Thyrotropin and cyclic AMP regulation of ras proto‐oncogene expression in cultured thyroid cells

Abstract
We examined the effect of thyrotropin (TSH) on intracellular levels of c‐ras mRNA in a line of differentiated rat thyroid cells obtained from normal Fischer rat thyroids. These cells are totally dependent on TSH for growth. TSH stimulation of quiescent cells increased c‐ras mRNA content, with a maximal response (730% of basal) after 6 h, and a decline towards basal levels after 24 h. Dibutyryl cAMP and forskolin mimicked this stimulatory effect of TSH on c‐ras, but did not enhance β‐actin mRNA content. This study demonstrates hormonal and cyclic nucleotide control of c‐ras expression in a well‐differentiated, non‐tumorogenic mammalian cell.