Urokinase-type plasminogen activator: a potent marker of metastatic potential in human cancers

Urokinase-type plasminogen activator (uPA) is a serine protease that is causally involved in cancer progression, especially invasion and metastasis. Multiple studies have shown that breast cancer patients whose primary cancer contains high levels of uPA have a significantly worse outcome than patients with low levels. As a prognostic marker for breast cancer the information supplied by uPA is both independent of traditionally used factors and significant in the important subgroup of axillary-node patients. Paradoxically, high levels of plasminogen activator inhibitor-1 (PAI-1), an endogenous inhibitor of uPA, also predict for aggressive disease. Recently, the prognostic impact of both uPA and PAI-1 in axillary node-negative breast cancer was confirmed using two different Level 1 Evidence studies, i.e. in both a randomized prospective trial and a pooled analysis. Therefore, uPA and PAI-1 appear to have fulfilled all the criteria for the routine assessment of prognosis in newly diagnosed breast cancer patients.     

Tumor-associated urokinase-type plasminogen activator: biological and clinical significance.

Evidence has accumulated that invasion and metastasis in solid tumors require the action of tumor-associated proteases, which promote the dissolution of the surrounding tumor matrix and the basement membranes. Receptor-bound urokinase-type plasminogen activator (uPA) appears to play a key role in these events. uPA converts plasminogen into plasmin and thus mediates pericellular proteolysis during cell migration and tissue remodeling under physiological and pathophysiological conditions. uPA is secreted as an enzymatically inactive proenzyme (pro-uPA) by tumor cells and stroma cells. uPA exerts its proteolytic function on normal cells and tumor cells as an ectoenzyme after having bound to a high-affinity cell surface receptor. After binding, pro-uPA is activated by serine proteases (e.g. plasmin, trypsin or plasma kallikrein) and by the cysteine proteases cathepsin B or L, resp. Receptor-bound enzymatically active uPA converts plasminogen to plasmin which is bound to a different low-affinity receptor on tumor cells. Plasmin then degrades components of the tumor stroma (e.g. fibrin, fibronectin, proteoglycans, laminin) and may activate procollagenase type IV which degrades collagen type IV, a major part of the basement membrane. Hence receptor-bound uPA will promote plasminogen activation and thus the dissolution of the tumor matrix and the basement membrane which is a prerequisite for invasion and metastasis. Tissues of primary cancer and/or metastases of the breast, ovary, prostate, cervix uteri, bladder, lung and of the gastrointestinal tract contain elevated levels of uPA compared to benign tissues. In breast cancer uPA and PAI-1 antigen in tumor tissue extracts are independent prognostic factors for relapse-free and overall survival.     

Limited prognostic value of c-erbB-2 compared to uPA and PAI-1 in primary breast carcinoma

In a retrospective study of 488 women with primary breast cancer, after a median follow-up of 10 years, we sought interactions between disease-free survival (DFS) and overall survival (OS) and tumor antigen levels of two components of the plasminogen system, urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1, and the transmembrane growth factor receptor c-erbB-2. We used ELISAs (American Diagnostica, Greenwich, CT, USA) to quantify uPA and PAI-1 antigen levels in cytosols, and a double monoclonal antibody-based assay (EIA) (Ciba Corning Diagnostics, Alameda, CA, USA) to quantify c-erbB-2 in membrane extracts of the same tissues. Weak positive correlations were found between uPA and c-erbB-2 (r(s) = 0.146; p = 0.001) and between PAI-1 and c-erbB-2 (r(s) = 0.154; p < 0.001). In the overall population, using univariate analyses, c-erbB-2 overexpression and high uPA and PAI-1 antigen levels (> 300 IU/mg, > 1.40 ng/mg and > 5.53 ng/mg, respectively) were significantly associated with shorter DFS (p = 0.003, p < 0.001 and p < 0.001, respectively) and OS (p < 0.001 in all cases). Using multivariate analyses, PAI-1, node status and tumor size were independent predictors of DFS and c-erbB-2 was retained in the model only for OS. In the node-negative subgroup, PAI-1 was the strongest significant survival predictor both for OS (p = 0.003; HR 2.52) and DFS (p < 0.001; HR 2.39). This study shows that in primary breast cancer c-erbB-2 offers no additional prognostic information when uPA and/or PAI-1 are candidates in the multivariate analyses.     

