TREM1+ tumor-associated macrophages secrete CCL7 to promote hepatocellular carcinoma metastasis.

Purpose: Tumor-associated macrophages (TAMs) play a critical role in hepatocellular carcinoma (HCC) progression and metastasis. Systematic investigation of the cross-talk between TAMs and HCC may help in searching for the critical target to guard against HCC metastasis.

Methods and results: Herein, we found that TREM1 highly expressed in HCC tissue by analyzing the data obtain from GEO database. Interestingly, the results indicated that TREM1 was primarily expressed by monocytes. Immune infiltration studies further validated that TREM1 expression was positively related with increased infiltration of macrophages in HCC tissues. In vitro, we observed that TREM1 knockdown significantly abrogated the effect of TAMs in promoting the metastasis and epithelial-mesenchymal transition (EMT) of HCC cells. Additionally, cytokine array detection identified CCL7 as the main responsive cytokine following with TREM1 knockdown in TAMs.

Conclusion: Taken together, our findings strongly suggested that high expression of TREM1 was positively associated with metastasis and poor prognosis of HCC. Furthermore, TAMs expressing TREM1 contribute to EMT-based metastasis through secreting CCL7. These results provide a novel insight into the potential development of targeting the TREM1/CCL7 pathway for preventing metastatic HCC.