MicroRNA-302a Stimulates Osteoblastic Differentiation by Repressing COUP-TFII Expression

Chicken ovalbumin upstream promoter transcription factor II (COUP‐TFII) is a potent transcription factor that represses osteoblast differentiation and bone formation. Previously, we observed that stimuli for osteoblast differentiation, such as bone morphogenetic protein 2 (BMP2), inhibits COUP‐TFII expression. This study was undertaken to identify BMP2‐regulated and COUP‐TFII‐targeting microRNAs (miRNAs), and to explore their regulatory roles in osteoblast differentiation. Based on in silico analysis, 12 miRNAs were selected and their expression in BMP2‐treated MC3T3‐E1 cells was examined. BMP2 induced miR‐302a expression in dose‐ and time‐dependent manners with the decrease in COUP‐TFII expression. Runx2, a BMP2‐downstream transcription factor, specifically regulated miR‐302a expression and its promoter activity. A computer‐based prediction algorithm led to the identification of two miR‐302a binding sites on the 3′‐untranslational region of COUP‐TFII mRNA (S1: 620–626 bp, S2: 1,016–1,022 bp), and a luciferase assay showed that miR‐302a directly targeted S1 and S2. Transfection of miR‐302a precursor significantly enhanced expression of osteogenic marker genes with decreasing COUP‐TFII mRNA and protein level, alkaline phosphatase activity and matrix mineralization. On the other hand, inhibition of miR‐302a significantly attenuated BMP2‐induced osteoblast specific gene expression, alkaline phosphatase activity, and matrix mineralization with increasing COUP‐TFII mRNA and protein level. These results indicate that miR‐302a is induced by osteogenic stimuli and promotes osteoblast differentiation by targeting COUP‐TFII. MiR‐302a could be a positive regulator for osteoblast differentiation. J. Cell. Physiol. 230: 911–921, 2015. © 2014 Wiley Periodicals, Inc.