Abstract 1630: Dysregulation of Hippo pathway in metastatic prostate cancer

Abstract

Abstract Background: Prostate cancer (PCa) is prevalently diagnosed and more than 80% of late stage PCa patients develop bone metastases. We hypothesized that the selective lodging of the PCa cells in the bone can be contributed by increased RANK-mediated cell signaling network. Cancer cell-derived RANKL orchestrates a complex bone-remodeling program facilitating PCa bone colonization through the activation of specific transcription factors (TFs) promoting PCa-bone microenvironment interaction through increased epithelial to mesenchymal transition (EMT), cell growth, and osteomimicry. Overexpression of RNAKL in indolent LNCaP cells drives cancer bone and soft tissue metastases. Methods and Results: Microarray gene expression was performed to compare RANKL- and Neo-vector- transfected LNCaP cells, LNCaPRANKL and LNCaPneo, respectively. qRT-PCR and western blot were performed to confirm the expression of RANKL-targeted genes in these cells. We found the new extracellular diffusible signal mediated by RANKL, regulating Hippo pathway in the aggressive PCa cells. Recombinant RANKL-treated indolent PCa cells, LNCaP and LAPC4, were shown to gain increased aggressiveness. The RANKL-treated indolent PCa cells exhibited down-regulation of Hippo pathway core kinases (Mst1/2 and Lats1/2) but up-regulation of YAP/TAZ expressions. By deleting downstream effectors of Hippo pathway, YAP/TAZ, interrupted the aggressive PCa cells to migrate, proliferate and invade and reversed their EMT phenotype. Inhibitions of YAP/TAZ in aggressive PCa cells via genetic knockdown approach resulted in E-cadherin increase and Vimentin decrease. With the identification of crosstalk between Hippo and TGF-β, or Wnt pathways, this opened up a new network and targeting opportunity for PCa bone metastasis. The metastatic PCa cells with YAP/TAZ deletions were illustrated for sensitization to other therapeutic agents such as TGF-β inhibitors. These results prompted us to study the mechanism, validate the functional significance, and devise potential targeting strategies of Hippo pathway in PCa bone metastasis. Conclusions: Our results showed that dysregulated Hippo pathway in the aggressive PCa cells. With deletions of YAP/TAZ, PCa metastatic abilities were inhibited. Our findings might explain why PCa cells prefer bone as primary metastatic sites. In addition, targeting YAP/TAZ could be a potential therapy for PCa bone metastasis. Citation Format: Jen-Ming Huang, Gina C-Y Chu, Hyung L. Kim, Haiyen E. Zhau, Leland W.K. Chung. Dysregulation of Hippo pathway in metastatic prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1630.