Abstract 3883: Robo1, a new target, by Wnt and androgen receptor signaling in castration resistant prostate cancer.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Androgen receptor (AR) and β-catenin/TCF-4 signaling both play a critical role during prostate cancer progression to castration-resistance and cross-talk with each other. Therefore, identifying novel down-stream targets that are co-regulated by AR and β-catenin/TCF-4 signaling is important for understanding the development of castration-resistant prostate cancer (CRPC). Robo1, a transmembrane receptor of Slit, is known for its roles in neurogenesis and angiogenesis. Previous studies have shown that Robo/Slits are aberrantly expressing in different cancers. We have shown that Robo1 is over-expressed in androgen-insensitive prostate cancer cell lines (C4-2B, PC3, 22RV1) compared to androgen-sensitive lines (LNCaP and LAPC-4), and absent in normal prostate epithelial cells. Androgen deprivation resulted in enhanced expression of Robo1 and addition of synthetic androgen R1881decreased Robo1 expression in LNCaP cells. In addition, Wnt 3A and 5A conditioned medium stimulation increased Robo1 mRNA expression in LNCaP cells. Inhibition of Wnt signaling by overexpression of secreted Wnt antagonists Wnt-inhibitory factor-1 (WIF-1) and Frzb/sFRP3 in two CRPC cell lines, decreased the expression of Robo1. Using GenBank and MatInspector software, we have identified potential binding sites for TCF-4 in the 5’ flanking promoter region of the ROBO1 gene. Chromatin immunoprecipitation followed by real-time PCR analysis revealed that TCF-4 binds to the ROBO1 promoter at two predicted sites, and that WIF-1 and Frzb/sFRP3 expression inhibited its promoter binding. Overexpression of WIF-1 and Frzb/sFRP3 also inhibited the promoter activity of Robo1. Knock-down of Robo1 by short-hairpin RNA in PC3 cells resulted in dramatic morphological changes with increased cell aggregation and adhesion. Taken together, our results indicate that Robo1 is a co-target of Wnt and AR signaling. Further studies are in progress to define the functional role of Robo1 in CRPC. Citation Format: Noriko N. Yokoyama, Zheng Sun, Toshinori Sakai, Bang H. Hoang, Xiaolin Zi. Robo1, a new target, by Wnt and androgen receptor signaling in castration resistant prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3883. doi:10.1158/1538-7445.AM2013-3883