The ER alpha-NRF2 signalling axis promotes bicalutamide resistance in prostate cancer

Background: Bicalutamide is a nonsteroidal antiandrogen widely used as a first-line clinical treatment for advanced prostate cancer (PCa). Although patients initially show effective responses to bicalutamide treatment, resistance to bicalutamide frequently occurs and leads to the development of castration-resistant PCa (CRPC). This research investigated the roles of the oestrogen receptor alpha (ER alpha)-nuclear factor E2-related factor 2 (NRF2) signalling pathway in bicalutamide resistance in PCa cells. Methods: We performed bioinformatic analysis and immunohistochemical staining on normal and cancerous prostate tissue to evaluate ER alpha and NRF2 expression and their correlation. Gene expression and localization in PCa cell lines were further investigated using real-time reverse transcription PCR/Western blotting and immunofluorescence staining. We treated PCa cells with the ER inhibitor tamoxifen and performed luciferase reporter assays and chromatin immunoprecipitation (ChIP) assays to understand ER alpha-dependent NRF2 expression. Overexpression and knockdown of ER alpha and NRF2 were used to explore the potential role of the ER alpha-NRF2 signalling axis in bicalutamide resistance in PCa cells. Results: We found that the expression of ER alpha and NRF2 was positively correlated and was higher in human CRPC tissues than in primary PCa tissues. Treatment with oestrogen or bicalutamide increased the expression of ER alpha and NRF2 as well as NRF2 target genes in PCa cell lines. These effects were blocked by pretreatment with tamoxifen. ChIP assays demonstrated that ER alpha directly binds to the oestrogen response element (ERE) in the NRF2 promoter. This binding led to increased transcriptional activity of NRF2 in a luciferase reporter assay. Activation of the ER alpha-NRF2 signalling axis increased the expression of bicalutamide resistance-related genes. Inhibition of this signalling axis by knockdown of ER alpha or NRF2 downregulated the expression of bicalutamide resistance-related genes and inhibited the proliferation and migration of PCa cells. Conclusions: We demonstrated the transcriptional interaction between ER alpha and NRF2 in CRPC tissues and cell lines by showing the direct binding of ER alpha to the ERE in the NRF2 promoter under oestrogen treatment. Activation of the ER alpha-NRF2 signalling axis contributes to bicalutamide resistance in PCa cells, suggesting that the ER alpha-NRF2 signalling axis is a potential therapeutic target for CRPC.