S100A8/A9 mediate the reprograming of normal mammary epithelial cells induced by dynamic cell-cell interactions with adjacent breast cancer cells.

Background: Tumor microenvironment drive the progression of solid tumors. Among the various cell types in the breast cancer microenvironments, non-tumorigenic mammary epithelial cells are often located in the vicinity of malignant cancer cells. However, the biologic characteristics of non-tumorigenic mammary epithelial cells adjacent to breast cancer cells are poorly understood. Methods: Non-tumorigenic mammary epithelial MCF10A cells were co-cultured with various breast cancer cells and the extent of cell-cell interactions was evaluated by time-lapse imaging. The molecular and functional traits of the co-cultured MCF10A cells were investigated by using RNA sequencing, phosphor-protein arrays, pathway analysis, and various in vitro assays. The molecular changes observed in vitro were validated using breast cancer xenograft mouse models. The phenotype changes in the S100A8/A9-overexpressing MCF10A cells were investigated to determine the causal relationship of S100A8/A9 upregulation observed in co-cultured MCF10A cells. Results: When the cells were co-cultured directly, there were dynamic cell-cell interactions between the MCF10A cells and breast cancer cells including lamellipodia- or nanotube-like contacts and transfer of extracellular vesicles. MCF10A cells exhibited features of epithelial-mesenchymal transition, and showed increased capacity of cell proliferation, migration, colony formation, and 3-dimensional sphere formation upon the direct co-culture with breast cancer cells. Transcriptome analysis and phosphor-protein array suggested that several cancer-related pathways are significantly dysregulated in MCF10A cells after the direct co-culture with breast cancer cells. S100A8/A9 showed distinct up-regulation in the co-cultured MCF10A cells and orthotropic xenograft of syngeneic mouse mammary tumors. When S100A8/A9 overexpression was induced in MCF10A cells, the cells showed phenotypic features of directly co-cultured MCF10A cells in terms of in vitro cell behaviors and signaling activities. Conclusions: This study suggests the possibility of dynamic cell-cell interactions between non-tumorigenic mammary epithelial cells and breast cancer cells that could lead to a substantial transition of molecular profiles and functional characteristics in mammary epithelial cells. S100A8/A9, along with other dysregulations in cancer-related signaling pathways, may mediate this phenotype transition of non-tumorigenic mammary epithelial cells.