Inhibition of in Vitro Ovarian Cancer Cell Invasion by Modulation of Urokinase-type Plasminogen Activator and Cathepsin B

HOC-I ovarian cancer cells express the single-chain form of the urokinase-type plasminogen activator (uPA) and cathepsin B (cath B) on their cell surface. The significance of the expression of cell surface uPA/cath B activity to the invasive potential was examined by preincubating with uPA/cath B-modulating agents in in vitro invasion assay. The anti-uPA monoclonal antibody 394 effectively inhibited invasion in a dose-dependent manner. On the contrary, anti-cath B antibody did not affect the invasive potential of the cells. E-64, a specific inhibitor for cysteine proteases, blocked invasion as effectively as monoclonal antibody 394. The data reveal that the uPA and cysteine proteases contribute significantly to the invasive capacity of the cells. We suggest that the cysteine proteases facilitate the action of uPA, possibly by activating proenzyme uPA produced by cancer cells. Evidence for the role of a cathepsin-uPA activation cascade in HOC-I cell invasion is provided.