Tumor tissue concentrations of the proteinase inhibitors tissue inhibitor of metalloproteinases-1 (TIMP-1) and plasminogen activator inhibitor type 1 (PAI-1) are complementary in determining prognosis in primary breast cancer

The purpose of this study was to investigate the association between tumor tissue levels of total tissue inhibitor of metalloproteinases-1 (TIMP-1) and prognosis in patients with primary breast cancer and to analyze whether measurement of TIMP-1 in tumor extracts added prognostic information to that obtained from measurements of urokinase-type plasminogen activator and plasminogen activator inhibitor type 1 (PAI-1). An established sandwich enzyme-linked immunosorbent assay was thoroughly validated for the measurement of total TIMP-1 in tumor tissue extracts and used to determine levels of total TIMP-1 in 341 detergent-extracted tumor tissue samples from patients with primary breast cancer. The median age of the patients was 56 years (range, 29-75 years), and 164 were lymph node-negative, and 177 were lymph node-positive. The median follow-up time of the patients was 8.5 years (range, 7.3-11.3 years), and during follow-up 153 patients experienced recurrence of disease, and 136 patients died. In univariate survival analysis, we found a significant association between tumor tissue TIMP-1 level and both shorter recurrence-free survival (p = 0.0004) and shorter overall survival (p = 0.03). In multivariate survival analysis, higher tumor tissue TIMP-1 levels significantly and independently predicted shorter recurrence-free survival (p < 0.05, hazard ratios >1, comparing quartiles II-IV with I). In addition, we found that measurement of TIMP-1 levels added prognostic information to that obtained from measurement of PAI-1. In conclusion, high levels of TIMP-1 in tumor tissue extracts are significantly associated with a poor prognosis in patients with primary breast cancer. Furthermore TIMP-1 adds prognostic information to that obtained from PAI-1. However, further validation in independent data sets is needed.     

The plasminogen activator inhibitor PAI-1 controls in vivo tumor vascularization by interaction with proteases, not vitronectin. Implications for antiangiogenic strategies

The plasminogen (Plg)/plasminogen activator (PA) system plays a key role in cancer progression, presumably via mediating extracellular matrix degradation and tumor cell migration. Consequently, urokinase-type PA (uPA)/plasmin antagonists are currently being developed for suppression of tumor growth and angiogenesis. Paradoxically, however, high levels of PA inhibitor 1 (PAI-1) are predictive of a poor prognosis for survival of patients with cancer. We demonstrated previously that PAI-1 promoted tumor angiogenesis, but by an unresolved mechanism. We anticipated that PAI-1 facilitated endothelial cell migration via its known interaction with vitronectin (VN) and integrins. However, using adenoviral gene transfer of PAI-1 mutants, we observed that PAI-1 promoted tumor angiogenesis, not by interacting with VN, but rather by inhibiting proteolytic activity, suggesting that excessive plasmin proteolysis prevents assembly of tumor vessels. Single deficiency of uPA, tissue-type PA (tPA), uPA receptor, or VN, as well as combined deficiencies of uPA and tPA did not impair tumor angiogenesis, whereas lack of Plg reduced it. Overall, these data indicate that plasmin proteolysis, even though essential, must be tightly controlled during tumor angiogenesis, probably to allow vessel stabilization and maturation. These data provide insights into the clinical paradox whereby PAI-1 promotes tumor progression and warrant against the uncontrolled use of uPA/plasmin antagonists as tumor angiogenesis inhibitors.     

