Abstract PR08: The N-Myc transcriptional program driving the neuroendocrine prostate cancer phenotype

Abstract

Abstract Emerging observations from clinical trials suggest that a subset of castration resistant prostate adenocarcinomas (CRPC) eventually evolve or progress to a predominantly small cell carcinoma or neuroendocrine phenotype [1]. Neuroendocrine prostate cancer (NEPC) does not typically express the androgen receptor (AR) or secrete prostate specific antigen (PSA), and often expresses markers of neuroendocrine lineage [2]. NEPC is clinically aggressive and carries a poor prognosis with an average survival of less than one year [3, 4]. Identification of effective treatment strategies for this lethal subtype of prostate cancer represents a significant unmet need in the clinic. We have previously discovered significant over-expression and gene amplification of AURKA (encoding Aurora-A) and MYCN (encoding N-Myc) in NEPC as compared to prostate adenocarcinoma [5, 6]. As in neuroblastoma [7], N-Myc interacts with Aurora-A in NEPC which leads to a co-stabilization of both proteins and that ectopic expression of N-Myc or Aurora-A induces neuroendocrine transformation of prostate adenocarcinoma cells [5]. However, the molecular mechanisms that underlie N-Myc driven NEPC have yet to be characterized. We performed RNA-sequencing (RNAseq) and ChIP-sequencing from multiple stable prostate adenocarcinoma cells with and without N-Myc over-expression. RNAseq reads were aligned to the hg19 reference genome using TopHat. Based on GSEA , pathway analysis and further validation of our N-Myc signature, we found that N-Myc is recruited to AR-bound enhancers and AR target genes, dramatically reduces AR signaling and induces a profile enriched in pro-metastatic, dedifferentiation and Polycomb Repressive Complex deregulated genes as well as other genes encoding targetable proteins. RNAseq data from 128 clinical samples (17 NEPC, 10 castrate resistant prostate cancer, 68 prostate adenocarcinoma patient tumors and 33 matched benign prostate samples) were used to assess clinical relevance and a novel Nanostring assay, targeted RT-PCR and ChIP-PCR to validate our findings. We used DESeq and MISO to identify differential expressed genes and differential exon expression. We have identified a signature of deregulated genes including specific alternatively spliced mRNA variants and splicing factors associated with N-Myc over-expression that are both biologically and clinically relevant. This included several variant transcripts from genes that are implicated in cancer-related signaling (e.g.PIK3C2A,ATM,HUWE1) and an up-regulation of the splicing factor NOVA1 (neuro-oncological ventral antigen 1). In conclusion, our findings have the potential to ultimately lead to the identification of a new class of disease specific biomarkers and therapeutic alternatives for this aggressive subgroup of prostate cancer.