CRISPR screening identifies regulators of enhancer mediated androgen receptor transcription in advanced prostate cancer (ATAC-Seq)

Amplification of the androgen receptor (AR) locus is the most frequent alteration in metastatic treatment resistant prostate cancer. Recently it was discovered that an enhancer of the AR is co-amplified with the AR gene body and contributes to increased AR transcription and resistance to androgen deprivation therapy. However, the mechanism of enhancer activation in advanced disease is unknown. Here, we used functional genetic screening to identify transcription factors that bind to the AR enhancer and are required for enhancer mediated AR transcription. We validated binding of the transcription factors, HOXB13, GATA2, and TFAP2C in patient derived xenografts and demonstrated differential effects on features associated with active chromatin state including H3K27ac, DNA accessibility, and enhancer-promoter interaction frequency. Interestingly, the AR enhancer belongs to a set of regulatory elements that requires HOXB13 to maintain FOXA1 binding, uncovering a novel role for HOXB13 in castration-resistant prostate cancer. This work provides a framework to functionally identify trans-acting factors required for activation of disease related noncoding regulatory elements.