ROLE OF BETA-1 INTEGRINS IN TUMOR-CELL ADHESION TO CULTURED HUMAN ENDOTHELIAL-CELLS

We investigated the effects of beta-1, integrins on tumor cell (TC) adhesion to unstimulated and interleukin-1 (IL-1) activated endothelial cells (EC). IL-1 treatment (20 units/ml for 6 hours) of cultured human umbilical vein EC significantly increased adhesion of seven human TC lines of different origin. A goat antiserum raised to purified alpha-5-beta-1 integrin abolished the IL-1 induced increment in adhesion of two osteosarcomas, one melanoma, one lung, and one kidney carcinoma, whereas it did not affect adhesion of two colon carcinoma cell lines. Further studies were performed on MG63 osteosarcoma cells. Adhesion of MG63 osteosarcoma cells to EC was dependent on time of EC treatment with IL-1: it was maximal at 12 hours and declined at 24 hours. Alpha-5-beta-1 antiserum blocked IL-1 induced increase in MG63 adhesion at any time of EC treatment. This effect appears to be mainly directed to MG63 integrins since selective incubation of the antiserum with EC, but not with MG63, did not modify TC adhesion. Using a series of antibodies to different alpha and beta-chains, we found that only monoclonal antibodies (mAb) to alpha-4, alpha-5, and beta-1, could inhibit MG63 adhesion to IL-1 activated EC, whereas alpha-2, alpha-6, and beta-3 antibodies were ineffective. Antibodies to fibronectin had very little activity on MG63 adhesion to EC matrix and did not significantly affect MG63 adhesion to control or IL-1 treated EC. Antibodies to alpha-4, alpha-5, and beta-3, were only partially effective in inhibiting MG63 adhesion to EC matrix. These data indicate that the capacity of alpha-4-beta-1 and alpha-5-beta-1 integrins to bind fibronectin contributed verv little to MG63 adhesion to EC. The importance of beta-1 integrins in promoting a direct interaction between EC and MG63 was further shown by inhibition of rosette formation among these cells in suspension by the alpha-5-beta-1 antiserum. Only a VCAM-1/INCAM110 mAb, but not ELAM-1 or ICAM-1 mAbs, could inhibit MG63 adhesion to IL-1 activated EC. Overall these data indicate that at least two members of the beta-1 integrin subfamily (alpha-4-beta-1 and alpha-5-beta-1) are involved in MG63 adhesion to cytokine treated EC. This integrin function might be important at early stages of TC interaction with the vessel wall.