Tanikawa Rena, Tanikawa Takahisa, Okada Yosuke, Nakano Kazuhisa, Hirashima Mitsuomi, Yamauchi Akira, Hosokawa Ryuji, Tanaka Yoshiya
First Department of Internal Medicine, University of Occupational and Environmental Health, School of Medicine, Kitakyushu, Japan.
J Bone Miner Res. 2008 Feb;23(2):278-86. doi: 10.1359/jbmr.071008.
Galectin-9 is a beta-galactoside-binding lectin expressed in various tissues, including bone. The role of galectin-9 in human osteoblasts, however, remains unclear. This study showed that galectin-9 interacts with lipid rafts and induces osteoblast proliferation through the c-Src/ERK signaling pathway.
Galectin-9 is a beta-galactoside-binding lectin that modulates many biological functions by interacting with particular carbohydrates attached to proteins and lipids. However, the role of galectin-9 in bone metabolism and osteoblast proliferation remains unclear. This study investigated the effects of galectin-9 on osteoblast proliferation and its signaling mechanisms.
The effect of galectin-9 on osteoblast proliferation was tested by measuring the conversion of tetrazolium salt WST-8 to formazan. Protein phosphorylation was assayed by western blotting and confocal microscopy was used to localize lipid rafts.
Galectin-9-induced proliferation of the obtained osteoblasts in a dose-dependent manner, whereas galectin-1, -3, and -4 did not. Galectin-9-induced phosphorylation of c-Src and subsequent ERK1/ERK2 in the osteoblasts. The galectin-9-induced phosphorylation and proliferation were inhibited by PP2, a selective inhibitor of c-Src. Galectin-9-induced clustering of lipid rafts detected by cholera toxin B (CTB; binding the raft-resident ganglioside GM1) using confocal microscopy. Cross-linking of the GM1 ganglioside with CTB by anti-CTB antibody-induced phosphorylation of c-Src, whereas disruption of galectin-9-induced lipid rafts by beta-methylcyclodextrin reduced c-Src phosphorylation and proliferation of the cells.
These results suggest that galectin-9, but not other galectins, induced proliferation of human osteoblasts through clustering lipid rafts on membrane and subsequent phosphorylation of the c-Src/ERK signaling pathway.
半乳糖凝集素-9是一种在包括骨骼在内的多种组织中表达的β-半乳糖苷结合凝集素。然而，半乳糖凝集素-9在人成骨细胞中的作用仍不清楚。本研究表明，半乳糖凝集素-9与脂筏相互作用，并通过c-Src/ERK信号通路诱导成骨细胞增殖。
半乳糖凝集素-9是一种β-半乳糖苷结合凝集素，通过与附着在蛋白质和脂质上的特定碳水化合物相互作用来调节多种生物学功能。然而，半乳糖凝集素-9在骨代谢和成骨细胞增殖中的作用仍不清楚。本研究调查了半乳糖凝集素-9对成骨细胞增殖及其信号机制的影响。
通过测量四唑盐WST-8转化为甲臜来测试半乳糖凝集素-9对成骨细胞增殖的影响。通过蛋白质印迹法检测蛋白质磷酸化，并使用共聚焦显微镜对脂筏进行定位。
半乳糖凝集素-9以剂量依赖性方式诱导所获得的成骨细胞增殖，而半乳糖凝集素-1、-3和-4则没有。半乳糖凝集素-9诱导成骨细胞中c-Src的磷酸化以及随后的ERK1/ERK2磷酸化。PP2（一种c-Src的选择性抑制剂）抑制了半乳糖凝集素-9诱导的磷酸化和增殖。使用共聚焦显微镜通过霍乱毒素B（CTB；结合脂筏驻留神经节苷脂GM1）检测到半乳糖凝集素-9诱导的脂筏聚集。抗CTB抗体使GM1神经节苷脂与CTB交联诱导c-Src磷酸化，而β-甲基环糊精破坏半乳糖凝集素-9诱导的脂筏则降低了c-Src磷酸化和细胞增殖。
这些结果表明，半乳糖凝集素-9而非其他半乳糖凝集素通过使膜上的脂筏聚集以及随后的c-Src/ERK信号通路磷酸化来诱导人成骨细胞增殖。
