Urokinase plasminogen activator as a predictor of aggressive disease in breast cancer

The Role of Fibrinolytic System in Health and Disease

The fibrinolytic system is composed of the protease plasmin, its precursor plasminogen and their respective activators, tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), counteracted by their inhibitors, plasminogen activator inhibitor type 1 (PAI-1), plasminogen activator inhibitor type 2 (PAI-2), protein C inhibitor (PCI), thrombin activable fibrinolysis inhibitor (TAFI), protease nexin 1 (PN-1) and neuroserpin. The action of plasmin is counteracted by α2-antiplasmin, α2-macroglobulin, TAFI, and other serine protease inhibitors (antithrombin and α2-antitrypsin) and PN-1 (protease nexin 1). These components are essential regulators of many physiologic processes. They are also involved in the pathogenesis of many disorders. Recent advancements in our understanding of these processes enable the opportunity of drug development in treating many of these disorders.

The Role of MMP8 in Cancer: A Systematic Review

Matrix metalloproteinases (MMPs) have traditionally been considered as tumor promoting enzymes as they degrade extracellular matrix components, thus increasing the invasion of cancer cells. It has become evident, however, that MMPs can also cleave and alter the function of various non-matrix bioactive molecules, leading to both tumor promoting and suppressive effects. We applied systematic review guidelines to study MMP8 in cancer including the use of MMP8 as a prognostic factor or as a target/anti-target in cancer treatment, and its molecular mechanisms. A total of 171 articles met the inclusion criteria. The collective evidence reveals that in breast, skin and oral tongue cancer, MMP8 inhibits cancer cell invasion and proliferation, and protects patients from metastasis via cleavage of non-structural substrates. Conversely, in liver and gastric cancers, high levels of MMP8 worsen the prognosis. Expression and genetic alterations of MMP8 can be used as a prognostic factor by examination of the tumor and serum/plasma. We conclude, that MMP8 has differing effects on cancers depending on their tissue of origin. The use of MMP8 as a prognostic factor alone, or with other factors, seems to have potential. The molecular mechanisms of MMP8 in cancer further emphasize its role as an important regulator of bioactive molecules.

High Levels of Cathepsin B Predict Poor Outcome in Patients with Breast Cancer

Cathepsin B (CB) is a thiol-stimulated protease implicated in cancer invasion and metastasis. Other proteases involved in cancer spread such as urokinase-type plasminogen activator (uPA) and cathepsin D have previously been shown to be prognostic markers in breast cancer. CB was assayed by ELISA in 193 patients with primary breast cancer. CB levels were significantly higher in both primary and metastatic breast tumors than in fibroadenomas (p=0.0001). In the primary carcinomas, CB levels showed no significant correlation with either nodal status, tumor size or estrogen receptor (ER) status. Patients with primary breast cancers containing high levels of CB had a significantly shorter disease-free interval (p=0.01, chi-square=6.61) and overall survival (p=0.014, chi-square=6.08) than patients with low levels of the protease. However, in multivariate analysis, using nodal status, tumor size, ER status and urokinase plasminogen activator (uPA), CB was not an independent prognostic marker. In contrast, nodal status, ER status and uPA were prognostic in multivariate analysis. In conclusion, CB, like certain other proteases implicated in cancer metastasis, correlates with poor outcome in patients with breast cancer. These results thus support the evidence from model systems linking CB to cancer spread. Inhibition of CB expression or activity might therefore be exploited for anti-metastatic therapies.

uPAR enhances malignant potential of triple-negative breast cancer by directly interacting with uPA and IGF1R

BACKGROUND

Due to lack of a targeted therapy for the triple-negative breast cancer (TNBC) patients, it is important to explore this aggressive breast cancer type in more detail and to establish novel therapeutic approaches. TNBC is defined negative for the protein expression of oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2). One prominent feature of this cancer type is the frequent overexpression of major components of the urokinase-type plasminogen activator system (uPAS) including uPA, its receptor uPAR and the inhibitor PAI-1, which may be valuable as therapeutic targets.

