title: Inhibition of Wnt signaling by the osteoblast-specific transcription factor Osterix.
abstract: The recent identification of the genes responsible for several human genetic diseases affecting bone homeostasis and the characterization of mouse models for these diseases indicated that canonical Wnt signaling plays a critical role in the control of bone mass. Here, we report that the osteoblast-specific transcription factor Osterix (Osx), which is required for osteoblast differentiation, inhibits Wnt pathway activity. First, in calvarial cells of embryonic day (E)18.5 Osx-null embryos, expression of the Wnt antagonist Dkk1 was abolished, and that of Wnt target genes c-Myc and cyclin D1 was increased. Moreover, our studies demonstrated that Osx bound to and activated the Dkk1 promoter. In addition, Osx inhibited beta-catenin-induced Topflash reporter activity and beta-catenin-induced secondary axis formation in Xenopus embryos. Importantly, in calvaria of E18.5 Osx-null embryos harboring the TOPGAL reporter transgene, beta-galactosidase activity was increased, suggesting that Osx inhibited the Wnt pathway in osteoblasts in vivo. Our data further showed that Osx disrupted binding of Tcf to DNA, providing a likely mechanism for the inhibition by Osx of beta-catenin transcriptional activity. We also showed that Osx decreased osteoblast proliferation. Indeed, E18.5 Osx-null calvaria showed greater BrdU incorporation than wild-type calvaria and that Osx overexpression in C2C12 mesenchymal cells inhibited cell growth. Because Wnt signaling has a major role in stimulating osteoblast proliferation, we speculate that Osx-mediated inhibition of osteoblast proliferation is a consequence of the Osx-mediated control of Wnt/beta-catenin activity. Our results add a layer of control to Wnt/beta-catenin signaling in bone.
authors.affiliation: Department of Molecular Genetics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Kyucheol
authors.initials: K
authors.lastname: Cho
authors.forename: Yehong
authors.initials: Y
authors.lastname: Huang
authors.forename: Jon P
authors.initials: JP
authors.lastname: Lyons
authors.forename: Xin
authors.initials: X
authors.lastname: Zhou
authors.forename: Krishna
authors.initials: K
authors.lastname: Sinha
authors.forename: Pierre D
authors.initials: PD
authors.lastname: McCrea
authors.forename: Benoit
authors.initials: B
authors.lastname: de Crombrugghe
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D015536:Down-Regulation; D005260:Female; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D051379:Mice; D008954:Models, Biological; D009928:Organ Specificity; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D055232:Proline-Rich Protein Domains; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D015398:Signal Transduction; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus; D051176:beta Catenin / Q000235:genetics
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin