Modification of the amounts of G proteins and of the activity of adenylyl cyclase in human benign thyroid tumours

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Abstract
The possibility that a TSH post-receptor-binding defect is responsible for the pathogenesis of benign thyroid tumours was studied. Thus, we attempted to determine in hyperfunctioning (hot) nodules and non-functioning (cold) nodules whether the functional activity or the amount of G proteins were modified in comparison with surrounding normal tissues. The adenylyl cyclase response to agonists that bypass the TSH–receptor complex (forskolin, guanosine 5′- (β.γ-imido)triphosphate (Gpp(NH)p) or [A1F4]−) was studied on membranes from tumorous and adjacent normal thyroid tissues. We also examined the ability of G proteins to be ADP-ribosylated by cholera toxin (CT) or pertussis toxin (PT), and quantified G proteins by Western blot analysis with specific antisera directed against Gsα and Giα subunits. Basal adenylyl cyclase activity was unchanged in hot tumours compared with normal tissue whereas the stimulation of adenylyl cyclase by Gpp(NH)p or [A1F4]− (which act directly on Gs) as well as by forskolin (which acts on the catalyst) was significantly (PPPPJournal of Endocrinology (1992) 132, 477–485

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