT negative), the presence of mammary tumors significantly reduced the bone volume fraction, trabecular thickness, and bone mineral density while it increased the structure model index in femurs, but not in vertebrae. Moreover, mammary tumorigenesis decreased plasma concentrations of osteocalcin. Supplementation with MSeA did not affect these changes in MMTV-PyMT mice. In conclusion, mammary tumorigenesis caused bone loss in MMTV-PyMT mice. However, dietary supplementation with MSeA did not attenuate mammary tumor-associated bone loss in this model of male breast cancer.

The plasminogen activator inhibitor-1 paradox in cancer: a mechanistic understanding

The paradoxical pro-tumorigenic function of plasminogen activator inhibitor 1 (PAI-1, aka Serpin E1) in cancer progression and metastasis has been the subject of an abundant scientific literature that has pointed to a pro-angiogenic role, a growth and migration stimulatory function, and an anti-apoptotic activity, all directed toward promoting tumor growth, cancer cell survival, and metastasis. With uPA, PAI-1 is among the most reliable biomarkers and prognosticators in many cancer types. More recently, a novel pro-tumorigenic function of PAI-1 in cancer-related inflammation has been demonstrated. These multifaceted activities of PAI-1 in cancer progression are explained by the complex structure of PAI-1 and its multiple functions that go beyond its anti-fibrinolytic and anti-plasminogen activation activities. However, despite the multiple evidences supporting a pro-tumorigenic role of PAI-1 in cancer, and the development of several inhibitors, targeting PAI-1, has remained elusive. In this article, the various mechanisms responsible for the pro-tumorigenic functions of PAI-1 are reviewed with emphasis on its more recently described contribution to cancer inflammation. The challenges of targeting PAI-1 in cancer therapy are then discussed.

Plasminogen activator inhibitor-2 (PAI-2) overexpression supports bladder cancer development in PAI-1 knockout mice in N-butyl-N- (4-hydroxybutyl)-nitrosamine- induced bladder cancer mouse model

BACKGROUND

Accumulating evidence suggests that plasminogen activator inhibitor-1 (PAI-1) plays an important role in bladder tumorigenesis by regulating cell cycle. However, it remains unclear whether and how inhibition of PAI-1 suppresses bladder tumorigenesis.

METHODS

To elucidate the therapeutic effect of PAI-1 inhibition, we tested its tumorigenicity in PAI-1 knockout (KO) mice exposed to a known bladder carcinogen.

RESULTS

PAI-1 deficiency did not inhibit carcinogen-induced bladder cancer in mice although carcinogen-exposed wild type mice significantly increased PAI-1 levels in bladder tissue, plasma and urine. We found that PAI-1 KO mice exposed to carcinogen tended to upregulate protein C inhibitor (PAI-3), urokinase-type plasminogen activator (uPA) and tissue-type PA (tPA), and significantly increased PAI-2, suggesting a potential compensatory function of these molecules when PAI-1 is abrogated. Subsequent studies employing gene expression microarray using mouse bladder tissues followed by post hoc bioinformatics analysis and validation experiments by qPCR and IHC demonstrated that SERPING1 is further downregulated in PAI-1 KO mice exposed to BBN, suggesting that SERPING1 as a potential missing factor that regulate PAI-2 overexpression (compensation pathway).

CONCLUSIONS

These results indicate that serpin compensation pathway, specifically PAI-2 overexpression in this model, supports bladder cancer development when oncoprotein PAI-1 is deleted. Further investigations into PAI-1 are necessary in order to identify true potential targets for bladder cancer therapy.

Tocotrienols Modulate Breast Cancer Secretomes and Affect Cancer-Signaling Pathways in MDA-MB-231 Cells: A Label-Free Quantitative Proteomic Analysis

Tocotrienols (T3), a family of vitamin E, are reported to possess potent anti-cancer effects but the molecular mechanisms behind these effects still remain unclear. The aim of this study was to investigate how T3 exert anti-cancer effects on MDA-MB-231 human breast cancer cells. The MDA-MB-231 cells were chosen for this study as they are triple-negative and highly metastatic cells, which form aggressive tumors in experimental models. The MDA-MB-231 cells were treated with varying concentrations (0-20 µg mL^-1) of gamma (γ) or delta (δ) T3 and the secretome profiles of these cells treated with half maximal inhibitory concentration (IC₅₀) of γT3 (5.8 µg mL^-1) or δT3 (4.0 µg mL^-1) were determined using label-free quantitative proteomic strategy. A total of 103, 174 and 141 proteins were identified with ProteinLynx Global Server (PLGS) score of more than 200 and above 25% sequence coverage in the untreated control and T3-treated cell culture supernatant respectively. A total of 18 proteins were dysregulated between untreated control and T3 (δT3 or γT3) treated conditions. The results showed that T3 treatment downregulated the exogenous Cathepsin D and Serpine1 proteins but upregulated Profilin-1 protein, which play a key role in breast cancer in the MDA-MB-231 cells. These findings strongly suggest that T3 may induce differential expression of secreted proteins involved in the cytoskeletal regulation of RHO GTPase signaling pathway.

