A CRISPR-based high-throughput screening system identifies bromodomain inhibitors as transcriptional suppressors of CYP11B1.

CYP11B1 encodes steroid 11β-hydroxylase, the final rate-limiting enzyme for cortisol biosynthesis in the adrenal cortex. Excessive cortisol production is a hallmark of Cushing's disease (CD). While direct enzymatic inhibitors have been explored, achieving specificity remains a challenge due to the high homology between CYP11B1 and CYP11B2, highlighting transcriptional suppression of CYP11B1 as an alternative therapeutic strategy. To identify transcriptional regulators of CYP11B1, we generated genome-edited H295R adrenal cells carrying a luciferase reporter knocked into the endogenous CYP11B1 locus. Using this reporter cell line, we established a high-throughput screening (HTS) platform and screened a focused chemical library targeting epigenetic-related factors, given the importance of epigenetic mechanisms in gene regulation. Among eight candidate compounds identified, we focused on JQ1, a bromodomain inhibitor. JQ1 significantly suppressed Forskolin-induced CYP11B1 promoter activity and mRNA expression without causing cytotoxicity, suggesting the involvement of epigenetic readers in the transcriptional regulation of steroidogenic genes. Furthermore, the reporter-based HTS platform developed here, when combined with our previously established CYP11B2-luciferase system, may facilitate the identification of compounds that selectively modulate adrenal steroidogenic pathways. These findings provide a foundation for the development of novel transcription-targeted therapies for CD.