Sclerostin inhibition of Wnt-3a-induced C3H10T1/2 cell differentiation is indirect and mediated by bone morphogenetic proteins.
High bone mass diseases are caused both by activating mutations in the Wnt pathway and by loss of SOST, a bone morphogenetic protein (BMP) antagonist, leading to the activation of BMP signaling. Given the phenotypic similarity between mutations that activate these signaling pathways, it seems likely that BMPs and Wnts operate in parallel or represent components of the same pathway, modulating osteoblast differentiation. In this study, we show that in C3H10T1/2 cells, Wnt-3A and BMP-6 proteins were inducers of osteoblast differentiation, as measured by alkaline phosphatase (ALP) induction. Surprisingly, sclerostin, noggin, and human BMP receptor 1A (BMPR1A)-FC fusion proteins blocked Wnt-3A-induced ALP as well as BMP-6-induced ALP activity. Dkk-1, a Wnt inhibitor, blocked Wnt-induced ALP activity but not BMP-induced ALP activity. Early Wnt-3A signaling as measured by beta-catenin accumulation was not affected by the BMP antagonists but was blocked by Dkk-1. Wnt-3A induced the appearance of BMP-4 mRNA 12 h prior to that of ALP in C3H10T1/2 cells. We propose that sclerostin and other BMP antagonists do not block Wnt signaling directly. Sclerostin blocks Wnt-induced ALP activity by blocking the activity of BMP proteins produced by Wnt treatment. The expression of BMP proteins in this autocrine loop is essential for Wnt-3A-induced osteoblast differentiation.
Winkler
David G
DG
Department of Gene Function and Target Validation, Celltech R&D Inc., Bothell, Washington 98119, USA.
Sutherland
May S Kung
MS
Ojala
Ethan
E
Turcott
Eileen
E
Geoghegan
James C
JC
Shpektor
Diana
D
Skonier
John E
JE
Yu
Changpu
C
Latham
John A
JA
D048868:Adaptor Proteins, Signal Transducing; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins / Q000378:metabolism / Q000494:pharmacology*; D002454:Cell Differentiation; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005819:Genetic Markers; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008809:Mice, Inbred C3H; D008954:Models, Biological; D009154:Mutation; D010006:Osteoblasts / Q000378:metabolism; D010641:Phenotype; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; D051176:beta Catenin
D048868:Adaptor Proteins, Signal Transducing; C525816:BMP6 protein, human; C525817:Bmp6 protein, mouse; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins; C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; D005819:Genetic Markers; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; C486030:Sost protein, mouse; D015534:Trans-Activators; C555510:WNT3A protein, human; D051153:Wnt Proteins; D060508:Wnt3 Protein; D060509:Wnt3A Protein; C555511:Wnt3a protein, mouse; D051176:beta Catenin; D000469:Alkaline Phosphatase