Abstract 88: The Nkx3.1 homeobox gene maintains prostatic identity while its loss leads to prostate cancer initiation

Background Maintenance of epithelial cell identity is tightly coordinated by tissue-specific gene expression programs, which are often deregulated during tumorigenesis. The homeodomain-containing transcription factor, Nkx3.1, is a key regulator of normal prostatic development and is frequently lost at early stages of prostate cancer initiation. In this study, we aim to elucidate detailed mechanisms governing Nkx3.1-driven maintenance of prostate identity and how deregulation of such can lead to prostate tumorigenesis. Models and Methods We evaluated the consequences of Nkx3.1 loss or gain of function in vivo using genetically-engineered mouse models and cell-recombination assays. RNA sequencing was performed to generate gene expression profiles, which were analyzed using Gene Set Enrichment analysis (GSEA), and validated by quantitative real-time PCR. In parallel, protein expression was assessed by immunofluorescence and western blot. Immunoprecipitation (IP) and chromatin-immunoprecipitation (ChIP) assays were performed using RWPE1 prostate epithelial cells. Results Here, we show that loss of function of Nkx3.1 leads to the progressive down-regulation of a prostate-specific gene expression program and to aberrant expression of genes that are not typically expressed in the prostate epithelium. Conversely, gain of function of Nkx3.1 in non-prostatic epithelium leads to the acquisition of a prostate-like morphology and expression of prostate-related genes. Our findings indicate that the underlying mechanism by which Nkx3.1 promotes prostatic identity is via epigenetic regulation of gene expression. In particular, we show that Nkx3.1 interacts with the histone methyl-transferase complex G9a/Glp. Finally, we demonstrate that this interaction is necessary for maintenance of prostate identity in vivo and that Nkx3.1 and G9a cooperate to control expression of genes that coordinate prostatic epithelial integrity. Conclusions Our results suggest that Nkx3.1 promotes prostatic identity by interacting with histone modifying enzymes to coordinate the expression of prostate-specific genes and that the loss of this function results in a failure to maintain prostate identity associated with early stages of prostate tumorigenesis. Citation Format: Clémentine Le Magnen, Aditya Dutta, Cory Abate-Shen. The Nkx3.1 homeobox gene maintains prostatic identity while its loss leads to prostate cancer initiation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 88. doi:10.1158/1538-7445.AM2015-88