Cell cycle signaling networks in prostate cancer: E2F target genes play a predominant role in radiation response and are potentially co-regulated by p53 and WT1

Delineating signaling pathways active in prostate epithelial cells will lead to a better understanding of those processes essential for prostate cancer progression, such as uncontrolled proliferation, survival as a consequence of resistance to cell death, invasion and metastasis, and for development of resistance to therapies such as androgen ablation and radiation therapy. Additionally, once mechanistic information is acquired, identified gene products can be used as determinants of high-grade tumor development leading to acquisition of prognostic biomarkers or therapeutic targets for intervention. Our approach involves identifying gene expression pathways that regulate these essential functions, especially focusing on those genes related to proliferation and genotoxic stress response, examining interactions of transcription factors (TFs) such as androgen receptor (AR), p53, retinoblastoma (Rb), E2F, and WT1. Although many gene targets regulated by these TFs are known, there is relatively little information available about common regulatory pathways shared between these genes. Thus, we have sought evidence of overlapping target genes common between these TFs. A mechanistic understanding of how these key TFs regulate their gene targets, such as identification of essential cofactors and other cooperating or competing TFs will lead to additional therapeutic and diagnostic applications. Here, we describe our global gene expression studies applied to prostate cancer epithelial cells using LNCaP derivative C4-2 cells, with altered androgen responsiveness. Irradiation used as a prototypic genotoxic stress response model system has revealed many induced and repressed genes. For those genes repressed by genotoxic stress that are candidate radiation sensitive genes we seek a better understanding of their mechanisms of coordinate expression. A list of genes repressed at two-fold level or higher among irradiated C4-2 cells was identified, and functional groups of genes were designated using Gene Ontology annotations. Additionally, promoter sequences of genes from the top two functional clusters were examined to identify the presence of TF binding sites (TFBS) of interest. Genes with detected TFBS were further considered as candidates for functional studies as potential target genes. Here we report the cooccurrence of predicted TFBS for E2F, p53, and WT1 within the promoters of radiation suppressed mitotic genes. Examining relationships between TFs and their potential target genes will provide important insight into pathways essential for prostate cancer progression that could lead to the development of the next generation of diagnostics and therapeutics.