miR‐28‐5p‐IL‐34‐macrophage feedback loop modulates hepatocellular carcinoma metastasis

UNLABELLED: MicroRNAs (miRNAs) play a critical role in regulation of tumor metastasis. However, the role of these molecules in hepatocellular carcinoma (HCC) has not been fully elucidated. In this study, we employed miRNA-sequencing and identified 22 miRNAs involved in HCC metastasis. One of these, miR-28-5p, was down-regulated in HCCs. This down-regulation correlated with tumor metastasis, recurrence, and poor survival. Biofunctional investigations revealed that miR-28-5p deficiency promoted tumor growth and metastasis in nude mice without altering the in vitro biological characteristics of HCC cells. Through gene expression profiles and bioinformatics analysis, we identified interleukin-34 (IL-34) as a direct target of miR-28-5p, and the effects of miR-28-5p deficiency on HCC growth and metastasis was dependent on IL-34-mediated tumor-associated macrophage (TAM) infiltration. Moreover, we found that TAMs induced by miR-28-5p-IL-34 signaling inhibit miR-28-5p expression on HCC cells by transforming growth factor beta 1, resulting in an miR-28-5p-IL-34-macrophage-positive feedback loop. In clinical HCC samples, miR-28-5p levels were inversely correlated with IL-34 expression and the number of TAMs. Patients with low miR-28-5p expression, high IL-34 levels, and high numbers of TAMs had a poor prognosis with shorter overall survival and time to recurrence. CONCLUSION: A miR-28-5p-IL-34-macrophage feedback loop modulates HCC metastasis and serves as a novel prognostic factor as well as a therapeutic target for HCC.