| Abstract: | Previous studies have indicated that thyrotropin may induce general increases in RNA and protein synthesis in calf thyroid tissue slices. In this report, we show that thyrotropin selectively stimulates 35S]methionine incorporation into small numbers of specific cytoplasmic and nuclear proteins. We provide data on the time course of stimulation and on relative molecular masses and isoelectric points of hormone-response proteins. Calf thyroid tissue slices were incubated for 3 h, 6 h or 9 h in the presence or absence of thyrotropin (50 mU/ml); 35S]methionine (50-75 microCi/ml) was added for the final 3 h of incubation. Cytoplasmic and nuclear fractions were then prepared, and analyzed by two-dimensional polyacrylamide gel electrophoresis and fluorography. Thyrotropin increased 35S]methionine incorporation into two cytoplasmic and four nuclear proteins within 3 h; hormonal effects on the labeling of five of these six proteins were transient, and no longer evident after 6-9 h. In contrast, a second group of two cytoplasmic and four nuclear proteins exhibited increased labeling after a delay of 6-9 h. Our results suggest that thyrotropin selectively stimulates the synthesis of specific cytoplasmic and nuclear proteins in calf thyroid tissue slices, and that stimulation involves at least two mechanisms (one rapid, the other delayed). |
