Abstract
Cell cycle-dependent growth regulation by hydrocortisone (HC) and specific glucocorticoid binding were studied in human embryonic lung fibroblasts (HEL) in a serum-free, defined medium. Confluent and quiescent HEL cells could stimulate DNA synthesis when polypeptide growth factors (EGF, insulin, and transferrin) were present.
HC promoted DNA synthesis only in the presence of EGF. When cells were exposed to HC after being refed growth factor-containing, serum-free medium (RITC 80-7), the rate of entry of cells into DNA synthesis was increased and, thus, the cell number.
The cell cycle period was not altered by an addition of HC. HC-induced 3H-thymidine incorporation was found in the prereplicative phase of the cell cycle in kinetic pulse experiments. 3H-dexamethasone binding activity persisted throughout the cell cycle, high activity being noted during the middle G1 phase and at the Gl/S boundary. Our results show a close relation between the presence of specific glucocorticoid binding and hormonal responsiveness in a defined medium.
