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Antagonism of glucocorticoid action in cultured hepatoma cells
Abstract:
We report here our recent data on the effects of antiglucocorticoids in two established cell lines (HTC, FAZA). These steroid hormone target tissues were designed to consider the problem of differential antagonism and lack of correlation between antiglucocorticoid activity and competition for the glucocorticoid receptor. In the systems chosen, several responses were considered which may be differentially antagonized: induction of tyrosine aminotransferase (TAT), alanine aminotransferase (AAT) and tryptophan oxygenase (TPO). By testing the anti-inducing capacities of a number of steroids, we found a few synthetic compounds like promegestone and R 25055 which exert a stronger antagonism against TAT and AAT induction than natural steroids like progesterone. The availability of highly radioactive antagonists (promegestone, progesterone) has greatly facilitated our "whole cell" study and allowed us to detect the antagonists in isolated nuclei whose purity and morphological integrity were controlled by specific criteria; our results suggest that the binding of the antagonists to the nucleus proceeds via the glucocorticoid receptor. The appearance of promegestone and progesterone in the nucleus suggests that the nucleus may be involved in the mechanism of action of anti-glucocorticoids.
Insights
Synthetic antiglucocorticoids like promegestone show stronger antagonism against key enzyme induction than natural steroids. These compounds bind to the glucocorticoid receptor in the nucleus, suggesting a nuclear role in antiglucocorticoid action.
Area of Science:
- Endocrinology
- Molecular Pharmacology
- Cell Biology
Background:
- Antiglucocorticoids modulate cellular responses to glucocorticoids.
- Differential antagonism and receptor binding present challenges in understanding antiglucocorticoid mechanisms.
- Key enzymes like tyrosine aminotransferase (TAT), alanine aminotransferase (AAT), and tryptophan oxygenase (TPO) are targets of glucocorticoid action.
Purpose of the Study:
- To investigate the effects of antiglucocorticoids on specific cellular responses.
- To compare the antagonistic potency of synthetic and natural steroids.
- To elucidate the role of the glucocorticoid receptor and nuclear localization in antiglucocorticoid activity.
Main Methods:
- Utilized HTC and FAZA cell lines as steroid hormone target tissues.
- Assessed the anti-inducing capacities of various steroids on TAT, AAT, and TPO induction.
- Employed whole-cell studies with radiolabeled antagonists (promegestone, progesterone).
- Analyzed antagonist binding in isolated nuclei, controlling for purity and integrity.
Main Results:
- Synthetic compounds (promegestone, R 25055) exhibited stronger antagonism against TAT and AAT induction compared to progesterone.
- Radiolabeled antagonists were detected in isolated nuclei.
- Nuclear binding of antiglucocorticoids appears to occur via the glucocorticoid receptor.
Conclusions:
- The nucleus is likely involved in the mechanism of action of antiglucocorticoids.
- Promegestone and progesterone localization within the nucleus supports a nuclear role.
- Glucocorticoid receptor mediates nuclear binding of antiglucocorticoids.