Whereas dimerization of the DNA‐binding domain of the androgen receptor (AR) plays an evident role in recognizing bipartite response elements, the contribution of the dimerization of the ligand‐binding domain (LBD) to the correct functioning of the AR remains unclear. Here, we describe a mouse model with disrupted dimerization of the AR LBD (ARLmon/Y). The disruptive effect of the mutation is demonstrated by the feminized phenotype, absence of male accessory sex glands, and strongly affected spermatogenesis, despite high circulating levels of testosterone. Testosterone replacement studies in orchidectomized mice demonstrate that androgen‐regulated transcriptomes in ARLmon/Y mice are completely lost. The mutated AR still translocates to the nucleus and binds chromatin, but does not bind to specific AR binding sites. In vitro studies reveal that the mutation in the LBD dimer interface also affects other AR functions such as DNA binding, ligand binding, and co‐regulator binding. In conclusion, LBD dimerization is crucial for the development of AR‐dependent tissues through its role in transcriptional regulation in vivo. Our findings identify AR LBD dimerization as a possible target for AR inhibition.

The androgen receptor (AR) plays a central role in the development and maintenance of the male phenotype. The binding of androgens to the receptor induces interactions between the carboxyterminal ligand-binding domain and the highly conserved 23FQNLF 27 motif in the amino-terminal domain. The role of these so-called N/C interactions in AR functioning is debated. In vitro assays show that mutating the AR in the 23FQNLF 27 motif (called AR NoC) attenuates the AR transactivation of reporter genes, has no effect on ligand binding, but does affect protein-protein interactions with several AR coregulators. To test the in vivo relevance of the N/C interaction, we analyzed the consequences of the genomic introduction of the AR NoC mutation in mice. Surprisingly, the AR NoC/Y mice show a normal male development, with unaffected male anogenital distance, normal accessory sex glands as well as male circulating androgen levels, body composition and fertility. The responsiveness of androgen target genes in kidney, prostate and testes was also unaffected. We thus conclude that the N/C interactions in the AR are not essential for the development of a male phenotype under normal physiological conditions.

Treatment of prostate cancer relies predominantly on the inhibition of androgen receptor (AR) signaling. Despite the initial effectiveness of the antiandrogen therapies, the cancer often develops resistance to the AR blockade. One mechanism of the resistance is glucocorticoid receptor (GR)-mediated replacement of AR function. Nevertheless, the mechanistic ways and means how the GR-mediated antiandrogen resistance occurs have remained elusive. Here, we have discovered several crucial features of GR action in prostate cancer cells through genome-wide techniques. We detected that the replacement of AR by GR in enzalutamide-exposed prostate cancer cells occurs almost exclusively at pre-accessible chromatin sites displaying FOXA1 occupancy. Counterintuitively to the classical pioneer factor model, silencing of FOXA1 potentiated the chromatin binding and transcriptional activity of GR. This was attributed to FOXA1-mediated repression of theNR3C1(gene encoding GR) expressionviathe corepressor TLE3. Moreover, the small-molecule inhibition of coactivator p300’s enzymatic activity efficiently restricted GR-mediated gene regulation and cell proliferation. Overall, we identified chromatin pre-accessibility and FOXA1-mediated repression as important regulators of GR action in prostate cancer, pointing out new avenues to oppose steroid receptor-mediated antiandrogen resistance.