Role of EDA Fibronectin and Toll-like Receptor 5 in the Development of the Tumor Microenvironment in Triple Negative Breast Cancer

Background/Objectives: Triple negative breast cancer remains the most difficult breast cancer to treat as there are no specific targeted therapies. The tumor stroma is recognized as essential for the development of solid tumors. Cancer associated myofibroblasts are known to play a major role in the construction of a tumor microenvironment conducive to tumor progression. Therefore, we established a co-culture system to identify potential molecular targets controlling myofibroblast conversion. Methods: Co-cultures of MDA-MB-468 triple negative breast cancer cells and skin fibroblasts were either mixed prior to seeding or seeded individually on opposite sides of a culture dish and incubated in complete medium. Inhibitors were preincubated with cells for 1 h. Inflammatory cytokines were measured by ELISA. Proteins were analyzed using the Wes-Protein Simple System. Immunostaining was visualized using a Hamamatsu Photonics Nanozoomer. Statistical analysis was done by student’s t-test and one-way ANOVA. Results: The data indicate that co-culturing the cells promotes myofibroblast differentiation and cytokine release and this requires direct contact between the two cell types. Both myofibroblast conversion and cytokine release were prevented by inhibitors of TLR5, TGF-β and EDA-fibronectin. Conclusions: Data suggest that the TLR5 receptor on the MDA-MB-468 cells binds to EDA-fibronectin expressed by fibroblasts thus inducing inflammatory cytokine expression. Expression of EDA fibronectin is regulated through TGF-β whose synthesis is induced by TLR5 signaling in the tumor cells. The data are consistent with a model in which TLR5-mediated crosstalk between the cancer cells and the stromal fibroblasts creates a tissue microenvironment conducive to tumor growth and metastasis.