OVEREXPRESSION OF GS-ALPHA SUBUNIT IN THYROID-TUMORS BEARING A MUTATED GS-ALPHA GENE

Point mutations occurring at codon 201 of the gene coding for the a su bunit of the stimulatory G protein impair intrinsic GTPase activity an d lead to a constitutive activation of adenylate cyclase. We have exam ined thyroid follicular and papillary carcinomas and follicular adenom as and found samples that bear this mutation at codon 201 of the Gsa g ene. Both mutation-positive and mutation-negative tissue samples were investigated for the level of Gsa expression relative to a pool of nor mal thyroid tissue, using immunoblotting against two (mid-region-speci fic and C-end-specific) antipeptide antibodies. Using 8000 g and 100 0 00 g membrane fractions of homogenized tissues we have demonstrated th at the Gsa proteins in normal ad neoplastic thyroid tissues are repres ented by three isoforms: 43 kDa, 45 kDa and 52 kDa. We have quantified and compared the amount of Gs alpha protein and find it is overexpres sed in mutation-bearing tissue samples.