Events in glucocorticoid hormone action

To approach experimentally changes of chromatin structure introduced by glucocorticoids, the histone H1 compositions of hormone‐treated and non‐treated mouse mammary tumor cells of the GR line [Ringold, G., Lasfargues, E. Y., Bishop, J. M. and Varmus, H. E. 1975) Virology 65 , 135–147] were compared. To define the biologically important hormone concentration range, the cells were exposed to different concentrations of triamcinolone, a synthetic glucocorticoid. The induction of mouse mammary tumor virus (MMTV) RNA was measured by cDNA excess hybridization, and the amount of hormone bound to nuclei was determined by a filter‐binding assay. Between 0.3 nM and 30 nM triamcinolone the relative increase in nuclear bound hormone corresponded well with the relative induction of MMTV RNA. The half‐life of triamcinolone in nuclei of growing cells was 1 h, as measured by a pulse‐chase experiment. Reversed‐phase high‐performance liquid chromatography of histone H1 resulted in its separation into four subfractions. The treatment of cells with biologically active glucocorticoid, 3 nM or 30 nM triamicinolone or 1 μM dexamethasone, resulted in changes in the relative amounts of two subfractions and to a positional shift of two subfractions as compared to untreated cells. No changes were observed after exposure to 3 nM dexamethasone, a concentration which does not induce MMTV RNA [Ringold, G. M., Yamamoto, K. R., Tomkins, G. M., Bishop, J. M. and Varmus, H. E. (1975) Cell 6 , 299–305].