METHODS

Direct interactions of uPAR with interactors were demonstrated by immunoprecipitations and proximity ligation assays. For stable knockdowns of target proteins, lentiviral vectors were used and the effects were analysed by immunoblottings and using in vitro cell viability, migration and invasion assays. Immunohistochemical and statistical analyses of biomarkers and clinical parameters were conducted in a TNBC cohort (n = 174).

RESULTS

Direct tumour-promoting interactions of uPAR with uPA and the insulin-like growth factor receptor 1 (IGF1R) were shown in TNBC cells and these interactions were significantly reduced (p = 0.001) when uPAR was downregulated. The combined knockdown of uPAR and uPA or IGF1R additively and significantly reduced cell viability, migration and invasion of the model cell lines. In TNBC tissue, the complexes formed by uPAR with uPA or with IGF1R significantly correlated with the histological grade (p = 0.0019) as well as with cathepsin B and D (p ≤ 0.0001) that are implicated in cell invasion and metastasis.

CONCLUSIONS

Our outcomes show that not only overexpressed biomarkers promote tumourigenesis, but rather their interactions further potentiate tumour progression. This study emphasises the potential of combined approaches targeting uPAR and its interactors with regard to an improved therapy of TNBC.

uPA and PAI-1 as biomarkers in breast cancer: validated for clinical use in level-of-evidence-1 studies

Urokinase plasminogen activator (uPA) is an extracellular matrix-degrading protease involved in cancer invasion and metastasis, interacting with plasminogen activator inhibitor-1 (PAI-1), which was originally identified as a blood-derived endogenous fast-acting inhibitor of uPA. At concentrations found in tumor tissue, however, both PAI-1 and uPA promote tumor progression and metastasis. Consistent with the causative role of uPA and PAI-1 in cancer dissemination, several retrospective and prospective studies have shown that elevated levels of uPA and PAI-1 in breast tumor tissue are statistically independent and potent predictors of poor patient outcome, including adverse outcome in the subset of breast cancer patients with lymph node-negative disease. In addition to being prognostic, high levels of uPA and PAI-1 have been shown to predict benefit from adjuvant chemotherapy in patients with early breast cancer. The unique clinical utility of uPA/PAI-1 as prognostic biomarkers in lymph node-negative breast cancer has been confirmed in two independent level-of-evidence-1 studies (that is, in a randomized prospective clinical trial in which the biomarker evaluation was the primary purpose of the trial and in a pooled analysis of individual data from retrospective and prospective studies). Thus, uPA and PAI-1 are among the best validated prognostic biomarkers currently available for lymph node-negative breast cancer, their main utility being the identification of lymph node-negative patients who have HER-2-negative tumors and who can be safely spared the toxicity and costs of adjuvant chemotherapy. Recently, a phase II clinical trial using the low-molecular-weight uPA inhibitor WX-671 reported activity in metastatic breast cancer.

Targeting fibroblast growth factor receptors blocks PI3K/AKT signaling, induces apoptosis, and impairs mammary tumor outgrowth and metastasis

Members of the fibroblast growth factor receptor (FGFR) family have essential roles in normal physiology and in cancer where they control diverse processes. FGFRs have been associated with breast cancer development. Thus, models to study the role of FGFR in breast cancer and their targeting potential are important. We present an in vitro and in vivo analysis of FGFRs in the breast cancer model cell lines 67NR and 4T1. We show that both tumor cell lines coexpress FGFRs and ligands and display autocrine FGFR signaling activity. Fibroblast growth factor receptor substrate 2 (FRS2), a downstream mediator of FGFR, is constitutively tyrosine phosphorylated and multiple signaling pathways are active. Treatment of 67NR and 4T1 cultures with TKI258, an FGFR tyrosine kinase inhibitor (TKI), caused a rapid decrease in FRS2 phosphorylation; decreased the activity of extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and phospholipase Cgamma; and blocked proliferation of both tumor lines. Furthermore, TKI258 induced 4T1 apoptotic cell death via blockade of the phosphoinositide 3-kinase/AKT pathway. In vivo, one dose of TKI258 rapidly lowered FRS2 phosphorylation and ERK1/2 and AKT activity in mammary tumors. Long-term TKI258 treatment of 4T1 tumor- and 67NR tumor-bearing mice had a significant effect on primary tumor outgrowth and 4T1 tumor-induced lung metastases. A microarray analysis was carried out to identify targets with roles in TKI258 antitumor activity and potential prognostic markers in human breast tumors. Of interest are the downregulated matrix metalloproteases (MMP), in particular MMP9, which is essential for metastatic spread of 4T1 tumors.

