Stimulation and inhibition of cellular functions by glucocorticoids. Correlations with rapid influences on chromatin structure

Abstract

The effect of media conditions on the glucocorticoid response has been examined in three types of cultured cells. In rat pituitary tumor cells (GC cells) growth hormone production was stimulated by glucocorticoids provided fresh culture media was present (enriched media conditions). In contrast, dexamethasone either failed to induce or deinduce growth hormone synthesis if added to cultures which had not received fresh media for 3 days (depleted media condition). With human skin fibroblasts, cortisol stimulated [3H]thymidine incorporation in the enriched condition but inhibited this response in the depleted condition. In mouse lymphoma (S49) cells the enriched media conditions significantly delayed the killing response to glucocorticoids (20% killing after 24 h versus 90% killing after 24 h for the depleted condition). Thus, the magnitude and in some cases, the direction of the glucocorticoid response are sensitive to the conditions to which the cells are exposed. In all three cell types the steroid also rapidly (detectable by 15 min, maximal by 2 h) altered chromatin structure as detected by a change in the number of initiation sites for Escherichia coli RNA polymerase assayed under cell-free conditions. This early nuclear response could be in a positive or negative direction and was also affected by the culture conditions; enriched media favored a positive or less negative effect on the initiation sites by the steroid, while depleted media favored a steroid-induced inhibition of this chromatin function. In S49 and GC cells the kinetics and magnitude of the change in chromatin closely followed receptor . glucocorticoid complex binding to nuclei while removal of dexamethasone from the culture media resulted in a rapid (t 1/2 = approximately 20 min) disappearance of the effect which paralleled loss of bound hormone from the nucleus. The glucocorticoid effect on chromatin was not observed in two lines of glucocorticoid-resistant mutant S49 cells. One line (R-) lacks detectable glucocorticoid receptors; the other line (Nti) has receptors that bind the hormone normally, but the receptor . glucocorticoid complexes bind more avidly to the nucleus. These results suggest that the receptor is involved in both the stimulatory and the inhibitory effects on chromatin. The findings in the Nti cells and of a slight lag between nuclear binding of receptors and initiation site alteration implies that some receptor property, in addition to nuclear binding per se, is responsible for the influence on chromatin. These results are discussed in terms of a model in which steroid hormones initiate their actions by influencing a reaction that modifies chromatin structure. The direction and magnitude of the reaction, and its effect on the expression of specific genes, are dictated by the metabolic state and differentiation of the cell.