Tumor-associated macrophages promote migration and invasion via modulating IL-6/STAT3 signaling in renal cell carcinoma

Tumor-associated macrophages (TAMs) promote tumor cell growth and metastasis in various human cancers. However, the role of TAMs in renal cell carcinoma (RCC) is rarely investigated. Herein, we observed that the infiltration of TAMs was obviously elevated in RCC tumor tissues, high infiltration of TAMs was closely associated with tumor progression and poor prognosis in RCC patients. In vitro assays further indicated that the conditioned medium of TAMs (TAMs CM) facilitated migration, invasion, and epithelial-mesenchymal transition (EMT) in RCC cells. Moreover, we found that IL-6 was involved in the functions of TAMs in RCC; IL-6 neutralizing antibody (IL-6NA) partly abolished the effect of TAMs on RCC cells. In addition, we demonstrated that TAMs might exert their roles by activating STAT3 signaling in RCC, and IL-6 was responsible for TAMs-induced STAT3 signaling activation. In conclusion, our results revealed that high infiltration of TAMs may promote RCC cells migration, invasion, and EMT via modulating IL-6/STAT3 signaling, further suggesting a potential of novel treatment strategies targeting TAMs or IL-6 for metastatic RCC.