TY - JOUR
T1 - Inhibition of Wnt signaling by the osteoblast-specific transcription factor Osterix
AU - Zhang, Chi
AU - Cho, Kyucheol
AU - Huang, Yehong
AU - Lyons, Jon P.
AU - Zhou, Xin
AU - Sinha, Krishna
AU - McCrea, Pierre D.
AU - De Crombrugghe, Benoit
PY - 2008/5/13
Y1 - 2008/5/13
N2 - 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 β-catenin-induced Topflash reporter activity and β-catenin-induced secondary axis formation in Xenopus embryos. Importantly, in calvaria of E18.5 Osx-null embryos harboring the TOPGAL reporter transgene, β-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 β-catenin transcriptional activity. We also showed that Osx decreased osteoblast proliferation. Indeed, E18.5 Osx-null calvaria showed greater BrdU incorporation than wildtype 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/β-catenin activity. Our results add a layer of control to Wnt/β-catenin signaling in bone.
AB - 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 β-catenin-induced Topflash reporter activity and β-catenin-induced secondary axis formation in Xenopus embryos. Importantly, in calvaria of E18.5 Osx-null embryos harboring the TOPGAL reporter transgene, β-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 β-catenin transcriptional activity. We also showed that Osx decreased osteoblast proliferation. Indeed, E18.5 Osx-null calvaria showed greater BrdU incorporation than wildtype 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/β-catenin activity. Our results add a layer of control to Wnt/β-catenin signaling in bone.
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U2 - 10.1073/pnas.0710831105
DO - 10.1073/pnas.0710831105
M3 - Article
C2 - 18458345
AN - SCOPUS:44349125905
SN - 0027-8424
VL - 105
SP - 6936
EP - 6941
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 19
ER -