Long-term follow-up confirms prognostic impact of PAI-1 and cathepsin D and L in primary breast cancer

After long-term follow-up, the prognostic impact of the following proteolytic factors associated with tumor invasion and metastasis was evaluated in 276 primary breast cancer patients: uPA (urokinase-type plasminogen activator), PAI-1 (uPA inhibitor type 1), and cathepsins B, D and L. The median follow-up of patients still alive at the time of analysis was 109 months. To date 119 patients (43%) have relapsed and 117 (42%) have died. Antigen levels of uPA and PAI-1 were determined by ELISA in detergent extracts; cathepsin B, D, and L content was determined in cytosol fractions of the primary tumor: cathepsin D by ELSA and cathepsin B and L by ELISA. In multivariate analysis (Cox model) for disease-free survival (DFS), lymph node status (p < 0.001; RR = 3.8), cathepsin L (p < 0.001; RR = 2.6) and PAI-1 (p = 0.027; RR = 1.7) were significant factors in all patients. In addition to these factors, grading was significant for overall survival (OS). In another multivariate approach, CART (Classification And Regression Trees) analysis, lymph node status (p < 0.001) turned out to be the strongest discriminator for patients at high risk of relapse. In the node-negative patient subset, PAI-1 was the strongest risk group discriminator (p < 0.001): in this subset, patients with low levels of both PAI-1 and cathepsin D had a very low relapse rate of only 3.2% compared to 39% in the remaining node-negative patients. In node-positive patients cathepsin L gave the best risk group assessment (p = 0.001). In conclusion, tumor-associated PAI-1 and cathepsins D and L provide significant, statistically independent prognostic information for DFS and OS in primary breast cancer, even after a median follow-up period of almost 10 years.     

Transforming growth factor beta1 stimulates urokinase plasminogen activator system on prostate cancer cells

The effect of TGFbeta1 on the proliferation and plasminogen activator system (PA) of two prostate carcinoma cell lines, PC3 and DU145, was investigated. PA, particularly urokinase plasminogen activator (uPA), has been implicated in extracellular proteolysis, local invasiveness, metastatic spread and angiogenesis. High levels of uPA and plasminogen activator inhibitor-1 (PAI-1) correlate with poor prognosis in several cancers. TGFbeta1 had no significant effect on the proliferation of either cell line. TGFbeta1 increased the production of uPA in PC3 and DU145 cells. Despite the very low PAI-1 protein levels in both cell lines, TGFbeta1 treatment resulted in a remarkable increase in PAI-1 secretion. PAI-2 protein was also increased by 59% in the PC3 cells. A divergent effect of TGFbeta1 on the uPA enzyme activity was observed (28% decrease in PC3 and 131% increase in DU145 cells). Overall, TGFbeta1 treatment did not affect the invasion of reconstituted basement membrane of PC3 cells. In addition to the uPA:PAI-1 ratio, the presence of PAI-2 may be an important factor in the determination of metastatic sites for prostate cancer cells. In conclusion, the potential contribution of TGFbeta1 to tumor invasion may be considered as positive, based on both loss of growth inhibition and stimulation of components of the invasive system of prostate carcinoma.     

Prognostic value of plasminogen activator inhibitors in breast cancer

The prognosis of cancer is primarily dependent on its potential to invade and metastasize. Data from both preclinical and clinical studies strongly suggest that serine proteases, as well as their inhibitors and receptor, play a central role in the processes leading to metastasis. We therefore investigated the prognostic value of plasminogen activator inhibitors type 1 (PAI-1) and type 2 (PAI-2) and the combination of both inhibitors in 332 patients with operable breast cancer. PAI-1 and PAI-2 content was measured in the primary tumor cytosols using an enzyme-linked immunosorbent assay. For PAI-1 the median value (3.9 ng/mg protein) was used as cutoff, while the optimized cutoff for PAI-2 (6.5 ng/mg protein) was obtained using the log-rank statistic. After a median follow-up of 46 months 96 (29%) patients relapsed. In univariate analysis patients with a high PAI-1 or a low PAI-2 content had an increased risk of relapse. The difference was statistically significant for PAI-1 (p<0.0001) and almost statistically significant for PAI-2 (p=0.057). Stage, tumor size, differentiation grade, lymph node status and hormone receptor status also showed significant univariate impact on disease-free survival (DFS). In multivariate analysis (Cox model) PAI-1 (p<0.0001, RR=2.78), PAI-2 (p=0.0075, RR=2.17), UICC stage (p=0.0014, RR=2.2), differentiation grade (p=0.0097, RR=1.91) and nodal status (p<0.0001, RR=2.9) retained their significance. When both inhibitors were combined the worst prognosis was observed in patients with simultaneous high PAI-1 and low PAI-2 levels, whereas low PAI-1 in combination with high PAI-2 values indicated a very favorable prognosis. In conclusion, our study showed that both PAI-1 and PAI-2 had independent prognostic value in breast cancer. Combination of both inhibitors further improved the differentiation of patients with respect to prognosis.     

