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Interactions of glucocorticoids with the AtT-20 cell: effect on protein accumulation
Abstract:
In order to investigate the mechanism through which glucocorticoids downregulate the number of their own receptors in the AtT-20 cell, the effect of glucocorticoids on cell protein metabolism was studied. Glucocorticoids were found to inhibit cellular protein accumulation when included in long-term cultures. The concentrations of agonists that cause a mid-maximal effect are similar to those needed to half-saturate the glucocorticoid receptor, suggesting that the growth-inhibiting effect is receptor-mediated. Two-dimensional electrophoresis of cytosolic extracts of treated and control cells suggested that the effect reflected a general suppression of overall protein accumulation rather than a selective effect on certain classes. Comparison of the protein to DNA ratio of control and dexamethasone-treated cells showed that the latter have higher ratios suggesting that cell composition may be altered by agonists. However, time-course studies of this effect indicated that this is basically an expression of a glucocorticoid effect on cell growth rather than a selective effect on protein metabolism. It is concluded that glucocorticoids inhibit overall AtT-20 cell growth and that this, in turn, manifests itself as a decrease in the rate of protein accumulation. It is suggested that this change in protein metabolism may be a minor component in the mechanism through which glucocorticoids decrease AtT-20 cell ACTH secretion and glucocorticoid receptor number.
Insights
Glucocorticoids inhibit AtT-20 cell growth, reducing protein accumulation. This receptor-mediated effect on cell growth, not protein metabolism, may influence ACTH secretion and receptor numbers.
Area of Science:
- Endocrinology
- Cell Biology
- Molecular Pharmacology
Background:
- Glucocorticoids are key regulators of cellular functions.
- Understanding glucocorticoid receptor (GR) downregulation is crucial for endocrine research.
- AtT-20 cells are a model for studying pituitary hormone regulation.
Purpose of the Study:
- To investigate the mechanism of glucocorticoid-induced downregulation of glucocorticoid receptors in AtT-20 cells.
- To determine the effect of glucocorticoids on AtT-20 cell protein metabolism.
- To elucidate the role of receptor-mediated effects in glucocorticoid action.
Main Methods:
- Long-term cell cultures of AtT-20 cells.
- Treatment with varying concentrations of glucocorticoid agonists.
- Analysis of cellular protein accumulation.
- Two-dimensional gel electrophoresis of cytosolic extracts.
- Measurement of protein to DNA ratios.
- Time-course studies.
Main Results:
- Glucocorticoids inhibit overall cellular protein accumulation in AtT-20 cells.
- The growth-inhibiting effect is receptor-mediated, correlating with GR binding affinity.
- Electrophoresis revealed a general suppression of protein accumulation, not selective effects.
- Dexamethasone treatment increased the protein to DNA ratio, indicating altered cell composition.
- Time-course studies confirmed the effect is primarily on cell growth, not protein metabolism.
Conclusions:
- Glucocorticoids inhibit AtT-20 cell growth, leading to decreased protein accumulation.
- This suppression of cell growth is a key factor in glucocorticoid's impact on protein metabolism.
- Altered protein metabolism may play a minor role in glucocorticoid-induced reduction of ACTH secretion and GR number.