UPA induces adhesion of tumor cells in vitro

We previously reported that the addition of uPA to a tumor cell suspension enhances cell adhesion to matrix. The interaction between tumor cells and their matrix is presently investigated in the human colon cancer cell line RKO in culture. By flow cytometry, we observed that these cells express integrins pi, a.3, a.5, and aV, with minimal expression of p3. Cell adhesion studies were carried out by adding cells and culture media containing different concentrations of uPA to 24-weIl plates, coated respectively with vitronectin and with fibronectin, and incubating for 24 h at 37C. The cells were then sonicated, incubated with Hoescht Dye and analyzed on a fluorometer. The results show that uPA at concentrations of 10-24 units/ml increased cell adhesion to the respective matrices by 10-20%. Further studies of the mechanism of this effect were carried out by flow cytometry to assay the levels of surface integrins. The results show that uPA, at concentrations of 1 10 units/ml, increases the expression of a5 and aV. This may explain why uPA enhances the cell adhesion to the respective ligands, fibronectin and vitronectin, of these integrins. Various disintegrins including kistrin and several ROD peptides were found to inhibit these adhesions. Since tumor invasion and metastasis require pericellular proteolysis, tumor cell migration and adhesion, our findings show that uPA participates in all of these steps. The results that disintegrins can block the uPA-induced cell adhesions to these matrices open the way to a new approach in control tumor cell invasion and metastasis.