Modulation of androgen receptor DNA binding activity through direct interaction with the ETS transcription factor ERG

Significance Progress in studying the androgen receptor (AR), the primary drug target in prostate cancer, has been hampered by challenges in expressing and purifying active multidomain AR for use in cell-free biochemical reconstitution assays. Here we successfully express full-length and truncated AR variants and demonstrate that the oncogenic ETS protein ERG, responsible for half of all prostate cancers, enhances the ability of AR to bind DNA through direct interaction with AR. In addition to providing a biochemical system to evaluate AR activity on different DNA templates, our findings provide insight into why ERG-positive prostate cancers have an expanded AR cistrome. The androgen receptor (AR) is a type I nuclear hormone receptor and the primary drug target in prostate cancer due to its role as a lineage survival factor in prostate luminal epithelium. In prostate cancer, the AR cistrome is reprogrammed relative to normal prostate epithelium and particularly in cancers driven by oncogenic ETS fusion genes. The molecular basis for this change has remained elusive. Using purified proteins, we report a minimal cell-free system that demonstrates interdomain cooperativity between the ligand (LBD) and DNA binding domains (DBD) of AR, and its autoinhibition by the N terminus of AR. Furthermore, we identify ERG as a cofactor that activates AR’s ability to bind DNA in both high and lower affinity contexts through direct interaction within a newly identified AR-interacting motif (AIM) in the ETS domain, independent of ERG’s own DNA binding ability. Finally, we present evidence that this interaction is conserved among ETS factors whose expression is altered in prostate cancer. Our work highlights, at a biochemical level, how tumor-initiating ETS translocations result in reprogramming of the AR cistrome.