The role of RANK-signaling in breast cancer development and metastasis

4200 RANK (Receptor Activator of NFκB) is a member of TNFα receptor super family. RANKL (RANK Ligand) activates RANK and its down-stream kinase IKKα, controlling osteoclast differentiation, mammary gland development as well as breast cancer tumorigenesis. Inhibition of RANK leads to reduction in tumor colonization and growth in bones in several mouse tumor metastasis models. However, the underlying mechanism underlying is still largely unknown. The purpose of the current study is to monitor and understand the influence of RANK-signaling on step-wise tumor development and metastasis. We used orthotopic tumor transplantation models with green fluorescent protein (GFP) and red fluorescent protein (DsRed2)-labeled Her2/neu transformed tumor cells which are under the control of RANK signaling. With the aid of real-time fluorescence imaging we can measure tumor growth, and monitor invasion, trafficking and colonization of tumor cells in real-time. To understand the mechanisms involved, we employed Western-blotting, RT-PCR, cell fractionation and transient transfection reporter assays. We found RANKL stimulation increased the nuclear accumulation of IKKα and expression of a group of genes involved in inflammation. However, genes which control the cell cycle and proliferation remained unchanged. This observation is consistent with that RANKL stimulation does not influence tumor-cell proliferation tumor growth. It is of great importance to analyze how blockage of RANK and RANK down-stream effectors, including IKKα and responsive genes affect tumor behavior and tumor-host interaction.