The activities of progesterone receptor isoform A and B are differentially modulated by their ligands in a gene-selective manner

It is known that progesterone receptor (PR) isoform A (PR-A) and isoform B (PR-B) may mediate different effects of progesterone. The objective of this study was to determine if the functions of PR isoforms also vary in response to different PR modulators (PRM). The effects of 7 synthetic PRM were tested in MDA-MB-231 cells engineered to express PR-A, PR-B, or both PR isoforms. The effects of progesterone were similar in cells expressing PR-A or PR-B in which it inhibited growth and induced focal adhesion. On the other hand, synthetic PRM modulated the activity of the PR isoforms differently. RU486, CDB4124, 17alpha-hydroxy CDB4124 and VA2914 exerted agonist activities on cell growth and adhesion via PR-B. Via PR-A, however, these compounds displayed agonist effect on cell growth but induced stellate morphology which was distinct from the agonist's effect. Their dual properties via PR-A were also displayed at the gene expression level: the compounds acted as agonists on cell cycle genes but exhibited antagonistic effect on cell adhesion genes. Introduction of ERalpha by adenoviral vector to these cells did not change PR-A or PR-B mediated effect of PRM radically, but it causes significant cell rounding and modified the magnitudes of the responses to PRM. The findings suggest that the activities of PR isoforms may be modulated by different PRM through gene-specific regulatory mechanisms. This raises an interesting possibility that PRM may be designed to be PR isoform and cellular pathway selective to achieve targeted therapy in breast cancer.

The fibrinolytic system facilitates tumor cell migration across the blood-brain barrier in experimental melanoma brain metastasis

BACKGROUND

Patients with metastatic tumors to the brain have a very poor prognosis. Increased metastatic potential has been associated with the fibrinolytic system. We investigated the role of the fibrinolytic enzyme plasmin in tumor cell migration across brain endothelial cells and growth of brain metastases in an experimental metastatic melanoma model.

METHODS

Metastatic tumors to the brain were established by direct injection into the striatum or by intracarotid injection of B16F10 mouse melanoma cells in C57Bl mice. The role of plasminogen in the ability of human melanoma cells to cross a human blood-brain barrier model was studied on a transwell system.

RESULTS

Wild type mice treated with the plasmin inhibitor epsilon-aminocaproic acid (EACA) and plg-/- mice developed smaller tumors and survived longer than untreated wild type mice. Tumors metastasized to the brain of wild type mice treated with EACA and plg-/- less efficiently than in untreated wild type mice. No difference was observed in the tumor growth in any of the three groups of mice. Human melanoma cells were able to cross the human blood-brain barrier model in a plasmin dependent manner.

CONCLUSION

Plasmin facilitates the development of tumor metastasis to the brain. Inhibition of the fibrinolytic system could be considered as means to prevent tumor metastasis to the brain.

Invasion and metastasis markers in cancers

Over 90% of all adults human cancers are of epithelial origin comprising mainly of skin and aero-digestive tract cancers. A significant proportion of our discipline's workload consists of management of these cancers. This review article is to provide clinicians with a summary of the current research findings in invasion and metastasis of epithelial cancers and the translation of some of this information to clinical use particularly related to skin and head and neck cancers (HNSCC). Metastasis is the leading cause of death in cancer patients. Although surgical resection of isolated metastases is beneficial for some patients, the overall efficacy of surgery, chemotherapy or radiotherapy is limited. Clearly, with today's advances in surgery a majority of these primary cancers are resectable and a cure attainable if surgeons could control or inhibit metastasis.

