Nrf1 and Nrf2 Mediated Regulation of Androgen Receptor Signaling in Castration Resistant Prostate Cancer

The role that oxidative stress and antioxidant signaling plays in prostate cancer (PCa) aggressiveness has not been clearly defined. Studies have shown that aggressive PCa cells have an increased capacity to produce ROS and differentially regulate antioxidant proteins that interact with the androgen receptor (AR). AR mediates mitogenic and survival signaling in PCa cells. Hence, androgen deprivation therapy (ADT) is used to inhibit AR activity and PCa cell growth. Castration resistant prostate cancer (CRPC) cells have enhanced AR signaling that is activated by low dihydrotestosterone (DHT) levels and resistant to ADT. While several studies have investigated the effects of antioxidant proteins on AR signaling in PCa, few have investigated the role of Nrf1 and Nrf2, two transcription factors that regulate antioxidant gene expression, on AR signaling and PCa aggressiveness. We examined the role of Nrf1 and Nrf2 in regulating AR signaling in androgen dependent LNCaP cells and castration resistant C4-2B cells. We observed that DHT stimulated AR signaling and nuclear localization are enhanced in C4-2B cells. Also, Nrf1 nuclear localization was inherently stimulated by DHT in C4-2B cells but not in LNCaP cells. Nrf2 nuclear localization was not androgen responsive in our cells. Furthermore, overexpression of p65 Nrf1 enhanced DHT stimulated AR activity in LNCaP cells and inhibition of Nrf1 expression decreased activity in C4-2B cells. In addition, Nrf2 overexpression decreased DHT mediated AR activity in both LNCaP and C4-2B cells. Nrf1 and Nrf2 may directly interact with AR because neither AR expression nor AR nuclear localization were affected by changes in Nrf1 or Nrf2 expression. However, in DHT treated C4-2B cells, Nrf2 overexpression increased the nuclear localization of p120 Nrf1, which also decreased AR activity in these cells. Gel shift assays also showed that Nrf1 and AR directly interact to bind the ARE in DHT treated C4-2B cells. Our studies implicate Nrf1 in enhanced AR signaling in castration resistant PCa cells and provide a rationale for decreased Nrf2 expression in aggressive PCa cells. After validation in human tissues, Nrf1 and Nrf2 may be used as biomarkers for CRPC or targets for therapies designed to enhance the efficacy of ADT.