Endothelial miR-30c suppresses tumor growth via inhibition of TGF-β-induced Serpine1

In tumors, extravascular fibrin forms provisional scaffolds for endothelial cell (EC) growth and motility during angiogenesis. We report that fibrin-mediated angiogenesis was inhibited and tumor growth delayed following postnatal deletion of Tgfbr2 in the endothelium of Cdh5-CreERT2 Tgfbr2fl/fl mice (Tgfbr2iECKO mice). ECs from Tgfbr2iECKO mice failed to upregulate the fibrinolysis inhibitor plasminogen activator inhibitor 1 (Serpine1, also known as PAI-1), due in part to uncoupled TGF-β-mediated suppression of miR-30c. Bypassing TGF-β signaling with vascular tropic nanoparticles that deliver miR-30c antagomiRs promoted PAI-1-dependent tumor growth and increased fibrin abundance, whereas miR-30c mimics inhibited tumor growth and promoted vascular-directed fibrinolysis in vivo. Using single-cell RNA-Seq and a NanoString miRNA array, we also found that subtypes of ECs in tumors showed spectrums of Serpine1 and miR-30c expression levels, suggesting functional diversity in ECs at the level of individual cells; indeed, fresh EC isolates from lung and mammary tumor models had differential abilities to degrade fibrin and launch new vessel sprouts, a finding that was linked to their inverse expression patterns of miR-30c and Serpine1 (i.e., miR-30chi Serpine1lo ECs were poorly angiogenic and miR-30clo Serpine1hi ECs were highly angiogenic). Thus, by balancing Serpine1 expression in ECs downstream of TGF-β, miR-30c functions as a tumor suppressor in the tumor microenvironment through its ability to promote fibrin degradation and inhibit blood vessel formation.

Increased Umbilical Cord PAI-1 Levels in Placental Insufficiency Are Associated with Fetal Hypoxia and Angiogenesis

In intrauterine growth restriction (IUGR), a subset of pregnancies undergoes placental vascular dysregulation resulting in restricted blood flow and fetal hypoxemia. Altered transcription of hypoxic regulated plasminogen activator inhibitor 1 (PAI-1) has been associated with pregnancy complications and angiogenic regulation. Here we assessed circulating PAI-1 as an indicator of placental insufficiency. Venous umbilical PAI-1 of hypoxemic (VpO2 20 versus 35 mmHg, p < 0.0001) placental insufficient pregnancies (resistance index 0.9 versus 0.63, p < 0.05) (n = 18) was compared to controls (n = 12). PAI-1 was increased (~10-fold, p < 0.001) and had a positive predictive ratio of 6.7. Further, PAI-1 levels correlated to blood oxygen (r = -0.68, p < 0.0001). The plasma's angiogenic potency measured in vitro was associated with umbilical cord blood PAI-1 levels (r = 0.65, p < 0.01). This association was attenuated by PAI-1 inhibiting antibody (p < 0.001). The results demonstrate PAI-1 as a potential marker of placental insufficiency and identify its close association with pathological hypoxia and angiogenesis in a subset of growth restricted pregnancies.

Plasminogen Activator Inhibitor-1 in Cancer: Rationale and Insight for Future Therapeutic Testing

Despite its function as an inhibitor of urokinase and tissue-type plasminogen activator (PA), PA inhibitor-1 (PAI-1) has a paradoxical protumorigenic role in cancer, promoting angiogenesis and tumor cell survival. In this review, we summarize preclinical evidence in support of the protumorigenic function of PAI-1 that has led to the testing of small-molecule PAI-1 inhibitors, initially developed as antithrombotic agents, in animal models of cancer. The review discusses the challenges and the opportunities that lay ahead to the development of efficacious and nontoxic PAI-1 inhibitors as anticancer agents.

Spontaneous lung and lymph node metastasis in transgenic breast cancer is independent of the urokinase receptor uPAR

Urokinase-type plasminogen activator (uPA) is an extracellular protease that plays a pivotal role in tumor progression. uPA activity is spatially restricted by its anchorage to high-affinity uPA receptors (uPAR) at the cell surface. High tumor tissue expression of uPA and uPAR is associated with poor prognosis in lung, breast, and colon cancer patients in clinical studies. Genetic deficiency of uPA leads to a significant reduction in metastases in the murine transgenic MMTV-PyMT breast cancer model, demonstrating a causal role for uPA in cancer dissemination. To investigate the role of uPAR in cancer progression, we analyze the effect of uPAR deficiency in the same cancer model. uPAR is predominantly expressed in stromal cells in the mouse primary tumors, similar to human breast cancer. In a cohort of MMTV-PyMT mice [uPAR-deficient (n = 31) or wild type controls (n = 33)], tumorigenesis, tumor growth, and tumor histopathology were not significantly affected by uPAR deficiency. Lung and lymph node metastases were also not significantly affected by uPAR deficiency, in contrast to the significant reduction seen in uPA-deficient mice. Taken together, our data show that the genetic absence of uPAR does not influence the outcome of the MMTV-PyMT cancer model.

Heritable IUGR and adult metabolic syndrome are reversible and associated with alterations in the metabolome following dietary supplementation of 1-carbon intermediates

Metabolic syndrome (MetS), following intrauterine growth restriction (IUGR), is epigenetically heritable. Recently, we abrogated the F2 adult phenotype with essential nutrient supplementation (ENS) of intermediates along the 1-carbon pathway. With the use of the same grandparental uterine artery ligation model, we profiled the F2 serum metabolome at weaning [postnatal day (d)21; n = 76] and adulthood (d160; n = 12) to test if MetS is preceded by alterations in the metabolome. Indicative of developmentally programmed MetS, adult F2, formerly IUGR rats, were obese (621 vs. 461 g; P < 0.0001), dyslipidemic (133 vs. 67 mg/dl; P < 0.001), and glucose intolerant (26 vs. 15 mg/kg/min; P < 0.01). Unbiased gas chromatography-mass spectrometry (GC-MS) profiling revealed 34 peaks corresponding to 12 nonredundant metabolites and 9 unknowns to be changing at weaning [false discovery rate (FDR) < 0.05]. Markers of later-in-life MetS included citric acid, glucosamine, myoinositol, and proline (P < 0.03). Hierarchical clustering revealed grouping by IUGR lineage and supplementation at d21 and d160. Weanlings grouped distinctly for ENS and IUGR by partial least-squares discriminate analysis (PLS-DA; P < 0.01), whereas paternal and maternal IUGR (IUGR(pat)/IUGR(mat), respectively) control-fed rats, destined for MetS, had a distinct metabolome at weaning (randomForest analysis; class error < 0.1) and adulthood (PLS-DA; P < 0.05). In sum, we have found that alterations in the metabolome accompany heritable IUGR, precede adult-onset MetS, and are partially amenable to dietary intervention.