MMP-10 is overexpressed, proteolytically active, and a potential target for therapeutic intervention in human lung carcinomas

Matrix metalloproteinase (MMP)-mediated degradation of the extracellular matrix is a major factor for tumor development and expansion. This study analysed MMP-10 protein expression and activity in human lung tumors of various grade, stage, and type to address the relationship between MMP-10 and tumor characteristics and to evaluate MMP-10 as a therapeutic target in non small cell lung carcinoma (NSCLC). Unlike the majority of MMPs, MMP-10 was located in the tumor mass as opposed to tumor stroma. MMP-10 protein was observed at low levels in normal human lung tissues and at significantly higher levels in all types of NSCLC. No correlation was observed between MMP-10 protein expression and tumor type, stage, or lymph node invasion. To discriminate between active and inactive forms of MMP-10 in samples of human NSCLC, we have developed an ex vivo fluorescent assay. Measurable MMP-10 activity was detected in 42 of 50 specimens of lung cancer and only 2 of 10 specimens of histologically normal lung tissue. No relationship was observed between MMP-10 activity levels and clinicopathologic characteristics. Our results suggest that MMP-10 is expressed and active at high levels in human NSCLC compared to normal lung tissues, and, as such, is a potential target for the development of novel therapeutics for lung cancer treatment.

Geldanamycins exquisitely inhibit HGF/SF-mediated tumor cell invasion

Induction of the urokinase-type plasminogen activator (uPA) by hepatocyte growth factor/scatter factor (HGF/SF) plays an important role in tumor cell invasion and metastasis that is mediated through the Met receptor tyrosine kinase. Geldanamycins (GA) are antitumor drugs that bind and inhibit HSP90 chaperone activity at nanomolar concentrations (nM-GAi) by preventing proper folding and functioning of certain oncoproteins. Previously, we have shown that a subset of GA derivatives exhibit exquisite potency, inhibiting HGF/SF-induced uPA-plasmin activation at femtomolar concentrations (fM-GAi) in canine MDCK cells. Here, we report that (1) inhibition of HGF/SF-induced uPA activity by fM-GAi is not uncommon, in that several human tumor glioblastoma cell lines (DBTRG, U373 and SNB19), as well as SK-LMS-1 human leiomyosarcoma cells are also sensitive to fM-GAi; (2) fM-GAi drugs only display inhibitory activity against HGF/SF-induced uPA activity (rather than basal activity), and only when the observed magnitude of uPA activity induction by HGF/SF is at least 1.5 times basal uPA activity; and (3) not only do fM-GAi derivatives strongly inhibit uPA activity but they also block MDCK cell scattering and in vitro invasion of human glioblastoma cells at similarly low drug concentrations. These effects of fM-GAi drugs on the Met-activated signaling pathway occur at concentrations well below those required to measurably affect Met expression or cell proliferation. We also examined the effect of Radicicol (RA), a drug with higher affinity than GA for HSP90. RA displays uPA activity inhibition at nanomolar levels, but not at lower concentrations, indicating that HSP90 is not likely the fM-GAi molecular target. Thus, we show that certain GA drugs (fM-GAi) in an HGF/SF-dependent manner block uPA-plasmin activation in tumor cells at femtomolar levels. This inhibition can also be observed in scattering and in vitro invasion assays. Our findings also provide strong circumstantial evidence for a novel non-HSP90 molecular target that is involved in HGF/SF-mediated tumor cell invasion.

