Aubin J E, Gupta A K, Bhargava U, Turksen K
Department of Anatomy and Cell Biology, University of Toronto, Ontario, Canada.
J Cell Physiol. 1996 Dec;169(3):468-80. doi: 10.1002/(SICI)1097-4652(199612)169:3<468::AID-JCP7>3.0.CO;2-M.
Galectin 3 is an endogenous soluble beta-galactoside-specific lectin originally identified and termed epsilon BP or IgE-binding protein in rat basophilic leukemia cells, but its wide tissue distribution and the multiple contexts in which it has been isolated have suggested that its function may not be limited to IgE binding but may include a role in cell growth regulation and differentiation, neoplastic transformation, and cell adhesion (Liu, 1990, Crit. Rev. Immunol., 10:289-306; Barondes et al., 1994, J. Biol. Chem., 269:20807-20810). After immunoscreening of a lambda gt11 cDNA expression library made from bone-nodule forming cultures of fetal rat calvaria (RC) cells with an antibody raised against osteoblastic cells (Turksen et al., 1992, J. Histochem. Cytochem., 40:1339-1352), three cDNA clones were isolated and sequenced; the sequence matched that of rat galectin 3. Galectin 3 mRNA was detected in various fetal and adult rat tissues, including calvaria and cultured RC cells. In RC cells and the rat osteosarcoma cell line ROS 17/2.8, galectin 3 mRNA expression increased with time in culture, in contrast to its behavior in fetal rat skin fibroblasts (RSF) in which its expression decreased with time in culture. In a second rat osteosarcoma line, UMR 106.01, galectin 3 mRNA was almost nondetectable. The synthetic glucocorticoid dexamethasone (Dex) enhanced galectin 3 expression in RSF cell cultures, while 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) had no significant effect. In contrast, Dex downregulated and 1,25(OH)2D3 upregulated galectin 3 expression in RC and ROS 17/2.8 cells, especially at later time points in culture when expression of osteoblast-associated differentiation markers by these cell types is most marked. Immunolabeling with an antibody against rat galectin 3 to identify galectin 3 protein showed that cells labelled within both the ROS 17/2.8 and RC populations but with marked intercellular heterogeneity of intensity. Our data support the conclusion that galectin 3 is a previously unrecognized product of osteoblastic cells, that galectin 3 mRNA and protein expression increases with time in vitro concomitant with other markers of osteogenesis, including formation of bone nodules and expression of osteoblast-associated markers such as alkaline phosphatase, bone sialo-protein, and osteocalcin, and that its expression is regulated by hormones such as glucocorticoids and 1,25(OH)2D3 that modulate other aspects of the osteoblast phenotype.
半乳糖凝集素-3是一种内源性可溶性β-半乳糖苷特异性凝集素，最初在大鼠嗜碱性白血病细胞中被鉴定并称为εBP或IgE结合蛋白，但它广泛的组织分布以及被分离出来的多种环境表明，其功能可能不限于IgE结合，还可能包括在细胞生长调节和分化、肿瘤转化及细胞黏附中发挥作用（Liu，1990年，《免疫评论》，10:289 - 306；Barondes等人，1994年，《生物化学杂志》，269:20807 - 20810）。在用抗成骨细胞抗体对由胎鼠颅骨（RC）细胞的骨结节形成培养物构建的λgt11 cDNA表达文库进行免疫筛选后（Turksen等人，1992年，《组织化学与细胞化学杂志》，40:1339 - 1352），分离并测序了三个cDNA克隆；其序列与大鼠半乳糖凝集素-3的序列匹配。在各种胎鼠和成年大鼠组织中检测到了半乳糖凝集素-3 mRNA，包括颅骨和培养的RC细胞。在RC细胞和大鼠骨肉瘤细胞系ROS 17/2.8中，半乳糖凝集素-3 mRNA表达随培养时间增加，这与其在胎鼠皮肤成纤维细胞（RSF）中的行为相反，在RSF中其表达随培养时间下降。在另一个大鼠骨肉瘤细胞系UMR 106.01中，几乎检测不到半乳糖凝集素-3 mRNA。合成糖皮质激素地塞米松（Dex）增强了RSF细胞培养物中半乳糖凝集素-3的表达，而1,25 - 二羟基维生素D3（1,25(OH)2D3）没有显著影响。相反，Dex下调而1,25(OH)2D3上调了RC和ROS 17/2.8细胞中半乳糖凝集素-3的表达，尤其是在培养后期，此时这些细胞类型中成骨细胞相关分化标志物的表达最为明显。用抗大鼠半乳糖凝集素-3抗体进行免疫标记以鉴定半乳糖凝集素-3蛋白，结果显示ROS 17/2.8和RC细胞群体中均有细胞被标记，但细胞间强度存在明显异质性。我们的数据支持以下结论：半乳糖凝集素-3是成骨细胞以前未被认识的产物，半乳糖凝集素-3 mRNA和蛋白表达在体外随时间增加，同时伴有其他成骨标志物，包括骨结节形成以及成骨细胞相关标志物如碱性磷酸酶、骨唾液蛋白和骨钙素的表达，并且其表达受糖皮质激素和1,25(OH)2D3等激素调节，这些激素可调节成骨细胞表型的其他方面。
