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Stabilization of androgen receptor protein is induced by agonist, not by antagonists
Takashi Furutani1, Tomoyuki Watanabe, Kyouko Tanimoto
1Metabolic Diseases Research, Pharmacology Laboratories, Institute for Drug Discovery Research, Yamanouchi Pharmaceutical Co. Ltd., Tsukuba 305-8585, Japan.
Abstract:
The action of nuclear receptor ligands in target tissues is specified mainly by the expression levels of their cognate nuclear receptors. The expression levels of these receptors are controlled through transcriptional and post-transcriptional events. Among post-transcriptional events, the effect of ligand on nuclear receptor protein turnover still remains largely unknown. Therefore, we studied the effects of agonist and antagonists on the turnover of the human androgen receptor (hAR) protein in stably transformed Chinese hamster ovary cells expressing exogenous hAR. Western blot analysis showed that the most potent androgen, dihydrotestosterone (DHT), stabilizes hAR with the induction of the transactivation function of hAR. However, this androgen-induced stabilization of hAR protein was abrogated by well-known androgen antagonists, hydroxyflutamide and bicalutamide (BIC), with inhibition of the transactivation function of hAR. Thus, the present study suggests that androgen antagonists exert their effects through, at least in part, abrogating the agonist-induced stabilization of hAR protein as well as blocking the ligand-induced transactivation function of hAR.
Insights
Androgen agonists like DHT stabilize the human androgen receptor (hAR) protein, enhancing its function. Androgen antagonists block this stabilization and function, revealing a key mechanism of action for these drugs.
Area of Science:
- Molecular Endocrinology
- Nuclear Receptor Signaling
- Pharmacology
Background:
- Nuclear receptor ligand action is primarily determined by receptor expression levels.
- Receptor expression is regulated by transcriptional and post-transcriptional mechanisms.
- The impact of ligands on nuclear receptor protein turnover is not well understood.
Purpose of the Study:
- To investigate the effects of androgen agonists and antagonists on human androgen receptor (hAR) protein turnover.
- To elucidate the role of ligand-induced stabilization in hAR protein regulation.
- To understand the mechanism by which androgen antagonists inhibit hAR function.
Main Methods:
- Utilized stably transformed Chinese hamster ovary (CHO) cells expressing exogenous hAR.
- Employed Western blot analysis to assess hAR protein levels and stability.
- Examined the impact of dihydrotestosterone (DHT), hydroxyflutamide, and bicalutamide (BIC) on hAR turnover and transactivation.
Main Results:
- The potent androgen dihydrotestosterone (DHT) significantly stabilized hAR protein and induced its transactivation function.
- Androgen antagonists, hydroxyflutamide and bicalutamide (BIC), abrogated DHT-induced hAR stabilization.
- Antagonists also inhibited the ligand-induced transactivation function of the hAR.
Conclusions:
- Androgen antagonists exert their effects, at least partly, by preventing agonist-induced stabilization of the hAR protein.
- Antagonists block both the stabilization and the transactivation function of the hAR in response to ligands.
- This study provides critical insights into the post-transcriptional regulation of nuclear receptors by their ligands.