Methylation status of uPA promoter as a molecular mechanism regulating prostate cancer invasion and growth in vitro and in vivo

Urokinase plasminogen activator (uPA) promotes tumor invasion and metastasis in several malignancies including prostate cancer, one of the most commonly detected male cancers that result in a high incidence of mortality. In the present study we have examined the differential regulation of uPA gene expression in different stages of prostate cancer by DNA methylation. We determined levels of uPA expression in normal prostate epithelial cells (PrEC) and in hormone-responsive (LNCaP) and -insensitive (PC-3) prostate cancer cell lines. We found that uPA is expressed only in the highly invasive PC-3 cells where the uPA promoter is unmethylated. The lack of uPA expression in PrEC and LNCaP cells, where uPA promoter is highly methylated, is due to suppression of uPA gene transcription by DNA methylation. Treatment of LNCaP cells with 5'-azacytidine, a potent demethylating agent, resulted in induction of uPA mRNA expression, uPA activity, and higher invasive capacity in vitro. Additionally, a marked increase in tumor volume was observed after inoculation of these cells into the flank of male BALB/c (nu/nu) mice. Collectively these studies have demonstrated that DNA methylation is the underlying molecular mechanism responsible for uPA gene silencing in normal and early stages of prostate cancer, which has a direct effect on tumor cell invasion and growth in vitro and in vivo.

Comparison of potential biological markers cathepsin B, cathepsin L, stefin A and stefin B with urokinase and plasminogen activator inhibitor-1 and clinicopathological data of breast carcinoma patients

Cysteine, serine and metalloproteinases and their respective inhibitors are involved in tumor cell invasion and may have prognostic value for the outcome of malignant disease. The aim of the study was to compare the expression of new potential biological tumor markers, the lysosomal cysteine proteinases and their endogenous inhibitors, with that of the serine proteinases and their inhibitors in breast cancinoma and to relate their levels to the clinicopathological factors of the disease. Enzyme-linked immunosorbent assays (ELISAs) were used to measure cysteine cathepsin B (CatB) and cathepsin L (CatL) and their inhibitors, stefin A (StA) and stefin B (StB), together with urokinase (u-PA) and plasminogen activator inhibitor-1 (PAI-1), in 150 cytosols of primary invasive breast carcinoma. A good correlation was found between the levels of the two cysteine proteinases but only a moderate one between those of the cysteine and serine proteinases. u-PA and PAI-1 levels correlated positively with histological grade and negatively with estrogen receptor (ER) status. PAI-1 correlated with most clinicopathological factors that indicate the progression of the disease, while cathepsins and stefins were independent of these factors. In the total group of patients, high u-PA and PAI-1 and low StB levels correlated significantly with shorter disease-free survival (DFS), while CatB, CatL and StA did not. In lymph node negative patients, high CatB and CatL were also associated with shorter DFS, while u-PA remained the most significant of all these biological markers. In conclusion, this retrospective study showed u-PA to be of better prognostic relevance than the cysteine proteinases, though CatB and CatL were relevant for prognosis in lymph node negative breast cancer patients.

Differential expression of c-jun and c-fos mRNAs in squamous cell carcinoma of the head and neck: associations with uPA, gelatinase B, and matrilysin mRNAs

BACKGROUND

Head and neck squamous cell carcinomas (HNSCC) are known for their invasive behavior. The invasiveness of these tumors requires proteases, some of which as urokinase-type plasminogen activator (uPA), gelatinase B and matrilysin are regulated through AP-1 dependent transcriptional mechanisms. AP-1 consists of several proteins, including those encoded by the proto-oncogenes c-jun and c-fos. The aim of this study was to: first, evaluate the expression levels of matrix metalloproteases (matrilysin and gelatinase B) and uPA mRNAs; second, examine whether these genes might be associated with c-jun and c-fos expression; third, examine the relationship between the expression of these genes and HNSCC clinico-pathological features.

METHODS

We have analyzed 38 HNSCC primary tumors and matched mucosa tissues for uPA, gelatinase B, matrilysin, c-fos, and c-jun by Northern-blot analysis.

RESULTS

uPA, gelatinase B, matrilysin, and c-jun mean levels were statistically higher in the tumors than in the normal adjacent mucosa, whereas no difference was found when c-fos mRNA values were compared, c-jun mRNA expression correlated directly with gelatinase B and matrilysin mRNA levels, but no association with uPA mRNA was observed, c-fos mRNA levels were not associated with the tested proteases, but low levels were determined in tumors from older patients who subsequently developed a 2(nd) tumor. No evidence of correlation between expression of uPA, matrilysin, and c-jun in tumors and clinico-pathological features was found. Gelatinase B mRNA high levels were associated to presence of cervical recurrences.