Pleiotropic functions of the tumor- and metastasis-suppressing matrix metalloproteinase-8 in mammary cancer in MMTV-PyMT transgenic mice

INTRODUCTION

Matrix metalloproteinase-8 (MMP-8; neutrophil collagenase) is an important regulator of innate immunity that has oncosuppressive actions in numerous tumor types.

METHODS

We have intercrossed Mmp8-null mice with the Polyoma virus middle T oncogene-driven (MMTV-PyMT) mouse model of mammary cancer to explore the effects of loss of MMP-8 on the incidence and progression of mammary carcinomas.

RESULTS

In this aggressive mouse model of breast cancer, loss of MMP-8 accelerated tumor onset even further, such that 90% of MMTV-PyMT; Mmp8-null female mice were tumor-bearing at the time of weaning. Throughout the 14 weeks of the model, tumor burden increased in homozygous Mmp8-null mice compared to Mmp8-wild-type and -heterozygote animals. Likewise, lung metastasis dramatically increased in the MMTV-PyMT; Mmp8-null mice. Immunohistochemistry revealed that tumors in wild-type, Mmp8-heterozygotes and -null animals had similar vascular density at 8 weeks, but at 10 weeks Mmp8-wild-type tumors had a lower vascularity than their heterozygote and null counterparts. No differences in macrophage infiltration were apparent throughout primary tumor development, though at 10 weeks a drop in neutrophil infiltrates was observed in Mmp8-wild-type tumors. Using quantitative real-time RT-PCR, we tracked the expression of the entire Mmp and Timp gene families, observing a significant decrease in Mmp3 expression in Mmp8-null tumors compared to wild-type and heterozygotes throughout the time course of the model, which was confirmed at the protein level.

CONCLUSIONS

These findings provide novel insight into the suppressive action of MMP-8 on mammary tumorigenesis and metastasis, and indicate that the loss of MMP-8 likely has pleiotropic effects on innate immunity and angiogenesis that are reflected in changes in the protease web.

Effects of a high-fat diet on spontaneous metastasis of Lewis lung carcinoma in plasminogen activator inhibitor-1 deficient and wild-type mice

This study investigated the effects of a high-fat diet on spontaneous metastasis of Lewis lung carcinoma (LLC) in plasminogen activator inhibitor-1 deficient (PAI-1^−/−) and wild-type mice. The high-fat diet increased the number of pulmonary metastases by 60% (p<0.01), tumor cross-sectional area by 82% (p<0.05) and tumor volume by 130% (p<0.05) compared to the AIN93G diet. Deficiency in PAI-1 reduced the number of metastases by 35% (p<0.01) compared to wild-type mice. In mice fed the high-fat diet, PAI-1 deficiency reduced tumor cross-sectional area by 52% (p<0.05) and tumor volume by 61% (p<0.05) compared to their wild-type counterparts; however, PAI-1 deficiency affected neither area nor volume in mice fed the AIN93G diet. Adipose and plasma concentrations of PAI-1 were significantly higher in high-fat fed wild-type mice than in their AIN93G-fed counterparts. Adipose and plasma PAI-1 were not detectable in PAI-1^−/− mice regardless of the diet. Mice deficient in PAI-1 showed significantly greater plasma concentrations of monocyte chemotactic protein-1, tumor necrosis factor-α, leptin, vascular endothelial growth factor, tissue inhibitor of metalloproteinase-1 and insulin compared to wild-type mice, indicating a compensatory overproduction of inflammatory cytokines, angiogenic factors and insulin in the absence of PAI-1. We conclude that PAI-1 produced by the host, including that by adipose tissue, promotes high-fat enhanced metastasis of LLC.

Protumorigenic activity of plasminogen activator inhibitor-1 through an antiapoptotic function

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) is a protease inhibitor but is paradoxically associated with poor outcomes in cancer patients. However, the mechanisms of its effects on tumor cells have not been explored.

METHODS

Endogenous PAI-1 in human tumor cell lines (HT-1080, A549, HCT-116, and MDA-MB-231) was suppressed by small interfering RNAs (siRNAs) and PAI-039, a small molecule inhibitor of PAI-1, and the effects on apoptosis were examined. Tumorigenicity of PAI-1 knockdown (KD) tumor cells was examined in immunodeficient PAI-1 wild-type and knockout (KO) mice (9-15 per group), and event-free survival was analyzed by the Kaplan-Meier method. The effect of PAI-1 suppression on HT-1080 xenotransplanted tumors was evaluated for cell proliferation, apoptosis, and angiogenesis. All statistical tests were two-sided.

RESULTS

Genetic and pharmacological inhibition of PAI-1 in the four tumor cell lines increased spontaneous apoptosis (mean fold increase relative to control: HT-1080, siRNA#1, mean = 4.0, 95% CI = 2.6 to 5.3, P < .001; siRNA#2, mean = 2.6, 95% CI = 2.4 to 2.9, P < .001, Student t test), which was blocked in the presence of recombinant PAI-1, a caspase-8 inhibitor, or Fas/FasL neutralizing antibodies and was partially attenuated by a plasmin inhibitor-aprotinin. PAI-1 KO mice implanted with PAI-1 KD HT-1080 cells had decreased tumorigenesis and prolonged survival compared with control mice (P = .002, log-rank test), and their tumors exhibited decreased cell proliferation and angiogenesis and increased apoptosis. Furthermore, five of 15 PAI-1 KO mice implanted with PAI-1 KD HT-1080 cells never developed tumors.

CONCLUSIONS

These data suggest that PAI-1 exerts a protective effect against tumor cell apoptosis by a mechanism that, in part, involves plasmin activation and inhibition of Fas/Fas-L-mediated apoptosis and may be a promising therapeutic target.

