surface on the androgen receptor that allosterically regulates coactivator binding

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 41; pp. 16074 - 16079
• Main Authors: Estébanez-Perpiñá, Eva, Arnold, Alexander A, Nguyen, Phuong, Rodrigues, Edson Delgado, Mar, Ellena, Bateman, Raynard, Pallai, Peter, Shokat, Kevan M, Baxter, John D, Guy, R. Kiplin, Webb, Paul, Fletterick, Robert J
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 09.10.2007; National Acad Sciences
• Subjects: Allosteric Site - genetics; Androgen Receptor Antagonists; Androgens; Animals; Binding sites; Biochemistry; Biological Sciences; Crystallography, X-Ray; Crystals; Drug interactions; Drug regulation; Electron density; Genetic mutation; In Vitro Techniques; Libraries; Ligands; Mice; Models, Molecular; Molecules; Mutation; Nuclear Receptor Coactivator 2 - metabolism; Nuclear receptors; Prostate cancer; Protein Structure, Tertiary; Receptors, Androgen - chemistry; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0708036104

Current approaches to inhibit nuclear receptor (NR) activity target the hormone binding pocket but face limitations. We have proposed that inhibitors, which bind to nuclear receptor surfaces that mediate assembly of the receptor's binding partners, might overcome some of these limitations. The androgen receptor (AR) plays a central role in prostate cancer, but conventional inhibitors lose effectiveness as cancer treatments because anti-androgen resistance usually develops. We conducted functional and x-ray screens to identify compounds that bind the AR surface and block binding of coactivators for AR activation function 2 (AF-2). Four compounds that block coactivator binding in solution with IC₅₀ [almost equal to] 50 μM and inhibit AF-2 activity in cells were detected: three nonsteroidal antiinflammatory drugs and the thyroid hormone 3,3',5-triiodothyroacetic acid. Although visualization of compounds at the AR surface reveals weak binding at AF-2, the most potent inhibitors bind preferentially to a previously unknown regulatory surface cleft termed binding function (BF)-3, which is a known target for mutations in prostate cancer and androgen insensitivity syndrome. X-ray structural analysis reveals that 3,3',5-triiodothyroacetic acid binding to BF-3 remodels the adjacent interaction site AF-2 to weaken coactivator binding. Mutation of residues that form BF-3 inhibits AR function and AR AF-2 activity. We propose that BF-3 is a previously unrecognized allosteric regulatory site needed for AR activity in vivo and a possible pharmaceutical target.