Cbl-b enhances Runx2 protein stability and augments osteocalcin promoter activity in osteoblastic cell lines
✍ Scribed by R. Ampornaramveth Salingcarnboriboon; P. Pavasant; M. Noda
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 158 KB
- Volume
- 224
- Category
- Article
- ISSN
- 0021-9541
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Cbl‐b is a member of Cbl family of E3 ubiquitin (Ub) ligase. Besides the important role in ubiquitination process, other members of Cbl family have been suggested to show non‐ubiquitination‐related function in regulation of osteoblastic differentiation. However, the role of Cbl‐b in regulation of osteoblastic function has not been known yet. To elucidate the role of Cbl‐b in regulation of osteoblastic function, we examined its effects on Runx2, a master gene of osteoblastic differentiation. We co‐expressed Cbl‐b and Runx2 in osteoblastic cell lines and tested their effects on osteocalcin promoter activity together with the expression of Runx2 and its downstream genes. Luciferase assay demonstrated that Cbl‐b synergistically enhances osteocalcin promoter activity in conjunction with the effect on Runx2. Co‐transfection of Cbl‐b and Runx2 further upregulated Runx2 protein levels without any alteration in Runx2 mRNA expression. The upregulation of Runx2 protein by Cbl‐b was inhibited by the treatment with lactacystin, a specific inhibitor of the 26S proteasome. These results indicated that Cbl‐b would control Runx2 protein levels at the post‐translational event. Moreover, the upregulation of downstream genes of Runx2 such as osteocalcin and alkaline phosphatase mRNA was also observed. These data propose the involvement of Cbl‐b in the regulation of osteoblast‐related genes expression. J. Cell. Physiol. 224: 743–747, 2010. © 2010 Wiley‐Liss, Inc.