ZNNT1/osteopontin/S100A9 feedback loop promote hepatocellular carcinoma progression via mediating crosstalk between hepatocellular carcinoma cells and macrophages

Abstract Background Macrophages are the major components of tumour microenvironment, which play critical roles in tumour development. Long noncoding RNAs (lncRNAs) also contribute to tumour progression. However, the potential roles of lncRNAs in modulating the interaction between cancer cells and macrophages in hepatocellular carcinoma (HCC) are poorly understood. Methods The expression of lncRNA ZNNT1 in tissues and cells was measured using qRT-PCR. The roles of ZNNT1 in HCC cells and macrophages were investigated using in vitro and in vivo assays. The molecular mechanisms of ZNNT1 were explored using qRT-PCR, RNA immunoprecipitation, RNA pull-down, chromatin immunoprecipitation, enzyme linked immunosorbent assay, and dual-luciferase reporter assays. Results ZNNT1 was identified as an HCC-related lncRNA, which was upregulated and associated with poor prognosis of HCC. ZNNT1 promoted HCC cellular growth, migration, and invasion, and suppressed apoptosis in vitro. ZNNT1 promoted HCC xenograft growth in vivo. Furthermore, ZNNT1 recruited and induced M2 polarization of macrophages. Mechanistically, ZNNT1 upregulated SPP1 expression and osteopontin (OPN) secretion via sponging miR-181a/b/c/d-5p and miR-33a/b-5p. Functional rescue assays identified OPN as the mediator of the oncogenic roles of ZNNT1 in HCC cells and also the effects of ZNNT1 on macrophages. M2 Macrophages-recruited by ZNNT1 enhanced malignant phenotypes of HCC cells, which was mediated by S100A9 secreted by M2 macrophages. Intriguing, S100A9 secreted by M2 macrophages also upregulated ZNNT1 expression in HCC cells via AGER/NF-κB signaling. Conclusions ZNNT1, OPN, and S100A9 formed a positive feedback loop, which promoted macrophages recruitment and M2 polarization, and enhanced malignant features of HCC cells. The ZNNT1/OPN/S100A9 feedback loop represents potential therapeutic target for HCC.