Lung metastasis fails in MMTV-PyMT oncomice lacking S100A4 due to a T-cell deficiency in primary tumors.

Interactions between tumor and stroma cells are essential for the progression of cancer from its initial growth at a primary site to its metastasis to distant organs. The metastasis-stimulating protein S100A4 exerts its function as a stroma cell-derived factor. Genetic depletion of S100A4 significantly reduced the metastatic burden in lungs of PyMT-induced mammary tumors. In S100A4(+/+) PyMT mice, massive leukocyte infiltration at the site of the growing tumor at the stage of malignant transition was associated with increased concentration of extracellular S100A4 in the tumor microenvironment. In contrast, in S100A4(-/-) PyMT tumors, a significant suppression of T-cell infiltration was documented at the transition period. In vitro, the S100A4 protein mediated the attraction of T cells. Moreover, S100A4(+/+), but not S100A4(-/-), fibroblasts stimulated the invasion of T lymphocytes into fibroblast monolayers. In vivo, the presence of S100A4(+/+), but not S100A4(-/-), fibroblasts significantly stimulated the attraction of T lymphocytes to the site of the growing tumor. Increased levels of T cells were also observed in the premetastatic lungs of tumor-bearing mice primed to metastasize by S100A4(+/+) fibroblasts. Treatment of T cells with the S100A4 protein stimulated production of cytokines, particularly granulocyte colony-stimulating factor and eotaxin-2. The same cytokines were detected in the fluid of S100A4(+/+) PyMT tumors at the transition period. We suggest that release of S100A4 in the primary tumor stimulates infiltration of T cells and activates secretion of cytokines, thus triggering sequential events that fuel tumor cells to metastasize. Similar processes could occur in the premetastatic lungs, facilitating generation of inflammatory milieu favorable for metastasis formation.