Effects of let-7e on the cell activities of monocytic cell line THP-1 and the possible mechanism

Objective\r\nTo investigate the effects of a microRNA family member, let-7e, on monocytic cell line THP-1 with regard to cell apoptosis and cytokine secretion and to analyze the possible mechanism.\r\n\r\n\r\nMethods\r\nTHP-1 cells were transfected with mimic negative control (cy3) and observed with immunofluorescence microscopy for the evaluation of transfection rate. The expression of let-7e in THP-1 cells respectively transfected with let-7e mimic, mimic negative control, let-7e inhibitor and inhibitor negative control were detected by qRT-PCR. MTT assay and flow cytometry analysis were used to detect the activities and apoptosis of transfected THP-1 cells. Western blot assay was performed to measure the expression of the genes encoding interferon alpha-inducible protein 6 (IFI6), enhancer of zeste homolog 2 (EZH2) and caspase-3 that were target genes of let-7e predicted by bioinformatics analysis. THP-1 cells were transfected with let-7e mimic and mimic negative control for 48 h and then stimulated with LPS for 2 h for further detection. The supernatants of cell culture were collected for the detection of secreted cytokines by Human Cytokine Array.\r\n\r\n\r\nResults\r\nThe monocytic THP-1 cells were transfected with mimic negative control with a transfection efficiency of about 75%. There were 8.551±0.365, 83.893±15.941, 38.858±2.743 and 0.594±0.174, 2.427±1.229, 3.053±0.207 fold increases in let-7e expression after the transient transfection of THP-1 cells with let-7e mimic and let-7e inhibitor for 12 h, 24 h and 48 h, respectively. The transfection of let-7e mimic into THP-1 cells enhanced the cell activities and inhibited the apoptosis of the transfected cells. Bioinformatics analysis showed that let-7e bound to the genes encoding EZH2, IFI6 and caspase-3 with the mirSVR scores of -0.1608, -0.5693 and -0.9423, suggesting them as the predicted target genes of let-7e. The expressions of IFI6, EZH2 and caspase-3 in let-7e mimic transfected THP-1 cells were decreased as indicated by Western blot assay. The results of Human Cytokine Array showed that the expression of LPS-induced cytokines including CD154, G-CSF, CD54, IL-13, IL-1RA and IL-23 were inhibited in let-7e mimic transfected THP-1 cells.\r\n\r\n\r\nConclusion\r\nLet-7e had an anti-apoptosis effect on monocytic THP-1 cells and influenced the secretion of LPS-induced cytokines in THP-1 cells. Let-7e might regulate the biological function of THP-1 cells through inhibiting the expression of target genes encoding caspase-3, IFI6 and EZH2.\r\n\r\n\r\nKey words: \r\nTHP-1 cell; let-7e; Apoptosis; Cytokine