[miR-125b promotes proliferation of human acute myeloid leukemia cells by targeting Bak1]

To investigate miR- 125b regulation mechanism by identifying miR-125b target genes and its function in acute myeloid leukemia (AML).

The bioinformatics software and database were applied to predict and analyze target genes of miR-125b. The vector contained the target gene 3'-UTR portion cloned into a luciferase reporter construct. A luciferase reporter assay was performed following co-transfection of small molecular miR-125b mimics and target gene wild-type or mutant plasmid into HEK-293T cells. Further in leukemia cell lines NB4 and HL-60, the protein level of target gene was measured by Western blot after overexpression miR-125b. Finally, the viabilities of NB4 and HL-60 cells were measured by CCK-8 assay at 24 h, 48 h, 72 h, 96 h after electroporation.

Bcl-2-antagonist/killer 1 (Bak1), a pro-apoptotic gene, was a target gene of miR-125b by software predicts. Reporter vector containing the 3'-UTR Bak1 wild and mutation sites were co-transfected with small molecule analogues of miR-125b in HEK-293T cells. Dual luciferase reporter gene assay system showed that miR-125b significantly suppresses the reporter gene activity containing Bak1 3'-UTR by about 53.8% (P<0.05), but it didn't suppresses the reporter gene activity containing 3'-UTR Bak1 mutation. Western blot showed that miR-125b mimics significantly down-regulated the expression of Bak1 in human leukemia cell lines NB4 and HL-60. Meanwhile, the growth rate of cells treated with miR-125b obviously increased compared with that in control by CCK-8 test (P<0.05).

Our findings strongly indicated that BAK1 was a downstream target gene of miR-125b, and miR-125b promoted proliferation in human AML cells at least partially by targeting Bak1, so we speculated that miR-125b as an oncogene could be a potential therapeutic target for treating AML.