Spontaneous metastasis in congenic mice with transgenic breast cancer is unaffected by plasminogen gene ablation

Plasminogen (Plg) plays a central role in tissue remodeling during ontogeny, development, and in pathological tissue remodeling following physical injury, inflammation and cancer. Plg/plasmin is, however, not critical for these processes, as they all occur to a varying extent in its absence, suggesting that there is a functional redundancy with other proteases. To explore this functional overlap in the transgenic MMTV-PyMT breast cancer metastasis model, we have combined Plg deficiency and a pharmacological metalloprotease inhibitor, which is known to reduce metastasis in this model, and has been shown to synergistically inhibit other tissue remodeling events in Plg-deficient mice. While metalloprotease inhibition dramatically reduced metastasis, we found no effect of Plg deficiency on metastasis, either independently or in combination with metalloprotease inhibition. We further show that Plg gene deficiency is of no significant consequence in this metastasis model, when analyzed in two different congenic strains: the FVB strain, and a F1 hybrid of the FVB and C57BL/6J strains. We suggest that the extensive backcrossing performed prior to our studies has eliminated the confounding effect of a known polymorphic metastasis modifier gene region located adjacent to the Plg gene.

PAI-1, progress in understanding the clinical problem and its aetiology

Plasminogen activator inhibitor-1 (PAI-1, also known as SERPINE1) is a member of the serine protease inhibitor (SERPIN) superfamily and is the primary physiological regulator of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) activity. Although the principal function of PAI-1 is the inhibition of fibrinolysis, PAI-1 possesses pleiotropic functions besides haemostasis. In the quarter century since its discovery, a number of studies have focused on improving our understanding of PAI-1 functions in vivo and in vitro. The use of Serpine1-deficient mice has particularly enhanced our understanding of the functions of PAI-1 in various physiological and pathophysiological conditions. In this review, the results of recent studies on PAI-1 and its role in clinical conditions are discussed.

Quantitative secretome analysis reveals that COL6A1 is a metastasis-associated protein using stacking gel-aided purification combined with iTRAQ labeling

In cancer metastasis, secreted proteins play an important role in promoting cancer cell migration and invasion and thus also in the increase of cancer metastasis in the extracellular microenvironment. In this study, we developed a strategy that combined a simple gel-aided protein purification with iTRAQ labeling to quantify and discover the metastasis-associated proteins in the lung cancer cell secretome. Secreted proteins associated with lung cancer metastasis were produced using CL1-0 and CL1-5 cells with different metastatic abilities. Quantitative secretomics analysis identified a total of 353 proteins, 7 of which were considered to be metastasis-associated proteins. These included TIMP1, COL6A1, uPA, and AAT, all of which were higher in CL1-5, and AL1A1, PRDX1, and NID1, which were higher in CL1-0. Six of these metastasis-associated proteins were validated with Western blot analysis. In addition, pathway analysis was performed in building the interaction network between the identified metastasis-associated proteins. Further functional analysis of COL6A1 on the metastatic abilities of CL1 cells was also carried out. An RNA interference-based knock-down of COL6A1 suppressed the metastatic ability of CL1-5 cells; in contrast, a plasmid-transfected overexpression of COL6A1 increased the metastatic ability of CL1-0 cells. This study describes a simple and high throughput sample purification method that can be used for the quantitative secretomics analysis of metastasis-associated proteins.

Use of mouse models to study plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is the main inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) and therefore plays an important role in the plasminogen/plasmin system. PAI-1 is involved in a variety of cardiovascular diseases (mainly through inhibition of t-PA) as well as in cell migration and tumor development (mainly through inhibition of u-PA and interaction with vitronectin). PAI-1 is a unique member of the serpin superfamily, exhibiting particular unique conformational and functional properties. Since its involvement in various biological and pathophysiological processes PAI-1 has been the subject of many in vivo studies in mouse models. We briefly discuss structural and physiological differences between human and mouse PAI-1 that should be taken into account prior to extrapolation of data obtained in mouse models to the human situation. The current review provides an overview of the various models, with a focus on cardiovascular disease and cancer, using wild-type mice or genetically modified mice, either deficient in PAI-1 or overexpressing different variants of PAI-1.

Unimpeded skin carcinogenesis in K14-HPV16 transgenic mice deficient for plasminogen activator inhibitor

Angiogenesis, extracellular matrix remodeling and cell migration are associated with cancer progression and involve at least, the plasminogen activating system and its main physiological inhibitor, the plasminogen activator inhibitor-1 (PAI-1). Considering the recognized importance of PAI-1 in the regulation of tumor angiogenesis and invasion in murine models of skin tumor transplantation, we explored the functional significance of PAI-1 during early stages of neoplastic progression in the transgenic mouse model of multistage epithelial carcinogenesis (K14-HPV16 mice). We have studied the effect of genetic deletion of PAI-1 on inflammation, angiogenesis, lymphangiogenesis and tumor progression. In this model, PAI-1 deficiency neither impaired keratinocyte hyperproliferation or tumor development nor affected the infiltration of inflammatory cells and development of angiogenic or lymphangiogenic vasculature. We are reporting evidence for concomitant lymphangiogenic and angiogenic switches independent to PAI-1 status. Taken together, these data indicate that PAI-1 is not rate limiting for neoplastic progression and vascularization during premalignant progression, or that there is a functional redundancy between PAI-1 and other tumor regulators, masking the effect of PAI-1 deficiency in this long-term model of multistage epithelial carcinogenesis.

Does plasminogen activator inhibitor-1 drive lymphangiogenesis?

