title: Osteoactivin acts as downstream mediator of BMP-2 effects on osteoblast function.
abstract: 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.
authors.affiliation: Department of Anatomy and Cell Biology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Samir M
authors.initials: SM
authors.lastname: Abdelmagid
authors.forename: Mary F
authors.initials: MF
authors.lastname: Barbe
authors.forename: Israel
authors.initials: I
authors.lastname: Arango-Hisijara
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Owen
authors.forename: Steven N
authors.initials: SN
authors.lastname: Popoff
authors.forename: Fayez F
authors.initials: FF
authors.lastname: Safadi
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D002113:Calcification, Physiologic / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D051898:Smad1 Protein / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; C503043:Gpnmb protein, rat; D008562:Membrane Glycoproteins; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D051898:Smad1 Protein; D016212:Transforming Growth Factor beta