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The non-activated glucocorticoid receptor: structure and activation
J A Gustafsson1, A C Wikström, M Denis
1Department of Medical Nutrition, Karolinska Institute, Huddinge University Hospital, Sweden.
Journal of Steroid Biochemistry
|January 1, 1989
Summary
Glucocorticoid receptors exist as large, inactive complexes with heat shock protein 90 (hsp90). Ligand binding and heat treatment dissociate this complex, enabling DNA interaction and receptor activation.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- Glucocorticoid receptors (GRs) are crucial for cellular response to glucocorticoids.
- In target cells, GRs exist as large, soluble complexes unable to bind DNA.
- These complexes involve a steroid/DNA-binding polypeptide and heat shock protein 90 (hsp90).
Purpose of the Study:
- To characterize the interaction between GRs and hsp90.
- To elucidate the mechanism of GR activation and DNA binding.
- To determine the role of hsp90 in GR function.
Main Methods:
- Purification of hsp90 from rat liver cytosol.
- Biochemical characterization of purified hsp90, including its role as a dimer.
- Development of monospecific antibodies against hsp90.
- DNA-binding assays and sucrose gradient ultracentrifugation.
- In vitro translation of GR mRNA.
Main Results:
- hsp90 was purified and identified as a dimer in the large GR complex.
- Dissociation of the GR-hsp90 complex and subsequent DNA binding were induced by ligand binding and heat treatment.
- hsp90 was shown to interact with the steroid-binding domain of the GR.
- In vitro translation demonstrated that GR is synthesized in an inactive, hsp90-associated form.
Conclusions:
- The glucocorticoid receptor is synthesized and maintained in a non-activated state through association with hsp90.
- hsp90 binding prevents GR interaction with DNA until ligand binding and heat-induced dissociation occur.
- This mechanism ensures that GRs are poised for activation upon hormonal stimulation.