Invasion of the Human Lung Carcinoma Cell Lines A549 and Endogenous Receptor-bound Urokinase Mediates Tissue

Macrophage colony-stimulating factor ((SI -I i increases the tissue invasive potential of the CSF-1 receptor-bearing lung carcinoma cell lines A549 and Calu-1 by increasing the number of endogenous!) bound urokinase-type plasminogen activators (u-PA)s on these cells. CSF-1, at concentrations which optimize invasion of A549 and Calu-1 cells into human amnion membranes (250 ng/ml), maximally augments the number of u-PA receptors occupied by endogenous!)1 produced urokinase. Preincubation of A549 and Calu-1 cells with the anti-u-PA monoclonal anti body MPW5UK (25 fig/ml) or with a 20to 40-fold stoichiometric excess of fluid phase type 2 plasminogen activator inhibitor abrogates invasiveness, indicating that functionally active cell surface u-PA is essential for tissue invasion. In contrast, fluid phase type 1 plasminogen activator inhibitor (PAI-1, 5-15 units/ml) does not inhibit invasiveness unless preincubated with the amnion membranes. Inhibition of invasion by I' VI1 is abolished by presaturating the amnion membranes with antiitronectin monoclonal antibody (10 MR/ml) which prevents binding of PAI-1 to tissue-associated vitronectin. Binding of PAI-1 to tissue vitronectin is therefore a prerequisite for its inhibitory action. Thus, endogenously receptor-bound u-PA is the primary protease mediating CSF-1induced tissue invasiveness of the lung carcinoma cell lines A549 and Calu-1.