The urokinase-type plasminogen activator (u-PA) system consists of the serine proteinases plasmin and u-PA; the serpin inhibitors alpha2-anti-plasmin, PAI-1 and PAI-2; and the u-PA receptor (u-PAR). Two lines of evidence have strongly suggested an important and apparently causal role for the u-PA system in cancer metastasis: results from experimental model systems with animal tumor metastasis and the finding that high levels of u-PA, PAI-1 and u-PAR in many tumor types predict poor patient prognosis. We discuss here recent observations related to the molecular and cellular mechanisms underlying this role of the u-PA system. Many findings suggest that the system does not support tumor metastasis by the unrestricted enzyme activity of u-PA and plasmin. Rather, pericellular molecular and functional interactions between u-PA, u-PAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors and growth factors appear to allow temporal and spatial re-organizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. Differential expression of components of the system by cancer and non-cancer cells, regulated by paracrine mechanisms, appear to determine the involvement of the system in cancer cell-directed tissue remodeling. A detailed knowledge of these processes is necessary for utilization of the therapeutic potential of interfering with the action of the system in cancers.

The urokinase-type plasminogen activator system in cancer metastasis: a review

Integrin function is central to inflammation, immunity, and tumor progression. The urokinase-type plasminogen activator receptor (uPAR) and integrins formed stable complexes that both inhibited native integrin adhesive function and promoted adhesion to vitronectin via a ligand binding site on uPAR. Interaction of soluble uPAR with the active conformer of integrins mimicked the inhibitory effects of membrane uPAR. Both uPAR-mediated adhesion and altered integrin function were blocked by a peptide that bound to uPAR and disrupted complexes. These data provide a paradigm for regulation of integrins in which a nonintegrin membrane receptor interacts with and modifies the function of activated integrins.

https://science.sciencemag.org/content/sci/273/5281/1551.full.pdf

Regulation of Integrin Function by the Urokinase Receptor

Acquisition of invasive/metastatic potential through protease expression is an essential event in tumor progression. High levels of components of the plasminogen activation system, including urokinase, but paradoxically also its inhibitor, plasminogen activator inhibitor 1 (PAI1), have been correlated with a poor prognosis for some cancers. We report here that deficient PAI1 expression in host mice prevented local invasion and tumor vascularization of transplanted malignant keratinocytes. When this PAI1 deficiency was circumvented by intravenous injection of a replication-defective adenoviral vector expressing human PAI1, invasion and associated angiogenesis were restored. This experimental evidence demonstrates that host-produced PAI is essential for cancer cell invasion and angiogenesis.

Absence of host plasminogen activator inhibitor 1 prevents cancer invasion and vascularization

Identification of the urokinase receptor as an adhesion receptor for vitronectin.

Fibroblast activation protein, a dual specificity serine protease expressed in reactive human tumor stromal fibroblasts.

We have studied the prognostic value of urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), and type 1 plasminogen activator inhibitor (PAI-1) in tumor extracts from 84 patients with squamous cell lung carcinoma and 38 patients with large cell lung carcinoma, measuring each molecule with sandwich enzyme-linked immunosorbent assays. High uPAR levels were significantly associated with short overall survival in patients with squamous cell lung carcinomas when the median value was used as a cutoff point (P = 0.038), while no statistically significant prognostic impact of uPA and PAI-1 levels was found in this group of patients. The combination of high uPAR and high PAI-1 levels did, however, have a particular significant association with short overall survival (P = 0.008). None of the 3 components was found to have a statistically significant prognostic impact in the group of 38 large cell lung cancer patients. There was a positive correlation between uPAR and PAI-1 levels in both groups and between uPA and uPAR levels in the large cell carcinoma patients. In a multivariate analysis, high uPAR was found to be an independent prognostic variable in squamous cell carcinoma patients, with a relative risk of 2.1 (95% confidence interval, 1.1-4.0) and tumor size the only other significant prognostic parameter. These data suggest that uPAR is an important prognostic factor in squamous cell lung carcinoma. In addition to the potential direct clinical usefulness, this information could be helpful in understanding the biology of this disease and developing new therapeutic approaches.

https://cancerres.aacrjournals.org/content/canres/54/17/4671.full.pdf

Prognostic Impact of Urokinase, Urokinase Receptor, and Type 1 Plasminogen Activator Inhibitor in Squamous and Large Cell Lung Cancer Tissue

