miR-148a Affects Polarization of THP-1-Derived Macrophages and Reduces Recruitment of Tumor-Associated Macrophages via Targeting SIRPα

PURPOSE: The objective of this study was to investigate the effect of miR-148a on the polarization and recruitment of tumor-associated macrophages (TAMs). METHODS: In human monocyte THP-1 cells, M1 or M2 differentiation was induced by phorbol 12-myristate 13-acetate (PMA) with specific induction supplements and identified using flow cytometry and ELISA. To alter cellular miR-148a expression level, THP-1 cells were transfected with miR-148a mimics or inhibitors. A dual-luciferase assay was used to determine whether miR-148a could directly regulate the expression of signal regulatory protein α (SIRPα). Expression of miR-148a and SIRPα was detected with RT-PCR or Western blot. A co-culture system of THP-1 cells and colorectal cancer SW480 cells was used for TAM induction. The recruitment of macrophage to SW480 cells was measured using chemotaxis assay. In SW480 cells, apoptosis induced by macrophages was detected using flow cytometry and a xenograft assay. Macrophage infiltration was detected by immunofluorescence assay in tumor tissues. RESULTS: miR-148a over-expression increased M1-related CD86 expression in THP-1 cells and promoted differentiation to M1-like macrophages. Inhibition of miR-148a increased M2-related CD206 expression and promoted differentiation to M2-like macrophages. In the co-culture system, THP-1 cells were induced to the M2-like state by SW480 cells. The level of miR-148a negatively correlated with the levels of M2-related cytokines. Additionally, miR-148a expression level was negatively associated with macrophage recruitment by colorectal cancer cells. Furthermore, in miR-148a over-expression, the number of macrophages recruited by SW480 cells was reduced. Meanwhile, cancer cell apoptosis induced by macrophages was enhanced. Thus, miR-148a expression was beneficial for the transformation of macrophages, from an immune-suppressive status to an immune-promoting status. These anti-cancer effects of miR-148a were related to the down-regulation of SIRPα in macrophages, directly targeted by miR-148a. A xenograft assay showed that the co-inoculation of macrophages over-expressing miR-148a reduced subcutaneous tumorigenesis and M2 macrophage infiltration. CONCLUSION: miR-148a promoted the differentiation of M0 macrophages into anti-tumor classical activation type M1, and reduced TAM recruitment by targeting SIRPα to inhibit colorectal cancer cell viability.