CONCLUSION

Expression of c-jun seems to be involved in the regulation of gelatinase B and matrilysin being not related to uPA. Lack of association with c-fos may indicate that other fos family members might play a role in the transcriptional activity of the analyzed proteases in HNSCC tumors.

Urokinase-receptor/integrin complexes are functionally involved in adhesion and progression of human breast cancer in vivo

Interactions between specific cell-surface molecules, which include the urokinase receptor (uPAR) and integrins, are crucial to processes of tumor invasion and metastasis. Here we demonstrate that uPAR and beta1-integrins may cluster at distinct sites at the cell surface of metastatic MDA-MB-231 breast cancer cells and form functional complexes. Attachment assays performed in the presence of a synthetic peptide (p25), which interferes with the formation of uPAR-integrin complexes, reveal that uPAR is able to regulate the adhesive function of integrins in breast cancer cells. On dissociation of the uPAR-integrin complexes by p25, tumor cell attachment to the extracellular matrix was either decreased (vitronectin) or increased (fibronectin). Moreover, the tumor cells display remarkable morphological changes when cultured on fibronectin in the continuous presence of p25, leading to increased cell spreading and attachment. In marked contrast to control conditions, increased cellular adhesion to fibronectin after p25 treatment was entirely beta1-integrin-mediated. The role of uPAR-integrin complexes in tumor progression was studied in an in vivo bone xenograft model. Stably transfected MDA-MB-231 cells that overexpress p25 showed a significant reduction in tumor progression in bone (P < or = 0.0001 versus mock-control). In line with these observations, continuous administration of p25 (25 microg/mouse/day, osmotic minipumps) for 28 days resulted in significantly reduced tumor progression of MDA-MB-231 cells in bone (P < or = 0.005) when compared to scrambled control peptide. In conclusion, our data demonstrate that uPAR can act as an adhesion receptor in breast cancer and is capable of regulating integrin function. Our findings strongly suggest that adhesive and proteolytic events are tightly associated in metastatic breast cancer cells and that functional integrin-uPAR complexes are involved in tumor progression in vivo.

Tumour progression and angiogenesis in bone metastasis from breast cancer: new approaches to an old problem

Breast cancer metastasizes frequently to the skeleton and causes considerable morbidity and deterioration of the quality of life. The clinical consequences of skeletal metastases are bone pain, pathological fractures, hypercalcaemia and nerve compression syndromes. From the moment breast cancer cells are located in the bone microenvironment, they may release factors which stimulate bone resorption and angiogenesis leading to growth of skeletal metastases and a subsequent selective increase in the attraction of new cancer cells to bone. In this review, emerging new concepts of breast cancer-bone interactions, in particular the involvement of angiogenesis, proteolysis and the role of cancer-induced bone resorption in skeletal metastasis are discussed. Better understanding of the processes involved in the metastasis of cancer cells to bone, local tumour growth and subsequent destruction of skeletal architecture can lead to optimal methods for the prevention and treatment of metastatic bone disease.

Urokinase plasminogen activator: a prognostic marker in multiple types of cancer

Urokinase plasminogen activator (uPA) is a serine protease causally involved in cancer invasion and metastasis. Consistent with its role in cancer spread, uPA has been shown to be a prognostic marker in a variety of malignancies, especially breast cancer. Approximately 20 different groups have shown that high levels of uPA in breast tumor tissue predict poor outcome. As a prognostic marker in breast cancer, uPA provides information that is independent of traditionally used factors such as tumor size, tumor grade, axillary node status and estrogen receptor status. Furthermore, uPA is prognostic in node-negative patients, and a clinical trial is currently under way to assess whether uPA and its inhibitor, plasminogen activator inhibitor-1, can differentiate between the majority of node-negative breast cancer patients who are cured by surgery from the minority who might benefit from adjuvant therapy. uPA is also prognostic in other malignancies, such as gastric, colorectal, esophageal, renal, endometrial, and ovarian cancers. uPA may thus be a prognostic indicator for multiple types of adenocarcinoma.