The purpose of this study is to explore the function of plasminogen activator inhibitor-1 (PAI-1) during pathological lymphangiogenesis. PAI-1, the main physiological inhibitor of plasminogen activators is involved in pathological angiogenesis at least by controlling extracellular proteolysis and by regulating endothelial cell survival and migration. Protease system's role in lymphangiogenesis is unknown yet. Thus, based on its important pro-angiogenic effect, we hypothesized that PAI-1 may regulate lymphangiogenesis associated at least with metastatic dissemination of cancer cells. To address this issue, we studied the impact of PAI-1 deficiency in various murine models of tumoral lymphangiogenesis. Wild-type PAI-1 proficient mice were used as controls. We provide for the first time evidence that PAI-1 is dispensable for tumoral lymphangiogenesis associated with breast cancers either induced by mammary carcinoma cell injection or spontaneously appearing in transgenic mice expressing the polyomavirus middle T antigen (PymT) under the control of a mouse mammary tumor virus long-terminal repeat promoter (MMTV-LTR). We also investigated inflammation-related lymphatic vessel recruitment by using two inflammatory models. PAI-1 deficiency did neither affect the development of lymphangioma nor burn-induced corneal lymphangiogenesis. These novel data suggest that vascular remodelling associated with lymphangiogenesis and angiogenesis involve different molecular determinants. PAI-1 does not appear as a potential therapeutic target to counteract pathological lymphangiogenesis.

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.

Plasminogen activator inhibitor-1 (PAI-1) facilitates retinal angiogenesis in a model of oxygen-induced retinopathy

PURPOSE

Angiogenesis, or the formation of new retinal blood vessels, is a key feature of many proliferative retinal diseases including diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity. The aim of the present study was to investigate the role of the serine proteinase inhibitor plasminogen activator inhibitor -1 (PAI-1) in facilitating retinal angiogenesis.

METHODS

The temporal expression of PAI-1 was examined by real-time PCR, Western blot analysis, and immunohistochemistry in retinal tissues from mice with oxygen-induced retinopathy. The requirement for PAI-1 in facilitating the retinal angiogenic response in this model was examined by quantitating the angiogenic response with wild-type and PAI-1 null mice. The mechanism by which PAI-1 mediates angiogenesis was further investigated with isolated human retinal vascular endothelial cells.

RESULTS

PAI-1 expression was upregulated in the retinas of mice with oxygen-induced retinopathy, which coincided with a significant increase in the expression of vitronectin in the retina of the experimental mice. There was significant reduction in the angiogenic response of PAI-1(-/-) mice compared with wild-type mice. PAI-1 promotes endothelial cell migration in vitro and facilitates the migration of cells on a vitronectin substrate by regulating alpha v integrin cell surface expression.

CONCLUSIONS

These observations suggest a role for PAI-1 during retinal angiogenesis and point to a potential new therapeutic target in the prevention or treatment of retinal neovascularization seen in many ocular diseases.

Metastasis is strongly reduced by the matrix metalloproteinase inhibitor Galardin in the MMTV-PymT transgenic breast cancer model

Matrix metalloproteinases (MMP) have several roles that influence cancer progression and dissemination. However, low molecular weight metalloproteinase inhibitors (MPI) have not yet been tested in transgenic/spontaneous metastasis models. We have tested Galardin/GM6001, a potent MPI that reacts with most MMPs, in the MMTV-PymT transgenic breast cancer model. We followed a cohort of 81 MMTV-PymT transgenic mice that received Galardin, placebo, or no treatment. Galardin treatment was started at age 6 weeks with 100 mg/kg/d, and all mice were killed at age 13.5 weeks. Galardin treatment significantly reduced primary tumor growth. Final tumor burden in Galardin-treated mice was 1.69 cm3 compared with 3.29 cm3 in placebo-treated mice (t test, P = 0.0014). We quantified the total lung metastasis volume in the same cohort of mice. The median metastasis volume was 0.003 mm(3) in Galardin-treated mice compared with 0.56 mm(3) in placebo-treated mice (t test, P < 0.0001). Thus, metastasis burden was reduced more than 100-fold, whereas primary tumor size was reduced only 2-fold. We also found that primary tumors from Galardin-treated mice exhibited a lower histopathologic tumor grade, increased collagen deposition, and increased MMP-2 activity. MMPs are known to have tumor-promoting and tumor-inhibitory effects, and several clinical trials of broad-spectrum MPIs have failed to show promising effects. The very potent antimetastatic effect of Galardin in the MMTV-PymT model does, however, show that it may be possible to find broad-spectrum MPIs with favorable inhibition profiles, or perhaps combinations of monospecific MPIs, for future clinical application.

The plasminogen activator inhibitor "paradox" in cancer

Proteolysis in general and specifically the plasminogen activating system regulated by urokinase (uPA) its specific receptor, the GPI membrane anchored urokinase receptor (uPAR) and the specific plasminogen activator inhibitor 1 (PAI-1) plays a major role in tumorigenesis, tumor progression, tumor invasion and metastasis formation. This is exemplified by a body of published work showing a positive correlation between the expression of uPA or uPAR in several tumors and their malignancy. It is generally assumed that such a "pro-malignant" effect of the uPA-uPAR system is mediated by increased local proteolysis thus favoring tumor invasion, by a pro-angiogenic effect of this system and also by uPA-uPAR signaling towards the tumor thereby shifting the tumor phenotype to a more "malignant" one. However, when tumor patients are analyzed for long term survival, those with high levels of the inhibitor of the system, PAI-1 have a much worse prognosis than those with lower PAI-1 levels. This indicates that increased overall proteolysis alone cannot be made responsible for the adverse effects of the plasminogen activating system in tumors. Moreover, it becomes increasingly evident that components of the fibrinolytic system secreted by the tumor cells themselves are not solely responsible for a correlation between the plasminogen activating system and tumor malignancy; components of the plasminogen activating system secreted by stroma cells or cells of the immune system such as macrophages contribute also to the impact of fibrinolysis on malignancy. This review summarizes the evidence for the role of plasminogen activator inhibitor-1 in mediating the malignant phenotype and possible mechanism thereby trying to explain the "PAI-1 paradox in cancer" on a molecular level.

