Abstract 281: Hsp27 is an essential effector of EGF-induced epithelial to mesenchymal transition in prostate cancer.

Introduction: Prostate cancer (PCa) is the most common cancer and the second leading cause cancer death in North American men. An important determinant for metastasis is epithelial to mesenchymal transition (EMT) which is known to be correlated to castrate resistant prostate cancer (CRCP). Previous report demonstrated the overexpression of Hsp27 and its phosphorylated form in poor diagnosis prostate cancer. In addition, both epidermal growth factor (EGF) and its receptor (EGFR) are up–regulated in PCa during progression to CRPC. However, the role of EGF and EGFR in PCa progression remains unclear. Our objective is to establish that Hsp27 is a central “node” for several signaling pathways activated by EGF and known to modulate EMT. Methods: To assess the role of Hsp27 in EMT, gain and loss of Hsp27 function has been conducted in LNCaP cells with or without EGF stimulation. EMT markers expression has been evaluated at the protein (WB) and mRNA level (qRT–PCR). Furthermore, invasion, migration assays in addition with MMP–9 activity have been done to evaluate the migratory capacity of those cells. Also, to better understand the molecular mechanism involved in EMT induction, transactivation and Chip assays have been performed. The in vitro results have been confirmed with an in vivo study using an Hsp27 antisense oligonucleotide (OGX-427) in a murine model. Results: We found that Heat shock protein 27 (Hsp27) is up–regulated with CRPC progression and drives EMT in PCa cells by decreasing epithelial cell markers, up–regulating mesenchymal markers and enhancing cell migration and MMP–9 activity. Hsp27 knockdown induces sequestration of beta–catenin in the cytoplasm by increasing its binding to GSK–3beta and abrogating EGF induced beta–catenin nuclear translocation. Additionally, by decreasing the nuclear translocation of beta-catenin, Hsp27 knockdown decreases the binding of beta–catenin to slug promoter thereby lessening its transcriptional activity. As Slug is known to be a critical key in EMT induction, we confirmed the role of EGF and Hsp27 in EMT induction and our capacity to abrogate the EGF-induced EMT effect by Hsp27 knockdown. Finally, targeting Hsp27 using antisense oligonucleotide OGX-427 in vivo, significantly reduced tumor cell metastasis in a PCa murine model. Conclusion: This study shows that EGF through Hsp27 induces modifications in gene expression and morphology toward a mesenchymal phenotype. The mechanism involving Hsp27, β-catenin, nuclear β-catenin/TCF and EGF signaling cascades described in the present study contribute to the comprehension of mechanisms driving metastasis in aggressive castration-resistant prostate cancer. This study reveals that Hsp27 is a crucial effector of EGF–dependent and independent EMT and suggests that targeting Hsp27 holds promises for a new strategy in metastatic PCa. Citation Format: Thomas D. Cordonnier, Jennifer L. Bishop, Masaki Shiota, Ario Takeuchi, Ka Mun Nip, Martin Gleave, Amina Zoubeidi. Hsp27 is an essential effector of EGF-induced epithelial to mesenchymal transition in 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 281. doi:10.1158/1538-7445.AM2013-281