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Updated: May 29, 2026

Biochemical Reconstitution of Steroid Receptor•Hsp90 Protein Complexes and Reactivation of Ligand Binding
Published on: September 21, 2011
BAG-1 diversely affects steroid receptor activity
Regina T Knapp1, Andrea Steiner, Ulrike Schmidt
1Max Planck Institute of Psychiatry, Kraepelinstrasse 10, 80804 Munich, Germany.
Bcl-2-associated athanogene 1 (BAG-1) isoforms BAG-1L and BAG-1M inhibit progesterone receptor (PR) activity, requiring the heat-shock protein 70-binding domain. BAG-1M also binds and inhibits the mineralocorticoid receptor (MR).
Area of Science:
- Molecular Biology
- Cellular Biology
- Endocrinology
Background:
- Bcl-2-associated athanogene 1 (BAG-1) is a co-chaperone for heat-shock protein 70 (HSP70).
- BAG-1 modulates steroid receptor activity, inhibiting the glucocorticoid receptor (GR) and stimulating the androgen receptor (AR).
- BAG-1's differential effects on GR and mineralocorticoid receptor (MR), despite their homology, are not fully understood.
Purpose of the Study:
- To investigate the effect of BAG-1 on progesterone receptor (PR) activity.
- To elucidate the mechanisms underlying BAG-1's differential regulation of steroid receptors.
- To explore the interaction between BAG-1 and the MR.
Main Methods:
- Analysis of transcriptional activity of progesterone receptor (PR) and mineralocorticoid receptor (MR) in the presence of BAG-1 isoforms.
- Mutational analyses of PR and BAG-1 isoforms to identify interaction domains.
- Assessment of BAG-1 binding to PR and MR.
Main Results:
- BAG-1 long (BAG-1L) and middle (BAG-1M) isoforms inhibit PR transcriptional activity, similar to their effect on GR.
- Inhibition of PR by BAG-1 requires the HSP70-binding domain of BAG-1.
- BAG-1M binds to and inhibits the transcriptional activity of the MR, contrary to previous reports.
Conclusions:
- BAG-1 isoforms BAG-1L and BAG-1M regulate PR activity through a mechanism distinct from GR.
- The HSP70-binding domain of BAG-1 is crucial for PR inhibition.
- BAG-1M interacts with and inhibits MR, necessitating a re-evaluation of its physiological role in steroid receptor regulation.
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