Ectopic Osx+ Cells Affect Tumor Growth

Tumor growth and metastases are dependent on interactions between cancer cells and the local environment. Expression of the cell-cell adhesion molecule N-cadherin (Ncad) is associated with highly aggressive cancers, and its expression by osteogenic cells has been proposed to provide a molecular “dock” for disseminated tumor cells to establish pre-metastatic niches within the bone. Contrary to expectations, the breast cancer cells were able to form tumors in bone and to induce osteolysis in Cdh2-cKO as well as in control mice. Notably, subcutaneous tumors grew larger in Cdh2-cKO relative to control littermates. Cell tracking experiments using the Ai9 reporter revealed the presence of Osx+ and Ncad+ cells in the stroma of extra-skeletal tumors and in a small population of lung cells, a frequent site of breast cancer metastasis. Gene expression analysis by RNAseq of CD45- Osx+ cells isolated from extra-skeletal tumors revealed alterations of pro-tumorigenic signaling pathways in Cdh2-cKO cells relative to control Osx+ cells. Also surprisingly, we find Osx+ cells present in the circulation, and the majority of tumor-associated and circulating Osx+ cells express the hematopoietic marker CD45, have a phenotypic profile resembling that of tumor infiltrating myeloid and lymphoid populations, but with higher expression of lymphocytic immune suppressive genes. Our results indicate that Osx marks distinct tumor promoting CD45- and CD45+ populations and challenge the dogma that osteogenic and hematopoietic markers are mutually exclusive. They also show that Ncad in CD45- Osx+ cells is not necessary for the establishment of bone metastases, but in extra-skeletal tumors it regulates pro-tumorigenic support by the microenvironment. Overall design: Profiling mRNA expression in Osx+ cells (CD45+ and CD45-) isolated from the stromal component of subcutaneous tumors grown in Cdh2-cKO and wild type mice