Osteoactivin acts as downstream mediator of BMP-2 effects on osteoblast function

• Published in: Journal of cellular physiology Vol. 210; no. 1; pp. 26 - 37
• Main Authors: Abdelmagid, Samir M., Barbe, Mary F., Arango-Hisijara, Israel, Owen, Thomas A., Popoff, Steven N., Safadi, Fayez F.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.01.2007
• Subjects: Animals; Animals, Newborn; Bone Morphogenetic Protein 2; Bone Morphogenetic Proteins - genetics; Bone Morphogenetic Proteins - metabolism; Bone Morphogenetic Proteins - pharmacology; Calcification, Physiologic - drug effects; Cell Differentiation - drug effects; Cells, Cultured; Dose-Response Relationship, Drug; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Oligonucleotides, Antisense - genetics; Oligonucleotides, Antisense - metabolism; Osteoblasts - cytology; Osteoblasts - drug effects; Osteoblasts - metabolism; Osteogenesis - drug effects; Rats; Recombinant Proteins - pharmacology; RNA, Messenger - metabolism; RNA, Small Interfering - genetics; RNA, Small Interfering - metabolism; Signal Transduction - drug effects; Smad1 Protein - genetics; Smad1 Protein - metabolism; Time Factors; Transfection; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism; Transforming Growth Factor beta - pharmacology; Up-Regulation - drug effects
• ISSN: 0021-9541; 1097-4652
• DOI: 10.1002/jcp.20841

Our laboratory previously showed that osteoactivin (OA) is a novel, osteoblast‐related glycoprotein that plays a role in osteoblast differentiation and function. The purpose of this study was to examine the regulation of OA expression by BMP‐2 and the role OA plays as a downstream mediator of BMP‐2 effects in osteoblast function. Using primary osteoblast cultures, we tested different doses of BMP‐2 on the regulation of OA expression during osteoblast development. To test whether Smad‐1 signaling is responsible for BMP‐2 regulation of OA expression, osteoblast cultures were transfected with Smad1 siRNA, treated with 50 ng/ml of BMP‐2 and analyzed by Western blot. BMP‐2 treatment increased OA mRNA and protein expression in a dose‐dependent manner and this upregulation was blocked in Smad1 siRNA transfected cultures. We next examined whether the role of OA as a downstream mediator of BMP‐2 effects on osteoblast differentiation and matrix mineralization. Osteoblast cultures were transfected with OA antisense oligonucleotides and treated with 50 ng/ml of BMP‐2. Cultures transfected with OA antisense oligonucleotides and treated with BMP‐2 showed a reduction of OA expression associated with a significant reduction in early and late differentiation markers induced by BMP‐2. Therefore, OA acts, at least in part, as a downstream mediator of BMP‐2 effects on osteoblast differentiation and matrix mineralization. Our findings suggest that BMP‐2 regulates OA expression through the Smad1 signaling pathway. Our data also emphasize that OA protein acts as a downstream mediator of BMP‐2 effects on osteoblast differentiation and function. J. Cell. Physiol. 210: 26–37, 2007. © 2006 Wiley‐Liss, Inc.