uPA、PAI-1的表达和MVD计数与浸润性乳腺癌侵袭性的关系

目的：探讨尿激酶型纤溶酶原激活剂（uPA）、纤溶酶原激活物抑制剂（PAI-1）的表达和血管形成与浸润性乳腺癌侵袭性的关系。方法：应用免疫组化SP法检测80例浸润性乳腺癌、20例良性乳腺肿瘤组织中uPA、PAI-1的表达情况并进行微血管计数。结果：uPA和PAI-1在浸润性乳腺癌组的阳性表达显著高于良性肿瘤组,且其高表达率与乳腺癌的临床病理参数密切相关（P〈0.05）;微血管计数在乳腺癌组和良性肿瘤组分别为30.87±7.64、20.28±8.72,两组比较有显著性差异（P〈0.01）。uPA与PAI-1在浸润性乳腺癌中的表达呈正相关（P〈0.05）。结论：uPA、PAI-1的高表达与浸润性乳腺癌的浸润、转移相关,uPA、PAI-1的高表达和MVD计数可作为评价浸润性乳腺癌侵袭性、评估预后和确定治疗方案的生物学指标。     

Prognostic significance of plasminogen activator inhibitor-1 in breast cancer, with special emphasis on locoregional recurrence-free survival

The independent prognostic value of protease uPA and its inhibitor PAI-1 for survival in breast cancer patients is firmly established. However, there is very little data on the prognostic value of serine proteases and their inhibitors for locoregional recurrence in breast cancer. The prognostic value of PAI-1 for local control in a group of 766 patients treated at our institute with either breast conserving treatment or modified radical mastectomy was evaluated. The locoregional recurrence-free survival (LRFS) of patients with PAI-1 values above the median value was significantly worse than that of patients with PAI-1 values below the median value (log-rank; p=0.0078). In multivariate analysis PAI-1 levels proved to be of independent statistical significance for LRFS (p=0.0401, relative risk 2.28, 95% confidence interval 1.04-5.02). The independent prognostic value of PAI-1 for metastasis-free survival and overall survival was also confirmed. In addition, our data suggest that PAI-1 antigen levels in tumor tissue might be of prognostic value for survival after locoregional recurrence (log-rank; p=0.0618). According to our findings, PAI-1 levels could be used as a biological marker that could facilitate the identifation of patients with a higher risk of local relapse already at the time of primary treatment. These patients should then be offered more aggressive treatment.     

Tumor-biological factors uPA and PAI-1 as stratification criteria of a multicenter adjuvant chemotherapy trial in node-negative breast cancer

In axillary node-negative primary breast cancer, 70% of the patients will be cured by locoregional treatment alone. Therefore, adjuvant systemic therapy is only needed for those 30% of node-negative patients who will relapse after primary therapy and eventually die of metastases. Traditional histomorphological and clinical factors do not provide sufficient information to allow accurate risk group assessment in order to identify node-negative patients who might benefit from adjuvant systemic therapy. In the last decade various groups have reported a strong and statistically independent prognostic impact of the serine protease uPA (urokinase-type plasminogen activator) and its inhibitor PAI-1 (plasminogen activator inhibitor type 1) in node-negative breast cancer patients. Based on these data, a prospective multicenter therapy trial in node-negative breast cancer patients was started in Germany in June 1993, supported by the German Research Association (DFG). Axillary node-negative breast cancer patients with high levels of either or both proteolytic factors in the tumor tissue were randomized to adjuvant CMF chemotherapy versus observation only. Recruitment was continued until the end of 1998, by which time 684 patients had been enrolled. Since then, patients have been followed up in order to assess the value of uPA and PAI-1 determination as an adequate selection criterion for adjuvant chemotherapy in node-negative breast cancer patients. This paper reports on the rationale and design of this prospective multicenter clinical trial, which may have an impact on future policies in prognosis-oriented treatment strategies.     