A guide to murine fibrinolytic factor structure, function, assays, and genetic alterations

The components and functions of the murine fibrinolytic system are quite similar to those of humans. Because of these similarities and the adaptability of mice to genetic manipulation, murine fibrinolysis has been studied extensively. These studies have yielded important information regarding the function of the several components of fibrinolysis. This review presents information on the structure, function and assay of mouse fibrinolytic parameters and it discusses the results of the extensive studies of genetically modified mice. It is intended to be a convenient reference resource for investigators of fibrinolysis.

Extracellular proteolysis in transgenic mouse models of breast cancer

Growth and invasion of breast cancer require extracellular proteolysis in order to physically restructure the tissue microenvironment of the mammary gland. This pathological tissue remodeling process depends on a collaboration of epithelial and stromal cells. In fact, the majority of extracellular proteases are provided by stromal cells rather than cancer cells. This distinct expression pattern is seen in human breast cancers and also in transgenic mouse models of breast cancer. The similar expression patterns suggest that transgenic mouse models are ideally suited to study the role of extracellular proteases in cancer progression. Here we give a status report on protease intervention studies in transgenic models. These studies demonstrate that proteases are involved in all stages of breast cancer progression from carcinogenesis to metastasis. Transgenic models are now beginning to provide vital mechanistic insight that will allow us to combat breast cancer invasion and metastasis with new protease-targeted drugs.

A Novel Function of Plasminogen Activator Inhibitor-1 in Modulation of the AKT Pathway in Wild-type and Plasminogen Activator Inhibitor-1-deficient Endothelial Cells

Cell proliferation, an event associated with angiogenesis, involves coordinated activities of a number of proteins. The role of plasminogen activator inhibitor-1 (PAI-1) in angiogenesis remains controversial. Utilizing proliferating PAI-1-/- endothelial cells (EC), the impact of a host PAI-1 deficiency on Akt activation was evaluated. Hyperactivation of Akt(Ser(P)473) was observed in PAI-1-/- EC, and this was probably due to enhanced inactivation of tumor suppressor PTEN, thus rendering the cells resistant to apoptotic signals. Higher levels of inactivated caspase-9 in PAI-1-/- EC led to lower levels of procaspase-3 and cleaved caspase-3, thereby promoting survival. These effects were reversed when recombinant PAI-1 was added to PAI-1-/- EC. Additional studies demonstrated that regulation of proliferation is dependent on its interaction with low density lipoprotein receptor-related protein. Thus, PAI-1 is a negative regulator of cell growth, exerting its effect on the phosphatidylinositol 3-kinase/Akt pathway and allowing controlled cell proliferation.

Exploring the tumour environment: cancer-associated fibroblasts as targets in cancer therapy

Stroma cells contribute to the microenvironment that is essential for cancer growth, invasion and metastatic progression. Fibroblasts, often termed myofibroblasts or cancer-associated fibroblasts (CAFs), represent the most abundant cell type in the tumour stroma. The demonstrated tumour-promoting capacities of CAFs has increased the interest to exploit them as drug targets for anticancer therapy. Although single factors, such as platelet-derived growth factor, transforming growth factor-beta1, hepatocyte growth factor and matrix metalloproteinases have been identified as mediators in the fibroblast tumour interaction, the morphological and functional differences of CAFs compared with their normal counterparts are only incompletely understood. Recently, novel global methods for gene expression profiling were applied to comprehensively characterise CAFs from breast, pancreas, colon and basal cell cancer in their in situ environment. The analysis of different CAF preparations revealed regulated genes that were previously not described in the tumour-stroma context. Additionally, besides a few striking overlaps, the comparison of the gene lists indicates a high level of heterogeneity in the expression pattern of CAFs from different tumour types. Together, these studies emphasise the importance of cross-talk between stromal and malignant cells of the tumour. It is likely that the continued characterisation of this interaction, and the molecular identification of key mediators, will provide insights into tumour biology and suggest novel therapeutic options.

[New prognostic and predictive factors in advanced colorectal cancer]

Cancer patients often show a clinical tendency to thromboembolic events. This tendency is due to tumor cell-related factors together with the damage of the vascular endothelial exerted by chemotherapy treatment. Gastrointestinal tumors especially contribute to these types of events. More recently, the implication of tumor angiogenesis in clotting/fibrynolisys and plasminogen systems activation has been addressed in cancer patients. Finally, some hemostasis and angiogenesis-related factors such as platelets, von Willebrand factor, fibrinogen, plasminogen activator inhibitor type-1, D dimer, and vascular endotelial growth factor have been highlighted as new potential response and survival predictors in colorectal cancer patients. In this review article, the current evidence supporting the use of these proteins in assessing prognosis in colorectal cancer patients is critically exposed and discussed.

Enhanced spontaneous metastasis in bikunin-deficient mice

Previously, we showed that bikunin, a Kunitz-type protease inhibitor, inhibits invasion and metastasis in several types of cancer cells possibly through suppression of upregulation of urokinase-type plasminogen activator (uPA) expression. Bikunin corresponds to a light chain of the inter-alpha inhibitor. To explore critical role of endogenous bikunin, we used bikunin knockout (Bik-/-) mice. Here, we show that 1) higher frequency of spontaneous 3LL lung metastasis was observed in Bik-/- mice compared to Bik+/+ mice, suggesting that bikunin deficiency increases the sensitivity of mice to lung metastasis; 2) administration of exogenous bikunin caused a significant reduction of lung metastasis in Bik-/- and Bik+/+ mice; 3) primary and metastatic tumors significantly upregulated uPA and PAI-1 expression in Bik-/- mice relative to Bik+/+ mice at least through phosphorylation of ERK1/2 and 4) exogenous bikunin suppressed phosphorylation of ERK1/2 and upregulation of uPA and PAI-1 expression in 3LL cells in response to G-CSF. These data allow us to conclude that the increased sensitivity of Bik-/- mice to lung metastasis in vivo is due to a lack of circulating proteins of the inter-alpha inhibitor family, especially bikunin.

