Figure 5.

miR-574-3p inhibits proliferation and promotes apoptosis of U937 leukemia cells and suppresses tumorigenesis. (A) U937 cell proliferation is repressed by miR-574-3p and rescued by hnRNP L. U937 cells (1 × 10⁶ cells) were transfected with miR-574-3p (or control miR, 50 nM), pcDNA3-Myc-hnRNP L (or empty vector, 500 ng), or both, for up to 4 days and cell number determined by hemocytometer. (B) Effects of miR-574-3p, miR-297, and hnRNP L on U937 cell proliferation and apoptosis. (Top) U937 cells (1 × 10⁶ cells) were transfected with miRNAs (50 nM) as indicated in the presence or absence of hnRNP L or its mutant (500 ng). Cell proliferation rate was determined by MTT assay after 48 h transfection. (Bottom) Caspase 3/7 activity was measured using luminescent assay after 48 h. (C) miR-574-3p reduces anchor-independent U937 cell colony formation. U937 cells were transfected as in Figure 5B and seeded (5 × 10³ cells) in 0.35% soft agarose gel containing RPMI with 10% serum. Cells were incubated for 2 weeks and stained with crystal violet and cell colonies imaged (above) and quantified (below). Data information: In (A–C), data are presented as mean ± SD (n = 3; *P ≤ 0.05, Student's t-test). (D) miR-574-3p represses tumor growth in mouse xenograft tumor model. miR-574-3p was transfected into U937 cells stably expressing hnRNP L (or pcDNA3 vector) for 48 h. Transfected cells (1 × 10⁷ cells) were injected into flanks of nude mice, and tumor growth monitored for 23 days. Data are presented as mean ± SD (n = 20; *** P ≤ 0.001, two-way ANOVA).