title: Wnt signaling during BMP-2 stimulation of mesenchymal chondrogenesis.
abstract: Members of both the Wnt and bone morphogenetic protein (BMP) families of signaling molecules have been implicated in the regulation of cartilage development. A key component of the Wnt signaling pathway is the cytosolic protein, beta-catenin. We have recently shown that the chondrogenic activity of BMP-2 in vitro involves the action of the cell-cell adhesion protein, N-cadherin, which functionally complexes with beta-catenin. The aim of this study is to test the hypothesis that Wnts may be involved in BMP-2 induced chondrogenesis, using an in vitro model of high-density micromass cultures of the murine multipotent mesenchymal cell line, C3H10T1/2. Expression of a number of Wnt members was detected in these cultures, including Wnt-3A and Wnt-7A, whose levels were up- and downregulated, respectively, by BMP-2. To assess the functional involvement of Wnt signaling in BMP-2 induced chondrogenesis, cultures were treated with lithium chloride, a Wnt-7A mimetic that acts by inhibiting the serine/threonine phosphorylation activity of glycogen synthase kinase-3beta (GSK-3beta). Lithium treatment significantly inhibited BMP-2 stimulation of chondrogenesis as well as GSK-3beta enzymatic activity, and decreased the levels of N-cadherin protein and mRNA. Furthermore, lithium decreased BMP-2 upregulation of total and nuclear levels of LEF-1 and beta-catenin as well as their interaction during later chondrogenesis; similarly, the interaction of beta-catenin with N-cadherin was also decreased. Interestingly, lithium treatment did not affect the ability of BMP-2 to decrease ubiquitination of beta-catenin, although it did reduce the interaction of beta-catenin with GSK-3beta during late chondrogenesis (days 9-13). We suggest that the chondro-inhibitory effect of lithium on BMP-2 induced chondrogenesis indicates antagonism between lithium-like Wnts and BMP-2 during mesenchymal condensation.
authors.affiliation: Department of Orthopaedic Surgery and Graduate Programs of Biochemistry and Molecular Biology, and Cell and Tissue Engineering, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Leslie
authors.initials: L
authors.lastname: Fischer
authors.forename: Genevieve
authors.initials: G
authors.lastname: Boland
authors.forename: Rocky S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015820:Cadherins / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002460:Cell Line; D020219:Chondrogenesis / Q000187:drug effects* / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D008094:Lithium / Q000494:pharmacology*; D008648:Mesoderm / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D051379:Mice; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; C495267:CTNNB1 protein, mouse; D015820:Cadherins; D003598:Cytoskeletal Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; C555511:Wnt3a protein, mouse; C490508:Wnt7a protein, mouse; D029961:Zebrafish Proteins; D051176:beta Catenin; D008094:Lithium; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3