Parathyroid Hormone Increases β-Catenin Levels through Smad3 in Mouse Osteoblastic Cells

Abstract

PTH, via the PTH/PTH-related protein receptor type 1 that couples to both protein kinase A (PKA) and protein kinase C (PKC) pathways, and the canonical Wnt-beta-catenin signaling pathway play important roles in bone formation. In the present study we have examined the interaction between the PTH and Wnt signaling pathways in mouse osteoblastic MC3T3-E1 cells. PTH dose- and time-dependently increased the concentrations of beta-catenin. The PKA activator, forskolin, and the PKC activator, phorbol 12-myristate-13-acetate, as well as the PTH analog, [Nle(8,18),Tyr(34)]human PTH-(3-34)amide, all increased beta-catenin levels. Both H-89, a specific PKA inhibitor, and PKC inhibitors, staurosporine and calphostin C, antagonized PTH stimulation of beta-catenin levels. TGF-beta as well as transfection of the TGF-beta-signaling molecule, Smad3, enhanced beta-catenin levels, and this was antagonized by transfection of a dominant-negative Smad3. The transcriptional activity of transfected dominant-active beta-catenin was enhanced by PTH, an effect that was antagonized by cotransfection of a dominant-negative Smad3. PTH as well as LiCl(2), which mimics the effects of the Wnt-beta-catenin pathway, rescued the dexamethasone- and etoposide-induced apoptosis of osteoblastic cells. In conclusion, the data demonstrate that PTH stimulates osteoblast beta-catenin levels via Smad3, and that both PKA and PKC pathways are involved. The canonical Wnt-beta-catenin pathway is likely to be involved in the antiapoptotic actions of PTH by acting through Smad3 in osteoblasts.

Na+/H+ Exchanger Regulatory Factor 1 (NHERF1) Directly Regulates Osteogenesis

“…The Wnt/␤-catenin signaling pathway plays a pivotal role in osteoblast differentiation and maturation from MSCs (39), and PTH increases the ␤-catenin level in osteoblasts (40). Interestingly, active ␤-catenin increased markedly in NHERF1-null MSC cells (Fig.…”

Gsα enhances commitment of mesenchymal progenitors to the osteoblast lineage but restrains osteoblast differentiation in mice

“…Therefore, the inhibition of Wnt signaling may contribute to the dramatic decrease in the pool of osteoprogenitors in G s α OsxKO mice. In addition to sclerostin and Dkk1, several laboratories have demonstrated other points of interaction between the PTH/PPR/PKA and Wnt signaling pathways (21,47). PTH is able to activate β-catenin targets in osteoblasts even in the absence of Dkk1 suppression (25,26), implicating other actions downstream of the PPR in regulating Wnt signaling.…”

Parathyroid Hormone-responsive Smad3-related Factor, Tmem119, Promotes Osteoblast Differentiation and Interacts with the Bone Morphogenetic Protein-Runx2 Pathway

“…Moreover, we showed that PTH stimulates osteoblast ␤-catenin levels via Smad3 (10,11). In that study, PTH * This work was supported by a grant from Mitsui Life Social Welfare Foundation (to H. K.), Grants-in-aid 17590961 and 21591179 from the Ministry of Science, Education, and Culture of Japan (to H. K.), the Global COE Program F11 from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, and Canadian Institutes of Health Research Grant MOP-9315 (to G. N. H.).…”

“…SB431542 and anti-Osterix antibody were from Tocris Cookson Ltd. (Bristol, UK) and Abcam Inc. (Cambridge, MA), respectively. The vectors expressing Myc-tagged Smad3 and a mutant, Smad3⌬C, in which the MH2 domain corresponding to amino acid residues 278 -425 had been removed, were described previously (9,10). All other chemicals used were of analytical grade.…”