Abstract 1502: PDEF inhibits prostate cancer progression by promoting luminal differentiation

Abstract Background: The emergence of metastatic castration-resistant prostate cancer (PCa) is accompanied by the loss of prostate luminal cell identity. Cell identity is defined by key transcription factors by association with enhancer and super-enhancer elements. Our previous studies have shown that Sam Pointed Domain Ets Transcription Factor a.k.a. Prostate-Derived Ets Factor (SPDEF/PDEF), inhibits tumor metastasis in vivo. Recently, PDEF has been reported as one of the super enhancer related transcription factors in the luminal PCa cell line LNCaP and observed to be highly expressed in prostate luminal cells. We propose that PDEF functions as a putative tumor metastasis suppressor and inhibits tumor progression by restoring luminal cell identity. The present study was designed to investigate the role of PDEF in metastatic PCa progression. Methods: PC3 and DU145 cells were stably transfected with PDEF/control pBABE retroviral vectors. Global gene expression changes were probed using Affymetrix microarray. Microarray was analyzed with GSEA. qRT-PCR was performed to confirm the differential gene expression profile and immunohistochemistry, immunofluorescence and immunoblot were performed to visualize protein expression. ChIP-seq data were extracted from SRP002475 and aligned with Bowtie. Peaks were identified by MACS2. Clinical data were extracted from GSE16560, GSE21034 and TCGA database. Statistical analysis was performed with GraphPad and R. Results: Analysis of our microarray studies revealed that PDEF expression resulted in the negative enrichment of metastasis-related gene sets and the positive enrichment of gene sets involved in luminal differentiation. Especially, PDEF restores canonical AR signaling in PC3 cells. Confirmed with qPCR, IB and IF, PDEF also inhibits the expression of neuroendocrine-related genes, stemness-related genes while promoting the expression of prostate luminal differentiation-related genes. Furthermore, PDEF ChIP-seq analysis revealed a novel PDEF binding site at the putative promoter region of prostate luminal cell marker cytokeratin 18 while no significant peaks were identified within the regulatory elements of EMT related transcription factors. Our data suggest that PDEF promotes the expression of cytokeratin 18 in vitro and in vivo. Knockdown of cytokeratin 18 by siRNA increases the expression of Twist1 while decreases the expression of E-Cadherin while PDEF expression level is not affected. Moreover, data analysis from multiple clinical prostate cancer cohorts suggests the loss of PDEF is associated with tumor metastasis, tumor progression, and poor survival. Conclusions: PDEF expression leads to luminal differentiation phenotype in advanced prostate cancer cells. PDEF inhibits cell migration and metastasis in part by down-regulating EMT related transcription factors in part through directly promoting the expression of cytokeratin 18. Citation Format: Fengtian Wang, Sweaty Koul, Hari K. Koul. PDEF inhibits prostate cancer progression by promoting luminal differentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1502.