Effects of parathyroid hormone on Wnt signaling pathway in bone
Article first published online: 16 JUN 2005
Copyright © 2005 Wiley-Liss, Inc.
Journal of Cellular Biochemistry
Volume 95, Issue 6, pages 1178–1190, 15 August 2005
How to Cite
Kulkarni, N.H., Halladay, D.L., Miles, R.R., Gilbert, L.M., Frolik, C.A., Galvin, R.J.S., Martin, T.J., Gillespie, M.T. and Onyia, J.E. (2005), Effects of parathyroid hormone on Wnt signaling pathway in bone. J. Cell. Biochem., 95: 1178–1190. doi: 10.1002/jcb.20506
- Issue published online: 20 JUL 2005
- Article first published online: 16 JUN 2005
- Manuscript Accepted: 25 FEB 2005
- Manuscript Received: 30 NOV 2004
- Wnt signaling
The Wnt signaling pathway has recently been demonstrated to play an important role in bone cell function. In previous studies using DNA microarray analyses, we observed a change in some of the molecular components of the canonical Wnt pathway namely, frizzled-1 (FZD-1) and axil, in response to continuous parathyroid hormone (PTH) treatment in rats. In the present study, we further explored other components of the Wnt signaling pathway in rat distal metaphyseal bone in vivo, and rat osteoblastic osteosarcoma cells (UMR 106) in culture. Several Wnt pathway components, including low-density lipoprotein-receptor-related protein 5 (LRP5), LRP6, FZD-1, Dickkopf-1 (Dkk-1), and Kremen-1 (KRM-1), were expressed in bone in vivo and in osteoblasts in vitro. Continuous exposure to PTH (1–38) both in vivo and in vitro upregulated the mRNA expression of LRP6 and FZD-1 and decreased LRP5 and Dkk-1. These effects in UMR 106 cells were associated with an increase in β-catenin as measured by Western blots and resulted in functional activation (three to six-fold) of a downstream Wnt responsive TBE6-luciferase (TCF/LEF-binding element) reporter gene. Activation of the TBE6-luciferase reporter gene by PTH (1–38) in UMR 106 cells was inhibited by the protein kinase A (PKA) inhibitor, H89. Activation was mimicked by PTH (1–31), PTH-related protein (1–34), and forskolin, but both PTH (3–34) and (7–34) had no effect. These findings suggest that the effect of PTH on the canonical Wnt signaling pathway occurs at least in part via the cAMP-PKA pathway through the differential regulation of the receptor complex proteins (FZD-1/LRP5 or LRP6) and the antagonist (Dkk-1). Taken together, these results reveal a possible role for the Wnt signaling pathway in PTH actions in bone. © 2005 Wiley-Liss, Inc.