Abstract 5287: Prostate-derived Etsfactor modulates AR-mediated gene expression and promotes luminal differentiation

Introduction: Transcription regulation, governed by the presence of transcription factors and the accessibility of regulatory elements such as enhancers is crucial in restricting lineage plasticity. Deregulated expression of differentiation-related transcription factors leads to cancer progression and poor prognosis. Prostate-derived ETS factor (PDEF) is one of the cell identity-related transcription factors characterized by the abundance of H3K27ac near its genomic locus. Highly expressed in prostate luminal cells, PDEF has been shown to promote the transcription of PSA in collaboration with AR. Our previous studies showed loss of PDEF is associated with higher Gleason score and tumor metastasis through MMP9 and Twist1. However, the role of PDEF, as a transcription factor, remains poorly understood. In this study, we evaluated the effects of PDEF on modulation of AR cistrome and luminal/epithelial differentiation. Methods: TCGA data were extracted from cBioportal and analyzed using R. Gene set enrichment analysis (GSEA) was performed using default settings and gene sets were downloaded from MySigDB. Genomic coverage analysis was performed using SeqPlots. ChIP-seq analysis was performed using GALAXY. PC3 cells were grown in DMEM/F12 medium and retroviral expression was used to generate cells with stable PDEF expression. ChIP experiments were performed using Chromatrap ChIP-seq kit followed by standard qPCR with SYBR-Green. Gene track was visualized with IGV. Results: Despite the oncogenic role of AR signaling, it plays a pivotal part in prostate luminal differentiation. We observed that prostate cancer progression is associated with loss of PDEF accompanied by a transcription switch from canonical AR targets to non-canonical in TCGA database. Moreover, AR genomic coverage in prostate luminal cell-specific enhancer regions is decreased in tumor tissues compared with the paired adjacent normal tissue. Stable-expression of PDEF in PC3 cells restored the expression of canonical AR targets as well as the enhancer pattern similar to LNCaP cells. PDEF ChIP-seq analysis of multiple cell lines revealed that PDEF co-localize with H3K4me1. ChIP-qPCR confirmed that PDEF co-localized with AR at the PSA enhancer region. We hypothesize that PDEF is critical for maintaining prostate luminal specific enhancers. Expressing PDEF in LNCaP-abl cells also increased the transcription of canonical AR targets and inhibited the transcription of non-canonical AR targets. Independent of AR, we discovered that PDEF binds to the promoter region of CK18. Moreover, a positive correlation was observed between PDEF and CK18 in cell culture and prostate cancer samples in the TCGA database. Conclusion: These results show that PDEF plays an important role in the maintenance of canonical AR signature and luminal cell differentiation in prostate cancer in-part by rewiring the transcriptional program. Citation Format: Fengtian Wang, Hari K. Koul. Prostate-derived Etsfactor modulates AR-mediated gene expression and promotes luminal differentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5287.