Genome-scale CRISPR screens identify PTGES3 as a direct modulator of androgen receptor function in advanced prostate cancer.

The androgen receptor (AR) is a critical driver of prostate cancer (PCa). Here, to study regulators of AR protein levels and oncogenic activity, we developed a live-cell quantitative endogenous AR fluorescent reporter. Leveraging this AR reporter, we performed genome-scale CRISPRi flow cytometry sorting screens to systematically identify genes that modulate AR protein levels. We identified and validated known AR protein regulators, including HOXB13 and GATA2, and also unexpected top hits including PTGES3-a poorly characterized gene in PCa. PTGES3 repression resulted in loss of AR protein, cell-cycle arrest and cell death in AR-driven PCa models. Clinically, analysis of PCa data demonstrates that PTGES3 expression is associated with AR-directed therapy resistance. Mechanistically, we show PTGES3 binds directly to AR, regulates AR protein stability and is necessary for AR function in the nucleus at AR target genes. PTGES3 represents a potential therapeutic target for overcoming known mechanisms of resistance to existing AR-directed therapies in PCa.