ADAMTS8 and ADAMTS15 expression predicts survival in human breast carcinoma

We recently undertook expression profiling of all 19 human ADAMTS metalloproteinases (a disintegrin and metalloproteinase with thrombospondin motifs) in malignant and non-neoplastic breast tissue and showed that 11 of the ADAMTS genes are dysregulated in breast carcinoma. We identified a subgroup of ADAMTSs, based on functional and amino acid sequence similarity (ADAMTS1, 4, 5, 8 and 15), to be the focus of further study in breast carcinoma. Further RNA expression analysis by real-time PCR on a different cohort of 229 patients with breast cancer has identified ADAMTS8 as a predictor of poor overall survival (OS) (hazard ratio (HR) = 2.20, 95% C.I. = 1.29-3.74, p = 0.004) and confirmed ADAMTS15 as a predictor of prolonged relapse-free survival (RFS) (HR = 0.54, 95% C.I. = 0.32-0.89, p = 0.016). We explored the differences in survival of the 4 groups that could be categorized based on the expression levels of ADAMTS8 and ADAMTS15. For both RFS and OS, the group with high ADAMTS8 and low ADAMTS15 expression had a particularly poor prognosis. This group had a 3-fold higher chance of recurrence (HR = 3.03, 95% C.I. = 1.49-6.15, p = 0.001) and a greater than 5-fold higher chance of death (HR = 5.40, 95% C.I. = 2.16-13.5, p < 0.001) than the most favorable prognostic group. This prediction of poor prognosis by ADAMTS8 and ADAMTS15 expression was found to be independent of other classical clinicopathological factors. Results observed in FVB-PyMT mice, a robust transgenic model of highly metastatic breast carcinoma, fitted the expectation that relatively high expression levels of ADAMTS8 together with low expression levels of ADAMTS15 seen in human breast carcinoma are associated with a poor clinical outcome. In summary, ADAMTS8 and ADAMTS15 have emerged as novel predictors of survival in patients with breast carcinoma.

Host plasminogen activator inhibitor-1 promotes human skin carcinoma progression in a stage-dependent manner

Angiogenesis and tumor expansion are associated with extracellular matrix remodeling and involve various proteases such as the plasminogen (Plg)/plasminogen activator (PA) system. Recently, several experimental data have implicated the plasminogen activator inhibitor-1 (PAI-1) in tumor angiogenesis in murine systems. However, little is known about PAI-1 functions in human skin carcinoma progression. By generating immunodeficient mice (in Rag-1-/- or nude background) deleted for PAI-1 gene (PAI-1-/-), we have evaluated the impact of host PAI-1 deficiency on the tumorigenicity of two malignant human skin keratinocyte cell lines HaCaT II-4 and HaCaT A5-RT3 forming low-grade and high-grade carcinomas, respectively. When using the surface transplantation model, angiogenesis and tumor invasion of these two cell lines are strongly reduced in PAI-1-deficient mice as compared to the wild-type control animals. After subcutaneous injection in PAI-1-/- mice, the tumor incidence is reduced for HaCaT II-4 cells, but not for those formed by HaCaT A5-RT3 cells. These data indicate that PAI-1 produced by host cells is an important contributor to earlier stages of human skin carcinoma progression. It exerts its tumor-promoting effect in a tumor stage-dependent manner, but PAI-1 deficiency is not sufficient to prevent neoplastic growth of aggressive tumors of the human skin.

Plasminogen activator inhibitor-1 (PAI-1) modifies the formation of aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis is a mesenchymal neoplasm associated with mutations, resulting in beta-catenin-mediated transcriptional activation. We found that plasminogen activator inhibitor-1 (PAI-1) was upregulated fourfold in aggressive fibromatosis. We investigated the ability of beta-catenin to regulate a PAI-1 reporter, and found that PAI-1 is an indirect target. To determine the role of PAI-1 in vivo, a mouse containing a targeted deletion in Pai-1 was crossed with a mouse that develops aggressive fibromatosis and gastrointestinal tumors (Apc/Apc1638N mouse). Pai-1 deficiency reduced the number of aggressive fibromatosis tumors formed, but not the number of gastrointestinal tumors. Deficiency of Pai-1 reduced tumor cell proliferation and motility rate. Although PAI-1 can alter cell motility by competing for a common binding site on vitronectin, blocking this site did not alter the motility rate. The number of cells moving through matrigel (invasion rate) did not change with Pai-1 deficiency, but because of the low motility rate the invasion index (invasion rate/motility) was increased in Pai-1-deficient cells. This suggests a proteolytic effect for PAI-1 regulating cell invasiveness. Our study found that, although PAI-1 has cellular effects that could inhibit or enhance tumor growth, on balance, it acts as a tumor enhancer in aggressive fibromatosis.

Extracellular protease mRNAs are predominantly expressed in the stromal areas of microdissected mouse breast carcinomas

Solid tumors synthesize a number of extracellular matrix-degrading proteases that are important for tumor progression. Based on qualitative in situ hybridization studies in human cancer tissue, a range of components involved in proteolysis appear to be expressed by stromal cells rather than cancer cells. We have now used laser capture microdissection and real-time PCR to quantify the mRNA expression of components of matrix-degrading proteolytic systems in cancer and stromal areas of mouse mammary tumors genetically induced by the polyoma virus middle T (PyMT) antigen. We examined the mRNA levels of urokinase plasminogen activator, plasminogen activator inhibitor 1 and the matrix metalloproteases MMP-2, -3, -11, -13 and -14, and found that all these seven genes are predominantly expressed by stromal cells. Our results were qualitatively supported by in situ hybridization analysis of the expression of mRNAs for MMP-2, -3 and -13 in the PyMT tumors. Statistical analyses indicated that the quantitative expression patterns observed in cancer and stromal cells isolated from individual tumors from different PyMT mice are quite reproducible. The methodology described in this study provides excellent tools to study the possible interactions between cancer and stromal cells during the development of breast cancer, and the results suggest that stromal cells are involved in carcinogenesis and tumor progression, which may have important implications for the biology and therapy of cancer.

