This Article Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by BERKOVITZ, G. D. Articles by BROWN, T. R. Search for Related Content PubMed PubMed Citation Articles by BERKOVITZ, G. D. Articles by BROWN, T. R.

Down-Regulation of the Glucocorticoid Receptor by Dexamethasone in Cultured Human Skin Fibroblasts: Implications for the Regulation of Aromatase Activity^*

Division of Pediatric Endocrinology, The Johns Hopkins Hospital Baltimore, Maryland 21205

Address all correspondence and requests for reprints to: Dr. Gary Berkovitz, CMSC 3-110, The Johns Hopkins Hospital, 600 North Wolfe Street, Baltimore, Maryland 21205.

Human genital skin fibroblasts grown in cell culture contain aromatase activity and glucocorticoid receptors, providing a model for studying the relationship between changes in levels of dexamethasone (DEX) receptor binding and changes in the response of aromatase to DEX. Incubation of cells with media containing DEX produced a time-dependent decline in receptor number, with a nadir at 18–24 h. When DEX was removed from the media, only 40–60% of the lost receptor content was recovered. Binding of DEX to its receptor declined in a dose-dependent fashion after 24-h exposure to this glucocorticoid; the concentration of DEX that produced a half-maximal decline (2.2 nmol/L) was in the same range as the K_d for the receptor-DEX complex (14 nmol/L). Incubation of cells with DEX for 20 h also reduced the level of DEX receptor binding in purified nuclei and nuclear matrix by 76% and 89%, respectively. When subcellular fractions were prepared after incubation of cells with DEX for 1–24 h, whole cell, cytosolic and nuclear DEX receptor binding declined in parallel with time. Incubation of skin fibroblasts with DEX resulted in progressive stimulation of aromatase activity, with a peak at 24 h followed by a return to baseline at 72 h. The initial stimulation of aromatase was mediated by DEX receptors. However, the decline in aromatase activity after prolonged DEX exposure did not appear to be due to a decline in the level of DEX receptor binding. The data supporting this last conclusion included the following. When cells were washed free of DEX after 48 h, DEX receptor binding recovered within 24 h, whereas aromatase activity could not be maximally restimulated until 36 h; when cells were incubated with media containing DEX and cycloheximide for 1–48 h, DEX receptor binding declined to a nadir by 24 h, whereas aromatase activity rose continuously up to 48 h. These findings are consistent with the concept that the aromatase gene in skin fibroblasts is subject to both positive and negative regulation.

^* This work was supported in part by NIH Grants R01-DK-35339, R01-HD-19536, and R01-DK-00180.

Received September 24, 1987.