Prognostic and predictive value of the urokinase-type plasminogen activator (uPA) and its inhibitors PAI-1 and PAI-2 in operable breast cancer

The present study on the prognostic and predictive value of serine proteases was conducted in 460 early breast cancer patients mostly treated with some kind of adjuvant systemic therapy: 156 received chemotherapy, 141 hormone therapy and 111 a combination of both. Already in univariate analysis PAI-1 was the only proteolytic factor with a significant impact on DFS, which was retained in multivariate analysis (p = 0.020); PAI-2 showed borderline significance in univariate analysis (p = 0.0503) and uPA did not present as a significant prognostic factor for DFS in our patient series. In a separate univariate analysis of DFS on patient subgroups defined by adjuvant systemic therapy, a higher risk of relapse associated with higher uPA and PAI-1 levels was found in the subgroup of patients who did not receive any treatment; this difference did not reach the level of significance, probably due to the small number (n = 52) of patients in this group (HR 1.37; p = 0.71 and HR 2.14; p = 0.321, respectively). A higher risk of relapse was also found in the subgroup of patients treated with adjuvant chemotherapy (HR 1.44; p = 0.381 and HR 2.48; p = 0.003, respectively). In contrast, the bad prognostic impact of high uPA and PAI-1 levels was lost in the subgroup of patients treated with adjuvant hormone therapy (HR 0.79; p = 0.693 and HR 0.26; p = 0.204, respectively). The same observations were made for the uPA/PAI-1 combination. Our study confirmed the prognostic value of serine proteases in early breast cancer. In addition, it pointed to a possible predictive value of these tumor markers for response to adjuvant hormone therapy with tamoxifen, which should be confirmed in further studies.     

Expression of active plasminogen activator inhibitor-1 reduces cell migration and invasion in breast and gynecological cancer cells

Urokinase-type (uPA) plasminogen activator is regulated by serine protease inhibitors (serpins), especially plasminogen activator inhibitor-1 (PAI-1). In many cancers, uPA and PAI-1 contribute to the invasive phenotype. We examined the in vitro migration and invasive capabilities of breast, ovarian, endometrial, and cervical cancer cell lines compared to their plasminogen activator system profiles. We then overexpressed active wild-type PAI-1 and an inactive "substrate" P14 form of PAI-1 (T333R) using stable transfection and adenoviral gene delivery. We also upregulated endogenous uPA and PAI-1 in these cells by treatment with transforming growth factor-beta. Some breast and ovarian cancer cell lines with natural expression of uPA, PAI-1, and urokinase receptor showed substantial migration and invasion compared to other cell lines that lack expression of these proteins. However, overexpression of active wild-type PAI-1, but not P14-PAI-1 (T333R), in these cell lines showed reduced migration and invasion. Since vitronectin binding by both forms of PAI-1 is equivalent, these results imply that PAI-1-vitronectin interactions are less critical in altering migration and invasion. Our results show that the in vitro migratory and invasive phenotype in these breast and ovarian cancer cell lines is reduced by active PAI-1 due to its ability to inhibit plasminogen activation.     

uPA and PAI-1-Related Signaling Pathways Differ between Primary Breast Cancers and Lymph Node Metastases

