RANKL-elicited RANK activity plays critical roles in many biological and pathological conditions, including osteoclast differentiation/bone remodeling, lymph node/thymic development, central thermoregulation and progesterone-driven mammary gland maturation, differentiation and carcinogenesis. RANKL can be derived from osteoblasts, infiltrating inflammatory cells and stromal fibroblasts. We previously showed that malignant prostate cancer (PCa) cells expressed RANKL and that its expression was correlated with clinical PCa progression and bone metastasis. The present study examined whether PCa-derived RANKL acts on RANK+ PCa cells to promote PCa bone metastasis. We demonstrated several interesting key findings for RANKL-RANK signaling in PCa cells: 1) RANKL overexpression in human PCa LNCaP and ARCaPE cells results in increased RANKL-RANK signaling within PCa cells and confers PCa bone and soft tissue metastases in a tumor cell RANK-dependent manner since RANK knockdown in RANKL-expressing PCa cells fails to induce bone colonization or metastasis. 2) RANKL amplifies downstream signaling by activating RANKL and c-Met expression through a common transcription factor complex, c-Myc/Max, which was identified by site-directed mutagenesis and transcription factor deletion/interference assays. 3) Even a few RANKL+ PCa cells are sufficient to initiate the in vivo metastatic cascade by recruiting non-tumorigenic RANKL PCa cells to participate in the metastatic process via downstream signaling amplification. This is supported by the observation that recombinant RANKL protein alone is sufficient to induce bone colonization and growth of RANKL and non-metastatic PCa cells. 4) RANKL also promotes EMT and confers stem and neuroendocrine (NE) cell properties on participating cancer cells determined by changes in their specific markers. 5) In support of the roles of RANKL-RANK signaling in PCa bone metastasis, RANKL expression at the single cell level in primary PCa specimens predicts PCa patient survival. Collectively, these results demonstrated that autocrine/paracrine RANKL-RANK signaling in PCa cells establishes a premetastatic niche through a “vicious cycle," inducing RANKL and c-Met expression via activation of c-Myc/Max, and this promotes PCa EMT progression, stem and NE cell properties, and PCa bone and soft tissue metastases. RANKL expression status therefore offers new insights for dissecting the mechanism by which PCa cells exhibit propensity for bone colonization/metastasis.

(Funding supported in part by R01 CA122602 and P01 CA098912 grants)

Citation Format: Gina C.Y. Chu, Haiyen E. Zhau, Ruoxiang Wang, Andre Rogatko, Xu Feng, Majd Zayzafoon, Leland W.K. Chung. Autocrine/paracrine RANKL-RANK signaling promotes cancer bone metastasis and establishes premetastatic niche recruiting bystander cancer cells to participate in the metastatic process. [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 3942. doi:10.1158/1538-7445.AM2013-3942