Previously we reported that suppression of type I collagenase synthesis in human melanoma cells with antisense RNA significantly reduced proteolysis of type I and type IV collagen matrices (Durko et al., 1997, Biochim. Biophys. Acta 1356, 271). Because plasmin is a major activator of the type I collagenase, we assessed the impact of type I collagenase suppression on the urokinase/plasmin system of proteolysis. Gel zymography revealed the appearance of two new caseinolytic bands of Mr 81-83000 in conditioned media of type I collagenase-depleted, but not of wild-type cells and these were identified as plasmin bands. This increased extracellular plasmin activity coincided with reduced membrane-associated plasminogen levels and decreased expression of the urokinase-type plasminogen activator receptor at both the mRNA (up to 83% reduction) and cell-surface (up to 48% reduction) levels, while urokinase mRNA levels remained unchanged. The results indicate that in these cells the urokinase/plasmin system is regulated by type I collagenase levels.
Copyright 1998 Academic Press.