ACTION OF CYCLIC NUCLEOTIDES ON PROTEIN AND RNA SYNTHESIS IN THE THYROID

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Abstract
Thyrotropin (TSH) regulates the biosynthesis of thyroid protein and RNA. This action is mediated by adenylate cyclase and cyclic[c]AMP. In this study the action of cGMP and cCMP was investigated in beef slices. Both cAMP and cGMP significantly increased incorporation of [3H]uridine into RNA. These effects were blocked by actinomycin D, suggesting that their action is located at a pre- or at a transcriptional step. The PCA [perchloric acid] soluble fraction radioactivity followed in parallel with the variations observed in the RNA fraction, supporting the view that cyclic nucleotides may regulate RNA by modulating the nucleotide precursors pool. cCMP in concentrations between 0.35-1.5 mM progressively decreased the RNA labeling, and the values of the PCA soluble radioactivity again followed those of RNA. cCMP also blocked the in vitro stimulatory action of cAMP on the incorporation of [3H]leucine into protein, and of [3H]uridine into RNA. The present results provide the 1st information on the action of cAMP on RNA synthesis and suggest that negative signals may also play a part in the regulation of thyroid function.

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