Abstract 1387: Convergent CREB1/FoxA1 transcriptional activity defines castration-resistant prostate cancer gene expression profile

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA To identify novel pathways and therapeutic targets in lethal, castration-resistant prostate cancer (CRPC), we extended our previous findings that the overexpression of several G1/S and G2/M phase cell cycle genes in CRPC vs. androgen-dependent prostate cancer (ADPC) cells relies on the cooperative activity of the transcription factors (TFs) FoxA1 and CREB1, and sought to comprehensively characterize their role in supporting CRPC growth. We have taken an integrated genomics approach to reveal the CREB1/FoxA1-coregulated gene expression profile of ADPC (LNCaP) and CRPC (LNCaP-abl) cell line models. Chromatin-immunoprecipitation combined with high-throughput sequencing (ChIP-seq) was performed using antibodies against CREB1 and FoxA1 to reveal genome-wide TF binding sites. Our results indicate that these factors adopt divergent binding patterns in each cell line and that the CREB1 and FoxA1 cistromes exhibit a higher degree of overlap in CRPC vs. ADPC. RNA-seq was also performed in each cell line following transfection with Control-, FoxA1-, or CREB1-targeting small interfering RNA (siRNA) molecules. We identified putative direct CREB1/FoxA1-coregulated genes by noting instances of TF binding near cooperatively coregulated genes (i.e. those up- or down-regulated by both CREB1 and FoxA1 knockdown). Unlike previous analyses, which found that cooperative TF activity occurs primarily in the event of TF co-occupancy of gene regulatory elements, we found that non-overlapping as well as overlapping CREB1/FoxA1 binding events were significantly enriched within cooperatively coregulated target gene loci compared to genes that were unresponsive to TF knockdown. Gene Ontology (GO) analysis of LNCaP-abl-coregulated genes found that CREB1/FoxA1 enhance the expression of critical CRPC pathways including “DNA Repair” and “Aurora Kinase,” while they repress pathways such as “Apoptosis” and, consistent with previous findings, “Androgen Receptor Signaling.” Importantly, CREB1/FoxA1-up-regulated and down-regulated pathway elements exhibit overexpression or under-expression, respectively, in LNCaP-abl vs. LNCaP as well as in public gene expression datasets of metastatic vs. primary prostate cancer. Finally, we performed several proof-of-concept analyses to demonstrate that the CREB1/FoxA1-coregulatory pathway is sensitive to compounds that target CREB1 phosphorylation, a critical event in the transactivation of CREB1 mediated in large part by the related AGC kinase family members PKA and Akt/PKB. Together these results reveal that CREB1 and FoxA1 assume overlapping roles in determining the expression of genes/networks relevant to experimental models and clinical cases of advanced prostate cancer, and though targeting transcription factors has proven challenging, this coregulatory pathway may in fact represent a therapeutic target owing to its kinase-dependent activation. Citation Format: Benjamin D. Sunkel, Dayong Wu, Xiangtao Liu, Zhenqing Ye, Victor Jin, Qianben Wang. Convergent CREB1/FoxA1 transcriptional activity defines castration-resistant prostate cancer gene expression profile. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1387. doi:10.1158/1538-7445.AM2014-1387