The supporting role of urokinase-type plasminogen activator (uPA) and its inhibitor plasminogen activator inhibitor 1 (PAI-1) in migration and invasion is well known. In addition, both factors are key components in cancer cell-related signaling. However, little information is available for uPA and PAI-1-associated signaling pathways in primary cancers and corresponding lymph node metastases. The aim of this study was to compare the expression of uPA and PAI-1-associated signaling proteins in 52 primary breast cancers and corresponding metastases. Proteins were extracted from formalin-fixed paraffin-embedded tissue samples of the primary tumors and metastases. Protein lysates were subsequently analyzed by reverse phase protein array for the expression of members of the PI3K/AKT (FAK, GSK3-β, ILK, pGSK3-β, PI3K, and ROCK) and the MAPK pathways (pp38, pSTAT3, and p38). A solid correlation of uPA expression existed between primary tumors and metastases, whereas PAI-1 expression did not significantly correlate between them. The correlations of uPA and PAI-1 with signaling pathways found in primary tumors did not persist in metastases. Analysis of single molecules revealed that some correlated well between tumors and metastases (FAK, pGSK3-β, ILK, Met, PI3K, ROCK, uPA, p38, and pp38), whereas others did not (PAI-1 and GSK3-β). Whether the expression of a protein correlated between tumor and metastasis or not was independent of the pathway the protein is related to. These findings hint at a complete deregulation of uPA and PAI-1-related signaling in metastases, which might be the reason why uPA and PAI-1 reached clinical relevance only for lymph node-negative breast cancer tissues.     

Structural basis for recognition of urokinase-type plasminogen activator by plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1), together with its physiological target urokinase-type plasminogen activator (uPA), plays a pivotal role in fibrinolysis, cell migration, and tissue remodeling and is currently recognized as being among the most extensively validated biological prognostic factors in several cancer types. PAI-1 specifically and rapidly inhibits uPA and tissue-type PA (tPA). Despite extensive structural/functional studies on these two reactions, the underlying structural mechanism has remained unknown due to the technical difficulties of obtaining the relevant structures. Here, we report a strategy to generate a PAI-1·uPA(S195A) Michaelis complex and present its crystal structure at 2.3-Å resolution. In this structure, the PAI-1 reactive center loop serves as a bait to attract uPA onto the top of the PAI-1 molecule. The P4–P3′ residues of the reactive center loop interact extensively with the uPA catalytic site, accounting for about two-thirds of the total contact area. Besides the active site, almost all uPA exosite loops, including the 37-, 60-, 97-, 147-, and 217-loops, are involved in the interaction with PAI-1. The uPA 37-loop makes an extensive interaction with PAI-1 β-sheet B, and the 147-loop directly contacts PAI-1 β-sheet C. Both loops are important for initial Michaelis complex formation. This study lays down a foundation for understanding the specificity of PAI-1 for uPA and tPA and provides a structural basis for further functional studies.     

Altered expression of urokinase-type plasminogen activator and plasminogen activator inhibitor in high-risk soft tissue sarcomas

In recent years, classification of soft-tissue sarcomas (STS) has improved with cytogenetic analyses, but their clinical behavior is still not easily predictable. The aim of this study was to detect alterations in the urokinase-type plasminogen system, involved in tumor growth and invasion, by comparing mRNA levels of its components with those of paired normal tissues, and relating them with patient clinical course. Real-time PCR was performed on human STS cell lines and tissues from highly malignant STS, including leiomyosarcomas and malignant fibrous histiocytomas, to evaluate the expression of urokinase-type plasminogen activator (uPA), uPA receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1). Immunohistochemistry of gene products was also performed. Median mRNA values of all genes studied were higher in tumors than in paired normal tissues. In agreement with data on STS cell lines, significant up-regulation for uPA and PAI-1 genes compared to reference values was seen. Moreover, different levels of expression were related to histotype and metastatic phenotype. There was accordance between uPA mRNA and protein expression, while immunodetection of PAI-1 product was weak and scattered. Clearly, the controversial role of PAI-1 protein requires further biological analyses, but evident involvement of uPA/PAI-1 gene overexpression in STS malignancy may highlight a molecular defect useful in discriminating STS high-risk patients.     

