Abstract
The androgen receptor (AR) plays a central role in prostate cancer. Development of castration resistant prostate cancer (CRPC) requires androgen-independent activation of AR, which involves its large N-terminal domain (NTD) and entails extensive epigenetic changes depending in part on histone lysine demethylases (KDMs) that interact with AR. The AR-NTD is rich in low-complexity sequences, including a polyQ repeat. Longer polyQ sequences were reported to decrease transcriptional activity and to protect against prostate cancer, although they can lead to muscular atrophy. However, the molecular mechanisms underlying these observations are unclear. Using NMR spectroscopy, here we identify weak interactions between the AR-NTD and the KDM4A catalytic domain, and between the AR ligand-binding domain and a central KDM4A region that also contains low-complexity sequences. We also show that the AR-NTD can undergo liquid-liquid phase separation in vitro, with longer polyQ sequences phase separating more readily. Moreover, longer polyQ sequences hinder nuclear localization in the absence of hormone and increase the propensity for formation of AR-containing puncta in the nucleus of cells treated with dihydrotestosterone. These results lead us to hypothesize that polyQ-dependent liquid-liquid phase separation may provide a mechanism to decrease the transcriptional activity of AR, potentially opening new opportunities to design effective therapies against CRPC and muscular atrophy.
Highlights
Prostate cancer is one of the most common forms of cancer in men [1]
Almost no perturbations on the 1H-15N TROSY-heteronuclear single quantum coherence (HSQC) spectrum of 15N-KDM4A(1–350) were caused by fragments containing the androgen receptor (AR) ligand-binding domain (LBD) alone (AR-LBD; residues 663–919) or from the DNA-binding domain (DBD) to the LBD (AR-DBD-LBD; residues 554–919) (Fig 1D and 1E). These results show that, under these conditions, the catalytic domain of KDM4A binds weakly to AR-N-terminal domain (NTD) and that such binding is enhanced by the DBD, while there is no appreciable binding to the LBD or to the DBD in the absence of the NTD
Regulation of androgen receptor activity by self-association into liquid droplets at 100 μM concentration [37]. These findings, together with the known importance of the AR-NTD for development of castration resistant prostate cancer (CRPC), the notion that longer polyQ sequences in the AR-NTD may protect against prostate cancer, and our finding that low complexity sequences mediate AR-KDM4A interactions, led us to investigate how polyQ length affects the ability of AR-NTD to phase separate
Summary
Prostate cancer is one of the most common forms of cancer in men [1]. Survival and proliferation of prostate cancer cells depend critically on signaling through the androgen receptor (AR). The NTD has attracted much attention because of its known participation in transcriptional activity and, and in particular, because diverse C-terminally truncated splice variants of AR lacking the LBD have been identified in prostate cancer cell lines and in clinical specimens [19] These variants can explain the development of androgen-independent AR activity in CRPC. We find that nuclear localization is decreased by longer polyQ sequences in the absence of hormone, and that such sequences increase the formation of AR-containing puncta in nuclei of cells treated with dihydrotestosterone (DHT) Based on these results, we propose that longer polyQ sequences in AR may have a protective role against prostate cancer by enhancing self-association processes that reduce the AR transcriptional activity
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