Analysis of Ligand-Specific Co-repressor Binding to the Androgen Receptor

The recruitment of co-repressors to the androgen receptor is an important mechanism for reducing androgen-mediated gene activation. Importantly, co-repressors play a major role in the treatment of hormone-dependent growing tissue, such as prostate cancer and breast cancer. In line with this, co-repressor dysfunction seems to be a major player for development of castration-resistant prostate cancer or therapy-resistant breast cancer. The molecular basis of hormone therapy by particular antihormones (antagonists) for the androgen receptor (AR) is mediated by enhanced recruitment and activity of co-repressors that cause repression of AR target genes that regulate proliferation and alteration of cancer cells. Therefore co-repressor recruitment is a crucial molecular mechanism of gene repression as well as inhibition of cancer growth. Here we describe different strategies to investigate co-repressor recruitment to the AR. First, we developed a modified mammalian two-hybrid system to investigate the recruitment of co-repressors to the AR within mammalian cells. This assay is very useful for the identification of the molecular mechanism of new AR antagonists and for molecular analysis of castration-resistant prostate cancer expressing the AR. Second, we describe a technique to analyze the interaction of AR isolated from human prostate cancer cells with a newly generated AR-specific co-repressor peptide, which is bacterially expressed and affinity purified by glutathione-S-transferase affinity precipitation assays in vitro. In summary, these methods can greatly facilitate the study of AR–co-repressor interactions.