Reduced metastasis of transgenic mammary cancer in urokinase-deficient mice

A prominent phenotype of plasmin deficiency in mice is reduced metastasis in the MMTV-PymT transgenic breast cancer model. Proteolytically active plasmin is generated from inactive plasminogen by one of 2 activators, uPA or tPA. We now find that uPA deficiency alone significantly reduces metastasis >7-fold in the MMTV-PymT model. We studied a cohort of 55 MMTV-PymT transgenic mice, either uPA-deficient or wild-type controls. Tumor incidence, latency, growth rate and final primary tumor burden were not significantly affected by uPA deficiency. In contrast, average lung metastasis volume was reduced from 1.58 mm(3) in wild-type controls to 0.21 mm(3) in uPA-deficient mice (p = 0.023). Tumor cell dissemination to brachial lymph nodes was also reduced from 53% (28/53) in wild-type controls to 31% (17/54) in uPA-deficient mice (p = 0.032). Mice without plasminogen display a severe pleiotropic phenotype. By comparison, spontaneous phenotypes are modest in uPA-deficient mice, probably because they still have active tPA. We show that metastasis is strongly and selectively decreased in uPA-deficient mice, suggesting that uPA-directed antimetastatic therapy would be efficacious and have limited side effects.

Pleiotropic functions of plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1), a 45-kDa serine proteinase inhibitor with reactive site peptide bond Arg345-Met346, is the main physiological plasminogen activator inhibitor. It occurs in human plasma at an antigen concentration of about 20 ng mL(-1). Besides the active inhibitory form of PAI-1 that spontaneously converts to a latent form, also a substrate form exists that is cleaved at the P1-P1' site by its target enzymes, but does not form stable complexes. Besides its role in regulating hemostasis, PAI-1 plays a role in several biological processes dependent on plasminogen activator or plasmin activity. Studies with transgenic mice have revealed a functional role for PAI-1 in wound healing, atherosclerosis, metabolic disturbances such as obesity and insulin resistance, tumor angiogenesis, chronic stress, bone remodeling, asthma, rheumatoid arthritis, fibrosis, glomerulonephritis and sepsis. It is not always clear if these functions depend on the antiproteolytic activity of PAI-1, on its binding to vitronectin or on its intereference with cellular migration or matrix binding.

Host-derived plasminogen activator inhibitor-1 (PAI-1) concentration is critical for in vivo tumoral angiogenesis and growth

Plasminogen activator inhibitor type 1 (PAI-1) plays a key role in tumor progression and is believed to control proteolytic activity and cell migration during angiogenesis. We report here that host PAI-1, at physiological concentration, promotes in vivo tumor invasion and angiogenesis. In sharp contrast, inhibition of tumor vascularization was observed when PAI-1 was produced at supraphysiologic levels, either by host cells (transgenic mice overexpressing PAI-1) or by tumor cells (after transfection with murine PAI-1 cDNA). This study provides for the first time in vivo evidence for a dose-dependent effect of PAI-1 on tumor angiogenesis. Of great interest is the finding that PAI-1 produced by tumor cells, even at high concentration, did not overcome the absence of PAI-1 in the host, emphasizing the importance of the cellular source of PAI-1.

Membrane associated proteases and their inhibitors in tumour angiogenesis

Cell surface proteolysis is an important mechanism for generating biologically active proteins that mediate a range of cellular functions and contribute to biological processes such as angiogenesis. Although most studies have focused on the plasminogen system and matrix metalloproteinases (MMPs), recently there has been an increase in the identification of membrane associated proteases, including serine proteases, ADAMs, and membrane-type MMPs (MT-MMPs). Normally, protease activity is tightly controlled by tissue inhibitors of MMPs (TIMPs) and plasminogen activator inhibitors (PAIs). The balance between active proteases and inhibitors is thought to determine the occurrence of proteolysis in vivo. High concentrations of proteolytic system components correlate with poor prognosis in many cancers. Paradoxically, high (not low) PAI-1 or TIMP concentrations predict poor survival in patients with various cancers. Recent observations indicate a much more complex role for protease inhibitors in tumour progression and angiogenesis than initially expected. As knowledge in the field of protease biology has improved, the unforeseen complexities of cell associated enzymes and their interaction with physiological inhibitors have emerged, often revealing unexpected mechanisms of action.

The myofibroblast is the predominant plasminogen activator inhibitor-1-expressing cell type in human breast carcinomas

The tumor level of plasminogen activator inhibitor-1 (PAI-1) is an informative biochemical marker of a poor prognosis in several cancer types. However, the tumor biological functions of PAI-1 and the identity of PAI-1-expressing cells are controversial. With the aim of immunohistochemically localizing PAI-1 in formalin-fixed, paraffin-embedded invasive ductal breast carcinoma samples, we raised new polyclonal antibodies against PAI-1 from different expression systems. The antibodies were affinity purified by absorption on immobilized preparations of PAI-1 different from those used for immunization. The specificity of the antibodies was ensured by immunoblotting analysis. In immunohistochemistry, the staining pattern obtained with the antibodies showed a good correlation with the PAI-1 mRNA expression pattern. In all 25 cases analyzed, PAI-1 immunoreactivity was predominantly localized in fibroblast-like cells. Double-immunofluorescence analyses showed co-expression of PAI-1 and alpha-smooth muscle actin in these cells, suggesting that they are myofibroblasts. PAI-1 was also seen in some myoepithelial cells surrounding occasional foci of ductal carcinoma in situ (9 of 25), some endothelial cells (8 of 25), some cancer cells (3 of 25), and some mast cells (6 of 25). In conclusion, we have provided a robust immunohistochemical procedure for detection of PAI-1 and shown that the majority of the PAI-1-expressing cells in invasive ductal breast carcinomas are myofibroblasts.