The androgen receptor (AR) is a key driver of prostate cancer development. Antiandrogens effectively inactivate the AR, but subsequent AR reactivation progresses the disease to castrate-resistant prostate cancer (CRPC). Constitutively active AR splice variants (AR-V) that function unchallenged by current AR-targeted therapies are key drivers of CRPC. Currently, very little is known about the regulation of AR-Vs at the chromatin level. Here, we show that the pioneer factor GATA2 is a critical regulator of AR-Vs. Furthermore, we demonstrate that the GATA2 cistrome in CRPC shares considerable overlap with bromodomain and extraterminal (BET) proteins and is codependent for DNA binding. GATA2 activity is compromised by BET inhibitors, which attenuates the pioneering role of GATA2 in CRPC. In all, this study indicates that GATA2 is a critical regulator of AR-V-mediated transactivation and is sensitive to BET inhibitors, signifying these agents may be efficacious in patients with CRPC which overexpress GATA2. Implications:We have defined novel mechanisms of AR-V and GATA2 regulation in advanced prostate cancer that could be therapeutically exploited.

<p>qPCR primers</p>

<p>siRNA sequences</p>

<p>S1: GATA2 depletion down-regulates AR-V target genes S2: Chromatin occupancy of AR-Vs is not perturbed by GATA2 depletion S3: Overlapping GATA2 and AR-V transcriptomes S4: Gene ontology of GATA2 and AR-V transcriptomes S5: Assessing GATA2 and BET protein interplay in prostate cancer cell lines S6: Global cistromic analysis of GATA2 S7: Overlapping cistromes of GATA2 and BET family members S8: Assessing overlap of GATA2 and BET protein-regulated transcriptomes S9: GATA2 regulates splicing activity in prostate cancer cells</p>

<div>Abstract<p>The androgen receptor (AR) is a key driver of prostate cancer development. Antiandrogens effectively inactivate the AR, but subsequent AR reactivation progresses the disease to castrate-resistant prostate cancer (CRPC). Constitutively active AR splice variants (AR-V) that function unchallenged by current AR-targeted therapies are key drivers of CRPC. Currently, very little is known about the regulation of AR-Vs at the chromatin level. Here, we show that the pioneer factor GATA2 is a critical regulator of AR-Vs. Furthermore, we demonstrate that the GATA2 cistrome in CRPC shares considerable overlap with bromodomain and extraterminal (BET) proteins and is codependent for DNA binding. GATA2 activity is compromised by BET inhibitors, which attenuates the pioneering role of GATA2 in CRPC. In all, this study indicates that GATA2 is a critical regulator of AR-V–mediated transactivation and is sensitive to BET inhibitors, signifying these agents may be efficacious in patients with CRPC which overexpress GATA2.</p>Implications:<p>We have defined novel mechanisms of AR-V and GATA2 regulation in advanced prostate cancer that could be therapeutically exploited.</p></div>