Effect of geldanamycin on androgen receptor function and stability

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Steroid receptors, including the androgen receptor (AR), function within heterocomplexes involving heat shock proteins (HSPs).
• Hsp90 is crucial for maintaining the native state of steroid receptors, but its specific role in AR activity compared to other steroid receptors was unclear.
• Hsp90 inhibitors, like geldanamycin (GA), can disrupt steroid receptor activity and promote degradation.

Purpose of the Study:

• To investigate the role of Hsp90 in the function of the androgen receptor (AR) heterocomplex using the Hsp90 inhibitor geldanamycin (GA).
• To determine the effects of GA on AR protein levels, ligand-binding ability, and transcriptional activity in prostate cancer cells.

Main Methods:

• LNCaP prostate cancer cells were treated with GA in the presence of a synthetic androgen (mibolerone).
• AR protein levels, androgen-induced gene expression (FKBP51, PSA), and reporter gene transactivation were measured.
• Degradation rates of AR were assessed using 35S-labeling and proteasomal inhibitors (lactacystin).

Main Results:

• GA treatment significantly reduced androgen-induced AR protein levels and suppressed the expression of androgen-upregulated genes, including PSA.
• AR-mediated transactivation of reporter genes was reversibly inhibited by GA.
• GA treatment increased AR degradation via the proteasomal pathway, disrupting both hormone-binding ability and receptor stability.

Conclusions:

• Hsp90 activity is essential for maintaining the androgen receptor's (AR) proper folding into a high-affinity ligand-binding conformation.
• Hsp90 inhibition by GA leads to AR instability, degradation, and a significant loss of androgen-induced gene activation.
• These findings underscore the critical role of Hsp90 in AR functional activity and protein homeostasis.