Overexpression of miR­21 is involved in acute monocytic leukemia­associated angiogenesis by targeting IL­12.

ABSTRACT

Angiogenesis is important in pathophysiological processes, including the pathogenesis of acute monocytic leukemia (AML). MicroRNA­21 (miR­21) is overexpressed and exhibits oncogenic activity in cancer. However, the biological mechanism underlying the effect of miR­21 in AML remains to be fully elucidated. In the present study, the expression levels of miR­21 and vascular endothelial growth factor (VEGF) were determined in 26 patients with AML and 28 healthy individuals. The secretion of VEGF was also measured following the transfection of THP­1 cells with miR­21 mimic or inhibitor. The supernatants of the THP­1 cells, which were transfected with miR­21 mimic, inhibitor or small interfering RNA (si)VEGF, respectively, were used to incubate human umbilical vein endothelial cells (HUVECs), following which tube formation of the HUVECs was measured. miR­21 targets were predicted using a biological target prediction website and confirmed using a luciferase assay. The effects of interleukin (IL)­12 were investigated by examining the tube formation of HUVECs and the secretion of VEGF following recombinant human (rh) IL­12 pretreatment. The results revealed that miR­21 and VEGF expression was significantly increased in the peripheral blood monocytes of the patients, compared with the healthy controls. There was negative correlation between the expression of IL­12 and miR­21 in the serum of patients with AML. Furthermore, supernatant VEGF levels from the miR­21 mimic­transfected THP­1 cells were increased, whereas a decreasing trend was observed in the miR­21 inhibitor group. The angiogenic ability of the HUVECs pretreated with supernatant from the THP­1 cells transfected with miR­21 mimic was higher, and was lower in THP­1 cells co­transfected with miR­21 mimic and siVEGF, compared with the miR­21 mimic only group. A luciferase assay demonstrated that IL­12 was the direct target of miR­21, and the level of IL­12 in the supernatant of THP­1 cells transfected with miR­21 mimic was increased. IL­12 pretreatment increased VEGF expression and angiogenic ability in HUVECs. The inactivation of miR­21 or activation of its target gene may be a potential therapeutic strategy in human AML.