Thyroid hormones regulate G-protein β-subunit mRNA expression in vivo

Thyroid hormones exert 'permissive effects' on the hormone-sensitive adenylate cyclase. Regulation of the expression of G(i) (G(iα2)) and G(s) by thyroid hormones in vivo was investigated at the level of mRNA. Steady-state levels of the mRNA for G(iα2) and G(sα), as well as the G(β)-subunits, were quantified using DNA excess solution hybridization analysis. Regulation of protein and mRNA expression in adipose tissue was investigated in hypothyroid, euthyroid, and hyperthyroid rats. In euthyroid animals, steady-state levels of mRNA (amol/μg RNA) were 13.8, 5.9, and 5.7 for G(sα), G(iα2), and G(β1,2), respectively. Activation of adenylate cyclase by G(s) is unaffected by thyroid status. Both G(sα) and G(sα) mRNA levels in hypothyroid rats were the same as those of controls (euthyroid). The inhibitory control of adenylate cyclase, in contrast, is markedly potentiated in hypothyroid rats. The expression of G(1α)s and G(β)-subunits was increased in hypothyroidism. Whereas G(iα2) mRNA levels remained essentially unchanged, G(β1,2) mRNA levels were observed to increase 45% in the hypothyroid state. In the hyperthyroid state G(β1,2) mRNA levels were observed to decline by 35%. Regulation of G-protein subunit expression, at the level of mRNA, appears to be one component of permissive hormone action on transmembrane signaling.