Recognition and Accommodation at the Androgen Receptor Coactivator Binding Interface

Abstract

Prostate cancer is a leading killer of men in the industrialized world. Underlying this disease is the aberrant action of the androgen receptor (AR). AR is distinguished from other nuclear receptors in that after hormone binding, it preferentially responds to a specialized set of coactivators bearing aromatic-rich motifs, while responding poorly to coactivators bearing the leucine-rich “NR box” motifs favored by other nuclear receptors. Under normal conditions, interactions with these AR-specific coactivators through aromatic-rich motifs underlie targeted gene transcription. However, during prostate cancer, abnormal association with such coactivators, as well as with coactivators containing canonical leucine-rich motifs, promotes disease progression. To understand the paradox of this unusual selectivity, we have derived a complete set of peptide motifs that interact with AR using phage display. Binding affinities were measured for a selected set of these peptides and their interactions with AR determined by X-ray crystallography. Structures of AR in complex with FxxLF, LxxLL, FxxLW, WxxLF, WxxVW, FxxFF, and FxxYF motifs reveal a changing surface of the AR coactivator binding interface that permits accommodation of both AR-specific aromatic-rich motifs and canonical leucine-rich motifs. Induced fit provides perfect mating of the motifs representing the known family of AR coactivators and suggests a framework for the design of AR coactivator antagonists.

Mechanisms of androgen receptor activation in advanced prostate cancer: differential co-activator recruitment and gene expression

“…In the presence of androgen all the ARs were able to interact with the LxxLL, FxxLY and FxxFF motifs, and interaction was stronger with phenylalanine-rich motifs than the LxxLL motif (Figure 2,compare (b) and (c) to (a)), in accordance with published studies (Hur et al, 2004). In the presence of MIB, there was no significant difference in the strength of interaction of AR WT , compared to any of the mutant receptors, with either FxxFF or FxxLY (Figures 2b and c).…”

“…However, the AR is idiosyncratic in that it appears to interact preferentially with phenylalanine-rich motifs, found in several AR co-activators including ARA70, FHL2 and gelsolin (Hsu et al, 2003;Dubbink et al, 2004;Hur et al, 2004;van de Wijngaart et al, 2006). We therefore next looked at whether the mutant receptors showed altered relative affinity for different interaction motifs in the presence of alternative ligands.…”

“…The main chain atoms at either end of the FxxLF motif form electrostatic interactions with both charge clamp residues. In contrast, the LxxLL motif forms hydrogen bonds with only one-Lys720 (Hur et al, 2004). Previous studies using computer modelling of AR LBD in complex with androgen or SARMs, that were complete agonists in transcriptional assays, showed that these ligands had distinct effects on the size and shape of the co-activator cleft and the distance between the charge clamp residues (Kazmin et al, 2006).…”

“…We therefore used a two-hybrid assay to study the effects of mutations and ligands on AR binding to three different interaction motifs-LxxLL, FxxLY or FxxFF. These motifs had previously been identified by phage display and interact with AR LBD in the presence of androgen (Hur et al, 2004).…”

“…Many co-activators, including the p160 protein SRC-1, interact with the LBD of nuclear receptors via conserved, helical leucine-rich motifs (LxxLL, L, leucine and x, any amino acid (reviewed in McKenna et al, 1999)). Recently the AR LBD has also been demonstrated to interact with similar phenylalanine-rich motifs (Hsu et al, 2003;Dubbink et al, 2004;Hur et al, 2004). However, SRC-1 and other co-activators can also interact with and promote activity of AF1 (reviewed in McEwan, 2004).…”