A ROLE OF DYSTROGLYCAN IN SCHWANNOMA CELL-ADHESION TO LAMININ

Dystroglycan is encoded by a single gene and cleaved into two proteins alpha- and beta-dystroglycan by posttranslational processing. Recentl y, alpha-dystroglycan was demonstrated to be an extracellular laminin- binding protein anchored to the cell membrane by a transmembrane prote in beta-dystroglycan in striated muscle and Schwann cells. However, th e biological functions of the dystroglycan-laminin interaction remain obscure, and in particular, it is still unclear if dystroglycan plays a role in cell adhesion. In the present study, we characterized the ro le of dystroglycan in the adhesion of schwannoma cells to laminin-l. I mmunochemical analysis demonstrated that the dystroglycan complex, com prised of alpha- and beta-dystroglycan, was a major laminin-binding pr otein complex in the surface membrane of rat schwannoma cell line RT4. It also demonstrated the presence of alpha-dystroglycan, but not beta -dystroglycan, in the culture medium, suggesting secretion of alpha-dy stroglycan by RT4 cells. RT4 cells cultured on dishes coated with lami nin-1 became spindle in shape and adhered to the bottom surface tightl y. Monoclonal antibody IIH6 against alpha-dystroglycan was shown previ ously to inhibit the binding of laminin-l to alpha-dystroglycan. In th e presence of IIH6, but not several other control antibodies in the cu lture medium, RT4 cells remained round in shape and did not adhere to the bottom surface. The adhesion of RT4 cells to dishes coated with fi bronectin was not affected by IIH6. The known inhibitors of the intera ction of a dystroglycan with laminin-l, including EDTA, sulfatide, fuc oidan, dextran sulfate, heparin, and sialic acid, also perturbed the a dhesion of RT4 cells to laminin-l, whereas the reagents which do not i nhibit the interaction, including dextran, chondroitin sulfate, dermat an sulfate, and GlcNAc, did not. Altogether, these results support a r ole for dystroglycan as a major cell adhesion molecule in the surface membrane of RT4 cells.