RIG-I Promotes Cell Death in Hepatocellular Carcinoma by Inducing M1 Polarization of Perineal Macrophages Through the RIG-I/MAVS/NF-κB Pathway

BACKGROUND: The development and metastasis of cancer cells are regulated by tumor-associated macrophages (TAMs) present in the surrounding tumor microenvironment. RIG-I is a key pathogen recognition receptor against RNA viruses that regulates innate immunity in cancer progression. Till now, the mechanism of RIG-I regulation of the polarization of TAMs in the progression of hepatocellular carcinoma (HCC) has not been understood. MATERIALS AND METHODS: Levels of RIG-I and the key proteins in the NF-κB pathway in HCC and paired paracancerous tissues were detected by Western blotting. The transfection efficiency of RIG-I was observed by fluorescence microscopy. The M1 and M2 markers were detected by real-time polymerase chain reaction and FACS assays. Apoptosis of RIG-I lentivirus-infected HCC cells was detected by flow cytometry assay. Death of Hepa1-6 and H22 cells was analyzed by lactate dehydrogenase releasing assay. RESULTS: The level of RIG-I was decreased in HCC tissues as compared to that in the paired paracancerous tissues. Overexpression of RIG-I in mouse peritoneal macrophages increased the expression of the biomarkers CD16/32 and CD11c associated with M1 macrophages. The relative levels of IL-1β, TNF-α, IL-6, and iNOS were significantly increased in RIG-I lentivirus-infected macrophages, whereas the levels of Arg-1 and IL-10 were not significantly different in RIG-I-overexpressed peritoneal macrophages. Moreover, overexpression of RIG-I in peritoneal macrophages promoted apoptosis of Hepa1-6 and H22 cells. Furthermore, overexpression of RIG-I increased the levels of phosphorylated p65 and p-IκB and decreased the level of IκB in peritoneal macrophages. Importantly, the expression of MAVS and TRAF2 was significantly increased in RIG-I lentivirus-infected macrophages. CONCLUSION: Our results demonstrate that overexpression of RIG-I promoted apoptosis and death of HCC cells. Moreover, RIG-I promoted the polarization of M1 through the RIG-I/MAVS/TRAF2/NF-κB pathway in mice peritoneal macrophages, suggesting that RIG-I may be a novel target in the immunotherapy of HCC.