Cell surface-associated and released proteolytic activities of bovine aorta endothelial cells

We have demonstrated cell surface-associated and released proteolytic activity on bovine aorta endothelial cells, representing normal cells with regulated invasive properties. To demonstrate these proteolytic activities on viable cells grown in monolayer cultures, a new method was developed. The method consists of rolling modified plastic beads carrying covalently-linked [125I]-labeled casein in contact with the cell surfaces or adjacent to the cell monolayers without actual contact. The rate of radioactive peptide release is proportional to the proteolytic activity. Released proteases are detected when no contact occurs between the substrate and the cells. When the bead-substrate complex is rolled over the surface of endothelial cells, a significant increase in released labeled peptides is observed which represents a cell surface-associated proteolytic activity. These activities may be relevant to the endothelial cell's invasive capacity and appear to be similar to the neutral proteolytic activity of transformed cells.