Modulation of murine B16F10 melanoma plasminogen activator production by a synthetic peptide derived from the laminin A chain.

Laminin is a large multidomain protein with diverse biological activities. We previously demonstrated that intact laminin as well as an A chain synthetic peptide (LamA2091-2108) stimulate tissue plasminogen activator (t-PA)-catalyzed plasminogen activation. Here we report that LamA2091-2108 increases t-PA production by the highly metastatic murine melanoma cell line B16F10, with no effect on the parental B16F1 line, which has a low metastatic capacity. Incubation of plasminogen with B16F10-conditioned medium results in direct activation of the zymogen to plasmin. Furthermore, following incubation of B16F10 cells with plasminogen, plasmin is eluted from the cell surface, suggesting that these cells contain binding sites for plasminogen/plasmin in close proximity to t-PA binding sites. Quantitation of t-PA activity using the synthetic substrate Val-Leu-Lys-p-nitroanilide indicates a minimal 10-fold increase in t-PA in the conditioned medium of B16F10 cells grown in the presence of LamA2091-2108, with no increased t-PA activity observed in B16F1-conditioned medium. Similar results were obtained in immunocapture experiments which are specific for t-PA antigen. In addition, B16F10 melanoma-associated t-PA catalyzes the plasminogen-dependent hydrolysis of laminin. Together these data suggest that degradation of basement membrane proteins by metastatic melanoma cells may release fragments (such as LamA2091-2108) which stimulate both the production and activity of metastasis-associated proteinases such as t-PA, providing a mechanism for augmentation of the metastatic capacity of B16F10 melanoma cells.