Elevated levels of urokinase-type plasminogen activator and its receptor during tumor growth in vivo.

Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) are important in the regulation of tumor tissue progenesis, cell differentiation, tumor cell motility, and tumor cell invasiveness. We have recently reported that the levels of uPA and uPAR were higher in malignant astrocytomas than in low-grade gliomas. In the present study, we measured the levels of uPA and uPAR during the growth of glioblastomas in nude mice. Using fibrin zymography, densitometry, and an enzyme-linked immunosorbent assay, we found that the enzyme activity and content of uPA were increased 4- to 10-fold during tumor formation. Using a receptor assay and an enzyme linked immunosorbent assay, we found the numbers and content of uPAR were increased 5- to 15-fold during tumor formation. In addition, immunohistochemical staining for uPA and uPAR revealed strong immunoreactivity in tumor cells with the staining more intense on day 28 than on day 14. These results suggest that the upregulation of uPA and uPAR plays a major role in the formation of gliomas.