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

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

Expression of plasminogen activator and plasminogen activator inhibitor mRNA in human fibroblasts grown on different substrates

mRNA levels for urokinase type plasminogen activator (uPA), tissue type plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator inhibitor-2 (PAI-2) were examined in human diploid (neonatal foreskin) fibroblasts grown in 200-ml microcarrier suspension culture. Four different substrates were used. These included gelatin-coated polystyrene plastic, DEAE-dextran, glass-coated polystyrene plastic and uncoated polystyrene plastic. Our previous studies have shown that culture fluids from diploid fibroblasts grown on DEAE-dextran contained higher levels of plasminogen-dependent fibrinolytic activity than culture fluids from the same cells grown on other substrates. The increased plasminogen activator activity was due largely to elevated amounts of tPA (In Vitro Cell. Develop. Biol. 22: 575–582, 1986). The present study shows that there is a corresponding elevation of tPA mRNA in diploid fibroblasts cultured on DEAE-dextran relative to the other substrates. There does not appear to be any difference in uPA mRNA or in mRNA for PAI-1 or PAI-2 produced by the same cells on the four substrates. These data suggest that the influence of the substrate on plasminogen activator production is mediated at the genetic level.     

Tissue plasminogen activator and plasminogen activator inhibitor 1 contribute to sonic hedgehog-induced in vitro cerebral angiogenesis

The molecular mechanisms underlying cerebral angiogenesis have not been fully investigated. Using primary mouse brain endothelial cells (MBECs) and a capillary-like tube formation assay, we investigated whether the sonic hedgehog (Shh) signaling pathway is coupled with the plasminogen/plasmin system in mediating cerebral angiogenesis. We found that incubation of MBECs with recombinant human Shh (rhShh) substantially increased the tube formation in naïve MBECs. This was associated with increases in tissue plasminogen activator (tPA) activation and reduction of plasminogen activator inhibitor 1 (PAI-1). Blockage of the Shh pathway with cyclopamine abolished the induction of tube formation and the effect of rhShh on tPA and PAI-1. Addition of PAI-1 reduced rhShh-augmented tube formation. Genetic ablation of tPA in MBECs impaired tube formation and downregulated of vascular endothelial growth factor (VEGF) and angiopoietin 1 (Ang1). Addition of rhShh to tPA−/− MBECs only partially restored the tube formation and upregulated Ang1, but not VEGF, although rhShh increased VEGF and Ang1 expression on wild-type MBECs. Complete restoration of tube formation in tPA−/− MBECs was observed only when both exogenous Shh and tPA were added. The present study provides evidence that tPA and PAI-1 contribute to Shh-induced in vitro cerebral angiogenesis.     

Increased vascular endothelial growth factor may account for elevated level of plasminogen activator inhibitor-1 via activating ERK1/2 in keloid fibroblasts

Keloids are characterized as an "overexuberant" healing response in which disequilibrium between production and catabolism of extracellular matrix (ECM) occurs. Previous studies from our laboratory and others demonstrate an intrinsically higher level of plasminogen activator inhibitor-1 (PAI-1) expression in keloid tissues and cultured fibroblasts compared with normal bordering skin. These findings support the concept that an altered balance of activator and inhibitor activities in the plasminogen system, in particular, an overexpression of PAI-1, may partly contribute to keloid formation and tissue fibrosis. Vascular endothelial growth factor (VEGF) has been implicated as a critical factor in regulating angiogenesis and inflammation under both physiological and pathological conditions. This study was designed to assess whether VEGF plays a role in keloid fibrosis. We report that VEGF was expressed at higher levels in keloid tissues and their derived fibroblasts compared with their associated normal skin. We have further demonstrated that VEGF stimulated the expression of PAI-1, but not urokinase plasminogen activator (uPA), in keloid fibroblasts at both mRNA and protein levels, in a dose- and time-dependent manner. However, treatment of normal skin fibroblasts with VEGF exerted little effects on PAI-1 gene expression. Additionally, we have characterized for the first time that the extracellular signal-regulated kinase (ERK)1/2 signaling pathway is mainly involved in VEGF-induced PAI-1 expression and have demonstrated its potential as a target molecule for modulation of scar fibrosis. These findings suggest that VEGF may play an important role in keloid formation by altering ECM homeostasis toward a state of impaired degradation and excessive accumulation. urokinase plasminogen activator; extracellular matrix; fibrosis