162 POSTER Effects of SOD2 silencing on androgen receptor function and gene regulation: implications for castration-resistant prostate cancer

Abstract

Purpose—Advanced prostate cancer is first treated with androgen deprivation therapy. However, tumors become resistant to and grow despite castrate levels of testosterone. Growth and proliferation of castration-resistant prostate cancer (CRPC) is mediated by gain-of-function changes in the androgen receptor (AR) and AR reactivation. Expression of manganese superoxide dismutase (SOD2), which regulates cellular reactive oxygen species (ROS), is markedly downregulated in CRPC when compared to hormone responsive tumors. Experimental Design—Here, we knocked down SOD2 expression in AR-expressing LNCaP prostate cancer cells and determined gene expression changes, transcription factor binding and AR transcription activity in SOD2 knockdown cells. Results—SOD2 knockdown results in an increase in ROS. Gene expression changes induced by SOD2 knockdown results in the upregulation of genes which are also androgen responsive and 46% of genes upregulated two-fold by the androgen ligand R1881 are also upregulated to the same extent with SOD2 knockdown. The induction of many of these genes with SOD2 knockdown, such as VEGFA and FKBP5, is reversible with the antioxidant N-acetylcysteine (NAC), suggesting that this mechanism is directly linked to ROS. Furthermore, an array for transcription factor DNA binding activity shows that SOD2 knockdown induces DNA binding by several transcription factors, including AR. SOD2 knockdown-induced AR activation was confirmed by electrophoretic mobility shift assay (EMSA) and luciferase activity and both were readily reversible with NAC. Conclusions—These findings show that downregulation of SOD2 induces AR activity in a ROSdependent manner, and suggests that there may be a role for antioxidant therapy in CRPC.