Interaction of the thyrotropin receptor on rat FRTL-5 thyroid cells with thyrotropin and a thyrotropin-stimulating autoantibody from Graves' patients

FRTL-5 rat thyroid cells were either surface-labeled with ¹²⁵I or biosynthetically labeled with [³H]N-acetylglucosamine, solubilized by lithium diiodosalicylate and immunoprecipitated after sequential exposure to bovine thyrotropin and anti-bovine thyrotropin. Autoradiography of polyacrylamide gels run under denaturing conditions and in the presence of a reducing agent revealed two prominant bands with approximate molecular weights of 66-70 kDa and 47 kDa. Immunoprecipitation of the same radiolabeled and solubilized membrane preparations with a Graves' disease IgG having thyroid stimulating but no thyrotropin-binding inhibiting activity revealed only one major band, migrating near the 47 kDa component reactive with thyrotropin. No bands were immunoprecipitated in control incubations using normal human IgG or substituting radiolabeled, solubilized membranes from a rat thyroid cell line with no thyrotropin receptor activity. Thin layer chromatography of Folch extracts of the [³H]-N-acetylglucosamine-labeled immunoprecipitates obtained by either procedure indicated that a specific thyroid ganglioside was coprecipitated with the immunoprecipitated proteins in both cases.