Role of miR‑let‑7c‑5p/c‑myc signaling axis in the committed differentiation of leukemic THP‑1 cells into monocytes/macrophages.

In a preliminary experiment, it was found that c-myc expression was decreased following the differentiation of THP-1 cells into monocytes/macrophages induced by phorbol 12-myristate 13 acetate (PMA) + lipopolysaccharide (LPS) + interferon (IFN)-γ. The expression of miR-let-7c-5p was then found to be elevated by cross-sectional analysis using TargetScan and PubMed and differential microarray analysis. The present study aimed to investigate the role of the miR-let-7c-5p/c-myc signaling axis in the committed differentiation of THP-1 leukemic cells into monocytes/macrophages induced by PMA + LPS + IFN-γ. Human THP-1 leukemic cells were induced to differentiate into monocytes/macrophages by PMA + LPS + IFN-γ. Following induction for 48 h, the growth density of the THP-1 cells was observed directly under an inverted microscope, cell proliferation was measured using Cell Counting Kit-8 assay and the cell cycle and the expression of differentiation-related antigens (CD11b and CD14) were measured using flow cytometry. The mRNA expression of miR-let-7c-5p and c-myc was detected using reverse transcription-quantitative PCR and the protein expression of c-myc was detected using western blot analysis. Dual luciferase reporter gene analysis was used to detect the targeted binding of miR-let-7c-5p on the 3'UTR of c-myc. The relative expression of miR-let-7c-5p and c-myc genes in THP-1 cells induced by PMA + LPS + IFN-γ was found to be up- and downregulated respectively, and expression of miR-let-7c-5p was negatively correlated with the expression of c-myc gene. Dual luciferase reporter gene assays confirmed that miR-let-7c-5p targeted the 3'UTR of c-myc and inhibited luciferase activity. Following transfection with miR-let-7c-5p mimics, the expression of c-myc was markedly downregulated and the proliferative ability of the THP-1 cells was decreased, while the expression rate of CD11b and CD14 was significantly increased. The rescue experiment revealed that the effects of miR-let-7c-5p mimics on the proliferation and differentiation of THP-1 cells were attenuated by transfection with c-myc overexpression vector. Together, the findings of the present study demonstrated that miR-let-7c-5p can target the 3'UTR region of c-myc and that the miR-let-7c-5p/c-myc signaling axis is one of the critical pathways involved in the directional differentiation of leukemic cells into monocytes/macrophages.