Nuclear 3,5,3'-triiodothyronine receptor concentration increases during deoxyribonucleic acid synthesis in partially synchronized GC cell cultures.

Abstract

The relationship between DNA synthesis and the appearance of nuclear T3-binding sites was examined in cultured GC cells which were partially synchronized by incubation with 2 mM thymidine for 25 h. After removal of thymidine, 75–85% of the cells actively synthesized DNA, and mitoses were absent until 4–6 h later. Nuclear T3-binding capacity (BC) was measured in paired asynchronous control cultures (C) and thymidine- blocked cultures 0–3 h after removal of thymidine (early S phase), after 3–6 h (mid-S phase), and after 18 h when all of the thymidine-blocked cells had divided. Compared to asynchronous controls, cells in the early S phase had a significant increase in the mean DNA content from 13.53 ± 0.42 to 16.55 ± 0.79 (±SEM) μg/106 cells (P < 0.007), and this was associated with an increase in the mean concentration of nuclear T3-binding sites from 46.8 ± 2.8 to 61.1 ± 3.8 fmol/106 cells (P < 0.001). There was, however, no significant change in the concentration of T3-binding sites per 100 μg DNA (C, 344...