BACILLUS-CALMETTE-GUERIN INTERACTS WITH THE CARBOXYL-TERMINAL HEPARIN-BINDING DOMAIN OF FIBRONECTIN - IMPLICATIONS FOR BCG-MEDIATED ANTITUMOR-ACTIVITY

Intravesical bacillus Calmette-Guerin (BCG) has been shown to be an ef fective treatment for superficial transitional cell carcinoma of the b ladder. The mechanisms by which BCG achieves this effect remain unclea r. Reports have attributed an important role to fibronectin both in th e initial attachment of BCG to bladder surfaces and in the limitation of tumor cell motility. In the present study, using limited protease c athepsin B degradation followed by Western blot analyses with antibodi es to various domains of the fibronectin molecule, we showed that BCG appears to bind to fibronectin near the carboxyl terminal and adjacent to the heparin binding domain. Furthermore a 51-chromium release assa y with human bladder cancer cell line T24 as target cells and lymphoki ne activated killer (LAK) cells as effector cells showed that fibronec tin was needed for tumor cytotoxicity by the LAK cells. By using antib odies and peptides to various domains of the fibronectin molecule, the heparin binding domain, but not the cell binding domain, carboxyl ter minal region, or the amino terminal region of the fibronectin molecule , was identified as essential to tumor cell lysis by the LAK cells. Fl ow cytometric analysis showed that both peripheral blood lymphocytes a nd the LAK cells express fibronectin receptors VLA-3, VLA-4 and VLA-5 on their surfaces. However, the numbers of receptors are not significa ntly different in the two cell populations. We conclude that, by bindi ng near the carboxyl terminal region and adjacent to the heparin-bindi ng domain of the fibronectin molecule, BCG may protect this region of the molecule from tumor proteases, and may thus allow the antitumor ac tivity of the host immune cells to take place.