Abstract 3645: Epigenetic regulation of oncogenic transcription mediated by aberrantly activated enhancers in prostate cancer
Authors: Sato Hiroaki , Sugiura Masahiro , Kanesaka Manato , Okabe Atsushi , Fukuyo Masaki , Sakamoto Shinichi , Komiya Akira , Ichikawa Tomohiko , Kaneda Atsushi 
Published: September 2020

Since androgen receptor (AR) is a master transcription factor of prostate gland in both normal development and carcinogenesis, androgen deprivation therapy (ADT) is quite effective for primary prostate cancer (PC) even in advanced disease. During ADT, however, PC tumors generally acquire resistance through oncogenic activation independent from androgen-AR signaling, and progress to lethal castration-resistant PC (CRPC). Transcription factors (TFs) such as AR regulate gene expression through binding regulatory elements of genome called as enhancers. Aberrantly activated enhancers regulating oncogenes could be one of the mechanisms of cancer therapy resistance.

In this study, to clarify how aberrant enhancer activation contribute to genesis of CRPC, we performed comprehensive transcriptome and epigenome analyses by RNA-seq and ChIP-seq for H3K4me1, H3K4me3, H3K27ac, H3K79me2, BRD4, AR, FOXA1 and RNA polymerase 2 (RNApol2). Using androgen dependent PC cells LNCaP and its derivative CRPC cells LNCaP95, we extracted BRD4(+)/AR(+)/FOXA1(+) enhancers and super enhancers (SEs) defined by cluster of H3K27ac regardless of BRD4, AR, FOXA1 binding. SE neighboring genes were mostly targeted by BRD4(+)/AR(+)/FOXA1(+) enhancers in LNCaP (57.5%), but markedly less in LNCaP95 (25.3%), suggesting a shift from AR-dependent to AR-independent regulation. In contrast, SE neighboring genes were mostly epigenetically modified with H3K79me2 in both LNCaP (77.4%) and LNCaP95 (76.2%). In addition, the mRNA expression levels of H3K79methyltansferase DOT1L was upregulated in CRPC clinical tissues. While BRD4 inhibition was quite effective for suppressing cell growth in LNCaP, but less effective in LNCaP95, DOT1L inhibition was markedly effective to both cells, inducing marked cell cycle arrest and apoptosis. Furthermore, precise analyses of RNApol2 behavior and transcriptome alteration revealed that BRD4 and DOT1L regulated different genes in a different manner. Mechanistically, while BRD4 inhibition suppressed AR target genes through reducing initiation of transcriptional elongation, DOT1L inhibition suppressed SE neighboring genes through reducing termination of transcriptional elongation.

In conclusion, our results indicated that BRD4 and DOT1L played critical role in regulating transcription mediated by aberrantly activated enhancers, and could be targeted as an epigenetic therapeutic strategy for CRPC.

Citation Format: Hiroaki Sato, Masahiro Sugiura, Manato Kanesaka, Atsushi Okabe, Masaki Fukuyo, Shinichi Sakamoto, Akira Komiya, Tomohiko Ichikawa, Atsushi Kaneda. Epigenetic regulation of oncogenic transcription mediated by aberrantly activated enhancers in prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3645.