Uncovering Androgen Responsive Regulatory Networks in Prostate Cancer

Abstract

An important goal for prostate cancer therapy is to identify novel mechanisms of androgen signaling that may provide new targets for androgen blockade therapy. Androgen regulated target genes continue to be identified, and include genes with regulatory regions containing 1) classical dimeric androgen receptor elements, or 2) sites for other transcription factors that tether androgen receptor to a regulatory region lacking androgen receptor binding sites, or 3) non-canonical half-sites. The latter category of half-sites is becoming increasingly important, because up to 80% of potential androgen receptor regulatory regions identified by chromatin immunoprecipitation microarray technology contain these monomeric half-sites [1-3]. Determining which of these predicted target genes and androgen pathways are functional is very important, as they contribute to our understanding of prostate cancer progression. Microarray analyses were used to identify genes expressed in laser captured prostate cancer epithelial cells [4], leading to identification of pathways of co-regulated genes. It is expected that important regulatory regions would be conserved between mammalian genomes, thus, comparative evolutionary analyses were used to identify evolutionary conserved transcription factor binding sites [5]. Notably, non-canonical androgen receptor half-sites were identified in a majority of the gene promoters analyzed, and these sites were adjacent to evolutionary conserved zinc finger transcription factor sites. Subsequent ChIP assays showed that indeed SP1, WT1 and AR proteins all bind to a common regulatory region, indicating potential for interaction between these transcription factors that in turn can modulate hormone responsiveness. Overall, our bioinformatics screening coupled with experimental validation has revealed critical components of regulatory networks important in prostate cancer cells and disease progression.