Retinoic acid enhances plasminogen activation on the cell surface

The importance of cell-associated plasminogen activation in the extracellular matrix degradation processes is becoming increasingly evident. To elucidate the modulators of net plasminogen activation on the cell surface, we have recently established an assay system. Using this system, we examined the effects of several candidate modulators on cell surface plasminogen activator in the human fibrosarcoma cell line HT-1080 and the SV40-transformed human lung fibroblast cell line WI-38 VA 13 2RA. Although the majority of the candidates had no effect or a selective effect on either cell line, only retinoic acid markedly enhanced cell surface plasminogen activator activity in both HT-1080 and WI-38 VA13 2RA cells in a time-dependent manner. The effect of retinoic acid was neutralized by actinomycin D. The enhanced activity was inhibited by anti-uPA IgG and by pretreatment with phosphatidylinositol-specific phospholipase C. These findings suggest that retinoic acid increases the amount of receptor-bound uPA via de novo synthesis, and that it plays an important role in modulating cell-associated plasminogen activation.