Abstract 1584: Wnt/beta-catenin and Foxa2 axis activates AR signaling in castration resistant prostate cancer
Authors: Connelly Zachary M. , Yang Shu , Li Jiahe , Matusik Robert , Yu Xiuping 
Published: July 2017

Background: Prostate cancer (PCa) is the leading cancer among men in the world. Androgen deprivation therapy is a common treatment to cease prostate growth. However, androgen deprivation eventually fails and PCa relapses, evolving into castration resistant prostate cancer (CRPCa). It has been established that androgen receptor (AR) continues to be the central player in mediating CRPCa. However, the mechanism by which the AR signaling remains active is unclear. We have reported that activation of Wnt/beta-catenin signaling pathway promotes castrate-resistant progression. Our study has also shown that activation of the Wnt/beta-catenin pathway induces the expression of Foxa2, a fork-head transcription factor that is expressed in embryonic prostate & advanced stage PCa. Here, we study the Wnt pathway and the role of Foxa2 in retaining active AR signaling in advanced PCa in the absence of androgens. TRAMP mice, SV40 T-antigen transgenic mouse models for PCa, were used. It has been recognized that in this model, T-antigen, which is driven by androgen-responsive probasin promoter, remains expressed following androgen ablation. In this study, we identified a mechanism that sustains an active AR signaling in CRPCa.

Methods: To study whether the Wnt/beta-catenin pathway is active in advanced stage PCa, we crossed the TRAMP mice with GFP-Wnt reporter mice. Some of the TRAMP/Wnt-reporter mice were castrated to study how androgen deprivation affects Wnt/beta-Catenin signaling and promotes PCa progression. Prostates were analyzed using IHC and IF staining. We also established a prostate epithelial cell line that stably expresses Foxa2. Cell proliferation was examined with IncuCyte Zoom software. The expression of AR target genes was assessed by using quantitative RT-PCR and Western blotting. ChIP was conducted to assess the recruitment of transcriptional machinery to the promoters of AR-regulated genes.

Results: Utilizing the TRAMP/Wnt mouse model, we show that Wnt/beta-Catenin signaling is active in advanced stage PCa. Additionally, our data showed that Foxa2, the downstream target of Wnt/beta-Catenin signaling, drives the expression of androgen-responsive genes, regardless of androgen deprivation. Furthermore, cell proliferation assays revealed that the expression of Foxa2 enabled an androgen-independent growth of prostatic cells. Using this model system, we further explored the mechanism that activates the transcription of AR-responsive genes in the absence of androgens. Our data indicated that Foxa2 is capable of recruiting H3k27Ac to AR-responsive promoters.

Conclusion: Together, these data indicate that Wnt signaling is activated in advanced stage PCa, driving Foxa2 expression, and promoting AR signaling to persist. This represents a novel mechanism that enables advanced PCa to retain AR signaling pathway following androgen ablation. Targeting both Wnt signaling and Foxa2 may pose as novel therapeutics for CRPCa.

Citation Format: Zachary M. Connelly, Shu Yang, Jiahe Li, Robert Matusik, Xiuping Yu. Wnt/beta-catenin and Foxa2 axis activates AR signaling in castration resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1584. doi:10.1158/1538-7445.AM2017-1584