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Glucocorticoids regulate the glucocorticoid receptor in the AtT-20 cell
Abstract:
Incubation of AtT-20/D-1 mouse pituitary tumor cells with glucocorticoids leads to a progressive diminution in the number of cellular glucocorticoid receptors. Control incubations demonstrate that non-glucocorticoids don't cause this depletion and that the decrease is not due to deleterious alterations in the incubation medium or degradation of the steroid. Incubation of cells with 0.5 micrograms/ml of cycloheximide alone does not dramatically diminish receptor content. However, incubation of cells with both cycloheximide and dexamethasone results in receptor depletion, suggesting that depletion involves enhanced receptor degradation. The cell's ability to bind glucocorticoids can be regenerated by a 24- to 48-h incubation in steroid-free medium. However, unlike the depletion step, the repletion process is sensitive to cycloheximide.
Insights
Glucocorticoids reduce glucocorticoid receptors in mouse pituitary cells by increasing receptor degradation. Receptor levels can be restored in steroid-free media, but this process requires protein synthesis.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Biology
Background:
- Glucocorticoids are crucial hormones regulating various physiological processes.
- Cellular responses to glucocorticoids are mediated by specific receptors.
- Understanding glucocorticoid receptor regulation is key to comprehending steroid hormone action.
Purpose of the Study:
- To investigate the mechanism by which glucocorticoids decrease cellular glucocorticoid receptor levels.
- To determine if glucocorticoid receptor depletion involves enhanced degradation.
- To examine the process of glucocorticoid receptor replenishment.
Main Methods:
- Incubation of AtT-20/D-1 mouse pituitary tumor cells with glucocorticoids (dexamethasone) and cycloheximide.
- Assessment of cellular glucocorticoid receptor levels.
- Incubation in steroid-free medium to observe receptor regeneration.
- Evaluation of cycloheximide's effect on receptor depletion and replenishment.
Main Results:
- Glucocorticoid treatment led to a progressive decrease in cellular glucocorticoid receptors.
- This depletion was specific to glucocorticoids and not caused by medium alterations.
- Co-incubation with cycloheximide and dexamethasone suggested enhanced receptor degradation.
- Receptor binding capacity was restored after incubation in steroid-free medium.
- The replenishment process was found to be sensitive to cycloheximide, indicating a requirement for protein synthesis.
Conclusions:
- Glucocorticoid-induced reduction in receptor number involves enhanced receptor degradation.
- Receptor levels can be replenished, but this process is dependent on ongoing protein synthesis.
- These findings provide insights into the dynamic regulation of glucocorticoid receptors.