The urokinase pathway of plasminogen activation is involved in proteolytic degradation of various tissues, including dissolution of the extracellular matrix and basement membranes during the process of cancer cell invasion. We have studied the prognostic value of urokinase-type plasminogen activator (uPA) and type-1 plasminogen activator inhibitor (PAI-1) in tumor extracts from 106 patients with adenocarcinoma of the lung. uPA and PAI-1 levels were determined by sandwich enzyme-linked immunosorbent assays. No correlation was found between uPA and PAI-1 (r = 0.23). High PAI-1 levels were significantly associated with short-duration overall survival (P = 0.017), while uPA levels showed no significant association with overall survival. Relating the levels of PAI-1 to other prognostic factors such as stage and age, no significant correlations were found. The prognostic impact of uPA and PAI-1 were investigated together with other prognostic factors in Cox multivariate analysis. PAI-1 was found to be an independent prognostic variable for survival, the relative risks being 1.5 (low versus medium PAI-1 values (95% confidence interval, 1.2-1.8) and 2.2 (low versus high (95% confidence interval, 1.8-2.6)). In patients with stage I disease (69 patients) high levels of PAI-1 were significantly associated with poor prognosis compared to low levels (P = 0.037). These data indicate that PAI-1 is a potentially important prognostic factor in pulmonary adenocarcinoma and may as such be used to select patients with low stage and poor prognosis for adjuvant therapy subsequent to complete surgical resection.

/pdf/urokinase-and-plasminogen-activator-inhibitor-type-1-in-v0curxqqun.pdf

Urokinase and Plasminogen Activator Inhibitor Type 1 in Pulmonary Adenocarcinoma

Urokinase plasminogen activator (uPA) is a proteolytic enzyme involved in degradation of the extracellular matrix during cancer invasion. The levels of uPA and its inhibitor PAI-1 in tumor extracts have previously been demonstrated to be of prognostic value in breast cancer as well as other types of cancer. We have previously characterized a specific cell surface receptor for uPA (uPAR) which strongly enhances the catalytic activity of uPA and is expressed during mammary cancer invasion. In order to quantitate uPAR in breast cancer tissue, we have now developed a sensitive enzyme-linked immunosorbent assay (ELISA), with polyclonal catching antibodies and three monoclonal detecting antibodies. The detection limit of the assay is approximately 0.16 fmol of uPAR in a volume of 100 µl (1.6 pM). There is a linear relationship between signal and uPAR concentration up to at least 6.6 fmol per 100 µl (66 pM). Both free uPAR and uPAR in complex with uPA is detected. The recovery of an internal uPAR standard in breast cancer tissue extracts is above 87%. The intra-assay and inter-assay variation coefficients are 7% and 13%. In order to find a suitable buffer for extraction of various components of the uPA-system from breast cancer tissue, we tested buffers which previously have been used for optimal extraction of estrogen receptor (A), uPA (B), and uPAR (C). Buffer A and B extracted approximately 30% and 50%, respectively, of the amount of uPAR extracted with buffer C. Extracts of samples of breast cancer tissue from 94 patients all contained uPAR in amounts above the detection limit of the present assay, which appears suitable for studies of the potential prognostic value of uPAR in this disease. Significant correlations were found between uPAR, uPA and PAI-1 tumor levels.

Urokinase receptor in breast cancer tissue extracts. Enzyme-linked immunosorbent assay with a combination of mono- and polyclonal antibodies.

The present invention relates to methods for inhibiting malignant tumour growth, invasion and/or metastasis in a patient, the method comprising suppressing the inhibitory activity of an inhibitor of a protease or of a non-proteolytic matrix-degrading enzyme (IPNME) in malignant tumour tissue or potential malignant tumour tissue. The suppression may be brought about by administering compounds interacting with the IPNME, but also administration of compounds interacting with transcription of genes encoding the IPNME is a possibility. The invention also relates to methods of selecting and identifying compounds in the therapeutical methods, as well of the use of such compounds in the treatment of malignancies.

Helle Pedersen

Papers

Prognostic Impact of Urokinase, Urokinase Receptor, and Type 1 Plasminogen Activator Inhibitor in Squamous and Large Cell Lung Cancer Tissue

Urokinase and Plasminogen Activator Inhibitor Type 1 in Pulmonary Adenocarcinoma

Urokinase receptor in breast cancer tissue extracts. Enzyme-linked immunosorbent assay with a combination of mono- and polyclonal antibodies.

Suppression of inhibitors

Urokinase-type receptor in breast cancer tissue extracts. Enzyme-linked immunosorbent assay with a combination of mono- and polyclonal antibodies