Regulation of proliferation and apoptosis in human osteoblastic cells by microRNA-15b.

MicroRNAs (miRNAs) play an important role in proliferation and differentiation of osteoblasts. We recently reported that miR-15b acts as a positive regulator of osteoblast differentiation, whereas its functional role in osteoblastic proliferation remains not known. In this study, we found that there was increased proliferation of human osteoblastic cells (MG63) when they were transiently transfected with miR-15b inhibitor. A significant level of cell population was found to be decreased at G0/G1 phase, and increased at S and G2/M phase by miR-15b inhibitor treatment. Cyclin E1 was found to be one of the putative target genes of miR-15b, and miR-15b mimic and miR-15b inhibitor treatments in cells decreased and increased cyclin E1 expression, respectively. We further identified that the cyclin E1 3'UTR is directly targeted by miR-15b using the luciferase reporter gene system. No significant effect was found on apoptosis of MG63 cells with miR-15b inhibitor. Thus, these findings provide new insights in understanding the role of miR-15b expression as negative regulator of osteoblast proliferation.