miR-203 inhibits cell growth and regulates G1/S transition by targeting Bmi-1 in myeloma cells

The oncogene B-cell-specific Moloney murine leukemia virus insertion site-1 (Bmi-1) is overexpressed in multiple myeloma (MM). Our previous study demonstrated that Bmi-1 silencing sensitized MM cells to bortezomib. Translational regulation has emerged as a prominent underlying mechanism of Bmi-1 regulation, particularly via microRNA targeting. The present study determined that Bmi-1 may be directly targeted by miR-203 using a luciferase assay. In addition, enforced expression of miR-203 led to significant downregulation of Bmi-1 protein and mRNA expression levels. Furthermore, restoration of miR-203 significantly inhibited cell growth and G1/S transition in MM cells. miR-203 was downregulated in MM patients, and a negative correlation between the expression of miR-203 and Bmi-1 was observed. The results of the present study indicated that miR-203 exerts growth-inhibiting effects in MM through the suppression of Bmi-1 expression. In conclusion, the present study demonstrated that Bmi-1 is a direct functional target of miR-203 in MM.