Cbfb enhances the osteognic differentiation of both human and mouse mesenchymal stem cells induced by Cbfa-1 via reducing its ubiquitination-mediated degradation

¹ Institute of Biopharmaceutical Science, National Yang-Ming University, Taipei, R.O.C.
² Institute of Biopharmaceutical Science, National Yang-Ming University, Taipei, Taiwan, R.O.C; Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan, R.O.C.; Institute of Clinical Medicine, National Yang-Ming University, Taipei, Taiwan, R.O.C.

^* To whom correspondence should be addressed. E-mail: yeusu{at}ym.edu.tw.

	Abstract

Core-binding factors (CBFs) are a small family of heterodimeric transcription factors that play critical roles in development. While Cbfa-1, one of the three subunits in the family, is essential for osteogenesis, Cbfb, the only subunit, forms heterodimers with different Cbfas to increase their DNA binding affinity by inducing conformational changes. Although defective bone formation was found in both Cbfa-1 and Cbfb knockout animals, the precise role of the latter in osteogenesis remains unclear. To dissect the contribution of Cbfb in osteogenic differentiation of mesenchymal stem cells (MSCs), recombinant adenoviruses carrying Cbfb (AdHACbfb) and Cbfa-1 (AdCbfa-1) were generated and used to infect both the mouse C3H10T1/2 cells and human bone marrow-derived MSCs. Although Cbfb alone failed to trigger osteogenesis of MSCs, it markedly enhanced the gene expression and enzyme activity of alkaline phosphatase (ALP) as well as osteocalcin activation in those cells over-expressing Cbfa-1. Enhancement of the osteogenic differentiation-inducing effect of Cbfa-1 by Cbfb was resulted from an increase in stability of the former due to the suppression of ubiquitination-mediated proteasomal degradation by the latter. Taken together, in addition to defining the role of Cbfb in osteogenic differentiation of MSCs, our results also suggest that the Cbfa-1 and Cbfb co-expressing MSCs might be an appropriate strategy for bone repairing and regeneration therapies.