Cell cycle regulation of glucocorticoid binding and proliferation of human diploid fibroblasts in a serum-free defined medium.

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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 [epidermal growth hormone], 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 G1/S boundary. A close relation between the presence of specific glucocorticoid binding and hormonal responsiveness in a defined medium was shown.

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