Transcriptional regulation of urokinase (uPA) gene expression in breast cancer cells: role of DNA methylation

Carcinoma of the breast is a leading hormone-dependent malignancy, resulting in a high rate of morbidity and mortality. During the complex multi-step process of tumor promotion, this common cancer is initiated as hormone-responsive (HR), non-metastatic cancer, followed by a gradual transition into a highly metastatic hormone-insensitive (HI) variety which lacks the functional estrogen receptor. This transition of cancer cells causes them to become refractory to hormonal treatment. Urokinase (uPA), a member of the serine protease family has been implicated in the progression of several malignancies including breast cancer. In the current study, we have examined the correlation between hormone sensitivity and uPA expression in HR normal mammary epithelial cells (HMEC) and in MCF-7 and T-47D breast cancer cell lines. Comparison was made with HI breast cancer cells MDA-231. uPA mRNA expression was seen only in the highly invasive, HI breast cancer cells MDA-231. Lack of uPA expression in HR normal (HMEC) and in minimally invasive, HR cells (MCF-7 and T-47D) was due to transcriptional suppression of uPA gene expression as determined by nuclear run-off assays. Since alteration of the DNA methylation status of CpG island in the 5' sequence of oncogenes and tumor suppressor genes has been demonstrated to change their expression, we examined DNA methylation as a potential molecular mechanism for regulating uPA gene transcription in these cancer cells. Southern blot analysis using methylation sensitive enzymes revealed that CpG island of uPA gene are methylated in HR, HMEC, MCF-7 and T-47D cells, whereas they are hypomethylated in HI and MDA-231 cells. Treatment of HR MCF-7 cells with cytosine DNA methyltransferase inhibitor 5' azacytidine caused a dose-dependent induction of uPA mRNA due to demethylation of the CpG island of the uPA gene which led to increased invasive ability of these HR cancer cells. Our results demonstrate that DNA methylation can regulate the transcription of the uPA gene to alter the invasive behaviour of these HR breast cancer cells.

Clinical relevance of the urokinase plasminogen activator system in breast cancer

Until recently clinical features and the hormone-receptor status were the only factors used to select systemic (adjuvant) treatment for breast cancer patients. Other biological factors are needed as well to predict the probability of relapse and response with more certainty. The uPA-system is such a prognostic and predictive factor in breast cancer. In this review, the results of research groups that have related relapse-free survival to the quantitative levels of uPA-system proteins and/or activities are discussed. Only studies that described the results from assays on cytosols or triton extracts of breast tumours were included. The levels of uPA-system proteins help to predict the probability of relapse and response, and knowledge of the expression levels of the various components of the uPA-system may lead to new treatment modalities targeted on specific properties of the uPA-system.

Prognosis and prediction of response in breast cancer: the current role of the main biological markers

In the medical literature there are frequently conflicting reports on the utility of biological tumour markers available in the clinical management of breast cancer. In this review we analyse current information on the relationships between the most widely investigated breast cancer biological markers including oestrogen and progesterone receptors, p53, Bcl-2, c-erbB-2, cyclin expression, proliferative activity, DNA ploidy and the urokinase plasminogen activation system, as well as their relevance to prognosis and response to clinical treatment. By biological prognostic indicator, we mean a marker that correlates with survival and disease-free survival; the term predictor marker indicates a marker that is capable of predicting tumour sensitivity or resistance to various therapies. Similarly to other authors' experiences, our analysis suggests that oestrogen receptors are weak prognostic indicators and good predictors of response to endocrine therapy. Furthermore, there are consistent data suggesting that proliferation indices are good indicators of prognosis, and that they are directly related to response to chemotherapy and closely related to response to hormonotherapy. On the contrary, there is no evidence or conflicting data for all of the other biological markers. These should be considered in the context of randomized trials in order to precisely define their prognostic and predictive roles. p53 and c-erbB-2 seem to be the most promising factors, but their use in routine practice still needs validation.