Gene expression profiling using a unique murine mammary tumor model reveal role of novel genes regulating tumor‐stromal interaction in mammary tumor‐induced osteolysis

Abstract

Bone metastases from breast cancer are predominantly osteolytic and develop as a result of interaction between tumor cells and bone cells. We used murine mammary tumor with different aggressiveness and examined their ability to grow and induce osteolytic changes in bone microenvironment. This model has been extremely useful in allowing us to identify key factors driving tumor-induced bone lesions and tumor-stromal interactions in vivo. Regardless of their aggressiveness, all murine mammary tumor cell lines showed strong bone resorption, induction of osteoclasts and intracranial penetration at the tumor bone-interface (TB-interface). We examined the factors critical for osteolytic changes by Affymetrix gene chip analysis using RNA isolated from microdissected samples at tumor-bone (TB) interface and tumor alone area. Further analysis of the data using BRB array tools and robust multiarray average (RMA) revealed 78 commonly upregulated genes in all the three cell lines at the TB-interface with 2-fold or greater changes and p-value less than 0.001 (paired t-test with random variance model). The strongly upregulated gene included receptor activator of NF-kB ligand (RANKL), insulin growth factor binding protein (IGFBP)-5, and integrin binding sialoprotein (IBSP) in the whole data set. We confirmed the expression by real-time reverse transcriptase assay and immunohistochemistry. These data demonstrate that tumor-stromal interaction play a role in tumor-induced osteolysis and RANKL, IGFBP-5 and IBSP may play a role in mammary tumor-induced osteolysis and growth in the bone microenvironment.