Galectin-9 induces osteoblast differentiation through the CD44/Smad signaling pathway |
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Authors: | Rena Tanikawa Mitsuomi Hirashima Yoshiya Tanaka |
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Institution: | a First Department of Internal Medicine, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan b Department of Cell Regulation, School of Medicine, Kagawa University, Kagawa, Japan c Department of Immunology and Immunopathology, School of Medicine, Kagawa University, Kagawa, Japan |
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Abstract: | Galectin-9 is a β-galactoside-binding lectin expressed in various tissues. It binds various glycoconjugates and modulates a variety of biological functions in various cell types. Although galectin-9 is expressed in bone, its function in human osteoblasts remains unclear. We demonstrate that galectin-9 induces osteoblast differentiation through the CD44/Smad signaling pathway in the absence of bone morphogenetic proteins (BMPs). Galectin-9 increases alkaline phosphatase activities in human osteoblasts and induces the phosphorylation of Smad1/5/8 and translocation of Smad4 to the nucleus in the absence of BMPs. Galectin-9 also induces binding of Smad4 to the Id1 promoter and increases its activity. Anti-CD44 antibody inhibits Smad1/5/8 phosphorylation by galectin-9. Galectin-9 binds to CD44 and induces the formation of a CD44/BMP receptor complex. Because Smad1 is phosphorylated by BMP receptors, we propose that formation of the CD44/BMP receptor complex induced by galectin-9 may provide a trigger for the activation of Smads. |
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Keywords: | Galectin-9 Osteoblast CD44 Smad |
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