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Submitted on June 26, 2007
Accepted on August 15, 2007
Phosphorylation and Promotes Osteoblast Differentiation and Bone Formation
Women's Health & Musculoskeletal Biology, Wyeth Research, Collegeville, PA and Biological Technologies, Wyeth Research, Cambridge, MA
* To whom correspondence should be addressed. E-mail: billiaj{at}wyeth.com.
Ror2 receptor plays a key role in bone formation, but its signaling pathway is not completely understood. We demonstrate that Ror2 homo-dimerizes at the cell surface, and that dimerization can be induced by a bivalent antibody. Antibody-mediated dimerization causes receptor autophosphorylation and induces functional consequences of its signaling, including osteogenesis in mesenchymal stem cells (MSC) and bone formation in organ culture. We further show that Ror2 associates with and phosphorylates 14–3-3
scaffold protein. Endogenous Ror2 binds 14–3-3
in U2OS osteosarcoma cells, and purified intracellular domain of Ror2 interacts with 14–3-3
in vitro. 14–3-3
is tyrosine phosphorylated in U2OS cells, and this phosphorylation is inhibited by down-regulating Ror2 and enhanced by over-expressing the kinase. Purified Ror2 phosphorylates 14–3-3
in vitro, confirming 14–3-3
as the first identified Ror2 substrate. Down-regulating 14–3-3
potentiates osteoblastogenesis in MSC and increases bone formation in calvarial cultures, indicating that 14–3-3
exerts a negative effect on osteogenesis. This raises a possibility that Ror2 induces osteogenic differentiation at least in part through a release of the 14–3-3
-mediated inhibition. Our research forms a foundation for several new areas of investigation, including the molecular regulation of 14–3-3 by tyrosine phosphorylation and the role of this scaffold in osteogenesis.
tyrosine phosphorylation
receptor tyrosine kinase
receptor dimerization
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