BINDING OF UROKINASE TO ITS RECEPTOR PROMOTES MIGRATION AND INVASION OF HUMAN-MELANOMA CELLS IN-VITRO

Previously, we reported that urokinase-type plasminogen activator (uPA ) plays a pivotal role in extracellular matrix dissolution by malignan t melanoma cells. Here, we demonstrate that a highly metastatic melano ma cell line (M24met) that secretes uPA expresses high levels of the u PA receptor (uPAR), 2.4 x 10(6) binding sites/cell with a K-D of 5.67 x 10(-10) M. The receptor was identified as a 55,000-60,000 kDa cell s urface protein. Although M24met cells secrete uPA, they are unable to efficiently utilize this enzyme for invasion, unless it is bound to it s receptor. This contention is based on the finding that an antibody a gainst uPAR (monoclonal antibody 3936) inhibited invasion of M24met ce lls through a reconstituted basement membrane (Matrigel) up to 33%, wh ile a reduction of uPA catalytic activity by its plasminogen activator inhibitor-2 resulted in 46% inhibition of invasion. Furthermore, uPAR is involved in signal transduction events in M24met cells, since both uPA and its amino-terminal fragment stimulated the migration of melan oma cells toward Matrigel, resulting in maximal increases of 32 and 72 %, respectively. Our results indicate that both uPA and uPAR are invol ved in melanoma metastasis and that uPAR contributes to at least two i mportant steps in this process, matrix dissolution and migration.