EXPRESSION OF FUNCTIONAL STIMULATORY GUANINE-NUCLEOTIDE-BINDING PROTEIN IN NONFUNCTIONING THYROID ADENOMAS IS NOT CORRELATED TO ADENYLATE-CYCLASE ACTIVITY AND GROWTH OF THESE TUMORS

In thyroid cells, the alpha-subunit of the stimulatory guanine nucleot ide binding protein (G(s alpha)) acts as signal transducer between the TSH receptor and the adenylate cyclase (AC), and it regulates both gr owth and function. In order to analyze G(s alpha) expression by both W estern blot analysis and in situ, we generated an antibody raised agai nst a recombinant human G(s alpha) protein. With this antibody, a stro ng cytoplasmic G(s alpha)-immunostaining was detectable in cultured hu man thyroid cells and in TSH-stimulated rat thyroids, in contrast to n ormal human thyroids and to T-4-treated rat thyroids, which showed onl y weak immunoreactivity. We obtained the;following results by immunohi stochemistry and Western blot analysis of 32 actively growing human th yroid adenomas: 1) strong G(s alpha) expression in 11 adenomas, includ ing 4 hyperfunctioning nodules, 1 of these with a point mutation in co don 201 of the G(s alpha) gene; 2) no expression or only weak G(s alph a) expression in 13 adenomas; and 3) a pattern of G(s alpha)-positive and G(S alpha)-negative cells in the remaining 8 adenomas, In addition , we analyzed ADP-ribosylation of G(s alpha) and AC activity in 9 nonf unctioning adenomas and found a significant correlation between G(s al pha) immunoreactivity and ADP-ribosylation and no correlation of both with basal and TSH-stimulated AC activity. In both types of adenomas, i.e. those with high as well as low G(s alpha), an indistinguishably h igh fraction of proliferating cells was detectable. We conclude that e xpression of functional G(s alpha) protein in nonfunctioning thyroid a denomas is neither correlated to the basal or TSH-stimulated AC activi ty nor to the proliferation rate of these tumors.