Transcriptional networks downstream of the AR identify clinically relevant prostate cancer targets

The AR signalling axis is central to Prostate Cancer (PrCa) biology, shown by its use in both screening (PSA) and treatment of the disease (androgen deprivation therapy). Identifying direct target genes of the AR will provide a better understanding the key signalling pathways controlled by the AR in PrCa and could lead to improved biomarkers and future therapeutic targets for the disease. To this end we have performed fine mapping of androgen responsive gene expression in prostate cancer cell lines using Illumina bead-arrays, coupled with AR chromatin-immunoprecipitation and Solexa sequencing technology (ChIP-seq). This approach generated over ten thousand candidate AR target genes. We have then undertaken large scale, cross-platform validation using BioTrove Realtime PCR panels which allow the measurement of >600 transcripts simultaneously. Using this combination of approaches we have identified and validated several hundred AR regulated genes. We found that metabolic enzymes and kinases were significantly enriched in the set of direct AR regulated genes. In nine independent clinical gene expression studies we found that the most consistently up-regulated AR target gene was a calcium regulated kinase. At the protein level this kinase showed increased expression in two independent patient cohorts. A small molecule inhibitor of this kinase reduced the growth of a panel of PrCa cell lines in vitro and tumour growth in xenograft models. Interestingly, we found that the levels of this AR regulated kinase were reduced in clinical PrCa following androgen deprivation therapy, but were raised in Castrate Resistant disease. Therefore, we have identified an AR regulate kinase which contributes to tumour growth and is a potential marker and therapeutic target in both hormone naïve and anti-androgen resistant disease. In summary, these data show that combining expression analysis, ChIP-seq and high through-put validation has identified a framework to understand the oncogenic functions of the AR in prostate cancer.