Abstract
Prostate cancer (PCa) is the leading cancer among men. Androgen Deprivation Therapy (ADT) is a common treatment for advanced PCa. However, ADT eventually fails and PCa relapses, developing into castration-resistant prostate cancer (CRPCa). Although alternative pathways such as cancer stem-cell pathway and neuroendocrine differentiation bypass androgen receptor (AR) signaling, AR remains the central player in mediating CRPCa. In this study, we identified a mechanism that retains AR signaling after androgen deprivation. The TRAMP SV40 T antigen transgenic mouse is a model for PCa. The expression of SV40 T-antigen is driven by the androgen-responsive, prostate specific, Probasin promoter. It has been recognized that in this model, T-antigen is still expressed even after androgen ablation. It is unclear how the androgen-responsive Probasin promoter remains active and drives the expression of T-antigen in these tumors. In our study, we found that the expression of Foxa2, a forkhead transcription factor that is expressed in embryonic prostate and advanced stage prostate cancer, is co-expressed in T-antigen positive cells. To test if Foxa2 activates AR-responsive promoters and promotes the expression of T-antigen, we established the prostate epithelial cells that stably express Foxa2, NeoTag1/Foxa2 cells. Neotag1 cells were derived from the Probasin promoter driven SV40 T-antigen transgenic mouse. We found ectopic expression of Foxa2 drives the T-antigen expression regardless of the presence of androgens. Using this model system, we further explored the mechanism that activates AR-responsive promoters in the absence of androgens. Chromatin immunoprecipitation revealed the occupancy of both H3K27Ac, an epigenetic mark of an active transcription, and Foxa2 at the known AR target promoters, Probasin and FKBP5, in the absence of androgen stimulation. In conclusion, we have identified a mechanism that enables PCa to retain the AR signaling pathway after androgen ablation.