Human urokinase receptor concentration in malignant and benign breast tumors by in vitro quantitative autoradiography. Comparison with urokinase levels

We measured the tissue concentration of human urokinase receptor (uPAR) in 22 breast carcinomas and 9 benign breast lesions using in vitro quantitative autoradiography. Tissue sections were incubated with increasing concentrations of 125I-pro-urokinase in the presence or absence of unlabeled competitor. Breast carcinomas were found to contain 5 times more uPAR that benign breast lesions with respect to their protein content (523+/- 72 versus 108 +/- 20 (SE) fmol/mg (p<0.001). Simultaneous quantitation of urokinase (uPA) by immunoenzymatic assay on tissue extracts from the same specimens showed that breast carcinomas also contain 19 times more uPA than benign lesions. (611 +/- 134 versus 32 +/- 8 fmol/mg) (p<0.001). The reliability of quantitative autoradiography measurements was confirmed by uPAR cross-linking assay on membrane fractions from either U937 histolytic lymphoma cells or breast carcinomas and immunoperoxidase staining with an anti-uPAR monoclonal antibody on tumor sections. Also, immunoperoxidase staining with an anti-uPA monoclonal antibody showed that uPA is indeed localized on the plasma membrane of epithelial tumor cells in confined areas of breast carcinomas whereas cells from benign breast lesions were devoid of uPA under the same experimental conditions. In conclusion, our findings support the hypothesis that uPAR play a central role in the acquisition of an invasive phenotype and favor its potential use as a prognostic factor in patients with breast carcinomas.