The Pro-Tumorigenic Role of Chemotherapy-Induced Extracellular HSP70 from Breast Cancer Cells via Intratumoral Macrophages

SIMPLE SUMMARY: Resistance to chemotherapy is an important problem to be solved in breast cancer research. Tumor-associated macrophages (TAMs) contribute to breast cancer progression, including chemoresistance, and it is important to clarify the altered functions of macrophages following chemotherapy to improve prognosis of breast cancer patients. Here, we conducted in vitro experiments and immunohistochemistry in 116 breast carcinoma tissues to determine whether the secretion of heat shock protein (HSP) 70 from breast cancer cells following chemotherapy affects macrophage function. It was revealed that extracellular HSP70 levels increased following chemotherapy and enhanced the pro-tumorigenic effects of TAMs either directly or indirectly by regulating the expression of transforming growth factor (TGF)-β in breast cancer cells. Immunohistochemistry demonstrated that HSP70 functions as a poor prognostic factor in conjunction with macrophage infiltration. Targeting HSP70 may therefore be useful in regulating the tumor microenvironment in breast cancer tissues and improving the prognosis of breast cancer patients following chemotherapy. ABSTRACT: Tumor-associated macrophages (TAMs) contribute to tumor progression and chemoresistance; it is therefore important to clarify the altered functions of macrophages following chemotherapy. While extracellular heat shock protein (HSP) 70 is associated with therapeutic resistance, the effects of HSP70 on TAMs remain largely unknown. Here, we conducted in vitro experiments and immunohistochemistry in 116 breast carcinoma specimens to determine whether the secretion of HSP70 from breast cancer cells following chemotherapy affects macrophage function. It was revealed that the interaction of epirubicin (EPI)-exposed breast cancer cells with macrophages enhanced tumor progression, and EPI promoted the secretion of extracellular HSP70 from breast cancer cells. The expression of pro-tumorigenic macrophage marker CD163 was decreased in macrophages treated with a conditioned medium (CM) from HSP70-silenced breast cancer cells. Breast cancer cells treated with CM from HSP70-silenced breast cancer cells showed decreased expression of transforming growth factor (TGF)-β, and the pro-tumorigenic effects of macrophages were impaired when TGF-β signaling was inhibited. Immunohistochemistry demonstrated that HSP70 served as a poor prognostic factor in conjunction with macrophage infiltration. It was therefore concluded that extracellular HSP70 levels increased following chemotherapy and enhanced the pro-tumorigenic effects of TAMs, either directly or indirectly, by regulating TGF-β expression in breast cancer cells.