Dynamic phase separation of the androgen receptor and its coactivators key to regulate gene expression

Abstract

Numerous cancers, including prostate cancer (PCa), are addicted to transcription programs driven by specific genomic regions known as super-enhancers (SEs). The robust transcription of genes at such SEs is enabled by the formation of phase-separated condensates by transcription factors and coactivators with intrinsically disordered regions. The androgen receptor (AR), the main oncogenic driver in PCa, contains large disordered regions and is co-recruited with the transcriptional coactivator mediator complex subunit 1 (MED1) to SEs in androgen-dependent PCa cells, thereby promoting oncogenic transcriptional programs. In this work, we reveal that full-length AR forms foci with liquid-like properties in different PCa models. We demonstrate that foci formation correlates with AR transcriptional activity, as this activity can be modulated by changing cellular foci content chemically or by silencing MED1. AR ability to phase separate was also validated in vitro by using recombinant full-length AR protein. We also demonstrate that AR antagonists, which suppress transcriptional activity by targeting key regions for homotypic or heterotypic interactions of this receptor, hinder foci formation in PCa cells and phase separation in vitro. Our results suggest that enhanced compartmentalization of AR and coactivators may play an important role in the activation of oncogenic transcription programs in androgen-dependent PCa.

Phase-separation: a possible new layer for transcriptional regulation by glucocorticoid receptor

“…Similarly, condensates modulated by AR are described as active transcriptional regions that depend on AR's multi-domain, a marked feature of GR LLPS and other transcription factors. The splice variant AR-v7 that lacks LBD and is incapable of forming foci reveals that this domain mediates critical interaction in AR-mediated LLPS (93,106). Not surprisingly, PS with PR has also been proposed as a molecular event involved in transcriptional regulation, which was corroborated by evidence that PR dimers act as important functional units, similarly to what happens with GR (100).…”

Transcription factor condensates and signaling driven transcription

“…[ 16 , 25 , 77 ]. Similarly, other nuclear receptors like AR and GR also form nuclear condensates in a hormone-dependent manner [ 19 , 47 , 117 ].…”

Advances in Nucleotide Repeat Expansion Diseases: Transcription Gets in Phase

“…For TBP, the disease-associated glutamine repeat expansion originated a decrease in the phase separation capacity of this TF [ 62 ]. Interestingly, it has been reported that the androgen receptor (AR), harboring a CAG repeat that when expanded causes spinal bulbar muscular atrophy (SBMA), has the ability to form phase separation condensates [ 90 ]. Curiously, the AR transcription factor interacts with MED1 by forming condensates where active transcription occurs.…”

“…Curiously, the AR transcription factor interacts with MED1 by forming condensates where active transcription occurs. It is reported that point mutations in several AR domains inhibit the co-condensation with MED1, altering its transcriptional activity [ 90 ]. Thus, if the CAG repeat expansion goes beyond a given threshold, as occurs in SMBA, this could impair the AR/MED1 condensate formation and, consequently, lead to transcriptional dysregulation, although no evidence for this has been reported so far.…”