Regulation of the inflammatory profile of stromal cells in human breast cancer: prominent roles for TNF-α and the NF-κB pathway

Introduction: Breast cancer progression is promoted by stromal cells that populate the tumors, including cancer-associated fibroblasts (CAFs) and mesenchymal stem/stromal cells (MSCs). The activities of CAFs and MSCs in breast cancer are integrated within an intimate inflammatory tumor microenvironment (TME) that includes high levels of tumor necrosis factor a (TNF-alpha) and interleukin 1 beta (IL-1 beta). Here, we identified the impact of TNF-alpha and IL-1 beta on the inflammatory phenotype of CAFs and MSCs by determining the expression of inflammatory chemokines that are well-characterized as pro-tumorigenic in breast cancer: CCL2 (MCP-1), CXCL8 (IL-8) and CCL5 (RANTES). Methods: Chemokine expression was determined in breast cancer patient-derived CAFs by ELISA and in patient biopsies by immunohistochemistry. Chemokine levels were determined by ELISA in (1) human bone marrow-derived MSCs stimulated by tumor conditioned media (Tumor CM) of breast tumor cells (MDA-MB-231 and MCF-7) at the end of MSC-to-CAF-conversion process; (2) Tumor CM-derived CAFs, patient CAFs and MSCs stimulated by TNF-alpha (and IL-1 beta). The roles of AP-1 and NF-kappa B in chemokine secretion were analyzed by Western blotting and by siRNAs to c-Jun and p65, respectively. Migration of monocytic cells was determined in modified Boyden chambers. Results: TNF-alpha (and IL-1 beta) induced the release of CCL2, CXCL8 and CCL5 by MSCs and CAFs generated by prolonged stimulation of MSCs with Tumor CM of MDA-MB-231 and MCF-7 cells. Patient-derived CAFs expressed CCL2 and CXCL8, and secreted CCL5 following TNF-alpha (and IL-1 beta) stimulation. CCL2 was expressed in CAFs residing in proximity to breast tumor cells in biopsies of patients diagnosed with invasive ductal carcinoma. CCL2 release by TNF-alpha-stimulated MSCs was mediated by TNF-RI and TNF-RII, through the NF-kappa B but not via the AP-1 pathway. Exposure of MSCs to TNF-alpha led to potent CCL2-induced migration of monocytic cells, a process that may yield pro-cancerous myeloid infiltrates in breast tumors. Conclusions: Our novel results emphasize the important roles of inflammation-stroma interactions in breast cancer, and suggest that NF-kappa B may be a potential target for inhibition in tumor-adjacent stromal cells, enabling improved tumor control in inflammation-driven malignancies.