Inhibitory role of Myeloid Elf-1 like Factor(MEF) on osteoblast differentiation

Objective: Runx and Ets family proteins control the expression of genes that are critical for biological processes such as proliferation, differentiation and cell death. Previous studies indicated that there are interactions between Runx and Ets family proteins and some of those interactions are important gene expressions and the cell differentiation. Myeloid elf-1 like factor (MEF) is a member of the Ets transcription factor family. In this study, we investigated the inhibitory role of MEF on osteoblast differentiation through functional regulation of Runx2. Method: Mouse calvairal cell line MC3T3-E1 cells were used to understand the expression profile of MEF in osteoblast differentiation and by BMP2 treatment. MEF, Runx2 or both MEF and Runx2 overexpressing C2C12 and MC3T3-E1 cells were established to determine the role of MEF on osteoblast differentiation. Results: MEF expression was higher at early time in the osteoblast differentiation and reduced by BMP2 treatments. MEF upregulated cell cycling components such as cycline A2 and D1 and facilitated proliferation of cells. The expression of MEF suppresses the alkaline phosphatase activity induced by BMP-2 stimulation and mediated by Runx2. MEF downregulated Dlx5, a positive regulator of osteoblast differentiation, and upregulated Msx2 and Mab21, negative regulators in osteoblast differentiation. MEF physically interact with Runx2 and competed out Runx2 binding on cis-element of osteocalcin. MEF diminished 6xOSE2-luciferase reporter activity induced by Runx2. We found that the MEF-mediated suppression of osteoblast differentiation is critically related with Runx2 regulation Conclusion: Together our findings suggest that MEF functions as a negative regulator of osteoblast differentiation through functional regulation of Runx2 transcription factor by protein to protein interaction as well as transcriptional regulation on both activators and repressors for osteoblast differentiation.