Abstract
The monocytic MDSC (M-MDSC) is one of the major types of MDSCs, which play important roles in suppression of antitumor immunity. However, the mechanisms underlying how M-MDSCs so heavily accumulate in patients with cancer are still poorly understood. The purpose of this study was to identify miRNAs that regulate the proliferation and differentiation of M-MDSCs. Microarray analysis was performed to identify differentially expressed miRNAs between tumor-induced M-MDSCs (TM-MDSCs) and their counterparts from tumor-free mice. The miRNAs and their target genes that regulate the proliferation and differentiation of myeloid cells were predicted by bioinformatics analysis and validated by RT-qPCR. Luciferase reporter assays were used to analyze the relationships between miRNAs and target genes. Overexpression of candidate miRNAs and target genes in myeloid cells was conducted to verify their functions in cell proliferation, differentiation, and apoptosis. Our data showed that miR-486 was overexpressed in TM-MDSCs. Cebpa was predicted to be one of the target genes of miR-486 that regulates the proliferation of myeloid cells. Expression of Cebpa was inversely correlated with miR-486 in TM-MDSCs, and we found that overexpression of miR-486 suppressed the expression of Cebpa in both 293T cells determined by luciferase reporter assays and in myeloid cells determined by RT-qPCR. Overexpression of miR-486 promoted proliferation and suppressed apoptosis in myeloid cells, as opposed to overexpression of Cebpa, which promoted the opposing phenotype. Overexpression of either miR-486 or Cebpa inhibited differentiation of myeloid cells. This study indicates that miR-486 promotes proliferation and suppresses apoptosis in myeloid cells by targeting Cebpa in vitro, suggesting that miR-486 and Cebpa might be involved in the expansion of TM-MDSCs in tumor-bearing mice.